Optimal Antenna Cluster Size in Cell-Free Distributed Large-Scale Antenna Systems with Imperfect CSI and Inter-Cluster Interference

LANGUAGE English

SOURCE IEEE Trans. Vehicular Tech, vol. 64, no. 7, pp. 2834-2845, Jul. 2015

Published Date:2015

ABSTRACT

In cell-free large-scale distributed antenna systems
(L-DASs), the antennas are distributed over the intended coverage
area. Introducing cooperation among the antennas can
significantly improve the system throughput. However, only finitecluster-
size (limited) cooperation with L-DAS antenna clusters is
realistic due to practical limitations. In this paper, the impact
of antenna cluster size on the downlink sum rate of frequencydivision
duplex (FDD) cell-free L-DASs is analyzed, considering
imperfect channel state information (CSI) and intercluster
interference (ICLI). We investigate the optimal cluster size in
terms of maximizing the downlink sum rate with respect to the
overhead of imperfect channel training and feedback. When the
number of users is sufficiently large, closed-form lower bounds
of the ergodic sum capacity, which are leveraged to analyze the
system performance, are derived by constructing different rateachieving
user-scheduling schemes. Both analog and digital feedback
schemes are considered to evaluate the imperfect channel
feedback. Based on these, closed-form expressions of the optimal
cluster size for 1-D antenna topology systems and the corresponding
achievable rates are derived. The scaling law of the optimal
cluster size for 2-D antenna topology systems is also given. Numerical
results demonstrate the impact of the signal-to-noise ratio
(SNR) and the block length on the achievable rates and the optimal
cluster size, which agree with our analytical results.
Index Terms—Broadcast channel (BC), frequency-division duplex
(FDD), imperfect channel state information (CSI), large-scale
distributed antenna systems (L-DASs).