We study the performance of the IEEE 802.11p medium access protocol for platooning of connected vehicles in the presence of interruptions from human-driven Motorised Two Wheelers (MTWs). We invoke specific mobility models for the movement of the vehicles—car-following models for connected vehicle platoons and gap-acceptance model to capture the interruptions by the MTWs—and use them to configure (i) the traffic setup and (ii) the rate at which data packets related to safety-critical messages are generated. A control-theoretic analysis of the car-following models yields a bound on the admissible communication delay to ensure non-oscillatory convergence of the platoon headway. We then use suitable Markov chain models to derive the distribution of the MAC access delay experienced by packets pertaining to safety-critical events as well as routine safety messages. Using the delay distribution and the bound on the admissible delay we compute the reliability of the 802.11p MAC protocol in terms of traffic and protocol parameters. It is seen that the MAC protocol may not always ensure timely delivery of packets for safe platooning. Our study highlights the need for redesign of MAC protocols for vehicular communications in heterogeneous conditions.

Motivated by the need to study platooning under heterogeneous traffic conditions, we study a platoon comprising two classes of vehicles: (i) connected cars (CC) equipped with vehicle-to-vehicle communication, (ii) human-driven motorcycles (HDM) that cannot communicate with surrounding vehicles. While the cars can be controlled through appropriate inputs to achieve platooning, the dynamics of the motorcycles are governed solely by the driver’s action. We use control- and graph-theoretic tools to design decentralised controllers for the connected cars, that can ensure safe spacing despite the presence of the motor-cycles. We first model the longitudinal dynamics of each CC and HDM individually, and then capture the information exchange required for platooning using a two-layer graph structure. Using the dynamics model and the graph-theoretic model, we design a controller, synthesised by solving the parametric Algebraic Riccati equation, for each CC so as to achieve a desired spacing in the platoon. The theoretical results are corroborated with numerical simulations.

We study Compound TCP (C-TCP), the default TCP in the Windows operating system, with Random Exponential Marking (REM) and the widely used Drop-Tail queue policy. The performance metrics we consider are stability of the queue size, queuing delay, link utilization, and packet loss. We analyze the following models: 1) a nonlinear model for C-TCP with Drop-Tail and small buffers; 2) a stochastic variant of REM along with C-TCP; and 3) the original REM proposal as a continuous-time nonlinear model with delayed feedback. We derive conditions to ensure local stability and show that variations in system parameters can induce a Hopf bifurcation, which would lead to the emergence of limit cycles. With Drop-Tail and small buffers, the Compound parameters and the buffer size both play a key role in ensuring stability. In the stochastic variant of REM, larger thresholds for marking/dropping packets can destabilize the system. With the original REM proposal, using Poincaré normal forms and the center manifold analysis, we also characterize the type of the Hopf bifurcation. This enables us to analytically verify the stability of the bifurcating limit cycles. Packet-level simulations corroborate some of the analysis. Some design guidelines to ensure stability and low latency are outlined.