Ethernet.Метод доступа,структура кадра - download pdf or read online

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This is typically done on a time scale of about two to twenty milliseconds. , not for speech users. Laakso et al. (1998) formulate the packet scheduling problem as an optimization problem. A special mode of WCDMA in which higher data rates can be accomplished at the price of less fairness is discussed by Kolding et al. (2002). • Channel Switching handles users who already have a session. During the session, a user’s channel conditions and the load of the base stations change. To adapt to these changes, channel switching increases and decreases the users’ maximum transmission rate.

Each user is stuck at using his assigned frequencies, even if there is locally heavy interference on this frequency band or the power gain is locally exceptionally low on these frequencies due to multipath fading. The second generic technique, Time Division Multiple Access (TDMA), splits the radio spectrum in time, instead of in frequency. This technique requires precise synchronization between all users (which in some areas and applications even means taking the propagation time into account).

Therefore, a simplified version of the reality, a model, is used. A criteria for the model is that it will provide a statistically correct description of the attenuation. Instead of modeling the attenuation, its inverse, power gain , is often modeled. The received signal power can comprehensively be expressed as transmitted power times the power gain. The model is often separated into three components. The product of these three is the power gain g = gp gs gmp < 1, where gp represents path gain 1 , gs shadow fading and gmp multipath fading.

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Ethernet.Метод доступа,структура кадра

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