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RRC層信令傳輸解析過程

如問題，誰能給講解一下LTE/LTE-A的RRC層信令的傳輸解析過程，比如eNodeB向UE傳輸信令是個什么過程啊不明白啊求講解！

提問者: jtth 提問時間: 2013-10-22

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問題答案 ( 3 )

RRC層信令包括：RRCConnectionRequest、RRCConnectionSetup、RRCConnectionSetupComplete等，其中包含AttachRequest消息。eNodeB和UE進(jìn)行信令交互，你可以看一下LTE的信令流程。其實我這些天也在愁信令解析，信令的消息格式以各個字段、字長劃分，從那些抓取的一大長串碼流中，如何分析出各個字段字節(jié)所代表的含義。我還沒有研究明白，共同學(xué)習(xí)吧！

回答者：初辰回答時間：2013-10-22 15:42

To a first approximation, the downlink channel for FDD appears as a sequence of 1ms subframes. The first few (typically 3, or 1 or 2 or 4 depends on number of RS) symbols are used for control signaling (PDCCH) and the remaining of the 14 symbols is the share channel (PDSCH) which carries both signaling an the data traffic.
The UE checks the PDCCH for its C-RNTI or P-RNTI (0XFFFE) or SI-RITI (0XFFFF). The C-RNTI is unique to the UE in a cell. The P-RNTI and SI-RNTI are common to all UEs. (P-RNTI Pagin RNTI, SI-RNTI System Information RNTI)

Technically speaking, the PDCCH has its 16 bit CRC scrambled by the appropriate RNTI.
The check for P-RNTI or SI-RNTI is not done in every PDCCH frame but only on selected,”paging occasion” sub-frame ( once every DRX cycle).

if the UE finds its C-RNTI in the PDCCH channel, then it knows that there is a control plane (RRC) or user-plane (PDCP) message for it in the PDSCH portion (symbols 4-14) of the subframe. The PDCCH also points to which part of the PDSCH subframe contains the message for the UE.
The UE then goes to that part of the PDSCH to find out what the message is.
The MAC header in the PDSCH tells the UE whether it is an RRC message or a Data message.

Logical Channel ID 0 >> CCCH (SRB0)
Logical Channel ID 1,2 >> DCCH (SRB1 and SRB2)
Logical Channel ID 3-10 >> DTCH

How does the UE find out what RRC message is being sent to it in DL direction?

if Logical Channel ID 0 == 0 (SRB0) : The “message type” field in RRC message tells the UE what the message is :

            DL-CCCH-Message Type::= CHOICE {
                                                                   rrcConnectionReestablishment
                                         rrcConnectionReestablishmentReject
                                                                   rrcConnectionReject
                              rrcConnectionSetup
                                }

if Logical Channel ID 0 == 1:2 (SRB1 and SRB2) : The “message type” field in RRC message tells the UE what the message is :

            DL-DCCH-Message Type::= CHOICE {
                                                                   csfbParametersResponseCDMA2000
                               dlInformationTransfer
                                                                    ….
                                                                    counterCheck
                        ueInformationRequest-r9
                                }

If Logical Channel ID == 3:10 (DRBs): The message is a data traffic channel

回答者： dancerinbright 回答時間：2013-10-22 23:02

謝謝！

jtth 2013-10-23 09:02

你好~我想問一下，這些話是在哪個協(xié)議里么？

微微一笑:-) 2013-11-25 10:34

通過ASN.1編解碼來解析。。。

回答者： expsive 回答時間：2013-10-31 08:52

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