are thus only limited by noise, implying that, especially in interfere with each other. This will limit the achievable smaller cells, very high broadcast data rates can be broadcast-transmission signal-to-interference ratio and achieved. Furthermore, in contrast to the explicit (in the thus limit the achievable broadcast data rates. receiver) multi-cell soft combining of WCDMA MBMS, One way to mitigate this and further improve the the OFDM receiver does not need to explicitly identify provisioning of broadcast/multicast services in a mobile- the cells to be soft combined. Rather, all transmissions communication network is to ensure that the broadcast that fall within the cyclic prefix will 'automatically' be transmissions from different cells are truly identical and captured by the receiver. Equivalence as seen from the mobile terminal Figure 4.4-22 Equivalence between simulcast transmission and multi-path propagation. This page intentionally left blank Chapter 4.5 Scheduling, link adaptation and hybrid ARQ Erik Dahlman, Stefan Parkvall, Johan Skold and Per Beming One key characteristic of mobile radio communication is received data packets, is therefore useful. This can be the typically rapid and significant variations in the in- seen as a mechanism for handling variations in the stantaneous channel conditions. There are several reasons instantaneous radio-link quality after transmission and for these variations. Frequency-selective fading will nicely complements channel-dependent scheduling and result in rapid and random variations in the channel link adaptation. Hybrid ARQ also serves the purpose of attenuation. Shadow fading and distance-dependent path handling random errors due to, for example, noise in the loss will also affect the average received signal strength receiver. significantly. Finally, the interference at the receiver due to transmissions in other cells and by other terminals will also impact the interference level. Hence, to summarize, 4.5.1 Link adaptation: Power and there will be rapid, and t