Broadband Fixed Wireless Access Systems Research Articles

Experimental distribution functions for analysis of coherence bandwidth fluctuations for a fixed broadband wireless access system

In this study the authors propose three methods of analysis in order to develop an in-depth study of the temporal or spatial coherence bandwidth fluctuations in a real environment. Firstly, the authors review the classical coherence bandwidth (CB) estimation that offers constant single values under the assumption of an ergodic radio channel model. Secondly, the authors introduce the estimation of the experimental cumulative distribution function for CB as a method to characterise and parameterise the fluctuations that this frequency channel parameter can undergo in real environments where the ergodicity condition cannot be fully ensured. Finally, the authors estimate the probability distribution functions regarding the correlation level α in order to determine the operations quality to be expected of a specific channel bandwidth. The CB trial values are the result of experimental measurements conducted in diverse scenarios which used different antenna pattern and polarisations within the frequency band of 40 GHz. The proposed statistical analysis reveals important information about this channel parameter that can determine the accurate design and performance of a broadband system operating within this spectrum region; besides, this method can also be extrapolated to other frequencies.

Climate-Driven Fuzzy Inference System for Downlink Power Control in CDMA Millimeter Wireless Access Networks

Broadband Fixed Wireless Access (BFWA) systems operating at millimeter frequencies and using orthogonal direct sequence code division multiple access (DS-CDMA) have been proposed as an alternative technology for the enhancement of the network capacity. The major limiting factors of the capacity are the propagation phenomena (rain attenuation for frequencies above 10GHz) and intercell interference. Several power control schemes have been proposed to mitigate these factors and decrease the outage time. In this Letter we propose a new Climate-Driven Fuzzy Inference System for downlink power control with engineering inputs such as the rain induced attenuation on the wanted and the interfering links, the deterministic path loss and the clear-sky carrier-to-interference ratio. The proposed FIS scheme has different parameters based on the statistics of rain rate and is more energy efficient. Numerical calculations highlight the superiority of the proposed downlink power control compared to existing schemes.

A Comparison Study for the BER in Broadband Fixed Wireless Access Systems Based on Using M-QAM

An analytical model for the bit error rate with different values of M-ary quadrature amplitude modulation (M-QAM) for broadband fixed wireless access (BFWA) is presented. The expressions/relations are derived and investigated for different values of M: 4, 8, 16, 32, 64, 128, and 256 to evaluate conditional probability of error, bit error probability and average of the probability of error. The analyses are presented for coherent and non-coherent detection schemes and comparisons between their performances are given. The achieved results show that with keeping a fixed amount of symbols energy for all considered levels/symbols the degradation in BER is remarkable with low SNR with using non-coherent detection compared with utilizing coherent one for all M-ary values. Also, less power is needed in order to achieve the same BER with utilizing non-coherent detection method.

Computation of Bit-Error Rate of Coherent and Non-Coherent Detection M-Ary PSK With Gray Code in BFWA Systems

In this paper we examined the broadband fixed wireless access (BFWA) systems by coherent and non-coherent detection using M-ary PSK with Gray code. A closed form for the exact symbol error rate and bit error rate (BER) of M-ary PSK is presented. We show through analysis the physical limitations of the BFWA channels over different values of M (2,4,8,16,32) and the performance difference between the two type of detection (coherent and non-coherent).

Empirical Analysis of Broadband 2×2 MIMO Channels in Outdoor-Indoor Scenarios

This paper presents the experimental characterization of a wideband 2×2 MIMO channel in typical indoor-outdoor scenarios in the 3.5 GHz band. The transmitter array emulates a base station positioned on the terrace of a building, and the receiver array, situated inside a nearby building, represents the end-user terminal. In a previous work, the authors analyzed the advantages attainable with a 2×2 MIMO channel compared to a SISO channel for the case of narrowband wireless systems in these types of environments without line-of-sight (NLOS). The new results for the wideband channel show that as in the narrowband case, the capacity degradation due to penetration losses can be practically compensated for by the gain of a 2×2 MIMO channel. Furthermore, the frequency diversity attainable in the case of wideband systems appears as a new contribution, reinforcing the conclusion obtained for the narrowband case. This paper also presents a stochastic 2×2 MIMO wideband channel-modeling method that represents a novel simplification with respect to other wideband MIMO models. The resulting models are accurate, but also easy to implement and computationally efficient, Using this method, outdoor-indoor channel models are obtained from a measurements campaign on real MIMO channels in different environments. The empirical data and the models presented in the paper will be very useful in the deployment of future and present broadband fixed wireless-access systems (BFWAS).

