Abstract:
Differential Unitary Space-Time Modulation (DUSTM) and its earlier
nondifferential counterpart, USTM, permit
high-throughput MIMO communication entirely without the possession of
channel state information (CSI) by either
the transmitter or the receiver. For an isotropically random unitary input
we obtain the exact closed-form expression
for the probability density of the DUSTM received signal, which permits the
straightforward Monte Carlo evaluation
of its mutual information. We compare the performance of DUSTM and USTM
through both numerical computations
of mutual information and through the analysis of low- and high-SNR
asymptotic expressions. In our comparisons
the symbol durations of the equivalent unitary space-time signals are both
equal to T, as are the number of receive
antennas N. For DUSTM the number of transmit antennas is constrained by the
scheme to be M = T/2, while
USTM has no such constraint. If DUSTM and USTM utilize the same number of
transmit antennas at high SNR's
the normalized mutual information of the differential and the
nondifferential schemes expressed in bits/sec/Hz are
asymptotically equal, with the differential scheme performing somewhat
better, while at low SNR's the normalized
mutual information of DUSTM is asymptotically twice the normalized mutual
information of USTM. If, instead,
USTM utilizes the optimum number of transmit antennas then USTM can
outperform DUSTM at sufficiently low
SNR's.
Status:
Bell Labs Technical Memo, submitted to Transactions on Information
Theory, 2004.
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