Optimal Noncoherent Detection for Physical-Layer Network Coding

The Feher quadrature phase shift keying (FQPSK) modulation based Physical-layer Network Coding (PNC) is investigated in this paper, by which the nonlinear distortion effects resulted from the high power amplifier (HPA) in the system can be avoided. In our presented framework, a novel remapping rule for the FQPSK modulation in the PNC system is proposed to make a better bit error rate (BER) performance. Moreover, a joint demapping-and-demodulation scheme based on Low Density Parity Check (LDPC) is employed to recover the data bits with a low computational burden. Numerical results demonstrate the efficiency of the proposed method.

Physical-Layer Network Coding (PNC) employed on a conventional two-way relay communications is an active research area due to the potential doubling of the throughput compared with traditional routing. In this paper, we investigate the effects of impulsive noise added at the relay and sink nodes of a TWRC employing link-by-link coded PNC. The Gaussian mixture model is chosen to model the impulsive noise and the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) and turbo codes on the conventional two-way relay communications is evaluated through simulation results for different mixtures, , of impulsive noise. For high and low values of the turbo codes outperform trellis BICM, but it is shown that for values between = 0.1 and = 0.5, a PNC system with trellis BICM outperforms a comparable PNC system with turbo codes, where both coding schemes have the same block size, code rate and constraint length.

In this paper, we consider a decode-and-forward (DF) two-way relay (TWR) system in power line communication (PLC). The DF TWR employs physical- layer network coding (PNC). We derive analytic expressions for the average capacity and the outage probability of the system over a log-normal fading channel. Analytic results are verified through Monte Carlo simulations. From the results, the TWR is able to mitigate the half-duplex (HD) spectral efficiency loss incurred by one-way relaying. The impact of the impulsive noise on the system performance is also highlighted in the simulation results. It is shown that higher impulsive probability degrades system performance.

A key issue in physical-layer network coding (PLNC) is how to recover the network-coded packet by the relay from the superimposed signals transmitted simultaneously by multiple transmitters. In order to decode correctly, the asynchrony between signals must be perfectly dealt with. That is, symbols transmitted by different transmitters could arrive at the receiver with relative carrier frequency offset (CFO), relative carrier phase offset and different channel fading. In this paper, we propose an algorithm to estimate the relative carrier offset from the PLNC signals, and investigate two decoding schemes, JCNC and M-JCNC, to construct the XORed packet. As shown in the simulation results, the algorithm can efficiently estimate the relative carrier offsets and significantly reduce the SNR penalty due to asynchrony.

Applying physical-layer network coding (PNC) to vehicular ad-hoc networks (VANETs) can theoretically boost the network throughput by 100%, thus partially addressing the intermittent node connectivity and short contact time issues caused by high speed vehicle motions. However, the application of OFDM modulated PNC in VANETs faces detrimental effects caused by carrier frequency offsets (CFOs) and time-frequency-selective channels. CFOs may destroy the orthogonality of OFDM subcarriers, resulting in inter-carrier interference (ICI). The CFOs of two transmitters may also be different, and cannot be removed by CFO tracking and equalization at the receiver as in conventional single-user communication even if the CFOs are known. In addition, time-frequency- selective channels due to delay and Doppler spreads are difficult to estimate and non-accurate channel estimations will increase the detection bit error rate (BER). To address the two challenges, this paper proposes an ICI-aware approach that jointly exploits pilot and data for channel estimation and data detection. Specifically, our approach jointly uses the belief propagation (BP) algorithm to mitigate the CFO/ICI effect for data detection, and the expectation maximization (EM) algorithm to accurately estimate the channels. A linear interpolation method and an ICI compensation method are simulated as benchmarks. Simulation results indicate that our approach improves the BER performance compared to the two benchmarks (more than 2 dB SNR gain in most cases), especially in the high SNR regime.

In this paper, we investigate the performance of the so-called Cross Network operating under diverse Network Coding (NC) techniques. We study the impact of Medium Access Control (MAC) layer fairness on the throughput performance of the network for the cases of pure relaying, digital NC with and without overhearing and physical layer NC with and without overhearing. We provide a comparison among these techniques and we discuss the throughput bounds, due to MAC layer limitations, imposed to the system operation by broadly adopted short range communication protocols that provide for fair resource allocation such as IEEE 802.11. Furthermore, we show that significant coding gains are achieved with digital and physical layer NC and we discuss on the energy efficiency performance of each NC case when applied on the Cross Network.

