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     

Capacity and delay of hybrid wireless broadband access networks

An optical network is too costly to act as a broadband access network. On the other hand, a pure wireless ad hoc network with n nodes and total bandwidth of W bits per second cannot provide satisfactory broadband services since the pernode throughput diminishes as the number of users goes large. In this paper, we propose a hybrid wireless network, which is an integrated wireless and optical network, as the broadband access network. Specifically, we assume a hybrid wireless network consisting of n randomly distributed normal nodes, and m regularly placed base stations connected via an optical network. A source node transmits to its destination only with the help of normal nodes, i.e., in the ad hoc mode, if the destination can be reached within L (L /spl geq/ 1) hops from the source. Otherwise, the transmission will be carried out in the infrastructure mode, i.e., with the help of base stations. Two transmission modes share the same bandwidth of W bits/sec. We first study the throughput capacity of such a hybrid wireless network, and observe that the throughput capacity greatly depends on the maximum hop count L and the number of base stations m. We show that the throughput capacity of a hybrid wireless network can scale linearly with n only if m = Ω(n), and when we assign all the bandwidth to the infrastructure mode traffics. We then investigate the delay in hybrid wireless networks. We find that the average packet delay can be maintained as low as Θ(1) even when the per-node throughput capacity is Θ(W).     

Optimized bandwidth allocation in broadband wireless access networks

Towards satisfying the requirements of International Mobile Telecommunications–Advanced, both the Institute of Electrical and Electronics Engineers (IEEE) and Third Generation Partnership Project (3GPP) introduced revolutionary wireless technologies, exploiting advanced technologies and architectures. Both IEEE's 802.16 (Worldwide Interoperability for Microwave Access (WiMAX)) and 3GPP's Long Term Evolution have been introduced to accommodate the increasing demand for mobile services and applications. To realize the true potential of these technologies, however, opportunistic frameworks for radio resource management must be designed to exploit the adaptive nature of mobile traffic. The utility optimized quality‐of‐service (QoS) framework proposed in this paper for the mobile WiMAX networks achieves this objective. To maintain support for QoS guarantees, the framework capitalizes on the adaptive nature of WiMAX traffic by individually linking connections with a utility function designed to both uphold the end users’ perceived performance and determine bandwidth allocations by a search tree maximization algorithm. In doing so, bandwidth utilization is maximized for all active connections, and blocking and dropping probabilities for new and handover calls, respectively, are minimized. The framework is evaluated through an extensive simulation model and is shown to outperform state‐of‐the‐art solutions. Copyright © 2014 John Wiley & Sons, Ltd.     

Capacity analysis of reservation-based random access for broadband wireless access networks

In this paper we propose a novel model for the capacity analysis on the reservation-based random multiple access system, which can be applied to the medium access control protocol of the emerging WiMAX technology. In such a wireless broadband access system, in order to support QoS, the channel time is divided into consecutive frames, where each frame consists of some consequent mini-slots for the transmission of requests, used for the bandwidth reservation, and consequent slots for the actual data packet transmission. Three main outcomes are obtained: first, the upper and lower bounds of the capacity are derived for the considered system. Second, we found through the mathematical analysis that the transmission rate of reservationbased multiple access protocol is maximized, when the ratio between the number of mini-slots and that of the slots per frame is equal to the reciprocal of the random multiple access algorithm?s transmission rate. Third, in the case of WiMAX networks with a large number of subscribers, our analysis takes into account both the capacity and the mean packet delay criteria and suggests to keep such a ratio constant and independent of application-level data traffic arrival rate.     

