1 Codebook Design for Noncoherent MIMO Communications Via Reflection Matrices Daifeng Wang and Brian L. Evans {wang, bevans}@ece.utexas.edu Wireless Networking and Communications Group The University of Texas at Austin IEEE Global Telecommunications Conference November 28, 2006
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Codebook Design for Noncoherent MIMO Communications Via Reflection Matrices
Codebook Design for Noncoherent MIMO Communications Via Reflection Matrices. Daifeng Wang and Brian L. Evans {wang, bevans}@ece.utexas.edu Wireless Networking and Communications Group The University of Texas at Austin IEEE Global Telecommunications Conference November 28, 2006. - PowerPoint PPT Presentation
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Codebook Design for Noncoherent MIMO Communications Via Reflection Matrices
Daifeng Wang and Brian L. Evans{wang, bevans}@ece.utexas.edu
Wireless Networking and Communications GroupThe University of Texas at Austin
IEEE Global Telecommunications ConferenceNovember 28, 2006
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Problem Statement What problem I have solved?
Design an optimal codebook for noncoherent MIMO communications.
What mathematical model I have formulated? Inverse Eigenvalues Problem
What approach I have taken? Using Reflection matrices
What goal I have achieved? Low searching complexity without any limitation
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Noncoherent Communications Unknown Channel State Information (CSI) at the
receiver Fast Fading channel
e.g. wireless IP mobile systems
No enough time to obtain CSI probably Difficult to decode without CSI
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Noncoherent MIMO Channel Model Noncoherent block fading model [Marzetta and Hochwald, 1999]
Channel remains constant over just one block
Mt transmit antennas, Mr receive antennas, T symbol times/block T ≥ 2 Mt
Y = HX + W X – Mt×T one transmit symbol block
Y – Mr×T one receive symbol block
H – Mr× Mt random channel matrix
W – Mr×T AWGN matrix having i.i.d entries
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Grassmann Manifold Grassmann Manifold [L. Zheng, D. Tse, 2002]
Stiefel Manifold S(T,M) – the set of all M-dimensional subspaces in a T-dimensional hyberspace.
Grassmann Manifold G(T,M) – the set of all different M-dimensional subspaces in S(T,M). X, an element in G(T,M), is an M×T unitary matrix
Chordal Distance [J. H. Conway et. al. 1996]
P, Q in G(T,M)
2( , ) H
c Fd M P Q PQ
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Codebook Model Codebook S with N codewords
Codeword Xi is an element in G(T,Mt)
Optimal codebook S Maximize the minimum distance in S
1 2{ , ,..., }NS X X X
( , )
2
( , )
arg max {min ( , )}
arg min {max }
t
t
c i jG T M
Hi jG T M F
d
S
S
S X X
X X
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Theoretical Support Majorization
Schur-Horn Theorem If ω majorizes λ, there exists a Hermitian matrix with diagonal
elements listed by ω and eigenvalues listed by λ.
ω majorizes λ => , with eigenvalues of
“
”, from [R. A. Horn & C. R. Johnson, 1985]
1
2
n
1 2 n[ ]
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Optimal Codebook Design
Gram Matrix G of Codebook S
Optimal S The diagonal elements of G are identical Power for the entire codebook P
Allocated P/T to each codeword equally. Nonzero eigenvalues of G = P/T
Optimal Codebook Design G => Xs => S
Given eigenvalues, how to reconstruct such a Gram matrix that it has identical diagonal elements?
1 2, [ ]H H H H Hs s s NG = X X X = X X X
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Reflection Matrix Reflection Angle θ
Equivalent to rotate by 2
Reflection matrix F Unitary matrix
Application Modify the first diagonal element of a matrix
, some value we desired
Reflect by θ
Rotate by 2θ
cos sin
sin cos
11 12 11 12
21 22 21 22
cos sin cos sin
sin cos sin cos
x x y y
x x y y
11y
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t
t
tM K
M K-TT
P[1 1 ... 1] (1)
M K
P P P[0 0 ... 0 ... ] (2)
T T T
Flow Chart of Codebook Design
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Comparison with other designsAlgorithm Searching
complexityDecoding method
Computational complexity
Notes
DFT [B. Hochwald et. al. 2000]
O(2RTMt) GLRT O(2RT)
Coherent Codes [I. Kammoun & J. –C. Belfiore, 2003]
O(2RT(T-Mt)) GLRT O(2RT)
PSK [V. Tarokh & I. Kim, 2002]
O(2RTMt) ML O(MtMr) T=2Mt
Orthogonal matrices [V. Tarokh & I. Kim, 2002]
O(2RTlog2Mt) ML O(Mt2Mr) T=2Mt
Mt=1,2,4,8
Training [P. Dayal et. al., 2004]
O(2RTT) MMSE O(Mt3Mr
3)
Reflection matrices O(2RTMt) GLRT O(2RT)
R: transmit data rate in units of bits/symbol period; T: coherent time of the channel in units of symbol period; Mt : number of transmit antennas; Mr: number of receive antennas.
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Simulation Mt=1, Mr=4, P=4, T=3
is the standard code from http://www.research.att.com/~njas/grass/index.html.
, Q is a unitary matrix. Thus, are the same point in G(T,Mt)