ffected by the strategy chosen using HSDPA, depending on whether it is introduced as a high bit rate service for top users or as a way to improve efficiency and capacity of background NRT traffic. Advanced Cellular Network Planning and Optimisation Edited by Ajay R Mishra © 2007 John Wiley & Sons, Ltd HSDPA B.2 HSDPA Performance In terms of performance, in a 5 MHz channel HSDPA can provide maximum peak rates of up to 14.4 Mbps with 15 spreading codes and with no channel coding. However, this would mean that one unique subscriber will have to use all available codes on the high speed downlink share channel (HSDSCH). This is not a realistic approach, especially for initial implementations, since typically the capacity is also shared with regular UMTS DCH channels. Codes allocated for HSDPA are fixed, and not usable for DCH, SO in practice implementations with 15 codes will require at least several 5 MHz carriers to be available in the system. It is expected that HSDPA realisations will follow a progressive approach, starting with five codes, and evolving to 10 or 15 as higher capacity or resources to support it become available. Additionally, it is important to consider that not all UE classes will support 10 or 15 codes, SO in order to get the full benefit from maximum throughputs, terminal availability needs to be considered. A realistic data rate will be about 600-800 kbps, taking real network conditions into account, while an estimated network round trip time (RTT) would be 80-100 ms. As a summary, the overall performance of an HSDPA network will depend on: the number of spreading codes (support of 5, 10 or 15 multicodes); the modulation mode (QSPK (quadrature phase shift keying), 16-QAM (quadrature amplitude modu- lation)), where 16-QAM is optional for the network and also for the UE; the error correction level; capabilities of end user devices. On the other hand, the impact of HSDPA on WCDMA R99 will be driven by sharing resources and the allocation of fixed codes and constant transmission power to HSDPA. HSD