Vietnam Spectrum Occupancy Measurements andAnalysis for Cognitive Radio Applications

Vo Nguyen Quoc Bao∗, Le Quoc Cuong∗, Le Quang Phu∗, Tran Dinh Thuan∗,Nguyen Thien Quy†, Lam Minh Trung†

∗School of TelecommunicationsPosts and Telecommunications Institute of Technology

Email: {baovnq, lequoccuong, phulq, tdthuan}@ptithcm.edu.vn† Radio Frequency Directorate

Vietnam Ministry of Information and CommunicationsEmail: {thienquy, trunglm}@rfd.gov.vn

Abstract—The rapid growth of demand for wireless transmis-sion has placed great pressure on the scarce radio spectrum dueto the fixed spectrum allocation policy and cognitive radio (CR)is considered as a promising solution to such the problem. Themain idea behind a cognitive radio network is for the unlicensedusers (also called secondary users) to exploit opportunistically theunderutilized spectrum licensed to a licensed network (referredto as a primary network). Before investigating the technical andpolitical implications of CR, it is important to know to whatextent the licensed bands are temporally unoccupied. In thispaper, for the first time, we investigate the spectrum usage patternin Vietnam in the frequency bands ranging from 20 MHz to3000 MHz in Ho Chi Minh City and Long An province. Thepurpose of the measurement is to find how the scarce radiospectrum allocated to different services is utilized in Vietnam andidentify the bands that could be accessed for future opportunisticuse due to their low or no active utilization. These analysesindicate that, on average, the actual spectral usage in all bandsis 13.74% and 11.19% for Ho Chi Minh City and Long Anprovince, respectively. The experiment results also show that thespectrum band assigned for analog television (470-806) is thehighest occupancy band with 58%.

I. INTRODUCTION

Radio frequency spectrum is a resource of fundamentalimportance in wireless communication systems. During recentyears, a multitude of wireless applications and services hasbeen developed resulting in a collision with the compre-hensive, well-established, but increasingly obsolescent policyfor the allocation and utilization of the radio spectrum [1].In principle, international regulatory bodies like the FederalCommunications Commission (FCC) coordinate and properlyregulate the usage of radio spectrum resources and the reg-ulation of radio emissions [2]–[4]. In Vietnam, based on therecommendations of the FCC, the radio frequency directorate(RFD) assigns spectrum to licensed holders, also known asprimary users, on a long-term basis [5]1 2 3.

Such the policy partitions the overall radio spectrum intonon-overlapping frequency bands corresponding to differentpurposes, i.e. government, public safety, national defense,

1http://rfd.gov.vn/Danh sach/Quy hoach moi2http://rfd.gov.vn/Danh+sach+Quy+hoach+bang+tan/Quy hoach bang tan3http://rfd.gov.vn/Danh sach/Quy

television radio, cellular, and unlicensed consumers. Althoughthe fixed allocation approach ensures that competing wirelessapplications do not interfere with each other’s, it seems tobe inappropriate since the current spectrum use is inefficientwith some bands heavily subscribed and others rarely used.One of the most promising solutions for such the problem iscognitive radio, invented by Mitola [6], being able to detectan unoccupied frequency band to use temporarily, and thenvacate when necessary [7]. To realize CR networks as wellas to quantify their potential benefits accurately, the currentspectrum usage should be known. Therefore, the crucial stepis the study of the availability of temporarily unoccupiedspectrum not only in terms of frequency but also in termstime and space.

Till now, several measurement campaigns were conductedin USA [8], New Zealand [9], Germany [10], Singapore [11],China [12], Spain [13], and Qatar [14]. A shared findingamong these studies is that a large portion of the assignedspectrum remains underutilized. In this paper, for the first time,we report the detail results of a spectrum survey conductedin Vietnam with an aim not only to fill the gaps today inknowledge about the use of spectrum but also to identify themost suitable and interesting bands for CRNs. The spectrummeasurement campaign covers the frequency range from 20MHz to 3000 MHz in two locations: Ho Chi Minh City andLong An province. The rest of this paper is organized asfollows. In section II, we introduce the measurement setupand procedure. Section III presents the measurement resultsand provides some observation and discussion. Finally, thepaper is closed in section IV.

II. MEASUREMENT SETUP AND PROCEDURE

The equipment used for the measurement consists of a setof antenna, an R&S EM550 VHF / UHF digital widebandreceiver4, and a server installed R&SARGUS monitoringsoftware5. The set of antennas including HE0166, HE3097,

4http://www2.rohde-schwarz.com/product/em550.html5http://www2.rohde-schwarz.com/product/ARGUS.html6http://www2.rohde-schwarz.com/product/HE016.html7http://www2.rohde-schwarz.com/product/HE309.html

2011 International Conference on Advanced Technologies for Communications (ATC 2011)

978-1-4577-1207-4/11/$26.00 ©2011 IEEE 135

Matrix Switch

HE015 HE309 HE314A1 HF214 HF902

Fig. 1. The measuarement system.

