Antenna
Selection in Space-Time Block Coded Systems: Performance Analysis and
Low-Complexity Algorithm
Abstract:
This paper presents outage probability analysis and a practical
algorithm for antenna selection in multiple-input multiple-output
wireless communication systems employing space-time block codes (STBC).
First, to minimize the outage probability in these systems, a
satisfactory antenna selection criterion for an STBC is to maximize the
channel Frobenius norm. Analysis shows that the more receive antennas
are selected, the better the performance. However, the performance of
transmit antenna selection heavily depends on how fast the channel
changes. When the channel changes slowly, since STBC averages the
channel gains of the selected transmit antennas, selecting more
transmit antennas causes lower coding gain and thus higher outage
probability. When the channel is fast changing, it is shown
analytically that the system can no longer provide transmit selection
diversity in the high SNR regime. Since the transmit diversity can be
still provided by using STBC, the best STBC scheme varies with SNR.
Although the outage analysis helps determine the STBC scheme, finding
the optimal antenna subsets with maximum channel Frobenius norm for
each fading state is still a challenging problem. This is because
solving the problem optimally requires an exhaustive search with
exponentially growing complexity. When the numbers of antennas are
large, the problem becomes intractable. To reduce the complexity, this
problem is formulated as a quadratically constrained quadratic
programming (QCQP) problem. Despite the fact that the problem is
nonconvex, a semidefinite relaxation of QCQP enables the problem to be
solved approximately in polynomial time. Simulation results indicate
that the loss of semidefinite relaxation to optimal selection is
negligible.
