In this paper, the multi-way relaying scenario is considered with M users who want to exchange their information with each other with the help of N relays (N ≫ M) among them. There are no direct transmission channels between any two users. Particularly, all users transmit their signals to all relays in the first time slot and M - 1 relays are selected later to broadcast their mixture signals during the following M - 1 time slots to all users. Compared to the transmission with the help of single relay, the multi-way relaying scenario reduces the transmit time significantly from 2M to M time slots. Random and semiorthogonal relays selections are applied. Rician fading channels are considered between the users and relays, and analytical expressions for the outage probability and ergodic sum rate for the proposed relaying protocol are developed by first characterizing the statistical property of the effective channel gain based on random relays selection. Also, the approximation of ergodic sum rate at high signal-to-noise ratio regime is derived. In addition, the diversity order of the system is investigated for both random and semiorthogonal relay selections. Meanwhile, it is shown that when the relays are randomly separated into L groups of M - 1 relays, the group with maximum average channel gain can achieve the diversity order L, which will increase when more relays considered in the scheme. Furthermore, when semiorthogonal selection (SS) algorithm is applied to select the relays with semiorthogonal channels, it is shown that the system will guarantee that all the users can decode the others information successfully. Moreover, the maximum of channel gain after semiorthogonal relays selection is investigated by using extreme value theory, and tight lower and upper bounds are derived. Simulation results demonstrate that the derived expressions are accurate.
Xue, J., Sellathurai, M., Ratnarajah, T., & Ding, Z. (2015). Performance Analysis for Multi-Way Relaying in Rician Fading Channels. IEEE Transactions on Communications, 63(11), 4050-4062. https://doi.org/10.1109/TCOMM.2015.2477085