Mobile WiMAX System Research Articles

An overview of next-generation mobile WiMAX technology

The growing demand for mobile Internet and wireless multimedia applications has motivated the development of broadband wireless access technologies in recent years. Mobile WiMAX has enabled convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. Since January 2007, the IEEE 802.16 working group has been developing a new amendment of the IEEE 802.16 standard (i.e., IEEE 802.16m) as an advanced air interface to meet the requirements of ITU-R/IMT-advanced for 4G systems, as well as for the next-generation mobile network operators. Depending on the available bandwidth and multi-antenna mode, the next-generation mobile WiMAX will be capable of over-the-air data-transfer rates in excess of 1 Gb/s and of supporting a wide range of high-quality and high-capacity IP-based services and applications while maintaining full backward compatibility with the existing mobile WiMAX systems to preserve investments and continuing to support first-generation products. This tutorial describes the prominent technical features of IEEE 802.16m and the potential for successful deployment of the next generation of mobile WiMAX in 2011+.

데이터 서비스를 위주로 하는 이동통신 망에서의 주파수 소요량 산출 모델

WiMax, WiBro 등의 무선망에서의 데이터 서비스들은 더 빠른 이동성 확보와 더 높은 데이터 전송 속도의 실현을 목표로 변화와 발전을 계속하고 있다. 이러한 서비스 진화에서는 무선 데이터 통신망에서 가입자의 트래픽 수요를 충족시키고 무선망 구축을 위한 정확한 주파수 소요량 예측이 무엇보다 중요하다. 따라서 본 논문에서는 기존기술 연구의 문제점을 분석하여 데이터 서비스를 위주로 하는 이동 통신망의 주파수 소요량 산출시 고려해야 할 핵심 요소들을 제안하였다. 그것은 첫째 데이터 트래픽의 자기 유사성 특징, 둘째, QoS(Quality of Service)가 고려된 처리용량, 셋째, 기지국 부하율의 비균일 특성, 그리고 마지막으로 FA 증설구조이다. 또한 데이터 서비스를 위주로 하는 이동통신 망에서는 이러한 핵심 요소들을 적용하여 주파수 소요량 산출 표준 모델을 제안하였다. Today, as various access technologies appear, for example WiMax, WiBro, the demand for spectrum is increasing rapidly. Spectrums are a national resource with scarcity value so that we need to a]locate them effectively for the national economy and industry. Accordingly, In the paper, we proposed several factors and new model for estimating spectrum requirements of a next generation mobile network with multimedia data services. These are self-similarity characteristics of data traffic, engineered capacity considering QoS, structure of FA increase, asymmetry of data traffic between uplink and downlink, handoff traffic, and uneven traffic pattern among base stations. It can applied mobile WiMax or other wireless broadband systems in general.

Optimal energy-efficient pair-wise cooperative transmission scheme for wimax mesh networks

Recently, there has been a steady trend toward the development of subscriber stations (SSs) to enable the ubiquitous communications. In the mobile environment, the power consumption of an SS is an important performance indicator because its battery life is limited. Many existing power-saving schemes for the IEEE 802.16e Mobile WiMax system have been proposed, such as scheduling algorithms for the sleep intervals. However, this type of approaches may be unrealistic for heavy network traffic since the SSs almost always have data to transmit. In this paper, we propose a new power-saving scheme by introducing the pair-wise matching procedure between the SSs prior to uplink data transmission in the WiMax mesh mode. According to the quality-of-service (QoS) requirement, we can preset the desired packet error rate (PER) or signal-to-interference-plus-noise-ratio (SINR) at the receiver end. Given the network topology and the channel state information, the required transmitting power per coded bit at each SS can be calculated. Then we may establish a cost function associated with the required transmitting power per coded bit and thus the optimal matching can be achieved by our proposed minimum weight matching algorithm. The numerical results show the significant improvement of the transmitting power consumption using our proposed method over the conventional scheme when we consider three aspects such as channel effects, coding/modulation options and network topology.