Training sequence design for frequency offset and frequency-selective channel estimation

We consider the problem of data-aided frequency-offset and channel estimation in the case of frequency-selective channels. More precisely, we address the problem of training sequence selection with the goal of providing accurate frequency offset and channel estimates. Toward this end, we consider the Crame/spl acute/r-Rao bound (CRB), for which we derive a closed-form expression. Since the CRB is a complicated function of the training sequence and the channel parameters, a much simpler asymptotic CRB is derived. Two criteria for training sequence design based on the asymptotic CRB are proposed, and a minmax approach is presented to optimize them. Our main contribution is to show that a white sequence is minmax optimal for both criteria considered, and that the quest for a generally optimal sequence is hardly motivated.     

Network-assisted diversity for random access wireless networks

A novel viewpoint to the collision resolution problem is introduced for wireless slotted random access networks. This viewpoint is based on signal separation principles borrowed from signal processing problems. The received collided packets are not discarded in this approach but are exploited to extract each individual user packet information. In particular, if k users collide in a given time slot, they repeat their transmission for a total of k times so that k copies of the collided packets are received. Then, the receiver has to resolve a k×k source mixing problem and separate each individual user. The proposed method does not introduce throughput penalties since it requires only k slots to transmit k colliding packets. Performance issues that are related to the implementation of the collision detection algorithm are studied. The protocol's parameters are optimized to maximize the system throughput     

Interference management using basestation coordination in broadband wireless access networks

This paper proposes a transmission‐scheduling algorithm for interference management in broadband wireless access networks. The algorithm aims to minimize the cochannel interference using basestation coordination while still maintaining the other quality of service (QoS) requirements such as packet delay, throughput and packet loss. The interference reduction is achieved by avoiding (or minimizing) concurrent transmission of potential dominant interferers. Dynamic slot allocation based on traffic information in other cells/sectors is employed. In order to implement the algorithm in a distributed manner, basestations (BSs) have to exchange traffic information. Both real‐time and non‐real‐time services are considered in this work. Results show that significant reduction in the packet error rate can be achieved without increasing the packet delay at low to medium loading values and with a higher but acceptable packet delay at high loading values. Since ARQ schemes can also be used for packet error rate reduction, we compare the performance of the proposed scheme with that of ARQ. Results indicate that although ARQ is more effective in reducing packet error rate, the proposed algorithm incurs much less packet delay particularly at medium to high loading. Copyright © 2006 John Wiley & Sons, Ltd.     

宽带CDMA无线接入系统及基站设计

宽带固定无线接入指的是从交换节点到固定用户终端部分或全部采用了无线方式.这里仅讨论对核心数据网络的接入.与有线接入比较,固定无线接入有如下显著特点:对自然条件适应性强.用户只要在覆盖区内,不需要特别定位和精确规划.在地形地物不适于架线铺缆的环境中,FWA系统显得尤其适合,建设速度快.     

Evaluation of OFDMA resource allocation algorithms in broadband wireless access networks

Broadband Wireless Access (BWA) is gaining interest due to the increasing demand of high-quality mobile wireless systems. In this context Orthogonal Frequency Division Multiple Access (OFDMA) is one of the most promising and researched physical transmission technologies. In OFDMA, data have to be mapped into a time-frequency matrix before the actual transmission. Efficiency, power consumption, Quality of Service (QoS) and complexity factors should be taken into account by mapping algorithms. In this paper, we focus on the OFDMA resource allocation problem in BWA networks. Through extensive simulation in different scenarios, performance of several resource allocation algorithms is evaluated.     

Signaling stack design for wireless ATM access networks

One of the challenges in designing a wireless ATM network is to specify control functions capable of managing data and signaling connections of moving mobile terminals. The challenge is tough, due to the facts that such control functions neither exist in the current state-of-the-art wireless networks nor are included in the existing ATM specifications and implementations. This article describes the design principles of a wireless ATM signaling stack created in the WAND project. The article identifies some common problems and presents possible solutions to the problems. To justify the feasibility of the ideas presented, some details of a reference implementation, the Wireless ATM Network Demonstrator (WAND) signaling stack, are revealed     

An iterative beamforming and decoding procedure for wireless networks with uncoordinated channel access

We propose an iterative receiver algorithm to cope with nonstationary cochannel interference, as e.g. arising in wireless ad hoc networks with uncoordinated channel access. The receiver incorporates an adaptive beamforming by a sample matrix inversion (SMI) technique on the information-bearing signals from an array antenna, and an a posteriori probability (APP) computation. The APPs are utilized to successively reconstruct and eliminate the reliably decoded signal parts from the samples. This allows to perform the SMI on a small number of snapshots, for the sake of adaptability, while evading a dramatic performance degradation due to the presence of the signal of interest.     

