1. CJK-B3G #11
2 and 4 Tx MIMO System
10-11 April 2006

2. Contents 1. Introduction 2. MIMO scheme set Two Tx scheme
Four Tx scheme
Closed-loop scheme for rate-1
STC-HARQ scheme

3. Downlink Multi-user MIMO Decoding and Demodulation
1. Introduction
1.1 Overall system
Feedforward
Feedback
MIMO
OFDM Tx
Coding and Modulation
LDC scheme
MIMO-Pilot
Downlink Multi-user MIMO
PAPR reduction scheme
Channel coder
Modulation
Uplink MIMO
Sub-carrier allocation
Scheduler
H-ARQ, Power control, MCS adaptation, Bit loading,
Per stream power control, Per antenna rate control,
OFDM mode change, MIMO mode change
Channel
Feedback overhead reduction
OFDM Rx
Decoding and Demodulation
MIMO Demodulator
Synchronization
MLD or QRM-MLD
Decoder
Demapper
Channel estimation
MMSE
CINR measurement

4. 1. Introduction
1.2 LDC (Linear dispersion code) [’02 Heath, ’02 Hassibi]
Nt, Nr : number of transmit and receive antennas
T : LDC period
Q : number of symbols
Aq, Bq : T x Nt dispersion matrix
ai, bi : real and imaginary value of ith symbol
Every multi-antenna transmit scheme can be expressed in form of LDC
Ex. Alamouti scheme

5. Equivalent channel model
1. Introduction
1.3 Design criterion
Pairwise error probability (PEP)
Capacity
Equivalent channel model

6. 2. MIMO scheme set 2.1 Two Tx Rate-1 Scheme [’98 Alamouti]
2.2 Two Tx Rate-2 Scheme [LGE proposal]
2.2.1 Another candidates

7. 2. MIMO scheme set 2.2.2 Simulation result
CF> IEEE Matrix-C has identical performance with the proposal

8. 2. MIMO scheme set 2.3 Advantages SM IEEE802.16e Matrix C Proposal
Decoding complexity
High(2x2 ML)
Low (2x2 MMSE)
High (4x4 ML)
Moderate (4x4 MMSE)
Encoding complexity
Low
(no manipulation on signal)
High
(signal multiplication & addition)
Moderate
(signal rotation & reconstruction)
Performance
Better, especially in high code rate

9. 2. MIMO scheme set 2.4 Four Tx Rate-1 scheme [’04 Sethuraman]
2.4.1 Another candidates

10. 2. MIMO scheme set
2.4.2 Simulation result
MMSE receiver

11. 2. MIMO scheme set 2.5 Four Tx Rate-2 scheme [’04 Sethuraman]

12. 2. MIMO scheme set 2.7 Closed-loop MIMO 2.7.1 Codebook
A set of pre-defined precoding matrices
Moderate feedback overhead (3~6 bits)
Selection criteria [‘03 Love] ML
MMSE Rx Nr Nt
Feedback information
Precoding W s1 s2 . sm

13. 2. MIMO scheme set
2.7.2 Four tx rate-1 closed-loop scheme [LGE proposal]
2.7.3 Advantage over codebook approach
Low feedback overhead (1 bit)
Less sensitive to mobility because of using channel statistics

14. 2. MIMO scheme set 2.7.4 Simulation Codebook size: 8
30km/h & 2ms feedback delay or
20km/h & 3ms feedback delay
30km/h & 5ms feedback delay
Codebook size: 8
(3bit feedback required)
Proposed scheme
(1bit feedback required)

15. 2. MIMO scheme set 2.8 STC-HARQ (IEEE802.16e) Initial transmission
Odd retransmission
Even retransmission
2 Tx
4 Tx
Alamouti
pair

16. 2. MIMO scheme set Alternative 1 Alternative 2 Alternative 3
2.8.1 Adaptive STC-HARQ [LGE proposal]
Alternative 1
Alternative 2
Alternative 3
ACK/NACK signals (2bits):
ACK,
NACK w/ alt 1,
NACK w/ alt 2,
NACK w/ alt 3

17. 2. MIMO scheme set 2.8.2 Simulation Results 802.16e system
20ms difference between transmission and retransmission

18. Thanks