CDIT-Based Constrained Resource Allocation for Mobile WiMAX Systems

Adaptive resource allocation has been shown to provide substantial performance gain in OFDMA-based wireless systems, such as WiMAX, when full channel state information (CSI) is available at the transmitter. However, in some fading environments (e.g., fast fading), there may not be a feedback link sufficiently fast to convey the CSI to the transmitter. In this paper, we consider resource allocation strategies for downlink multiuser mobile WiMAX systems, where the transmitter has only the channel distribution information (CDI), but no knowledge of the instantaneous channel realization. We address the problem of subchannel assignment and power allocation, to maximize the ergodic weighted-sum rate under long-term fairness, minimum data rate requirement and power budget constraints. This problem is formulated as a nonlinear stochastic constrained optimization problem. We provide an analytical solution based on the Lagrange dual decomposition framework. The proposed method has a complexity of (KM) for K users and M subchannels. Simulation results are provided to compare the performance of this method with other allocation schemes and to illustrate the tradeoff between maximized weighted-sum rate and the constraints.

A Paging Indicator Transmission Technique for Mobile WiMAX Systems

In a cellular system, efficient power saving techniques for a mobile station (MS) are necessary because of its inherently limited battery capacity. The paging indicator (PI) transmission scheme in CDMA cellular systems is known to be an effective power saving strategy. However, in OFDM-based cellular systems, the MS has to operate FFT for PI symbol detection, resulting in a significant power consumption. In this letter, a PI transmission technique with reduced power consumption using the preamble in OFDM-based cellular systems, especially for mobile WiMAX systems, is proposed for the MS under power saving mode. Simulations indicate a 30-50% power saving from our proposed PI transmission technique, at the expense of a slight increase in paging response delay.

Highest Urgency First (HUF): A latency and modulation aware bandwidth allocation algorithm for WiMAX base stations

The mobile WiMAX systems based on IEEE 802.16e-2005 provide high data rate for mobile wireless networks. However, the link quality is frequently unstable owing to mobility and air interference and therefore impacts the latency requirement of real-time applications. In the WiMAX standard, the modulation/coding scheme and the boundary of uplink/downlink sub-frames could be adjusted subject to channel quality and the traffic volume, respectively. This provides us a chance to design a MAC-layer uplink/downlink bandwidth allocation algorithm that is QoS/PHY-aware. This work takes into account the adaptive modulation and coding scheme (MCS), uplink and downlink traffic volume, and QoS parameters of all five defined service classes to design a bandwidth allocation algorithm that calculates the slot allocation in two phases. The first phase decides the boundary of uplink and downlink sub-frames by satisfying requests with pending latency violation and proportionating according to traffic volume, while the second phase allocates slots to mobile stations considering urgency, priority and fairness. Simulation results show our algorithm achieves zero latency violation and higher system throughput compared to existing non-QoS/PHY-aware or less-QoS/PHY-aware approaches.

E‐CLEMA: A cross‐layer design for improved quality of service in mobile WiMAX networks

AbstractIn this paper, an efficient cross‐layer design that performs joint adaptation of the physical (PHY) and application layers of a mobile WiMAX network is proposed. The design takes into account channel state and performance information from the PHY and medium access control (MAC) layers, respectively. It uses a decision algorithm to evaluate this information, specify unfavorable conditions regarding low channel quality and increased congestion, and take measures by coordinating modulation order, transmission power, and media encoding rate, toward improved overall quality of service (QoS) offered to the user. Extensive simulation results show that the proposed design achieves considerably reduced packet loss and power consumption, combined with increased throughput as compared to a typical mobile WiMAX system. Copyright © 2008 John Wiley & Sons, Ltd.

Fast and Efficient QoS-Guaranteed Adaptive Transmission Algorithm in the Mobile WiMAX System

In this paper, we propose a fast and efficient adaptive transmission algorithm for the mobile WiMAX system. In our algorithm, we select the position of the boundary between the downlink and uplink subframes, the positions of the service flows within the frame, the coding and modulation schemes, and the transmission power values. Our algorithm gains high spectral efficiency, satisfies quality-of-service (QoS) requirements for the service flows, and has low computational complexity. The algorithm includes a frame boundary position optimization procedure, downlink and uplink optimization procedures, as well as a procedure that selects a transmission power value that enables satisfaction of the QoS requirements. All these procedures are novel, efficient, and fast. We evaluate the adaptive transmission algorithm by performing a system-level simulation of the mobile WiMAX system with multisector topology. We show that our algorithm has high spectral efficiency and low computational complexity, enabling QoS provisioning.

