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  1. 1. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® TOPICS IN RADIO COMMUNICATIONS Deployment and Coverage of Cognitive Radio Networks in TV White Space Kyu-Min Kang, Jae Cheol Park, Sang-In Cho, and Byung Jang Jeong, Electronics and Telecommunications Research Institute Young-Jin Kim, Hyoung-Jin Lim, and Gi-Hong Im, Pohang University of Science and Technology ABSTRACT ongoing [5]. Many countries also have regulatory requirements for both fixed and This article presents experimental and simu- personal/portable TV band devices (TVBDs) to lation results for the use of TV band devices operate in the TVWS without a license. (TVBDs) in TV white space, considering the When wireless networks are deployed in the presence of interference by incumbent services. attractive TVWS, incumbent services, especially Digital TV (DTV) services are major incumbent digital TV (DTV), should preferentially be pro- services currently operating in the TV bands. tected in a specified service area. Each country With DTV service, co-channel and adjacent has its own service contour for DTV stations to channel deployment scenarios of TVBD net- protect DTV service from interference. Some works are introduced. To safely protect the countries employ a DTV protected contour incumbent service, a minimum separation dis- based on the field strength level of a DTV tance from the DTV protected contour, which is received signal, whereas others allow DTV ser- called the keep-out distance, is required. We vice depending on the local administrative area. estimate the keep-out distance for different A TVBD operating on co-channel (N) or adja- ranges of TVBD transmit antenna height by cent channels (N±1) must be located outside using several propagation models and measure- the DTV protected contour with an additional ments of ultra-high-frequency signals in Korea. separation called a keep-out distance to safely We also investigate the hidden node problem for protect DTV services from interference by the spectrum sensing operation mode of TVBDs. TVBDs. Exceptionally, a personal/portable According to the results of these measurements, TVBD operating on channels (N±1) adjacent to the hidden node margin should be at least 38 dB an active DTV channel N may be allowed to in order to protect DTV service. Finally, the ser- operate within the protected contour if its vice coverage reduction of TVBD networks transmit power level is sufficiently low not to caused by neighboring DTV service is discussed. cause harmful interference to the DTV service It is shown that the service coverage of a wire- at its position. less local area network system decreases about Within the regulatory requirements, a TVBD 50 percent by co-channel interference from can be operated on available channels in TVWS neighboring DTV service when the field strength at its current location. When the TVBD tries to of the DTV received signal is 41 dBu. acquire information on the available channels, three different approaches (i.e., geo-location INTRODUCTION and database access, spectrum sensing, and beacon approaches) are generally considered. Cognitive radio (CR) technology is greatly val- Most countries allowing the operation of ued as a method of enhancing the current low TVBDs presently aim for TVWS recognition usage of limited frequency resources [1–4]. TV using the geo-location and database access white space (TVWS) is perceived as the most mechanism. In addition, the spectrum sensing suitable frequency bands for CR, although the mechanism will be widely used in the near technology is conceptually workable in any fre- future. In the spectrum sensing mode, the quency band. TVWS refers to the TV bands at a TVBD regards a TV band as an available chan- particular time in a particular geographic area nel at its current location via the threshold- that are not being used by licensed services. The based hypothesis test of licensed signals [4]. Federal Communications Commission (FCC) Ofcom has recently raised a hidden node prob- suggested opening TVWS for unlicensed opera- lem in TV bands to determine the reasonable tion and released a notice of proposed rulemak- spectrum sensing threshold level of a DTV sig- ing (NPRM) in May 2004. Standardization nal [6]. On the basis of various measurements activities such as IEEE 802.22, 802.11af, and analyses of DTV signals in the UK, Ofcom 802.15.4m, and 802.19.1 aimed at employing recommended a hidden node margin of 35 dB unlicensed practical applications in TVWS are in the UK. We also conduct a measurement 88 0163-6804/12/$25.00 © 2012 IEEE IEEE Communications Magazine • December 2012C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
