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This paper investigates the decode-and-forward two-way relaying channel without direct link and proposes a protocol based on the physical-layer network coding PNC protocol. The proposed protocol termed ORT introduces one retransmission into PNC, aiming at enhancing its outage performance. To manifest the merits of ORT, we compare it with PNC and the time-division broadcast TDBC protocol, in terms of outage performance, expected rate, and diversity-multiplexing tradeoff DMT. Firstly, we derive the outage probability of the three protocols and then the expected rate. Secondly, asymptotic analysis is conducted to shed light on the diversity and coding gains. Finally, the DMT is obtained for the three protocols. The numerical results reveal the following: i that ORT performs better than PNC in both outage and expected rate performance when the nodes transmit with different powers. However, it has the same DMT performance with PNC; ii that ORT possesses improved DMT performance over TDBC whereas its expected rate is only better than the latter at medium to high signal-to-noise ratio. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY This paper investigates two-way relaying with direct link transmission. We propose to combine incremental relaying (IR) with the time division broadcast protocol (TDBC) to form a new scheme, termed TDBC-IR, to increase the spectral efficiency of TDBC. Assuming half-duplex decode-and-forward relaying, the performance of three protocols, that is, TDBC, TDBC-IR, and physical-layer network coding (PNC), are studied and compared, in terms of outage probability, expected rate (ER), and diversity-multiplexing tradeoff. First, we reveal that the outage probability performance of TDBC-IR is the same as that of TDBC and better than that of PNC. Second, we compare the ER and diversity-multiplexing tradeoff performance of the three protocols based on the derived outage probability. The numerical results reveal that (1) the ER of TDBC-IR is greater than that of TDBC and PNC in the whole signal-to-noise ratio (SNR) region, that is TDBC-IR has improved spectral efficiency performance; (2) the ER performance of TDBC is better than PNC in the low SNR region but worse in the high SNR region; (3) the maximum achievable diversity order of TDBC-IR and TDBC are both two whereas that of PNC is one; (4) the maximum achievable multiplexing gain of TDBC-IR is one, which is better than TDBC (its maximum achievable is 2/3) and achieves the maximum of PNC (its maximum achievable is one). Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents a joint physical-layer network coding (PNC) and serially concatenated continuous phase modulation (SCCPM) scheme in a two-way relay (TWR) channel. This proposed scheme can be viewed as a serial concatenated codes (SCCs) scheme in which the joint CPM and PNC is the inner code and the convolutional code (CC) is the outer code. It aims to improve the spectral efficiency, error performance and power efficiency of the PNC system by utilizing the technical advantage of CPM and SCCs. An iterative decoding algorithm for the relay receiver over AWGN channels is investigated. Emphasis is put on the extrinsic logarithmic likelihood ratios (LLRs) of the XORed codewords generated by the soft input soft output (SISO) inner decoder. Simulation results are also provided to show the error performance of the joint scheme.

This paper investigates two-way relaying with direct link transmission. We propose to combine incremental relaying (IR) with the time division broadcast protocol (TDBC) to form a new scheme, termed TDBC-IR, to increase the spectral efficiency of TDBC. Assuming half-duplex decode-and-forward relaying, the performance of three protocols, TDBC, TDBC-IR, and physical-layer network coding (PNC), are studied and compared, in terms of outage probability, expected rate (ER), and diversity-multiplexing tradeoff (DMT). It is found that 1)TDBC-IR has the same outage performance as that of TDBC and better than PNC; 2) the ER of TDBC-IR is greater than TDBC and PNC in the whole signal-to-noise ratio region, i.e., TDBC-IR has improved spectral efficiency performance; 3) the maximum achievable diversity order of TDBC-IR and TDBC are both two whereas that of PNC is one; 4) the maximum achievable multiplexing gain of TDBC-IR is one, which is better than TDBC (its maximum achievable is 2/3) and achieves the maximum of PNC (its maximum achievable is one). Since multiplexing gain reflects spectral efficiency, the DMT analysis confirms the spectral efficiency advantage of TDBC-IR over TDBC.

The following paper is a comment on the paper titled "Performance of Two-Way Opportunistic Relaying With Analog Network Coding Over Nakagami-m Fading". In the original paper, the authors investigated the performance of the outage-optimal two-way opportunistic relaying scheme with analog network coding over independent but not identically distributed Nakagami-m fading channels. For the relay-selection process, the authors declared that the two distributed methods, given by eqs. (6) and (7) in the original paper, were equivalent. According to Kun Xu and Yuanyuan Gao, the equivalence of the two criteria cannot be guaranteed, even for the high-signal-to-noise ratio (SNR) regime.