Improving reliable transport and handoff performance in cellular wireless networks

TCP is a reliable transport protocol tuned to perform well in traditional networks where congestion is the primary cause of packet loss. However, networks with wireless links and mobile hosts incur significant losses due to bit-errors and handoffs. This environment violates many of the assumptions made by TCP, causing degraded end-to-end performance. In this paper, we describe the additions and modifications to the standard Internet protocol stack (TCP/IP) to improve end-to-end reliable transport performance in mobile environments. The protocol changes are made to network-layer software at the base station and mobile host, and preserve the end-to-end semantics of TCP. One part of the modifications, called the snoop module, caches packets at the base station and performs local retransmissions across the wireless link to alleviate the problems caused by high bit-error rates. The second part is a routing protocol that enables low-latency handoff to occur with negligible data loss. We have implemented this new protocol stack on a wireless testbed. Our experiments show that this system is significantly more robust at dealing with unreliable wireless links than normal TCP; we have achieved throughput speedups of up to 20 times over regular TCP and handoff latencies over 10 times shorter than other mobile routing protocols.This work was supported by ARPA Contract J-FBI-93-153. This paper was in part presented at the ACM Mobile Computing and Networking Conference (Mobicom '95), Berkeley, California, 14–15 November 1995.     

Roaming times of multi‐wireless systems for software defined radio

In this paper, we evaluate the roaming time performance for a reconfigurable multi‐mode mobile station (MS) that experiences possible transition from one kind of wireless system standard to another. In future software defined radio systems (SDR) (IEEE Commun Mag 2000; 138–143, IEE 1998; 1–6, IEEE 1999; 1212–1216, IEEE Commun Mag 1995; 33 ), reconfigurability of the MS is achieved by downloading the system configuration software code over the wireless channel. For evaluation of the roaming times, a generalized state diagram of the multi‐mode MS is presented. We focus on evaluating the times for sensing the universal pilot channel, classic base station pilot channel, association and connection establishment signaling are included. We investigate the effects of packet successful transmission probability over the wireless channel. We also consider the effects of the system resource blocking probability, MS resource blocking probability, and signaling bit rate over the universal base station channel for different cases and design scenarios. Such evaluations are important for prior design of SDR mobile terminal and universal base station in global roaming situations. We include some analysis results from many obtained. These show the feasibility of wireless software download, and switching between different wireless standard as the mobile station roams. Copyright © 2003 John Wiley & Sons, Ltd.     

Development of the Base Station Transceiver Subsystem in the CDMA Mobile System

The base station transceiver subsystem (BTS) of the CDMA Mobile System is interfaced to mobile stations over the air and to the wired network through a packet switched interconnection network. The potential benefits of CDMA technology are achieved when the transmitter and the receiver are properly designed and implemented. The physical layer of the air interface at the base station is implemented with the CDMA ASICs and control circuits in the channel card of the BTS. We present the design perspectives and structural illustration of the BTS. Base station modem ASICs and their control to implement the CDMA receiver, baseband and RF signal processing blocks, and BTS controller are described. Elaborate power control is essential to ensure the high capacity which is one of advantages of the CDMA technology. The closed loop reverse link power control and the forward link power control operated in the BTS are described.     

Forward high-speed wireless packet data service in IS-2000 - 1/spl times/EV-DV

This article describes enhancements to the physical layer design of single-carrier (1/spl times/) cdma2000/sup /spl reg// wireless networks introduced by Revision C of the IS-2000 standard (commonly referred to as 1/spl times/EV-DV). These improvements are mainly for the support of high-speed wireless packet data service on the forward (base station to mobile station) link. A new shared channel, the forward packet data channel, F-PDCH, is introduced to significantly increase spectral efficiency. This is accomplished through smart, channel-dependent scheduling of base station, BS, resources by taking advantage of the delay-tolerant nature of data traffic. This shared channel utilizes fast link adaptation through adaptive modulation and coding supported by the feedback of channel quality information. A form of hybrid ARQ type II technique commonly referred to as asynchronous adaptive incremental redundancy compensates for frame error events due to imperfect link adaptation. The impact of the new channel on voice capacity of the system is designed to be minimal because the F-PDCH utilizes resources that are not consumed by real-time users.     

