Adaptrum and Microsoft NAB Show Demonstration

Adaptrum and Microsoft NAB Show Demonstration

1. Overview Adaptrum and Microsoft demonstrated a complete TV whitespace system at the NAB Show April 11 th April 14 th in Las Vegas. The demonstration attracted significant interests from industry participants. The demonstration was conducted under Microsoft STA 0140-EX-ST- 2011. Microsoft coordinated with the local SBE and the TV channels allowed for the demonstration included 31, 33, 34, 36, 38 and 39. Only channels 34 and 39 were actually used in the demonstration. Internet Microsoft Research TVWS Database Zune Video Marketplace on XBOX Live TV Whitesapce Link Ethernet Control PC Adaptrum TVBD Basestation Splitter Adaptrum TVBD Client Control PC XBOX 360 Display Spectrum Analyzer Figure 1: Adaptrum and Microsoft NAB Show TV whitesapce demonstration system. The demonstration system, comprised of an Adaptrum TVBD base station, an Adaptrum TVBD client station and a prototype whitespace database software developed by Microsoft Research, is illustrated in Figure 1. The base station and the client station form a whitespace system where the base station is connected directly to the Internet and acts as an access gateway for the client station. An XBOX 360 with a TV display is connected to the Internet through the client station. Once online, the XBOX allows a user to browse and stream live HD videos from the Zune Video Marketplace on XBOX Live. To monitor output signal spectrum during operation, a spectrum analyzer is connected to the output of the client station through a 2-way splitter whose other output is connected to the client antenna. 2. System Description Adaptrum TVBD system The Adaptrum TVBD system employs innovative TDD OFDMA technology with tunable carrier frequency between 400 and 1000 MHz and flexible channel bandwidth up to 10 MHz. In the NAB demonstration, the transmit signal uses 5.65 MHz out of the 6 MHz available

channel bandwidth achieving a channel utilization efficiency of 94 percent and an aggregated data rate up to 11 Mbps while meeting the current FCC TVBD emission mask requirement. 1 In addition, the Adaptrum TVBD system is built upon a fully flexible OFDM SDR platform supporting programmable FFT size, OFDM cyclic prefix size, and modulation mode, as well as variable downlink and uplink frame sizes on a frame-by-frame basis. Both the base station and the client station are capable of delivering maximum conducted output power of 1 W. In the demonstration, both the base station output and the client station output were attenuated by 15 db so there was more than 30 db total attenuation in the signal path between the stations, noting the additional 3 db loss due to the 2-way splitter. In other words, the equivalent transmit signal power seen at the receiving station considering the total path attenuation was less than 1 mw. Both the base station and the client station were connected to PCB Bowtie antennas that have close to 0 dbi antenna gains. Microsoft Research TVWS Database The complete TVBD system demonstration also included a prototype whitespace database software developed by Microsoft Research. 2 The Microsoft Research whitespace database software has an advanced core computation engine (WS Engine) combined with an ASP.NET based web service frontend. Using the TV towers and other TV band transmitters information obtained from the FCC CDBS and ULS databases together with registered wireless microphones information maintained locally in the Microsoft database, the software computes a list of available TV whitespace channels at any geographic location based on a specified propagation model and terrain elevation data obtained from NASA. Currently, several advanced propagation models are supported including Longley Rice, Egli and Okumura-Hata. In a recent filing with the FCC, Microsoft stated interest in becoming an official TVBD database administrator and plans to incorporate the propagation model adopted in the current TVBD rules in its production database. 3 To interact with the computation engine, the software defines a set of web service API calls for device and database related operations. 4 For example, the API call GetSpectrumMap is used to retrieve the list of available TV whitespace channels at a specified geographic location. 3. Demonstration Description In the NAB demonstration, referring to Figure 1, the Adaptrum TVBD base station was connected to the Internet and constantly communicating with the Microsoft whitespace database. 1 See 47 C.F.R. 15.709 (c). 2 More information about the software is available at http://whitespaces.msresearch.us. 3 See ex parte filing by Microsoft on April 18, 2011, available at http://fjallfoss.fcc.gov/ecfs/document/view?id=7021239289. 4 See web service API definitions at http://whitespaces.msresearch.us/wsweb/driver.asmx.

