Inter-relay Interference Research Articles

Inter-Relay Interference in Two-Path Digital Relaying Systems: Detrimental or Beneficial?

This Letter studies the two-path digital relaying systems, where two relay nodes alternately forward messages from the source to the destination. By applying the signal space diversity (SSD) technique, a novel adaptive scheme is proposed to deal with the inter-relay interference (IRI). Our work reveals that, with careful protocol design, the IRI becomes a beneficial resource that can be utilized rather than a detrimental factor that has to be suppressed. Simulation results demonstrate that, in high average SNR regions, the proposed method outperforms the existing alternatives in terms of symbol error probability.

Approaching MISO Upper Bound: Design of New Wireless Cooperative Transmission Protocols

While various cooperative protocols have been developed for the simple scenario with one source-destination pair, most of them still suffer a significant loss compared with the optimal multiple-input single-output (MISO) upper bound. The diversity-multiplexing tradeoff will be used as the criterion for performance evaluation. In this paper, we propose two new half-duplex decode-forward cooperative transmission protocols, whose performance can approach the optimal MISO bound, and achieve a better diversity-multiplexing tradeoff when compared with existing cooperative protocols, particularly for large multiplexing gains. Firstly, a simple protocol of cooperative transmission is devised by combining opportunistic strategies with non-orthogonal transmission. When the number of relays is large, the proposed opportunistic decode-forward cooperative protocol can approach the optimal MISO upper bound. Due to the inter-relay interference constraint, each relay can only be used once, which limits the achievable diversity gain. Such an observation motivates our second transmission protocol which can further push the performance of cooperative transmission close to the optimal upper bound. Secondly, a relaying protocol is proposed for a four-node network where two multiple-antenna relays alternately forward messages to the destination when they can successfully cancel the inter-relay interference using the zero forcing method. Monte-Carlo simulation has also been provided to demonstrate the performance of both protocols and comparable ones.

Full Interference Cancellation for Two-Path Relay Cooperative Networks

This paper proposes the full interference cancellation (FIC) algorithm to cancel the interrelay interference (IRI) in the two-path cooperative system. Arising from simultaneous data transmission from the source and relay nodes, IRI may significantly decrease performance if it is not carefully handled. Compared with the existing partial interference cancellation scheme, the FIC approach is more robust yet is not as complex. Numerical results are also given to verify the proposed scheme.

On the Diversity-Multiplexing Tradeoff of Amplify-and-Forward Half-Duplex Relaying

In this paper, an amplify-and-forward (AF) two-path half-duplex relaying scheme is considered in which one of the relays additionally performs inter-relay interference cancellation. We first generalize lower bounds for the diversity-multiplexing tradeoff (DMT) of an arbitrary block lower triangular channel matrix. We then characterize the diversity-multiplexing tradeoff for the AF two-path relaying scheme and show that the DMT achieves the multiple-input single-output (MISO) upper bound. The analysis also demonstrates that, with a careful choice of the coding strategy, the DMT of this scheme is achievable for finite codeword lengths. We then propose using an equivalent linear space time code at the source, which does not require any form of channel state information, as a simple and effective coding strategy to achieve the full DMT of the scheme. From the DMT perspective, the proposed AF two-path relaying with the equivalent linear space time coding outperforms existing schemes. Our analysis is then extended to the slotted-amplify-and-forward (SAF) scheme with multiple relays, where we provide a stronger result by deriving the DMT while taking into account inter-relay interference.

Spectral efficient half-duplex relaying with interference suppression

Two-hop relaying systems suffer spectral efficiency loss due to the half-duplex property of relays. This paper proposes an efficient relaying protocol which can recover the spectral efficiency loss but still work with half-duplex relays. However, there exists inter-relay interference which degrades the performance of the protocol. With this consideration, a power control policy is derived to suppress the interference using game theory, and then an algorithm is given to facilitate distributed implementation. Furthermore, impact of deploying more destination antennas on performance of the relaying protocol is investigated. Simulation results show that, with the power control policy, the proposed relaying protocol can achieve high spectral efficiency.

