Selective physical layer network coding in bidirectional relay channel (original) (raw)
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IEEE Transactions on Vehicular Technology
In bidirectional relaying using Physical Layer Network Coding (PLNC), it is generally assumed that users employ same modulation schemes in the Multiple Access phase. However, as observed by Zhang et al. [1], it may not be desirable for the users to always use the same modulation schemes, particularly when user-relay channels are not equally strong. Such a scheme is called Heterogeneous PLNC. However, the approach in [1] uses the computationally intensive Closest Neighbour Clustering (CNC) algorithm to find the network coding maps to be applied at the relay. Also, the treatment is specific to certain cases of heterogeneous modulations. In this paper, we show that, when users employ heterogeneous symmetric-PSK modulations, the network coding maps and the mapping regions in the fade state plane can be obtained analytically. Performance results are provided in terms of Relay Error Rate (RER) and Bit Error Rate (BER).
Joint Physical Layer Coding and Network Coding for Bidirectional Relaying
IEEE Transactions on Information Theory, 2000
We consider a communication system where two transmitters wish to exchange information through a central relay. The transmitter and relay nodes exchange data over synchronized, average power constrained additive white Gaussian noise channels with a real input with signal-to-noise ratio (SNR) of snr. An upper bound on the capacity is 1 2 log(1 + snr) bits per transmitter per use of the multiple access phase and broadcast phase of the bi-directional relay channel. We show that, using lattice codes and lattice decoding, we can obtain a rate of
Physical Layer Network Coding with Multiple Antennas
2010 IEEE Wireless Communication and Networking Conference, 2010
The two-phase MIMO NC (network coding) scheme can be used to boost the throughput in a two-way relay channel in which nodes are equipped with multiple antennas. The obvious strategy is for the relay node to extract the individual packets from the two end nodes and mix the two packets to form a network-coded packet. In this paper, we propose a new scheme called MIMO PNC (physical network coding), in which the relay extracts the summation and difference of the two end packets and then converts them to the network-coded form. MIMO PNC is a natural combination of the single-antenna PNC scheme and the linear MIMO detection scheme. The advantages of MIMO PNC are many. First, it removes the stringent carrier-phase requirement in single-antenna PNC. Second, it is linear in complexity with respect to the constellation size and the number of simultaneous data streams in MIMO. Simulation shows that MIMO PNC outperforms the straightforward MIMO NC significantly under random Rayleigh fading channel. Based on our analysis, we further conjecture that MIMO PNC outperforms MIMO NC under all possible realizations of the channel. I. INTRODUCION In wireless networks, the use of relay has many advantages. It can lead to better coverage and connectivity. With a smaller distance for node-to-node transmissions, the power consumption can be reduced. At the same time, the detrimental effects of the interferences from other transmissions can be alleviated, leading to higher capacity per unit area. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2010 proceedings.
Performance analysis of relay networks with channel code in low SNR regime
2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013
This paper analyzes the performance of relay networks with channel coding in low and medium Signal-to-Noise Ratio (SNR) regime. In particular, we study the three-node relay network in the quasi-static block Rayleigh fading channel plus additive white Gaussian noise. Estimate-and-forward (EF) relay protocol is used. In order to achieve high spectrum efficiency, the relay can either forward the whole or a part of the estimated codeword to the destination. The contributions of the paper are as follows: i) First, we compute an upper bound of the Bit Error Rate (BER) of the proposed scheme. ii) Second, from the upper bound, we derive a so-called instantaneous diversity order in low and medium SNR region which is essential to practical systems. The instantaneous diversity depends on both the amount of information forwarded by the relay and the minimum distance of the channel code. Interestingly, the proposed scheme can achieve full diversity gain in a given SNR region of interest (such as BER 10 5) while obtaining 32% spectrum efficiency improvement compared to classical relay network under appropriate conditions. The analysis is checked by simulation.
On Constellations for Physical Layer Network Coded Two-Way Relaying
2013
Modulation schemes for two-way bidirectional relay network employing two phases: Multiple access (MA) phase and Broadcast (BC) phase and using physical layer network coding are currently studied intensively. Recently, adaptive modulation schemes using Latin Squares to obtain network coding maps with the denoise and forward protocol have been reported with good end-to-end performance. These schemes work based on avoiding the detrimental effects of distance shortening in the effective receive constellation at the end of the MA phase at the relay. The channel fade states that create such distance shortening called singular fade states, are effectively removed using appropriate Latin squares. This scheme as well as all other known schemes studied so far use conventional regular PSK or QAM signal sets for the end users which lead to the relay using different sized constellations for the BC phase depending upon the fade state. In this work, we propose a 4-point signal set that would always require a 4-ary constellation for the BC phase for all the channel fade conditions. We also propose an 8-point constellation that gives better SER performance (gain of 1 dB) than 8-PSK while still using 8-ary constellation for BC phase like the case with 8-PSK. This is in spite of the fact that the proposed 8-point signal set has more number of singular fade states than for 8-PSK.
