arXiv subjects

Seong-Cheol Kim

Publications and source records attributed to Seong-Cheol Kim.

10 recordsLinked to original sources

arXiv2022

Joint Vehicle Tracking and RSU Selection for V2I Communications with Extended Kalman Filter

We develop joint vehicle tracking and road side unit (RSU) selection algorithms suitable for vehicle-to-infrastructure (V2I) communications. We first design an analytical framework for evaluating vehicle tracking systems based on the extended Kalman filter. A simple, yet effective, metric that quantifies the vehicle tracking performance is derived in terms of the angular derivative of a dominant spatial frequency. Second, an RSU selection algorithm is proposed to select a proper RSU that enhances the vehicle tracking performance. A joint vehicle tracking algorithm is also developed to maximize the tracking performance by considering sounding samples at multiple RSUs while minimizing the amount of sample exchange. The numerical results verify that the proposed vehicle tracking algorithms give better performance than conventional signal-to-noise ratio-based tracking systems.

cs.IT↗

arXiv2021

Adaptive Beam Design for V2I Communications using Vehicle Tracking with Extended Kalman Filter

Vehicle-to-everything communication system is a strong candidate for improving the driving experience and automotive safety by linking vehicles to wireless networks. To take advantage of the full benefits of vehicle connectivity, it is essential to ensure a stable network connection between roadside unit (RSU) and fast-moving vehicles. Based on the extended Kalman filter (EKF), we develop a vehicle tracking algorithm to enable reliable radio connections. For the vehicle tracking algorithm, we focus on estimating the rapid changes in the beam direction of a high-mobility vehicle while reducing the feedback overhead. Furthermore, we design a beamforming codebook that considers the road layout and RSU. By leveraging the proposed beamforming codebook, vehicles on the road can expect a service quality similar to that of conventional cellular services. Finally, a beamformer selection algorithm is developed to secure sufficient gain for the system's link budget. Numerical results verify that the EKF-based vehicle tracking algorithm and the proposed beamforming structure are more suitable for vehicle-to-infrastructure networks compared to existing schemes.

cs.IT↗

arXiv2017

Deep Learning Based NLOS Identification with Commodity WLAN Devices

Identifying line-of-sight (LOS) and non-LOS (NLOS) channel conditions can improve the performance of many wireless applications, such as signal strength-based localization algorithms. For this purpose, channel state information (CSI) obtained by commodity IEEE 802.11n devices can be used, because it contains information about channel impulse response (CIR). However, because of the limited sampling rate of the devices, a high-resolution CIR is not available, and it is difficult to detect the existence of an LOS path from a single CSI measurement, but it can be inferred from the variation pattern of CSI over time. To this end, we propose a recurrent neural network (RNN) model, which takes a series of CSI to identify the corresponding channel condition. We collect numerous measurement data under an indoor office environment, train the proposed RNN model, and compare the performance with those of existing schemes that use handcrafted features. The proposed method efficiently learns a non-linear relationship between input and output, and thus, yields high accuracy even for data obtained in a very short period.

cs.NI↗

arXiv1998

Use-it or Lose-it Policies for the Available Bit Rate (ABR) Service in ATM Networks

The Available Bit Rate (ABR) service has been developed to support 21st century data applications over Asynchronous Transfer Mode (ATM). The ABR service uses a closed-loop rate-based traffic management framework where the network divides left-over bandwidth among contending sources. The ATM Forum traffic management group also incorporated open-loop control capabilities to make the ABR service robust to temporary network failures and source inactivity. An important problem addressed was whether rate allocations of sources should be taken away if sources do not use them. The proposed solutions, popularly known as the Use-It-or-Lose-It (UILI) policies, have had significant impact on the ABR service capabilities. In this paper we discuss the design, development, and the final shape of these policies and their impact on the ABR service. We compare the various alternatives through a performance evaluation.

