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Sarris, I

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Power Azimuth Spectrum Measurements in Home and Office Environments at 62.4 GHz

The high demand for unlicensed spectrum mandates the use of higher frequencies, such as the 60 GHz band, where large amounts unlicensed bandwidth exists. In this paper, the results from Power Azimuth Spectrum (PAS) measurements in a home and an office environment are presented with a view of revealing the amount of scattering power at that frequency and its relative power to the Line-of-Sight (LoS) signal. More-over, a tractable scheme is proposed for the estimation of the Power Azimuth Spectrum from absolute power measurement data which produces a very close fit with the measured PAS. A discussion is made on the accuracy of this method which is dependent on the directionality of the antenna elements, the fading in the channel and the presence of nois

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                          Sarris, I., & Nix, A. R. (2007). Power Azimuth Spectrum measurements inhome and office environments at 62.4 GHz. In International Symposium onPersonal, Indoor and Mobile Radio Communications (PIMRC), Athens,Greece. (pp. 1 - 4). Institute of Electrical and Electronics Engineers (IEEE).10.1109/PIMRC.2007.4394455Link to published version (if available):10.1109/PIMRC.2007.4394455Link to publication record in Explore Bristol ResearchPDF-documentUniversity of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only the publishedversion using the reference above. Full terms of use are available:http://www.bristol.ac.uk/pure/about/ebr-terms.htmlTake down policyExplore Bristol Research is a digital archive and the intention is that deposited content should not beremoved. However, if you believe that this version of the work breaches copyright law please contactopen-access@bristol.ac.uk and include the following information in your message:• Your contact details• Bibliographic details for the item, including a URL• An outline of the nature of the complaintOn receipt of your message the Open Access Team will immediately investigate your claim, make aninitial judgement of the validity of the claim and, where appropriate, withdraw the item in questionfrom public view.The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’07)POWER AZIMUTH SPECTRUM MEASUREMENTS IN HOME AND OFFICEENVIRONMENTS AT 62.4 GHZDr. Ioannis SarrisMitsubishi Electric ITE B.V.Visual Information LaboratoryGuildford, U.K.ioannis.sarris@vil.ite.mee.comProf. Andrew R. NixUniversity of BristolCentre for Communications ResearchBristol, U.K.andy.nix@bristol.ac.ukABSTRACTThe high demand for unlicensed spectrum mandates the useof higher frequencies, such as the 60 GHz band, where largeamounts unlicensed bandwidth exists. In this paper, the re-sults from Power Azimuth Spectrum (PAS) measurements ina home and an office environment are presented with a viewof revealing the amount of scattering power at that frequencyand its relative power to the Line-of-Sight (LoS) signal. More-over, a tractable scheme is proposed for the estimation of thePower Azimuth Spectrum from absolute power measurementdata which produces a very close fit with the measured PAS.A discussion is made on the accuracy of this method whichis dependent on the directionality of the antenna elements, thefading in the channel and the presence of noise.I. INTRODUCTIONThe large penetration of Wireless Local Area Networks(WLANs) in the residential and office environments along withthe ever increasing demand for higher bandwidth is expectedto eventually overflow the already congested radio spectrum atmicrowave frequencies [1]. A potential solution to this prob-lem, from a technological point–of–view, is a combination ofspectrum efficiency enhancing techniques (such as Multiple–Input Multiple–Output (MIMO) technology) with the exploita-tion of additional (higher) frequency bands.This paper examines the potential of the 60 GHz frequencyband for indoor WLAN applications. This band is viewed bymany as a very attractive candidate for future communicationsystems due to a high reuse factor which is the result of in-creased signal attenuation from free-space propagation, scat-tering and oxygen attenuation compared to lower (microwave)frequencies. The high reuse factor has allowed for an enormousbandwidth (between 5 and 7 GHz) to be allocated globally forunlicensed use [2, 3], however, it is undisputable that the suc-cessful employment and utilisation of this bandwidth requiresprofound knowledge of the propagation characteristics in thisfrequency range.The authors have a specific interest in the area of MIMOtechnology where multiple antenna elements are employed inboth ends of a communication link. A crucial parameter thatgoverns the performance of such systems is the existence ofscatterers in a given environment [4]. Information about thescattering objects can be derived from the Power AzimuthSpectrum (PAS) which determines the spatial distribution ofthe received power over the azimuth domain. Hence, it is of vi-tal importance to identify accurately the spatial channel prop-Figure 1: Measurement systemerties to ultimately be able to make accurate predictions on thepotential performance of MIMO systems at that frequency.Recently, the deconvolution scheme was proposed for theestimation of the PAS from complex electric field pattern mea-surements [8, 9]. In this paper, a number of (real valued) powermeasurements were performed and therefore a deconvolutionscheme was found unsuitable. Instead, a simplified serial can-cellation scheme is employed which is based on an iterativeprocess of Multipath Power Component (MPC) identification.II. MEASUREMENT DESCRIPTIONThe measurement equipment employed in this study was bor-rowed from the University of Glamorgan (U.K.) and has beenused in numerous measurements in the past [10, 11, 12]. A de-scription of this equipment is presented in the following para-graphs.A. Measurement equipmentThe system employs Phase Locked Loop (PLL) synthesiserswhich have an enhanced frequency stability (±1 kHz) that al-lows the use of a narrow IF filter at the receiver. The transmitterconsists of a 20.8 GHz PLL whose signal frequency is multi-plied by a factor of three by means of a frequency multiplier,leading to an output frequency of 62.4 GHz. This signal is fedto a waveguide attenuator and subsequently to an appropriatetransmitting antenna.The received signal is mixed with a 61.8 GHz PLL local os-cillator obtaining a very stable IF of 600 MHz. This IF signal isthen used to evaluate the received signal strength via a logarith-mic amplifier (LogAmp). To further decrease the noise floor ofthe 600 MHz DAQ data logger, an IF band pass filter is used toreduce the noise power at the LogAmps input which lowers thenoise floor to -57 dBm.A laptop computer was responsible for the control of the twoservomotors where the transmitter and receiver modules weremounted. Moreover, this laptop employed a data–acquisitioncard with 4 channels and 100 ksamp/s sampling frequency that1-4244-1144-0/07/$25.00 c©2007 IEEEThe 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’07)Table 1: Omni antenna characteristicsSpecified Frequency Range 59 to 64 GHzGain Variation Elevation 2 ± 1.5 dBGain Variation Azimuth ± 1 dBPolarisation VerticalNominal 3 dB Beamwidth Greater than 600−180 −135 −90 −45 0 45 90 135 180−60−50−40−30−20−100Angle (degrees)Power (dBm)Figure 2: Normalised field pattern on the E planewas used to perform the data acquisition. The turn tables wereconnected to the PC serial port and were controlled via a ded-icated indexer with a proprietary control language. This lan-guage was programmed into the measurement software code,allowing the software to fully control the turn tables. All themeasured data was recorded into a structured Matlab data filefor further processing.B. Antenna ElementsFor both measurement campaigns two different types of an-tennas were used; at the transmitter (Tx) an omni–directionalantenna was deployed while the receiver (Rx) was connectedto a custom–made 36 dBi directional lens horn antenna. Theomni antenna has been specifically designed to provide a verti-cally polarised 3600 field of view in the azimuth with the widestpossible acceptance angle in the elevation. The main character-istics of this antenna are given in Table 1.On the other hand, the lens horn antenna had a 3 dB–beamwidth of approximately 1.50 and was used to measure thereceived power by obtaining power samples over 3600 in theazimuth plane in steps of 10. The normalised field response onthe E plane is illustrated in Fig. 2.III. MEASUREMENT RESULTSTwo different propagation environments were investigated inthis study; namely a home and an office environment. For thehome environment a 4.7 m × 3.5 m lounge area was employedwith a number pieces of furniture and a staircase Fig. 3. The of-Figure 3: Home environment floor–plan showing the receivedpower distribution after the log–amp.Figure 4: Office environment floor–plan showing the receivedpower distribution after the log–amp.fice environment was an 18 m× 12.4 m office at the Universityof Bristol with several desks, chairs and computer equipmentseparated by partitions as shown in Fig. 8.By rotating the lens antenna in the azimuth plane it was pos-sible to identify the strength of the LoS signal and individualreflected signals at two different receiver locations in each en-vironment. The measured PASs are superimposed in Fig. 3 and8.In the home environment a significant difference between thepower of the LoS and the reflected components can be easilyobserved. In detail, differences of approximately 15 dB wereobserved between the LoS signal and the strongest (first–order)reflections. In the office environment the results are similarwith differences of around 13 dB between the powers of theLoS signal and the strongest reflection at a Tx–Rx distance of5 m. For an increased T–Rx distance however (10 m) a smallerdifference of 8 dB was observed.The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’07)Table 2: Effective MPCsLocation Number of effective MPCsHome 1 41Home 2 43Office 1 28Office 2 27IV. POWER AZIMUTH SPECTRUM ESTIMATIONThe measured powers from this measurement campaign werepost-processed using a PAS estimation technique. In detail, aserial cancellation algorithm was used to remove the antennapattern effect from the received PAS. Since the Tx antenna hadan omni pattern this process was performed directly on the re-ceived power. The algorithm used for this study is shown belowusing MATLAB notation.Input: Measured Power Spectrum (PASmeas)Antenna Pattern (AP )Output: Estimated Multipath Power Components (MPC)Reconstructed Power Spectrum (PASrec)for i=1:q do[maxV alue maxIndex] = max(PASmeas);MPC(i,:) = [maxV alue maxIndex];tempAP = circshift(AP , maxIndex).