Cognitive Radio Products and Applications

 
Cognitive Radio Products and Applications
As the last section in this chapter, we would like to discuss a currently available cognitive radio
product developed by Adapt4 XG1, where “XG” stands for “Next-Generation” Communications. The
appearance of XG1 is shown in Figure 9.18.
The Adapt4 Inc. is a Florida based organization started in early 2003 as an affiliate of Data Flow
Systems, Inc., which is the largest manufacturer of wireless turn-key Supervisory Control and Data
Acquisition (SCADA) systems for water utilities in the Southeastern US. The XG1 is the world’s
first cognitive radio. The XG1 Cognitive Radio’s technology allows it to adapt to its surroundings and time-share existing licensed channels, but only when they are not in use. XG1 cognitive radios provide
the opportunity to implement new networks or to expand existing ones that are currently restricted
by the scarcity of licencable FCC frequencies. This is accomplished without resorting to unreliable,
unlicensed alternatives. The XG1 operates within licensed frequency bands on a secondary user basis.
In fact, the XG1 project was largely funded by DARPA. Its aim is to develop technology that
allows multiple users to share spectra in a way that coexists with and complements sharing protocols
included in today’s Wi-Fi technologies. The XG1 explores the idea in the most extreme way. The
product can work on a dc-to-daylight box, covering a broad range of frequency bands up to the
microwave area, and it can use any spectrum at any time and adapt accordingly.
The XG1 is also well suited for military applications. From a military perspective, the ability of
the cognitive radio to handle functions that best serve its user translates to sufficient situational and
mission awareness to help the soldiers reach an objective. It has to be admitted that the kind of data
required for this is still in the labs. Academia are studying this and industry wants to work with them.
Examples of data for a soldier could include local topography, mission objectives and timescales for
those objectives, as well as the knowledge of, and access to, the radio networks in the area as well
as the location of friendly and enemy positions and artillery.
Now, we would like to discuss the way the product works and its key technical features.
The XG1 uses its Automatic Spectrum Adaptation Protocol (ASAP) technology to manage time,
space, frequency, and power to provide reliable communications without causing interference to other
licensed users. A patent-pending feature in XG1 allows all XG1 Adaptive radios within a network
to monitor activity by other users in a specified band and identify unused bandwidth. The network
generates a set of parallel carriers and transmits on these channels when they are not in use. When
another licensed user is sensed, the network stops using that frequency until it becomes dormant once
more. Two additional features are used to further reduce the likelihood of interference to other users.
A frequency hopping technique is used to minimize the amount of time that any single frequency
utilizes and the radios’ transmit power is dynamically regulated so that the minimum amount of
power needed to establish solid communications is used. Three key technologies have been used in
the XG1 terminal, and they are introduced in the following text.
Dynamic frequency selection and avoidance
The XG1 uses advanced signal processing techniques to identify unused bandwidth, normally licensed
to others, and creates a selection of channels available for use by the XG1 network. Individual XG1  sites detect non-XG1 radio users and relay this information to the central radio. This information is
processed by the central radio to create a composite usage map covering the entire XG1 network.
Networks with XG1 adaptive radios can span a radius of over 50 miles.
This map is continuously updated and distributed throughout the network. Using a spectrum
usage policy in accordance with FCC and network operator guidelines, the XG1 determines opportunities
to use these channels on a shared, noninterfering basis. When any XG1 adaptive radio in the
network recognizes the presence of another licensed user within the specified band, that frequency
is immediately removed from the selection of available channels until the network determines that
it is not being used once more. The network also employs a programmable keep away feature that
allows the operator to determine the amount of white space buffer to maintain around other primary
users.
Dynamic power management
The adaptive radios in an XG1 network regulate their power output to further decrease the chance
of interference to licensed users. Each remote radio in the network uses the minimum amount
of transmit power needed to maintain reliable communications with the central radio, dynamically
adjusting as necessitated by the variables in the environment. The central radio maintains
an output power equal to the level demanded by the network link with the highest wattage requirement.
Frequency hopping
In order to further reduce the likelihood of causing interference to primary channel users, the network
employs a frequency hopping technique that minimizes the amount of time the network uses
a particular frequency. Typically, these bursts use up to 40 channels simultaneously, but only spend
about 10 continuous milliseconds on any one channel.
Additional features
The XG1 Adaptive Radio employs unique modulation techniques to achieve unequaled transmission
efficiency. It uses multiple, narrow band carriers to maximize the use of available channels and
throughput within the defined band. Networks support a variety of architectures such as mobile,
point-to-multipoint and point-to-point with multihopping. The radio’s software-defined features allow
them to easily adapt to meet unique networking traffic requirements.
A feature-rich network management system is available for providing software downloads over
the air, traffic monitoring, fault reporting, policy engine updates, and complete configuration. Link
transmission parameters such as the TPC (up to FCC limits) transmitter disable and frequency blocking
are provided.
User data can be supplied over the Ethernet port (10/100 MHz) or a serial RS-232 port. In
addition to a DSP, the XG1 includes a Power PC microprocessor and software to support a wide
variety of user data processing, including encryption, protocol emulation, and network management.
Adapt4 has made use of the fourth dimension, time, to provide highly reliable, interference-free
wireless communications solutions for a nearly limitless variety of applications. Operating on FCClicensed
channels, Adapt4’s XG1 cognitive radio effectively manages space, frequency, power, and
time, to provide adjustable throughput rates approaching 200 kbps, even in the presence of other
primary users. The XG1 provides protected QoS communications without interference to or from
other users, whether licensed or not.