Reham Almesaeed

TVWS extension of the 3GPP/ITU channel model

Recently many cellular and WLAN standards are considering operation in the TV bands due to enhanced coverage and access to additional bandwidth. To accurately assess the performance of wireless communication systems operating in the TeleVision White Space (TVWS) spectrum, a new channel model is required that accounts for the unique propagation characteristics in the UHF band. This paper proposes an extension to the existing 3GPP/ITU channel model for operation at frequencies from 400 MHz (bottom of the TVWS band) up to 5 GHz (top of the WLAN band). The channel model is suitable for urban environments and the raw propagation data was generated using a state-of-the-art 3D ray-tracing tool. Results are presented as cumulative distribution functions of total received power, RMS delay spread, K-factor and RMS angular spread (azimuth and elevation). The probability of line-of-sight as function of distance and best-fit parameters for large and small scale fading are also presented.

A comparison study of 2D and 3D ITU channel model

Recently there has been strong interest in extending MIMO signal processing from the azimuth dimension to include the elevation plane. However, many channel models, such as the 3GPP/ITU model, focus on two dimensional propagation, i.e. propagation in the azimuth plane only. The assumption of 2D propagation may lead to inaccurate estimation of channel capacity, spatial correlation and system level performance in environments where the distribution of the elevation angles is significant. In this paper, we implement a 3D extension of the 3GPP/ITU 2D channel model by adding elevation angle statistics generated by a state-of-the-art 3D ray tracer. The paper also presents a comparison study between the implemented 3D 3GPP/ITU model and the ray tracer channel statistics. We also show the impact of considering 3D components on the channel ergodic capacity, antenna spatial correlation and large/small scale parameters (total received power, delay spread, angular spread, and K-factor).

Exploiting the elevation dimension of MIMO system for boosting handset capacity

Recently there has been strong interest in extending the MIMO signal processing from the azimuth dimension to include the elevation plane. Therefore a 3D channel model is required for an accurate evaluation of MIMO performance. The MIMO system can also be deployed at the user terminal according to the LTE-Advanced system specifications. Therefore, this study exploits the elevation dimension at the user equipment (UE) MIMO receiver and proposes an antenna switching strategy to achieve the highest performance among the MIMO spatial streams. This study is considered as one of the solutions toward boosting MIMO capacity and enhancing end user experience for 5G systems. The study considers different types of user handsets such as smartphone and tablet where different scenarios of antennas placements are implemented and different number of antennas elements are deployed. The consideration of the 3D component in the modelling of the MIMO channels results in performance differences in the MIMO system in terms of ergodic capacity and spatial correlation as the handset rotates. The paper suggests the best arrangement of antenna elements for the UE handset manufacturers to achieve the highest channel capacity when exploiting the elevation plane.

3D Channel Models: Principles, Characteristics, and System Implications

This article presents a comprehensive review of the principles and characteristics of 3D channel models. We propose a framework for a 3D channel extension of the widely used 2D 3GPP/ ITU generic channel model. We describe the main components and challenges of the newly proposed 3D channel model and the motivations that lie behind them. 3D channel models specify multipath elevation angles as well as azimuth (or horizontal plane) angles. This enables the evaluation of 3D MIMO techniques such as FD MIMO and per user 3D beamforming. We also provide a state-of-the-art review on the evolution of channel models. The article ends with a discussion on the impact of 3D channel modeling on system-level performance.

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.

Impact of 3D propagation on Wi-Fi performance in MIMO system

One of the research activities in 5G communication systems is the extension of the MIMO processing from the 2D to the 3D plane by exploiting the elevation dimension which gives an additional degree of freedom to meet the high capacity demands. Despite the growing researches concerning 3D space propagation, there are few studies that evaluate the impact of 3D propagation on MIMO performance at the PHY level and the capacity gained from exploiting the elevation component. The aim of this paper is to evaluate, quantify and compare the downlink BER performance experienced by users in an urban environment in cases of 2D and 3D channel models, where the impact of the 3D component on MIMO performance is evaluated. Results indicate that 3D modelling implies lower correlation between MIMO spatial streams and consequently lower BER. Therefore, the full benefits of MIMO cannot be accurately predicted in 2D model where high correlated MIMO spatial streams are observed. The study also compares two different orientations of linear MIMO arrays (horizontal and vertical). In this study, we are also implementing our enhanced 3D channel model which is an extension of the well-known 3GPP/ITU channel model. The proposed channel model is made available to the public through SourceForge.

Exploiting MIMO vertical diversity in a 3D vehicular environment.

Recently there has been strong interest in extending the MIMO processing from the azimuth dimension to include the elevation plane. This paper compares vertically and horizontally oriented dual polar MIMO LTE-A base station antennas pairs, and studies the performance among large set of users and channel predictions. The study also considers a 2D planar MIMO antenna array arrangement which is compared against the horizontal and vertical configuration for a 4×4 MIMO system. In order to study accurately the performance of such 3D MIMO systems, a 3D ITU propagation channel model is employed in addition to the 3D antenna radiation patterns. Bit level simulations are performed for the downlink physical shared channel (PDSCH) in LTE-A operating at 2.6GHz for a vehicle moving at 35kmph in an urban macro environment. The paper examines the best arrangement for LTE base station dual polarised antenna arrays to achieve the lowest spatial correlation values in a MIMO system.

Infrastructure to Vehicle Throughput Performance in LTE-A Using 2D and 3D 3GPP/ITU Channel Models

This paper considers infrastructure to vehicle communications using Advanced-LTE. The paper compares the downlink throughput performance experienced by mobile users in an urban-macro-cell in cases of 2D and 3D channel models, where the impact of the 3D component on MIMO performance is investigated. Recently there has been strong interest in extending the MIMO processing from the azimuth dimension to include the elevation plane. Therefore, a 3D channel model is required in the evaluation of elevation MIMO performance. Bit level simulation is performed for the downlink physical shared channel (PDSCH) in LTE-A operating at 2.6GHz. Results indicate the accuracy of the 3D channel model and implies correct estimation of the 3D channel. The difference in the small scale parameters for the SISO case and the lower spatial correlation parameters for the MIMO case result in higher predicted capacity for the 3D channel model. The study has been carried out for different mobility speeds, packet sizes and MCSs modes.

How much can White-Fi networks deliver to cellular operators?

In order to alleviate the mobile data explosion problem, a Wi-Fi offloading strategy has been proposed. Given the recent deployment of Wi-Fi like systems in the TVWS (TV White Space), the mobile offloading to White-Fi networks is an attractive solution to mobile operators to provide full broadband coverage in dense urban environments. To quantify the amount of throughput and coverage gain achieved from users offloading, this paper conducts a simulation-based analysis for a range of carrier class access points (AP) densities considering practical deployment of the IEEE 802.11af and 802.11g networks. The study takes into account a realistic modelling of the TV channels availability and wireless channel propagation. The interference from co-channel operation and DVB-T systems are also considered. The paper shows that the opportunistic deployment of White-Fi networks generally results in high throughput gain and coverage probability at various AP densities as compared to Wi-Fi only networks. It also grants a higher fraction of users with high throughput capability as compared to 802.11g only networks. In addition, the study provides the mobile operators with a range of performance statistics that can help them to select the suitable range of AP deployment to meet certain performance thresholds.