  2. 2. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® campaign regarding the hidden node attenua- INCUMBENT SERVICES IN TV BANDS tion of DTV signals to determine the hidden To effectively solve node margin in Korea. There are several types of TV stations, such as the coexistence The FCC opened up vacant TV airwaves to full-service analog/digital TV stations, Class A enable mobile wireless devices such as “super TV, lower power TV, TV translators, and TV problem among the Wi-Fi” technologies to utilize the attractive very booster stations. TV services must be protect- family of IEEE 802 high frequency (VHF)/ultra high frequency ed from harmful interference within specified (UHF) bands, which have good propagation contours that depend on the type of TV sta- wireless standards, characteristics. Accordingly, the service cover- tion and the operating frequency band. In the IEEE 802.19.1 age of a wireless local area network (WLAN) addition, many incumbent services exist in the TG is currently system can theoretically increase about 10 times TV bands: TV translator receive sites, cable compared to existing coverage assuming the TV headends, multichannel video program dis- developing methods free-space path loss when the 500 MHz TV tributors, radio astronomy services, and low- of coexistence bands are used for WLAN signal transmission power auxiliary stations, including wireless instead of the 5 GHz frequency bands. Howev- microphones. Digital multimedia broadcasting among dissimilar or er, TVBD service coverage may be somewhat (DMB) services in the TV bands are now in independently reduced because TVBD networks are affected operation in some countries. For example, the operated TVBD by interference from DTV signals. In this arti- commercial terrestrial DMB service of Korea, cle, we deal with the service coverage reduction with a frequency bandwidth of 1.536 MHz on networks and caused by interference from a neighboring DTV the high VHF TV channels (7–13), was dissimilar TVBDs. service. launched in 2005. The community access TV (CATV) service should also be considered as an incumbent service in the TV bands because IEEE STANDARDIZATION CATV systems typically utilize spectrum below 1 GHz (VHF/UHF bands). Hence, direct pick- ACTIVITIES ON TVWS up interference may occur when a TVBD After the FCC suggested the operation of unli- transmit antenna is placed near a cable-con- censed TVBDs in vacant TV bands, IEEE 802.22 nected TV. Above all, DTV service is the most first developed a standard for wireless regional important incumbent service, especially after area network (WRAN) systems using CR tech- the digital switchover. In this article, we focus nology [5]. The 802.22 WRAN systems can pro- on DTV service among various incumbent ser- vide broadband wireless access to regional, rural, vices in the TV bands. and remote areas without causing harmful inter- ference to incumbent services. This standard specifies both the physical layer (PHY) and TVBD DEPLOYMENT medium access control layer (MAC) functionali- ties of point-to-multipoint WRANs operating in SCENARIOS IN TVWS the VHF/UHF bands between 54 MHz and Figure 1 shows both co-channel and adjacent 862 MHz. The 802.22 WRAN adopts a simple, channel deployment scenarios between DTV optimized orthogonal frequency-division multi- services and TVBDs. TVBDs must protect ple access (OFDMA) waveform and meets all DTV services within the well-known DTV the regulatory requirements such as protection noise-limited contour (grade B contour) or of incumbent services, database access, and administrative contour; the service contour is transmit spectrum mask. The IEEE 802.11af specified by the regulatory body of each coun- task group (TG) is also developing a standard try [6, 7]. Thus, TVBDs that intend to operate for WLAN operation in TVWS, which modifies on the same frequency band should be located both the 802.11 PHY and MAC to meet the outside the contour by at least the keep-out dis- legal requirements for channel access and coex- tance to guarantee DTV reception within the istence in TVWS. The 802.15 working group has DTV protected contour. Even if TVBDs oper- researched TVWS service models and wireless ate on channels (Npm1) adjacent to an active personal area network (WPAN) applications DTV channel (N), they must also maintain the operating in TVWS. The 802.15 TG 4m is cur- keep-out distance or reduce their transmit rently modifying the existing 802.15.4 PHY and power level to prevent adjacent channel inter- MAC specifications to realize power-efficient ference. In the adjacent channel, the FCC for- device command and control applications on bids a low-power operation mode for fixed TVWS between 54 MHz and 862 MHz. TVBDs [7]. When multiple systems are intended to use the TVWS, a coexistence problem occurs in CO-CHANNEL DEPLOYMENT SCENARIOS the use of the available frequency band owing In co-channel deployment scenarios, TVBD net- to differences in radio access methods between works should be located outside the DTV pro- the different systems. Frequency sharing in tected contour by the keep-out distance to TVWS should be performed by utilizing the protect DTV services from TVBD interference. available TV band without interfering with To obtain the keep-out distance, we consider the incumbent services. To effectively solve the desired-to-undesired signal (D/U) ratio for co- coexistence problem among the family of channel TVBD interference to DTV service. IEEE 802 wireless standards, the IEEE Although the required D/U ratios for co-channel 802.19.1 TG is currently developing methods interference to DTV services vary depending on of coexistence among dissimilar or indepen- the interferers (other DTV stations and/or dently operated TVBD networks and dissimi- TVBDs), the difference is less than 0.5 dB. It is lar TVBDs. reasonable to set the D/U ratio to 15.5 dB at IEEE Communications Magazine • December 2012 89C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
  3. 3. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® To operate on the Personal/portable TVBD (100 mW) Channel (N) Channel Channel adjacent channels, (N±1) (N) TVBDs must maintain ce istan the keep-out dis- -out d Keep tance from the DTV Protected protected contour as contour Channel (N±1) in the co-channel TV station Fixed TVBD (4W) deployment case. To Channel (N) determine the keep- Keep -out d out distance for istan ce adjacent channel Channel (N) deployment, the same off-axis Ch. (N±1) antenna discrimina- Ch. (N) tion factor as in the Ch. (N) Ch. (N±1) Ch. (N±1) Ch. (N±1) co-channel case is employed. Personal/portable TVBD (40 mW) Figure 1. Deployment scenarios of co-channel and adjacent channel TV band devices in TV white space. locations where the signal-to-interference-plus- ADJACENT CHANNEL DEPLOYMENT SCENARIOS noise ratio (SINR) is 28 dB or greater. The co- To operate on the adjacent channels, TVBDs channel D/U ratio should be 23 dB around the must maintain the keep-out distance from the edge of the DTV noise-limited contour, where DTV protected contour as in the co-channel the SINR is 16 dB or less [8]. The field strength deployment case. To determine the keep-out dis- of TVBD signals measured at a DTV receiver tance for adjacent channel deployment, the same varies depending on the antenna direction off-axis antenna discrimination factor as in the and/or polarization of both the TVBD transmit- co-channel case is employed. The recommended ter and the DTV receiver. Thus, we should also D/U ratio for adjacent channel protection is consider this antenna discrimination between –33 dB [8]. Additionally, the FCC has allowed the TVBD transmitter and the DTV receiver in personal/portable TVBDs to operate on adjacent determining the keep-out distance [8]. For channels within the DTV protected contour only example, in co-channel use of 4W fixed TVBDs if their maximum conducted output power does in 802.22 WRAN systems, the main lobes of the not exceed 40 mW (Fig. 1). In this case, the off- directional DTV receive antenna and the direc- axis antenna discrimination between the DTV tional customer premise equipment (CPE) receive antenna and the TVBD transmit antenna transmit antenna are assumed to be looking in would no longer be available. Note that, for opposite directions because the CPE is located operation in an adjacent channel within the outside the DTV contour. An off-axis antenna DTV protected contour, the nominal minimum discrimination of 28 dB is exploited in the fixed separation distance between the DTV receive CPE deployment scenario. On the other hand, antenna and the TVBD transmit antenna is in the fixed base station (BS) scenario, 14 dB assumed to be 10-20 m [7, 8]. off-axis antenna discrimination is taken into account in