Earticle

In this paper, a new ultra-wideband (UWB) receiver is proposed and analyzed in indoor wireless channels. We consider pulse position modulation-time hopping (PPM-TH) UWB systems. A double binary turbo coding scheme is used for detecting and correcting errors occurring in wireless channels. Also, we employ a delay diversity receiver for enhancing the system performance with reasonable cost and complexity. A conventional receiver equipping an antennas diversity scheme requires additional hardware and space for installing multiple antennas in accordance with increase in the number of antennas. If the number of antennas increases, not only the system performance but also hardware complexity rise. Then, it is difficult to make the receiver practically. Therefore, we adopt the delay diversity receiver for solving problems of the conventional receiver using antenna diversity. We derive analytical expressions for bit error probability performance of the proposed system. From the simulation results, it is demonstrated that the delay diversity receiver has almost half complexity and shows similar performance as compared with that employing the antenna diversity scheme. Therefore, the proposed receiver structure can be a practical solution for enhancing the performance of the UWB systems. The results of this paper can find its applications to legacy UWB systems with simple modifications.

Cognitive radio network is proposed as a solution to fully utilize the valuable spectrum. In this paper, we propose a new spectrum access scheme using buffer for new secondary user (SU) and interrupted SU calls, and analyze the corresponding Erlang capacity of cognitive radio system, which is defined as a set of supportable offered traffic loads of primary users (PUs) and SUs. As a result, it is observed that the Erlang capacity can be improved extremely using a suitable buffer length.

The term “Ubiquitous Sensor Networks” (USN) is used to describe networks of intelligent sensor nodes that could be deployed “anywhere, anytime, by anyone and anything”. The technology has huge potential as it could generate applications in a wide range of civilian and military fields, including ensuring safety and security, environment and habitat monitoring, and realtime healthcare. Earlier research shows that it is highly suitable for monitoring purposes in military use and also biomedical applications. However, there isn’t any flexible and robust communication infrastructure to integrate these devices into an emergency care setting. An efficient wireless communication substrate for medical devices that addresses ad hoc or fixed network formation, naming and discovery, security and authentication, as well as filtration and aggregation of vital sign data need to be studied. This research is aimed at developing a system that is able to provide continuous monitoring of patients outside the hospital environment. The potential application outcomes among others; cutting the cost of medical services and saves many important lives.

In this paper, a longitudinal transmission-line model for two section distributed feedback (DFB) lasers is developed. The characteristic impedances of active periodic structures are derived. A two section DFB laser is described as a transmission-line network, with each section represented by a transmission-line segment with a corresponding characteristic impedance. Static and dynamic analysis of two section DFB lasers is demonstrated. The reflections at the junctions between sections are evaluated more accurately. The resonant condition of the equivalent transmission-line network is used to reformulate the rate equations.

This paper proposes the joint optimization of power allocation, subcarrier assignment and relay selection strategy for cooperative OFDM system to maximize the total capacity. We use Lagrangeandual approach for relaxing some available constraints and also make use of the simple greedy algorithm to perform lesser iterations to converge. Extensive experiments with realistic data prove that the subgradient dual method is approriate to dynamic resource allocation.