*maxV alue;PASmeas = PASmeas − tempAP ;PASrec = PASrec + tempAP ;endIn order to determine the number of MPC (q) that were ef-fectively contributing to the PAS, the minimum Root MeanSquared Deviation (RMSD) between the measured PAS andthe reconstructed PAS was calculated as follows for differentvalues of q.RMSD =√(PASmeas − PASrec)2(1)The number of MPCs that corresponded to the minimumRMSD are shown in Table 2.The measured and the reconstructed PAS along with theidentified MPCs are shown in the following figures for the twolocations in each environment.It is clear that there is a very close fit between the recon-structed and the measured PAS. In detail, it was found that theRMSD was less than 1 % in all the examined scenarios. How-ever, as far as the identified MCSs are concerned it is also clearthat there is a number of cases where the number of detectedMPCs is more than one for each peak of the received PAS. Thisunavoidable inaccuracy can be attributed to the noise in the en-vironment and the limited directionality of the system. More-over, the effect of multipath fading decreases the accuracy ofthe method even more especially in the non-LoS orientations.To increase the accuracy, a higher directionality antenna could0 45 90 135 180 225 270 315 360−55−50−45−40−35−30−25−20−15−10−50Angle (degrees)Power (dBm)Measured PASReconstructed PASPower componentsFigure 5: Received and reconstructed PAS for home environ-ment, Location 10 45 90 135 180 225 270 315 360−55−50−45−40−35−30−25−20−15−10−50Angle (degrees)Power (dBm)Measured PASReconstructed PASPower componentsFigure 6: Received and reconstructed PAS for home environ-ment, Location 20 45 90 135 180 225 270 315 360−55−50−45−40−35−30−25−20−15−10−50Angle (degrees)Power (dBm)Measured PASReconstructed PASPower componentsFigure 7: Received and reconstructed PAS for office environ-ment, Location 1The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’07)0 45 90 135 180 225 270 315 360−55−50−45−40−35−30−25−20−15−10−50Angle (degrees)Power (dBm)Measured PASReconstructed PASPower componentsFigure 8: Received and reconstructed PAS for office environ-ment, Location 2be employed and several measurements in adjacent positions tocounteract for the effect of the noise and the channel fading.For the purposes of our investigation, the results are provensufficiently accurate and demonstrate very clearly that the LoSsignal along with the first and second order reflections dom-inate the PAS. In non-LoS locations, the dynamic range thatwas available in the measurement system (≈ 48 dB at a 5 mdistance) did not allow us to receive any signals above the noisefloor.V. CONCLUSIONThis paper presented the procedure and the outcomes of a mea-surement campaign conducted in a home and an office envi-ronment at 62.4 GHz. The PAS was measured in two locationsin each environment using an omnidirectional transmitting an-tenna and a highly directional lens horn antenna at the receiver.In the post-processing stage a serial cancellation algorithm wasused to estimate the MPCs. The exact number of these MPCswas decide from calculations of the RMS deviation betweenthe measured response and the reconstructed PAS.By comparison of the measured and the reconstructed PASthe aforementioned method was shown to provide sufficientlyaccurate results for the purpose of our investigations. How-ever, it was also shown that the procedure is inherently ill-conditioned due to the real-valued information that was avail-able from the measurement and also that the method’s accuracywas highly dependant on the antenna directivity.To increase the accuracy of this method a larger number ofspatially discrete measurements is suggested so that the effectof noise and fading could be minimised.ACKNOWLEDGMENTSThe authors would like to thank Prof. M. Al.Nuaimi,Dr. J. Richter and Dr. T. R. Fernandes from the University ofGlamorgan, U.K. for their invaluable help throughout this mea-surement campaign. Moreover, the authors would also like tothank Mr. M. Matthaiou for a number of useful technical dis-cussions. This work was partly performed under the IST FP-6 ASTRALS project by Mitsubishi Electric ITE-VIL and theUniversity of Bristol, U.K.REFERENCES[1] C. Williams (editor) et.al., “Antenna Array Technology and MIMO Sys-tems”, doc. 8366CRCR, deliverable to Ofcom, Jun 2004.[2] E. R. 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Antenna Pattern Deconvolution for Precise Power Density Pattern Measurement,” in

Capacity Bounds and Estimates for the Finite Scatterers MIMO Wireless Channel,”

Coherence bandwidth characterisation and estimation for indoor Rician multipath wireless channels using measurements at

Diffuse channel model ans experimental results for antenna arrays in mobile environments,”

Multipath delay spread and signal level measurements for indoor wireless radio channels at 62.4 GHz,”

Overview of spatial channel models for array communcation systems,”

Report 95-499,” tech. rep., Federal Communications Commission,

Spatial Channel Characteristics in Outdoor Environments and their

The european table of frequency allocations and utilisations covering the frequency range 9 KHz to 275 GHz,” tech. rep.,

Wideband propagation measurements forfuturemillimetre60GHzwirelessLANs,” ElectronicsLetters,

Power Azimuth Spectrum measurements in home and office environments at 62.4 GHz

https://research-information.bris.ac.uk/files/3008071/sarris_IEEE_PIMRC_2007.pdf

Power Azimuth Spectrum measurements in home and office environments at 62.4 GHz

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