We study the data reliability problem for devices forming a dynamic distributed storage system. Such systems are commonplace in traditional cloud storage applications where storage node failures and updates are frequent. We consider the application of regenerating codes for file maintenance. Such codes require lower bandwidth to regenerate lost data fragments compared to file replication or reconstruction. We investigate threshold-based repair strategies where data repair is initiated after a threshold number of data fragments have been lost. We show that at a low departure-to-repair rate regime, in which repairs are initiated after several nodes have left the system outperforms if repairs are initiated after a single node departure. This optimality is reversed when the node turnover is high. We further compare distributed and centralized repair strategies and derive the optimal repair threshold for minimizing the average repair cost per unit of time. In addition, we examine cooperative repair strategies and show performance improvements. We investigate several models for the time needed for node repair including a simple fixed time model and a more realistic model that takes into account the number of repaired nodes. Finally, an extended model where additional failures are allowed during the repair process is investigated.

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 study the data reliability problem for a community of devices forming a mobile cloud storage system. We consider the application of regenerating codes for maintaining a file within a geographically-limited area. Such codes require lower bandwidth to regenerate lost data fragments compared to file replication or reconstruction. We investigate threshold-based repair strategies where data repair is initiated after a threshold number of data fragments have been lost due to node mobility. We show that at a low departure-to-repair rate regime, a lazy repair strategy in which repairs are initiated after several nodes have left the system outperforms eager repair in which repairs are initiated after a single departure. This optimality is reversed when nodes are highly mobile. We further compare distributed and centralized repair strategies and derive the optimal repair threshold for minimizing the average repair cost per unit of time, as a function of underlying code parameters.

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.