determining the keep-out distance because the DTV receive antenna main lobe is HOW TO looking away from the omni-directional BS transmit antenna. For 100 mW PROTECT DIGITAL TV SERVICE personal/portable TVBDs, because the DTV To guarantee the protection of the incumbent receive antenna main lobe is looking away from DTV services, a TVBD should be located out- the omni-directional CPE or the BS transmit side the DTV protected contour by the keep-out antenna, only 14 dB off-axis antenna discrimina- distance. This distance depends mainly on the tion is considered [8]. The keep-out distance maximum allowable equivalent isotropically radi- should be determined using the required D/U ated power (EIRP), the operation mode (fixed ratio, antenna discrimination associated with the or personal/portable mode), and the transmit deployment scenario of TVBDs and DTV antenna height of the TVBDs. The transmit receivers, and transmit power level of the power of TVBDs deployed within the protected TVBDs in order to protect DTV reception from contour on adjacent channels should be suffi- co-channel TVBD interference. Co-channel ciently reduced not to cause harmful interfer- operation is allowed when the TVBD networks ence to the incumbent DTV service. A TVBD maintain at least this separation distance from using the spectrum sensing mode identifies avail- the DTV protected contour. able channels via the threshold-based hypothesis 90 IEEE Communications Magazine • December 2012C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
  4. 4. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® test of incumbent signals [4]. If the sensing threshold is improperly chosen, the TVBD may Okumura, open, large city misjudge an occupied TV band as an available Okumura, Quasi open, medium city Okumura, Quasi open, large city channel and thus cause severe interference to 50 Okumura, suburban, medium city the incumbent service. Therefore, the geographi- Okumura, suburban, large city Okumura, urban, medium city cal characteristics, local shape of each area, and Okumura, urban, large city radio propagation environments of each country ITU-R 1546-4 40 FCC should be considered when determining the Keep-out distance (km) Measured in Korea spectrum sensing threshold level of incumbent services. 30 DTV PROTECTED CONTOUR A DTV station’s service coverage depends on the DTV transmission effective radiated power 20 (ERP), transmit antenna height above average terrain (HAAT), operating frequency band, and so on. When an Advanced Television Systems 10 Committee (ATSC) DTV system operates on channel 38 (614–620 MHz) with a transmit antenna HAAT of 500 m and a 1000 kW ERP, 0 the service coverage is expected to be about 0 20 40 60 80 100 120 135 km, as estimated by the International TVBD transmitting antenna HAAT (m) Telecommunication Union Radiocommunication Sector (ITU-R) P.1546-4 propagation model [9]. Figure 2. Comparison of co-channel keep-out distances of fixed TVBDs from In the US and Canada, DTV service is available the DTV contour for different ranges of TVBD transmitting antenna HAAT in the area within the grade B contour, where estimated using the Okumura propagation model, FCC F(50,10) propagation the field strength values are 28 dBu (low VHF), curve, ITU-R P.1546-4 propagation model, and propagation measurement of 36 dBu (high VHF), and 41 - 20log[615/channel UHF signals in Korea. mid-frequency in MHz] dBu (UHF) [8]. Howev- er, in other countries, such as Korea, where TV broadcasting services are based on local TV net- required D/U ratio for co-channel protection at works, a DTV service is allowed within a prede- the contour is 23 dB. The antenna discrimina- termined local administrative area instead of an tion between the DTV receive and the TVBD area defined by the field strength level of the transmit antennas is 14 dB. As shown in the fig- DTV received signal. Thus, the field strength of ure, the estimated keep-out distances calculated a DTV signal operating on the UHF TV broad- with the FCC propagation curve are similar to cast band would be much larger than 60 dBu in the results using the ITU-R P.1546-4 propaga- some fringe areas of the administrative contour tion model. In addition, the estimated keep-out in Korea, whereas the field strength can be less distances based on the measurements in Korea than 41 dBu in other areas of the administrative have many similarities with the results for the contour. In this case, it is desirable to carefully “quasi-open, large