IST-2003-507581 WINNER D2.5 v1.0 Duplex ... - Celtic-Plus

WINNER D2.5 v1.06) It is also possible to use a FDMA or a CDMA multiplexing schemes to separate AP/RS-cells, but inthis case FNs are required that relay traffic between AP/RS-cells. Otherwise MTs would need to havebandswitching capabilities and there would be a severe MT-MT interference issue as depicted forscheme H in Figure 4-17.4.3 Approaches to Interference ManagementThere are two approaches that can be taken when managing interference for a cellular system:interference averaging and interference avoidance.4.3.1 Interference AveragingThe ethos behind interference averaging is that every receiver in a cell will see the minimum amount ofinterference from users in its own cell, but every receiver should see an equal amount of interference fromtransmitters in other cells.There are a number of techniques to average interference between cells• Frequency hopping• Time slot hopping• Spreading• There is also some averaging which comes about as a result of statistical multiplexing of packet data.4.3.1.1 Frequency HoppingFrequency hopping is a technique that has been used successfully in narrow band cellular systems (e.g.GSM). The technique assumes that the multiple access scheme has a frequency component. Thefrequency of a link is changed on a frame-by-frame basis picked from a set of frequencies using a pseudorandomsequence.FrequencyFigure 4-19: Frequency HoppingThis averages adjacent channel interference between cells and leads to capacity benefits.In Orthogonal Frequency Division Multiple Access (OFDMA), frequency hopping can be implemented assub-carrier hopping.Time4.3.1.2 Time Slot HoppingTime slot hopping uses the same basis as frequency hopping (section 4.3.1.1), averaging the interferenceseen from links in another cell. This technique is of course only applicable for a system using a TDMAstructure.Page 65 (121)