[Abstract]: Wireless local area network applications may include the use of bodyworn or handportable terminals. For the first time, this paper compares measurements and simulations of a narrowband 5.2-GHz radio channel incorporating a fixed transmitter and a mobile bodyworn receiver. Two indoor environments were considered,

an 18-m long corridor and a 42-m2 office. The modeling

technique was a site-specific ray-tracing simulator incorporating the radiation pattern of the bodyworn receiver. In the corridor, the measured body-shadowing effect was 5.4 dB, while it was 15.7 dB in the office. First- and second-order small-scale fading statistics

for the measured and simulated results are presented and compared with theoretical Rayleigh and lognormal distributions. The root mean square error in the cumulative distributions for the simulated results was less than 0.74% for line-of-sight conditions and less than 1.4% for nonline-of-sight conditions

Evans, N. E.

Scanlon, W. G.

Ziri-Castro, K. I.

English

University of Southern Queensland ePrints

IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 3, 2004 219Indoor Radio Channel Characterization and Modelingfor a 5.2-GHz Bodyworn ReceiverK. I. Ziri-Castro, W. G. Scanlon, Member, IEEE, and N. E. EvansAbstract—Wireless local area network applications may includethe use of bodyworn or handportable terminals. For the first time,this paper compares measurements and simulations of a narrow-band 5.2-GHz radio channel incorporating a fixed transmitter anda mobile bodyworn receiver. Two indoor environments were con-sidered, an 18-m long corridor and a 42-m2 office. The modelingtechnique was a site-specific ray-tracing simulator incorporatingthe radiation pattern of the bodyworn receiver. In the corridor, themeasured body-shadowing effect was 5.4 dB, while it was 15.7 dBin the office. First- and second-order small-scale fading statisticsfor the measured and simulated results are presented and com-pared with theoretical Rayleigh and lognormal distributions. Theroot mean square error in the cumulative distributions for the sim-ulated results was less than 0.74% for line-of-sight conditions andless than 1.4% for nonline-of-sight conditions.Index Terms—Bodyworn antennas, channel characterization,finite-difference time-domain (FDTD), radio propagation, raytracing.I. INTRODUCTIONWIRELESS local area networking systems, such asHiperLAN type 2 and IEEE 802.11a, operate at 5 GHzand provide high bandwidth services within the indoor envi-ronment. Although most terminal equipment will be designedfor stationary use, future applications will include bodyworn orhandportable devices. Under these close proximity conditionsthe terminal’s radiation pattern is significantly distorted bycoupling to the user’s body and additional signal attenuationmay occur. These effects are not only frequency dependent butwill vary with the design of the terminal, its antenna and theexact positioning with respect to the body surface [1]. Underthe multipath conditions present in the indoor environment,the distorted radiation pattern of the bodyworn terminal can beconsidered as a form of spatial filter.Several multipath models have been suggested to explainthe observed statistical nature of the mobile channel. Manyresearchers have also evaluated electromagnetic interactionsbetween the human body and handset antennas or portabledevices [2], [3]. In [3], Toftgard et al. show the effect of thehuman body on the performance of antennas for hand-heldportable telephones. They suggest that an average system lossof 3–4 dB should be considered in the link budget and pointout that there is considerable fading when users move aroundManuscript received December 10, 2003; revised June 10, 2004.K. I. Ziri-Castro and W. G. Scanlon are with the School of Electrical andElectronic Engineering, The Queen’s University of Belfast, Belfast BT9 5AH,Northern Ireland (e-mail: w.scanlon@ee.qub.ac.uk).N. E. Evans is with the School of Electrical and Mechanical Engineering,University of Ulster, Newtownabbey BT37 0QB, Northern Ireland.Digital Object Identifier 10.1109/LAWP.2004.836119TABLE ISPECIFICATION AND MEASURED RF PERFORMANCE OF CUSTOM RECEIVERin a natural manner. This work compares measurements andray-tracing simulations in a narrowband indoor propagationchannel at 5.2 GHz for a bodyworn terminal moving at a mod-erate walking speed of 0.5 m/s. Practical signal-level resultswere obtained using a bodyworn power-measurement receiverand datalogger.II. MEASUREMENT SYSTEMThe transmitter (TX) consisted of an R&S SMIQ03B signalgenerator, a GaAs frequency doubler (Hittite HMC189MS8), aGaAs InGaP power amplifier (Hittite HMC406MS8G), and asleeve dipole antenna ( dBi, Mobile Mark model PSTN3-5250). The transmitter was adjusted to deliver dBm to theantenna’s input port, taking account of cable losses. The radi-ating system was placed on a wheeled cart to facilitate move-ment around the selected measurement locations. The transmitantenna was vertically polarized and mounted 1.35 m abovefloor level on a wooden support. The bodyworn module (RX)consisted of a custom 5.2-GHz measurement receiver (RX), a12-bit analog-to-digital converter (ADC) and a notebook PC fordata recording. The receive antenna was a sleeve dipole iden-tical to that used at