LTE上行链路反馈MCS（计算MCS、调制阶数、编码速率、频谱效率关系表格）



计算MCS、调制阶数、编码速率、频谱效率关系表格

参考网址：http://4g-lte-world.blogspot.tw/2012/12/transport-block-size-code-rate-protocol.html

参考网址：http://blog.richliu.com/2013/10/22/1545/

（1）前提：

因此，efficiency可简化为下式：

TBS=传输块的大小（表7.1.7.2.1-1）

CRC=附加的用于检错的比特数量=24

RE=分给PDSCH或PUSCH信道的Resource elaments数量（认为全部RE中，有90%用于共享信道）

Bits per RE=调制阶数

（2）举例

若eNB根据CQI分配该PUSCH传输的配置为：MCS index=20，2个RB。则有：

1）表7.1.7.1-1，TBS index=18

2）表7.1.7.2.1-1 计算TBS（传输块大小，单位bits）

3）计算code rate

Bits per RE=调制阶数=(MCS index=20)6阶=6

4）计算efficiency

（3）

计算RB数=12时，MCS

对应表

MCS index	modulation	code rate×1024	efficiency
0	QPSK	99.329806	0.194003527
1	QPSK	126.4197531	0.24691358
2	QPSK	153.5097002	0.299823633
3	QPSK	198.659612	0.388007055
4	QPSK	243.8095238	0.476190476
5	QPSK	297.989418	0.582010582
6	QPSK	352.1693122	0.687830688
7	QPSK	424.4091711	0.828924162
8	QPSK	478.5890653	0.934744268
9	QPSK	532.7689594	1.040564374
10	16QAM	266.3844797	1.040564374
11	16QAM	297.989418	1.164021164
12	16QAM	343.1393298	1.340388007
13	16QAM	388.2892416	1.51675485
14	16QAM	442.4691358	1.728395062
15	16QAM	496.64903	1.940035273
16	16QAM	514.7089947	2.010582011
17	64QAM	343.1393298	2.010582011
18	64QAM	367.2192828	2.151675485
19	64QAM	415.3791887	2.433862434
20	64QAM	451.4991182	2.645502646
21	64QAM	487.6190476	2.857142857
22	64QAM	523.7389771	3.068783069
23	64QAM	565.8788948	3.315696649
24	64QAM	609.5238095	3.571428571
25	64QAM	657.6837155	3.85361552
26	64QAM	681.7636684	3.994708995
27	64QAM	705.8436214	4.135802469
28	64QAM	826.2433862	4.841269841

参考文章附于此处

（1）CQI and MCS

LTE UE 會使用 CQI (Channel Quality Indicator) 動態調整 MCS 以降低傳輸錯誤率.

UE 測量 PRB (Physical Resource Block)的接收功率和干擾得到 SINR 值, 在 BLER 值不超過 10%. 將測量值轉換成 CQI. eNodeB 會根據 CQI 值選擇最合適的 MCS.
CQI 報告是由 eNodeB 主動發起, 可以是定時或是不定時.

不同的 CQI Index 有不同的 Code Rate.
如下表

CQI	Modulation	Bits/Symbol	REs/PRB	N_RB	MCS	TBS	Code Rate
1	QPSK	2	138	20	0	536	0.101449
2	QPSK	2	138	20	0	536	0.101449
3	QPSK	2	138	20	2	872	0.162319
4	QPSK	2	138	20	5	1736	0.318841
5	QPSK	2	138	20	7	2417	0.442210
6	QPSK	2	138	20	9	3112	0.568116
7	16QAM	4	138	20	12	4008	0.365217
8	16QAM	4	138	20	14	5160	0.469565
9	16QAM	4	138	20	16	6200	0.563768
10	64QAM	6	138	20	20	7992	0.484058
11	64QAM	6	138	20	23	9912	0.600000
12	64QAM	6	138	20	25	11448	0.692754
13	64QAM	6	138	20	27	12576	0.760870
14	64QAM	6	138	20	28	14688	0.888406
15	64QAM	6	138	20	28	14688	0.88840

MCS

Table 7.1.7.1-1: Modulation and TBS index table for PDSCH

MCS Index	Modulation Order	TBS Index
0	2	0
1	2	1
2	2	2
3	2	3
4	2	4
5	2	5
6	2	6
7	2	7
8	2	8
9	2	9
10	4	9
11	4	10
12	4	11
13	4	12
14	4	13
15	4	14
16	4	15
17	6	15
18	6	16
19	6	17
20	6	18
21	6	19
22	6	20
23	6	21
24	6	22
25	6	23
26	6	24
27	6	25
28	6	26
29	2	reserved
30	4
31	6

TBS Index (部份)

Table 7.1.7.2.1-1: Transport block size table (dimension 27×110)

