A principal objective of recent U.S. Department of Defense telecommunication transmission policy is to simplify its integrated wireless networks. To reach that objective, DoD policy includes a reduction in the number of available wireless waveforms and corresponding network hardware.

The objective is to field fewer types of wireless network devices, while providing improved network interoperability to accommodate the emergence of Internet Protocol (IP) as a connectivity standard.

At the same time, the Department of Defense wants to continue to encourage innovation. Interoperability does not mean that SATCOM users should be faced with only a plain vanilla set of choices for their networking, rather that those choices should meet an underlying ability to interoperate with other similar network devices.

A number of features and choices remain when considering wireless networking equipment like the satellite communications modems that form the backbone of many wireless networks. There is no “one size fits all” modem, as many networks require features that may be advantageous to one operating environment, but are inefficient or detrimental to another. However within common networks, interoperability with efficiency is the goal.

MIL-STD-188-165B
A new element of DoD Frequency Division Multiple Access (FDMA) modem policy is the creation of MIL-STD-188-165B, which includes new, more-efficient operating modes. Though this new standard is often thought of as catching the military up to commercial standards and technology, the new -165B standard is actually enhanced beyond pure commercial technology. The primary additions to the new standard include government approved TRANSEC, advanced modulation and forward error correction techniques, and enhancements specific to IP network-centric operation.

The MD-1366 EBEM
To implement this new standard for high-speed, high-performance, flexibility, and interoperability, the U.S. Department of Defense and its coalition defense partners have selected the ViaSat MD-1366 EBEM, the only modem certified to the MIL-STD. The objective is to field fewer types of wireless network devices, while providing improved network interoperability to accommodate the emergence of Internet Protocol (IP) as a connectivity standard.

At the same time, the Department of Defense wants to continue to encourage innovation. Interoperability does not mean that SATCOM users should be faced with only a plain vanilla set of choices for their networking, rather that those choices should meet an underlying ability to interoperate with other similar network devices.

A number of features and choices remain when considering wireless networking equipment like the satellite communications modems that form the backbone of many wireless networks. There is no “one size fits all” modem, as many networks require features that may be advantageous to one operating environment, but are inefficient or detrimental to another. However within common networks, interoperability with efficiency is the goal.


MIL-STD-188-165B
A new element of DoD Frequency Division Multiple Access (FDMA) modem policy is the creation of MIL-STD-188-165B, which includes new, more-efficient operating modes. Though this new standard is often thought of as catching the military up to commercial standards and technology, the new -165B standard is actually enhanced beyond pure commercial technology. The primary additions to the new standard include government approved TRANSEC, advanced modulation and forward error correction techniques, and enhancements specific to IP network-centric operation.

The MD-1366 EBEM
To implement this new standard for high-speed, high-performance, flexibility, and interoperability, the U.S. Department of Defense and its coalition defense partners have selected the ViaSat MD-1366 EBEM, the only modem certified to the MIL-STD-188-165B standard. This Single Channel Per Carrier (SCPC) SATCOM modem incorporates the latest technology in advanced modulation and coding, while providing backwards interoperability with the majority of SCPC modems in the government inventory. The U.S. and coalition partners adoption of the -165B standard waveform has made the MD-1366 EBEM the most widely used FDMA modem for government applications and networks since the OM-73.

The bottom line advantage of the MD-1366 efficiency is that more carriers can be placed on a single satellite transponder and those carriers can be better utilized, enabling more warfighters to gain access to more data when and where they need it. A few key improvements over MIL-STD-188-165A modems create this additional efficiency:

• Increased symbol rates to 60 Msps providing single carrier data rates up to 155 Mbps.
• Open-standard interoperable Turbo codes
• Advanced modulation techniques including 8-PSK and 16-APSK
• Information Throughput Adaptation
• Radio Aware Routing

The main advantage of turbo coding is that it reduces the Eb/No needed to close a link at a given code rate. Known turbo codes at reasonable block size and complexity can come quite close to the Shannon channel capacity limit (within about 1 to 2 dB). For instance, an R=1/3 turbo code can achieve a BER of about 1 in 10-7 at an Eb/No = 1 dB with a block size of less than 2000 bits. Reducing the code rate to R=1/4 would reduce the Eb/No required to about 0.7 dB. Providing an open standard for this enhanced forward error correction technique means that efficiency and interoperability can finally coexist.

Demonstrations of the modem have shown the value of the new modulation and coding choices. In one, the MD-1366 EBEM, (operating at 16-APSK R=7/8), achieved 205 Mbps total capacity on a single XTAR transponder, the highest capacity ever achieved on a 72 MHz X-band transponder. EBEM also operates on C-, Ku-, and Ka-band transponders, including certification for the new WGS satellites.

