Method and apparatus for providing interference measurements for device to-device communication

An approach for providing interference measurements for device-to-device communication is disclosed. A logic generates a control signal to instruct a plurality of stations to perform measurement relating to interference or path loss by the stations. The logic then receives measurement information from the stations and determines, based on the measurement information, whether resources are to be scheduled to provide direct communication between two of the stations.

BACKGROUND

Radio communication systems, such as a wireless data networks (e.g., Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, spread spectrum systems (such as Code Division Multiple Access (CDMA) networks), Time Division Multiple Access (TDMA) networks, WiMAX (Worldwide Interoperability for Microwave Access), etc.), provide users with the convenience of mobility along with a rich set of services and features. This convenience has spawned significant adoption by an ever growing number of consumers as an accepted mode of communication for business and personal uses. To promote greater adoption, the telecommunication industry, from manufacturers to service providers, has agreed at great expense and effort to develop standards for communication protocols that underlie the various services and features. One area of effort involves ensuring minimal or no signal interference among user terminals, while observing the constraints of network resources. For example, device-to-device (D2D) communication can utilize the same resources with a cellular network; and hence, there is a need to coordinate the D2D and cellular communication to optimize the use of resources as to offer guaranteed service levels to the users in the cellular network and minimize the interference between the cellular users and D2D communication.

Therefore, there is a need for an approach for efficiently utilizing network resources while minimizing interference.

SOME EXAMPLE EMBODIMENTS

According to one embodiment, a method comprises generating a control signal to instruct a plurality of stations to perform measurement relating to interference or path loss by the stations. The method also comprises receiving measurement information from the stations. The method further comprises determining, based on the measurement information, whether resources are to be scheduled to provide direct communication between two of the stations.

According to another embodiment, a computer-readable medium carries one or more sequences of one or more instructions which, when executed by one or more processors, cause an apparatus to generate a control signal to instruct a plurality of stations to perform measurement relating to interference or path loss by the stations. The apparatus is also caused to receive measurement information from the stations. The apparatus is further caused to determine, based on the measurement information, whether resources are to be scheduled to provide direct communication between two of the stations.

According to another embodiment, an apparatus comprises a logic configured to generate a control signal to instruct a plurality of stations to perform measurement relating to interference or path loss by the stations. The apparatus is also caused to receive measurement information from the stations. The apparatus is further caused to determine, based on the measurement information, whether resources are to be scheduled to provide direct communication between two of the stations.

According to another embodiment, an apparatus comprises means for generating a control signal to instruct a plurality of stations to perform measurement relating to interference or path loss by the stations. The apparatus also comprises means for receiving measurement information from the stations. The apparatus further comprises means for determining, based on the measurement information, whether resources are to be scheduled to provide direct communication between two of the stations.

According to another embodiment, a method comprises receiving a control signal from a base station. The method also comprises performing measurement of interference or path loss in response to the control signal. The method further comprises initiating transmission of measurement information to the base station. The method further comprises receiving a resource allocation message specifying whether resources can be utilized to establish a direct connection to a user equipment.

According to another embodiment, a computer-readable medium carries one or more sequences of one or more instructions which, when executed by one or more processors, cause an apparatus to receive a control signal from a base station. The apparatus is also caused to perform measurement of interference or path loss in response to the control signal. The apparatus is further caused to initiate transmission of measurement information to the base station. The apparatus is further caused to receive a resource allocation message specifying whether resources can be utilized to establish a direct connection to a user equipment.

According to another embodiment, an apparatus comprises a logic configured to receive a control signal from a base station. The apparatus is also caused to perform measurement of interference or path loss in response to the control signal. The apparatus is further caused to initiate transmission of measurement information to the base station. The apparatus is further caused to receive a resource allocation message specifying whether resources can be utilized to establish a direct connection to a user equipment.

According to yet another embodiment, an apparatus comprises means for receiving a control signal from a base station. The apparatus also comprises means for performing measurement of interference or path loss in response to the control signal. The apparatus further comprises means for initiating transmission of measurement information to the base station. The apparatus further comprises means for receiving a resource allocation message specifying whether resources can be utilized to establish a direct connection to a user equipment.

DESCRIPTION OF SOME EMBODIMENTS

Although the embodiments of the invention are discussed with respect to a wireless network compliant with the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) architecture, it is recognized by one of ordinary skill in the art that the embodiments of the inventions have applicability to any type of communication system and equivalent functional capabilities.

FIGS. 1A and 1Bare, respectively, a diagram of a communication system capable of providing interference sensing, and a ladder diagram of the interference sensing process, according to an exemplary embodiment. As shown inFIG. 1A, a communication system100includes one or more user equipment (UEs)101a-101ncommunicating with a base station103, which is part of an access network (e.g., 3GPP LIE or E-UTRAN, etc.). Under the 3GPP LIE architecture (as shown inFIGS. 10A-10D), the base station103is denoted as an enhanced Node B (eNB). The UEs101a-101ncan be any type of mobile stations, such as handsets, terminals, stations, units, devices, multimedia tablets, Internet nodes, communicators, Personal Digital Assistants (PDAs) or any type of interface to the user (such as “wearable” circuitry, etc.). The UEs101a-101neach include a transceiver105(e.g., transceivers105aand105n) and an antenna system107(e.g., antenna system107aand107n) that couples to the transceiver105to receive or transmit signals from the base station103. The antenna system107can include one or more antennas. For the purposes of illustration, the time division duplex (TDD) mode of 3GPP is described herein; however, it is recognized that other modes can be supported, e.g., frequency division duplex (FDD).

