l – band propagation measurements for fixed and mobile reception of satellite digital emission

8/7/2019 L Band Propagation Measurements for Fixed and Mobile Reception of Satellite Digital Emission

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JOURNAL OF COMPUTING, VOLUME 3, ISSUE 2, FEBRUARY 2011, ISSN 2151-9617HTTPS://SITES.GOOGLE.COM/SITE/JOURNALOFCOMPUTING/ WWW.JOURNALOFCOMPUTING.ORG

184

L Band Propagation Measurements for

Fixed and Mobile Reception of SatelliteDigital Emission

P.K.Chopra 1 S. Jain 2

K.M. Paul 3, S. Sharma

Abstract:

The nature of variations of L-band satellite signal strength for direct reception both in fixed as well as in mobile scenario areimportant technical parameters for the planning of satellite broadcast and communication services network. These parameters havebeen assessed through field experiment using L-band signal from the Asia star satellite of Worldspace, USA. Variation of signal

strength due to vegetation; urban structures; etc. as well as the building penetration LOSs along with the Standard Deviation of each of these variations has been assessed based on the data collected during the fixed and mobile reception .

Keywords : Satellite, L-band, Signal, Mobile, World space

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1. Introduction

1.1

The characteristics of the radio wavepropagation channel (terrestrial orsatellite) always play an importantrole in planning and designing the

communication/broadcasting servicenetwork. It is more so when the radiofrequency contains digitalinformation. Satellite emission ofdigital multimedia signal for directreception is one of the most importanttrends in the field of InformationCommunication technology (ICT).The signal can be in

1. HoD ECE Ajay Kumar Garg EngineeringCollege, Ghaziabad, India

(M) 09350023027 Fax: 0120-2761846 2. HoD ECE, IGIT, New Delhi3. Former E-in- C, All India Radio4. Becil, INDIA

UHF; L-band; S-band; Ku-band or evenat higher frequency [1]. It is thereforenecessary to study the characteristics ofthe propagation channel involved in the

satellite emission of the digital RF signalat these RF frequencies.

Such propagation studies have beenmade in different countries in differentfrequency bands. Nevertheless there arescopes to make further observations inthis field in various ITU-RadioFrequency Regions.

1.2 Background, Objective andEnvironment of Measurements:

After the introduction of Satellite radioservices in India through the use of AsiaStar Satellite of World Space, USA, itwas considered necessary to study thecoverage area and discover spots wherethe reception was not up to the desired


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level. Initially the World Spaceorganization was offering the service atfixed locations and the signal wasreceived using a small patch antennawhich was required to be installed on aSouth facing window or on roof-top,facing the satellite. As the service atfixed locations was stabilized, it wasdecided to probe the possibility of usingthe satellite radio in Cars and othermoving vehicles in cites and onhighways and even extend this study inmoving trains across the country. Beforesuch a service is offered for commercialuse it was necessary to evaluate the

effects of foliage; shadows of thebuildings; mobile reception (vehiclespeed); etc. on the received signal.

In the present study programmed anattempt has been made in general tomeasure the propagation channelcharacteristics in L-band both for fixedas well as for mobile reception of digitalsatellite emission. L band satellitedigital signal from the World space AsiaStar Satellite which employs ITU Digitalsystem Ds has been used as the signalsource. Primarily the service is intendedfor fixed and portable reception.However the measurement objectiveincluded assessment of propagationchannel characteristics of this satelliteservice both for fixed as well as formobile reception.

Measurements for fixed reception werecarried out for a period of about afortnight in congested city areas ofcentral Delhi and the Ridge area withundulating terrain and moderately thickvegetation. While measuring the signalattenuation under fixed reception,different types of environments like

Roadside vegetation; Multistorybuilding area; Interior of building; etc.were taken into account (as given inTable 2).

Measurements for mobile receptionwere carried out on board the fastexpress train operating between New-Delhi and Trivandrum. The total routelength is about 3000 KM andmeasurements have been conducted allalong the route for 2 days and 2 nights.This is a North-South route and themeasurements have covered the satelliteelevation from about 42 o (New-Delhi) to

about 80o

2.1 The radio wave propagation channelcharacteristics can be broadly classifiedinto three categories. In the firstcategory the reception of the radiosignal is in a Line-of-sight (LOS) withthe transmitting source and there is noreflected signal component (i.e. nomultipath signal). Here the propagationchannel is called Gaussian Channel .This is because the signal distribution insuch a channel follows the Gaussiandistribution. Here the signal at aparticular reception location remainsfixed and it steadily gets attenuated asthe distance from the transmittingsource increases. In the second categorythe received signal is a combination ofboth LOS signal as well as reflectedsignal components from multiplereflecting objects like buildings, hills,other structures and also the mobileobjects such as motor vehicles etc. Herethe signal level at a particular location is

(Trivandrum).

