The Influence of Link Adaptation in Multi-User OFDM.

We examine the performance gains from two variants of adaptive coding and modulation (ACM) in an OFDM-based cellular system with realistic system parameters. In this system a channel-aware scheduler allocates to each active user a set of subchannels, upon which the users may perform link adaptation with ACM. We investigate the achievable performance gain by frequency-selective ACM, in comparison to non frequency-selective adaptation. Since the scheduler, which is aware of the channel and the traffic conditions, already exploits the multi-user diversity and tends to allocate similar subchannels to a given user, it is not obvious that frequency-selective link adaptation achieves a signifi- cant performance gain, especially when realistic ACM with limited granularity is considered. In this paper, we evaluate the gain of frequencyadaptive vs. non frequency-adaptive transmission for the uplink under realistic conditions for a 4G system proposal. [ABSTRACT FROM AUTHOR]