System and method for a long-term evolution (LTE)-compatible subframe structure for wideband LTE

A system and method of scheduling transmissions. A wireless device such as an eNodeB (eNB) may schedule a transmission of a wideband (WB) signal on a micro-frame selected from a plurality of WB micro-frames of a WB carrier. A narrowband (NB) subframe may span a portion of the selected WB micro-frame in the frequency-domain, and the selected WB micro-frame may overlap at least a portion of the NB subframe in the time-domain. The WB signal and an NB signal may be transmitted over the WB micro-frame and the NB subframe in accordance with a first numerology and a second numerology, respectively. A WB subframe may be divided into a plurality of micro-frames. The transmission direction of the WB micro-frame may be scheduled according to a transmission rule based on the contents of a payload in the NB subframe.

TECHNICAL FIELD

The present invention relates generally to managing the allocation of resources in a network, and in particular embodiments, to techniques and mechanisms for a long-term evolution (LTE)-compatible subframe structure for wideband LTE.

BACKGROUND

The current spectrum allocation for cellular systems is becoming inadequate in capacity as the number of users and the amount of traffic increase. While more frequency bands can be included for the cellular communication, these frequency bands are usually higher in frequency (e.g., 3.5 gigahertz (GHz)-6 GHz) than the traditional cellular bands (e.g., 1100 MHz to 2.5 GHz), typically larger in contiguous bandwidth (e.g., up to 400 MHz) compared to the typical maximum of 20 MHz, and often unpaired such that only one band may be available for transmission and reception.

SUMMARY OF THE INVENTION

Technical advantages are generally achieved, by embodiments of this disclosure which describe a system and method for an LTE-compatible subframe structure for wideband LTE.

In accordance with an embodiment, a method for scheduling transmissions is provided, as may be performed by an eNodeB (eNB). In this example, the method includes selecting a wideband micro-frame from a plurality of wideband micro-frames of a wideband carrier. A narrowband subframe spans a portion of the selected wideband micro-frame in the frequency-domain, and the selected wideband micro-frame overlaps at least a portion of the narrowband subframe in the time-domain. The method further includes scheduling a wideband transmission to be performed on resources of the selected wideband micro-frame in accordance with a transmission direction of signaling carried in the portion of the narrowband subframe that overlaps the selected wideband micro-frame in the time-domain. A downlink wideband transmission is scheduled to be performed on the resources in the selected wideband micro-frame when downlink signaling is carried in the portion of the narrowband subframe that overlaps the selected wideband micro-frame in the time-domain. An uplink wideband transmission is scheduled to be performed on the resources in the selected wideband micro-frame when uplink signaling is carried in the portion of the narrowband subframe that overlaps the selected wideband micro-frame in the time-domain. The method further includes signaling the wideband transmission scheduling to a user equipment (UE). An apparatus for performing this method is also provided.

In accordance with another embodiment, a method for wireless communications is provided, as may be performed by wireless devices. The method includes transmitting, by a first wireless device, to a second wireless device a wideband subframe consisting of N micro-frames. The N micro-frames have a combined duration that is equal to a duration of a single narrowband subframe. The method further includes transmitting, by the second wireless device, to the first wireless device an acknowledgement or a negative acknowledgement on the earliest available micro-frame at least a predetermined number of subframes after the corresponding wideband subframe. An apparatus for performing this method is also provided.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments of this disclosure are discussed in detail below. It should be appreciated, however, that the concepts disclosed herein can be embodied in a wide variety of specific contexts, and that the specific embodiments discussed herein are merely illustrative and do not serve to limit the scope of the claims. Further, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of this disclosure as defined by the appended claims.

Some frequency bands that were not utilized for cellular systems are being considered to be used for future cellular systems. To operate at these frequencies, one option is to enhance the physical layer of the existing LTE systems to operate with larger bandwidths. This design may reduce latency and overhead, as well as increase throughput. Thus, a compatible frame structure that accommodates these frequency bands is desired.

