Sounding reference signal cell specific sub-frame configuration

A method of wireless communication including a plurality of fixed basestations and a plurality of mobile user equipment with each basestation transmitting to any user equipment within a corresponding cell a sounding reference signal sub-frame configuration indicating sub-frames when sounding is permitted. Each user equipment recognizes the sounding reference signal sub-frame configuration and sounds only at permitted sub-frames. Differing cells may have differing sounding reference signal sub-frame configurations. There are numerous manners to encode the transmitted information.

TECHNICAL FIELD OF THE INVENTION

The technical field of this invention is wireless communication.

BACKGROUND OF THE INVENTION

FIG. 1shows an exemplary wireless telecommunications network100. The illustrative telecommunications network includes base stations101,102and103, though in operation, a telecommunications network necessarily includes many more base stations. Each of base stations101,102and103are operable over corresponding coverage areas104,105and106. Each base station's coverage area is further divided into cells. In the illustrated network, each base station's coverage area is divided into three cells. Handset or other user equipment (UE)109is shown in Cell A108. Cell A108is within coverage area104of base station101. Base station101transmits to and receives transmissions from UE109. As UE109moves out of Cell A108and into Cell B107, UE109may be handed over to base station102. Because UE109is synchronized with base station101, UE109can employ non-synchronized random access to initiate handover to base station102.

Non-synchronized UE109also employs non-synchronous random access to request allocation of up-link111time or frequency or code resources. If UE109has data ready for transmission, which may be traffic data, measurements report, tracking area update, UE109can transmit a random access signal on up-link111. The random access signal notifies base station101that UE109requires up-link resources to transmit the UE's data. Base station101responds by transmitting to UE109via down-link110, a message containing the parameters of the resources allocated for UE109up-link transmission along with a possible timing error correction. After receiving the resource allocation and a possible timing advance message transmitted on down-link110by base station101, UE109optionally adjusts its transmit timing and transmits the data on up-link111employing the allotted resources during the prescribed time interval.

FIG. 2shows the Evolved Universal Terrestrial Radio Access (E-UTRA) time division duplex (TDD) Frame Structure. Different sub-frames are allocated for downlink (DL) or uplink (UL) transmissions. Table 1 shows applicable DL/UL sub-frame allocations.

SUMMARY OF THE INVENTION

This invention addresses the timing aspects of sounding reference signal (SRS) transmission, also with the goal of reducing SIB (broadcast) and the radio resource control (RRC) overhead. Overall, the parameters related to SRS timing are: SRS sub-frame configuration (SIB signaled); SRS duration (RRC signaled); SRS periodicity (RRC signaled) and sub-frame offset (RRC signaled).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Sounding involves exchange of signals between the base station and the connected UE. Each sounding uses a reference resource identifier selected from an available reference resource identifier map h(t, L) and a portion of the spectrum selected from an available spectrum identifier map f(t, N); where L is a group of shared parameters signaled to each UE from the group; and N is a group of shared parameters signaled to each UE from the group. Some examples utilize Constant Amplitude Zero Auto-Correlation (CAZAC) sequences as the reference sequences. CAZAC sequences are complex-valued sequences with: constant amplitude (CA); and zero cyclic autocorrelation (ZAC). Examples of CAZAC sequences include: Chu sequences, Frank-Zadoff sequences, Zadoff-Chu (ZC) sequences and generalized chirp-like (GCL) sequences. CAZAC (ZC or otherwise) sequences are presently preferred.

In this invention each basestation101,102and103transmits a sounding reference signal (SRS) to connected UEs109in the corresponding cell. The UE receiving the SRS then conducts sounding in accordance with the SRS sub-frame configuration.

The SRS sub-frame configuration is broadcast by basestation101in SIB. This sub-frame configuration indicates which sub-frames are SRS sub-frames. Broadcast of the SRS sub-frame configuration is useful even for UEs109which do not transmit any SRS. SRS shouldn't collide with physical uplink shared channel (PUSCH) transmission. Thus non-SRS UEs109can extract some of their silent symbol periods from the SRS sub-frame configuration. These silent periods are useful for performing some measurements at UE109. In general each cell107and108would employ a different SRS sub-frame configuration. Ideally, basestations101,102and103would select SRS sub-frame configurations to minimize cross-cell interference.

