1. Prakshep Mehta (03307909) Guided By: Prof. R.K. Shevgaonkar
MIMO Antenna Systems for
Wireless Communication
Prakshep Mehta ( )
Guided By:
Prof. R.K. Shevgaonkar

2. Outline Introduction...Why MIMO?? What is MIMO ?? From SISO to MIMO
The ”pipe” interpretation
To exploit the MIMO channel
BLAST
Space Time Coding
Special Cases
Still to Conquer
Foschini, Bell Labs 1996
Tarokh, Seshadri & Calderbank 1998

3. What is MIMO ??

4. Initial Assumptions Flat fading channel (Bcoh>> 1/ Tsymb)
Slowly fading channel (Tcoh>> Tsymb)
nr receive and nt transmit antennas
Noise limited system (no CCI)
Receiver estimates the channel perfectly
We consider space diversity only

5. ”Classical” receive diversity
H11
H21
= log2[1+(PT/s2)·|H|2] [bit/(Hz·s)]
H = [ H11 H21]
Capacity increases logarithmically
with number of receive antennas...

6. Multiple Input Multiple Output systems
H11
H21
H12
H22
C = log2det[I +(PT/2s2 )·HH†]=
Where the i are the
eigenvalues to HH† l1 l2
m=min(nr, nt) parallel channels,
equal power allocated to each ”pipe”
Interpretation:
Receiver
Transmitter

7. MIMO capacity in general
H unknown at TX
H known at TX
Where the power distribution over
”pipes” are given by a water filling
solution l1 l2 l3 l4 p1 p2 p3 p4
Test tes

8. The Channel Eigenvalues
Orthogonal channels HH† =I, 1= 2= …= m= 1
Capacity increases linearly with min( nr , nt )
An equal amount of power PT/nt is allocated
to each ”pipe”
Transmitter
Receiver

9. To Exploit the MIMO Channel
Bell Labs Layered
Space Time Architecture
Time s0 s1 s2
V-BLAST
D-BLAST
Antenna s3
nr  nt required
Symbol by symbol detection. Using nulling and symbol cancellation
V-BLAST implemented -98 by Bell Labs (40 bps/Hz)
If one ”pipe” is bad in BLAST we get errors ...
{G.J.Foschini, Bell Labs Technical Journal 1996 }

10. Solution: BLAST algorithm
Idea: NON-LINEAR DETECTOR
Step 1: H+ = (HH H)-1 HH
Step 2: Find the strongest signal
(Strongest = the one with the highest post detection SNR)
Step 3: Detect it (Nearest neighbor among Q)
Step 4: Subtract it
Step 5: if not all yet detected, go to step 2

11. Space Time Coding Use parallel channel to obtain diversity not
spectral efficiency as in BLAST
Space-Time trellis codes : coding and diversity gain (require Viterbi detector)
Space-Time block codes : diversity gain
(use MMSE at Decoder)
*{V.Tarokh, N.Seshadri, A.R.Calderbank
Space-time codes for high data rate wireless communication:
Performance Criterion and Code Construction
, IEEE Trans. On Information Theory March 1998 }

12. Orthogonal Space-time Block Codes
Block of T symbols
Constellation
mapper
STBC
Data in
nt transmit
antennas
K input symbols, T output symbols T K
R=K/T is the code rate
If R=1 the STBC has full rate
If T= nt the code has minimum delay
Detector is linear !!!
Block of K symbols
*{V.Tarokh, H.Jafarkhani, A.R.Calderbank
Space-time block codes from orthogonal designs,
IEEE Trans. On Information Theory June 1999 }

13. STBC for 2 Transmit Antennas
Full rate and
minimum delay
[ c0 c1 ] 
Antenna
Time
Assume 1 RX antenna:
Received signal at time 0
Received signal at time 1

14. Still to Conquer !! Backward Compatibility Antenna Spacing
Complexity at Receiver

15. ”Take- home message”
MIMO is the FUTURE