the TX. The RX unit was built as a portabledevice enclosed in a 150 80 50 mm conducting box; it de-livered an output voltage linear with input power measured indBm. The specification and measured RF performance parame-ters are given in Table I. The received power indication from thereceiver was sampled at 10-ms intervals using the 12-bit ADCand the results stored on the notebook PC.Two indoor scenarios were considered, both situated onthe fifth floor of a university building. Location 1 was a1.3 m 18 m corridor, and location 2 was a 6 7-m rect-angular office (Fig. 1). The measurement environments wererelatively complex, i.e., metallic ducting and lockers set into thecorridor walls and fluorescent lighting in the office. For conve-nience, however, the ray-tracing simulations assumed a regulargeometric structure with the following material parameters:walls, relative permittivity 4.0, conductivity 0.001 S/m; for thefloor and ceilings, relative permittivity 2.7 and conductivity0.005 S/m.1536-1225/04$20.00 © 2004 IEEE220 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 3, 2004Fig. 1. Measurement locations. (a) Location 1 (corridor). (b) Location 2 (small room). Trajectories are shown dotted.Fig. 2. Finite-difference time-domain (FDTD) computational model andcalculated azimuthal radiation pattern (E ).Measurements were performed by fixing the transmitter asshown in Fig. 1 and recording received power using the mea-surement receiver described above. The RX unit was positionedtoward the front of the user’s body at the hip (see Fig. 2), whilethe ADC circuitry and notebook PC were carried in a back-pack. Two types of measurement were recorded in both loca-tions: LOS, where the user was walking toward the transmitter,and NLOS, with the user walking away. In all scenarios the userwalked along the trajectories shown in Fig. 1, at approximately0.5 m/s. Therefore, the selected sampling interval of 10 ms cor-responds to a spatial resolution of better than .III. SIMULATION MODELA three-dimensional (3-D) image-based propagation pre-diction technique [4] was used; although this is capable ofmodeling the effect of pedestrian movement within the in-door environment, pedestrians were excluded from the presentstudy. Human body proximity effects were included in thesimulation as the receiver’s polar pattern was obtained fromFDTD modeling of the complete bodyworn system. The FDTDmodel was composed of a human body phantom, conductingbox (representing the receiver) and a thin-wire dipole antenna(Fig. 2). The overall FDTD grid was 499 93 154 with cubic3.6-mm voxels. The body phantom was for a 1.75-m tall adultmale and incorporated 21 tissue types. The sleeve-dipole an-tenna was modeled as a centre-fed 25.2-mm (0.36-mm radius)thin-wire element with a minimum antenna-body spacing of14.4 mm. Body losses were relatively low, with an FDTD-com-puted radiation efficiency of 83.3% at 5.2 GHz. Fig. 2 alsoshows the calculated azimuthal pattern for vertical polarization. The entire 3-D radiation pattern was generated for 5intervals of both azimuth and vertical angles.IV. RESULTSA. General ObservationsAn example of the measured and received power profiles isgiven in Fig. 3 for both LOS and NLOS conditions in location 1.The correlation between measurements and simulations for theseresults was better in the LOS case, with a correlation coefficientof 0.52, than for NLOS, where the corresponding value was0.25. Table II compares the overall body-shadowing effect (thedifference between mean LOS and NLOS powers) obtainedthrough measurement and simulation for both locations. Body-shadowing is dominated by attenuation of the direct ray, causedby reduced antenna gain in the through-body direction. However,it is worthwhile noting that the measured body-shadowingeffect (15.7 dB) was significantly more severe in location 2than in location 1. The variation in body shadowing effectbetween locations suggests that the propagation channel isstrongly influenced by the characteristics of the immediateenvironment.There is a low correlation between the overall NLOS mea-sured and simulated received power in both locations, althoughtheir mean values are similar. A potential cause of the discrep-ancy between measurements and simulations is the significantnatural variability in the volunteer’s posture as he walked. ThisZIRI-CASTRO et al.: INDOOR RADIO CHANNEL CHARACTERIZATION AND MODELING 221Fig. 3. Measured and simulated received power for location 1 under LOS andNLOS conditions.TABLE IICOMPARISON OF SIMULATED AND MEASURED RECEIVED POWER ANDBODY-SHADOWING EFFECTcauses a quasi-random variation in the direct ray azimuth angle,leading to rapid fluctuations in ray attenuation. In contrast, thedirect ray azimuth angle in the simulation model was constantthroughout, with the vertical angle gradually increasing towardthe end of the location. The effects of these natural variations inbody posture become more significant in NLOS scenarios.B. First-Order StatisticsAll of the statistical measures in this letter correspond tosmall-scale fading, and were calculated with reference to localmean values (determined by averaging received signal powerover 460 samples, ). The CDF was calculated for thesimulated and measured data sets in both locations (Fig. 4). Theresults were compared to theoretical Rayleigh and lognormaldistributions, since it is generally accepted that the receivedenvelope is Rayleigh distributed over a spatial distance of lessthan and lognormally distributed over larger areas.In location 1, LOS measured and simulated CDFs were ingood agreement [root-mean square (rms) error of 0.65%] andboth were lognormally distributed above the median, whilebelow it they were Rayleigh distributed. However, measuredand simulated NLOS results were in less agreement with anrms error of 1.4%. The simulated NLOS results were closerto Rayleigh because of the constant direct ray attenuationFig. 