Michael J. Neve

A Frequency-Selective Wall for Interference Reduction in Wireless Indoor Environments

Modifying the indoor wireless physical propagation environment to reduce the interference level was investigated and demonstrated in this research. A common office partition wall (that was in the main propagation path) was transformed into a frequency-selective (FS) wall by attaching a custom-designed band-stop frequency-selective surface (FSS) as a cover on the wall surface. In-situ measurements showed that this frequency-selective wall filtered out signals operating at 5.4-6.0 GHz (IEEE 802.11a) by an additional attenuation of 10-15 dB compared to the unmodified wall, for incident angles ranging from 0deg-55deg in the azimuth plane and 0deg-20deg in the elevation plane. An attenuation of 10-15 dB in signal strength in the stop band is considered to be significant and beneficial in interference reduction, whereas in the pass-band region (such as 1.8 GHz for cellular telephones), signals experienced only marginally more attenuation than that through the unmodified wall. Results also suggest that the interactions between the FSS and the wall surface can be minimized with an appropriate FSS design, which leads to a feasible and practical product solution: frequency-selective wallpapers. In addition, installation issues, such as misalignment of FSS sheets on the wall, were also examined

Modeling the Effects of Nearby Buildings on Inter-Floor Radio-Wave Propagation

Two buildings (A and B) have been modeled and analyzed with a 2D TEz implementation of the finite-difference time-domain (FDTD) algorithm in order to identify and characterize the mechanisms allowing signals to propagate between floors, specifically reflection and scattering from nearby buildings. Results have been extended to 2.5D by assuming isotropic spreading in the third dimension. In both scenarios considered, reflections from surrounding buildings are found to increase the average received power on adjacent floors-up to 9.7 dB and 32 dB for buildings A and B respectively. Measurements of the impulse response in Building A, made with a sliding correlator channel sounder, show a number of long-delay pulses, which can be attributed to specific reflection paths. Based on these findings, a simple two-component propagation model to predict the sector-average signal strengths is proposed and validated against measurements of the received power. The direct component is modeled as free space with a 22 dB/floor attenuation factor, and the reflected component is modeled as free space with reflection/transmission coefficients of 0.5. The RMS prediction error for this model is 3.2 dB.

Modeling Propagation in Multifloor Buildings Using the FDTD Method

A three-dimensional parallel implementation of the finite-difference time-domain (FDTD) method has been used to identify and isolate the dominant propagation mechanisms in a multistorey building at 1.0 GHz. A novel method to visualize energy flow by computing streamlines of the Poynting vector has been developed and used to determine the dominant propagation mechanisms within the building. It is found that the propagation mechanisms depend on the level of internal clutter modeled. Including metallic and lossy dielectric clutter in the environment increases attenuation on some propagation paths, thereby altering the dominant mechanisms observed. This causes increases in the sector-averaged path loss and changes the distance-dependency exponents across a floor from 2.2 to 2.7. The clutter also reduces Rician K-factors across the floor. Directly comparing sector-averaged path loss from the FDTD simulations with experimental measurements shows an RMS error of 14.4 dB when clutter is ignored. However, this is reduced to 10.5 dB when the clutter is included, suggesting that the effects of clutter should not be neglected when modeling propagation indoors.

A technique for approximating the location of surface- and leaky-wave poles for a lossy dielectric slab

An approximation technique for locating the surface- and leaky-wave poles for a lossy dielectric slab is presented. The problem is reduced to the simultaneous solution of two transcendental equations (for each of the perfect magnetic conductor (PMC) and perfect electric conductor (PEC) cases) which is shown to yield a simple approximate solution for the poles, and which can subsequently be refined using numerical optimization. The technique yields both surface-wave and leaky-wave poles, and results are presented for a typical example to demonstrate the approach. The greatest approximation accuracy was observed for surface-wave and leaky-wave poles well removed from the spectral gap. For poles either within or in close proximity to the spectral gap, an alternative iterative technique is proposed. Expressions for the number of proper plus improper surface-wave poles in a given problem are also derived.

