International audience

The paper proposes a novel cross-layer signaling mechanism to provide unprecedented Quality of Experience (QoE) in next generation mobile networks. The number of network-connected cameras is rapidly increasing, especially on the widely and globally deploying cellular networks (i.e. LTE). In many cases, the video traffic can be considered as a real-time traffic, as the video traffic generating service may require continuous real-time human interaction or may be a part of the remote control system. Meanwhile, throughput and delay can vary rapidly due to changes in a radio network, thus affecting service QoE. The novel cross-layer signaling mechanism presented requires minimal modification to the networking stack at the client side for faster feedback of wireless link capacity variations. The proposed mechanism has been evaluated via simulation with video traffic. The results show outage rate decreased from 1.3 outages/sec to zero and reduction in self-inflicted delay, from 60 ms to 14 ms.

The paper describes the principles of a novel mechanism that is aiming at providing unprecedented Quality of Experience (QoE) in next generation mobile networks. The main benefits include: (i) enabling dynamic IP tunnel management (establishing and tearing down) with terminating point in the mobile device instead of the traditional base station; (ii) enabling multiple parallel tunnels (e.g., Generic Routing Encapsulation (GRE)) between an anchor node and a mobile device, where a specific tunnel may support differentiated Quality of Service (QoS) requirements for a targeted service class; (iii) enabling advanced network protocol support for service flows split across multiple Radio Access Technologies (M-RATs), whenever it may be deemed necessary to support and maintain a targeted QoS level per service flow; (iv) allowing to aggregate the necessary bandwidth to meet the QoS requirements per service flow if no single RAT can fulfill them alone; (v) supporting massive M-RAT capacity aggregation for enhanced scalability and very large throughput.

3GPP LWIP Release 13 technology and its pre- standard version Wi-Fi Boost have recently emerged as an efficient LTE and Wi-Fi integration at the IP layer, allowing the combined use of LTE and Wi-Fi radio resources by the user. This solves the contention problems of Wi-Fi cell by routing uplink traffic over LTE, thus enabling an optimum usage of the unlicensed band for downlink. In this paper, we present a new feature of Wi-Fi Boost, its radio link management, which allows to smartly steer the downlink traffic between both LTE and Wi-Fi upon congestion detection. This customised congestion detection algorithm is based on IP probing, and can work with any Wi-Fi access point. Simulation results in a typical enterprise scenario show that LWIP R13 and Wi-Fi Boost can enhance network performance up to 5x and 6x over LTE-only, and 4x and 5x over Wi-Fi only networks, respectively, and that the proposed traffic flow control can further improve Wi-Fi Boost performance over LWIP R13 up to 19%. Based on the promising results, this paper suggests to enhance LWIP R13 user feedback mechanisms in future LTE releases.

Wireless fidelity (Wi-Fi) benefits from large downlink bandwidth but suffers from inefficient uplink contention, while long term evolution (LTE) benefits from efficient scheduling in the uplink but suffers from bandwidth scarcity in the downlink. In this paper, we quantify the performance gain of Boost, a new technology that blends the advantages of Wi-Fi and LTE in an efficient manner to overcome their individual disadvantages. By redirecting uplink traffic from Wi-Fi to LTE, Boost avoids resource waste due to Wi-Fi contention in the uplink. Since the radio channel is now fully under the control of an scheduler, downlink controlled by Wi-Fi AP scheduler and uplink controlled by LTE scheduler, delays and rates can be guaranteed. Simulation results show that in typical enterprise scenarios, Boost significantly decreases packet delay up to 85 % and increases user throughput up to 3.5x, which is beneficial for delay-sensitive and best effort applications, respectively. This positions Boost as a strong candidate for realising the all-wireless enterprise.

Wi-Fi is providing hotspot capacity in conjunction with broadband cellular networks. We propose to divert uplink 802.11 MAC layer traffic to the cellular uplink towards improving range and downlink efficiency. This architecture uses the large unlicensed spectrum on the downlink, and the higher power and other advanced media access and physical layer techniques of the LTE uplink. Initial measurements show an improvement in Wi-Fi efficiency of about 30 percent due to the otherwise large airtime spent on TCP acknowledgements. Based on propagation and 802.11n receiver models, indoor area coverage at high bit rate (100 Mbps) is improved by a factor of 20. Maximum range is improved by a factor of 4 for indoor-to-outdoor scenarios. These are examples of gains beyond the federation of bandwidth.

