Understanding TV White Spaces

Transcription

1 Understanding TV White Spaces

2 On December 6, 2010, the Federal Communications Commission finalized the rules and regulations that will allow the unused spectrum in the TV bands to be available for unlicensed broadband devices. This unused spectrum is commonly referred to as the TV white spaces was opened up in June, 2009 when TV broadcast stations transitioned from analog to digital television. According to the FCC, access to this spectrum could enable more powerful public internet connections super Wi-Fi hot spots with extended range, fewer dead spots. This particular spectrum has excellent propagation characteristics that allow signals to reach further and penetrate walls and other structures and is ideally suited for outdoor and long distance networking. The Commission s actions are expected to spur investment and innovation in applications and devices. The rules governing the use of unlicensed devices in TV white spaces will officially go into effect January 15, Initial interest in this new unlicensed spectrum by technology companies such as Google, Intel, Microsoft and Motorola is geared towards developing a sort of Wi-Fi on steroids, for enhanced broadband access and rural ISP service (White-Fi), other unlicensed, low powered devices can also take advantage of this spectrum to promote new services, applications and products. This could include wireless control and sensors, public safety equipment, smart grid applications, and M2M applications. Compared to 2.4 GHz Wi-Fi, white spaces devices can expect to provide a 4x range improvement with the same transmit power and receiver sensitivity. White Spaces Wi-Fi (2.4 GHz) Wi-Fi (5.8 GHz) Spectrum Availability 282 MHz 80 MHz 240 MHz Max. Channel Bandwidth 6 MHz 20 MHz 20 MHz # of Non-Overlapping Channels Low High Low Congestion/Interference 4X 1X ¼X Building Penetration 4X 1X ¼X Building Penetration Excellent Poor Poor World Wide Acceptance No Yes Yes Operation Location Dependent Yes No No Design Complexity High Low Medium FCC Part 15 TV Band Device Compliance Requirements Overview Television Band Devices (s) Television band devices, called s will be authorized to operate on available channels in the broadcast television band at MHz (TV channel 2), MHz (TV channels 5-6), MHz (TV channels 7 13), MHz (TV channels 14 36) and MHz (TV channels 38 51). Unlike many of the other unlicensed bands these new s can only utilize those portions of the spectrum not being used by other incumbent devices such as broadcast television, wireless microphones and private land mobile radios. The technical rules outlined by the FCC in 47CFR Part 15, Subpart H Television Band Devices addresses these issues by making distinctions between fixed and portable devices, specifying channels of operation, limiting the transmitter power levels and prescribing the methods needed for identifying unoccupied spectrum. A must determine television channel availability either from geo-location where devices are required to communicate their coordinates to a centralized database set up to track occupied TV channels or via spectrum sensing where devices are required to assess the channel for incumbent devices prior to transmission. The FCC classifies s as either fixed or personal/portable devices. Fixed devices are intended to operate at a fixed location like an outdoor access point while personal/portable devices can operate in unspecified or mobile locations that may change, similar to a cell phone or laptop. Fixed Devices Fixed devices can initiate a network by sending enabling signals to one or more fixed and/or personal/portable s. Fixed devices can utilize all TV band frequencies but may not operate above 512 MHz (above TV channel 20) if those available channels are adjacent to occupied TV channels. Fixed s can utilize an external antenna up to 30 meters above the ground and are allowed a higher transmitter power of 1 watt or up to 4 watts EIRP with a 6 dbi gain antenna. These devices are not allowed to be located at a site where the ground height above the average terrain (HAAT) exceeds 76 meters, so use in hilly areas may be restricted. Personal/Portable Devices Personal/portable device transmissions are restricted to available channels in the frequency bands MHz (TV channels 21-36) and MHz (TV channels 38-51). These devices are limited to a maximum EIRP of 100 mw (20 dbm) or 40 mw (16 dbm) if the device is operating on a channel adjacent to an occupied TV channel. Personal/portable s are further differentiated into Mode I and Mode II devices. Mode I Personal/Portable Devices A Mode I device is not required to use geo-location or have access to the TV bands database. Instead, it obtains a list of available channels from either a fixed or Mode II personal/portable device. A Mode I device may not initiate a network nor may it provide a list of available channels to another device.

