Yunpeng Cheng

On the Capacity of Dual-Hop Multiple Antenna AF Relaying Systems with Feedback Delay and CCI

In this letter, we develop a unified framework for the ergodic capacity of dual-hop multiple antenna amplify-and-forward (AF) relaying systems employing transmit beamforming and maximum ratio combining (TB/MRC) with feedback delay and co-channel interference (CCI). Over Rayleigh fading channels, a new closed-form expression for the exact cumulative distribution function (CDF) of the end-to-end SINR is derived. Based on this, we present the exact expression and the closed-form upper and lower bounds of the ergodic capacity, respectively. The derived analytical results provide an efficient mathematical tool for the fast evaluation of the ergodic capacity of the system as well as for the investigation of the impact of key parameters such as feedback delay, number of antennas and CCI on the ergodic capacity of the system. Monte Carlo simulations are also provided to verify the correctness of the exact results and demonstrate the tightness of the proposed bounds.

Effective Capacity of Cognitive Radio Systems with GSC Diversity under Imperfect Channel Knowledge

In this paper, we investigate the effective capacity of opportunistic spectrum sharing with generalized selection combining (GSC) diversity at the secondary receiver in fading environments. In particular, we study the impact of outdated channel information between the secondary transmitter and the primary receiver on the performance of the secondary user. An exact closed-form expression for the effective capacity of the secondary user with GSC diversity is derived under the peak interference constraint at the primary receiver. Comparisons done using simulations show the effect of the uncertainty of channel information on the effective capacity. Specially, the performance gap due to imperfect channel information becomes smaller with the increase of the number of selected antennas {k}. Theoretic analysis and simulations show that the system performance is robust against imperfect channel information and selection combining (SC) should be adopted under strict delay quality of service (QoS) requirements.

Low-Complexity ML Detection for Spatial Modulation MIMO With APSK Constellation

Spatial modulation (SM) is a promising multiple-input- multiple-output (MIMO) transmission technology, which exploits the indexes of the transmit antennas for encoding information into the spatial dimension and, thus, for increasing the transmission rate. Optimal demodulation is realized by using a maximum-likelihood (ML) detector, which jointly estimates the information bits encoded into the transmit antenna indexes and into the transmitted symbol. If a large number of transmit antennas and/or a large modulation size are used; however, the computational complexity of ML demodulation may not be affordable for some applications. Against this background, we propose two novel near-ML but low-complexity detection schemes for SM-MIMO systems, which use M-ary amplitude and phase-shift keying (APSK) digital modulation. The proposed algorithms exploit specific features of the M-ary APSK constellation diagram, in order to avoid searching among all constellation points. It is shown, in particular, that the complexity of the proposed detection schemes is independent of the constellation size and that it only depends on the number of rings that constitute the APSK constellation. Simulation results are also provided, which confirm that the proposed detection schemes provide bit error probability performance close to that of ML demodulation but with lower demodulation complexity.

Joint subcarrier and power allocation for physical layer security in cooperative OFDMA networks

In this paper, a joint subcarrier and power allocation algorithm is proposed to improve the physical layer security in cooperative orthogonal frequency division multiple access (OFDMA) networks, where several source-destination pairs and one untrusted relay are involved. The relay is friendly and intends to help these pairs to enhance their communications. However, it may be overheard by a malicious eavesdropper at the same time. To optimize the joint subcarrier and power allocation with low complexity, we divide the optimization problem into two simpler subproblems. Firstly, the subcarriers are assigned to the source-destination pairs by employing the dual approach under the assumption that the relay power is equally allocated to all the subcarriers. Then, the relay power is allocated to the subcarriers based on the alternative ascending clock auction mechanism. In addition, we prove that the two subproblems can converge after a finite number of iterations. We also find that the proposed auction is cheat-proof and, thus, can avoid the cheating behaviors in the auction process. Numerical results demonstrate that our proposed algorithm can effectively improve the system sum secrecy rate, and the convergence performance is also desirable.

Combine non-binary LDPC codes with M-ary orthogonal spread spectrum modulation

Low-density parity-check (LDPC) codes are playing more and more important roles in wireless communications due to their excellent error correction performance. In this paper, we study the combination of non-binary LDPC codes with M-ary orthogonal spread spectrum modulation for bandwidth efficient transmission over AWGN channel. Specifically, we investigate an algorithm for computing symbol soft metric based on Maximum a Posteriori Probability (MAP) criterion. To justify the performance of our proposed scheme, we made extensive simulations for various code rates and codeword lengths.