cs.NI↗

arXiv1998

UBR+: Improving Performance of TCP over ATM-UBR service

ATM-UBR switches respond to congestion by dropping cells when their buffers become full. TCP connections running over UBR experience low throughput and high unfairness. For 100% TCP throughput each switch needs buffers equal to the sum of the window sizes of all the TCP connections. Intelligent drop policies can improve the performance of TCP over UBR with limited buffers. The UBR+ service proposes enhancements to UBR for intelligent drop. Early Packet Discard improves throughput but does not attempt to improve fairness. Selective packet drop based on per-connection buffer occupancy improves fairness. The Fair Buffer Allocation scheme further improves both throughput and fairness.

cs.NI↗

arXiv1998

Performance of TCP over ABR on ATM backbone and with various VBR traffic patterns

We extend our earlier studies of buffer requirements of TCP over ABR in two directions. First, we study the performance of TCP over ABR in an ATM backbone. On the backbone, the TCP queues are at the edge router and not inside the ATM network. The router requires buffer equal to the sum of the receiver window sizes of the participating TCP connections. Second, we introduce various patterns of VBR background traffic. The VBR background introduces variance in the ABR capacity and the TCP traffic introduces variance in the ABR demand. Some simple switch schemes are unable to keep up with the combined effect of highly varying demands and highly varying ABR capacity. We present our experiences with refining the ERICA+ switch scheme to handle these conditions.

cs.NI↗

arXiv1998

Performance of TCP/IP Using ATM ABR and UBR Services over Satellite Networks

We study the buffering requirements for zero cell loss for TCP/IP over satellite links using the available bit rate (ABR) and unspecified bit rate (UBR) services of asynchronous transfer mode (ATM) networks. For the ABR service, we explore the effect of feedback delay (a factor which depends upon the position of the bottleneck), the switch scheme used, and background variable bit rate (VBR) traffic. It is shown that the buffer requirement for TCP over ABR is independent of the number of TCP sources, but depends on the aforementioned factors. For the UBR service, we show that the buffer requirement is the sum of the TCP receiver window sizes. We substantiate our arguments with simulation results.

cs.NI↗

arXiv1998

Performance and Buffering Requirements of Internet Protocols over ATM ABR and UBR Services

The Asynchronous Transfer Mode (ATM) networks are quickly being adopted as backbones over various parts of the Internet. This paper analyzes the performance of TCP/IP protocols over ATM network's Available Bit Rate (ABR) and Unspecified Bit Rate (UBR) services. It is shown that ABR pushes congestion to the edges of the ATM network while UBR leaves it inside the ATM portion.

cs.NI↗

arXiv1998

Performance of TCP over ABR with Long-Range Dependent VBR Background Traffic over Terrestrial and Satellite ATM networks

Compressed video is well known to be self-similar in nature. We model VBR carrying Long-Range Dependent (LRD), multiplexed MPEG-2 video sources. The actual traffic for the model is generated using fast-fourier transform of generate the fractional gaussian noise (FGN) sequence. Our model of compressed video sources bears similarity to an MPEG-2 Transport Stream carrying video, i.e., it is long-range dependent and generates traffic in a piecewise-CBR fashion. We study the effect of such VBR traffic on ABR carrying TCP traffic. The effect of such VBR traffic is that the ABR capacity is highly variant. We find that a switch algorithm like ERICA+ can tolerate this variance in ABR capacity while maintaining high throughput and low delay. We present simulation results for terrestrial and satellite configurations.

cs.NI↗

arXiv1998

Performance of Bursty World Wide Web (WWW) Sources over ABR

We model World Wide Web (WWW) servers and clients running over an ATM network using the ABR (available bit rate) service. The WWW servers are modeled using a variant of the SPECweb96 benchmark, while the WWW clients are based on a model by Mah. The traffic generated by this application is typically bursty, i.e., it has active and idle periods in transmission. A timeout occurs after given amount of idle period. During idle period the underlying TCP congestion windows remain open until a timeout expires. These open windows may be used to send data in a burst when the application becomes active again. This raises the possibility of large switch queues if the source rates are not controlled by ABR. We study this problem and show that ABR scales well with a large number of bursty TCP sources in the system.

cs.NI↗