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Capacity scaling laws in MIMO relay networks
Authors
Helmut Bölcskei, Rohit U. Nabar, Özgür Oyman, and Arogyaswami J. PaulrajReference
IEEE Transactions on Wireless Communications, Vol. 5, No. 6, pp. 1433-1444, June 2006
DOI: 10.1109/TWC.2006.1638664
[BibTeX, LaTeX, and HTML Reference] Abstract
The use of multiple antennas at both ends of a wireless link,
popularly known as multiple-input multiple-output (MIMO) wireless,
has been shown to offer significant improvements in spectral
efficiency and link reliability through spatial
multiplexing and space-time coding, respectively. This
paper demonstrates that similar performance gains can be obtained in
wireless relay networks employing terminals with MIMO capability. We
consider a setup where a designated source terminal communicates
with a designated destination terminal, both equipped with M
antennas, assisted by K single-antenna or multiple-antenna relay
terminals using a half-duplex protocol. Assuming perfect
channel state information (CSI) at the destination and the relay
terminals and no CSI at the source, we show that the corresponding
network capacity scales as C = (M/2)log(K) + O(1) for fixed M,
arbitrary (but fixed) number of (transmit and receive) antennas N
at each of the relay terminals, and K going to infinity. We
propose a protocol that assigns each relay terminal to one of the
multiplexed data streams forwarded in a "doubly coherent'' fashion
(through matched filtering) to the destination terminal. It is shown
that this protocol achieves the cut-set upper bound on network
capacity for fixed M and K going to infinity (up to an
O(1)-term) by employing independent stream decoding at the
destination terminal. Our protocol performs inter-stream
interference cancellation in a completely decentralized fashion,
thereby orthogonalizing the effective MIMO channel between source
and destination terminals. Finally, we discuss the case where the
relay terminals do not have CSI and show that simple
amplify-and-forward relaying, asymptotically in K, for
fixed M and fixed N >= 1, turns the relay network into a
point-to-point MIMO link with high-SNR capacity C =(M/2)log(SNR)+O(1),
demonstrating that the use of relays
as active scatterers can recover spatial multiplexing gain in poor
scattering environments.Keywords
Relay channel, adhoc network, distributed orthogonalization, MIMO, fading channelsCorrection: The argument right after Eq. (4) stating "... where conditioning on the t_k in the first term can be dropped since neither s nor the r_k depend on the t_k." is misleading. It should be replaced by "The first term on the RHS of Eq. (4) is upper-bounded by I(s;r_1,...,r_K) as s-{r_i}-{t_i} forms a Markov chain." Furthermore in the fifth line of the proof of Theorem 1 "C_u=" should be removed and the sentence "We can therefore ..." starting in line 6 after Eq. (4) should be "We can therefore summarize our result as the capacity of the MIMO relay network being upper bounded by ...".
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