24.2 Study on Synchronized e-dch for utra fdd uid_370042

Resources: R1

References

Document	Title/Contents
WID(s)
RP-070678	SID on Synchronized E-DCH for UTRA FDD
Impacted Specifications
-	-
New Dedicated Specifications/Reports
TR 25.823	Feasibility study on synchronized E-DCH for UTRA FDD

Supporting Individual Members: Nokia, Nokia Siemens Networks, Qualcomm, T-Mobile International, Ericsson.

The goal of RAN1 Rel-5 study TR 25.854 Uplink Synchronous Transmission Scheme (USTS) was to improve orthogonality of the uplink signals by sharing a common scrambling code and assigning different channelization codes to UEs similarly to downlink. In order to achieve the improved orthogonality at the receiving side (Node B), the transmission time on the UE side needs to be adjusted so that the arrival times in Node B are sufficiently synchronized.

This study did not lead to an implementation work item due to lack of orthogonal codes space (as too many users with DTX would require multiple parallel codes) and at that time all resource allocation resided in RNC.

Since then 3GPP has introduced MAC layer functionality in the BTS to control radio resources with HSDPA and HSUPA, and thus the limitation of RNC-only control of resource allocation was removed. Also the use of 16QAM in the uplink offers potential for putting more data on an individual code channel.

As a consequence, the potential of synchronized uplink transmission should be studied to see what additional benefits could be obtained combining synchronized uplink transmission and BTS based uplink resource allocation. The original focus was on the resulting low data rate capacity (such as speech).

This work studies whether HSUPA-like uplink resource allocation allows more potential of synchronized uplink transmission to be achieved for uplink packet data transmission compared to Rel-5 TR 25.854, with the focus on:

• Resulting performance from BTS based dynamic uplink code allocation;

• Resulting L1/MAC signalling needs to enable BTS based code allocation and uplink synchronization on top of the Rel-7 specification;

• This study did not repeat the basic USTS analysis already existing in TR 25.854 on e.g. synchronization sensitivity.

TR 25.823 conclusion

Synchronised E-DCH study has investigated methods for increasing the capacity of WCDMA uplink, including CDM based Synchronized E-DCH, TDM based Synchronized E-DCH and interference cancellation.

Performance evaluation has been carried out at link and system level, comparing Synchronised E-DCH against Rel-7 HSUPA. At 80-90% HARQ throughput, the CDM based Synchronised E-DCH showed link level gains of 0.75-1dB in a multipath rich channel and 1-2dB in low dispersion channel, while 3 stage parallel IC on HSUPA showed link level gains of 2dB in both kinds of channel. Parallel IC on CDM based Synchronised E-DCH showed additional gains of 1.8dB in TU6 and <0.1dB in PedA (the OVSF already removed most of the interference in the latter case). At low HARQ throughput levels (25%), Synchronised E-DCH and IC showed link level gains of <0.5dB.

System level full buffer simulations were also performed in order to assess the capacity gains available with each of the techniques. Comparing the simulations at 6dB RoT, CDM based Synchronised E-DCH showed capacity gains of 50% in Pedestrian A and 10-15% in TU6. TDM based Synchronised E-DCH showed gains of 50% in Pedestrian A and 30-40% in TU6. Interference cancellation on Rel-7 HSUPA based on a realistic group serial/parallel algorithm showed gains of 50-60% in cell throughput and 40-75% in cell edge user throughput in both dispersive TU6 and non dispersive Pedestrian A channels.

The CDM and TDM approaches effectively share the time/OVSF code resources between users, whereas conventional HSUPA allows each user access to a full OVSF tree. At cell throughput levels of ≥2Mbps, higher coding rates or higher order modulation compared to asynchronous HSUPA would be needed if pure CDM or TDM operation is to be maintained.

Interference cancellation may be applied to CDM based or TDM based Synchronised E-DCH or to HSUPA. Simulations indicated that application of IC to CDM based Synchronised E-DCH could reduce the number of interference cancellation stages required in a parallel interference canceller by 1 compared with an application to HSUPA. TDM based Synchronised E-DCH could benefit from the fact that the inter-cell interference is dominated by a low number of users in order to further boost capacity, e.g. by being able to operate at a higher RoT level by cancelling or suppressing these dominant interferers.

In terms of complexity, CDM based Synchronised E-DCH increases CM and PAPR at the UE transmitter and requires code scheduling and synchronisation at NodeB. TDM synchronisation requirements are looser, and scheduling may be more straightforward. Interference cancellation implies additional NodeB baseband processing complexity.

Impact on specifications is greatest for CDM based Synchronised E-DCH, significantly lower for TDM and zero for interference cancellation on Rel-7 HSUPA.

Last Status Report in RP-080068

NOTE: TR 25.823 and Status Report provide no Work Plan.