As with the UE101, the base station103employs a transceiver, which transmits information to the UE101. Also, the base station103can employ one or more antennas for transmitting and receiving electromagnetic signals. For instance, the Node B103may utilize a Multiple Input Multiple Output (MIMO) antenna system111, whereby the Node B103can support multiple antenna transmit and receive capabilities. This arrangement can support the parallel transmission of independent data streams to achieve high data rates between the UE101and Node B103. The base station103, in an exemplary embodiment, uses OFDM (Orthogonal Frequency Divisional Multiplexing) as a downlink (DL) transmission scheme and a single-carrier transmission (e.g., SC-FDMA (Single Carrier-Frequency Division Multiple Access) with cyclic prefix for the uplink (UL) transmission scheme. SC-FDMA can also be realized using a DFT-S-OFDM principle, which is detailed in 3GGP TR 25.814, entitled “Physical Layer Aspects for Evolved UTRA,” v.1.5.0, May 2006 (which is incorporated herein by reference in its entirety). SC-FDMA, also referred to as Multi-User-SC-FDMA, allows multiple users to transmit simultaneously on different sub-bands.

As seen, the UEs101a-101ncan also establish device-to-device (D2D) communication, in addition to communicating over the system100. It is assumed that the base station103assigns resources separately for each group of UEs101a-101nrequesting D2D communication. In the approach described herein, resource scheduling of the base station103to cellular users can utilize knowledge of the interference levels or path loss estimates between UEs101a-101nengaged in D2D communication and UEs101a-101nengaged in cellular communication on the same network. As used herein, path loss is defined to include: (i) distance-dependent path loss, (ii) shadow fading, (iii) antenna gains, and (iv) penetration loss—exclusive of fast fading. For example, the base station103can attempt to schedule the cellular communication on resources with low interference from and to UEs101a-101nengaged in D2D communication. The base station103can also schedule the D2D groups on resources with low interference from and to UEs101a-101nengaged in cellular communication.

In network scenarios with high site density, the uplink sector throughput is limited by the rise of interference, and not by the UE101transmit power. By way of example, one approach of controlling inter-cell interference is to only compensate for a fraction of the path loss (fractional power control in LTE). The fractional power control algorithm involves trading off the throughput of a particular UE101and that of the other UEs101. Compared with other conventional approaches, this approach allows for more power for UEs101whose path loss is small—i.e., UEs101situated close to the base station101because these UEs101generate little inter-cell interference. However, the extent to which transmit power can be increased without penalizing other users on the network (e.g., other UEs101) is not explicitly taken into account. If the UE101can also estimate path loss to all interfering entities (e.g., other UEs101), an estimate of how much interference in other sectors or cell in total can be determined. When the UE101transmit power increases, the corresponding interference also increases—but due to the background noise floor, the effect on signal to interference ratio (SINR) of a transmit power increase depends on the absolute path loss to the base station103being interfered.

If, for example, D2D communication takes place on uplink (UL) resources, interference caused by D2D communication can be limited by applying power back-off relative to the normal UL transmission directed to the base station103. However, interference measurements would be needed in order to find out, on one hand, which cellular UEs101would produce so much interference to the D2D receiver that they could not be scheduled on the same resources with the D2D users or, on the other hand, which cellular UEs101would produce so little interference to the D2D receiver that they should be scheduled on the same resources with the D2D users.

If D2D communication employ downlink (DL) resources, interference measurements are important in order to find out those UEs101that would be interfered by the D2D communication.

It is recognized that defining a system for estimating path loss or interference between the cellular and D2D users can be problematic. Further, it is noted that there are several standards that support D2D operation in the same band as the base station103, access point, and/or central controller. For example, in Hiperlan 2, Tetra and WiMAX systems, interference is of no concern, because D2D communication happens on resources that are not used for other transmission. In wireless local area network (WLAN) ad-hoc and direct link modes, the D2D communication utilizes the same resources as communication that occurs through access points. However, the access points are not coordinating resources. Instead, resource reservation is based on beacons and sensing of free resources. All the nodes of the WLAN thus apply the same contention based carrier sensing multiple access scheme.

Communications between the UE101and the base station103(and thus, the network) is governed, in part, by control information exchanged between the two entities. Such control information, in an exemplary embodiment, is transported over a control channel on, for example, the downlink from the base station103to the UE101.

By way of example, a number of communication channels are defined for use in the system100. The channel types include: physical channels, transport channels, and logical channels. For instance in LIE system, the physical channels include, among others, a Physical Downlink Shared channel (PDSCH), Physical Downlink Control Channel (PDCCH), Physical Uplink Shared Channel (PUSCH), and Physical Uplink Control Channel (PUCCH). The transport channels can be defined by how they transfer data over the radio interface and the characteristics of the data. In LIE downlink, the transport channels include, among others, a broadcast channel (BCH), paging channel (PCH), and Down Link Shared Channel (DL-SCH). In LIE uplink, the exemplary transport channels are a Random Access Channel (RACH) and UpLink Shared Channel (UL-SCH). Each transport channel is mapped to one or more physical channels according to its physical characteristics.

Each logical channel can be defined by the type and required Quality of Service (QoS) of information that it carries. In LTE system, the associated logical channels include, for example, a broadcast control channel (BCCH), a paging control channel (PCCH), Dedicated Control Channel (DCCH), Common Control Channel (CCCH), Dedicated Traffic Channel (DTCH), etc.

In LTE system, the BCCH (Broadcast Control Channel) can be mapped onto both BCH and DL-SCH. As such, this is mapped to the PDSCH; the time-frequency resource can be dynamically allocated by using L1/L2 control channel (PDCCH). In this case, BCCH (Broadcast Control Channel)-RNTI (Radio Network Temporary Identities) is used to identify the resource allocation information.

To ensure accurate delivery of information between the eNB103and the UE101, the system100utilizes error detection in exchanging information, e.g., Hybrid ARQ (HARQ). HARQ is a concatenation of Forward Error Correction (FEC) coding and an Automatic Repeat Request (ARQ) protocol. Automatic Repeat Request (ARQ) is an error detection mechanism used on the link layer. As such, this error detection scheme, as well as other schemes (e.g., CRC (cyclic redundancy check)), can be performed by error detection modules and within the eNB103and UE101, respectively. The HARQ mechanism permits the receiver (e.g., UE101) to indicate to the transmitter (e.g., eNB103) that a packet or sub-packet has been received incorrectly, and thus, requests the transmitter to resend the particular packet(s).

