Sithamparanathan Kandeepan

Cooperative Shared Spectrum Sensing for Dynamic Cognitive Radio Networks

Cooperative spectrum sensing for cognitive radio networks is recently being studied to simultaneously minimize uncertainty in primary user detection and solve hidden terminal problem. Sensing wideband spectrum is another challenging task for a single cognitive radio due to large sensing time required. In this paper, we introduce a technique to tackle both wideband and cooperative spectrum sensing tasks. We divide the wideband spectrum into several subbands. Then a group of cognitive radios is assigned for sensing of a particular narrow subband. A cognitive base station is used for collecting the results and making the final decision over the full spectrum. Our proposed algorithm minimizes time and amount of energy spent for wideband spectrum scanning by a cognitive radio, and effectively detects the primary users in the wideband spectrum thanks to cooperative shared spectrum sensing.

Bayesian Tracking in Cooperative Localization for Cognitive Radio Networks

In this paper we consider cooperative localization and tracking of primary users (PU) in a cognitive radio network using Bayesian techniques. We use particle filtering methods to track the location of a PU in the network using cooperative localization techniques and present some results for noisy measurements. The cognitive radio (CR) nodes estimate the information related to the geographical position of the PU based on existing location identification and localization techniques and forward the noisy information to a cognitive radio base station (CRB), which then fuses the information to estimate the position of the PU in the network in order to perform a radio scene analysis. We propose a particle filtering approach that is suitable for tracking Gaussian and non-Gaussian noisy signals at the CRB to estimate the position of a PU, two importance-functions relative to the particle filtering algorithm are also presented. Simulations are performed on the proposed tracking algorithm and the results are presented in terms of the mean squared error of the positional estimates.

Steady state distribution of a hyperbolic digital tanlock loop with extended pull-in range for frequency synchronization in High Doppler environment

A hyperbolic arctan based Digital Tanlock Loop (D-TLL) operating with complex signals at base-band or intermediate frequencies in high Doppler environments is treated here. The arctan based loop, known as the tanlock loop (TLL), is used in software defined radio architectures for frequency acquisition and tracking. The hyperbolic nonlinearity intentionally introduced within the phase detector extends the pull-in range of the frequency for a given loop, compared to the normal D-TLL, allowing a wider frequency acquisition range which is suitable for high Doppler communications environment. In this paper we study the steady state phase noise performances of such a feedback loop for additive Gaussian noise using stochastic analysis. The stochastic model of a first-order hyperbolic loop and the theoretical analysis for the corresponding statistical distribution of the closed loop steady state phase noise are presented. The theoretical results are also verified by simulations. Index Terms Digital Tanlock Loop, D-TLL, arctan, hyperbolic loop, steady state distribution, steady state phase noise, pull-in range, Frequency SynchronizationA hyperbolic arctan based digital tanlock loop (D-TLL) operating with complex signals at base-band or intermediate frequencies in high Doppler environments is treated here. The arctan based loop, known as the tanlock loop (TLL), is used in software defined radio architectures for frequency acquisition and tracking. The hyperbolic nonlinearity intentionally introduced within the phase detector extends the pull-in range of the frequency for a given loop, compared to the normal D-TLL, allowing a wider frequency acquisition range which is suitable for high Doppler communications environment. In this paper we study the steady state phase noise performances of such a feedback loop for additive Gaussian noise using stochastic analysis. The stochastic model of a first-order hyperbolic loop and the theoretical analysis for the corresponding statistical distribution of the closed loop steady state phase noise are presented. The theoretical results are also verified by simulations.

Frequency jitter of a digital phase-locked loop and comparison with a modified CRB

The steady state (SS) noise performance of a digital phase locked loop (DPLL) is of very much interest, while tracking carrier signals. In the literature the SS performance is very well examined in terms of the SS phase jitter, however the SS frequency jitter of a DPLL is unexamined up to now. In this paper we analyse the SS performance of a DPLL in terms of the frequency jitter. We derive a linearised expression for the SS frequency jitter of a DPLL, and verify it by simulations.

