Tag Archives: Communication Delays

Communication delays modelled as Gamma distributions for space-earth applications

H. Chen, Z. Liu, P. Huang and Z. Kuang, Time-Delay Modeling and Simulation for Relay Communication-Based Space Telerobot System, IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 52, no. 7, pp. 4211-4222, July 2022 DOI: 10.1109/TSMC.2021.3090806.

In a space telerobot system (STS), effectiveness of the control method in eliminating the time delay\u2019s influences is advisable to be verified under the real circumstance. However, it is difficult and costly for many scholars to obtain confidential information that would allow them to establish an STS. It may be feasible, using some existing results, to model the time delay as close to reality as possible, and to then program a simulation system to generate the simulated time delay, thus verifying validity. In this article, time-delay modeling and simulation problems for relay communication-based STS are first studied. The time delay in relay communication-based STS consists of both processing and communication time delays; the latter is divided into ground and ground-space parts. By extending the available results, processing and ground communication time delays are modeled with the probability distribution function modeling approach. An optimal communication link identification and minimum time-delay realization (OCLIMTDR) method is proposed to model the ground-space communication time delay. In this method, the novel point\u2013vector\u2013sphere (PVS) algorithm serves to judge link connectivity. The PVS algorithm is based on geometric theory, which gives the OCLIMTDR method good extensibility and renders it suitable for any relay communication network in theory. All three parts of the time-delay models are integrated to form the loop time-delay model of the STS. Subsequently, a time-delay simulation system is created by programming the loop time-delay model. Finally, the correctness of the simulation system is further authenticated based on simulations and some prior knowledge.

Kalman filter with time delays

H. Zhu, J. Mi, Y. Li, K. -V. Yuen and H. Leung, VB-Kalman Based Localization for Connected Vehicles With Delayed and Lost Measurements: Theory and Experiments, EEE/ASME Transactions on Mechatronics, vol. 27, no. 3, pp. 1370-1378, June 2022 DOI: 10.1109/TMECH.2021.3095096.

Traditionally, connected vehicles (CVs) share their own sensor data that relies on the satellite with their surrounding vehicles by vehicle-to-vehicle (V2V) communication. However, the satellite-based signal sometimes may be lost due to environmental factors. Time-delays and packet dropouts may occur randomly by V2V communication. To ensure the reliability and accuracy of localization for CVs, a novel variational Bayesian (VB)-Kalman method is developed for unknown and time varying probabilities of delayed and lost measurements. In this VB-Kalman localization method, two random variables are introduced to indicate whether a measurement is delayed and available, respectively. A hierarchical model is then formulated and its parameters and state are simultaneously estimated by the VB technique. Experimental results validate the proposed method for the localization of CVs in practice.

NOTE: See also S. Guo, Y. Liu, Y. Zheng and T. Ersal, “A Delay Compensation Framework for Connected Testbeds,” in IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 52, no. 7, pp. 4163-4176, July 2022, doi: 10.1109/TSMC.2021.3091974.

Modelling network delay in the remote estimation of the robot state for networked telerobots

Barnali Das, Gordon Dobie, Delay compensated state estimation for Telepresence robot navigation, Robotics and Autonomous Systems, Volume 146, 2021 DOI: 10.1016/j.robot.2021.103890.

Telepresence robots empower human operators to navigate remote environments. However, operating and navigating the robot in an unknown environment is challenging due to delay in the communication network (e.g.,�distance, bandwidth, communication drop-outs etc.), processing delays and slow dynamics of the mobile robots resulting in time-lagged in the system. Also, erroneous sensor data measurement which is important to estimate the robot\u2019s true state (positional information) in the remote environment, often create complications and make it harder for the system to control the robot. In this paper, we propose a new approach for state estimation assuming uncertain delayed sensor measurements of a Telepresence robot during navigation. A new real world experimental model, based on Augmented State Extended Kalman Filter (AS-EKF), is proposed to estimate the true position of the Telepresence robot. The uncertainty of the delayed sensor measurements have been modelled using probabilistic density functions (PDF). The proposed model was successfully verified in our proposed experimental framework which consists of a state-of-the-art differential-drive Telepresence robot and a motion tracking multi-camera system. The results show significant improvements compared to the traditional EKF that does not consider uncertain delays in sensor measurements. The proposed model will be beneficial to build a real time predictive display by reducing the effect of visual delay to navigate the robot under the operator\u2019s control command, without waiting for delayed sensor measurements.

A ROS module that improves real-time aspects of network communication among distributed ROS machines, and a nice analysis of wireless network characteristics and limitations

Danilo Tardioli, Ramviyas Parasuraman, Petter Ögren, Pound: A multi-master ROS node for reducing delay and jitter in wireless multi-robot networks, Robotics and Autonomous Systems, Volume 111, 2019, Pages 73-87, DOI: 10.1016/j.robot.2018.10.009.

The Robot Operating System (ROS) is a popular and widely used software framework for building robotics systems. With the growth of its popularity, it has started to be used in multi-robot systems as well. However, the TCP connections that the platform relies on for connecting the so-called ROS nodes presents several issues regarding limited-bandwidth, delays, and jitter, when used in wireless multi-hop networks. In this paper, we present a thorough analysis of the problem and propose a new ROS node called Pound to improve the wireless communication performance by reducing delay and jitter in data exchanges, especially in multi-hop networks. Pound allows the use of multiple ROS masters (roscores), features data compression, and importantly, introduces a priority scheme that allows favoring more important flows over less important ones. We compare Pound to the state-of-the-art solutions through extensive experiments and show that it performs equally well, or better in all the test cases, including a control-over-network example.