tarve' the mobile ter- scheduling. Since the radio conditions for the minal with the bad channel conditions, and the mobile different radiolink within a cell typically vary in- terminal with bad channel conditions will never be dependently, at each point in time there is almost always scheduled. This is illustrated in Figure 4.5-3a where a radio link whose channel quality is near its peak (see a max-C/I scheduler is used to schedule between two Figure 4.5-2). Thus, the channel eventually used for different users with different average channel quality. transmission will typically have a high quality and, with Virtually all the time the same user is scheduled. rate control, a correspondingly high data rate can be used. Although resulting in the highest system capacity, this This translates into a high system capacity. The gain situation is often not acceptable from a quality-of-service obtained by transmitting to users with favorable radio- point-of-view. link conditions is commonly known as multi-user An alternative to the max-C/I scheduling strategy is diversity; the gains are larger, the larger the channel so-called round-robin scheduling, illustrated in variations and the larger the number of users in a cell. Figure 4.5-3b. This scheduling strategy let the users take Hence, in contrast to the traditional view that fast fading, turns in using the shared resources, without taking the that is, rapid variations in the radio-link quality, is an instantaneous channel conditions into account. Round- undesirable effect that has to be combated, with the robin scheduling can be seen as fair scheduling in the possibility for channel-dependent scheduling fading is in sense that the same amount of radio resources (the same fact potentially beneficial and should be exploited. amount of time) is given to each communication link. CHAPTER 4.5 Scheduling, link adaptation and hybrid ARQ Figure 4.5-3 Example of three different scheduling behaviors for two users with different average channel quality: (a) max C/I, (b) round robin a