A Guidebook for Mitigating Disruptive WiFi Interference at Airports (2015)

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76 A P P E N D I X B Within an airport terminal environment, all wireless airport and passenger communica- tions systems must operate harmoniously with “tolerable” interference, albeit some func- tions serviced by wireless fidelity (WiFi) may need better protection against interference (for example, baggage check-in and aircraft routing ticketing, security checks, and other defined airport critical operations). The expected growth of the WiFi environment and other com- mercial communications at airport terminals is likely to produce an increase in interference- related reports, but not all may be sufficiently severe to be noticed or to warrant a complaint. For those interference complaints made, interference mitigation should be accomplished in the best interest of all concerned to restore interference-free operations needed for airport ter- minal and passenger communications. Best practices to ensure accessible WiFi service focus on establishing a reporting system, a cooperative analysis process between all concerned to determine the root cause of the interference source, and a cooperative process to mitigate interference that considers the responsibilities and perspectives of the airport authority as well as the users. Airport WiFi Environment The researchers focused on best practices to prevent, detect, and resolve WiFi interfer- ence issues within the terminal; however, there may be some interference from or to external sources. The largest impact is related to the operation and security of the airport, but passen- ger WiFi usage is also a concern. The following is a list of areas where WiFi is used inside the airport, as well as a few areas exterior to the airport. The list is not exhaustive. • WiFi in the 2.4 GHz band provides operationally critical services to airports both inside the terminal (e.g., security check and other terminal functions) and possibly on the tarmac. • Baggage tag scanning can be accomplished both within the terminal at the passenger check-in line and often in outdoor apron areas of airports. • Kiosks or check of boarding passes at gates. • Vendor wireless credit card payments. • Future demands may include WiFi access for commercial vendors and passengers (i.e., to access food menus and place orders via the WiFi system), to order supplies, con- duct inventory, and maintain sales records. • Passenger use in departure lounges and other areas of airports to conduct business or con- nect to the Internet for pleasure. Best Technical Practices to Ensure Accessible WiFi Service

Best Technical Practices to Ensure Accessible WiFi Service 77 Airport Organizational Approach to Managing the WiFi Environment Research to date indicates there is a large diversity in the ways the WiFi environment is man- aged. WiFi was not included in the initial design of the airport environment as part of the airport infrastructure or guidelines to connect and distribute communications. The WiFi unlicensed technology opened the possibility to economically do business without expensive cable instal- lations. As a consequence, many airports and businesses took advantage of this opportunity and took individual steps to install their own WiFi systems without any overarching airport guidance. Airports have their own unique WiFi networks using unique equipment and network designs, with the main implications for network management as follows: • Airports in the planning stage or airports being modernized may present the only possibil- ity of establishing an optimized WiFi network architecture based on managing interference. Optimizing existing airport WiFi networks may be addressed when the system requires updat- ing or when resources permit. • WiFi networks will change over time with advances in technology along with the introduction of new devices using the same spectrum. • Benefits and potential interference issues will change created by growth or congestion within the unlicensed 2.4 GHz band and eventually this may occur in the 5 GHz band as well. Approach Taken to Identifying Best Practices Airport architectural structures and sizes differ widely. Spectrum measurements conducted by traveling study team members within the U.S. present unique environments for each airport from a radio propagation point of view. The best practices to prevent, identify, and resolve WiFi interference issues were formulated using: 1. Research on the Internet for airport WiFi interference-related information for the U.S. and abroad. 2. Network design systems and tools to map the WiFi radio frequency (RF) in the airport environment. 3. Network management systems that attempted to identify symptoms of interference and resolutions. 4. Commercial tools that could assist in identifying and confirming interference sources. 5. Past national and international experience of professionals who worked in identifying and resolving interference for the Department of Defense and other government entities at the federal, state, and local levels. 6. Synergistic analyses that leveraged past experience for interference mitigation to formulate the best practices. The framework used to organize the best practices includes a generalized grouping method- ology and formulation approach based on separating the functional areas. The notional break- down included: • Passengers using WiFi for business and entertainment will mostly be in gate areas, food courts, and business lounges. Anticipate heaviest passenger-related use of WiFi use here. • Check-in and baggage handling will be near the entrance. • Commercial businesses (newsstands, vending machines, miscellaneous sales and services) will likely be in wings of most airports somewhat separated from flight waiting areas. Wireless credit card services will be common to most of these areas.