HE314A18, HF2149 and HF90210 is connected to the EM550receiver via a switch matrix as shown in Fig. 1. Via theR&SARGUS monitoring software, we can configure the sys-tem to measure the received signal power in all range offrequency (of interest) from 20 MHz to 3000 MHz as wellas stored all the measurement results in the server in realtime for further processing. The detail characteristics of eachantenna are provided in Table I. Depending on the measuredspectrum band, the appropriate antenna is manually chosen,i.e. it is directly connected to the receiver. For example, weuse an active vertical dipole (HE309) for the frequency rangebetween 20MHz to 1300 MHz while HF902 should be usedif the frequency range from 1 to 3 GHz is considered.

The measurements were conducted over a 4-month timespan from Oct. 2010 to Feb. 2011 at two different locations.The first location as shown in Figs. 2 is the roof top (the 6thfloor) of the RFD office building in An Phu, District 2, Ho ChiMinh City with coordinate 10◦47′42.3′′ and 106◦44′25.9′′. Asa reference, the second location (Long An province with co-ordinate 10◦38′12.50′′ and 106◦29′36.00′′) is chosen roughly50km far away the first location considered as a rural area.Both the chosen measurement sites almost have almost nohigh buildings surrounding enabling us to accurately measurethe spectral activity of all possible transmitters.

The utilization of spectrum is usually quantitatively ex-amined by the most used metric - spectrum occupancy. Ina particular location, it is defined as the probability that ameasured signal of a certain bandwidth is unused by primaryusers. To determine whether a given frequency is occupiedor not, spectrum sensing is usually used. There are threecommon methods proposed in the literature so far includingmatched filter detection, cyclostationary feature detection andenergy detection [15], [16]. Among them, energy detection isthe most popular method measuring only the received signal

8http://www2.rohde-schwarz.com/product/HE314A1.html9http://www2.rohde-schwarz.com/en/products/antennas/HF214.html10http://www2.rohde-schwarz.com/en/products/antennas/HF902.html

Fig. 2. The measurement system.

Fig. 3. The antenna system.

power [17]. In this paper, we use the energy detection forall measurements. In energy detection approach, a frequencyband is considered ”unused” if the power of measured signalsis above a predefined power threshold, i.e. the noise levelat the receiver. Otherwise, it is reported as an ”available”band for cognitive applications. Therefore, determining thelevel of background noise is a critical step towards spectrumoccupancy measurement. According to [2], [10], [14], a marginof 3dB is considered for determining the final threshold valuein order to account any unforeseen effects and variations.

III. MEASUREMENT RESULTS AND ANALYSIS

In this section, we present some selective spectral measure-ment results. We start with the Fig. 5 and 6 where the averagePSD over the whole frequency range of measurement studyare plotted. Due to the characteristics of the antennae used,the measured frequency is divided into two non-overlapping

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Fig. 4. The aerial map showing Ho Chi Minh City measurement site(Courtesy of Google Inc.).

Type of an-tenna

Antenna characteristics

HE016 Active antenna system, omnidirectional reception of ver-tically and horizontally polarized signals with bandwidth10 kHz to 80 MHz (vertical) and 600 kHz to 40 MHz(horizontal).

HE309 Active vertical dipole, high sensitivity, large bandwidthand wide dynamic range from 20MHz to 1300 MHz.

HE314A1 Active omnidirectional antenna, reception of horizontallypolarized waves from 20 MHz to 500 MHz.

HF214 Omnidirectional antenna, designed for the reception ofhorizontally polarized waves 500 MHz to 1300 MHz.

HF902 Omnidirectional antenna designed for the reception ofvertically and horizontally polarized waves from 1-3GHz.

TABLE IANTENNA CHARACTERISTICS.

100 200 300 400 500 600 700 800 900 1000

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0

Frequency [MHz]

PS

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Fig. 5. Average power spectral density vs. frequency at Ho Chi Minh City20-1000 MHz.