2. Propagation Channels & Factorsinfluencing Mobile Reception


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no longer fixed. It fluctuates about thesteady LOS value. As the distance fromthe transmitter increases, the amount ofsignal fluctuation (from the steady LOSvalue) varies depending upon thecombined effect of all the multipathsignal components prevailing at theparticular receiving location. Such apropagation channel with mixed signalcomponents is called Rice-NakagamiChannel. The third category of channelis considered as the most severe. Herethe receiving location is totally obscuredfrom the transmitting source byobstacles like- buildings, hills or other

structures. In such a situation there is noLOS signal component. Whatever signalis received by the receiver is thecombined effect of all the reflectedmultipath signal components.Obviously the received signal level at aparticular location is very unsteady andwith change of distance from thetransmitting source the signal levelfluctuates very deeply. Such apropagation channel is called RayleighChannel and is considered to be themost severe channel condition.

2.2 In fixed reception, the radio wavepropagation channel condition more orless remains fixed. It means that thechannel will follow either the GaussianDistribution i.e. direct line-of sight(LOS) channel or a Rice-Nakagamichannel , giving both direct LOS signalas well as reflected multipath signalcomponents or it will follow aRayleigh channel i.e. only reflectedsignal.

2.3 In a mobile reception, the channeldoes not remain fixed. It goes onchanging with the variable

environmental conditions of thereceiving locations as rapidly as thespeed of mobility. When it is satellitemobile reception, it rapidly changes thechannel conditions sometimes directLOS; sometimes under shadow ofbuildings, trees or other structures andsometimes inside the buildings. Hencethe reception has to encounter all typesof radio wave propagation channelconditions including the worst one i.e.the Rayleigh channel.

The second important factor in mobilereception is the Doppler Frequency

Shift of the R.F.carriers. The Dopplercarrier shift with mobility of receiverproduces additional Bit Error Ratio(BER) and hence more noise and signalaberrations. Depending on the receivercharacteristics in terms of required C/N,it can tolerate this bit error/ additionalnoise, up to certain extent which limitsthe maximum speed of the reception.Beyond this speed, the DopplerFrequency Shift of the carriers crossesthe safe limit and producesirrecoverable signal aberrations.

The third factor of mobile reception iscontained in the fact that the serviceplanning of mobile reception is notbased on reception with roof-topantenna, as in the case of fixedreception. The receiving device in themobile services being a hand-set withbuilt-in antenna, the reception isexpected anywhere- inside the building,building basement, congested urbanbuilt-up areas etc. In all theseenvironments, the received signalstrength; the error-correction coding etc.should be strong enough to lay a robust


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received signal at the mobile receiverinput to enable an error free reception.

3. Source of L-band Satellite Emission

3.1 World Space-USA launched three L-band geo-stationary broadcast satellites Asia Star (105 o East); AfriStar (21 o East); Ameri Star (95 o

3.3 Digital audio is being broadcast byall three World Space satellites usingITU-R Digital System DS. Theprogrammes can be encoded either inMPEG 1 layer III, MPEG 2 layer III orMPEG 2.5 layer III and are time divisionmultiplexed in a bit stream of 1.536Mbps. This bit stream is encoded witherror protection scheme employingReed Solomon block codes and 1/2 FEC

code to form a bit stream of 3.68 Mbps.This digital stream is then QPSKmodulated on an IF and occupiesa bandwidth of 2.5 MHz. This IF is upconverted to L-Band in 1467 to 1492MHz bands and broadcast fromsatellite. Salient technical parameters ofWorld Space satellite are given in Table1.West). This

attempt of World Space-USA is historicand extremely significant because, thiscan be termed as the maiden venture forthe direct reception of satellite broadcastservice (sound). This was a successfulventure which provided digital satellite

radio service in multiple channels over awide global area in Asia; Africa; Europeand American continents.

3.2 World Space geo-synchronoussatellites AmeriStar, AfriStar and AsiaStar- are planned to illuminate South &Central America, Africa & Middle Eastand Asia respectively, usingthree beams from each satellite. Eachbeam comprises of left and right handcircular polarizations and bothpolarizations have different frequencies.Each beam can carry about 50 broadcastchannels and each broadcast channelcan carry up to 8 programmes togetherwith Programme Associated Data(PAD) to indicate type of programme.