78 A Guidebook for Mitigating Disruptive WiFi Interference at Airports • Security, maintenance personnel, and handicap transport will be present throughout the air- port, with expected light to moderate WiFi use. Best Technical Practices Best technical practices to ensure accessible WiFi service are summarized below, reflecting the accompanying spreadsheet and list of references. 1. Identify airport user groups based on airport areas or primary user functions to sup- port baselining WiFi installations and prioritizing response. Schedule periodic spectrum/ performance measurements to compare with baseline and assist with interference investiga- tion using spectrum analyzer tools. a. Develop candidate grouping of WiFi services. b. Individual airports can prioritize the WiFi electromagnetic interference impact thresh- olds for each group (decibel measures that can be compared with planning/periodic “tool” output map or spectrum analyzer tools). c. Execute measurements applicable to the airport areas based on prioritization. 2. On smaller airports, grouping may not be an option because all WiFi uses may be on various systems in the same floor space. In this case, a priority response based on type of service, security, baggage, etc., may be a better choice. 3. Analyze collected data to identify when a particular WiFi hotspot is frequently nearing its “usage” saturation point during its prime operational period. This can be an indication that it is time to upgrade the device or all devices in a grouping before interference becomes a problem. 4. Identify the IEEE 802.xx specification of the equipment in place and plan for an upgrade to the 802.11 or other newer specification device for better throughput/spectral efficiency. This step can be executed at signs of WiFi equipment operating frequently near the satura- tion point. 5. Perform periodic upgrades to existing WiFi equipment as they become available and afford- able. This replaces aged equipment and supports increased growth requirements. 6. Acquire one or two inexpensive commercial spectrum analyzer tools and use to identify, isolate, and confirm interference. For groupings that could possibly be affected by interfer- ence external to the airport (e.g., curbside baggage check-in), repeat the measurement near the check-in point. 7. Establish a database and map showing current WiFi installations within the airport, associ- ated equipment information, and primary users. Airports may want to consider granting access to all individual airport databases through the creation of a centralized database pos- sibly sponsored by the ACRP in order to leverage previous airport interference experiences and resolutions. a. Include all WiFi hotspots and information on all WiFi equipment. b. List all reported incidences of interference and resolution. c. Include in the database the WiFi baseline and periodic spectrum/performance measure- ments. Include reported WiFi interference reports (especially interference spectrum ana- lyzer traces), status, and resolution. d. Include interference analyses results of each investigation documented with date, time, problem description, investigation measurements made, etc. Even if a repetition occurs from the suspected same source, document results for historical comparison. Analyze results periodically for patterns, anomalies, or unusual behavior. e. Look for and confirm interference with the latest affordable spectrum analyzer tools and vice networking tools. Interference can be accurately identified at the physical layer (transmitter/receiver) vice using networking tools; e.g., networking can provide a reduc- tion in throughput which is not uniquely associated with interference.