Propagation theory is developed to get analytic expressions for both guided and diffusely scattered 3-D fields in common indoor environments, with access points (APs) placed along a hallway and mobile nodes in the rooms. Resulting predictions agree with measurements of both path loss and single-user multiple-input-multiple-output link capacity. In particular, the model reproduces the observed reduction in normalized channel capacity with increasing range. This effect, occurring in a common indoor environment, can be beneficial. Interfering APs, which tend to be further away, occupy channel dimensions corresponding to low-order hallway modes, causing total interference to concentrate in a small subset of the channel dimensions, in a manner reminiscent of interference alignment. The channel for the desired signal has a greater number of effective degrees of freedom (EDOFs) due to a shorter distance from its serving AP. The disparity in the number of EDOFs between the signal and the interference leads to higher rates, which can be further increased through water filling applied individually to each link, with no interlink coordination. The resulting rates are on the order of 30% greater than would be anticipated in range-independent scattering models.

Heterogeneous cellular networks are composed of a mixture of macro and small (pico) cells embedded in the macro network. A greedy strategy is proposed to maximize network capacity. Picos placement and either macro or pico transmit power are optimized jointly, as picos are deployed. The scaling of area spectral efficiencies (ASE) as pico densities are increased is studied. Median ASEs grow linearly with density and are comparable to cell-splitting given fixed pico power -20dB EIRP relative to the macro. The effectiveness of the pico at such low power is due in part to the improvement in area coverage of an omni vs. a 3 sectored antenna.

We present inner and outer bounds of the rate region for the multiple-input-multiple-output mutiple access channel with imperfect channel estimates. We then employ them to compare different channel estimation techniques. We show that the benefit of using traditional compressed sensing recovery techniques, specifically orthogonal matching pursuit, for multipath wireless channels is dominant for high signal to noise ratio regimes, but does not provide a good performance for low signal to noise ratio regime.

Cognitive and experiential factors in human–computer interaction have been the focus of significant recent attention, but there is a lack of a much needed integrated approach to these issues. The current article proposes such an approach and applies this, combined with the person–task–artifact model (Finneran & Zhang, 2003), to the modeling of web navigation. In an experiment, artifact complexity and task complexity were manipulated. The effects of the experimental manipulations and intrinsic motivation on flow experience, task performance and task outcome were tested. The main effects of the manipulations were confirmed. Further analyses demonstrated that flow was a mediator of the effect of experimental manipulations on task performance, and task performance was a mediator of the effect of flow on task outcome. Overall, the results in the domain of web navigation that are presented here demonstrate the need for taking an integrated cognitive-experiential approach in the modeling of human–computer intera...

In many situations, people make judgments on the basis of incomplete information, inferring unavailable attributes from available ones. These inference processes may also well operate when judgments about a product’s user-experience are made. To examine this, an inference model of user-experience, based on Hassenzahl and Monk’s [2010], was explored in three studies using Web sites. All studies supported the model’s predictions and its stability, with hands-on experience, different products, and different usage modes (action mode versus goal mode). Within a unified framework of judgment as inference [Kruglanski et al. 2007], our approach allows for the integration of the effects of a wide range of information sources on judgments of user-experience.

Diffusion theory is found to provide a simple yet accurate expression for the average received radio power loss indoors in non-line-of-sight propagation. Effective specific absorption is the sole parameter. Agreement with extensive indoor power measurements is found at all ranges. Use of the standard power-law to describe the data is found to lead to power exponents that vary from near 2 at short ranges to around 11 at 100 m. Extending the diffusion model to account for variation in scatterer density provides a stochastic mechanism explaining the log-normal nature of observed average power variations, usually termed "shadow fading". The standard deviation of power variation is found to increase with range (as r1/2at short ranges), in agreement with measurements and unlike accepted models. Exponential absorption in diffusion is determined to have a large impact on the signal-to-interference-and noise behavior, materially affecting conclusions on the value of increasing cell density as a method of increasing wireless network capacity.

