Huahui Wang

Anti-Jamming Message-Driven Frequency Hopping—Part I: System Design

This is Part I of a two-part paper that considers anti-jamming system design in wireless networks based on message-driven frequency hopping (MDFH), a highly efficient spread spectrum technique. In this paper, we first analyze the performance of MDFH under hostile jamming. It is observed that while MDFH is robust under strong jamming, it experiences considerable performance losses under disguised jamming from sources that mimic the true signal. To overcome this limitation, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit a secure ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver, it is then exploited by the receiver for effective signal extraction. It is shown that AJ-MDFH can effectively reduce the performance degradation caused by disguised jamming, and is also robust under strong jamming. In addition, we extend AJ-MDFH to the multi-carrier case, which can increase the system efficiency and jamming resistance significantly through jamming randomization and frequency diversity, and can readily be used as a collision-free multiple access system. Part II of the paper focuses on the capacity analysis of MDFH and AJ-MDFH under disguised jamming.

On PHY-layer security of cognitive radio: Collaborative sensing under malicious attacks

In cognitive radio networks, physical layer spectrum sensing plays a key role in helping cognitive radios adapt to changes in spectrum availability. However, it raises significant security issues at the physical layer as well. In this paper, we investigate collaborative sensing of cognitive radio networks under malicious attacks, and analyze the system performance in a generalized framework. The system design goal is to improve efficiency of spectrum access on a non-interfering basis, which is formulated as a constrained parameter optimization problem. A numerical algorithm is provided to resolve the problem. The system performances are evaluated under various conditions, and discussions are provided to help better understand the effectiveness of the attacks and their countermeasures.

Hybrid ALOHA: A Novel MAC Protocol

This paper considers cross-layer medium access control (MAC) protocol design in wireless networks. Taking a mutually interactive MAC-PHY perspective, we aim to design an MAC protocol that is in favor of the physical (PHY) layer information transmission, and the improved PHY, in turn, can improve the MAC performance. More specifically, we propose a novel MAC protocol, named hybrid ALOHA, which makes it possible for collision-free channel estimation and simultaneous multiuser transmission. The underlying argument is as follows: As long as good channel estimation can be achieved, advanced signal processing does allow effective signal separation given that the multiuser interference is limited to a certain degree. Comparing with traditional ALOHA, there are more than one pilot subslots in each hybrid ALOHA slot. Each user randomly selects a pilot subslot for training sequence transmission. Therefore, it is possible for different users to transmit their training sequences over nonoverlapping pilot subslots and achieving collision-free channel estimation. Relying mainly on the general multipacket reception (MPR) model, in this paper, quantitative analysis is conducted for the proposed hybrid ALOHA protocol in terms of throughput, stability, as well as delay behavior. It is observed that significant performance improvement can be achieved in comparison with the traditional ALOHA protocol based either on the collision model or the MPR model.

Spectrally Efficient Jamming Mitigation Based on Code-Controlled Frequency Hopping

This paper considers spectrally efficient anti-jamming system design based on code-controlled frequency hopping. Unlike conventional frequency hopping systems where hopping patterns are determined by preselected pseudo-random sequences, in the proposed scheme, part of source information is passed through a block encoder, and used to determine the selected frequency bands for signal transmission. By exploiting the redundancy provided by the block coding, the receiver can retrieve the hopping pattern without a priori knowledge. Through an integrated decoding-and-encoding process, the receiver can also perform partial jamming detection. It is observed that due to the combination of dynamic frequency hopping and coding diversities, the proposed system can effectively mitigate random jamming interference while maintaining high spectral efficiency.