In the system100, the base station103determines the UE101to UE101path loss or expected level of interference by requesting the devices to perform interference power measurements. The path loss or interference estimates (as determined via the measurement modules (e.g. measurement modules113aand113n) are used for coordinating the D2D and cellular transmission on the same band. The coordination can be performed using a D2D module115within a resource allocation logic117and includes several approaches.

As shown inFIG. 1B, the base station103can instruct UEs101aand101nto take measurements relating to interference or path loss by generating a control signal (step121) and transmitting it to the UE101a(step123) and the UE101n(step125). On receipt of the control signal, the UE101a(step127) and the UE101n(step129) each take measurements relating to interference or path loss over the network. By way of example, the measurement can be performed over randomly selected resources or all the resources of the network. The measurement information may also include relative power with respect to one of the UEs101or relative power with respect to a link power. These measurements are then transmitted to the base station103(steps131and133). In one embodiment, the interference measurements are reported to the base station103so that the base station can perform resource allocation relating to the D2D communication (step135). In other words, the measurement information (e.g., path loss or interference estimates) can be used for deciding if D2D communication needs dedicated resources or if the D2D communication can take place on resources that are used also for cellular communication. It is noted that interference estimates may be more readily obtainable than path loss estimates, as path loss estimates require the UE101to have knowledge of the transmitted signal power.

In one embodiment, the path loss or interference estimates can be utilized for determining whether D2D communication should share UL or DL resources. If D2D communication takes place on UL resources, the path loss or interference estimates can be used for scheduling the D2D and cellular communication such that the interference experienced by the D2D communication due to cellular communication is minimized. Accordingly, D2D communication avoids UL frequency and time resources that are scheduled for nearby UEs101for cellular communication. If D2D communication takes place on DL resources, the path loss or interference estimates can be used for scheduling of the resources such that the interference caused by the D2D communication to the cellular communication is minimized. This means that D2D communication is scheduled on such DL resources that are not received by the nearby cellular UEs101. Furthermore, the measurements can be used also for determining whether two UEs101are at such proximity that D2D connection between them is sensible (i.e., practical). In the example ofFIG. 1B, the base station103determines based on the measurement information to scheduling of resources for D2D communication between the UE101aand UE101n(steps137and139). In one embodiment, if the base station103determines that measurement information is not available from the either the UE101aor UE101n, the base station may instruct the UE101aor UE101nwith no measurement information to use a dedicate resource to establish a D2D connection. In response, the UE101aand101nestablish a D2D connection using the scheduled resources (step141).

There are several options for arranging the interference measurements, as next described with respect toFIGS. 2-5.

FIG. 2is a flowchart of a process for performing interference and path loss measurements based on a list of UEs, according to an exemplary embodiment. In one embodiment, the process of200ofFIG. 2is performed by the UE101. In step201, the UE101receives a list of UE identities from the base station on which to perform interference and path loss measurements. By way of example, when requesting interference measurements to be performed by the UE101, the base station103provides a list of UE101identities. In an exemplary embodiment, the UE101identities are Cell Radio Network Temporary Identifiers (CRNTIs), within an LIE system. Under this scenario, the UE101receiving the list can search on or read the DL control channel for UL resource grants for the listed UEs101(step203). This searching, particularly in a LIE system, uses minimal additional processing for the active UEs101, as these listed UEs101are checking the control channel for their own UL or DL grants anyhow. Because the grants can be addressed by masking cyclic redundancy check (CRC) words with CRNTIs, simultaneously checking grants for the listed UEs101does not entail unreasonable additional decoding load (e.g., simply involving one XOR operation of the length of CRNTI for each listed UE identity).

In one embodiment, if the UE101that is performing the measurements is following, e.g., a discontinuous reception (DRX) cycle, the UE101can be moved to the mode of continuous reception to perform measurements without delay. When the UE101finds an UL grant with a listed UE101identity, the UE101measures, for instance, the power density or, alternatively, the pilot power density over the resource indicated in the grant (step205). It is contemplated that the UE101may also measure any other parameter indicative of interference or path loss. The UE101then reports the measurements and corresponding UEs101from which the measurements were taken to the base station (step207). After receiving the measurement reports, the base station103, for instance, determines the scheduling restrictions that ensure sufficiently suppressed interference between the cellular and D2D communication.

In certain embodiments, the receiving UE's ability to measure absolute power is rather limited and, depending on the power level, up to 10 dB errors are allowed. Therefore, in one embodiment, the power density measurements are provided in relative terms, such that receiving UE101reports the power densities relative to the power of the first of the listed UEs101or relative to the power received in the D2D communication (if that is already ongoing) or relative to the received downlink power of the base station103.

FIG. 3is a flowchart of a process for performing interference and path loss measurements based on a list of resources, according to an exemplary embodiment. In one embodiment, the process300ofFIG. 3is performed by the UE101. With respect toFIG. 3, instead of signaling the list of UE101identities, the base station103can provide a list of resources on which the UE101should perform the measurements. Accordingly, at step301, the UE101receives the list of resources from the base station. Under this approach, the base station103schedules, in the case of the UL, the UL transmission to the listed resources for a number of UEs101in a certain subframe during which the receiving UE101makes the measurements. In contrast to the approach involving the list of UE identities, there is a scheduling restriction that all the UEs101associated with the listed resources should transmit on some frequency resource at least in one subframe during a reasonably short period, e.g., 10-20 ms. Next, the receiving UE101performs the measurements on the listed resources (step303). As described with respect toFIG. 2, these measurements include, for instance, the power density or, alternatively, the pilot power density over the listed resource. The UE101then reports the measurements along with the listed resources to the base station103(step305). The base station103then uses the interference and path loss measurements to determine whether resources are to be scheduled to provide direct communication between, for instance, two of the UEs101associated with the listed resources.