Cellular Systems with Non-Regenerative Relaying and Cooperative Base Stations

In this paper, the performance of cellular networks with joint multicell processing and dedicated relay terminals is investigated. It is assumed that each relay terminal is capable of full-duplex operation and receives the transmission of relay terminals in adjacent cells. Focusing on intra-cell time division multiple access and non-fading channels, a simplified relay-aided uplink cellular model is considered. Addressing the achievable per-cell sum-rate, two non-regenerative relaying schemes are considered. Interpreting the received signal at the base stations as the outcome of a two-dimensional linear time invariant system, the multicell processing rate of an amplify-and-forward scheme is derived and shown to decrease with the inter-relay interference level. A novel form of distributed compress-and-forward scheme with decoder side information is then proposed. The corresponding multicell processing rate, which is given as a solution of a simple fixed-point equation, reveals that the compress-and-forward scheme is able to completely eliminate the inter-relay interference, and it approaches a "cut-set-like" upper bound for strong relay terminal transmission power. The benefits of base-station cooperation via multicell processing over the conventional single site processing approach is also demonstrated for both protocols.

On achievable rates of two-path successive relaying

This letter studies the achievable rates of the two-path relay channel (TPRC), where two half-duplex relays successively in turn forward messages from a source to a destination. It is shown that the conventional analogue and digital relaying schemes incur non-negligible throughput losses due to a socalled "inter-relay-interference (IRI)" phenomenon. This letter presents a new digital relaying scheme at the source transmitter to mitigate the IRI by applying the "dirty-paper-coding (DPC)" technique. It is shown that the proposed scheme achieves the capacity of the symmetric TPRC.

Cooperative OFDM Channel Estimation in the Presence of Frequency Offsets

Channel estimation in the presence of frequency offsets is developed for cooperative orthogonal frequency-division multiplexing (OFDM) systems. A two-time-slot cooperative channel estimation protocol is proposed. The source broadcasts the training sequence to the relays and the destination (first time slot), and the relays retransmit the training sequence (second time slot). Pilot designs for amplify-and-forward (AF) and decode-and-forward (DF) relays are derived. These designs eliminate interrelay interference (IRI), which occurs due to the simultaneous relay retransmissions, and minimize the mean square error (MSE). Consequently, the number of AF and DF relays is constrained to be less than lfloorN/(2L - 1)rfloor and lfloorN/Lrfloor, respectively, where N is the total number of subcarriers, L is the channel order, and lfloorarfloor is the maximum integer part of alpha. The pairwise error probability (PEP) of orthogonal space-time coding in cooperative OFDM due to both frequency offset and channel-estimation errors is also evaluated. The optimal power allocation ratio between the source and the relays to minimize the PEP is derived for AF and DF relays. When L < 16, DF relays outperform AF relays in terms of PEP. With L = 4 and 16 active relays, the gap is 9 dB for a frequency offset error variance of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , and this gap increases to about 11.3 dB when the variance increases to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> .

AF two-path half duplex relaying with inter-relay self interference cancellation: diversity analysis and its improvement

In this paper, we consider a network consisting of one source, one destination and two relays, under a half duplex constraint. We analyze an amplify-and-forward (AF) two-path relaying scheme where one of the relays additionally performs inter-relay interference cancellation. With this inter-relay self interference cancellation, we show that degradation in performance can be significantly reduced when inter-relay channel gain increases. By treating the AF two-path relaying as an equivalent MIMO space time code, we derive an upper bound for the pairwise error probability (PEP) of this system. Previous works indicate that only a diversity order of two can be achieved even though physically there are three possibly independent spatial paths to the destination. From our analysis of the PEP, we analytically prove and identify the reason to the limited diversity order of two. We then propose a simple but novel precoding scheme which allows the system to achieve a full diversity order of three while maintaining the spectral efficiency gain of the two-path relaying protocol. A robust precoding design to achieve full diversity order with high coding gain is also proposed.