探究LTE网络典型建设场景中的传输接入方案

随着当前互联网、无线通信和多媒体等高线技术的不断融合，各种互联网和多媒体业务层出不穷，对移动互联网的要求也越来越高。本文结合工作经验，从LTE网络结构和对传输的影响出发，并主要就LTE网络典型建设场景中的传输接入方案进行了分析与探讨。     

爱立信:移动多媒体亟待市场驱动

自今年年初爱立信把多媒体业务独立成一个专门的事业部,针对多媒体业务做开发,并于今年6月在大中华区成立移动多媒体事业部之后,爱立信在移动多媒体上进一步提出了"无缝覆盖"的概念.     

无线内容自适应技术研究

介绍和分析内容自适应相关技术,重点讨论自适应策略及其分类、网络监控方法以及构架设计方面的内容.在此基础上,研究内容自适应技术在无线领域应用的问题,并以移动多媒体传输为例研究其网络局限性,并讨论适应移动多媒体内容分发的网络感知策略.     

UMTS的IP多媒体子系统

基于IP的多媒体业务将成为未来移动通信网的主要业务，为了适应未来移动通信网的发展，必须在核心网中增加专门处理IP多媒体业务的功能实体。本文详细介绍了UMTS的IP多媒体子系统及其提供的多媒体业务。     

基于网络的媒体流同步算法研究

同步是多媒体业务中一个重要的服务质量(QoS).分析网络中多媒体传输同步的基本问题,提出一种媒体内自适应缓冲控制方案.该方案采用接收瑞缓存媒体单元补偿网络的时延抖动,缓冲区采用循环队列的结构,当缓冲区达到要求预取数时,开始从缓冲区取帧.测试结果表明,应用该缓冲区方案能够补偿由于网络传输时延特性变化而引起的失步,从而使接收端播放平滑连续,对媒体通信质量有较大提高.     

IMS多媒体彩像业务网关模式的设计与实现

1引言 IMS是基于SIP的IP多媒体基础设施,通过一个完整的架构提供多媒体业务,可以同时支持固定和移动多种接入方式,实现固定与移动网络的融合。IMS的出现不仅能带来丰富的移动多媒体业务,     

NGN中的移动多媒体业务平台

IP多媒体子系统作为下一代网络的重要平台实现了固定网络与移动网络的无缝业务传递,丰富了移动多媒体的各种增值业务.IP多媒体子系统具有控制功能与承载能力分离、呼叫与会晤分离、应用与服务分离、业务与网络分离、移动网与互联网业务融合的主要特征,既适用于基于IP的移动多媒体业务,也适用于传统语音、数据和视频业务,是未来移动多媒体业务的发展方向.     

未来移动多媒体网络之间无缝切换的挑战

第三代移动通信系统的主要目标是提供多媒体业务,在移动多媒体通信系统中的切换问题非常重要,本文介绍了多媒体业务的特点,移动多媒体业务切换的特殊要求,不同网络间的切换协议。重点介绍了基于IP网络的移动多媒体网络之间无缝切换的各种水平切换和垂直切换方式以及无线TCP的优化。     

TD—SCDMA移动多媒体业务及终端

介绍了TD-SCDMA的系统及关键技术，阐述了TD-SCDMA所能提供的独具特色的移动多媒体业务，并介绍了TD-SCDMA移动多媒体终端的技术，最后探讨了TD-SCDMA移动多媒体终端的发展前景。     

TD-SCDMA的MBMS技术演进浅析

MBMS作为在第三代移动通信网络中提供多媒体广播组播业务的一种技术,能够有效地利用无线接入网的资源,特别是提高空中接口的传输效率。MBMS技术使移动网络运营商能够利用现有3G网络方便灵活地提供移动电视业务,满足日益增长的移动多媒体业务需求。对TD无线接入网中的R7MBMS关键技术进行了综述和研究分析。     

Medium access protocol design for delay-guaranteed multicode CDMA multimedia networks

