ain size and after transmitting the page, there is no more data to be transmitted to the terminal in question It should be noted that there is little difference between until the users requests a new page by clicking on a link. different scheduling algorithms at low system load, that In this case, a max-C/I scheduler can still provide a cer- is when only one or, in some cases, a few users have data tain degree of fairness. Once the buffer for the user with waiting for transmission at the base station at each the highest C/I has been emptied, another user with non- scheduling instant. The differences between different empty buffers will have the highest C/I and be scheduled scheduling algorithms are primarily visible at high load. and SO on. This is the reason for the difference between However, not only the load, but also the traffic behavior full buffer and web-browsing traffic illustrated in affects the overall scheduling performance. Figure 4.5-4. The proportional-fair scheduler has similar As discussed above, channel-dependent scheduling performance in both scenarios. tries to exploit short-term variations in radio quality. Clearly, the degree of fairness introduced by the traffic Generally speaking, a certain degree of long-term fairness properties depends heavily on the actual traffic; a design in service quality is desirable, which should be accounted made with certain assumptions may be less desirable in for in the scheduler design. However, since system an actual network where the traffic pattern may be dif- throughput decreases the more fairness is enforced, ferent from the assumptions made during the design. a trade-off between fairness and system throughput is Therefore, relying solely on the traffic properties for necessary. In this trade-off, it is important to take traffic fairness is not a good strategy, but the discussion above CHAPTER 4.5 Scheduling, link adaptation and hybrid ARQ Full buffer Web browsing Max C/I Max C/I User throughput User throughput Figure 4.5-4 Illustration of the principle 