city” case in the Okumura determine interference protection requirements propagation model. Note that the FCC recently based on both the administrative contour and revised the keep-out distances between fixed the noise-limited contour (grade B contour) TVBDs and the DTV protected contour of co- because the DTV service available area is quite channel and adjacent channel TV stations for different from the permissible area. antenna HAAT values ranging from less than 3 m to a maximum of 250 m [7]. KEEP-OUT DISTANCE Figure 2 compares the co-channel keep-out dis- HIDDEN NODE MARGIN tances of 4 W fixed TVBDs from the DTV con- Currently, most countries opening up the TVWS tour for different ranges of TVBD transmitting have an initial plan to detect available TV chan- antenna HAAT estimated using the Okumura nels by the geo-location and database access propagation model, FCC F(50,10) propagation mechanism. In the near future, a TVBD is curve, ITU-R P.1546-4 propagation model, and expected to obtain information on the available propagation measurement of UHF signals in TV channels from a TV band database in areas Korea [8, 10]. The Okumura model is one of the where it can access the database. In other areas, most popular macroscopic propagation models the TVBD can obtain available TV channels by based on measurements in and around Tokyo the spectrum sensing mechanism. In the spec- [10]. This model was designed for use in the fre- trum sensing mode, the TVBD may miss to quency range between 150 MHz and 1920 MHz detect DTV signals because of surrounding and mostly in urban areas. For various propaga- buildings or barriers even though DTV service is tion environments, the correction factors by area active in the area. When the TVBD uses the types, such as suburban, quasi-open, and open, DTV frequency band, regarding it as an avail- are also included in the model. F(50,10) means able TV channel according to wrong sensing that the field strength is obtained by the FCC result, it may cause severe interference to the propagation curve at 50 percent of the potential DTV service. To address this problem, a hidden receiver locations for at least 10 percent of the node margin should be considered when deter- time. In the estimation of co-channel keep-out mining the DTV sensing threshold level. distances, we assume that the field strength We investigated the hidden node margin (channel 38) of the DTV contour is 41 dBu. The required to efficiently utilize TVBD networks in IEEE Communications Magazine • December 2012 91C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
  5. 5. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® the TVWS and also to protect DTV service in 100 Korea. To determine the hidden node margin, 90 each country should consider its own geographi- cal characteristics, the local shape of each area, 80 and the radio propagation environment. First, we classified the radio propagation environment 70 into urban, basin, and coastal areas on the basis Percentile (percent) 60 of the geographical characteristics. We also con- sidered eight local shapes: commercial buildings, 50 apartments, residential and commercial build- 40 ings, villas, housing, parks, quasi-open fields, and Commercial building industrial complexes. We then measured and 30 Apartment analyzed hidden node attenuation for each local Residential and commercial building Villa shape in each classified geographic area. Figure 20 Housing 3 shows the hidden node attenuation of DTV Park 10 Quasi-open field signals for the eight local shapes in Korea. Industrial complex Because commercial buildings or apartments in 0 0 5 10 15 20 25 30 35 40 large cities in Korea are located in close proxim- Hidden node attenuation (dB) ity to each other, the hidden node margin should be at least 38 dB in order to safely protect DTV Figure 3. Hidden node attenuation of DTV signals in Korea; measurements service. This result is 3 dB higher than the 35 dB were conducted for eight local shapes in each classified geographic area hidden node margin in the UK suggested by (urban, basin, and coastal areas) in Korea. Ofcom [6]. TVBD SERVICE COVERAGE CHANGE Interference (I) DUE TO NEIGHBORING DTV SERVICE Undesired signal (U) Desired As discussed earlier, DTV service can be provid- signal Data ed without harmful interference from TVBD (D) signal networks when the TVBD networks are (S) deployed outside the DTV protected contour by DTV station DTV user MS BS more than the keep-out distance. However, it