802.18 Study Group 1 Unlicensed Reuse of Broadcast TV Channels

1. 802.18 Study Group 1Unlicensed Reuse of Broadcast TV Channels John Notor, Cadence Design Systems, Inc.

2. Introduction Overview of the Opportunity Approaches to TV Channel Reuse Identifying Incumbent Users Service Profiles Air Interface Options Four Protocols for Spectrum Etiquette Cognitive vs Non-Cognitive Radios Wrap Up Outline John Notor, Cadence Design Systems, Inc.

3. On December 20, 2002, the Federal Communications Commission (FCC) released a Notice of Inquiry (NOI)1 regarding "...the feasibility of allowing unlicensed devices to operate in TV broadcast spectrum at locations and times when spectrum is not being used...". The FCC’s NOI on TV band reuse envisions: New opportunities for more commercial utilization of existing spectrum. The right mix of radio technologies to avoid interfering with incumbent users (i.e., TV broadcasters). Without attempting to predict the outcome of the FCC proceedings, this presentation explores the architectural issues related to exploiting unused TV spectrum from a radio design perspective. Introduction 1. “Notice of Inquiry: Additional Spectrum for Unlicensed Devices Below 900 MHz and in the 3 GHz Band”, ET Docket No. 02-380, December 11, 2002 John Notor, Cadence Design Systems, Inc.

4. According to the FCC NOI: “During and after the digital television transition, there will be a number of TV channels in a given geographic area not being used … because such stations will not be able to operate without causing interference to co-channel or adjacent channel stations.” Unused TV channels in any geographic area could be reused by unlicensed systems under an appropriate (TBD) regulatory regime. A central feature of the reuse strategy is the protection of incumbent users from interference by unlicensed devices. Overview of the Opportunity John Notor, Cadence Design Systems, Inc.

5. The current Digital TV (DTV) plan: Only channels 2-51 will be available for DTV broadcasts after the transition to digital. All analog TV broadcasts will be shut down. Spectrum for channels 52-69 will be reallocated to other uses: Channels 52-67 (700 MHz band: 698-794 MHz) are currently being auctioned off for other services: Lower 700 MHz auction (Ch 52-59: 698-746 MHz) complete except blocks A, B, & E, which are currently not scheduled. Upper 700 MHz auction (Ch 60-67: 746-794 MHz) currently not scheduled. Scheduled DTV roll-out to be complete by the end of 2006. Overview of the Opportunity (con) John Notor, Cadence Design Systems, Inc.

6. The Basic principles of reuse: Select a channel unoccupied by an incumbent to establish the network. Minimize impact to other unlicensed networks using the same channel by Keeping aggregate network transmit power low to avoid interference with other nearby networks. Implementing a burst mode transmission scheme to allow other networks access to the channel. Mitigate interference from other unlicensed networks occupying the same channel by using spectrum spreading, error correction, and data retransmission signaling schemes. The Ideal Solution: a “cognitive radio” system, i.e., a radio system with the ability to adapt to it’s communications environment automatically. Approaches To TV Channel Reuse John Notor, Cadence Design Systems, Inc.

7. Accurate identification of incumbent users in a given geographic area is the key to interference management and channel reuse. Some approaches to creating a database of unused or infrequently used channels: Geolocation: use GPS or some other location technology along with a pre-programmed database. Autonomous detection: scan all channels, identify any incumbent users based on signal characteristics, and create a database automatically. Preprogram network devices: manual or operator-initiated broadcast programming of each device to create the database. A fully cognitive radio system would implement autonomous detection as the most adaptive approach. In some situations, geolocation or preprogramming may be cheaper. Identifying Incumbent Users John Notor, Cadence Design Systems, Inc.

8. The TV Channel Bandwidth is now and will continue to be 6 MHz. 6 MHz will support a wide variety of unlicensed communications services: Narrowband symmetrical voice and/or data access (Example: 240 narrowband channels at 25 kHz channel spacing) Broadband symmetrical data access (1–30 Mbps), supporting broadband networking, local teleconferencing, Voice Over IP, and similar Internet-style applications. Short range proprietary video services including security monitoring, campus educational services, and other similar applications. Low to medium rate burst mode telemetry services which take advantage of transient channel availability. The FCC might allow radio systems to aggregate two or more unassigned TV channels to support higher data rates for video distribution, shared multi-media experiences (games, group training in simulated environments, etc.). Service Profiles John Notor, Cadence Design Systems, Inc.

