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Type 1 PDCCH Common Search Space

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The 5G New Radio (NR) protocol introduces several new concepts, one of which is the PDCCH (Physical Downlink Control Channel). The PDCCH is crucial for signaling and control information exchange between the base station (gNB) and the User Equipment (UE).

Let's delve into the Type 1 PDCCH Common Search Space in detail:

PDCCH in 5G NR:

PDCCH is part of the 5G NR physical layer and is used for transmitting downlink control information (DCI). DCI includes parameters like resource allocations, HARQ feedback, and other control information necessary for the UE to operate in the network.

Search Space:

The search space concept in 5G NR is introduced to efficiently search for PDCCH candidates due to the vast number of potential candidates. The search space defines the locations where the UE needs to look for PDCCH.

Type 1 PDCCH Common Search Space:

Type 1 PDCCH Common Search Space is a specific configuration where the UE looks for PDCCH candidates within a predefined set of locations in the frequency-time grid. This is designed to handle common control information that is applicable to multiple UEs.

Here are some technical details:

  1. Resource Blocks (RBs): The search space is defined in terms of a set of RBs in the frequency domain and a set of symbols in the time domain. The UE is configured to search for PDCCH candidates within this RB-symbol grid.
  2. Aggregation Level (AL): The Type 1 common search space is associated with specific aggregation levels, which determine the number of contiguous control channel elements (CCEs) the PDCCH can occupy. An aggregation level is chosen based on the amount of control information that needs to be transmitted.
  3. Mapping and Monitoring: The gNB maps the DCI to the PDCCH and distributes it across the configured search space. The UE is then responsible for monitoring this search space to detect PDCCH candidates. The UE uses demodulation reference signals (DMRS) to decode the PDCCH.
  4. Frequency-Time Structure: The common search space is structured in a way that allows for efficient detection of common control information across UEs. The frequency and time structure of the search space are defined based on the system bandwidth, subcarrier spacing, and other parameters.
  5. UE Configuration: The UE receives configuration information from the gNB regarding the Type 1 common search space. This includes parameters like the starting RB, the number of RBs, symbols, aggregation level, and other relevant parameters.