【導讀】了解CDMA反向業(yè)務信道.理解反向碼分信道的概念及其與前向碼分信道的區(qū)別.論述反向信道的解調.用于在呼叫期間發(fā)送：。用戶對來自基站的命令和查詢的響應。支持可變速率操作。反向業(yè)務信道的生成。1/3速率卷積編碼器。反向業(yè)務信道塊交織。20ms符號塊被按序重新排列?4800bps和4800bps以下速率的重復符號被隔離開來。改善了符號數(shù)據(jù)對衰落的抵抗性能。分散了突發(fā)干擾的影響。六個符號被轉換為一個0-63的十進制數(shù)。對應該數(shù)的64位沃氏碼被輸出

　　

【正文】 =1/2,K=9 Mcps User Address Mask Long PN Code Generator ksps Orthogonal Modulation Data Burst Randomizer kcps Mcps Q PN (no offset) I PN (no offset) D 1/2 PN Chip Delay Direct Sequence Spreading Convolutional Encoder amp。 Repetition Block Interleaver Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 反向信道解調 ? IS95A/JSTD008移動臺調制過程的反過程 ? 多徑分量有益于 CDMA處理 ? 來自多個接收單元的信號可以被矢量合并以改善總的接收信號質量 U/D Command DeInterleaver Speech Output Combiner BTS Receiver BSC Demodulator Search Correlator Demodulator Search Correlator Demodulator Search Correlator Demodulator Search Correlator Power Control Decision Viterbi Decoder 聲碼器 來自 Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) CDMA概述 第四課 : CDMA反向信道 4a: 反向業(yè)務信道 復習 Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 4a: Review Questions 1. What is the size of the block interleaving arrays used in the Reverse CDMA Channels? Their size is 32 rows by 18 columns (576 modulation symbols). 2. What is the modulation symbol rate input to the Orthogonal Modulation step, what is the chip rate out, and how does this rate change happen? ksps in, kcps out. Every six modulation symbols are interpreted as a Walsh index (063), and they are replaced by the corresponding 64bit Walsh code. Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) CDMA概述 第四課 : CDMA反向信道 4b: 接入信道 Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 4b: 接入信道 課程目標 ? 論述接入信道的作用 ?明確接入信道的主要調制參數(shù) ?了解接入信道的產生 ?了解接入信道和尋呼信道的關系 Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 接入信道 ? 移動臺用接入信道： ? 與基站建立初始通信 ? 對尋呼信道消息作出響應 ?固定數(shù)據(jù)率： 4800bps ?每個接入信道僅與一個尋呼信道相關 ?每個尋呼信道最多可支持 32個接入信道 (031) 4800 bps Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 接入信道的生成 ? 請求消息被隨機化以降低沖突的可能性 ?兩類消息 : ? 響應消息 (響應基站的消息 ) ? 請求消息 (移動臺自動發(fā)送 ) ksps Convolutional Encoder amp。 Repetition R = 1/3 Mcps Access Channel Long Code Mask Long PN Code Generator ksps Orthogonal Modulation kcps Mcps Q PN (No Offset) I PN (No Offset) D 1/2 PN Chip Delay Block Interleaver Access Channel Information (88 bits/Frame) kpbs Direct Sequence Spreading Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 接入信道試探 Seq 2 Seq 3 Seq MAX_REQ_SEQ (15 max) PD Request message ready for transmission Access Attempt System Time Access Probe Sequence 1 REQUEST ATTEMPT RS PD RS PD ACCESS PROBE SEQUENCE IP (Initial Power) TA RT TA RT TA RT PI TA Access Probe 1 Access Probe 2 Access Probe 3 Access Probe 4 Access Probe 1 + NUM_STEP (16 max) PI PI System Time Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) CDMA概述 第四課 : CDMA反向信道 4b: 接入信道 復習 Course 809 Lesson 4: CDMA反向信道 Issue (January 1998) 4b: Review Questions 1. What are Access Channels used for? Access Channels are used by mobile stations to initiate munication with the base station or to respond to Paging Channel messages. 2. How many Access Channels are there, and how are they differentiated from other forward and reverse channels on the same CDMA frequency? Up to 32 Access Channels for every Paging Channel can be supported on a CDMA frequency. Each Access Channel is differentiated from all other forward and reverse channels on that frequency by the mask applied to the long PN code before the orthogonal modulation step. This mask bines the Access and Paging Channel numbers with the base station specific BASE_ID and PILOT_PN parameters. (Notice that two different mobile stations might choose to transmit to the same base station using exactly the same Access Channel at the same time. They would, therefore, use the same mask, which would result in a collision?.