Best Technical Practices to Ensure Accessible WiFi Service 79 8. Treat high-power interference sources as the highest priority and isolate them using spec- trum analyzer tools. The source could be an already installed WiFi system that is malfunc- tioning or possibly a rogue WiFi hotspot being used by a transiting customer or waiting passenger. This could be a potential security threat as well as an interference threat. 9. Use an airport employee for the WiFi oversight administrator that has access to all real-time information and status of the WiFi network, leaving the responsibility to operate the WiFi to a hired company. The rationale is twofold: first, the airport has real-time knowledge of the health, status, and evaluation of a severe interference occurrence within the airport. Secondly, any potential security threat with connection to WiFi can be directed to airport security efficiently. If the airport manages its own WiFi networks, tie the airport employee administrator role to security. 10. When purchasing new WiFi equipment, invest in upper end/high quality WiFi hardware. Usually the higher end equipment is made with better components and designed to take precautions to control spectrum emissions (i.e., receiver noise floor). The result is better spectrum efficiency and less likelihood of causing interference. 11. Support is needed for the National Telecommunications and Information Administration and FCC “Out of Band (OOB)” Interference Limits Policy effort that is intended to identify where the interference mitigation falls; i.e., if the transmitter OOB exceeds the established limit, then the transmitter is to be responsible for the fix. If it is within the limit, then the fix is in the receiver. Note while this is in the early stages of consideration, it is a relatively simple and efficient method for resolving who fixes the interference issue. 12. ACRP research can potentially influence airport construction designs as appropriate based on the WiFi study and implementation findings. The present WiFi study, practices, and analyses of interference efforts may support surface airport layouts and construction that minimize interference and enhance WiFi (or future replacement) and security, as well as operations and businesses within the airport. Potential contributions are as follows: a. Groupings into business areas, such as baggage handling, ticketing, and food court, may influence the layouts of the occupied areas to reduce opportunities for interference. b. Groupings of WiFi areas can be further influenced by the use of RF-absorbing materials to confine the RF signal and preclude occasions of potential interference to other areas. RF-absorbing materials can be paint, transparent coatings, or built into materials that serve as area dividers. The goal is to minimize RF interference leakage in the WiFi bands into adjacent areas. c. RF-absorbing materials may also be used in entrance and access entry points for baggage or other similar functionality to minimize RF leakage in the WiFi bands in and out of the airport building. Interference internally created by WiFi commercial usage can be blocked by proper layout and absorbing material at access points to the tarmac. 13. Establish local airport policies to govern installation and use of WiFi systems. a. Local policies can address equipment transmit power limits, procedures/processes to request and install WiFi systems, interference problem reporting, and user participation. b. This provides a set of rules/guidance that all users are required to follow if they wish to install WiFi systems to support their operations or business. 14. Establish a formal airport stakeholders’ council to address WiFi problems and future requirements. This makes everyone part of the process, which will help minimize future problems as well as resolve any interference issues that may arise. The following is a spreadsheet that presents an abstracted summary of the above discussion. The spreadsheet provides numerical references to the basis of each best practice, followed by a list of the references.

