Joint design of physical layer network coding and channel decoding based on trellis coded modulation in two-way relay channel

In this paper, a vertical physical-layer network coding (VPNC) scheme based pulse amplitude modulation (PAM) for two-way relay channel (TWRC) is proposed. Different from the conventional physical layer network coding (PNC) scheme in which the relay superimposes two users' signals of the same constellation, in the proposed VPNC scheme two users transmit PAM signals with vertical constellation and the relay superimposes two signals of vertical constellation in the multiple access (MA) phase. In addition, when the VPNC is exploited in conjunction with channel coding, joint channel VPNC is proposed to further improve the BER performance. Simulation results show that the proposed VPNC scheme outperforms the conventional PNC scheme on BER performance.

we propose a novel iterative physical layer network and channel decoding scheme based on XOR network coding and turbo code for the multiple-access relay channel. Firstly, the system model of two access nodes and one terminal with a relay between them is presented. At the relay node physical-layer network coding (PNC) is employed to combine the data information transmitted from resource, then at the terminal with the help of a check node an iterative scheme of soft information exchanging between PNC decoding and channel decoding is implemented. Meanwhile the complexity of the relay node also could be significantly reduced. And as the simulation results depict this scheme outperforms other joint decoding schemes and the complexity at the relay node is also reduced, especially in the case the channel condition between one transmitter and receiver is poor. Then multiple access nodes model is presented, also the scheme could propose good performance by contrast with other schemes only perform better in two sources case.

In this paper, we propose a joint design of MIMO-PNC (multiple-input multiple-output physical layer network coding) and channel decoding in two way relay channels. The paper shows that if we adopt the same Repeat Accumulate (RA) channel code at the two end nodes, there would be a compatible decoder at the relay which can transform the received superimposed packet to the network coding form of the two packets efficiently. Specifically, we redesign the belief propagation decoding algorithm of the RA code for traditional point-to-point channel to suit the need of the MIMO PNC channel. The simulation results show that our new scheme outperforms the previously proposed schemes which combined MIMO NC with channel coding/decoding significantly in terms of BER with little added complexity.

A two-way relay (TWR) channel is considered where two users exchange their messages with the help of a single relay. With the assumption of separate relay power budget and user power budget, we maximize the sum-rate of the TWR channel using physical-layer network coding (PNC) with flexible time fraction. We propose an optimal power allocation scheme between users and find that in high signal-to-noise ratio (SNR) regime, the user power should be allocated inversely proportional to the channel gains. Moreover, the bidirectional streams of the PNC-TWR enjoy full diversity gain. The analysis of the equal time fraction case and the numerical results of the flexible time fraction case both imply that the PNC relaying performs better than the decode-and-forward based TWR (DF-TWR) if the channel gains are similar, while the DF relaying performs better if the channel gains are quite different.

In this paper, we consider the two-way relay channel (TWRC) over which communication is performed using space-time block codes (STBC) with physical-layer network coding (PNC) protocol. The three-node two-way relaying (TWR) model consists of two end nodes (sources) simultaneously communicating with each other over a relay node where each node is equipped with two antennas and uses Alamouti's STBC to provide diversity. We consider non-reciprocal channels where fading channel coefficients are independent for opposite directions of the same link. We first derive closed form expressions for the outage probability of the STBC-TWR system and uncoded TWRC assuming equal transmit power at each node and decode-and-forward (DF) strategy at the relay. We show that the STBC-TWR system significantly improves the uncoded TWRC outage performance. Then, to further improve the performance, we propose an optimal power allocation in TWR scheme employing Alamouti's STBC and PNC protocol. The optimal power allocation is obtained by maximizing the sum-rate under the total power constraint. We show that the optimal power allocation considerably improve the outage performance as well as the sum-rate compared to the equal-power case.

We propose a new joint channel coding and physical layer network coding (CPNC) scheme for multiple-input multiple-output (MIMO) two-way relay channels (TWRCs). At the heart of the scheme lies a key technique referred to as eigen-direction alignment (EDA) precoding. This technique efficiently creates multiple aligned parallel channels which facilitates the deployment of multi-stream CPNC. Our analysis shows that the achievable rate of the scheme can approach the capacity upper bound in the median to high signal-to-noise (SNR) region when n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> > n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> , where n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> and n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> denote the number of antennas of each user and that of relay, respectively. The gap to the capacity upper bound diminishes as n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> /n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> increases. Numerical results demonstrate that the proposed scheme significantly outperform other well-known schemes in the literature.

