SER performance optimisation of AF cooperative communication system based on directional antenna

Aiming at the cooperative communication system with directional antenna, this paper has studied the SER (Symbol Error Rate) performance under AF (Amplify-and-Forward protocol). The model of AF cooperative communication system using directional antenna was firstly established to deduce the closed-form expression of SER in this model as well as the upper limit of SER. Then, the OPA (Optimum Power Allocation) was also analysed on the purpose of minimising SER. Combining specific simulation numerical values, SER performance of established model was thoroughly researched in this paper. Simulation results demonstrate that system SER obviously decreases by adopting cooperative communication system with directional transmitting and directional receiving. Each node's directional gain, channel quality and power allocation method all have great influence on system's overall performance. And the OPA is also proved to be superior to EPA (Equal Power Allocation).

In this paper, the Symbol Error Rate (SER) performance formulation which suited to multi-node amplify-and-forward cooperative communication M-PSK constellation systems with the mean channel gains is derived. Firstly, the closed-form theory symbol error rate formulation with M-PSK modulation is derived. Then, a Low Bound (LB) is established to show the asymptotic performance of the cooperation protocol which tightens the theory SER under the both low and high Signal to Noise Ratio (SNR) conditions. Thirdly, the optimal power allocation algorithm for multi-node cooperative communication systems which minimizes the SER performance based on the Low Bound (LB) is formulated. SER comparison between the proposed approximate optimal power allocation method and the traditional Equal Power Allocation (EPA) method, the SER performance for the approximate optimal power allocation is better than the EPA's, especially under the channel conditions which the relay nodes are near the middle locations between the source and destination node or near the destination node.

This paper presents the symbol error rate (SER) vs. signal-to-noise (SNR) ratio performance of OFDM system with QAM modulation. It has been observed that the optimal power allocation between pilot and information symbols can improve the performance gain by 2.3 dB relative to the equal power allocation between pilot and information symbols, for a system with N=3D512 sub-carriers, and a channel with L=3D40 taps. The SER performance is then compared with Rayleigh-faded as well as Rician-faded channels. It has been further concluded that the SER vs. SNR performance graph in Rayleigh-faded channel environment is better than that in Rician-faded channel. This idea implies that in OFDM case, the SER vs. SNR performance is better in scattered rich channel environments. The SER vs. SNR performance graph is degraded by equal magnitude for both equal-power and optimal-power cases, which implies that the difference between the equal-power and optimal power case is independent of the channel fading model being used. It is also observed that by varying the standard-deviation of the channel, the SER vs. SNR performance graph is not going to be affected if the channel is considered Rayleigh-faded.

For specific military use of the environment, this paper study the performance change of the system used directional antennas and exploratory study the power optimization based on the symbol error rate(SER) under amplify-and-forward protocol (AF). Firstly, cooperative communication system model based on the directional antenna was established, and then the closed-form expression of the model was derived theoretically. Secondly, it analyzed the optimal power allocation (OPA) problem in order to minimize system SER. Finally, it analyzed and compared the performance of the SER combining with specific numerical and simulation in detail. The results showed that in the condition of using directional transmission and directional reception, system had smaller SER. Directional gain, channel quality and power distribution of each node had enormous impact on the whole system performance. OPA had better performance than equal power allocation (EPA).

Optimal power allocation to minimize SER for multinode amplify-and-forward cooperative communication systems

In this paper, we analyze the symbol-error-rate (SER) performance for a two-user amplify-and-forward cooperative system. The closed-form SER formulation and corresponding upper bound with PSK signals are derived first. Moreover, we develop an optimum power allocation for the cooperative system to minimize the SER. With the optimum and equal power allocation methods, we discuss the impact of relay location to the SER performance by making use of a characteristic ellipse topology. With the equal power allocation, the SER curve shows an interesting symmetric characteristic and the optimum relay location is just in the middle with respect to the source and destination, while the optimum relay location is near the destination with the optimum power case.

In this paper, we propose an optimum power allocation method (OPA) which to minimize the the symbol-error-rate (SER) performance for a two-user amplify-and-forward cooperative system. With this optimum and equal power allocation (EPA) methods, we also discuss the impact of relay location to the SER performance and ergodic capacity by making use of two characteristic rectangle and ellipse topologies. With the EPA method, the ergodic capacity and SER curves show an interesting symmetric characteristic and the optimum relay location is just in the middle with respect to the source and destination. While a different conclusion is drown with the OPA method, the optimum relay location is near the destination in this case.