4. Measuring set-up for Fixed SatelliteReception

4.1 Figure 1(a), (b) and (c) gives theblock schematic diagram and

photographs of measuring set-up forfixed satellite reception. A calibrated L-Band yagi antenna having a gain of 9dBi mounted on 1.5 m high woodentripod was used for receiving satellitesignals. The received signal was firstamplified using a Low Noise Amplifier(LNA). The amplified signal wasdivided in two signal paths of equalsignal strength using signal splitter. One

output of the splitter was used as inputto the World Space compatible receiverand other one was connected to fieldstrength meter for simultaneousmeasurement of field strength andchecking sound quality.

4.2 For the measurements under fixedreceiving condition, the measuringsetup was taken to various types oflocations in and around New-Delhi andthe data collected broadly under threeenvironmental conditions, viz. (1)Vegetation area (2) Urban areasurrounded by high rise buildings and(3) Inside the building.

4.3 Median Value & StandardDeviation: As explained earlier the


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received signal is always fluctuatingwhether received in a stationary modeor in mobile mode. Therefore in boththese modes of reception, instead oftaking a single reading for the signalstrength, a set of readings are taken foreach location or each environment andMedian value of that set of readings iscalculated and that is taken as themeasured signal level of that location /environment.

For the purpose of service planning, theabsolute signal strength in a particularlocation/environment is necessary. But

characteristically the signal level is ingeneral not steady but fluctuatingowing to presence of multipath effect.The amount of such fluctuation ordeviation from the mean level is animportant parameter for serviceplanning. While designing thetransmission system, provision has to bekept, so that the available signal levelcan offset the effect of signal deviationand satisfy the receiver in terms ofthreshold for satisfactory reception.Conventionally such deviation of signalis derived from the StandardDeviation (SD) of a set of signalstrength readings.

For all the above environments, sets ofmeasurements were made to derive themedian value of satellite signalattenuation due to environment as wellas the standard deviation of the receivedsignal.

4.4 For building penetration LOSs,signal measurements were made insideand outside the buildings of differentcategories of structures like- concrete,bricks, etc. The measurements were

made in the direction of the satellitebeam in a manner that only one wallobstructs the satellite beam. It wasobserved that reception of good qualityaudio is possible even if the signalattenuation inside the building is of theorder of 9-11 dB.

4.5 The data collected under the threeenvironmental conditions wereanalyzed and the median value of signalattenuation (dB) as well as the standarddeviation of the signal was computed.The results are presented in Table 2.

Several countries like Canada, UnitedKingdom, etc., have conducted similarexperiments and the results of thestudies are available in ITU-R SpecialPublication Terrestrial and satelliteDigital Sound broadcasting to vehicular,portable and fixed receivers in theVHF/UHF bands. Results of studiescarried out in India are in closeagreement with the results obtained inthese countries.

5. Digital Satellite Signal Receptionunder Mobile condition

5.1 World Space Asia Star satellite islocated at 105E longitude. West Beamof the satellite operating on 1487.885MHz provides coverage to entire Indiaand its neighboring countries. Itemploys Digital System DS, which isprimarily intended for portable andfixed reception. Though service for fixedand portable reception in India isworking satisfactorily, experimentswere required to ascertain itsperformance during mobile conditionparticularly in a fast moving train.


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5.2 Therefore, a study to assessreception of digital satellite radio serviceunder mobile condition was carried outin a fast moving train over a path lengthof about 3 000 km between New Delhiand Trivandrum. The selection ofrailway track was made to include thefollowing different conditions:

Track with and withoutelectric traction

Urban and ruralenvironment

Plain and hilly terrain

Track with and without tree-

line

Track with overhead bridgesand tunnels.

5.3 The desired satellite signal wastuned in to feed input signal to thereceiver and the measuring equipment.Figure 2 gives the block schematic of themeasuring set-up installed in a coach offast moving train. Two numbers ofpatch antennas mounted on magnetwere installed on two ends of rooftop ofthe coach. R.F. cables from antennaswere brought inside the coach whereoutputs from both the antennas werecombined with the help of a T-connectoras shown in Figure 3. The combinedantenna output was fed to a bufferamplifier for amplification. The outputof buffer amplifier was divided with thehelp of a 4-way connector to provideinput to radio receiver, spectrumanalyzer and field strength meter asshown in the Figure2. The receiveroutput was fed to a monitoringamplifier of the Public Address (PA)system installed in the train.