A generalized concept of interference suppression is introduced for multiuser systems with a known memoryless transmit non-linearity, such as in the downlink amplifier of a satellite communication system. By considering the operation of commonly used multiuser detection techniques from a viewpoint of constellation structure, we extend these notions to nonlinear multiuser systems. We also analyze the performance of such multiuser detectors in terms of their asymptotic multiuser error exponents, which reduce to the asymptotic multiuser effective energies for the respective detectors in the absence of nonlinearity. The asymptotic conditional error exponent is introduced as a quantitative measure for evaluating nonlinear multiuser detectors based on the conditional probability of error at high signal-to-noise ratio (SNR). The optimal affine detector that maximizes the asymptotic error exponent for a given user is derived along with a successive interference annulment (SIA) scheme that maximizes the asymptotic conditional error exponent at each stage of successive detection. We have shown that the optimal affine detector (and hence the SIA detector) is a generalization of existing linear (and successive interference canceller) detectors to include the possibility of nonlinearity and therefore, nonadditive multiuser interference. We introduce the concept of joint successive interference annulment (JSIA) for nonlinear systems, which uses the joint structural relationship between two or more users in an ordered set to achieve higher performance gains in terms of the asymptotic conditional error exponent. We generalize the joint successive interference annulment detector to include more than two users at each stage of JSIA detection to scale the tradeoff between detection complexity and performance gain. We also introduce the decorrelating detector for nonlinear systems which essentially employs a successive interference canceller with a decorrelation kernel in an equivalent but higher-order linear system. Finally, we analyze the optimal affine detector and hence, the family of proposed joint successive interference annulment detectors when the multiuser system is perturbed with noise inside the nonlinearity. Simulation results demonstrate that the proposed detectors based on successive interference annulment consistently outperform conventional multiuser detectors based on successive interference cancellation.

In this paper, we propose a new linear physical- layer network coding (NC) scheme for the fading Y- channel, assuming that the channel state information (CSI) is not available at transmitters. In this scheme, each user transmits one message to a relay and intends to obtain both other two users' messages. Based on the receiver- side CSI, the relay determines two NC generator vectors for linear network coding, and reconstructs the associated two linear NC codewords. For the case when there is one time- slot in the uplink phase, we present an explicit solution for the generator vectors that minimizes the error probability at a high SNR, and a lower bound of the error performance of the proposed scheme using our optimized generator vectors. Extending to multiple time-slots in the uplink, two typical scenarios are discussed. Numerical results show that the proposed scheme significantly outperforms existing schemes, and match well with our analytical results.

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Near-far resistance is one of the most important performance measures in a multiuser communication system, especially in a code division multiple access (CDMA) system. The optimum multiuser detector can achieve the optimum near-far resistance. However, due to its high computational complexity, the optimum detector is impractical to implement. Nevertheless, computation of the near-far resistance of the optimum multiuser detector is still important since it is the least upper bound on the near-far resistance of any detector, as well as a benchmark for relative performance of any suboptimum detector. Lupas et al. and Zvonar et al. provided the computation of the optimum near-far resistance in the asynchronous AWGN and unipath channel case. In this paper, we extend the above results to the asynchronous multipath channel case. We derive the optimum near-far resistance under the assumption of a common identifiability condition in the blind multiuser detection/equalization literature. We also derive the ideal near-far resistance of three typical methods in blind multiuser detection/equalization (subspace, linear prediction, and constrained optimization) and compare them with that of the optimum detector. Two methods to enhance near-far resistance of suboptimum detectors are also presented. Furthermore, one possible cause that may affect the near-far resistance in a practical setting is analyzed. The computational complexity of the proposed methods is analyzed and compared. Simulations confirm the theoretical findings.

Optimum detectors for CPM use in general a large number of filters in order to calculate the optimum metrics. In this paper, we propose correlation detectors that calculate its metrics in a subspace of the signal space. The subspace is selected such that the asymptotic error performance is optimized for the given dimensionality. We focus on noncoherent detectors but show also some results for coherent detectors. The subspace metric calculation is combined with previously published reduced complexity decoding algorithms such as the SAN(B) and RSSD algorithms. Optimum subspace correlation detectors with different number of filters are found for both binary and quaternary CPM schemes. Their error performance on an AWGN channel is derived analytically through the use of a minimum Euclidean distance approach and is also simulated through the symbol error probability. Comparison is done with the optimum detectors. A close agreement between minimum distance and simulated symbol error probability is found for all considered detectors. We find that in most cases only 4 to 6 matched filters are needed in order to obtain a performance that is close to optimum. This corresponds to at least a five‐fold reduction in number of filters and with the reduced complexity search algorithms for making symbol decisions this leads to a dramatic reduction in overall complexity.

