Broadband Fixed Research Articles

General N-State Markov Model for Rain Attenuation Time Series Generation

Nowadays and mainly in the near future the wireless point-to-point or point-to-multipoint connections are operating in high frequency. These systems are applied in feeder network for future cellular mobile communication systems or BFWA (Broadband Fixed Wireless Access) networks. Besides the obvious benefits of the applied high carrier frequency there is a significant disadvantage, the considerable attenuation caused by precipitation, especially by rain. For accurate planning of the proposed microwave links the statistics of the expectable rain attenuation is highly important. Applying our previous research results the this work provides a general N-state Markov Chain model to generate rain attenuation time series on a proposed microwave link according to the link parameters. The first and second order rain attenuation statistics of the generated time series can be derived directly from the Markov model parameters, so the N-state Markov model can be applied for prediction of rain attenuation on the proposed link even in the early planning phase. With our proposed model very accurate realisation of the physical fade process can be achieved.

Quality of Service of Broadband Fixed Wireless Access QPSK Channels Interfered by Adjacent Terrestrial Links

A physical model is presented concerning the quality of service (QoS) statistics of broadband fixed wireless access (BFWA) QPSK channels interfered by adjacent terrestrial links operating at the same frequency. The QoS is quantified in terms of the bit-error probability (BEP) of the link. BFWA networks of current interest are mainly operated above 10 GHz assuming line-of-sight (LoS) connection between the base station and the subscriber terminal. In these network configurations, rain attenuation is the dominant fading mechanism and its statistical behavior severely aggravates the nominal interference environment due to the spatial inhomogeneity of rain. The BEP of a coherent QPSK demodulator in the presence of Gaussian noise, cochannel interference and rain attenuation is determined and is related to the relevant performance masks recommended by ITU-R. Numerical results of the proposed model examine how the frequency of operation, the clear-sky interference levels, the length of the interfering path and the climatic conditions affect the QoS of BFWA channels. The spectral and spatial coexistence of BFWA networks and point-to-point links is investigated

An Integrated AP for Seamless Interworking of Existing WMAN and WLAN Standards

Broadband Fixed Wireless Access (BFWA) systems represent a potential technological foundation for the Fourth Generation of Wireless Mobile Communication Systems (4G) as they can replace wired broadband and, with sufficient widespreading deployment, can significantly cut into the usage of cellular networks in many areas. In this context, the seamless interworking of Wireless Metropolitan Area Network (WMAN) and Wireless Local Area Network (WLAN) technologies is an efficient solution to provide the indoor extension of BFWA systems coverage, which would largely contribute to their success and penetration in the market. In this paper, we introduce a novel Access Point (AP), called WMAN/WLAN AP (WWAP), which essentially integrates in a compact device a WMAN Subscriber Station (SS) and a WLAN AP in order to extend the WMAN coverage in-house and to guarantee the end-to-end Quality of Service (QoS). Besides the technical features, the market trends and the usage scenarios where the WWAP might be a cost-effective and a very efficient solution are outlined. Finally, simulation results are carried out in order to demonstrate the effectiveness of the proposed AP.

Editorial: Special Issue on “Increasing Efficiency in Broadband Fixed Wireless Access Systems: From Physical to Network Layer Solutions”

Editorial: Special Issue on “Increasing Efficiency in Broadband Fixed Wireless Access Systems: From Physical to Network Layer Solutions”

A Joint MAC-PHY Approach for Medium Access Control in VBR MC-CDMA Broadband Indoor Connections

Multicarrier Code Division Multiple Access (MC-CDMA) techniques were originally proposed at mid of 90's for wideband multi-user communications in wireless environments characterized by hostile propagation characteristics. In this work, the design of a MC-CDMA-based infrastructure is considered for VBR broadband indoor connections with real-time asynchronous multiple access. At the present time, Broadband Fixed Wireless Access (BFWA) standards like IEEE 802.16 and HIPERMAN can bring broadband services inside buildings, but indoor access should be conveniently provided by a local area connection. The capability of MC-CDMA of supporting asynchronous multi-user variable-bit-rate (VBR) transmission is exploited jointly with an efficient and real-time Medium Access Control (MAC) strategy in order to allow a significant number of indoor VBR users to transmit information in CDMA modality with different quality of service (QoS) profiles. Different classes of users are defined at the MAC level. The available radio resources (i.e. the orthogonal subchannels) are selectively attributed to transmitting users depending on their performance achieved at MAC level and measured by an "intelligent" gateway. When the quality level is not satisfactory for one or more users, the AP issues a decrease of the data rate for such users while providing them with an increased number of subcarriers, guaranteeing a slower transmission fostered against frequency-selective channel distortions. The paper presents an overview of the system and tests its performance through extensive simulations. The proposed joint MAC-PHY approach demonstrates good performance in terms of achieved throughput and high flexibility in radio resource management.

Crossing the digital divide: cost-effective broadband wireless access for rural and remote areas

The use of wireless, DSL, and cable for broadband access has become increasingly prevalent in metropolitan areas. While these technologies are being successfully utilized in terms of both service quality and economics in densely populated areas, there are still vast geographic regions where broadband services are either prohibitively expensive or simply unavailable at any price. The article examines several alternatives for using 2.4 GHz 802.11b (WiFi) technology to provide fixed broadband access in rural areas consisting of towns, smaller remote communities, clusters of subscribers separated by large intercluster distances, as well as widely scattered users. Our approach is to model a network based on realistic demographics, equipment and operations costs, service revenues, and customer demand and usage, and calculate the lifecycle economics in terms of capital investment and profitability. We consider the cost benefits of several emerging technologies and architectures, including high gain antennas, dynamically steerable beamforming antennas, and multihop routing. Our results show that cost-effective affordable high-speed wireless Internet access can be provided in rural and remote areas using nontraditional and innovative approaches, bridging the so-called digital divide.