LTE: Resource Allocation

The information on which Resource Blocks (RBs) are allocated (Resource Allocation) for both Uplink and Downlink needs to be signalled to the UE.

The Resource Allocation information is carried on Downlink Control Information (DCI) by Physical Downlink Control Channel (PDCCH). Resource Allocation field is one of the major field in the DCI.

In the case of Uplink, the allocated RBs have to be contiguous in order to guarantee single-carrier property (SC-FDMA is used in the Uplink). The contiguous nature of resource allocation requires less number of bits but the scheduler in the eNB will have less flexibility in allocating the resources.

  

In the case of Downlink, the allocated RBs doesn’t need to be contiguous which will require more bits to signal the Resource Allocation but the eNB’s scheduler will have more flexibility in allocating the resources.

In LTE, ResourceAllocation Type 0, Resource Allocation Type 1 and Resource Allocation Type 2 are defined.

Resource Allocation Type 0 and Resource Allocation Type 1 are used for non-contiguous resource allocation (only for Downlink) which uses bit-map based signaling. 

For allocating contiguous resource blocks in the Uplink, Resource Allocation Type 0 is used where as same for downlink it is called as Resource Allocation Type 2.

The UE shall interpret the Resource Allocation field depending on the PDCCH DCI Format detected. 

For Uplink, Resource Allocation information is conveyed on PDCCH DCI Format 0 using Resource Allocation Type 0.

In the Downlink, PDCCH DCI Formats 1, 2, 2A and 2B uses Resource Allocation Type 0 or Type 1  whereas PDCCH DCI Formats 1A, 1B, 1C and 1D uses Resource Allocation Type 2

Click here for Resource Allocation Type 0 in the Downlink. Check here for Downlink Resource Allocation Type 1. 

Uplink Type 0 and Downlink Type 2 are explained in post 'Downlink Resource Allocation Type2 and Uplink Resource Allocation Type0'.

Reference: 3GPP TS 36.213