maxi- Link adaptation in the frequency domain implies that, mum tolerable interference level at the receiver is based on knowledge about the instantaneous channel reached. This strategy maximizes the air interface utili- conditions in the frequency domain, that is knowledge zation but is achieved at the cost of potentially large about the attenuation as well as the noise/interference differences in data rates between users. In the extreme level of, in the extreme case, every OFDM subcarrier, the case, a user at the cell border with poor channel condi- power and/or the data rate of each OFDM carrier can be tions may not be allowed to transmit at all. individually adjusted for optimal utilization. Strategies between greedy filling and max-C/I can also Similarly, channel-dependent scheduling in the fre- be envisioned, for example different proportional-fair quency domain implies that, based on knowledge about strategies. This can be achieved by including a weighting the instantaneous channel conditions in the frequency factor for each user, proportional to the ratio between domain, different subcarriers are used for transmission to the instantaneous and average data rates, into the greedy or from different mobile terminals. The scheduling gains filling algorithm. from exploiting variations in the frequency-domain are The schedulers above all assume knowledge of the similar to those obtained from time-domain variations. instantaneous radio-link conditions; knowledge that can Obviously, in situations where the channel quality varies be hard to obtain in the uplink scenario as discussed in significantly with the frequency while the channel quality Section 4.5.2.4 below. In situations when no information only varies slowly with time, channel-dependent sched- about the uplink radio-link quality is available at the uling in the frequency domain can enhance system ca- scheduler, round-robin scheduling can be used. Similar to pacity. An example of such a situation is a wideband the downlink, round-robin implies terminals ta