Denys Berkovskyy

Cross-layer design of raptor codes for video multicast over 802.11n MIMO channels

This paper explores the benefits of application layer forward error correction (AL-FEC) based on Raptor codes for high quality video multicasting over 802.11n multiple-input multiple-output (MIMO) channels. A cross-layer Wi-Fi simulator in combination with a state-of-the-art ray tracing propagation tool was used to analyse the performance of spatial multiplexing (SM) and space time block coding (STBC) MIMO techniques under different channel conditions. Simulation results showed that with the use of Raptor code AL-FEC, the operation range of the SM system was increased, i.e., the outage probability was driven to zero even though the MIMO channels were highly correlated. Furthermore, the spectral efficiency was also increased since the SNR gain can be increased up to 10 dB depending on the channel conditions. This results in a higher MCS mode to be selected for the transmission of data. We also presented a MIMO switching algorithm which implements Raptor codes as a means to improve the SM performance and then we evaluated the system under realistic wireless channel conditions.

Evaluation of 802.11 and LTE for Automotive Applications

This paper evaluates coverage prediction and radio performance for automotive infotainment applications. The work compares IEEE 802.11af operating in the TV White Space (TVWS) bands with LTE operating at 800MHz and 2.6GHz. Real world rural and urban databases are incorporated into a 3D ray tracing tool for the purposes of exploring signal coverage and data rates along with virtual drive tests. Results are presented as a function of radio standard, operating band, vehicle speed, user location and packet size. LTE is shown to outperform 802.11af since it is less affected by the multipath channel and the significant levels of Doppler Spread experienced by vehicular users. Results also indicate that 802.11af systems provide superior coverage, especially in rural environments.

Multicast Wi-Fi Raptor-enabled data carousel design: simulation and practical implementation

Multicast is an efficient way of transmitting the same set of data to multiple interested users. Unlike the 3rd Generation Partnership Project (3GPP) cellular standards, for Wi-Fi, there is no standardised solution for reliable multicast data transmission. Multicast packets are delivered to multiple users as a broadcast service without support for automatic repeat request. Hence, multicast transmission often results in high packet loss. In order to improve the reliability of multicast delivery, a fixed low-speed (robust) transmission mode can be used. However, this results in the inefficient use of scarce and valuable radio bandwidth. This paper presents a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. An application layer forward error correction (AL-FEC)-enabled data carousel is proposed to enhance reliability. For multicast transmission, we demonstrate that limitations in the Wi-Fi clients are a major source of packet loss, even in ideal channel conditions. Client limitations (particularly data rate limitations) were found to vary as a function of modulation and coding mode, Raptor code parameters and multicast server rate. Our initial Raptor-enabled carousel designs are based on computer simulations and lab-based trials. Analysis is then extended to field trials using a practical implementation of the recommended design. These trials were performed in central Bristol with parameters such as received signal level, packet loss traces and file download times recorded at the clients. Finally, we compare our site-specific simulated results against real-world measurements.

A raptor enabled data carousel for enhanced file delivery and QoS in 802.11 multicast networks

802.11 WLANs do not provide any standardized solution for reliable data multicast. Multicast packets are delivered to multiple clients as a simple broadcast service without support for Automatic Repeat Request. Hence, a fixed low speed (robust) transmission mode is generally used to improve the reliability of multicast files. However, this results in the inefficient use of bandwidth. This paper details a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. We propose an Application Layer Forward Error Correction enabled data carousel for reliable multicast transmission over standard 802.11 WLANs. To quantify the benefits of the proposed system, results are reported from a cross-layer simulator combining novel outdoor ray-tracing, a Physical layer abstraction simulator (to rapidly quantify the radio performance), a RaptorQ enabled multicast data carousel simulator and an optimal access point deployment tool. The simulation results demonstrate that RaptorQ enabled carousels (compared to standard carousels) significantly reduce the average response time and increase the percentage of satisfied users in a multicast network.

