Source: http://patents.com/us-9521019.html
Timestamp: 2018-01-23 08:05:03
Document Index: 6340601

Matched Legal Cases: ['Application No. 2', 'Application No. 2008800090392', 'Application No. 10', 'Application No. 2012', 'Application No. 08005035', 'Application No. 2', 'Application No. 2014', 'Application No. 5564', 'Application No. 2015']

US Patent # 9,521,019. Efficient uplink feedback in a wireless communication system - Patents.com
United States Patent 9,521,019
Khan , et al. December 13, 2016
Efficient uplink feedback in a wireless communication system
Khan; Farooq (Allen, TX), Pi; Zhouyue (Richardson, TX)
Family ID: 1000002288923
13/663,809
US 20130064217 A1 Mar 14, 2013
11907944 Oct 18, 2007 8451915
60919311 Mar 21, 2007
Current CPC Class: H04L 25/03343 (20130101); H04L 2025/03414 (20130101); H04L 2025/03426 (20130101); H04L 2025/03802 (20130101)
Field of Search: ;375/220,260,267,295,316 ;370/204,329,330,335
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1. A method for transmitting control information by a user equipment (UE), the method comprising: receiving a reference signal from a first transceiver; in response to the reception of the reference signal, determining a plurality of control information based upon the received reference signal; jointly encoding the plurality of control information using a block code; modulating the encoded control information to generate a plurality of modulated symbols using a modulation scheme; multiplying a selected sequence with the modulated symbols to generate a plurality of multiplied sequences; mapping the plurality of multiplied sequences into two sets of resource elements in time and frequency domains in a subframe, the two sets of resource elements allocated to the UE, a first set of the two sets of resource elements being located in one edge of the subframe in the frequency domain and in a first half of the subframe in the time domain, and a second set of the two sets of resource elements being located in an opposite edge of the subframe in the frequency domain and in a second half of the subframe in the time domain; and converting the mapped sequences to radio frequency signals for transmission.
4. The method of claim 1, further comprising: applying a constant amplitude zero autocorrelation (CAZAC) sequence to the modulated symbols to generate a plurality of CAZAC-modulated sequences; and transmitting the plurality of CAZAC-modulated sequences using a number of subcarriers, wherein the number of subcarriers is an integer multiple of a length of the CAZAC sequence, and wherein the length of the CAZAC sequence is 12.
5. The method of claim 1, further comprising: applying a constant amplitude zero autocorrelation (CAZAC) sequence to the modulated symbols to generate a plurality of CAZAC-modulated sequences; and transmitting the plurality of CAZAC-modulated sequences using a number of subcarriers, wherein the number of subcarriers is an integer multiple of a length of the CAZAC sequence, wherein the plurality of CAZAC-modulated sequences are mapped into the two sets of resource elements.
6. A user equipment (UE), comprising: a receiver configured to receive a reference signal from a first transceiver; and a controller configured to: in response to the reception of the reference signal, determine a plurality of control information based upon the received reference signal, jointly encode the plurality of control information using a block code, modulate the encoded control information to generate a plurality of modulated symbols using a modulation scheme, multiply a selected sequence to with the modulated symbols to generate a plurality of multiplied sequences, map the plurality of multiplied sequences into two sets of resource elements in time and frequency domains in a subframe, the two sets of resource elements allocated to the UE, a first set of the two sets of resource elements being located in one edge of the subframe in the frequency domain and in a first half of the subframe in the time domain, and a second set of the two sets of resource elements being located in an opposite edge of the subframe in the frequency domain and in a second half of the subframe in the time domain, and convert the mapped sequences to radio frequency signals for transmission.
9. The UE of claim 6, wherein the controller configured to: apply a constant amplitude zero autocorrelation (CAZAC) sequence to the modulated symbols to generate a plurality of CAZAC-modulated sequences; and cause transmission of the plurality of CAZAC-modulated sequences using a number of subcarriers, wherein the number of subcarriers is an integer multiple of a length of the CAZAC sequence, and wherein the length of the CAZAC sequence is 12.