There are two main ways of signaling and interpreting the SRS sub-frame configuration parameters. Sub-frame configuration can be defined by two parameters: the periodicity TSFC; and the offset ΔSFC. Both UEs109and basestation101keep a sub-frame counter CSFCpermitting UE109and basestation101to determine which sub-frames are configured for SRS transmission. A sub-frame is an SRS sub-frame if and only if ΔSFC=(CSFC)mod TSFC. The exact range of values of ΔSFCand TSFCneed to be defined with the number of bits and encoding for each. For example, TSFCcould be selected from the set {1, 2, 3, 4, 5, . . . , 32} allowing flexible system deployment ΔSFCcould be selected from the same set. This yields maximum flexibility, but requires 10 bits of broadcast SIB signaling, which can be very costly. A reduced overhead alternative encodes and signals TSFCfirst. This requires greatest integer in log2(TSFC) (ceil[log2(TSFC)]) bits. The bits required for ΔSFCwould be either the ceil[log2(TSFC)] or the least integer in log2(TSFC) (floor[log2(TSFC)]) because 0≦ΔSFC<TSFC. This reduces the number of required bits for signaling ΔSFC, but only for certain scenarios where TSFCis small. Another reduced overhead alternative hard codes a value for ΔSFCsuch as zero. In that case, only TSFCis signaled.

Several examples of combined TSFC, ΔSFCcoding are listed in the following tables. In these examples the SRS sub-frame configuration is encoded using either 4 or 5 bits in SIB using joint source coding in TSFCand ΔSFC. Thus a unique 4 or 5 bit combination maps into a particular pair (TSFC, ΔSFC).

Table 2 lists a 4 bit example suitable for use in frequency division duplex (FDD) systems.

TABLE 2DecimalBinaryTSFCΔSFC00000101000120200102130011504010051501015260110100701111018100010291001200101010201111011202121100400131101401141110402151111Inf.NA
In Table 2 a coding of decimal 15 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA).

Table 3 lists another 4 bit example suitable for use in FDD systems.

TABLE 3DecimalBinaryTSFCΔSFC000001010001202001021300115240100535010154601101057011110681000107910012081010102091110112010121100401113110140121411104013151111Inf.NA
In Table 3 a coding of decimal 15 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA).

Table 4 lists a 5 bit example suitable for use in FDD systems.

TABLE 4DecimalBinaryTSFCΔSFC000000101000012020001021300011504001005150010152600110537001115480100010090100110110010101021101011103120110010413011011051401110106150111120016100002011710001202181001020319100112042010100205211010120622101104002310111401241100040225110014032611010404271101140528111004062911101Optional3011110Optional3111111Inf.NA
In Table 4 codings decimal 29 and 30 are optional and not defined in this example. In Table 4 a coding of decimal 31 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA).

Table 5 lists another 5 bit example suitable for use in FDD systems.

TABLE 5DecimalBinaryTSFCΔSFC00000010100001202000102130001150400100515001015260011053700111548010001009010011011001010102110101110312011001041301101105140111010615011111071610000200171000120118100102021910011203201010020421101012052210110206231011120724110004002511001401261101040227110114032811100404291110140530111104063111111Inf.NA
In Table 5 a coding of decimal 31 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA).

Table 6 lists another 5 bit example suitable for use in FDD systems.

TABLE 6DecimalBinaryTSFCΔSFC00000010100001202000102130001150400100515001015260011053700111548010001039010011041001010105110101110612011001071301101108140111010915011112010161000020111710001201218100102013191001120142010100201521101012016221011040172310111401824110004019251100140202611010402127110114022281110040232911101Optional3011110Optional3111111Inf.NA
In Table 6 codings decimal 29 and 30 are optional and not defined in this example. In Table 6 a coding of decimal 31 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA).

Table 7 lists a 4 bit example suitable for use in time division duplex (TDD) systems.