Disclosed herein is an embodiment LTE-compatible subframe structure for wideband LTE that allows a wideband (WB) signal and a narrowband (NB) signal to be simultaneously transmitted in accordance with a first numerology and a second numerology, respectively. The NB signal may be transmitted over a legacy LTE carrier bandwidth and the WB signal may be transmitted over the LTE frequency band in addition to previously unused frequency sub-bands. Both the WB signal and the NB signal may be transmitted simultaneously over the same center frequency with the NB signal spanning a subset of subcarrier frequencies spanned by the WB signal. A WB subframe may be further divided into a plurality of micro-frames, while a total duration of the WB subframe stays the same as a duration of a single NB subframe.

Micro-frames of a WB subframe may be scheduled according to a transmission rule based on the contents of a payload in an NB subframe. For example, the transmission rule may prohibit uplink (UL) transmissions from being scheduled on the one or more micro-frames of the WB subframe when the payload of the NB subframe carries downlink (DL) data, and vice versa. One or more leading micro-frames of the WB subframe may be statically assigned to carry DL transmissions, and one or more trailing micro-frames of the WB subframe may be dynamically assigned to carry DL transmissions, UL transmissions, or combinations thereof. On the other hand, one or more leading micro-frames of the WB subframe may be statically assigned to carry UL transmissions, and one or more trailing micro-frames of the WB subframe may be dynamically assigned to carry UL transmissions, DL transmissions, or combinations thereof. These and other aspects are disclosed in greater detail below.

FIG. 1illustrates a network100for communicating data. The network100comprises a base station110having a coverage area112a plurality of mobile devices120(120a,120b), and a backhaul network130. As shown, the base station110establishes uplink (dashed line) and/or downlink (dotted line) connections with the mobile devices120, which serve to carry data from the mobile devices120to the base station110and vice-versa. Data carried over the uplink/downlink connections may include data communicated between the mobile devices120, as well as data communicated to/from a remote-end (not shown) by way of the backhaul network130. As used herein, the term “base station” refers to any component (or collection of components) configured to provide wireless access to a network, such as an enhanced Node B (eNB), a macro-cell, a femtocell, a Wi-Fi access point (AP), or other wirelessly enabled devices. The terms “eNB” and “base station” are used interchangeably throughout this disclosure. Base stations may provide wireless access in accordance with one or more wireless communication protocols, e.g., long term evolution (LTE), LTE advanced (LTE-A), High Speed Packet Access (HSPA), Wi-Fi 802.11a/b/g/n/ac, etc. As used herein, the term “mobile device” refers to any component (or collection of components) capable of establishing a wireless connection with a base station, such as a user equipment (UE), a mobile station (STA), and other wirelessly enabled devices. In some embodiments, the network100may comprise various other wireless devices, such as relays, low power nodes, etc.

FIG. 2Aillustrates an embodiment wideband (WB)-LTE architecture that can accommodate legacy UEs. Legacy UEs may transmit and receive an NB signal220over the legacy LTE carrier bandwidth. Next generation UEs may transmit and receive a WB signal210over the WB LTE carrier bandwidth. As shown, the NB signal220spans a subset of subcarrier frequencies spanned by the WB signal210.FIG. 2Billustrates the WB signal210(individually), andFIG. 2Cillustrates the NB signal220(individually). As shown, the WB signal210may include a zero power portion212and two non-zero power portions214,216; the zero power portion212of the WB signal210may span the same set of subcarrier frequencies as the NB signal220. The NB signal220may span a subset of subcarrier frequencies spanned by the zero power portion212. The zero power portion212of the WB signal210may be positioned in between the non-zero power portions214,216of the WB signal210in the frequency domain. In the example, the zero power portion212of the WB signal210spans the center frequency of the WB signal210. In other examples, the zero power portion212of the WB signal210does not span the center frequency of the WB signal210. In such examples, the zero power portion212may be partially offset from the center carrier frequency of the WB signal210such that one of the non-zero power portions214,216is wider than the other. Alternatively, the zero power portion212may be located at the edge of the WB LTE bandwidth such that the WB signal210includes a single non-zero power portion. Other configurations are also possible.

LTE operations over the legacy carrier bandwidth may stay compliant with existing LTE standards. The overall radio frame structure of the WB signal210may also be compliant with the existing LTE standards. Table 1 lists some possible bandwidth configurations for the WB signal210.