1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

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Frequency [MHz]

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Fig. 6. Average power spectral density vs. frequency at Ho Chi Minh City1000-3000 MHz.

frequency ranges, i.e. from 20 to 1000 Mhz and from 1001MHz to 3000 MHz. From the figures, there are some importantpoints that is worth noting as follows. The level of backgroundnoise is a little higher than the theoretical ambient noise.Importantly, it is not constant and slightly increases withfrequency resulting in an increase on the decision threshold.It is due to the fact that the decision threshold is chosen 3-dBabove the system noise floor as mentioned previously. Besides,we can also observe that the actual spectrum usage patternis not uniform, i.e, the spectrum below 1 GHz seems to beheavily utilized while the spectrum from 2 to 3 GHz is foundto be lightly used.

Although Fig. 5 and 6 provide us some overview aboutspectrum utilization, they is insufficient to provide a detaildescription on how spectrum is used in different bands. There-fore, for a better view, we participate the overall spectrumunder consideration into 15 sub-bands and study its associatedspectrum activity in Figs. 7-22. In particular, Fig. 7, 8 and 9show the received power versus frequency plot for 30-54 MHz,54-68 MHz and 68-87 MHz, respectively. Clearly observedfrom the figures, the band allocated to FM radio is found tobe most quiet as compared to the other bands.

In Fig. 10, 12 and 15, we show the PSD in the broadcasting(FM, TV) bands: 87-108 MHz, 174-230 MHz and 490-806MHz. As can be seen, they are the most heavily utilized bandsobserved in this study. The typical maximum signal power ofFM bands is from 0 dBM to -20 dBm. With TV channels,the maximum power is around -60dBm to -40 dBm. From thefigures, we can also identify some spectrum of signals comingfrom some popular FM and TV channels, e.g. VOV1, VOV2,VOV3, VOV5, FM99.9 , HTV7, HTV9, TayNinh, DongNai,etc.

Along with the broadcasting bands, cellular mobile servicebands (Fig. 14, 16 and 21) are the other ones having aconsiderably higher occupancy rate compared with other typeof frequency allocations. If we consider land mobile bands824-960 MHz and 1710-2300 MHz, it is easy to identify thespectrum of downlink GSM/E-GSM signals that are located in950MHz and 1800MHz bands. Furthermore, the spectrum ofdownlink 3G/IMT2000 signals of four 3G service providers,i.e. Mobile, Viettel, EVN&HT, and Vinaphone, are observedranging from 2110Mhz to 2200 MHz. It appears that thedownlink channels in point-to-multipoint mobile applicationsare identified as mostly occupied. This is due to the activecontrol channels constantly broadcasted by base stations tomaintain cellular service coverage of GSM900, GSM1800and WCDMA networks. Unlike downlink channels alwaystransmitting with relatively high power, the usages in theuplink channels depend on the actual number of active mobileusers in the measurement area and more intermittent accordingto their behaviors. From the figure, we can see that as expectedtransmit power of GSM900 mobile stations is higher thanthat of GSM1800 mobile stations. Besides, from Fig. 21, wealso observe that 3G uplink channels seem to be completelyunused. Here, it should be noted that due to the nature ofWCDMA technology the transmit power of uplink channels

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in 3G system is very low, and might not be detectable by themeasurement system.

Next, we focus on Fig. 11 and 13 where the spectrumactivity of the frequency bands 108-174 and 230-406 is shows.As can be seen, most part of these bands band is unoccupiedsuggesting some opportunities for cognitive radio accesses.However, recalling that the whole band from 230 to 406 MHzis exclusively reserved for security services and systems ofthe Vietnam ministry of public security (MPS). Therefore,in principle, such spectrum bands should be precluded bysecondary access.

The average PSD of the well-known unlicensed Industrial,Scientific and Medical (ISM) band (2400 to 2500 MHz) isillustrated in Fig. 22. Allocated for unlicensed spectrum use,the ISM band is considered as the most open band. Withinthis band, many wireless applications are operated includingWiFi transmitters, cordless telephones, microwave ovens, andvarious consumer products. Therefore, it is believed to be themost heavily used frequency band. However, from Fig. 22,it is observed that this band appears to be unoccupied. Itcan be explained by the fact that this frequency band isusually occupied in indoor environments and signals at suchfrequencies are severely attenuated by walls. The rest ofspectrum between and 3 GHz remains mostly unused, withthe exception of some signals with very low duty cyclein bands allocated to aeronautical and satellite radiolocationand radionavigation, (960-1350 and 1610-1710 MHz), DECTcordless phones (1880-1900 MHz) and military radars (2700-2900 MHz).

To this end, we show the band-by-band average spectrumoccupancy in Ho Chi Minh City in Fig. 23. The results of thesemeasurements indicate that some spectrum bands are subjectedto exhaustive usage while some others are sparsely used orshow temperate utilization, and, in some cases, are not usedat all. In general, the average spectrum occupancy observed inHo Chi Minh City is 13.74% for the whole frequency rangebetween 20MHz and 3000 MHz and the band assigned fortelevision broadcasting is the highest occupancy band with58%. Stated another way, 86.25% of this spectrum is unused.