ESEM = True Modem Pair Compatibility
When it comes to satellite modem interoperability, it takes more than waveform commonality to ensure modem pair compatibility. Using different modems that have an open-standard waveform, but proprietary baseband interfaces is just as ineffective as using two different proprietary modems.

The presence of an Ethernet interface to deliver IP data over a wireless network also does not necessarily mean that heterogeneous modems are compatible. The manner in which a satellite modem converts digital data to analog signals for delivery over the air and then retranslates that data back to a digital format must be the same on each side of a satellite link.

To create true Ethernet compatibility between virtually any modem pair, the government created an open-standard option for the MD-1366, the Ethernet Service Expansion Module (ESEM). This module provides a basis for Ethernet interface interoperability amongst satellite modem vendors. Within the MD-1366 EBEM, it extends FDMA modem capability far beyond traditional fixed-channel operation.

Information Throughput Adaptation
What’s the number one bandwidth-killing aspect of most SCPC modem links? It’s link margin, thrown away in the name of contingency for harsh operating environments. Information Throughput Adaptation (ITA) is a way to keep that built-in safety margin, but use it for enhanced data throughput when that margin is not needed.

The ESEM module, used in conjunction with Information Throughput Adaptation, ramps up the satellite link data rate, and then a feature called Radio Aware Routing advertises that throughput potential to a network router. Together, the features maximize overall network throughput across the satellite link when little or no margin is needed.

If downlink power decreases, ITA then automatically and dynamically decreases the link data rate using more robust waveforms to maintain the link connection. During a demonstration, the EBEM has shown its seamless, error-free adaptation to data rates from 28 to over 155 Mbps without operator intervention.

These features allow users to make use of the many dBs of FDMA link margin that typically go unutilized in a fixed-channel rate environment. In traditional fixed-channel military satellite communication environments, where a 3-4 dB link margin is typical, these features can provide more than a 100 percent improvement in data throughput. The ESEM plug-in interface also enables the concurrent transmission of Internet Protocol (IPv4 or IPv6) Ethernet baseband traffic as well as non-IP data flows for maximum interoperability.

The EBEM with ESEM is certified for use over Defense Satellite Communication System and WGS satellites. Already, U.S. Army, Navy, Marine, and Air Force customers have recently ordered large quantities of MD-1366 modems equipped with the ESEM interface.

Beyond The MIL-STD
In the CENTCOM AORs, soldiers are short more than 500 MHz of bandwidth, as compared to what they need for the most basic of communications. This type of shortage provides an ideal opportunity for the ability of the MD-1366 EBEM to close this gap. But while the MD-1366 EBEM performance gains and cost savings are impressive to be sure, the “bandwidth problem” that the military faces — as well as the constantly growing need for more of it — requires further innovation, consistent with the DoD desire to encourage performance beyond MIL-STD operation.

Bandwidth Re-Use — PCMA
Combining the uplink and downlink transmissions into the same bandwidth is another way to boost the capacity of satellite transponders. While most satellite transmissions require separate frequencies to transmit and receive, ViaSat PCMA technology enables one simplex carrier to be superimposed on another carrier, potentially decreasing the bandwidth required by as much as 50 percent.

The technology uses an adaptive self-interference cancellation technique to subtract the transmitted signal and recover the desired signal. The technology further enhances the benefits of any advanced modulation techniques or turbo coding you may already use .

However, it’s important to keep in mind that frequency re-use techniques are icing on the bandwidth efficiency cake. They are appropriate only when certain conditions apply:

Link requirements

• Must use full-duplex circuits (symmetric or asymmetric)
• Must be able to receive your own uplink signal (doesn’t work with on-board processed, cross-strapped, cross-banded, or otherwise non-loopback transponders)

Implementation considerations

• More power is required with the dual simplex frequency pair approach (~3dB total composite transponder power)
• An implementation power loss exists (0.15 t0.5 dB depending on near/far ratio)
• May need to change existing coding rates and modulation to take advantage of bandwidth reduction

PCMA is best used to overcome Power Equivalent Bandwidth imbalances. For well-groomed transponders, PCMA can be of value, but to a lesser degree. Link budget analysis can determine feasibility, link configuration, and the possible overall savings of power and bandwidth with PCMA. Where PCMA does provide value, it’s the closest thing to a free lunch in satellite communications today.

More Efficiency + Control
DoD efforts to simplify networking hardware and operation are not intended to be limiting to the overall capabilities of the network. Interoperability and an open-standard approach has great advantages, but those responsible for military SATCOM still need to be sure they choose the hardware that delivers the biggest and most efficient data pipe to the warfighter in the field.

The MD-1366 EBEM/ESEM with Information Throughput Adaptation and Radio Aware Routing features, as well as PCMA bandwidth re-use technologies, moves networks and users beyond the traditional “fixed channel data rate” environment of FDMA communications. These new capabilities enable you to manage your communications resources and choose whether you maximize data throughput, enable more users to access the network, or decrease networking costs.