5.4 Observations during the Trial: Monitoring of reception quality of AllIndia Radio's digital satellite service viaAsia Star satellite was conducted duringto-and-fro railway journey from Delhi toTrivandrum using World Spacecompatible receivers. The programmeoutput was fed in the rail compartmentsusing existing PA system also in thetrain. The salient observations of thetrial are listed below:

The reception quality ingeneral was found to beexcellent.

The radio reception was notpossible in some cases whenthe train was passingthrough tunnels or under theoverhead bridges.

Muting of receiver inpresence of R.F. interferencewas noticed in some of theareas usually in theproximity of large citieswhere several other servicesare operating in L-Band.

Muting of receiver was alsonoticed in presence of multi-path signals from man-madeor natural objects.

Objective measurementsusing field strength metershowed that if there are noobstacles from overheadbridges, buildings, trees,tunnels, etc., signal leveldoes not change beyond 3 dBover entire path length of 3000 km.

5.5 India has a vast railway networkserving millions of people across thecountry. During the journey, commuters


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are not able to avail of the live radiobroadcast service and as such not able tolisten to the latest update on news,current affairs and other importantevents, which are available on fixed andportable receivers. During thisexperiment on board the IndianRailways, the live digital satellite radioservice was fed to the existing PAsystem of the train. The passengers werevery happy to taste this new service onthe moving train and they appreciatedthe superior quality of the digital radio.

6. Conclusion

6.1 Fixed and Portable Reception -For the measurements under fixedreceiving condition, the measuringsetup was taken to various types oflocations in and around New-Delhi andthe data was collected broadly underthree environmental conditions, viz.Vegetation area, urban area surroundedby high rise buildings and inside the

building. The signal was analysed undervarious conditions and detailed analysiscarried out.

Signal attenuation was higher in areaswhere vegetation is thick as comparedto areas of thin vegetation. Medianattenuation was found to be 7.6 dB withstandard deviation of 3.22 dB whenLine-of-Sight (LOS) is obstructed by

vegetation. Signal attenuation was alsohigh in presence of multi-storeybuildings in urban areas resulting in themuting of receivers. Median value ofattenuation in case of LOS obstructed byhigh-rise building was of the order of7.8 dB with standard deviation of 4.35dB.Median building penetration LOSs

inside the room was observed as 11 dBwith standard deviation of 3.40 dB.

6.2 Mobile reception A study to assessreception of digital satellite radio serviceunder mobile condition was carried outin a fast moving train over a path lengthof about 3 000 km between New Delhiand Trivandrum(India). Experimentshows that excellent quality of digitalsatellite radio reception is possible ona fast train moving at a speed of 120km/hour or beyond. However, in someof the extreme cases, like tunnels, therewere small breaks in reception due to

muting of receivers. Objectivemeasurements using field strengthmeter showed that if there are noobstacles from overhead bridges,buildings, trees, tunnels, etc., signallevel does not change beyond 3 dB overentire path length of 3000 km. Thereceived satellite programme was fed tothe existing PA system of the train and,the passengers from different walks of

life appreciated the programme quality.Acknowledgement:

I sincerely thank UNIVERSITYSCHOOL OF ENGINEERING &TECHNOLOGY, Guru Govind SinghIndraprastha University, New Delhi forproviding the opportunity and guidancefor research work.References1. ITU-R special publication on Terrestrial and

satellite digital sound ITU-R

Broadcasting to vehicular, portable and fixed receiversin the VHF/UHF bands , Radio CommunicationBureau, Geneva, 1995.

2. Goldhrish, J. Vogel, W.J.: Mobile Satellite system FadeStatistics for Shadowing and Multipath from Roadside Treesat UHF and L-band, IEE Transactions on Antennas &propagation, vol. 37, no. 4 April, 1989, pp 489-498


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3. De Gaudenzi, R.; Fanucci, L.; Giannetti, F.; Luise, M.;Rovini, M.; Satellite mobile communications spread-spectrum receiver Aerospace and Electronic SystemsMagazine, IEEE Volume 18, Issue 8, Aug 2003Page(s):23 304. Blas, J.M.; De Pablos, J.; Ramos, J.; Perez, F.; Alonso,J.I.;Closed loop adaptive antenna for satellite mobile

communications Electrotechnical Conference, 1996.MELECON '96., 8th Mediterranean Volume 1, 13-16May 1996 Page(s):538 - 541 vol.1

5. Al Salameh, M.S.; Jarandal, A.H.; Impact ofbuildings on the performance of MEO satellitemobile communication systems for low bit rateapplications Microwaves, Antennas and Propagation, IEEProceedings - Volume 151, Issue 2, Apr 2004 Page(s):161 166

