Broadband Fixed Wireless Access Research Articles

Using WiMAX to Improve Volcano Monitoring during an Emergency: A Feasibility Study of the WEIRD System Applied to the Campi Flegrei Volcanic Area Scenario (Southern Italy)

IEEE Standard for Local and Metropolitan Area Networks (hereafter IEEE 802.16; online at http://standards.ieee.org/getieee802/802.16.html) is one of the most promising mobile and fixed broadband wireless access technologies for next-generation all-IP networks in the 3.5 GHz band (European spectrum profile). Commonly known as Universal WiMAX (worldwide inter-operability for microwave access), this access technology reaches a high bit rate and covers large areas with a single base station, making it possible to offer connectivity to end users in a cost-effective way. A further useful property of the WiMAX technology is that the transmission can be used both in line-of-sight (LOS) and non-line-of-sight (NLOS) environments, allowing highly feasible communications (WiMAX Forum 2004). Thanks to these features, IEEE 802.16 opens the way to the use of wireless technologies in the environmental monitoring of areas such as seismic and volcanic zones. Volcanic eruptions, in particular, are among the highest natural risks in the world. About 600 volcanoes have erupted in historical times, and many are located near densely populated areas. An adequate monitoring system is essential to understanding the physical processes preceding an eruption and for mitigating the risk of such an event. Active volcano surveillance is primarily based on the analysis of geophysical and geochemical parameters gathered by monitoring networks. Seismological methods are among the most useful methods for monitoring volcanoes. In fact, several types of seismic signals, e.g. , volcano-tectonic earthquakes (VT), long-period events (LP), and volcanic tremors, can occur before and during an eruption (McNutt 2005). The analysis and interpretation of these seismic signals is a very important task for volcanic eruption forecasting. WiMAX technology can be applied to provide broadband wireless access in volcano monitoring scenarios to solve some of the problems that prevent us from improving surveillance of volcanic activities during emergencies. In particular, this paper focuses on a novel …

On the applicability of MIMO principle to 10-66GHz BFWA networks: capacity enhancement through spatial multiplexing and interference reduction through selection diversity

This paper investigates the applicability of multiple-input-multiple-output (MIMO) technology to broadband fixed wireless access (BFWA) systems operating in the 10-66 GHz frequency range. In order to employ the MIMO principle at these frequencies, the spatial channel benefits that may arise from the rainfall spatial inhomogeneity are more relevant since multipath is insignificant. Therefore, a special MIMO/BFWA channel may be implemented if every subscriber is equipped with multiple antennas and communicates with multiple base stations. The exact relationship between conventional MIMO and the proposed 10-66 GHz MIMO/BFWA channels is established. Then, emphasis is put on two different topics from the field of MIMO applications: (i) capacity enhancement for spatial multiplexed MIMO/BFWA systems; and (ii) interference reduction for MIMO/BFWA diversity systems employing receive antenna selection. More specifically, in the first case, a communication-oriented single-user capacity analysis of a 2 times 2 MIMO/BFWA spatial multiplexing system is presented, the relevant optimal power allocation policy is explored and useful analytical expressions are derived for the outage capacity achieved in the asymptotically low and high SNR regions. The effect of feedback on the capacity is investigated and quantified through Monte Carlo simulations. In the second case, a 2 times 2 MIMO/BFWA diversity system with receive selection combining is considered and its efficiency to mitigate intrasystem/intersystem cochannel interference over the downstream channel is studied from a propagation point of view. A general analytical prediction model for the interference reduction obtained by such a 2times2 MIMO/BFWA diversity system is presented along with a numerical validation.

Packet error statistics of LOS broadband fixed wireless access channels

In broadband fixed wireless access (BFWA) networks mainly operating above 20 GHz, a clear line-of-sight (LOS) path is necessary between the base stations (BS) and the subscribers (S). In this letter, a Markov-based method to estimate the packet loss rate (PLR) statistical characteristics over a dynamically, due to propagation, varying LOS BFWA channel is presented. The method is verified by means of information theoretic metrics and tested against simulation results.

