Sanjay Dhar Roy

Performance Evaluation of Cooperative Spectrum Sensing Scheme with Censoring of Cognitive Radios in Rayleigh Fading Channel

In this paper, the performance of cooperative spectrum sensing (CSS) with censoring of cognitive radio (CR) users in Rayleigh fading channel is analyzed. More precisely, CR users which employ energy detectors are censored depending on the quality of radio channels between them and a fusion center (FC). Each CR makes a hard decision about primary user (PU) using energy detection and transmits the information to FC using BPSK signaling if that CR user is selected to transmit. A training based channel estimator is used at the FC to estimate the complex Gaussian fading coefficients characterizing the channels between the CR users and the FC. This channel state information on fading coefficients is used for censoring the CR users. Two fusion rules such as majority logic fusion and maximal ratio combining (MRC) fusion rules are applied at the FC for estimating the performance in terms of probability of missed detection (Pm). We develop a simulation test bed for evaluating the performance of CSS scheme. Probability of missed detection has been evaluated for both perfect and imperfect channel estimation for various probabilities of false alarm (Pf), reporting and sensing channel SNR values.

Performance of energy detection based spectrum sensing in fading channels

In order to enable access to underutilized licensed spectrum, a secondary user has to monitor licensed bands and detects occupancy of primary users in the different parts of the spectrum. However, detection is compromised when a user experiences shadowing or fading effects. In this paper we evaluate the performance of cognitive radio with energy detection based spectrum sensing (ED-SS) in AWGN, and several fading scenarios such as log-normal shadowing, Rayleigh, Nakagami, and Weibull fading environments. The performance has been assessed in terms of miss detection (Pm) and false detection probabilities (Pf). The performances of energy detector for different values of average SNR are characterized through complementary receiver operating characteristic (ROC) curves (plot of Pm vs. Pf). A simulation test bed has been developed to evaluate performance of ED-SS in different fading environments. A comparative performance of ED-SS has been studied for various fading channels.

Performance of cooperative spectrum sensing in fading channels

Detection is compromised when a cognitive radio (CR) user experiences deep shadowing or fading effects. In order to detect the primary user (PU) more accurately, we allow the CR users to cooperate by sharing their information. In this paper we investigate performance of cooperative spectrum sensing scheme using energy detection (ED-CSS) to improve the sensing performance in channels such as log-normal shadowing and Nakagami fading channels. Hard decision combining rule (OR-rule, AND-rule and MAJORITY-rule) is performed at fusion center (FC) to make the final decision about primary user present or not. Comparison among data fusion rules has been investigated for a wide range of average SNR values. The performance has been assessed in terms of miss detection (Pm) and false detection probabilities (Pf). A simulation model has been developed to evaluate performance of ED-CSS in different fading environments. A comparative performance of ED-CSS has been studied for various data fusion rules in Nakagami fading as well as shadow faded channels.

Detection performance of cooperative spectrum sensing with hard decision fusion in fading channels

In this paper, we investigate the detection performance of cooperative spectrum sensing (CSS) using energy detector in several fading scenarios. The fading environments comprise relatively less-studied Hoyt and Weibull channels in addition to the conventional Rayleigh, Rician, Nakagami-m and log-normal shadowing channels. We have presented an analytical framework for evaluating different probabilities related to spectrum sensing, i.e. missed detection, false alarm and total error due to both of them, for all the fading/shadowing models mentioned. The major theoretical contribution is, however, the derivation of closed-form expressions for probability of detection. Based on our developed framework, we present performance results of CSS under various hard decision fusion strategies such as OR rule, AND rule and Majority rule. Effects of sensing channel signal-to-noise ratio, detection threshold, fusion rules, number of cooperating cognitive radios (CRs) and fading/shadowing parameters on the sensing performance have been illustrated. The performance improvement achieved with CSS over a single CR-based sensing is depicted in terms of total error probability. Further, an optimal threshold that minimises total error probability has been indicated for all the fading/shadowing channels.

Throughput of a Cognitive Radio Network With Energy-Harvesting Based on Primary User Signal

In this letter, we analyze an energy-harvesting-based cognitive radio (CR) system. The CR system harvests energy from the radio frequency (RF) signal of primary user (PU) during sensing time as well as the transmission time of a detection cycle if PU is present. The CR accesses the spectrum band of PU opportunistically using the energy harvested over the frames with PU present, while maintaining a quality of service (QoS) constraint on PU in terms of a collision probability. An optimal sensing time is found, which maximizes the harvested energy. The performance is investigated in terms of harvested energy, outage probability, and throughput of the network. Novel analytical expressions for average harvested energy and average throughput are developed under such a scenario, which are validated by simulation.

PERFORMANCE ANALYSIS OF CELLULAR CDMA IN PRESENCE OF BEAMFORMING AND SOFT HANDOFF

The present paper proposes a scheme of combining soft handoff (HO) and beamforming in physical layer and automatic repeat request (ARQ) in link layer for improving the performance of data service in cellular CDMA. A stop and wait ARQ scheme has been assumed for data service. Joint effects of beamforming and soft handoff reduce delay, BER and increase throughput significantly. Impact of several parameters of soft handoff and beamforming on data performance has been evaluated. Both the cases of perfect and imperfect beamforming have been investigated. Effects of DOA (Direction of arrival) estimation error have also been indicated on data service.

