We discuss the design rules of an energy-efficient wireless wiretap channel in this paper. On the transmitter side, we investigate the optimal power control policy for secrecy rate maximization over wiretap channels with the bit-interleaved coded modulation scheme. On the receiver side, an energy harvesting algorithm is used to collect wireless signal energy without degrading the secrecy rate performance. These objectives are challenging as the closed-form solution to the mutual information of finite-alphabet input schemes remains unknown. In this paper, we derive a closed-form relationship between the secrecy rate and the signal-to-noise ratio (SNR) by transforming the SNR from the linear domain to the logarithm domain. The optimal power control policy (PCP) can be easily obtained by exhaustive search in a small interval, whereas the traditional search is performed over the entire SNR range. We also propose a sub-optimal PCP algorithm that significantly reduces the search complexity with only a minor performance loss. The optimal power splitting ratio is studied to save energy while achieving the target secrecy rate. We show that if the transmission power is too high, the receiver is unable to simultaneously harvest energy from the wireless signals and achieve the target secrecy rate.

Spatial diversity is an effective method to mitigate the effects of fading, and when used in conjunction with low-density parity-check (LDPC) codes, it can achieve excellent error-correcting performance. Noise added at each branch of the diversity combiner is generally assumed to be additive white Gaussian noise, but there are many applications where the received signal is impaired by noise with a non-Gaussian distribution. In this paper, we derive the exact bit-error probability of different linear combining techniques on Rayleigh fading channels with impulsive noise, which is modeled using symmetric alpha-stable distributions. The relationship for the signal-to-noise ratios of these linear combiners is derived and then different non-linear detectors are presented. A detector based on the bi-parameter Cauchy-Gaussian mixture model is used and shows near-optimal performance with a significant reduction in complexity when compared with the optimal detector. Furthermore, the threshold signal-to-noise ratio of LDPC codes for different combining techniques on these channels is derived using density evolution and an estimation of the waterfall performance of LDPC codes is derived that reduces the gap between simulated and asymptotic performance.

This paper investigates secrecy rate optimization problems for a multiple-input-single-output (MISO) secrecy channel in the presence of multiple multiantenna eavesdroppers. Specifically, we consider power minimization and secrecy rate maximization problems for this secrecy network. First, we formulate the power minimization problem based on the assumption that the legitimate transmitter has perfect channel state information (CSI) of the legitimate user and the eavesdroppers, where this problem can be reformulated into a second-order cone program (SOCP). In addition, we provide a closed-form solution of transmit beamforming for the scenario of an eavesdropper. Next, we consider robust secrecy rate optimization problems by incorporating two probabilistic channel uncertainties with CSI feedback. By exploiting the Bernstein-type inequality and S-Procedure to convert the probabilistic secrecy rate constraint into the determined constraint, we formulate this secrecy rate optimization problem into a convex optimization framework. Furthermore, we provide analyses to show the optimal transmit covariance matrix is rank-one for the proposed schemes. Numerical results are provided to validate the performance of these two conservative approximation methods, where it is shown that the Bernstein-type inequality-based approach outperforms the S-Procedure approach in terms of the achievable secrecy rates.

This paper proposes an alternating optimization algorithm for addressing the secrecy rate optimization problem for a multi-input-multi- output (MIMO) secrecy channel in the presence of a multiantenna eavesdropper, where a multiantenna cooperative jammer will be employed to confuse the eavesdropper by introducing jamming signal. We investigate the secrecy rate maximization problem, which is a non-convex problem in terms of transmit covariance matrices of the legitimate transmitter and the cooperative jammer. In order to circumvent this issue, we develop an optimization algorithm by alternating optimizing the transmit covariance matrices of the legitimate transmitter and the cooperative jammer where each transmit covariance matrix is optimized while other is fixed. Based on this algorithm, we develop a robust scheme by incorporating channel uncertainties associated with the eavesdropper. By exploiting S-Procedure, we show that these robust optimization problems can be formulated into semidefinite programming (SDP). Simulation results have been provided to validate the convergence and the performance of the alternating algorithm.

This paper investigates robust beamforming techniques for a multiple-input-single-output (MISO) secrecy transmission with a cooperative jammer by incorporating two different types of channel uncertainties. We solve the worst-case signal-to-interference-plus-noise ratio (SINR) maximization of the legitimate user with the worst-case SINR constraint of the eavesdropper and the transmit power constraint. The original problems are not convex in terms of transmit covariance matrices, and cannot be solved directly. Thus, we present two approaches to convert these problems into semidefinite programmings (SDPs) by exploiting S-Procedure and deriving the corresponding Lagrangian dual problem. Numerical results are provided to validate the performance of the proposed robust schemes.

