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标题: 对于MAC Random Access过程的一点理解，请高手指教 [查看完整版帖子] [打印本页]

时间: 2012-2-21 07:41

作者: Charlesl0420 标题: 对于MAC Random Access过程的一点理解，请高手指教

1. Contention Based Random Access
过程 1: RRC establishment or RRC reestablishment
            CCCH logical channel (RRC establishment or RRC reestablishment)
过程 2: RRC handover on DCCH1 without the rach-ConfigDedicated configed
               NONE- CCCH logical channel
过程 3: PDCCH order
               NONE- CCCH logical channel

2. None-Contention Based Random Access
过程 4: RRC handover on DCCH1 with the rach-ConfigDedicated configed
            NONE- CCCH logical channel (PDCCH order or RRC handover on DCCH1)

《过程描述》
过程 1: If CCCH logical channel (the CCCH SDU is included in Msg3)
                  - MAC initializes random access
                  - ENB sends random access response (with temporary-CRNTI and UL-Grant) to UE
                  - MAC sends the Msg3 with CCCH-SDU (with RRC connection establishment or reestablishment request message UEID: 5bytes ;Establishment cause: 1 byte) to ENB on the received temporary-CRNTI
                  - MAC starts contention resolution timer
                  - ENB sends RRC connection establishment or reestablishment response message with MAC control element (UE Contention Resolution Identity) to UE on DL-SCH on the temporary-CRNTI
                  - MAC matches the UE Contention Resolution Identitywith the CCCH-SDU (checking the UEID)
                  - If matches
                        a. Stop contention resolution timer
                        b. Set the temporary-CRNTI to the C-RNTI
                        c. Send the RRC connection establishment or reestablishment response message to RRC
                        d. Random Access procedure successfully completed
                  - Else
                        a. Random Access procedure failed

过程 2, 3, 4: If NONE- CCCH logical channel (the C-RNTI MAC control element is included in Msg3)
                              - MAC initializes random access
                              - ENB sends random access response (with temporary-CRNTI and UL-Grant) to UE
                              - if ra-PreambleIndex was explicitlysignalled and it was not 0 (handover with the rach-ConfigDedicated message configed) <过程 2>
                                    a. MAC does not start contention resolution timer
                                    b. MAC sends the ULdata (e.g. RRC Connection Reconfiguration Complete- handover complete message on DCCH1)by the assigned UL-Grant on the C-RNTI (not temporary-CRNTI)
                                    c. The Random Access procedure successfully completed
                           NOTE: I think no Msg3 transmission in this procedure<过程 2>.
                              - Else (PDCCHorder or handover without the rach-ConfigDedicated message configed) < 过程 3, 4>
                                    a. MAC sends the Msg3 with C-RNTI MAC control element (original C-RNTI for PDCCH or the assigned C-RNTI for handover) to ENB on the received temporary-CRNTI
                                       b. MAC starts contention resolution timer
                                       c. If ENB sends PDCCH notification on C-RNTI (the C-RNTI sent in the MAC control element , not temporary-CRNTI)
                                    · stop mac-ContentionResolution Timer
                                    · discard the Temporary C-RNTI (use the original C-RNTI or the assigned C-RNTI for handover)
                                    · use the UL grant included in this notification for a new transmission
                                    · Random Access procedure successfully completed
                              Else 《对应 c if》
                                    If mac-ContentionResolution Timer expires
                                       Random Access procedure failed

[ 本帖最后由 Charlesl0420 于 2012-2-21 09:14 编辑 ]

时间: 2012-2-21 08:44

作者: ieai0011

这么早发帖支持一下

时间: 2012-2-21 09:15

作者: Charlesl0420

重新编辑了一下

时间: 2012-2-22 20:07

作者: illidan

PDCCH order can also include a ra-PreambleIndex which was explicitlysignalled and not 0

b. MAC sends the ULdata (e.g. RRC Connection Reconfiguration Complete- handover complete message on DCCH1)by the assigned UL-Grant on the C-RNTI (not temporary-CRNTI)

This is exactly the msg3 which is sent on UL-SCH with UL grant given in RAR. So you can see that there is always an msg3 in contention-based or -free random acess.

时间: 2012-2-23 04:39

作者: Charlesl0420 标题: 回复 4# 的帖子

这里是MAC协议的内容：
- if ra-PreambleIndex was explicitly signalled and it was not 000000 (i.e., not selected by MAC):
      - consider the Random Access procedure successfully completed.
- else, if the Random Access Preamble was selected by UE MAC:
      - set the Temporary C-RNTI to the value received in the Random Access Response message no later than at the time of the first transmission corresponding to the UL grant provided in the Random Access Response message;
      - if this is the first successfully received Random Access Response within this Random Access procedure:
            - if the transmission is not being made for the CCCH logical channel, indicate to the Multiplexing and assembly entity to include a C-RNTI MAC control element in the subsequent uplink transmission;
            - obtain the MAC PDU to transmit from the "Multiplexing and assembly" entity and store it in the Msg3 buffer.

可见，在Random Access Response过程中，如果ra-PreambleIndex 被设置了并且不是0，MAC认为Random Access完成，不需要再生成msg3 buffer了。只有ra-PreambleIndex未被设置或为0时，才生成Msg3 buffer。并且MAC一旦送出Msg3，就要启动ContentionResolutionTimer。

时间: 2012-2-23 12:37

作者: illidan

原帖由 Charlesl0420 于 2012-2-23 04:39 发表
这里是MAC协议的内容：
-       if ra-PreambleIndex was explicitly signalled and it was not 000000 (i.e., not selected by MAC):
      -       consider the Random Access procedure successfully completed.
-       else ...

