B. Fong

On the scalability of fixed broadband wireless access network deployment

Fixed broadband wireless access systems, such as the local multipoint distribution service, use an open system architecture that supports a scalable solution for the Internet services over IEEE 802.16 wireless networks. This article presents an overview of various features of BWA systems toward realizing a high level of scalability to support a potentially fast expanding network. This is achieved by optimizing various network resources, which include utilizing the available bandwidth efficiency, making a minor enhancement to an existing system that minimizes the disruption to network services during the network expansion process, and combining the benefits of different features to increase network capacity.

Factors causing uncertainties in outdoor wireless wearable communications

Wearable computers are becoming increasingly popular as new features emerge and device portability improves-making them suitable for accessing multimedia services on the move. Wireless LANs are compatible with Ethernet and asynchronous-transfer-mode-based fiber-optic networks, providing high mobility to user nodes while integrated and connected to high-speed networks wired with broadband. With a range covering several kilometers, WLANs are advantageous for providing multimedia services to wearable computers. Various factors influence the operation of wirelessly connected wearable computers, but we emphasize the rainfall influence.

Polarization of received signals for wideband wireless communications in a heavy rainfall region

Wireless fixed network access offers many advantages such as scalability and ease of deployment in low population density areas. However, its coverage is greatly affected by rainfall. In this letter, we study the effects of rain attenuation on the radio channel in a heavy rainfall region for wideband signals in the 10-40-GHz frequency range. We conclude that although a lower frequency of <10 GHz is more affected by multipath due to a longer wavelength, it is still optimal in a heavy rainfall region due to high losses associated with higher frequency signals. In addition, for a path of over 1.5 km, the difference in horizontal and vertical polarization becomes significant.

On the performance of telemedicine system using 17-GHz orthogonally polarized microwave links under the influence of heavy rainfall

This paper describes the design of a telemedicine system based on next-generation wireless local area networks (WLANs) operating at 17 GHz. Seventeen gigahertz is proposed for next-generation WLAN services offering numerous advantages over traditional IEEE 802.11 networks that operate in the range of 2.4-5 GHz. Orthogonal polarization is often used to increase spectrum efficiency by utilizing signal paths of horizontal and vertical polarization. Radio waves exceeding 10 GHz are particularly vulnerable to signal degradation under the influence of rain which causes an effective reduction in isolation between polarized signal paths. This paper investigates the influence of heavy rain in a tropical region on wide-band microwave signals at 17 GHz using two links provided by a fixed broad-band wireless access system for two-way data exchange between paramedics attending an accident scene and the hospital via microwave equipment installed in the ambulance. We also study the effects of cross polarization and phase rotation due to persistent heavy rainfall in tropical regions.

An intelligent video categorization engine

Purpose – We describe an intelligent video categorization engine (IVCE) that uses the learning capability of artificial neural networks (ANNs) to classify suitably preprocessed video segments into a predefined number of semantically meaningful events (categories).Design/methodology/approach – We provide a survey of existing techniques that have been proposed, either directly or indirectly, towards achieving intelligent video categorization. We also compare the performance of two popular ANNs: Kohonens self‐organizing map (SOM) and fuzzy adaptive resonance theory (Fuzzy ART). In particular, the ANNs are trained offline to form the necessary knowledge base prior to online categorization.Findings – Experimental results show that accurate categorization can be achieved near instantaneously.Research limitations – The main limitation of this research is the need for a finite set of predefined categories. Further research should focus on generalization of such techniques.Originality/value – Machine understandin...

The effect of rain attenuation on orthogonally polarized LMDS systems in tropical rain regions

The effect of rainfall is to reduce the link reliability of local multipoint distribution service (LMDS) systems. We study the effects of rain attenuation on the microwave channel in two heavy rainfall tropical cites in Asia for wideband signals using a line-of-sight LMDS link with orthogonal polarizations. This is performed by transmitting signals with horizontal and vertical polarizations with carrier frequencies commonly used in LMDS systems. It is noted that the effect of depolarization due to rain is minimal at around 10 GHz; it is also observed that the rainfall rate has little effect on the difference in attenuation with different polarizations.

Forward error correction with Reed-Solomon codes for wearable computers

High-speed multimedia data transmission is vulnerable to burst errors primarily due to its frame structure. Forward error correction (FEC) codes mitigate the effects of multipath fading as some form of time diversity by adding redundancies into the transmitted data. This paper evaluates the performance of Reed-Solomon codes on transmitting ATM data for lightweight wearable computers using single carrier modulation. The aim is to maximize link and minimize the impact of atmospheric conditions on bit error rate (BER) performance. The performance is compared with signals transmitted without any forward error correction scheme. This scheme is particularly suitable for small wearable computers with high portability due to simplicity of circuitry making it suitable for consumers on the move.

Measurement of attenuation and phase on 26-GHz wide-band point-to-multipoint signals under the influence of rain

This letter presents the results of a study on rain attenuation of an outdoor radio propagation channel at 26 GHz, which is widely used for local multipoint distribution service deployment. The difference in attenuation between vertical and horizontal polarization is compared for wide-band signals using a line-of-sight radio link with alternate polarizations by transmitting signals with horizontal and vertical polarizations. It is shown that attenuation difference due to depolarization becomes much more significant when the rainfall exceeds 70 mm/h.

On performance of an equalization algorithm based on space and time diversity for wireless multimedia services to home users

Wireless networks often operate under harsh environmental conditions with many uncontrollable factors causing data corruption and network outage. Atmospheric phenomena such as rain and snow make signal reception difficult for such systems. Furthermore, factors such as multipath fading and depolarization due to rain attenuation can severely and adversely impact the performance of wireless networks. This paper presents an equalization algorithm that uses spatial and temporal diversity. By using such information of the received signal, it is possible to minimize the effects of intersymbol interference, and leads to a reduction in computational complexity. Results show that the proposed equalization algorithm offers a noticeable improvement with single-carrier modulated signals.

Error localization for robust video transmission

The convergence of Internet, multimedia and mobile applications has led to an increased demand for efficient and reliable video data transmission over heterogeneous networks. Due to their coding efficiency, variable-length codes (VLC) are usually employed in the entropy coding stage of video compression standards. However, error propagation is a major problem associated with VLC. We propose the use of a class of self-synchronizing VLC (SSVLC) to achieve the dual goal of optimal coding efficiency and optimal error localization. Performance evaluation has confirmed that the use of SSVLC provides better performance than standard VLC techniques.