It has been shown that diamond relaying networks offer higher multiplexing gain than conventional cooperative networks. In diamond relaying networks, a relay-pair cooperates to deliver two messages to the destination within only two-time slots using non-orthogonal multiple access (NOMA). It was recently shown that rate-splitting multiple access (RSMA) has superior performance over NOMA. In this paper, the benefits of using rate-splitting in the diamond relaying model is explored for improving the achievable sum data rate. A hybrid rate-splitting/NOMA diamond relaying system model is proposed. The system's sum data rate can be maximized by optimizing the power allocation coefficients for both the rate-splitting and the NOMA phases. Our results show that the proposed hybrid model outperforms the conventional full NOMA diamond relaying systems.

Non-orthogonal multiple access (NOMA) emerges as a strong candidate for the next wireless generation as it promises large spectral efficiency. However, as the number of the users increases, the interference increases. This limits the rate per user. In this paper, the maximum number of users that can be admitted in a NOMA system, under a total power constraint and a minimum rate requirement per user, is sought. A lower bound for the achievable sum-rate is first obtained. A power allocation scheme that maximizes the sum-rate, under the aforementioned constraints, is then proposed. Using the proposed scheme, an efficient algorithm to obtain the maximum number of users is developed. The performance is compared with the orthogonal multiple access (OMA) schemes. Our results show that the proposed scheme efficiently computes the number of users and provides significant gain compared to the OMA schemes.

Energy-efficiency has been always a concern in wireless sensor network. Since sensor clustering was proposed as a technique for energy-efficient routing in hierarchical wireless sensor networks, many algorithms were proposed for the formation of clusters, the selection of cluster heads, and routing data within and between clusters. The use of Genetic algorithm is proposed to obtain the optimal number of clusters as well as the position of each cluster head during the network's lifetime. In this paper, we propose an algorithm based on the use of genetic algorithms to improve the network lifetime, especially in sensor networks that can tolerate the loss of some nodes without affecting the functionality of the whole network. Simulation results show that the proposed algorithm almost 1.5 times the network's lifetime.

In this paper, we study cognitive radio and propose mathematical and behavioral modeling of the LTE downlink signal of primary users in order to facilitate spectrum decisions of the secondary users. Auto-regressive integrated moving average (ARIMA) time series model, non-linear autoregressive exogenous input (NARX) neural network (NN) are investigated and a hybrid system is proposed. Using the proposed model instead of the ARIMA model results in a decrease in the average mean square error (MSE) by 23.23% in addition to a decrease of 9.68% in the number of the classifier's misclassification. The hybrid model yields a 29.25% improvement in the average MSE compared to the random NN, it also offers an advantage of 15.15% decrease in the number of misclassifications. Results show that using predictive models and previous instances of sensed data, the behavior of the primary user could be captured and the secondary user could decide about usable parts of the spectrum accordingly.

A unified performance analysis is presented for dual-hop amplify-and-forward (AF) relaying systems operating over non-identically distributed Rician fading channels. A general, two-parameter AF relaying model is used such as to cover various AF relaying schemes, namely, variable-gain AF relaying, fixed-gain AF relaying, and channel-assisted relaying, as well other unconventional schemes. Although, in some applications, systems operating over Rician fading links can be approximated and analyzed using equivalent systems operating over Nakagami- m fading links, we show that this is not sufficiently accurate in the case of AF relaying systems. Therefore, single-fold infinite-series expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the instantaneous end-to-end received signal-to-noise ratio (SNR) of such systems are derived, and Monte-Carlo simulations are used to verify the precision of the derived expressions. In addition, the effects of the relaying model parameters, as well as the channel fading parameters, on system performance are studied.

A direct evaluation method is proposed to obtain numerical solutions for the performance metrics of dual-hop amplify-and-forward relaying systems. The proposed method accommodates any link fading distributions. The results obtained are precise while requiring less computational time than simulation, about 40 times less. The proposed solution is used to obtain precise results for the average symbol error probability, ergodic capacity and outage probability of systems operating over Nakagami-m fading links with arbitrary, non- integer fading parameter m. The new direct solution method allows the accurate assessment of the case of Nakagami-0.5 fading, the worst case fading scenario of Nakagami-m fading.

Closed-form expression for the outage probability of dual-hop amplify-and-forward (AF) systems with relay selection from N independent and non-identically (i.ni.d.) distributed dual-hop branches is obtained. Closed-form expression for the probability density function of the end-to-end signal-to-noise ratio (SNR) is also obtained for such systems, and is used to obtain the exact average symbol error probability for systems operating over i.ni.d. Nakagami-m fading links. It is found that the limiting slopes of the outage probability and the average symbol error probability curves are proportional to the sum of the minimums of the fading parameters of the source-to-relay and relay-to-destination links of each branch. The modified generalized transformed characteristic function (M-GTCF) is used to obtain exact, integral solutions for the outage probability and the average symbol error probability of multihop AF relaying systems operating over N i.ni.d. Nakagami-m fading links. It is found that the limiting slopes of the performance metrics curves are proportional to the minimum of the fading parameters of the individual links. Dual-hop AF systems with relay selection from N available relays are compared to multihop AF systems with N intermediate relays. It is found that dual-hop AF systems can significantly outperform multihop AF systems. The findings are used to propose multiple criteria for practical design of wireless cooperative systems.

