A wireless LAN standard developed by IEEE committee P802.11 operates in the unlicensed 2.4 GHz ISM band. This band is a very hostile environment due to many unpredictable interference sources, such as microwave ovens, utilizing the same frequency bands. At the same time the allowed signal power density that can be used is limited in order to minimize the interference to other users in the same band. In order to avoid these interference and keep a low signal power density the standard supports both direct sequence (DS) and frequency hopping (FH) modulation for these applications. The new test beds for multimedia wireless (WLANs) also use FH modulation. We analyze the performance of a modification of the FH multiple frequency shift keying (MFSK) system that includes a multitone multiamplitude MFSK signal, designated as amMFSK modulation. In this case, in order to meet the transmitted power density limits imposed in the ISM band, the signal energy is split into m separate tones. This makes the system more vulnerable to noise and fading, but still the overall flow of useful information will be increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance.

In this paper, an average bit error rate (BER) analysis of the free-space optical (FSO) system applying subcarrier intensity modulation with binary differential phase-shift keying is presented. Multiple receiver apertures are considered, when maximal-ratio combining (MRC) is employed. Intensity fluctuations due to atmospheric turbulence are modeled by Melaga (M) distribution, taking the pointing errors effect into account. Novel closed-form average BER expression is derived in terms of Meijer's G-function. Utilizing derived expression, numerical results are presented and confirmed by Monte Carlo simulations. The effects of atmospheric turbulence and pointing errors parameters, as well as the number of photodetectors, on the average BER performance are discussed. Employing multiple receivers with MRC leads to the improvement of the FSO system performance. Numerical results illustrate that this improvement depends on the FSO channel conditions. In addition, it is proved that SNR unbalance scenario can seriously deteriorate system performance.

This paper investigates the performance of an unmanned aerial vehicle (UAV)-assisted wireless power transfer (WPT)-enabled communications for energy-constrained wireless devices. Herein, a UAV serves as a radio-frequency (RF) energy harvesting transmitter for a pair of Internet of Things devices (IoDs). It also provides relay cooperation to IoDs using decode-and-forward operation. The composite fading channels associated with the UAV and IoDs are modeled by considering the probability of line-of-sight (LoS)/non-LoS and shadowing components, assuming log-normal distribution. Besides, the small-scale fading scenarios for LoS and non-LoS communications are assumed to follow Nakagami-m and Rayleigh distributions, respectively. In addition, considering relative mobility between the UAV and IoDs, we exploit the first-order autoregressive process to model the fading channels during the information transmission phase. For such a realistic system setup, we derive the expressions for the outage probability at the IoDs using Gauss-Hermite quadrature under different shadowing and fading channel combinations. The system throughput and energy efficiency are also quantified using the derived outage probability expressions. The analytical findings are verified through numerical and simulation results. Our results highlight the impact of various system/channel parameters on the system’s performance and provide significant insights into the system’s behavior.

In this paper, we address the challenges in facilitating the intra-band coexistence of WiFi and LTE technologies in multi-RAT networks and propose a semantic coordination protocol that improves the communication performance among inter-network devices. Effective communication in LTE networks is a critical task to achieve as the heterogeneity of the devices and coexisting technologies arises. This paper introduces an internetwork spectrum coordination across Wi-Fi and LTE systems based on an ontological framework as a possible solution for improved coexistence. We develop and evaluate our approach under real-world settings. The results we obtained using the proposed semantic coordination protocol have shown significant gains for both the under-study Wi-Fi and LTE networks.

In this paper we consider performance of a dual hop amplify-and-forward system, with co-channel interference at relay. We consider channel state information assisted system in Nakagami-m channel. The outage probability and the average bit error probability of the system are determined. The influence of the interference, as well as the influence of other system's parameters, such as the fading parameter m and outage probability threshold γ _th on the system's performance is considered.