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 (本题), 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 ( ) for lack of bandwidth.„„
