Multi-channel MAC (MMAC) protocols are designed to coordinate multi-user access to several non-overlapping frequency bands. They are primarily tasked with the efficient and fair bandwidth utilization under a variety of traffic load conditions, presuming that terminals follow the protocol specifications. However, selfish terminals can manipulate the protocol parameters to gain an unfair share of the common bandwidth. The problem of selfish MAC-layer misbehavior is well-studied for single-channel MAC protocols, but little attention has been paid when channel access is coordinated across multiple channels. In this paper, we address the problem of MAC-layer misbehavior in the multi-channel domain. We identify misbehavior strategies for popular classes of MMAC protocols (split-phase and dedicated control channel MMACs) and evaluate their impact on network throughput and fairness. We show that selfish terminals can easily isolate frequency bands for exclusive use without violating the protocol specifications. We develop corresponding detection and mitigation strategies that greatly reduce the throughput gains due to misbehavior.

Distributed wireless networks often employ voting to perform critical network functions such as fault-tolerant data fusion, cooperative sensing, and reaching consensus. Voting is implemented by sending messages to a fusion center or via direct message exchange between participants. However, the delay overhead of message-based voting can be prohibitive when numerous participants have to share the wireless channel in sequence, making it impractical for time-critical applications. In this paper, we propose a fast PHY-layer voting scheme called PHYVOS, which significantly reduces the delay for collecting and tallying votes. In PHYVOS, wireless devices transmit their votes simultaneously by exploiting the subcarrier orthogonality of OFDM and without explicit messaging. Votes are realized by injecting energy to pre-assigned subcarriers. We show that PHYVOS is secure against adversaries that attempt to manipulate the voting outcome. Security is achieved without employing cryptography-based authentication and message integrity schemes. We analytically evaluate the voting robustness as a function of PHY-layer parameters. We extend PHYVOS to operate in ad hoc groups, without the assistance of a fusion center. We discuss practical implementation challenges related to multi-device frequency and time synchronization and present a prototype implementation of PHYVOS on the USRP platform. We complement the implementation with larger scale simulations.

We address the problem of improving the throughput and security of multi-channel MAC (MMAC) protocols. We design a protocol called FD-MMAC that exploits recent advances in full duplex (FD) communications to coordinate channel access in a distributed manner. Compared with prior MMAC designs, our protocol eliminates the use of dedicated in-band or out-of-band control channels for resolving contention, discovering the resident channel of destinations, and performing load balancing. The elimination of the control channel improves spectral efficiency and mitigates denial-of-service attacks that specifically target the exchange of control information. Moreover, FD-MMAC enables the operation of multi-channel exposed terminals. To achieve these goals, we integrate an advanced suite of PHY-layer techniques, including self interference suppression, error vector magnitude and received power measurements, and signal correlation. We validate the proposed PHY-layer techniques on the NI USRP testbed. Furthermore, we theoretically analyze the throughput performance of FD-MMAC and verify our analysis via packet level simulations. Our results show that FD-MMAC achieves significantly higherthroughput compared with prior art. Finally, we analyze the resilience of FD-MMAC to reactive jamming attacks.

We address the problem of improving the throughput and delay efficiency of distributed multi-channel MAC (MMAC) protocols. We design an MMAC protocol called FD-MMAC that exploits recent advances in full-duplex (FD) communications to coordinate channel access in a distributed manner. Compared with prior MMAC designs, the FD-MMAC protocol eliminates the use of in-band or out-of-band control channels for combating the multi-channel hidden terminal problem, discovering the resident channel of destinations, and performing load balancing. Furthermore, FD-MMAC improves the spectral efficiency by enabling the operation of multi-channel exposed terminals. To achieve its goals, FD-MMAC integrates an advanced suite of PHY-layer techniques, including self interference suppression, error vector magnitude and received power measurements, and signal correlation techniques. We validate the proposed PHY-layer techniques on NI USRP devices. Further, we show via simulations that FD-MMAC achieves significantly higher throughput and lower delay compared with prior art.

We address the problem of MAC-layer misbehavior in distributed multi-channel MAC protocols. We show that selfish users can manipulate the protocol parameters to gain an unfair share of the available bandwidth, while remaining undetected. We identify optimal misbehavior strategies that can lead to the isolation of a subset of frequency bands for exclusive use by the misbehaving nodes and evaluate their impact on performance and fairness. We develop corresponding detection and mitigation strategies that practically eliminate the misbehavior gains. To the best of our knowledge, this is the first attempt in characterizing the impact of misbehavior on multi-channel MAC protocols.