In certain embodiments, if is the processes ofFIGS. 2 and 3are utilized, the base station103can reduce the measurement and signaling load by leaving out those UEs101that are known to be sufficiently far away so that there would be no risk of interference. This determination of sufficiency in proximity and level of interference can be set using predetermined values (e.g., based on historical and/or simulated data). Also, there may be no need for measurements on those “close” UEs101that would suffer significant interference by their proximity.

FIG. 4is a flowchart of a process for minimizing measurement signaling by measuring random or all resources, according to an exemplary embodiment. In one embodiment, the process400ofFIG. 4is performed by the UE101. Under some scenarios, the signaling load may increase in the link where measurements are reported (e.g., UL) because the UEs101would more likely do unnecessary measurements. For example, the measurements may be unnecessary if multiple UEs101are performing measurements on the same resources or communication links. Also, there may be a longer time delay until all relevant UEs101have been measured; meanwhile the base station103would have incomplete information about interfering UEs101. In addition, since the allocated frequency band cannot be assumed to be constant, synchronizing to the pilot signals for accurate measurements would be difficult (if not impossible). Therefore, in one embodiment, instead of reporting all measurements, the measuring UE101reports only the best observed frequency blocks (with least interference), the worst observed frequency blocs (with highest interference), or both, thereby reducing signaling associated with measurement reporting.

Accordingly, at step401, the measuring UE101selects either a random selection of resources or the entire resource bandwidth to measure (step401). In most cases, selecting a random selection is sufficient because the UE101will only be reporting either the best or worst interfering measurements. The UE101then performs measurements (e.g., relative power, etc.) on the selected resources (step403). The measurements are then evaluated to determine the highest or lowest levels of interference associated with the measured resources (step405). The UE101then reports the selected measurements to the base station103(step407). For example, if the base station103receives measurement information on the lowest measured interference, the base station103will know that the corresponding resources can support D2D communication. Conversely, if the base station103receives measurement information on the high measured interference, the base station103will that the corresponding resources cannot support D2D communication and that dedicated resources should be allocated instead.

FIG. 5is a flowchart of a process for correlating measurements with UEs by identifying the UEs from a control channel, according to an exemplary embodiment. In one embodiment, the process500is performed by the UE101. At step501, the UE101performs interference and path loss measurements on the entire bandwidth resource. In this example, the UE101performs the measurements without knowing which specific other UEs101are using a particular resource or portion of the bandwidth. To correlate specific UEs101with the measurements, the measuring UE101identifies the UEs from an associated control channel (step503). By way of example, in LTE, the UE101can read the other UE's resource allocations from the control channel if the UE knows the other UE's CRNTI. In other embodiments, knowledge of the CRNTI is not necessary for reading the control channel, and the UE101can identify the other UE's resource allocations from the control channel without the CRNTI. After identifying each UE101corresponding to the measurements, the measuring UE101reports the both the UE101identities and the measurements to the base station103(step505).

In the above processes ofFIG. 2-5, according to one embodiment, the base station103can continually update a table of UE101to UE101interference estimates so that when a D2D connection is needed, the optimal coordination scheme would be immediately available. The measurements may also be initiated only after D2D connection is requested. This would not necessarily entail any delay, but D2D communication could be started on a dedicated resource, and optimization would be performed after measurements.

From the perspective of the base station103, measurement reports and interference coordination can be executed in a variety of ways. One approach to overcome the UE's limitation in measuring absolute powers is to perform relative measurements. For example, if the UE101already has an ongoing D2D connection, the UE101can measure the power received by the other UEs101relative to power received on the D2D connection. Where a D2D connection is yet not established, measurements values can be relative to, for instance, the received power on the downlink control channel.

Under the scenario in which measurements are performed during UL transmissions, the physical layer technology utilized in the UL may be taken into account. As mentioned, in LTE, UE101transmissions use SC-FDMA, while UEs101are equipped with OFDMA receivers only. No substantial modifications are necessary at the UE101side to implement the approach described herein, since actual decoding of the UL transmission is not needed, and power measurements can be performed using the standard OFDMA receiver. Even for pilot power measurements the UE101need only know the pilot sequence of the UEs101in question.

In fact, the measuring UE101need not report precise measurements to the base station103, but rather an indication of which UEs101generate more interference. Such indication can be quantized to a small set of values, for example {0, 1, 2, 3}, where 0 indicates no interference and 3 indicates high interference. Alternatively, 1 bit indication can be used to differentiate UEs causing low interference from the ones causing large interference.

FIG. 6is a diagram of an exemplary communication system in which the user equipment are influenced by power control on interference measurements, according to an exemplary embodiment. In one embodiment, UL power control can be taken into account as well. For example, power control (e.g., uplink power) aims to optimize UE101transmit power according to the following criteria: maximum throughput, limited interference (increase throughput for other UE's), and maximum battery lifetime. The conventional approach focuses on the UE's throughput as the optimization criteria. In this case, the UE101should transmit with maximum power except when its signal to interference ratio (SINR) is beyond the required SINR for the maximum modulation and coding scheme (MCS); in other words, there is no need to waste power when no further throughput can be obtained.

For example, in the scenario600ofFIG. 6, a UE101auses more power than a UE101ddue to UL power control. Hence, a UE101cperceives stronger interference from the UE101a, even though the path loss from the UE101aand the UE101dto the UE101cmight be approximately the same. Accordingly, the measurements do not allow deducing a map of the node locations, unless the UL power control information is considered at the base station103, which in turn adds complexity to the system—although UE101reporting of power headroom (maximum minus the actual power) is included already in LIE Rel'8. However, such a map is not needed, since the interference measurements already provide the information needed for coexistence of D2D with the cellular network.

