Broadband Wireless Access Networks Research Articles

A stochastic geometrical vector model of macro- and megacellular communication channels

This paper describes a physically based stochastic approach that allows to predict the narrowband fading statistics for macro- and megacellular networks operating in urban areas. On one hand, macrocellular channels have been mainly covered in the literature by means of empirical models. On the other hand, megacells are typical of upcoming communication systems, such as broadband wireless access and high-altitude platform-based networks. Generally, the path gain of a wireless fading channel can be statistically characterized by a Ricean distribution, which includes Rayleigh fading as a particular case. The key parameter of the distribution is the K-factor K, defined as the ratio of the dominant component to the scatter contribution. The K-factor is estimated by means of a physical model, conditionally to a set of geometrical parameters, such as the building height, the street width and the base station-to-terminal distance. These parameters are statistically described by analytical distributions. The model is successfully compared with experimental data at 1.6 GHz and typical applications are presented. Finally, because of its physical background, the model performs very well in analyzing polarization (MIMO) multiplexing schemes.

Technologies and performance for non-line-of-sight broadband wireless access networks

This article presents emerging technologies for upcoming non-line-of-sight fixed or stationary broadband wireless access systems. We describe design trade-offs for overall maximization of the radio capacity and coverage of fixed wireless access (FWA) in multicell interference- and fading-prone environments. We characterize quantitatively the impact of key emerging radio technologies on the overall performance.

Permittivity and Conductivity Measurements of Building Materials at 5.8 GHz and 41.5 GHz

The results of various experiments performed to characterize electromagnetic properties of typical building materials at BRAN (Broadband Radio Access Networks) and MVDS (Multipoint Video Distribution System) bands are presented and compared. Transmission and reflection coefficients were measured as functions of the angle of incidence, using a wideband sounder based on the swept frequency technique. A high precision angular positioning system was built and used in co-ordination with the measurement equipment. The dielectric constants (er) were estimated by comparing values predicted with a multiple successive internal reflection model and measured transmission and reflection coefficients. It has been found that the variation of the dielectric constant value with the frequency does not necessarily follow the same trend for different materials. For example, the measured er for plasterboard presents an increment with frequency (2.02 at 5.8 GHz, 2.5 at 41.5 GHz – measured by the authors –, 2.58 at 59.5 GHz, and 2.81 at 60.2 GHz – given by literature –), while the values for glass follow a wandering pattern (6.06 at 5.8 GHz, 5–10 at 10 GHz, 3.41 at 41.5 GHz, 7.51 at 57.6 GHz, and 5.29 at 60.2 GHz). Moreover, the measured er for a brick wall at 5.8 GHz (3.58) shows differences with values reported at 2 GHz (4.44).

HYPERFLOW: An Efficient Error Control Protocol for Wireless Broadband Access Networks

The subject of this paper is the design and evaluation of an efficient error control scheme for indoor cellular wireless broadband access networks, which can be considered as the wireless extension of a fixed quality-of-service oriented network (e.g., based on the ATM- (asynchronous transfer mode-) protocol). In order to improve the high and time-variant probability of transmission errors, a novel error control scheme is developed. The protocol called HYPERFLOW (Hybrid Partial sElective Repeat ARQ with Flow control) represents an efficient combination of a selective repeat and a Go-Back-N ARQ- (automatic repeat request-) scheme while keeping the implementation complexity within limits. Additionally, it features a flow control mechanism which prevents the channel from being blocked by a user with momentarily high transmission error probability and thus considerably increases the total system throughput. Furthermore, the HYPERFLOW-protocol is combined with an adaptive forward error control code. The resulting type II hybrid ARQ-scheme is based on the principle of incremental redundancy with redundant symbols being sent only when they are required. A realistic model for the fluctuations of the transmission quality is used for the performance evaluation of the HYPERFLOW-protocol. It turns out that the adaptive FEC-based error correction scheme can considerably improve the system performance. The mean transmission delay, for instance, can be reduced by a factor of up to 10 when the FEC-scheme is properly applied.

Study of LMDS Videoconferencing System

LMDS is one kind of fixed broadband wireless access network. It uses radio spectrum between 10GHz and 40GHz to transmit voice, video, and data signals within small cell 3-10 miles in diameter. This paper proposes some key technical scenarios to support videoconferencing services transported on LMDS. Firstly, two kinds of typical LMDS lower layer standards made by DAVIC and 802.16 separately are discussed from the angle of supporting video conferencing services. Then, H.323 is studied and recommended as the standard of LMDS video conferencing system. And some strategies are proposed to support H.323 services on LMDS. After that, IP multicast technology, the key supporting technology of H.323, is studied from the angle of running on LMDS. Scenarios for IGMP, RMTP protocol running on LMDS are suggested and analyzed with Markov network queuing theory. The technical scenarios proposed by this paper make use of the transporting property of LMDS to support LMDS videoconferencing system more effectively.