To enable multimedia real-time applications over next-generation wireless code-division multiple access (CDMA) packet-switching networks, previous efforts show a proper scheduling policy is the key to provide delay-guaranteed access services to various traffic types with different bit error rate (BER) requirements. Considering the support of the prevailing Internet protocol (IP) with variable-length packets in future mobile networks, we develop a mathematically delay-optimal medium access control (MAC) protocol over multicode CDMA (MC-CDMA) environments under the continuous-time assumption. From our investigations, we suggest that a good MAC protocol should be designed by using a proper single-server scheduling policy to guarantee packet-delay, and controlling the maximal number of simultaneous spreading-code transmissions to maintain the required BER. We further evaluate the performance of some MC-CDMA MAC protocols supporting QoS on BER and packet-delay, and show that MAC schemes conforming to our design rules give better performance on packet-delay when maintaining acceptable BER of various traffic types.     

基于TDD-CDMA的集成可变速率多媒体业务传输的MAC协议

文章给出了一种应用于移动多媒体通信的无线媒体接入控制(MAC)协议.该MAC协议采用混合TDMA/CDMA结构,以提高资源利用率;采用多码并行传榆提供可变速率,以支持集成多媒体业务.系统仿真表明,该协议具有较高的码利用率和良好的灵活性,适用于可变速率多媒体业务集成传输.     

Design of spread spectrum multicode CDMA transport architecture formultimedia services

We investigate a new application of the well-known spread spectrum code division multiple access (SS-CDMA) techniques to multimedia services related to the development of the next-generation wireless mobile networks interconnecting with a wireline ATM-based broadband network. Such services allow users to share novel multimedia applications without any geographical restrictions. However, since the mobile radio channel has a fixed limited bandwidth, the traditional SS-CDMA system may not be sufficient to accommodate the variable bit rate (VBR) multimedia services requested by multiple mobile users simultaneously. Moreover, the traffic load at the base station can change dynamically due to the time-varying throughput requirement of these requested multimedia services. To tackle this difficulty, a multicode CDMA (MC-CDMA) technique is proposed to provide multirate multimedia services by varying the number of spreading codes assigned to each user in order to meet its throughput requirement. In MC-CDMA, a spreading code can be used to transmit information at a basic bit rate. Users (video or data) who need higher transmission rates can use multiple codes in parallel. Meanwhile, the maximum available number of codes in the MC-CDMA system is still limited. Hence, a cost-effective dynamic code allocation scheme has then been proposed to dynamically assign an appropriate number of codes to each user for achieving the maximum resource utilization for multiuser multimedia services via the mobile radio channel. Finally, a number of real multimedia titles generated from the well-known MacroMind Director are conducted to evaluate performance     

Multicast for mobile hosts in IP networks: progress and challenges

In the past few years, multimedia applications have become very popular on the Internet, and a growing number of users have shown interest in this type of communications. IP multicasting has logically been considered to support such transmissions, mainly because its inherent nature is to efficiently minimize the bandwidth required to deliver multimedia data to a large set of targeted receivers. In the meantime, there has been a steady increase in the number of mobile wireless devices connected to the Internet. It has also clearly appeared that mobile Internet users will expect to have access to the services and applications available in traditional wired networks, and these services will surely include multimedia applications. Consequently, many efforts are being made to provide efficient mobility and multicasting support, and to bring the two together in the next generation of IP networks.     

A multicarrier CDMA architecture based on orthogonal complementarycodes for new generations of wideband wireless communications

This article is a review of our ongoing research effort to construct a new multicarrier CDMA architecture based on orthogonal complete complementary codes, characterized by its innovative spreading modulation scheme, uplink and downlink signaling design, and digital receiver implementation for multipath signal detection. There are several advantages of the proposed CDMA architecture compared to conventional CDMA systems pertinent to current 2G and 3G standards. First of all, it can achieve a spreading efficiency (SE) very close to one (the SE is defined as the amount of information bit(s) conveyed by each chip); whereas SEs of conventional CDMA systems equal 1/N, where N denotes the length of spreading codes. Second, it offers MAI-free operation in both upand downlink transmissions in an MAI-AWGN channel, which can significantly reduce the co-channel interference responsible for capacity decline of a CDMA system. Third, the proposed CDMA architecture is able to offer a high bandwidth efficiency due to the use of its unique spreading modulation scheme and orthogonal carriers. Lastly, the proposed CDMA architecture is particularly suited to multirate signal transmission due to the use of an offset stacked spreading modulation scheme, which simplifies the rate-matching algorithm relevant to multimedia services and facilitates asymmetric traffic in up- and downlink transmissions for IP-based applications. Based on the above characteristics and the obtained results, it is concluded that the proposed CDMA architecture has a great potential for applications in future wideband mobile communications beyond 3G, which is expected to offer a very high data rate in hostile mobile channels     