Further, it is assumed that a UE101c, the UE101c, and the UE101dhave measured interference caused by each of the other UEs101a-101d, and that this information is reported to the base station103, using one of the processes ofFIGS. 2-5. If 2-bit feedback is received from the UEs101a-101d, the interference table at the base station103would be similar to Table 1, where each row corresponds to the interference reports from a given UE101a-101d. It can be seen in Table 1 that the interference observed from the UEs101a-101dis not symmetric (due to UL power control). In Table 1, no measurements are available from the UE101a, but the other UEs101b-101chave measured interference from the UE101atransmissions. This represents the case where the UE101ais a legacy terminal, which is not capable of performing and reporting interference measurements.

It is assumed that the UE101band the UE101care engaged in D2D communications. From Table 1, the UE101cexperiences significant interference from UE101a, and hence the UE101aand the UE101cshould not share resources. On the other hand, the pair (UE101b, UE101c) and the UE101dperceive low interference from each other, and thus are good candidates for resource sharing. Moreover, it can be concluded that the UE101band the UE101care close by and require low power for D2D communication; this scenario suggests that resource sharing is possible.

Table 1 is an interference table at the base station103(e.g., quantized to 2 bits). The row indicates the interference victim and the column indicates the interference source

Similar conclusions can be drawn in the case of the interference information being quantized to only one bit, as shown in Table 2.

Again, the effect of UL power control is clear from the asymmetry in the table. In this case the only information missing is the quality of the link between the UE101band the UE101c, even though this information can be estimated from the table due to the symmetry of the estimates of the UE101band the UE101cwith respect to each other. Table 2 enumerates an interference table at base station103quantized to 1 bit.

To evaluate the effects of the uplink power control on the scheduling decisions, the full interference matrix of Table 3 is considered. If measurements from the UE101dare not available, and the UE101ais establishing a D2D connection, the base station103may conclude that the UE101adoes not generate interference to the UE101d(which is not true). This occurs because the UE101duses low power in the uplink since it is very close to the base station103. However, it should be observed that if the UE101aand the UE101dshare resources in downlink, the effect of the interference caused to the cellular connection of the UE101dis indeed low, since it has a very good connection to base station103. Also, if the UE101aand the UE101dshare resources in uplink, interference caused to the cellular connection of the UE101dcan be controlled by applying power back-off relative to the normal UL transmission directed to the base station103. Moreover, from Table 3 it is observed that the UE101ddoes not generate interference on the D2D reception of the UE101a.

Table 3 provides a full interference table at the base station103quantized to 2 bits. The row indicates the interference victim, and the column indicates the interference source.

Hence, the correct scheduling decisions can be made even without interference reports from terminals communicating only with the cellular network. This implies that the schemes ofFIGS. 2-5can operate well even when legacy terminals are present in the network or if measurements are not available from some terminals for any other reason.

According to one embodiment, the following design rules can also be used in order to improve the quality of scheduling and sharing decisions by the base station103. First, the transmit power is requested from the UEs101a-101d. This information is then used to properly weight the interference reports from other UEs101a-101d. This is particularly relevant for the UEs101(e.g., the UE101d) that are close to the base station103. Second, smaller transmit power is applied to the D2D link that is sharing resources with a UE101whose interference reports are not available. Thirdly, dedicated resources can be used for D2D connection, if reports from cellular UEs101are not available.

If the full interference matrix is known, the base station103can make more accurate and sophisticated scheduling decisions. For example, if the UE101aand the UE101cengage in D2D communications, they will cause interference to the UE101d(from the UE101a) and to the UE101b(from the UE101c). In this case, the base station103may coordinate transmissions such that D2D transmissions from the UE101ashare resources with the UE101b, while D2D transmissions from the UE101cshare resources with the UE101d. It should be noted that such level of coordination of D2D transmissions might introduce large overhead to the system.

FIGS. 7A and 7Bare diagrams of an exemplary communication system in which the user equipment provide timing estimates, according to various exemplary embodiments. It is noted that in addition to estimating a pilot power of another UE101, the measuring UE101can also estimate its timing as well. For example, assuming that the UE101a(to be measured) sends a signal at time t1, which is equal to t0−TA1, where t0is the reference time at the base station103, when the base station103is receiving the signal. In other words, TA1is the timing advance of the UE101a. When the UE101bis performing the measurement, the UE101bknows its own TA2, so that the UE101bcan perform a measurement at the time that the signal is expected to reach the base station103.

However, the time when the signal reaches the UE101bmay be different. For example, if the two UEs101aand101band the base station103form an equilateral triangle (as shown), the signal from the UE101areaches the UE101band the base station103simultaneously, as shown inFIG. 7A. However, if the UE101bis on a line between the UE101aand the base station103, the signal from the UE101areaches the UE101bat t0−TA2as shown inFIG. 7B. In other cases (e.g., depending on the spatial arrangement of the UEs101a-101band the base station103), the signal from the UE101ais either later or earlier than the example ofFIG. 7B. For example, the earliest time a signal can reach the UE101bis t0−maxTA, where maxTA is the maximum Timing Advance in the cell. This is realized when both the UEs101aand101bare at the cell border, and almost in the same location. The latest possible time is roughly t0+maxTA, both in 3-sectorized and omni systems.

In one embodiment, timing for reception of signal from the UE101ain the UE101bdepends on relative position of the UEs101a-101band the base station103. In both cases, the signal is received at the UE101bat t0−TA2. Three approaches are described for determining the timing of the measurement at either of the UEs101aor101b. In the first approach, the UE (e.g., either the UE101aor101b) may base a timing estimate on the base station103clock and on its own TA. In particular, if the own TA (TA2) is small compared to maxTA, it is best to measure at t0−TA2. Also, if the own TA is large (i.e., close to maxTA), it is best to measure at a time t0+r*TA2, where r is a number between 0 and 1. This parameter may depend on the cellular deployment, and on how close TA2is to maxTA.

