Multimode Transmission in Network MIMO Downlink with Incomplete CSI
Journal article, 2011
We consider a cooperative multi-cell MIMO (a.k.a network MIMO) downlink system with multiantenna
base stations (BSs), which are connected to a central unit and communicate with multi-antenna
users. In such a network, obtaining perfect channel state information (CSI) of all users at the central unit
to exploit opportunistic scheduling requires a substantial amount of feedback and backhaul signaling.
In this paper, we propose a scheduling algorithm based only on the knowledge of the average received
SNR at each user from all the cooperating BSs, denoted as incomplete CSI. Multi-mode transmission is
applied that is able to adaptively adjust the number of data streams transmitted to each user. Utilizing
the results of random matrix theory, an analytical framework is proposed to approximate the ergodic
rate of each user with different number of data streams. Using these approximate ergodic rates, a joint
user and mode selection algorithm is proposed, where only the scheduled users need to feed back
instantaneous CSI. Simulation results demonstrate that the developed analytical framework provides
a good approximation for a practical number of antennas. While substantially reducing the feedback
overhead, it is shown that the proposed scheduling algorithm performs closely to the opportunistic
scheduling algorithm that requires instantaneous CSI feedback from all users.