1 research outputs found
LOS-based Conjugate Beamforming and Power-Scaling Law in Massive-MIMO Systems
This paper is concerned with massive-MIMO systems over Rician flat fading
channels. In order to reduce the overhead to obtain full channel state
information and to avoid the pilot contamination problem, by treating the
scattered component as interference, we investigate a transmit and receive
conjugate beamforming (BF) transmission scheme only based on the line-of-sight
(LOS) component. Under Rank-1 model, we first consider a single-user system
with N transmit and M receive antennas, and focus on the problem of
power-scaling law when the transmit power is scaled down proportionally to
1/MN. It can be shown that as MN grows large, the scattered interference
vanishes, and the ergodic achievable rate is higher than that of the
corresponding BF scheme based fast fading and minimum mean-square error (MMSE)
channel estimation. Then we further consider uplink and downlink single-cell
scenarios where the base station (BS) has M antennas and each of K users has N
antennas. When the transmit power for each user is scaled down proportionally
to 1/MN, it can be shown for finite users that as M grows without bound, each
user obtains finally the same rate performance as in the single-user case. Even
when N grows without bound, however, there still remains inter-user LOS
interference that can not be cancelled. Regarding infinite users, there exists
such a power scaling law that when K and the b-th power of M go to infinity
with a fixed and finite ratio for a given b in (0, 1), not only inter-user LOS
interference but also fast fading effect can be cancelled, while fast fading
effect can not be cancelled if b=1. Extension to multi-cells and
frequency-selective channels are also discussed shortly. Moreover, numerical
results indicate that spacial antenna correlation does not have serious
influence on the rate performance, and the BS antennas may be allowed to be
placed compactly when M is very large.Comment: 32 pages, 11 figure