4. Small-scale fading cumulative distribution functions (CDFs).(a) Location 1 LOS. (b) Location 1 NLOS. (c) Location 2 LOS. (d) Location2 NLOS.described earlier. There was good agreement between measure-ment and simulation in location 2, with an rms error of 0.74%for the LOS case and 0.87% for the NLOS case, respectively.All measured and simulated CDFs in location 2 were lognor-mally distributed. Simulation and measurement results fromboth locations tend to be distributed following a mixture ofRayleigh and lognormal distributions. Some researchers [5], [6]have compared cumulative distributions of experimental dataand have suggested the Suzuki distribution, a mixture of theRayleigh and lognormal distributions, to represent the statisticsof mobile radio signals. However, a practical limitation to thisdistribution is that no closed form has been found to solve theCDF integral [7].C. Second-Order StatisticsLevel-crossing rate (LCR) and average fade duration (AFD)were calculated for both simulated and measured data sets in lo-cation 1. Results were compared to theoretical Rayleigh and log-normal distributions with a maximum Doppler frequency, ,of 8.67 Hz, which corresponds to a receiver speed of 0.5 m/s.Although measured and simulated LCR results had similarprofiles (Fig. 5), for LOS conditions the peak of the measuredLCR curve was 53% higher than that of the simulated curve.Both measured and simulated peak LCR values were signifi-cantly higher under NLOS conditions and were comparable tothe theoretical Rayleigh maximum LCR. In particular, the simu-lated results were relatively well matched to the Rayleigh curve.Overall the LCR curves were more similar to Rayleigh thanthey were to lognormal. Inspection of the raw fading profilesconfirmed that the measured results experienced significantlymore fading than was predicted by the simulation tool. Thissuggests that the additional body movements associated withwalking led to more rapid envelope variation. As only lateralmovement is considered, the simulation tool was unable to faith-fully represent these variations. The AFD results [Fig. 5(c) and222 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 3, 2004Fig. 5. Second-order statistics for location 1. (a) LOS level crossing rate.(b) NLOS level crossing rate. (c) LOS average fade duration. (d) NLOS averagefade duration.(d)] indicate that the predicted LOS fade duration was consis-tently longer than that measured. Again, variations in posture orwalking speed during measurements may have contributed tothese differences.V. CONCLUSIONMeasurement and simulation results for an indoor narrow-band channel using a bodyworn receiver at 5.2 GHz havebeen presented: body shadowing caused 5–16 dB extra pathloss across the locations considered. For small-scale fading,the first-order channel statistics in the corridor tended to beRayleigh distributed below the mean and lognormally dis-tributed above it, while in the small room, first-order statisticswere all lognormally distributed. The second-order statistics inthe corridor tended toward Rayleigh even for LOS conditions.The accuracy of the simulation tool used in this work wassufficient in LOS scenarios with an rms error of 0.7% or lessin the cumulative distributions. However, it was not suitablefor NLOS comparisons due to the inability of the tool tomodel natural variations in posture during walking. Overall,these results provide an insight into the characteristics of bodyshadowing for bodyworn terminals in wireless communicationsystems design at 5 GHz.REFERENCES[1] W. G. Scanlon and N. E. Evans, “Numerical analysis of bodyworn UHFantenna systems,” IEE Electron. Comm. Eng. J., vol. 13, pp. 53–64,2001.[2] F. L. Lin and H.-R. Chuang, “Performance evaluation of a portable radioclose to the operator’s body in urban mobile environments,” IEEE Trans.Veh. Technol., vol. 49, pp. 614–621, Feb. 2000.[3] J. Toftgard, S. N. Hornsleth, and J. B. Andersen, “Effects on portableantennas of the presence of a person,” IEEE Trans. Antennas Propagat.,vol. 41, pp. 739–746, June 1993.[4] F. Villanese, W. G. Scanlon, N. E. Evans, and E. Gambi, “A hybridimage/ray-shooting UHF radio propagation predictor for populated in-door environments,” Electron. Lett., vol. 35, no. 21, pp. 1804–1805,1999.[5] H. Suzuki, “A statistical model for urban radio propagation,” IEEETrans. Commun., vol. COMM-25, pp. 673–80, July 1977.[6] F. Hansen and F. I. Meno, “Mobile radio fading—Rayleigh and log-normal superimposed,” IEEE Trans. Veh. Technol., vol. VT-26, pp.332–335, Apr. 1977.[7] R. Vaughan and J. B. Andersen, Channels Propagation and Antennasfor Mobile Communications, London, U.K.: Inst. Elect. Eng., 2003.

