Delay-based Algorithm Research Articles

Trajectory-Based Signal Control in Mixed Connected Vehicle Environments

The emerging connected vehicle (CV) technology has introduced the opportunity to improve traditional traffic signal operation. Real-time vehicle trajectory information (location, speed, and heading) from CV technology can provide information about the nearby traffic conditions which potentially can be utilized for enhanced traffic signal control operation. However, implementation of CV technology still is impractical due to the lower penetration rate of CV-enabled vehicles on the road and the limited deployment of vehicle-to-infrastructure (V2I) communications. This paper developed an approach to use vehicle trajectory data with traditional traffic signal controllers to improve intersection operational performance, even with the limited use or absence of V2I communications. Two signal control algorithms, the delay-based algorithm (DBA) and the weighted delay-based algorithm (WDBA), were developed to demonstrate delay optimization at a signalized intersection. The intersection was modeled in Vissim microsimulation, and simulation scenarios were tested for various traffic demands. Analysis results showed that both proposed algorithms outperformed existing free timing operation, and statistically significant improvement was observed in terms of vehicle delay, stop delay, and queue length.

Measuring Passenger Car Equivalents (PCE) for Heavy Vehicle on Two Lane Highway Segments Operating Under Various Traffic Conditions

Passenger Car Equivalent (PCE) is essential for transportation engineering to assess heavy vehicles’ (HV) impact on highway operations and capacity planning. Highway Capacity Manual 2010 (HCM 2010) used PCE values and percent of heavy vehicles to account the impacts on both highway planning and operation, however, PCE values in the latest version of HCM derived based on the steady and balanced two-lane-two-way (TLTW) traffic flows. The objective of the study is to identify PCE values for TLTW highway at various traffic volume with an emphasis on congestion conditions. This study introduces an analytical model, combining a headway-based and a delay-based algorithms, for estimating PCEs of HV on a TLTW highway. This study contributes to the literature by providing relationships among PCE, the traffic volume level (TVL) of both lanes, and the TVL duration on a TLTW highway. Traffic volume was categorized into five levels: TVL A (<250 pc/h), TVL B (250–375 pc/h), TVL C (375–600 pc/h), TVL D (600–850 pc/h), and TVL E (>850 pc/h). The results indicate that on a TLTW highway, the TVLs of both lanes and their durations have significant impact on PCE values. In general, PCE values increase as TVL duration increases. Trucks have much higher impacts on operation under unbalanced conditions of TVL A with D, TVL B with C, and TVL D with B, when duration time is greater than one hour. When both lanes are saturated, trucks’ effect on capacity diminishes over time, and PCE values are approaching to 1.0.

Receiver-Side TCP Countermeasure in Cellular Networks.

Cellular-based networks keep large buffers at base stations to smooth out the bursty data traffic, which has a negative impact on the user’s Quality of Experience (QoE). With the boom of smart vehicles and phones, this has drawn growing attention. For this paper, we first conducted experiments to reveal the large delays, thus long flow completion time (FCT), caused by the large buffer in the cellular networks. Then, a receiver-side transmission control protocol (TCP) countermeasure named Delay-based Flow Control algorithm with Service Differentiation (DFCSD) was proposed to target interactive applications requiring high throughput and low delay in cellular networks by limiting the standing queue size and decreasing the amount of packets that are dropped in the eNodeB in Long Term Evolution (LTE). DFCSD stems from delay-based congestion control algorithms but works at the receiver side to avoid the performance degradation of the delay-based algorithms when competing with loss-based mechanisms. In addition, it is derived based on the TCP fluid model to maximize the network utility. Furthermore, DFCSD also takes service differentiation into consideration based on the size of competing flows to shorten their completion time, thus improving user QoE. Simulation results confirmed that DFCSD is compatible with existing TCP algorithms, significantly reduces the latency of TCP flows, and increases network throughput.

A Spectrum Switching Delay-Aware Scheduling Algorithm for Centralized Cognitive Radio Networks

We formulate a scheduling problem that takes into account different hardware delays experienced by the secondary users (SUs) in a centralized cognitive radio network (CRN) while switching to different frequency bands. We propose a polynomial-time suboptimal algorithm to address our formulated scheduling problem. We evaluate the impact of varying switching delay, number of frequencies, and number of SUs. Our simulation results indicate that our proposed algorithm is robust to changes in the hardware spectrum switching delay and its performance is very close to its upper bound. We also compare our proposed method with the corresponding constant switching delay-based algorithm and demonstrate that our suggestion of taking into account the different hardware delays while switching to different frequency bands is essential for scheduling in CRNs.

Performance Improvement of Delay-Based TCPs in Asymmetric Networks

Delay-based TCPs detect network congestion in the early stage and successfully prevent periodic packet loss that usually occurs in loss-based TCPs. It has been demonstrated that delay-based algorithms outperform loss-based schemes in many aspects. However, a delay-based TCP may not prevent unnecessary throughput degradation in asymmetric networks and when the congestion occurs in the backward path over symmetric links. In this letter, we modify the mechanism of measuring RTT value for delay-based TCPs without clock synchronization. Based on the simulation results, we show the effectiveness and utilities.

Improving performance of delay-based TCPs with rerouting

Delay-based TCPs detect network congestion in the early stage and successfully prevent periodic packet loss that usually occurs in loss-based mechanisms. It has been demonstrated that delay-based algorithms outperform loss-based schemes in many aspects. However, a delay-based TCP may not prevent unnecessary throughput degradation when rerouting occurs and in mobile IP networks and mobile ad hoc networks because it could not differentiate whether the increased RTT is due to route change or network congestion. This work investigates how to improve the performance of delay-based TCPs with rerouting and proposes a mechanism for delay-based TCPs. The proposed mechanism is able to re-measure the BaseRTT if necessary by detecting the change of TTL value of two end-hosts. Based on the simulation results, we demonstrate the effectiveness and utilities

High-Precision Algorithms for Astrometry: A Comparison of Two Approaches

This paper discusses the correspondence between two approaches to astrometric observational reductions: the approach based on angular observables used for optical observations, and the approach based on the interferometric delay observable used for very long baseline radio interferometry (VLBI) observations. A procedure is presented by which VLBI algorithms can be used for optical observations. This scheme can help to guarantee consistent treatment of observational results in the two regimes. Differences between angle- and delay-based algorithms in current use are shown to be less than 1 μas. However, the physical models used as the bases for the algorithms must be improved to reach external accuracies at such levels.