FIG. 3illustrates an embodiment method300for scheduling a WB signal, as may be performed by a wireless device such as a controller (e.g., base station, central controller, etc.). As shown, the method300begins at step310, where a WB micro-frame is selected by the controller from a plurality of WB micro-frames of a WB carrier. A NB subframe may span a portion of the selected WB micro-frame in the frequency-domain, and the selected WB micro-frame may overlap at least a portion of the NB subframe in the time-domain. Thereafter, the method300proceeds to step320, where a WB transmission is scheduled by the controller to be performed on resources of the selected WB micro-frame in accordance with a transmission direction of signaling carried in the portion of the NB subframe that overlaps the selected WB micro-frame in the time-domain. A downlink WB transmission may be scheduled to be performed on the resources in the selected WB micro-frame when downlink signaling is carried in the portion of the NB subframe that overlaps the selected WB micro-frame in the time-domain. Similarly, an uplink WB transmission may be scheduled to be performed on the resources in the selected WB micro-frame when uplink signaling is carried in the portion of the NB subframe that overlaps the selected WB micro-frame in the time-domain.

Subsequently, the method300proceeds to step330, where a WB signal is transmitted over the selected WB micro-frame. The controller may communicate the micro-frame scheduling assignments to a UE with the capability of transmitting and/or receiving WB signals. A wireless device with the capability of transmitting and/or receiving WB signals, such as the controller or a UE, may transmit a WB signal in accordance with a first numerology. The subset of physical layer parameters used to communicate a signal over a carrier are collectively referred to as the “numerology” of the carrier, and may include a combination, or subset, of a transmission time interval (TTI) used to transmit the signal over the carrier, a symbol duration of symbols transmitted over the carrier, a cyclic prefix (CP) length of symbols transmitted over the carrier, and a sub-carrier spacing between sub-carrier frequencies over which the signal is transmitted.

The wireless device may transmit an NB signal in accordance with a second numerology that is different than the first numerology. The WB signal and at least a portion of the NB signal may overlap in the time-domain. For example, both the WB signal and the NB signal may be transmitted simultaneously over the same center frequency. As discussed above, the NB signal may span a subset of subcarrier frequencies spanned by the WB signal.

The first numerology and the second numerology may include a common subset of physical layer parameters for communicating over the NB bandwidth and the WB bandwidth. The common subset of physical layer parameters may include a common subcarrier frequency spacing between subcarriers in both the NB bandwidth and the WB bandwidth, a common symbol duration for symbols in both the NB bandwidth and the WB bandwidth, a common duration of a radio frame, a common duration of a subframe, and/or some other physical layer parameter.

Some features of the cellular systems allow uplink (UL)-downlink (DL) configuration for time division duplexing (TDD) mode to change periodically, for example every 10 ms. Alternatively, the UL-DL configuration may be chosen from one option in Table 2.

In Table 2, “D” represents a DL subframe, “U” represents an UL subframe, and “S” represents a special subframe. In current systems, a subframe may be defined as 30,720 samples where the sample rate (1/Ts) is 30,720,000 samples/second. In the special subframe, the samples are grouped into three sets. The first set of samples forms the downlink pilot timeslot (DwPTS), the second set of samples forms the guard period (G), and the last set forms the uplink pilot timeslot (UpPTS). The number of samples in each set is defined by the standards. The guard period allows the device to switch from receiving DL transmissions to transmitting UL transmissions as well as allowing timing advance.

With dynamic switching of the uplink-downlink configuration, one or more capable UEs may monitor downlink control information (DCI) format 1C to determine the uplink-downlink configuration for the next radio frame. DCI format 1C is transmitted on the physical downlink control channel (PDCCH) using the common search space rules. There are certain uplink-downlink configurations that can be grouped together, such as ((4, 0, 1, 3, 6), (5, 0, 1, 2, 3, 6), (2, 0, 1, 6)).

