Nor Fadzilah Abdullah

Spatial Diversity for IEEE 802.11p Post-Crash Message Dissemination in a Highway Environment

In this paper, we evaluate the performance of broadcast safety applications in a vehicular-to-vehicular (V2V) communication scenario using a BER-based reception model from a detailed IEEE 802.11p physical layer simulator for a more accurate interpretation of the vehicular communication system, instead of the prebuilt SNR threshold model available in a typical network simulators. Our main contribution is the spatial diversity analysis provided using MIMO-STBC, that is specific to modulation types, vehicular speeds and range of SNR values. To further improve the accuracy of the analysis, realistic vehicular traces from a bidirectional highway are used as the mobility model. Finally, we included post-crash warning message prioritization over periodic status updates by enabling a hybrid EDCA MAC. Our analysis shows that MIMO-STBC achieves up to 80% range extension of the 1-hop safety broadcast in a V2V when compared against single antenna system.

Channel Parameters and Throughput Predictions for mmWave and LTE-A Networks in Urban Environments

Spectrum shortage in the conventional microwave bands coupled with the need for multi-gigabit per- cell capacities has motivated the use of the mmWave bands in future 5G networks. In this paper 3D ray tracing is used to derive key statistical parameters for the mmWave channel. These include path loss, LoS probability, K-factor, RMS delay spread and angular spreads. The mmWave parameters are directly compared to the microwave channel present in LTE-A. Cellular deployment in both bands is then simulated for a 500 m by 500 m regqasion of central Bristol. The impact of different antenna geometries is also studied. Due to the trade-offs between the number of required BSs and the cost of network deployment, we propose a converged mmWave/microwave network for improved user experience.

Raptor code for wireless ad hoc vehicular safety broadcast

This paper proposes an implementation of systematic Raptor code in an ad hoc V2V (vehicular-to-vehicular) environment for post-crash safety broadcast. This is to address the latency problem caused by use of repetition code in a high speed vehicular environment for time-sensitive safety applications. The highly dynamic topology and challenging RF behavior of vehicular networks necessitate the use of a robust error control mechanism even with the use of spatial diversity techniques such as STBC-MIMO scheme. A cross-layer simulator model is used to evaluate the delay performance of Raptor codes against a low complexity repetition code. The numerical analysis demonstrates that the end-to-end delay performance is significantly reduced when Raptor codes are used, especially at higher distances from the source node. This is true in the case of single antenna as well as multiple antenna schemes.

Car-to-Car Safety Broadcast with Interference Using Raptor Codes

Car-to-car safety applications that demand real-time and reliable communications in vehicular ad hoc networks (VANETs) requires a new paradigm of coding techniques. In this paper, we propose a novel coding approach using a systematic Raptor code for car-to- car post-crash warning broadcast applications. A cross-layer simulator model is developed to evaluate the performance of Raptor codes against repetition codes using also multiple antennas spatial diversity techniques. The end-to-end delay and packet delivery ratio are used as performance metrics to demonstrate the latency and reliability problems of repetition codes that are addressed using Raptor codes.

Raptor Codes for Infrastructure-to-Vehicular Broadcast Services

One of the important applications to be available in vehicular ad-hoc networks are value-added or infotainment services. However, vehicular communication suffers from high packet loss due to challenging channel characteristics such as huge Doppler spread and multipath fading. This makes current IEEE 802.11p standard for vehicular network based on the ARQ scheme inefficient. Therefore, the highly scalable and fault-tolerant properties offered by rateless code makes this a promising area of research. This paper investigates the implementation of a systematic Raptor codes for a broadcast service in infrastructure-to-vehicular communications. The code performance in terms of the decoding probability of success, mean decoding time and mean aggregate throughput are presented.

Path-Loss and Throughput Prediction of IEEE 802.11ad Systems

This paper presents a path-loss prediction analysis and a performance evaluation of the 60GHz IEEE 802.11ad standard. Received signal strength measurements were performed in indoor locations and the decay coefficients were estimated over a number of measured routes. Furthermore, real world maps were incorporated into a 3-D mm wave ray- tracing tool for the purpose of employing realistic channel matrices into an 802.11ad bit level simulator. Finally, performance metrics for various MCS modes are presented and analyzed for both Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier (SC) transmissions.

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.

Systematic raptor codes for safety broadcast in an unsaturated vehicular highway environment

Active safety broadcast is one of the most fundamental services in intelligent transportation systems. The repetition code proposed in wireless access for vehicular environment (WAVE) standard is inefficient in realistic channel conditions and rapidly changing network topologies. In this study, we propose the use of systematic raptor codes as a forward error correction (FEC) scheme at the MAC layer. This code is optimised for short packet lengths, as are expected in safety applications. We have developed a multi-layered simulator that consists of realistic IEEE 802.11p physical layer results, an analytical random access MAC model and FEC codes implemented at different OSI layers. The model considers safety messages under non-saturated channel conditions according to the vehicular IEEE 802.11p standard. Issues such as the hidden nodes problem, interference and vehicles leaving the communication area are considered. The performance evaluation of raptor codes against repetition codes in the shared control channel with different antenna schemes is also presented.

A Throughput Study of White-Fi Networks in Rural Environment under Realistic Conditions and Mobility

The regulatory framework for secondary utilization of TV white spaces (TVWS) is well underway in the United Kingdom, while important steps in this direction are taken within the European Union and elsewhere. Mobile network operators are interested in the use of TVWS for cellular extension and rural access, where TVWS is seen as a significant new opportunity for operators to provide new wireless services. The governments plan to close the digital divide between the urban and rural communities has motivated the efforts to develop Wi-Fi like operation in TVWS for better coverage in rural areas. The IEEE currently has a working group developing 802.11af amendment which will allow for WLAN operations in the TVWS. This paper presents a quantitative analysis of downlink throughput performance of IEEE802.11af, also known as White-Fi in a rural environment while taking into account realistic modelling of TV channel availability, wireless channel, AP density, and the effect of co-channel interference caused by secondary APs and DVB-T transmitters. The paper shows that the low operating frequency of White-Fi offers a wide coverage in a rural environment, where there is limited cellular coverage due to the cost-inefficiency of base stations deployment. The presented results also show that there are more available TVWS channels and less co-channel interferers in a rural environment, resulting in a significant throughput performance even in high mobility if suitable channel estimation is considered, making it ideal for vehicular communications with White-Fi.

Performance evaluation of 802.11 standards operating in TVWS and higher frequencies under realistic conditions

The digital switch-over has triggered the development of new wireless standards which are expected to use unoccupied TV channels known as TV white space. Wi-Fi like systems in TVWS are foreseen as cost effective high data rate communication systems which might provide significant coverage compared to existing 802.11 Wi-Fi systems. This paper presents a quantitative analysis of downlink throughput of three 802.11 standards, namely 802.11af in the TV band, 802.11g in the 2.4GHz band and 802.11p in the 5.9GHz band. The study is the first to compare the three standards considering realistic conditions such as availability of TV channels, realistic modelling of wireless channels and considering the effect of AP and DVB-T interference in rural and urban environments in the United Kingdom. We have shown that the overall benefit of operation in TVWS is mainly governed by the AP density, number of available TV channels and the AP transmission power.