Method and apparatus for coexistence among wireless transmit/receive units (WTRUs) operating in the same spectrum

A method and apparatus for coexistence among wireless transmit/receive units (WTRUs) operating in the same spectrum are disclosed. A WTRU includes a memory, a receive unit, a transmit unit and a control unit. The memory stores coexistence gap patterns. Each of the coexistence gap patterns defines a pattern of transmission periods and silent periods for the WTRU and corresponds to a respective duty cycle. The receive unit receives from a base station information regarding a duty cycle for a wireless cell operated by the base station. The control unit selects one of the coexistence gap patterns based on the received information regarding the duty cycle for the wireless cell and controls the transmit unit to transmit information during the transmission periods and not transmit information during the silent periods of the selected one of the plurality of coexistence gap patterns.

BACKGROUND

Wireless networks were originally designed for use with targeted applications, such as voice or data, for an envisioned load (e.g., based on a predicted consumer acceptance of the technology). However, such networks are now being subject to increasingly more uses, and actual consumer acceptance of such technologies has been unexpected. For example, wireless networks are commonly used for streaming video and web browsing, wireless local area networks (WLANs) are commonly used to provide hotspot coverage in coffee shops and restaurants, many businesses are foregoing wiring Ethernet LANs for the simplicity of wireless LANs and most residential homes have at least one WiFi access point.

SUMMARY

A method and apparatus for coexistence among wireless transmit/receive units (WTRUs) operating in the same spectrum are disclosed. A WTRU includes a memory, a receive unit, a transmit unit and a control unit. The memory stores coexistence gap patterns. Each of the coexistence gap patterns defines a pattern of transmission periods and silent periods for the WTRU and corresponds to a respective duty cycle. The receive unit receives from a base station information regarding a duty cycle for a wireless cell operated by the base station. The control unit selects one of the coexistence gap patterns based on the received information regarding the duty cycle for the wireless cell and controls the transmit unit to transmit information during the transmission periods and not transmit information during the silent periods of the selected one of the plurality of coexistence gap patterns.

DETAILED DESCRIPTION

The serving gateway144may also be connected to the PDN gateway146, which may provide the WTRUs102a,102b,102cwith access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs102a,102b,102cand IP-enabled devices.

Today's wireless networks have evolved over time to meet the increasing demands of available applications, but they are beginning to reach their limits in terms of maximum throughput offered. To address the increasing demand, wireless networks have been evolved, for the most part, to use their licensed spectrum more efficiently. In some cases, this is reaching a point where the gains are small compared with the effort or changes necessary to achieve those gains. One solution to this may be to find new spectrum on which to operate. The potential spectrum may be available in many bands (e.g., licensed and license exempt or dynamic spectrum sharing (DSS) bands). With this new spectrum, the throughput shortage may be addressed by a number of mechanisms. For instance, the wireless systems may use some form of load balancing, thereby allowing certain users to operate in this new spectrum. Alternatively the wireless systems may use carrier aggregation in which transmissions to/from users may be aggregated over multiple chunks of spectrum, where one or more of these chunks may be over license exempt spectrum. In the embodiments described herein, a cell operating in carrier aggregation mode over license exempt spectrum may be referred to as a supplementary cell and a carrier may be referred to as a supplementary carrier.

An example of a license exempt band that may be used as this potential new spectrum (for example for carrier aggregation) is referred to as the television white space (TVWS). Generally speaking, the TVWS represents spectrum in the ultra high frequency (UHF) and very high frequency (VHF) bands that is not reserved for other uses (e.g., TV distribution or wireless microphone use). At least a portion of the TVWS resulted from the transition from analog to digital TV transmissions, which freed up certain portions of the spectrum that are no longer used for TV transmissions. The Federal Communications Commission (FCC) has opened up the TVWS frequencies for a variety of unlicensed uses, given that the unlicensed (or secondary) users take steps to minimize interference to incumbent (or primary) users.

Due to the need for wireless networks to keep up with increasing demands, implementation of wireless networks such as long term evolution (LTE) in DSS bands has been considered. However, because such bands are available for use by users other than, for example, the LTE network, such networks need to be adapted so that co-existence between the wireless network and other users of the same spectrum is possible. Embodiments described herein provide enhancements to wireless networks such as LTE networks to enable co-existence between the wireless network or small cell operators (such as LTE-Time Division Duplex (LTE-TDD) operators in standalone small cells) and other users of the same spectrum (e.g., WiFi).

Non-coordinated methods for LTE coexistence with other secondary users in DSS bands may include the use of coexistence gaps. Such methods may include the use of silent periods (or coexistence gaps) in an LTE transmission to provide opportunities for other networks to operate in the same band. During each coexistence gap, all LTE entities may cease transmitting. At the end of each coexistence gap, the LTE eNB may resume downlink (DL) transmission without attempting to assess channel availability.

FIG. 2is a signal diagram200of an example periodic coexistence gap pattern202. The example periodic coexistence gap pattern202illustrated inFIG. 2has a periodic ON-OFF transmission, including alternating LTE DL transmission periods204(LTE ON, LTE active periods or TON) and coexistence gaps206(LTE OFF, LTE DTX periods or TOFF). The period of the coexistence pattern (CPP) illustrated inFIG. 2may be defined by:
CPP=TON+TOFF.  (1)
The duty cycle of the coexistence pattern (CPDC) may be defined by:
CPDC=TON/(TON+TOFF)  (2)

The CPP may be fixed (e.g., statically set during radio resource configuration (RCC) with a value set based on a trade-off between the frequency of gaps and the impact on latency and quality of service (QoS) of LTE) or dynamically changed to adapt to traffic conditions and the presence of other users (e.g., WiFi users). The CPDC may be a semi-static parameter that may change as a function of the traffic and presence of other secondary users.

FIG. 3is a signal diagram300of the example periodic coexistence gap pattern ofFIG. 2including variations where all nodes experience the same interference and where nodes experience localized interference. In embodiments where all nodes experience the same interference, the hidden node problem, which occurs when a node is visible from, for example, a wireless access point (AP) but not from other nodes communicating with the AP, does not occur. However, the hidden node problem may occur in embodiments where nodes experience localized interference. In the example illustrated inFIG. 3, the periodic coexistence gap pattern202is the same as illustrated inFIG. 2. Elements304,306and308are different example transmission patterns for other networks (e.g., WiFi).

With respect to transmission patterns304and306, all nodes experience the same interference and, therefore, the hidden node problem does not occur. Here, during the coexistence gaps206aand206b, WiFi or other network nodes may detect the available channel and start transmitting packets. For pattern304, the WiFi nodes transmit longer packets, and for pattern306, the WiFi nodes transmit shorter packets. For pattern304where WiFi nodes use longer packets, the last WiFi packet transmitted during a coexistence gap may overlap on the next LTE DL transmission (314a), thus creating interference. However, for pattern306where WiFi nodes use shorter packets, the last WiFi packet transmitted during a coexistence gap may overlap on the next LTE DL transmission (314b) to a lesser extent than longer WiFi packet transmissions or not at all. Accordingly, the longer the WiFi packets are, the longer the potential duration of LTE-WiFi interference at the beginning of the LTE ON period. It is, therefore, expected that WiFi transmission using long packets may result in more degradation of LTE throughput as compared to shorter WiFi packet transmissions.

With respect to transmission pattern308, interference between nodes is localized, in which case the hidden node problem may occur. Here, WiFi nodes may not detect or defer to the LTE transmission and, thus, they may transmit both during LTE coexistence gaps206aand206band LTE ON periods204aand204b, resulting in random periods of overlap interference314c,314d,314e,314f,314g,314hand314i. A WiFi node may not detect LTE transmissions during LTE ON periods because, for example, WiFi may use a high threshold for detection of non-WiFi systems (e.g., a −62 dBM threshold for a 20 MHz bandwidth), so, in this scenario, any LTE transmission below the −62 dBM threshold will not be detected by the WiFi node.

FIGS. 4A and 4Bare diagrams of periodic coexistence gap patterns having different duty cycles and different alignments with respect to LTE active periods for a DL operating mode. For these examples, the license exempt spectrum is used in carrier aggregation mode, where the aggregation is with a primary cell (PCell) in the licensed band. The example primary cell402and410in each ofFIGS. 4A and 4Bhas a frame size of 10 ms, with each frame including ten 1 ms sub-frames numbered 0-9. Each of the supplementary cells404/412,406/414and408/416has a different duty cycle. The supplementary cells404and412, for example, have a 5:5 or 50% duty cycle. As illustrated inFIGS. 4A and 4B, this means that a 5 ms coexistence gap occurs every 10 ms. The supplementary cells406and414, for another example, have a 7:3 or 30% duty cycle. As illustrated inFIGS. 4A and 4B, this means that a 3 ms coexistence gap occurs every 10 ms. The supplementary cells408and416, for another example, have a 9:1 or 10% duty cycle. As illustrated inFIGS. 4A and 4B, this means that a 1 ms coexistence gap occurs every 10 ms. InFIG. 4A, coexistence gaps across the supplementary carriers404,406and408are aligned at the start of the LTE active periods. InFIG. 4B, coexistence gaps across the supplementary carriers412,414and416are aligned at the end of the LTE active periods. For supplementary carriers aligned at the start of an LTE active period, the first sub-frame in the active period may be set to sub-frame #9. This may ensure that sub-frame0, which may carry the supplementary cell synchronization signals, is the second sub-frame in the LTE active period, and, as a result, may be somewhat protected from harmful secondary user interference that may be present at the start of an active period.

For each of the supplementary carriers illustrated inFIGS. 4A and 4B, the eNB/HeNB may use a non-zero duty cycle, where the LTE active period is at least one sub-frame. This mode of operation may be referred to herein as Mode B. The eNB/HeNB may use this mode of operation as soon as one WTRU is actively using the carrier. The eNB/HeNB may transmit reference symbols and data during the LTE active periods. For Mode B operation with short duty cycles, the eNB/HeNB may reduce the frequency of transmission of synchronization signals, for example, to once every 10 ms.

Supplementary carriers may also operate with a special 0% duty cycle referred to hereafter as Mode A. In this mode, the eNB/HeNB may refrain from using the supplementary carriers for data traffic. Rather, the eNB/HeNB may limit transmission on the supplementary carrier to regularly transmit synchronization signals (e.g., PSS and SSS) and a limited set of pilot or reference symbols. For instance, this may be done in the first slot of sub-frame0. As activity on Mode A carriers may be limited, it may cause minimal interference to other secondary users on this carrier. The mode may be used by the eNB/HeNB to configure inter-frequency measurements on supplementary carriers, which may still not be in operation (e.g., for testing the signal reception on these carriers). An eNB/HeNB may activate a number of Mode A carriers and configure a WTRU to perform inter-frequency measurements for these carriers.

FIG. 4Cis a diagram400C of an example Mode A carrier480with a 0% duty cycle and an example Mode B carrier482with a 50% duty cycle. For the example Mode A carrier480, a cell may transmit only a single slot Sync and RS to allow for RSRP/RSRQ measurements. For the example Mode B carrier482, a cell may transmit Sync, RS and data during an ON cycle.

The coexistence gap used by a DSS cell may be cell-wide. In an embodiment, the eNB or home eNB (HeNB) may configure multiple coexistence gaps for a DSS cell, only one of which may be active at a given time. The eNB/HeNB may, however, change the size of the coexistence gap depending, for example, on the presence or absence of secondary user systems (e.g., WiFi). An eNB or HeNB may be able to measure the load on the secondary system to further tailor the coexistence gap size.

In another embodiment, one or more WTRUs in a cell may require a different coexistence gap size than the one the cell is currently operating in. For example, an eNB/HeNB may sense no secondary user interference on the spectrum and, accordingly, may operate the cell with a very short coexistence gap (e.g., 1 ms every 10 ms). However, a particular WTRU may require a longer coexistence gap to perform actions on another radio access technology (RAT). Here, a cell may dynamically change the coexistence gap for the entire cell or may keep the existing coexistence gap but schedule the requesting WTRU in such a manner as to effectively allow it to use the requested longer coexistence gap (e.g., 5 ms every 10 ms), allowing the requesting WTRU more time to perform the required actions.

In a more specific example, a WTRU may be using both WiFi and LTE simultaneously. As the WiFi and LTE systems run independently, the WTRU may be both a WiFi WTRU and an LTE WTRU and may need to run concurrent procedures on either system that are not compatible. For example, the WiFi WTRU may enter a power saving mode and monitor only one beacon out of every x and then go to sleep. Here, the RRC may configure two different coexistence gaps for the WTRU. When the WTRU enters WiFi power saving mode, it may signal this to the eNB/HeNB, and the eNB/HeNB may send a message changing the coexistence gap to another pre-configured coexistence gap (e.g., the lowest idle duty cycle). When coming out of the WiFi power saving mode, or when the station detects that it needs to increase the amount of data to be sent over the WiFi, the WTRU may signal this to the eNB/HeNB. The eNB/HeNB may send a message changing the coexistence gap to the other pre-configured coexistence gap (e.g., the highest idle duty cycle).

FIG. 5Ais a flow diagram500A of an example method of an eNB/HeNB managing WTRU requests for control over coexistence gap selection. In the example illustrated inFIG. 5A, WTRUs502and506and eNB/HeNB504exchange system information (SI) (508). The WTRU502needs to operate on a different coexistence gap than the one the eNB/HeNB504is currently using for the cell, and it informs the eNB/HeNB504that it needs control over coexistence gap selection (510). In an embodiment, this may be part of the capability transfer of the WTRU502or may be sent via a dedicated RRC message. Upon receipt of this information from the WTRU502, the eNB/HeNB504may configure the WTRU502with the currently used cell-wide coexistence gap as well as other pre-configured but idle coexistence gaps for the cell (512). The WTRU502may later determine that it can no longer operate using the cell-wide gap but would prefer to use one of the other pre-configured but idle gaps (514). Here, the WTRU502may send its preference to the eNB/HeNB504using a MAC control element (CE) or other signaling mechanism (516).

As described above, there may be different options available to the eNB/HeNB504for resolving the request from the WTRU502to use one of the other pre-configured but idle gaps. In option518, the eNB/HeNB504may change the cell-wide coexistence gap (520). Here, the eNB/HeNB504may reconfigure the coexistence gap for all WTRUs in the cell by, for example, informing each of the WTRUs (e.g., WTRUs502and506) of the new coexistence gap (522/524). In option526, the eNB/HeNB504may decide to only configure the coexistence gap for the WTRU502(528). Here, the eNB/HeNB504may send a MAC CE or other signaling mechanism to the WTRU502informing it that it may use the requested pre-configured coexistence gap (530). The eNB/HeNB504may manage the new coexistence gap for the WTRU502through effective scheduling (532).

In some situations, LTE cells may operate only over dynamic and shared spectrum. For example, new entrants may not have access to licensed spectrum and, therefore, may need to deploy LTE in DSS bands. For another example, small cells may be deployed in dynamic and shared spectrum only with a macro cell overlay operating in licensed spectrum. In this example, since the macro cell and small cell may operate in different bands, this may eliminate any interference issue between them. However, since the small cell itself may not operate in the licensed spectrum, the cell operating in the DSS may not be able to anchor the LTE system to a cell in licensed spectrum. This situation may be referred to herein as a small cell operating in standalone DSS bands.

New entrants may be motivated to deploy their own networks for a number of reasons. Cellular operators are often gatekeepers and may block new services that new entrants may wish to provide. But a new entrant's deployment of its own network may enable it to showcase or introduce such new services to the end customer. Further, new entrants may not have a monthly billing relationship with the end customer, and the basic connectivity provided by a small cell network may enable these new entrants to charge the end customer a monthly fee. Additionally, new entrants often make devices that do not have cellular connectivity to address market segments that do not want to pay high monthly fees (e.g., users of tablet personal computers (PCs) and electronic book readers). Finally, some new entrants may have already made considerable investments in developing and lobbying TVWS technology. To allow such new entrants to deploy their own networks, cellular technologies may need to be adapted so that they can be deployed using small cells and shared and dynamic spectrum such as the TVWS.

Embodiments are described herein that may enable or improve coexistence between LTE cells that operate only over dynamic and shared spectrum (e.g., new entrants and small cells operating in standalone BSS) and other users of the shared spectrum (such as WiFi users). One such embodiment includes the use of sub-frame-based coexistence gaps. Another such embodiment includes the use of frame-based coexistence gaps. Another such embodiment includes the use of coexistence gaps using a non-repeating pattern based approach. Another such embodiment includes the use of a new discontinuous reception (DRX) cycle for creation of coexistence gaps.

For each of these embodiments, any number of different coexistence gap patterns may be defined and provided to WTRUs. The WTRUs may select one of the defined coexistence gap patterns to apply with respect to transmissions at a given time based on information provided to the WTRU by an eNB. For an embodiment where a WTRU requests to use a different gap size, for example, the information provided to the WTRU by the eNB may include signaling configuring all of the WTRUs in a cell to use a particular one of the different coexistence gap patterns, or signaling instructing the requesting WTRU to operate using the particular one of the different coexistence gap patterns. For embodiments where sub-frame-based or frame-based coexistence gaps are used, the information provided to the WTRU by the eNB may include information regarding a particular duty cycle to apply that may, for example, correspond to a particular one of the different coexistence gap patterns.

