IEEE P802.22Wireless RANs
The IEEE 802 would like to acknowledge FCC’ s leadership for proposing the use of new and novel technologies such as Dynamic Spectrum Access (DSA), spectrum sensing, geolocation & database and beacons for spectrum sharing and enhanced usage of the spectrum for licensed and un-licensed use.
In response to the FCC Notice of Inquiry (FCC NoI 10-198), here is some information and suggestions that we would like to make:
Clause 18: Information on the Current State of the Art in Dynamic Spectrum Access Radios
Question: What is the current state of equipment, system development?
Response:
IEEE 802 has no knowledge of any commercially available Dynamic Spectrum Access (DSA) equipment. However, over the last five years IEEE 802 has gained tremendous amount of knowledge on the technologies that are necessary to successfully develop standards for efficient usage of the spectrum using new technologies such as DSA, spectrum sensing, access to a database, beaconing, etc.
For example, the IEEE 802.22 standard project (www.ieee802.org/22) has developed a PHY / MAC air interface to provide cognitive radio (CR) and DSA based broadband wireless access in the TV White spaces. This project has been concurrent with the FCC’ s proceeding on un-licensed operation in the TV Whitespaces and the resulting proposed standard has optimized robustness and spectrum utilization in line with the requirements identified in the FCC proceeding.
The IEEE 802.22 membership comprises the entire ecosystem of interested parties such as TV broadcasters, service providers, chip manufacturers, device manufacturers, Department of Defence contractors, Govt. and non-Govt., academic institutions and universities. The 802.22 member organizations not only bring state of the art research to convert these technologies into products but also the knowledge on how to successfully develop and deploy these systems.
The IEEE 802.22 project on cognitive radio based Wireless Regional Area Networks (WRANs) has three projects under its umbrella.
1. The IEEE 802.22.1-2010 standard on enhanced protection of low power licensed devices using a beacon technology was completed and published in Nov. 2010.
2. The IEEE 802.22 standard, specifying the broadband wireless air-interface, is on-track to be completed in the 2011 time-frame.
3. The IEEE 802.22.2 standard for recommended practice for deployment of 802.22 systems is being developed in parallel.
For more information on the Overview of the IEEE 802.22 Standard, please refer to our website at www.ieee802.org/22 (under the Core Technologies)
Question: What approaches have developers taken with respect to mitigating hidden nodes where shadowing may make it appear that the spectrum is unoccupied when in fact it is being used nearby? Which methods have met with the most success? What solutions are available for dynamic radio operations in the vicinity of (primarily) receive-only sites?
Response:
The IEEE 802.22 standards project has recognized the challenge posed by the hidden node issues (e. g., protecting wireless microphones in the TV bands). Spectrum sensing is more suitable than database registration to protect wireless microphone usage due to the dynamic and unpredictable nature of on-location news and emergency reporting. However, because of the fade margin allowed in the operation of the microphones, the detection range of the low-power signals is unacceptably shorter than the potential range of interference from a 4 W EIRP White Space Device (WSD). The IEEE 802.22 standards project has accounted for this difficulty by publishing the IEEE 802.22.1-2010 standard for enhanced protection of low-power devices. IEEE 802.22.1 specifies a beaconing system that indicates the presence in a channel of protected wireless microphones in an area. The IEEE 802.22 protocol detects and reacts to the IEEE 802.22.1 beacon. IEEE 802.22 uses a combination of cognitive techniques (e.g. spectrum sensing, database service and beacons) to protect the primary users and to avoid the hidden node issues.
Clause 21: Spectrum Sensing Technologies:
Questions: What innovations to sensing are contemplated? Has there been any industry wide consensus regarding methods of implementing sensing? Have there been studies regarding which sensing methods work best among using matched filters, simple energy detection, or cyclostationary detection or other techniques? Are there ways to generalize sensing requirements, or do they need to be determined band-by-band based on the incumbent services? Advocates for band by band requirements should also address methods for updating sensing algorithms based on usage changes over time. How has filter technology advanced such that false positive detections due to adjacent channel signals can be minimized? Can a common standard for spectrum sensing be developed? What would need to be included in such a standard? How should the detection threshold for spectrum sensing be determined? How can dynamic spectrum access radios avoid adjacent channel interference to incumbent systems? Upon detection, should a minimum frequency offset be established to avoid adjacent channel interference? What factors impact detection time and how do they vary for different incumbent radio services (e.g., land mobile systems versus radar systems)?
Response:
IEEE 802.22 investigated a variety of spectrum sensing techniques such as cyclostationary approaches, higher order statistics, covariance based approaches, matched filter, energy detection etc. to detect and recognize the signals of interest. The proposed standard has created a dedicated Annex that describes these techniques and provides detailed quantitative performance comparisons for various techniques using over-the-air captured signals that were provided to the various participants. The IEEE 802.22 standard specification accommodates the use of spectrum sensing for deployment of the WRAN systems. In fact the IEEE 802.22 standard specification recommends signal type determination/ characterization in addition to the basic signal detection for security reasons in order to ensure protection against cognitive attacks such as primary user emulation and spoofing.
