Dual-Trigger Handover Algorithm for WiMAX Technology

IEEE 802.16e is a Worldwide Interoperability Microwave Access (WiMAX) standard that supports mobility. Handover is one of the most important factors that affect the performance of a WiMAX network. Various handover schemes have been proposed and implemented. In this paper, we propose Dual-Trigger Handover (DTHO) algorithm for WiMAX networks. The proposed handover algorithm depends on the computation of signal to noise ratio (SNR) received at the Mobile Station (MS) from various Base Stations (BSs). Relying on SNR measurements and free capacity measurements of the serving BS and the target BS improves the accuracy of handover decisions. The handover is not triggered by the MS node or the BS node individually. Instead, it is a combined decision between the two nodes. The proposed algorithm is implemented in both MS and BS nodes. We implemented the proposed algorithm using OPNET Modeler version 14 running on Windows operating system. The algorithm was simulated using multiple scenarios with various channel parameters

Cognitive Radio: Energy Sensing Analysis and Dynamic Spectrum Access modeling

Efficient utilization of the spectrum has become a fundamental requirement in modern wireless networks, due mainly to spectrum scarcity and the ever-increasing demand for higher data rate applications and internet services. A particularly interesting proposal to meet this requirement is the cognitive radio (CR) system which can adapt its transmission parameters according to the environment. CRs, as will be shown in later chapters, are very efficient in maximizing spectrum utilization due to their inherent spectrum sensing capability.The purpose of this dissertation is to investigate and analyze two main components of CR. First is the sensing or exploring component, which is the core of a CR device as it is the first stage to discover spectrum holes (SHs) in a spectrum band. For this component, a new algorithm to compute the detection probability in the case of odd degrees of freedom and a closed-form expression for the detection probability in Nakagami-m fading channels are presented, both for a local spectrum sensing scenario. For a cooperative scenario, the errors of CRs decisions which are caused by erroneous feedback channels are analyzed. In addition, the optimal number of CRs that are required to mitigate against such errors is derived. The second component is the access or exploiting component, i.e. how a CR device can exploit SHs efficiently. To study the second component, the interactions between the primary users (PUs) and secondary users (SUs) are modeled as a continuous time Markov chain (CTMC). Based on the CTMC model, the effect of two inevitable sensing errors (misdetection and false alarm) on the blocked call probability, the dropped call probability and system utilization is investigated for two access schemes. In the first scheme, the PUs are considered to access the system using a standard access policy. In the second scheme, the PUs use non-standard access policies. In both schemes, the overall (primary and secondary) system utilization is analyzed and compared under both perfect and imperfect sensing. The simulation results obtained concur with the analytical ones and it is determined that spectrum utilization can be improved by choosing a suitable non-standard access policy

A novel handover algorithm design in WiMAX networks

In this paper, we propose a handover algorithm for WiMAX networks. The algorithm relies on the computation of the received signal-to-noise ratio (SNR) at a Mobile Station (MS) from neighboring Base Stations (BSs) combined with the capacity estimation of the targeting cell. The proposed handover algorithm is implemented by a joint decision between the MS and BS nodes. The performance of the proposed algorithm is evaluated in terms of call dropping ratio and system throughput. A comparison with the conventional hard handover algorithm is presented