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**Prakshep Mehta (03307909) Guided By: Prof. R.K. Shevgaonkar**

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

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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 (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

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**”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...

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**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

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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 l1 l2 l3 l4 p1 p2 p3 p4 Test tes

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**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

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**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 }

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**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

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**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 }

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**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 }

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**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

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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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