New, exact closed-form expressions are derived for the probability density function (PDF) and the cumulative distribution function (CDF) of the instantaneous end-to-end signal-to-noise ratio (SNR) of amplify-and-forward (AF) relaying systems with “full” selection diversity. The direct path, from the source to the destination, as well as multiple dual-hop paths, through intermediate relays, are considered in the selection set. The selection process follows a maximum SNR policy, such that the path of the maximum end-to-end SNR is used as the communication link, whether this path is the direct path or one of the dual-hop paths. The derived expressions are used to obtain the first exact results for the average error probability and the outage probability of such AF relaying systems. The results are verified through simulations for identically distributed as well as non-identically distributed Nakagami-m fading links. The system performance is compared to that of conventional wireless systems which use only the direct link between the source and the destination for communication. The system performance is compared also to that of an opportunistic dual-hop AF system with maximum end-to-end SNR relay selection that excludes the direct path from the selection set. Results show that the full selection system performance is superior to those in the comparison. For example, in the case of Nakagami-m fading links with m = 4 and N = 2 candidate intermediate relays, an average error probability of 2×10-4in the case of AF relaying with full selection, occurs at 4.06 dB less than it occurs in the case of only direct transmission and at 0.95 dB less than it occurs in the case of maximum end-to-end SNR relay selection that excludes the direct path from selection. Results show also that the system provides diversity gain, proportional to the selection set size, N +1.

A new transform method, the generalized transformed characteristic function (GTCF), gives an exact, integral solution for the probability density function of the end-to-end received signal-to-noise ratio (SNR) of multihop amplify-and-forward (AF) relaying systems. The results are precise for any number of hops and can accommodate any channel fading distribution. The theory provides the first exact theoretical solutions when the number of hops N >; 2. Both cases of identically and non-identically distributed links are investigated. The case of dissimilar links, in which the link fadings follow different distributions, is also studied. The effect of the number of hops, N, on the performance metrics is studied.

Novel exact closed-form expressions are derived for the probability density function (PDF) and the cumulative distribution function (CDF) of the instantaneous received end-to-end signal-to-noise ratio (SNR) of dual-hop amplify-and-forward (AF) relaying systems operating over Rayleigh, Nakagami-m and Rician fading channels. New exact closed-form expressions are also obtained for opportunistic dual-hop AF relaying systems, with maximum relay-to- destination SNR relay selection. The average symbol error probability, ergodic capacity and outage probability are calculated using the derived PDF and CDF expressions. It is found that the opportunistic dual-hop AF system, with relay selection pool size M = 2, has at least 2.84 dB power advantage over the dual-hop AF system without relay selection for average error probabilities less than 10^-2 in the case of Rayleigh fading links. It is shown that although the performance of a dual-hop AF system with maximum relay-to-destination SNR relay selection is improved by increasing the selection pool size, the improvement has diminishing returns and a relay selection pool of more than 6 relays is not of practical benefit.

A new theoretical method, the generalized transformed characteristic function (GTCF) approach gives an exact, integral solution for the probability density function of the end-to-end received signal-to-noise ratio in multihop amplify-and-forward relaying systems. In turn, the GTCF approach is used to obtain exact integral solutions for the ergodic capacity, outage probability and average symbol error probability of multihop amplify-and-forward relaying systems. The results are precise for any number of hops and can accommodate any channel fading distribution. The theory provides the first exact theoretical solutions for numbers of hops larger than 2.

New, exact closed-form expressions are derived for the probability density function and the cumulative distribution function of the end-to-end signal-to-noise ratio (SNR) of opportunistic dual-hop amplify-and-forward (AF) relaying systems with relay selection. The expressions are used to obtain the first exact integral solutions for the ergodic capacity and average symbol error probability, and the first exact closed-form solution for outage probability of an opportunistic AF relaying system where the best node is selected from a number of candidate intermediate nodes to relay the data signal between the source and the destination. The selection follows a maximum end-to-end SNR policy, based on the available channel state information. The results are precise for any number of candidate relays and Rayleigh, Nakagami-m or Rician fading distributions. The effects of different channel fading parameters and the number of relays in the relay selection pool are studied. The system performance is compared to that of dual-hop AF systems without relay selection and to dual-hop AF relaying systems with maximum relay-to-destination SNR relay selection. The adopted selection method provides diversity gain over dual-hop AF relaying systems without relay selection and over maximum relay-to-destination SNR relay selection. The diversity gain is proportional to the relay selection pool size.