An experiment, using two versions of a Web site varying in usability, tested three models of user experience: an interaction experience model, a technology acceptance model and an integrated experience-acceptance model. We found that the perceptions of three product attributes (Pragmatic Quality, Hedonic Quality-stimulation and Hedonic Quality-identification) and technology acceptance variables (the beliefs of Perceived Ease of Use, Perceived Enjoyment and Perceived Usefulness, and Intention to Use) are separate underlying psychological dimensions. A positive effect of usability on task performance, interaction experience and acceptance was found. In the interaction experience model, the evaluation of Goodness (overall interaction quality) was less stable and influenced by both Pragmatic Quality and Hedonic Quality, but the evaluation of Beauty was more stable and only influenced by Hedonic Quality. In the technology acceptance model, Perceived Ease of Use was a determinant of Perceived Enjoyment and Perceived Usefulness, and the latter two were independent determinants of Intention to Use. In the integrated model, perceptions of product attributes were independent determinants of beliefs, but evaluations were not independent determinants of Intention to Use. Future modelling work should address a range of interactive systems, information architecture and individual differences.

A new multihop protocol is devised for cellular networks. Mobiles transmit and receive on uplink time slots assisting in-building users that are experiencing high pathloss. Wireless capacity indoors is improved by 3× to 8× compared to direct transmission. A central feature of the protocol, is that interference to existing or primary" communication may be controlled. Power control by the source mobile, using a measurement of basestation pilots, minimizes uplink interference on a shared multihop uplink slot. Likewise interference cancelation at the basestation, allows the a slot normally reserved for downlink multihop messages to be reused. This paper presents outage analysis of interference at the relay and the source mobile for the two hop link.

Recent research into user experience has identified the need for a theoretical model to build cumulative knowledge in research addressing how the overall quality or ‘goodness’ of an interactive product is formed. An experiment tested and extended Hassenzahl’s model of aesthetic experience. The study used a 2 × 2 × (2) experimental design with three factors: principles of screen design, principles for organizing information on a web page and experience of using a web site. Dependent variables included hedonic perceptions and evaluations of a web site as well as measures of task performance, navigation behaviour and mental effort. Measures, except Beauty, were sensitive to manipulation of web design. Beauty was influenced by hedonic attributes (identification and stimulation), but Goodness by both hedonic and pragmatic (user-perceived usability) attributes as well as task performance and mental effort. Hedonic quality was more stable with experience of web-site use than pragmatic quality and Beauty was more stable than Goodness.

Downlink cellular packet systems utilizing opportunistic scheduling and adaptive modulation must deal with outdated channel state information. A fade margin is part of the link budget which is used to mitigate the effect of channel variation. Channel prediction reduces this margin, improving the transmission rate. We derive a fade margin which keeps packet outage constant for any prediction error variance. In our model both the signal and the interferer powers are modeled as autoregressive stochastic processes and predicted. The MMSE power predictor is also derived. Improvement in system throughput due to channel prediction is shown for a proportional fair scheduled downlink packet system, and compared to systems without prediction and opportunistic scheduling.

Wireless systems exploiting multi-user diversity require accurate channel state information. In this paper we examine channel prediction as a method to improve the performance of these systems. We model the outdoor channel by the Rician model, which combines diffuse spectra with a single specular component. Prediction accuracy is determined for the Rician model given various ratios (K factors) of specular to diffuse power. Simulation results show that accurate channel prediction further than one wavelength can be achieved at 30 dB SNR when the channel K factor is greater than ten. The predictor was evaluated on measured channels, and the Rician model was found to be appropriate as prediction intervals of the measured data are similar to those of synthetic data with same K factor. Using measurements some results regarding channel stationarity and optimal filter order are presented. We show for a proportionally fair scheduled downlink packet system that the predictor reduces fade margin at fixed packet outage leading to an improvement in throughput.

The effects of design parameters of rating scales on the perceived quality of interaction with web sites were investigated, using four scales (Disorientation, Perceived ease of use, Perceived usefulness and Flow). Overall, the scales exhibited good psychometric properties. In Experiment 1, psychometric results generally converged between two response formats (visual analogue scale and Likert scale). However, in Experiment 2, presentation of one questionnaire item per page was better than all items presented on a single page and direct interaction (using radio buttons) was better than indirect interaction (using a drop-down box). Practical implications and a framework for measurement are presented.

