Cognitive radio (CR) is projected as a technology (or solution) that will raise the spectrum utilization considerably by allowing low-priority or secondary user (SU) to utilize the spectrum of high-priority or primary user (PU) opportunistically. Spectrum handoff is a different type of handoff necessitated by the reappearance of the primary user on the frequency channels occupied by the secondary user at that time and location. In this paper, a hybrid type of spectrum handoff algorithm is proposed where proactive decision and reactive decision approaches are combined. Depending on the arrival rate of primary user (i.e. PU activity), the algorithm switches from reactive decision mode to proactive decision mode and vice versa. The switching from one mode to another mode depends on threshold value of PU activity and we evaluated the threshold value through analysis for switching of the algorithm to be 0.37. Simulated results show that the proposed hybrid spectrum handoff algorithm reduces the total service time of secondary user considerably compared to conventional proactive decision or reactive decision handoff approaches.

Cognitive Radio, a software defined radio, is an emerging technology which uses opportunistic spectrum access (OSA) for the efficient utilization of the spectrum. Its main aim is to utilize the unused portions of the spectrum by allowing unlicensed users (secondary users) to transmit data in absence of primary users. In this paper the assignment of multiple primary and secondary users in a multiple channel system is addressed with the sole aim of optimizing the total throughput. We have considered an optimal spectrum access (OSA) algorithm for the allotment of both the primary and secondary users in a multiple channel system and compared the results with the well-known meta-heuristic techniques such as Simulated Annealing (SA) and Tabu Search (TS). The results reveal that OSA algorithm is more efficient as compared to SA and TS as far as throughput optimization is considered.

Multiple input multiple output (MIMO) is one of the key technology to accomplish the goal of the future wireless broadband communication.This paper deals with the bit error rate (BER) and capacity performance of the Vertical Bell laboratories layered space-time (VBALST) MIMO systems with a linear receiver such as minimum mean-square error (MMSE) and zero forcing (ZF) over Nakagami-m channel. Both the BER and the capacity of MIMO systems have been analyzed for different modulation techniques and also with various configurations of MIMO systems. We have also analyzed the VBLAST MIMO system performance in a higher SNR region.

The optimal capacity expansion of base station subsystems in Next Generation Wireless Network (NGWN) problem with respect to multi-demand type and system capacity constraints is known to be NP-complete. In this paper, we propose a novel ant colony optimization algorithm to solve a network topology has two levels in which mobile users are sources and both base stations and base station controllers are concentrators. There are two important aspects of upgrading to NGWN. The first importance of backward compatibility with pre-existing networks, and the second is the cost and operational benefit of gradually enhancing networks, by replacing, upgrading and installing new wireless network infrastructure elements that can accommodate both voice and data demand. Our objective function is the sources to concentrators connectivity costas well as the cost of the installation, connection, replacement, and capacity upgrade of infrastructure equipment. We evaluate the performance of our algorithm with a set of real world and data randomly generated. Numerical results show that our algorithms is a promising approach to solve this problem.