is not guaranteed that the TVBD networks are Protected Keep-out distance Coverage properly operated in this deployment scenario. contour for portable TVBD Thus, we investigated the service coverage change in a TVBD network considering interfer- Keep-out distance for fixed TVBD ence from neighboring DTV stations. Noise (N) Figure 4 illustrates the simulation model for estimating the service coverage of an 802.11- D/U SINR ratio [S/(I+N)] TGaf-based TVBD network. We consider the worst-case coverage scenario in which the high- Figure 4. Simulation methodology for estimating the worst-case TVBD service est interfering power from a DTV station can be coverage. measured at a personal/portable TVBD mobile station (MS). The simulation parameters are summarized in Table 1. In Korea, because the protected contour of DTV service is determined 2 by the local administrative area, the received In the absence of DTV interference PDTV RX = -94 dBm power of an incumbent DTV service at the pro- 1.8 PDTV RX = -84 dBm (grade B) tected contour may not meet the exact grade B PDTV RX = -74 dBm 1.6 PDTV RX = -64 dBm level (e.g. 41 dBu). Thus, we consider different levels of the received power of DTV signals, P DTV RX , near that of the grade B in order to TVBD service coverage (km) 1.4 consider the various protected contours, i.e. 1.2 P DTV RX [dBm] Œ {–94, –84, –74, –64}. From P DTV RX, we obtained the protected contour of 1 the DTV service by using the ITU-R P.1546-4 propagation model at 50 percent of the locations 0.8 for 90 percent of the time in the simulation [9]. 0.6 To evaluate the keep-out distance for a fixed TVBD BS, the Okumura propagation model for 0.4 a quasi-open area and a large city in Fig. 2 was used. Considering the keep-out distance, the 0.2 location of the TVBD BS can be determined as in Fig. 4. The transmit powers of the fixed 0 0 20 40 60 80 100 TVBD, portable TVBD, and DTV station are Height of TVBD BS antenna (m) 100 mW, 100 mW, and 2.5 kW, respectively. In this scenario, we assume that the transmit power Figure 5. Service coverage of a TVBD network for different ranges of TVBD level of the fixed TVBD BS is 100 mW instead BS transmitting antenna height with various protected contours. of 4 W EIRP to avoid downlink-uplink coverage 92 IEEE Communications Magazine • December 2012C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
  6. 6. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® imbalance with the personal/portable TVBD MS DTV Parameter Value of 100 mW. The transmit antenna height of the DTV station is 500 m. When the service cover- age of a TVBD network is calculated, the ITU-R Center frequency of DTV Tx 617 MHz (Ch. 38) P.1411-4 propagation model assuming the lower bound in a line-of-sight environment [11] is used Field strength at grade B contour 41 dBu (–84 dBm) to estimate the received signal power. The rea- son is that an 802.11 TGaf system is expected to D/U ratio at noise-limited contour 23 dB cover the short range as a micro cell outdoors. The path loss of the interfering signal from the DTV Rx antenna discrimination 14 dB DTV station to the TVBD MS is calculated using the ITU-R P.1546-4 model [9] at 50 per- DTV ERP 2.5 kW cent of the locations for 10 percent of the time. Then, we can obtain a SINR of the TVBD MS Height of DTV Tx antenna 500 m located dBS–MS. The packet error ratio of 802.11 systems must be 10 percent or less when the Height of DTV Rx antenna 10 m physical layer service data unit length is 1000 octets. We assume that the SINR required to TVBD Parameter Value support the lowest level of the modulation and coding set for 802.11-TGaf-based systems (e.g. Channel spacing of TVBD 4 MHz binary phase shift keying and 1/2 code-rate) is 4 dB, with a receiver noise figure of 10 dB and TVBD BS EIRP 100 mW an implementation margin of 5 dB [12]. Thus, when the received SINR of the TVBD MS at TVBD MS EIRP 100 mW the position of the MS with a separation of dBS–MS from the BS meets the target value, the Height of TVBD BS antenna 3, 10, 20, 30, …, 90, 100 m service coverage of a TVBD network can be esti- mated as the distance between the BS and the Height of TVBD MS antenna 1.5 m MS. Figure 5 shows the estimated service cover- Thermal noise (for 4 MHz bandwidth) –108 dBm age of a TVBD network for different ranges of the TVBD BS transmitting antenna height with Receiver noise figure 10 dB various protected contours. The result of PDTV RX = –84 dBm corresponds to TVBD ser- vice coverage with the grade B level of the Noise power [N] –98 dBm DTVprotected contour. The service coverage with the grade B contour is about 500 m when Target SINR for coverage estimation 4 dB the transmit antenna height of the TVBD BS is Table 1. Simulation parameters. 