The wireless communication channel between vehicular nodes in an ad-hoc network was assessed in a comprehensive measurement and modeling effort. Nodes were equipped with roof mounted azimuthally omnidirectional antennas, and measurements were taken at both short (line-of-sight) and long ranges, at a center frequency of 2.5 GHz. The median MIMO capacity with 8 transmitters and 10 receivers (8 times10) was found to be about five times the corresponding 1times1 SISO capacity, and three times the corresponding 1times10 SIMO capacity. Wideband soundings of such channels were conducted, where the median rms delay spread was found to be 0.6 mus. Measurements, spatial correlation scales, an empirical model of pathloss, and cross- polarization properties of peer-to-peer channels in a rural area are reported.

We examine the prediction of the signal to interference ratio by the mobile as a means of improving the channel feedback in adaptive radio links. A cellular system is considered where the pilots of the desired and interfering basestation are available to obtain channel estimates. Both are modeled as auto-regressive (AR) stochastic processes. We derive the density function of the conditional SIR in order for the mobile to determine the backoff margin required for a percentage of packets to be decoded successfully.

Propagation of radio signals from a base above clutter, such as buildings and trees to a mobile immersed in clutter, is treated theoretically by accounting for random diffuse scattering at the mobile. Closed form expressions are derived for path gain as well as for angular spectrum at the base. The resulting predictions are in close agreement with widely accepted models and empirical results. The angular spectrum at the base is found to be Lorentzian of width close to that reported for urban measurements in Aarhus. Small-scale fading and distance-depedent loss are treated in a unified way, as opposed to the heuristic methodologies, which formulate them as separate factors.

Channel prediction is an appealing approach to mitigate channel mismatch in wireless downlink packet systems. Channel mismatch arises due to the delay in the feedback loop. Both synthetic and measured channels were used to assess the accuracy of channel prediction for various ratios of specular to diffuse power. The power spectrum was estimated rather than assumed known. It has been found that high ratios (K factors) greater than ten are necessary for prediction greater than one wavelength. K factors of measured channels gave prediction accuracy similar to that of the synthetic channel given by the same K factor.

In high speed downlink packet access systems (HS-DPA), opportunistic beamforming has been proposed as a viable technique for improving the system capacity by taking advantage of the multiuser diversity due to the time varying fluctuations of the mobile users channels. In opportunistic beamforming with proportional fair scheduling, mobile users who have the largest rates when compared with their averaged throughputs, are scheduled over preferred spatial beams, thereby yielding improved throughput-delay tradeoffs. In this paper, we consider cellular architectures where base stations coordinate to service users. These base stations are assumed equipped with smart antenna systems which generate pilot beams according to a predefined algorithm, collect only an SINR report from the users, and provide opportunistic scheduling. We propose schemes where the base stations coordinate to generate beams that reduce the inter-cell interference to the users considered for service. Through computer simulations we show that the proposed base station coordination technique provides significant performance gains in downlink packet access cellular systems. Furthermore this is achieved with the use of only modest feedback (SINR) from the users i.e. without the need for excessive channel state information feedback.

We examine the effect of measurement delays on the throughput of certain downlink data packet systems operating over Rayleigh fading channels. In these systems the base station (BS) schedules a single user at a time and transmits at a rate which is based on measurements of the BS's received power performed by the user. The same subject was also discussed in a recent paper, titled "Asymptotically fair transmission scheduling over fading channels" by Berggren and Jantti (2004). They studied the effects of measurement delays on the operation of the scheduler. As a consequence of the delay, it is possible that by the time the BS actually transmits data, the propagation channels might have changed, such that the scheduler's choice no longer conforms to the desired scheduling policy, resulting in loss of system throughput and multi-user gain. Berggren and Jantti assume that perfect link adaptation is nevertheless always assured, i.e., that the BS transmits at a rate that matches precisely the current state of the selected user's channel. However, measurement delays lead also to mismatch between the data rate the BS transmits to the chosen user, and the current state of the propagation channel to that user. We believe that this mismatch must also be taken into account. In this letter we propose to use a backoff factor and analyze its mitigating effect on losses introduced by measurements delay in a Rayleigh fading environment. We then show the resulting gain in system throughput for optimal choices of the backoff factor

We address the problem of downlink throughput improvement for IEEE 802.11a/g systems by using a modified access point (AP) equipped with multiple antennas. The main restriction is that the standard terminals should not be modified in any way. An alternating time-offset space division multiple access (SDMA) solution is considered for a conference room scenario. A simulation is based on channel models approved by the IEEE 802.11 Standard Group and takes into account the main features of the IEEE 802.11a/g standard. It is demonstrated that a near doubling of downlink capacity can be achieved in a conference room environment.

