Resource Allocation Type in a Nutshell

Resource Allocation Type in Detail

Resource Allocation Type indicates a method for resource allocation in frequency domain. Similar concept is used in LTE Resource Allocation as well. So if you are familiar with LTE Resource Allocation Type, you would easily understand the concepts on NR Resource Allocation Type.

• What kind of resource allocation types are supported ?
• How to determine Resource Allocation Type ?
• Allocation Type 0
• Allocation Type 1
• Dynamic Switch

What kind of resource allocation types are supported ?

NR Resource Allocation Type is specified in the following specification.

• Downlink : 38.214 - 5.1.2.2 Resource allocation in frequency domain
• Uplink : 38.214 - 6.1.2.2 Resource allocation in frequency domain

Resource Allocation Type specifies the way in which the scheduler allocate resource blocks for each transmission. Just in terms of flexibility, the way to give the maximum flexibility of resource block allocation would be to use a string of a bit map (bit stream), each bit of which represent each resource block. This way you would achieve the maximum flexibility, but it would create too much complication of resource allocation process or too much data (too long bit map) to allocate the resources.

As mentioned above, LTE also use similar concept. Following table shows the comparision of NR and LTE Resource Allocation Type.

How to determine Resource Allocation Type ?

According to 38.214 - 5.1.2.2, the Resource Allocation Type is determined implcitely by DCI format or by RRC layer message as described below.

•   The UE may assume that when the scheduling grant is received with DCI format 1_0 downlink resource allocation type 1 is used.
•   If the scheduling DCI is configured to indicated the downlink resource allocation type as part of the Frequency-domainPDSCHresource field, the UE shall use downlink resource allocation type 0 or type 1 as defined by this field. Otherwise the UE shall use the downlink frequency resource allocation type as defined by the RRC configured parameter Resource-allocation-config for PDSCH.

Allocation Type 0

In this type, we bundle multiple number of consecutive RBs into RBG(Resource Block Group) and allocate PDSCH / PUSCH only in the multiples of RBG. The number of RBs within a RBS varies depending on Bandwidth Part Size and Configuration as shown in the following table. The configuration type is determined by rbg-size field in PDSCH-Config in a RRC message. We specify the bitmap in DCI indicating the RBG number that carries PDSCH or PUSCH data. Since this is the bitmap, it is not required for the RBGs to be consecutive.

<  38.214 - Table 5.1.2.2.1-1: Nominal RBG size P, Table 6.1.2.2.1-1: Nominal RBG size P >

Allocation Type 1

In this type, the resource is allocated to one or more consecutive RBs. The resource allocation area is defined by two parameters RB_Start and Number of Consecutive RBs within a specific BWP(BandWidth Part). When the resource allocation is specified in DCI, RB_Start and Number of Consecutive RBs within the BWP is combined into a specific single value called RIV(Resource Indicator Value).

When the resource allocation for type 1 is configured in DCI, it is specified as a specific number called RIV. RIV is a number to specify PDSCH or PUSCH resource allocation. In more intuitive form,  we normally use two values (i.e, Number of RBs and Start RB) for the resource allocation. But with RIV, we can represent Number of RBs and Start RB in a single value. It would have some advantage in terms of number of bits to carry the information.. but it causes some confusion for us to convert RIV into Number of RBs and Start RB

The RIV is calculated in following formula.

< Downlink >

< Uplink >

NOTE : For easy conversion between RIV and RB, check out this site.

Dynamic Switch

Whether to use Type 0 or Type 1 is determined by DCI at the time of each transmission.

In 38.214-5.1.2.2, it is stated as follows.

If the scheduling DCI is configured to indicate the downlink resource allocation type as part of the Frequency domain resource assignment field by setting a higher layer parameter resourceAllocation in pdsch-Config to 'dynamicswitch', the UE shall use downlink resource allocation type 0 or type 1 as defined by this DCI field. Otherwise the UE shall use the downlink frequency resource allocation type as defined by the higher layer parameter resourceAllocation.

In 38.212-7.3.1.2.2, it is stated as follows.

If both resource allocation type 0 and 1 are configured, the MSB bit is used to indicate resource allocation type 0 or resource allocation type 1, where the bit value of 0 indicates resource allocation type 0 and the bit value of 1 indicates resource allocation type 1.

Reference

[1]