Achievable Sum-Rate of MU-MIMO Cellular Two-Way Relay Channels: Lattice Code-Aided Linear Precoding

Joint Precoder and Receiver Design for AF Non-Simultaneous Two-Way MIMO Relaying

“…We assume that all the channel matrices are frequencyflat and quasi-static. The quasi-static channel model, wherein channels are assumed to be unchanged over one cycle of multiple-access and broadcast phases, and to vary independently across multiple cycles, is widely used in the study of two-way MIMO relay communications [10], [24], [25]. The terms n u ∈ C N u ×1 and n b ∈ C N b ×1 are circularly-symmetric complex Gaussian noise vectors at the RUE and BS with E(n u n H u ) = σ 2 u I N u and E(n b n H b ) = σ 2 b I N b , respectively.…”

“…We use a high-SNR approximation commonly made in the literature [25], [29]: R(δ δ δ,λ λ λ u ,λ λ λ b ) ≈ 1 2 ∑ i∈{u,b} ∑ N n=1 w i,n log 2 ( SNR i, n (δ δ δ, λ λ λ¯i ) ) (a) = − 1 2 log 2 ∏ i∈{u, b} ∏ N n = 1 (ISNR i, n (δ δ δ,λ λ λ¯i) w i,n . The term ISNR i,n in (a) denotes the inverse of SNR i,n , that is ISNR i,n = 1/SNR i,n .…”

Towards the Asymptotic Sum Capacity of the MIMO Cellular Two-Way Relay Channel

“…To avoid the aforementioned disadvantages, the authors in [21] proposed a DF-based relaying scheme for the MIMO cTWRC involving linear precoding and nested lattice coding at the BS and users, and dirty-paper coding at the RS. It was shown that the achievable sum-rate of this scheme is much higher than the AF based schemes in [17]- [19], and this scheme can achieve the cut-set outer bound of the MIMO cTWRC if only the second phase is concerned.…”

“…It was shown that the achievable sum-rate of this scheme is much higher than the AF based schemes in [17]- [19], and this scheme can achieve the cut-set outer bound of the MIMO cTWRC if only the second phase is concerned. However, the scheme in [21] can perform far away from the capacity of the MIMO cTWRC, especially for a relatively large MIMO setup. This performance gap is largely due to the following fact: In the first phase, linear precoding can be applied only at the BS (as the users cannot cooperate), whereas the BS precoder alone fails to provide enough freedom to align the signals efficiently for interference-free PNC decoding at the relay.…”

“…Compared to [21], a major difference and contribution of this work is a new non-linear precoding technique, called lattice precoding, employed in the first-phase system design. We show that, together with linear precoding, nested lattice coding, and successive interference cancellation (SIC), the proposed lattice precoder at the BS efficiently pre-compensates for the inter-stream interference (ISI) seen at the relay, such that interference-free lattice decoding can be performed at the relay.…”