Abstract — In HSDPA, a single logical channel is shared amongst multiple contending users. Besides better link utilization, scheduling disciplines seek to achieve fair allocation of this shared resource. However, these two criteria can potentially be in conflict. This paper investigates these two criteria performances in a heavy load scenario using FTP traffic with achievable maximum data rate of 14.4 Mbps, simulating different scheduling algorithms in order to find the best solution for this scenario. Comparison is also made with previous given simulation results with achievable maximum data rate of 3.6 Mbps for three schedulers. Simulation results show that Proportional Fair Time scheduling algorithm provides the best results comparing link utilization and fairness among the users, under heavy load conditions. Keywords — HSDPA, Scheduling algorithm, Scheduling optimization, Simulation, Terminal Category. I. INTRODUCTION SDPA is a 3.5G wireless system standardized as a set of technological advancements to UMTS in order to improve network capacity and increases the peak data rates up to 14.4 Mbps for downlink packet traffic [1] -[4]. HSDPA utilizes a common downlink shared channel known as high speed downlink shared channel (HS- DSCH), and employs fast link adaptation for downlink data transfer to mobiles, based on adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ) and a shorter minimum allocation time (transmission time interval, TTI) of 2ms. In addition to these physical layer features, the packet scheduling functionality is moved from the centralized radio network controller (RNC) to the base station (Node B), where it is embedded in a new MAC entity known as MAC-hs. Packet Scheduling functionality plays a key role in HSDPA. The features included in HSDPA and the new location of the scheduler in the Node-B open new possibilities for the design of this functionality for the evolution of WCDMA. The main goal of the Packet Scheduler is to maximize the network throughput while satisfying the Quality of Service (QoS) requirements of the users. Dr. Toni Janevski is Professor at the Faculty of Electrical Engineering and Information Technologies, Ss. Cyril and Methodius University, Karpos 2 bb, 1000 Skopje, Macedonia, (e-mail: tonij@feit.ukim.edu.mk). Kire Jakimoski is Ph.D. student at the Faculty of Electrical Engineering and Information Technologies, Ss. Cyril and Methodius University, Karpos 2 bb, 1000 Skopje, Macedonia, (e-mail: kire_jakimoski@yahoo.com). In UMTS, the bearers do not set any absolute quality guarantees (such can never be given in a wireless transmission) in terms of data rate for interactive and background traffic classes. The introduction of minimum service guarantees for users is a relevant factor, and it is taken into consideration in the performance evaluation of the different HSDPA schedulers. The service guarantees interact with the notion of fairness and the level of satisfaction among users. Very unfair scheduling mechanisms can lead to the starvation of the least favourable users in highly loaded networks, and as described in [1], the starvation of users could have negative effects on the performance of higher layer protocols, like TCP. These concepts and their effect on the HSDPA performance are thus important for our investigation. A number of different scheduling algorithms have been proposed to address these issues [2-6], all with their respective advantages and trade-offs. Several simulation experiments were conducted in this paper for evaluating the performance of different algorithms. We evaluate the system performance of different groups of schedulers using CAT 10 UEs (offering up to 14.4 Mbps theoretical bit rate) in a heavy load scenario with FTP traffic in terms of system throughput and fairness. Section II discusses scheduling in HSDPA, and the main performance measures related to scheduling. Section III presents the simulation results of the scheduling algorithms. In our simulations experiments, the performance of CAT 10 UEs is determined under 14 scheduling schemes. The results are given in average throughput and delay and overall cell throughput. Finally, Section IV contains summary of the work done. II. SCHEDULING IN HSDPA AND PERFORMANCE MEASURES The process of scheduling refers to the process of allocation of transmitter time and power (at Node-B) to the randomly time-varying mobile data connections (mobile users, UE). Scheduling decisions control the allocation of resources amongst users, and this allocation determines the overall performance of a system. In HSDPA, the packet scheduler is moved from the Radio Network Controller (RNC) to Node B, with the resulting advantage of fast link adaptation techniques. The idea is to enable scheduling such that, if required, most of the cell capacity may be allocated to one user, when its conditions are favorable. In the optimum scenario, scheduling should be able to track fast fading of users. In HSDPA, the User Equipment (UE) sends its downlink channel quality feedback to Node B in the form Scheduling Optimization in HSDPA Networks Simulating Maximum Terminal Capabilities Toni Janevski, Senior Member, IEEE, and Kire Jakimoski H 17th Telecommunications forum TELFOR 2009 Serbia, Belgrade, November 24-26, 2009. 206