Neighbor discovery is important for docking applications, where mobile nodes communicate with static nodes situated at various rendezvous points. Among the existing neighbor discovery protocols, the probabilistic methods perform well in average cases but they have aperiodic, unpredictable, and unbounded discovery latency. Yet, deterministic protocols can provide bounded worst-case discovery latency by sacrificing the average-case performance. In this study, we propose a mobility-assisted slot index synchronization (MASS), which is a new synchronization technique that can improve the average-case performance of deterministic neighbor discovery protocols via slot index synchronization without incurring additional energy consumption. Furthermore, we propose an optimized beacon strategy in MASS to mitigate beaconing collisions, which can lead to discovery failures in situations where multiple neighbors are in the vicinity. We evaluate MASS with theoretical analysis and simulations using real traces from a tourist tracking system deployed at the Mogao Grottoes, which is a famous cultural heritage site in China. We show that MASS can reduce the average discovery latency of state-of-the-art deterministic neighbor discovery protocols by up to two orders of magnitude.

Duty-cycling is generally adopted in existing sensor networks to reduce power consumption and these networks depend on neighbor discovery protocols to ensure that nodes wake up and discover each other. For different neighbor discovery protocols, the discovery latency is determined by two factors: the wake-sleep pattern and slot size. To the best of our knowledge, previous works on neighbor discovery have thus far been focused on improving the wake-sleep pattern. In this paper, we investigate the extent to which we can improve discovery latency by reducing the slot size. We found that by reducing the slot size, i.e., reducing the listening time in active slots, the collisions between beacons and synchronization between nodes become more severe, which can lead to discovery failures that are not predicted by existing theoretical models. We show that we can mitigate these effects by reducing the number of beacons and introducing randomization. We propose a new continuous-listening-based neighbor discovery algorithm called Spotlight. Our evaluations with a practical sensor testbed suggest that Spotlight can achieve a 50% reduction in discovery latency over existing state-of-the-art neighbor discovery protocols without increasing power consumption in existing sensor networks.

TCP does not work well in modern cellular networks because the current congestion-window-based (cwnd-based) congestion control mechanism intimately couples congestion control and packet dispatch, which provides TCP with only indirect control of the effective data rate. The throughput degradation arising from the cwnd-based mechanism is especially serious when the uplink is congested. We describe PropRate, a new rate-based TCP algorithm that directly regulates the packets in the bottleneckbuffer to achieve a trade-off in terms of delay and throughput along a more efficient frontier than conventional cwnd-based TCP variants. To the best of our knowledge, PropRate is the first TCP algorithm that allows an application to set and achieve a target average latency, if the network conditions allow for it. Also, unlike the cwnd-based TCP mechanism, our new rate-based TCP mechanism is significantly more resilient to saturated uplinks in cellular networks. PropRate does not require modifications at the receiver and is amenable to practical deployment in the base stations and proxies in mobile cellular networks.

Neighbor discovery is essential for docking applications, where mobile nodes communicate with static nodes situated at various rendezvous points. In existing neighbor discovery protocols, the probabilistic protocols perform well in the average-case but have a periodic, unpredictable and unbounded discovery latency. While the deterministic protocols can provide a bounded worst-case discovery latency, they achieve this by sacrificing the average-case performance. In this paper, we propose a new synchronization technique, called Mobility-Assisted Slot index Synchronization (MASS). MASS improves the average-case performance of deterministic neighbor discovery protocols via slot index synchronization, without incurring additional energy consumption. We evaluate MASS through both theoretical analysis and simulations of the real traces from a tourist tracking system deployed at Mogao Grottoes, a famous cultural heritage site in China. We show that MASS can reduce the average discovery latency of state-of-the-art deterministic neighbor discovery protocols by up to 2 orders of magnitude.

It is not uncommon for the uplink buffers of cellular data networks to be saturated when the uplink bandwidths are low. This can cause the ACK packets for a downlink TCP flow to be severely delayed. Since existing TCP implementations are ACK-clocked, the downstream flow will suffer significant degradation, causing the downlink to be under-utilized. We present a new TCP variant, called TCP Receiver-Rate Estimation (TCP-RRE), that addresses this problem directly by eliminating ACK clocking. Instead, it uses TCP timestamps to estimate the receiving rate at the receiver, which it then uses to determine the sending rate. We show that TCP-RRE is able to improve download speeds by 2 to 4 times compared to existing TCP variants in both simulation and on real commercial cellular data networks. Our solution is practical because it is compatible with existing TCP implementations, requires no modifications to existing mobile devices, and is thus immediately deployable in existing ISP proxies.