FIG. 5Bis a flow diagram of an example method500B of coexistence among WTRUs operating in the same spectrum. In the example method illustrated inFIG. 5B, a WTRU stores a number of coexistence gap patterns (550). Each of the coexistence gap patterns may define a pattern of transmission periods and silent periods for the WTRU and may correspond to a respective duty cycle of a plurality of duty cycles. The WTRU may receive information regarding a duty cycle from a base station (e.g., an eNB or HeNB) regarding a duty cycle for a wireless cell operated by the base station (552). The WTRU may select one of the coexistence gap patterns based on the received information regarding the duty cycle for the wireless cell (554). The WTRU may transmit during the transmission periods and not transmit during the silent periods of the selected one of the plurality of coexistence gap patterns (556).

In an embodiment, the silent periods are periods during which all transmission to and from the WTRU is absent. However, in some embodiments, minimal transmission of reference and/or synchronization symbols (e.g., PSS/SSS) may be permitted. The plurality of duty cycles may include a pre-determined number k of duty cycles, each of which may represent a range of percentages of the transmission periods to the silent periods in the corresponding coexistence gap pattern.

There may be advantages to using TDD instead of frequency division duplexing (FDD) in the DSS bands. TDD only needs one frequency band, and it may be easier to find a single suitable DSS frequency channel than finding a pair of separated frequency channels for UL and DL operation. Further, the nature of DSS bands may make it difficult to define fixed duplex separation between the UL and DL that are currently used in FDD systems. In addition, with two frequency bands used by FDD, there are more chances to interfere with incumbent users on any of the two channels than for TDD and its single channel. Further, detection of incumbent users on a single frequency band is easier than for two bands. Finally, allowing asymmetric DL/UL data connection on a single frequency band may fit better with a dynamic spectrum assignment system where channel bandwidth is being optimized. Accordingly, at least some of the embodiments described herein rely on the use of TDD, and, therefore, embodiments are also described herein that introduce changes to existing hybrid automatic repeat request (HARQ) procedures in TDD-LTE that may be required due to the relation between UL and DL sub-frames involved in the HARQ procedures.

FIG. 6is a diagram of a Type 2 frame structure600for TDD. In the illustrated Type 2 frame structure600, each radio frame602is 10 ms long and is made up of 10 sub-frames610,611,612,614,616,618,619,620,622and624, each of which is 1 ms long, and two half frames604, each of which is 5 ms long. Each sub-frame is made up of two slots606.

In TDD, a sub-frame may be either a UL sub-frame, a DL sub-frame or a special sub-frame. In the illustrated Type 2 frame structure600, the sub-frames611and619are special sub-frames, each of which includes a DL pilot time slot (DwPTS)626and a UL pilot time slot (UpPTS)630as well as a guard period628for the transition from DL to UL for interference avoidance. Certain restrictions may be placed on the types of channels that may be transmitted in the special sub-frame for the Type 2 format. For example, the special sub-frame may not have the physical UL control channel (PUCCH) mapped to it. The difference in frame structure may result in different placement/location of certain channels and signals, such as reference signals and shared channel (SCH).

TDD may allow for seven possible UL/DL configurations (e.g., arrangements of UL, DL and special sub-frames), which may be statically configured on a per-cell basis. For each of the seven UL/DL configurations0-6, a maximum number of DL HARQ processes and UL HARQ processes for TDD may be specified. Table 1 below specifies an example maximum number of DL HARQ processes for each of the seven UL/DL configurations0-6, and Table 2 below specifies an example maximum number of UL HARQ processes for each of the seven UL/DL configurations0-6.

In an embodiment, coexistence gaps may be defined as a collection of blank TDD sub-frames (sub-frame based approach). A blank sub-frame may be a UL, DL or special sub-frame during which neither the eNB nor any of the WTRUs under the control of the eNB may transmit. DL blank sub-frames may include no physical control or data channels (e.g., including physical DL control channel (PDCCH) and physical control format indicator channel (PCFICH)) and no DL reference symbols).

All WTRUs under the control of an eNB may be made aware of the presence of the blank sub-frames. For UL sub-frames, WTRUs may not be allowed to transmit on blank sub-frames. As a result, PUCCH and PUSCH may not be defined on these sub-frames, and the WTRU may not send a radio access channel (RACH) or sounding reference signal (SRS) on these sub-frames either.

The sub-frame-based approach to defining coexistence gaps for TDD may include deriving the specific sub-frames in each TDD UL/DL configuration in order to define configurations that allow existing physical layer (PHY) procedures for TDD-LTE to be performed with minimal impact and to allow sufficient length gaps for WiFi systems to coexist on the same channel. Coexistence gaps may be defined by introducing blank sub-frames into existing LTE configurations to create new variants of the existing TDD UL/DL configurations defined for each of high, medium and low duty cycles. In addition, the special sub-frame in TDD may be replaced by a new special sub-frame where the UpPTS is removed from the special sub-frame to increase the consecutive duration of the coexistence gaps.

FIG. 7is a signal diagram700of a method of changing a channel using sub-frame-based coexistence gaps in an LTE system that includes WTRUs750, an eNB760, a coexistence manager770and a WiFi AP780. In an embodiment, channel usage information may be exchanged between the eNB760and the coexistence manager770(702). The LTE system may be initially operating in a DSS without coexistence, or, alternatively, the LTE system may be operating with a minimal gap time that allows it to perform sensing for WiFi on the channel. To achieve the minimal amount of gap time, the eNB760may select a high duty cycle gap configuration in the gap pattern design, which may be associated with the current TDD UL/DL configuration being used by the eNB760(704). In either of these cases, the eNB760may signal both the TDD UL/DL configuration and the coexistence gap pattern (e.g., high or none) using system information (SI) so that the WTRUs750that try to attach to the eNB760are aware of the current gap pattern (if any) that is being used (706). One or more WTRUs750may then perform network discovery and attachment to eNB760(708), and the eNB760may configure those WTRUs760for sensing (710).

Periodically, the LTE system may evaluate the best suited coexistence gap configuration to be used in the system (712). The coexistence gap configuration may include, for example, a high duty cycle configuration where the majority of the frame is used by the LTE system, a medium duty cycle configuration where the frame is evenly (or close to evenly) split between the LTE system and a coexistence gap meant for WiFi operation, and a low duty cycle configuration, where the majority of the frame is dedicated to a coexistence gap and only a few sub-frames may be used for LTE transmission. The actual frame format to be used for each configured gap state (e.g., high, medium, or low) may depend on the UL/DL configuration chosen by the eNB760. The eNB760may choose a TDD UL/DL configuration based on the traffic profile (e.g., UL heavy, DL heavy, balanced) and may change the TDD UL/DL configuration if the traffic profile changes. Each TDD UL/DL configuration may have corresponding high, medium, and low gap states that define which sub-frame is used as a gap sub-frame and which sub-frame maintains its use as a normal sub-frame in LTE (UL or DL as defined by the current TDD UL/DL configuration).

The eNB760may make periodic decisions with respect to the preferred duty cycle for the gap configuration based on sensing, for example, to detect the presence of secondary signals such as WiFi signals. Such sensing may be performed by the eNB760or by one or of the WTRUs750(714). In an embodiment, the sensing may be performed during coexistence gap sub-frames. A duty cycle determination algorithm may then be triggered to determine the required duty cycle configuration (e.g., high, medium, low) to be used (716). In an embodiment, the algorithm may use an averaged sensing result to determine the required duty cycle. The algorithm may also use direct information about the WiFi system(s) that may be made available by an entity that is aware of the WiFi system or may be used to manage the coexistence of systems in the DSS bands (e.g., a coexistence manager) to make the determination.

The algorithm may account for knowledge of the continuously monitored LTE traffic load in making the determination. If the determined configuration does not match the current configuration, the eNB760may decide to change the duty cycle configuration. This process may be repeated periodically (724/726), and each time the eNB decides to change the duty cycle, it may signal each of the WTRUs750the change of duty cycle (728). The signaling may indicate a target frame at which the duty cycle configuration change will take place. Alternatively, the duty cycle change may take place immediately, or some fixed time following, transmission of the duty cycle configuration change message.

At the time that the duty cycle configuration change is to take effect, the eNB760and WTRUs750may transition from use of the old duty cycle to the new duty cycle. For example, if the eNB760is currently using the medium duty cycle and wants to change to the high duty cycle, the eNB760and WTRUs750may change from using a frame format that is defined by the medium duty cycle configuration to a frame format that is defined by a high duty cycle configuration (730).

The eNB760may determine the actual sequence of normal UL and DL sub-frames and blank sub-frames that make up the coexistence gap based on, for example, the current TDD UL/DL configuration and the determined coexistence duty cycle (e.g., high, medium, low). The WTRUs750may be aware of the mapping from the UL/DL configuration and the duty cycle to the actual sequence so that the eNB760does not need to signal the sequence but only the duty cycle and the TDD UL/DL configuration. The eNB760may periodically signal the duty cycle configuration to all WTRUs750(e.g., through SI) so that all WTRUs750are aware of the current duty cycle configuration. In addition, a WTRU750that wishes to attach or connect (e.g., following an initial cell search or when exiting IDLE mode) may be able to obtain the duty cycle prior to the attach procedure.

Sub-frames that are defined as blank sub-frames and that are part of the coexistence gap may not be used for transmission by either the eNB760or WTRUs750. If the blank sub-frames were previously DL sub-frames in the original TDD UL/DL frame format, the eNB760may not transmit PDCCH, PDSCH, reference signals, or any SI in these sub-frames. During sub-frames that were previously DL sub-frames and that are defined as sub-frames in the coexistence gap, the WTRUs750may not attempt to decode the PDCCH. The WTRUs750may also not attempt to measure any reference symbols (e.g., CRS), and channel quality indicator (CQI) measurements may not be made for these sub-frames. If the blank sub-frames were previously UL sub-frames in the original TDD UL/DL frame format, the WTRUs750may not transmit on PUCCH, PUSCH, or any SRS or DMRS signals. No WTRU750may transmit during blank sub-frames that were previously UL sub-frames in the original TDD UL/DL frame format.

Sub-frames that are not defined as blank sub-frames may continue to be either DL or UL sub-frames in TDD, and during these sub-frames, the WTRUs750may behave as they otherwise would. A WTRU750that wishes to send a RACH may first determine the coexistence gap pattern being used by the eNB760from received SI. In any sub-frame that was previously defined as a UL sub-frame in the original TDD UL/DL configuration but is a blank sub-frame according to the coexistence gap, a WTRU750may not transmit RACH. RACH may only be transmitted on RACH opportunities, which may fall on a UL sub-frame that is not a blank sub-frame (e.g., not part of a coexistence gap).

DL and UL HARQ rules may depend on the frame formats. In general, UL HARQ timing may not change, and DL HARQ timing for each coexistence gap configuration may be fixed for a TDD UL/DL configuration. All other signaling applicable to normal TDD sub-frames may be applied to non-blank sub-frames (e.g., transmission of reference signals (RSs) in DL sub-frames).

WhileFIG. 7illustrates the inclusion of a coexistence manager770in the LTE system, use of a coexistence manager770is optional but may provide additional guidance to the eNB760for choosing the duty cycle to be used based on knowledge of whether any WiFi systems are using the channels. Regardless of the presence of the coexistence manager770, the eNB760may choose an initial duty cycle to operate on based either on information from the coexistence manager, some initial sensing, or a default coexistence gap. The eNB760may send the duty cycle information as part of the SI.

Any WTRU750that attaches to the eNB may be asked to perform continual sensing to help the eNB760maintain the best duty cycle configuration for the given channel usage conditions. A WTRU750that has been configured to perform sensing may do so during the coexistence gap (e.g., during the blank sub-frames) and may send the results to the eNB760as dictated by the sensing configuration sent by the eNB760. The eNB760may use the sensing information from the WTRUs750, as well as sensing information it may have also collected itself, to determine the best coexistence duty cycle by running the coexistence duty cycle determination algorithm. If the algorithm determines the need to change the duty cycle (e.g., between high, medium, and low), the eNB760may signal this through SI.

The eNB760may signal the duty cycle to the WTRUs750by using or extending one of the existing methods of SI signaling. In an embodiment, a new SIB may be used that includes the required duty cycle. In another embodiment, the duty cycle information may be added to an existing SIB. Sequence Listing 1 below is a sequence listing for the duty cycle being added to the coexistenceGapConfiguration information element (IE) (where the value none represents the absence of any coexistence gaps).

In an embodiment, a WTRU750may be required to read the duty cycle currently used by a cell before it attempts to perform RACH on the cell (e.g., for initial attachment). As a result, the coexistence duty cycle may be transmitted in SIB1, or, alternatively, in a new SIB that a WTRU750may be required to read prior to the attach procedure. A change in duty cycle may, therefore, only take place at the start of an SIB1modification period (e.g., every 80 ms).

Other signaling methods, such as a new MAC control element (CE), may be used to change the duty cycle on a faster time frame if needed. If the new MAC CE is used, it may be sent independently to each WTRU750that is connected to the eNB760in order to obtain a faster change in the duty cycle. Here, however, it may be assumed that the duty cycle configuration is still transmitted in an SIB so that non-connected WTRUs (or WTRUs that may attach later) may not transmit RACH on sub-frames that fall in a coexistence gap.

In an embodiment, the coexistence manager770and a WiFi access point (AP)780may exchange channel usage information in between the periodic sensing and duty cycle change determinations (718). The WiFi AP780may then start operation on the same DSS channel (720), and the coexistence manager770may send change of channel usage information to the eNB760(722).

In an embodiment, sub-frame-based gap pattern designs using blank sub-frames may be backward compatible. In this embodiment, the gap pattern designs may comply with certain hard and soft constraints. The hard constraints may be essential to system operation, and, therefore, gap pattern designs that do not comply with the hard constraints may result in significant impacts to LTE standards and/or system operation. The soft constraints may have less impact on LTE standards and/or system operation as the hard constraints.

Example hard constraints may be related to UL HARQ, primary and secondary synchronization signals (PSS/SSS), MIB and SIB1. An example UL HARQ constraint is that the gap pattern should not result in changes to the UL HARQ timing or to the synchronous property of the UL HARQ. With respect to PSS/SSS constraints, to enable the WTRUs to receive PSS and SSS for synchronization and cell search purposes, sub-frame0and the DwPTS part of sub-frame1may not be configured within a gap. Further, although PSS/SSS may be sent twice in each frame (e.g., in sub-frame0/1and sub-frame5/6), cell ID and timing may be obtained entirely through a single PSS/SSS pair. With respect to MIB constraints, the MIB may be transmitted in sub-frame0, and sub-frame0may not be configured within a gap to enable the WTRUs to monitor the MIB. With respect to SIB1constraints, SIB1may be transmitted in sub-frame5of every other frame, and sub-frame5may not be configured within a gap to enable the WTRUs to monitor SIB1. In other words, sub-frame5may be used as a coexistence gap in every other frame when it does not carry SIB1.

Example soft constraints may be related to DL HARQ timing, paging and UL/DL ratio. An example DL HARQ timing constraint includes maintaining the timing of the DL HARQ consistent with LTE Release 8 and 10 specifications where possible, including timing of UL ACK/NACK feedback. With respect to paging-related constraints, for TDD, paging opportunities may occur in sub-frames0,1,5and6. It is possible that sub-frame5and6may be configured as gaps, in which case mitigation mechanisms may be implemented for WTRUs that map to paging opportunities in sub-frames5and6. With respect to UL/DL ratio-related constraints, the UL/DL ratio resulting after applying the coexistence pattern may be kept comparable to that of the original TDD DL/UL configuration. Further, whenever possible, the coexistence gaps may be defined in consecutive sub-frames. Additionally, to protect the MIB in sub-frame0, as well as the PSS/SSS of sub-frames0and5, from WiFi interference, gaps should not be scheduled for sub-frames9and4whenever possible. Finally, given that a WiFi system may gain access to the channel during the guard period (GP) of a special sub-frame, the GP of a special sub-frame may be in a gap to reduce the interference to the LTE system following a gap when possible.

High, medium and low duty cycles, as described above, may correspond to particular duty cycle ranges that an eNB may choose from. Table 3 below provides example duty cycles ranges that may be defined for each of the high, medium and low duty cycle categories. The example provided in Table 3 assumes that three duty cycles are defined for each TDD UL/DL configuration. However, any number of different duty cycle categories may be defined for eNBs to use and configure. The number of allowable UL/DL configurations may be known a-priori by the WTRU, and, therefore, the eNB may only need to configure the duty cycle to be used at a given time.

TABLE 3Duty Cycle CategoryDuty Cycle RangeHigh~80% to 90%Medium~50% to 60%Low~30% to 40%

In some circumstances, defining low duty cycle coexistence patterns (e.g., in the 30% to 40% duty cycle range) may not always be possible without significant impacts to backward compatibility (e.g., with LTE standards). Accordingly, a low duty cycle coexistence pattern may not always be available for use by the eNB.