FIG. 4illustrates an embodiment scheduling scheme for WB signals. Micro-frames412and421may be used for control channel transmissions, for example physical downlink control channel (PDCCH). As shown in Case 1, when a payload415of an NB subframe410is scheduled for DL transmissions, micro-frames422-428of a corresponding WB subframe420may also be scheduled for DL transmissions. In Case 2, when a payload of an NB subframe430is scheduled for UL transmissions, micro-frames of a corresponding WB subframe440may also be scheduled for UL transmissions. In Case 3, when a payload of an NB subframe450is empty, micro-frames of a corresponding WB subframe460may be scheduled for either DL or UL transmissions. It should be noted that in some embodiments, some micro-frames of a WB subframe may be scheduled for UL transmissions, and the remaining microframs of the WB subframe may be scheduled for DL transmissions. Some micro-frames of a WB subframe may be pre-scheduled, and the remaining micro-frame of the WB subframe may be scheduled dynamically. In an example, the start symbols of a WB subframe may be 2×ceiling(control format indicator (CFI)/2) where a CFI indicates the length of the control region (number of symbols used for PDCCH).

A guard interval may be transmitted between the UL micro-frames and DL micro-frames. The guard interval between micro-frames carrying UL data and micro-frames carrying DL data in the WB subframe may be defined as one symbol duration, half a symbol duration, or some other duration. Initial access to the WB subframe may be performed by transmitting WB configurations over NB subframes. For example, the base station110may communicate parameters of the WB signal, such as the bandwidth, subcarrier spacing, and/or center carrier frequency of the WB signal, to the UE120aor120bover the NB signal. Configurations of the WB signal may be transmitted in broadcast messages and/or radio resource control (RRC) messages.

An acknowledgement/negative acknowledgement (A/N or ACK/NACK) may be sent by a UE on the earliest available micro-frame at least a predetermined number of subframes after the corresponding DL micro-frame. The predetermined number may be four, two, or some other number. However, for some DL micro-frames, if the next subframe(s) is DL only, then the A/N may be delayed. A WB device may need to know the NB subframe configuration, which may be obtained by decoding the NB signals. Alternatively, the WB capable device may operate in a WB mode only. In such a case, the NB subframe configuration may need to be known and/or signaled to WB devices. This could be done, e.g., in a physical control format indicator channel (PCFICH) in the first micro-frame of the first subframe of a radioframe or in some other location.

FIG. 5illustrates an embodiment method500for transmitting WB signals, as may be performed by wireless devices (e.g., eNBs, UEs, etc.). As shown, the method500begins at step510, where a first wireless device transmits to a second wireless device a WB subframe consisting of N micro-frames. The N micro-frames may have a combined duration that is equal to a duration of a single NB subframe. Thereafter, the method500proceeds to step520, where the second wireless device transmits to the first wireless device an acknowledgement/negative acknowledgement on the earliest available micro-frame at least a predetermined number of subframes after the corresponding wideband subframe.

FIG. 6illustrates three embodiment WB transmission time intervals (TTIs)601,602,603. A TTI of the WB signal may have the same duration as, or a different duration than a TTI of an NB signal. As shown, the WB TTI601has a one symbol duration (e.g., one fourteenth of a millisecond (ms)), the WB TTI602has a two symbol duration (e.g., one seventh of a ms), and the WB TTI603has a seven symbol duration (e.g., half a ms). Other durations are also possible.

FIG. 7illustrates an embodiment micro-frame structure700for WB signals. As shown, the durations of radio frames, subframes, and symbols of WB signals may stay the same as those of legacy LTE radio frames, subframes, and symbols. A radio frame for the WB signal may be ten ms long and comprises ten subframes that each is one ms long. In an embodiment, each WB subframe may be further divided into micro-frames, for example into six, seven, eight, or some other number of micro-frames. A micro-frame may comprise six, seven, or some other number of symbols, depending at least partially on whether a guard interval is needed between UL and DL micro-frames. A micro-frame structure, e.g. the number of symbols in the micro-frame and so on, may be predetermined and/or based on a subframe index.

FIG. 8illustrates an embodiment WB subframe800. In this example, the first four micro-frames of the WB subframe800carry downlink transmissions and the last two micro-frames of the WB subframe800carry uplink transmissions. Other configurations are also possible. As shown, the first UL micro-frame starts half a symbol duration (guard interval) after the last DL micro-frame. The last symbol may be uplink control indicator (UCI) symbol reserved for carrying control information. It should be noted that the UCI symbol may be located elsewhere, e.g., the first symbol of the UL section of the subframe. Some acknowledgement and negative acknowledgement indicators for hybrid automatic repeat request (HARD) processes may be transmitted as HARQ-ACK bits in the UCI sent on the physical uplink control channel (PUCCH).

