Fixed Wireless Access Systems Research Articles

Downlink Cell-Free Fixed Wireless Access: Architectures, Physical Realities, and Research Opportunities

Recently a new paradigm of wireless access, termed as cell-free massive multiple-input multiple-output (MIMO), has drawn significant research interest. Its primary distinction from conventional massive MIMO aided cellular networks is the ability to eliminate the detrimental inter-cell interference (ICI), or to convert ICI into extra power for the intended signal via a multi-cell cooperation approach originated from network MIMO. However, the information-theoretical limit of cell-free access is achieved at the expense of large network configuration overhead and high MIMO processing complexity. Because of the dynamic nature of wireless channels, the global channel state information (CSI) invoked for network MIMO quickly becomes outdated, leading to performance degradation. This paper focuses on the cell-free implementation of fixed wireless access (FWA), a complementary solution to fibre-to-the-premise (FTTP) where the latter is prohibitively expensive. In particular, we discuss the centralisation architectures and channel characteristics of cellfree FWA, as well as their joint implications on imperfect CSI performance. Moreover, measurement-based offline simulations show that the long coherence time ('quasi-static') assumption of real-world FWA channels is only valid against a completely motionless background, and thus it should not be used in FWA system design or performance analysis. Finally, we present new research opportunities for cell-free FWA in terms of physical infrastructure, data processing as well as machine learning.

Planning 5G Networks for Rural Fixed Wireless Access

We study the planning of a rural 5G multi-user massive MIMO fixed wireless access system to offer fixed broadband service to homes. Specifically, we aim to determine the user limit, i.e., the maximum number of homes that can simultaneously receive target minimum bit rates (MBRs) on the downlink (DL) and on the uplink (UL) given a set of network resources and a cell radius. To compute that limit, we must understand how resources should be shared between the DL and UL and how user and stream selection, precoding and combining, and power distribution should be performed. We use block diagonalization and propose a static grouping strategy that organizes homes into fixed groups (of possibly different sizes) in the DL and UL; then we develop a simple approach to compute the user limit that we validate numerically. We study the impact of group size and show that smaller groups yield larger user limits in a 3.5 GHz band. We show how the user limit at different cell radii is impacted by the system bandwidth, the number of antennas at the base station and homes, the transmit power, and the DL and UL MBRs. Lastly, we offer insights into how the network could be operated.

Maximum-Likelihood-Based Location, Orientation, Transmitted Power, and Antenna Beamwidth Estimator Utilizing the Angle-of-Arrival and Received Power for Spectrum Sharing at Millimeter Wave Bands

The fifth-generation (5G) system utilizing millimeter wave is available in Japan, but more bandwidth is demanded by the mobile phone operators to accommodate the demand for high data rate. Allocation of the vacant spectrum is impossible due to the past spectrum allocation to other radio systems. For example, 24.25-27.5 GHz has been allocated for the fixed wireless access (FWA) and license exempt small power data communication system in Japan. Although Japanese government is considering to license a part of the band for 5G under the spectrum sharing scheme, the coexistence design is quite challenging due to unavailable operation data of such systems in a form of database for the coexistence study. For this purpose, this paper introduces a maximum-likelihood estimator (MLE), which utilizes the angle-of-arrival (AoA) and received power of the line-of-sight (LOS)/diffraction paths as well as the map database to simultaneously estimate these unknown parameters via the spectrum sensing. It was applied to the measurement data obtained from a sub-urban environment where a commercial fixed wireless access system with similar operational parameters is under operation. Its performance was evaluated for a different number of receiver (Rx) points. The results showed that the parameter estimation accuracy is proportional to the number of receiver points. The distance and orientation errors of 45 m and 5 deg were achieved at 90th percentile with 40 Rx points. Furthermore, the prediction performance of the effective isotropic radiated power (EIRP) was decent, albeit a slight underestimation of the beamwidth.