In addition to defining specific sub-frames in the TDD UL/DL configuration as a blank sub-frame that may become part of the coexistence gap, a sub-frame based method for creation of coexistence gaps may also include enhancements to the special TDD sub-frame to create coexistence gaps. Since the constraint related to sub-frame1, which is a special sub-frame in all TDD UL/DL configurations, stems from the synchronization symbols transmitted in the DwPTS, the UpPTS and the GP may form part of the coexistence gaps by disabling the use of the UpPTS in the WTRU. In an embodiment, the new special sub-frame may be combined with a gap sub-frame following it to provide a contiguous gap, which may eliminate the need for a separate GP for UL timing advance. This combination may be more bandwidth efficient than using separate coexistence gaps (for coexistence) and GP (for timing advance).

FIG. 8is a diagram800of an example special TDD sub-frame that may be used to create coexistence gaps. The new special TDD sub-frame806is formed from a number of OFDM symbols802. As described above, the DwPTS portion810of the special sub-frame806includes the synchronization symbols, including the OFDM symbol804used for PSS. The remaining OFDM symbols802in the special sub-frame806, along with the following gap sub-frame808, form the coexistence gap812.

In an embodiment, a minimum allowable DwPTS for any special sub-frame configuration may be used, leaving nearly 80% of the special sub-frame for coexistence. In another embodiment, the amount of DwPTS may remain configurable to give the system flexibility on whether DL data should be transmitted within the special sub-frames.

In an embodiment, unenhanced special sub-frames (e.g., an LTE release 8 special sub-frame) may also be used by an eNB when creating sub-frame based coexistence gaps. A WTRU may know whether a special sub-frame is a new special sub-frame (e.g., special sub-frame806) or an unenhanced special sub-frame based on knowledge of the gap pattern sequence attached to each TDD UL/DL configuration and duty cycle configuration. During a new special sub-frame, a WTRU may behave according to LTE release 8 rules during the DwPTS and follow the special sub-frame configuration to determine the length of the DwPTS. The WTRU may not transmit RACH or SRS during the UpPTS of a new special sub-frame such that no WTRU transmissions are to occur during the UpPTS.

Gap patterns for TDD configurations1-5may be designed by starting with the existing frame formats for each TDD UL/DL configuration and selectively changing specific sub-frames to blank sub-frames. The new frame formats for the high, medium and low duty cycle configurations may be created by blanking out an increased number of sub-frames. UL and DL sub-frames that are replaced by blank sub-frames may be selectively chosen for each TDD UL/DL configuration from all sub-frames except sub-frame0as well as sub-frame5in odd system frame number (SFN) frames.

Selection and placement of blank sub-frames may be determined by observing UL HARQ timing. To maintain backward compatibility as described above, blank sub-frames may be selected in such a way so as to not affect the UL HARQ timing. In addition, DL HARQ timing may be maintained similar to LTE release 8 timing, for example, while ensuring that the high, medium and low frame formats are defined with the same DL HARQ timing (e.g., only the number of ACK/NACK bits that need to be sent in each UL sub-frame may be changed for a given TDD UL/DL configuration when the duty cycle is changed).

UL sub-frames may be selected by ensuring that at least one UL HARQ process is maintained (e.g., the pair of one UL sub-frame and the corresponding DL sub-frame where HARQ ACK is sent may not be replaced with blank sub-frames). DL sub-frames may be selected so that they create a gap pattern, which may result in the configuration with the most consecutive blank sub-frames, while adhering to the constraints described above.

In an embodiment, high, medium and low duty cycle sub-frame based coexistence gap patterns may be configured for each of the TDD UL/DL configurations0-6by selecting a UL process that favors consecutive gaps to be defined with consecutive sub-frames and removing that UL process. This may allow for definition of coexistence gaps without modifying UL HARQ timing because only sub-frames associated with certain processes are removed. Selection may be subject to hard constraints on sub-frames0,1and5. Both UL data sub-frames and corresponding DL PHICH sub-frames may be incorporated into the gap, if possible. DL sub-frames with no PHICH may be used as needed when creating the gap.

If DL sub-frames remain without a corresponding UL for ACK in the original timing (e.g., because the UL sub-frame is now part of the coexistence gap), a new DL HARQ timing may be defined (which may optimize the throughput but impact backward compatibility to previous standards) or the DL sub-frame may not be used for eNB transmission (the DL sub-frames may only be used for transmitting SI, RSs, etc.).

Definition of new DL HARQ timing may be consistent across all duty cycles used. Dynamic changes to DL HARQ timing may not be preferable because it avoids potential HARQ issues if signaling for change in duty cycle is not reliably received by every WTRU. Where possible, the new special sub-frame may be used to allow the GP to be part of the coexistence gap. This may result in more efficient usage of the medium by the LTE system when considering UL/DL transitions and also the need to provide coexistence gaps to the WiFi systems.

Special treatment may be given to TDD UL/DL configurations0and6. For example UL HARQ RTT may be kept greater than 10. For another example, such special treatment may include definition of the gap pattern over multiple frames or special consideration by the scheduler.

FIG. 9is a diagram900of UL HARQ and DL HARQ timing relationships and HARQ processes for TDD UL/DL configuration2for LTE Releases 8 and 10. The first row gives the sub-frame number, and the second row indicates whether the associated sub-frame is UL, DL or a special sub-frame (S). In the first row of the UL HARQ section, a shading scheme is used to associate the sub-frames used for UL transmission and the associated sub-frames where ACK/NACK may be sent for the corresponding UL transmission. The following rows show the actual UL process numbers and associated ACKs for these processes. The HARQ process numbers are arbitrary and may be used to differentiate the different processes themselves. In addition, the scheduler may or may not choose to use a given HARQ process, and the HARQ process identifiers, therefore, show the scenario that would be employed in the case of full buffer traffic. The DL HARQ section is the same except that it represents the transmissions in the DL and the associated ACK/NACK in the UL (along with the process numbers). As an example of the information portrayed by the shading scheme, sub-frames4,5,6and8are all DL sub-frames whose data are acknowledged using UL sub-frame2(in the next frame).

FIGS. 10A and 10Bare diagrams1000A and1000B of UL HARQ and DL HARQ timing relationships and HARQ processes for medium and low duty cycle gap patterns, respectively, for TDD UL/DL configuration2. Consistent with the procedure described above, it may be necessary for both the medium and low duty cycle coexistence gap configurations to remove exactly one of the two UL HARQ processes. One of the UL HARQ processes should remain present to allow UL transmission, but one should also be removed to ensure that the UL/DL ratio does not become skewed toward the DL after creating the gap. In an embodiment, process H1(associated with sub-frames3and7) may be removed because doing so may allow for definition of continuous coexistence gaps more easily by configuring sub-frames3and7in a gap. In effect, apart from the need to maintain sub-frame5as a DL sub-frame in every other frame for transmission of SIB1, all sub-frames from3to7, inclusive, may be used to define a coexistence gap.

The second row inFIGS. 10A and 10Bindicates the coexistence gap by specifying a blank gap sub-frame as G and a new special sub-frame as S1. The medium duty cycle coexistence gap may span sub-frames3to7inclusive with sub-frame5being part of the gap during every odd sub-frame (e.g., where SIB1is not transmitted). Eliminating UL sub-frame7may result in a change in the DL HARQ timing to send ACK/NACK for data transmissions in sub-frames9and10. Alternatively, these sub-frames may not be used for DL transmission, and LTE Release 8 and 10 DL HARQ timing may be maintained. The configurations illustrated in FIGS.10A and10B assume the former option and illustrate the new DL HARQ timing that results.

FIG. 10Cis a diagram1000C of UL HARQ and DL HARQ timing relationships and HARQ processes a high duty cycle gap pattern for TDD UL/DL configuration2. For the high duty cycle case, and considering the use of 90% duty cycle as the target, sub-frames6(the special sub-frame) may be selected in order to have the minimum impact on the UL/DL ratio and provide a coexistence gap pattern that may be used when the LTE traffic is reasonably high without impacting the LTE throughput. As a result, the high duty cycle configuration may include a coexistence gap in sub-frames6of each frame.

In the examples illustrated inFIGS. 10A,10B and10C, the DL HARQ timing is also modified despite all UL sub-frames still being available for transmission of DL HARQ ACK/NACK in order to avoid problems that may stem from a change in duty cycle by a system. A system may need to transition between low, medium, and high duty cycle configurations as the detected WiFi traffic on the channel changes. Some of the methods used to signal a change in duty cycle may not guarantee errorless signaling of a duty cycle change. If the HARQ timing (e.g., which ACK/NACK is associated with which DL transmissions) were to change dynamically during operation of the system, there may be a reasonable risk that a WTRU may transmit the HARQ ACK/NACK associated with a given sub-frame at the wrong time following a request to change the duty cycle. It may also mean that a WTRU may need to keep separate DL HARQ tables for each duty cycle, which may increase implementation complexity compared to using a single DL HARQ timing that is consistent across the duty cycles configured. Accordingly, in the illustrated embodiment, the DL HARQ timing is fixed across the different UL/DL configurations (high, medium and low). As a result, definition of the DL HARQ timing for a given UL/DL configuration may be dictated by the low or medium duty cycle. When both the low and medium duty cycles have the same number of available UL sub-frames, the timing may be constrained by either of them; otherwise, the timing may always be constrained by the low duty cycle.

In another embodiment, the system may support only the medium and high duty cycle coexistence gaps and, accordingly, may not configure a low duty cycle coexistence gap. In this case, the DL HARQ timing may be designed for the medium duty cycle, and the DL HARQ timing for the high duty cycle may be designed so as not to change when a change in the duty cycle occurs. This same alternate embodiment may be used for each of the TDD UL/DL configurations1-5.

In another embodiment, the system may support different DL HARQ timings depending on the currently configured duty cycle. In that case, the system may need to change the DL HARQ timing when the duty cycle is changed. This is shown as option2inFIG. 10C.

FIGS. 10D,10E,10F,10G,10H,10I,10J,10K,10L,10M,10N and10O are diagrams1000A,1000B,1000C,1000D,1000E,1000F,1000G,1000H,1000I,1000J,1000K,1000L,1000M,1000N and1000O of UL HARQ and DL HARQ timing relationships and HARQ processes for high, medium and low duty cycle gap patterns for TDD UL/DL configurations1,3,4and5, which were developed using the above-described procedures While specific examples of duty cycle gap patterns are illustrated inFIGS. 10A-10O, other embodiments may be implemented following the same procedure and may easily be derived by someone skilled in the art following such procedures.

FIGS. 11A,11B and11C are diagrams1100A,1100B and1100C of the gap configurations for each of TDD UL/DL configurations1-5for medium, high and low duty cycles, respectively. The coexistence gaps are shaded in the sub-frames. As illustrated inFIGS. 11A,11B and11C, there are similarities in the gap configurations between different TDD UL/DL configurations since many of the constraints used are the same across configurations. For example, the medium duty cycle patterns for configurations2and5, as well as configurations3and4, are the same. The difference in the gap configuration between the odd and even frames may be eliminated by ensuring that sub-frame5does not fall in a gap. However, in this scenario, flexibility with the target duty cycle percentage and WiFi performance may suffer as a result. Further, following the introduction of coexistence gaps, several different TDD UL/DL configurations (especially for the medium and low duty cycles) tend to have the same UL/DL ratio. It may also be possible for an overall design to consolidate these UL/DL configurations and have a system operating in DSS actually support a reduced set of TDD UL/DL configurations.

With respect to TDD UL/DL configurations0and6, these configurations have a UL RTT that is larger than 10 sub-frames. Accordingly, for these configurations, a UL process may occupy a different sub-frame for any given frame, which may make it difficult to remove a UL process as was done for configurations1-5since every UL process will move to a different sub-frame from one frame to the next. In addition, since configurations0and6are balanced or UL heavy configurations, it may be difficult to create a reasonable gap configuration by removing only DL sub-frames.

In one embodiment, the gap pattern for configurations0and6may be defined over several frames instead of over a single frame as was done for configurations1-5. The blank sub-frames used on a particular frame may, therefore, change from one frame to the next in order to follow the HARQ process movement from one frame to the next. As a result, the gap pattern may be defined over a number of frames, which may be equal to the repetition period associated with the placement of the HARQ process numbers to each sub-frame (e.g., 7 frames for configuration0and 6 frames for configuration6). In defining these configurations, a DL sub-frame with no corresponding UL sub-frame to send HARQ ACK in may be used. For this sub-frame, the eNB may either not transmit DL data or may assume NACK on any data transmission sent on this sub-frame.

In another embodiment, the LTE Release 8 and 10 HARQ timing may be changed, and the same coexistence gap pattern may be kept in each frame. Here, a new UL HARQ timing may be defined, which may change on a frame-by-frame basis.

FIGS. 12A,12B and12C are diagrams1200A,1200B and1200C of UL HARQ and DL HARQ timing relationships and HARQ processes for medium, high and low gap patterns, respectively, for TDD UL/DL configuration6. As can be seen from the first two frames shown inFIGS. 12A,12B and12C, the gap pattern is changed on a per-frame basis to avoid collision of the maintained HARQ process retransmissions and the chosen gap pattern. The overall gap pattern that results is, therefore, defined over a period of 6 frames since this is the periodicity of the UL HARQ processes, which is the number of frames required for the HARQ processes to return to their initial sub-frame position.

In addition, since a single ACK/NACK is sent for each UL sub-frame for the DL HARQ, the DL HARQ timing from LTE Releases 8 and 10 may be used by introducing, on average, one DL sub-frame that is un-usable for data transmission (e.g., the DL sub-frame does not fall in the coexistence gap but can not be scheduled by the eNB for data due to the lack of corresponding non-gap UL sub-frame to carry ACK/NACK). For example, inFIG. 12A, sub-frame0of the second frame may not be used for data transmission because of the lack of a corresponding UL sub-frame that may send ACK/NACK. This sub-frame may still, however, be used to transmit SI (e.g., MIB and SIBs other than SIB1).

As an alternative to using a sub-frame that may not be used for data transmission, DL data may be transmitted in sub-frame0(e.g., a DL HARQ process may be used in sub-frame0) but an ACK/NACK may not be sent for this process by the WTRU. Here, the eNB may assume a NACK for this DL transmission and transmit a new redundancy version for the same transport block at the next available opportunity for the DL HARQ process. The WTRU may then use the data received for both redundancy versions (e.g., using soft combining) to decode the transport block before sending the ACK/NACK to the second transmission. The same embodiment may be applied for other cases that may not use sub-frames that may not be used for data transmission (e.g., TDD UL/DL configuration0and other duty cycles for TDD UL/DL configuration6).

FIGS. 13A,13B and13C are diagrams1300A,1300B and1300C of medium, high and low gap patterns, respectively, for TDD UL configuration0. Shaded sub-frames are part of the coexistence gap. A sub-frame with gradual shading is used to denote the new special sub-frame (S1).

For the embodiment where UL HARQ timing is changed in order to create coexistence gaps that do not change from one frame to another, both the UL HARQ RTT and timing may be changed to take into account the presence of the coexistence gaps. In addition, the UL HARQ timing may also be changed dynamically from one duty cycle to another. A coexistence gap for each of the high, medium and low duty cycles, as well as new UL HARQ timing that changes from one frame to the next, may be defined by one of ordinary skill in the art by applying the procedures described herein.

FIGS. 14A,14B and14C are diagrams1400A,1400B and1400C of UL HARQ and DL HARQ timing relationships and HARQ processes for medium, high and low gap patterns, respectively, for TDD UL/DL configuration0. The gap patterns for configuration0may be similar to the gap patterns for configuration6illustrated inFIGS. 12A,12B and12C except that the configuration0repetition pattern is 7 frames instead of 6 and DL HARQ timing remains fixed but with a larger number of sub-frames that are un-usable for data transmission. The corresponding medium, high and low gap patterns for TDD UL configuration0are given in diagrams1500A,1500B and1500C inFIGS. 15A,15B and15C.

A sub-frame based approach to coexistence gaps may also be applicable to new carrier type (NCT). In one embodiment, an eNB may ensure that no DL or UL transmission occurs during the coexistence gap. This may be done, for example, through smart scheduling, limited configuration of RACH occasions, CSI RS, SRS, etc. Corresponding coexistence gap patterns may be defined in such a way that the sub-frames on which the CRS is to be transmitted based on NCT (e.g., every 5 ms) occurs on sub-frames that do not fall on a gap. In another embodiment, procedures defined above for sub-frame based approaches may be applied despite the use of NCT.

For the embodiment of NCT where the eNB ensures that no DL or UL transmission occurs during the coexistence gap, gap patterns defined above may be used and modified such that sub-frames0and5are non-gap sub-frames under the assumption that the CRS is transmitted on the NCT in sub-frames0and5. Here, the eNB may decide to not signal the coexistence gap to the WTRUs, and the WTRUs may continue to decode the PDCCH on gap sub-frames. Alternatively, the eNB may signal the coexistence gap to the WTRUs so that the WTRUs may abstain from decoding PDCCH during gap sub-frames. This may achieve both power savings and also avoid falsely detected PDCCH, which may result in data decoding errors or unexpected WTRU UL transmissions.