10. The UE of claim 6, wherein the controller configured to: apply a constant amplitude zero autocorrelation (CAZAC) sequence to the modulated symbols to generate a plurality of CAZAC-modulated sequences; and cause transmission of the plurality of CAZAC-modulated sequences using a number of subcarriers, wherein the number of subcarriers is an integer multiple of a length of the CAZAC sequence, and wherein the plurality of CAZAC-modulated sequences are mapped into the two sets of resource elements.
11. A method for receiving control information from a user equipment (UE) at a base station, comprising: transmitting a reference signal from a first transceiver; and receiving signals from the UE at the base station, the signals generated by: receiving the reference signal at the UE; in response to the reception of the reference signal, determining a plurality of control information based upon the received reference signal, jointly encoding the plurality of control information using a block code, modulating the encoded control information to generate a plurality of modulated symbols using a modulation scheme, multiplying a selected sequence with the modulated symbols to generate a plurality of multiplied sequences, mapping the plurality of multiplied sequences into two sets of resource elements in time and frequency domains in a subframe, the two sets of resource elements allocated to the UE, a first set of the two sets of resource elements being located in one edge of the subframe in the frequency domain and in a first half of the subframe in the time domain, and a second set of the two sets of resource elements being located in an opposite edge of the subframe in the frequency domain and in a second half of the subframe in the time domain; and converting the mapped sequences to radio frequency signals for transmission.
14. The method of claim 11, wherein the received signals are generated by: applying a constant amplitude zero autocorrelation (CAZAC) sequence to the modulated symbols to generate a plurality of CAZAC-modulated sequences; and transmitting the plurality of CAZAC-modulated sequences using a number of subcarriers, wherein the number of subcarriers is an integer multiple of a length of the CAZAC sequence, and wherein the length of the CAZAC sequence is 12.
15. The method of claim 11, wherein the received signals are generated by: applying a constant amplitude zero autocorrelation (CAZAC) sequence to the modulated symbols to generate a plurality of CAZAC-modulated sequences; and transmitting the plurality of CAZAC-modulated sequences using a number of subcarriers, wherein the number of subcarriers is an integer multiple of a length of the CAZAC sequence, and wherein the plurality of CAZAC-modulated sequences are mapped into the two sets of resource elements.
The plurality of modulated sequences may be mapped into the available transmission resources by dividing the available transmission resources into a plurality of equal duration resource elements in time and frequency domain, with each resource element formed with a plurality of subcarriers, and the number of subcarriers in each resource element being equal to the length of each of the plurality of modulated sequences; selecting a plurality of continuous time-domain subframes for control channel transmission, selecting two sets of resource elements in each time-domain subframe, with a first set of resource elements being located in one edge of the subframe in time and frequency domain, and a second set of resource elements being located in the opposite edge of the subframe in time and frequency domain, and the relationship between the number of resource elements in the two sets of resource elements in each selected subframe the number of the plurality of modulated sequences being established by: M=X.times.N where M is the number of the modulated sequences, X is the number of the selected subframe, and N is the number of resource elements in the two sets of resource elements is each selected subframe; and mapping the plurality of modulated sequences into the selected resource elements in the selected subframes.
FIG. 11 is an illustration of an example of MIMO layer ordering on different subbands for a 2.times.2 MIMO system suitable for the practice of the principles of the present invention;
In a communication link, a multi-path communication channel results in a frequency-selective fading. Moreover, in a mobile wireless environment, the channel also results in a time-varying fading. Therefore, in a wireless mobile system employing OFDM/DFT-Spread-OFDM based access, the overall system performance and efficiency can be improved by using, in addition to time-domain scheduling, frequency-selective multi-user scheduling. In case of frequency-selective multi-user scheduling, a contiguous set of subcarriers potentially experiencing an upfade is allocated for transmission to a user. Upfade is a situation where multipath conditions cause a radio signal to gain strength. The total bandwidth is divided into multiple subbands, and each subband contains multiple contiguous subcarriers. As shown in FIG. 3, subcarriers f.sub.1, f.sub.2, f.sub.3 and f.sub.4 are grouped into a subband 201 for transmission to a user in frequency-selective multi-user scheduling mode. The frequency-selective multi-user scheduling is generally beneficial for low mobility users for which the channel quality can be tracked.
