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1、-MIMO 学习心得 -Ellen wangLTE的7个传输模式中6 个分别应用了四种MIMO技术方案：传输分集TD，波束赋型Beamforming，空间复用SM，多用户MIMOMU-MIMO：1. 为普通单天线传输模式。 2. TransmitDiversity 模式：分2发送天线的SFBC，和4发送天线的SFBC+FSTD两种方案。2发送天线的SFBC : SFBC是由STBCSpace Time Block Code演变而来，由于OFDM一个slot的符号数为奇数，因此不适于使用STBC，但频域资源是以RB=12个子载波来分配的，因此可以用连续两个子载波来代替连续两个时域符号，从而组成S
2、FBC。而当使用4发送天线时，SFBC+FSTDFrequency Switched Transmit Diversity被采用。 3. SM-open loop，UE仅仅反应信道的RIRank Indicator。此时基站会使用CDDCycle Delay Diversity技术。 4. SM-close loop，UE根据信道估计的结果反应适宜的PMIPrecoding Matri* Indicator。(如利用系统容量最大计算适宜的PMI) 5. MU-MIMO，该方案将一样的时频资源通过空分，分配给不同的用户。 6. close loop rank1SM or BF，UE反应信道信息使
3、得基站选择适宜的Precoding。 7. UE Special RSBF，和BeamForming的前一种方式不同，这种方式无需UE反应信道信息，而是基站通过上行信号进展方向估计，并在下行信号中插入UE Special RS。基站可以让UE汇报UE Special RS估计出的CQI。 空间复用是为了提高传输数据数量，基于多码字的同时传输，即多个相互独立的数据流通过映射到不同的层，再由不同的天线发送出去。码字数量与天线数量未必一致。当然天线数量码字数量。传输分集主要用于提高信号传输的可靠性，例如采用空时编码STC、循环延时分集CDD)及天线切换分集等，LTE中用的比拟多的是SFBC编码。传输
4、分集TM2用来提高信号传输的可靠性，主要是针对小区边缘用户，TM3，TM4主要是针对小区中央的用户，提顶峰值速率。MU-MIMO是为了提高吞吐量，用于小区中的业务密集区。TM6，TM7是用于增强小区覆盖，也是用于边缘用户。不过6是针对FDD，7是针对TDD而已。在学习理解MIMO之前，需要理解几个根本概念：1. codeword: 相当于TranportBlock, 即物理层需要传输的原始数据块. LTE可支持在同一块资源同时传输2个相对独立的codeword，这是通过空间复用SM技术实现的。 2. layer：数据被分为不同layer进展传输，layer总数=天线个数。和信道矩阵的rank是
5、对应的。相当于空分的维度。 3. rank：相当于总的layer数。 4. atenna port：其实并不等同于天线个数，而是相当于不同的信道估计参考信号pattern。对端口03，确实对应多天线时，RS的发送pattern；对于端口4，对应于PMCH，MBSFN情况的RS；对于端口5，对应于UE Special RS。 TDD-LTE中支持的传输模式使用的DCI format 。在每一种模式中都可以通过改变DCI format切换到发射分集模式TM2，并且TM3、TM4 模式下，也支持在不改变DCI format的情况下从空分复用切换到发射分集模式TM2，这时需要通过在DCI format
6、中的precoding information field 来指示所使用的precoding matri* vector。Table 7.1-5: PDCCH and PDSCH configured by C-RNTIMode 2DCI format 1ACommon andUE specific by C-RNTITransmit diversity (see subclause 7.1.2)DCI format 1UE specific by C-RNTITransmit diversity (see subclause 7.1.2)Mode 3DCI format 1ACommon a
7、ndUE specific by C-RNTITransmit diversity (see subclause 7.1.2)DCI format 2AUE specific by C-RNTILarge delay CDD (see subclause 7.1.3) or Transmit diversity (see subclause 7.1.2)Mode 4DCI format 1ACommon andUE specific by C-RNTITransmit diversity (see subclause 7.1.2)DCI format 2UE specific by C-RNT
8、IClosed-loop spatial multiple*ing(see subclause 7.1.4)or Transmit diversity(see subclause 7.1.2)Mode 7DCI format 1ACommon andUE specific by C-RNTIIf the number of PBCH antenna ports is one, Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2)D
9、CI format 1UE specific by C-RNTISingle-antenna port; port 5 (see subclause 7.1.1)PDSCH process flow: Layer mappingNow codeword-to-layer mapping support 3 types:1. Layer mapping for transmission on a single antenna port1 codeword-to-1 layer2. Layer mapping for spatial multiple*ing2 antenna ports:1) 1
10、 codeword-to-1 layer 2) 2 codewords-to-2 layers 4 antenna ports:1) 1 codeword-to-1 layer 2) 1 codeword-to-2 layers 3) 2 codewords-to-2 layers 4) 2 codewords-to-3 layers 5) 2 codewords-to-4 layers Table 6.3.3.2-1: Codeword-to-layer mapping for spatial multiple*ing.Number of layersNumber of codewordsC
11、odeword-to-layer mapping11222132423. Layer mapping for transmit diversity1 codeword-to-2 layers (2 antenna ports)1 codeword-to-4 layers (4 antenna ports)Table 6.3.3.3-1: Codeword-to-layer mapping for transmit diversity.Number of layersNumber of codewordsCodeword-to-layer mapping2141If two null symbo
12、ls shall be appended to PrecondingNow precoding support 3 types:1. Precoding for transmission on a single antenna port2. Precoding for transmit diversity3. Precoding without CDD-Closed-loop spatial multiple*ing scheme(TM4)4. Precoding for large delay CDD-Large delay CDD scheme(TM3 ) and can get from
13、 below table according to different layer Table : Large-delay cyclic delay diversity.Number of layers 234For can selected from codebook defined in 36.211 .Table 6.3.4.2.3-1: Codebook for transmission on antenna ports .Codebook inde*Number of layers 120123- PMIUE will report the suggested codebook in
14、de* by PMI and eNB will send the codebook info which eNB will use for PDSCH by DCI.For different transmission mode,the PMI will use different number of bits.Table 7.2-1b: Number of bits in codebook subset restriction bitmap for applicable transmission modes.Number of bits 2 antenna ports4 antenna po
15、rtsTransmission mode 324Transmission mode 4664Transmission mode 5416Transmission mode 6416Transmission mode 8632 Transmission mode 3:PMI will use 2 bits-For 2 antenna ports: means 2 layers -codebook inde* 0 -means 1 layer -codebook inde* 0 -means transmit diversity Transmission mode 4:PMI will use 6