Measuring, modeling, and characterizing of indoor radio channel at 5.8 GHz

Wide-band indoor radio channel characterization for broadband radio access networks and unlicensed national information infrastructure has been performed at 5.8 GHz, and results are given in this paper. Delay spreads of 8.8 and 17.2 ns and coherence bandwidths of 9.6 and 4 MHz have been found for line-of-sight (LoS) and obstructed line-of-sight (OLoS) situations, respectively. Results have been compared with predictions made using a ray-tracing tool. To get accurate predictions, a good description of the electromagnetic properties of the obstacles present in the environment is needed. Several experiments were made in order to characterize the electromagnetic parameters of six typical building materials. Transmission and reflection coefficients were measured using the free-space technique. A multiple successive internal reflection model was used to estimate the permittivity and conductivity by comparing the measured and predicted values of the coefficients. Several samples of each material were measured, and the results vary from sample to sample. This variation has been characterized by the calculation of confidence bands for the parameters. The influence of both the dielectric parameters and the order of reflections considered in the ray-tracing tool has been analyzed. The effect is reduced on narrow-band predictions but is more important on wide-band parameters as the delay spread. It is shown that the measured delay spread cumulative distribution function falls within the band predicted using the measured maximum and minimum values of permittivity.

Broadband wireless access and future communication networks

This paper presents a vision for wireless communication systems beyond the third generation, which comprises a combination of several optimized access systems on a common IP-based medium-access and core network platform. These different access systems will interwork via horizontal and vertical handover, service negotiation, and global roaming. The different access systems are allocated to different cell layers in the sense of hierarchical cells with respect to cell size, coverage, and mobility to provide globally optimized seamless services to all users. This vision requires extensive international research and standardization activities to solve many technical challenges. Key issues are the global interworking of different access systems on a common platform, the implementation of multimode and multiband terminals and base stations by software-defined radio concepts as well as advanced antenna concepts.

BRAIN?an architecture for a broadband radio access network of the next generation

The tremendous growth rates of the Internet as well as the area of mobile communications give rise to the chance that the mobile Internet is most promising by combining both the Internet and mobile communications. These prospects are the motivation for the European research project BRAIN (Broadband Radio Access for IP-based Networks), which is developing an open architecture for a broadband wireless mobile access network offering an integrated communication platform across heterogeneous networks and, thus, goes beyond current third generation systems and towards the mobile Internet. The project covers three major technical areas: support of seamless service provision in a mobile environment; the design of an IP-based access network that will support non-cellular technologies such as wireless LANs; and requirements of a broadband air interface suitable for hot spots. BRAIN is going to integrate HIPERLAN/2 with UMTS by means of an IP access network. The work is guided by a user-centric top-down approach ensuring that user functionality is the key driver of the project. This article will focus on that part of the BRAIN work which specifies the main interfaces of the BRAIN architecture and deals with aspects related to the support of Quality of Service and mobility. Copyright © 2001 John Wiley & Sons, Ltd.

Contention-free distributed dynamic reservation MAC protocol with deterministic scheduling (C-FD/sup 3/R MAC) for wireless ATM networks

This paper proposes a novel MAC protocol for wireless ATM networks, which is characterized by a contention-free mechanism of the reservation request and a deterministic nature of mobile-assisted (distributed) uplink scheduling under a framework of the dynamic reservation TDMA, as discussed in the current standardization activities of ETSI Project BRAN (broadband radio access network) and the wireless ATM working group in the ATM Forum. The design objective of the proposed MAC protocol is to guarantee the real-time constraint of the real-time VBR (rt-VBR) traffic class while maximizing the multiplexing gain among all ATM traffic classes, especially with a fixed length frame. The proposed deterministic scheduling scheme for the rt-VBR traffic class lends itself to implementing the minimal configuration of control data units for reservation request as desired under the limited wireless resources. Simulation experiments using statistically multiplexed MPEG-2 video streams are performed for a 25 Mbits/s wireless ATM access link scenario. It has been shown that the proposed framework guarantees the delay constraint of rt-VBR sessions along with its cell loss rate significantly reduced, while improving the average delay performance of the nrt-VBR in the range of 10%-30% without compromising the channel utilization as compared to the DSA++ system.