Improved VoIP capacity in mobile WiMAX systems using persistent resource allocation

Efficient support of voice traffic has always been one of the key metrics for evaluating and selecting radio access technologies. Even for next-generation broadband wireless technologies primarily focused on the mobile Internet, special handling of VoIP traffic in the physical and MAC layers is required to maximize voice capacity. While Mobile WiMAX Release 1.0 and 802.16e have all the key features necessary to support mobile VoIP traffic, special attention is given in Mobile WiMAX Release 1.5 and 802.16REV2 to further optimizing VoIP capacity through reduction in the MAC layer overhead associated with signaling messages. This article focuses on features and solutions used in Mobile WiMAX and the 802.16 standard to support voice traffic and the expected performance in Release 1.0/802.16e-2005, as well as gains from optimization concepts such as persistent allocation added in Release 1.5/802.16REV2. In each case, MAP overhead reduction and the projected improvements in VoIP capacity are presented using typical industry accepted models and assumptions. The results show about 15 percent increase in bidirectional VoIP capacity.

Mobile WiMAX systems: performance and evolution

Mobile WiMAX was successfully adopted by ITU as one of the IMT-2000 technologies in November 2007. Since then mobile WiMAX (a.k.a. IP-OFDMA) has officially become a major global cellular wireless standard along with 3GPP UMTS/HSPA and 3GPP2 CDMA/ EVDO. Mobile WiMAX is an OFDM-based technology available for deployment today, and new WIMAX devices come to market at much reduced cost than that of current 3G solutions. Currently over 260 service providers are deploying fixed, portable and mobile WiMAX networks in 110 countries. This article provides an overview of the mobile WiMAX system and its performance under various configurations, channel conditions, and types of data traffic. Furthermore, the article provides an overview of mobile WiMAX evolution.

An adaptive cross-layer design for multiservice scheduling in OFDMA based mobile WiMAX systems

We consider a cross-layer scheme for the downlink multiuser Orthogonal Frequency Division Multiple Access (OFDMA) for mobile WiMAX (Worldwide Interoperability for Microwave Access) based on IEEE802.16e standard. We propose an intelligent Medium Access Control (MAC) that adapts with the physical layer (PHY) in response to the different QoS requirements of the diverse service flows in the system. This adaptation is represented by a joint packet scheduling and slot allocation scheme interaction in both MAC and PHY layers. Based on this interaction, a fair and efficient QoS guaranteed resource allocation for a mixture of real-time and non real-time service flows is achieved. We provide extensive simulation results showing the performance aspects of the proposed cross-layer scheme.

Cross-layer mobile WiMAX MAC designs for the H.264/AVC scalable video coding

To effectively provide the QoS of streaming services in mobile WiMAX systems, this paper proposes a cross-layer design between the streaming server and mobile WiMAX base stations. We will show that for each user the implementation of multiple connections with feedback information of the available transmission bandwidth is critical for supporting H.264/AVC-based scalable video coding in which the transmission packets can be further separated into multiple levels of importance. To quantify the performance, a mobile WiMAX simulation platform including both the video encoder/decoder and IEEE 802.16e MAC controls is developed.

Channel estimation in mobile WiMAX systems

Abstract:The use of channel adaptive transmission techniques requires accurate channel stateinformation (CSI) which may not easily be achievable particularly near the cellboundary in multi-cell environments. In this paper, we consider the improvement of CSIestimation accuracy by exploiting the preamble signal as well as the pilot signal inODFM based wireless systems. We first estimate the CSI from both the receivedpreamble signal and the received pilot signal. By exploiting the channel correlationbetween the preamble and pilot signaling, we combine the two CSIs estimated from thepreamble and pilot signals. The combining weight is analytically determined tominimize the mean squared error. For the interference cancellation with the use multiplereceive antennas, we also consider the estimation of interference channel in a similarmanner. Simulation results show that when applied to the mobile-WiMAX system, theproposed scheme is quite effective near the cell boundary.

Energy-efficient packet scheduling algorithms for real-time communications in a mobile WiMAX system

Broadband wireless access systems usually provide flexible sleep-mode operations for mobile stations to conserve their energy during idle or active mode. For example, Mobile WiMAX, i.e. the IEEE 802.16e, offers several power-saving classes that can be associated with different types of network connections to minimize power consumption of mobile stations. Unfortunately, previous studies did not fully utilize the sleep-mode features to save the energy of a mobile station with multiple real-time connections, and power consumption of a mobile station is not yet optimized. In this work, two energy-efficient packet scheduling algorithms for real-time communications in a Mobile WiMAX system are proposed. The schemes not only guarantee the quality of services (QoSs) of real-time connections but also minimize power consumption of mobile stations. Simulation results demonstrate that the proposed schemes outperform the traditional approach.

