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

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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

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What is MIMO ??

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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

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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...

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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

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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

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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

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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 }

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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

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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 }

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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 }

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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

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

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”Take- home message” MIMO is the FUTURE

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