A Guidebook for Mitigating Disruptive WiFi Interference at Airports (2015) / Chapter Skim
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Pages 7-28
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7 C H A P T E R 2 Wireless communication, most commonly encountered through the use of either wireless fidelity (WiFi) or the cell phone, has become a routine tool for daily life.
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8 A Guidebook for Mitigating Disruptive WiFi Interference at Airports Service expectations of WiFi networks vary widely among both airport network managers and travelers. Some airport managers and travelers have come to view WiFi as part of the necessary infrastructure.
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Table 1. At-a-glance WiFi summary of case study airports.
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10 A Guidebook for Mitigating Disruptive WiFi Interference at Airports that is interference. If the communication is slower than it should be when another device is transmitting, that also is considered interference.
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WiFi Service at Airports and the Problem of Interference 11 in their product. In a recent technology trends article published in Electronic Design, "Bluetooth and Wi-Fi Rule the Airwaves," Louis E
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12 A Guidebook for Mitigating Disruptive WiFi Interference at Airports WiFi Traffic Distribuon by Channel All 5GHz traffic 20% Channel 11 44% Channels 7 10 5% Channel 6 9% Channels 2 5 9% Channel 1 13% Figure 8. Traffic distribution among WiFi channels.
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WiFi Service at Airports and the Problem of Interference 13 Figure 10. Percent of packet retransmission as a function of access point (AP)
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14 A Guidebook for Mitigating Disruptive WiFi Interference at Airports A result of the 2.4 GHz band crowding is low data rates, reported in Figure 12, and a high level of transmission errors requiring packet retransmission, reported in Figure 13. The realized data rates are very slow compared to the specified maximum rates for WiFi, and those in the 2.4 GHz band are approximately half of those experienced in the 5 GHz band.
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WiFi Service at Airports and the Problem of Interference 15 An examination of WiFi use at airports shows that the trend toward band congestion is pronounced. Table 3 gives a sampling of the band usage at 28 airports.
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16 A Guidebook for Mitigating Disruptive WiFi Interference at Airports both more opportunities to connect in other bands must become available and an increasing number of network users must be incentivized to use those opportunities. Adjacent Channel Interference Radio frequency devices do not have perfect frequency boundaries.
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WiFi Service at Airports and the Problem of Interference 17 in a shared distributed antenna system. Strong RF signals can create intermodulation products and a variety of related problems.
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18 A Guidebook for Mitigating Disruptive WiFi Interference at Airports power by spreading the same total transmit power over the antennas to achieve an array gain that improves the spectral efficiency (more bits per second per hertz of bandwidth) and the link reliability.
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WiFi Service at Airports and the Problem of Interference 19 Other WiFi and Network Problems Interoperability Issues Interoperability issues have also been sources of problems. Vendors implement the same requirements in different ways.
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20 A Guidebook for Mitigating Disruptive WiFi Interference at Airports viewpoint, there are those WiFi users that, with agreement between the airport and the users, potentially could be coordinated but currently are not coordinated. A second category of uncoordinated use is those situations where getting an agreement between the airport and the user is unlikely to be feasible because the user is transient.
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WiFi Service at Airports and the Problem of Interference 21 trigger the CCA protocol. With adjacent channel operation, the result is similar to what happens when non-WiFi transmitters are in the area.
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22 A Guidebook for Mitigating Disruptive WiFi Interference at Airports capacity of the access points near it. These kinds of specialized access points can be integrated into the regular network and create an independent testing sub-network.
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WiFi Service at Airports and the Problem of Interference 23 Most access points come with installation instructions and grounding planes, and are designed to operate from ceilings or elevated mounts. However, a common problem is for architectural or aesthetic considerations to conflict with optimal placement of access points.
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24 A Guidebook for Mitigating Disruptive WiFi Interference at Airports Dynamic Frequency Selection and Transmit Power Control Requirements Dynamic frequency selection (DFS) is the process of detecting signals (i.e., radar)
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WiFi Service at Airports and the Problem of Interference 25 what is shown here, there are other bands used by WiFi: the new TV White Space band, and the 3.6 GHz, 4.9 GHz, and 60 GHz bands. Spectrum Reuse and Load Distribution Spectrum reuse and load distribution are important aspects of network planning.
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26 A Guidebook for Mitigating Disruptive WiFi Interference at Airports Table 4 shows the frequency assignments at a gate in one of the largest U.S. airports.
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WiFi Service at Airports and the Problem of Interference 27 away or because of interference from other transmitters, the system backs off, dropping to a slower speed but more reliable modulation methods. Some systems will track the availability of other access points and switch access points when the signal from one becomes better than the current connection.
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28 A Guidebook for Mitigating Disruptive WiFi Interference at Airports Next, the power levels and field strength need to be checked over the coverage area. Power levels at the low end of the power range are likely to result in poor coverage and decreased performance.
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