Optimal Power Allocation Strategies in Two-Hop X-duplex Relay Channel

We consider a dual-hop, decode-and-forward network where the relay can operate in FD or HD mode (X-duplex relay). We model the residual self-interference as an additive Gaussian noise with variance proportional to the relay transmit power, and we assume a Gaussian input distribution at the source. Unlike previous work, we assume that the source is only aware of the transmit power distribution adopted by the relay, but not of the symbols that the relay is currently transmitting. {\color{black} This assumption better reflects the practical situation where the relay node forwards data traffic but modifies physical-layer or link-layer control information.} We then identify the optimal power allocation strategy at the source and relay, which in some cases coincides with the HD transmission mode. We prove that such strategy implies either FD transmissions over an entire time frame, or FD/HD transmissions over a variable fraction of the frame. We determine the optimal transmit power level at the source and relay for each frame, or fraction thereof. We compare the performance of our scheme against reference FD and HD techniques, which assume that the source is aware of the symbols instantaneously transmitted by the relay, and show that our solution closely approaches such strategies

A practical feasibility study of a novel strategy for the Gaussian half-duplex relay channel

This paper presents a practical feasibility study of a novel two-phase three-part-message strategy for half-duplex relaying, which features superposition coding and interference-aware cancellation decoding. Aiming to analyze the performance of the proposed scheme in the non-asymptotic regime, this paper evaluates the spectral efficiency with finite block-length and discrete constellation signaling and compares it with the theoretical performance of Gaussian codes with asymptotically large block-lengths. The performance evaluation is carried out on an LTE simulation test bench. During each transmission phase, the modulation and coding scheme is adapted to the channel link qualities to enhance the overall spectral efficiency. A single-antenna source and relay, and a multi-antenna destination are assumed. The static Gaussian and two frequency selective channel models are considered for the proposed scheme. A spectral efficiency comparison with a baseline scheme (non-cooperative two-hop transmission, i.e., the source-destination link is absent) and with the point-to-point transmission strategy (no relay) is presented. The results confirm that physical-layer cooperation and multi-antennas are critical for performance enhancement in heterogeneous networks. Moreover, they show that physical layer cooperation advantages are within practical reach with existing LTE coded-modulation and interference-mitigation techniques, which are prevalent in modern user-equipment.This paper was presented at the 2015 IEEE International Conference on Communications.This work was supported in part by the Eurecom’s Industrial Partners: BMW Group Research & Technology, IABG, Monaco Telecom, Orange, SAP, ST Microelectronics, and Symantec. It was also partially funded by the EU Celtic+ Framework Program Project SHARING. Other partially funded sources include the National Research Foundation (NRF) in South Africa and the National Science Foundation. The work of R. R. Thomas was supported in part by NRF under Grant 89803, and in part by the National Research Foundation (NRF) in South Africa. The work of M. Cardone was supported by NSF under Grant 1314937 and Grant 1514531. The work of D. Tuninetti was supported by NSF under Award 1218635.http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=7742hj2018Electrical, Electronic and Computer Engineerin