Combined Dynamic Channel Simulator for High Capacity Broadband Fixed Wireless Access Systems

We present a time dynamic channel simulator for broadband fixed wireless access systems which properly combines earlier reported models for single degradation effects. The wideband model combines the effect of rain, scintillation, vegetation and multipath propagation. The objective is to specify the relationship between propagation effects and combine them to construct a comprehensive channel model suitable for designing fade mitigation techniques and evaluating system performance. The dynamics of rain attenuation is done using the Maseng-Bakken model. The multipath propagation is modeled using the geometrical based single bounce elliptical channel model. The spatial correlation between multipath taps during rain is incorporated using a space-time rain attenuation model. A lowpass filter which models the power spectral density of scintillation is used to describe the dynamic characteristics of scintillation. The signal fading due to swaying vegetation is described by utilizing a multiple mass-spring system to represent a tree and a turbulent wind model. In addition, numerical results under different combinations of propagation impairments are presented.

Planning of Efficient Wireless Access with IEEE 802.16 for Connecting Home Network to the Internet

The emergence of IEEE802.16 wireless standard technology (WiMAX) has significantly increased the choice to operators for the provisioning of wireless broadband access network. WiMAX is being deployed to compliment with xDSL in underserved or lack of the broadband network area, in both developed and developing countries. Many incumbent operators in developing countries are considering the deployment of WiMAX as part of their broadband access strategy. This paper presents an efficient and simple method for planning of broadband fixed wireless access (BFWA) with IEEE802.16 standard to support home connection to Internet. The study formulates the framework for planning both coverage and capacity designs. The relationship between coverage area and access rate from subscriber in each environment area is presented. The study also presents the throughput and channel capacity of IEEE802.16 in different access rates. An extensive analysis is performed and the results are applied to the real case study to demonstrate the practicality of using IEEE 802.16 for connecting home to Internet. Using empirical data and original subscriber traffic from measurement, it is shown that the BFWA with IEEE802.16 standard is a capacity limited system. The capacity of IEEE802.16 is related to different factors including frequency bandwidth, spectrum allocation, estimation of traffic per subscriber, and choice of adaptive modulation from subscriber terminal. The wireless access methods and procedures evolved in this research work and set out in this paper are shown to be well suited for planning BFWA system based on IEEE802.16 which supports broadband home to Internet connections.

Performance-complexity tradeoff of convolutional codes for broadband fixed wireless access systems

In this study, the authors investigate the performance-complexity tradeoff of convolutional codes for broadband fixed wireless access systems by considering the effects of quantisation and path metric memory in practical Viterbi decoding implementations. They show that in systems with limited antenna diversity, low-memory codes achieve a better error-rate performance compared to that of high-memory codes. Only in systems with considerable antenna diversity, can the performance of a convolutional code be improved by increasing its memory size. Nevertheless, the authors demonstrate that the coding advantage offered by the high-memory codes is not large enough to justify the significant increase in implementation complexity. In particular, memory-2 convolutional codes achieve a coding gain of up to 1.2 dB over their memory-8 counterparts in single-input single-output fixed wireless access systems. The situation is reversed when multiple antennas are used, but the decoder of memory-8 codes occupies at least 130 times more silicon area than that of memory-2 codes.