An overview of configurable computing machines for software radio handsets

The advent of software radios has brought a paradigm shift to radio design. A multimode handset with dynamic reconfigurability has the promise of integrated services and global roaming capabilities. However, most of the work to date has been focused on software radio base stations, which do not have as tight constraints on area and power as handsets. Base station software radio technology progressed dramatically with advances in system design, adaptive modulation and coding techniques, reconfigurable hardware, A/D converters, RF design, and rapid prototyping systems, and has helped bring software radio handsets a step closer to reality. However, supporting multimode radios on a small handset still remains a design challenge. A configurable computing machine, which is an optimized FPGA with application-specific capabilities, show promise for software radio handsets in optimizing hardware implementations for heterogeneous systems. In this article contemporary CCM architectures that allow dynamic hardware reconfiguration with maximum flexibility are reviewed and assessed. This is followed by design recommendations for CCM architectures for use in software radio handsets.     

Optimizing Web delivery over wireless links: design, implementation, and experiences

World over wide-area wireless Global System for Mobile Communication (GSM) networks have been upgraded to support the general packet radio service (GPRS). GPRS brings "always-on" wireless data connectivity at bandwidths comparable to that of conventional fixed-line telephone modems. Unfortunately many users have found the reality to be rather different, experiencing very disappointing performance when, for example, browsing the Web over GPRS. In This work, we show what causes the web and its underlying transport protocol TCP to underperform in a GPRS wide-area wireless environment. We examine why certain GPRS network characteristics interact badly with TCP to yield problems such as: link underutilization for short-lived flows, excess queueing for long-lived flows, ACK compression, poor loss recovery, and gross unfairness between competing flows. We also show that many Web browsers tend to be overly aggressive, and by opening too many simultaneous TCP connections can aggravate matters. We present the design and implementation of a web optimizing proxy system called GPRSWeb that mitigates many of the GPRS link-related performance problems with a simple software update to a mobile device. The update is a link-aware middleware (a local "client proxy") that sits in the mobile device, and communicates with a "server proxy" located at the other end of the wireless link, close to the wired-wireless border. The dual-proxy architecture collectively implements a number of key enhancements-an aggressive caching scheme that employs content-based hash keying to improve hit rates for dynamic content, a preemptive push of Web page support resources to mobile clients, resource adaptation to suit client capabilities, delta encoded data transfer of modified pages, DNS lookup migration, and a UDP-based reliable transport protocol that is specifically optimized for use over GPRS. We show that these enhancements results in significant improvement in web performance over GPRS links.     

Dynamic rate adaptation and integrated rate and error control in cellular WCDMA networks

Optimal dynamic rate allocation among mobile stations for variable rate packet data transmission in a cellular wireless network is an NP-complete problem; therefore, suboptimal solutions to this problem are sought for. In this paper, three novel suboptimal dynamic rate adaptation schemes, namely, peak-interference-based rate allocation, sum-interference-based rate allocation, and mean-sense approximation-based rate allocation, are proposed for uplink packet data transmission in cellular variable spreading factor wide-band code division multiple access (WCDMA) networks. The performances of these schemes are compared to the performance of the optimal dynamic link adaptation for which the rate allocation is found by an exhaustive search. The optimality criterion is the maximization of the average number of radio link level frames transmitted per frame time under constrained signal-to-interference-plus-noise ratio (SINR) at the base station receiver. Two different error control alternatives for variable rate packet transmission environment are presented. We demonstrate that the dynamic rate adaptation problem under constrained SINR can be mapped into the radio link level throughput maximization problem with integrated rate and error control. Performance evaluation is carried out under random and directional micromobility models with uncorrelated and correlated long-term fading, respectively, in a cellular WCDMA environment for both the homogeneous (or uniform) and the nonhomogeneous (or nonuniform) traffic load scenarios.     