On the feasibility of bandwidth estimation in wireless access networks

Bandwidth estimation refers to the measurement of a bandwidth-related metric over a network path, performed only by the end hosts, without access to the intermediate routers. The problem of fast bandwidth estimation has been extensively studied in the wired Internet. More recently, researchers have shown that tools developed for the wired Internet cannot be used in wireless networks, due to the different characteristics of these networks which invalidate many of the assumptions made for the wired Internet. This observation has led to new tools that take into account the different characteristics of wireless networks. These tools have only been evaluated in controlled environments, under controlled settings and interferers, and only for 802.11 CSMA-based WLANs. In addition, no tool has been reported so far in the literature for cellular networks. This paper presents the first study of the feasibility of fast bandwidth estimation in wireless networks “in the wild”, i.e., in deployed operational networks. We discuss the challenges associated with bandwidth measurements in operational networks in contrast to in controlled lab environments. We study the applicability of a state-of-the-art probe-based tool for 802.11 WLANs in a commercial 1 × EVDO network. In addition, we evaluate the accuracy of the tool in three different WLAN environments, i.e., lab, home, and hotspot. Our results show that bandwidth estimation using a probe-based tool can be challenging in certain WLAN environments, and practically infeasible in EVDO cellular networks, due to the short-scale dynamics in this type of networks.     

High‐resolution compressive channel estimation for broadband wireless communication systems

Broadband channel is often characterized by a sparse multipath channel where dominant multipath taps are widely separated in time, thereby resulting in a large delay spread. Accurate channel estimation can be done by sampling received signal with analog‐to‐digital converter (ADC) at Nyquist rate and then estimating all channel taps with high resolution. However, these Nyquist sampling‐based methods have two main disadvantages: (i) demand of the high‐speed ADC, which already exceeds the capability of current ADC, and (ii) low spectral efficiency. To solve these challenges, compressive channel estimation methods have been proposed. Unfortunately, those channel estimators are vulnerable to low resolution in low‐speed ADC sampling systems. In this paper, we propose a high‐resolution compressive channel estimation method, which is based on sampling by using multiple low‐speed ADCs. Unlike the traditional methods on compressive channel estimation, our proposed method can approximately achieve the performance of lower bound. At the same time, the proposed method can reduce communication cost and improve spectral efficiency. Numerical simulations confirm our proposed method by using low‐speed ADC sampling. Copyright © 2012 John Wiley & Sons, Ltd.     

IIDWBA algorithm for integrated hybrid PON with wireless technologies for next generation broadband access networks

Optical and wireless technology integration has been proposed as one of the most promising nominees for the next-generation broadband access networks for quite some time. Integration scheme merges the high-speed and high-capacity of the optical networks with the low-cost, wide-coverage and mobility features of the wireless counterparts for the Subscriber Stations (SSs). It is also financially viable for the telecommunication service providers, particularly in the rural area where the development of optical infrastructure or expansion of the existing telecommunication solutions such as Digital Subscriber Line (DSL), Cable Modem (CM) or T-1/E-1 networks are either too costly or unreachable. In order to successfully integrate the two technologies, there are some technical concerns in terms of Architectural aspects, Physical Layer features and Media Access Control (MAC) related issues, which need to be addressed efficiently in order to provide the smooth end-to-end (e2e) integration. This paper is mainly focused upon the analysis of the key topics in MAC-related issues such as E2E wavelength/bandwidth requests and allocations over the converged scenario. It proposes an Inter-channel and Intra-channel Dynamic Wavelength/Bandwidth Allocation (IIDWBA) algorithm where the hybrid Passive Optical Network (PON) acts as a back haul technology for the wireless counterpart. The proposed algorithm works in three phases, namely, Initialisation, Intra-channel bandwidth allocations and Inter-channel bandwidth allocations and is capable of allocating wavelength/bandwidth efficiently and effectively over the converged scenario. Performance of the proposed algorithm is evaluated through conducted simulation scenarios under different simulation parameters, traffic patterns and load values. According to the captured results, IIDWBA algorithm shows a better performance when it is compared to the scenario in which it has not been employed.     

