[移动通讯]【Carrier Aggregation-9】【 Radio Resource Control (RRC) Aspects】

前言：

  CA 分析辅助工具： UE Capabilities

目录： 

1.    总体流程
2.    Radio Resource Control (RRC) Aspects
3.    SCell addition and removal
4.     Handover

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一     总体流程

     1.1  CA 总体流程

   

      1.2 CA 和 NSA 区别

           NSA 我理解也是一种特殊的CA 方案，但是无线资源管理，以及终端影响到了PDCP,SDAP,

RLC 层。

    

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二  Radio Resource Control (RRC) Aspects

     为了更灵活使用CA, E-UTRAN 必须了解UE 支持CA 的情况.  

这里面我们重点解读一下 UE Capability Information OTA 信令

UL_DCCH / UECapabilityInformation

    2.1 UE category

         The category that UE support is indicated in UE Capability Information message as shown below. Notice that ue-Category can specify only up to Cat 4.

        The category higher than 4 should be assinged to another IE (Information Element) ue-Category-v1020. (Here we are having similar confusing IEs as in WCDMA/HSPA. So many different places to check to figure out exact category)）

       CA support is implied by UE categories 6, 7, and 8

       The UE category (without suffix) defines a combined uplink and downlink radio throughput capability

 例：我们OTA 里面看到如下信息

ue-Category	4
ue-Category-v1020  总体信息	6
ue-CategoryDL-r12  具体上下行	13
ue-CategoryUL-r12  具体上下行	5

36.306 defines the maximum throughput for each category as follows :

 

         Note : Following throughput does not make difference about the number of Carriers. When you are talking about Categories about Carrier Aggregation throughput, you would be clear on whether you are talking about the category for each component carrier or categories of aggregated carriers.

      This tables tells you only about the maximum throughput, it doesn't tell in detail about how you achieve it. Many people tries to associate this table to a specific MIMO configuration or Carrier Aggregation(CA) configuration. But there is no direction connection between this table and MIMO/CA condition.

   简单的说，这个标志位跟载波聚合没关系

注意事项：

Note 1 :

            The number shown in this table is the number of bits that can be transmitted in 1 TTI (1 ms). So you have to multiply this number by 1000 to get the rate in 'bps'. For example, Table 4.1-1 Category 3 says 102048. If you convert this number into bps, it is 102048 x 1000 = 102,048,000 bps.

Note 2 :

         You should be very careful when you talk about the throughput in Kbps, Mbps unit. A lot of people do the conversion by dividing the number by 1000, 1000000. But in digital theory (especially in computer world) 1 Kbps is 2^10 bits and 1 Mbps is 2^20 bits. When the number is small, you don't see much difference, however when the number is very big, the difference between the two different conversion would give you huge difference.

Note 3 :

          The number shows in this table is based on the assumption that all the DL/UL TTI carries only user data (U-Plane Data), but in really you cannot allocate 100% of resources for user data only. There should be a certain portion of overhead (like SIBs, MAC CE, Signaling etc). So real throughput you get will be less than the one listed in this table.

 下行：3GPP 36.306 V14.5-Table 4.1A-A<   Downlink physical layer parameter values set by the field ue-CategoryDL >

上行：< 36.306 v13.4 - Table 4.1A-2: Uplink physical layer parameter values set by the field ue-CategoryUL >

  

2.2 Cross-carrier scheduling support

      指示UE 可以从PCell 上面接收SCell的PDCCH 调度信息。 PCell PDCCH 里面包含

SCell 的PDCCH 信息

   （A heterogeneous network is a network connecting computers and other devices with different operating systems and/or protocols. For example, local area networks (LANs) that connect Microsoft Windows and Linux based personal computers with Apple Macintosh computers are heterogeneous.）  

构网络主要是针对目前现在无线接入网络的差异性。例如宏基站（Macro Basestation）、小基站(Micro Basestation)以及家庭基站（Femto  Basestation）覆盖的区域。这类基站主要是接入协议是相同的

     Cross-carrier scheduling is an important feature in heterogeneous networks (HetNet) where inter-cell interference is significant when the cells within HetNet are deployed on the same carrier frequency.(不同Band 频点相同）

      The PDCCH, carrying Downlink control information (DCI), must be received by the UEs at the cell edge, so, PDCCH may be transmitted with higher power than the traffic channels. This causes inter-cell interference on the PDCCH of the respective carrier. In CA, cross-carrier scheduling enables the UE connected to different nodes to receive the PDCCH on different carriers to eliminate inter-cell interference on the PDCCH

     Cross-carrier scheduling may also be used to balance the loads from traffic and scheduling across different component carriers.

   This technique is also effective in scenarios where scheduling of PDCCH on a carrier which has larger bandwidth compared to the carrier of relatively small bandwidth, due to the fact that carriers with smaller bandwidths have relatively low frequency diversity gain.

    Without cross-carrier scheduling, the downlink scheduling assignments on PDCCH are valid for the component carrier (CC) on which they were transmitted. 
      Similarly, for uplink grants, there is an association between downlink and uplink CCs (provided in cell 's system information) such that each uplink CC has
an associated downlink CC. Thus, from the uplink–downlink association, the UE will know to which uplink CC the DCI relates to.

     With cross-carrier scheduling, the PDSCH is received on a CC other than the one on which PDCCH/EPDCCH is received. Similarly, the PUSCH would be transmitted on an associated CC other than the one on which uplink grant is received.

    The cross-carrier scheduling feature is optional for the UE introduced in Release-10. The UE indicates its support of this feature with parameter crossCarrierScheduling-r10 under PhyLayerParameters-v1020 during the UE capability transfer procedure.