For the embodiment of NCT where procedures defined above for sub-frame based approaches are applied despite the use of NCT, the eNB may not need to further restrict, for example, RACH and CSI-RS configurations. The WTRU may simply be aware, for example, that RACH may not be allowed on sub-frames that fall in a gap. The CRS may then be transmitted as defined for NCT (e.g., every 5 ms). If transmission of the CRS would not adversely impact the coexistence gaps, the current definition of NCT with respect to CRS and PSS/SSS may be maintained. Alternatively, the frequency of occurrence of CRS and/or PSS/SSS may be reduced, or transmissions of CRS and PSS/SSS may be avoided when they coincide with a gap. For example, assuming the CRS on the NCT is transmitted in sub-frames0and5, the PSS/SSS and CRS may be transmitted only in sub-frame0in configurations where sub-frame5is a gap sub-frame.

Gap configurations defined using a sub-frame based approach may result in a DL HARQ timing that requires more than four DL sub-frame to be acknowledged with a single UL frame. In an embodiment, the number of sub-frames to be acknowledged may not exceed 9 (e.g., for LTE Release 8 embodiments), which may result in restricting the WTRU to using only bundling and may have some performance impacts. In an embodiment, a new partial temporal bundling may be used that reflects the current association table and allows multiplexing to be used to some extent. In another embodiment, multiple PUCCH resources may be used on a single sub-frame for sending ACK/NACK. In another embodiment, temporal bundling may be used when necessary to account for the additional bits that may need to be sent.

For the embodiment where a new partial temporal bundling may be used, instead of taking the approach where bundling is applied to the entire new association table, ACK/NACK may be sent by applying temporal bundling only partially to the sub-frames according to the LTE Release 8 association table, and the resulting bundled ACK/NACK bits may then be sent using PUCCH format1a/1bor1bwith channel selection, as applicable. As a result, the transmission of ACK/NACK in a UL sub-frame where more than four ACK/NACK bits may need to be transmitted may include performing bundling across sets of up to four of the ACK/NACK bits and transmitting the ACK/NACK bits using multiplexing (e.g., format1aor format1bwith channel selection). This may avoid bundling across a window of an entire frame, which may be required if LTE Release 8 and 10 rules were applied to the DL HARQ timings derived for the configurations with coexistence gaps. This may also improve the performance of the system.

Although it is expected that the PHY may require some changes compared to LTE Release 8, the group of bundled ACK/NACK bits may be defined such that they correspond to the LTE Release 8 association table and, therefore, minimize the change to the current implementation of the standards. In particular, a WTRU may already have the capability to perform the temporal bundling required to perform bundling across sets of up to four of the ACK/NACK bits and across the same sub-frames.

Table 4 below provides the LTE Release 8 and coexistence gap association set for low, medium and high duty cycles for configuration4.

In Table 4, the association set indices 12, 8, 7 and 11 for the LTE Release 8 (in the second row of the table) and the association set indices 9, 12 and 13 for the coexistence gap association set (in rows 3,4, and 5 of the table) correspond to the same DL sub-frames. The one sub-frame offset in the indices are due to the fact that the ACK/NACK for these sub-frames is now being sent one sub-frame later.

For LTE Release 8, the WTRU may be configured to perform at least one of sending the four ACK/NACK bits in sub-frame2and sub-frame3using multiplexing and format1bwith channel selection (spatial bundling may be used across transport blocks for a single TTI), bundling each of the four ACK/NACK bits in each sub-frame to create a single bit in each of the two sub-frames and sending that bit using either format1a(single transport block) or format1b(TX diversity), or using multiplexing and format3to send the ACK/NACK bits if multiple cells are configured.

The WTRU may first perform bundling across the indices corresponding to the sub-frames that may have been bundled in LTE Release 8 had the WTRU been configured with bundling. For the high duty cycle (row 3 of the table), ACK/NACK for indices 4,5,7,8 may be bundled into a single ACK/NACK, and sub-frames9,12, and13may be bundled into a single ACK/NACK. The two ACK/NACK bits may then be sent using format1bwith channel selection using LTE Release 8 rules (these rules support up to 4 bits). Similarly, in the low duty cycle (row 5 of the table), indices 4 and 8 may be bundled to create a single ACK/NACK bit, and index 13 may be considered as is without bundling. The two ACK/NACK bits may be sent using format1bwith channel selection.

Format3may also be used with the same scheme. Since the total number of bits being sent in each UL sub-frame is less than 4, the following may be used for format3. If TX diversity is being used, the WTRU may not be required to perform spatial bundling, and separate ACK bits may be sent for each transport block where a maximum number of cells are being transmitted. Further, the number of bits used for format3may be halved by creating a new format and requiring spatial bundling to be used if the number of ACK/NACK bits exceeds 10.

For the embodiment where multiple PUCCH resources are used on a single sub-frame for sending ACK/NACK, the number of resource blocks used by PUCCH may be configured semi-statically by the eNB. A PUCCH resource to be used by a WTRU may then be assigned using either the CCE index of the grant that was used or through tables that select one of multiple PUCCH resources configured by higher layers for use by the WTRU. In order to use multiplexing, the WTRU may need to send more than the maximum number of bits supported by each PUCCH format (e.g., format1band format3).

Since changing the coding for a specific PUCCH format (e.g., allowing format1bto send more than two bits) may have a significant impact on both HW and standards, a less drastic mechanism may be to define additional PUCCH resources to be used by the WTRU. For instance, the WTRU in LTE Release 8 may be assigned two separate PUCCH resources in order to transmit from different antenna ports (resources p and p+1 are assigned). In a similar fashion, the WTRU may be assigned additional resources to be used for sending multiple PUCCH resources per sub-frame. In the example given for solution 1, a similar approach may be taken to send the ACK/NACKs associated with the same set of DL sub-frames as would be used for LTE Release 8. For example, for UL/DL configuration4and high duty cycle, ACK/NACK for indices 9, 12, and 13 may be sent using one PUCCH resource (e.g., 1b with channel selection) and ACK/NACK for indices 4, 5, 7 and 8 may be sent using a different PUCCH resource.

For the embodiment where temporal bundling may be used when necessary to account for the additional bits that may need to be sent, bundling may be used to solve the increase in the number of ACK bits to be sent. As a result, there may be no changes made with respect to LTE Release 8 except for placing restrictions on using bundling only in certain configurations (e.g., rather than allowing the eNB to configure either of the two approaches). The HW/SW impacts may, therefore, be restricted to redefining procedures for low, medium, and high duty cycles.

For a single serving cell using PUCCH format1b, bundling may be used more often with the new gap configurations than may be used in LTE Releases 8 and 10. For instance, an LTE Release 8 or 10 LTE served by single cell may not use spatial bundling (except in configuration5). With gap configurations defined herein, spatial bundling may be required in UL/DL configuration1(for medium and high duty cycles), UL/DL configuration2(for medium and high duty cycles), UL/DL configuration3(for high duty cycle) and UL/DL configuration4(for medium and high duty cycles).

In another embodiment, coexistence gaps may be defined as a transparent frame (frame-based approach) or an integer number of transparent frames. For example, a full LTE frame (e.g., 10 ms) may be defined as a blank frame with no transmissions in either the UL or DL during the blank frame. Since the coexistence gap in this embodiment is defined on an entire frame, the resulting gap patterns may be independent of the TDD UL/DL configuration and may have a minimal impact on HARQ and other transmission timing rules.

Because the TDD UL/DL configuration may be repeated in each frame, in a frame-based approach, a gap that spans over an entire frame or an integer number of frames may make it easier to adapt the timing and rules of the TDD HARQ in such a manner that the HARQ timing may be delayed by exactly the number of frames in the coexistence gap. As a result, in an embodiment, the existing HARQ rules (e.g., LTE Release 8 HARQ rules) may be used for the timing of grants, transmissions and acknowledgements, with the added condition that counting of sub-frames associated with this timing may be frozen on frames that are part of the coexistence gap.

FIG. 16Ais a diagram of a high duty cycle coexistence gap pattern1600A for a frame-based approach to defining coexistence gap patterns. The illustrated high duty cycle coexistence gap pattern1600A includes a number of consecutive frames, each of which is assigned an SFN1-31. At least one of the frames may be a transparent frame. In the illustrated example, frames with SFNs7,15,23and31have been designated as the transparent frames.

FIG. 16Bis a diagram of a medium duty cycle coexistence gap pattern1600B for a frame-based approach to defining coexistence gap patterns. The illustrated high duty cycle coexistence gap pattern1600B includes a number of consecutive frames, each of which is assigned an SFN1-31. At least one of the frames may be transparent frames. In the illustrated example, frames with SFNs1,3,5,7,9,11,13,15,17,19,21,23,25,27,29and31have been designated as the transparent frames.

Low duty cycle patterns may not be included in a frame-based approach due to a high RTT for both the DL and UL traffic that may result if more than one consecutive frame would be unusable by an LTE system due to a coexistence gap. Instead, in an embodiment, a medium duty cycle gap configuration may be used even under low LTE traffic.

For each coexistence gap pattern, the gap may be achieved by introducing a transparent frame. Although this frame may exist in the timing of the actual system (e.g., it occupies 10 ms of time like a normal frame), a transparent frame may not be usable by the system and, therefore, may not exist from the point of view of transmission and sub-frame timing.

In order to minimize the impact on SI timing, a transparent frame may still be assigned an SFN. Accordingly, the schedules for MIB, SIB1and SI messages (as defined in LTE Release 8, for example) may remain unchanged. In other words, SI may not be received less frequently if it is transmitted with the same period as in LTE Release 8.

Another alternative to defining a transparent frame may be to not assign a transparent frame an SFN (e.g., to freeze the SFN counter during the transparent frame). However, such an embodiment may have more significant impacts on the overall timing of the system, as the effective duration of a set of sub-frames with such a system may now change compared to LTE Release 8 and may also change based on the configured duty cycle. For example, under an implementation where a transparent sub-frame is not assigned an SFN, the period of time from SFN0to SFN10may last 110 ms when the system is configured with the high duty cycle and 200 ms when the system is configured with the medium duty cycle. In addition, SFN alignment across multiple cells when doing carrier aggregation may not be possible. As a result, it may be preferable that the transparent frame be allocated an SFN.

Gap patterns may be defined by introducing transparent frames in such a way that they minimize the impact on SI. Since SI messages are transmitted within a configurable window that may be as large as 40 ms, the concern may only be to ensure transmission of MIB and SIB1using the schedule currently defined.

Since an MIB may be transmitted every 4 frames and repeated each frame within this time (where each repetition may be independently decoded), the use of transparent frames may impact transmission of the MIB. The same 4-frame MIB period may be maintained, but repetitions that fall in a transparent frame may not be made by the system. As a result, some MIB repetitions may not be sent due to the presence of coexistence gaps. In this case, it may be preferred to prioritize the first transmission of the MIB in order to increase the average speed with which a WTRU may be able to acquire new MIB information. As a result, SFN numbers that are divisible by 4 may not fall in a gap. Similarly, in order to allow transmission of SIB1, all frames with an even SFN may not be defined as a transparent frame.

A WTRU may execute a method of coexistence among WTRUs operating in the same spectrum such as the example method illustrated and described with respect toFIG. 5Babove when transparent frames are configured. In an embodiment, the eNB may signal the duty cycle using SI. During a transparent frame, a WTRU may not try to decode the PDCCH or reference symbols and may not transmit in the UL. In addition, the eNB may not transmit PHY layer signals during a transparent frame. In an embodiment, the eNB may transmit MIB with the same repetition cycle (e.g., 40 ms) as described in LTE Release 8. However, the MIB may not be transmitted during a transparent frame. Accordingly, fewer than 4 MIB repetitions may be transmitted during the repetition cycle. In an embodiment, the eNB may ensure that SIB1does not collide with a transparent frame. As a result, SIB1may be transmitted as in LTE Release 8.

A WTRU may follow HARQ timing rules and measurement timing rules defined in LTE Release 8 except that the timing may be frozen during the transparent frame. In other words, sub-frames in a transparent frame may not be counted when determining the time (in sub-frames) elapsed between two different events related to the WTRU procedures. The freezing of the sub-frame counter is described in more detail below. For example, sub-frames that are part of a transparent TDD frame may not be counted when calculating one of a delay between a transmission and ACK/NACK of the transmission or a delay between an ACK/NACK and a retransmission in a HARQ. The sub-frame counter may also be frozen with respect to calculating delays for other LTE operations (e.g., channel quality reporting operations, power control operations and RACH operations) such that sub-frames that are part of a transparent TDD frame are not counted when calculating delays for such operations.

SI in LTE includes the MIB and SIB1, which may be in fixed locations, and higher order SIBs, whose locations may be specified by the timing sent in SIB1and may be detected using normal PDCCH grants in the common search space. Due to the absence of any DL data or signaling in the transparent frame, SI may not be transmitted on transparent frames. The timing of the coexistence gaps given in LTE Release 8 may guarantee that SIB1will be scheduled in non-transparent frames. In addition, SI messages that include higher order SIBs (e.g., SIB2and above) may be scheduled by the eNB in such a way that the SI window may not fall on transparent frames or that each SI window may always include at least one non-transparent frame. The SIBs may then be scheduled in the DL sub-frames of non-transparent frames only. As a result, from the WTRU perspective, the WTRU may not decode any SIBs in a transparent frame.

Because the MIB in LTE Release 8 is transmitted in every frame (with a four frame repetition period), the eNB in the coexistence gap design may be altered to not transmit MIB on a transparent frame. In an embodiment, a WTRU may decode the MIB by reading the MIB from each frame that is not a transparent frame. A new transmission of MIB may still be assumed at values of the SFN that satisfy SFN mod 4=0 (same as LTE Release 8). The number of repetitions of the MIB that the WTRU may expect may depend on the configured duty cycle, since transparent frames may not include any MIB transmissions.

FIG. 17Ais a diagram1700A of MIB transmissions for a high duty cycle. In the example illustrated inFIG. 17A, MIB is transmitted on every frame other than transparent frames1702,1704,1706and1708. For the high duty cycle, the WTRU may receive four MIB transmissions or repetitions that start on (SFN/2) mod 4−0, such as MIB repetition1710. It may receive three MIB transmissions for MIB repetitions that start on any other SFN that does not satisfy (SFN/2) mod 4=0, such as MIB repetition1712. In an alternate high duty cycle configuration (not shown), the WTRU may always receive three MIB repetitions.

FIG. 17Bis a diagram1700B of MIB transmissions for a medium duty cycle. In the example illustrated inFIG. 17B, MIB is transmitted on every frame other than transparent frames1712,1714,1716,1718,1720,1722,1724,1726,1728,1730,1732,1734,1736,1738,1740and1742. For the medium duty cycle configuration, the WTRU may receive two MIB transmissions every MIB repetition period, such as MIB repetition1744.

In another embodiment, the eNB may transmit MIB only in the even sub-frames, which may yield an identical MIB schedule, regardless of the duty cycle being used.

Since operation on small cells may be assumed, reception of two repetitions of the MIB may not result in a significant degradation of the PBCH performance. As a result, no specific robustness enhancements to the MIB may be required to offset the shorter number of repetitions that the WTRU may take advantage of. Further, in addition to some aspects related to timing, the SI in the SIBs may need to change slightly to allow for the ability to change the duty cycle dynamically as described herein.

The change in duty cycle (e.g., from low to medium) may be affected by the surrounding WiFi systems as well as the relative LTE traffic currently being handled. As a result, the system may want to change its duty cycle (e.g., from high to medium and vice versa) fairly often to manage the change in traffic pattern. As a result, it may be desirable to avoid the need to read the entire SI when a change in duty cycle occurs. In addition, it may be desirable to send the change in duty cycle over SI whose timing is not changed from the coexistence gap so that the behavior of a WTRU is more predictable when a change in the duty cycle occurs. For these reasons, the proposed design may be to send the current duty cycle configuration as an information element in SIB1.

The WTRU may read SIB1at every repetition period (e.g., 80 ms) in order to check the value of the systemInfoValueTag. In addition, the WTRU may determine the current duty cycle being applied by the small cell eNB by reading the duty cycle IE that is to be added to SIB1. To enable operation in the case of spectrum where a coexistence gap is not required, the duty cycle IE may be added as an optional IE in SIB1, or a special value of the duty cycle may be used to indicate the absence of coexistence gaps. On a condition that the duty cycle indicates that there is no duty cycle information, the WTRU may operate under normal LTE rules (e.g., decode MIB/SIBs as in a standard such as LTE Release 8 and assume no transparent frames are present). On a condition that the configured duty cycle indicates a specific value of the duty cycle information, the WTRU may respect that specific duty cycle and apply procedures described above during transparent frames.