FADE MARGINS PREDICTION FOR BROADBAND FIXED WIRELESS ACCESS (BFWA) FROM MEASUREMENTS IN TROPICS

The fade margins for 15, 23, 26 and 38GHz frequency bands are predicted based on one-minute rain rate measurements for four years at Universiti Teknologi Malaysia (UTM) Skudai and the speciflcations of the given four MINI-LINKS. The availabilities of terrestrial microwave links are also investigated based on rain attenuation data collected from seven operational microwave links at 15GHz and one at 23GHz for more than one year. The fade margins for all eight links are measured based on the rain attenuation data collected with difierent hop lengths. In this paper, the feasibility to design outage-free wireless broadband radio link also highlighted. These results will contribute to the better design of outage-free Broadband Fixed Wireless Access (BFWA) system such as, Local Multipoint Distribution Service (LMDS) and IEEE802.16 in tropical regions.

Broadband wireless real time communication

Today's Internet access technologies are not able to provide broadband connectivity to all areas in a cost-effective way for telecom operators. Wired technologies still require a noteworthy investment in cabling infrastructures, whereas wireless access technologies cannot deliver high-speed connections to several users simultaneously. To address this issue, a very interesting solution has been defined by the IEEE 802.16 working group, in particular the IEEE 802.16-2004 and IEEE 802.16e-2005 standards. IEEE 802.16-2004 is a fixed broadband wireless access technology, capable to provide high data rate connections over large areas.

Optimal placement and channel assignment of relay stations in heterogeneous wireless mesh networks by modified Bender’s decomposition

Fixed Broadband Wireless Access (FBWA) technology is designed to serve as a wireless DSL replacement to provide broadband Internet access in underserved areas where no other access technology exists. Due to the enormousness of the target service area, relay equipment play an important role in such networks, and the installation and maintenance cost of the network is directly proportional to the cost of the relay equipment. To minimize the network operational cost, an optimization framework which computes the minimum number of relay stations and their corresponding placements and channel assignments in the network is desired. Because the problem is NP-hard, we propose an efficient optimization algorithm based on a modified version of Bender’s decomposition to iteratively compute converging bounds to the problem solution. Our numerical results show that by using a few relay stations in a rural community, broadband Internet access can be established in a cost effective manner.

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.

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.

Co-channel interference effects as applied to broadband fixed wireless access channel capacity statistical distribution

Channel Capacity is of primary importance in broadband fixed wireless access (bfwa) networks due to the ever increasing demand for multimedia services and the possibility of providing wireless Internet. One of the major factors limiting capacity in such systems is interference originating from adjacent terrestrial applications belonging to the same bfwa network or to another. Moreover, the performance of broadband fixed wireless access links operating above 10 GHz is predominantly controlled by rain attenuation. The purpose of this paper is the presentation of a physical model for the evaluation of the fraction of the time where the capacity distribution of a broadband fixed wireless access channel under rain fade conditions suffering from co-channel interference, non-exceeds a specified level in (bps/Hz). The proposed analysis examines the capacity distribution properties focusing on the spatial inhomogeneity of rainfall medium. The impact of various operational and geometrical parameters on the performance of interfered broadband wireless access channel capacity distribution is investigated through extended simulations.

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.

Data Transmission over Rain-Faded Broadband Fixed Wireless Access Channels

The performance evaluation of communication protocols in broadband fixed wireless access (BFWA) networks needs the accurate description of the statistical properties of the packet error process. In BFWA networks mainly operating above 20 GHz, a clear line-of-sight (LOS) path is necessary between the base stations (BS) and the subscribers (S). Rain attenuation is the dominant fading mechanism at these frequencies. In this paper, a Markov- based method to estimate the packet loss rate (PLR) performance over a dynamically, due to propagation, varying LOS BFWA channel is presented and tested against simulation results. The proposed method is based on the first- order Markovian modeling of the rain attenuation process. The proposed method can serve as a performance evaluation tool of various modulation and coding schemes (MCS) and is also applicable even when adaptive fade mitigation techniques are employed in the BFWA network.

Rain Scatter Interference in mm-Wave Broadband Fixed Wireless Access Networks Caused by a 2-D Dynamic Rain Environment

The classical Mie scattering theory together with the bistatic radar equation has been applied in this paper to quantify interference levels in broadband fixed wireless access (BFWA) for two different network topologies: mesh and cellular. The complete scattering analysis takes into account the realistic variations of rainfall along the propagation paths and inside the common volume. The interfering element is a rain cell model that follows closely the experimental characteristic dimension, decay and movement obtained in recent research by the authors. The signal-to-interference power ratios (S/I) for two different frequencies, 28 and 42 GHz, and several scattering angles have been calculated. They show that, when two beams cross each other, rain-induced interference must be taken into account for an efficient planning of radio communication systems operating at these millimeter-wave frequencies as well as for an adequate design and implementation of fade mitigation techniques.