In the second approach, the UE (e.g., either the UE101aor101b) may base a timing estimate on the base station103clock, its own TA, and on the TA of the UE to be measured. By way of example, for the process200ofFIG. 2, the base station103may signal the TAs of the UEs101to be measured. Regarding the process300ofFIG. 3, the base station may signal the TAs to be used when measuring the indicated resources.

As for the process400ofFIG. 4, there may be a DL control channel where the TAs of all UEs101are indicated, which the measuring UE101may read.

Under the third approach, the UE101may measure the timing of the other UE101. For example, it may be considered that at most x% of the pilot power may be lost due to timing error. Corresponding to this, a maximum measurement timing error maxErr is defined. The base station103may signal maxTA, so that the measuring UE101knows the earliest and latest possible arrival times of other-UE101signals. In one embodiment, if the difference of these is larger than twice maxErr, the UE101considers more than one timing, and selects the timing which gives the highest power.

In the above process, there may be significant errors in the timing of the measurement. Depending on the length of the cyclic prefix (CP), and the length of the pilot symbols, the timing error is a more or less serious problem. For example, if the CP is of the order of 5 us, distance differences up to 1.5 km may be easily tolerated. If the timing of the measurement is more in error than CP, the timing starts to degrade the reliability of the measurement. If d is the excess measurement timing error (error above CP, measured in units in the payload symbol duration), the wanted signal part of the received power is (1−d)2, and the inter-symbol interference (ISI) and inter-carrier interference (ICI) arising from timing error is 1−(1−d)2. Hence half of the pilot power would be lost to ICI and ISI if d=1−1/√{square root over (2)}≈0.3, i.e., if the measurement time difference is approximately equal to CP+0.3*payload. With LTE numerology, this would mean that with a measurement timing difference of ˜25 us, corresponding to a distance difference of 7.5 km, half of the pilot power is lost. At measurement timing error CP+payload, corresponding to 21 km, all of the pilot power is lost.

From these computations, it is understood that if the disclosed approaches were to be used in a large LIE macro cell, the accuracy of the timing of the measurement becomes an issue. In that case, an implementation of timing measurement according to second approach or the third approach can be used. In smaller cells, the first approach is sufficient.

It should be noticed as well that if the timing differences of other UEs101(including both the one(s) measured and the possible non-measured) at the measuring UE101are larger than CP, orthogonality of the other UE101signals is lost. This lost can cause multiple access interference which may render the pilot power measurements unreliable.

FIG. 8is a graph showing performance when device-to-device (D2D) communication shares downlink resources. The potential benefits of interference measurements can be observed in graph800, where exemplary cumulative distribution functions (CDFs)801-815of the cellular DL SINR are shown. Table 4 shows the plots for the various scenarios:

TABLE 4LabelDescriptionFunction 801P = 5 dBm, uncoordinatedFunction 803P = 0 dBm, uncoordinatedFunction 805P = 5 dBm, coordinatedFunction 807P = −10 dBm, uncoordinatedFunction 809P = 0 dBm, coordinatedFunction 811P = −10 dBm, coordinatedFunction 813No D2DFunction 815No D2D
The CDFs801-815are shown for different levels of D2D transmit power, and for uncoordinated (e.g., when the base station103is not aware of interference to cellular UE101) and coordinated transmissions (e.g., when the base station103uses the information of the interference to the cellular UE101when scheduling the cellular UEs101). It can be seen that the same cellular DL SINR is achieved for coordinated transmissions with a D2D transmit power P=0 dBm and for uncoordinated transmissions with a D2D transmit power P=−10 dBm, thus representing a gain of 10 dB in the tolerable D2D transmission power. In graph800, it is assumed that the path loss and shadow fading from all links are known at the base station103, and performance degradation is expected in a practical scenario, but still most of the gains should be retained.

As mentioned, the described processes may be implemented in any number of radio networks.

FIGS. 9A and 9Bare diagrams of an exemplary WiMAX architecture, in which the system ofFIG. 1A, according to various exemplary embodiments of the invention. The architecture shown inFIGS. 9A and 9Bcan support fixed, nomadic, and mobile deployments and be based on an Internet Protocol (IP) service model. Subscriber or mobile stations901can communicate with an access service network (ASN)903, which includes one or more base stations (BS)905. In this exemplary system, the BS905, in addition to providing the air interface to the mobile stations901, possesses such management functions as handoff triggering and tunnel establishment, radio resource management, quality of service (QoS) policy enforcement, traffic classification, DHCP (Dynamic Host Control Protocol) proxy, key management, session management, and multicast group management.

The base station905has connectivity to an access network907. The access network907utilizes an ASN gateway909to access a connectivity service network (CSN)911over, for example, a data network913. By way of example, the network913can be a public data network, such as the global Internet.

The ASN gateway909provides a Layer 2 traffic aggregation point within the ASN903. The ASN gateway909can additionally provide intra-ASN location management and paging, radio resource management and admission control, caching of subscriber profiles and encryption keys, AAA client functionality, establishment and management of mobility tunnel with base stations, QoS and policy enforcement, foreign agent functionality for mobile IP, and routing to the selected CSN911.

The CSN911interfaces with various systems, such as application service provider (ASP)915, a public switched telephone network (PSTN)917, and a Third Generation Partnership Project (3GPP)/3GPP2 system919, and enterprise networks (not shown).

The CSN911can include the following components: Access, Authorization and Accounting system (AAA)921, a mobile IP-Home Agent (MIP-HA)923, an operation support system (OSS)/business support system (BSS)925, and a gateway927. The AAA system921, which can be implemented as one or more servers, provide support authentication for the devices, users, and specific services. The CSN911also provides per user policy management of QoS and security, as well as IP address management, support for roaming between different network service providers (NSPs), location management among ASNs.

