Physical layer processes a single transport block for each resource allocation.
There are 2 types of resource allocations: dynamic allocation and configured grant allocation.
Dynamic allocation
For every PUSCH transmission, network sends DCI format 0_0 or 0_1 to specify allocated resources. These resources can be changed for every transmission.
These dynamic allocations are adaptive to current radio conditions, user requirements and network load, but have drawback of increased PDCCH signaling load which creates system overhead.
There are two types of dynamic allocation:
- UE requests allocations by using Scheduling Request (SR)/Buffer Status Report (BSR)/Random Access Procedure (RACH).
This approach involves higher latency as UE may have to wait before being permitted to send requests for uplink resources.
- Base station allocates resources in proactive manner. Base station provides uplink resource allocations without relaying upon UE.
This helps UE to ensure that uplink resources are available when UE has to send uplink data. These grants are called proactive grants. Proactive grants increase uplink interference levels unless skipping is enabled.
When a proactive grant is received to UE and there is no uplink data, it transmits packets of padding.
Configured grant allocations
In this method, PDCCH transmissions are not required prior to sending PUSCH transmissions.
There are two types of configured grant allocations:
- Type 1 resource allocations: The resource allocation is fully configured and released using RRC signaling. UE can do PUSCH transmissions periodically.
PDCCH transmissions used only for retransmissions. This type1 allocations are designed for longer term requirements.
IoT devices could be provided using type 1 resource allocations. Uplink data can be transferred without Scheduling requests (SRs) and PDCCH
transmissions.
- Type 2 resource allocations: Type 2 is partially configured using RRC signaling but activated/deactivated using PDCCH transmissions.
While activating PDCCH provides time and resource allocations.
Type 2 is used for rapid activation and deactivation.
eg. voice service. Activate when user speaking, deactivate when listening.
Both dynamic and configured grant uses both time and frequency resource allocations.
Configured grant and PC(Power control)
ConfiguredGrantConfig IE is used configure uplink transmission without PDCCH DCI format 0_0 or 0_1 transmissions. This IE is used in configured grant resource allocations.
The actual uplink grant may either be configured via RRC (Type 1) or via PDCCH (type 2).
ConfiguredGrantConfig IE has two fields related to power control: powerControlLoopToUse and p0-PUSCH-Alpha.
The powerControlLoopToUse and p0-PUSCH-Alpha information elements provide information related to PUSCH power control.
UE capabilities
The network initiates the procedure to a UE in RRC_CONNECTED when it needs (additional) UE radio access capability information. In response UE sends its UE capabilities to network.
The IE Phy-Parameters is used to convey the physical layer capabilities. Phy-ParametersCommon IE has two fields configuredUL-GrantType1 and configuredUL-GrantType2. If UE is not supporting configured grant resource allocations, this info will not be set.
Time domain resource allocation (TDRA)
Time domain resources can be allocated through DCI format 0_0/0_1 or through RRC signaling.
Time domain resources can be allocated for the PUSCH using Downlink Control Information (DCI) Formats 0_0 and 0_1. DCI is transferred to the UE using the PDCCH physical channel. Alternatively, in the case of Type 1 Configured Grants, time domain resources are allocated for the PUSCH using RRC signaling.
The ‘Time Domain Resource Assignment’ field within the DCI defines a pointer towards a row within a look-up table. Similarly, the ‘timeDomainAllocation’ information element (in ConfiguredGrantConfig IE) within the RRC signaling protocol defines a pointer towards a row within a look-up table.
These fields value m provides a row index m+1 to an allocated look-up tables described here.
Each row entry has slot offset(K2), PUSCH mapping type and start and length Indicator (SLIV) or start symbol and length.
PUSCH slot offset is calculated based on PDCCH slot number(n), PDCCH SCS , PUSC SCS and K2 values.
Type 1 Configured Grants use the timeDomainOffset, periodicity information elements from within the ConfiguredGrantConfig parameter structure.
When using Configured Grant Type 1, a transmission occasion starts when the following equation is satisfied:
(SFN x SlotsPerFrame x SymbolsPerSlot) + (SlotNumber x SymbolsPerSlot) + SymbolNumber =
(timeDomainOffset x SymbolsPerSlot + S + N x periodicity) MOD (1024 x SlotsPerFrame x SymbolsPerSlot)
where, timeDomainOffset and periodicity are both specified within the ConfiguredGrantConfig parameter structure. ‘S’ corresponds to the starting symbol deduced from the TimeDomainAllocation information element. ’N’ is an integer corresponding to the Nth transmission occasion.
When using Configured Grant Type 2, a transmission occasion starts when the following equation is satisfied:
(SFN x SlotsPerFrame x SymbolsPerSlot) + (SlotNumber x SymbolsPerSlot) + SymbolNumber =
[(SFNstart x SlotsPerFrame x SymbolsPerSlot + Slotstart x SymbolsPerSlot + Symbolstart) + N x periodicity] MOD (1024 x SlotsPerFrame x SymbolsPerSlot)
where, SFNstart, Slotstart and Symbolstart are the SFN, slot and symbol during which the first PUSCH transmission occurs according to the resource allocation within the activation PDCCH.
Frequency domain resource allocation is explained in next post.
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