Performance Analysis of 5G Fixed Wireless Access Networks with Antenna Diversity Techniques

An increase in the network interconnection has been observed across the world because of multimedia applications and services transmission over the Internet. Nonetheless, a huge number of homes are still experiencing irregular or no broadband connections. Fixed wireless access (FWA) offers an attractive wireless solution for offering multimedia services to various homes compared with fixed-line broadband solutions. However, matching the performance levels of the fixed-line broadband is comparatively demanding for the current access networks. Compared with the fourth-generation (4G) networks, the fifth-generation (5G) technological implementation in FWA is envisioned to give significant enhancements regarding the system capacity, coverage, and connectivity at low-latency. To fulfill the network requirements, 5G systems are anticipated to exploit higher frequency bands. However, radio propagation conditions at higher frequency bands are relatively demanding, owing to the path-loss (PL). In this paper, we discuss different network requirements of the 5G FWA system. Also, a comprehensive overview of the broadband schemes’ technical challenges is presented and we proffer viable solutions for achieving cost-effective and scalable 5G FWA solutions. Moreover, we exploit diversity scheme and present a closed-form expression for the multiple-input, multiple-output scheme in which the PL and beamforming schemes are considered. The accuracy of the proposed closed-form expression is validated by Monte-Carlo simulation over different antenna configurations and signal-to-noise ratios. Based on the presented models, we evaluate and simulate the PL and average transmission rates for different use cases. Simulation results show significant performance improvement compared with a single-input single-output configuration. Apart from being capable of enhancing system performance, the proposed model can be employed for an arbitrary number of transmit and receive antennas. The model is anticipated to pave the way for more robust performance evaluation of multi-antenna-based 5G use cases.

Design and analysis of triple band circular patch antenna

This paper presents a circular slotted patch antenna resonating at three frequencies namely 1.8 GHz, 2.4 GHz and 5.4 GHz. The antenna is fabricated using Roger RT Duroid 5870 substrate having a thickness of 1.5 mm. The multiband behavior is achieved by etching slots on the patch. The measured antenna gains at the three frequencies are 5.5 dBi, 7.8 dBi and 7.9 dBi respectively. This paper extends its contribution by incorporating and discussing the resonation using the higher order modes. The designed antenna is suitable to be used for Global System for Mobile communication (GSM), Wi-Fi applications, Bluetooth, WLAN, Radio Local Area Network (RLAN) and Fixed Wireless Access systems (FWAS).

Evaluating the interference from fixed wireless access TDMA systems into HAPS systems: a probabilistic approach

This study presents a probabilistic model to assess the co-channel interference produced by multiple transmitters of a fixed wireless access network into a high altitude platform stations (HAPS) victim receiver. The authors propose an alternative probabilistic approach that avoids the worst case assumptions usually considered in traditional interference calculation methods, by considering the random modelling of some of the technical parameters involved. More specifically, the geographic positions of fixed wireless access system transmitters are modelled by a two-dimensional point process and their antenna gains in the sidelobe region are modelled as gamma distributed random variables. The proposed method is validated by comparing the minimal operating distance resulting from the traditional deterministic interference calculation methods and that obtained with th proposed approach. Results corresponding to the four possible interfering scenarios indicate that the proposed probabilistic approach leads to a reduction in coordination distances.

Modeling of Dynamic Effect of Vegetation for Fixed Wireless Access System

This paper presents the results of investigation of fixed wireless access performance based on IEEE802.16 standard in wide campus environment. Measurements have been conducted at 5.8 GHz that includes various parameters in different outdoor environments to study the effect of vegetation, street and building. The primary goal of this work is to investigate the performance of received signal strength during daytime and night. Based on the measurement result, small signal deviation recorded for daytime and night. The channel capacity is found varied with environment conditions, wind speed, humidity and temperature. The extent of changes based on blockage is examined as well. The excess loss due to vegetation is ranging from 5.14 to 31.17 dB. Within the research framework, the empirical values obtained are to be scintillated with the statistical models. Henceforth, it is vital to discover the interrelation within the outstanding statistical distributions, such as log-normal, Gaussian, Rayleigh, Rician and Nakagami distributions. In such models, it is found that log-normal distribution best fit the path and excess loss models.

IJIREEICE - Electrical, Electronics, Instrumentation and Control

3 Abstract: The article presents a structure of human shape microstrip patch antenna operating at dual frequencies. In this paper a rectangular patch of human shape cutting is proposed. The human shape antenna is designed for wireless applications, which works at 2.4 GHz and 5.4 GHz frequencies. This proposed antenna can be widely used for Wi-Fi (IEEE 802.11 standard), BLUETOOTH, WLAN, WiMAX (IEEE 802.16 and 802.20 standards. Radio Local Area Networks (RLAN), Fixed Wireless Access Systems (FWA) and NLOS applications.

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.

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.

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.

