nalytically. There are many open questions, even for relatively simple channels. In this section we will discuss some principles for multiuser communication in a network. One focus will be the modeling and analysis of interference between users. Without interference, one could apply theoretical results from wireline communications, where the network is often modeled as a collection of point-to-point links. However, neglecting the impact of interference can lead to significant performance losses. In gen- eral, the performance of one link can depend on the chosen strategy of other links. All users are potentially coupled by interference. Therefore, a joint optimization approach involving cooperation between users is generally favorable, although it also complicates the analysis of wireless networks. In the following, some basic strategies for cooperative network communication, which are far from comprehensive, will be discussed. Relaying. The distance from source to destination can be bridged by using a relay. Compared to a single link, less transmission power is needed per transmitter. This advantage can be exploited in different ways. For given power limits, relaying increases the coverage of the system. For a given coverage area, relaying reduces the peak power and therefore the interference radiated to other users. A possible relaying strategy is "amplify and forward," where the received signal is amplified and retransmitted. This strategy is simple but has the disadvantage that noise is amplified. This is avoided by decoding the information before retransmis- sion. This is known as "decode and forward." In Figure 7.4, a simple relaying channel is depicted, where the relay assists the direct link. Even for this basic channel, the information-theoretical capacity is not fully known (e.g., Cover and Gamal [43]). Network coding. The core notion of network coding is to allow mixing of data at intermediate network nodes. A receiver sees these data packets and deduces from them the messages that were originally inten