9 Layer 2/3 protocol aspects

25.2023GPP7.68 Mcps Time Division Duplex (TDD) optionOverall description: Stage 2Release 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

9.1 Protocol architecture

The protocol architecture for 7.68 Mcps TDD is the same as the protocol architecture for 3.84 Mcps TDD. Section 5.1 of [7] provides an overview of the radio interface protocol architecture.

9.2 Signalling

9.2.1 General

There are signalling differences between 7.68 Mcps TDD and 3.84 Mcps TDD. These differences concern L2/MAC and L3/RRC (see Section 5.1 of [7]) only. L2/RLC, L2/BMC, L2/PDCP and L3 U-plane information are not impacted.

9.2.2 L2/MAC differences

The L2/MAC differences between 7.68Mcps TDD and 3.84Mcps TDD are due to the support of a higher capability HSDPA UE at 7.68Mcps (20.4Mbps) and a higher capability E-DCH UE at 7.68Mcps (17.7Mbps). The L2/MAC differences concern:

– the maximum number of PDUs transmitted in a single TTI (636 at 7.68Mcps compared to 318 for3.84 Mcps TDD).

– HSPDA transport block size signalling. The maximum transport block size that can be signalled at 7.68Mcps is twice that at 3.84Mcps. A new table and formula for transport block size signalling for 7.68 Mcps TDD HS-DSCH is included in [9].

– E-DCH transport block size signalling. The maximum transport block size that can be signalled at 7.68Mcps is approximately twice that at 3.84Mcps. A new table and formula for transport block size signalling for 7.68 Mcps TDD E-DCH is included in [9].

9.2.3 L2/RRC differences

The L2/RRC differences concern:

Use of SF 32: The signalling is extended to include support for SF32. The 7.68 Mcps cell will be configured to use SF 16 or 32 for PRACH and E-RUCCH rather than SF 8 and 16 as 3.84 Mcps

Open Loop Power Control: Configuration of a cell for use of SF 16 or 32 with respect to the PRACH impacts calculation of the uplink transmit power for PRACH and requires the UE to add 3dB to the RACH Constant Value in the equation:

P_PRACH = L_PCCPCH + I_BTS + PRACH Constant value

for the case where RACH Spreading Factor = 16.

The same applies for open loop power control of E-RUCCH.

Capability Update Requirement: A new IE "UE radio access 7.68 Mcps TDD capability update requirement" is used.

Uplink Timing Advance: A different Uplink Timing Advance IE is required at 7.68Mcps to account for the number of bits used to signal timing advance at 7.68Mcps. A number of RRC messages are impacted due to the use of a different Uplink Timing Advance IE for 7.68 Mcps TDD to 3.84 Mcps TDD.

DL Physical Channel Capability: The physical channel capability at 7.68Mcps is extended in order to account for the greater number of physical channels supported at 7.68Mcps.

Burst Types and Midambles: Signalling related to burst types is modified since burst type 2 at 7.68Mcps supports K_cell of 4 or 8.

9.3 HSDPA related issues

The highest UE capability at 7.68Mcps is double that at 3.84Mcps, hence the maximum transport block size and the maximum number of PDUs that can be transmitted in a single TTI are double that of 3.84 Mcps. The range of UE capabilities is extended and the maximum UE capablitity for 7.68 Mcps is 20.4 Mbits/s.

9.4 Mobility

Inter RAT and intra RAT handover for 7.68 Mcps TDD is as for 3.84 Mcps TDD with handover between 3.84 Mcps TDD and 7.68 Mcps TDD cells also supported. Bands a), b), c), a + b), a + c), b + c) and a + b + c) can be configured for 7.68 Mcps TDD or 3.84 Mcps TDD or 1.28 Mcps TDD.

9.5 Idle Mode Procedures

Idle mode procedures are as for 3.84 Mcps TDD.

9.6 E-DCH related issues

The highest UE capability at 7.68Mcps is approximately double that at 3.84Mcps, hence the maximum transport block size and the maximum number of PDUs that can be transmitted in a single TTI are increasedwith respect to that of 3.84 Mcps. The range of UE capabilities is extended and the maximum UE capablitity for 7.68 Mcps is 17.7 Mbits/s.