Longxiang Yang

Superposition coding cooperative relaying communications: Outage performance analysis

User cooperative is a powerful tool to combat fading and to increase robustness for communications over wireless channels. For cooperative relaying communications, the outage probability and the expected rate (throughput) can be greatly improved when the superposition coding relaying (SC-relaying) strategy is employed. Under the assumption of high signal-to-noise ratio (SNR), this work contributes to a comprehensive investigation on the outage probability and the throughput of cooperative relaying communications system with only two-level rate SC. Through strict mathematical process and deduction, the approximated close-form expressions of the outage probabilities and the throughput of system are obtained for the first time. Based on the results, the impact of power and channel allocation fractions on system performance is carried out. With the aim of maximal throughput, a set of optimal solutions of system parameters are obtained by employing difference evolution arithmetic. The comparative numerical analyses show that the approximation results are feasible and correct. Copyright

Outage Balancing in Downlink Nonorthogonal Multiple Access With Statistical Channel State Information

This paper considers a downlink nonorthogonal multiple access (NOMA) system where the source intends to transmit independent information to the users at target data rates under statistical channel state information. The outage balancing problem is studied with the issues of power allocation, decoding order selection, and user grouping being taken into account. Specifically, with regard to the max-min fairness criterion, we derive the optimal power allocation in closed form and prove the corresponding optimal decoding order for the elementary downlink NOMA system. By assigning a weighting factor for each user, the analytical results can be used to evaluate the outage performance of the downlink NOMA system under various fairness constraints. Furthermore, we investigate the case with user grouping, in which each user group can be treated as an elementary downlink NOMA system. The associated problems of intergroup power and resource allocation are solved. The implementation complexity issue of NOMA is also considered with focus on that caused by successive interference cancellation and user grouping. The complexity and performance tradeoff is analyzed by simulations, which provides fruitful insights for the practical application of NOMA. The simulation results substantiate our analysis and show considerable performance gain of NOMA when compared with orthogonal multiple access.

Spectrum and Energy Efficiencies for Multiuser Pairs Massive MIMO Systems With Full-Duplex Amplify-and-Forward Relay

To achieve insights about the impact of amplified loop interference, we consider a dual-hop fullduplex (FD) massive multiple-input multiple-output (MIMO) amplify-and-forward (AF) relaying system in terms of achievable ergodic rates for each user pair as well as spectrum and energy efficiencies. It is assumed that the base station (or relay) is equipped with MRx receive antennas and MTxtransmit antennas, while all sources and destinations have a single antenna. For such FD massive MIMO AF relaying systems, the closedform expressions of the lower bounds of achievable ergodic rates are derived first with a finite number of receive and transmit antennas at base station. Then, the asymptotic performance analysis is performed by considering three different power-scaling schemes: 1) P_S = E_S/M_Rx and P_R = E_R; 2) P_S = E_S and P_R = E_R/M_Tx; and 3) P_S = E_S/M_Rx and P_R = E_R/M_Tx, where E_S and E_R are fixed, and P_S and P_R denote the transmit powers of each source and relay, respectively. Our results show that only when the power-scaling 2) is utilized, do the FD massive MIMO AF relay systems have the ability to restrict the loop interference, so that the system performance is free of loop interference when the number of antennas at the relay is large enough. On the contrary, with the power-scaling cases 1) and 3), the systems have no ability to cancel the loop interference even if M_Rx or M_Tx (or both) goes to infinity. The insight is different from the results in the FD massive MIMO decode-and-forward relaying systems where the loop interference can be entirely eliminated for the three power-scaling cases.

Upper and Lower Bounds of Two-Way Opportunistic Amplify-and-Forward Relaying Channels

With the high signal-to-noise ratio (SNR) approximation, the statistical descriptions of the two-way opportunistic relaying amplify-and-forward channels (TWOR-AF) are investigated through the appropriate mathematic proof and simulations. Firstly, we obtain the tractable closed-form expressions of the cumulative distribution function (CDF) and outage probability by defining the equivalent instantaneous end-to-end channels variance {λ _{eq - k}}(θ ), where 2 ≤ θ ≤ 3. Then, we study the performance bounds of the TWOR-AF systems. The simulations show that, in high SNR, the derivation is the tight lower bound of the outage probability when θ=2, and is the upper bound when θ=3. Finally, we present the approximate analysis of the outage probability by taking θ=2.3 and θ=2.5, respectively. The results show that we can obtain the more precise approximate evaluation of the systems performance when θ=2.3, especially in low SNR region. However, when θ=2.5, we can approximately evaluate the upper bound of the systems performance over the entire SNR region. This yields that the TWOR-AF systems can achieve about 1dB of SNR gain at 10^{-4} of outage probability over θ=3 case.