FIG. 18is a diagram1800of timing associated with a change in duty cycle as signaled by a change in the duty cycle IE in SIB1. Four SIB1repetition periods1822,1824,1826and1828are illustrated inFIG. 18. Four SIBs1830,1832,1834and1836indicating a medium duty cycle are transmitted in repetition period1822, four SIBs1838,1840,1842and1844indicating a high duty cycle are transmitted in repetition period1824, four SIBs1846,1848,1850and1852indicating a high duty cycle are transmitted in repetition period1826, and four SIBs1854,1856,1858and1860indicating a high duty cycle are transmitted in repetition period1828. In an embodiment, the duty cycle IE may be changed by the eNB at the boundary of an SIB1repetition period. A WTRU may detect a change in the duty cycle IE within the SIB1838during the SIB1repetition period1824. When the WTRU detects a change in the duty cycle IE within an SIB1repetition period, it may assume that the eNB will start to use the new duty cycle at the start of the next SIB1repetition1826. This may avoid any potential for a change in duty cycle that is not properly decoded by all WTRUs, resulting in possible transmission by a WTRU in the UL during a transparent frame.

In an embodiment, the WTRU may read the duty cycle field in SIB1at the boundary of the SIB1repetition period. If necessary, this may be read from the other repetitions of SIB1within the SIB1repetition period. If a change in the currently assumed duty cycle is detected by the WTRU (e.g., the value of the duty cycle changes from medium to high), the WTRU may assume that the agreed on pattern of transparent frames will move to high duty cycle pattern at the beginning of the next SIB1repetition period (1826inFIG. 18).

In another embodiment, the duty cycle may be signaled within the MIB by modifying the MIB to include this additional field. Alternatively, SIB2may be used to carry the duty cycle SI and find out about a change in the duty cycle from the eNB.

In order to modify the UL and DL HARQ timing in the presence of transparent frames, in an embodiment, sub-frames that are part of a transparent frame may not be counted when calculating HARQ delays. Accordingly, when counting sub-frames in order to determine, for example, the sub-frame that will carry ACK for a particular transmission, all sub-frames that fall in a transparent frame may not be counted. The HARQ timing counters in the eNB and the WTRU may be frozen during the transparent frames. In effect, the HARQ timing counters may be frozen at the start of a coexistence gap and for the duration of the coexistence gap. The timers may then be restarted at the end of the gaps and may resume at the values they were prior to being frozen. Effectively, this may be considered as introducing a TDM aspect into the LTE system, whereby sub-frames associated with a coexistence gap do not belong to the LTE system (and may, therefore, not be counted for timing of PHY and MAC operations). The same mechanism may also be used for other operations in LTE (such as CQI measurements) that are defined in terms of over-the-air time in order to account for the presence of transparent frames with minimal impact to the rules defining LTE Release 8 and 10 procedures.

Table 5 below is a DL association set index for TDD UL/DL configuration 1. Based on Table 5, for a given sub-frame n corresponding to a UL sub-frame carrying ACK/NACK for DL HARQ, the value k given in Table 5 corresponds to the sub-frames n-k that are the DL transmissions ACK/NACK'd in sub-frame n. When computing n-k, all sub-frames that occur before n that fall in a transparent frame may be ignored.

FIG. 19is a diagram1900of an example ACK/NACK procedure for TDD UL/DL configuration1. In the example illustrated inFIG. 19, DL transmissions in sub-frames1908and1910in frame1902may be ACK/NACK'd using sub-frame1912in frame1906(instead of frame1904). In other words, an ACK/NACK message may be transmitted in a next non-transparent TDD frame following a frame in which a transmission is made or make a retransmission in a next non-transparent TDD frame following a frame in which the corresponding ACK/NACK was received. Since the actual sub-frame relationship between transmission and acknowledgments has not changed when the entire transparent frame is ignored, the HARQ timing rules may not be impacted except for the inclusion of a frame offset when two related sub-frames are separated by a transparent frame that needs to serve as a gap. For this reason, the HARQ timing rules specified in LTE Release 8 remain effectively unchanged, and none of the signaling of ACK/NACK or grant/allocations needs to be changed.

In an embodiment, the HARQ counter (which counts the number of sub-frames between transmissions and expected ACK/NACKs) may be frozen when sub-frames that are part of a transparent frame are being traversed. When the transparent frame has been traversed, the HARQ sub-frame counter is then re-enabled to continue the counting associated with the HARQ procedure. The same approach may be used to handle the timing of other procedures in LTE, such as RACH opportunities. A transparent frame may not include any RACH resources, and the WTRU may only be allowed to use the RACH resources defined on non-transparent frames. As a result, for any procedures whose timing is defined at the sub-frame level, these procedures may be modified to account for the fact that the sub-frame counter is effectively frozen during a transparent frame. On the other hand, for procedures defined at the frame level, these procedures may simply not be applied on transparent frames.

In an embedment, the definition of transparent frames may require that a WTRU not make any UL transmissions during a transparent frame, which may include any potential transmission of RACH by a WTRU. As a result, the WTRU procedures may need to be changed to ensure that the WTRU does not send a RACH preamble during a transparent frame. Instead, it may wait for the next PRACH resource after the transparent frame to send its preamble since it has knowledge of the location of transparent frames via SIB1. In LTE Release 10, if a WTRU fails to receive a preamble response, it waits a random time between 0 and a configured back-off time and then re-transmits during the next available PRACH occasion. Accordingly, in an embodiment, the WTRU may pause its random access back-off timer during a transparent frame, since, unaltered, the WTRU may attempt to send each preamble attempt during a transparent frame.

After the preamble, the eNB may schedule the preamble response over the PDCCH and use normal PUSCH resources thereafter. If the preamble response falls on a transparent frame, the eNB may schedule the response in the next frame since it cannot transmit during a transparent frame. The WTRU may wait for the next frame to listen for the response to arrive since it has knowledge of the location of the transparent frame via SIB1.

Use of coexistence gaps may have an impact on paging. For frame-based methods, there may be an impact on the calculation for the paging frame, which could occur on a transparent frame. If an eNB is to page a WTRU during a specific sub-frame number in a transparent frame, it may instead wait until the next active frame and use the same specific sub-frame number. Similarly, from the perspective of a WTRU that is to receive a page during a specific sub-frame number in a transparent frame, it may wait until the next frame and listen to the page during the same specific sub-frame number. Since smaller cells may have on average fewer WTRUs per cell, limited paging resource may suffice.

In an embodiment, the way the WTRU determines the paging frame (PF) may be changed. For example, in LTE Release 10, a WTRU uses equation (3) to calculate PF:
SFN modT=(TdivN)*(UE_ID modN), whereNis set in the SIBs.  (3)
In the embodiment for calculating the PF when transparent frames are used, the WTRU may calculate PF as follows. If “SFN mod T” lands on a transparent frame (which may be known from the SIBs), SFN mod T may be incremented by one frame (or looped back to 0) such that it lands in a non-transparent frame. In this embodiment, the WTRU may determine the PF to occur in a frame immediately following the transparent frame.

In at least some of the embodiments described above, application of LTE Release 10 was assumed, and, therefore, the presence of regular CRS and CSI-RS was also assumed (regardless of whether WTRUs were scheduled or not). For these embodiments, no transmission of CRS or CSI-RS may be made by the eNB during the CRS, and, therefore, the WTRU may not expect or measure these reference symbols during the transparent frame. For NCT embodiments, however, CRS on the NCT may only be transmitted every 5 sub-frames. In addition, during sub-frames in which CRS is transmitted, the transmission may occur only in the six center resource blocks (rather than, for example, the entire bandwidth).

The transparent frame definition may be changed when it is applied to an NCT. Due to the reduced CRS overhead allowed by the NCT, the CRS may be transmitted during the transparent frame in the locations dictated by the NCT (e.g., every 5 sub-frames and, in an embodiment, on the center 6 resource blocks rather than the entire bandwidth) rather than blanked out during the entire transparent frame. The CSI-RS, however, may follow the same rules as the HARQ (e.g., its transmission period may be frozen during the transparent frame so that sub-frames in the transparent frame may not count as time expired in determining the period of the CSI-RS). Alternatively, the eNB may schedule the period of the CSI-RS so that it does not coincide with the occurrence of the transparent frame.

In order to maintain the definition of the NCT with respect to transmission of reference symbols and synchronization symbols, the transparent frame definition in the context of NCT may be defined without any UL or DL transmission, with the following exceptions. A transparent frame may still include the PSS/SSS at the locations agreed on by the final definition of NCT. Further, a transparent frame may still include port0CRS1out of every 5 sub-frames. In this embodiment, sub-frames0and5may be assumed for the sub-frames in the transparent frame where CRS port0is to be transmitted. This may not preclude embodiments where sub-frames other than0and5are chosen by the NCT definition as the sub-frames that include the CRS.

As a result, the WTRU and eNB procedures for the transparent frame in the context of NCT may be slightly modified with respect to LTE Release 10. For example, the PSS/SSS may not be transmitted in all frames, including the transparent frames. For another example, the CRS may be transmitted the same way in all frames (transparent and non-transparent) and may follow the definition of the NCT CRS symbol transmissions, which may only include CRS port0transmissions sent in sub-frames0and5of every frame. The rules for CSI-RS for the transparent frames in this embodiment may be the same as those defined for the transparent frame in the context of LTE Release 10 (e.g., the WTRU decodes CSI-RS according to the schedule given by the eNB and does not assume CSI-RS during a transparent frame).

In an embodiment, when the WTRU performs an initial cell search, it may search for PSS/SSS on the channel as normal. However, WTRU synchronization and channel estimation procedures may take into account the transparent frames by operating according to the following rules. When the WTRU is connected, it may maintain synchronization using only the PSS/SSS and the CRS on all frames (both transparent and non-transparent). The rules for SRS for the transparent frames may be the same as those defined for the transparent frame in the context of LTE Release 10.

In another embodiment, the eNB may decide to not transmit the CRS at all during the transparent frame on the NCT. In this embodiment, the WTRU's behavior may need to change compared to LTE Release 12 in the context of using the CRS for synchronization. In other words, the WTRU may not perform synchronization (e.g., it may not assume the presence of the CRS) on the transparent frame, and all synchronization may be performed during non-transparent frames only.

In the context of small cells, intra and inter-frequency measurements may be performed to trigger handovers in one of a number of different embodiments. In one embodiment, a WTRU may perform intra-frequency measurements on a small cell that is to measure and potentially trigger handover to another small cell. In another embodiment, a WTRU may perform inter-frequency measurements by a WTRU on a small cell that is to measure and potentially trigger handover to another small cell. In another embodiment, a WTRU may perform inter-frequency measurements on a macro cell that is to measure and potentially trigger handover to small cells. In another embodiment, a WTRU may perform inter-frequency measurements on a small cell that is meant to measure and potentially trigger handover to a macro cell.

In each of these embodiments, the WTRU measurements should consider the potential presence of transparent frames that serve as coexistence gaps, and the restrictions on how these measurements are performed may depend on which of the above embodiments are being considered. As described above, it may be assumed that small cells managed by a single macro cell will be synchronized (in frame timing and SFN number). However, different small cells may have different duty cycles configured in each cell since this may depend on traffic and proximity to a WiFi system.

For intra-frequency measurements, a WTRU should be aware of the coexistence gap duty cycle of a neighboring small cell before it attempts the measurements in order to avoid measurements on a transparent frame where there are no reference symbols on which to perform the measurements. To avoid using a worst case duty cycle assumption (e.g., assuming that the neighboring small cell is using a 50% duty cycle and measuring only on even SFN numbers), a WTRU may be required to read SIB1of the neighbor cell prior to doing intra-frequency measurements. Thus, a WTRU may first receive the duty cycle configuration of the neighbor cell, and, with the assumption of synchronized operation for small cells under control of the same macro cell, a WTRU may be able to perform measurements on the neighbor small cell and avoid the transparent frames configured in the small cell. Accordingly, intra-frequency measurement performance may be optimized with respect to the available amount of potential measurement time (e.g., non-gap time) on the neighbor cell.

In an embodiment, a WTRU may make intra-frequency measurements as follows. A small cell eNB may configure a WTRU to perform intra-frequency measurements. In an embodiment, the eNB may choose only even SFNs to do measurements. If the neighbor has a higher duty cycle, the WTRU may perform intra-frequency measurements during a transparent frame where the neighbor may also be transmitting.

A WTRU may perform intra-frequency measurement a follows. The WTRU may find and decode PSS/SSS of a small cell on the same frequency to determine the cell ID of the neighbor small cell and read SIB1on the neighbor small cell whose cell ID was identified in order to determine the coexistence gap duty cycle/pattern being used on the small cell. The WTRU may perform measurements on the small cell using reference symbols on frames that are not transparent frames (e.g., based on the duty cycle configuration obtained from SIB1). In an embodiment, this may be done periodically, in which case SIB1may be read prior to each measurement. The WTRU may not measure any part of the target eNB that coincides with a transparent frame and may report the intra-frequency measurements of neighboring small cells detected.

FIG. 20Ais a diagram2000A illustrating times available for WTRUs associated with an eNB2002with a high duty cycle and an eNB2004with a medium cycle to make intra-frequency measurements. In the example illustrated inFIG. 20A, WTRUs associated with both the eNBs2002and2004may perform intra-frequency measurements during frames corresponding to SFNs0,2,4,6,8,10,12,14and16. The best time for WTRUs associated with eNB2004is during frames corresponding to SFNs1,3,5,9,11,13and17. During frames corresponding to SFNs7and15, no intra-frequency measurements may be made.

Inter-frequency measurements may require a WTRU to tune to a different frequency and may, therefore, be enabled through the use of measurement occasions in LTE, which span 6 ms and may be configured every 40 ms or 80 ms. Since each measurement occasion may be used by the WTRU to measure PSS/SSS and reference symbols of cells on a different frequency, and may be limited to 6 ms, a WTRU may not use these measurement occasions to read SIB1and to find the coexistence gap configuration when the inter-frequency measurements are being performed to measure small cells. For inter-frequency measurements performed to measure the macro-cell, there may be no issue as there are may be no transparent frames configured for the macro-cell.

In order to avoid having the WTRU perform inter-frequency measurements at a time when a neighbor small cell has a coexistence gap configured, an assumption of synchronized operation, in addition to the known potential location of coexistence gaps, may used. Based on these assumptions, measurement occasions may be restricted by the eNB of a small cell to occur on frames that may not fall in a coexistence gap (e.g., cannot be a transparent frame). Given the allowable timing of coexistence gaps described above, coexistence gaps may occur in the worst case every other frame (e.g., the 50% duty cycle case). In that scenario, every odd-numbered SFN in a small cell may represent a transparent frame and, therefore, may represent a time period where WTRUs cannot perform inter-frequency measurements on that cell. Since a serving small cell for a WTRU and a neighbor (e.g., inter-frequency) small cell may frame and SFN synchronized, the serving small cell eNB may schedule measurement occasions only on even SFN frame numbers (e.g., since the period of the measurement occasions is 40 ms and 80 ms, all measurement occasions for a given configuration may land on an even SFN). The measurement occasion may be scheduled at different times within the even SFN frames on a per WTRU basis, as long as the entire measurement occasion remains within the even SFN frame. This may guarantee that the neighbor inter-frequency small cell transmits reference symbols during the entire measurement occasion.

FIG. 20Bis a diagram2000B illustrating times available for three different WTRUs2010,2012and2014associated with small cell2018having a high duty cycle with a neighboring small cell2016having a medium duty cycle. In the example illustrated inFIG. 20B, each of WTRUs2010,2012and2014has different measurement occasion timing within SFN8.

In an embodiment, a macro eNB may configure a WTRU camped on a macro cell to perform inter-frequency measurements on the small cells. In order to do this, the macro cell may configure measurement occasions. Since the macro cell may be aware of the duty cycle configured on each of the small cells (e.g., the small cells communicate to the macro cell each time a change in duty cycle is decided), the macro cell may configure the measurement occasions based on the coexistence gap configuration of the one or more small cells to be measured. For example, if a cluster of small cells is configured without coexistence gaps (e.g., operation with no gaps), the macro eNB may have the flexibility of configuring measurement occasions on any SFN.

In another embodiment, the small cell may configure inter-frequency measurements to enable measurement of the macro cell. Since the macro cell has no limitation on the location of these measurement occasions (e.g., there are no gaps on the macro cell), the small cell may configure the measurement occasions in any frame. This may include the transparent frame or the coexistence gap occurring on the serving cell of the small cell.

Since measurement occasions may take time away from normal transmissions, it may be beneficial for the small cell to configure inter-frequency measurements to measure the macro cell during a transparent frame since the small cell eNB may not transmit or control at that time. As a result, the configured measurement occasion may not take any usable data transmission time away from the small cell but rather may force the WTRU to perform inter-frequency measurements during the time when it is already silent and not transmitting on the small cell frequency.

FIG. 20Cis a diagram2000C illustrating best times for a small cell eNB2032with a medium duty cycle and a neighboring macro eNB2030to perform inter-frequency measurements. In the illustrated embodiment, the best times for WTRUs associated with the small cell eNB2032to perform inter-frequency measurements is during frames having SFNs1,3,5,7,9,11,13,15and17.

In an embodiment, all small cells under the control of a macro cell may be frame synchronized. In some embodiments, this may be required to ensure that coexistence gaps left by neighboring small cells allow WiFi coexistence at the intersection of the coverage of the two cells.