Comparison of Convolutional and Turbo Coding for Broadband FWA Systems

It has been demonstrated that turbo codes substantially outperform other codes, e.g., convolutional codes, both in the non-fading additive white Gaussian noise (AWGN) channel as well as multiple-transmit and multiple-receive antenna fading channels. Moreover, it has also been reported that turbo codes perform very well in fast fading channels, but perform somewhat poorly on slow and block fading channels of which the broadband fixed wireless access (FWA) channel is an example. In this paper, we thoroughly compare the performance of turbo-coded and convolutional-coded broadband FWA systems both with and without antenna diversity under the condition of identical complexity for a variety of decoding algorithms. In particular, we derive mathematical expressions to characterize the complexity of turbo decoding based on state-of-the-art Log-MAP and Max-Log-MAP algorithms as well as convolutional decoding based on the Viterbi algorithm in terms of the number of equivalent addition operations. Simulation results show that turbo codes do not offer any performance advantage over convolutional codes in FWA systems without antenna diversity or FWA systems with limited antenna diversity. Indeed, turbo codes only outperform convolutional codes in FWA systems having significant antenna diversity.

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

On the Coexistence of DS-UWB Systems with Wi-Max/IEEE-802.16 Based Systems

In this paper the coexistence issue between the DS-UWB systems and Wi-Max/IEEE-802.16 based Fixed Broadband Wireless Access (FBWA) systems has been investigated. The aim is to evaluate the impact that the interference resulting from a realistic UWB hot spot scenario may have on the performance of a FBWA receiver. A mathematical model is developed through which the interference power produced by the UWB hot spot can be calculated. The benchmarks against which the UWB interference is assessed are also developed using the specifications of Wi-Max/IEEE-802.16 systems. Several simulations have been done to both validate the analytical results and calculate the UWB interference. In doing so, the effects of parameters like victim receiver bandwidth, carrier frequency, activity factor, the number of users and the distance from victim receiver in a realistic hot spot scenario have been studied.

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.

Characterization of Line-of-Sight MIMO Channel for Fixed Wireless Communications

In this letter, we proposed an approach to construct multiple-input-multiple-output (MIMO) channel in line-of-sight (LOS) environment. It could be a potential technique for high-speed data transmission in fixed broadband wireless access (BWA). Based on Ricean fading channel model, our research is focused on the characteristics of the channel matrix such as the condition number. The initial discussion starts from a 4 times 4 MIMO scheme that the four antennas formed a square array on each side. A design constraint for antenna arrangement as a function of frequency and distance is derived for the LOS MIMO communication. Since rigorous constraint is difficult to achieve in practice, simulation results of the acceptable deviation from optimal design in different cases are presented. Smart geometrical arrangement and multipolarization may also weaken this constraint

Characterization and Modeling of BFWA Channels in Outdoor--Indoor Environments

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter presents the experimental characterization and modeling of the radio channel for outdoor-indoor communications, within the framework of broadband fixed wireless access (BFWA) systems. Five models based on tapped delay lines have been proposed. These models provide a good fit of the measured rms delay spread. The time delay values are considerably lower than the typical values for outdoor channels in urban and suburban environments. In quasi-line-of-sight (LOS) situations, it is not necessary to distinguish between open and closed environments, while this is necessary in the case of NLOS and hard-NLOS situations. </para>

Empirical analysis of a 2 x 2 MIMO channel in outdoor-indoor scenarios for BFWA applications

The unquestionable advantages of multiple-input multiple-output (MIMO) systems are having a strong influence on the development of new wireless systems, both in wireless local-area networks (WLANs), and in those designed to offer broadband fixed wireless access (BFWA) services in wireless metropolitan-area networks (WMANs). The MIMO channel characterization in different environments and for different operating frequency bands is a crucial factor in the design of new systems and standards, and for adequate planning of existing systems. This article makes two main contributions. First, the experimental characterization of a 2 times 2 MIMO channel at a frequency of 2.4 GHz in a canonical outdoor-indoor scenario is presented. The channel characterization performed includes the analysis of the spatial correlation between the MIMO system subchannels and its impact on the channel capacity. Second, on the basis of the capacity results obtained, a proposal is made for the use of a 2 times 2 MIMO system in outdoor-indoor scenarios for BFWA applications in metropolitan environments. The proposal is based on the experimentally verified hypothesis that the path loss due to building penetration can be practically compensated for by the diversity gain of 2 times 2 systems

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