Design and Verification of a Virtual Drive Test Methodology for Vehicular LTE-A Applications

In this paper, a virtual drive test (VDT) emulation methodology for vehicle-to-infrastructure long-term evolution-advanced (LTE-A) communications is proposed, evaluated, and compared against a traditional drive test approach. A generic antenna and radio test process is developed based on 3-D ray-traced channel models, theoretic and measured antenna patterns, radio frequency (RF) channel emulation, and hardware-in-the-loop (HIL) radio measurements. The spatial and temporal multipath components of the radio propagation channel between the multiple-input and multiple-output (MIMO)-enabled LTE-A base stations (BS) and the vehicle under test are accurately modeled for a site-specific virtual environment. Measured BS and LTE-A vehicular antenna patterns are incorporated into the system via spatial and polarimetric convolution with the synthetic ray data. The resulting channels are streamed into a wideband channel emulator that connects a multichannel LTE-A BS emulator to a smartphone representing the vehicular on-board-unit (OBU). The laboratory-based LTE-A HIL system is used to study the handover process between two serving LTE-A BSs according to the received RF powers at the vehicular OBU. Emulated RF powers and data throughputs are compared with data from a traditional drive test to verify the legitimacy of the proposed methodology. Our VDT results in terms of reference signal received power and physical downlink shared channel throughput match well the real-world LTE-A measurements for single-input and single-output and MIMO operation. This new process benefits from being repeatable and via the use of ray-tracing scales to support a wide range of urban and rural operating environments.

LTE-A Virtual Drive Testing for Vehicular Environments

In this paper, a Virtual Drive Testing (VDT) methodology for a MIMO LTE Vehicle to Infrastructure (V2I) urban scenario is proposed and compared with actual road drive tests. We have developed a unique and generic radio performance analysis process based on 3D ray traced channel models, theoretic or measured antenna patterns, RF channel emulation and hardware-in-the-loop radio measurements. A 3D ray-tracing channel model is used to predict the spatial and temporal multipath ray components of the radio propagation channel between an LTE BS and the vehicle. Measured LTE vehicular antenna patterns were then applied using a spatial and polarimetric convolution process. The resulting channels were streamed into a Keysight PropSim F8 channel emulator, which was programmed to communicate with the multi-channel LTE BSs emulator and a Samsung S5 mobile client performing a handover procedure. The VDT emulation method proposed in this paper is shown to be reliable and repeatable and the accuracy of the emulated throughput agreed well with real measurements for MIMO operation.

Large-Scale Modeling and Cell-Edge Coverage for Future HetNet Deployments

This paper evaluates the large-scale channel parameters and the cell-edge coverage for various LTE-WiFi based, heterogeneous networks. Real world urban databases are incorporated into two separate 3D ray tracing software tools, specifically designed for the characterization of both microwave and millimeter (mm)-wave radio links. The study is performed for both LTE-800MHz and LTE-2.6GHz macro-cell configurations whereas it demonstrates the coverage enhancement attained by deploying 802.11n/ac/ad micro-cell structures. The significance of this study lies on the radio planning aspects of future heterogeneous networks.

Infrastructure-to-vehicle throughput in TVWS for urban and rural environments

Currently TV whitespace is being considered by WLAN standards, namely the IEEE 802.11af or WhiteFi for enhanced coverage and access to additional bandwidth. The TV bands are harmonised worldwide and the white space is expected to be available globally, making it suitable for vehicular communications. This paper utilises a state-of-the-art 3D ray tracing tool, where road routes are defined in an urban and a rural environment to model realistic infrastructure-to-vehicle propagation in different scenarios. Based on the propagation analysis and link adaptation of SISO, STBC 2×2 and SM 2×2 schemes, the paper compares the coverage and throughput performance of WhiteFi against the legacy WiFi system. Results indicate that WhiteFi has better propagation characteristics than WiFi due to its lower operating frequency. Besides that, it is also shown that the performance of MIMO is critically dependent on the availability of independent spatial channels. Therefore, the full benefits of MIMO cannot be exploited in highly correlated channels especially in a rural scenario.