We propose and analyze the performance of the full-duplex multiple-input multiple-output singular value decomposition (FD-MIMO-SVD) based relay with self-interference-cancellation (SIC). The effects of channel estimation errors for the source-to-relay and self-interference channels are considered. The performance of the system is investigated in the presence of additive white Gaussian noise (AWGN) over Rayleigh fading channels. Analytical results are presented for this system by exploiting SVD as a dominant eigenmode transmission for maximizing the signal-to-noise ratio (SNR) of the desired signal, in addition to mitigating the self-interference (SI). Furthermore, exact, closed-form solutions for the signal-to-interference-plus-noise-ratio (SINR) distribution and outage probability are derived and evaluated along with the average symbol error rate (ASER) for M-ary phase-shift keying (MPSK) modulation schemes.

In this paper, an enhanced orthogonal frequency division multiplexing (OFDM) with offset quadrature amplitude modulation (OQAM) system utilising Walsh-Hadamard transform (WHT) is presented. This system demonstrates high resistance to the multipath transmission. The simulation results over standard ITU channels for pedestrian and vehicular confirm the improvement of the proposed system over the conventional OFDM and OFDM/OQAM systems by approximately 6 dB in terms of Eb/Noat 10-3of bit error rate (BER). Furthermore, the computational complexity is reduced by 50% for the integration of the WHT in the system.

We propose a cross-layer strategy that jointly optimizes user scheduling and resource allocation for adaptive modulation and coding (AMC) based orthogonal frequency multiple access (OFDMA). The objective of this paper is to maximize the system throughput as a function of the bit error rate (BER) and the spectral efficiency based on selected modulation and coding schemes (MCSs). The proposed optimal user scheduling and resource allocation (OSRA) strategy arranges the users in distinct queues according to their priorities and selects users in an optimal manner that guarantees fair services for users among different priority levels. Moreover, it allocates the available resources optimally over the utilized sub-channels. The transmitter of the investigated AMC-OFDMA system at the assigned base station (BS) divides the transmitted OFDMA frame into sub-channels depending on the number of the considered priority levels. Simulation results show that the performance of the investigated AMC-OFDMA system based on the proposed OSRA strategy outperforms the conventional approaches.

In this paper, we propose a bit and power allocation strategy for adaptive modulation and coding (AMC) based spatial multiplexing multi-input-multi-output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. This strategy aims to maximize the average system throughput by allocating the available resources optimally among the utilized bands depending on the corresponding channel conditions and the total transmission power constraints. The average system throughput is represented as a trade-off criterion between the spectral efficiency and bit error rate (BER). The considered AMC technique utilizes distinct modulation and coding scheme (MCS) options rather than adopting fixed or uncoded approaches. The transmitter divides the OFDMA frame at each transmit antenna into bands depending on the number of active users in an assigned base station (BS). The simulation results show superior performance of the MIMO-AMC-OFDMA system, which adopts the proposed strategy, over other conventional schemes.

In a cooperative communication network, individual users are encouraged not only to transmit their own data, but also relay other user's data. This relaying transmission creates spatial diversity to combat the effect of individual severe fading and path loss. Since cooperative users utilize some degree of their transmission freedom for relaying other user's data, cooperative transmission results in lowering each user's transmission spectral efficiency. Therefore, a coding scheme with high spectral efficiency and optimized performance would be desirable for a cooperative network. This paper proposes the Trellis Coded Modulation (TCM) scheme to be incorporated with the cooperative Amplify-and- Forward (AF) systems. A criterion for designing good TCM codes for AF systems is also derived and two cooperative AF systems achieving 1 bits/sec/Hz and 1.5 bits/sec/Hz for each user are presented. Analyses in this paper show that cooperative TCM schemes can not only achieve high spectral efficiency, but also outperform convolutional codes with a high order modulation scheme.

We propose a novel iterative decoder for block turbo codes (BTCs). The proposed decoder combines soft-input/softoutput (SISO) and hard-input/hard-output (HIHO) constituent decoders in order to obtain better error performance and reduce the computational complexity compared to classical BTC decoders. We show that the new decoder, called 'hybrid decoder', offers a better complexity/performance tradeoff than a classical BTC decoder.

Selected mapping (SLM) is a technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. SLM requires the transmission of several side information bits for each data block, which results in some data rate loss. These bits must generally be channel-encoded because they are particularly critical to the error performance of the system. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of several OFDM systems using either QPSK or 16-QAM modulation, we show that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output provided that the number of subcarriers is large enough.

Selected mapping (SLM) is a technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. SLM requires the transmission of several side information bits for each data block, which results in some data rate loss. These bits must be channel-encoded because they are particularly critical to the error performance of the system. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of several OFDM systems using either QPSK or 16-QAM modulation, we show that the proposed method performs very well in terms of bit error rate at the receiver output provided that the number of subcarriers is large enough.