Two-way denoise-and-forward network coding opportunistic relaying with jointing adaptive modulation relay selection criterions

To improve the performance of the two-way denoise-and-forward network coding opportunistic relaying systems (TW-DNF-OR), two novel best-relay selection criterions are presented, which are the jointing adaptive modulation max-min criterion (AM-MM) and the jointing adaptive modulation maximum harmonic mean criterion (AM-MHM). In the proposed AM-MM and AM-MHM criterions, the effect of the modulation schemes used at both sources is exploited perfectly by integrating the adaptive modulation with the max-min and maximum harmonic mean criterions. On the basis of the proposed AM-MM and AM-MHM criterions, the authors analyse the symbol error probability (SEP) of the TW-DNF-OR systems under independent and non-identically distributed Rayleigh fading channels, and obtain the analytical expressions to the approximate upper bounds of the overall average SEPs. The comparison analyses show that the average SEP of TW-DNF-OR is improved greatly when the proposed jointing adaptive modulation best relay selection criterions are used. Moreover, in certain channel realisations or signal-to-noise ratio regions, the adaptive modulation non-selection TW-DNF-OR systems outperform the conventional best relay selection systems in which the adaptive modulation is not integrated with the best relay selection criterions.

Comparison of average symbol error rate and optimal power allocation for two-way opportunistic relaying with amplify-and-forward protocol

In this paper, we investigate the statistical characteristics of the equivalent end-to-end signal-to-noise ratios SNRs, the average symbol error ratios SERs, and the optimal power allocation OPA for two-way amplify-and-forward opportunistic relaying TWOR-AF systems. First, with strict mathematic manipulation, we obtain the closed-form solutions to the PDF, CDF, and moment generating function of the end-to-end SNRs. Then, based on the obtained statistical results, we present the total average SER of the Non-OPA TWOR-AF systems by using the appropriate approximation, in which only the greater segment of the two terminal SERs is considered. Finally, by aiming at minimizing the total average SER and using the SNRs balancing condition at both transceivers, we study the OPA problem subject to a total transmission power constraint. The comparison analysis shows that, for the Non-OPA TWOR-AF systems, we can only evaluate exactly the greater segment of the two SERs of the received signals at two transceivers by using the derivations. However, for the OPA TWOR-AF systems, with our derivations we can evaluate exactly not only each segment of the two terminal SERs but also the sum SER exact total SER. Moreover, the simulations show the OPA TWOR-AF systems outperform the Non-OPA TWOR-AF systems. Copyright

Tight performance bounds for two-way opportunistic amplify-and-forward wireless relaying networks with TDBC protocols

Based on amplify-and-forward network coding (AFNC) protocol, the outage probability and ergodic capacity of two-way network coding opportunistic relaying (TWOR-AFNC) systems are investigated as well as the corresponding closed-form solutions. For the TWOR-AFNC systems, it is investigated under two scenarios, namely, the TWOR-AFNC systems without direct link (TWOR-AFNC-Nodir) and the TWOR-AFNC systems with direct link (TWOR-AFNC-Dir). First, we investigate TWOR-AFNC-Nodir systems by employing the approximate analysis in high SNR, and obtain closed-form solutions to the cumulative distribution function (CDF) and the probability density function (PDF) of the instantaneous end-to-end signal-to-noise ratio (SNR) with very simple expressions. The derived simple expressions are given by defining an equivalent variable ωeq-k (θ), 2 ≤ θ ≤ 3. When θ = 2, the derived results are the tight lower bounds to CDF and PDF. The sequent simulation demonstrates that the derived tight lower bounds are also very effective over the entire SNR region though which the results are derived in high SNR approximation. Then, with the derived tight closed-form lower bound solutions (θ = 2) in TWOR-AFNC-Nodir systems, we investigate TWOR-AFNC-Dir systems as well as the overall comparison of the outage probability and the ergodic capacity between the two system models. The comparison analysis performed over path loss model basis shows that, in urban environment, due to utilizing the direct link the TWOR-AFNC-Dir outperform considerably the TWOR-AF-Nodir systems. However, when the value of path loss exponent is relatively large, the achievable gain is very small and the direct link can be omitted. In this case, the TWOR-AFNC-Dir model can be displaced by TWOR-AFNC-Nodir model having lower implementation complexity.