In Table 7 codings decimal 1, 2, 5, 6, 9, 10, 13 and 14 are encoded with respect to Uplink Pilot Transmission Slot (UpPTS) orthogonal frequency division multiplexing (OFDM) symbols. If UpPTS contains two OFDM symbols: 1(a) means the first OFDM symbol is used for SRS to determine ΔSFC; and 1(b) means the second of OFDM symbol is used for SRS to determine ΔSFC. In Table 7 a coding of decimal 15 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA).

Table 8 lists a 5 bit example suitable for use in TDD systems.

TABLE 8DecimalBinaryTSFCΔSFC0000001010000151 (a)20001051 (b)30001151 (a) + 1 (b)400100525001015360011054700111101 (a)801000101 (b)901001101 (a) + 1 (b)100101010211010111031201100104130110110714011101081501111201 (a)1610000201 (b)1710001201 (a) + 1 (b)181001020219100112032010100204211010120722101102082310111401 (a)2411000401 (b)2511001401 (a) + 1 (b)261101040227110114032811100404291110140730111104083111111Inf.NA
In Table 8 codings decimal 1, 2, 3, 7, 8, 9, 15, 16, 17, 23, 24 and 25 are encoded with respect to UpPTS OFDM symbols. If UpPTS contains two OFDM symbols: 1(a) means the first OFDM symbol is used for SRS to determine ΔSFC; 1(b) means the second of OFDM symbol is used for SRS to determine ΔSFC; and 1(a)+1(b) means that both OFDM symbols are used for SRS to determine ΔSFC. In Table 8 a coding of decimal 31 indicates no SRS thus TSFCis infinite, ΔSFCis meaningless and not applicable (NA). For TDD, if the SRS sub-frame period is 1, all UL sub-frames and UpPTS can contain SRS. If UpPTS is used for short random access channel (RACH) transmission in some sub-frames, then there is no SRS. Thus basestation101does not assign any SRS UEs in RACH UpPTS sub-frames.

Table 9 lists another 5 bit example suitable for use in TDD systems.

Table 10 lists another 4 bit example suitable for use in FDD systems. Sounding reference signal sub-frames are the sub-frames satisfying └ns/2┘ mod TSFCεΔSFC.

Table 11 lists another 4 bit example suitable for use in TDD systems. Sounding reference signal sub-frames are the sub-frames satisfying └ns/2┘ mod TSFCεΔSFC. Sounding reference signals are transmitted only in configured UL sub-frames or UpPTS.

For TDD, a SRS sub-frame period of 1 means that all UL sub-frames and UpPTS can contain SRS. If UpPTS is used for short RACH transmission in some sub-frames, then there is no SRS. Thus basestation101does not assign any SRS UEs in RACH UpPTS sub-frames. For TDD, it is not clear how to have SRS sub-frame configuration with period2.

Broadcasting both ΔSFCand TSFCsupports flexible SRS sub-frame configuration. Different values of ΔSFCcan be assigned in different cells. Thus SRS transmission in one cell does not interfere with a neighboring cells. Because the set of UL sub-frames varies with DL/UL sub-frame configuration, ΔSFCis needed for SRS sub-frame configuration in TDD. Note binary tree300illustrates inFIG. 3is just an example. Different trees can be used with different depths and configurations and different joint source-encodings of (ΔSFC, TSFC).

FIG. 3illustrates a manner of jointly encoding ΔSFCand TSFCwith an efficient source code to support multiple values for the offset ΔSFCfor each TSFCusing an underlying structure.FIG. 3illustrates a binary tree based structure300. Binary tree300has exactly 2x−1 nodes, where x is 4 in this example. Identifying any point on the binary tree requires exactly x bits, 4 bits in this example. A reserved codeword may be defined meaning no SRS, for example. Each node in the binary tree is assigned a mapping to a pair of (ΔSFC, TSFC). The simplest mapping is that nodes at a certain depth are assigned a unique value of TSFC. Referring toFIG. 3, for node 1 TSFC=L, for nodes (2, 3) TSFC=2, for nodes (4, 5, 6, 7) TSFC=3, and for nodes (8, 9, 10, 11, 12, 13, 14 and 15) TSFC=3. Thus the depth identifies TSFC. In this example offset ΔSFCis derived from the value of the node mod TSFC. Such code is even simpler if we consider binary values for labeled nodes. The position of the most significant 1 bit in the binary value of a node equals the value of TSFC. This is illustrated inFIG. 3. The remaining less significant bits identify offset ΔSFC. This same binary code can be used to encode frequency position (offset and bandwidth) of SRS.