The base station software polled the database every 40 seconds using the channel list query GetSpectrumMap to get the updated whitespace channels at the demonstration location. The base station used in the demonstration can be classified as a Mode II TVBD 5 considering its low output power level. When the base station receives the returned channel list from the database after the query, it selects one of the channels for its normal radio operation. During the normal radio operation, the base station will constantly broadcast a sync signal on the operating channel, which can be considered as the contact verification signal (CVS) as specified in the rules. 6 The client station used in the demonstration can be classified as a Mode I TVBD. 7 At startup, the client station is in the search mode when it actively scans all TV channels looking for the sync signal or CVS. Once the client station detects the CVS on a TV channel, it will send a connection request to the base station on the same channel. Under the rules, once the base station receives the connection request, it must contact the database to verify the FCC ID of the client station and retrieve a channel list on behalf of the client. 8 This step, however, was skipped in the demonstration assuming both stations have valid FCC IDs and the same returned channel list. The base station immediately accepts the connection request from the client station. The connection between the base station and the client station has been established and the client enters the normal operation mode. During the normal operation mode, the client station is constantly tracking the CVS from the base station. If the CVS is not received within a 20-second period, the client station will re-enter into the search mode when it scans all TV channels looking for the CVS. 9 To reduce the search time, the base station periodically advertises a set of candidate channels a subset of the channels in the channel list received from the database. The client station will search the advertised candidate channels first upon losing contact with the base station. The XBOX was connected to the Internet through the whitespace system when the base and client stations were in the normal operation modes. Rate adaptation was enabled so the system monitors the link quality between the stations and adaptively changes the modulation mode to maximize the data throughput. Throughout the demonstration, the aggregated data throughput of the whitespace system was maintained at the maximum achievable rate of 11.1 Mbps with approximately 8.8 Mbps downlink and 2.3 Mbps uplink, allowing the XBOX to stream live HD movies from the Zune Video Marketplace on XBOX Live. Approximately 3.6 GB of data were transferred through the whitespace system each hour and approximately 144 GB over the 4 day demonstration period. 5 See 47 C.F.R. 15.703 (f). 6 See 47 C.F.R. 15.703 (b). 7 See 47 C.F.R. 15.703 (e). 8 See 47 C.F.R. 15.711 (b) (3) (iv). 9 47 C.F.R. 15.711 (b) (3) (iv) requires Mode I TVBD to receive the contact verification signal from a fixed or Mode II TVBD at least once every 60 seconds.

As part of the demonstration, we emulated the scenario of a forced channel switching when the whitespace system was forced to vacate its current operating channel and move to another channel. In the demonstration, the whitespace system was originally operating on Channel 34 when a faked wireless microphone registration on Channel 34 was entered into the database. In the next channel list query (40 seconds apart from the last one), the base station discovered that Channel 34 was no longer in the returned channel list and immediately ceased operation on Channel 34 and began operation on Channel 39 the next available channel in the channel list. After about 20 seconds, the client station discovered it had lost the CVS on Channel 34. The client station then switched to Channel 39 which was the next candidate channel in the last advertisement from the base station. The CVS was detected on Channel 39 and the client station resumed normal operation. We noticed that channel switching didn t cause any noticeable disruption in the video streaming likely because of the deep play-out buffer used by the XBOX streaming software. 4. Demonstration Pictures Figure 2: Client side setup. The XBOX is connected to the Adaptrum TVBD client station and streaming HD movies from the Zune Video Marketplace on XBOX Live.

Figure 3: Screen shot of HD 1080p video streaming.

Figure 4: Microsoft Research TVWS database GUI. Figure 5: Adaptrum TVBD link status monitor.