An 8.29 mm<formula formulatype="inline"><tex>$^{2}$</tex> </formula> 52 mW Multi-Mode LDPC Decoder Design for Mobile WiMAX System in 0.13 <formula><tex>$\mu$</tex></formula>m CMOS Process

This paper presents a multi-mode decoder design for Quasi-Cyclic LDPC codes for Mobile WiMAX system. This chip can be operated in 19 kinds of modes specified in Mobile WiMAX system, including block sizes of 576,..., 2304. There are four proposed design techniques: reordering of the base matrix, overlapped operations of main computational units, early termination strategy and multi-mode design strategy. Based on overlapped decoding mechanism, the decoding latency can be reduced to 68.75% of non-overlapped method, and the hardware utilization ratio can be enhanced from 50% to 75%. Besides, the proposed early termination strategy can dynamically adjust the number of iterations when dealing with communication channels of different SNR values. The proposed multi-mode LDPC decoder design is implemented and fabricated in TSMC 0.13 mum 1.2 V 1P8M CMOS technology. The maximum operating frequency is measured 83.3 MHz and the corresponding power dissipation is 52 mW. The core size is 4.45 mm2 and the die area only occupies 8.29 mm2.

Full-rate full-diversity 2 x 2 space-time codes of reduced decoder complexity

Multiple-input multiple-output (MIMO) techniques have become an essential part of broadband wireless communications systems. For example, the recently developed IEEE 802.16e specifications for broadband wireless access include three MIMO profiles employing 2x2 space-time codes (STCs) and two of those are mandatory on the downlink of Mobile WiMAX systems. Conventional approaches to STC design are based on performance criteria such as coding gain, diversity gain, multiplexing gain, and ignore the decoder complexity. In this paper, we take an alternative approach and present a full-rate full-diversity 2x2 STC design leading to substantially lower complexity of the optimum detector than existing schemes. This makes the implementation of high performance full-rate codes realistic in practical systems.

Performance Evaluation of Energy-Saving Mechanism Based on Probabilistic Sleep Interval Decision Algorithm in IEEE 802.16e

While the legacy power-saving mechanism in wireless networks usually uses a predetermined and fixed sleep interval to enhance the energy conservation of mobile stations, the IEEE 802.16e Mobile WiMAX system adopts a power-saving mechanism with a binary truncated exponent (BTE) algorithm for determining sleep intervals. Although the BTE algorithm allows more flexibility in determining sleep intervals, it still does not consider the delay of the response packet. Thus, in this paper, we suggest a new power-saving mechanism, which is the probabilistic sleep interval decision (PSID) algorithm, in the context of an IEEE 802.16e Mobile WiMAX system. While the length of sleep interval is restricted by the upper and lower bounds, irrespective of response packet's arrival time under the BTE algorithm, the PSID algorithm determines sleep interval placement by using the distribution function of the response packet's arrival time so that the response packet may arrive at the base station during each sleep interval with the same probability. To compare the two algorithms, the main properties of the BTE algorithm and the proposed PSID algorithm are discussed, and a theoretical framework for analyzing its performance is provided. Analytical and simulation results show that under the BTE algorithm, energy consumption and buffering delay converge to a saturation point, and a short buffering delay can be obtained at the expense of sacrificing energy consumption. Meanwhile, the PSID algorithm performs better with respect to energy consumption and buffering delay than the BTE algorithm.

Radio resource management of heterogeneous services in mobile WiMAX systems [Radio Resource Management and Protocol Engineering for IEEE 802.16

IEEE 802.16e, known as mobile WiMAX, has gained much attention recently for its capability to support high transmission rates in cellular environments and QoS for different applications. Beyond what the standard can define, in order to effectively support video streaming, VoIP, and data services, proprietary radio resource management, including multiconnection assignment, scheduling controls, and call admission controls, are essential. In this study we evaluate the downlink performance of a mobile WiMAX cellular system with different radio resource management, especially the scheduler for QoS control and the implementation of multiconnection for streaming applications