Abbas Mohammed

The Role of High-Altitude Platforms (HAPs) in the Global Wireless Connectivity

Since 1990s, the investigations of aerospace communication segment have not only been concerned with satellites, but increasingly with lower altitude repeaters flying in the stratosphere. They are the so-called high-altitude platforms (HAPs) with important advantages with respect to satellites in terms of reduced cost of implementation, deployment, and launch. However, HAPs are characterized by a reduced coverage, as compared with satellites. Nevertheless, in recent literature, HAPs are not regarded as competitors of the satellite technology. On the contrary, the emphasis is on the effective and seamless integration among heterogeneous aerospace segments (GEO, LEO, and HAP) and aerospace segments with terrestrial wireless networks in order to globally extend the broadband wireless connectivity. This paper is focused on the role of HAPs in providing global connectivity in future communication systems and services. Potentialities, enabling technologies, and challenges are presented from the perspective of the integrated terrestrial/HAPs/satellite communications infrastructure.

Performance Evaluation of Uplink Closed Loop Power Control for LTE System

Uplink power control is a key radio resource management feature in the 3GPP Long Term Evolution (LTE). In order to adapt to changes in the inter-cell interference situation or to correct power amplifier errors, closed-loop adjustments should be applied. In this paper the performance of closed loop power control combined with fractional path loss compensation factor is studied, and an optimal value for the path loss compensation factor is investigated. The closed loop power control with fractional path loss compensation factor is found to improve the system performance in terms of mean bit rate by 68% and utilizes the battery power more effectively.

On Spectrum Sharing and Dynamic Spectrum Allocation: MAC Layer Spectrum Sensing in Cognitive Radio Networks

One of the most critical issues regarding wireless networks regulation agencies is how to manage the available electromagnetic radio spectrum in a way that satisfies the needs of the huge growing in wireless systems both economically and technically, especially with the recent crowding in the available spectrum. Hence, building cognitive radio systems supporting dynamic access to the available spectrum has appeared recently as a novel solution for the wireless system huge expansion. In this paper we investigate the MAC layer sensing schemes in cognitive radio networks, where both reactive and proactive sensing are considered. In proactive sensing the adapted and non-adapted sensing periods schemes are also assessed. The assessment of these sensing schemes has been held via two performance metrics: available spectrum utilization and idle channel search delay. Simulation results show that with proactive sensing adapted periods we achieve the best performance but with an observable overhead computational tasks to be done by the network nodes.

Advanced Communication Techniques and Applications for High-Altitude Platforms

1Department of Signal Processing, Blekinge Institute of Technology, 372 25 Ronneby, Sweden 2Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, 84105 Beer-Shiva, Israel 3Department of Electronics, The University of York, York YO10 5DD, UK 4Dipartimento di Elettronica, Politecnico di Torino, 10129 Torino, Italy 5Adaptive Communications Research laboratories, Advanced Telecommunications Research Institute International (ATR), Kyoto 619-0288, Japan

Performance of a Multiple HAP System Employing Multiple Polarization

In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. In addition, we evaluate the performance of the system for different separation angles between HAPs, and determine the optimal separation angle that maximizes the total capacity of the system.

High Altitude Platforms for Wireless Sensor Network applications

In this paper, we investigate the performance of using high altitude platforms (HAPs) for low power wireless sensor network (WSN) applications. In our study, HAPs are employed to replace the sink usually deployed on the ground and collect data from sensor nodes. Two scenarios of employing the HAP as the sink in the WSN are established. Multiple sensor nodes are organized in an ad-hoc manner or in a cluster fashion. Due to the advantages of HAP systems, integrating HAPs into WSN can efficiently extend the deployment coverage area of WSN and reduce complexity of the WSN structure. Simulation results show that HAPs can be effectively employed to provide communications for WSNs.

Performance of Multi-Channel MAC Incorporating Opportunistic Cooperative Diversity

This paper proposes a medium access control (MAC) protocol, termed as CD-MMAC, for wireless networks that utilizes multiple channels and incorporates opportunistic cooperative diversity dynamically to improve its performance. The IEEE 802.11b standard protocol allows the use of multiple channels available at the physical layer but its MAC protocol is designed only for a single channel. The proposed protocol utilizes multiple channels by using single interface and incorporates opportunistic cooperative diversity by using a cross-layer MAC. The new protocol leverages the multi-rate capability of IEEE 802.11b and allows wireless nodes far away from destination node to transmit at a higher rate by using intermediate nodes as a relays. The protocol incorporates opportunistic cooperative diversity by the design of a cross-layer MAC. The protocol improves network throughput and packet delivery ratio significantly and reduces packet delay. The performance improvement is further evaluated by simulation and analysis.

WCDMA uplink interference assessment from multiple high altitude platform configurations

We investigate the possibility of multiple high altitude platform (HAP) coverage of a common cell area using a wideband code division multiple access (WCDMA) system. In particular, we study the uplink system performance of the system. The results show that depending on the traffic demand and the type of service used, there is a possibility of deploying 3–6 HAPs covering the same cell area. The results also show the effect of cell radius on performance and the position of the multiple HAP base stations which give the worst performance.

Performance Evaluation of a Low-Complexity OFDM UMTS-LTE System

Research towards meeting the higher demands for higher data rates was the main reason for the birth of an evolution technology towards the 4th generation mobile communication systems. This evolution to the current 3rd generation UMTS systems was given the name E-UTRA/UTRAN long term evolution (LTE) by the 3GPP. This paper analyzes the requirements for this evolution and evaluates the performance of the OFDM-LTE system under different propagation impairments (AWGN and multipath fading channels involving pedestrian and vehicular scenarios) in terms of bit and symbol error rates (BER and SER) for different modulation formats.

Uplink closed loop power control for LTE system

The role of uplink power control is to suppress interference. Power control refers to set output power levels of transmitters, base stations in the downlink and User Equipment (UE) in the uplink. In this paper the performance of 3GPP Long Term Evolution (LTE) closed loop power control combined with fractional path loss compensation factor is evaluated by simulating the effects of open loop error, Transmit Power Control (TPC) command delay and power headroom reporting. Simulation results show that the closed loop power control with fractional path loss compensation factor is advantageous compared to closed loop power control with full path loss compensation. The closed loop power control with fractional path loss compensation factor is found to improve the system performance in terms of mean bit rate by 63%.