LTE PDCCH忙检测，并补充
PDCCH中承载的是各种各样的控制信息。由于系统部署和运行过程中的多样性，控制信息的内容也是非常多样的。为了简化起见，LTE中将DCI分成如下几种类型：
UE一般不知道当前PDCCH占用的CCE的数目大小，传送的是什么DCI format的信息，也不知道自己需要的信息在哪个位置。但是UE知道自己当前在期待什么信息，例如在Idle态UE期待的信息是paging, SI；发起Random Access后期待的是RACH Response；在有上行数据等待发送的时候期待UL Grant等。对于不同的期望信息UE用相应的X-RNTI去和CCE信息做CRC校验，如果CRC校验成功，那么UE就知道这个信息是自己需要的，也可以进一步知道相应的DCI format，调制方式，从而解出DCI内容。这就是所谓的盲检过程。
如果UE按照CCE的顺序依次搜索过去，那么UE侧的计算量是相当可观的，尤其是对于带宽比较大，CCE数目比较多的系统。为此协议中定义了搜索空间的概念，对系统中不同格式的PDCCH可能的摆放位置进行了一些限制，降低了UE进行盲检的复杂度。每个不同格式的PDCCH，对应不同的搜索空间。前面我们已经提到过，对于CCE数目为N的PDCCH，其起始位置的CCE号必须是N的整数倍。而且对于不同大小的PDCCH，其搜索空间的大小（定义为搜索需要覆盖的CCE数目，也就是可能的搜索位置数目与PDCCH格式对应的CCE数目之积）并不相同。更进一步，LTE中还划分了公共搜索空间（Common Search Space）和UE特定搜索空间（UE-Specific Search Space）。如下图所示：
| 类型 |
PDCCH类型[in CCEs] |
搜索空间大小 [in CCEs] |
可能的PDCCH数目 |
| UE-specific |
1 |
6 |
6 |
| 2 |
12 |
6 |
|
| 4 |
8 |
2 |
|
| 8 |
16 |
2 |
|
| Common |
4 |
16 |
4 |
| 8 |
16 |
2 |
下图为PDCCH搜索空间示意图：
其中每个方框代表一个CCE，并按照逻辑上排列好顺序了。
搜索的起点Z计算公式如下：
其中，A=39827,D=65537, Y(-1)=UE ID, α=UE 聚合等级,NCCE=可用的CCEs总数目,K = TTI索引。
所谓公共搜索区间是指所有UE都需要监听的区间，通常用来发送寻呼，RAR，系统消息，以及部分UE公用的上行功率控制消息等。公共搜索区间占据从0开始到最大数目为16的CCE，公共搜索区间内的PDCCH只有4CCE和8CCE两种类型的大小，UE需要在公共搜索区间内，从0开始，按CCE粒度为8进行搜索2次，按CCE粒度为4搜索4次，至多需要进行6次PDCCH的搜索。
LTE系统中，可用于PDCCH的CCE数目取决于系统带宽，PHICH配置，天线端口数，PCFICH配置等。上述因素确定后，PDCCH的CCE数目就可以确定，公共搜索区间就可以随之确定，从0开始占据至多16个CCE。公共搜索区间不随子帧的变化而变化。UE特定的搜索区间则不同，UE特定的搜索空间的起始点取决于UE的ID（C－RNTI），子帧号，以及PDCCH的类型，因而，随着子帧的不同，UE特定的搜索空间也有所不同。而且UE特定的搜索空间和公共的搜索空间有可能是重叠的。对于大小为N的PDCCH，在某一子帧内，对应某UE的特定搜索区间的起点就可以确定（起点可能落入公共搜索区间的范围内），UE从起始位置开始，依次进行对应大小PDCCH的盲检（也就是满足大小为N的PDCCH，其起始点的CCE号必须为N的整数倍），至多进行的盲检数目如上图所示，此时如果到了CCE的末端，UE特定的搜索空间有可能从CCE 0 开始，继续进行。从上图还可以看到，在UE特定的搜索区间内，UE需要进行的搜索次数至多为16。
对于公共搜索区间和UE特定搜索区间重叠的情形，如果UE已经在公共搜索区间成功检测，那么UE可以跳过重叠部分对应的特定搜索区间。
UE在PDCCH搜索空间进行盲检时，只需对可能出现的DCI进行尝试解码，并不需要对所有的DCI格式进行匹配。UE进行PDCCH盲检的总次数不超过44次。
博文源地址：http://blog.sina.com.cn/s/blog_673b30dd0100ksx5.html
盲检测与DCI和RNTI关系如下多张表：
UE根据在子帧中检测到的具有DCI格式1，1A，1B，1C，1D，2,2A或者UE扩展的DCI格式2B的PDCCH，使用上层定义的传输块数目限制条件来解码在同一子帧中相应的PDSCH。
UE可能设想定位参考信号不在根据用DCI格式1A或者1C的SI-RNTI或者P-RNTI做CRC扰码的PDCCH解码的PDSCH的资源块中出现。
如果UE被高层设置解码具有用SI-RNTI扰码CRC的PDCCH时，UE将根据表7.1-1中定义的任意组合来解码PDCCH和对应的PDSCH。对应于这些PDCCH的PDSCH用SI-RNTI来进行扰码初始化。
Table 7.1-1: PDCCH and PDSCH configured by SI-RNTI
| DCI format |
Search Space |
Transmission scheme of PDSCH corresponding to PDCCH |
| DCI format 1C |
Common |
If the number of PBCH antenna ports is one, Single-antenna port, port 0 is used, otherwise Transmit diversity. |
| DCI format 1A |
Common |
If the number of PBCH antenna ports is one, Single-antenna port, port 0 is used, otherwise Transmit diversity |
同样道理：
Table 7.1-2: PDCCH and PDSCH configured by P-RNTI
| DCI format |
Search Space |
Transmission scheme of PDSCH corresponding to PDCCH |
| DCI format 1C |
Common |
If the number of PBCH antenna ports is one, Single-antenna port, port 0 is used （see subclause 7.1.1）, otherwise Transmit diversity |
| DCI format 1A |
Common |
If the number of PBCH antenna ports is one, Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |
Table 7.1-3: PDCCH and PDSCH configured by RA-RNTI
| DCI format |
Search Space |
Transmission scheme of PDSCH corresponding to PDCCH |
| DCI format 1C |
Common |
If the number of PBCH antenna ports is one, Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |
| DCI format 1A |
Common |
If the number of PBCH antenna ports is one, Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |
Table 7.1-5: PDCCH and PDSCH configured by C-RNTI
| Transmission mode |
DCI format |
Search Space |