Precoded spatial multiplexing multiple-input multiple-output (MIMO) systems using limited feedback have been extensively studied to reduce the feedback information based on the notion of delay-free feedback channel. In order to reduce performance degradation of precoded spatial multiplexing MIMO systems due to delay in the feedback channel, in this paper, we take into account the time varying nature of the channel, and consider the feedback delay problem. We propose the use of a linear predictor at the receiver to provide the precoder at the transmitter with predicted channel state information, and hence, mitigate the effect of feedback delay. The predictor is implemented using Kalman filter. The performance of this method is evaluated using computer simulation, and the achieved results demonstrate improved bit error rate performance in frequency selective Rayleigh fading channels.

Selected mapping (SLM) is a well-known method for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of this technique is that, for each data block, it requires the transmission of several side information bits, which results in some data rate loss. These redundant bits are so critical to the error performance of the system that they need in practice to be protected by a powerful channel code. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of an OFDM system using 16-QAM modulation, it is shown that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output.

Selected mapping (SLM) is a well-known method for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of this technique is that, for each data block, it requires the transmission of several side information bits, which results in some data rate loss. These redundant bits are so critical to the error performance of the system that they need in practice to be protected by a powerful channel code. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of an OFDM system using 16-QAM modulation, it is shown that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output.

This paper introduces a new technique for combining constellation shaping and bit-interleaved turbo-coded modulation (BITCM) over additive white Gaussian noise channel. The proposed scheme consists of serial concatenation of a binary turbo code, short-length binary shaping code, and mapping function using Gray labeling. The corresponding receiver is made up of four blocks (demapper, shaping decoder, and two constituent RSC decoders) exchanging extrinsic information in order to optimize error performance. A BITCM scheme employing 16-PAM constellation to achieve a rate of 3 bits/dim is considered as an example. It is shown that, by careful selection of the shaping code parameters, shaping gains almost equal to 0.8 dB can be obtained at a little cost in terms of system complexity.

In this paper, the performance of a computationally efficient adaptive MMSE receiver is investigated for asynchronous MC-CDMA systems over multipath fading channels. According to Wiener filter and LMS algorithm theories, we prove that the proposed computationally efficient MMSE receiver has the same BER and convergence performance as that of the conventional MMSE receiver, assuming the sampling rate per symbol is equal to the number of subcarriers. When the sampling rate per symbol is increased, the proposed receiver can outperform the conventional MMSE receiver without sacrificing the convergence speed. The theoretical analysis is verified by the results through Monte-Carlo simulation

We investigate the association between constellation shaping and bit-interleaved coded modulation with iterative decoding (BICM-ID). To this end, we consider a technique which consists of inserting shaping block codes between mapping and channel coding functions in order to achieve constellation shaping. By assuming the example of a 2-bit/s/Hz 16-QAM BICM-ID, it is demonstrated using computer simulations that this technique can improve the performance of BICM-ID schemes by a few tenths of decibels.

We present a new and simple method for combining constellation shaping and bit-interleaved coded modulation over Gaussian channels. By considering the example of a 3-bit/dim turbo coding scheme using a 16-PAM constellation, it is shown that this technique can provide shaping gains of 0.7 dB, and that error performance within 1.6 dB of the continuous-input channel capacity limit is achieved.

Bit-interleaved coded modulation (BICM) is a bandwidth-efficient coding technique consisting of serial concatenation of binary error-correcting coding, bit-by-bit interleaving, and high-order modulation. BICM is capable of achieving excellent error performance provided that powerful codes, such as for example turbo codes or low-density parity-check (LDPC) codes, are employed. We address the problem of finding the signal sets that are the most suitable ones for designing power-efficient BICM schemes over an additive white Gaussian noise (AWGN) channel. To this end, we exploit the expression of the BICM capacity limit, and evaluate it for several 8- and 16-ary constellations. The bit-error rate (BER) performance of some BICM schemes made up of turbo codes and various signal sets is also investigated by computer simulations so as to illustrate the theoretical results. We show that, for spectral efficiencies of practical interest, the most attractive signal sets are those for which Gray mapping is possible, provided that their symbol error rate performance is "sufficiently close" to the optimum. This explains why some constellations having a simple structure, such as 8-PSK and 16-QAM, perform very well when combined with a powerful code. At the same time, the constellations displaying optimal error performance without coding are, generally, not of interest for BICM.

Bit-interleaved turbo-coded modulations (BITCM) have been shown to achieve bit error rate performance very close to the capacity limit over both additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. So far, most studies have been done on BITCM systems designed using rectangular QAM signal sets. In this paper, we address the problem of finding some constellations that would be more suitable than rectangular QAM for designing power efficient BITCM. When the parameter M is in the form M=2/sup 2p/ where p is an integer, we show that rectangular QAM constellations are surprisingly the most attractive signal sets for the design of power-efficient BITCM schemes over AWGN channels. This is not necessarily true with Rayleigh fading channels.