3 Mode II Personal/Portable Devices A Mode II device uses internal geo-location capability and access to the TV bands database, either through a direct connection to the internet or through an indirect connection by way of a fixed or another Mode II. A Mode II device may select a channel itself and initiate and operate as part of a network of s, transmitting to and receiving from one or more fixed or personal/ portable TVDBs. It may provide a list of available channels to a Mode I device. In other words, a network can only be initiated by a fixed or Mode II TVDB not a Mode I. General Technical Requirements All s will need to incorporate transmit power control to limit their operating power to the minimum necessary for successful communication. The maximum conducted output power is the total transmit power over the occupied bandwidth. If multiple antennas are used, the power must be summed across all antennas. All TVDB devices must incorporate the capability to display a list of identified available channels and its operating channels. The power spectral density shall not be greater than the following values when measured during any time interval of continuous transmission: Fixed devices: 12.2 dbm Personal/portable devices when operating adjacent to occupied TV channels: -1.8 dbm Sensing-only devices: -1.8 dbm All other personal/portable devices: 2.2 dbm Each 6 MHz television channel, which is not being used by an authorized service at or near the same geographic location as the is acceptable for use by an unlicensed device. Utilizing OFDM, data rates up to 10 Mbps could be achieved. The above PSD limits indicate that in order to utilize the maximum allowed transmitter power, the full 6 MHz channel would need to be occupied by the modulated spectrum - so wideband modulation is implied. The PSD limits would also restrict subdividing the channel to allow multiple narrow band devices to share the spectrum. Interference Avoidance Methods Channel availability for a is determined based upon geolocation and database access but spectrum sensing can also be used. Geo-location For fixed and Mode II devices, geographic coordinates need to be determined to an accuracy of +/- 50 meters by utilizing incorporated geo-location capability. Fixed devices that are professionally installed do not need geo-location capability if the coordinates are provided at the time of installation. All devices must register their coordinates with the database and must re-establish their position each time it is activated from a power-off condition. Fixed devices shall access and update their database at least once every day and personal/portable device must check its location at least once every 60 seconds. Operation on a channel must cease immediately if the database indicates the channel is no longer available. Mode II personal/portable devices also must re-check its position if it changes location during operation by more than 100 meters. A Mode II device can also establish a bounded area in which a channel is available at all locations within the area and operate on a mobile basis within that area. Database Access Fixed devices are intended to access the database from the Internet but those fixed devices that do not have a direct Internet connection can access the database from another fixed device within the network. A Mode I personal/portable may only transmit upon receiving a list of available channels from a fixed or Mode II that has contacted a database and verified that the FCC identifier (FCC ID) of the Mode I device is valid. Interference Protection Requirements for Incumbent Services Incumbent services are to be protected from interference by s. These include digital and analog TV services within the propagation curve contours provided by the FCC in Part The required separation from the protected contour can range from 6 to 14.4 km, depending upon antenna height. Fixed s are not permitted to operate within 1km, and personal/portable s will not be permitted to operate within 400 meters, of registered low power auxiliary stations, including wireless microphones, during the designated times that they are in use. Other constraints may apply to operation near the border areas of Canada and Mexico as well as radio astronomy observatory sites. TV Bands Database Information A TV bands database maintains records for all authorized services that operate in the TV bands. The data base contains the following information for all television stations and other broadcast devices: including transmitter coordinates, effective radiated power (EIRP), antenna height above terrain (HAAT), antenna pattern, beam tilt, channel number and call sign. A TV bands database administrator may charge a fee for the provision of lists of available channels and for registering fixed s. The FCC will designate one of more entities to administer the database(s). The database provider must establish protocols, procedures and security for all s and provide service for a five-year term. Spectrum Sensing Spectrum sensing can be used in lieu of geo-location and database access but devices must submit an application for certification and demonstrate with a high degree of confidence that they will not cause harmful interference to incumbent radio services. Applicants must submit a pre-production device to the FCC and a full explanation of how the device will protect other users. The application will be placed on public notice and the Commission will conduct laboratory and field tests to evaluate proof of performance. s that meet the spectrum sensing requirements for personal/ portable devices are limited to a maximum EIRP of 50 mw and do not have to comply with the geo-location and database access requirements. All fixed and personal/ portable s must be capable of detecting ATSC digital TV, NTSC analog TV and wireless microphone signals using analog or digital modulation methods. The required detection thresholds are:

4 ATSC digital TV signals: -114 dbm, averaged over a 6 MHz bandwidth NTSC analog TV signals: -114 dbm, averaged over a 100 khz bandwidth Low power auxiliary & wireless microphone signals: -107 dbm, averaged over a 200 khz bandwidth. A spectrum sensing may start operating on a TV channel if no TV, wireless microphone or other low power auxiliary device signals above the detected threshold are detected within a minimum time of 30 seconds. A must perform in-service monitoring of an operating channel at least once every 60 seconds. After a TV, wireless microphone or other low power auxiliary device signal is detected, transmissions by the must cease within two seconds. Regulatory Approval Requirements for s s must be certified by the FCC. Telecommunication Certification Bodies (TCBs) will not be permitted to certify s until the FCC has more experience with them and can properly advise the TCBs on how to apply the applicable rules. White Space Solutions With the rules governing the use of unlicensed devices in TV white spaces officially going into effect January 15, 2011, solutions for white spaces devices are expected to be available in late 2011 and early TV Database Administration Companies including Google, Comsearch, Frequency Finder, KB Enterprises, Neustar, Spectrum Bridge, Telecordia and White Spaces DB have all filed with the FCC to provide databases but the FCC has yet to select a provider. Spectrum Mapping Tools The following general planning tools can be used determine where available spectrum is located throughout the US. Spectrum Bridge - an online interactive TV white spaces map and available channel calculator and a free showmywhitespace app for iphone and Android. aspx Broadband-Mapping.com - a Google Earth mapping tool that can be used to determine the availability of TV white spaces spectrum. Test Sites Currently, trial installations of white spaces devices involving Google, Spectrum Bridge, Dell and Microsoft are in operation including a broadband Smart City project in Wilmington, N.C., and a SmartGrid application in Plumas-Sierra County. Standards Based Applications The IEEE standards association has officially chartered an af task group to determine the modifications to both the physical layers (PHY) and Medium Access Control Layer (MAC) needed to meet the legal requirements for channel access and coexistence in the TV white space. White Spaces Technical Challenges and Limitations Spectrum Availability In major metro areas, the available spectrum may be very limited; often just one or two 6 MHz channels and in many instances restricted to 40 mw personal/portable devices only. This severely limits the use of the white space spectrum for consumer applications like home networking or wireless video distribution. Although the unused channels vary in each local market, much of the spectrum will only be available in sparsely populated rural areas where there are fewer TV broadcasters and it is highly unlikely that any company could use the spectrum to build a nationwide network. Location Fixed (1 watt) Portable (100 mw) Portable (40 mw) Chicago Boston New York Los Angeles North Dakota Source: database from Spectrum Bridge Indoor Applications Geo-location also implies that a GPS receiver is incorporated into the fixed or Mode II personal/portable device. Since GPS does not work indoors this could be pretty problematic for commercial use of white spaces where an internet connection is not always available and an external GPS antenna impractical. Transmission Range While common Wi-Fi ranges are typically less than 100 meters and require line-of-sight operation, white spaces devices can reach as far as several miles depending upon terrain and antenna height, are less impacted by weather and more easily penetrate obstacles such as buildings. If s are constrained to 40 mw due to limited spectrum availability, the transmission range performance will be even less. One area where s may have a distinct advantage is in propagation through heavy masonry such as concrete or cinder block buildings commonly found in schools and industrial applications Coexistence and Robustness In large metro areas, limited channel availability may result in poor radio link robustness, especially if other TVDB devices are in use. Despite the efforts to protect incumbent devices, the FCC has no process in place to coordinate operation or mitigate interference amongst multiple users. In addition, because incumbent devices are given a higher priority for spectrum use, s would always be subject to secondary use requirements as they must cease transmission if a channel is in use by protected device. Will White Spaces Succeed or Will It Become Another WiMax? First, technology companies need to prove that with proper engineering, they can develop solutions that meet the interference

5 avoidance requirements and still provide cost effective solutions. Second, like many other new technologies, what is initially touted as a platform for a variety of applications will eventually settle down to providing a solid technical solution for a very specific niche market like rural broadband. Reference: 47 CFR Parts 0 and 15, Unlicensed Operation in the TV Broadcast Bands; Final Rule, December 6,