9. Multiple access air interface choices for TV Channel reuse are constrained by the likely operating environment: Competing Players: uncoordinated heterogeneous systems sharing the same channelized spectrum: telemetry, narrowband voice, broadband data, etc. The usual multiple access suspects – TDMA, FDMA, CDMA – require disciplined, highly coordinated sharing protocols within a common network structure – not a fit for an unlicensed scenario. Air Interface Options John Notor, Cadence Design Systems, Inc.

10. A “Listen-Before-Talk” communications etiquette using a burst mode transmission scheme works best for uncoordinated networks. No requirement for disciplined timing across heterogeneous networks. Uses RSSI2 or other techniques to determine if a channel is quiet, i.e., available for use. Includes some kind of receive acknowledgement mechanism to identify data corruption due to collisions between network signals. Depends on random backoff/retry mechanisms to minimize the probability of a collision when retransmitting data. Air Interface Options (con) 2. RSSI: Received Signal Strength Indicator, a mechanism for determining the signal level at the receiver input. John Notor, Cadence Design Systems, Inc.

11. Network Frequency Allocation (NFA, aka “DFS”): Survey and monitor spectrum use patterns. Avoid incumbents, operate the network on an unused or lightly used channel. Link Power Control (LPC, aka “TPC”): Keep network transmitter power low while maintaining good link quality. LPC mitigates interference and promotes frequency reuse with networks located nearby. Incumbent Profile Detection (IPD, historically subsumed under DFS): Detect incumbent users based on specific spectrum signature (supports NFA) Example: detecting the presence of a sound carrier in NTSC (analog TV) systems or a pilot tone in ATSC (DTV) systems. Four Protocols for Spectrum Etiquette John Notor, Cadence Design Systems, Inc.

12. Collision Detection And Avoidance (CDAA, aka “CCA”): Transmitters wait until the channel is quiet before transmitting (“listen before talk”). A receiving node acknowledges valid data by transmitting a response. A transmitting node “detects” a collision if it does not receive an acknowledgement for a data transmission. The protocol implements an appropriate backoff/retry timing mechanism for retransmission when a collision is detected. Note: These protocols resemble those presently adopted or proposed for IEEE 802.11x wireless networks (“DFS”, “TPC”, “CCA”), but are generalized here to avoid confusion with the specifics of pre-existing implementations. Four Protocols for Spectrum Etiquette (con) John Notor, Cadence Design Systems, Inc.

13. A fully cognitive network should have the ability to do the following: Tune to any TV channel in the band (up to 50 channels after the DTV changeover). Establish links and operate in all or part of a 6 MHz channel. Implement NFA, LPC, IPD, and CDAA protocols. Implement adaptive transmission bandwidths, data rates, and error correction schemes to obtain the best throughput possible. Implement adaptive antenna steering to focus transmitter power in the direction required and optimize received signal strength. For data network applications where reliability and throughput are overriding system values, the fully cognitive approach is the best. Cognitive vs. Non-Cognitive Radios John Notor, Cadence Design Systems, Inc.

14. The simplest non-cognitive approach to TV channel reuse requires the ability to do the following: Operate on one or more unoccupied channels selected by the system operator during network deployment. Implement IPD and CDAA protocols. Operate with low transmit power by design. Use a simple antenna system. For applications like telemetry, or applications fielded in remote areas with little chance of interference, the non-cognitive approach makes the most economic sense. Cognitive vs. Non-Cognitive Radios (con) John Notor, Cadence Design Systems, Inc.

15. This presentation identifies radio network strategies and protocols which support frequency reuse of TV spectrum by unlicensed devices as suggested by the FCC’s NOI. These same strategies and protocols are generally applicable to any sharing environment where licensed and unlicensed radio systems interoperate on a non-interfering basis. Fully cognitive unlicensed radio systems support high data rate, moderately high throughput networks in densely occupied spectrum environments. In rural areas, and other low density spectrum environments, simple, low cost, non-cognitive radios can reuse fallow spectrum effectively. Wrap Up John Notor, Cadence Design Systems, Inc.