Abstract
A novel coding strategy is proposed for a broadcast setting with two transmitter (TX) antennas and two single-antenna receivers (RX). The strategy consists of using space-time block coding to send a common message (to be decoded by both RXs) across the two TX antennas, while each TX antenna also sends a private message to one of the RXs. The relative weight of the private and common messages from each TX antenna is tuned to maximize the instantaneous achievable sum-rate of the channel. Closed-form expressions for the optimal weight factors are derived. In terms of the generalized degrees of freedom (GDoF) metric, the new scheme is able to achieve the sum-GDoF with finite precision channel state information at the transmitter (CSIT) of the two user broadcast channel. Moreover, as opposed to the existing rate-splitting schemes, the proposed scheme yields instantaneous achievable rates that are independent of the channel phases. This property is instrumental for link adaptation when only magnitude CSIT is available. Our numerical results indeed demonstrate the superiority of the scheme for the 2-user setting in case of magnitude CSIT. Extension to a more general K-user scenario is briefly discussed.
Highlights
Multi-antenna terrestrial base stations [1] and multi-beam satellite systems [2] play a key role in both current and forthcoming high-throughput communication networks
Under full channel state information at the transmitter (CSIT), the Shannon capacity region of the MISO-BC is achieved by means of dirty-paper coding (DPC) [3], [4]
For a generic number of users K, the MISO-BC is modeled as y = Hx + w, with y ∈ CK×1 the received values at the K single-antenna user terminals, H ∈ CK×K the square channel matrix, x ∈ CK×1 the symbol vector transmitted by the K antennas, and w ∈ CK×1 a vector of zero-mean unit variance additive white Gaussian noise (AWGN) samples, such that E wwH = IK
Summary
Multi-antenna terrestrial base stations [1] and multi-beam satellite systems [2] play a key role in both current and forthcoming high-throughput communication networks. It may be the case that cooperation among different transmit antennas can be limited due to the lack of phase coherence or precise time alignment among the different radio frequency chains, so that only channel magnitude is to be entrusted for the design of the transmit scheme and joint selection of information rates. This limitation can be more commonly found in multibeam communication satellites [2]. E [·] and tr{·} are the expectation and matrix trace operators, respectively
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