This paper investigates how multiuser dimensions can effectively be exploitedfor target degrees of freedom (DoF) in interfering broadcast channels (IBC)consisting of K-transmitters and their user groups. First, each transmitter isassumed to have a single antenna and serve a singe user in its user group whereeach user has receive antennas less than K. In this case, a K-transmittersingle-input multiple-output (SIMO) interference channel (IC) is constitutedafter user selection. Without help of multiuser diversity, K-1 interferingsignals cannot be perfectly removed at each user since the number of receiveantennas is smaller than or equal to the number of interferers. Only withproper user selection, non-zero DoF per transmitter is achievable as the numberof users increases. Through geometric interpretation of interfering channels,we show that the multiuser dimensions have to be used first for reducing theDoF loss caused by the interfering signals, and then have to be used forincreasing the DoF gain from its own signal. The sufficient number of users forthe target DoF is derived. We also discuss how the optimal strategy ofexploiting multiuser diversity can be realized by practical user selectionschemes. Finally, the single transmit antenna case is extended to themultiple-input multiple-output (MIMO) IBC where each transmitter with multipleantennas serves multiple users.
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