We consider a broadcast channel, in which a multi-antenna transmitter (Alice) sends K confidential information signals to K legitimate users (Bobs) in the presence of L eavesdroppers (Eves). Alice uses MIMO precoding to generate the information signals along with her own (Tx-based) friendly jamming. Interference at each Bob is removed by MIMO zero-forcing. This, however, leaves a "vulnerability region" around each Bob, which can be exploited by a nearby Eve. We address this problem by augmenting Tx-based friendly jamming (TxFJ) with Rxbased friendly jamming (RxFJ), generated by each Bob. Specifically, each Bob uses self-interference suppression (SIS) to transmit a friendly jamming signal while simultaneously receiving an information signal over the same channel. We minimize the powers allocated to the information, TxFJ, and RxFJ signals under given guarantees on the individual secrecy rate for each Bob. The problem is solved for the cases when the eavesdropper's channel state information is known/unknown. Simulations show the effectiveness of the proposed solution. Furthermore, we discuss how to schedule transmissions when the rate requirements need to be satisfied on average rather than instantaneously.Under special cases, a scheduling algorithm that serves only the strongest receivers is shown to outperform the one that schedules all receivers.
Index termsBroadcast channel, channel correlation, friendly jamming, full-duplex, physical layer security
I. INTRODUCTIONAs wireless systems continue to proliferate, confidentiality of their communications becomes one of the main concerns due to the broadcast nature of the wireless medium. Cryptographic techniques can be utilized to address these concerns, but such techniques often assume adversaries with limited computational capabilities. Physical (PHY) layer security, on the other hand, can be implemented regardless of the adversary's computational power. It also takes advantage of the characteristics of the wireless medium.The authors are with the The origins of PHY-layer security dates back to the pioneering work of Wyner [1] that studied the concept of secrecy capacity for the degraded wiretap channel. The authors in [2] extended Wyner's work to non-degraded discrete memoryless broadcast channels. Later on, the secrecy capacity of MIMO (multiple-input multiple-output) wiretap channel was obtained in [3]. The secrecy region of the Gaussian MIMO broadcast channel was studied in [4], [5], and [6]. The authors in [7] and [8] studied the problem of secure communications over broadcast channels under individual secrecy constraint, which guarantees that the information leakage to eavesdroppers from each information message vanishes. Even though the joint secrecy constraint, which ensures that the information leakage to eavesdroppers from all information messages vanishes, is stronger than the individual one, it is not always possible to satisfy. Moreover, the individual secrecy constraint still offers an acceptable secrecy level, while increasing transmission rates [7]. T...