30 m. Note that the calculated DTV protected contour becomes shorter as the received power of the DTV signal at the contour increases. The TVBD has the longest coverage when the TVBD networks. The coverage of TVBD net- received power is –94 dBm because the interfer- works was estimated considering the interfer- ence power is lowest then. When the transmit ence from a neighboring DTV service. antenna height of the TVBD BS is 50 m, the coverage with P DTV RX = –94 dBm is almost 1 km and has a gap of about 400 m compared to ACKNOWLEDGEMENT that without DTV interference. From the simu- This research was supported by the KCC (Korea lation results, we conclude that the service cov- Communications Commission), Korea, under the erage of a TVBD network has various ranges R&D program supervised by the KCA (Korea when the field strength of the DTV protected Communications Agency) (KCA-2012-09911- contour is fixed not at the exact grade B level 01105). This research was also supported by but at various levels according to local adminis- Basic Science Research Program through the trative contours. National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2012-0005457). CONCLUSIONS In this article, we presented co-channel and REFERENCES adjacent channel deployment scenarios of [1] S. Haykin, “Cognitive Radio: Brain-empowered Wireless TVBDs or TVBD networks in the TVWS. Communications,” IEEE JSAC, vol. 23, no. 2, Feb. 2005, TVBDs should be operated outside the DTV pp. 201–20. protected contour by at least the keep-out dis- [2] T. W. Yune et al., “SC-FDMA with Iterative Multiuser tance to guarantee DTV service. We calculated Detection: Improvements on Power/Spectral Efficiency,” IEEE Commun. Mag., vol. 48, no. 3, Mar. 2010, pp. co-channel keep-out distances from the DTV 164–71. contour for various ranges of TVBD transmit [3] D. Y. Seol, T. W. Yune, and G. H. Im, “Primary Network antenna height by using several propagation Cognition with Spatial Diversity Signature,” IEEE Com- models and measurements of UHF signals in mun. Lett., vol. 13, no. 5, May 2009, pp. 321–23. [4] H. J. Lim, D. Y. Seol, and G. H. Im, “Joint Sensing Adap- Korea. 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  7. 7. C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® [5] K. G. Shin et al., “Cognitive Radios for Dynamic Spec- include cognitive radio and cooperative networks, mobile trum Access: from Concept to Reality,” IEEE Wireless communications, and MIMO systems. From the simulation Commun., vol. 60, no. 4 Dec. 2010, pp. 64–74. [6] Ofcom, “Digital Dividend: Cognitive Access, Statement SANG-IN CHO received the B.S., and M.S. degrees in infor- results, we conclude on License-Exempting Cognitive Devices using Inter- mation and telecommunication engineering from Chonbuk that the service leaved Spectrum,” Statement, July 2009. National University, Korea, in 1997, and 1999, respectively. [7] FCC, “Third Memorandum Opinion and Order, In the Since 1999, he has been with Electronics and Telecommu- coverage of a TVBD Matter of Unlicensed Operation in the TV Broadcast nications Research Institute (ETRI), Daejeon, Korea. His cur- Bands, Additional Spectrum for Unlicensed Devices rent research interests include spectrum engineering, VLSI network has various Below 900 MHz and in the 3 GHz Band,” ET Docket digital signal processing and digital communications. No. 12-036, Apr. 2012. ranges when the [8] G. L. StÅNuber, S. M. Almalfouh, and D. Sale, “Interfer- BYUNG JANG JEONG received his B.S. degree from Kyungpook field strength of the ence Analysis of TV-Band Whitespace,” Proc. IEEE, vol. National University, Daegu, Korea, in 1988, and his M.Sc. 97, no. 4, pp. 741–54, Apr. 2009. and Ph.D. degrees in electrical engineering from Korea DTV protected [9] ITU-R Recommendation P.1546-4, “Method for Point-to- Advanced Institute of Science and Technology (KAIST) in Area Predictions for Terrestrial Services in the Frequency 1992 and 1997, respectively. He was with Samsung contour is fixed not Range 30 MHz to 3000 MHz,” Tech. Rep., the ITU Advanced Institute of Technology (SAIT) from 1994 to Radiocommunication Assembly, 2009. 