一种实现VEM总线结构的软件无线电方案

为了解决无线电通信领域内多体系并存、不同体系间无法制订统一标准等问题,在介绍了软件无线电提出的背景、硬件系统结构和软件系统结构的基础上,采用WiMAX802.16技术给出了一种实现VEM总线结构的软件无线电基站方案,以便满足用户在任何时间、地点的通信需求。研究了其对多种软件无线电标准的适应性,能够覆盖多个频段,能进行软件重构和复用。     

Using OBSAI to Build the Baseband-RF Interface of Multi-Mode Base Stations

The unique frame structure of Open Base Station Architecture Initiative (OBSAI) is well-suited to transmitting data of different wireless standards. In a multi-mode base station built with OBSAI,the baseband-RF interface can effectively screen out the influence of different wireless standards over the data transport link. It can also support multiple wireless standards on a single hardware platform. With such an interface,the Baseband Unit (BBU) and Remote RF Unit (RF) need only be changed to support a new ...     

Syndrome: a light‐weight approach to improving TCP performance in mobile wireless networks

It is well known that the performance of TCP deteriorates in a mobile wireless environment. This is due to the fact that although the majority of packet losses are results of transmission errors over the wireless links, TCP senders still take packet loss as an indication of congestion, and adjust their congestion windows according to the additive increase and multiplicative decrease (AIMD) algorithm. As a result, the throughput attained by TCP connections in the wireless environment is much less than it should be. The key problem that leads to the performance degradation is that TCP senders are unable to distinguish whether packet loss is a result of congestion in the wireline network or transmission errors on the wireless links. In this paper, we propose a light‐weight approach, called syndrome, to improving TCP performance in mobile wireless environments. In syndrome, the BS simply counts, for each TCP connection, the number of packets that it relays to the destination host so far, and attaches this number in the TCP header. Based on the combination of the TCP sequence number and the BS‐attached number and a solid theoretical base, the destination host will be able to tell where (on the wireline or wireless networks) packet loss (if any) occurs, and notify TCP senders (via explicit loss notification, ELN) to take appropriate actions. If packet loss is a result of transmission errors on the wireless link, the sender does not have to reduce its congestion window. Syndrome is grounded on a rigorous, analytic foundation, does not require the base station to buffer packets or keep an enormous amount of states, and can be easily incorporated into the current protocol stack as a software patch. Through simulation studies in ns‐2 (UCB, LBNL, VINT network simulator, http://www‐mash.cs.berkeley.edu/ns/ ), we also show that syndrome significantly improves the TCP performance in wireless environments and the performance gain is comparable to the heavy‐weight SNOOP approach (either with local retransmission or with ELN) that requires the base station to buffer, in the worst case, a window worth of packets or states. Copyright © 2001 John Wiley & Sons, Ltd.     

Evaluation of a Split-Connection Mobile Transport Protocol

A performance evaluation is presented for a split-connection protocol for wireless Internet access which is denoted Split-Connection Mobile Tranport Protocol (SCMTP). It uses the general approach of the previously introduced Mobile End Transport Protocol (METP) but with differences that include a wireless-link channel-access protocol better matched with current cellular networks and more general ARQ methods for error control in the wireless link. In common with METP, SCMTP uses a standard TCP protocol on the wire-line connection and isolates the data flow in the wire-line network from the effect of wireless packet errors.Performance is considered for the important case of a single SCMTP split connection between a fixed host and a mobile host with heavy downlink traffic from the fixed host to the mobile host. It is shown for these conditions that if the wire-line packet-error rate is small, a steady state is reached in which the connection's data flow in the wire-line network remains under the control of the receiver-advertised window of the TCP entity at the base station. Performance is evaluated for the steady-state operation of the SCMTP protocol, and relationships are established between the key properties of the split connection and the end-to-end performance of the connection.It is shown that for heavy downlink traffic, the delay in the wire-line part of the connection does not affect steady-state throughput if the receiver buffer is sized appropriately. It is also shown that use of the go-back-N ARQ protocol on the wireless link yields better performance than the stop-and-wait ARQ protocol, although the performance with go-back-N ARQ is more sensitive to the characteristics of the wireless channel. It is shown that under a broad range of conditions, SCMTP with go-back-N ARQ provides nearly optimal utilization of the capacity of the wireless link.     

