This paper studies the information-theoretic limits of a secondary or
cognitive radio (CR) network under spectrum sharing with an existing primary
radio network. In particular, the fading cognitive multiple-access channel
(C-MAC) is first studied, where multiple secondary users transmit to the
secondary base station (BS) under both individual transmit-power constraints
and a set of interference-power constraints each applied at one of the primary
receivers. This paper considers the long-term (LT) or the short-term (ST)
transmit-power constraint over the fading states at each secondary transmitter,
combined with the LT or ST interference-power constraint at each primary
receiver. In each case, the optimal power allocation scheme is derived for the
secondary users to achieve the ergodic sum capacity of the fading C-MAC, as
well as the conditions for the optimality of the dynamic
time-division-multiple-access (D-TDMA) scheme in the secondary network. The
fading cognitive broadcast channel (C-BC) that models the downlink transmission
in the secondary network is then studied under the LT/ST transmit-power
constraint at the secondary BS jointly with the LT/ST interference-power
constraint at each of the primary receivers. It is shown that D-TDMA is indeed
optimal for achieving the ergodic sum capacity of the fading C-BC for all
combinations of transmit-power and interference-power constraints.

本文研究了在现有主要无线电网络下采用频谱共享的辅助或认知无线电（CR）网络的信息论极限。研究了多个辅助用户在在其各自的传输功率约束和一个应用于主要接收器之一的干扰功率约束下，向辅助基站（BS）发送信号的信道模型。在辅助发射机的不同状态下，以及每个主要接收器应用的长期或短期干扰功率约束下，导出了辅助用户的最优功率分配方案，以实现信道容量的无穷期望总和。对于辅助网络的动态时分多址（D-TDMA）方案的优化条件也得到了研究探讨。研究了在辅助基站下行链路传输的信道模型（C-BC），并论证了对于所有传输功率和干扰功率约束的组合，D-TDMA 都是实现信道容量的无穷期望总和的最优方案。