Title: Fundamental overview and simulation of MIMO systems for SpaceTime coding and Spatial Multiplexing
1Fundamental overview and simulation of MIMO
systems for Space-Time coding and Spatial
Multiplexing
- EE381k-11 Wireless Communication
May 3, 2003
Hoo-Jin Lee, Shailesh Patil, and Raghu G. Raj
2Introduction I
- Multiple Input Multiple Output (MIMO)
- Multiple antennas at source and destination.
- Motivation Current wireless systems 1, 2
- Capacity constrained networks.
- Issues related to quality and coverage.
3Introduction II
- MIMO increases capacity 3
- MIMO uses independent channel fading due to
multipath propagation to increase capacity. - No extra expenive bandwidth required !!
- MIMO gives reliable communication 4
- Multiple independent samples of the same signal
at the receiver give rise to diversity.
C ? NT log2(1 SNR)
4Introduction III
- Diversity exhibited
- Spatial diversity
- spacing between antennas
- Transmit diversity
- space time coding
- Receive diversity
- receive antennas
5System Model I
- MIMO system with NT transmit and NR receive
antennas - received vector
- quasi-static channel matrix
- transmitted vector
- white Gaussian noise vector
6System Model II
- Rayleigh channel model multi-path
- Channel between any two pair of antennas is
independent - Each hik is complex Gaussian with unit variance
- Ricean channel model line of sight (K 0dB)
5
7MIMO LabVIEW demo
- Intuition to MIMO system
- Presented at WNCG open house
- Modified for project presentation
- MIMO demo
8Goals
- Study and simulate basic MIMO systems
- Space-Time coding Better error performance
- Trellis codes
- Alamouti code
- Spatial Multiplexing Higher data rate
- Maximum likelihood receiver
- Linear receiver
- Successive interference cancellation or V-BLAST
- Ricean channel model (Prof. Rappaports
suggestion) - Application of MIMO systems
9 Space-Time Coding I
- What is Space-Time coding?
- Coding schemes allow for the adjusting and
optimization of joint encoding across space and
time in order to maximize the reliability of a
wireless link.
- Space-Time codes allow us to achieve this goal by
exploiting - Spatial diversity in order to provide coding and
diversity gains over an uncoded wireless link
10Space-Time Coding II
- Space-Time Block Codes
- These codes are transmitted using an orthogonal
block structure which enables simple decoding at
the receiver. - Space-Time Trellis Codes
- These are convolutional codes extended to the
case of multiple transmit and receive antennas.
11Design Criteria for Space-Time Codes
- Error matrix B for code words c and e
- Diversity criterion Maximize diversity
orderrNR - where r is the rank of B
- Maximum diversity obtained is NTNR
- Coding gain criterion Maximize coding gain
where, eigenvalues of B
12Probability of Error 6
- Rayleigh channel
- Ricean channel
where,
eigenvalues of code separation matrix B
Ricean K factor between antenna i and j symbol
energy noise power
13Space-Time Trellis Coding
- Example of a 2 transmit space-time trellis code
with 4 states - (4-PSK constellations, spectral efficiency of
2bps/Hz)
14Simulation Results for Trellis Codes
Increase in number of states ? increases coding
gain Increase in number of receive antennas ?
increases diversity gain
15Space-Time Block Code Alamouti 7
- Encoding and Transmission
- Decoding
- Linearly combine received symbols
- Perform Maximum Likelihood (ML) detection
- Diversity order of 2NR guaranteed
The received symbols
16Simulation Results for Alamouti Scheme
Increase in number of receive antennas ?
increases diversity order
17Comparison of Alamouti and Trellis
- SpaceTime Trellis codes perform better than
Alamouti scheme. - Alamouti code is lot simpler to decode than
trellis codes
18Ricean Channel Simulations
For both Alamouti and Trellis codes the
performance improves with Ricean channel.
19Spatial Multiplexing Overview
- Multiple data streams are transmitted
simultaneously and on the same frequency using a
transmit array - Different data sub-streams are transmitted from
different antennas - The transmitter needs no channel state
information - No need for fast feedback links.
20Spatial Multiplexing Detection I 8
- Maximum Likelihood (ML) optimum and most complex
detection method -
- Linear detection
- Zero-Forcing (ZF) pseudo inverse of the channel,
simplest - Minimum mean-squared error (MMSE) intermediate
complexity and performance
where C is the constellation size.