In general we believe that no one technique is sufficient to accurately detect and characterize the signals with reasonable computational complexity and for all types of signals. For example, cyclostationary and higher order statistics based approaches are suitable to detect and characterize a wide variety of signals at low Signal to Noise Ratios (SNR) however they suffer from relatively high computational complexity. In cases where signals are above the noise floor, simple techniques such as energy detection and interference detection (Clause 23 – correlation in the rise of the noise floor) may be used. IEEE 802.22 had to investigate techniques that would allow detection of signals some 20 dB below the noise floor. As a result, the use of a combination of techniques such as energy (interference) detection, Receiver Signal Strength Indication (RSSI) monitoring as well as more complex feature based techniques as described above may be needed to detect and determine the signal types.
We continue to believe that spectrum sensing will play a very important role in DSA systems.
Member companies of the IEEE 802.22 are working with Government agencies such as DARPA to continue the advancements in spectrum sensing technologies.
Clause 29: Policy Radios
Questions: How should policies be developed for these dynamic radios? Who should be responsible for developing these policies? Should the policies be incorporated as part of individual service rules? What is the appropriate hierarchy among the Federal Government, industry, and users of policy radios? If policies are developed by non-governmental entities, should the Commission or other appropriate agencies have the option to review or modify policies before they become effective? What factors should be considered in developing dynamic radio policies? How often should policies be reviewed for possible modification? How do we ensure that dynamic policies are distributed to all devices in a timely manner? What procedures can be used to ensure the distributed polices are implemented properly?
Response: IEEE 802.22 has devoted a significant effort into the issues of enforcing the policies in Cognitive Radios. While developing the policies for the radios, the Working Group considered aspects such as how to ensure policy enforcement and security, minor differences in policies proposed by various regulatory domains, etc. Although other generic formats of defining these policies may be available, IEEE 802.22 currently uses rule-based policies specific to the bands in which these system are likely to operate. The policy frame-work has been made generic enough to allow its operation in various regulatory domains. The policies are driven by certain regulatory dependent parameters (e.g. Channel Move Time, Database Refresh Time, etc.) which are pre-configured by the manufacturer before coming on the market to ensure appropriate operation in the given regulatory domain. An integrated cognitive engine called the “Spectrum Manager” has been defined that is responsible for enforcing the policies of the given regulatory domain. In addition the Spectrum Manager is also responsible for accessing, processing and executing other cognitive inputs and functions such as database service, sensing etc.
Clause 38: Secondary Market Mechanisms - Time, Frequency and Spatial Approach for Interference Management and Spectrum Sharing
IEEE 802 supports FCC’ s position that effective spectrum sharing and interference management may require the use of all the dimensions that may be available and that are best suited for effective re-use of the band (e.g., frequency, time, space, sub-space, etc.).
Clause 48: Real-time Database Service:
Question: We seek comment on whether such an approach (use of real time database service) would also work in fixed microwave bands. How might such an approach be instituted in these bands? Should the Commission consider promoting such an approach, and if so, how? Are there other candidate bands? How would a real-time database be maintained so that it contains up-to-date information? Similarly, we seek comment on whether and how such an approach would work in highly mobile bands.
Response:
Although the real-time database service approach is suitable for the TV bands, IEEE 802 recommends the following considerations:
a. Access model of the TV bands database needs to be defined, developed and fully tested before extending this model to other services.
b. Push technologies such as those used for synchronous audio and video conferencing as well as instant messaging have been successfully developed and are widely used today. Push technology needs to be considered for DSA systems where the spectrum usage patterns are likely to change more rapidly. Push technology will also reduce the amount of internet traffic, since the database service provider can selectively send messages to the interested parties in case changes to transmit characteristics (e. g. frequency, power etc.) of the devices are needed rather than the devices continuously querying the database.
c. Security aspects and database access – Entities that are present on the internet are susceptible to various kinds of Denial of Service (DoS), cyber attacks and information assurance issues. The level of effort required to stage such attacks are low and the risk of system failure is very high. Another issue of manual entry database is that of trust. Adequate considerations need to be made to establish a secure connection between the DSA device and the database service. Security aspects such as authorization to access, authentication, identification, data integrity, non-repudiation, confidentiality and privacy need to be considered.
Clause 50: Real-time Spectrum Monitoring
Questions: Generally, we seek comment on whether such a system of monitoring equipment could be deployed at a reasonable cost. Should such a network be administered by the U.S. Government or the private sector? If the private sector, how should the collected information be disseminated? For example, should a fee be charged? Could a low-cost sensor be developed to effectively detect the presence of weak radio signals? How would a system of sensors perform in urban areas or in areas where there is irregular terrain?
Response:
The development of a country-wide network of distributed sensors that monitors the spectrum and reports any unauthorized signals to the FCC official database for further investigation could be beneficial to complement other techniques of interference avoidance such as use of database and beacons. It may also help to act as a sentry on the ground to corroborate the information that has been provided to the database service. This will further help to make the proposed DSA network more robust. For a example, IEEE 802.22 has incorporated distributed sensing features into the standard to complement the interference avoidance techniques and enhance security.
Concluding Remarks:
IEEE 802 appreciates this opportunity to provide information on our standards projects related to dynamic spectrum use. As these standards are deployed and implementation experience is gained, we will continue to apprise the Commission of our progress.
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