Cross-carrier scheduling does not apply to PCell i.e. PCell is always scheduled via its own PDCCH. As shown in the figure below, cross-carrier scheduling is only used to schedule resources on a Secondary CC without PDCCH.

     For each UE, the eNodeB can either enable or disable the cross-carrier scheduling independently for each CC, via RRC signaling.
     When cross-carrier scheduling is active, the UE needs to know to which CC a certain DCI relates. The carrier responsible for delivering scheduling information should add an indication in the DCI, which SCell the DCI is intended for.

     A new 3-bit Carrier Indicator Field (CIF) is added at the beginning of Release-8 PDCCH DCI formats. Whether CIF is present in a serving cell’s PDCCH DCI or not is configured by eNodeB via RRC signaling. CIF value ‘zero’ indicates PCell, while the other SCell can be addressed with ServCellIndex i.e., CIF value is the same as ServCellIndex.

       The cif-Presence-r10 in physicalConfigDedicated (PCell configuration) indicates whether CIF is present in the PDCCH DCI of the PCell.
         Similarly, each SCell may be configured with cross-carrier scheduling as part of SCell addition or modification. crossCarrierSchedulingConfig is responsible for this and is part of PhysicalConfigDedicatedSCell.

      schedulingCellInfo under crossCarrierSchedulingConfig indicates whether cross-carrier scheduling is enabled or not. If schedulingCellInfo indicates ‘own’, it means that the SCell will be transmitting its own PDCCH i.e., cross-carrier scheduling not enabled. On the other hand, if cross-carrier scheduling is enabled, then schedulingCellInfo indicates ‘other’, which means that some ‘other’ serving cell would be transmitting PDCCH DCI.
The parameter schedulingCellId informs the UE about which cell signals the downlink allocations and uplink grants for the concerned SCell.
      As discussed above, when the cross-carrier scheduling is enabled on an SCell, the UE wouldn’t be decoding PDCCH on that SCell, so UE doesn’t need to decode PCIFH on the concerned SCell. This implies that the UE does not know how many OFDM symbols in the beginning of each subframe are used for control data. Hence, this information referred to as pdsch-Start needs to be informed to the UE at the time of activating cross-carrier scheduling.
pdsch-Start is the starting OFDM symbol of PDSCH (data region) for the concerned SCell. Values 1, 2, 3 are applicable when dl-Bandwidth for the concerned SCell is greater than 10 resource blocks, values 2, 3, 4 are applicable when dl-Bandwidth for the concerned SCell is less than or equal to 10 resource blocks.
          Also, it is important to note that, when cross-carrier scheduling is active for an SCell, it can only be scheduled by one CC. Considering the same example above, it is not possible for SCell1 to receive scheduling information on PDCCH from both PCell and SCell2.
         The common search space is always on the primary cell, but the UE-specific search space can be on the primary cell or on any of the secondary cells.
        A UE configured with the CIF for a given serving cell shall assume that the CIF is not present in any PDCCH of the serving cell in the common search space. On the other hand, the UE shall assume that CIF is present in PDCCH located in the UE specific search space.

2.3 Simultaneous PUCCH and PUSCH transmission support

           For CA-capable UEs, implies that the UE can support
simultaneous PUCCH and PUSCH transmission on different CCs.

2.4 Multi-cluster PUSCH within a CC support 

    Indicates baseband (non-band-specific) support for multi-cluster
PUSCH transmission within CCs. (Explained in testing section)

2.5 Non-contiguous uplink resource allocation within a CC support

     Indicates that RF (band- specific) supports noncontiguous
uplink resource allocations within CCs.

2.6Supported band combinations

 – Indicates the specific frequency band and channel bandwidth configurations that
the UE can utilize in support of CA.

2.7 Event A6 reporting support

– Indicates that the UE is able to report Event A6, which occurs when a neighbor PCell
becomes stronger than a serving SCell by an offset.

2.8 SCell addition during handover to E-UTRA support

   – Indicates that the UE can support E-UTRAN inbound interradio

2.9  access technology (IRAT) handover directly into CA mode.
     Periodic SRS transmission on all CCs support – Indicates that the UE can transmit periodic SRSs on all SCells.

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三 SCell addition and removal

       SCells are added and removed from the set of serving cells through the RRC Connection Reconfiguration procedure.
      Note that, since intra-LTE handover is treated as an RRC connection reconfiguration, SCell “handover” is supported.
       The CA-related information sent by the base station pursuant to this the RRC Connection Reconfiguration procedure is summarized below.

       Cross-carrier scheduling configuration – Indicates, among other things, if scheduling for the referenced,SCell is handled by that SCell or by another cell.
    • SCell PUSCH configuration – Indicates, among other things, whether resource block group hopping is  utilized on the SCell.
• SCell uplink power control configuration – Carries a number of primitives related to SCell uplink TPC,  including the path loss reference linking parameter.
       • SCell CQI reporting configuration – Carries a number of primitives related to CQI measurements reporting  for SCells.

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四   Handover

     Handover processing for LTE in Release-10 is largely the same as Releases 8 and 9, except that clarifications are made to refer to PCell in the measurement-related RRC signaling messages.
     Release-10 does introduce one new measurement event: Event A6. As indicated above, Event A6 occurs when a neighboring cell’s strength becomes better than an SCell’s strength by an offset.
   In the case of Intra-Band SCell’s, this event is less useful, as the strength of the PCell and the SCells usually is very  similar. However, with Inter-Band serving cells, the strength of a neighbouring PCell could be significantly different from a serving SCell. Depending on network conditions – such as traffic load distribution – it could be advantageous to
execute a handover to the cell identified by Event A6.     

Intra-Band scenario

    Intra-Band Contiguous and Non Contiguous

Inter-Band scenario

参考：

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