How MAC Protocol Work In LTE?

The MAC protocol provides the following services:
  • Logical Channel to Transport channel mapping
  • Scheduling:
    There is no dedicated channel allocated to a UE. Time and frequency resources are dynamically shared between the users in DL and UL. The scheduler is part of the MAC layer and controls the assignment of uplink and downlink resources.
  • Multiplexing/Demultiplexing of RLC PDU
  • The scheduler (in the eNodeB) determines dynamically, each 1 ms, which UEs are supposed to receive data on the DL shared channel and on the UL shared channel and on what resources. 
  • The basic time-frequency unit is the resource block. 
  • To select the adapted modulation and coding rate, the scheduler needs measurement reports in DL and UL.
In downlink, the scheduler needs the following inputs to schedule data:
  • Amount of data
  • Nature of the data
  • Radio resource available
  • Radio Condition in DL The UE reports regularly
its measurement report,called Channel Quality Indicator (CQI).
In uplink, the mechanism is similar but:
  • Measurements are made by the eNodeB
  • The eNodeB scheduler controls the UE transmission
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