Multiple Input Multiple Output (MIMO) schemes use multiple transmit antennas and multiple receive antennas to improve the capacity and reliability of a wireless communication charnel. A MIMO system promises linear increase in capacity with K where K is the minimum of number of transmit (M) and receive antennas (N), i.e. K=min(M,N). A simplified example of a 4.times.4 MIMO system is shown in FIG. 5. In this example, four different data streams are transmitted separately from the four transmission antennas. The transmitted signals are received at the four reception antennas. Some form of spatial signal processing is performed on the received signals in order to recover the four data streams. An example of spatial signal processing is vertical Bell Laboratories Layered Space-Time (V-BLAST) which uses the successive interference cancellation principle to recover the transmitted data streams. Other variants of MIMO schemes include schemes that perform some kind of space-time coding across the transmit antennas (e.g., diagonal Bell Laboratories Layered Space-Time (D-BLAST)) and also beamforming schemes such as Spatial Division multiple Access (SDMA).
The MIMO channel estimation consists of estimating the channel gain and phase information for links from each of the transmit antennas to each of the receive antennas. Therefore, the channel for M.times.N MIMO system consists of an N.times.M matrix:
where a.sub.ij represents the channel gain from transmit antenna j to receive antenna i. In order to enable the estimations of the elements of the MIMO channel matrix, separate pilots are transmitted from each of the transmit antennas.
An optional precoding protocol that employs a unitary pre-coding before mapping the data streams to physical antennas is shown in FIGS. 8A and 8B. The optional precoding creates a set of virtual antennas (VA) 171 before the pre-coding. In this case, each of the codewords is potentially transmitted through all the physical transmission antennas 172. Two examples of unitary precoding matrices, P.sub.1 and P.sub.2 for the case of two transmission antennas 172 may be:
Assuming modulated symbols S.sub.1 and S.sub.2 are transmitted at a given time through stream 1 and stream 2 respectively. Then the modulated symbol T.sub.1 after precoding with matrix P.sub.1 in the example as shown in FIG. 8A and the modulated symbol T.sub.2 after precoding with matrix P.sub.2 in the example as shown in FIG. 8B can be respectively written as:
.function..function..times..function..times..times..function..function..t- imes..function..times..times..times..times. ##EQU00003## Therefore, the symbols
.times..times..times..times. ##EQU00004## will be transmitted via antenna 1 and antenna 2, respectively, when precoding is done using precoding matrix P.sub.1 as shown in FIG. 8A. Similarly, the symbols
.times..times..times..times..times..times..times..times. ##EQU00005## will be transmitted via antenna 1 and antenna 2, respectively, when precoding is done using precoding matrix P.sub.2 as shown in FIG. 8B. It should be noted that precoding is done on an OFDM subcarrier level before the IFFT operation as illustrated in FIGS. 8A and 8B.
An example of MIMO precoding is Fourier-based precoding. A Fourier matrix is a N.times.N square matrix with entries given by: P.sub.N=e.sup.j2.pi.mn/Nm,n=0,1, . . . (N-1) (4) A 2.times.2 Fourier matrix can be expressed as:
e.pi. ##EQU00006## Similarly, a 4.times.4 Fourier matrix can be expressed as:
e.pi.e.pi.e.pi.e.pi.e.pi.e.pi.e.pi.e.pi.e.pi. ##EQU00007## Multiple precoder matrices can be defined by introducing a shift parameter (g/G) in the Fourier matrix as given by:
e.times..times..times..pi..times..times..times..times..times..times..time- s. ##EQU00008## A set of four 2.times.2 Fourier matrices can be defined by taking G=4. These four 2.times.2 matrices with g=0, 1, 2 and 3 are written as:
e.pi.e.pi.e.pi.e.pi.e.pi.e.pi. ##EQU00009##
When the total bandwidth in an OFDM system is divided into a plurality of subbands, each subband being a set of consecutive subcarriers, due to frequency-selective fading in the OFDM system, the optimal precoding for different subbands (SBs), can be different, as shown in one example illustrated in FIG. 9. In FIG. 9, different SBs use different precoding matrix. Subband 1 (SB1) which includes continuous OFDM subcarriers 1 through 64, uses precoding matrix P.sub.2.sup.2; SB2 which includes continuous OFDM subcarriers 65 through 128, uses precoding matrix P.sub.2.sup.1, etc. Therefore, the precoding feedback information is transmitted on a subband basis. Moreover, due to feedback errors, the base station also needs to inform the user equipment of the precoding information used on transmitted subbands. This results in additional signaling overhead in the downlink.
