华为CDMA2000中的反向接入信道(R-ACH)

反向接入信道(R-ACH) 4.8 ksps (307.2kbps) PN 码片 1.2288 Mcps 正交扩频 重复的符号流 28.8 kbps Code symbol 14.4 kbps 4.4 kbps 4.8 kbps 每帧增加8bit编码尾比特 卷积编码 r=1/3,K=9 符号重复 接入信道信息比特 (80 bits/frame) 块交织 28.8 kbps 数据突发随机化 长码生成器 长码掩码 重复的符号流 用于MS在反向接入系统和响应寻呼 I Q I 信道PN序列 1.2288 Mcps Q 信道PN序列 1.2288 Mcps 基带滤波 基带滤波 I(t) Q(t) + + X X ∑ QPSK 调制 Sin(2pfct) Cos(2pfct) 1/2 PN 码片 时延=406.9ns Walsh码 CDMA 空中接口 Note that a reverse channel is first spread with WALSH to 307.2Kbps and then becomes 1.2288Mcps after long code modulation. The long code here not only spreads spectrum, but implements the function of channelization. “Data burst randomizer” means discarding repeated chips during the transmission according to a certain algorithm and implementing discontinuous transmission so as to reduce the transmission rate and increase the capacity of reverse channels. In OQPSK reverse modulation, as opposed to the data modulated by I channel PN sequence, the data modulated by Q channel PN sequence has the delay of half a PN chip (406.901ns). Thus, the maximum phase change of four-phase modulation is 90 degrees instead of 180-degree mutation.