FIG. 4illustrates another embodiment of this invention. Binary tree400illustrated inFIG. 4identifies sub-frames having periodicities TSFCof (1, 2, 4, 8, 16) ms. Each node in binary tree400is mapped to a pair of (ΔSFC, TSFC). The simplest mapping assigns a unique value of TSFCto all nodes at a certain depth.FIG. 4illustrates this assignment. A simple 5-bit code identifies the node. The position of most significant 1 identifies TSFCas 2(N-1). The remaining bits identify the offset ΔSFC. If all 0 is signaled (00000), this identifies no SRS (infinity) or alternatively a one-shot SRS.

In another embodiment of the invention, the pair (ΔSFC, TSFC) is coded jointly (source encoding) and broadcast in the SIB. In this embodiment the tree structure is not necessary. For example, if TSFCtakes on values from the set (1, 2, 4, 5, 10) ms, then there are 1+2+4+5+10=22 possible values for the combination (ΔSFC, TSFC). Each one of these combinations is mapped to a unique number Y out 22 numbers and can be represented by 5 bits. Broadcasting the unique number identifies the (ΔSFC, TSFC) pair. Broadcasting the unique number could be in binary. In this example, 5 bits are need to represent the 22 possible values of Y. One option maps the range of Y into TSFC. Then (Y)mod TSFCidentifies ΔSFC.

Suppose TSFCcan have values from the set (A1, A2, . . . , AN) ms. There are A1+A2+ . . . +ANvalues for the communicated number Y. This requires ceil[log2(A1+A2+ . . . +AN)] bits to represent. The values of TSFCand ΔSFCare encoded as follows. If Y is in the range 1 to A1then TSFCis A1. If Y is in the range 1+A1to A1+A2then TSFCis A2. If Y is in the range 1+A1+ . . . +AKto A1+ . . . +AK+AK+1then TSFCis AK+1. The value of ΔSFCis determined as (Y)mod TSFC. Any remaining values of Y which do not map into (ΔSFC, TSFC) can be used to communicate re-configuration, one-shot SRS or other options.

In another embodiment of the invention, the SRS sub-frame configuration may not be exactly qui-spaced. In this embodiment introduces another parameter δSFC. Then, the SRS sub-frames are the sub-frames CSFCfor which any of the following equations hold:
ΔSFC=CSFCmodTSFC
1+ΔSFC=CSFCmodTSFC
2+ΔSFC=CSFCmodTSFC
δSFC+ΔSFC=CSFCmodTSFC
The value of the parameter δSFCcan be pre-determined and fixed. In this case the value of δSFCcan be inferred from the cell ID. Alternatively, the value of δSFCcan be signaled in the SIB. As a further alternative, the value of δSFCcan be encoded jointly or separately with TSFCand ΔSFC.

In other embodiments of the invention, multiple values for TSFC, ΔSFCand δSFCare possible. These values can also be broadcast via SIB.

RRC signaled SRS timing parameters include: duration having a range from one-shot to infinite; periodicity indicating the SRS transmission period from the UE109; and sub-frame offset identifying the offset within the SRS transmission period from the UE.

In a first embodiment the RRC overhead for SRS timing parameters include: duration is one-shot to infinite and can be encoded in one bit; periodicity selected from (2, 5, 10, 20, 40, 80, 160, 320) ms which can be encoded in 3 bits; and sub-frame offset which must be designed according to the worst case of the longest possible periodicity thus requiring ceil[log2(320)] or 9 bits to encode. Thus the number of UE specific bits signaled via RRC to describe the SRS configuration in this example equals 1+3+9=13 bits. Since the cell wide sub-frame configuration is separate from the UE specific parameters listed above, there are either two possibilities.

