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

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Presentation on theme: "Prakshep Mehta (03307909) Guided By: Prof. R.K. Shevgaonkar MIMO Antenna Systems for Wireless Communication."— Presentation transcript:

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

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 (B coh >> 1/ T symb ) Slowly fading channel (T coh >> T symb ) n r receive and n t transmit antennas Noise limited system (no CCI) Receiver estimates the channel perfectly We consider space diversity only

5 H 11 H 21 ”Classical” receive diversity = log 2 [1+(P T  2 )·|H| 2 ] [bit/(Hz·s)] H = [ H 11 H 21 ] Capacity increases logarithmically with number of receive antennas...

6 H 11 H 22 Multiple Input Multiple Output systems H 12 H 21 C = log 2 det[I +(P T  2 )·HH † ]= Where the i are the eigenvalues to HH †   m=min(n r, n t ) 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     p1p1 p2p2 p3p3 p4p4

8 The Channel Eigenvalues Orthogonal channels HH † = I, 1 = 2 = …= m = 1 Capacity increases linearly with min( n r, n t ) An equal amount of power P T /n t is allocated to each ”pipe” Transmitter Receiver

9 To Exploit the MIMO Channel Time s0 s1 s2 V-BLAST D-BLAST Antenna s1 s2 s3 n r  n t 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... Bell Labs Layered Space Time Architecture {G.J.Foschini, Bell Labs Technical Journal 1996 }

10 Solution: BLAST algorithm Idea: NON-LINEAR DETECTOR  Step 1: H + = (H H H) -1 H H  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 diversity Use parallel channel to obtain diversity not spectral efficiency as in BLAST trellisand Space-Time trellis codes : coding and diversity gain (require Viterbi detector) block 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 STBC Block of K symbols K input symbols, T output symbols T  K code rate R=K/T is the code rate full rate If R=1 the STBC has full rate If T= minimum delay If T= n t the code has minimum delay Detector is linear !!! Detector is linear !!! Block of T symbols n t transmit antennas Constellation mapper Data in *{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 [ c 0 c 1 ]  Time Antenna Full rate Full rate and minimum delay 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


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