Aniruddha Chandra

Wireless Relays for Next Generation Broadband Networks

Wireless radio relays are one of the possible contenders to extend the capacity and reliability of broadband data channels envisaged for 4G and above. Several research and standardization groups are engaged in evaluating and evolving the range of applications with radio relays. There are both pros and cons of this technology, which needs to be carefully addressed before its actual implementation. Its cost effectiveness will also be a decid ing factor in a particular application sce nario with respect to other competing technologies.

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.

Performance of Non-coherent MFSK with Selection and Switched Diversity Over Hoyt Fading Channel

A closed-form expression of cumulative distribution function (CDF) of the instantaneous signal to noise ratio (SNR) in Hoyt fading channel is derived. This CDF and associated formulas are then used to find out the error probability of non-coherent M-ary frequency shift keying with multichannel reception. Simple finite-range integral expression for the symbol error probability (SEP) with selection diversity is found through CDF method. Next, closed-form expressions of moment generating functions (MGF) are presented for the switched diversity case and SEP values are calculated using the derived MGFs. Some other performance parameters like, outage probability and average SNR with switched diversity, are provided. In addition, analytic frameworks are presented for calculation of optimum switching thresholds that ensure minimum outage probability or minimum SEP. The analysis is quite general in the sense that it covers switch and stay combining and Rayleigh fading as special cases.

Energy Efficient Relay Placement in Dual Hop 802.15.4 Networks

IEEE 802.15.4 has emerged as a popular standard for short range wireless sensor networks used in industrial, military, health, and environmental sectors. The limited lifetime of such networks is one of the critical design challenges. This paper examines the how relaying through intermediate sensor nodes can enhance the lifetime of an 802.15.4 network. In particular, novel energy consumption models for both AF and DF relays have been developed. Different relay gain scaling mechanisms and forwarding strategies under each of the relay categories were also considered and their energy efficiencies were compared. For every relaying protocol, it was found that there exists an optimum location where energy saving is maximum and this location is not necessarily different for different modes. In summary, it has been observed that the optimum location for AF relays is the equidistant point from source and destination. In contrast, the optimal location for DF relays is closer to source. The effect of different PHY level (outage probability, path loss) and MAC level parameters (frame length) on the energy efficiency are also studied.

Error performance of RS coded binary FSK in PLC channels with Nakagami and impulsive noise

Power line communication (PLC) systems are being standardized over the globe and some of these standards recommended frequency shift keying (FSK) as their modulation choice. Broadband transmission over a PLC channel is mainly affected by the ever-present background noise and the occasional high-amplitude impulses. It has been recently found that the background noise in PLC can be suitably modelled with Nakagami-m distribution while a standard model for characterizing impulses is to assume Gaussian distributed amplitude and Poisson distributed arrivals. Considering such a model, at first, simple analytical bit error rate (BER) expressions of uncoded binary FSK (BFSK) signals are derived in the paper. Next, a unified analytical framework is presented for evaluating BER when a Reed Solomon (RS) code is used to mitigate the noise effects. The results reveal that when the signal to background noise ratio (SNR) is low, the noise parameter m and the demodulation scheme affects the performance of the coded system. On the contrary, at higher SNR, impulsive noise dominates over background noise, and these effects vanish as the BER curve becomes flat. Numerical evaluations dictated that by allowing a lower code rate (0.7) this error floor may be reduced significantly (up to 10-15). The code gain of the system was found to be an inverse function of the code rate and codeword length.

