Brahmjit Singh

Comparative Performance Evaluation of Spectrum Sensing Techniques for Cognitive Radio Networks

Cognitive radio is the key technology for future wireless communication. Spectrum sensing is one of the most important functions in cognitive radio (CR) applications. It involves the detection of primary user (PU) transmissions on a preassigned frequency band. PU licensed band can be sensed via appropriate spectrum sensing techniques. In this paper, we consider three basic spectrum sensing techniques of transmitter detection: Matched filter detection, Energy detection, and Cyclostationary feature detection. Using simulations, a comparative analysis of the three techniques has been carried out in terms of probability of false alarm Pf, probability of detection alarm Pd, and probability of miss detection Pm. Finally, Numerical result shows that at low signal to noise ratio (SNR), cyclostationary feature detection outperforms other two techniques, thus have some difficulties like implementation is complex, long observation time, etc. For simulation we used MATLAB software.

An improved handover algorithm based on signal strength plus distance for interoperability in mobile cellular networks

In future generation mobile cellular systems, position location of mobile terminal is expected to be available. In this paper, we propose an initiation algorithm for intersystem handover based on the combination of position location of mobile terminal and the absolute signal strength thresholds. Global System for Mobile communication (GSM) and Universal Mobile Telecommunication Systems (UMTS) networks are considered for interworking. The proposed algorithm reduces the handover rate by around 50% and thus improves the network resource efficiency as compared to that based on signal strength thresholds only.

Performance Enhancement of Cellular Network Using Adaptive Soft Handover Algorithm

Mobility management is the most important feature of a wireless cellular communication system. Continuation of an active call is one of the most important quality measurements in the cellular systems. Handover makes it possible for a user to travel between various networks or cells while having a seamless connection. This paper shows that, performance of cellular network can be increased with proposed adaptive soft handoff algorithm, which dynamically calculates the Soft handover margin based on the received signal strength and distance. Performance is evaluated in terms of the performance metrics active set update rate, active set size, soft handover region and probability of outage. Simulation results show that soft handover algorithm gives better performance with adaptive soft handoff margin compared to that of fixed soft handover margin in varied propagation conditions.

Sensitivity analysis of handover performance to shadow fading in microcellular systems

In this paper, we carry out a simulation study of the sensitivity of handover performance to standard deviation of lognormal shadow fading in a mobile radio environment. The handover algorithm is based on received signal strength measurements. Handover rate and initiation delay are used as performance metrics. It is shown that the performance metrics depend on standard deviation of shadow fading. In a nonuniform environment, the standard deviation may be different at different places and a given handover scheme with fixed design parameters cannot give optimum results consistently in the entire cellular service area. Through numerical results, it is further shown that the effect of hysteresis margin on handover performance depends on its relative value as referred to standard deviation of lognormal shadow fading in the prevailing cellular propagation environment. To achieve optimum handover performance, hysteresis margin as a handover design parameter is determined in terms of standard deviation of shadow fading in varied radio propagation environments.

Routing in Wireless Mesh Networks: Three New Nature Inspired Approaches

Multi radio, multi hop, self organizing and self configuring wireless technology are the characteristic features of wireless mesh networks (WMNs) to offer last mile access to end users. The emergence of stochastically varying network environments critically affects routing in WMNs. Any routing policy meant for WMNs must be quickly adaptive and evolve in a decentralized self organizing and self configuring manner. This paper firstly proposes formulation of a soft computing i.e. fuzzy logic based hybrid performance metric which includes per flow (throughput, delay and jitter) as well as per node (residual energy of the node) parameters. This fuzzy logic based hybrid performance metric enumerates the integrated link cost (ILC) which is used as distance measure between two adjacent nodes. The paper further proposes three routing algorithms based upon nature inspired computing approaches namely firefly algorithm, Big Bang Big Crunch and Ant Colony Optimization. The proposed routing approaches aim at finding the minimal ILC path within a stipulated time constraint. The time constraint is governed by the mobility of network nodes. Extensive simulations were conducted for various WMN topologies. The results of the proposed approaches have been compared with two commonly used conventional approaches and were found to be far more superior. It was also observed that the self organizing capability of the proposed nature inspired routing approaches effectively reduces the complexity and makes a network quite adaptive to the dynamic network behavior found in WMNs.

