Multi-Code TDMA (MC-TDMA) for Multimedia Satellite Communications
用于多媒体卫星通信的MC--TDMA（多码时分多址复用）
R. Di Girolamo and T. Le-Ngoc
Department ofa Electricl and Computer Engineering - Concordia University
1455 de Maisonneuve Blvd. West, Montreal, Quebec, Canada, H3G 1M8
ABSTRACT
摘要
In this paper, we propo a multiple access scheme bad
on a hybrid combination of TDMA and CDMA,在这篇文章中，我们提出一种基于把时分多址复用和码分多址复用集合的多址接入方案。 referred to
as multi-code TDMA (MC-TDMA). 称作多码—时分多址复用The underlying TDMA
frame structure allows for the transmission of variable bit
rate (VBR) information,以TDMA技术为基础的帧结构允许传输可变比特率的信息 while the CDMA provides inherent
statistical multiplexing.和CDMA提供固有的统计特性多路复用技术 The system is studied for a multimedia
satellite environment with long-range dependent
data traffic,and VBR real-time voice and video traffic研究这个系统是为了在远程环境下依赖数据传输和可变比特率的语音和视频传输的多媒体卫星通信系统 . Simulation
results show that with MC-TDMA, the data packet
delay and the probability of real-time packet loss can be
maintained low. 仿真结果表明：采用MC-TDMA的多媒体卫星通信，数据包延时和实时数据丢失的可能性可以保持很低。The above advantages are achieved at the
expen of soft blocking, which occurs when many packets
are transmitted simultaneously, but on different spreading
codes.上述的优点是以软阻塞为代价达到的，当很多数据包以不同的扩频码同时传输时会发生软阻塞。海洋环境 Similar conclusions are drawn for simulations
where the channel propagation conditions, adjacent beam
interference, and imperfect power control are considered.当仿真时考虑到信道传播条件，相邻的电波干扰和非理想功率控制等因素也会有相似的结论。
1 INTRODUCTION介绍
The nature of satellite channels make them ideally suited
for broadcast and multipoint transmissions. 卫星信道的性质非常适合广播和多点传输The envisioned
satellite systems do not only provide a backup to
the terrestrial wire and wireless networks, but in many situations
they are the only feasible alternative.未来卫星系统不只是给地面上有线和无线网络提供一个备份，在很多状况他们还是唯一可行的替代 This is particularly
true in cas where the infrastructure基础设施 to support the
terrestrial systems is not in place. 在支持地面的系统的基础设施不到位的情况下上面的说法就更正确了In such environments,在这种情况下
the satellite provides a means of communication which is
innsitive to the location and the distance between the
communicating urs.卫星会提供一种通信方式，这种通信方式对在通信的用户所在的位置和他们之间的距离不敏感
With the incread emphasis placed on multimedia, 现在重点放在多媒体上，any
propod systemmust be able to support a mixture of voice,
video, and data. 任何被提议的系统都必须可以支持语音，视频和数据的混合Typical applications could include video
conferencing, LAN interconnection, medical imaging, remote
踏平东京
video monitoring, and the like典型的技术包括视频会议，局域网互联，医学影像，远程视频监控和类似于这类的技术。. As a conquence, the
satellite system must be able to support all the rvices，and any future rvices which may become popular.所以，卫星系统必须可以支持所有这些服务和未来可能很受欢迎的服务。The problem lies in the characterization of this multimedia traffic
and in the different quality of rvice (QoS) 牛肉韭菜饺子requirements
for each of the. 问题就在于这种多媒体交换的描述和服务质量的不同要求不同。Packetized data, for instance, is generally
jitter tolerant but loss nsitive, 比如，封包化的数据通常可以容错但是不够敏感。涉县特产and often requires the retransmission
of packets which are received incorrectly.而且经常要求重新发送在接收端被错误接受的数据包 In addition,此外 recent traffic studies have shown that data traffic
exhibits long-range dependence [ll. 最近在通信交换的研究表明数据的交换存在一种长期的依赖，On the other hand,另一方面
voice and video are delay nsitive (real-time), 语音和视频信号对延迟是敏感的，but normally
can sustain a certain level of packet loss.但是一般情况下他可以支撑到数据包丢失的某个电平 Furthermore,此外 as
a result of the coding techniques ud,作为编码技术被利用的结果 the real-time traffic
can be of variable bit rate (VBR). 它可以实现可变比特率的实时交换Any designed system
should address the above issues.任何一个设计的系统都应该考虑上述问题。
The cond issue to be resolved is the method of multiple
双面上班族
Access.第二个要解决的问题就是多址接入的方法 How to geographically disperd earth stations(or urs) supporting multimedia traffic, 在地理上怎么划分可以支持多媒体交换的区域或者用户efficiently share the available fixed uplink bandwidth怎么有效的分享可利用的固定的上行带宽. One of the
关于国庆节的画simplest approaches is to u a form of demand assigned
TDMA or multi-frequency TDMA (MF-TDMA),where an
earth station periodically requests capacity, 最简单的方法就是使用一种按需求分配的形式的TDMA或者多频 TDMA。地面的无线站周期性的请求信道带宽 ，有一个中心程序机来响应这些请求and a central
套报
scheduler honors the requests [2]. A cond broad class
of technique which has recently been gaining momentum,
has CDMA as a basis. 最近已经蓄势待发的以CDMA为基础的第二大类技术，The spread spectrum approaches
require very high transmission 雅尔塔协议chip rates, and are hampered
with problems dealing with synchronization and unequal