Adaptive terminal to base station assignment in BFWA systems

In point-multipoint systems the signal to interference plus noise ratio highly depends on the assignment of terminal stations (TS) to base stations (BS). The Broadband Fixed Wireless Access (BFWA) systems operate at high carrier frequencies. In this frequency range wave propagation is highly influenced by precipitation. Applying site diversity can mitigate rain attenuation effects. Present contribution provides a special site diversity method adopting genetic algorithm to adaptively optimize TS-BS assignments from point of view of the interference in BFWA service area. Rain events are generated with a Markov modeled simulation of the rain cell translations.

Performance comparison of low density parity check codes using square root Kalman equalisation and orthogonal frequency division multiplexing techniques for broadband fixed wireless access systems

Broadband fixed wireless access (BFWA) systems enable services such as high-speed data communication, high quality voice/video conferencing and high-speed internet access in areas where a wired link is not possible. However, the BFWA channel is a slow-fading channel having deep frequency-selective fading caused by clusters of scatterers in the environment that introduce inter-symbol interference (ISI) at the receiver. Low density parity check (LDPC) codes, optimised for the single-input single-output BFWA channel, are designed using the structured balance incomplete block design method. The use of both quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM) are investigated theoretically. To help overcome the ISI effects of the channel, equalisation techniques are employed separately with LDPC decoding for a system employing QPSK and 16-QAM modulation schemes. The equaliser single carrier approach is then replaced with orthogonal frequency division multiplexing (OFDM) and the performance of these two approaches is evaluated in terms of bit-error rate. The simulation results show that equalisation with LDPC coding has a measurable performance gain over LDPC coding with OFDM.

Channel-Aware Scheduling for QoS and Fairness Provisioning in IEEE 802.16/WiMAX Broadband Wireless Access Systems

In the last few years, standardization activities within the IEEE 802.16 Working Group have resulted in the publication of specifications for an air interface of Fixed broadband wireless access systems. WiMAX is the commercial name of products compliant with the approved IEEE 802.16 standard. Although the standard suggests the main principles in designing a QoS architecture to support multimedia broadband services, implementation details are left to manufacturers. This article addresses a channel-aware scheduling algorithm conceived for a point-to-multipoint WiMAX architecture. It aims at enabling downlink traffic delivery with differentiated service treatment, even in nonideal channel conditions. A technique to compensate for channel errors is proposed to preserve QoS and fairness of a WF2Q+ based scheduling algorithm. The performance behavior of the proposed algorithm is confirmed by the outputs of a comprehensive simulation campaign.

Rician K-Factor Distribution in Broadband Fixed Wireless Access Channels under Rain Fades

The performance of broadband fixed wireless access (BFWA) systems operating at frequencies above 10 GHz is adversely influenced by rainfall, which introduces severe attenuation and a short-term variation to the received signal. In this letter, the fading channel of a BFWA link is modeled as Rician with a strong Rician K-factor. A novel analytical model relating the Rician K-factor with the rain fading effects is presented based on which, an analytical prediction model for the cumulative distribution of the Rician K-factor is derived. Experimental data is necessary to validate the proposed models. The presented methodology provides an efficient way to incorporate the mathematically intractable physical input of rain fading into the easy-to-simulate Rician channel model. The proposed models can be applied on a global scale and incorporate the impact of various crucial operational and geometrical parameters of a BFWA system on the wideband multipath behavior of the channel. Useful numerical results regarding the validity of the presented models are also provided

Theoretical performance analysis of single and multiple antenna BFWA systems

The systems under investigation are broadband fixed wireless access (BFWA) systems operating in multipath fading channels. Conventional detection methods, for example, coherent detection for single-input single-output systems and the Alamouti algorithm for multiple-input multiple-output systems are examined theoretically and shown to yield unsatisfactory performance. The theoretical analyses are validated by Monte-Carlo simulations and are demonstrated to be accurate. The asymptotic performance of the space–time block coded (STBC) system with the–Alamouti transmission scheme is also evaluated. However, the results indicate that the performance lower bound cannot be obtained in an uncoded system due to the error propagation problem, which can be tackled by concatenating the STBC system with an outer channel code and applying the turbo processing principle. Theoretical performance analysis provides an insight into the physical limitations imposed by BFWA channels and suggest solutions to improve the capacity and performance of future BFWA systems.

