Zhihua Lai

A new approach to solve angular dispersion of discrete ray launching for urban scenarios

Ray-based methods such as ray tracing and ray launching have been increasingly used in radio wave propagation modelling. Ray tracing is used for point-to-point multipath prediction (for few receivers) while ray launching, being more adaptable, is more suitable for multi-point prediction. However, ray launching suffers from angular dispersion which causes rays to miss pixels when the distance from the emitter increases. Several solutions such as beam tracing or ray splitting have been proposed to resolve this, but this paper presents a new approach, which is suitable for discrete ray launching, to avoid the problem. Results show that by this approach, discrete ray launching is suitable for radio wave propagation modelling. Significant speedups are observed compared to traditional ray-based models via parallelization techniques such as multi-threading and distributed computing. Complex channel characteristics due to multipaths in the urban environment can be obtained via this method.

Implementation and validation of a new combined model for outdoor to indoor radio coverage predictions

A new model used to compute the outdoor to indoor signal strength emitted from an outdoor base station is presented. This model is based on the combination of 2 existing models: IRLA (Intelligent Ray Launching), a 3D Ray Optical model especially optimized for outdoor predictions, and MR-FDPF (Multiresolution Frequency Domain ParFlow), a 2D Finite Difference model initially implemented for indoor propagation. The combination of these models implies the conversion of the ray launching paths on the border of the buildings, into virtual source flows that will be used as input for the indoor model. The performance of the new combined model is evaluated via measurements at 2 frequencies (WiMAX and WiFi). This solution appears to be efficient for radio network planning, in term of both accuracy and computational cost.

Indoor Massive MIMO Channel Modelling Using Ray-Launching Simulation

Massive multi-input multioutput (MIMO) is a promising technique for the next generation of wireless communication networks. In this paper, we focus on using the ray-launching based channel simulation to model massive MIMO channels. We propose one deterministic model and one statistical model for indoor massive MIMO channels, both based on ray-launching simulation. We further propose a simplified version for each model to improve computational efficiency. We simulate the models in indoor wireless network deployment environments and compare the simulation results with measurements. Analysis and comparison show that these ray-launching based simulation models are efficient and accurate for massive MIMO channel modelling, especially with application to indoor network planning and optimisation.

A Performance Evaluation of a Grid-Enabled Object-Oriented Parallel Outdoor Ray Launching for Wireless Network Coverage Prediction

The use of parallel technologies to solve complex scientific problems has gained increased popularity. The ray optical methods are deterministic propagation approaches that are based on geometrically searching paths between emitter and receivers. They offer higher accuracy than empirical models, but suffer from slow calculations on exhausted rays that have to be searched. In this paper, an object-oriented scheme based on POP-C++ for parallel objects to accelerate outdoor ray launching is described. Performance evaluation is presented to show that this parallel scheme is promising in outdoor wireless propagation modeling. The possibility of running this model in the distributed grid environment is also discussed. Results have shown the great potential of using such a parallel model to predict accurate outdoor wireless propagation scenarios within a short time.

The Development of a Parallel Ray Launching Algorithm for Wireless Network Planning

Propagation modeling has attracted much interest because it plays an important role in wireless network planning and optimization. Deterministic approaches such as ray tracing and ray launching have been investigated, however, due to the running time constraint, these approaches are still not widely used. In previous work, an intelligent ray launching algorithm, namely IRLA, has been proposed. The IRLA has proven to be a fast and accurate algorithm and adapts to wireless network planning well. This article focuses on the development of a parallel ray launching algorithm based on the IRLA. Simulations are implemented, and evaluated performance shows that the parallelization greatly shortens the running time. The COST231 Munich scenario is adopted to verify algorithm behavior in real world environments, and observed results show a 5 times increased speedup upon a 16-processor cluster. In addition, the parallelization algorithm can be easily extended to larger scenarios with sufficient physical resources.

A novel indoor localization scheme

Ultra-wideband (UWB) receivers can resolve individual multipath components (MPCs), due to the signal occupied a large bandwidths, so they are capable of accurately estimating the time of flight of the signal. To realize high-accuracy indoor localization, a novel UWB locating scheme through estimating the round trip time (RTT) of UWB signal is proposed. Each reference station (RS) transmits the baseband pulse modulated UWB signals. The signals are received by the user terminals (UT) and sent back to the original RS using a different carrier frequency. We can easily calculate the position of the UT by detecting the time gap between the feedback signal and the origin signal. Meanwhile, the multi-path detection algorithm for RTT estimation is presented and the localization performance of the proposed scheme is tested under IEEE 802.15.4a channel models. Experiments demonstrate that the proposed scheme can realize high accuracy localization with an error around the centimeter level.

Performance comparison of MR-FDPF and ray launching in an indoor office scenario

Radio-wave propagation modelling plays a fundamental role in the wireless network planning and optimization. In this work, the performance of two propagation models which are based on different mechanisms are compared in an indoor office scenario in terms of speed and accuracy. Firstly, the office building is modelled and the properties of materials are tuned according to the measurement data so that they are more fit to the real environment. Then the two models are used to predict the coverage and the performance is analysed. Finally, a summary of the simulation results and the model recommendations are given.

The Characterisation of Human Body Influence on Indoor 3.5 GHz Path Loss Measurement

This paper investigates the influence of the human body on indoor measurements of radio wave path loss at 3.5 GHz and proposes a solution to improve the accuracy of measurement. The presence of the human body causes measurement errors to radio wave field strength, which is of concern for analysis. The reduction of errors due to measurement process enhances the accuracy of measurement data that is used to validate propagation models. Also, the characterisation of signal strengths at nearby-locations will be presented, which may be used as a proof to develop new propagation models that take advantage of fast calculation based on the observation of relations between geographically-related signal levels. This is also used to analyse the human body influence depending on the locations.

Sharing experiences with using next generation knowledge portals for advancing web communities

In this article, we discuss the development of two repositories of shared knowledge using intra- and inter-tagging functionality. The functionality enables web user communities to upload, search, navigate through and tag multiple documents in multiple ways at a macro and micro level. Users can tag the whole document as well as parts there-in, as they deem appropriate. Our development process employed a unique, specifically designed community user needs approach (CUNA) to allow elicitation of diverse user communities needs. This included an iterative, rapid application development approach, which in turn, allowed lessons learned from the testing phase to be implemented in the following building phase. Results from in-house testing and an independent consultancy suggest that the web communities perceive the portals as beneficial not just during the project lifecycle but quite likely in future ventures.

A dual-polarisation modelling method for simulation-based propagation models

In this paper, we propose a universal dual-polarisation modelling method for the simulation-based propagation models. We adopt the universal definition of dual-polarisation radiation pattern and apply the definition to model the dual-polarised propagation channel. By adopting the universal definition of dual-polarisation using the ray reference, we clarify the misunderstanding caused by the widely accepted polarisation definition using ground reference. Furthermore, we integrate the universal dual-polarised model to a simulation-based propagation model. Simulation results demonstrate the effectiveness and potential of this dual-polarisation model in the simulation-based propagation models.