Transmission scheme of PDSCH corresponding to PDCCH |
| Mode 1 |
DCI format 1A |
Common and UE specific by C-RNTI |
Single-antenna port, port 0 (see subclause7.1.1)
|
| DCI format 1 |
UE specific by C-RNTI |
Single-antenna port, port 0 (see subclause7.1.1) |
|
| Mode 2 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 1 |
UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
|
| Mode 3 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 2A |
UE specific by C-RNTI |
Large delay CDD (see subclause 7.1.3) orTransmit diversity (see subclause 7.1.2) |
|
| Mode 4 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 2 |
UE specific by C-RNTI |
Closed-loop spatial multiplexing (see subclause 7.1.4)or Transmit diversity (see subclause 7.1.2) |
|
| Mode 5 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 1D |
UE specific by C-RNTI |
Multi-user MIMO (see subclause 7.1.5) |
|
| Mode 6 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 1B |
UE specific by C-RNTI |
Closed-loop spatial multiplexing (see subclause 7.1.4) using a single transmission layer |
|
| Mode 7 |
DCI format 1A |
Common and UE specific by C-RNTI |
If the number of PBCH antenna ports is one,Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |
| DCI format 1 |
UE specific by C-RNTI |
Single-antenna port; port 5 (see subclause 7.1.1) |
|
| Mode 8 |
DCI format 1A |
Common and |
If the number of PBCH antenna ports is one,Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |
| DCI format 2B |
UE specific by C-RNTI |
Dual layer transmission; port 7 and 8 (see subclause 7.1.5A) or single-antenna port; port 7 or 8 (see subclause 7.1.1) |
Table 7.1-6: PDCCH and PDSCH configured by SPS C-RNTI
| Transmission mode |
DCI format |
Search Space |
Transmission scheme of PDSCH corresponding to PDCCH |
| Mode 1 |
DCI format 1A |
Common and UE specific by C-RNTI |
Single-antenna port, port 0 (see subclause 7.1.1)
|
| DCI format 1 |
UE specific by C-RNTI |
Single-antenna port, port 0 (see subclause 7.1.1) |
|
| Mode 2 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 1 |
UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
|
| Mode 3 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 2A |
UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
|
| Mode 4 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| DCI format 2 |
UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2)
|
|
| Mode 5 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| Mode 6 |
DCI format 1A |
Common and UE specific by C-RNTI |
Transmit diversity (see subclause 7.1.2) |
| Mode 7 |
DCI format 1A |
Common and UE specific by C-RNTI |
Single-antenna port; port 5 (see subclause 7.1.1) |
| DCI format 1 |
UE specific by C-RNTI |
Single-antenna port; port 5 (see subclause 7.1.1) |
|
| Mode 8 |
DCI format 1A |
Common and |
Single-antenna port; port 7(see subclause 7.1.1) |
| DCI format 2B |
UE specific by C-RNTI |
Single-antenna port; port 7 or 8 (see subclause 7.1.1) |
Table 7.1-7: PDCCH and PDSCH configured by Temporary C-RNTI
| DCI format |
Search Space |
Transmission scheme of PDSCH corresponding to PDCCH |
| DCI format 1A |
Common and UE specific by Temporary C-RNTI |
If the number of PBCH antenna port is one, Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |
| DCI format 1 |
UE specific by Temporary C-RNTI |
If the number of PBCH antenna port is one, Single-antenna port, port 0 is used (see subclause 7.1.1), otherwise Transmit diversity (see subclause 7.1.2) |