The use of a comprehensive set of psychometric instruments for measuring the quality of interaction in Web sites is proposed. Five existing scales for Web site evaluation, each measuring a key construct in human-computer interaction, were used together. The set of 5 scales demonstrated good distinguishability of factor structure, and all scales possessed adequate reliability. Evidence for validity of the scales was obtained, but additional work is necessary to establish the conditions under which these properties are best demonstrated. Aesthetic quality emerged as a separate scale that moderately correlated with other scales and level of task performance, highlighting the importance of aesthetics in interaction with Web pages. The results suggest the 5 scales can be used to measure the quality of interaction in Web sites for both monitoring and continual improvement of these sites.

Abstract Coexistence of different access technologies, hierarchical cellular deployment, a wide variety of data services, requirements for transparent operation across different technologies, adaptivity to varying network conditions and mobility and quality of service (QoS) constraints introduce a number of challenges in the design of future generation systems and the specification of new air interfaces, such as efficiency and flexibility in the utilization of spectrum, dynamic resource allocation and exploitation of the multiuser diversity and reconfigurable interference management and inter‐cell coordination. In this paper, three critical issues for the design of next generation systems are addressed: (i) duplexing, (ii) scheduling and resource allocation and (iii) interference and inter‐cell coordination. A number of research directions are presented, which constitute promising potential candidates for next generation systems specification. Copyright © 2005 John Wiley & Sons, Ltd.

Opportunistic scheduling (OS) has been proposed as a technique to improve the downlink throughput of high speed packet systems. OS attempts to use the time varying propagation channels between the base station (BS) and the mobile stations (MSs) when they reach their peak rate capability and defer using channels when in bad state. It exploits the fact that the propagation channels between the BS and the MSs fade independently and the tolerance of many data services to delay and delay jitter. However, when the fading is slow in comparison with an acceptable packet delay, or weak, OS is not very useful. In such cases, opportunistic beamforming (OBF), a recently proposed scheme, may offer additional gains. OBF is a "natural" enhancement to OS. The enhancement amounts to replacing the BS antenna with multiple antennas and implementing an algorithm that generates a different radiation pattern every timeslot. In this paper we propose to tie the sequence of radiation patterns to the waiting times of the served MSs. We show through simulations that the scheme we propose leads to both, reduced probability of excessive packet delay and improved throughput. This can be achieved by additional processing of the feedback received from the MSs, with no additional signaling on the air interface.

The proportional fair (PF) scheduling algorithm has been proposed as a technique to improve the throughput of multiple packet-data users sharing a wireless downlink channel while preserving fairness. It exploits the fact that the propagation channels between the base station (BS) and the mobile stations (MS) fade independently giving rise to "multi-user diversity". The gain offered is significant when the allowed packet delay exceeds the de-correlation time of the fading channels and the number of users is high. We analytically investigate the "time allocation" property and the multi-user diversity gain of the PF algorithm under certain conditions in the context of the HSDPA standard. Since in practical systems a certain latency is unavoidable, we have studied the use of a "backoff' factor to reduce the probability that when the transmission takes place, the channel cannot support it.

Technological developments in Virtual Reality (VR) appear to outpace progress in design methodology of VR. The theory of Perceptual Opportunities (POs) has previously been proposed as a basis of such a design methodology (Blade and Padgett, 2002). This paper presents the first empirical study investigating the effect of representation of POs on users' behaviour in Virtual Environments (VEs). The current study has a methodological focus, using POs as a framework and desktop VR as a experimental environment. The application of an experimental paradigm is illustrated with two experiments. Evidence was found for an effect of movement type on choice of objects in a simple VE. Implications for VE design and the methodology of empirical research in the framework of POs are discussed.