Joint scheduling and resource allocation in uplink OFDM systems for broadband wireless access networks

Orthogonal Frequency Division Multiplexing (OFDM) with dynamic scheduling and resource allocation is a key component of most emerging broadband wireless access networks such as WiMAX and LTE (Long Term Evolution) for 3GPP. However, scheduling and resource allocation in an OFDM system is complicated, especially in the uplink due to two reasons: (i) the discrete nature of subchannel assignments, and (ii) the heterogeneity of the users' subchannel conditions, individual resource constraints and application requirements. We approach this problem using a gradient-based scheduling framework. Physical layer resources (bandwidth and power) are allocated to maximize the projection onto the gradient of a total system utility function which models application-layer Quality of Service (QoS). This is formulated as a convex optimization problem and solved using a dual decomposition approach. This optimal solution has prohibitively high computational complexity but reveals guiding principles that we use to generate lower complexity sub-optimal algorithms. We analyze the complexity and compare the performance of these algorithms via extensive simulations.     

浅谈宽带无线接入技术的应用

0 引言 随着通信技术的飞速发展及社会生活水平的不断提高，传统的、纯粹的话音业务已经不能满足人们的需求，特别是随着互联网的迅猛发展，人们更希望享受到多媒体化、多样化、个性化的电信业务，数据业务量的猛增使人们对通信带宽的需求日益高涨。光纤接入虽然代表了未来宽带接入的方向，但其庞大的工程量和巨额的资金投入使其难以在近期一蹴而就。应运而生的宽带无线接入技术，以其建网的快速灵活和经济特性受到了广泛关注，新老运营商均对其表现出浓厚的兴趣。     

An overview of MIMO-oriented channel access in wireless networks [medium access control protocols for wireless LANs]

The integration of MIMO technology in WLANs has recently been the locus of extensive research. The main objectives of this technology are to improve channel reuse and or reduce energy consumption. In this article, we give an overview of MIMO systems and their use in WLANs. We highlight the different types of gains that MIMO offers and then discuss some of the work that has been done on MAC design. We conclude by outlining several open issues thai must be addressed for MIMO-based systems.     

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.     

Optimal DLC protocol configuration for realistic broadband fixed wireless access networks based on ATM

DLC protocols, scheduling, and multiplexing issues for broadband fixed wireless access networks based on ATM are discussed. The established DSA++ mac protocol has been developed at ComNets and has been widely applied within the German project ATMmobil. It has been a fundamental contribution to the etsi bran standardisation of HIPERLAN /2. The DSA++ is here modified to perform optimal within the fixed wireless access network environment. Therefore, realistic traffic as well as radio channel models for the respective scenarios are introduced. Simulation results are presented, showing the feasibility of the respective protocol stack for offering broadband multimedia services with reasonable quality of service. In addition to this advanced protocol approach, two systems are discussed which are currently under standardisation process. The IEEE 802.16 as well as the European hiperaccess systems are both proposed for fixed wireless access networks. Expected scenarios and applications are presented and basic requirements the standards have to fulfil are derived. As another aspect of access networks, their impact on the global information society is discussed.