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11.4 Interference-Controlled Behavior: S... > 11.4.1 Underlay in Small Networks: A... - Pg. 320

320 CHAPTER 11 Information theoretical limits on cognitive radio networks at the primary receivers. In [494] a sum-rate maximization problem for single- input, multiple-output multiple-access channels (SIMO-MAC) under interference constraints for the primary users as well as a peak transmission power constraint for each secondary user is considered. The authors wish to maximize the rate of the secondary users subject to interference constraints on the primary users as well as peak power constraints for the secondary users. Other works that similarly exploit multiple antennas to avoid or control the interference seen by primary users may be found in [495­497]. The scenarios considered in these papers can be considered an interference-avoiding scheme if the tolerable interference at the primary receivers is set to zero; otherwise, it falls under the interference-controlled paradigm we look at in the next section. 11.4 INTERFERENCE-CONTROLLED BEHAVIOR: SPECTRUM UNDERLAY When the interference caused by the secondary users on the primary users is permitted when below a certain level or while guaranteeing a certain level of