Wireless personal communications have expanded at an incredible rate over the last 2 decades. The technological advances in hardware and software are truly remarkable. With these technological changes have also come the standardization of these technologies, including: GSM and CDMA for cell phones, Ethernet for wired computer connectivity, USB for wired computer and cell phone connectivity, and IEEE 802.11 Wi-Fi(TM) for wireless high speed data connectivity. With this standardization has come interoperability – the ability to develop products that can be used across multiple platforms, operating systems, and with imagination to grow into unexpected new products and services.

Wi-Fi has become the preferred wireless data communication link for many high speed data applications. Wi-Fi is now used globally in businesses, homes, hotels, coffeehouses, stadiums, and of course airports and airplanes. With smartphones, tablet computers, laptops and even the lowly desktop computer coming equipped with Wi-Fi, it has become the standard for short distance, wireless high speed data communications.

However, data now takes many forms from accounting information to audio and video, from databases to Netflix and Pandora, with Wi-Fi being used to move this “data” wirelessly.

With these opportunities and services on the ground, it’s clear why we expect the same level of connectivity and data communications in the air.

Many of our readers know a small amount about their Wi-Fi wireless access points (A/P) because they all use them – few really know about how they differ from ground units. As a result, IFExpress contacted Robert Guidetti, VP/GM Commercial Division, of VT Miltope for help to better understand the technology driving airborne wireless connectivity.

1. IFExpress: Many readers aren’t familiar with airborne wireless access points.  To begin, could you could give a short summary about the differences your engineers have to consider in designing a wireless access point (A/P) that works on an airplane? Basically, we are asking if there is anything different about an aircraft A/P from one used on the ground.

VT Miltope: Yes, there are a number of differences between airborne and ground-based wireless access points (A/Ps).

• Safety comes first. First, there are the usual airworthiness certifications typical for flight safety; these deal with both environmental as well as electrical. In addition, 802.11 wireless access points include transmitting radios, which must be rigorously proven to be safe on airplanes. Therefore, multiple industry specifications have been developed to guide the design, testing and installation of these devices on airplanes. Those specifications include, but are not limited to:

• Working with congestion. As we all know so well, the cabin is a congested environment with many people in a small space. This leads to a very high density Wi-Fi environment. There are few ground-based applications as densely populated with Wi-Fi A/Ps and client devices as an airplane. This is an increasing challenge as more passengers bring multiple Wi-Fi devices on board; progressively more passengers are connecting multiple Wi-Fi devices to the airplane network.

We need to keep in mind: The aircraft cabin dimensions stay roughly the same over decades, but the demand for bandwidth grows exponentially each year driven by:

a) Continuous increase in numbers of passenger devices
b) Higher quality of service expectations by passengers
c) Continuous increase in the kind of services in the cabin that use Wi-Fi network.

The on-board A/P network must not just survive the congested wireless environment; it must manage and optimize the data throughput, while embracing the plethora of different client devices, and the different needs of streaming video, e-mail, games, etc. VT Miltope’s solution to these networking challenges is Cognitive Hotspot(TM) Technology (CHT) – an advanced embedded software solution specifically developed to optimize wireless network performance. With CHT, nMAP2 units share information such as the number of associated clients, the QoS of those clients, data rate throughput, RF noise and interference, etc.  With this information, the nMAP2 network performs load balancing, band selection (2.4 or 5 GHz), channel selection, RF power management, etc.  Thus, CHT reduces interference and congestion, while significantly improving data throughput and network capacity.

• Beyond the safety and congestion aspects, hardware designs are tailored for airborne applications. For example, multiple A/Ps are often used on airplanes to provide full coverage across the entire cabin. To help reduce weight, Ethernet and power cables are “daisy-chained” from A/P to A/P. Designing for daisy-chaining is just one of several hardware design differences between airborne and ground-based systems. Other hardware differences also include:

o Unique power supplies
o Aviation grade connectors
o Designing for damp environments
o Designing for shock and vibration

• Adding more A/Ps may reduce network performance. I mentioned multiple A/Ps, but in the confined tube of the cabin, the interferences between A/Ps will grow when the number of A/Ps gets too high. Again, it is therefore important to not just add A/Ps but rather aim to have as few as possible, but to manage the available capacity more effectively.

