Two-way relaying (TWR) improves the spectral efficiency of cellular systems by enabling data exchange between two nodes via a relay station (RS) in two channel uses. It is assumed in TWR that a user has data to send and receive from the base station (BS) at the same time. This paper considers a non-simultaneous traffic scenario observed in cellular systems, where one user sends data to the BS and another user receives data from the BS. We consider a novel multiple-input multiple-output (MIMO) TWR protocol to enable communication between two users and the BS in two channel uses. By designing a linear precoder at the decode-And-forward RS, we maximize the sum-rate of this protocol by formulating a sequence of semidefinite programs. The sum-rate performance of this protocol is evaluated in two coverage-limited scenarios in a cellular framework by extensive numerical simulations. It is shown that the protocol results in a dramatic performance gain over conventional protocols. © 2014 IEEE.

Bhaskar Ramamurthi

Department of Electrical Engineering

Cellular arrays

Cellular telephone systems

Communication channels (information theory)

Electronic data interchange

MIMO systems

signal processing

TELECOMMUNICATION REPEATERS

Cellular system

DECODE - AND - FORWARDS

LINEAR PRECODERS

NON-SIMULTANEOUS

Performance Gain

SEMIDEFINITE PROGRAMS

Spectral efficiencies

TWO-WAY RELAYING

Mobile telecommunication systems

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Two-way MIMO DF relaying for non-simultaneous traffic in cellular systems

2014 International Conference on Signal Processing and Communications, SPCOM 2014

In conventional two-way relaying (TWR), it is assumed that a user has data to send and receive simultaneously from the base station (BS) via a relay. In cellular systems, data flow between the BS and a user is usually not simultaneous, e.g., a transmit-only user (say, TUE) may have uplink data to send in the multiple access (MAC) phase, but may not have downlink data to receive in the broadcast (BC) phase. Such one-way data flow will reduce TWR to spectrally inefficient one-way relaying. The multiple-input-multiple-output (MIMO) asymmetric TWR (ATWR) protocol considered here restores the two-way data flow via a relay. In ATWR, the BC phase following the MAC phase of a TUE is used to send downlink data to a receive-only user (say, RUE). However, the RUE will not be able to cancel the back-propagating interference. We design a structured precoder at the relay to cancel this interference. The proposed precoder also triangularizes the end-to-end MIMO channels. The channel triangularization reduces the weighted sum-rate maximization and relay power minimization problems to power allocation problems, which are then cast as geometric programs. Simulation results illustrate the effectiveness of the proposed precoder when compared with conventional solutions. © 2014 IEEE.

Fulltext

IEEE Transactions on Wireless Communications

Linear precoders for nonregenerative asymmetric two-way relaying in cellular systems

Two-way relaying reduces the loss in spectral efficiency caused in a conventional half-duplex relay due to two channel uses per data unit transmitted to the destination. Two-way relaying is possible when two nodes exchange data simultaneously through a relay. In the case of cellular systems, data exchange between base station (BS) and users (UE) is usually not symmetric, e.g., a user (UE1) might have uplink data to transmit during multiple access (MAC) phase, but might not have downlink data to receive during broadcast (BC) phase. This asymmetry in data exchange will reduce the gains of two-way relaying. In the case of infrastructure relays, where there are multiple users communicating through a relay, we propose that the BC phase following the MAC phase of UE 1 be used by the relay to transmit downlink data to a second user (UE2). Conventional two-way relaying with symmetric MAC and BC phases must now be modified to asymmetric MAC (BS → RS ← UE1) and BC phases (BS ← RS → UE2), respectively. This will result in UE2 not being able to cancel the back-propagating interference in the usual way. We design precoders using conventional zero-forcing and linear minimum-mean-square-error criteria to mitigate the back-propagating interference at UE2 for an amplify-and-forward (AF) relay. We also propose a novel precoder appropriate for the asymmetric two-way relaying. The sum-rate performance of the proposed precoder is shown to be better than the conventional precoders. © 2013 IEEE.

IEEE International Conference on Communications

Precoder design for asymmetric multi-user two-way AF relaying in cellular systems

Journal	Data powered by Typeset2014 International Conference on Signal Processing and Communications, SPCOM 2014
Publisher	Data powered by TypesetInstitute of Electrical and Electronics Engineers Inc.
Open Access	No