LTE: Downlink Resource Allocation Type 2 and Uplink Resource Allocation Type 0

This type of resource allocation is mainly used for contiguous RB allocations for uplink (RA Type0) and for compact scheduling of downlink assignments (RA Type 2).

In this type, the resource block assignment information indicates to a scheduled UE a set of contiguously allocated localized VRBs or distributed VRBs.

In case of resource allocation signaled with PDCCH DCI format 1A, 1B or 1D, one bit flag indicates whether localized VRBs or distributed VRBs are assigned (value 0 indicates Localized and value 1 indicates Distributed VRB assignment) . In the case of resource allocation signaled with PDCCH DCI format 1C, only distributed VRBs are assigned.

Localized VRB allocations for a UE vary from a single VRB up to a maximum number of VRBs spanning the system bandwidth.

For indicating contiguous RB assignment, starting position of the RB (RB_start) and the number of RBs is required. Let us consider RB_start = 0^th RB, the number of combinations possible = N_RB. Similarly when RB_start = 1^st RB, then the number of possible combinations are N_RB – 1 and so on. There are N_RB.(N_RB + 1)/2 combinations possible in total.

For downlink, PDCCH DCI format 1A, 1B or 1D, a type 2 resource allocation field consists of a Resource Indication Value (RIV) corresponding to a starting resource block (RB_start) and a length in terms of virtually contiguously allocated resource blocks L_CRBs.

For uplink, a resource allocation (type 0) field in the scheduling grant consists of a resource indication value (RIV) corresponding to an RB_start and a length in terms of contiguously allocated physical resource blocks (L_CRBs ≥ 1). The RIV value for both uplink and downlink is defined by:

        RIV = N_RB (L_CRBs — 1) + RB_start                                            if (L_CRBs — 1) ≤ ⎿ N_RB /2⏌

                = N_RB (N_RB — L_CRBs + 1) + (N_RB — 1 — RB_start)         otherwise

Example:

Let us consider N_RB = 6 ⇨ N_RB.(N_RB + 1)/2 = 21 ⇨  5-bits are required for indicating any RIV value ranging from 0 to 20. The RIV values for N_RB = 6 are illustrated below. Let RB_start = 2 and L_CRBs = 3, from the above equations RIV = 14

Reference: 3GPP TS 36.213