OFDM技术在GSM语音信道中的应用

远距离数据传输以及数据传输的保密性向来是人们比较关注的问题,使用语音信道传输数据信息是一种可选的方案。利用GSM信道,结合OFDM技术,将电脑、手机、A/D、D/A组成一个系统,可以实现一种远距离数据传输平台。针对OFDM技术特点,实现了GSM语音信道OFDM调制解调系统,经过多次实验测试,平均误码率曲线表明设计达到了最初的设计要求,在话音保密数据通信及其他数据传输上有较好的应用前景。     

A Channel Access Protocol for Integrated Voice/Data Applications

A new multiaccess protocol is proposed for an integrated voice/data application. The protocol, which is a variation of virtual time CSMA (VT-CSMA), takes advantage of the periodicity of voice packets and possesses a number of important features. With this protocol, voice stations appear to have a dedicated time-division multiplexed (TDM) slot, and the delay of a voice packet is bounded by the length of a frame (defined to be the period between two consecutive voice packets from a voice station). Also, the amount of data added to the channel has little effect on the voice traffic. When silence detection is used, many more voice conversations can be supported without losing the dedicated-slot characteristic. This is in contrast to a movingboundary TDM system where the excessive bandwidth saved by silence detection can only be used for data. The protocol requires no global synchronization and is easy to implement. Simulation results are presented to evaluate its performance.     

GSM话音质量提升方案综述

传统的话音业务仍是目前GSM网络业务收入的主要来源,通话质量也越来越为移动用户所关注,本文通过对GSM网络MOS话音质量评估标准及其影响因素的分析,重点给出提升GSM网络话音质量的方案。     

Channel equalization for the GSM system

This article presents first the generic structure and the formulation for the maximum likelihood detection of signals corrupted by intersymbol interference. Then, simplifications are made for the application of the technique in the mobile communication environment using the GSM specifications for which a channel memory length of 4 is used for equalizing over 4 bits. This work was done while the author was with Motorola.     

一种基于GSM／GPRS的动态信道分配策略

针对GSM／GPRS网络中某些小区因频繁切换导致掉话率高的问题,提出了一种新的动态信道分配策略。该方案将信道划分为数据业务专用信道和语音／数据业务共享信道,并在共享信道中为切换型语音呼叫预留保护信道以降低其呼叫失败率。对于数据业务采用FIFO排队机制。最后利用一种近似计算方法求取该策略的呼叫阻塞率等指标。实验结果表明该方案能有效降低语音呼叫掉话率。     

GSM语音业务容量的演进

随着新技术的应用,现有GSM系统的频谱效率已经获得了很大提高;伴随着GSM向3G的演进,还需要运用一些新技术来平滑提高其频谱效率。首先介绍GSM演进中的一些关键技术:跳频、部分负载和AMR等,并揭示这些技术提高频谱效率的机理:逐步降低频率复用系数。仿真表明,这些技术可以使得GSM系统频率复用模式从传统的4/12逐步下降到1/1,从而给出了一个清晰的GSM系统频谱效率(即容量)的演进轨迹。最后,给出了1/1复用下GSM-AMR网络相对传统GSM网络的频谱效率增益。     

移动通信端到端语音传输安全问题与对策分析

随着移动通信的广泛应用,语音通信安全问题日益突出.移动通信网的现有安全机制仅对无线信道进行了加密,未能提供地面核心网络的安全措施.文中针对移动语音通信安全现状,探讨了实现端到端语音保密通信的方法,分析了加密语音在移动网内传输面l临的主要问题,研究了加密语音基于移动数据业务信道传输和基于话音业务信道传输的两种实现方案,分析了方案的可行性,指出了下一步的研究方向.     

话带Modem与多媒体通信

本文介绍话带Ｍｏｄｅｍ技术的最新进，讨论了它与多媒体通信之间的相互促进关系。     

Towards Security of GSM Voice Communication

Wireless Personal Communications - Global system for mobile communication (GSM) is widely used digital mobile service around the world. Although GSM was designed as a secure wireless system, it is...     