2003. Since 2003, he has been with Electronics and at the exact grade B [10] Y. Okumura et al., “Field Strength and Its Variability in Telecommunications Research Institute (ETRI) as a principal level but at various VHF and UHF Land-Mobile Radio Service,” Review of member of research staff. His research interests include sig- the Electrical Comm. Laboratory, vol. 16, no. 9–10, nal processing for wireless communications, MIMO sys- levels according to Sept.–Oct. 1968, pp. 825–73. tems, and cognitive radio networks [11] ITU-R Recommendation P.1411-4, “Propagation Data local administrative and Prediction Methods for the Planning of Short- HYOUNG-JIN LIM received the B.S. degree in electronic and Range Outdoor Radiocommunication Systems and electrical engineering from Pohang University of Science contours. Radio Local Area Networks in the Frequency Range 300 and Technology (POSTECH), Kyungbuk, Korea, in 2006. He MHz to 100 GHz,” Tech. Rep., the ITU radiocommuni- is currently working toward the Ph.D. degree at Communi- cation assembly, 2007. cations Research Laboratory, POSTECH. His current research [12] IEEE Draft P.802.11-REVmb/D9.0, “IEEE Standard for interests are radio resource management, dynamic spec- Information Technology, Telecommunications and trum access, and cognitive radio networks. Information Exchange between Systems, Local and Metropolitan Area Networks, Specific Requirement Part G I -H ONG I M [M’87, SM’94] (igh@postech.ac.kr) was with __________ 11: Wireless LAN MAC and PHY Specifications,” May AT&T Bell Laboratories, Holmdel, NJ, where he was respon- 2011. sible for the design and implementation of high-speed dig- ital transmission systems for loop plant, local area network, BIOGRAPHIES and broadband access applications (1990–1996). He has authored or co-authored more than twenty standards con- KYU-MIN KANG received the B.S., M.S., and Ph.D. degrees in tributions to standards organizations such as ANSI T1E1.4, electronic and electrical engineering from Pohang Universi- ETSI, IEEE 802.9, ANSI X3T9.5, and the ATM Forum. These ty of Science and Technology (POSTECH), Kyungbuk, Korea, contributions have led to the adoption of three AT&T pro- in 1997, 1999, and 2003, respectively. Since 2003, he has posals for new standards for high-speed LANs and broad- been with Electronics and Telecommunications Research band access. In 1995, he was appointed as Distinguished Institute (ETRI), Daejeon, Korea. His current research inter- Member of Technical Staff at AT&T Bell Laboratories. Since ests include cognitive radio networks, spectrum engineer- 1996, he has been with POSTECH as a professor. From ing, digital signal processing, and high-speed digital 1996 to 2000, he was a Bell Laboratories Technical Consul- transmission systems. tant. From 2002 to 2003, he was a visiting vice president of Samsung Electronics, where he worked on 4G wireless Y OUNG -J IN K IM received the B.S. degree in electronic and communication systems. His current research interests electrical engineering from Pohang University of Science include signal processing and digital communications with and Technology (POSTECH), Kyungbuk, Korea, in 2007. He applications to high-speed digital transmission systems. He is currently working toward the Ph.D. degree at Communi- received the 1996 Leonard G. Abraham Prize Paper Award cations Research Laboratory, POSTECH. His current research from the IEEE Communications Society for the paper enti- interests are MIMO systems, spectrum sharing, and cogni- tled “Bandwidth-efficient digital transmission over unshield- tive radio networks. ed twisted pair wiring,” published in the IEEE Journal on Selected Areas in Communications, the 2000 LG Award JAE CHEOL PARK received the B.S. degree in electronics engi- from LG Electronics, and the 2005 National Scientist Award neering and the M.S.E. degree in electronics and radio from the Korean government. From 2004 to 2010, he engineering from the Kyung Hee University, Yongin, Korea, served as an editor for the IEEE Transactions on Communi- in 2009 and 2011, respectively. He is currently a member cations and an associate editor for IEEE Communications of engineering staff at the Radio Technology Research Letters. Currently, he is serving as a division editor for the Department, Electronics and Telecommunications Research Journal of Communications and Networks. He has 24 U.S. Institute (ETRI), Daejeon, Korea. His research interests patents granted or pending. 94 IEEE Communications Magazine • December 2012C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®

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