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This paper investigates the decode-and-forward two-way relaying channel without direct link and proposes a protocol based on the physical-layer network coding PNC protocol. The proposed protocol termed ORT introduces one retransmission into PNC, aiming at enhancing its outage performance. To manifest the merits of ORT, we compare it with PNC and the time-division broadcast TDBC protocol, in terms of outage performance, expected rate, and diversity-multiplexing tradeoff DMT. Firstly, we derive the outage probability of the three protocols and then the expected rate. Secondly, asymptotic analysis is conducted to shed light on the diversity and coding gains. Finally, the DMT is obtained for the three protocols. The numerical results reveal the following: i that ORT performs better than PNC in both outage and expected rate performance when the nodes transmit with different powers. However, it has the same DMT performance with PNC; ii that ORT possesses improved DMT performance over TDBC whereas its expected rate is only better than the latter at medium to high signal-to-noise ratio. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY This paper investigates two-way relaying with direct link transmission. We propose to combine incremental relaying (IR) with the time division broadcast protocol (TDBC) to form a new scheme, termed TDBC-IR, to increase the spectral efficiency of TDBC. Assuming half-duplex decode-and-forward relaying, the performance of three protocols, that is, TDBC, TDBC-IR, and physical-layer network coding (PNC), are studied and compared, in terms of outage probability, expected rate (ER), and diversity-multiplexing tradeoff. First, we reveal that the outage probability performance of TDBC-IR is the same as that of TDBC and better than that of PNC. Second, we compare the ER and diversity-multiplexing tradeoff performance of the three protocols based on the derived outage probability. The numerical results reveal that (1) the ER of TDBC-IR is greater than that of TDBC and PNC in the whole signal-to-noise ratio (SNR) region, that is TDBC-IR has improved spectral efficiency performance; (2) the ER performance of TDBC is better than PNC in the low SNR region but worse in the high SNR region; (3) the maximum achievable diversity order of TDBC-IR and TDBC are both two whereas that of PNC is one; (4) the maximum achievable multiplexing gain of TDBC-IR is one, which is better than TDBC (its maximum achievable is 2/3) and achieves the maximum of PNC (its maximum achievable is one). Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we investigate the outage probability performance of dual-hop Alamouti transmission with channel estimation error in Rayleigh fading channels. The cumulative density function-based method is adopted to obtain the outage probability expression in closed-form. Power allocation between the source and relay is also studied. Furthermore, asymptotic analysis is conducted to shed light on the diversity order. Finally, simulation results are presented to verify the analysis. Copyright © 2012 John Wiley & Sons, Ltd.

The decoupled coherent Maximum Likelihood (ML) detection algorithm presented in this letter can sharply reduce the complexity of the receiver as well as provide better error performance under the precondition that channel should be estimated first. Considering the bandwidth inefficiency of Frequency Shift Keying (FSK), the acquisition of channel state information through training sequences will further decrease the transmission efficiency. This letter presents a blind channel estimation algorithm based on noise subspace theory which can acquire channel information without any training symbols. The simulation shows that the algorithm brings about fewer channel estimation errors while the frequency efficiency can be increased.

The closed-form solutions for error rates of Space-Time Block Code (STBC) Multiple Phase Shift Keying (MPSK) systems are derived in this paper. With characteristic function based method and the partial integration based respectively, the exact expressions of error rates are obtained for (2,1) STBC with and without channel estimation error. Simulations show that the practical error rates accord with the theoretical ones, so closed-form error rates are accurate references for STBC performance evaluation. For the error of pilot assisted channel estimation, the performance of a (2,1) STBC system is deteriorated about 3dB.

In this letter a convolutional coded Direct-Sequence Code-Division Multiple Access(DS/CDMA) concept is introduced. The number of the users it can accommodate is greater than the spreading factor N. Each of the available orthogonal spreading sequences of length N is assigned to one of the first N users which employ a common Pseudo-Noise (PN) scrambling sequence. When the number of users K exceeds N, say K=N+M with M N. The proposed technique thus accommodates N users without any mutual interference and a number of additional users almost without signal-to-noise ratio penalty.

This paper presents a joint physical-layer network coding (PNC) and serially concatenated continuous phase modulation (SCCPM) scheme in a two-way relay (TWR) channel. This proposed scheme can be viewed as a serial concatenated codes (SCCs) scheme in which the joint CPM and PNC is the inner code and the convolutional code (CC) is the outer code. It aims to improve the spectral efficiency, error performance and power efficiency of the PNC system by utilizing the technical advantage of CPM and SCCs. An iterative decoding algorithm for the relay receiver over AWGN channels is investigated. Emphasis is put on the extrinsic logarithmic likelihood ratios (LLRs) of the XORed codewords generated by the soft input soft output (SISO) inner decoder. Simulation results are also provided to show the error performance of the joint scheme.