Physical layer network coding (PNC) with channel coding is a strategy that applies error correction at the relay nodes of a relay system to improve data communication reliability of the whole relay system. So far, channel coded PNC schemes have been studied for two-way relay systems, but have not been systematically proposed for general multiple-way relay systems. In this paper, joint channel coding network coding schemes (JCCNC) are proposed for compute-and-forward (CF) relaying scheme that is able to be applied to general types of PAM and QAM modulation systems. LDPC codes are used for channel coding. Numerical results from simulation show that these JCCNC schemes greatly improve the performance of the relay systems.

In this paper, compute-and-forward physical layer network coding (PNC) scheme is investigated for wireless two-way relay channel. The achievable rates are reviewed both for AWGN channel and fading channel. New transmit schemes by using channel inversion precoding are proposed over fading channel to achieve much higher rates. It is revealed that with the proposed channel aware precoding scheme, the performance of compute-and-forward improves enormously. For two-way relay channel, compute-and-forward can achieve the maximum degree of freedom (DoF) of 2 without the limitation of Diophantine tradeoff, which indicates that compute-and-forward is the most suitable relaying scheme for two-way relay channel.

Recently, in multi-way relay systems employing physical-layer network coding (PNC), channel condition-based pair selection for pairwise information exchange has drawn increased attention as it provides improved performance over the alternative approaches such as round-robin scheduling of node pairs. With pairwise information exchange, there is additional time diversity available due to transmission of the same coded information block of most of the nodes twice in two adjacent time slots. This additional time diversity can be exploited to further enhance the system performance by means of joint channel decoding-network coding. To this end, a joint belief propagation (BP)-based channel decoding-network coding algorithm was proposed by us in [9] for the relay node of low density parity check (LDPC)-coded multi-way relay systems. Even though the algorithm of [9] offers much superior performance over separate channel decoding, it is highly computational expensive and may not be suitable for applications in wireless sensor networks. Alternatively, bit-flipping (BF)-based LDPC decoding can be adopted at much lower computational complexity. In this paper, we develop a low complexity joint bit-flipping (BF)-based channel decoding and network coding algorithm for LDPC-based multi-way relay systems. The BER performance of the proposed algorithm is investigated using computer simulation for two commonly used LDPC codes. The simulation results demonstrate that superior BER performance can be achieved using the proposed joint decoding algorithm over separate and independent bit-flipping-based LDPC channel decoding at the relay. The simulation results also verify that our proposed algorithm is capable of harnessing the aforesaid additional time diversity available. Though the performance of the proposed joint decoding algorithm is inferior to the BP-based algorithm of [9], due to its low computationally complexity, this algorithm may be appealing for applications in relay nodes with low computational capabilities and memory constraints.

This paper applies the expectation-maximization (EM) algorithm to address the problem of joint channel estimation and channel decoding in Physical-layer Network Coding (PNC) systems. The use of PNC can significantly improve the throughput of a relay network. The throughput advantage, however, is predicated on the availability of accurate channel estimates. For channel-coded PNC systems, a major challenge is that the maximum a posteriori probability (MAP) channel estimation is nontrivial due to 1) the overlapping of signals from multiple users received at the relay; and 2) the correlations among data symbols introduced by channel coding. In this paper, we show that an EM algorithm implemented on a factor graph framework is well suited to tackle this problem. Through iterative message passing, the channel estimation component and the channel decoding component in the factor graph interact to improve each other's results progressively. Simulation results indicate that just one EM iteration of our algorithm can significantly improve the channel estimation accuracy as well as the BER performance of channel-coded PNC systems.

In this chapter, two-way relaying networks using Physical-Layer Net- work Coding (PLNC) are considered with practical constraints. In a Multiple Access (MA) phase, two users transmit messages simultaneously on the same physical resources. The relay constructs a relay message based on the superimposed receive signal of both users. This message is broadcasted to the users which are able to extract the desired data from the other user. However, as the relay is not able to resolve shifts in time and frequency for the individual channels, the transmission scheme needs to be adjusted, if perfect synchronization cannot be ensured. This chapter deals with the proper selection of waveforms for multi-carrier systems in the Two-Way-Relay Channel (TWRC) using PLNC. We address Generalized Frequency Division Multiplexing (GFDM) compared to Orthogonal Frequency Division Multi-plexing (OFDM) under practical constraints like Carrier Frequency Offsets (CFOs) and Timing Offsets (TOs) within double dispersive channels. For OFDM rectangular transmit filters are used, which have a broad spectrum shape and are sensitive to shifts, especially in frequency domain. GFDM applies Gaussian waveforms that are inherently less susceptible to synchronization offsets than theirs rectangular counterparts, but additional interference is introduced even in a perfectly synchronized and flat fading channel. Thus, interferences caused by the channel or by the non-orthogonal Gaussian impulse shape are treated by an equalizer at the relay. The simulation results show that the Gaussian waveform outperforms the conventional OFDM system if the nodes are not perfectly synchronized.