As a baseline for comparison, we also show the averagespectrum occupancy of New York and Long An in Fig. 24. Theobtained results demonstrate that Ho Chi Minh City spectrumutilization exceeds Long An by roughly 1.46%, which, inturns, exceeds New Yorks by 1.15%.

IV. CONCLUSION

The spectrum measurements presented here are part of alarger on-going measurement campaign conducted by PTIT inseveral cities in the south of Vietnam. The purpose of thisproject is to create a usage map for cognitive applicationsin Vietnam. The challenge of this campaign is not onlycost (equipment) but also time (deployment) where multiplelocations are to be measured to obtain local spectral patternusage.

Our measurement results suggest that in Vietnam most ofallocated frequencies are underutilized except for mobile and

broadcasting bands and CR applications can be realized by ex-ploiting bands with low measured occupancy rates. However,care must be taken to account for possible wireless channeleffects such as multi-path and hidden terminal problems.

ACKNOWLEDGMENT

This research was supported in part by the Science andTechnology Foundation of Ho Chi Minh City and by theVietnam’s National Foundation for Science and TechnologyDevelopment (NAFOSTED) (No. 102.99-2010.10).

REFERENCES

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[9] R. I. C. Chiang, G. B. Rowe, and K. W. Sowerby, “A quantitativeanalysis of spectral occupancy measurements for cognitive radio,” inProc. IEEE VTC2007-Spring Vehicular Technology Conf. (IEEE VTC65th, pp. 3016–3020.

[10] M. Wellens, J. Wu, and P. Mahonen, “Evaluation of spectrum occupancyin indoor and outdoor scenario in the context of cognitive radio,” inProc. 2nd Int. Conf. Cognitive Radio Oriented Wireless Networks andCommunications CrownCom 2007, pp. 420–427.

[11] M. H. Islam, C. L. Koh, S. W. Oh, X. Qing, Y. Y. Lai, C. Wang, Y.-C.Liang, B. E. Toh, F. Chin, G. L. Tan, and W. Toh, “Spectrum survey insingapore: Occupancy measurements and analyses,” May 2008.

[12] D. Chen, S. Yin, Q. Zhang, M. Liu, and S. Li, “Mining spectrum usagedata: a large-scale spectrum measurement study.” ACM, pp. 13–24.

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[15] A. Goldsmith, S. A. Jafar, I. Maric, and S. Srinivasa, “Breaking spectrumgridlock with cognitive radios: An information theoretic perspective,”Proceedings of the IEEE, vol. 97, no. 5, pp. 894–914, 2009.

[16] A. Ghasemi and E. S. Sousa, “Spectrum sensing in cognitive radio net-works: requirements, challenges and design trade-offs [cognitive radiocommunications],” IEEE Communications Magazine, vol. 46, no. 4, pp.32–39, 2008.

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30 35 40 45 50

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Frequency [MHz]

PS

D [d

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MeanMinMax

Fig. 7. Amateur 30-54 MHz.

54 56 58 60 62 64 66 68

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F [MH ]

PS

D [d

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MeanMaxMin

Fig. 8. Broadcasting (FM radio) 54-68 MHz.

68 70 72 74 76 78 80 82 84 86−100

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0Aero Nav., Analog TV.

Frequency [MHz]

PS

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Fig. 9. Aeronautical Radionavigation/Analog TV 68-87 MHz.

88 90 92 94 96 98 100 102 104 106 108

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Frequency [MHz]

PS

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Fig. 10. Broadcasting (FM radio) 87-108 MHz.

110 120 130 140 150 160 170

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Frequency [MHz]

PS

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Fig. 11. Aeronautical Radionavigation, Aeronautical Mobile (R), Mob. Sat. (S-E)/Fixed/Mobile, Amateur/Amateur Satellite, Fixed/Mobile 108-174 MHz.

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175 180 185 190 195 200 205 210 215 220 225 230

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Frequency [MHz]

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CH7:HTV7 CH9:HTV9 CH11:TAYNINH

CH12:DONGNAI

Fig. 12. Broadcasting (TV channels 7 to 13) 174-230 MHz.

240 260 280 300 320 340 360 380 400

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Frequency [MHz]

PS

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DataTransmisson

of MPS

Fig. 13. Fixed/Radionavigation Sat./Meteorological Aids 230-406 MHz.

410 420 430 440 450 460 470

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Frequency [MHz]

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UPLINKPMRTAXI

DOWNLINKPMRTAXI

CDMA400/EVN

Fig. 14. Fixed/Radiolocation/Land Mobile 406,1-470 MHz.

