Device-to-Device (D2D) networks would play a paramount role in meeting the steep operational targets of 5G. D2D networks enable proximity based communication links, allowing the cellular network to scale up substantially with minimal impact on core network resources. Adoption of Radio Environment Map (REM) would help in transcending the performance gains from upper layers to physical layer as well. In this paper, performance evaluation of prevalent REM techniques and sensor deployment strategies has been carried out in Nakagami-m and Nakagami-lognormal channels. The results obtained support adoption of Crowd-Sensing (CS) with Inverse Distance Weighting (IDW) in D2D scenario, especially in public safety applications.

In a cognitive radio environment, the optimality in channel selection by a secondary user (SU) is directly dependent on its spectrum‐sensing efficiency, and quality of experience (QoE) in terms of the channel‐switching frequency (CSF) and the interference caused to the primary users (PUs). Modelling the spectrum through statistical methods becomes, sometimes, difficult due to the lack of a‐priori information of the PU activity. This work proposes a framework for learning‐based prediction of the future idle times of the PUs thereby opportunistically allocating the channel with enhanced QoE of SUs. The idea is to minimise the spectrum‐sensing energy requirement by sensing only if the channel is predicted to be idle, thereby reducing the CSF and mitigating the SU–PU interference. Initially, the authors have tested the accuracy of the prediction approach in various traffic scenarios for a single PU channel case. Later, it is extended to the multiple channel case for a particular data traffic. Furthermore, a practical scenario has been considered where the efficacy of the proposed framework is validated for PU data traffic in GSM and ISM bands. The results highlight the practicability of prediction‐based opportunistic dynamic spectrum access with improvement in the SU QoE over random channel selection.

The TV white space (TVWS) or equivalently the spatially available unused TV spectrum has drawn much attention recently due to its availability for opportunistic access by unlicensed users in fulfilling the spectrum demands. In this paper, we have evaluated the capacity of secondary (unlicensed) user network meeting the constraint on the aggregated secondary interference power at the TV receiver. Particular importance has been given to the interference modeling to define the protection region around the TV-receiver as per the Federal Communications Committee (FCC) rules. The impact of different system parameters such as power, transmission range, and density of secondary users contending for the same TV channel are also explored in the paper for different channel scenarios.

Diversity reception schemes are well-known effective techniques for mitigating the adverse effects of multipath fading in wireless mobile channels. This paper analyzes the performance of an amplify-and-forward (AF) relay-based cooperative spectrum sensing system with generalized selection combining (GSC) over a Rayleigh fading channel and compare the results with those of the conventional diversity combining schemes such as maximal-ratio-combining (MRC) and selection combining (SC). Novel closed-form expression has been derived for the average detection probability over the independently and identically distributed (i.i.d) diversity paths. Receiver operating characteristics (ROCs) and the average detection probability versus the average signal-to-noise ratio (SNR) curves have been presented for different scenarios of interest.

We present numerical results relative to a bistable optical device comprised of an asymmetric Fabry-Perot cavity embedding a nonlinear optical medium. Both the real and imaginary part of the third order nonlinear susceptibility are considered in our calculations. Optimized device operation, expressed in terms of the contrast ratio between the two stable states, is then discussed as a function of the different cavity parameters. The presented method can be a useful tool for designing practical devices with application in the field of all-optical switching, optical regeneration and optical signal processing.

An analytical approach based on a reduced Markov chain (RMC) model of an optical packet switch with partially shared output buffer has been presented and a combined scheme for the contention resolution in optical packet switches has been proposed. The proposed scheme takes the advantage of output buffering, shared buffering and wavelength conversion to enhance the switch performance. The performance evaluation of the switch architecture based on RMC modelling has been validated through extensive simulation. Moreover, for a self-similar input traffic, the switch performance has been shown to achieve further improvement if a traffic shaping mechanism is incorporated at the input end of the switch architecture.

Performance of convolutionally coded M-ary pulse position modulation (M-PPM) systems in the presence of slot synchronization errors is evaluated for the shot-noise-limited photon-counting receiver and the avalanche photodetection receiver. Both hard and soft ( delta -max) demodulation results are given, and two soft-decision metrics are investigated.>

Several strategies for combining convolutional codes (CCs) and pulse position modulation (PPM) in a direct-detection optical channel are considered, including binary and 2/sup n/-ary PPM with rate-1/n CCs, 2/sup m/-ary PPM with a dual-m CC, and interleaved 2/sup L/-ary PPM with a rate-1/n CC. In the latter case, J.L. Massey's (1981) concept of coding of L separate component channels constituting a 2/sup L/-ary PPM erasure channel is carried out for both the ideal photon counting and the avalanche photodetection (APD) cases, providing a comparative evaluation of the various strategies in terms of bit error probability and achievable coding gain for different code structures and decoding schemes.>

This paper examines the problem of self bit synchronization employing nonlinear timing extraction schemes in optical receivers with avalanche photodetectors (APD) through digital computer simulation. A direct algorithm is developed for the simulation of sample functions of the APD output process with due consideration to intersymbol interference (ISI). Simulation of all the functional blocks used for synchronization is carried out in the discrete time domain. Performances of the nonlinear timing recovery schemes are evaluated in terms of the rms timing jitter for nonreturn-to-zero (NRZ) as well as return-to-zero (RZ) signaling formats.