Performance analysis of a correlator based maximum likelihood frequency estimator

In this paper we discuss the performance of a correlator based frequency estimator (CE). The estimator is statistically analysed for single-tone frequency estimation for an additive white Gaussian noise (AWGN) channel. The CE is a maximum likelihood estimator (ML) S. M. Kay (1993) which theoretically achieves the Cramer-Rao lower bound (CRB) S. M. Kay (1993) if properly implemented. Frequency estimates on the received single-tone signal are made by correlating the received signal with a locally generated signal by varying the frequency, and maximizing the energy at the output of the correlator. The statistical distribution of the frequency estimates, made by the CE is studied; we consider four different cases as discussed in the paper for the distribution, whilst providing simulation results to verify the analysis.

Phase detector models and their performances for IF/baseband frequency recovery for complex envelope based DSP implemented PLL

This paper discusses four phase detector (PD) models that could be used in DSP implemented phase locked loops (PLL) for frequency recovery at intermediate frequency (IF) or at baseband. The PD models, which are nonlinear functions in general, can be easily implemented in DSP. The steady state and the acquisition performances of the PD models are discussed and compared with each other, and the noise statistics are explored by means of computer experiments and numerical analysis.

Performance analysis of a Digital Phase-Locked Loop with a Hyperbolic Nonlinearity

The treatment of phase locked loops (PLL) has been heavily looked into over the past several decades on its performances and analysis, and is a very old topic. However the usage of it has never been reduced with the rapid evolvement of various open loop and closed loop systems. In this paper we analyse the performance of an arctan based digital phase locked loop (DPLL) with a hyperbolic nonlinearity for single-tone carrier tracking. We purposely introduce the nonlinearity for improved performance of the closed loop system. We look at the acquisition performance of the DPLL by considering the phase plane portrait and the lock-in range of the loop. The steady state (SS) performance of the loop is analysed by considering the open loop SS statistical distribution of the phase noise

DSP based symbol timing estimation techniques

This paper presents three symbol timing estimation techniques, using DSP (digital signal processing) methods. The techniques are easily implemented on digital signal processors or FPGAs (field programmable gate arrays). Two feedforward techniques and one feedback technique are presented. The relative performances of the techniques are compared, and the advantages and the disadvantages of the techniques are discussed as well.

Frequency tracking and acquisition with a four-quadrant arctan phase detector based digital phase locked loop

This paper discusses the performance of tracking and acquiring a single frequency sinusoid with a four-quadrant phase detector (PD) based digital phase locked loop (DPLL). Under tracking we analyse the open loop steady state phase error distribution of the DPLL at the output of the PD and the output phase noise. Acquisition is treated as a complete linear process under noise free conditions and the performance degradation is studied using computer experiments.

Timing Synchronization for Cooperative Communications with Detect and Forward Relaying

A non-data-aided near maximum likelihood (NDA-NML) symbol timing estimator is presented, which is applied to a cooperative communication system with a source, relay and destination. A Cramer rao bound (CRB) for the estimator for asymptotically low signal-to-noise (SNR) ratio case is derived. The timing complexity of the NDA-NML estimator is derived and compared with the correlation based data-aided maximum likelihood (DA-ML) estimator. It is demonstrated that the complexity of the NDA-NML estimator is much less than that of correlation based DA-ML estimator. The bit-error-rate (BER) performance of this system operating in a detect-and-forward (DAF) mode is studied where the channel state information (CSI) is available at the receiver and the symbol timings are estimated independently for each channel. SNR combining (SNRC) and equal ratio combining (ERC) methods are considered. It is found that timing estimation error has a significant effect on BER performance. It is also found that for large timing error the benefit of cooperative diversity could vanish. It is demonstrated that significant gains can be made with both combining methods with cooperation and timing estimation, where the gains are the same for both estimators.