Paging Indicator Channel PICH work in 3G

Paging Indicator Channel PICH main work in 3G as below.

  • Carrying Paging Indicators (PI)
  • Fixed rate (30kbps), SF = 256
  • N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72, or 144

Page Indicator Channel 3g

The Page Indicator Channel (PICH) is a fixed rate (30kbps, SF=256) physical channel used by the NodeB to inform a UE (or a group of UEs) that a paging information will soon be transmitted on the PCH. Thus, the mobile only decodes the SCCPCH when it is informed to do so by the PICH. This enables to do other processing and to save the mobiles’ battery.

The PICH carries Paging Indicators (PI), which are user specific and calculated by higher layers. It is always associated with the S-CCPCH to which the PCH is mapped.

The frame structure of the PICH is illustrated above. It is 10 ms long, and always contains 300 bits (SF=256). 288 of these bits are used to carry paging indicators, while the remaining 12 are not formally part of the PICH and shall not be transmitted. That part of the frame (last 12 bits) is reserved for possible future use.

In order not to waste radio resources, several PIs are multiplexed in time on the PICH. Depending on the configuration of the cell, 18, 36, 72 or 144 paging indicators can be multiplexed on one PICH radio frame. Thus, the number of bits reserved for each PI depends of the number of PIs per radio frame. For example, if there is 72 PIs in one radio frame, there will be 4 (288/72) consecutive bits for each PI. These bits are all identical. If the PI in a certain frame is “1”, it is an indication that the UE associated with that PI should read the corresponding frame of the S-CCPCH.

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