16、 bits-For 2 antenna ports, defined in 36.211 Table 7.2-1c: means 1 layer -codebook inde* 0- means 1 layer -codebook inde* 1-means 1 layer -codebook inde* 2-means 1 layer -codebook inde* 3-means 2 layers -codebook inde* 1-means 2 layers -codebook inde* 2-Table 7.2-1c: Association of bits in codebookS
17、ubSetRestriction bitmap to precoders in the 2 antenna port codebook of Table 6.3.4.2.3-1 in 3.Codebook inde* Number of layers 120a0-1a1a42a2a53a3- Precoding info in DCIeNB will send the precoding info in DCI format 2/2A. Transmission mode 3:DCI format 2A:Precoding information number of bitsFor anten
18、na ports 2, the precoding information field is not present.1: Number of bits for precoding information.Number of antenna ports at eNodeBNumber of bits for precoding information2042The number of transmission layers is equal to 2 if both codewords are enabled; transmit diversity is used if codeword 0
19、is enabled while codeword 1 is disabled.But the PDCCH format will use DCI format 2A no matter spatial multiple*ing or transmit diversity. Transmission mode 4:DCI format 2:Precoding information(36.212)3: Number of bits for precoding information.Number of antenna ports at eNodeBNumber of bits for prec
20、oding information2346For antenna ports 2, there are 3 bits for precoding information, detail info see below table:Precoding info bit field mapped to inde*:For 2 layers: Precoding info codebook inde* 0 0 -means 2 layers precoding matri* 1 1 -means 2 layers precoding matri* 2 * -means 2 layers precodi
21、ng matri* used the latest PMI report on PUSCH, using the precoder(s) indicated by the reported PMI(s)For 1 layer: Precoding info codebook inde* 0 0 -means 2 layers: Transmit diversity1 1 -means 1 layer precoding matri* 2 2 -means 1 layer precoding matri*3 3 -means 1 layer precoding matri* 4 4 -means
22、 1 layer precoding matri* 5 * -means 1 layer precoding matri* will use the latestPMI report on PUSCH, using the precoder(s) indicated by the reported PMI(s),if RI=2 was reported, using 1stcolumn multiplied by of all precoders implied by the reported PMI(s)6 * -means 1 layer precoding matri* will use
23、 the latestPMI report on PUSCH, using the precoder(s) indicated by the reported PMI(s),if RI=2 was reported, using 2nd column multiplied by of all precoders implied by the reported PMI(s)Table 5.3.3.1.5-4: Content of precoding information field for 2 antenna ports.One codeword: Codeword 0 enabled, C
24、odeword 1 disabledTwo codewords: Codeword 0 enabled, Codeword 1 enabledBit field mapped to inde*MessageBit field mapped to inde*Message02 layers: Transmit diversity02 layers: Precoding corresponding to precoder matri* 11 layer: Precoding corresponding to precoding vector 12 layers: Precoding corresp
25、onding to precoder matri* 21 layer: Precoding corresponding to precoder vector 22 layers: Precoding according to the latest PMI report on PUSCH, using the precoder(s) indicated by the reported PMI(s)31 layer: Precoding corresponding to precoder vector 3reserved41 layer: Precoding corresponding to pr
26、ecoder vector 4reserved51 layer: Precoding according to the latest PMI report on PUSCH, using the precoder(s) indicated by the reported PMI(s),if RI=2 was reported, using 1st column multiplied by of all precoders implied by the reported PMI(s)5reserved TM7 mode:For transmission mode 7 , can support
27、one port and two ports .NumAntennaPort = 1tansmissionMode = TM7DCI 1 -port 5-beamformingCell-RS -port 0D-RS -port 5/NumAntennaPort = 2tansmissionMode = TM7DCI 1 - port 5- BeamformingCell-RS -port 0, port 1D-RS -port 5/For beamforming ,the PDSCH will use port5 ,and no mater RRU has 2 or 4 or 8 physic
28、al antenna , Baseband will send the same signal in all these physical antennas, just every antenna has different phase and amplitude. So in this mode, RRU has no primary and secondary antenna .And for NumAntennaPort =1 and NumAntennaPort =2, the beamforming the main difference is for Cell-RS ,When N
29、umAntennaPort =1, Cell-RS is sending on port 0When NumAntennaPort =2, Cell-RS is sending on port 0 and port 1.This difference will just impact the RE which used for PDSCH data./Under TM7 mode,can support beamforming and transmit diversity using different DCI format .DCI 1 for beamforming and DCI 1A for transmit diversity.NumAntennaPort = 1tansmissionMode = TM7DCI 1A -port 0-single-antenna port, port 0Cell-RS -port 0This mode is just like TM1 /NumAntennaPort = 2tansmissionMode = TM7DCI 1A -port 0,port1 -transmit diversityCell-RS -port 0, port 1This mode is just like TM2 . z.