• Installation longevity: Aircraft cabins and IFE systems are being installed to last for several years, or decades. Yet much of the IFEC world for the airline passenger is driven more and more by short life-cycle consumer devices, with aircraft life-cycles being much longer. It is therefore paramount that the cabin Wi-Fi network has the inbuilt adaptability to support the rapidly evolving passenger device and content landscape.

2. IFExpress: Given the various standards (802.11a, b, g, n & ac) can you tell our readers what is the standard used most often today and please give us a bit of information about the number of available channels and the bandwidth available for each?

VT Miltope: IEEE 802.11 is just over 20 years old, with more than 50 revisions issued. 802.11 specifies everything from RF power to RF frequencies to modulation characteristics to security aspects. Although each new revision normally includes specifications from prior revisions, the popular approach is to discuss 802.11a, b, g, n & ac as separate characteristics.

Rapidly becoming the most popular implementation over the last two years is 802.11ac, operating in the 5 GHz band, with theoretical data rates exceeding 8 Gbps. Two RF bands are used for normal Wi-Fi connectivity, 2.4 GHz and 5 GHz. By far, the 5 GHz band provides the greatest bandwidth and the greatest opportunity for expanding data throughput. The latest 802.11ac only uses the 5 GHz band, with 802.11n supporting both 2.4 GHz and 5 GHz bands. Although actual data rates vary widely on the ground and on airplanes, the following table shows the theoretical maximum data rates for 802.11g, n and ac.

Both the 2.4 GHz and 5 GHz bands are divided into channels. The channels are of fixed bandwidth of 22 MHz in the 2.4 GHz band, but have bandwidths of 10 MHz, 20 MHz, 40 MHz, 80 MHz or 160 MHz (depending upon the channel) in the 5 GHz band.

Actual throughput varies by the amount of congestion, RF power level, number of spatial streams (antennas), number of channels used together (bonded), RF bandwidth, distance, RF noise, and many other factors.

In addition, country regulations vary widely regarding regulatory and legal requirements affecting the use of these RF bands. All countries restrict the use of at least some of the internationally allocated spectrum, and these restrictions tend to vary by country or region. To help with these differences in regulatory aspects, industry organizations including APEX, ARINC and RTCA are discussing how to harmonize the use of these bands for airborne applications. Although it will likely be several years before harmonization is realized, once completed, certification on airplanes will become easier and Wi-Fi performance can be further enhanced.”

3. IFExpress: Please tell our readers about the challenges of streaming video on inflight A/Ps.

VT Miltope: Streaming video is a challenge due to the relatively high bandwidth requirement, combined with a need for a very low error rate. Some data (such as e-mail) can be delayed without harm, and/or retransmitted if there are errors. However, video cannot be delayed without losing fidelity, and retransmission to correct errors uses a lot of bandwidth and delays the video stream.

One of the most severe wireless system tests is running continuous streaming video to every seat on an airplane. As you might imagine, this uses a lot of RF bandwidth, while creating interference and congestion across the cabin. Part of the A/P design challenge is to accommodate the large number of client devices within the airplane cabin. VT Miltope performs these tests as a routine part of our software verification and validation in the lab, and on airplanes in conjunction with our customers. Our customers what to know that the passenger and crew Wi-Fi performance meets and exceeds required benchmarks and expectations.

4. IFExpress: In today’s aircraft, how many A/Ps are typically used?

VT Miltope: This is a common question and the short answer is: it depends. It depends upon several parameters, including: the type of service required (e-mail, video, games, data loading, etc.), the number of passengers, how many passengers are expected to use which services, the data throughput requirements (speed and amount), the aircraft configuration, etc.

Fairly typical for a narrowbody airplane with 140 seats such as an A320 or B737 are 2 to 3 A/Ps distributed throughout the cabin, depending upon required services. Typical for a widebody airplane with 320 passengers such as an A350 or B787 are 5 to 7 A/Ps, again depending upon required services.”

