[信息与通信]移动通信发展和CDMA基本原理.ppt

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1、,移动通信发展和CDMA基本原理,2,移动通信的发展,AMPS,TACS,其它,第一代 80年代,模拟,模,拟,技,术,GSM,第二代 90年代,数字,需求驱动,数,字,技,术,语,音,业,务,第三代,IMT-2000,UMTS,WCDMA,CDMA,2000,需求驱动,宽,带,业,务,TD-SCDMA,第三代移动通信系统,IMT-2000 2000年在2000M频段实现2000K的数据通信IMT2000推荐的3种制式 WCDMA 欧洲 CDMA2000 美国 TD-SCDMA 中国3G对数据通信速率的要求室内环境至少2Mbps室内外步行环境至少384kbps室外车辆运动中至少144kbps,

2、主流技术：WCDMA CDMA2000 TD-SCDMA,3G,3G的发展概况,3G的演进,移动通信的发展,CDMA2000标准家族演进,CDMA20001xRel 0,CDMA20001xRel A,CDMA20001xRel B,CDMA20001xRel C,1999 2000 2002 2003 2004,2000,TIA/EIA-95-B,1995 1999,CDMA20001xRel D,CDMA2000 HRPDRev A,“1xEV-DV”,“1xEV-DO”,CDMA2000 HRPDRev B,2004,2006,CDMA2000 1X 网络结构,多径环境,衰落示意图,纠错

3、编码技术,纠错编码技术是在发射端按一定规则引入冗余信息，从而使得即使空中传输引入了误码，也能利用冗余信息将此错误纠正回来的技术。,在通信系统中，为了减少突发干扰对连续数据造成的大面积差错，常采用交织 来将突发干扰造成的连续差错化解为随机独立差错，使其适合于译码器的错误纠正。,交织技术,多址技术,几种流行的多址技术：FDMA 频分多址每个用户使用不同的频率一个信道对应一个频率TDMA 时分多址每个用户使用不同的时隙一个信道就是特定频率的特定时隙CDMA 码分多址一个信道对应一种独特的码序列。每个用户使用相同的频率，但采用不同的码序列。,多址技术：多个独立用户同时使用传输介质而互不影响。,扩频通信

4、的定义,扩展频谱（SS:Spread Spectrum)通信简称扩频通信。扩频通信技术:在发端采用扩频码调制，使信号所占的频带宽度远大于所传信息必须的带宽，在收端采用相同的扩频码进行相关解调来解扩以恢复所传信息数据。,结论：在信道容量C不变的情况下，信号频带宽度B与信噪比S/N完全可以互相交换，即可以通过增大传输系统的带宽以在较低信噪比的条件下获得比较满意的传输质量,扩频通信的理论基础,CDMA扩频原理,CDMA扩频原理,CDMA扩频原理,Interference Sources,Long&Short CodeSpreading,Encoding&Interleaving,Long&Short

5、 CodeCorrelator,Decode&Deinterleaving,BasebandData,BasebandData,Background Noise,External Interference,Other Cell Interference,Other User Noise,384 kbps,1152 kbps,4.096 mcps,4.096 mcps,1152 kbps,384 kbps,CDMA Transmitter,CDMA Receiver,5 MHz BW,f,c,5 MHz BW,f,c,390 kHz BW,0,390 kHz BW,0,5 MHz BW,5 MH

6、z BW,-100 dB/Hz,Spurious Signals,CDMA扩频原理,CDMA扩频原理,扩频通信的特点和分类,隐蔽性和保密性好多个用户可以同时占用相同频带,实现多址抗衰落、抗多径干扰抗干扰能力强,CDMA扩频码的选择,扩频码速率：1.2288Mcps；扩频码：前向为Walsh码和PN短码，反向为PN长码。,扩频码的使用是扩频通信的关键点,Walsh码的定义:,Walsh码的定义,Walsh函数是一种非正弦波的完备正交函数系统，可用哈达玛矩阵H通过递推关系构成。由于它仅有可能的取值是1和1（或0和1），比较适合于用来表达和处理数字信号。Walsh函数具有理想的互相关特性。在Wals

7、h函数中，两两之间的互相关函数为“0”，亦即它们之间是正交的。,Code#23 0110100101101001100101101001011001101001011010011001011010010110(Code#23)1001011010010110011010010110100110010110100101100110100101101001 Code#59 0110011010011001100110010110011010011001011001100110011010011001,正交与相关性,WALSH CODES#-64-Chip Sequence-0 0000000000

8、000000000000000000000000000000000000000000000000000000 1 0101010101010101010101010101010101010101010101010101010101010101 2 0011001100110011001100110011001100110011001100110011001100110011 3 0110011001100110011001100110011001100110011001100110011001100110 4 000011110000111100001111000011110000111100

9、0011110000111100001111 5 0101101001011010010110100101101001011010010110100101101001011010 6 0011110000111100001111000011110000111100001111000011110000111100 7 0110100101101001011010010110100101101001011010010110100101101001 8 0000000011111111000000001111111100000000111111110000000011111111 9 0101010