Cooperative communication has been recently proposed in wireless communication systems for exploring the inherent spatial diversity in relay channels.The Amplify-and-Forward (AF) cooperation protocols with multiple relays have not been sufficiently investigated even if it has a low complexity in term of implementation. We consider in this work a cooperative diversity system in which a source transmits some information to a destination with the help of multiple relay nodes with AF protocols and investigate the optimality of allocating powers both at the source and the relays system by optimizing the symbol error rate (SER) performance in an efficient way. Firstly we derive a closedform SER formulation for MPSK signal using the concept of moment generating function and some statistical approximations in high signal to noise ratio (SNR) for the system under studied. We then find a tight corresponding lower bound which converges to the same limit as the theoretical upper bound and develop an optimal power allocation (OPA) technique with mean channel gains to minimize the SER. Simulation results show that our scheme outperforms the equal power allocation (EPA) scheme and is tight to the theoretical approximation based on the SER upper bound in high SNR for different number of relays.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with an imperfectly-known relay fading channel. It is assumed that a pilot symbol assisted modulation (PSAM) scheme with linear minimum mean square estimator (LMMSE) is used for the channel estimation. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the choice of parameters in the PSAM scheme, i.e., the pilot spacing and the Wiener filter length. We also formulate an optimum power allocation problem for the considered system. The optimum power allocation can be found by means of a gradient search over a continuous range. Numerical simulations are presented to verify the correctness of the theoretical results and the benefits of the parameter optimization. The performance of amplify-and-forward (AF) cooperative systems has been studied in the past from different perspec- tives. However, most of the work on performance analysis of AF systems has assumed that the perfect channel state information (CSI) is available to both the relay and desti- nation terminal. More recently, (1) and (2) have studied the performance of AF cooperative communication systems with channel estimation error by means of Monte Carlo simulations. The accurate SER expression for cooperative communication systems with a pilot symbol assisted modulation (PSAM) scheme employing a linear minimum mean square estimator (LMMSE) is derived in (3). Furthermore, (4) propose a new channel estimation scheme and analyse the mean square error of the channel estimation. To the authors' best knowledge, no research has been conducted to solve the problem of parameter optimization and optimum power allocation for variable gain AF cooperative communication systems with a PSAM scheme. In this paper, we propose to use the asymptotic upper bound (AUB) of the SER to overcome these difficulties. In particular, we derive a tight expression for the AUB of the SER for the AF cooperative communication system with a PSAM scheme. Using the AUB of the SER, we present the criterion for the parameter choice in the PSAM scheme and show that two parameters used in this scheme, i.e., pilot spacing and Wiener filter length, can be chosen in a tradeoff between system performance, pilot overhead, and receiver complexity. With the derived tight AUB, an optimum power allocation problem is also formulated for the AF cooperative communication system. Since the optimization of the power allocation is very complicated, as it is related to many terms, and obtaining an analytical solution is unlikely, we propose to find the optimum power allocation by means of a gradient search over a continuous range. The rest of the paper is organized as follows. In Section II, we describe the system model and some preliminaries of the AF cooperative system with a PSAM scheme. In Section III, we derive an AUB of the SER for an AF cooperative com- munication system with LMMSE. In Section IV, we first deal with the parameter optimization for the PSAM scheme. Then, an optimum power allocation problem is formulated. Various simulation results and their discussions are presented in Section V. Finally, Section VI contains the conclusions. The following notation is used throughout the paper: (·) ∗ , (·) T , (·) H , and (·) −1 denote the complex conjugate, vec- tor (or matrix) transpose, conjugate transpose, and matrix inverse, respectively. The symbol E(·) denotes the expecta- tion operator, |z| represents the absolute value of a com- plex number z, and the complex Gaussian distribution with mean m and covariance P is denoted by CN(m, P). Finally, x ∼C N(m, P) denotes a complex random variable x with distribution CN(m, P).

An interference alignment (IA) and independent component analysis (ICA)-based semiblind scheme, referred to as IA-ICA, is proposed for downlink dual-user power-domain nonorthogonal multiple access (NOMA) systems in high-reliability low-latency (HRLL) Internet of Things (IoT). At the base station (BS), one user is converted to constructive interference to the other user via phase alignment of each symbol. At both user ends, ICA is used for semiblind signal detection. The phase rotation via nonredundant precoding at the BS does not introduce any spectral overhead, while only 1–2 pilot symbols are required for elimination of ICA incurred ambiguity. Closed-form expressions are derived for the users’ symbol error rate (SER) performance in Rayleigh fading with 4-quadrature amplitude modulation (4-QAM), which matches the simulation results very well. Based on the analytical results, we propose an efficient power allocation algorithm that is based on statistical channel state information (CSI) only, and therefore, the signaling overhead involved is negligible. In particular, a near-optimal SER performance can be achieved with equal power allocation between the two users. The proposed IA-ICA-based semiblind NOMA system demonstrates a much better SER performance than the existing approaches even though they are under perfect CSI. Hence, it is a feasible solution for HRLL IoT, with high reliability and very low spectral and signaling overheads.