5. IFExpress: Is there a difference in streaming from a server vs downloaded satcom streaming… we assume bandwidth is the issue?

VT Miltope: “In general, airborne servers are able to provide significantly higher network data rates than satcom links; although Ka band satellites are starting to change the dynamics due to the potentially higher data rates supported by Ka satcom. So for satcom connectivity, wireless A/Ps typically have greater bandwidth capabilities than the satcom link, therefore, the A/Ps are not the bottleneck. But for video on demand servers, A/Ps can become the bottleneck to these high bandwidth requirements. Beyond the data rate differences, the 802.11 A/Ps are simply a lower cost connection from an airborne server or satcom modem to the passengers’ client device than a wired solution.”

6. IFExpress: Do you have any idea about what percentage of passengers use your devices on any one flight?

VT Miltope: “Industry reports indicate an average take-up rate of 5 to 10 percent. This tends to vary by type of flight (domestic, international, business commuter, etc.), country and region, services available, and other factors. However, VT Miltope designs its A/P to support all passengers at an optimum data rate.”

7. IFExpress: Does the airplane internal structure effect the placement/number of wireless A/Ps – things like class of service dividers, for example?

VT Miltope: “Yes, at the Wi-Fi frequencies of 2.4 GHz and 5 GHz, aluminum and composite fiber are good reflectors of these RF signals. This leads to class dividers, monuments, lavatories, purser stations, bag bins, and other items needing to be considered when determining the best aircraft installation locations for A/Ps. A/Ps are normally located in the cabin overhead above the aisle(s), but can be located in bag bins, side panels, purser stations, or other imaginative locations.”

8. IFExpress: Can you tell our readers about any new technology or products coming along?

VT Miltope: “The greatest recent impact has been the increasing use of 802.11ac in mobile devices. Since 802.11ac uses the less congested 5 GHz band, and provides higher data rates, this provides significant opportunity to improve data throughput and overall wireless network performance.

VT Miltope’s approach has been to develop an A/P computing platform with high end performance, while developing a dynamic and flexible software solution providing real-time network connectivity optimization. We call this smart software solution Cognitive Hotspot(TM) Technology (CHT). Our nMAP2 combines the technology strides of 802.11ac performance with CHT to optimally manage today’s and tomorrow’s high density airborne connectivity requirements.”

9. IFExpress: What are the installation and certification aspects related to airborne wireless access points?

VT Miltope: “As mentioned above, the selection of A/P installation locations in the cabin needs to consider the RF characteristics of 802.11 radios and proximity to passengers’ Wi-Fi client devices. Certification aspects require testing of the A/P devices as components, and in addition there must be testing and certification of the aircraft for the safe use of Wi-Fi devices in flight. Testing at the component level shows compliance with RTCA DO-160, with aircraft certification including testing and evaluation to RTCA DO-294 or DO-307, or both.”

10. IFExpress: Does VT Miltope have any additional information you want to provide to our readers?

VT Miltope: “Yes, about Wi-Fi System performance measurement: We all know about the IFE system availability formulae of the past consisting of complex system diagnostic and reporting applications that give airlines the perception of control over more complex IFEC systems. CHT, our connectivity improvement technology, enables transparency to the system integrator and the airline with its unique CHT Manager application. Continuously measuring and recording key system availability parameters, the CHT Manager offers comprehensive system control and performance insight.”

VT Miltope will be at Aircraft Interiors booth 3B10 in the IFEC Zone

Featured Products:
• nMAP2 with CHT
• cTWLU with 4G LTE, 3G Cellular and 802.11a/g/n & ac

Notes:
Wi-Fi(TM) is a trademark of Wi-Fi Alliance
Cognitive Hotspot(TM) Technologies is a trademark of AOIFES Solutions

Contact:
Jeff Drader
Director, Business Development
VT Miltope
2082 Michelson Drive, Suite 100
Irvine, CA 92612

Jeff.Drader@Miltope.com
+1 (949) 752-8191

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