Narrowband multiple-input-multiple-output (MIMO) measurements using 16 transmitters and 16 receivers at 2.11 GHz were carried out in Manhattan. High capacities were found for full, as well as smaller array configurations, all within 80% of the fully scattering channel capacity. Correlation model parameters are derived from data. Spatial MIMO channel capacity statistics are found to be well represented by the separate transmitter and receiver correlation matrices, with a median relative error in capacity of 3%, in contrast with the 18% median relative error observed by assuming the antennas to be uncorrelated. A reduced parameter model, consisting of 4 parameters, has been developed to statistically represent the channel correlation matrices. These correlation matrices are, in turn, used to generate H matrices with capacities that are consistent within a few percent of those measured in New York. The spatial channel model reported allows simulations of H matrices for arbitrary antenna configurations. These channel matrices may be used to test receiver algorithms in system performance studies. These results may also be used for antenna array design, as the decay of mobile antenna correlation with antenna separation has been reported here. An important finding for the base transmitter array was that the antennas were largely uncorrelated even at antenna separations as small as two wavelengths.

This paper presents analysis for spatial and temporal variations of multiple-input-multiple-output (MIMO) channels at the mobile. The channel study is based on the narrowband measurements at 2.11 GHz in Manhattan, New York with 16 transmitting antennas and 16 receiving antennas. Doppler spread and angle of arrival (AOA) are derived from the temporal correlation of field components. The results show that the AOA at the mobile is not uniformly distributed. The restricted AOA distribution results in approximately twice the correlation distance and correlation time than the predicted values from the Jakes (1974) model. The measured median coherence time is at least a few seconds for stationary channels, and 90 ms at a mobile pedestrian speed of 3 km/hr. These observations hold for both vertically and horizontally polarized antennas. The measured median RMS angular spread at the mobile is 22.5/spl deg/ for horizontally polarized antennas and 25.5/spl deg/ for vertically polarized antennas.

Narrowband MIMO measurements using 16 transmitters and 16 receivers at 2.11 GHz were carried out in Manhattan. High capacities were found for full as well as smaller array configurations, all within 80% of the fully scattering channel capacity. It was found that two streets which might be considered near LOS, had different capacities, one about 45% of and the other about 75% of the fully scattering channel capacity.

We evaluate the performance of the VBLAST (vertical Bell Labs layered space-time) receiver algorithm in multiple-transmitter/multiple-receiver (MTMR) cellular W-CDMA systems. We assume that the VBLAST algorithm is executed on a symbol level (i.e., on the despread received signal), following a conventional bank of matched filters (correlators). Also, we introduce the concept of virtual antennas. Performance of the algorithm in the presence of intra- and inter-cell multiple-access interference (MAI) is evaluated. System capacity is also studied. The observed system is defined based on the UMTS physical layer and corresponding channel models.

Usability is paramount for the success of Web sites. This study aims to contribute towards Web design guidelines for usability through an empirical investigation into two Web page design parameters. Using a 2 × 4 mixed measures experimental design, we studied the effects of frame layout and background contrast on visual search performance. One hundred and eighty-nine undergraduates carried out a visual search task using mock Web pages. Analysis showed an effect of layout both on accuracy and speed measures, with frames located at the top or left of the screen leading to better performance. No main effect of contrast was found, although there was an interaction between layout and contrast in reaction time for hits. Preference for frame layout was dependent on background contrast. The results are discussed in terms of visual search processes and design recommendations are given.

We demonstrate the capacity growth of multiple-element antenna arrays (MEAs) in a realistic propagation environment using WiSE, an experimental ray tracing tool. WiSE is used to construct the channel response for MEAs operating at 1.9 GHz for two situations: (a) (16-16)-MEAs located inside an office building and (b) (4, 4)-MEAs located in an outdoor fixed wireless loop. We define effective degrees of freedom (EDOFs) as parallel spatial modes of transmission for an MEA. We quantify the increase in both the number of EDOFs and capacity with transmit power, received SNR, and antenna spacing. More EDOFs are present when receiving MEAs are physically closer to the transmitting MEA, regardless of the scattering effect.

Engineers designing and installing outdoor and indoor wireless communications systems need effective and practical tools to help them determine base station antenna locations for adequate signal coverage. Computer-based radio propagation prediction tools are now often used in designing these systems. We assess the performance of such a propagation tool based on ray-tracing and advanced computational methods. We have compared its predictions with outdoor experimental data collected in Manhattan and Boston (at 900 MHz and 2 GHz). The comparisons show that the computer-based propagation tool can predict signal strengths in these environments with very good accuracy. The prediction errors are within 6 dB in both mean and standard deviation. This shows that simulations, rather than costly field measurements, can lead to accurate determination of the coverage area for a given system design.