We investigate the Alamouti scheme with joint antenna selection and power allocation over flat-fading Rayleigh channels. Based on the channel state information (CSI) feedbacks, the transmitter selects the optimal two antennas out of all possible antennas to transmit data using space-time block coding (STBC). Then, the transmitter adaptively allocates transmit power among the selected antennas to minimize the symbol-error rate (SER). We derive the SER as either the closed-form expression or the single-fold finite integral when assuming perfect and delayed CSI feedbacks, respectively. Our results show that when the CSI feedback is perfect, the optimal power allocation is to assign all power to the single optimal antenna, such that the selection-combining (SC)-STBC reduces to the simpler selection-combining (SC) scheme. On the other hand, when taking the CSI feedback delay into account, the SC-STBC scheme with dynamic power allocation ensures the better SER performance than the conventional SC scheme and SC-STBC scheme with equal power (EP) allocation.

In this paper, we consider a space–time and amplify-and-forward (ST-AF) cooperative system which consists of two-antenna source, single-antenna relay and destination. Source transmits Alamouti space–time coding symbols to destination with cooperation of relay which adopts AF strategy. Closed-form symbol error rate (SER) is derived for the ST-AF system with PSK signals. Moreover, a SER approximation is developed to show the asymptotic performance of the ST-AF cooperative system in medium and high SNR regimes. For comparison, the SER approximation of another cooperative space–time coding (C-STC) scheme is also derived. Theoretical analysis shows that the ST-AF can obtain more diversity gain and achieve higher diversity order than C-STC. Statistical optimal power allocation (OPA) algorithm for the ST-AF cooperative system is presented based on the SER performance. It turns out the OPA only depends on the channel links related to the relay, not depend on the direct link between source and destination. Finally, numerical simulations validate the theoretical analysis.

In this paper, we consider a dual-hop wireless cooperative network with amplify-and-forward (AF) relaying. The output signal-to-noise ratio (SNR) at the destination of the AF cooperative networks is in the form of the sum of harmonic mean of the source-relay channel SNR and the relay-destination channel SNR. Instead of deriving the exact probability density function (PDF) of the output SNR, we study the series expansion of this PDF around zero. This result is then applied to evaluate the performance of the AF cooperative systems over Nakagami-m fading channels, and closed-form high-SNR approximations of the average symbol error rate (SER) and the outage probability are derived. Next, we investigate the optimal power allocation (OPA) among the source node and the relays to minimize the approximate SER as well as the outage probability. It is shown that the optimal power allocation depends on the channel mparameters and the ratio of the source-relay channel gain to the relay-destination gain. In addition to the optimal power allocation, we also propose a low complexity sub-optimal power allocation (SubOPA) scheme. The performance improvement with optimal and sub-optimal power allocation is analyzed and validated by numeric results. It is shown that equal power allocation is near optimal when the relays are close to the source, while significant performance improvement is observed by both the optimal and sub-optimal power allocation schemes when the relays are close to the destination.

Timing offset (TO) would introduce the misaligned interference which can influence the symbol error rate (SER) performance of the symbol detection. We extend joint detection (JD) to systems with TO, where the misaligned interference will be considered as noise and thus merged into the additive noise. However, the SER performance will also be degraded when the misaligned interference increases. In this paper, we propose an iterative technique, decision-aided reconstruction (DAR) to improve the SER performance. The proposed technique can mitigate the interference by making the symbol decision in the frequency domain and then converting the symbol back to the time domain. Simulation results show that DAR can improve the SER performance for MC-CDMA uplink with TO.

Wireless communication systems commonly use Rayleigh distribution to model a non-line of sight multipath channel. With the consideration of on-axis rotation, the probability of symbol error can be described by a different probability distribution. This study presents an evaluation of the Symbol Error Rate (SER) performance of M-ary Phase Shift Keying (MPSK) and M-ary Quadrature Amplitude Modulation (MQAM) in a mobile handheld device with random on-axis rotational motion using an extended Saleh and Valenzuela (S&V) channel model through simulations. The on-axis rotational motion pertains to the pitch and roll movement with respect to the mobile's embedded antenna. Furthermore, the SER performance of the MPSK and MQAM in Weibull distribution are derived and compared to the SER performance of the simulated system. The results show that the SER performance curves of the simulated system are not far from to the derived Weibull equations for MPSK and MQAM. Hence, the Weibull distribution is best to characterize the impairments caused by the on-axis rotational motion in a non-line of sight multipath propagation.