Media Synchronization and QoS Packet Scheduling Algorithms for Wireless Systems

Wireless multimedia synchronization is concerned with distributed multimedia packets such as video, audio, text and graphics being played-out onto the mobile clients via a base station (BS) that services the mobile client with the multimedia packets. Our focus is on improving the Quality of Service (QoS) of the mobile client's on-time-arrival of distributed multimedia packets through network multimedia synchronization. We describe a media synchronization scheme for wireless networks, and we investigate the multimedia packet scheduling algorithms at the base station to accomplish our goal. In this paper, we extend the media synchronization algorithm by investigating four packet scheduling algorithms: First-In-First-Out (FIFO), Highest-Priority-First (PQ), Weighted Fair-Queuing (WFQ) and Round-Robin (RR). We analyze the effect of the four packet scheduling algorithms in terms of multimedia packet delivery time and the delay between concurrent multimedia data streams. We show that the play-out of multimedia units on the mobile clients by the base station plays an important role in enhancing the mobile client's quality of service in terms of intra-stream synchronization and inter-stream synchronization. Our results show that the Round-Robin (RR) packet scheduling algorithm is, by far, the best of the four packet scheduling algorithms in terms of mobile client buffer usage. We analyze the four packet scheduling algorithms and make a correlation between play-out of multimedia packets, by the base station, onto the mobile clients and wireless network multimedia synchronization. We clarify the meaning of buffer usage, buffer overflow, buffer underflow, message complexity and multimedia packet delay in terms of synchronization between distributed multimedia servers, base stations and mobile clients.     

Integrated circuits for channel coding in 3G cellular mobile wireless systems

Error control coding is a key element of any digital wireless communication system, minimizing the effects of noise and interference on the transmitted signal at the physical layer. In 3G mobile cellular wireless systems, error control coding must accommodate both voice and data users, whose requirements vary considerably in terms of latency, throughput, and the impact of errors on the user application. At the base station, dedicated hardware or readily reconfigurable components are needed to address the concurrent coding and decoding demands of a large number of users with different call parameters. In contrast, the encoder and decoder at the user equipment (UE) are dedicated to a single call setup which changes infrequently. In designing encoder and decoder solutions for 3G wireless systems, not only are the performance issues important, but also the costs. Cellular wireless infrastructure manufacturers need to reduce costs, maximize system reuse, and increase flexibility in order to compete in the market. Furthermore, future-proofing a network is a primary concern due to the high cost of deployment. For the UE, power consumption (battery life) and size are key constraints in addition to manufacturing costs. This article considers the 3G decoder design problem and, using case studies, describes two 3G decoder solutions using ASICs. The first device is targeted for base station deployment and is based on a unified architecture for convolutional and turbo decoding. The second device is a dedicated high-speed radix-4 logMAP turbo decoder targeted for UE, motivated by the requirements for high-speed downlink packet access. Both devices have been fabricated in 0.18 /spl mu/m CMOS technology, and while optimized for either base station or UE, may be used in both applications.     

