On the asymptotic sum-rate in 2xNx2 dual-hop relaying with quality based channel reporting and relay selection

Abstract

In this paper, we prove the asymptotic sum-rate growth like 2 log log N can be achieved in 2 × N × 2 dual-hop relaying systems with 2 transmit antennas at a base station (or a source), N ≥ 2 single receive/transmit antenna relays and 2 destination users with a single antenna. The capacity is achieved when the base station transmits with zero-forcing beamforming and the relays that actively transmit are selected with semi-orthogonal relay selection principle. Since the base station should know the channel information to the relays, the feedback load grows prohibitively large if N → ∞. To reduce the feedback load from the relays to the base station, we use quality-based channel state reporting (QBR). Numerical results show that the sum-rate achieved by N relays gets close to its multiuser counterpart if the amplifying gain at the relay is large. We also show how QBR is effective in reducing the feedback load when N is large.