80 A Guidebook for Mitigating Disruptive WiFi Interference at Airports Best Pracces for WiFi Interference Migaon Best Pracce Airport Responsibility (Larger or Smaller) References Category Prevent or Accept Tolerable Interference Idenfy Interference Source Resolve Interference to Tolerable Level Idenfy Airport WiFi user groups based on airport areas or primary user funcons to support baselining WiFi installaons and priorizing response, and schedule periodic spectrum/performance measurements to compare with baseline and assist with interference invesgaon using spectrum analyzer based tools. Potenal grouping categories: Baggage, Tickeng, Security, Food Courts, Business Lounges, Passenger Waing Areas, Gates, etc. Subtasks/Pracces: i. Develop candidate grouping of WiFi services. ii. Individual airports can priorize the WiFi interference impact thresholds for each group (decibel measures that can be compared with planning/periodic “tool” output map or spectrum analyzer tools). iii. Execute measurements applicable to the airport areas based on priorizaon. Larger and Smaller 2, 3, 4, 5, 6, 8, 13, 14, 16, 17, 18, 19, 21, 22, 23, 24 X X Establish a database and airport map idenfying all WiFi installaons within the airport, associated equipment informaon, and primary users. Subtasks/Pracces: i. Include baseline, results of periodic measurements, and any WiFi interference reports, status, and resoluon. ii. Include analyses results of each invesgaon documented with date, me, problem descripon, invesgaon measurements made, and resoluon. Even if a repeon occurs from the suspected same source, Larger and Smaller Study Recommendaon X X X document for historical comparison. Analyze results for anomalies or unusual behavior. Acquire one or two inexpensive commercial spectrum analyzer tools to idenfy, isolate, and confirm interference vice networking tools. Subtasks/Pracces: Interference can be more accurately idenfied at the physical layer (WiFi transmi€er/receiver) vice using networking tools. Networking problems can provide a reducon in throughput which is not uniquely associated with interference. Larger and Smaller 4, 6, 8, 11, 12, 14, 16, 17, 18 X Analyze collected data to idenfy when a parcular WiFi hotspot is frequently nearing its “usage” saturaon point during its prime operaonal period. Comments/Raonale: This can be an indicaon that it is me to upgrade the device or all devices in a grouping before interference becomes a problem. Larger and Smaller 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 17, 18 19, 23, 24 X XIdenfy the 802.xx specificaon of the equipment in place and plan for an upgrade for be€er throughput/spectral efficiency. Comments/Raonale: This step can be executed at signs of WiFi equipment frequently near the saturaon point. These data should be included in the overall WiFi database. Larger and Smaller 9, 10, 13, 20

Best Technical Practices to Ensure Accessible WiFi Service 81 Best Pracce Airport Responsibility (Larger or Smaller) References Category Prevent or Accept Tolerable Interference Idenfy Interference Source Resolve Interference to Tolerable Level Treat high power interference sources as the highest priority and isolate with available spectrum analyzer tools. The source could be an already installed WiFi system that is malfunconing or possibly a rogue WiFi hotspot being used by a transing customer or waing passenger. Comments/Raonale: This could be a potenal security threat as well as an interference threat. Larger and Smaller 1, 4, 5, 6, 12, 14, 16, 18 X X Use an airport employee for the WiFi oversight administrator that has access to all real me informaon and status of the WiFi network vice, leaving all responsibility to a hired company to operate the WiFi. Comments/Raonale: First, the airport has real me knowledge of the health, status, and evaluaon of a severe interference occurrence within the airport WiFi system. Second, any potenal security threat with connecon to WiFi can be directed to airport security efficiently. If airport manages its own WiFi networks, e the airport employee administrator role to security. Larger and Smaller 1, 21, 22, 25 X X X When purchasing newWiFi equipment, invest in upper end/high quality WiFi hardware. Comments/Raonale: Usually the higher end equipment is made with be‰er components and designed to take precauons to control the spectrum emissions (i.e., receiver noise floor). The result is be‰er spectrum efficiency and less likelihood to cause interference. Larger and Smaller 9, 10 X ACRP research can support spectrum issues that benefit the WiFi implementaons and usage at airports. Comments/Raonale: Present support is needed for the NTIA and FCC Interference Limits Policy effort that influences and enables higher quality hardware. ACRP research can potenally influence airport construcon designs as appropriate based on WiFi study and implementaon findings. Subtasks/Pracces: i. Groupings into business areas such as baggage handling, ckeng, and foodcourt, etc., may influence the layouts of the occupied areas to reduce opportunies for interference. ii. Groupings of WiFi areas can be further influenced by the usage of RF absorbing materials to confine the RF signal and preclude occasions of potenal interference to other areas. RF absorbing materials can be paint, transparent coangs, or built into materials that serve as area dividers. The goal is to minimize RF interference leakage in the WiFi bands into adjacent areas Comments/Raonale: The present WiFi study, pracces, and analyses of interference efforts may support surface airport layouts and construcon that minimize interference and enhance WiFi (or future replacement) and security, as well as operaons and businesses within the airport. 2 X 1 X (continued on next page)