In other embodiments, neighboring small cells in a coverage scenario may be managed by different macro cells. In these embodiments, there is no guarantee that the two macro cells will have the same frame timing and SFN synchronization. As a result, the two underlying small cells may not have the same timing of transparent frames. Here, inter-frequency measurements made by a WTRU of a neighbor small cell belonging to a different macro cell may or may not allow a WTRU to properly measure the neighbor small cell (e.g., depending on the relative timing of transparent frames in the neighbor small cell and measurement occasions scheduled by the serving small cell). Since this handover scenario may not occur (e.g., a serving small cell may prefer a handover to the macro cell prior to allowing a handover to a small cell managed by a different macro cell), the ability to correctly measure the neighbor small cell and the quality of the measurements may not be critical in this case.

In embodiments described above, gap patterns are pre-defined and known a priori by the WTRU and eNB. Since the gap pattern may repeat and may depend on the duty cycle configured by the eNB, the eNB may need to signal the duty cycle to inform WTRUs of, for example, which pattern of blank sub-frames or transparent frames to use at a given time.

In other embodiments, the eNB scheduler may dynamically determine the need for a regular transmission or gap time based on its traffic and may dynamically notify the WTRU of this. Rather than coordinated patterns, the eNB scheduler may schedule a period of gap time (a few sub-frames, for example) when this may be possible based on the traffic load of the scheduler.

In order to allow coexistence for dynamically determined gap schedules, the eNB may broadcast the use of a set of ICIC frames or sub-frames. These ICIC frames or sub-frames2102may also be inherent in the communication (e.g., for an LTE Release 12 new carrier type where there are known sub-frames that carry no CRS). Regardless of the method used to communicate the ICIC frames or sub-frames, the eNB may be constrained to scheduling coexistence gaps during only these ICIC frames or sub-frames so that the coexistence gaps themselves (although scheduled dynamically) may become a subset of the set of ICIC sub-frames. The ICIC sub-frames may themselves be periodic and repeated patterns, but the coexistence gaps themselves may not be.

FIG. 21is a diagram2100illustrating a method of coexistence for a dynamically determined gap schedule. In the example illustrated inFIG. 21, an eNB broadcasts the use of a set of ICIC frames or sub-frames2102. At times2106,2108and2110selected dynamically by the eNB during the set of ICIC frames, the eNB may signal a coexistence gap and the length of that gap to the WTRUs. The WTRUs and eNB may cease transmitting during the signaled gap periods. In the example illustrated inFIG. 21, the eNB signals coexistence gap2104and its corresponding length at2106, signals coexistence gap2112and its corresponding length at2108and signals coexistence gap2114and its corresponding length at2110.

In an embodiment, the eNB may broadcast the usage of the ICIC sub-frames so that they are known to all WTRUs. For example, SI may be modified or added to broadcast the presence of the ICIC sub-frames. In another embodiment, the eNB may broadcast the presence of ICIC sub-frames, but the pattern of occurrence of the ICIC sub-frames may be known apriori by the eNB and WTRUs. In this embodiment, the presence of the ICIC sub-frames may be made more static.

In an embodiment, the eNB scheduler may determine, based on the traffic scenario and scheduling algorithm, the best opportunity to schedule a coexistence gap and a reasonable length for the gap. Dependency of HARQ processes may also affect the timing of the coexistence gap patterns scheduled by the eNB. For example, the eNB may abstain from scheduling a coexistence gap if WTRUs are expecting pending synchronous retransmissions in the UL.

In order to allow for synchronization and measurement by the WTRU, the WTRU measurement and synchronization procedures may be based on non-ICIC sub-frames. In an embodiment, a WTRU may abstain from measurement during the ICIC sub-frames and perform measurements only during the non-ICIC sub-frames, regardless of the presence of coexistence gaps. In addition, the WTRU may assume that any synchronization symbols (e.g., PSS/SSS and CRS) are not transmitted during the ICIC sub-frames, regardless of the actual coexistence gap patterns signaled by the WTRU. The eNB may or may not transmit synchronization symbols during the ICIC sub-frames, however, when a coexistence gap is scheduled by the eNB. All eNB transmissions (including any synchronization symbols) may be interrupted for the duration of the gap.

When an eNB determines the need for a coexistence gap, it may signal the presence of this gap to all WTRUs through PHY layer signaling. The duration of the gap may also be signaled to the WTRUs. When a WTRU receives this signaling, it may abstain from decoding the control channel (on DL sub-frames) or sending SRS (on UL sub-frames) until the coexistence gap expires.

In another embodiment, discontinuous reception may be used to create coexistence gaps. In order to use DRX to create coexistence gaps for the use of the channel by WiFi, for example, the eNB may synchronize the timing of DRX cycles among all WTRUs. As a result, all WTRUs in the control of an eNB may need to be configured with the same DRX cycle parameters at all times.

The LTE transmission time may correspond to the union of the active times for each of the WTRUs while the coexistence gap or time available for WiFi transmission may correspond to the intersection of the non-active DRX times of all WTRUs. In order to make the method most effective for the use of coexistence gaps, the scheduler may need to configure the DRX parameters such that traffic to the majority of the WTRUs may be full-buffer during the active time so that the WiFi system may see the channel as occupied during the entire active time and the configured duration time should reflect the expected load of the busiest WTRU so that the least busy WTRU is guaranteed to listen to the DL channels throughout the entire LTE transmission time.

FIG. 22is a signal diagram2200illustrating a method of using DRX to create coexistence gaps for different WTRUs2202,2204and2206. For all of the WTRUs2202,2204and2206, an onDurationTimer may specify the minimum amount of time the WTRU should remain on and monitor the PDCCH for each DRX cycle. When the timer expires without receiving an allocation or grant, the WTRU may go back to sleep. This is the case for WTRU2202. When a WTRU receives an allocation, the time in which the WTRU goes back to sleep may be dictated by a drxInactivityTimer, which may specify the amount of time following an allocation or grant that the WTRU will go back to sleep. This timer may be reset each time a new allocation or grant is received. The WTRUs2204and2206inFIG. 22receive grants2208and2210, respectively, for active transmissions. Since each of the WTRUs2204and2206receive their grants at different times during the on duration, however, the inactivity timer extends their on times to total different amounts of time. The time before the last WTRU is scheduled for active transmissions may be reserved as an LTE on period for coexistence purposes, and the time between the end of the last scheduled active transmission for a WTRU and the beginning of the next DRX on period may be reserved as a coexistence gap for use for transmissions by other WTRUs (e.g., for WiFi).

For traditional DRX, signaling and timing are applied on a per WTRU basis, and HARQ retransmissions may take place regardless of the DRX cycle. Further, for traditional DRX, the eNB may continue to operate regardless of the DRX cycle. As a result, the eNB may still transmit reference signals and PSS/SSS, regardless of how many and which WTRUs are currently in DRX. These features of traditional DRX may make it challenging to use traditional DRX as is for the creation of coexistence gaps due to the large signaling overhead for configuring DRX for all of the WTRUs, the interference that WiFi may cause on HARQ retransmissions that occur well after the bulk of active time retransmissions, and the interference that eNB RS and PSS/SSS transmissions may have on the WiFi system.

Since the coexistence gap length may need to depend on the relative amount of traffic between the entire LTE system (e.g., the eNB and all served WTRUs) and the WiFi system and not just the traffic experienced by a single WTRU (as is the case for traditional DRX), traditional DRX may be enhanced in order to create a new DRX capable of supporting coexistence with WiFi. For example, in an embodiment, a common configuration may be broadcast to all WTRUs (for example, through RRC signaling). The common DRX configuration may be used by all WTRUs to determine when to wake up and go to sleep in DRX. For another example, in an embodiment, WTRUs may not transition from a short DRX cycle to a long DRX cycle based on a timer related to traffic that is specific to a single WTRU. This may be done by defining only a single DRX cycle (short or long) and configuring the length of the DRX cycle and the on Duration timer based on the needs of the system as a whole. Alternatively, WTRUs may transition between short and long DRX cycles, but the transition between the two may be controlled by the eNB explicitly through a broadcast message such as a group-based MAC CE or PDCCH signaling addressed to all WTRUs. For another example, in an embodiment, the eNB may stop transmitted RSs and, in an embodiment, PSS and SSS, during the DRX period that is defined for coexistence. In addition, procedures may be defined for the WTRU to know when reference symbols have been turned off, since each WTRU may independently go to sleep at different times.

In an embodiment, the eNB may transmit PSS/SSS as long as at least one WTRU is known to be active. When all WTRUs are known to be in DRX (sleeping), the eNB may not transmit any reference signals or PSS/SSS. Each WTRU may assume valid PSS/SSS and reference symbols from the start of the DRX cycle to the end of the active time for that specific WTRU. The WTRU may not measure PSS/SSS and reference signals at any time outside the active period for that specific WTRU.

Additional restrictions on HARQ retransmissions during DRX may also be defined. For example, the last WTRU with pending retransmissions following the transmission of the bulk of traffic during the active time may suffer from WiFi interference since the WiFi may gain access to the channel before the retransmissions are successfully sent. Retransmissions may also adversely affect the WiFi itself, and the resulting coexistence scheme may be highly sub-optimal. To deal with this, in an embodiment, the number of allowable retransmissions may be reduced, the HARQ operation may be frozen and/or release mechanisms may be performed during retransmissions to keep the channel occupied.

In an embodiment, the number of retransmissions that occur at the end of an active period may be reduced. For example, a small value may be used for the drxRetransmissionTimer. For another example, retransmissions may be disabled altogether.

In another embodiment, HARQ retransmissions may be allowed to continue at the next active period following a coexistence gap, for example, to avoid upper layer retransmissions that may arise from reducing or eliminating HARQ retransmissions. Here, WTRUs with pending retransmissions may freeze and maintain their HARQ buffers and counters at the end of the maximum active period. In addition, UL procedures may be enhanced so that UL retransmissions that did not take place at the end of the active time may be made implicitly from the start of the next DRX cycle. In this case, the DRX procedure may be enhanced to hold the HARQ buffers, and the HARQ timing may be specified from the start of the next on Duration. In addition, the active time may be given a stipulated maximum period. For example, the active time may be defined based on a timer in which a WTRU may have no grants or allocations made. The WTRU may then move to DRX if the timer expires without a grant or allocation made. For another example, when a grant/allocation is made for a WTRU, the WTRU's active time may be further extended up to some maximum active time. Any pending retransmissions following the maximum active time may be suspended and continued at the next DRX cycle.

In an embodiment, the eNB may ensure a busy channel during the retransmission phase, which may occur at the end of the active period. This may involve the transmission of all redundancy versions prior to acknowledgement in order to keep the channel occupied during HARQ RTT time.

In addition to defining the coexistence gaps and patterns to reduce interference among different wireless systems operating in the same band, an eNB may also schedule WTRU transmissions during LTE active periods in such a way as to further reduce potential interference. In an embodiment, link adaptation may be used to help manage interference and maximize data throughput over a shared channel. For example, eNBs may use channel state information to determine how aggressively to schedule DL transmissions. Here, WTRUs may be configured to report CSI at both the beginning and end of an LTE ON period of a coexistence gap cycle. For each cell that it is measuring, a WTRU may report two different CQI values (CQIstartand CQIend), which may correspond to the start of an LTE active period or the end of an LTE active period, respectively. The two CQI values may allow an eNB/HeNB to more efficiently schedule the WTRUs at the start of an LTE active period.

When operating on a cell in a DSS band, the eNB/HeNB may provide both a periodic and an aperiodic CSI configuration. The eNB/HeNB may provide 2 periodic configurations (cqi-pmi-ConfigIndex and cqi-pmi-ConfigIndex3). The first of the 2 periodic configurations may apply for CQIend, and the second of the 2 periodic configurations may apply to CQIstart. The eNB/HeNB may guarantee that the periodicity and offset of these reports are configured so as not to occur in the same sub-frame. CSI resource sets may also be included to enable coexistence between neighbor LTE systems. The eNB/HeNB may also configure the reporting mode for the aperiodic CSI reports. As in LTE Release 10, the CSI trigger sets, which are applicable to aperiodic CSI reporting, may be configured only for primary cells. In the case of supplementary cells, the eNB/HeNB may segregate these into specific trigger sets (e.g., by grouping supplementary cells that may require similar CSI reporting feedback).

The eNB/HeNB may ensure that the request for aperiodic CSI is sent in the sub-frame that will guarantee the correct CSI reference resource is used by the WTRU. For example for the case of carrier aggregation with LTE active periods aligned at the end of the a coexistence gap, to request an update of CQIstart, the eNB/HeNB may request an aperiodic CSI report in the sub-frame corresponding to the start of the LTE active period in all supplementary cells. Similarly, to request an update to CQIend, the eNB/HeNB may request an aperiodic CSI report in a sub-frame corresponding to the latter sub-frames of an LTE active period (e.g., third or later sub-frame of an LTE active period).

At the WTRU, the CQI may be determined based on the CSI reference resource as defined in LTE Release 10, with the exception that if a WTRU is requested to send an aperiodic CSI report and the CSI trigger set includes a cell in an LTE DTX period, the WTRU may not return CSI information for this cell.

For periodic CSI reports, the WTRU may be configured with 2 periodic patterns. One of the 2 periodic patterns may be used for reporting on CQIstartand the other of the 2 periodic patterns may be used for reporting on CQIend. In determining the CQI for periodic CSI reporting in sub-frame n, the CSI reference resource may defined by a single downlink sub-frame n-nCQI—ref. For CQIstart, nCQI—refmay be the smallest value greater than or equal to 4 such that it corresponds to a valid DL sub-frame at the start of an LTE active period. For CQIend, nCQI—refmay be the smallest value greater than or equal to 4 such that it corresponds to a valid DL sub-frame at the end of an LTE active period. In an embodiment, the eNB may optimize the patterns so as to minimize nCQI—ref.

FIG. 23is a flow diagram2300of a method for supplementary cell CSI reporting at the eNB/HeNB. In the example method illustrated inFIG. 23, the eNB/HeNB is initially in a waiting state (2302). On a condition that it decides to add a supplementary cell for a WTRU, it may configure the periodic and aperiodic CSI reporting for the WTRU, including modifying the CSI trigger set for the Pcell if necessary (2304). On a condition that the eNB/HeNB receives a CSI report, it may cross-reference to determine which WTRU the report is from and what type of CQI it is (e.g., CQIendor CQIstart) (2306). The eNB/HeNB may store the CQI information for the WTRU according to CQI type (2308) and schedule a supplementary cell according to the CQI reported for the start and end of the LTE active period (2310). On a condition that the eNB/HeNB needs CQIendinformation for a particular WTRU, the eNB/HeNB may schedule an aperiodic CSI request for the WTRU in the last sub-frame of an active period. For example, for a case where the LTE active periods are aligned at the beginning of a coexistence gap, this may correspond to sub-frame9(2314).

FIG. 24Ais a flow diagram2400A of a method for supplementary cell CSI reporting at the WTRU. In the example method illustrated inFIG. 24A, the WTRU is initially in a waiting state (2402). On a condition that a supplementary cell is added for the WTRU, the WTRU may configure periodic CSI for up to 2 reporting configurations and aperiodic CSI reporting for the added supplementary cell (2404). On a condition that a CSI report is to be transmitted, the WTRU may transmit the CSI report (e.g., using LTE Release 10 rules) (2406). On a condition that the WTRU receives a request for an aperiodic CSI report, the WTRU may determine the CQI for each of the supplementary cells in the CSI trigger set and ignore those cells for which the supplementary cells are in a DTX period (2408). On a condition that a sub-frame for periodic CSIstartreference resource for a particular supplementary cell occurs, the WTRU may determine the CQI for the supplementary cell (2410). Similarly, on a condition that a sub-frame for a periodic CSIendreference resource for a particular supplementary cell occurs, the WTRU may determine the CQI for the supplementary cell (2412).

In addition to CSI reporting, coexistence gaps may also impact discontinuous reception (DRX) operation. For the case of carrier aggregation between a primary cell and a supplementary cell, a single common set of DRX parameters may be used for both cells. However, due to the presence of the LTE OFF periods, the interpretation of each DRX parameter by the WTRU may need to change as DRX active sub-frames (from the point of view of DRX) may fall within an OFF period. A WTRU configured in DRX mode may monitor PDCCH during the DRX active time. In these sub-frames, the WTRU may monitor PDCCH on the primary cell as well as PDCCH on the supplementary cell, if the supplementary cell is configured to transmit PDCCH for that WTRU and if that sub-frame does not fall within an LTE OFF period. When a WTRU wakes up following a short DRX cycle or a long DRX cycle, the eNB/HeNB may only schedule resources on the supplementary cell for sub-frames in the DRX active time that do not fall within the LTE Off period. For this reason, the eNB/HeNB may configure the DRX parameters such that the shortDRX-Cycle, if used, may have a minimum value of sf10 and the drxStartOffset may be such that the start of the DRX ON duration coincides with the second sub-frame of the LTE active period. The WTRU may interpret the drxRetransmissionTimer and the drxInactivityTimer differently depending on where the last transmission was received. If the last transmission was received from the primary cell, the number of PDCCH sub-frames to be counted, when compared with the timer, may be the absolute number of sub-frames (e.g., counted on the primary cell). If the last transmission was received from the supplementary cell (either through cross-carrier scheduling from the primary or through a Supplementary Cell PDCCH), the number of PDCCH sub-frames to be counted, when compared with the timer, may be the number of non-LTE-OFF sub-frames on the respective supplementary cell that have elapsed since the timer was started. If both a primary cell and supplementary cell allocation were received in the same sub-frame, the timers may be based on non-LTE-OFF sub-frames (e.g., as though the last transmission was received on the supplementary cell).