Joint Relay Selection and Power Allocation for Two-Way Relaying with Physical Layer Network Coding
We consider a two-way relay (TWR) network with multiple relays, where the relays adopt physical layer network coding based on decode-and-forward. A joint relay selection and power allocation (RS-PA) scheme is proposed to improve the symbol error probability (SEP) of the TWR network using BPSK modulation under the total power constraint. For the proposed scheme and the benchmark scheme performing RS without PA, the average SEP of the TWR network is derived analytically and confirmed with simulation results. It is shown that the proposed scheme provides an asymptotic SNR gain of about 1.76 dB over the benchmark scheme at the same diversity order.
Soft network coding in wireless two-way relay channels
Journal of Communications and Networks, 2008
Application of network coding in wireless Two-Way Relay Channels (TWRC) has received much attention recently because its ability to improve throughput significantly. In traditional designs, network coding operates at upper layers above (including) the link layer and it requires the input packets to be correctly decoded. However, this requirement may limit the performance and application of network coding due to the unavoidable fading and noise in wireless networks. In this paper, we propose a new wireless network coding scheme for TWRC, which is referred to as soft network coding (SoftNC), where the relay nodes applies symbol-by-symbol soft decisions on the received signals from the two end nodes to come up with the network coded information to be forwarded. We do not assume further channel coding on top of SoftNC at the relay node (channel coding is assumed at the end nodes). According to measures of the soft information adopted, two kinds of SoftNC are proposed: amplify-and-forward SoftNC (AF-SoftNC) and soft-bit-forward SoftNC (SBF-SoftNC). We analyze the both the ergodic capacity and the outage capacity of the two SoftNC schemes. Specifically, analytical form approximations of the ergodic capacity and the outage capacity of the two schemes are given and validated. Numerical simulation shows that our SoftNC schemes can outperform the traditional network coding based two-way relay protocol, where channel decoding and re-encoding are used at the relay node. Notable is the fact that performance improvement is achieved using only simple symbol-level operations at the relay node.
Generalized Joint Channel Coding and Physical Network Coding for Two-Way Relay Systems
2010 IEEE 71st Vehicular Technology Conference, 2010
In this paper we present a generalized joint channel and physical layer network coding scheme for two-way relay systems, where the two sources A and B desire to exchange information from each other through the relay R simultaneously. Physical network coding scheme allows the relay to decode the network-coded information of both sources from the superimposed received signal. A novel iterative decoding approach is developed for arbitrary linear channel code, e.g. Low-Density Parity-Check (LDPC) code. Simulation results show that the proposed scheme outperforms other recently proposed network coding schemes with slightly increased complexity.
Physical Layer Network Coding and Precoding for the Two-Way Relay Channel in Cellular Systems
IEEE Transactions on Signal Processing, 2011
In this paper, we study the application of physical layer network coding to the joint design of uplink and downlink transmissions, where the base station and the relay have multiple antennas, and all M mobile stations only have a single antenna. A new network coding transmission protocol is proposed, where 2M uplink and downlink transmissions can be accomplished within two time slots. Since each single antenna user has poor receive capability, precoding at the base station and relay has been carefully designed to ensure that co-channel interference can be removed completely. Explicit analytic results have been developed to demonstrate that the multiplexing gain achieved by the proposed transmission protocol is M, much better than existing time sharing schemes. To further increase the achievable diversity gain, two variations of the proposed transmission protocols have also been proposed when there are multiple relays and the number of the antennas at the base station and relay is increased. Monte-Carlo simulation results have also been provided to demonstrate the performance of the proposed network coded transmission protocol.
Wireless Personal Communications, 2019
In this paper, we adopt the relay selection (RS) protocol proposed by Bletsas, Khisti, Reed and Lippman (2006) with Enhanced Dynamic Decode-and-Forward (EDDF) and network coding (NC) system in a two-hop two-way multi-relay network. All nodes are single-input single-output (SISO) and half-duplex, i.e., they cannot transmit and receive data simultaneously. The outage probability is analyzed and we show comparisons of outage probability with various scenarios under Rayleigh fading channel. Our results show that the relay selection with EDDF and network coding (RS-EDDF&NC) scheme has the best performance in the sense of outage probability upon the considered decode-and-forward (DF) relaying if there exist sufficiently relays. In addition, the performance loss is large if we select a relay at random. This shows the importance of relay selection strategies. Index Terms Enhanced dynamic decode-and-forward (EDDF), network coding (NC), relay selection (RS), two-way relay channels.