文章标题

MIMO System

System utilizing multiple transmit and multiple receive antennas are commonly knowns as Multiple Input Multiple Output(MIMO) Systems

Performance improvements from multiple antennas at both transmitter and receiver

Array Gain —> SNR improvement

Diversity Gain —> fading mitigating

Spatial Multiplexing Gain —> channel capacity

Interference Reduction / Avoidance

Spatial Multiplexing

In rich scattering environments, independent data signals transmitted from different antennas can be uniquely decoded to yield an increase in channel capacity

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Capacity - now multipath is good

Recall SISO capacity in one-path

C=B*log_2(1+|h|^2 * SNR)

Now, MIMO channel capacity for N transmit antennas

C=B*log_2 det[I + (SNR/N) HH^H]

C=N_ss*log_2 (1+SNR)

MIMO Channel Model

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y(n)=Hd(n)+w(n)

where

y(n): M x 1 received vector

H: M x N channel Matrix with E{|H(k,l)|^2}=1

d(n): N x 1 data vector with E{d(n)d(n)^H}=P***I_N***

w(n): M x 1 noise vector with E{w(n)w(n)^H}= ρ^2 I_M

MIMO Receivers

z = G^H * y = G^H * H * d + G^H * w

MF(matched filter): G^H = H^H

LS(Least Square) or ZF(zero-forcing): G^H=(H^H* H)^(-1)* H^H

MMSE: G^H=(H^H * H+(1/Θ)I_N)^(-1) * H^H

= H^H(H H^H +(1/Θ) I _N)^(-1)

MIMO System