FIG. 24Bis a diagram2400B illustrating a supplementary cell duty cycle2450having a short DRX cycle configured of coexistence gaps2452and DRX ON periods. In the example illustrated inFIG. 24B, the eNB/HeNB may configure the DRX parameters such that the shortDRX-Cycle may have a minimum value of sf10and the drxStartOffset may be such that the start of the DRX ON duration coincides with the second sub-frame2462of the LTE active period2460.

The control of supplementary cells may be different from the control of licensed secondary cells used for LTE carrier aggregation. In an embodiment, an eNB/HeNB may control the operation of the supplementary cells at three different levels: configuration, operating mode and activation. The first (configuration) level pertains to the details of the supplementary cells, such as how the PHY is configured, how the MAC is configured, how often the WTRU is required to make measurements and how the measurements are to be reported. This level may be applicable to all WTRUs in a cell (i.e., it may be cell-wide). The second (operating mode) level relates to the operating mode of the configured cell (e.g., how the cell is used for carrier aggregation). The operating mode may be TDD based, FDD based or off. The details for each operating mode may be included in the cell configuration. This level may also be cell-wide. The third (activation) level deals with the activation/deactivation of a supplementary cell for an individual WTRU. As a result, the scope may be limited to a single WTRU.

Two embodiments of the different operating modes are described herein. In one embodiment, the different operating modes may be treated as different configuration parameters that pertain to one supplementary cell. Thus, the network and the WTRU see a single supplementary cell that is changing from one to another (also referred to as a Single-Cell interpretation). In another embodiment, the different operating modes may be considered as different supplementary cells (also referred to as Multi-Cell interpretation).

In a Single-Cell interpretation, a cell may be characterized by a configuration that includes the necessary information to function in each of its potential operating modes. A cell may have any number of operating modes, of which only one is the active mode and all others are dormant. When an operating mode is active, the WTRU may be expected to follow the operating procedures for this mode. For example, it may need to take measurements on the channel, monitor the DL control information, send channel quality feedback to the network, etc. The complete list of procedures may depend on the particular operating mode. In contrast, when an operating mode is dormant, the WTRU may not necessarily follow the operating procedures associated with this mode. In an embodiment, the following operating modes may be considered for a cell: FDD DL only, FDD UL only, FDD shared, enhanced TDD, and OFF. The OFF mode may deal with the case where the supplementary cell is configured for operation but is not being used for carrier aggregation.

FIG. 25is a signal diagram2500illustrating the relationship between the different levels of supplementary cell control. The example inFIG. 25illustrates three events: the addition of a supplementary cell2502, the reconfiguration of a supplementary cell2504and the release of a supplementary cell2506. In level1, supplementary cells1and2are configured (2508/2510). In level2, operating mode switching may be carried out, which may include making a dormant operating mode active and downgrading the current active mode to dormant. In the example illustrated inFIG. 25, three operating mode switches2518a,2518band2518coccur for supplementary cell configuration1to switch the operating mode from off (2512) to operating mode1(2520) to operating mode2(2522). Similarly, three operating mode switches2518d,2518eand2518foccur for supplementary cell configuration2to switch the operating mode from off (2514), to operating mode3(2524), to off (2516), to operating mode4(2518). In level3, a supplementary cell may be used actively by some WTRUs but not by others. Level3allows a WTRU to treat supplementary cells as either activated or deactivated. In the example illustrated inFIG. 25, supplementary cell configuration1has a period where it is activated (2530a) and periods where it is deactivated (2528aand2528b). Similarly, supplementary cell configuration2has periods where it is activated (2530band2530c) and periods where it is deactivated (2528band2528c).

In an embodiment, level1and level2control may be combined. In such a case, each individual operating mode switch may trigger supplementary cell reconfiguration. Although this may lead to potential increase in RRC load and may suffer from large latency to process the RRC message, it may be an acceptable solution in case where the operating mode changes infrequently.

With respect to level1, the network is responsible for determining the need for supplementary cells (e.g., based on demands from the WTRUs or availability of spectrum). The network relies on algorithms (e.g., running in some radio resource management (RRM) functionality) to determine whether to add or release a supplementary cell to a given eNB. As described above, these supplementary cells may have unique characteristics that make their configuration somewhat different from secondary cells. The re-used configuration fields of the cell are described in Table 6 below. The new or modified configuration fields of the cell are described in Table 7 below.

TABLE 6Supplementary cell indexIndex to the supplementary cell used to referto the cell at layers below the RRCCell identification (PhysicalAs defined for Secondary CellsCell ID and frequency ofoperation)

TABLE 7DescriptionType of SpectrumType of channel the WTRU will operate in (e.g.Sublicensed, Available or PU Assigned). In somecases, the WTRU may have to take additional stepsto use these channels. For example for PU Assignedspectrum, additional measurements and reportingmay have to be done by the WTRU.Bandwidth ofBandwidth of the cell (common to all operatingoperationmodes)This may be different for supplementary cells. Forinstance, the bandwidth information may includedetails regarding blacklisted sub-bands within theoperating bandwidth, For example, a cell may beallocated 2 TVWS channels (total of 12 MHz) buthave certain portions reserved for other secondaryusers (e.g., a narrowband wireless microphone or acompeting LTE system). This may be used forcoexistence purposes.PUCCHIn some cases, use of supplementary cells mayconfigurationrequire that the PUCCH be carried in a reservedportion of the licensed band PUSCH. The detailsmay need to be provided to the WTRU.PDCCHIn some cases, use of supplementary cells mayconfigurationrequire that the PDCCH be carried in a reservedportion of the licensed band PDSCH.UplinkUsed on UL only mode, shared mode, or TDD modeconfigurationIn some cases, the method of CQI reporting may bedetailsdifferent for supplementary cells (e.g., how toPower detailsmeasure or when to send feedback). In such cases,SRSthe CQI configuration may be tailored forconfigurationsupplementary cells.PUSCHSimilarly, power details specific to supplementaryconfigurationcell use may be required.CQI reportingDL ConfigurationUsed on DL only mode, shared mode, or TDD mode.detailsCSI configuration may be tailored forPHICHsupplementary cells (as a result, it may use aconfigurationdifferent configuration than that used for primary(if carried onand secondary cells).SupplementaryPHICH configuration (if carried) may be tailored forcell)supplementary cells (as a result, it may use aPDSCHdifferent configuration than that used for primaryconfigurationand secondary cells).CSI configurationCoexistence GapThe schedule for the coexistence gap to allowscheduleneighbor systems to use the LE spectrum. Theschedule may be defined based on a period and sizeof gap.MeasurementDetails for the type of measurements to beConfigurationperformed on the supplementary cells as well as thereporting of these measurements. For example, aWTRU may be told to monitor for TV signal powerabove a certain threshold.This is in addition to the inter-frequency and intra-frequency measurements that may already beperformed by the WTRU as part of an LTE Release10 measurement.

In Table 7, a sublicensed channel may be a TVWS channel that is sublicensed to an operator or user for a specific geographical area and for a specific time that is not used by any primary or other secondary users. Further, an available channel may be a TVWS channel that is free from primary users but may be used by any secondary users. Further, a PU assigned channel may be a TVWS channel used by a primary user that requires secondary users to leave the channel if a primary user is detected.

Although the information in Table 7 has been grouped according to functionality, it may also be grouped according to operating mode. For example, the supplementary cell configuration information may be grouped into configuration parameter sets pertaining to FDD DL only, FDD UL only, FDD shared, and enhanced TDD. Each parameter set may include the necessary configuration for that operating mode. For example, in the case of DL FDD only mode, the parameter set may include supplementary cell index, cell identification (e.g., physical cell ID and frequency of operation), type of spectrum, bandwidth of operation, PUCCH configuration, PDCCH configuration, coexistence gap schedule, measurement configuration and DL configuration details. Alternatively, the configuration details may be divided into those that are common to multiple operating modes and those that are operating mode specific. In such a case, the network may send the common parameters followed by a list of operating mode specific parameter sets. In either case, the sets may be numbered to allow the network to quickly refer to these in cases that a configuration needs to be changed.

For an embodiment with a DL only supplementary cell, the configuration of the cell may be achieved through an RRCConnectionReconfiguration message carrying a supplementary cell specific sCellToAddModList IE. This IE may be modified to take into account the unique features of supplementary cells as compared to secondary cells. For example, the potential need for duty cycle for each cell, the possibility to dynamically decide whether or not to transmit PBCH, PHICH, and/or PDCCH physical channels, if PDCCH transmission is supported, the modified configuration of this channel, the modified CQI reporting rules for the supplementary cells, and the modified cross-carrier scheduling rules for the supplementary cells. In addition, the IE may include a new flag to denote that the configuration applies to a supplementary cell. Table 8 below provides a list of configuration details for a DL only supplementary cell, divided into 3 categories: cell identification, common, and dedicated. Those fields which are new to supplementary cells are shown shaded.

Upon reception of an RRCConnectionReconfiguration message with a sCellToAddModList IE, a WTRU may first evaluate whether the configuration is for a supplementary cell (e.g., by verifying the presence of SupplementaryCellIndication). If present, the WTRU may know that the assigned EARFCN applies to the shared spectrum band, and the WTRU may determine the DL carrier frequency. All other aspects of the cell identification may be as defined for secondary cells. As part of the common configuration, the WTRU may obtain the common secondary cell configuration information. The WTRU may obtain knowledge of cell duty cycle duration. The WTRU may configure its PSS and SSS monitoring according to the duty cycle duration. The WTRU may determine whether the cell carries the PBCH physical channel by evaluating the PBCHPresenceIndication. If present, the RRC may configure its lower layers to monitor the PBCH. However, if not present, the RRC may configure the lower layers to process the PBCH slot (e.g., second slot of sub-frame0) as any other non-synchronization slot. The WTRU may determine the number of PHICH groups supported in the supplementary cell. Upon reception of a PHICH duration of 0, the RRC may configure the lower layers not to monitor the PHICH in the supplementary cell. The WTRU may determine the PDCCH configuration for the supplementary cell (e.g., by monitoring the Common PDSCH Configuration). If present, and if the WTRU is not configured for cross-carrier scheduling, the RRC may configure the lower layers with the location {low, mid, high} and BW {1.4, 3, 5} of the PDCCH within the shared spectrum channel.

As part of the dedicated configuration, the WTRU may obtain the dedicated supplementary cell configuration information and the WTRU may be provided with the details for cross-carrier scheduling and may be configured with a PDSCH symbol start set to 0. In such an embodiment, the RRC may configure its lower layers to begin receiving the PDSCH transmissions on the supplementary cell from OFDM symbol0. The WTRU may be configured with a periodic CSI reporting. The RRC may configure the MAC and PHY to determine the CQI based on the appropriate CSI Reference resources. The WTRU may optionally be provided the configuration details for a second periodic CQI report. This report may be geared for CQI reporting for sub-frames at start of LTE Active Period. Upon receiving this configuration, the RRC may configure the MAC and PHY to make the CQI calculations on the appropriate CSI Reference resources.

WTRUs capable of supporting supplementary cell operation may provide a capability indication to the network (either at time of initial registration or after being queried from the network). This may be an extension to the LTE UECapabilityInformation, which may include details as to the channel support in the LE band. As an example, for TVWS, the WTRU may include additional information in the supportedBandListEUTRA IE to indicate capability specific to supplementary cells. The WTRU may indicate whether UL only operation is supported. The WTRU may signal its spectrum sensing capabilities, which may describe what kind of spectrum sensing algorithm is supported. It may also signal whether primary user detection of DTV signal and wireless microphone are supported. It may also signal if feature detection for secondary users is supported. The WTRU may also signal the FCC ID of the device, for example to meet any regulatory requirements.

When a Node B initiates the operation of a supplementary cell or reconfigures a supplementary cell, the network may provide the cell's configuration information for all available operating modes to the capable WTRUs. Each WTRU may have a local store of supplementary cell configurations corresponding to each operating mode. Such mappings may exist for all supplementary cells for which the WTRU deems fit for aggregation. In such a case, the network may simply indicate an operating mode transition to ensure a successful cell transition. This may be accomplished using one or a combination of the following techniques. For example, the cell configuration information may be broadcast in the SI of the associated primary cell. For another example, the network may provide the information through dedicated signaling to all capable WTRUs (e.g., using an RRCConnectionReconfiguration message with a new supplementary cell specific IE). For another example, the network may use a new RRC message directed to a SuppCell specific RNTI. Here, capable WTRUs may monitor for this RNTI and be able to read the supplementary cell configuration details. This information may be sent periodically by the network in order to provide the configuration information to WTRUs entering connected mode. For another example, in cases where the supplementary cell carries some DL SI, the primary cell may need to only carry a pointer to the supplementary cell frequency. The WTRU may then be responsible for reading this SI from the supplementary cell.

Upon receiving a supplementary cell reconfiguration, the WTRU may need to stop the active operating mode in order to effect the requested change. For example, if a cell is operating in DL only mode and the network determines that it needs to change the operating frequency or PDSCH configuration, then the active operating mode may be temporarily suspended until a scheduled time after which the DL only mode may be restarted. However, if the reconfiguration is affecting a dormant operating mode, then the supplementary cell operation may not be effected. Here, the reconfiguration may happen transparently.

With respect to level2, operating mode switching may involve making a dormant operating mode active and downgrading the current active mode to dormant. This may occur as a result of decisions made in the network. For example, a cell operating in FDD DL only mode may suddenly begin to experience UL congestion. The algorithms in the network may decide to switch to FDD shared mode. As the WTRU already has the configuration details for shared mode operation (this is a dormant operating mode), it may only need to send an indication to the WTRUs to make the shared mode active and downgrade the FDD DL only mode to dormant.

Some of the operating modes may require only an indication from the network, while others may require that the network to provide some additional operating mode details. For example, a shared mode operation may require the network to provide the shared mode pattern to be used. For another example, an enhanced TDD operation may require the network to provide the TDD UL/DL configuration pattern to be used. The term indication may be used herein to refer to the operating mode to be made active as well any special details that may be specific to this operating mode.

The network may signal the operating mode to use by one or a combination of the following techniques. For example, the network may send the indication in an RRC control message. In this example, the indication may be carried either in a dedicated RRC message or in a multicast RRC message. For another example, the network may embed the indication in a MAC header. For example, in LTE, the indication may be included in a MAC control element (CE). The MAC CE may be sent individually to each WTRU. Alternatively, the MAC CE may be sent to a group of WTRUs through a group multicast address (e.g., SuppCell RNTI). To increase the likelihood that all WTRUs receive the indication, the network may send the message in repeated sub-frames. For another example, the network may send the indication in a PHY signal. This signal may be carried in the licensed band (e.g., on primary or secondary cells) or in the unlicensed band. In LTE, the indication may be carried in the PDCCH using a special DCI format. In order to quickly reach all WTRUs, the indication may be carried on a common PDCCH monitored by all WTRUs. This information may be sent to a group of WTRUs using a multicast address (e.g., SuppCell RNTI). An existing DCI format may be used for the indication, with the fields redefined for carrying the operating mode information. The WTRU may use the SuppCell RNTI to distinguish between the LTE Release 10 interpretation of the DCI and the new operating mode indication. For another example, the network may use a pre-configured operating mode schedule that is synchronized between the WTRU and the network (e.g., based on the SFN). The schedule may provide details as to the times and durations of certain operating modes. For example, the FDD DL only mode may start at time t1and end at time t2, the OFF mode may start at time t2and end at time t3, and the FDD UL may start at time t3and end at time t4. The schedule may be specified for a fixed duration or may be periodic. The schedule information may be sent, for example, through RRC signaling, MAC signaling, or PHY signaling using any of the techniques described for the activation mode. Alternatively, the schedule may be broadcast via MIB/SIB in the primary cell.

Upon reception of an operating mode switch, the WTRU may need to change the configuration of its lower layers (e.g., depending on the type of operating mode switch selected). For example, in an LTE system, this may impact the Hybrid ARQ entities at the MAC layer, the physical layer receive and transmit chains, and the PHY measurement entities. Table 9 below defines the major changes for a few potential operating mode changes. The WTRU may be required to complete these changes within a defined period of time (e.g., K sub-frames).

In some cases, the operating mode switch indication or signaling may need to be extremely robust. For example, use of a TVWS channel comes with very stringent requirements regarding incumbent user protection. As a result, a system may be asked to quickly evacuate a channel (e.g., stop transmitting so that the channel may be returned to the incumbent user). However, such a situation may be generalized to any spectrum that is shared between systems of different priorities. If a higher priority system requests spectrum already in use by a competing lower priority system, the lower priority system may be required to release (e.g., evacuate) the requested spectrum.

