Recent technological advances in electronics, sen- sors, and communications devices have facilitated the prolifer- ation of Unmanned Aircraft System (UAS)-aided applications. However, the UAS-aided communications networks are yet to receive sufficient research endeavor. In this paper, we address one of the most important research challenges pertaining to UAS-aided networks comprising adaptive modulation-capable nodes, namely how to fairly maximize the energy efficiency (throughput per energy). For the mobility pattern innate to the UAS, we demonstrate how the adaptive modulation behaves. Furthermore, we formulate the problem as a potential game that is played between the UAS and the network-nodes, and prove its stability, optimality, and convergence. Based upon the potential game, a data collection method is envisioned to maximize the energy efficiency with the fairness constraint. Additionally, we analyze the Price of Anarchy (PoA) of our proposed game. Extensive simulations exhibit the effectiveness of our proposal under varying environments. sensor nodes require only capabilities to communicate with the CHs. The mobility pattern of the UAS causes the distance between a CH and the UAS to vary. The distance between the CH and the UAS affects the Signal-to-Noise Ratio (SNR), which in turn affects the Bit Error Rate (BER) of the CH transmissions. Both SNR and BER affect the modulation scheme. This is because modulation schemes that transmit more bits per symbol require higher values of SNR for a given BER requirement (9). Moreover, if high levels of BER are acceptable, the achievable number of bits per symbol that a modulation scheme transmits can be increased.

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An Optimal Data Collection Technique for Improved Utility in UAS-aided Networks

An output-threshold multiple-relay-selection (OT-MRS) scheme for dual-hop multibranch cooperative wireless networks is proposed. In this scheme, the first Lc (nonordered) relays are sequentially selected out of L relays such that the SNR of the maximal ratio combined Lc relayed paths and the direct path exceeds a preset threshold. Analytical results for the performance bounds are derived. The numerical results verify the analyses and show that OT-MRS outperforms optimal single-relay selection and generalized-selection-combining-based multiple relay-selection for low to moderately high SNRs. The proposed scheme provides more flexibility in utilizing bandwidth and spatial diversity in cooperative wireless networks.

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Output-Threshold Multiple-Relay-Selection Scheme for Cooperative Wireless Networks

Optimization of the switching thresholds for constant-power adaptive five-mode M-ary quadrature amplitude modulation (M -QAM) transmission with an amplify-and-forward (AF) relay network is developed. The optimization criterion is the maximization of spectral efficiency subject to an average bit-error-rate (BER) constraint. This approach results in a constant-BER variable-rate M-QAM AF relay system, which requires feedback of log2(N) bits for N modes. The performance analysis is based on an upper bound on the total effective SNR. Expressions are derived for the outage probability, the achievable spectral efficiency, and the error-rate performance for the AF cooperative system over both independent identically distributed (i.i.d.) and non-i.i.d. Rayleigh fading environments. The tightness of the upper bound is validated by Monte Carlo simulation. Adaptive five-mode M-QAM with optimum switching levels is shown to offer performance gains of 2-2.5 dB compared with fixed switching in terms of the transmit SNR to achieve specific spectral efficiency. Furthermore, the spectral efficiency of adaptive five-mode M-QAM with optimized switching comes within ~6 dB of the theoretical Shannon channel capacity. However, this performance gain, which is obtained by employing adaptive M -QAM under cooperative diversity, comes at the cost of increased system complexity that is incurred due to the additional complexity of transmitter and receiver design.

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Performance of Optimum Switching Adaptive $M$ -QAM for Amplify-and-Forward Relays

We consider an amplify-and-forward (AF) cooperative-diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). in this paper, we analyze the system where N multiple relays that have the strongest signal strength at the destination are selected out of M relays and forward their received data from the source node to the destination node. We derive closed-form expressions for the average symbol error probability, the outage probability, the average channel capacity, the average signal-to-noise ratio (SNR), the amount of fading, and the SNR moments. In particular, closed-form expression for the moment generating function of the SNR at the destination node is determined. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Simulation results are also given to verify the analytical results. Results show that increasing N will slightly improves the error performance and degrade the outage probability and average channel capacity. In particular, N = M gives the best performance in terms of error performance and N = 1 (the best relay) gives the best performance in terms of outage probability and average channel capacity.