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Indoor radio channel characterization and modeling for a 5.2-GHz bodyworn receiver

Wireless local area network applications may include the use of bodyworn or handportable terminals. For the first time, this paper compares measurements and simulations of a narrowband 5.2-GHz radio channel incorporating a fixed transmitter and a mobile bodyworn receiver. Two indoor environments were considered, an 18-m long corridor and a 42-m/sup 2/ office. The modeling technique was a site-specific ray-tracing simulator incorporating the radiation pattern of the bodyworn receiver. In the corridor, the measured body-shadowing effect was 5.4 dB, while it was 15.7 dB in the office. First- and second-order small-scale fading statistics for the measured and simulated results are presented and compared with theoretical Rayleigh and lognormal distributions. The root mean square error in the cumulative distributions for the simulated results was less than 0.74% for line-of-sight conditions and less than 1.4% for nonline-of-sight conditions

Ziri-Castro, K.I.

Scanlon, William

Evans, N.E.

Queen's University Belfast Research Portal

Indoor radio channel characterisation and modelling for a 5.2 GHz bodyworn receiver

http://eprints.usq.edu.au/3004/1/Ziri-Castro_Scanlon_Evans_2_Publ_version.pdf

Indoor radio channel characterization and modeling for a 5.2-GHz bodyworn receiver

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