Protocol design and performance analysis for cognitive cooperative networks with multiple antennas

In this article, we deal with a novel access protocol design for cognitive cooperative networks with multiple antennas. According to the principles of cognitive radio, the secondary user (SU) can exploit the primary user (PU) burstiness to access the licensed spectrum in the proposed access protocol. To get more access opportunities to the licensed spectrum, the SU simultaneously relays the PU’s packets and transmits its own packets based on the superposition coding. Furthermore, to concurrent transmission of the PU’s packets and SU’s packets based on the superposition coding such that they are received without the interference at the primary receiver and secondary receiver respectively, two weight vectors at the SU equipped with multiple antennas are designed based on zero-forcing algorithm. Specifically, from a networking perspective, we analyze the performance of the proposed access protocol in terms of the maximum stable throughput and the average end-to-end delay for both the PU and SU based on the principles of queueing theory. In addition, to protect the PU’s performance and exhibit the advantage of adopting multiple antenna technology, we jointly optimize the parameter of superposition coding and the number of antennas, and define the maximum stable throughput cooperative gain compared to the non-cooperative access scheme. More importantly, the impact of imperfect channel state information (CSI) at the SU on the maximum stable throughput and the average end-to-end delay performance is evaluated in the simulations from a practical point of view. Analysis and simulation results demonstrate that the proposed access protocol achieves significant performance gains for both the PU and the SU, outperforms the existing cooperative access protocol based on the dirty-paper coding, and keeps robust against to the imperfect CSI.

Performance analysis of interference-limited dual-hop multiple antenna AF relaying systems with feedback delay

In this paper, we present a comprehensive performance analysis of dual-hop multiple antenna channel state information (CSI) assisted amplify-and-forward (AF) relaying systems over Rayleigh fading channels employing arbitrary transmit antenna selection (TAS) and receiver maximum ratio combining (MRC) with feedback delay in the presence of co-channel interference (CCI) at both the relay and destination. Specifically, an upper bound on the cumulative distribution function (CDF) of the end-to-end signal-to-interference ratio (SIR) is proposed, based on which closed-form expressions for the outage probability and the average symbol error rate (SER) are derived. To gain further insights, simple and high informative expressions for the outage probability and the average SER are obtained at the high SIR regime, which readily enable us to characterize the achievable diversity order and coding gain of the system. Moreover, we present new analytical upper and lower bounds for the ergodic capacity of the system, which apply to the system with arbitrary number of antennas, CCI and feedback delay at any SIRs. Finally, to minimize the outage probability of the system, an optimum power allocation scheme is devised under the total transmission power constraint between the source and the relay. The findings suggest that the feedback delay limits the diversity order to one, while the CCI degrades the outage performance by affecting the coding gain of the system.

Unified performance analysis of maximal-ratio combining for spectrum sharing systems with antenna correlation

A comprehensive analytical framework of a spectrum sharing system, in which secondary receiver SR is equipped with multiple antennas, is presented over Rayleigh fading channels. The impact of spatial fading correlation on the performance of spectrum sharing system with maximal-ratio combining at the SR is investigated. In particular, we explicitly derive the CDF and moment generating function of the end-to-end signal-to-noise ratio by assuming a correlation model with arbitrary eigenvalue multiplicities at the SR. On the basis of these results, we conduct an evaluation of secondary system performance in terms of the outage probability, the average symbol error probability, and the ergodic capacity. All analytical results are verified by Monte Carlo simulations. Furthermore, to obtain an insight of system performance, the asymptotic analysis is studied to obtain the diversity gain and the coding gain in the peak transmit power dominated region. Our results show that the diversity gain is unaffected by antenna correlation whereas the coding gain is degraded. Copyright

Secure transmission of cognitive untrusted relay networks with selection diversity

In this paper, we investigate the secrecy performance of a cognitive untrusted relay network with a direct link using selection combining (SC) scheme, where a secondary source communicates with a secondary destination through an untrusted relay. We first examine the connection outage probability (COP) and secrecy outage probability (SOP) to investigate the reliability and security performance of the considered system. Notably, the reliability level can be improved by loosing the interference temperature constraint, which unfortunately increases the risk that the untrusted relay succeeds in eavesdropping the source information. Then, we characterize the reliability and security in a unified manner by effective secrecy throughput (EST). In order to gain additional insights on the performance evaluation, we provide the asymptotic expressions for the COP, SOP, and EST in high signal-to-noise ratio (SNR) region. Finally, Monte Carlo simulation results validate our numerical analysis.

Low-Complexity Detection for GSM-MIMO Systems via Spatial Constraint

The optimal detection of generalized spatial modulation (GSM) technique is the maximum likelihood (ML) algorithm. However, the computational complexity of ML detection is high and increases dramatically with the increase of the number of transmit antennas and active antennas. To tackle this problem, we propose low-complexity suboptimum detectors by exploiting a special property of GSM-MIMO systems, i.e., the spatial constraint of active antennas. Specifically, the proposed detections are designed based on a greedy algorithm termed Multipath Matching Pursuit (MMP). Using the spatial constraint of active antennas, the proposed detections achieve better performance than that of the original MMP algorithm with lower computational complexity. Moreover, the numerical results are also provided to demonstrate the superiority of the proposed detections.