Performance Analysis of Generalized Selection Combining for Amplify-and-Forward Cooperative-Diversity Networks

Antenna selection schemes offer a good complexity versus performance tradeoff for amplify-and-forward (AF) relay network implementation. In this paper, we consider a dual-hop channel state information assisted AF relay network with a direct source-destination link and investigate the performance of two antenna selection schemes (one optimal and another suboptimal). We derive analytical expressions for the systems' rate outage probabilities and the average bit error rate (BER) that match perfectly with simulation based results in the medium to high signal-to-noise ratio (SNR) regimes. We also investigate the channel capacity of the two schemes by deriving tight upper bounds. In order to gain further insights, simple high SNR approximations for the outage probability and the average BER have also been developed. Our theoretical analysis shows that the performance gap between the optimal and suboptimal schemes largely diminishes in the high SNR regime by increasing the number of antennas at the source. Since the suboptimal scheme has a near optimal performance as well as low signaling overhead compared to the optimal scheme, it seems to be a promising solution for implementing future cellular networks expecting to support relay based communications.

Amplify-and-Forward Relaying with Optimal and Suboptimal Transmit Antenna Selection

In this letter, the use of adaptive source transmission with amplify-and-forward relaying is proposed. Three different adaptive techniques are considered: (i) optimal simultaneous power and rate adaptation; (ii) constant power with optimal rate adaptation; (iii) channel inversion with fixed rate. The capacity upper bounds of these adaptive protocols are derived for the amplify-and-forward cooperative system over both independent and identically distributed (i.i.d.) Rayleigh fading and non-i.i.d. Rayleigh fading environments. The capacity analysis is based on an upper bound on the effective received signal-to-noise ratio (SNR). The tightness of the upper bound is validated by the use of a lower bound and by Monte Carlo simulation. It is shown that at high SNR the optimal simultaneous power and rate adaptation and the optimal rate adaptation with constant power provide roughly the same capacity. Channel inversion is shown to suffer from a deterioration in capacity relative to the other adaptive techniques.

On the capacity of Rayleigh fading cooperative systems under adaptive transmission

The use of constant-power, rate-adaptive M-QAM transmission with an amplify-and-forward cooperative system is proposed. The upper bound expressions are derived for the outage probability, achievable spectral efficiency, and error rate performance for the amplify-and-forward cooperative system over both independent and identically distributed (i.i.d.) and non-i.i.d. Rayleigh fading environments. The analysis is based on an accurate upper bound on the total effective signal-to- noise ratio SNR at the destination. Adaptive continuous rate M-QAM achieves a capacity that comes within a constant gap of the Shannon capacity of the channel, but adaptive discrete rate M-QAM suffers additional performance penalties.

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Performance Analysis of Adaptive M-QAM for Rayleigh Fading Cooperative Systems

This paper considers the signal design problems for quaternary digital communications with nonuniform sources. The designs are considered for both the average and equal energy constraints and for a two-dimensional signal space. A tight upper bound on the bit error probability (BEP) is employed as the design criterion. The optimal quarternary signal sets are presented and their BEP performance is compared with that of the standard QPSK and the signal set previously designed for nonuniform sources. Results shows that a considerable saving in the transmitted power can be achieved by the proposed signal sets for a highly nonuniform source

Quarternary signal sets for digital communications with nonuniform sources

Clipping and filtering (CF) is a simple but effective technique for peak-to-average ratio (PAR) reduction of orthogonal frequency division multiplexing (OFDM) signals. This paper determines the optimal clipping value for the CF method in order to maximize the power efficiency of the high power amplifier (HPA). A transmission spectral mask is placed on the output of the HPA as a design constraint in determining the optimal clipping value. The optimal clipping value is obtained for each specified bit error rate (BER) level. Results show that the optimal clipping value maximizes the efficiency of the HPA modelled as a travelling wave tube amplifier (TWTA), without causing a deterioration in BER performance.

T. Nechiporenko

Papers

On the capacity of Rayleigh fading cooperative systems under adaptive transmission

Performance of Optimum Switching Adaptive $M$ -QAM for Amplify-and-Forward Relays

Performance Analysis of Adaptive M-QAM for Rayleigh Fading Cooperative Systems

Quarternary signal sets for digital communications with nonuniform sources

Optimal Clipping Value for PAR Reduction of OFDM