	1	2	3	4	5	6	7	8	9	10
0	16	32	56	88	120	152	176	208	224	256
1	24	56	88	144	176	208	224	256	328	344
2	32	72	144	176	208	256	296	328	376	424
3	40	104	176	208	256	328	392	440	504	568
4	56	120	208	256	328	408	488	552	632	696
5	72	144	224	328	424	504	600	680	776	872
6	328	176	256	392	504	600	712	808	936	1032
7	104	224	328	472	584	712	840	968	1096	1224
8	120	256	392	536	680	808	968	1096	1256	1384
9	136	296	456	616	776	936	1096	1256	1416	1544
10	144	328	504	680	872	1032	1224	1384	1544	1736
11	176	376	584	776	1000	1192	1384	1608	1800	2024
12	208	440	680	904	1128	1352	1608	1800	2024	2280
13	224	488	744	1000	1256	1544	1800	2024	2280	2536
14	256	552	840	1128	1416	1736	1992	2280	2600	2856
15	280	600	904	1224	1544	1800	2152	2472	2728	3112
16	328	632	968	1288	1608	1928	2280	2600	2984	3240
17	336	696	1064	1416	1800	2152	2536	2856	3240	3624
18	376	776	1160	1544	1992	2344	2792	3112	3624	4008
19	408	840	1288	1736	2152	2600	2984	3496	3880	4264
20	440	904	1384	1864	2344	2792	3240	3752	4136	4584
21	488	1000	1480	1992	2472	2984	3496	4008	4584	4968
22	520	1064	1608	2152	2664	3240	3752	4264	4776	5352
23	552	1128	1736	2280	2856	3496	4008	4584	5160	5736
24	584	1192	1800	2408	2984	3624	4264	4968	5544	5992
25	616	1256	1864	2536	3112	3752	4392	5160	5736	6200
26	712	1480	2216	2984	3752	4392	5160	5992	6712	7480

依公式

Transport block size is 776 bits for ITBS = 18 and NPRB=2

code rate = (TBS + CRC) / (RE x Bits per RE)

code rate = (776 + 24) / (302 * 6 ) = 0.4

詳情請見

http://4g-lte-world.blogspot.tw/2012/12/transport-block-size-code-rate-protocol.html

以下引用自書LTE 關鍵技術與無線性能
覺得整理的還不錯

Ref.
3GPP 36.213 : 最主要的 Document.
http://www.sharetechnote.com/html/Handbook_LTE_CQI.html

（2）Transport Block Size and Code rate

Since the size of transport block is not fixed, often a question comes to mind as to how transport block size is calculated in LTE.
Back Ground
If we only consider "Uplink direction" and we assume that the UE is already attached to the network, then data is first received by PDCP (Packet data compression protocol) layer. This layer performs compression and ciphering / integrity if applicable. This layer will pass on the data to the next layer i.e. RLC Layer which will concatenate it to one RLC PDU.
RLC layer will concatenate or segment the data coming from PDCP layer into correct block size and forward it to the MAC layer with its own header. Now MAC layer selects the modulation and coding scheme configures the physical layer. The data is now in the shape of transport block size and needed to be transmitted in 1ms subframe.

Transport Block size

Now how much bits are transferred in this 1ms transport block size? 

It depends on the MCS (modulation and coding scheme) and the number of resource blocks assigned to the UE. We have to refer to the Table 7.1.7.1-1 and Table 7.1.7.2.1-1 from 3GPP 36.213

Lets assume that eNB assigns MCS index 20 and 2 resource blocks (RBs) on the basis of CQI and other information for downlink transmission on PDSCH. Now the value of TBS index is 18 as seen in Table 7.1.7.1-1

After knowing the value of TBS index we need to refer to the Table 7.1.7.2.1-1 to find the accurate size of transport block (Only portion of the table is shown here while for the complete range of values refer to 3gpp document 36.213  http://www.quintillion.co.jp/3GPP/Specs/36213-920.pdf )

Now from the Table 7.1.7.2.1-1 the value of Transport block size is 776 bits for ITBS = 18 and NPRB=

Code Rate

In simple words, code rate can be defined as how effectively data can be transmitted in 1ms transport block or in other words, it is the ratio of actual amount of bits transmitted to the maximum amount of bits that could be transmitted in one transport block
code rate = (TBS + CRC) / (RE x Bits per RE)
where
TBS = Transport block size as we calculated from Table 7.1.7.2.1-1
CRC = Cyclic redundancy check i.e. Number of bits appended for error detection
RE = Resource elements assigned to PDSCH or PUSCH
Bits per RE = Modulation scheme used


While we know the values of TBS, CRC and bits per RE (modulation order), it is not easy to calculate the exact amount of RE used for PDSCH or PUSCH since some of the REs are also used by control channels like PDCCH, PHICH etc
In our case, lets assume that 10% of RE's are assigned for control channels then
TBS = 776
CRC = 24
RE = 2 (RB) x 12 (subcarriers) x 7 (assuming 7 ofdm symbols) x 2 (slots per subframe) x 0.9 (10% assumption as above) = 302 REs
Bits per RE = 6 (Modulation order from table 7.1.7.1-1)
So
code rate = (776 + 24) / (302 * 6 ) = 0.4