480 500 520 540 560 580 600 620 640

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650 700 750 800

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CH55 CH56CH54CH51 CH52 CH60CH50CH48CH44

CH36CH34CH32CH30CH28CH21 CH22 CH23 CH25 CH26 CH39 CH40 CH41 CH42

CH62

Fig. 15. Broadcasting (TV channels 14 to 20)/Fixed 470-806 MHz.

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820 840 860 880 900 920 940 960

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Mobile Data, PMR & Trunking

MeanMinMax

DLGSMVINA

DLGSM

VIETEL

DLGSMMOBI

DLE−GSMVNMOBUL

GSMUL

E−GSMCDMAVNPT

CDMAS−PHONE

Fig. 16. Fixed/Land mobile 810-960 MHz.

1000 1050 1100 1150 1200 1250 1300 1350−70

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DME

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DME 1260DME 1201 DME 1280 DME 1340DME 1024DME1003

Fig. 17. Aeronautical Radionavigation 960-1350 MHz.

1350 1360 1370 1380 1390 1400 1410 1420

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Radio Location, Radio Astronomy, Earth Exploration Sat., Space Research

MeanMinMax

Fig. 18. Radio location/Earth Expl. Sat./Radio Astronomy 1350-1427.

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VIBA VNPT1470.5 MHz

Fig. 19. Fixed 1427-1525 MHz.

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1540 1560 1580 1600 1620 1640 1660 1680 1700

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Mobile Satellite

Maritime Mobile Satellite (Space to Earth)

Maritime Mobile Satellite (Earth to Space)

Fig. 20. Mobile Satellite 1525-1660,5 MHz.

1750 1800 1850 1900 1950 2000−80

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IMT2000

GSM1800 (BT)

Vina Mobile Vietel GTelVina Mobile Vietel GTel

GSM1800 (BR)

Fig. 21. Radio Astronomy/Space Research/Meteological Aids/Mobile/Fixed 1710-2300 MHz.

2300 2400 2500 2600 2700 2800 2900 3000

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ISM, Radio Location, Maritime Radionavigation,Aeronautical Radionavigation, Meteorological Aids.

Frequency [MHz]

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Fig. 22. Fixed/Mobile/Aeronatical navigation/Radiolocation 2300-3000 MHz.

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0 10 20 30 40 50 60Fixed/Mobile/Aeronatical navigation/Radiolocation 2300−3100 MHz

GSM/Fixed 1710−2300MHzRadio Astronomy/Space Research/Meteological Aids/Fixed 1660,5−1710 MHz

Mobile Satellite 1525−1660,5 MHzFixed 1427−1525 MHz

Radio location/Earth Expl. Sat./Radio Astronomy 1350−1427 MHzAeronautical Radionavigation 960−1350 MHz

Land Mobile/Fixed 824−960 MHzFixed/Land mobile 806−824 MHz

Broadcasting (TV channels 14 to 20)/Fixed 470−806 MHzFixed/Radiolocation/Land Mobile 406,1−470 MHz

Fixed/Radionavigation Sat./Meteorological Aids 230−406,1 MHzBroadcasting (TV channels 7 to 13) 174−230 MHz

Fixed/Mobile 146−174 MHzAmateur/Amateur Satellite 144−146 MHz

Mob. Sat. (S−E)/Fixed/Mobile 137−144 MHzAeronautical Mobile (R) 117,975−137 MHz

Aeronautical Radionavigation 108−117,975 MHzBroadcasting (FM radio) 87−108 MHz

Aeronautical Radionavigation/Analog TV 68−87 MHzBroadcasting (FM radio) 54−68 MHz

Amateur 30−54 MHz

Fig. 23. Average spectrum occupancy by band Ho Chi Minh City.

0 10 20 30 40 50 60 70 802900−3000 MHz2686−2900 MHz2500−2686 MHz2390−2500 MHz2360−2390 MHz2300−2360 MHz2200−2300 MHz2110−2200 MHz1990−2110 MHz1850−1990 MHz1710 1850 MHz

1525−1710 MHz1400−1525 MHz1300−1400 MHz1240−1300 MHz960−1240 MHz

928−906 MHz902−928 MHz806−902 MHz698−806 MHz608−698 MHz512−608 MHz470−512 MHz406−470 MHz225−406 MHz216−225 MHz174−216 MHz138−174 MHz108−138 MHz

54−88 MHz30−54 MHz

Ho Chi Minh CityLong AnNew York

Fig. 24. Average spectrum occupancy by band Ho Chi Minh City vs. Long An vs. New York.

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