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

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prakshep mehta 03307909 guided by prof r k shevgaonkar

MIMO Antenna Systems for

Wireless Communication

Prakshep Mehta (03307909)

Guided By:

Prof. R.K. Shevgaonkar

outline
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

initial assumptions
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
slide5

= log2[1+(PT/s2)·|H|2] [bit/(Hz·s)]

H = [ H11 H21]

Capacity increases logarithmically

with number of receive antennas...

”Classical” receive diversity

H11

H21

slide6

Interpretation:

l1

Receiver

Transmitter

l2

m=min(nr, nt) parallel channels,

equal power allocated to each ”pipe”

Multiple Input Multiple Output systems

H11

H21

H12

H22

C = log2det[I +(PT/2s2 )·HH†]=

Where the i are the

eigenvalues to HH†

mimo capacity in general

H known at TX

Where the power distribution over

”pipes” are given by a water filling

solution

l1

p1

l2

p2

l3

p3

l4

p4

MIMO capacity in general

H unknown at TX

the channel eigenvalues
The Channel Eigenvalues

Orthogonal channelsHH† =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

to exploit the mimo channel

Time

s1

s1

s1

s1

s1

s1

V-BLAST

Antenna

s2

s2

s2

s2

s2

s2

s3

s3

s3

s3

s3

s3

s0

s1

s2

s0

s1

s2

D-BLAST

s0

s1

s2

s0

s1

s0

s1

s2

s0

To Exploit the MIMO Channel

Bell Labs Layered

Space Time Architecture

  • 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 }

solution blast algorithm
Solution: BLAST algorithm
  • Idea: NON-LINEAR DETECTOR
    • Step 1: H+ = (HHH)-1HH
    • 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
space time coding
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 }

orthogonal space time block codes
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= ntthe 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 }

stbc for 2 transmit antennas
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

still to conquer
Still to Conquer !!
  • Backward Compatibility
  • Antenna Spacing
  • Complexity at Receiver
take home message
”Take- home message”
  • MIMO is the FUTURE