GSM话音应用的未来

讨论在当前发展的三种无线通信网ＧＳＭ、ＧＰＲＳ和ＵＭＴＳ中,话音业务所承担的角色,介绍 ＧＳＭ话音应用的未来。     

基于Cable Modem技术的VoIP话音解决方案

目前,一些大、中城市的有线电视公司已经拥有庞大的有线电视宽带用户群,而基于HFC网的VoIP系统正是目前在有线电视宽带网条件下综合接入语音、数据和多媒体业务的最佳解决方案之一,其中语音业务可利用中继媒体网关设备完成媒体流转换,并通过标准的E1协议接入PSTN网络,以达到充分利用HFC及PSTN网络资源迅速开展话音业务的目的.同时,作为NGN(下一代网络)中的标准部件,VoIP是面向未来、可持续发展的解决方案之一,在有线电视宽带网所及之处,可以为商业和家庭用户提供质优价廉的IP语音服务.     

密话在INMARSAT数据信道上的传输

介绍了INMARSAT系统的发展与应用,提出了应用海事卫星数据信道进行加密话音双向传输的实现方案,给出了系统组成及功能实现,并对话音传输中应用的一些关键技术,包括:话音的流控实现、话音的实时转发及话音的存储与回放等,进行了详细介绍。经过方案论证及试验验证,实现了密话在数据信道上的双向传输,证明了该实现机制是切实可行的。     

GSM网络信道承载能力

3G到来的前夜,GSM网络的过度投资将大大增加成本风险,对网络资源配置进行评估和优化是目前工作的重点之一.既要提升网络服务能力,又要为今后降低经营成本提供有力条件.网络资源的利用率正在成为网络低成本运行的关键指标.本文就"GSM网络信道承载能力"问题进行一些分析.     

Channel de-allocation schemes for GSM/GPRS networks

Several channel de-allocation schemes for GSM/GPRS（General Packet Radio Service） networks are proposed in this paper. For DRA （Dynamical Resource Allocation） with de-allocation mechanism, if a new voice call arrives and finds that all the channels are busy, then one of the GPRS packets which occupy more than one channel for data transmission may release a channel for the new voice call. This paper presents 5 de-allocation mechanisms, i.e. DA-RANDOM, DA-RICHEST, DA-POOREST, DA-OLDEST and DA-YOUNGEST, to select the GPRS packet for releasing the appropriate channel. Simulation results show that DA-OLDEST achieves the best performance, especially in packets blocking probability, among all the de-allocation schemes. Although the performance of the proposed de-allocation schemes is not significantly different, they are all much better than that of the scheme without de-allocation.     

GSM系统中话音加密技术的研究

无线传播的特性使得用户的保密性和利益容易受到影响。重点分析了GSM系统在安全性管理功能上的缺陷,提出了GSM系统中话音加密的技术路线。     

关于GSM网络无线信道利用率的一种计算方法

主要介绍了一种从用户主观感知度、网络拥塞率的角度出发来计算GSM网络的每载频最佳话务区间，继而得出最佳无线信道利用率的方法。     

GSM移动网络话音质量问题分析

本文论述了GSM无线系统话音质量问题的原因,并根据在日常监控中的实际维护经验分析了话音质量问题的多种原因和采取的处理方法。讨论了GSM数字移动通信无线系统网络话音质量问题;总结了一些常见的优化方法及经验。     

A Battery-Powered Digital Modem for Telephone Transmission of ECG Data

We present the design of a battery-powered digital modem for transmitting ECG signals. It operates from a 5-V battery supply, uses a coil or acoustic coupler for a telephone interface, and consumes only 30 mW during transmission. We show error rates comparable to regular stand-alone modems, well within the acceptable limit of 1 bit per 100 kbits transmitted at a transmission speed of 300 Bd.     

A Low-rate Data Transfer Technique for Compressed Voice Channels

This study considers the problem of transmitting generic (non-speech) data through compressed voice channels such as those used in wireless communications networks. These networks employ voice codecs that are designed to efficiently encode and reproduce the relatively slow-changing signals of human speech, which leads to communication channels that are nonlinear and have long-term memory. A data modem is presented that utilizes finite alphabets of waveforms that are numerically optimized to be as separable as possible after passing through the voice codec. The optimization of the finite alphabet is performed using a pattern search algorithm. When used with the GSM Enhanced Full-Rate Voice Codec, this system demonstrated improved performance, in terms of error rates, compared to previously reported results. Simulation results for four other voice codecs are also presented.     

Data Performance in a System Where Data Packets are Transmitted During Voice Silent Periods--Single Channel Case

We develop a mathematical analysis for the steady state performance of a system where voice calls and data packets are transmitted over the same channel. The voice calls have priority over the data packets, in that the data packets are transmitted only when there are no voice calls present in the system or the voice conversation is in a long silent period.