Resource Allocation with Load Balancing for Cognitive Radio Networks

This paper considers channel and power allocation for cognitive radio (CR) networks. We assume that the total available spectrum is divided into several bands, each consisting of a group of channels. A centralized base station, enabled by spectrum sensing, is assumed to have the knowledge of all vacant channels, which will be assigned to various CRs according to their requests. The objective of resource allocation is to maximize the sum data rate of all CRs. Since the activities of primary users may cause heavy traffic in some bands while leaving other bands idle, load balancing is first performed to equalize the traffic. A multi-level subset sum algorithm as well as a simpler greedy algorithm is proposed to achieve excellent load balancing performance. After that, an algorithm incorporated with constant-power water filling is proposed to maximize the sum data rate. Simulation results are presented to illustrate the effectiveness of the proposed algorithms.

Hybrid Aloha: A Novel Medium Access Control Protocol

In this paper, a novel medium access control (MAC) protocol, name hybrid ALOHA, is proposed to improve the system performance by allowing collision-free channel estimation and simultaneous multiuser data transmission. The idea behind it is to design an MAC protocol that is in favor of the physical (PHY) layer information transmission, and the improved PHY layer, in turn, can improve the MAC performance. Using the general multipacket reception (MPR) model as an interface between the MAC layer and the PHY layer, the hybrid ALOHA protocol is analyzed in terms of throughput, stability, as well as delay behavior. Significant performance improvement is observed in comparison with the traditional ALOHA either with the MPR model or with the collision model

Jamming resistance reinforcement of message-driven frequency hopping

This paper considers spectrally efficient anti-jamming system design based on message-driven frequency hopping (MDFH). As a highly efficient frequency hopping scheme, MDFH is particularly robust under strong jamming. However, disguised jamming from sources of similar power strength can cause performance losses. To overcome this drawback, in this paper, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit an ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver. It is then exploited by the receiver for effective signal detection and extraction. It is shown that AJ-MDFH can effectively reduce the performance degradation caused by disguised jamming. Moreover, AJ-MDFH can be extended to a multi-carrier scheme for higher spectral efficiency and/or more robust jamming resistance. Simulation examples are provided to demonstrate the performance of the proposed approaches.

Jamming mitigation based on coded message-driven frequency hopping

This paper proposes an anti-jamming system based on coded message-driven frequency hopping. In each hopping period, multiple frequency bands are utilized for signal transmission. The selection of these bands is determined by a coded message sequence, hence the proposed scheme “hops” its frequencies randomly without a pre-defined pseudo-random sequence. Error correction codes are employed in an innovative way for accurate hopping pattern retrieving, and can also be exploited for jamming detection. The proposed scheme achieves strong jamming resistance while maintaining high spectral efficiency.

Code-controlled 3D frequency hopping for jamming mitigation

This paper considers spectrally efficient anti-jamming system design based on coded three-dimensional (3D) frequency hopping. Unlike conventional frequency hopping systems where the hopping pattern is determined by a preselected pseudo-random sequence, in the proposed scheme, part of the information is passed through a block encoder, and used to determine the selected frequency bands for signal transmission. The receiver is designed to retrieve the hopping pattern without a priori knowledge. The proposed system can effectively mitigate random jamming interference while maintaining high spectral efficiency. Simulation results are provided to illustrate the systems jamming mitigation performance.

Stability analysis of hybrid ALOHA

We perform stability analysis of a recently proposed MAC protocol, hybrid ALOHA, based on the multipacket reception (MPR) model. Hybrid ALOHA distinguishes from conventional slotted ALOHA by allowing conditional collision-free channel estimation and simultaneous transmissions, and hence improves the MPR capability of the system. The stability analysis of the two-user case () has been conducted in our previous work. In this paper, we study the stability region of hybrid ALOHA for the general N-user () system. By using the method of stochastic dominance and mathematical induction, we obtain the sufficient condition for the stability of hybrid ALOHA. As an illustration, we characterize the stability inner bounds for the case. In this particular situation, the results are derived by solving a nonhomogeneous Riemann-Hilbert problem. Potentially, the mathematical tools used in this paper can be exploited for obtaining closed-form results in stability analysis of wireless networks.