Dynamic bandwidth allocation for multimedia traffic with rate guarantee and fair access in WCDMA systems

Packet scheduling in a WCDMA system poses a new challenge due to its nature of variable bit rates and location-dependent, time-varying channel conditions. In this work, three new downlink scheduling algorithms for a WCDMA base station are proposed to support multimedia transmissions. Using a credit management and a compensation mechanism, our algorithms provide rate guarantee and fair access to mobile terminals. In particular, we propose to allow a user to simultaneously use multiple OVSF codes in a time-sharing manner, which we call a multicode, shared model. Using multiple codes allows us to compensate those users suffering from bad communication quality or even errors. The proposed schemes can tolerate a multistate link condition (compared to the typically assumed two-state, or good-or-bad, link condition) by adjusting the number of OVSF codes and the spreading factor of each code. Simulation results show that the proposed schemes do achieve higher bandwidth utilization while keeping transmission delay low.     

Capacity Analysis for Connection Admission Control in Indoor Multimedia CDMA Wireless Communications

In this paper, the capacity analysis for connection admission control is presented for the reverse-link transmission of a packetized indoor multimedia wireless communication system using direct sequence code division multiple access (DS/CDMA). Since CDMA is interference limited, the signal-to-interference-plus-noise ratio criterion is used to check if there is enough system resources (i.e., the CDMA channels and received signal power) for each new connection request. Taking into account the stochastical nature of multimedia traffic, the effective bit rate is used to characterize the resources required by each mobile user and a linear approximation is then used to find the total resources required by all the mobile users already admitted to the system and the new connection request. Transmission errors due to both base station buffer overflow and wireless channel impairments are considered. The capacity of multimedia traffic is determined in such a way that the utilization of the system resources is maximized and, at the same time, the required transmission bit error rate and transmission delay of all users admitted to the system are guaranteed. Computer simulation results are given to demonstrate the performance of the proposed method for capacity analysis.     

IEEE 802.11 handoff latency improvement using Fuzzy Logic

Multimedia transmissions are delay‐sensitive Internet applications. Because mobile stations are in continual motion, handoff processes are necessary and unavoidable in wireless network environments. Because handoff processes tend to break the communication link, the research has been conducted on reducing the break time and arrival delay during Internet multimedia applications. In this paper, we propose an approach based on Fuzzy Logic to evaluate the average variation in signal strength received by a mobile station and produce a FitAP factor. This factor indicates the possible handoff access point that is suitable for the mobile station. According to the FitAP factor, a mobile station needs only to execute an active scan process once. Therefore, smaller handoff latency is expected. We compare the results from the current cell search scheme with that of the Fuzzy Logic approach. The statistical results show that the proposed method outperforms the current cell search scheme with an improved handoff latency performance. Copyright © 2007 John Wiley & Sons, Ltd.     

Carrier aggregation for LTE-advanced mobile communication systems

In order to achieve up to 1 Gb/s peak data rate in future IMT-Advanced mobile systems, carrier aggregation technology is introduced by the 3GPP to support very-high-data-rate transmissions over wide frequency bandwidths (e.g., up to 100 MHz) in its new LTE-Advanced standards. This article first gives a brief review of continuous and non-continuous CA techniques, followed by two data aggregation schemes in physical and medium access control layers. Some technical challenges for implementing CA technique in LTE-Advanced systems, with the requirements of backward compatibility to LTE systems, are highlighted and discussed. Possible technical solutions for the asymmetric CA problem, control signaling design, handover control, and guard band setting are reviewed. Simulation results show Doppler frequency shift has only limited impact on data transmission performance over wide frequency bands in a high-speed mobile environment when the component carriers are time synchronized. The frequency aliasing will generate much more interference between adjacent component carriers and therefore greatly degrades the bit error rate performance of downlink data transmissions.