21Spatial Multiplexing Detection II 9
- V-BLAST
- extracts data streams by ZF or MMSE filter with
ordered successive interference cancellation
(SIC) - Steps for V-BLAST detection
- Ordering choosing the best channel
- Nulling using ZF or MMSE
- Slicing making a symbol decision
- Canceling subtracting the detected symbol
- Iteration going to the first step to detect the
next symbol
22Simulation Results of ML Receiver in Rayleigh and
Ricean Channels
- 4QAM, antenna configurations
- Increase of the Number of Rx antennas ? Increase
of the performance - The Ricean channel approximately 1dB gain more
than in the Rayleigh channel at SER of 10-4
23Simulation Results of ZF Receiver in Rayleigh and
Ricean Channels
- 4QAM, antenna configurations
- Increase of the Number of Rx antennas ? Increase
of the performance - The Ricean channel approximately 1dB gain more
than in the Rayleigh channel at SER of 10-2
24Simulation Results of MMSE Receiver in Rayleigh
and Ricean Channels
- 4QAM, antenna configurations
- Increase of the Number of Rx antennas ? Increase
of the performance - The Ricean channel approximately 1dB gain more
than in the Rayleigh channel at SER of 10-2
25Simulation Results of ZF V-BLAST Receiver in
Rayleigh and Ricean Channels
- 4QAM, antenna configurations
- Increase of the Number of Rx antennas ? Increase
of the performance - Performance in the Ricean fading channel gt
Performance in the Rayleigh fading channel
(approximately 0.5 dB increase in the Ricean
fading channel at SER of 10-2)
26Simulation Results of MMSE V-BLAST Receiver in
Rayleigh and Ricean Channels
- Increase of the Number of Rx antennas ? Increase
of the performance - Performance in the Ricean fading channel gt
Performance in the Rayleigh fading channel
27Comparison among Spatial Multiplexing Receivers
in Rayleigh Channel
- Performance and Complexity
- ML receiver gt MMSE V-BLAST (SIC) receiver
- gt ZF V-BLAST (SIC) receiver gt MMSE receiver gt
ZF receiver
28Applications and Conclusions
- Applications
- 3G UMTS (optional) 3GPP WCDMA and GSM/EDGE
- Wireless LAN IEEE 802.11 and HIPERLAN/2
- Strong candidate for 4G along with OFDM
- Conclusions
- Multipath is not enemy but ally.
- Space-time coding scheme Diversity and Coding
gains - ? error performance improvement
- Spatial multiplexing scheme V-BLAST is the most
suitable to use in practical scenario - MIMO is a promising technology for the next
generation wireless systems
29References I
- Al-Dhahir, N., Fragouli, C., Stamoulis, A.,
Younis, W., and Calderbank, R., Space-time
processing for broadband wireless access, IEEE
Communications Magazine, Volume 40, Issue 9,
pp. 136-142, 2002 - Gore, D. A., Heath, R. W. Jr., and Paulraj, A.
J., Performance Analysis of Spatial Multiplexing
in Correlated Channels, submitted to
Communications, IEEE Transactions March 2002. - Telatar, I. E., Capacity of multi-antenna
Gaussian channels, Tech. Rep. BL0112170-950615-0
7TM, ATT Bell Laboratories, 1995 - Foschini, G. J. and Gans, M. J., On limits of
wireless communications in a fading environment
when using multiple antennas, Wireless Personal
Communications, vol. 6, pp. 311-335, 1998 - Erceg, V., Soma, P., Baum, D.S., Paulraj, A.J.,
Capacity Obtained from Multi-Input-Multi-Output
Channel Measurements in fixed Wireless
Environments at 2.5GHz, Communications, 2002.
ICC 2002. IEEE International Conference on ,
Volume 1 , 2002, Page(s) 396 400
30References II
- Tarokh, V., Jafarkhani, H., and Calderbank, A.
R., Space-time Codes for High Data Rate Wireless
Communication Performance Criterion and Code
Construction, IEEE Trans. Inform. Theory, Vol.
44, No. 2, pp. 744-765, July 1998 - Alamouti, S. M., A simple transmit diversity
technique for wireless communications, Selected
Areas in Communications, IEEE Journal,16(8)14511
458, 1998 - Gore, D. A., Heath, R. W. Jr., and Paulraj, A.
J., Performance Analysis of Spatial Multiplexing
in Correlated Channels, submitted to
Communications, IEEE Transactions March 2002 - Golden, G. D., Foschini, C. J., Valenzuela, R.
A., and Wolniansky, P. W., Detection algorithm
and initial laboratory results using V-BLAST
space-time communication architecture, IEE
Lett., Vol. 35, No. 1, pp. 14-16, January 1999
31