Performance analysis for indoor wireless systems employing directional antennas in the presence of external interference

External interference can cause significant performance degradation in indoor wireless systems such as third/fourth-generation mobile systems and WLANs. Strategic deployment of simple antennas (e.g., the directional patch) at base stations is an attractive low-cost solution that can mitigate, to some extent, the effect of external interference by modifying the propagation of signals in the environment. An experimental investigation of the influence of external interference on the performance of an indoor wireless system is presented. Although appropriate deployment of directional antennas can reduce the impact of external interference, the effectiveness and the optimal antenna arrangement of this deployment strategy are dependent on the relative power level of the external interference.

The Impact of Structural Shielding on the Performance of Wireless Systems in a Single-Floor Office Building

Cochannel interference in indoor wireless communication systems can severely limit system capacity and performance. To reduce cochannel interference in indoor environments, electromagnetic shielding can be used to increase the radio isolation between physically adjacent systems. In this paper, the impact of structural (wall) shielding on the system performance of an interference-limited CDMA system is examined using a ray-tracing propagation model. A logarithmic relationship is observed between the average outage probability and the extent of shielding in a typical single-floor office environment. With an efficient deployment of shielding, the results obtained suggest that both the capacity and signal quality of a wireless system can be enhanced as the number of base stations increases. By incorporating shielding into the architecture of a building, wireless-friendly environments that facilitate better use of the available radio spectrum might be realized

Physical layer engineering for indoor wireless systems in the twenty-first century

Deploying wireless systems so that they offer the best performance for all stakeholders (e.g. users, service providers and shareholders) is identified as a critical issue in advancing the wireless industry into the second decade of the twenty-first century. An historical perspective of the key issues is initially presented, from which a set of societal expectations of future wireless performance are derived. The engineering challenge is to meet these expectations, and this has motivated a programme of research being undertaken at the universities of Auckland and Kent. Suggestions are made as to how this research might be encapsulated in the form of a wireless Code of Practice to assist practitioners charged to provide high performance wireless functionality to users in built environments.

A New Algorithm for Efficient Optimisation of Base Station Placement in Indoor Wireless Communication Systems

A new algorithm is proposed to efficiently find an optimal base station configuration for indoor CDMA networks from a set of potential base station sites. It considers both forward link and reverse link signal-to-interference ratio (SIR) constraints. The proposed algorithm is a combination of a heurisitc algorithm and selective brute force search. The heurisitc algorithm estimates the minimum number of base stations required to serve a set of mobiles. Brute force search analyzes forward link and reverse link SIR for the configurations, starting with the estimated minimum required number of base stations, to find the acceptable configurations and one optimal configuration. The proposed algorithm can be applied repeatedly to different sets of mobiles in an indoor system to find an overall optimal configuration. The efficiency of the proposed algorithm is compared with that of the Branch and Bound (B&B) Algorithm and the Genetic Algorithm to find an optimal configuration.

Reactance of Posts in Circular Waveguide

Experimental and numerical simulation results are presented for the reactance of centered variable-height single and double posts in a circular waveguide. The reactance is a function of the waveguide and post dimensions and frequency, and the results presented are useful in the design of a variety of circular waveguide devices involving these elements.

Antenna selection and deployment strategies for indoor wireless communication systems

Effective antenna selection and deployment strategies are important for reducing co-channel interference in indoor wireless systems. Low-cost solutions are essential, and strategies that utilise simple (passive) antennas (such as directional patches) are advantageous from this perspective. However, performance is always an issue and the improvements achievable through clever antenna deployment (both placement and orientation) need to be quantified. An experimental investigation of indoor propagation comparing the performance of directional and omni-directional antennas is reported. In the case study of a voice-based indoor communication system employing DS-CDMA radio access technique with BPSK modulation, the outage probability for base stations fitted with directional antennas was observed to change in the -54% to +66% range relative to the omni-directional case. The effective change in the distribution of carrier-to-interference ratios by the use of directional antennas is well established in outdoor micro cellular deployment scenarios; however, the magnitude of the influence is quantified for an indoor environment in this case study. It is also shown that obstacles in the environment can amplify the effectiveness of the antenna deployment by acting as physical cell boundaries that restrict interference. External interference has been shown to cause a significant degradation to the performance of an indoor system when the carrier-to-external-interference ratio. This performance degradation can be minimised by appropriate deployment of directional antennas at the base stations, although the optimum antenna orientations depends on the strength of external interference.