Yes, you are right, and I made a mistake. Though there will be a UL-SCH transmission in response to the RAR, it is not called msg3. Only the message sent on UL-SCH granted by an RAR in a contention-based random access is called 'msg3'.

But you should note that for a PDCCH order, it may a contention-free random access (which might also be more resonable though not mandatory), if the preamble and PRACH resources are indicated by the PDCCH order.

时间: 2012-2-24 03:42

作者: Charlesl0420 标题: 回复 6# 的帖子

多谢回复，我再重编辑一下

时间: 2012-2-24 04:01

作者: Charlesl0420 标题: 回复 6# 的帖子

我没有编辑权限了，不过的确存在PDCCH order contention-free random access。可修改如下：
- if ra-PreambleIndex was explicitlysignalled and it was not 0 (by PDCCH order or handover with the rach-ConfigDedicated message configed) <过程 2>

时间: 2012-2-24 04:59

作者: Charlesl0420 标题: 重新编辑

MAC Random Access 过程:

1. Contention Based Random Access

过程 1: RRC establishment or RRC reestablishment
            CCCH logical channel (RRC establishment or RRC reestablishment)

过程 2: RRC handover on DCCH1 without the rach-ConfigDedicated configed
            NONE- CCCH logical channel

过程 3: PDCCH order without ra-PreambleIndex signalled or ra-PreambleIndex=0
            NONE- CCCH logical channel

2. None-Contention Based Random Access

过程 4: RRC handover on DCCH1 with the rach-ConfigDedicated configed
            NONE- CCCH logical channel (PDCCH order or RRC handover on DCCH1)

过程 5: PDCCH order with ra-PreambleIndex explicitly signalled and is not 0
            NONE- CCCH logical channel (PDCCH order or RRC handover on DCCH1)

《过程描述》

过程 1: If CCCH logical channel (the CCCH SDU is included in Msg3)
            -  MAC initializes random access
            -  ENB sends random access response (with temporary-CRNTI and UL-Grant) to UE
            -  MAC sends the Msg3 with CCCH-SDU (with RRC connection establishment or reestablishment
               request message UEID: 5bytes ; Establishment cause: 1 byte) to ENB on the received temporary-CRNTI
            -  MAC starts contention resolution timer
            -  ENB sends RRC connection establishment or reestablishment response message with MAC control element
               (UE Contention Resolution Identity) to UE on DL-SCH on the temporary-CRNTI
            -  MAC matches  the UE Contention Resolution Identity with the CCCH-SDU (checking the UEID)
            -  If matches
                  a. Stop contention resolution timer
                  b. Set the temporary-CRNTI to the C-RNTI
                  c. Send the RRC connection establishment or reestablishment response message to RRC
                  d. Random Access procedure successfully completed
            -  Else
                  a. Random Access procedure failed

过程 2, 3, 4, 5: If NONE- CCCH logical channel (the C-RNTI MAC control element is included in Msg3)
                        - MAC initializes random access
                        - ENB sends random access response (with temporary-CRNTI and UL-Grant) to UE
                        - if ra-PreambleIndex was explicitly signaled and it was not 0 (by PDCCH order or handover with the rach-ConfigDedicated message configed)
                           <过程 4, 5>
                           a.  MAC does not start contention resolution timer
                           b.  MAC sends the UL data (e.g. RRCConnectionReconfigurationComplete - handover complete message on DCCH1) by the assigned UL-Grant on the C-RNTI (not temporary-CRNTI)
                           c.  The Random Access procedure successfully completed
                           NOTE: I think no Msg3 transmission in the procedures < Procedure 4, 5>.
                        - Else (PDCCH order or handover without the rach-ConfigDedicated message configed)
                           < 过程 2, 3>
                           a.  MAC sends the Msg3 with C-RNTI MAC control element (original C-RNTI for PDCCH or the assigned C-RNTI for handover) to ENB on the received temporary-CRNTI
                           b.  MAC starts contention resolution timer
                           c.  If ENB sends PDCCH notification on C-RNTI (the C-RNTI sent in the MAC control element , not temporary-CRNTI)
                                    •  stop mac-ContentionResolutionTimer
                                    •  discard the Temporary C-RNTI (use the original C-RNTI or the assigned C-RNTI for handover)
                                    •  use the UL grant included in this notification  for a new transmission
                                    •  Random Access procedure successfully completed
                                 Else 《对应 c if》
                                    If mac-ContentionResolutionTimer expires
                                       Random Access procedure failed

时间: 2012-7-11 15:51

作者: xiaomi 标题: 回复 9# 的帖子

正好在看终端的代码，以下是我的理解。
非竞争的ra（切换和pdcch order）理论上都不需要msg3。基站在配置竞争preamble数目时候，并没有把64个全用，剩下的可以做非竞争用，因此此时msg3和msg4用来“竞争解决”是没有必要的。
对于非竞争，我们代码中虽然msg2后就任务成功了，但还是会走msg3的流程，我认为这主要是协议不是很明确，这样做为了兼容。如果msg2中有grant，直接可以走msg3，不然等dci format 0的ul grant一样的。
另外一个值得注意的是，如果在第n子帧收到msg2，则对于FDD，在n+1，n
+2, 或者n+3（依赖于msg2中的ul delay属性）的dci format 0 的ul grant会覆盖msg2中的grant

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