Real Time Available-Bandwidth Estimation (ABE) Algorithm Based Selection in Heterogeneous Network for WiMAX and 3G

The increasing demand for broadband wireless service in todays wireless communications, especially with WiMAX technology being one of the 3G standards, is causing cellular network providers to consider the integration of different heterogeneous networks. Consequently, network selection techniques play a vital role in ensuring quality of service in heterogeneous networks. In this article we have developed a network selection scheme for an integrated 3G/WiMAX heterogeneous system. The design goal is to provide the user with the best available QoS at any time. The proposed algorithm selects network on the basis of available bandwidth estimation. Analysis of heterogeneous system with 3G and WiMAX network reveal that the proposed network selection method can effectively choose the suitable network by negotiating trade-offs among network dynamic condition and multimedia service application.

On the decision fusion for cooperative spectrum sensing in cognitive radio networks

Cooperation among different cognitive radios is used to enhance the sensing performance by exploiting the multiuser diversity. Soft and Hard decision fusion schemes are usually employed at the fusion center to detect the presence or absence of primary user. Soft decision fusion schemes perform better than hard fusion schemes but at the cost of increased bandwidth burden on the control channel. In this context, we propose a semi-soft fusion scheme to achieve a tradeoff between sensing performance and bandwidth cost. Under this scheme, each cognitive radio makes a local decision and sends one or two-bit data to the fusion center based on the observed test statistics. On the basis of received data, fusion center estimates the global test statistics which are then compared to a predetermined threshold to make the final decision. Furthermore, a closed form expression for average bandwidth cost for the proposed scheme is also derived. MATLAB simulation demonstrates that the performance of the proposed semi-soft fusion approaches to that of soft fusion scheme with a remarkable reduction in the bandwidth cost of control channel.

Vertical handoff decision in 4G wireless networks using multi attribute decision making approach

Multi-interface terminal in heterogeneous wireless networks will have network access from diverse access technologies. Multiple attribute for decision making including user preference will increase the complexity of handoff process. Various approaches have been proposed to solve the complexity problem of handoff decision. In this paper, multi attribute decision making algorithms Analytic Hierarchy Process (AHP) method, Simple Additive Weighting (SAW), Total Order Preference by Similarity to the Ideal Solution (TOPSIS), and Grey Relational Analysis (GRA) methods have been proposed for handoff decision in a WiMAX–WLAN environment to facilitate user with better quality of service. AHP has been used for calculation of weights of decision parameters. Numerical results show that SAW, TOPSIS and GRA provide almost similar performance. SAW is very simple to implement but probability of error is less in GRA because values of decision attribute are directly used for ranking of alternatives. TOPSIS is sensitive to the attribute with high score.

Performance Analysis of Modified RC4 Encryption Algorithm

RC4 is one of the most widely accepted stream cipher on account of its structural simplicity, encryption and decryption speed and efficiency. In this paper, we report on several vulnerabilities of RC4 algorithm and further propose a modified RC4 (MRC4) algorithm to overcome the weaknesses of RC4. Working of RC4 consists of two parts: key scheduling algorithm (KSA) and pseudo random number generator algorithm (PRGA). In MRC4, additional layers are added to both KSA and PRGA without modifying its basic structure. Performance analysis of the conventional RC4 algorithm and its proposed variant has been performed in terms of running time, security, and randomness analysis. Through numerical results it is shown that while retaining the simplicity of RC4, MRC4 enhances the security of the stream cipher.

Simulation study of double threshold energy detection method for cognitive radios

Cognitive Radio is a new paradigm in wireless communication to tackle the problem of spectrum underutilization. One of the important functions of cognitive radio is spectrum sensing. There are many spectrum sensing algorithms available in the literature out of which energy detection is widely used because it is easy to implement and it does not require prior information about PU (Primary User). However, the performance of the conventional energy detector deteriorates in low SNR region. Double threshold CSS (Cooperative Spectrum Sensing) was introduced to increase the reliability of decision but at the cost of some sensing information lost. In this paper, we are discussing a method of double threshold CSS in which each CR (Cognitive Radio) sends local decision or observed energy to the FC (Fusion Center) depending on the region in which the observed energy lies. FC then makes a final decision by combining local decisions and observed energy values. We have developed a simulation model to prove the superiority of the proposed algorithm and it has been observed that the proposed method outperforms the conventional CSS in low SNR region. There is almost a 10% improvement in the cooperative probability of detection at -8 dB SNR at 0.1 probability of false alarm.