Besides precoding information, another form of feedback information is rank information, i.e., the number of MIMO layers. A MIMO layer is a spatial channel that can carry data symbols. It is well known that even when a system can support 4.times.4 MIMO, rank-4 (4 MIMO layers) transmissions are not always desirable. The MIMO channel experienced by the UE generally limits the maximum rank that can be used for transmission. In general for weak users in the system, a lower rank transmission is preferred over a higher rank transmission from the throughput perspective. Moreover, due to frequency-selective fading, optimal rank may be different on different subbands. As shown in the example of FIG. 10, SB1 uses rank-1 transmission; SB2 uses rank-2 transmission, etc. Therefore, the UE needs to include the rank information in the feedback information on a subband basis. Also, due to a possibility of feedback errors, the base station additionally needs to indicate the transmitted MIMO rank on different subbands. The rank information can also be common across the subbands, that is, a single rank value is reported for all the subbands. In any case, this results in additional overhead on the downlink.
.function.e.times..times..pi..times..times..times..times..times..times..t- imes..times..times..times..times.e.times..times..pi..times..times..times..- times..times..function..times..times..times..times..times..times..times..t- imes..times. ##EQU00010## where p, the sequence index, is relatively prime to N (i.e. the only common divisor for p and N is 1). For a fixed p, the Zadoff-Chu (ZC) sequence has ideal periodic auto-correlation property (i.e. the periodic auto-correlation is zero for all time shift other than zero). For different p, ZC sequences are not orthogonal, but exhibit low cross correlation. If the sequence length N is selected as a prime number, there are N-1 different sequences with periodic cross-correlation of 1/ {square root over (N)} between any two sequences regardless of time shift.
In summary, with Zadoff-Chu sequence, N-1 different sequences with fixed periodic cross-correlation are available to be used as preambles, provided that N is a prime number. In addition, each of the sequence has ideal periodic auto-correlation property.
According to a first embodiment of the principles of the present invention, Table 1 lists eleven possible physical uplink control channel (PUCCH) formats. The PUCCH may contain seven fields: "Format", "Subbands CQI", "MIMO rank and selected layers", "MIMO precoding", "ACK/ACK", "Reserved" and "CRC". The PUCCH may have a total of five possible payload sizes, namely 60, 43, 36, 27 and 16 bits. We assume that the UE provides feedback when one (1), five (5) or ten (10) subbands over the total bandwidth are defined. The first possible control channel, i.e., control channel 1 carries subband CQI and subband based MIMO precoding information for the case of 10 subbands. The total payload size for control channel 1 is 60 bits. Control channel 2 carries subband CQI but no MIMO information for the case of 10 subbands. If we assume that MIMO rank information is common across the subbands, it is not necessary for the PUCCH to carry the information about the MIMO rank and the selected layers. Therefore, the number of bits in the field of "MIMO rank and selected layers" may be zero (0). The payload size for control channel 2 is 36 bits. Control channel 3 carries MIMO information for the case of 10 subbands but no CQI information. The payload size for control channel 3 is 36 bits. A UE may transmit control channel 2 and control channel 3 alternatively to provide the Node-B (i.e., the base station) information on both subband CQI and subband-based precoding. A 1-bit Format indication tells the Node-B which information is carried at a given time. This alternative transmission of control channel 2 and control channel 3 allows UE to transmit at a lower power compared to the case where UE uses control channel 1 for transmission of both subband CQI and subband precoding information. The Node-B does not need to blindly decode between control channel 2 and control channel 3 because of the presence of 1-bit format indication.