Research and developments of software-defined radio technologies inJapan

Software-defined radio technologies are attractive for future mobile communication systems because of reconfigurable and multimode operation capabilities. The reconfigurable feature is useful for enhancing functions of equipment without replacing hardware. Multimode operation is essential for future wireless terminals because a number of wireless communication standards will still coexist. Research efforts on SDR have become very active in Japan, and various kinds of SDR prototypes have been developed. This article introduces the trends of Japanese wireless communication systems and the role of SDR technologies for the future wireless systems. R&D activities for the SDR in the field of academia and industry are also presented including examples of SDR prototypes     

EGPRS网络中Abis链路优化提升PDCH承载效率的分析

随着智能终端的迅速普及,移动QQ与微博业务受到越来越多用户的青睐,EGPRS网络承载的用户与数据业务流量都呈现倍速增长.本文中指出EGPRS网络中导致PDCH承载效率低的几个原因,重点针对由于Abis链路受限影响PDCH承载效率的情况进行分析.     

A Pseudo-Bayesian ALOHA Algorithm with Mixed Priorities

In reservation-based multiple access protocols, before obtaining a contention-free access to the channel, a mobile terminal must wait for its request packet to be successfully sent to the base station. A pseudo-Bayesian ALOHA algorithm with multiple priorities is proposed in this paper to reduce the waiting time of delay sensitive request packets in a multimedia environment. Packets are transmitted in each slot according to a transmission probability based on the channel history and a priority parameter assigned to their respective priority class. An adaptation of the slotted protocol to the framed environment proposed for wireless ATM is also described. Simulation results are presented to show that the protocol offers a significant delay improvement for high priority packets with both Poisson and self-similar traffic while low priority packets only experience a slight performance degradation.     

软件无线电在移动通信基站接收分系统中的实现

软件无线电技术是用现代化软件来操纵、控制传统的"纯硬件电路"的无线通信。由于软件无线电技术软、硬件便于升级,具有很强的适应性与兼容性,因而得到广泛的发展和应用。介绍了移动通信基站接收分系统的一种宽带中频带通采样软件无线电技术实现方法。通过对宽带中频带通采样软件无线电结构的分析与研究,介绍了一种切实可行的方案,并取得了预期效果。     

Common packet data channel (CPDC) for integrated wireless DS-CDMAnetworks

A common packet data channel (CPDC) architecture is proposed to support bursty, packet-based services in direct sequence code-division multiple-access (DS-CDMA) integrated wireless access networks. The architecture employs an asynchronous transfer mode (ATM) strategy in the forward CPDC link and a spread ALOHA-type random access strategy in the reverse CPDC link. A congestion control algorithm using base station broadcast and portable terminal random delay call reattempt is described. A performance analysis of the CPDC architecture and algorithms is carried out, and formulas for the bit error rate, blocking probability, system delay time, transmission time, and waiting time for packet data calls are derived. The interference caused by a CPDC to stream services in the network is determined, and the capacity of a CPDC is evaluated in terms of the number of packet data subscribers that can be served with a specified grade of service (GOS)     

基于PLC和GSM短信技术移动通信基站监控系统研制

介绍了基于小型可编程序控制器(PLC)产品FP2实现的移动通信基站监控系统.移动通信基站监控系统由全球移动通信系统(GSM),多台移动通信基站监控仪、PC机和移动通信基站监控管理软件组成,本文侧重介绍移动通信基站监控系统的硬件和功能,分析了移动通信基站监控系统的短信平台以及短信收发处理实现.由于采用PLC作为数据采集器,所以该系统具有可靠性高,成本低等优点.     

智能超表面在波束及信息调控中的应用

现代移动通信中无线信道的随机性、不确定性和不可控性是影响通信质量的关键因素,往往会导致接收端信号质量降低,从而限制了信息传输的速率与范围。目前正兴起的6G技术研究中,智能超表面是被积极讨论的研究方向之一,其是由亚波长结构组成的超薄人工表面,具有现场可编程能力和时空信息调制能力,可精准、高效地操控电磁波,可被用于重塑无线传播环境。通过对智能超表面的概念、基于时空调制的波束调控方法、基于智能超表面的无线中继以及通信系统 4 个方面的综述和分析,展示了智能超表面在辅助移动通信中具有的应用潜力,为6G的发展提供了新的思路。