Exploiting Full-duplex Receivers for Achieving Secret Communications in Multiuser MISO Networks

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 Rx-based 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.Comment: IEEE Transactions on Communication

Price-based friendly jamming in a MISO interference wiretap channel

© 2016 IEEE. In this paper, we expand the scope of PHY-layer security by investigating TX-based friendly jamming (FJ) for the wiretap channel in multi-link settings. For the single-link scenario, creating a TX-based FJ is an effective and practical method in improving the secrecy rate. In a multi-link setting, several information signals must be transmitted simultaneously. Thus, the design must guarantee that the FJ signal of a given transmitter does not interfere with unintended but legitimate receivers. Under the assumption of exact knowledge of the eavesdropping channel, we first propose a distributed price-based approach to improve the secrecy sum-rate of a two-link network with one eavesdropper while satisfying an information-rate constraint for both link. Simulations show that price-based FJ control outperforms greedy FJ, and is close to the performance of a centralized approach. Next, we propose a method based on mixed strategic games that can offer robust solutions to the distributed secrecy sum-rate maximization problem under the assumption of an unknown eavesdropping channel. Lastly, we use simulations to show that in addition to outperforming the greedy approach, our robust optimization also satisfies practical network considerations. In particular, the transmission time for the robust optimization can be determined flexibly to match the channel's coherence time

Jamming attack on in-band full-duplex communications: Detection and countermeasures

© 2016 IEEE. Recent advances in the design of in-band full-duplex (IBFD) radios promise to double the throughput of a wireless link. However, IBFD-capable nodes are more vulnerable to jamming attacks than their out-of-band full-duplex (OBFD) counterparts, and any advantages offered by them over the OBFD nodes can be jeopardized by such attacks. A jammer needs to attack both the uplink and the downlink channels to completely break the communication link between two OBFD nodes. In contrast, he only needs to jam one channel (used for both uplink and downlink) in the case of two IBFD nodes. Even worse, a jammer with the IBFD capability can learn the transmitters' activity while injecting interference, allowing it to react instantly with the transmitter's strategies. In this paper, we investigate frequency hopping (FH) technique for countering jamming attacks in the context of IBFD wireless radios. Specifically, we develop an optimal strategy for IBFD radios to combat an IBFD reactive sweep jammer. First, we introduce two operational modes for IBFD radios: transmission reception and transmission-detection. These modes are intended to boost the anti-jamming capability of IBFD radios. We then jointly optimize the decision of when to switch between the modes and when to hop to a new channel using Markov decision processes. Numerical investigations show that our policy significantly improves the throughput of IBFD nodes under jamming attacks

Ganoderma boninense Pat. from basal stem rot of oil palm (Elaeis guineensis) in Peninsular Malaysia

Several hundred sporophores of Ganoderma were collected from 5 - 40 years old palm trees infected with basal stem rot in 5 oil palm estates in Peninsular Malaysia. Based on the morphometric studies of the pores, dessepiments and basidiospores dimensions and other morphological characteristics, the sporophores were identified as belonging to a single species, G. boninense Pat

Exploiting Microscopic Spectrum Opportunities in Cognitive Radio Networks via Coordinated Channel Access

Under the current opportunistic spectrum access (OSA) paradigm, a common belief is that a cognitive radio (CR) can use a channel only when this channel is not being used by any neighboring primary radio (PR). Therefore, the existence of a spectrum opportunity hinges on the absence of active cochannel PRs in a macroscopic region. In this paper, we propose the concept of microscopic spectrum opportunity and show that CRs can still utilize this type of opportunities without interfering with active cochannel PRs, even when these PRs are close to them. As a result, a channel may at the same time present different levels of availability to different CRs. Channel access needs to be carefully coordinated between these CRs to avoid collisions, and more importantly, ensure efficient utilization of the spectrum opportunity from a network’s standpoint. In this paper, we formulate the coordinated channel access as a joint power/rate control and channel assignment optimization problem, with the objective of maximizing the sum-rate achieved by the cognitive radio network (CRN). We develop both centralized and distributed algorithms to solve this problem. Our simulation results show that even when accounting for the implementation overhead, significant throughput gain is achieved under our designs.TRUEpu

Exploiting microscopic spectrum opportunities in cognitive radio networks via coordinated channel access

Under the current opportunistic spectrum access (OSA) paradigm, a common belief is that a cognitive radio (CR) can use a channel only when this channel is not being used by any neighboring primary radio (PR). Therefore, the existence of a spectrum opportunity hinges on the absence of active cochannel PRs in a macroscopic region. In this paper, we propose the concept of microscopic spectrum opportunity and show that CRs can still utilize this type of opportunities without interfering with active cochannel PRs, even when these PRs are close to them. As a result, a channel may at the same time present different levels of availability to different CRs. Channel access needs to be carefully coordinated between these CRs to avoid collisions, and more importantly, ensure efficient utilization of the spectrum opportunity from a network’s standpoint. In this paper, we formulate the coordinated channel access as a joint power/rate control and channel assignment optimization problem, with the objective of maximizing the sum-rate achieved by the cognitive radio network (CRN). We develop both centralized and distributed algorithms to solve this problem. Our simulation results show that even when accounting for the implementation overhead, significant throughput gain is achieved under our designs.TRUEpu