The traditional way of allocating a single channel among multiple competing users is to chop up its ( ) by using one of the multiplexing schemes such as FDM (Frequency
Division Multiplexing). If there are N users, the bandwidth is divided into N equal-sized portions, with each user being assigned one portion. Since each user has a private frequency ( ), there is no interference among users.When there is only a small and constant number of users, each of which has a steady stream or a heavy load of ( ), this division is a simple and efficient allocation mechanism. A wireless example is FM radio stations. Each station gets a portion of the FM band and uses it most of the time to broadcast its signal.However, when the number of senders is large and varying or the traffic is ( ), FDM presents some problems. If the spectrum is cut up into N regions while fewer than N users are currently interested in communicating, a large piece of valuable spectrum will be wasted. If more than N users want to communicate, some of them will be denied ( 本题 ) for lack of bandwidth.„„