A Radio Resource Allocation Scheme for Fixed Broadband Wireless Access Systems with Avoidance of Major Interferers

An improved radio resource allocation scheme with avoidance of major interferers is proposed and analyzed for the downlink of Fixed Broadband Wireless Access (FBWA) systems with full frequency reuse. The scheme is based on Enhanced Staggered Resource Allocation (ESRA) and permits the enhancement of the throughput per sector. Simulation results show a maximum downlink throughput per sector in excess of 44% and an increase of 10% with respect to ESRA is achieved, with Base Station (BS) selection procedure, while meeting a 15 dB signal-to-interference ratio (SIR).

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”

Analysis and performance evaluation of the OFDM-based metropolitan area network IEEE 802.16

Wireless last mile technology is becoming a challenging competitor to conventional wired last mile access systems like DSL and cable modems or even fiber-optic cables. The Institute of Electrical and Electronics Engineers has developed a standard for fixed broadband wireless access systems namely IEEE 802.16. Its OFDM mode targets frequency bands below 11 GHz. This paper gives an overview of the OFDM-based transmission mode of the IEEE 802.16 standard. The medium access control (MAC) and the physical layer are described in detail. Especially the MAC frame structure is elaborated. An analytical performance evaluation of an example scenario is performed which results in overall system performance measures. Especially the interaction of fragmentation and padding of OFDM symbols and its effect on the system capacity is evaluated. Furthermore, different MAC layer configurations with different levels of robustness are analyzed. Optional features to resist challenging channel conditions are outlined. Their trade off, i.e., a reduced MAC layer capacity is pointed out. It is shown that the system can be optimized while maintaining the necessary robustness against environmental challenges. A prototypical IEEE 802.16 protocol stack including a sophisticated channel model has been implemented. By means of this stochastic event-driven computer simulator, downlink and uplink delay as well as throughput evaluation is performed. Thus, performance results based on meaningful MAC configuration examples are provided. Simulative and analytical results are compared.

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.

A proposal of multihop mesh network architecture featuring adaptive network control for broadband fixed wireless access systems

AbstractAs a means of flexibly providing large‐capacity access infrastructure at a low cost, the broadband fixed wireless access (BFWA) system using millimeter‐wave and quasi‐millimeter‐wave frequencies is promising. In general, wireless channel quality variations are significant due to rainfall in wireless systems using millimeter‐wave and quasi‐millimeter‐wave frequencies. Hence, deterioration of the channel working rate is a problem. In this paper, a multihop wireless access system with a mesh configuration is proposed that can deploy a millimeter‐ and quasi‐millimeter‐wave BFWA system at a high quality and a high density. In the proposed system, deterioration of the channel working rate due to wireless channel quality variations is avoided. In addition, the capacity is maximized by adaptively assigning the network resources for variations of the traffic demand and wireless channel transmission capacity. Further, as an adaptive control used in the proposed system, wireless channel assignment for a wireless link and load distribution among several paths within the mesh network are discussed. The problem is formulated as a mixed nonlinear optimization problem. In addition, a heuristic solution is proposed for solving the problem within a realistic time for a network of the anticipated size. The proposed algorithm is applied to a mesh network and the behavior and the performance of the algorithm are evaluated to prove its effectiveness. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 22–33, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10133

Coverage enhancement methods for LMDS

The upper SHF and EHF radio bands (above about 20 GHz) offer abundant available bandwidth for access to metropolitan area networks by fixed broadband wireless access (FBWA) systems. However, these systems must withstand significant propagation impairments, especially shadowing by obstacles and rainfall attenuation. We describe the results of propagation measurements and modeling of coverage, and consequences for FBWA system design, notably antenna placement, use of repeaters, and diversity. High (> 90 percent) coverage generally requires line-of-sight placement, although some non-line-of-sight coverage is possible for short distance and with judicious use of repeaters and macrodiversity.