Frequency-Domain In-Vehicle UWB Channel Modeling

This paper aims to present a simple but robust model characterizing the frequency-dependent transfer function of an in-vehicle ultrawideband (UWB) channel. A large number of transfer functions spanning the UWB (3–11 GHz) are recorded inside the passenger compartment of a four-seated sedan. It is found that the complex transfer function can be decomposed into two terms, the first term being a real-valued long-term trend that characterizes frequency dependence with a power law and the second term forming a complex correlative discrete series that may be represented via an autoregressive (AR) model. An exhaustive simulation framework is laid out based on empirical equations characterizing trend parameters and AR process coefficients. The simulation of the transfer function is straightforward as it involves only a handful of variables; however, it is in good agreement with the actual measured data. The proposed model is further validated by comparing different channel parameters, such as coherence bandwidth, power delay profile, and root-mean-square delay spread, obtained from raw and synthetic data sets. It is also shown how the model can be compared with existing time-domain Saleh–Valenzuela-influenced models and related IEEE standards.

Double threshold-based cooperative spectrum sensing for a cognitive radio network with improved energy detectors

Performance of cooperative spectrum sensing in a cognitive radio (CR) network is investigated where each CR node uses an improved energy detector (IED) to sense the primary user (PU), and makes a local decision regarding the presence of PU using double thresholds (DTHs). The local hard decisions are combined at fusion centre (FC) to obtain the global decision. The advantage of a DTH-based system over a single threshold based one is, a CR node can opt for no decision when a decision variable lies in the fuzzy zone between two thresholds. Such censoring reduces the transmission overhead between CR and FC without significantly affecting the receiver operating characteristics. In this study, the performance of the abovementioned CR network has been assessed in terms of the average number of normalised transmitted sensing bits (k nor), the total error probability (P e,n ) and optimal number of CR users that ensures minimum Pe,n . It was observed that k nor increases as the signal power raise factor of IED increases or failed sensing probability decreases. Further, the agility of the network improves as the PU death rate increases. Impact of reporting channel on the sensing performance has also been indicated.

Performance of BFSK over a PLC channel corrupted with background Nakagami noise

Power line communication (PLC) is one of the preferred broadband high-speed data communication technology for its wide availability, low infrastructure cost, and robustness. However, PLC performance is limited by attenuation and background noise present in the medium. The frequency shift keying (FSK) modulation scheme is experimentally found to be more robust against such power line distortions. Further, it was shown earlier that the background noise in PLC follows Nakagami-m distribution. In this paper, we have evaluated bit error rate (BER) of coherent and non-coherent binary FSK, when corrupted with background Nakagami noise. The derived expressions are simple, involve only elementary functions, and the analytical BER values match perfectly with computer simulations. It is found that the noise parameter m has a marked influence on the BER performance.

Location Management in Cellular Mobile Networks

Increasing traffic generated from users and different QoE requirements has increased the importance of LM recently. This increasing importance has given way to the development of newer and intelligent schemes as well as the modification of the existing ones. In this article, we have discussed various methods proposed for the two important LM functions, LU and paging. The features, relative performances, and inherent disadvantages associated with each of them have been thoroughly dealt with. Studies reveal that the performance of different LU and paging schemes is largely affected by the user mobility pattern and call arrival characteristics. Further, the newly devised schemes are often associated with tremendous implementation complexity as well as large computational overhead, and require smarter MTs/ networks. For a given network, the best design will include a scheme, or a set of schemes, that provides the best compromise between performance and implementation constraints and is often sub-optimum for a different network.

BER Performance of Coherent PSK in Rayleigh Fading Channel with Imperfect Phase Estimation

In this paper average bit error rate (BER) of coherent phase shift keying (PSK) modulations with improper phase estimation have been derived. A simple slow flat wireless fading channel obeying Rayleigh distribution is assumed for channel modelling. In addition the channel is also perturbed by additive white Gaussian noise (AWGN). The phase distortions considered in the paper are random, unbiased, i. e. having zero-mean and follows a Gaussian distribution. Analytical BER is calculated for the first two members of the PSK family, namely binary PSK (BPSK) and quaternary PSK (QPSK), through Hermite’s method of integration. Extensive Monte Carlo simulations were also performed to validate the theoretical results. In order to demonstrate the advantages of modulation schemes that do not require phase synchronization, BER performances of BPSK and QPSK with phase error are compared with the corresponding differential PSK modulations (DPSK and DQPSK respectively) of same constellation size.