Received signal strength based vertical handoff algorithm in 3G cellular network

Next generation wireless networks need seamless handoff between different wireless networks. Suitable vertical handoff algorithm may make seamless handoff possible in heterogeneous networks. We evaluate performance of received signal strength (RSS) based vertical handoff (VHO) in a new heterogeneous network model. To compare RSS of different network, the method based on corresponding bandwidth in each network has been considered in this paper. Further the RSS based VHO algorithm has been modified considering averaging of RSS. We evaluate the performance of the modified VHO algorithms in our proposed network model in terms of decision delay and number of handoff. For comparison purposes, the performance of the VHO algorithm that does not consider averaging of RSS has also been shown.

A hybrid cooperative spectrum sensing for cognitive radio networks in presence of fading

In this paper, we study a hybrid fusion scheme for cooperative spectrum sensing (CSS) where we combine the hard decisions and soft decisions from cognitive radio (CR) users based on quality of their reporting channel (R-channel). The CR users transmit their hard decisions if the estimated R-channel between them and the fusion centre (FC) exceeds censoring threshold else they send soft decision, i.e. the energy values. Based on the received hard decisions, the FC derives an intermediate hard decision using majority rules while an intermediate soft decision is obtained by combining the received soft decisions following MRC or EGC. Finally the FC combines the intermediate decisions via an OR rule to obtain the final decision regarding the primary user (PU). Analytical expressions have been developed as well as simulation has been carried out to evaluate the performance of the proposed scheme in presence of Rayleigh fading in both the sensing channel (S-channel) and R-channel, in terms of detection probability and total error probability. The performance of the proposed scheme is studied and compared for two cases of soft combining such as MRC with majority logic and EGC with majority logic. Furthermore, the scheme is compared with CSS using hard decision fusion based on censoring and CSS using soft decision fusion only. Impact of several parameters such as number of CRs, S-channel and R-channel SNR, censoring threshold, sensing threshold on the performance of the proposed scheme is shown. Our scheme outperforms the hard decision fusion with censoring of CRs in faded R-channel.

Signal Strength Ratio Based Vertical Handoff Decision Algorithms in Integrated Heterogeneous Networks

In this paper, we propose the signal strength ratio (SSR) based vertical handoff (VHO) algorithms and the averaged received signal strength (ARSS) based VHO algorithms for integrated networks of wireless local area network (WLAN) and 3G network. The performance of our proposed VHO algorithms with hysteresis and dwell timer approaches has been investigated for two different topologies of integrated heterogeneous network. Two different network topologies consider two different types of radio cell arrangement. A mobile terminal (MT) is moving within the coverage area of WLAN and 3G with constant velocity. The received signal strength at the MT of interest is measured at different sampling instant. The received signal strength with other additional parameters is used to determine the condition of VHO. We evaluate the decision delay, and the number of vertical handoffs between WLAN and 3G network using the proposed VHO algorithms. We compare the performance of our proposed VHO algorithms with existing RSS based VHO algorithm. Our proposed SSR and ARSS based VHO algorithms provide less decision delay as compared to existing RSS based VHO algorithm. Further, ARSS with dwell timer based VHO algorithm provides better performance than other VHO algorithms.In this paper, we propose the signal strength ratio (SSR) based vertical handoff (VHO) algorithms and the averaged received signal strength (ARSS) based VHO algorithms for integrated networks of wireless local area network (WLAN) and 3G network. The performance of our proposed VHO algorithms with hysteresis and dwell timer approaches has been investigated for two different topologies of integrated heterogeneous network. Two different network topologies consider two different types of radio cell arrangement. A mobile terminal (MT) is moving within the coverage area of WLAN and 3G with constant velocity. The received signal strength at the MT of interest is measured at different sampling instant. The received signal strength with other additional parameters is used to determine the condition of VHO. We evaluate the decision delay, and the number of vertical handoffs between WLAN and 3G network using the proposed VHO algorithms. We compare the performance of our proposed VHO algorithms with existing RSS based VHO algorithm. Our proposed SSR and ARSS based VHO algorithms provide less decision delay as compared to existing RSS based VHO algorithm. Further, ARSS with dwell timer based VHO algorithm provides better performance than other VHO algorithms.

Performance of cooperative spectrum sensing with soft data fusion schemes in fading channels

Cognitive radio (CR) systems need to detect the presence of licensed primary user (PU) reliably. Cooperation among multiple CRs helps to enhance the reliability of detection of the PU in case of unreliable decision by a single CR due to channel uncertainties. In this paper, we consider cooperative spectrum sensing (CSS) based on energy detection in cognitive radio networks (CRN) which uses soft combination of the observed energy values from different CRs. More precisely, we study the performance of CSS with several soft data fusion schemes namely, (a) Square law selection (SLS) (b) Square law combining (SLC) (c) Maximal ratio combining (MRC) that can be implemented at fusion center (FC). The performance of CSS has been assessed under several cases of sensing (S) channels such as AWGN, log-normal shadowing, Rayleigh and Rician fading channels. Comparative performance of CSS for various soft data fusion schemes under different fading channels has been studied for various values of average S-channel SNRs, time-bandwidth products, different number of CRs. The impact of shadowing and fading parameters on missed detection performance of CSS is indicated. Further, the performance comparison between soft data fusion schemes and hard decision fusion schemes is also highlighted.