Dynamic channel allocation in wireless ATM networks

During the last few years extensive research has been carried out to extend fixed ATM networks to mobile users. Currently the European Telecommunications Standards Institute (ETSI) is standardising new types of Broadband Radio Access Networks (BRAN): HIPERLAN/2 and HIPERACCESS. In cellular systems like HIPERLAN/2 the aspect of channel allocation plays an important role. In this paper two approaches for channel allocation are introduced and compared with each other concerning the spectrum efficiency and their influence on the implementation of wireless ATM networks and wireless LANs.

Smart antennas for broadband wireless access networks

This article is an overview of smart antenna applications in fixed broadband wireless access networks. Different smart antenna techniques are described including advances such as "spatial multiplexing" that can dramatically increase the performance of BWA networks. The impact of SA techniques on capacity and throughput of BWA networks is discussed.

SDMA techniques for wireless ATM

The introduction of space-division multiple access techniques into wireless ATM systems is presented. The concepts are embedded in the framework of the HIPERLAN/2 system, which is currently under standardization by the ETSI Broadband Radio Access Networks (BRAN) project. HIPERLAN/2 aims at the provision of broadband services with guaranteed QoS. Originally started as a WATM standardization initiative, its scope has been broadened and now aims at core network independence. Essential system functions, such as scheduling algorithms and random access, are reviewed in light of the spatial dimension. To give an impression of their performance, some key results are discussed. Although adopted for HIPERLAN/2, the ideas are generally applicable and can be transferred to various systems.

A wideband two-layer radio access network using DECT technology in the uplink

This article describes a novel architecture of a broadband radio access network using the two-layer network solution. The proposed downlink is compliant with the DVB-S standards, and a DECT custom solution is used in the return channel. The idea we present is based on the use of a single carrier with equalization system in order to directly link the end-user terminal, avoiding the most expensive part of the cabling network: the last mile. The article reports, some considerations concerning the advantages and disadvantages of the novel architecture. Successively, aspects such as frequency plan, architecture of the base station, local repeater, and user terminal, in combination with some practical studies, are discussed.

A broadband wireless access network based on mesh-connected free-space optical links

Driven by the twin forces of industry-wide deregulation and the explosive demand for Internet access and bandwidth-intensive multimedia services, broadband local access has emerged as one of the key issues in modern telecommunications. We describe a broadband local access network consisting of small, densely spaced packet-switching nodes interconnected by focused free-space optical links in a multihop mesh arrangement. Each switch serves a client, which may be an office building (containing, for example, conventional PBXs and LANs), a picocellular base station, or both. It is the responsibility of our local access network to economically and reliably extend broadband local access service (perhaps OC-3 or OC-12 for building LANs and PBXs; perhaps several tens of megabits per second to base stations) from an infrastructure end office or fiber ring add/drop multiplexer without requiring the installation of new buried optical cabling. Computed is the capacity of the multihop mesh, defined to be the maximum number of virtual connections which can be delivered to the infrastructure access point such that, independent of the traffic distribution among clients, all quality of service guarantees are maintained.

HIPERACCESS: an access system for the information age

This paper introduces the ETSI Project on Broadband Radio Access Networks (EP-BRAN). BRAN systems will be used for local-area applications with limited mobility (HIPERLAN/2); fixed access with area coverage in urban and rural areas (HIPERACCESS); and short-range high-speed point-to-point links (HIPERLINK). They will support transport of either IP or ATM protocols, supporting managed quality of service. Such systems are needed to provide access to the future broadband core networks supporting multimedia applications. The paper focuses on HIPERACCESS. It addresses the motivation and market demand for broadband radio access networks; the objectives and scope of the Project; the operational and technical requirements; the types of networks to be standardised; the scope of the standards; and the issue of spectrum.

MAC protocols for wideband wireless local access: evolution toward wireless ATM

The wireless local area network (WLAN) and wireless ATM are emerging technologies for wideband wireless local access. Two standards, IEEE 802.11 and ETSI HIPERLAN type 1, are currently available for WLAN; the standardization process of wireless ATM, involving, among others, the wireless ATM Group of the ATM Forum and the broadband radio access networks project of the ETSI, is ongoing and related standards are expected to be released by mid-1999. This article focuses on the MAC protocol aspects of wireless local access networks. It first investigates, from a traffic performance point of view, the MAC protocol of the IEEE 802.11 and ETSI HIPERLAN type 1 standards, and then verifies to what extent these MAC protocols are suitable for wireless ATM. The analysis is then extended by considering a new MAC protocol, dynamic slot assignment (DSA++), which has been designed to explicitly support ATM technology over the radio interface. DSA++ is a candidate for the ETSI HIPERLAN type 2 standard, a developing ETSI standard for wireless ATM.