JP7116274B2 - Uplink signaling for coordinated multipoint communication - Google Patents

Description

The present embodiments relate to wireless communication systems, and more particularly to uplink signaling of control information in Cooperative MultiPoint (CoMP) communication systems.

Conventional cellular communication systems operate in a point-to-point, single-cell transmission scheme. In this scheme, a user terminal or equipment (UE) is uniquely connected to and served by one cellular base station (eNB or eNodeB) at any given time. An example of such a system is 3GPP Long Term Evolution (LTE Release 8). Modern cellular systems increase data rate by adopting coordinated multi-point (CoMP) communication, in which multiple base stations can coordinate downlink transmissions to serve UEs at the same time. and are intended to further improve performance. An example of such a system is the 3GPP LTE Advanced system (Release 10 and later). This greatly improves the received signal strength at the UE by transmitting the same signal to each UE from different base stations. This is especially beneficial for cell-edge UEs that experience strong interference from neighboring base stations. In CoMP, interference from nearby base stations becomes a useful signal, thus greatly improving reception quality. Therefore, UEs in CoMP communication mode are served much better when several nearby cells work together.

FIG. 1 shows an example wireless telecommunications network 100 . The illustrated telecommunications network includes base stations 101, 102 and 103, but in operation the telecommunications network should include many more base stations. Base stations 101, 102 and 103 (eNBs) are operable over corresponding coverage areas 104, 105 and 106, respectively. The coverage area of each base station is further divided into cells. In the network shown, the coverage area of each base station is divided into three cells. A handset or other user equipment (UE) 109 is shown in cell A 108 . Cell A 108 is within the coverage area 104 of base station 101 . Base station 101 transmits to and receives transmissions from UE 109 . As UE 109 moves out of cell A 108 and into cell B 107 , UE 109 may be handed over to base station 102 . Since UE 109 is synchronized with base station 101 , UE 109 may use asynchronous random access to initiate handover to base station 102 . UE 109 may also use asynchronous random access to request allocation of uplink 111 time or frequency or code resources. UE 109 may transmit a random access signal on uplink 111 when UE 109 has data ready for transmission, which may be, for example, traffic data, measurement reports, or tracking area update information. This random access signal informs the base station 101 that the UE 109 is requesting uplink resources to transmit the UE's data. Base station 101 responds by sending a message to UE 109 over downlink 110 containing parameters of resources allocated for UE 109 uplink transmission, along with possible timing error corrections. After receiving the resource allocation and possible timing announcement messages sent on the downlink 110 by the base station 101, the UE 109 optionally adjusts its transmission timing and uses this allocated resource for a predetermined time interval. Data is transmitted on the uplink 111 used. Base station 101 configures UE 109 for periodic uplink Sounding Reference Signal (SRS) transmission. Base station 101 estimates uplink channel quality information (CQI) from SRS transmissions.

Uplink (UL) Cooperative Multipoint (CoMP) communication requires coordination between multiple network nodes to facilitate improved reception from a UE. This involves efficient resource utilization and avoidance of high inter-cell interference. In particular, a non-uniform arrangement of small cells controlled by low power nodes such as pico eNBs and RRHs (Remote Radio Heads) are arranged within macrocells such as 108 . In a Coordinated Multi-Point (CoMP) wireless communication system, a UE receives signals from multiple base stations (eNBs). These base stations may be macro eNBs, pico eNBs, femto eNBs, or other suitable transmission points (TPs). For each UE, multiple channel state information reference signal (CSI-RS) resources are configured based on which UE can measure downlink channel state information. Each CSI-RS resource can be associated by E-UTRAN with a base station, a Remote Radio Head (RRH), or a distributed antenna. The UE then transmits to the eNB in OFDM frames using the assigned physical resource blocks (PRBs) in the uplink (UL).

Referring now to FIG. 2, there is a diagram of a prior art heterogeneous wireless communication system. The system includes macrocells A and B cells separated by a cell boundary 200 . Cell A includes a pico cell 204 controlled by a macro eNB 202 and controlled by a pico eNB 206 . Cell B includes a pico cell 222 controlled by a pico eNB 228 that communicates 226 with pico UEs 224 . Pico eNB 206 serves UEs such as pico UE 208 in region 204 . Pico eNB 206 communicates with pico UE 208 via data and control channel 210 . Cell A further includes macro UE 214 , which communicates directly with macro eNB 202 via data and control channel 218 . The introduction of pico eNB 206 within macrocell A provides cell or area split gains due to the creation of additional cells within the same geographical area. Non-uniform deployment can also be classified as a shared or unique Physical Cell Identity (PCID) scenario. Referring to FIG. 2, in a shared PCID scenario, both macro eNB 202 and pico eNB 206 share the same PCID. Therefore, the DL transmissions from both base stations to the UE can be arranged such that a single transmission emerges from the distributed antenna system. Alternatively, pico eNB 206 may have a different unique PCID than macro eNB 202 . These two scenarios result in different interference environments.

Uplink reference signals from the UE to the eNB are used to estimate uplink channel state information. These reference signals include control channel reference signals (RS), traffic channel demodulation reference signals (DMRS), and sounding reference signals (SRS). In LTE, control and traffic channels are known as physical uplink control channel (PUCCH) and physical uplink shared channel (PUSCH), respectively. Orthogonality of the reference signals within the cell is preserved by using a cyclic shift different from the base sequence. Uplink reference signals in communication systems are typically modulated with constant amplitude zero autocorrelation (CAZAC) sequences or pseudorandom noise (PN) sequences. However, different base sequences are not orthogonal and require good network planning to achieve low cross-correlation between neighboring cells. Inter-cell interference is mitigated by interference randomization techniques such as cell-specific based sequence hopping and cyclic shift hopping patterns. Also, different problems arise depending on whether all cells in a CoMP communication system have a unique cell ID or share the same cell ID.

In prior art non-uniform wireless communication systems, inter-cell interference is significantly increased due to short site-to-site or point-to-point distances. For UL cell selection, the UE should select the cell with the lowest path loss in terms of reducing UL interference. For example, macro UE 214 transmits uplink data and control and also receives downlink control information over wireless connection 218 with macro eNB 202 . However, communication link 212 between macro UE 214 and pico eNB 206 has a shorter path loss than communication link 218 . As such, macro UE 214 attempts to maintain acceptable link quality with macro eNB 202 while generating significant UL interference 212 to pico eNB 206 . Macro UEs 214 may also generate significant interference 220 to pico eNBs 228 when macro UEs 214 are near cell borders 200 . In a shared PCID scenario, all eNBs within a macrocell effectively form a supercell including a distributed antenna system thanks to a single PCID. Therefore, there is little or no inter-cell interference since the transmitted reference signals are cyclic shifts of the same base sequence. On the other hand, there is no area split gain for utilizing multiple co-located eNBs in the same geographical area. In a unique PCID scenario, macro UEs 214 may generate unacceptable UL interference to pico eNBs 206 . Conversely, pico eNB 206 degrades DL reception for macro UE 214 . Therefore, it is desirable that the macro UE 214 be configured to transmit to the pico eNB 206 to reduce interference and conserve battery life by reducing its UL transmit power. Thus, it can be seen that there is a trade-off between increasing network capacity and mitigating the resulting increase in inter-cell or point-to-point interference.

While previous approaches have provided steady improvements in wireless communication, the inventors recognize that further improvements in UL control information transmission are possible. Accordingly, the preferred embodiments described hereinafter are directed to improvements over the prior art as well.

A method of operating a wireless communication system is disclosed in a preferred embodiment of the present invention. The method includes receiving an identification parameter (ID) from a remote transmitter. A base sequence index (BSI) and a cyclic shift hopping (CSH) sequence are determined in response to the received ID. A first pseudorandom sequence is determined in response to the BSI. A subsequent pseudo-random sequence is selected in response to the CSH. The method further includes receiving a set of dedicated parameters from the remote transmitter for determining time/frequency regions for transmitting uplink control information or sounding reference signals.

1 is a diagram of a prior art wireless communication system; FIG.

1 is a non-uniform layout diagram of a prior art wireless communication system showing a macrocell and two picocells; FIG.

1 is a diagram of a wireless communication system of the present invention showing macrocells and picocells deployed within a macrocell area with reduced point-to-point interference; FIG.

4 is a block diagram illustrating logical resource block allocation for macrocells and picocells such as in FIG. 3; FIG.

Fig. 2 is a flow chart illustrating sequence selection for sounding reference signal (SRS) and PUCCH reference signal (RS);

Figure 4 is a flow chart illustrating determination of PUCCH resource mapping to logical resource blocks based on cell-specific or UE-specific PUCCH parameters;

Fig. 10 is a flow chart of inter-eNB signaling for determining UE specific configuration of PUCCH and SRS transmission parameters;

Inter-channel interference is a major problem in uplink control channels of LTE wireless communication systems.

The following abbreviations may be used herein.
BLER: Block Error Rate BSI: Base Sequence Index CQI: Channel Quality Indicator CRS: Cell Specific Reference Signal CRC: Cyclic Redundancy Check CSH: Cyclic Shift Hopping CSI: Channel State Information CSI-RS: Channel State Information Reference Signal DCI: Down Link Control Indicators DL: Downlink DMRS: Demodulation Reference Symbol or UE Specific Reference Symbol DPS: Dynamic Point Selection eNB: E-UTRAN Node B or Base Station EPDCCH: Enhanced Physical Downlink Control Channel E-UTRAN: Evolved Universal Terrestrial Radio Access Network HARQ-ACK: Hybrid Auto-Repeat Request Acknowledge IRC: Interference Rejection Combining JT: Joint Transmission LTE: Long Term Evolution MIMO: Multiple Input Multiple Output MRC: Maximum Ratio Combining PCFICH: Physical Control Format Indicator Channel
PCID: physical cell identification
PDCCH: Physical Downlink Control Channel
PDSCH: Physical Downlink Shared Channel
PMI: Precoding Matrix Indicator PRB: Physical Resource Block PUCCH: Physical Uplink Control Channel PUSCH: Physical Uplink Shared Channel QAM: Quadrature Amplitude Modulation RI: Rank Indicator RNTI: Radio Network Temporary Indicator RRC: Radio Resource Control SNR: Signal-to-Noise Ratio SRS: Sounding Reference Signal TPC: Transmit Power Control UE: User Equipment UL: Uplink UpPTS: Uplink Pilot Time Slot VCID: Virtual Cell Identifier

Embodiments of the present invention are directed to improving uplink control transmission on PUCCH and sounding reference signal transmissions in CoMP communication systems. The present invention describes a method for partitioning uplink control regions between cells such that inter-cell interference is minimized. UEs close to cell boundaries may generate severe UL interference in nearby cells due to transmission of non-orthogonal PUCCH reference signal-based sequences in nearby cells. The interference severity is proportional to the difference in path loss between UEs to the intended eNB and UEs to neighboring eNBs. Here, path loss is the reduction in power density or signal attenuation with respect to electromagnetic wave propagation. Referring to FIG. 3, pico eNB 206 measures received interference caused in part by macro UE 214, according to one embodiment of the present invention for the case where each cell has a unique physical cell ID. The pico eNB 206 informs the macro eNB 202 on the backhaul link 216 if the UL interference is greater than a predetermined threshold. One logical interface over which such inter-eNB signaling takes place is the X2 interface. Macro eNB 202 then instructs macro UE 214 to adopt the PCID of picocell 206 when initializing the pseudo-random sequence generator to generate the BSI and CSH sequences for PUCCH transmission. Macro UE 214 is here considered a CoMP UE, where inter-cell orthogonality between UE 214 and pico UE 208 is achieved and interference 212 (FIG. 2) is eliminated. However, one issue with this method is that the UE 214 determines its resource block allocation for uplink control transmissions based on the (macro eNB 202) PUCCH parameters of the cell it serves. This may result in PUCCH resource allocation conflicts between CoMP UEs and legacy UEs when sending channel state information reports, scheduling requests and HARQ-ACK feedback. One solution to this problem is to partition uplink control transmissions from CoMP UEs and legacy UEs into different RBs. This partition needs to be managed carefully to avoid increasing PUCCH overhead.

In an alternative embodiment of the invention where all cells in a CoMP cooperating set share a common PCID, PUCCH area splitting gain is achieved by configuring the UE to transmit to the closest eNB. Here there is a trade-off between increased point-to-point interference and area PUCCH capacity. According to this embodiment, clusters of UEs that are relatively close to each other and spatially isolated from other clusters have unique IDs to initialize pseudo-random sequence generators for PUCCH reference signals and sounding reference signals. assigned. A new set created by these UE clusters can be considered a virtual cell, and this dedicated ID is the corresponding virtual cell ID (VCID).

Other exemplary applications of this concept of virtual cells are possible. Referring to Figure 3, an alternative embodiment is as follows. eNB 202 forms macrocell A with PCID=123, pico eNB 206 forms its picocell with PCID=231, and pico eNB 228 forms its picocell with PCID=55. By configuring UE 214 with VCIDnID=500, an entirely new virtual cell under control of eNB 202 may be created.

Dynamic PUCCH resource allocation is significantly different from semi-static PUCCH resource allocation. Here, dynamic PUCCH resource allocation is determined from DL scheduling assignments sent on PDCCH or EPDCCH. The present invention uses existing parameters from LTE Releases 8-10 to compute a single parameter m to map PUCCH resource blocks (RBs) for both legacy and CoMP UEs. The concept taught by the present invention is a method of configuring UE-specific semi-static and dynamic PUCCH regions, the former of which results in CSI reports, scheduling requests, and HARQ-ACKs due to semi-persistent scheduling. The latter determines a region for dynamic HARQ-ACK feedback, whereas it determines a semi-static region for sending feedback.

Referring now to FIG. 4, there is a diagram showing logical resource block allocations m for macrocells and picocells such as in FIG. The parameter m increases vertically as shown. FIG. 4 illustrates a resource block (RB) allocation case where a macro UE is virtually transmitted to a pico eNB. By virtual transmission we mean that the macro UE is configured as a CoMP UE for transmitting uplink control information to the pico eNB. A logical RB map for the macro UE configuration is shown on the left side of FIG. Each RB contains a group of PUCCH resources, and the number of resources in an RB depends on the type of PUCCH transmission. Blocks 400-406 represent PUSCH, dynamic PUCCH formats 1a/1b, semi-static PUCCH regions for PUCCH formats 1/1a/1b, and semi-static PUCCH regions for PUCCH formats 2/2a/2b, respectively. The number of RBs allocated for the PUCCH format 2/2a/2b region is denoted by N(2) RB,m, while the starting offset for the dynamic PUCCH region is denoted by N(1) PUCCH,m. A logical RB map for pico UE configuration is shown on the right with similar definitions for semi-static and dynamic PUCCH regions. Block 410 represents the PUSCH, block 414 represents the dynamic PUCCH format 1a/1b region, block 416 represents the semi-static PUCCH format 1/1a/1b region, and block 418 represents the semi-static PUCCH format 2/2a2b region. LTE Releases 8-10 define PUCCH resource mapping for resource block m. These earlier release UEs determine the starting offset of the dynamic PUCCH region based on the parameters N(2) RB and N(1) PUCCH.

A CoMP UE in a macrocell may be configured to transmit UL control information in the CoMP dynamic PUCCH region indicated by block 412 in FIG. In this way, CoMP uplink control transmissions to the pico eNB do not collide with the pico cell's original uplink control transmissions. However, if the CoMP UE is equipped with only a new dedicated dynamic PUCCH offset parameter denoted as N(1) PUCCH, UE, the CoMP UE will set the macro CSI region parameter N (2) RB,m can be used. In this case, the CoMP UE's dynamic PUCCH transmissions may collide with other dynamic PUCCH resources or even PUSCH transmissions in picocells. Collisions are also possible when there are mixed RBs, where one RB contains PUCCH resources for both HARQ-ACK feedback and CSI reporting. Therefore, according to an embodiment of the present invention, both dynamic PUCCH offset and CSI region parameters are provided to the UE.

Referring now to FIG. 5, a flowchart is shown to illustrate how a UE determines the mapping of PUCCH resources to logical resource blocks. A UE receives an RRC message 500 . If one or more dedicated PUCCH parameters from N(1) PUCCH, UE and N(2) RB, UE are detected in message 500, the UE may select PUCCH resources to RB based on the detected parameters. Determine 504 the mapping. Otherwise, if the RRC message 500 does not include one or more dedicated PUCCH mapping parameters, the UE may, as at 506, set the N(1) PUCCH and N(2) RB serving cell common parameters to , determine the PUCCH resource-to-RB mapping.

In another embodiment of the invention, the UE is configured with a dedicated ID nID, which generates both base sequence index (BSI) and cyclic shift hopping (CSH) sequences for all PUCCH formats. used to The UE initializes the pseudo-random sequence generator with either PCID or nID. A binary flag is signaled to the UE to indicate whether the UE applies the serving cell's PCID or a dedicated ID to generate the BSI and CSH sequences. The UE is further configured with dedicated UE specific parameters N(1)PUCCH,UE and N(2)RB,UE to determine the starting offset of the dynamic PUCCH region.

Referring now to FIG. 6, a flow chart is shown to illustrate how a UE generates reference signals for PUCCH or SRS transmission. The UE monitors 600 for RRC messages. The UE determines at 602 whether the detected RRC message contains a dedicated PUCCH or SRS ID nID. If nID exists, the UE initializes 604 a pseudo-random number generator with nID for the base sequence group, sequence and cyclic shift hopping sequence. Otherwise, if no nID is detected in the RRC message, the UE initializes a pseudo-random sequence generator with the PCID 606 of the cell it serves for the base sequence group, sequence and cyclic shift hopping sequence. If block 608 determines that PUCCH is to be transmitted, the UE selects sequence 0 from the PUCCH sequence group and cyclic shift corresponding to time slot nS at block 610 . Otherwise, if block 608 determines that SRS is to be transmitted, the UE, at 612, responds to that time slot and the corresponding SRS SC-FDMA symbol within that time slot to generate a sequence Select group and cyclic shift. At block 614, the UE generates a suitable reference signal using the selected sequence.

CoMP enhancements can be further extended to SRS transmissions within CoMP cooperation areas. In a shared PCID scenario, this allows for increased SRS capacity, but at the expense of increased inter-cell interference. Therefore, ensuring sufficient SRS capacity while maintaining reasonable SRS overhead per cell becomes a major issue as the number of served UEs increases in CoMP coordinated areas. Area split gain can be achieved by configuring UEs clustered around a reception point with a virtual cell ID for SRS transmission to the desired reception point. As a result of introducing VCID for SRS transmission, the present invention also describes a new mechanism for improving SRS operation in non-uniform deployments. One case is when more UEs are transmitting to the macro eNB than to the pico eNB. Therefore, applying the same cell-specific SRS subframe configuration across macro and picocells disproportionately penalizes PUSCH transmission efficiency in picocells due to PUSCH rate matching in cell-specific SRS subframes. Another related issue arises to separate data and control, where the UE receives PDCCH from one eNB but transmits PUSCH to a different eNB. So, if the SRS subframe configurations are different between two cells, it needs to be determined which of these configurations should be adopted by the UE.

One embodiment of the present invention is the configuration of a dedicated UE specific ID for SRS transmission. The UE determines the base sequence group and sequence hopping pattern from the signaled SRS ID.

Another embodiment of the present invention is that the UE is further configured with dedicated SRS parameters. For example, a macro UE may be configured with cell-specific SRS parameters for pico cells to transmit SRS to pico eNBs. A UE may be configured with dedicated parameters for SRS subframe configuration, SRS bandwidth configuration, and parameters for enabling/disabling simultaneous SRS and HARQ-ACK transmissions. In TDD systems, the UE may be further configured with parameters that define the maximum uplink pilot time slot (UpPTS) region.

ここで、ＰＣＭＡＸ，ｃ（ｉ）は、セルｃをサービスするためのサブフレームｉの構成される最大送信電力である。ＰＳＲＳ＿ＯＦＦＳＥＴ，ｃ（ｍ）は、セルｃをサービスするためのｍ＝０及びｍ＝１でのより高次の層によりセミスタティックに構成される４ビットパラメータである。ここで、ｍは、ＳＲＳ送信を誘導するためのトリガタイプである。ＭＳＲＳ，ｃ（ｉ）は、セルｃをサービスするためのサブフレームｉにおけるＳＲＳ送信の帯域幅である。セルｃをサービスするためのサブフレームｉの現在の電力制御調節状態はｆｃ（ｉ）である。Ｐ０＿ＰＵＳＣＨ，ｃ（ｊ）及びαｃ（ｊ）は、セルｃをサービスするための、それぞれ、ＰＵＳＣＨ基準電力スペクトル密度及びフラクショナル電力制御パラメータである。ここで、ｊは、ＰＵＳＣＨ送信のタイプを示し、即ち、セミパーシステント、ダイナミック、又はランダムアクセス応答許可に応答する。ＰＬｃは、セルｃをサービスするためのＵＥにより計算されるダウンリンク経路損失推定である。 Both open-loop and closed-loop UL power control are closely related to CoMP operation. This is because the wireless network may configure one set of transmission points for the DL of the UE and a different set of reception points for the UL of the UE. Referring again to FIG. 3, for example, UE 214 may be configured to send UL transmissions to pico eNB 206 to minimize interference. However, UE 214 may still be configured to receive DL transmissions from macro eNB 202 . Power control issues arise when the path loss between UE 214 and pico eNB 206 is significantly different than the path loss between UE 214 and macro eNB 202 . The UE may be UL power controlled such that the reception at the pico eNB is below the desired threshold. However, macro eNB 202 may still monitor UL transmissions from UE 214 for radio resource management functions or for use in the DL in TDD systems where channel reciprocity between UL and DL may be used. . Therefore, reducing power just to meet the reception threshold at pico eNBs can degrade reception at macro eNBs. This problem typically arises when the transmission point (TP) and reception point (RP) for the UE are not collocated. One solution to this problem is to provide separate power control loops for UL and DL. A first power control loop may be used for PUSCH, PUCCH, and SRS transmissions to nearby eNBs. A second power control loop is used to ensure reliable reception at the second eNB, which has higher path loss to the UE compared to the first eNB. However, this creates other problems such as backward compatibility with legacy systems. For example, new mechanisms are needed for eNBs to signal independent transmit power control (TPC) commands to UEs. The SRS power control for LTE Release 10 is given by equation [1].

where PCMAX,c(i) is the configured maximum transmit power of subframe i for servicing cell c. PSRS_OFFSET,c(m) is a 4-bit parameter semi-statically configured by higher layers with m=0 and m=1 to service cell c. where m is the trigger type for inducing SRS transmission. MSRS,c(i) is the bandwidth of the SRS transmission in subframe i for serving cell c. The current power control adjustment state for subframe i to serve cell c is fc(i). P0_PUSCH,c(j) and αc(j) are the PUSCH reference power spectral density and fractional power control parameters, respectively, for serving cell c. where j indicates the type of PUSCH transmission, ie semi-persistent, dynamic, or responding to random access response grant. PLc is the downlink path loss estimate calculated by the UE for serving cell c.

Another embodiment of the present invention solves the power control problem described above and maintains backward compatibility with minimal impact on existing specifications. According to this embodiment, the UE is configured by higher layer signaling to transmit aperiodic SRS with offset PSRS_OFFSET(1) for UL transmission. The UE is configured by higher layer signaling to transmit aperiodic SRS with offset PSRS_OFFSET(2) for DL transmission. The power control parameters are substituted individually for a single power control parameter, corresponding to UL and DL power respectively.

The present invention describes a method of signaling two or more power control commands to a UE. A UE may be configured for aperiodic SRS transmission with dedicated power control commands in a group power control signal transmitted on the PDCCH in downlink control information (DCI) format. A UE may be configured with RRC signaling with two or more index positions in a bitmap containing transmit power control commands for multiple UEs. One TPC index indicates the TPC instruction for the first power control loop and the other TPC index indicates the TPC instruction for the second power control loop. Each TPC index can indicate a 1- or 2-bit TPC instruction. For example, in an LTE Release 10 system, 2-bit instructions are sent in DCI format 3 and 1-bit instructions are sent in DCI format 3A. When the CRC of the DCI format is scrambled by the PUCCH RNTI, one TPC index can indicate the TPC order for PUCCH, and the other TPC index indicates the TPC order for aperiodic SRS transmission. can be done. As a separate example, one or more sets of indices can be used to indicate different SRS TPC commands to the UE. Other variations are not excluded, the main idea being that the UE is configured with multiple indices in the group power control DCI to indicate TPC commands for different power control loops.

Prior art for CoMP operation is primarily based on ideal backhaul links where inter-eNB signaling in CoMP coordination areas is characterized by very high throughput and very low latency of approximately less than 1-2 ms. Target the scenario that occurs. This embodiment of the invention is also designed to work in deployments where the latency in inter-eNB signaling is at least on the order of tens of milliseconds. A base station may request via backhaul signaling (eg, using the X2 signaling protocol) that neighboring base stations transmit their PUCCH configurations. Alternatively, a base station may signal the PUCCH configuration of its controlled cell to one or more target cells controlled by other base stations via the X2 logical interface. At least the dynamic PUCCH offset parameter is indicated in the PUCCH information element signaled on the backhaul link. Also, the number of RBs allocated for transmitting CSI reports can be indicated to allow neighboring eNBs to accurately determine HARQ-ACK regions for cells controlled by different eNBs. . The number of PUCCH format 1/1a/1b resources that can be assigned in one RB, the number of cyclic shifts reserved for transmitting HARQ-ACK, and the resources used for mixed transmission of HARQ-ACK scheduling requests and CSI Other parameters may optionally be signaled, including scheduling requests in blocks.

In different embodiments of the present invention, the PUCCH configuration or some elements of this configuration may be signaled by the first base station when requested by the second base station. In an alternative embodiment, a first base station may convey preferred PUCCH configurations for neighboring cells under the control of the second base station to the second base station.

In SRS transmission, a first base station may indicate the SRS subframe configuration and SRS bandwidth configuration of the cell under its control to a second base station controlling a neighboring cell, eg, over the X2 interface. The second base station may consider this information when configuring cell-specific SRS configurations for neighboring cells, as well as dedicated SRS configurations for cell-edge UEs in that cell. For example, referring to FIG. 3, eNB 202 may configure macrocell A with a 5ms periodicity and a subframe offset of 0 for cell-specific SRS subframes. Upon receiving this information, the pico eNB 206 can configure pico cells with the same 5ms periodicity but different subframe offsets to avoid inter-cell interference. Also, in TDD systems, parameters defining the maximum UpPTS region may be signaled over a backhaul link such as the X2 interface.

Referring now to FIG. 7, an exemplary flowchart illustrating inter-eNB signaling to enable network operation in heterogeneous network deployments is shown. The eNB 702 controlling the cell serving the UE 700 sends a request for cell-specific PUCCH and/or SRS configuration for neighboring cells under control of the eNB 704 . A request message 708 is sent over the backhaul link using the X2 signaling protocol. The eNB 704 sends a reply message 710 acknowledging the previous request and also sends the requested PUCCH or SRS configuration over the backhaul link. Based on the information received from eNB 704 and based on UE measurement reports 706, eNB 702 makes a decision 712 whether the UE should be configured to transmit PUCCH and/or SRS to eNB 704. If this determination is positive, eNB 702 sends an RRC configuration message 714 to UE 700 with dedicated PUCCH or SRS parameters that match eNB 704's PUCCH or SRS configuration. For PUCCH transmission, UE 700 determines RB mapping at 716 and transmits 718 the required uplink control information on PUCCH. For aperiodic SRS request 720 targeting eNB 704 , the UE sends SRS 722 to eNB 704 . Based on the UE measurement reports 706, the eNB may alternatively determine at 712 that the UE 700 should continue to use the cross-cell PUCCH or SRS configuration. In this case, blocks 716, 718, 720, and 722 may be made according to the eNB's 702 cell common configuration.

Also, having provided such numerous examples, one of ordinary skill in the art will appreciate that the implementations described without departing from the scope of the invention as defined in the claims of the invention set forth hereinafter. It should be understood that various variations, substitutions, or alterations may be made to the examples. Other combinations will be apparent to those skilled in the art having reference to this specification.

Claims (14)

A method of transmitting an uplink reference signal, comprising:
receiving a radio resource control (RRC) message;
selecting a physical cell identity or virtual cell identity parameter in response to the status of the RRC message;
Said virtual cell identification parameterOn the basis ofto generate the base sequenceToinitializing a first pseudorandom sequence generatorWhen,
Said virtual cell identification parameterOn the basis ofto generate a cyclic shift hopping sequenceToinitializing a second pseudo-random sequence generatorWhen,
generating the uplink reference signal based on the base sequence and the cyclic shift hopping sequence;
on the physical uplink control channel (PUCCH) transmitting the uplink reference signalWhen,
A method, including The method of claim 1, wherein
configuring a user equipment with dedicated user-specific uplink control resource allocation parameters to determine an uplink control region for transmitting channel state information reports ;
determining the uplink control region for transmitting scheduling requests and hybrid auto-repeat request (HARQ) acknowledgment reports ;
The method further comprising: The method of claim 1, wherein
The method further comprising determining resource blocks for transmitting uplink control information on the PUCCH . 4. The method of claim 3 , wherein
The method, wherein the uplink control information is one of a hybrid automatic repeat request acknowledgment (HARQ-ACK) , a channel state information report , and a scheduling request. 5. The method of claim 4 , wherein
The method, wherein the HARQ-ACK is in response to one of a previous control signal scheduling downlink data transmission and a semi-persistently scheduled downlink data transmission. The method of claim 1, wherein
The method further comprising configuring a user equipment with dedicated sounding reference signal (SRS) resource allocation parameters to determine time-frequency resources for transmitting sounding reference signals. 7. The method of claim 6 , wherein
wherein the SRS resource allocation parameters include one or more of an SRS bandwidth configuration , an SRS subframe configuration , a hybrid auto-repeat request acknowledgment and an indication of whether simultaneous transmission of SRS is allowed within a subframe. including, method. A user equipment (UE),
receive a radio resource control (RRC) message;
selecting a physical cell identity or virtual cell identity parameter in response to the status of the RRC message;
initializing a first pseudo-random sequence generator to generate a base sequence based on the virtual cell identification parameter;
initializing a second pseudorandom sequence generator to generate a cyclic shift hopping sequence based on the virtual cell identity parameter;
generating the uplink reference signal based on the base sequence and the cyclic shift hopping sequence;
transmitting the uplink reference signal on a physical uplink control channel (PUCCH);
User equipment that is configured to A user equipment according to claim 8, comprising:
the user equipment is further configured with a dedicated user-specific uplink control resource allocation parameter for determining an uplink control region for transmitting channel state information reports;
A user equipment, wherein the user equipment is further configured to determine the uplink control region for transmitting scheduling requests and hybrid auto-repeat request (HARQ) acknowledgment reports. A user equipment according to claim 8, comprising:
A user equipment, wherein the user equipment is further configured to determine resource blocks for transmitting uplink control information on the PUCCH. A user equipment according to claim 10, comprising:
The user equipment, wherein said uplink control information is one of a hybrid automatic repeat request acknowledgment (HARQ-ACK), a channel state information report and a scheduling request. A user equipment according to claim 11, comprising:
The user equipment, wherein said HARQ-ACK is in response to one of a previous control signal scheduling downlink data transmission and a semi-persistently scheduled downlink data transmission. A user equipment according to claim 8, comprising:
A user equipment, wherein the user equipment is further configured with dedicated sounding reference signal (SRS) resource allocation parameters to determine time-frequency resources for transmitting sounding reference signals. 14. The user equipment of claim 13, comprising:
wherein the SRS resource allocation parameters include one or more of an SRS bandwidth configuration, an SRS subframe configuration, a hybrid auto-repeat request acknowledgment and an indication of whether simultaneous transmission of SRS is allowed within a subframe; including, user equipment.

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