82 A Guidebook for Mitigating Disruptive WiFi Interference at Airports References 1. BAA’s Response to Ofcom’s Consultation, Higher Power Limits for License Exempt Devices, 2006. 2. Bit-Error Analysis in WiFi Networks Based on Real Measurements, Gabor Feher, Budapest University of Technology and Economics, Department of Telecommunications and Informatics, 2011. 3. The Wireless Jungle, Howard Preston, Preston Cinema Systems, 2009. 4. 20 Myths of Wi-Fi Interference: Dispel Myths to Gain High-Performing and Reliable Wireless, Cisco, 2007. 5. The Future of Hotspots: Making Wi-Fi as Secure and Easy to Use as Cellular, Cisco, 2012. 6. Interference Limits Policy: The Use of Harm Claim Thresholds to Improve the Interference Tolerance of Wireless Systems, White Paper, Receivers and Spectrum Working Group, FCC Technological Advisory Council Version 1.0, 2013. 7. Cool-Tether: Energy Efficient On-the-Fly WiFi Hot-Spots Using Mobile Phones, Ashish Sharma, Vishnu Navda, Ramachandran Ramjee, Venkata N. Padmanabhan, and Elizabeth M. Belding, University of Califor- nia, Santa Barbara, Microsoft Research India, 2009. 8. Passive Measurement of Interference in WiFi Networks with Application in Misbehavior Detection, Utpal Paul, Anand Kashyap, Ritesh Maheshwari, and Samir R. Das. 9. IEEE 802.16 Broadband Wireless Access Working Group, Title 802.16b PHY: Spectral Mask Related Issues and Carrier Allocations; Date Submitted 2001-03-10, Source(s) Dr. Ir. Nico van Waes. 10. The IEEE 802.11 Standardization, Its history, Specifications, Implementations and Future, Justin Berg, Tech- nical Report GMU-TCOM-TR-8, 2011. 11. Promising Interference and Radio Management Techniques for Indoor Standalone Femtocells, INFSO- ICT-248523 BeFEMTO D3.2 12. A WiFi Measurement in 802.11g Networks, Jian Lin, Feilu Liu, Thanasis Korakis, Zhifeng Taoy, Elza Erkip, and Shivendra Panwar, Department of Electrical and Computer Engineering, Polytechnic Institute of NYU, Mitsubishi Electric Research Laboratories (MERL). 13. AirMagnet WiFi Analyzer PRO: Anytime, Anywhere, WLAN Monitoring and Troubleshooting. 14. AirMagnet Planner for Cisco Small Business and Air Magnet Spectrum XT, Fluke Networks. 15. Attack tool published for WiFi setup flaw; Cisco issues warning; Cisco. 16. Cisco Aims for Clean Air on Wi-Fi, Sean Michael Kerner, 2010. Best Pracce Airport Responsibility (Larger or Smaller) References Category Prevent or Accept Tolerable Interference Idenfy Interference Source Resolve Interference to Tolerable Level Perform updates on exisng WiFi equipment. Comments/Raonale: Replaces aged equipment and supports increased growth requirements. Larger and Smaller 15 X Establish local airport policies to govern installaon and use of WiFi system. Subtasks/Pracces: Local policies can address equipment transmit power, procedures/processes to request and install WiFi systems, interference problem reporng, and user parcipaon. Comments/Raonale: Provides a set of rules/guidance that all users are required to follow if they wish to install WiFi systems to support their operaons or businesses. Larger and Smaller Study Recommendaon X Establish a formal airport stakeholders’ council to address WiFi problems and future requirements. Comments/Raonale: Makes everyone part of the process, which will help minimize future problems as well as resolve any issues that may arise Larger and Smaller Study Recommendaon X

Best Technical Practices to Ensure Accessible WiFi Service 83 17. Cisco Spectrum Expert Wi-Fi. 18. Interference Identification Guide, Metageek. 19. The Future of Hotspots: Making Wi-Fi as Secure and Easy to Use as Cellular, Cisco, 2012. 20. Test MIMO Wi-Fi and LTE Radios over the Air, octoScope, 2012. 21. Airport Communications at Risk, ISCO International. 22. Guidelines and Tools for Migrating to the Cisco Unified Wireless Network, Cisco. 23. Visualize Your Wireless Network, TM. 24. Wireless Solution, Made in Sweden. 25. Protecting Wi-Fi Networks from Hidden Layer 1 Security Threats, David Coleman and Neil Diener, 2007.