This paper investigates the diversity-multiplexing tradeoff (DMT) performance of coded cooperation with incremental relaying (CCIR). First, the exact and closed-form DMT expression is derived for CCIR at arbitrary exchange ratio (ER), i.e., the ratio of the time duration of the first phase to that of the whole transmission phase. The result reveals that CCIR outperforms coded cooperation in terms of DMT. Compared with the slotted incremental decode-and-forward protocol, CCIR is more flexible in choosing ER, and performs better in DMT except for low multiplexing gain at high ER. Secondly, asymptotic power allocation, including both source and source-relay asymptotic power allocation, is carried out to improve the DMT performance under a long-term average power constraint. Finally, numerical results are provided to validate the analysis.

In this paper, diversity-multiplexing tradeoff (DMT) of three-user wireless multiple-antenna cooperative systems is investigated in general fading channels when half-duplex and decode-and-forward relay is employed. Three protocols, i.e., adaptive protocol, receive diversity protocol, and dual-hop relaying protocol, are considered. The general fading channels may include transmit and/or receive correlation and nonzero channel means, and are extensions of independent and identically distributed Rayleigh or Rician fading channels. Firstly, simple DMT expressions are derived for general fading channels with zero channel means and no correlation when users employ arbitrary number of antennas. Explicit DMT expressions are also obtained when all users employ the same number of antennas and the channels between any two users are of the same fading statistics. Finally, the impact of nonzero channel means and/or correlation on DMT is evaluated. It is revealed theoretically that the DMTs depend on the number of antennas at each user, channel means (except for Rayleigh and Rician fading statistics), transmit and/or receive correlation, and the polynomial behavior near zero of the channel gain probability density function. Examples are also provided to illustrate the analysis and results.

In this paper, a novel resource allocation algorithm is proposed for multi-service OFDMA systems. The multi-objective optimization model is established for resource allocation, according to the different QoS requirements of different services. In order to achieve the suboptimal solution for the multi-objective optimization problem, this paper proposes a novel hierarchical algorithm, and adopting some appropriate parameter can achieve the optimal performance practically. Simulation results explicitly verify our expectation that the proposed algorithm can meet the different QoS requirements and balance the fairness among users of the same service.

In this paper, a novel hierarchical algorithm is proposed for orthogonal frequency-division multiple-access wireless mesh networks (WMNs). The problem is to maximize the overall end-to-end rate with balancing the fairness among users, and find a new method as a substitute for Lee's resource allocation algorithm with high computational complexity. The proposed algorithm consists of two subproblems, where the mesh router (MR) allocates groups of subcarriers to the mesh clients (MCs) based on Nash bargaining solution according to the limited information, and each MC allocates subcarriers to each of its outgoing links based on the equal power allocation according to the full information of channel gains. The simulation results demonstrate that the proposed algorithm have a comparable overall end-to-end rate with the maximal rate algorithm. Moreover, compared to Lee's resource allocation algorithm, the proposed algorithm not only needs lower computational complexity, but also provides comparable fair opportunities for the respective users (MCs), and a comparable end-to-end rate of each user.

In this paper, we developed a loss-free handover scheme for IEEE802.16e based wireless broadband access networks. Minimized the handover delay and eliminates packet losses during handover. By integrating MAC and network layer handovers efficiently. Results of simulations show that it achieves loss-free packet delivery without packet duplication and increases system throughput significantly.

In this paper, closed-form solutions for error rates of MPSK modulated (2,1) STBC systems are derived. With the hypothesis of ideal channel estimation, a general method of formulating the (2,1) STBC MPSK systems' error rates is explicated and the closed-form solutions for symbol error rate and bit error rate are put forward, which provides the designers with a more accurate standard for evaluating STBC system's performance than the Chernoff bound. Computer simulations demonstrate the consistency between practical error rates and theoretical results.

The following paper is a comment on the paper titled "Performance of Two-Way Opportunistic Relaying With Analog Network Coding Over Nakagami-m Fading". In the original paper, the authors investigated the performance of the outage-optimal two-way opportunistic relaying scheme with analog network coding over independent but not identically distributed Nakagami-m fading channels. For the relay-selection process, the authors declared that the two distributed methods, given by eqs. (6) and (7) in the original paper, were equivalent. According to Kun Xu and Yuanyuan Gao, the equivalence of the two criteria cannot be guaranteed, even for the high-signal-to-noise ratio (SNR) regime.

Fiber Bragg gratings have has been widely used in sensors. We analyze the transmission and polarization properties of magneto-optical fiber Bragg gratings based on coordinate conversion. The simulations demonstrate the influence of magnetic field intensity on the transmission spectrum, the polarization properties by the coupled mode theory, and the Jones formalism. The results show that while a small magnetic field can hardly be detected in the grating amplitude response, it leads to significant polarization properties such as the third normalized Stokes parameter, polarization dependent loss, and ellipticity. We demonstrate that these polarization properties contain information about the magnetic field and can thus be used for magnetic field sensing purposes. The sensitivity and dynamic range depend on the physical parameters of the grating.