A noncoherent two-way relaying system is developed using physical-layer network coding for improved throughput over conventional relaying in a fading channel. Energy-efficient noncoherent operation is achieved using multitone frequency shift keying (FSK). A novel soft-output demodulator is developed for the relay, and corresponding achievable exchange rates are found for Rayleigh fading and AWGN channels. Bit-error rate performance approaching the achievable rate is realized using a capacity-approaching channel code and a receiver architecture, which iterates between demodulation and channel decoding. Iterative decoding is performed feeding information back from the channel decoder to the demodulator. In addition, the error-rate performance is made to approach the achievable rate more closely by optimizing LDPC codes for this system. The energy efficiency improvement obtained by increasing the modulation order is more dramatic for the proposed physical-layer network coding scheme than it is for a conventional point-to-point system. Using optimized LDPC codes, the bit-error rate performance is improved by as much as 1.1 dB over a widely known standardized LDPC code, and comes to within 0.7 dB of the limit corresponding to the achievable rate. Throughout this paper, the performance for physical-layer network coding is compared with conventional network coding. When noncoherent FSK is used, physical-layer network coding enables higher achievable rates, and conventional network coding exhibits better energy efficiency at low rates.

In this paper, the authors show that using physical layer network coding (PNC) in wireless relay systems does not always increase throughput performance, and to achieve maximum throughput, PNC should be exploited intelligently regarding to the channel conditions. In this study, they propose a selective PNC (SPNC) scheme in bidirectional relay systems for binary phase shift keying. In the proposed scheme, the relay chooses either to detect network-coded data from superimposed signal by PNC scheme or single source data by a so-called single node detection (SND) scheme, based on which offers more end-to-end throughput for current channel realisation. They analytically determine the region of channel state plane in which SPNC selects SND scheme. Also, they obtain expressions for instantaneous bit error rates (BERs) of PNC and SND protocols. Moreover, they derive upper bounds in closed-form for average BERs of PNC and SND schemes during multiple access phase at the relay. Then, they investigate SPNC with high-order modulations. Simulations and analytical results confirm that SPNC achieves considerable throughput gain over PNC in Rayleigh fading channels.

The physical-layer network coding (PNC) can greatly improve the throughput of wireless network communications. However, critical synchronization in both time domain and frequency domain is required. Orthogonal frequency division multiplexing (OFDM) solves the problem of the synchronization in time domain while more critical synchronization in frequency domain is required. In this paper, we investigate the inter-channel interference (ICI) issue for OFDM-based physical-layer network coding (FPNC) over the two-way relay channel (TWRC). An approximate formula that calculates the ICI is derived. The compensation frequency, used by intermediate node to obtain minimal ICI power, has also been calculated. We find that average compensation is the optimal compensation method in the symmetric TWRC system while a different compensation method should be adopted in the asymmetric TWRC system. In addition, it is observed that bit error rate (BER) performance is not only decided by the power of the ICI but also by the distribution of it. At last, numerical results indicate that our approximate formula is accurate enough to calculate the ICI and can be applied to other OFDM systems.

Recently, Network coding has been proved to be the breakthrough in the research field of network and communication. It is an effective technique to increase network capacity and improve the robustness and reliability of networks. In this paper, there is application of network coding in wireless network. In order to improve the reliability and the throughput of wireless network, we do extensive research on network coding incorporated with the multicast communication in WLAN, the routing optimization in multi-hop network and the retransmission efficiency for wireless broadcast system, and focus on the protocol design and the theory for the performance analysis. On the basis of introduction on basic idea and method of network coding, we proposes a new physical layer network coding scheme for two-way relay channel model based on a belief propagation approach. Then we make performance analysis through numerical simulation.