A novel cooperative transmission scheme based on superposition coding and partial relaying

This paper considered the single relay system and proposed a novel repetition coding decode-and-forward DF cooperative transmission scheme on the basis of superposition coding and partial relaying. In the proposed scheme, the link disparity due to the geometry of the relay network is emphasized, and only a fraction of the information is transmitted in relay mode with the rest being transmitted directly, which benefits from the utility of superposition coding SC in broadcast situation. The proposed scheme is analyzed in two cases, one assumes full channel state information at the source full CSIS, the other with only mean gain of each link known by the source partial CSIS. For both cases, the optimal design of system parameters is considered. We investigate the achievable rate and expected rate performance for these two cases, respectively. The proposed schemed is well compared with conventional repetition coding DF, parallel coding DF, as well as another promising superposition coding relaying. It is concluded that, by designing protocols that orients to certain network geometry, better trade-off between performance and complexity can be obtained. The analysis reveals that the gap between conventional repetition and parallel coding is largely mitigated by the proposed scheme, quite for the scenario that the relay locates relatively but not extremely closer to the source, at moderate SNR regime for both partial and full CSIS cases. The proposed scheme becomes more beneficial in severe path loss attenuation scenario. Copyright

Operator Profit-Aware Wireless Virtualization for Device-to-Device Communications Underlaying LTE Networks

This paper investigates the operator profit from virtual resource allocation in device-to-device (D2D) communications underlaying long-term evolution networks. By utilizing the power-bandwidth product model as the metric of operator cost, the virtual resource allocation is formulated as a binary integer programming to maximize the difference between the sum rate of all the users and the consumed resources. To reduce the complexity, the formulated problem is decomposed to two subproblems, and for each subproblem, a heuristic algorithm is proposed to transfer the complexity of exponent into polynomial. Simulation results show that the proposed scheme is close to the optimal solution with lower complexity. Meanwhile, it also outperforms the benchmark in terms of the total profit, and enables the desired tradeoff between the operator cost and sum rate of both cellular and D2D users.

Study on cognitive DF relaying cooperation with the mutual interference between primary and secondary users over Nakagami-m fading channels

In this paper, the cognitive relay cooperation CRC wireless communication systems are investigated over Nakagami-m fading channels. The decode-and-forward DF relay is employed to assist the communications between cognitive source and destination. Especially, to achieve full diversity order, we consider the case in which there is a direct path between cognitive source and destination. Besides the interference at primary users PUs created by secondary users SUs, the interference at SUs created by PUs is also considered. For the interested CRC systems, we first achieve the exact expression for the CDF of the equivalent end-to-end signal-to-interference ratio SIR of CRC systems. Then, with the exact CDF, the exact average symbol error ratio SER and outage performance of CRC systems are achieved. The derivation is of significance, by which we can obtain a detailed knowledge about CRC systems. Though a single integral included in the derivation, it can be calculated numerically by employing some mathematical tools such as Matlab. At the same time, to obtain the insight and highlight the effect of system parameters on the considered CRC systems, by using the high SIR approximation, we obtain the asymptotic closed-form expression of CDF as well as the ones of average SER and outage probability. From the asymptotic results, we can find the main factors that dominate the performance of CRC systems. The presented simulation results for outage probability and average SER show the derivations and simulations are in agreement. Moreover, in high SIR the achieved asymptotic results match well the exact ones. As a result, in high SIR we can employ the asymptotic closed-form solutions to evaluate the exact performance of CRC systems. This can reduce greatly the implementation complexity. Besides this, the simulations also show that the diversity order is dominated by the fading severities of the secondary systems, i.e. the diversity order be proportional to the summation of the minimum fading severity between the two hops and that of the direct link. In contrast, the parameters of the primary systems only affect the coding gain, not the diversity gain. Copyright