TABLE-US-00001 TABLE I Uplink PUCCH control channel formats MIMO Control Rank and channel Subbands selected MIMO ACK/ Total No. Format CQI Layers Precoding NACK Reserved CRC bits Subband CQI and 1 0 25 4 20 2 1 8 60 Subband precoding [10 subbands] Suband CQI and no 2 1 25 0 0 2 0 8 36 MIMO information [10 subbands] MIMO and 3 1 0 4 20 2 1 8 36 ACK/NACK (No- CQI information) [10 subbands] Suband CQI and 4 1 25 4 3 2 0 8 43 Common precoding [10 subbands] Average CQI and 5 2 5 4 3 2 3 8 27 common precoding [1 subband] Average CQI and no 6 2 5 4 0 2 6 8 27 (fixed) precoding [1 subband] Suband CQI and 7 1 15 4 10 2 3 8 43 Subband precoding [5subbands] Suband CQI and no 8 2 15 0 0 2 0 8 27 MIMO information [5 subbands] MIMO and 9 2 0 4 10 2 1 8 27 ACK/NACK (No- CQI information) [5- subbands] Average CQI, no 10 1 5 2 0 0 0 8 16 (fixed) precoding, no ACK/NACK Average CQI (3-bits 11 1 3 2 0 2 0 8 16 reduced granularity), no precoding, 2-bits ACK/NACK
In an example embodiment according to the principles of the present invention shown in FIG. 17, 8 tail bits are added to 36-bits of PUCCH information and the information is convolutional coded with a 1/3 coding rate. This results in a total of 132 coded bits. In the next step, 36 bits are punctured providing 96 coded bits. These 96 bits are QPSK modulated resulting in 48 complex modulated symbols. Each complex modulated symbol further modulates a CAZAC sequence and the resulting 48 sequences are mapped to 48 physical resource elements.
In a seventh embodiment according to the principles of the present invention shown in FIG. 23, multiple length 256 CAZAC sequences, i.e., 256 possible CAZAC sequences are transmitted over two hundred and fifty-six (256) subcarriers in twelve SC-FDMA blocks. Each of the 256 possible CAZAC sequences has 256 elements. Unlike the previous embodiments, the seventh embodiment uses a non-coherent transmission. As shown in FIG. 24, in the case of non-coherent transmission, the CAZAC sequence is mapped to the subcarriers at the input of IFFT. When FFT-precoding is used, the CAZAC sequence is mapped at the input of FFT and the samples at the output of FFT are mapped to subcarriers at the input of IFFT. In case of non-coherent reception, the receiver performs a correlation operation on the received frequency domain samples with all the possible CAZAC sequences expected. Then a decision is made on the received CAZAC sequence based on a threshold criterion. Since a single sequence from among multiple possible sequences is received, the received sequence indicates the information bits of PUCCH. Each of the 256 possible CAZAC sequences can be represented by 8-bits information because 2.sup.8=256. Among the 256 CAZAC sequences, a single sequence is selected to be transmitted in each of the twelve SC-FDMA blocks. This allows carrying 8-bits in each SC-FDMA block with a total of 96 coded bits in these twelve SC-FDMA blocks (12.times.8=96). It should be noted that in this case a non-coherent detection can be performed on the transmitted sequences without requiring pilot or reference signals transmitted with PUCCH.
In a seventh embodiment according to the principles of the present invention shown in FIG. 25, two length-16 CAZAC sequences, i.e., sixteen possible CAZAC sequences, are transmitted over thirty-two subcarriers in each of the twelve (12) SC-FDMA blocks. Among the sixteen CAZAC sequences, a single sequence is transmitted using 16 sub-carriers in each SC-FDMA block. This allows carrying 4 bits in each 16 sub-carriers in each SC-FDMA block. Therefore, a total of 96 coded bits can be carried in 32-subcarriers in the 12 SC-FDMA blocks (12.times.2.times.4=96). It should be noted that in this case a non-coherent detection can be performed on the transmitted sequences without requiring pilot or reference signals transmitted with PUCCH.