Discussed above is one option to operate at higher frequencies and wider bandwidths for cellular systems. Another option is to use carrier aggregation (CA) to enable multiple 20 MHz carriers to fill the available bandwidths.FIG. 9illustrates an embodiment WB signal structure with carrier aggregation. As shown, a fifteen kHz backward compatible carrier (a legacy carrier) in a high frequency band may be aggregated with another non-backward compatible carrier. The non-backward compatible carrier may have a different sub-carrier spacing, e.g., sixty kHz, as shown inFIG. 9. The legacy carrier may be used to support legacy UEs or provide assistance for UEs to access the new non-backward compatible carrier such as in initial access or random access. For example, prior to transmitting a WB signal on resources of a WB micro-frame selected for the wideband signal, configuration information of the WB micro-frame may be transmitted to a UE over an NB subframe. The benefit of this design includes that it just changes the carrier frequency to the higher frequencies while maintaining the design features of the current LTE system.

FIG. 10illustrates a block diagram of an embodiment processing system1000for performing methods described herein, which may be installed in a host device. As shown, the processing system1000includes a processor1004, a memory1006, and interfaces1010-1014, which may (or may not) be arranged as shown inFIG. 10. The processor1004may be any component or collection of components adapted to perform computations and/or other processing related tasks, and the memory1006may be any component or collection of components adapted to store programming and/or instructions for execution by the processor1004. In an embodiment, the memory1006includes a non-transitory computer readable medium. The interfaces1010,1012,1014may be any component or collection of components that allow the processing system1000to communicate with other devices/components and/or a user. For example, one or more of the interfaces1010,1012,1014may be adapted to communicate data, control, or management messages from the processor1004to applications installed on the host device and/or a remote device. As another example, one or more of the interfaces1010,1012,1014may be adapted to allow a user or user device (e.g., personal computer (PC), etc.) to interact/communicate with the processing system1000. The processing system1000may include additional components not depicted inFIG. 10, such as long term storage (e.g., non-volatile memory, etc.).

In some embodiments, one or more of the interfaces1010,1012,1014connects the processing system1000to a transceiver adapted to transmit and receive signaling over the telecommunications network.FIG. 11illustrates a block diagram of a transceiver1100adapted to transmit and receive signaling over a telecommunications network. The transceiver1100may be installed in a host device. As shown, the transceiver1100comprises a network-side interface1102, a coupler1104, a transmitter1106, a receiver1108, a signal processor1110, and a device-side interface1112. The network-side interface1102may include any component or collection of components adapted to transmit or receive signaling over a wireless or wireline telecommunications network. The coupler1104may include any component or collection of components adapted to facilitate bi-directional communication over the network-side interface1102. The transmitter1106may include any component or collection of components (e.g., up-converter, power amplifier, etc.) adapted to convert a baseband signal into a modulated carrier signal suitable for transmission over the network-side interface1102. The receiver1108may include any component or collection of components (e.g., down-converter, low noise amplifier, etc.) adapted to convert a carrier signal received over the network-side interface1102into a baseband signal. The signal processor1110may include any component or collection of components adapted to convert a baseband signal into a data signal suitable for communication over the device-side interface(s)1112, or vice-versa. The device-side interface(s)1112may include any component or collection of components adapted to communicate data-signals between the signal processor1110and components within the host device (e.g., the processing system1000, local area network (LAN) ports, etc.).

It should be appreciated that one or more steps of the embodiment methods provided herein may be performed by corresponding units or modules. For example, a signal may be transmitted by a transmitting unit or a transmitting module. A signal may be received by a receiving unit or a receiving module. A signal may be processed by a processing unit or a processing module. Other steps may be performed by a scheduling unit/module. The respective units/modules may be hardware, software, or a combination thereof. For instance, one or more of the units/modules may be an integrated circuit, such as field programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs).