WO2017075812A1

WO2017075812A1 - Srs base sequence for extended comb4 mode

Info

Publication number: WO2017075812A1
Application number: PCT/CN2015/094013
Authority: WO
Inventors: Bo Chen; Chao Wei; Guodong Li; Neng Wang
Original assignee: Qualcomm Incorporated
Priority date: 2015-11-06
Filing date: 2015-11-06
Publication date: 2017-05-11

Abstract

The present disclosure describes embodiments for reducing collisions for SRS transmitted to cells using comb4 mode and comb2 mode. In an embodiment, the SRS data included in the SRS signals is reordered such that SRS signals transmitted to a cell operating in comb4 mode do not collide with SRS signals transmitted to a cell operating in comb2 mode. In an additional or alternative embodiment, the SRS signals transmitted to a cell operating in comb4 mode are redefined such that the SRS signals transmitted to the cell operating in comb 4 mode do not collide with SRS signals transmitted to a cell operating in comb2 mode.

Description

SRS BASE SEQUENCE FOR EXTENDED COMB4 MODE

BACKGROUND Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly to configuring a sounding reference signal (SRS) base sequence for SRS transmission in comb4 mode.

Background

Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN) . The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS) , a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP) . Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs) . A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink.

As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

SUMMARY

In one aspect of the disclosure, a method of wireless communication includes determining a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two, and, in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, modifying the SRS transmissions communicated to a serving cell. The SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the serving cell using comb4 mode and SRS transmissions using comb2 mode to cells other than the serving cell. In an embodiment, modifying the SRS transmissions may include modifying a mapping of SRS data included in the SRS transmissions. In an additional or alternative embodiment, modifying the SRS transmissions may include defining a new base sequence for the SRS transmissions.

In an additional aspect of the disclosure, a computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to perform operations for wireless communication is disclosed. The operations may include determining a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two, and, in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, modifying the SRS transmissions communicated to a serving cell. The SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the serving cell using comb4 mode and SRS transmissions using comb2 mode to cells other than the serving cell. In an embodiment, modifying the SRS transmissions may include modifying a mapping of SRS data included in the SRS transmissions. In an additional or alternative embodiment, modifying the SRS transmissions may include defining a new base sequence for the SRS transmissions

In an additional aspect of the disclosure, an apparatus for wireless communication is disclosed and includes at least one processor and a memory coupled to the at least one processor. The at least one processor may be configured to determine a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two, and, in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, modifying the SRS transmissions communicated to a serving cell. The SRS transmissions may be modified to reduce sequence collisions between the SRS transmissions to the to the serving cell with comb4 and SRS transmissions with comb2 mode to cells other than the serving cell. In an embodiment, modifying the SRS transmissions may include modifying a mapping of SRS data included in the SRS transmissions. In an additional or alternative embodiment, modifying the SRS transmissions may include defining a new base sequence for the SRS transmissions.

In an additional aspect of the disclosure, an apparatus for wireless communication is disclosed and includes means for determining a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two, and means for modifying the SRS transmissions communicated to a serving cell in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode. The SRS transmissions may be modified to reduce sequence collisions between the SRS transmissions to the to the serving cell with comb4 and SRS transmissions with comb2 mode to cells other than the serving cell. In an embodiment, modifying the SRS transmissions may include modifying a mapping of SRS data included in the SRS transmissions. In an additional or alternative embodiment, modifying the SRS transmissions may include defining a new base sequence for the SRS transmissions.

The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. Characteristics of the concepts disclosed herein, both their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description, and not as a definition of the limits of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the present disclosure may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

FIG. 1 is a block diagram illustrating details of a wireless communication system.

FIG. 2is a block diagram conceptually illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure.

FIG. 3 is a block diagram illustrating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode；

FIG. 4 is a block diagram illustrating a first embodiment for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode；

FIG. 5 is a block diagram illustrating a second embodiment for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode；

FIG. 6 is a flow diagram illustrating an embodiment of a method performed at a mobile device for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode； and

FIG. 7 is a flow diagram illustrating an embodiment of a method performed at a base station for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the appended drawings and appendix, is intended as a description of various configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation.

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various possible configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation.

This disclosure relates generally to providing or participating in authorized shared access between two or more wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

A CDMA network may implement a radio technology such as universal terrestrial radio access (UTRA) , CDMA2000, and the like. UTRA includes wideband-CDMA (W-CDMA) and low chip rate (LCR) . CDMA2000 covers IS-2000, IS-95, and IS-856 standards.

A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM) . 3GPP defines standards for the GSM EDGE (enhanced data rates for GSM evolution) radio access network (RAN) , also denoted as GERAN. GERAN is the radio component of GSM/EDGE, together with the network that joins the base stations (for example, the Ater and Abis interfaces) and the base station controllers (A interfaces, etc. ) . The radio access network represents a component of a GSM network, through which phone calls and packet data are routed from and to the public switched telephone network (PSTN) and Internet to and from subscriber handsets, also known as user terminals or user equipments (UEs) . A mobile phone operator's network may comprise one or more GERANs, which may be coupled with UTRANs in the case of a UMTS/GSM network. An operator network may also include one or more LTE networks, and/or one or more other networks. The various different network types may use different radio access technologies (RATs) and radio access networks (RANs) .

An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA) , IEEE 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS) . In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from an organization named “3rd Generation Partnership Project” (3GPP) , and CDMA2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . These various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. For clarity, certain aspects of the apparatus and techniques may be described below for LTE implementations or in an LTE-centric way, and LTE terminology may be used as illustrative examples in portions of the description below； however, the description is not intended to be limited to LTE applications. Indeed, the present disclosure is concerned with shared access to wireless spectrum between networks using different radio access technologies or radio air interfaces.

A new carrier type based on LTE/LTE-A including unlicensed spectrum has also been suggested that can be compatible with carrier-grade WiFi, making LTE/LTE-A with unlicensed spectrum an alternative to WiFi. LTE/LTE-A, when operating in unlicensed spectrum, may leverage LTE concepts and may introduce some modifications to physical layer (PHY) and media access control (MAC) aspects of the network or network devices to provide efficient operation in the unlicensed spectrum and meet regulatory requirements. The unlicensed spectrum used may range from as low as several hundred Megahertz (MHz) to as high as tens of Gigahertz (GHz) , for example. In operation, such LTE/LTE-A networks may operate with any combination of licensed or unlicensed spectrum depending on loading and availability. Accordingly, it may be apparent to one of skill in the art that the systems, apparatus and methods described herein may be applied to other communications systems and applications.

System designs may support various time-frequency reference signals for the downlink and uplink to facilitate beamforming and other functions. A reference signal is a signal generated based on known data and may also be referred to as a pilot, preamble, training signal, sounding signal, and the like. A reference signal may be used by a receiver for various purposes such as channel estimation, coherent demodulation, channel quality measurement, signal strength measurement, and the like. MIMO systems using multiple antennas generally provide for coordination of sending of reference signals between antennas； however, LTE systems do not in general provide for coordination of sending of reference signals from multiple base stations or eNBs.

In some implementations, a system may utilize time division duplexing (TDD) . For TDD, the downlink and uplink share the same frequency spectrum or channel, and downlink and uplink transmissions are sent on the same frequency spectrum. The downlink channel response may thus be correlated with the uplink channel response. Reciprocity may allow a downlink channel to be estimated based on transmissions sent via the uplink. These uplink transmissions may be reference signals or uplink control channels (which may be used as reference symbols after demodulation) . The uplink transmissions may allow for estimation of a space-selective channel via multiple antennas.

In LTE implementations, orthogonal frequency division multiplexing (OFDM) is used for the downlink–that is, from a base station, access point or eNodeB (eNB) to a user terminal or UE. Use of OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates, and is a well-established technology. For example, OFDM is used in standards such as IEEE 802.11a/g, 802.16, High Performance Radio LAN-2 (HIPERLAN-2, wherein LAN stands for Local Area Network) standardized by the European Telecommunications Standards Institute (ETSI) , Digital Video Broadcasting (DVB) published by the Joint Technical Committee of ETSI, and other standards.

Time frequency physical resource blocks (also denoted here in as resource blocks or “RBs” for brevity) may be defined in OFDM systems as groups of transport carriers (e.g. sub-carriers) or intervals that are assigned to transport data. The RBs are defined over a time and frequency period. Resource blocks are comprised of time-frequency resource elements (also denoted here in as resource elements or “REs” for brevity) , which may be defined by indices of time and frequency in a slot. Additional details of LTE RBs and REs are described in the 3GPP specifications, such as, for example, 3GPPTS 36.211.

UMTS LTE supports scalable carrier bandwidths from 20 MHz down to 1.4 MHZ. In LTE, an RB is defined as 12 sub-carriers when the subcarrier bandwidth is 15 kHz, or 24 sub-carriers when the sub-carrier bandwidth is 7.5 kHz. In an exemplary implementation, in the time domain there is a defined radio frame that is 10 ms long and consists of 10 subframes of 1 millisecond (ms) each. Every subframe consists of 2 slots, where each slot is 0.5 ms. The subcarrier spacing in the frequency domain in this case is 15 kHz. Twelve of these subcarriers together (per slot) constitute an RB, so in this implementation one resource block is 180 kHz. Six Resource blocks fit in a carrier of 1.4 MHz and 100 resource blocks fit in a carrier of 20 MHz.

Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim.

FIG. 1 shows a wireless network 100 for communication, which may be an LTE-A network. The wireless network 100 includes a number of evolved nodeBs (eNBs) 105 and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB 105 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a pico cell, would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a femto cell, would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG) , UEs for users in the home, and the like) . An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB or a home eNB. In the example shown in FIG. 1, the eNBs105a, 105b and 105c are macro eNBs for the

macro cells

110a, 110b and 110c, respectively. The eNBs105x, 105y, and 105z are small cell eNBs, which may include pico or femto eNBs that provide service to

small cells

110x, 110y, and 110z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

The wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs 115 are dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, a lightning bolt (e.g., communication links 125) indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink, or desired transmission between eNBs.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, and 1200 for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz) , respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20MHz, respectively.

FIG. 2 shows a block diagram of a design of a base station/eNB 105 and a UE 115, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. For a restricted association scenario, the eNB 105 may be the small cell eNB105z in FIG. 1, and the UE 115 may be the UE115z, which in order to access small cell eNB105z, would be included in a list of accessible UEs for small cell eNB105z. The eNB 105 may also be a base station of some other type. The eNB 105 may be equipped with antennas 234a through 234t, and the UE 115 may be equipped with antennas 252a through 252r.

At the eNB 105, a transmit processor 220 may receive data from a data source 212 and control information from a controller/processor 240. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor 220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a through 232t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc. ) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 232a through 232t may be transmitted via the antennas 234a through 234t, respectively.

At the UE 115, the antennas 252a through 252r may receive the downlink signals from the eNB 105 and may provide received signals to the demodulators (DEMODs) 254a through 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc. ) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all the demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 115 to a data sink 260, and provide decoded control information to a controller/processor 280.

On the uplink, at the UE 115, a transmit processor 264 may receive and process data (e.g., for the PUSCH) from a data source 262 and control information (e.g., for the PUCCH) from the controller/processor 280. The transmit processor 264 may also generate reference symbols for a reference signal. The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by the modulators 254a through 254r (e.g., for SC-FDM, etc. ) , and transmitted to the eNB 105. At the eNB 105, the uplink signals from the UE 115 may be received by the antennas 234, processed by the demodulators 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by the UE 115. The processor 238 may provide the decoded data to a data sink 239 and the decoded control information to the controller/processor 240.

The controllers/

processors

240 and 280 may direct the operation at the eNB 105 and the UE 115, respectively. The controller/processor 240 and/or other processors and modules at the eNB 105 may perform or direct the execution of various processes for the techniques described herein with reference to FIGs. 4, 5, and 7. The controllers/processor 280 and/or other processors and modules at the UE 115 may also perform or direct the execution of the functional blocks illustrated in FIGs. 4-6, and/or other processes for the techniques described herein. The

memories

242 and 282 may store data and program codes for the eNB 105 and the UE 115, respectively. A scheduler 244 may schedule UEs for data transmission on the downlink and/or uplink.

Referring to FIG. 3, a block diagram illustrating a collision between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode is shown. As shown in FIG. 3, a first cell (labeled “CELL 1” ) may receive SRS transmissions from user equipments (UEs) on a plurality of subcarriers 310, and a second cell (labeled “CELL 2” ) may receive SRS transmissions from the user equipment (UEs) on a plurality of subcarriers 320. In FIG. 3, the first cell may be operating in comb4 mode, and the second cell may be operating in comb2 mode.

For cells operating in comb4 mode, such as the first cell of FIG. 3, a UE may be assigned a block of subcarriers for transmitting SRS to the first cell, and the UE may transmit SRS to the first cell on every 4^th subcarrier. For cells operating in comb2 mode, such as the second cell of FIG. 3, the UE may be assigned a block of subcarriers for transmitting SRS to the second cell, and the UE may transmit SRS to the first cell on every other subcarrier. For example, in FIG. 3, a first UE (e.g., UE1 in FIG. 3) may be assigned a block of subcarriers (e.g., the subcarriers above the line 302) for transmitting SRS (e.g., SRS 312 and 322) to the first cell and the second cell. For SRS transmissions to the firs cell, the UE may transmit the SRS 312 on every 4^th subcarrier of the block of subcarriers assigned to the UE, and for SRS transmissions to the second cell, the UE may transmit the SRS 322 on every other subcarrier. Assigning blocks of subcarriers to UEs for transmitting SRS allows additional UEs to send SRS to the respective cells. For example, a second UE (UE2 in FIG. 3) may be assigned a second block of subcarriers (e.g., subcarriers below the line 302) for transmitting SRS to the first cell and the second cell, respectively. The second UE may send SRS to the first cell using comb4 mode (e.g., on every 4^th subcarrier of the second block of subcarriers) and may send SRS to the second cell using comb2 mode (e.g., on every other subcarrier of the second block of subcarriers) , as described above. Additionally, using comb4 mode and/or comb2 mode allows even more UEs to transmit SRS. For example, in comb4 mode, 4 UEs may transmit SRS in a first block of subcarriers (e.g., each of the 4 UEs transmits on every 4^th subcarrier starting from a different subcarrier index, such as every 4^th subcarrier starting at subcarrier 0 of the block of subcarriers, every 4^th subcarrier starting at subcarrier 1 of the block of subcarriers, and so on) , and in comb2 mode UEs may transmit SRS in a first block of subcarriers (e.g., each of the 2 UEs transmits on every other subcarrier starting from a different subcarrier index, such as every other subcarrier starting at subcarrier 0 of the block of subcarriers, and every other subcarrier starting at subcarrier 1 of the block of subcarriers) .

SRS sequences are defined by 3 parameters: a cyclic shiftα, sequence length

and a base sequenc

where

The base sequences

are divided into groups, where u∈ {0， 1， ... 29} is the group number and v is the base sequence number within the group. For

the base sequence

is given by:

where the q^th root Zadoff-Chu sequence is defined by:

Where q is given by u and v,

and

For

and

the base sequence

is given by:

where the value of

is given by Table 5.5.1.2-1 and Table 5.5.1.2-2 in 3GPP TS36.211 for

and

In the expression above, the length

of the Zadoff-Chu sequence is given by the largest prime number such that

Assigning different u values for different cells may ensure low cross correlation between different SRS sequences of different cells due to the properties of Zadoff-Chu sequences. For example, when a first cell and a second cell are both operating in comb2 mode, the SRS transmitted for the first cell may be given by:

and the SRS transmitted for the second cell may be given by:

From equations 1 and 2 above it can be seen that, as long as u1 ≠ u2 (i.e., different group numbers for different cells) , there will be no SRS collision because q₁ ≠ q₂. However, when a first cell is operating in comb4 mode and a second cell is operating in comb2 mode, a collision may occur between SRS transmitted to the first cell and the second cell by a UE. For example, as shown in FIG. 3, at 330, a collision may occur between SRS transmitted to a first cell operating in comb4 mode and SRS transmitted to a second cell operating in comb2 mode. In this scenario, the SRS transmitted for the first cell may be given by:

and the SRS transmitted for the second cell may be given by:

From equations 3 and 4 above it can be seen that, if q₁ ＝ 4q₂, the SRS sequence of comb 0 in the first cell is a time domain shifted version of the SRS sequence of comb 0 in cell 2, causing a collision. In FIG. 3, this is illustrated by the subcarriers surrounded by the dashed line box, at 302. At present, the solution for the problem of collisions between SRS transmissions involving cells operating in comb4 and comb 2 modes, respectively, is to derive the SRS sequence index with 4 combs as q’ ₁ ＝ 4q₁, where q₁ is the SRS sequence index for comb2 mode. Under such solution, the SRS sequence with 4 combs based on q₁ is given by:

the SRS sequence with 2 combs is given by:

and

the collision parts of the SRS sequence with 2 combs is given by:

Under the current solution shown above, low cross correlation between

and

is achieved as long as q₁ ≠ q₂. However, this solution only applies to cases where

Unlike the current solution described above, which is limited by the length of the SRS sequence, the various embodiments of the present disclosure provide a solution that prevents collisions irrespective of the length of the SRS sequence, as described in more detail below with reference to FIGs. 4-7.

Referring to FIG. 6, aflow diagram illustrating an embodiment of a method performed at a mobile device for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode is shown as a method 600. In an embodiment, the method 600 may be performed by a mobile device (e.g., one of the UEs 115 of FIG. 1) . In an additional or alternative embodiment, the method 600 may be stored as instructions in a memory of a mobile device (e.g., the memory 282 of FIG. 2) , and the instructions may be executed by a processor of the mobile device (e.g., the controller/processor 280 of FIG. 2, the transmit processor 264 of FIG. 2, the transmit multiple input multiple output (MIMO) processor 266 of FIG. 2, etc. ) to perform the operations of the method 600 described below. Various concepts and features described in connection with operations of the method 600 are illustrated with reference to FIGs. 4 and 5, of which FIG. 4 is a block diagram illustrating a first embodiment for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode, and of which FIG. 5 is a block diagram illustrating a second embodiment for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode..

At 610, the method 600 include determining, at the mobile device, a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two. In an embodiment, the SRS transmission may be sent to a serving cell (e.g., CELL 1 in FIG. 4) that is operating in a comb4 mode (e.g., SRS transmission assigned with the extended comb value of four) , and other cells that are different from the serving cell (e.g., CELL 2 in FIG. 4) may be operating in a comb2 mode (e.g., SRS transmissions assigned with the standard comb value of two) . In an embodiment, the mobile device may determine the comb mode configuration based on control information communicated to the mobile device by the serving cell. At 620, the method 600 includes modifying the SRS transmissions communicated to the serving cell in response to a determination that the comb mode configuration for the SRS transmission is comb4 (e.g., the comb mode configuration for the SRS transmission is assigned with the extended comb value of four) . The SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the serving cell using comb4 mode and SRS transmissions using comb2 mode to cells other than the serving cell.

In an embodiment, modifying the SRS transmissions includes, at 622, modifying a mapping of the SRS data included in the SRS transmissions. For example, as shown in FIG. 4, a mapping of RS data 410 (e.g., SRS base sequences

u1, v (n) ) to physical resources (e.g., subcarriers) may be modified to generate SRS data 420 (e.g., SRS base sequences

Mod 2 ＝ 0) is transmitted using subcarriers included in a first block of subcarriers (e.g., the subcarriers above the line 302) , and SRS data 420 associated with odd indices (e.g., n Mod 2 ＝ 1) is transmitted using subcarriers included in a second block of subcarriers (e.g., the subcarriers below the line 302) , where the first block of subcarriers and the second block of subcarriers are different. In an embodiment, the first block of subcarriers may be assigned to a first mobile device for SRS transmission with respect to the first and second cells, and the second block of subcarriers may be assigned to a second mobile device for SRS transmission with respect to the first and second cells. As indicated by the arrows 430-442, by remapping the SRS data 410 to generate the SRS data 420, sequence collisions between SRS data transmitted in the first and second cells using comb4 mode and comb2 mode, respectively, may be avoided.

In an embodiment, the SRS data 410 is remapped to generate the SRS data 420 according to:

where

is the base sequence for SRS transmission using comb2 mode, and

where

is a base sequence for the SRS transmissions communicated to the first cell using comb4 mode, x_q is the qth root Zadoff-Chu sequence,

is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and

is the length of the Zadoff-Chu sequence. Remapping the SRS data 410, as shown in FIG. 4, provides additional advantages other than simply avoiding collisions with SRS data transmitted to cells using comb2 mode. For example, modifying the mapping of the SRS data to different subcarriers, rather than modifying how the SRS data is generated, may enable mobile devices to be more easily updated to implement embodiments of the present disclosure. As an additional example, although not shown in FIG. 4, using the SRS data 420 may avoid collisions between SRS data transmitted to a first and second cell, each of which is operating in comb4 mode. In an embodiment, the base station providing the first cell may transmit configuration information to the mobile device that indicates a mapping of the SRS data or information indicating the assigned comb mode configuration for the SRS transmission, and the configuration information may be used by the mobile device to generate the SRS data 420. It is noted that in FIG. 4, SRS transmissions with the same r’ values are found in the subcarriers for the top half (e.g., the subcarriers above the line 302) , and, for the bottom half (e.g., the subcarriers below the line 302) , the r’ value are different as well. While FIG. 3 indicates that different r’ values may result in a sequence collision, the sequences illustrated with respect to cell 1 and cell 2 in FIG. 4 do not collide because the respective SRS transmissions correspond to different root Zadoff-Chu sequences (e.g., different index q) .

In an additional or alternative embodiment, modifying the SRS transmissions includes, at 624, defining a new base sequence for the SRS transmissions. In an embodiment, the new base sequence for the SRS transmissions may be given by:

where

is the new base sequence for the SRS transmissions using the comb4 mode, x_q is the qth root Zadoff-Chu sequence,

is the length of the Zadoff-Chu sequence.

As indicated at 422 of FIG. 5, defining new base sequences for SRS transmissions may simplify the operations to map the SRS data to the subcarriers. For example, as shown in FIG. 5, the new base sequences 422 (e.g.,

) may not require remapping. That is, the new base sequence

may be transmitted on the first subcarrier (e.g., subcarrier 0) in accordance with comb4, the new base sequence

may be transmitted on the second subcarrier (e.g., subcarrier 4) in accordance with comb4, and so on. As indicated by the arrows 430-442, by generating the new SRS data 422, sequence collisions between SRS data transmitted in the first and second cells using comb4 mode and comb2 mode, respectively, may be avoided. It is noted that the new base sequence described above with reference to FIG. 5 can be regarded as another root Zadoff-Chu sequence that is generated by different mapping from the original root Zadoff-Chu sequence. Thus, there is no collision even if different SRS transmissions for a subcarrier occur since Zadoff-Chu sequences have low cross correlation properties.

At 630, the method 600 includes transmitting the SRS data to the serving cell based on the modifications to the SRS transmissions. In an embodiment, the SRS data transmitted to the serving cell may be transmitted using comb4 mode. In an embodiment, 630 may further include transmitting SRS data to the base station associated with the second cell based on non-modified SRS data using comb2 mode. In an embodiment, determining the comb mode configuration for the SRS transmission according to the method 600 may include determining a first comb mode configuration for type 0 periodic SRS transmission and a second comb mode configuration for type 1 aperiodic SRS transmission, and assigning the determined comb mode configuration to all transmission antenna ports associated with the SRS transmission. In an embodiment, the method 600 may further include determining a transmission comb value associated with a first antenna port for the SRS transmission using the comb4 mode based on K_TC or mod (K_TC+2， 4) , where K_TC is a configured transmission comb value for the first antenna port.

Referring to FIG. 7 is a flow diagram illustrating an embodiment of a method performed at a base station for reducing or eliminating sequence collisions between sounding reference signals (SRS) transmitted using a comb4 mode and SRS transmitted using a comb 2 mode is shown as a method 700. In an embodiment, the method 700 may be performed by a base station (e.g., one of the eNBs 105 of FIG. 1) . In an additional or alternative embodiment, the method 700 may be stored as instructions in a memory of a base station (e.g., the memory 242 of FIG. 2) , and the instructions may be executed by a processor of the mobile device (e.g., the controller/processor 240 of FIG. 2, the transmit processor 220 of FIG. 2, the transmit multiple input multiple output (MIMO) processor 230 of FIG. 2, etc. ) to perform the operations of the method 700 described below.

At 710, the method 700 includes determining, at a first cell, a comb mode configuration for an SRS transmission assigned with one of: an extended comb value of four and a standard comb value of two. In an embodiment, the SRS transmission may be configured for transmission to the first cell (e.g., a serving cell, such as CELL 1 in FIG. 4) , which is operating in a comb4 mode (e.g., SRS transmission assigned with the extended comb value of four) , and other cells that are different from the serving cell (e.g., CELL 2 in FIG. 4) may be operating in a comb2 mode (e.g., SRS transmissions assigned with the standard comb value of two) . At 720, the method 700 includes modifying SRS transmissions communicated to the first cell in response to a determination that the comb mode configuration for the SRS transmission is the comb4 mode (e.g., the comb mode configuration for the SRS transmission is assigned the extended comb value of four) . The SRS transmissions may be modified to reduce sequence collisions between the SRS transmissions using the comb4 mode and SRS transmissions using the comb2 mode (e.g., the comb mode configuration for the SRS transmission is assigned the standard comb value of two) .

In an embodiment, the method 700 includes, at 722, modifying a mapping of the SRS data included in the SRS transmissions. In an embodiment, the mapping may be modified in the manner described above with reference to FIG. 4. In an embodiment, the base station providing the first cell may transmit configuration information to a mobile device, and the configuration information may indicate the modifications to the mapping of the SRS data 410 to enable the mobile device to generate the SRS data 420. In an additional or alternative embodiment, modifying the SRS transmissions communicated to the first cell includes, at 724, defining a new base sequence for the SRS transmissions. In an embodiment, the new base sequence (s) for the SRS transmissions may be generated in the manner described above with reference to FIG. 5. In an embodiment, the base station providing the first cell may transmit configuration information to a mobile device, and the configuration information may indicate, to the mobile device, how to generate the new base sequences to enable the mobile device to generate the SRS data 422 of FIG. 5.

At 730, the method 700 includes receiving, by the base station, SRS transmissions from at least one mobile device in accordance with the information indicating the modifications to the SRS transmission. Although not shown in FIG. 7, in an embodiment, the method 700 may include determining a first comb mode configuration for type 0 periodic SRS transmission and a second comb mode configuration for type 1 aperiodic SRS transmission, and assigning the determined comb mode configuration to all transmission antenna ports associated with the SRS transmission. In an embodiment, not shown in FIG. 7, the method 700 may include determining a transmission comb value associated with a first antenna port for the SRS transmission using the comb4 mode based on K_TC or mod (K_TC+2， 4) , where K_TC is a configured transmission comb value for the first antenna port.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The functional blocks and modules in FIGs. 1-7 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. Skilled artisans will also readily recognize that the order or combination of components, methods, or interactions that are described herein are merely examples and that the components, methods, or interactions of the various aspects of the present disclosure may be combined or performed in ways other than those illustrated and described herein.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. Computer-readable storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, a connection may be properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, or digital subscriber line (DSL) , then the coaxial cable, fiber optic cable, twisted pair, or DSL, are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

In conjunction with the various embodiments disclosed herein, an apparatus for configuring transmission of sounding reference signals (SRS) is disclosed and includes means for detecting that a first cell is operating in a comb4 mode for SRS transmission and a second cell is operating in a comb2 mode for SRS transmission. In an embodiment, the means for detecting may be the control processor 240 of FIG. 2 (e.g., for a base station embodiment, as described with reference to 7) or the controller/processor 280 of FIG. 2 (e.g., for a mobile device embodiment, as described with reference to FIG. 6) . Further, the apparatus includes means for modifying SRS transmissions communicated to the first cell in response to detection that the first cell is operating in the comb4 mode and the second cell is operating in the comb2 mode. In an embodiment, the means for modifying the SRS transmissions may be the controller/processor 240, the scheduler 244, the transmit processor 220, the transmit MIMO processor 230, the MIMO detector 236, the receive processor 238, or a combination thereof. In an additional or alternative embodiment, the means for modifying the SRS transmissions may be the controller/processor 280, the transmit processor 264, the transmit MIMO processor 266, the MIMO detector 256, the receive processor 258, or a combination thereof. In an embodiment, the means for modifying the SRS transmissions may include means for modifying a mapping of the SRS data included in the SRS transmissions. In an embodiment, the means for modifying the mapping o the SRS data may include the controller/processor 240, the scheduler 244, the transmit processor 220, the transmit MIMO processor 230, the MIMO detector 236, the receive processor 238, or a combination thereof. In an additional or alternative embodiment, the means for modifying the mapping o the SRS data may be the controller/processor 280, the transmit processor 264, the transmit MIMO processor 266, the MIMO detector 256, the receive processor 258, or a combination thereof. In an additional or alternative embodiment, the means for modifying the SRS transmissions may include means for defining a new base sequence for the SRS transmissions. In an embodiment, the means for defining a new base sequence for the SRS transmissions may be the controller/processor 240, the scheduler 244, the transmit processor 220, the transmit MIMO processor 230, the MIMO detector 236, the receive processor 238, or a combination thereof. In an additional or alternative embodiment, the means for defining a new base sequence for the SRS transmissions may be the controller/processor 280, the transmit processor 264, the transmit MIMO processor 266, the MIMO detector 256, the receive processor 258, or a combination thereof. In an embodiment, the apparatus includes means for transmitting information indicating the modifications to the SRS transmissions to at least one mobile device being served by the first cell, and means for receiving SRS transmissions transmitted in accordance with the information indicating the modifications to the SRS transmissions. In an embodiment, the means for transmitting may be the transmit processor 220, the transmit MIMO processor 230, that antennas 234a-234t, the modulator/demodulators 232a-232t, or a combination thereof. In an embodiment, the means for receiving may be the receive processor 238, the MIMO detector 236, that antennas 234a-234t, the modulator/demodulators 232a-232t, or a combination thereof. In an embodiment, the apparatus includes means for receiving information indicating the modifications to the SRS transmissions to at least one mobile device being served by the first cell, and means for receiving SRS transmissions transmitted in accordance with the information indicating the modifications to the SRS transmissions. In an embodiment, the means for receiving information indicating the modifications to the SRS transmissions may be the receive processor 258, the MIMO detector 256, that antennas 252a-252r, the modulator/demodulators 254a-254r, or a combination thereof. In an embodiment, the apparatus includes means for transmitting SRS data in accordance with the modified SRS configuration. In an embodiment, the for transmitting SRS data in accordance with the modified SRS configuration may be the transmit processor 220, the transmit MIMO processor 230, that transmit antennas 252a-252r, the modulator/demodulators 254a-254r, or a combination thereof.

As used herein, including in the claims, the term “and/or, ” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone； B alone； C alone； A and B in combination； A and C in combination； B and C in combination； or A, B, and C in combination. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) or any of these in any combination thereof.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

WHAT IS CLAIMED IS:

Claims

A method of wireless communication comprising:

determining a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two； and

in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, modifying the SRS transmissions communicated to a serving cell, wherein the SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the serving cell using comb4mode and SRS transmissions usingcomb2 mode to cells other than the serving cell.
The method of claim 1, wherein modifying the SRS transmissions includes modifying a mapping of SRS data included in the SRS transmissions.
The method of claim 2, wherein the mapping is modified such that SRS data associated with even indices is transmitted using subcarriers included in a first block of subcarriers and SRS data associated with odd indices is transmitted using subcarriers included in a second block of subcarriers, wherein the first block of subcarriers and the second block of subcarriers are different.
The method of claim 2, wherein SRS data is mapped to subcarriers according to:

wherein
is a base sequence for the SRS transmissions using the comb2 mode,

wherein
is a base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The method of claim 1, wherein modifying the SRS transmissions includes defining a new base sequence for the SRS transmissions.
The method of claim 5, wherein the new base sequence for the SRS transmissions is given by:

wherein
is the new base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The method of claim 1, wherein determining the comb mode configuration for the SRS transmission includes determining a first comb mode configuration for type 0 periodic SRS transmission and a second comb mode configuration for type 1 aperiodic SRS transmission.
The method of claim 7, wherein the method includes assigning the determined comb mode configuration to all transmission antenna ports associated with the SRS transmission.
The method of claim 8, wherein the method includes determining a transmission comb value associated with a first antenna port for the SRS transmission using the comb4 mode based on K_TC or mod (K_TC+2， 4) , where K_TC is a configured transmission comb value for the first antenna port.
The method of any combination of claims 1-9.
A computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to perform operations for wireless communication, the operations comprising:

determining a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two； and

in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, modifying the SRS transmissions communicated to a serving cell, wherein the SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the serving cell with comb4 and SRS transmissions with comb2 mode to cells other than the serving cell.
The computer-readable storage medium of claim 11, wherein the operations to modify the SRS transmissions include operations for modifying a mapping of SRS data included in the SRS transmissions.
The computer-readable storage medium of claim 12, wherein the mapping is modified such that SRS data associated with even indices is transmitted using subcarriers included in a first block of subcarriers and SRS data associated with odd indices is transmitted using subcarriers included in a second block of subcarriers, wherein the first block of subcarriers and the second block of subcarriers are different.
The computer-readable storage medium of claim 12, wherein the SRS data is mapped to subcarriers according to:

wherein
is a base sequence for the SRS transmissions using the comb2 mode,

wherein r′_u，v (n) is a base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The computer-readable storage medium of claim 11, wherein the operations to modify the SRS transmissions include operations for defining a new base sequence for the SRS transmissions.
The computer-readable storage medium of claim 15, wherein the new base sequence for the SRS transmissions is given by:

wherein
is the new base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The computer-readable storage medium of claim 11, wherein determining the comb mode configuration for the SRS transmission includes determining a first comb mode configuration for type 0 periodic SRS transmission and a second comb mode configuration for type 1 aperiodic SRS transmission.
The computer-readable storage medium of claim 17, wherein the operations include assigning the determined comb mode configuration to all transmission antenna ports associated with the SRS transmission.
The computer-readable storage medium of claim 18, wherein the operations include determining a transmission comb value associated with a first antenna port for the SRS transmission using the comb4 mode based on K_TC or mod (K_TC+2， 4) , where K_TC is a configured transmission comb value for the first antenna port.
An apparatus for wireless communication comprising:

at least one processor configured to:

determine a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two； and

in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, modifying the SRS transmissions communicated to a serving cell, wherein the SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the to the serving cell with comb4 and SRS transmissions with comb2 mode to cells other than the serving cell； and

a memory coupled to the at least one processor.
The apparatus of claim 20, wherein the at least one processor is configured to modify the SRS transmissions by modifying a mapping of SRS data included in the SRS transmissions.
The apparatus of claim 21, wherein the mapping is modified such that SRS data associated with even indices is transmitted using subcarriers included in a first block of subcarriers and SRS data associated with odd indices is transmitted using subcarriers included in a second block of subcarriers, wherein the first block of subcarriers and the second block of subcarriers are different.
The apparatus of claim 21, wherein the SRS data is mapped to subcarriers according to:

wherein
is a base sequence for SRS transmission using the comb2 mode,

wherein
is a base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The apparatus of claim 20, wherein the at least one processor modifies the SRS transmissions by defining a new base sequence for the SRS transmissions.
The apparatus of claim 24, wherein the new base sequence for the SRS transmissions is given by:

wherein
is the new base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The apparatus of claim 20, wherein determining the comb mode configuration for the SRS transmission includes determining a first comb mode configuration for type 0 periodic SRS transmission and a second comb mode configuration for type 1 aperiodic SRS transmission.
The apparatus of claim 26, wherein the at least one processor is configured to assign the determined comb mode configuration to all transmission antenna ports associated with the SRS transmission.
The apparatus of claim 27, wherein the at least one processor is configured to determine a transmission comb value associated with a first antenna port for the SRS transmission using the comb4 mode based on K_TC or mod (K_TC+2， 4) , where K_TC is a configured transmission comb value for the first antenna port.
An apparatus for wireless communication comprising:

means for determining a comb mode configuration for an SRS transmission assigned with one of: an extended comb value four and a standard comb value two； and

means for modifying SRS transmissions communicated to a serving cell in response to a determination that the comb mode configuration for the SRS transmission is comb4 mode, wherein the SRS transmissions are modified to reduce sequence collisions between the SRS transmissions to the serving cell using comb4 mode and SRS transmissions using comb2 mode to cells other than the serving cell.
The apparatus of claim 29, wherein the means for modifying the SRS transmissions includes means for modifying a mapping of SRS data included in the SRS transmissions.
The apparatus of claim 30, wherein the means for modifying the mapping of the SRS data is configured to modify the mapping such that SRS data associated with even indices is transmitted using subcarriers included in a first block of subcarriers and SRS data associated with odd indices is transmitted using subcarriers included in a second block of subcarriers, wherein the first block of subcarriers and the second block of subcarriers are different.
The apparatus of claim 30, wherein the SRS data is mapped to subcarriers according to:

wherein
is a base sequence for the SRS transmissions using comb2 mode,

wherein
is a base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The apparatus of claim 29, wherein the means for modifying the SRS transmissions includes means for defining a new base sequence for the SRS transmissions.
The apparatus of claim 33, wherein the new base sequence for the SRS transmissions is given by:

wherein
is the new base sequence for the SRS transmissions using the comb4 mode, x_q is the q^th root Zadoff-Chu sequence,
is the SRS sequence length, u is the group number, v is the base sequence number within the group u, and
is the length of the Zadoff-Chu sequence.
The apparatus of claim 29, wherein the means for determining the comb mode configuration for the SRS transmission includes means for determining a first comb mode configuration for type 0 periodic SRS transmission and a second comb mode configuration for type 1 aperiodic SRS transmission.
The apparatus of claim 35, wherein the apparatus includes means for assigning the determined comb mode configuration to all transmission antenna ports associated with the SRS transmission.
The apparatus of claim 36, wherein the apparatus includes means for determining a transmission comb value associated with a first antenna port for the SRS transmission using the comb4 mode based on K_TC or mod (K_TC+2， 4) , where K_TC is a configured transmission comb value for the first antenna port.