移动通信发展和CDMA基本原理

,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-20002000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,主流技术：WCDMACDMA2000TD-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,CDMA20001xRel0,CDMA20001xRelA,CDMA20001xRelB,CDMA20001xRelC,19992000200220032004,2000,TIA/EIA-95-B,19951999,CDMA20001xRelD,CDMA2000HRPDRevA,“1xEV-DV”,“1xEV-DO”,CDMA2000HRPDRevB,2004,2006,CDMA20001X网络结构,多径环境,衰落示意图,纠错编码技术,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。,扩频通信的定义,扩展频谱（SS:SpreadSpectrum)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,InterferenceSources,Long&ShortCodeSpreading,Encoding&Interleaving,Long&ShortCodeCorrelator,Decode&Deinterleaving,BasebandData,BasebandData,BackgroundNoise,ExternalInterference,OtherCellInterference,OtherUserNoise,384kbps,1152kbps,4.096mcps,4.096mcps,1152kbps,384kbps,CDMATransmitter,CDMAReceiver,5MHzBW,f,c,5MHzBW,f,c,390kHzBW,0,390kHzBW,0,5MHzBW,5MHzBW,-100dB/Hz,SpuriousSignals,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Walsh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#230110100101101001100101101001011001101001011010011001011010010110(Code#23)1001011010010110011010010110100110010110100101100110100101101001Code#590110011010011001100110010110011010011001011001100110011010011001,正交与相关性,WALSHCODES#-64-ChipSequence-0000000000000000000000000000000000000000000000000000000000000000010101010101010101010101010101010101010101010101010101010101010101200110011001100110011001100110011001100110011001100110011001100113011001100110011001100110011001100110011001100110011001100110011040000111100001111000011110000111100001111000011110000111100001111501011010010110100101101001011010010110100101101001011010010110106001111000011110000111100001111000011110000111100001111000011110070110100101101001011010010110100101101001011010010110100101101001800000000111111110000000011111111000000001111111100000000111111119010101011010101001010101101010100101010110101010010101011010101010001100111100110000110011110011000011001111001100001100111100110011011001101001100101100110100110010110011010011001011001101001100112000011111111000000001111111100000000111111110000000011111111000013010110101010010101011010101001010101101010100101010110101010010114001111001100001100111100110000110011110011000011001111001100001115011010011001011001101001100101100110100110010110011010011001011016000000000000000011111111111111110000000000000000111111111111111117010101010101010110101010101010100101010101010101101010101010101018001100110011001111001100110011000011001100110011110011001100110019011001100110011010011001100110010110011001100110100110011001100120000011110000111111110000111100000000111100001111111100001111000021010110100101101010100101101001010101101001011010101001011010010122001111000011110011000011110000110011110000111100110000111100001123011010010110100110010110100101100110100101101001100101101001011024000000001111111111111111000000000000000011111111111111110000000025010101011010101010101010010101010101010110101010101010100101010126001100111100110011001100001100110011001111001100110011000011001127011001101001100110011001011001100110011010011001100110010110011028000011111111000011110000000011110000111111110000111100000000111129010110101010010110100101010110100101101010100101101001010101101030001111001100001111000011001111000011110011000011110000110011110031011010011001011010010110011010010110100110010110100101100110100132000000000000000000000000000000001111111111111111111111111111111133010101010101010101010101010101011010101010101010101010101010101034001100110011001100110011001100111100110011001100110011001100110035011001100110011001100110011001101001100110011001100110011001100136000011110000111100001111000011111111000011110000111100001111000037010110100101101001011010010110101010010110100101101001011010010138001111000011110000111100001111001100001111000011110000111100001139011010010110100101101001011010011001011010010110100101101001011040000000001111111100000000111111111111111100000000111111110000000041010101011010101001010101101010101010101001010101101010100101010142001100111100110000110011110011001100110000110011110011000011001143011001101001100101100110100110011001100101100110100110010110011044000011111111000000001111111100001111000000001111111100000000111145010110101010010101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