SIMULATION MODEL FOR COMPATIBILITY OF CO-SITED IMT-ADVANCED AND POINT TO MULTIPOINT SERVICES

GHz fixed wireless access system is a point-to- multipoint wireless technology providing broadband services. In this paper, point-to-multipoint fixed cellular service network structure such as Local Multipoint Distribution (LMDS) service is proposed to share same network area and frequency band (3400-3600 MHz) with the fourth generation of mobile (IMT-Advanced) represented by mobile Worldwide Interoperability for Microwave Access (WiMAX) service on base of co-sited systems. As a result of space and frequency domain sharing, harmful interference probability may be transpired between the two services. Different network cell sizes and different channel bandwidths were considered in dense urban area to investigate the intersystem interference effects based on the average interference to noise ratio INR as a fundamental criterion for coexistence and sharing coordination between different systems. Adjusting of antenna discrimination loss is also proposed to facilitate the frequency efficiency and accomplish frequency sharing.

Service Area Expansion of Quasi-Millimeter FWA Systems Through Site Diversity Based on Detailed Rainfall Intensity Data

Two years of high temporal- and spatial-resolution radar data is used to quantify the rain-attenuation diversity gain available in 26 GHz fixed wireless access systems having sight of the second transmitter. The service area defined by attenuation contours on the least-faded link is determined; the results show that an expansion of the service area is possible even over short paths. Service area contours with and without diversity are derived from radar observations of rainfall rate. Good agreement is obtained with similar results for a statistical model based on a gamma probability distribution and a negative-exponential spatial correlation function for rain rate (which are shown to fit observed data). For the service area defined by a bit error rate of 10-4 and availability of 4 times 10-1, site diversity expands the service area by up to 20% with a 10 km access point spacing.

Spectrum emission mask for coexistence between future WiMAX and existing fixed wireless access systems

This paper introduces a new coexistence study of the future WiMAX system and existing fixed wireless access (FWA) systems and investigates its feasibility. Spectrum emission mask as an interference mitigation technique is used as well as interference to noise ratio (I/N) of -6 dB as one of standard sharing criterion value at FWA systems recommended by international telecommunication union radio sector ITU-R. Three channel bandwidths of (3.5, 7, and 10 MHz) of WiMAX system in the band 3500 MHz are selected to be studied with 7 MHz FWA channel in dense urban area. All parameters of the two systems are presented and methodology is explained. It is well known that frequency distance rules are an important of frequency coordination process in most radio services, so frequency and distance separations are determined and analyzed for both terms co-channel interference and adjacent channel interference in the different interference scenarios which are supposed. This coexistence and spectrum sharing study is considered as an initial step toward beyond 3G or IMT-Advanced coexistence with FWA systems.

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.

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.

Route diversity effect on multipoint‐to‐multipoint (MP‐MP) fixed wireless systems with mesh network topologies recommended in ITU‐R F.1704

AbstractBroadband fixed wireless access (FWA) systems using submillimeter and millimeter bands are expected to function as large‐capacity access circuits supplementing wired broadband access networks. However, a major issue in handling high‐frequency bands such as the submillimeter and millimeter bands has been deterioration of circuit quality due to rain attenuation and the resulting degradation of operating efficiency. In order to deal with this issue, the authors proposed a multipoint‐to‐multipoint (MP‐MP) FWA system using a mesh topology that organically combines point‐to‐point (P‐P) wireless links, and quantitatively showed a diversity effect obtained on the mesh network to demonstrate the validity of the system. The proposed system was recommended for use as F.1704 by the ITU‐R (International Telecommunication Union‐Radiocommunication Sector), which promotes research into standardization of wireless communications and prepares recommendations. In this paper, we give theoretical evaluations of the diversity effect that formed the core of the recommendation, and present evaluation examples based on real data obtained from outdoor test networks, to demonstrate the validity of the diversity effect in the proposed system. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 61–70, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20334

A Proposal of Simplified Viterbi Equalizer Applied to FWA Systems Employing 64QAM Signals

We propose a novel simplified Viterbi equalizer for high symbol rate FWA (Fixed Wireless Access) systems carrying 64QAM signals. Reduced complexity and improved performance are achieved adopting two approaches. The first one is reducing the number of survival paths, taking advantage of the large D/U common in LOS (line of sight) communications. The second one is using a multi-stage process to generate desired signal replicas based on their likelihoods. Computer simulations confirm that the proposed replica generation method offers a performance improvement of about 1 dB and the proposed Viterbi equalizer offers reduced complexity with no performance penalty compared to full Viterbi equalizer.