Conference Paper

# BEM-Based Estimation for Time-Varying Channels and Training Design in Two-Way Relay Networks

Dept. of Electr. & Comput. Eng., Univ. of Alberta, Edmonton, AB, Canada

DOI: 10.1109/GLOCOM.2010.5683403 Conference: Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE Source: IEEE Xplore

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**ABSTRACT:**We study two-hop communication protocols where one or two relay terminals assist in the communication between two transceiver terminals. All terminals operate in half-duplex mode, i.e., may not receive and transmit simultaneously at the same time and frequency. This leads to a loss in spectral efficiency due to the pre-log factor 1/2 in corresponding expressions for the achievable rate (capacity). We propose and analyze two relaying protocols that avoid the pre-log factor 1/2 but still work with half-duplex relays. Firstly, we consider a relaying protocol where two half-duplex relays, either amplify-and-forward (AF) or decode-and-forward (DF), alternately forward messages from a source terminal to a destination terminal (two-path relaying). It is shown that the protocol can recover a significant portion of the half-duplex loss. Secondly, we propose a relaying protocol where a bidirectional connection between two transceiver terminals is established via one half-duplex AF or DF relay (two-way relaying). It is shown that the sum rate of the two-way half-duplex AF relay channel achieves the rate of the one-way full-duplex AF relay channel, whereas the sum rate of the two-way half-duplex DF relay channel achieves the rate of the one-way full-duplex DF relay channel only in certain cases.Circuits, Systems and Computers, 1977. Conference Record. 1977 11th Asilomar Conference on 01/2005; - [Show abstract] [Hide abstract]

**ABSTRACT:**In this paper, we consider distributed space-time coding for two-way wireless relay networks, where communication between two terminals is assisted by relay nodes. Relaying protocols using two, three, and four time slots are proposed. The protocols using four time slots are the traditional amplify-and-forward (AF) and decode-and-forward (DF) protocols, which do not consider the property of the two-way traffic. A new class of relaying protocols, termed as partial decode-and-forward (PDF), is developed for the two time slots transmission, where each relay first removes part of the noise before sending the signal to the two terminals. Protocols using three time slots are proposed to compensate the fact that the two time slots protocols cannot make use of direct transmission between the two terminals. For all protocols, after processing their received signals, the relays encode the resulting signals using a distributed linear dispersion (LD) code. The proposed AF protocols are shown to achieve the diversity order of min{N,K}(1- (log log P/log P)), where N is the number of relays, P is the total power of the network, and K is the number of symbols transmitted during each time slot. When random unitary matrix is used for LD code, the proposed PDF protocols resemble random linear network coding, where the former operates on the unitary group and the latter works on the finite field. Moreover, PDF achieves the diversity order of min{N,K} but the conventional DF can only achieve the diversity order of 1. Finally, we find that two time slots protocols also have advantages over four-time-slot protocols in media access control (MAC) layer.IEEE Transactions on Signal Processing 03/2009; · 3.20 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**This paper studies the wireless two-way relay channel (TWRC), where two source nodes, S1 and S2, exchange information through an assisting relay node, R. It is assumed that R receives the sum signal from S1 and S2 in one timeslot, and then amplifies and forwards the received signal to both S1 and S2 in the next time-slot. By applying the principle of analogue network coding (ANC), each of S1 and S2 cancels the so-called "self-interference" in the received signal from R and then decodes the desired message. Assuming that S1 and S2 are each equipped with a single antenna and R with multi-antennas, this paper analyzes the capacity region of the ANC-based TWRC with linear processing (beamforming) at R. The capacity region contains all the achievable bidirectional rate-pairs of S1 and S2 under the given transmit power constraints at S1, S2, and R. We present the optimal relay beamforming structure as well as an efficient algorithm to compute the optimal beamforming matrix based on convex optimization techniques. Low-complexity suboptimal relay beamforming schemes are also presented, and their achievable rates are compared against the capacity with the optimal scheme.IEEE Journal on Selected Areas in Communications 07/2009; · 4.14 Impact Factor

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