10、11010101001010101101010100101010110101010010101011010101010 001100111100110000110011110011000011001111001100001100111100110011 011001101001100101100110100110010110011010011001011001101001100112 000011111111000000001111111100000000111111110000000011111111000013 010110101010010101011010101001010101101

11、010100101010110101010010114 001111001100001100111100110000110011110011000011001111001100001115 011010011001011001101001100101100110100110010110011010011001011016 000000000000000011111111111111110000000000000000111111111111111117 010101010101010110101010101010100101010101010101101010101010101018 0011

12、00110011001111001100110011000011001100110011110011001100110019 011001100110011010011001100110010110011001100110100110011001100120 000011110000111111110000111100000000111100001111111100001111000021 010110100101101010100101101001010101101001011010101001011010010122 001111000011110011000011110000110011

13、110000111100110000111100001123 011010010110100110010110100101100110100101101001100101101001011024 000000001111111111111111000000000000000011111111111111110000000025 010101011010101010101010010101010101010110101010101010100101010126 001100111100110011001100001100110011001111001100110011000011001127 0

14、11001101001100110011001011001100110011010011001100110010110011028 000011111111000011110000000011110000111111110000111100000000111129 010110101010010110100101010110100101101010100101101001010101101030 001111001100001111000011001111000011110011000011110000110011110031 011010011001011010010110011010010

15、110100110010110100101100110100132 000000000000000000000000000000001111111111111111111111111111111133 010101010101010101010101010101011010101010101010101010101010101034 001100110011001100110011001100111100110011001100110011001100110035 01100110011001100110011001100110100110011001100110011001100110013

16、6 000011110000111100001111000011111111000011110000111100001111000037 010110100101101001011010010110101010010110100101101001011010010138 001111000011110000111100001111001100001111000011110000111100001139 011010010110100101101001011010011001011010010110100101101001011040 000000001111111100000000111111

17、111111111100000000111111110000000041 010101011010101001010101101010101010101001010101101010100101010142 001100111100110000110011110011001100110000110011110011000011001143 011001101001100101100110100110011001100101100110100110010110011044 00001111111100000000111111110000111100000000111111110000000011

18、1145 010110101010010101011010101001011010010101011010101001010101101046 001111001100001100111100110000111100001100111100110000110011110047 011010011001011001101001100101101001011001101001100101100110100148 000000000000000011111111111111111111111111111111000000000000000049 010101010101010110101010101

19、010101010101010101010010101010101010150 001100110011001111001100110011001100110011001100001100110011001151 011001100110011010011001100110011001100110011001011001100110011052 000011110000111111110000111100001111000011110000000011110000111153 01011010010110101010010110100101101001011010010101011010010

20、1101054 001111000011110011000011110000111100001111000011001111000011110055 011010010110100110010110100101101001011010010110011010010110100156 000000001111111111111111000000001111111100000000000000001111111157 010101011010101010101010010101011010101001010101010101011010101058 001100111100110011001100

21、001100111100110000110011001100111100110059 011001101001100110011001011001101001100101100110011001101001100160 000011111111000011110000000011111111000000001111000011111111000061 010110101010010110100101010110101010010101011010010110101010010162 00111100110000111100001100111100110000110011110000111100

22、1100001163 0110100110010110100101100110100110010110011010010110100110010110,Walsh码,CDMA中:用64阶Walsh函数进行前向扩频，区分扇区内前向码分信道,反向做正交调制。,WALSH码,PN码发生器,PN短码序列,短码序列I和Q均为32,768chip，短码序列可以看作具有I和Q两种不同成分序列的二维二进制矢量，每一个的长度为32,768chip每一个短码序列均与它自身完全相关，即与时间偏置为零的短码序列完全相关。一个零偏置短码序列与它自身的任何非零偏置的短码序列正交。实际中以64chips偏移做为一个偏移序号

23、(PN_OFFSET_INDEX),即可用的PN 码是0-511,PN短码序列,PN长码序列,每个移动台使用一个唯一的用户长码序列，该序列是根据42位长码寄存器的内容、32位的ESN及掩码生成的，长码寄存器在移动台初始化期间与CDMA系统建立同步速率1.2288Mcps，周期为41天10小时12分钟19.4秒通话期间，虽然不同移动台产生的用户长码不是严格正交的，但彼此非常不同，在反向链路上足以对其可靠解码,长码寄存器(1.2288 MCPS),公共长码掩码(静态),用户长码序列(1.2288 MCPS),PN码在CDMA中的应用,CDMA系统中有两个序列的PN码：PN长码：242 1(n=42)PN短码：215(n=15)不同的用途 前向信道 长码扰码，短码正交扩频（标识基站）反向信道 长码扩频（标识用户），短码正交调制,小结,移动通信的发展扩频理论 PN码及其应用 WALSH码及其应用,小结,