d to be a trade-off between performance and implementation complexity. For instance, a simple flow control implementation may consist in sending periodic capacity allocations that either follow a round-robin approach among the UEs or is based on the MAC-hs or has RLC buffer status. However, this kind of implementation can have constraints regarding the guaranteed bit rate and number of simultaneous users. On the other hand, a more a dvanced flow control may take into account the buffer status in Node B, the guaranteed bit rate, scheduling priority, the buffer status in the RNC, the air interface bit rate and the discard timer for sending the capacity allocation messages. B.4 Handset Capabilities HSDPA handsets are becoming more complex, due to the addition of several new features to existing 3G devices in order to achieve maximum capability, such as support of the 16-QAM modulation method, a roadmap for advanced receivers (equaliser, diversity), HARQ in layer 1, a gfaster turbo decoder, the need for increased and faster buffer memory, etc. The UE capabilities, presented in Table B.4, are sent from the serving RNC (SRNC) to Node B when the HSDSCH MAC-d flow is established. They include among others: The maximum number of bits a UE can receive within one TTI; The maximum number of HSDSCH codes the UE can receive simultaneously; The minimum inter-TTI arrival; The total buffer size minus the RLC AM buffer size; Five main parameters used to define the physical layer UE capability level (3GPP TS 25.306): - the maximum number of HSDSCH multicodes that the UE can simultaneously receive; at least five multicodes must be supported in order to facilitate efficient multicode operation; - the minimum inter-TTI interval, which defines the distance from the beginning of a TTI to the beginning of the next TTI that can be assigned to the same UE; e.g. if the allowed interval is 2 ms, this means that the UE can receive HSDSCH packets every 2 ms; the maximum number of HSDSCH transport channel bits that can be received within a sing