We revisit the problem of non-coherent signal detection in multipath scattering by exploring the effect of bandwidth and signaling duration on detection performance in doubly selective rich and sparse multipath. We begin with a general sampled representation of multipath channels that allows us to quantify the independent degrees of freedom (DoF) in non-uniform and sparse channels as a function of the physical propagation environment and the signaling parameters. We then develop the optimal non-coherent detector for such channels. Based on analytical and numerical results, we conjecture that detection performance is optimized in any multipath environment, rich or sparse, if two conditions are met: C1) the number of independent DoF induced by the transmit signal on the channel is approximately SNR/3, a condition empirically observed in earlier work, and C2) the variance of the channel coefficients (each corresponding to a DoF) is identical. We then show how to achieve these conditions given statistical characterization of the channel. In the most general setting of non-uniform power distribution across both delay and Doppler, it may not be possible to meet the two conditions above.

For the single-carrier M-ary differential phase-shift keying (MDPSK), the multiple-symbol differential detector, or the noncoherent maximum-likelihood sequence detector (NSD), and its three special cases, namely, the noncoherent one-shot detector, the linearly predictive decision-feedback (DF) detector, and the linearly predictive Viterbi receiver are reviewed based on a hierarchical interpretation. For the multicarrier transmission, the differential orthogonal frequency division multiplexing (OFDM) systems with diversity reception are discussed. It is well known that there are two types of differential OFDM systems, namely, the time domain differential OFDM (TD-OFDM) and the frequency domain differential OFDM (FD-OFDM). In this paper, the NSD and its special cases are incorporated to the differential OFDM systems. Furthermore, we provide a simple closed-form bit-error-rate (BER) expression for the differential OFDM systems utilizing the noncoherent one-shot detector with diversity reception in the time-varying multipath Rayleigh fading channels. Numerical results have revealed that, with multi-antenna diversity reception, the performance of the noncoherent one-shot detector is improved significantly. However, when only one or two receive antennas are available, the implementation of the linearly predictive DF detector or the linearly predictive Viterbi receiver is necessary for achieving better and satisfactory performance.

In order to satisfy the delay requirements of telecommunication systems, in this paper, we present a cooperative network with the short packet transmission in the Rayleigh fading channel. The desired relay can be implemented as a two-way half-duplex (HD) or a two-way full-duplex (FD). Also, for more accurate satisfaction and reduction of communication delays, sending and receiving with short packets is considered. Effective capacity appropriately measures the transmission rate under the delay constraint. Therefore, it is considered as a performance evaluation criterion here. With a two-way relay, two nodes exchange data with each other using a relay simultaneously. The priorities and requirements of the two nodes are not necessarily the same. Therefore, to increase performance, the system is modeled and solved as a multi-objective problem. In this way, the available power in the network is divided between the relay and two nodes, and the effective capacity of the two nodes is maximized. Depending on the different conditions, the optimal amount of allocated power to relay and nodes is calculated. However, due to the complexity and time consuming calculations, an approximate method which speeds up the calculation is presented. The approximated solution has a very close performance to the optimal allocated power. Finally, various comparisons have been made in different conditions between the performance of two-way HD and two-way FD relays. The improvement of multi-objective power allocation has been shown, especially when the relay is not located in the middle of two nodes.

This paper considers a short packet transmission scheme based on optical fiber sensing technology, which consists of a transmitter and K users. Considering that the error probability in short packet communication cannot be ignored, we first derive the expression of the block error probability of the receiver based on the approximation of the Gaussian function, then the delay boundary is analyzed based on stochastic network calculus, and the delay violation probability under the target delay constraint is finally obtained. According to the simulation results, it can be concluded that the block error probability of the receiver can be reduced by increasing the number of launchers and the length of the data packet, thereby improving the reliability of the short packet transmission system based on optical fiber sensing technology. In addition, by increasing the threshold of block error probability, increasing the information transmission rate and the accumulated departure of the system can be improved, and the waiting time of arriving data packets will be reduced, thereby improving the delay performance of the short packet transmission system based on optical fiber sensing technology.