eds to be flexible and adjustable by the parameters defined in 3GPP/release 5, including some indirect parameters such as complying with the power targets specified from the RNC. Different approaches have been proposed for the packet scheduler, as described in Table B.3.1 Typically the most simple approach is round-robin scheduling, or best effort, which performs a 'blind' allocation of resources without using quality information. It has low complexity and allows a fair distribution of power and code resources among users. On the other hand, algorithms like proportional fair scheduling (Figure B.4), use information of user quality and fast fading behaviour to select the most appropriate transmission turn for each user. This scheduler has a higher complexity, but can provide 20-60 % gains in throughput compared with round-robin scheduling. The gain depends on the number of HSDPA users in the cell, the radio conditions and transmitted power. UE capabilities also have an effect on scheduling. The UE's ability to receive data depends on the UE category it supports. Category 1 and 2 UEs can receive data in every third TTI. Categories 3, 4 and 11 UEs can receive data in every second TTI. The remaining UE categories can receive in every TTI. B.3.6 Code Multiplexing (Optional) Code multiplexing gives the possibility of sending data to several UEs in the same TTI by using different sets of codes for each UE. For example, if 10 codes are used in the HSPDSCH, five codes could be used to send data for UE1 and the remaining five codes could be used for UE2 in the same TTI. In the case of time multiplexing all 10 codes would be scheduled for one UE in a TTI. Combining time and code multiplexing makes scheduling algorithms much more complicated. This option will therefore probably not be used in early HSDPA implementations. HSDPA TTI 1 TTI 4 Scheduled user USER 2 Es/NO USER 1 Es/NO Figure B.4 Packet of proportional fair scheduling B.3.7 Impact on the lub Interface With higher throughputs in HSDPA, there is a high probability of