FIG. 9Bshows a reference architecture that defines interfaces (i.e., reference points) between functional entities capable of supporting various embodiments of the invention. The WiMAX network reference model defines reference points: R1, R2, R3, R4, and R5. R1is defined between the SS/MS901and the ASN903a; this interface, in addition to the air interface, includes protocols in the management plane. R2is provided between the SS/MS901and a CSN (e.g., CSN911aand911b) for authentication, service authorization, IP configuration, and mobility management. The ASN903aand CSN911acommunicate over R3, which supports policy enforcement and mobility management.

R4is defined between ASNs903aand903bto support inter-ASN mobility. R5is defined to support roaming across multiple NSPs (e.g., visited NSP929aand home NSP929b).

As mentioned, other wireless systems can be utilized, such as 3GPP LIE, as next explained.

FIGS. 10A-10Dare diagrams of communication systems having exemplary long-term evolution (LIE) architectures, in which the user equipment (UE) and the base station ofFIG. 1can operate, according to various exemplary embodiments of the invention. By way of example (shown inFIG. 10A), a base station (e.g., destination node) and a user equipment (UE) (e.g., source node) can communicate in system1000using any access scheme, such as Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), Orthogonal Frequency Division Multiple Access (OFDMA) or Single Carrier Frequency Division Multiple Access (FDMA) (SC-FDMA) or a combination of thereof. In an exemplary embodiment, both uplink and downlink can utilize WCDMA. In another exemplary embodiment, uplink utilizes SC-FDMA, while downlink utilizes OFDMA.

The communication system1000is compliant with 3GPP LIE, entitled “Long Term Evolution of the 3GPP Radio Technology” (which is incorporated herein by reference in its entirety). As shown inFIG. 10A, one or more user equipment (UEs) communicate with a network equipment, such as a base station103, which is part of an access network (e.g., WiMAX (Worldwide Interoperability for Microwave Access), 3GPP LIE (or E-UTRAN), etc.). Under the 3GPP LIE architecture, base station103is denoted as an enhanced Node B (eNB).

MME (Mobile Management Entity)/Serving Gateways1001are connected to the eNBs103in a full or partial mesh configuration using tunneling over a packet transport network (e.g., Internet Protocol (IP) network)1003. Exemplary functions of the MME/Serving GW1001include distribution of paging messages to the eNBs103, termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. Since the GWs1001serve as a gateway to external networks, e.g., the Internet or private networks1003, the GWs1001include an Access, Authorization and Accounting system (AAA)1005to securely determine the identity and privileges of a user and to track each user's activities. Namely, the MME Serving Gateway1001is the key control-node for the LIE access-network and is responsible for idle mode UE tracking and paging procedure including retransmissions. Also, the MME1001is involved in the bearer activation/deactivation process and is responsible for selecting the SGW (Serving Gateway) for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation.

A more detailed description of the LTE interface is provided in 3GPP TR 25.813, entitled “E-UTRA and E-UTRAN: Radio Interface Protocol Aspects,” which is incorporated herein by reference in its entirety.

InFIG. 10B, a communication system1002supports GERAN (GSM/EDGE radio access)1004, and UTRAN1006based access networks, E-UTRAN1012and non-3GPP (not shown) based access networks, and is more fully described in TR 23.882, which is incorporated herein by reference in its entirety. A key feature of this system is the separation of the network entity that performs control-plane functionality (MME1008) from the network entity that performs bearer-plane functionality (Serving Gateway1010) with a well defined open interface between them S11. Since E-UTRAN1012provides higher bandwidths to enable new services as well as to improve existing ones, separation of MME1008from Serving Gateway1010implies that Serving Gateway1010can be based on a platform optimized for signaling transactions. This scheme enables selection of more cost-effective platforms for, as well as independent scaling of, each of these two elements. Service providers can also select optimized topological locations of Serving Gateways1010within the network independent of the locations of MMEs1008in order to reduce optimized bandwidth latencies and avoid concentrated points of failure.

As seen inFIG. 10B, the E-UTRAN (e.g., eNB)1012interfaces with UE101via LTE-Uu. The E-UTRAN1012supports LTE air interface and includes functions for radio resource control (RRC) functionality corresponding to the control plane MME1008. The E-UTRAN1012also performs a variety of functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink (UL) QoS (Quality of Service), cell information broadcast, ciphering/deciphering of user, compression/decompression of downlink and uplink user plane packet headers and Packet Data Convergence Protocol (PDCP).

The MME1008, as a key control node, is responsible for managing mobility UE identifies and security parameters and paging procedure including retransmissions. The MME1008is involved in the bearer activation/deactivation process and is also responsible for choosing Serving Gateway1010for the UE101. MME1008functions include Non Access Stratum (NAS) signaling and related security. MME1008checks the authorization of the UE101to camp on the service provider's Public Land Mobile Network (PLMN) and enforces UE101roaming restrictions. The MME1008also provides the control plane function for mobility between LIE and 2G/3G access networks with the S3 interface terminating at the MME1008from the SGSN (Serving GPRS Support Node)1014.

The SGSN1014is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management, logical link management, and authentication and charging functions. The S6a interface enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME1008and HSS (Home Subscriber Server)1016. The S10 interface between MMEs1008provides MME relocation and MME1008to MME1008information transfer. The Serving Gateway1010is the node that terminates the interface towards the E-UTRAN1012via S1-U.

The S1-U interface provides a per bearer user plane tunneling between the E-UTRAN1012and Serving Gateway1010. It contains support for path switching during handover between eNBs103. The S4 interface provides the user plane with related control and mobility support between SGSN1014and the 3GPP Anchor function of Serving Gateway1010.

The S12 is an interface between UTRAN1006and Serving Gateway1010. Packet Data Network (PDN) Gateway1018provides connectivity to the UE101to external packet data networks by being the point of exit and entry of traffic for the UE101. The PDN Gateway1018performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening. Another role of the PDN Gateway1018is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMax and 3GPP2 (CDMA 1X and EvDO (Evolution Data Only)).