6. Ho, H.Y.-P.; A helical antenna array design formobile satellite communication system MicrowaveConference Proceedings, 1997. APMC '97., 1997 Asia-

Pacific2-5 Dec. 1997 Page(s):657 - 659 vol.2

7. Sofos, T.; Constantinou, P.; Propagation model forvegetation effects in terrestrial and satellite mobilesystems Antennas and Propagation, IEEE Transactions onVolume 52, Issue 7, July 2004 Page(s):1917 1920

8. Gollere M .; Application of GSM in high speedtrains: measurements and simulations Radiocommunications in Transportation, IEE Colloquium on 16May 1995 Pages (s) : 5/1-5/7

Biography:

Prof. Pradeep Kumar Chopra entered the field ofeducation in the year 2004 after 24 years of exemplaryservice in the technical branch of the Indian Air Force,He earned his Bachelors degree in Engineering(Electronics) from Delhi college of Engineering in theyear 1979 and Masters in Technology from IIT Delhi inthe year 1985. He also has a Masters degree in DefenceStudies from Madras University. While he was in theIndian Air Force he was part of, and headed a numberof important technical projects. For his exemplaryservices he was awarded Vishist Seva Medal by the

President of India in the year 1993. He took prematureretirement from the IAF in the year 2004 and enteredthe field of education. He is the Head of Dept.(Electronics and Communication) in Ajay Kumar GargEngineering College in Ghaziabad. AKGEC is rated asthe No 1 Engineering Colleges in U.P., Affiliated toUttar Pradesh Technical University, Lucknow.

BRIEF BIO - DATAPROF. P. K. CHOPRA,HOD-ECE Deptt,

AJAY KUMAR GARG ENGINEERING COLLEGE,GHAZIABAD, U.P.

TABLE 1

Technical parameters of Digital System D S
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Frequency (GHz) 1.48

SatelliteRepeater output power (w)Output LOSses (dB)OBO compression (dB)Antenna gain @ EOC (dB)

300.01.30.3

25.6

EIRP (dBW) 48.8

PropagationElevation ()Distance (km)Free space LOSses (dB)

Pointing LOSses (dB)Atmospheric LOSses (dB)

30.038612.6

187.6

0.00.1

Signal from the Asia Star satellite (105 degrees East) was taken as the source signal formeasurements of propagation channel characteristics.The satellite signal measurements were divided in two major categories: (1) Under FixedReceiving Condition and (2) Under Mobile Receiving Condition .

TABLE 2

Median value of Signal Attenuation (dB) and Standard Deviation (dB) underDifferent Environmental Conditions

Environmental condition Median value of Sig.Attn.

(dB)

Standard Deviation(dB)

Vegetation (tree-lined roads) 7.6 3.22

Urban area (surrounded by multi-storeybuildings) 7.8 4.35

Inside building (building penetrationLOSs) 11 3.40

Figure:1(a) - Block Schematic of Measuring Set-Up for Fixed Satellite Reception

Radio receiverPower flux density (dBW/m 2)G/T (dB/k)Received C/No (dBHz)

114.113.0

76.7

Radio receiverRequired Eb/No (dB @ 10-4)Hardware LOSses (dB)Intersymbol interference (dB)Bit rate (kHz)Required C/No (dBHz)

2.71.80.5

1 584.067.0

Margin (dB) 9.7


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Figure:1(b) - Measuring Set-Up for Fixed Satellite Reception

Figure:1(c) - Measuring Set-Up for Fixed Satellite Reception

ANTENNA

LNA

SPLITTER

F.S. METER RADIORECEIVER


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Figure:2- Experimental Setup for Digital Satellite Radio Reception in a Train of IndianRailways under Mobile Condition.

FIGURE 2

SPECTRUMANALYSER PRINTER

F.S. METER 12 VPOWERSUPPLY

4-WAYCONNECTOR BAND PASS

FILTER1 480-1 489

MHz

WORLDSPACERECEIVER-CUM-

CASSETTERECORDER

PA SYSTEM

BUFFERAMPLIFIER

SPEAKER

T-CONNECTOR RF FEEDER

RF FEEDER

PATCH ANTENNA-I(L-BAND)

MOUNTED ON COACH

PATCH ANTENNA-II(L-BAND)MOUNTED ON COACH

Train Roof

Inside Train Coach


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Figure:3 - Patch Antennas on Train Roof Top

l – band propagation measurements for fixed and mobile reception of satellite digital emission

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