Praveen Kaligineedi

Secure Cooperative Sensing Techniques for Cognitive Radio Systems

The most important task for a cognitive radio (CR) system is to identify the primary licensed users over a wide range of spectrum. Cooperation among spectrum sensing devices has been shown to offer various benefits including decrease in sensitivity requirements of the individual sensing devices. However, it has been shown in the literature that the performance of cooperative sensing schemes can be severely degraded due to presence of malicious users sending false sensing data. In this paper, we present techniques to identify such malicious users and mitigate their harmful effect on the performance of the cooperative sensing system.

Relay and Power Allocation Schemes for OFDM-Based Cognitive Radio Systems

In this letter, we investigate the relay and power allocation problem for OFDM-based cognitive radio (CR) systems with single antennae. We propose a method where the capacity of CR user employing relays is maximized while total transmission power is kept within a budget and the interference introduced to the primary user (PU) band is kept within a prescribed threshold. The optimization problem is a mixed-integer problem, which is NP-hard. Hence in this letter, we have proposed three sub-optimal schemes. The presented numerical results show that the performance of proposed suboptimal schemes is close to the optimal solution.

Distributed Detection of Primary Signals in Fading Channels for Cognitive Radio Networks

In this paper, we investigate cooperative sensing schemes to identify primary signals in fading environment for cognitive radio (CR) networks employing energy detectors. We consider a parallel fusion architecture in which all the sensing devices send their quantized sensing information to an access point, which then applies a fusion rule to determine the presence of the primary signal. We assume independent and identically distributed fading at various CR sensing devices. Considering identical binary quantization at the sensing devices, we study the optimal quantization and data fusion scheme. We compare the performance of the optimal binary data fusion scheme based on identical quantizers with the performances of other binary data fusion schemes commonly used in the literature for CR cooperative sensing networks. We further investigate the performance gain that could be obtained by using identical multi- bit quantization at the sensing devices.

Some research issues in cognitive radio networks

The cognitive radio (CR) technology will allow a group of potential users to identify and access available spectrum resources provided that the interference to the users for whom the band has been licensed is kept below a prescribed level. However, this research area is at a very immature stage because various research challenges have to be addressed and solved. In this paper our objective is to present an overview of some research issues for CR networks. Specifically, we present some research and development in CR networks with focus on i) information- theoretic aspects, ii) spectrum sensing, iii) link adaptation, iv) advanced transceiver design, and v) admission control. We also discuss some important research problems related to these specific topics that needs to be addressed before deployment of CR systems in practice.

Frequency-Domain Turbo Equalization and Multiuser Detection for DS-UWB Systems

One of the major challenges in direct sequence-ultra wideband (DS-UWB) receiver design is intersymbol interference (ISI). Several equalization schemes to eliminate ISI in DS-UWB systems have been proposed in the literature. It was shown that frequency-domain (FD) equalization techniques can offer better trade off between performance and complexity compared to time- domain equalization schemes for DS-UWB systems on highly dispersive channels. In this paper, we derive low-complexity FD minimum mean square error turbo equalization schemes for single-user binary phase shift keying (BPSK) and quaternary bi-orthogonal keying (4BOK) DS-UWB systems. For multiuser DS-UWB systems, we combine FD turbo equalization schemes with soft interference cancelation to obtain multiuser FD turbo detectors. The bit error rate performance gain due to turbo detection is shown to be significant, particularly for multiuser DS-UWB systems.

Joint Sensing and Power Loading Algorithms for OFDM-Based Cognitive Radio Systems

In this paper, we investigate joint sensing and power allocation schemes for OFDM-based cognitive radio (CR) systems. A CR system employing cooperative sensing based on energy detection is considered. Each primary user (PU) band is assigned a subset of sensors and equal gain combining is used at the access point to detect the presence of PU in that particular band. For such a system, we propose algorithms to jointly allocate sensing thresholds at the access point and power at the CR transmitters so that the throughput of the CR system is maximized while taking total transmit power, CR quality of service (QoS) constraints, and interference introduced to the PU band into consideration. The performance of the proposed schemes is compared to the schemes that only optimize either sensing thresholds or transmitted power. Presented numerical results demonstrate the strength of our proposed schemes.

WLC18-3: Frequency-Domain Equalization Techniques for DS-UWB Systems

Non-linear frequency domain equalization schemes which give better performance than linear frequency domain equalization schemes, have recently been proposed in the literature for single carrier (SC) systems. In this paper, we study performance of non-linear frequency domain equalization schemes, viz. decision feedback equalization (DFE) and iterative DFE, for DS-UWB systems. We compare bit error rate (BER) performance of various time domain and frequency domain equalization techniques and evaluate their computational complexity. We show that the frequency domain equalization techniques can offer better trade off between complexity and performance compared to the time domain equalization techniques for DS-UWB systems.