The S7 interface provides transfer of QoS policy and charging rules from PCRF (Policy and Charging Role Function)1020to Policy and Charging Enforcement Function (PCEF) in the PDN Gateway1018. The SGi interface is the interface between the PDN Gateway and the operator's IP services including packet data network1022. Packet data network1022may be an operator external public or private packet data network or an intra operator packet data network, e.g., for provision of IMS (IP Multimedia Subsystem) services. Rx+ is the interface between the PCRF and the packet data network1022.

As seen inFIG. 10C, the eNB103utilizes an E-UTRA (Evolved Universal Terrestrial Radio Access) (user plane, e.g., RLC (Radio Link Control)1015, MAC (Media Access Control)1017, and PHY (Physical)1019, as well as a control plane (e.g., RRC1021)). The eNB103also includes the following functions: Inter Cell RRM (Radio Resource Management)1023, Connection Mobility Control1025, RB (Radio Bearer) Control1027, Radio Admission Control1029, eNB Measurement Configuration and Provision1031, and Dynamic Resource Allocation (Scheduler)1033.

The eNB103communicates with the aGW1001(Access Gateway) via an S1 interface. The aGW1001includes a User Plane1001aand a Control plane1001b. The control plane1001bprovides the following components: SAE (System Architecture Evolution) Bearer Control1035and MM (Mobile Management) Entity1037. The user plane1001bincludes a PDCP (Packet Data Convergence Protocol)1039and a user plane functions1041. It is noted that the functionality of the aGW1001can also be provided by a combination of a serving gateway (SGW) and a packet data network (PDN) GW. The aGW1001can also interface with a packet network, such as the Internet1043.

In an alternative embodiment, as shown inFIG. 10D, the PDCP (Packet Data Convergence Protocol) functionality can reside in the eNB103rather than the GW1001. Other than this PDCP capability, the eNB functions ofFIG. 10Care also provided in this architecture.

In the system ofFIG. 10D, a functional split between E-UTRAN and EPC (Evolved Packet Core) is provided. In this example, radio protocol architecture of E-UTRAN is provided for the user plane and the control plane. A more detailed description of the architecture is provided in 3GPP TS 86.300.

The eNB103interfaces via the S1 to the Serving Gateway1045, which includes a Mobility Anchoring function1047. According to this architecture, the MME (Mobility Management Entity)1049provides SAE (System Architecture Evolution) Bearer Control1051, Idle State Mobility Handling1053, and NAS (Non-Access Stratum) Security1055.

One of ordinary skill in the art would recognize that the processes for interference sensing may be implemented via software, hardware (e.g., general processor, Digital Signal Processing (DSP) chip, an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Arrays (FPGAs), etc.), firmware, or a combination thereof. Such exemplary hardware for performing the described functions is detailed below.

FIG. 11illustrates exemplary hardware upon which various embodiments of the invention can be implemented. A computing system1100includes a bus1101or other communication mechanism for communicating information and a processor1103coupled to the bus1101for processing information. The computing system1100also includes main memory1105, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus1101for storing information and instructions to be executed by the processor1103. Main memory1105can also be used for storing temporary variables or other intermediate information during execution of instructions by the processor1103. The computing system1100may further include a read only memory (ROM)1107or other static storage device coupled to the bus1101for storing static information and instructions for the processor1103. A storage device1109, such as a magnetic disk or optical disk, is coupled to the bus1101for persistently storing information and instructions.

The computing system1100may be coupled via the bus1101to a display1111, such as a liquid crystal display, or active matrix display, for displaying information to a user. An input device1113, such as a keyboard including alphanumeric and other keys, may be coupled to the bus1101for communicating information and command selections to the processor1103. The input device1113can include a cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor1103and for controlling cursor movement on the display1111.

According to various embodiments of the invention, the processes described herein can be provided by the computing system1100in response to the processor1103executing an arrangement of instructions contained in main memory1105. Such instructions can be read into main memory1105from another computer-readable medium, such as the storage device1109. Execution of the arrangement of instructions contained in main memory1105causes the processor1103to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the instructions contained in main memory1105. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiment of the invention. In another example, reconfigurable hardware such as Field Programmable Gate Arrays (FPGAs) can be used, in which the functionality and connection topology of its logic gates are customizable at run-time, typically by programming memory look up tables. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software.

The computing system1100also includes at least one communication interface1115coupled to bus1101. The communication interface1115provides a two-way data communication coupling to a network link (not shown). The communication interface1115sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information. Further, the communication interface1115can include peripheral interface devices, such as a Universal Serial Bus (USB) interface, a PCMCIA (Personal Computer Memory Card International Association) interface, etc.

The processor1103may execute the transmitted code while being received and/or store the code in the storage device1109, or other non-volatile storage for later execution. In this manner, the computing system1100may obtain application code in the form of a carrier wave.

FIG. 12is a diagram of exemplary components of a user terminal configured to operate in the systems ofFIGS. 5 and 6, according to an embodiment of the invention. A user terminal1200includes an antenna system1201(which can utilize multiple antennas) to receive and transmit signals. The antenna system1201is coupled to radio circuitry1203, which includes multiple transmitters1205and receivers1207. The radio circuitry encompasses all of the Radio Frequency (RF) circuitry as well as base-band processing circuitry. As shown, layer-1 (L1) and layer-2 (L2) processing are provided by units1209and1211, respectively. Optionally, layer-3 functions can be provided (not shown). L2 unit1211can include module1213, which executes all Medium Access Control (MAC) layer functions. A timing and calibration module1215maintains proper timing by interfacing, for example, an external timing reference (not shown). Additionally, a processor1217is included. Under this scenario, the user terminal1200communicates with a computing device1219, which can be a personal computer, work station, a Personal Digital Assistant (PDA), web appliance, cellular phone, etc.

While the invention has been described in connection with a number of embodiments and implementations, the invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the claims. Although features of the invention are expressed in certain combinations among the claims, it is contemplated that these features can be arranged in any combination and order.