One of the main challenges already faced by communication networks is the efficient management of increasing complexity. Cognitive networks are put forwarded in the framework of evolution of network architectures as novel paradigms to provide autonomous in network reasoning to support end to end goals. This paper aims at proposing a new method for modifying spectral efficiency of topology control using new vertex coloring algorithm in Thomas cognitive networks.

One of the most important designing problems in cellular communication is the Channel assignment Problem (CAP). The goal of Channel assignment is to assign the required number of Channels to each cell, such that frequency spectrum utilization is maximized and frequency interference effect is minimized. Due to the limitation of the usable frequency spectrum, the optimal Channel assignment can improve capacity, quality, and performance of the system. Since in its simplest form this problem is known to be equivalent to a graph-coloring problem, belonging to the class of NP-complete optimization problems, different techniques such as heuristic techniques, neural networks, simulated annealing, and evolutionary algorithms have been used to solve it. In this paper, a modified Hopfield neural network has been proposed. The modifications, include structure of the network, initialization method, and the updating procedure. In the network structure, contrary to usual structures, there is also a connection from each neuron’s output to its input with negative weight and instead convergence is obtainable with the procedure of updating. Simulation results show better performance than the previous presented networks.

Spectrum shortage in Vehicular Communications has become an area of concern due to the diverse nature of applications served. Though the allocated 5.9GHz Dedicated Short Range Communication (DSRC) spectrum for vehicular communication is inefficiently utilized, the problem of congestion creates an impression that there is always a scarcity in the spectrum. The criticality of the issue becomes high when a safety message is unable to access the Channel or is dropped due to congestion. This paper proposes an approach to prioritize Channel access to safety messages through dynamic spectrum sharing. In case, when a safety message finds all the DSRC Sub-Channels occupied, then any one of the ongoing non-safety messages is switched over to the adjacent 5.8GHz ISM/UNII-3 band allowing the former to access the DSRC band. The proposed approach shows an increased QoS and reduced Channel access delay for safety messages compared to the previous works.

As one of the promising approaches to increase the network capacity, Full-duplex (FD) communications have recently gained a remarkable attention. FD communication enables wireless nodes to simultaneously send and receive data through the same frequency band. Thanks to the recent achievements in the self-interference (SI) cancellation, this type of communication is expected to be potentially utilized in cellular systems, especially in small cell networks. In this paper, we integrate the FD communications into femtocell networks where femtocell users (FUs) share the same spectrum with macro users (MUs). In particular, aiming to maximize the number of admitted FUs in the network and satisfying the target rate for FUs, we jointly study the problem of Sub-Channel allocation, duplexing-mode selection, and power control for FUs in both uplink (UL) and downlink (DL) transmissions. Moreover, we address the power control problem for macro-tier where the main goal is to minimize the transmission power of prioritized MUs while guaranteeing a target rate for them. To jointly address these problems for both tiers, we propose a distributed algorithm in which FBSs and admitted FUs choose whether to operate in half-duplex (HD) or FD mode so as to meet their target rate. The convergence and performance of the proposed algorithm are evaluated through simulation where it is demonstrated that the average admission ratio of FUs in our proposed distributed scheme surpasses the existing traditional HD approaches.

A low complexity dynamic Subcarrier and power allocation methodology for downlink communication in an OFDM-based multiuser environment is developed. The problem of maximizing overall capacity with constraints on total power consumption, bit error rate and data rate proportionality among users requiring different QOS specifications is formulated. Assuming perfect knowledge of the instantaneous Channel gains for all users, a new simple algorithm is developed to solve the mentioned problem. We compare the sum capacity, proportionality, and computational complexity of the proposed algorithm with the one presented by Wong et al. Numerical results demonstrate that the proposed algorithm offers a performance comparable with Wong's algorithm, yet complexity remains low and proportionality constraint will be tightly satisfied. As well, the proposed algorithm can provide a flexible trade-off between complexity, capacity and proportionality constraint.