The number of bits and source encoding required for UE specific parameters could depend on the actual sub-frame configuration transmitted via SIB. For example, if the sub-frame configuration notes every sub-frame is an SRS sub-frame, then 1+3+9=13 bits are required to specify the UE specific parameters. Alternatively, if the sub-frame configuration notes that every tenth sub-frame is an SRS sub-frame, then a smaller number of bits would be required to specify the UE specific parameters. This approach is more cumbersome. It likely would require a different definition of RRC configured parameters, depending on the sub-frame configuration. This would disadvantageously further complicate the specification. The number of bits required for UE specific RRC parameters can be independent of the actual sub-frame configuration transmitted via SIB. The worst case sub-frame configuration is when all sub-frames are SRS sub-frames. The number of RRC configured SRS timing parameters is this worst case is 1+3+9=13 bits.

In the second option there are two SRS periods that are not multiples of each other and cannot be multiplexed on a common SRS (frequency) resource. Possible SRS periods are selected from the set (2, 5, 10, 20, 40, 80, 160, 320) ms. Thus, since 2 ms and 5 ms cannot be multiplexed, any given SRS resource should be shared either with periodicities selected from the set S1(5, 10, 20, 40, 80, 160, 320) ms or set S2(2, 10, 20, 40, 80, 160, 320) ms.FIG. 5illustrates a resource sharing tree500for set S1. Tree500for set S1illustrated inFIG. 5has 8 levels including node 1. Each W is a binary tree with 5 levels. The tree for set S1has 1+5+10+20+40+80+160+320=636 nodes. This requires 10 bits to represent. Each node of the tree for set S1encodes both the periodicity and the offset. There are 5 nodes at level 2 (2, 3, 4, 5, 6). Each of these nodes has a periodicity TSFCof 5 ms. The offset ΔSFCincreases from left to right via a one-to-one mapping from (2, 3, 4, 5, 6) to (0, 1, 2, 3, 4). This example is a simple subtraction of 2. Alternatively, it can be a mod 5 operation. At level 3, there are 10 nodes (7 to 16) each having a periodicity of 10 ms. Offsets ΔSFCcan be derived either via subtraction or a mod 10 operation as previously described.

Table 12 lists the relationship between SRS periodicity TSFCand the node index for set S1. The SRS periodicity TSFCcan be extracted from the node index via a look-up table and a few comparisons. The SRS offset ΔSFCcan be extracted by performing (Node_Index)mod TSFC. Thus SRS periodicity TSFCand the SRS offset ΔSFCare easily found from node index.

FIG. 6illustrates resource sharing tree600for set S2. Tree600for set S2has 8 levels and each W is a binary tree with 5 levels. Tree600for set S1has 1+2+10+20+40+80+160+320=633 nodes. This requires 10 bits to represent. Each node of the tree encodes both periodicity TSFCand offset ΔSFC. There are 2 nodes at level 2 (2, 3). Each of these nodes has a periodicity TSFCof 2 ms. Offset ΔSFCincreases from left to right in a one-to-one mapping from (2, 3) to (0, 1). This could be implemented by a simple subtraction of 2. Alternatively, it can be a mod 2 operation. At level 3, there are 10 nodes (4 to 13) each having a periodicity TSFCof 10 ms. Offsets ΔSFCcan be derived either via subtraction or a mod 10 operation as previously described.

Table 13 lists the relationship between SRS periodicity TSFCand the node index for set S2for two alternative codings. The SRS periodicity TSFCcan be extracted from the node index via a look-up table and a few comparisons. The SRS offset ΔSFCcan be extracted by performing (Node_Index)mod TSFC. Thus SRS periodicity TSFCand the SRS offset ΔSFCare easily found from node index.

The designation of which tree is used (set S1or set S2) can be implicitly tied to some other system parameter. For example, set S1may be used for TDD and set S2used for FDD. This choice may be tied to some alternate system parameters, broadcast via SIB or tied to some specific values of SRS sub-frame configuration. Thus the number of required RRC signaling bits can be reduced from 13 bits to 11 bits. This is about a 15% overhead reduction. This overhead reduction carries no penalty and is achieved by employing efficient source encoding of the periodicity and sub-frame offset. This set of embodiments reduces SIB and RRC signaling overhead for parameters related to SRS timing using efficient data structures such as trees. This overhead reduction is especially important for SIB signaling due to coverage issues.