A Novel Cooperative Network Using Down-link Non-orthogonal Multiple Access Scheme

A novel downlink cooperative non-orthogonal multiple access (DC-NOMA) scheme is proposed in this paper to achieve higher performance in the spectral efficiency compared to the classical NOMA schemes. The communication system consists of one base station and two users (e.g., strong user and weak user). In down link phase, the base station transmits a superimposed signal to both users, and in the cooperative phase, the weak user sends its decoded message to the strong user. The main idea is how the weak user can help the strong user to improve the performance of both users. This occurs by enabling the weak user to perform a cooperative transmission with the strong user during the cooperative phase. The outage probability, outage throughput, and diversity order are derived and analyzed. Numerical results are provided to show that the spectral efficiency gain achieved through our proposed scheme is better than the conventional cooperative NOMA schemes.

Performance Analysis and Optimization of RIS-Assisted Networks in Nakagami-m Environment

This work studies and optimizes the performance of reconfigurable intelligent surface (RIS)-aided networks in Nakagami- m fading environment. First, accurate closed-form approximations for the channel distributions are derived. Then, closed-form formulas for the system outage probability, average symbol error probability (ASEP), and the channel capacity are obtained. Furthermore, we provide three different optimization approaches for finding the optimum number of reflecting elements to achieve a target outage probability. At the high signal-to-noise ratio (SNR) regime, a closed-form expression for the asymptotic outage probability is obtained to give more insights into the system performance. Results show that the considered system can achieve a diversity order of, where a is a function of the Nakagami- m fading parameter m and the number of reflecting elements N . Moreover, findings show that m is more influential on the diversity order than N . Finally, the achieved expressions are applicable to non-integer values of m and any number of meta-surface elements N .

Analyzing bit error rate of relay sensors selection in wireless cooperative communication systems

Cooperative communication systems, which make use of the intermediate relays between the transmitter and the receiver, have been employed as an effective technique to combat the channel fading and to enhance system performance. Cooperative systems have some drawbacks such as high latency and may diversity order not guaranteed. To alleviate the negative effects of these factors, the relay selection protocol is employed in cooperative communication systems to increase overall cooperative system performance. Relay selection in the cooperative systems enables the source to cooperate with the single relay node rather than multiple relay nodes which guaranteed the diversity order.

Performance Analysis of Cooperative Low-Power Wide-Area Network for Energy-Efficient B5G Systems

Low-power wide-area networks (LPWANs) have received extensive attention from both academia and industry, since they can efficiently provide massive connectivity to internet of things (IoT) devices in wide geographical areas with low cost and low power consumption. Recently, it was shown that macro-diversity among multiple gateways significantly improves the performance of uplink LPWANs by coherently combining multiple received signals at gateways. We call such networks cooperative LPWANs. In this paper, the error performance of an uplink cooperative LPWAN is mathematically analyzed in terms of outage probability, bit error rate (BER), and diversity order. It is assumed that there exist multiple (two or more) gateways that have multiple antennas and are located at arbitrary positions in the LPWAN area. Each gateway exploits the optimal maximum-ratio combining (MRC) technique to decode the received signal, and then the signals after MRC are delivered to the cloud fusion center for coherent combining in the cooperative LPWAN. The main results, the closed-form expressions of outage probability and BER, were derived by utilizing the hyper-Erlang distribution. Furthermore, the macro-diversity order was mathematically derived. The mathematical analysis was validated through extensive computer simulations. It worth noting that the mathematical analysis of the error performance of cooperative LPWANs is the first theoretical result in the literature to the best of our knowledge.

Bit Error Rate Closed-Form Expressions for LoRa Systems under Nakagami and Rice Fading Channels

We derive exact closed-form expressions for Long Range (LoRa) bit error probability and diversity order for channels subject to Nakagami-m, Rayleigh and Rician fading. Analytical expressions are compared with numerical results, showing the accuracy of our proposed exact expressions. In the limiting case of the Nakagami and Rice parameters, our bit error probability expressions specialize into the non-fading case.