CDMA原理介绍【荐】.pptVIP

* Schedulers handle how data gets transmitted to the access terminals. The goal of schedulers is to improve overall system throughput. The 1xEV-DO system allocates bandwidth to different access terminals based on their reported data rates. It is the responsibility of scheduler to allocate bandwidth to different ATs. The scheduler is implemented at the sector. For 1xEV-DO, there are four different schedulers available: round-robin best rate equal opportunity proportional fairness * * * * Proportional fairness The proportional fairness scheduler’s goal is to provide fairness to each user regardless of their data rates. The scheduler maintains a moving average of DRC (data rate control) values and the scheduler transmits data to the access terminal only when the DRC value is greater than or equal to the moving average. The scheduler functions as follows: If an access terminal reports less than average DRC values, it may appear the access terminal will not receive any data at all. The access terminal gains credits with the system increasing their priority to receive data. This increases overall throughput for individual users as well as the whole system. 接入鉴权 a. 建立空口会话，其中包括UATI 分配、会话配置协商和DH 密钥交换等过程。 b. AT 向AN 发送开启请求消息，请求开启AN 流；AN 返回开启响应消息，开启AN 流。 c. AN 与AT 之间进行PPP 和LCP 协商，主要协商PPP 数据分组的大小和鉴权协议类型（如CHAP）。通常，AN 配置CHAP 鉴权协议类型。 d. AN 发起接入鉴权，向AT 发送CHAP 查询消息，其中包含鉴权随机数。 e. AT 收到该消息后，根据鉴权随机数，使用MD5 算法计算鉴权结果，并向AN 发送CHAP响应消息，该消息中包含NAI、CHAP Password 和CHAP-Challenge 等接入鉴权参数。 f. AN 收到AT 上报的CHAP 响应消息后，向AN-AAA 发送A12 接入请求消息，其中包含NAI、CHAP Password、CHAP-Challenge 和AN-IP 等鉴权参数。 g. AN-AAA 根据A12 接入请求消息中的鉴权参数，使用MD5 算法计算鉴权结果，并与AT 上报的鉴权结果进行比较。若两者一致，则AN-AAA 向AN 发送A12 接入允许消息，允许AT 接入到1x EV-DO 网络，该消息中还包含MNID（或IMSI），用于建立和标识R-P 连接；否则，返回A12 接入拒绝消息，拒绝AT 接入到1x EV-DO 网络。若AN-AAA 收到的A12 接入请求消息中的鉴权密码为空，则直接丢弃该消息。 h. 若AN-AAA 允许AT 接入到网络，则AN 分析A12 接入允许消息的属性域得到IMSI，然后向AT 发送CHAP 鉴权成功消息；反之，AN 向AT 发送CHAP 鉴权失败消息 AT 发起位置更新 当配置属性中的RANHandoff=0x01 且AT 检测到位置变更（如ANID 改变）时，AT 会主动发起位置更新操作 a. AT 向AN 发送位置通告消息，上报AT 保存的ANID。