Some of the techniques for signal operating mode switch indications are very robust or can be made robust. For example, techniques that rely on dedicated RRC signaling are inherently robust as they are typically acknowledged at the RRC layer. In other cases, the network may be made aware of a failed operating mode switch and may retransmit the request. This may be applicable for cases where the operating mode switch is carried in a dedicated MAC CE.

These techniques, however, may not be applicable for broadcast/multicast operating mode switch indications. For these cases, in an embodiment, multicast and dedicated signaling mechanisms may be combined.

FIG. 26is a signal diagram2600of signaling operating mode switch indications for broadcast/multicast operating mode indications. In the example illustrated inFIG. 26, the network2602sends a multicast operating mode switch command2612(e.g., RRC layer, MAC layer (e.g., MAC CE), and PHY layer (e.g., PDCCH) to WTRUs2604,2606,2608and2610in the network, requiring all WTRUs receiving the command to send feedback to the network confirming reception. In the example illustrated inFIG. 26, WTRUs2604and2608receive the command and send switch confirm messages2614and2616to the network2602. The feedback may be, for example, an RRC message, a MAC control message, or a PHY layer indication. Upon receiving the feedback, the network2602may be aware of all the WTRUs that failed to receive the original message and may rely on dedicated signaling to send these WTRUs an operating mode switch. In the example illustrated inFIG. 26, the network2602sends dedicated operating mode switch messages2618and2622to the WTRUs2606and2610, respectively. Each of the WTRUs2606and2610acknowledges receipt of the operating mode switch message by sending a switch confirm message2620and2624, respectively, to the network2602.

In an embodiment, a WTRU may rely on consistent scheduling/assignment information for the supplementary cell as an indication that it has lost operating mode synchronization with the network (e.g., the network is operating in Operating Mode 1 while the WTRU thinks the cell is in Operating Mode 2) or that the network wants the WTRU to evacuate the channel and stop using the supplementary cell.

In an embodiment, the WTRU may treat reception of inconsistent information as an indication to transition to OFF mode. In FDD DL only mode, the WTRU may only expect DL scheduling assignments for the supplementary cell. On a condition that the WTRU receives a UL grant for the supplementary cell, the WTRU may transition to an OFF operating mode. In FDD UL only mode, the WTRU may only expect UL grants for the supplementary cell. On a condition that the WTRU receives a DL scheduling assignment for the supplementary cell, the WTRU may transition to an OFF operating mode. In FDD shared mode, the WTRU may know the UL and DL pattern that is expected for transmission.

FIG. 27is a diagram2700of an example UL and DL pattern that may be expected for transmission in FDD shared mode. In the illustrated example, the expected pattern is 4UL: 4DL. In the illustrated example, the WTRU expects to receive a DL scheduling assignment in sub-frames2702,2704,2706,2708,2718,2720,2722and2724. The WTRU does not expect a DL scheduling assignment in sub-frames2710,2712,2714,2716,2726,2728,2730or2732. If one is received, the WTRU may transition to an OFF operating mode.

With respect to level3, when a supplementary cell is configured and in a certain operating mode, it may be used for communication to and from LE capable WTRUs (depending on the specific operating mode). However, as a result of individual WTRU demands, at any given time, the supplementary cell may be used actively by some WTRUs and not by others. The final level of supplementary cell control may allow a WTRU to treat supplementary cells as either activated or deactivated. When activated, the WTRU may perform all the necessary procedures tied to that operating mode.

For an LTE Release 10 system employing carrier aggregation, activation of a secondary cell may be based on the reception of a MAC CE message or command. Deactivation of a secondary cell may be based either on reception of a similar MAC CE command or secondary cell inactivity (e.g., the WTRU has not received a DL scheduling assignment for the secondary cell or a UL grant for the secondary cell for the duration of the timer).

A similar mechanism (e.g., explicit signaling of activation, deactivation and timer based deactivation) may be used for supplementary cells but may be enhanced with an implicit activation of the supplementary cell. In an embodiment, a WTRU may activate a supplementary cell upon reception of a cross-carrier grant or scheduling information (carried on the licensed band). Here, the scheduler may need to consider the inherent latency in activating the supplementary cell. This may be especially true for an activation while in DL only mode because the WTRU may not be able to use the scheduling assignments for the first L sub-frames. As a result, the network may use dummy or empty scheduling assignments during this time. From the WTRU perspective, it may ignore all scheduling assignments received for these first L sub-frames after the implicit activation command.

In an embodiment, a WTRU may activate a supplementary cell upon reception of an operating mode switch. For example, a supplementary cell may be in FDD UL only mode and may be deactivated for a specific WTRU (WTRUk). If the network changes the operating mode of the supplementary cell (e.g., to FDD DL-only), the WTRU may decide to activate the supplementary cell. This may allow the WTRU to take measurements on the supplementary cell and send back some initial CQI measurements. This may allow the network to schedule DL traffic to the WTRU without sending an activation command, as well as to tailor the transmission to the WTRU based on more reliable CQI information.

Alternatively, the network may transmit a carrier aggregation schedule where activation of supplementary cells may be timer driven. Here, the network may relay the carrier aggregation schedule to each capable WTRU highlighting activation times (e.g., in frames and sub-frames) for all supplementary cells that may be aggregated. Since both the eNB/HeNB and WTRU are time aligned, the SFN (or the hyper frame number) may be used to accurately track activation times at which each WTRU may independently activate the concerned supplementary cell without an activation trigger (such as the ones described above) from the network.

In an embodiment, the carrier aggregation schedule may be transmitted aperiodically when the RRM detects a supplementary cell change (e.g., addition, modification or removal of a supplementary cell) for any of the supplementary cells that may be aggregated, or it may be transmitted periodically via a configurable CarrierAggregationScheduleTimer.

FIGS. 28A and 28Bare example carrier aggregation schedules2800A and2800B. In the example illustrated inFIG. 28A, the carrier aggregation schedule carries absolute time values at which the concerned CC will be activate (t1inFIG. 28A). It may be assumed that once active, the supplementary cell will continue to be active until explicitly signaled by the network. In the example illustrated inFIG. 28B, the carrier aggregation schedule carries activation time intervals (e.g., CC x will only be active between t1and t2) and will be deactivated otherwise.

Timer based activation via carrier aggregation schedule reception may operate as follows (e.g., using one or both of the absolute timer activation method or the interval based activation mechanism). For the interval based activation mechanism, t1may signify the lower bound of the interval. If supplementary cell x is to be activated at t1ms in a received CA Schedule, t1>CURRENT_TTI and supplementary cell x is not yet active, supplementary cell x may be activated at t1. If supplementary cell x is to be activated at t1ms as provided in a received CA schedule, t1>CURRENT_TTI and supplementary cell x is already active, supplementary cell x may be deactivated and activated at t1(may be tied to a configuration or operating mode change at t1) or the supplementary cell x may continue in activated state. If supplementary cell x is to be activated at t1ms as provided in a CA schedule and t1<CURRENT_TTI, SupplCellx may be deactivated if not already deactivated or the timing command may be ignored.

FIG. 29is a diagram2900of multiple pre-configured cells. In the illustrated example, a primary cell2902is pre-configured and includes a DL channel and a UL channel. Two supplemental cells2904and2906are also pre-configured. Supplemental cell2904is UL only, and supplemental cell2906is DL only.

Multi-cell transitions between different operating modes by switching between pre-configured cells may be an alternative approach to a single-cell approach that relies on an explicitly operating mode switch. It may be involved pre-configuration of a cell, for example, as illustrated inFIG. 29, using RRC messaging and quick Cell-Switch signaling to transition between the different operating modes (e.g., UL and DL inFIG. 15). This method may also include transition issues related to the HARQ buffers and measurement reporting that may occur during UL/DL and DL/UL transitions.

In an embodiment, the different operating modes may be implemented by adding up to K pre-configured cells. RRC signaling may be used to configure cells to include, for example, signaling, signaling reliability, control delay, extensibility and security control parameters for the cells. The pre-configured cells may be organized in one of a number of different ways.

FIG. 30is a diagram of an example system3000with pre-configured cells using a pool of K pre-configurations. In the example illustrated inFIG. 30, the pre-configured cell pool includes K pre-configurations3012,3014,3016,3018,3020,3022,3024,3026,3028and3030. Five of the configurations in the pool may become configured cells. In the example illustrated inFIG. 30, configured cell3002is pre-configured cell3012, configured cell3004is pre-configured cell3014, configured cell3006is pre-configured cell3016, configured cell3008is pre-configured cell3018and configured cell3010is pre-configured cell3020. The configured cells may be activated or deactivated, and measurements may only be taken on configured cells.

New signaling from the eNB/HeNB may prompt a WTRU to swap a configured cell with a supplementary cell from the pre-configured pool to enable a quick transition between operating modes or to change channels. In the example illustrated inFIG. 30, the WTRU swaps pre-configured cell3016for pre-configured cell3024in configured cell3006. During the swap, the configured cell may retain its active or deactivated status. For example, in the example illustrated inFIG. 30, if the pre-configured cell3024is swapped with pre-configured cell3016, the configured cell3006may remain active and may be used immediately (in some embodiments, with gaps). Alternatively, any swapped cell may default to an inactive or active state. The eNB/HeNB may have its own list of possible cells and may issue activation, deactivation and swap commands to the WTRU.

FIG. 31is a diagram3100of an example system illustrating activation and cell swap commands over time. In the example illustrated inFIG. 31, at time t1, the eNB/HeNB3102activates configured cells3106and3108. From the perspective of the WTRU3104, at t1, primary cells3112and3114are activated. At time t2, the eNB/HeNB3102may active cell3110. From the perspective of the WTRU3104, the primary cell3116may be deactivated and swapped for primary cell3118, which may be activated.

In another embodiment, WTRUs may use the five cells from LTE Release 10 as pre-configured cells. New signaling from the eNB/HeNB may prompt the WTRU to quickly switch operating modes.

In another embodiment, WTRUs may be configured with an increased set of pre-configured cells. For example, if there are 10 alternate channels and 3 operating modes, a WTRU may have 30 pre-configured cells. A maximum of 5 pre-configured cells may be activated/deactivated at any given time. Each WTRU may be configured independently, and legacy WTRUs (e.g., with a maximum of 5 CCs) may not be impacted. The first cell in the set of cells may be the primary cell. New signaling may be sent to WTRUs to activate a cell while simultaneously deactivating the old cell. Hence, a WTRU may transition between operating modes via a cell switch.

FIG. 32is a diagram3200illustrating example WTRU transitions between operating modes via a cell switch. In the example illustrated inFIG. 32, in a pre-configured cell pool, UL pre-configured cell3202is activated, DL pre-configured cell3204is activated, UL pre-configured cell3206is deactivated, and pre-configured cells3208and3210are not active. A cell switch occurs during which pre-configured cells3204and3206are switched such that pre-configured cell3206is activated and per-configured cell3204is deactivated.

The new signaling may be similar to the signaling used in the single-cell approach. In an embodiment, the network may signal a cell swap using one or more of the following. For example, the network may send the indication in an RRC control message. Here, the indication may be carried in a dedicated RRC message or in a multicast RRC message (e.g., using a multicast address such as SuppCell RNTI). For another example, the network may embed the indication in a MAC header. For example in LTE, the indication may be included in a MAC CE. The MAC CE may be sent individually to each WTRU or may be sent to a group of WTRUs through a group multicast address (e.g., SuppCell RNTI). To increase the likelihood that all WTRUs receive the indication, the network may send the message in repeated sub-frames. For another example, the network may send the indication in a physical layer signal. This signal may be carried in the licensed band (e.g., on primary or secondary cells) or in the unlicensed band. In LTE, the indication may be carried in the PDCCH using a special DCI format. In order to quickly reach all WTRUs, the indication may be carried on common PDCCH. This information may be sent to a group of WTRUs using a multicast address (e.g., SuppCell RNTI). An existing DCI format may be used for the indication, with the fields redefined for carrying the cell change information. The WTRU may use the SuppCell RNTI to distinguish between the LTE Release 10 interpretation of the DCI and the new cell change indication.

A format for the cell swap indication message may include one or more of the following. For example, if there are 5 pre-configured cells, 3 bits may be transmitted to indicate a cell switch. For example, a base station transmitting ‘000’ over a cell may indicate ‘no change,’ and a base station transmitting ‘101’ may indicate to switch the current cell with pre-configured cell5in the next frame (or sub-frame, etc). Up to 7 cells may be pre-configured using 3 bits. In another alternative, the base station may explicitly signal which cells to swap. For example, it may transmit ‘011’ ‘110,’ which may signal to replace cell3with pre-configured cell6. Adding extra bits may enable a larger pre-configuration set.

For another example, if there are 5 pre-configured cells, a bitmap of 5 bits may be transmitted. For example, cell1may be the primary cell, cell2may be a supplementary cell configured for UL, and cell3may be a supplementary cell configured for DL. A WTRU receiving the bit sequence ‘10100’ may know that the first and third cells are active. Hence, it may know that the supplementary carrier is acting in DL only. In this embodiment, the base station may continue to transmit ‘10100’ to indicate ‘no change’ until it needs to switch to UL. It may then transmit, for example, ‘11000’ to indicate that the next frame (or sub-frame, etc.) will be UL only. The bitmap format may allow multiple cells to be switched using the same command. This may be generalized to a bitmap of n bits if there are n pre-configured cells.

For another example, the UL/DL cell pairs may be grouped saving some bits. A bitmap may be used as in the previous technique. However, the first bit may be used to indicate UL or DL. For example, if there are 4 pre-configured cells (e.g., 2 supplementary UL cells and 2 supplementary DL cells), 1 bit may indicate UL or DL, and 2 bits may form a channel bitmap. For example, if the base station transmits ‘110,’ this may signal a WTRU to change supplementary channel 2 from a DL supplementary cell to a UL supplementary cell. This may form a total of 3 bits and may encode the same information as the earlier bitmap. This method may become significant if the number of pre-configured cells increases beyond 5. Also, this technique assumes that UL/DL cell pairs are configured equivalently except for their UL/DL property.

For another example, the indication message may be sent periodically or aperiodically. If it is sent periodically, then it may indicate ‘no change’ when there will be no transition.

When a transition is indicated, it may apply to the next frame. During a transition, the HARQ process may need to be taken into account. For example, the supplementary cell may want to ensure the HARQ buffers are all released before performing the switch from the DL-only mode to the UL-only mode. This may require additional transmissions of the NACK'd packets. Hence, the grace period may be defined for the completeness of HARQ processes.

Additionally there may be a need for a coexistence gap to coexist with CSMA-like systems (e.g., WiFi). This may coincide with the grace period or come directly after.

In an embodiment, operating mode transitions using cell switch may be combined with one or a combination of the following channel switching techniques. An example fast channel switching technique may include channel switching using pre-configured cells. This combination may require more than 5 pre-configured cells because the UL/DL transitions described above also use cell switch techniques using pre-configured cells and, as a result, the availability of cells may otherwise become scarce. The channel switch may be indicated using the MIB and/or SIB broadcast on the supplementary channel. As some information does not need to be broadcast over SuppCCs, these resources may be used for channels switching.

The carrier indicator (CI) may be transmitted on the PDCCH and may indicate which cell a control block is addressed to. The CI may not change without RRC signaling. For example, a WTRU may decode the PDCCH with a CI indicating a packet on cell4after a MAC CE has indicated to switch from cell4to cell5. The WTRU may implicitly know when a cell switch has occurred and should know to decode the packets scheduled to cell4until RRC signaling is complete. Otherwise, information may be lost.

Channel state measurement reports may be affected during transition periods. In LTE Release 10, measurements are taken on reference signals. The WTRU may take measurements on DL cell-specific reference signals (CRS) and report these results to the eNB/HeNB that is to use this information to make scheduling decisions. However, when operating in DL mode, the WTRU may not report the measurements on the same cell.

One or more of the following may be used for measurement reports. For example, measurement reports may be periodic or aperiodic. An eNB/HeNB may schedule an aperiodic measurement report as part of a PDCCH scheduling grant immediately before transitioning from DL to UL. The WTRU should know to wait a certain time for the transition after which it will transmit the report. For another example, if the operating mode transitions from UL to DL (and vice versa) often enough, the WTRU may take measurements during DL mode and implicitly know to report the measurements during UL mode. The eNB/HeNB may assume the same measurement information throughout the DL phase. For another example, reports during DL mode may be sent on the primary cell PUCCH.

In an example multi-cell embodiment without pre-configured supplementary cells, supplementary cell control may be similar to that used for secondary cell control, whereby the network may only configure and activate/deactivate these cells. However, supplementary cell control may have the following differences. First, the cell configuration details may be specific and tailored to supplementary cells. Second, the network may treat different operating modes as different configured cells. Consequently, in order to change the operating mode of a supplementary cell, the network may need to remove the old cell (e.g., old operating mode) and subsequently add the new cell (e.g., with the new operating mode) using RRCConnectionReconfiguration.