LTE基本原理介绍.pptVIP

* 一般而言，往来高层的数据实体称为SDU，相应的往来低层的实体称为PDU RLC PDU的大小由调度机制决定，对于高速率数据，采用大的PDU可以使得开销相对较小；对低速率数据，采用小的PDU使得payload不会显得太大。 RLC can also be configured in Unacknowledged Mode (UM) and Transparent Mode (TM). In UM, in-sequence delivery to higher layers is provided, but no retransmissions of missing PDUs are requested. UM is typically used for services such as VoIP where error-free delivery is of less importance compared to short delivery time. TM, although supported, is only used for specific purposes such as random access. * * * * * * * * MIMO空间复用的作用是把一个原来SINR较高的信道，分成若干个SINR较低的信道。香农容量公式表明，在SINR较低时，SINR的改善能够迅速提高频谱效率；在SINR较高时，SINR的改善对频谱效率的提高作用越来越弱。 * * * * * * * * * * * 2007年2月St. Louis会议上，Vodafone提出要求把PDCP功能下移，当时该提议遭到Ericsson和我司以及其他Operator的反对，由于Vodafone在3GPP的强势以及IETF阵营的支持，最终这个提议被通过，并且，又一次刷新了SAE的架构，其中MME和UPE进行了正式的分离，并且由于PDCP功能的下移导致UPE功能基本成为简单路由器所以做出了和3GPP Anchor的合一，并且重新命名为Serving GW。这个架构一直维持至今，而且成为了SAE的最终架构。 S1-MME: Reference point for the control plane protocol between E-UTRAN and MME. S1-U: Reference point between E-UTRAN and Serving GW for the per bearer user plane tunnelling and inter eNodeB path switching during handover. S3: It enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active state. S4: It provides related control and mobility support between GPRS Core and the 3GPP Anchor function of Serving GW. In addition, if Direct Tunnel is not established, it provides the user plane tunnelling. S5: It provides user plane tunnelling and tunnel management between Serving GW and PDN GW. It is used for Serving GW relocation due to UE mobility and if the Serving GW needs to connect to a non-collocated PDN GW for the required PDN connectivity. S6a: It enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME and HSS. Gx: It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging Enforcement Function (PCEF) i