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Digital Battlefield Communications
Hawaii Center for Advanced Communications
Department of Electrical Engineering
College of Engineering
University of Hawaii
Project Summary
This proposal discusses a four year project to be conducted at the University of Hawaii in
digital battlefield communications research. The goal of the project is to integrate research in
communication technology from the device and component levels to the communication, signal
processing, and networking levels for future combat systems. The future combat systems will
have communication systems that are easy to deploy, are mobile, and can seamlessly access
and send a variety of different bandwidth information sources. Research will be conducted to
build hardware devices and design algorithms to realize this complex wireless communication
network. The research will be conducted by members of the Hawaii Center for Advanced
Communications (HCAC). The HCAC was recently formed to bring together researchers from
diverse areas ranging from integrated circuit design to microwave and millimeter-wave devices
to communication systems to networking design and analysis to jointly work together on
advanced communication research projects.
Project Description
The future battlefield will require digital communication systems that are easy to deploy,
mobile, and can seamlessly access and send a variety of different bandwidth information
sources ranging from broadband multimedia applications to sensor and control information.
This proposal integrates a diverse set of researchers in the Department of Electrical
Engineering at the University of Hawaii to jointly work on several important aspects of digital
battlefield communications. We will analyze and develop devices, components, and algorithms
for future generation combat communication systems.
Digital communications in a battlefield environment will cover a wide range of the frequency
spectrum. Individual units will carry small, hand-held radios. Operating at lower carrier
frequencies (below 5 GHz), these radios will be inexpensive and useful in urban, forested,
smoky, or other environments where direct line-of-sight links are not possible. Line-of-sight
communications between rapidly deployed base stations or from base stations to satellites can
be achieved with higher carrier frequencies (5 to 30 GHz). These higher operating frequencies
will provide the bandwidth necessary for higher data rates. Finally, very high millimeter-wave
frequencies (30 to 100 GHz) can be used for secure satellite cross-links to convey information
from the battle theater to a centralized command.
To implement communications systems over these vast range of frequencies, researchers will
develop novel hardware devices and components that can achieve stringent size, power, and
bandwidth requirements. An important aspect of battlefield communications is secure
communications. Here we combine expertise from millimeter-wave systems and the physical
propagation channel with advanced signal processing, communication, and coding algorithms
to analyze and implement secure communication systems. Finally, we examine network
architectures for a deployed battlefield communication system. These networks will be mobile
with dynamic network topologies requiring optimization, routing, and signal processing
algorithms for transmitting different sources of information.
Novel Hardware
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Developing novel hardware for use over this wide frequency spectrum is a major focus of our
effort. We will develop hardware at both the device level and the component level. Our efforts
at the device level will research the fundamental electronic, microelectromechanical systems
(MEMS), and photonic technology necessary to enable broadband communications. We will
explore innovative semiconductor passivation techniques that promise to improve the
performance and reliability of high-speed compound semiconductor devices. We will develop
tiny electromechanical switches and variable tuning elements that could revolutionize
microwave integrated circuits. We will also explore millimeter-wave photonic crystals that
enhance the performance and functionality of high-speed components. Our efforts at the
component level will develop key building-block circuitry for high-speed communications. We
will develop novel integrated circuits to process the baseband data. These baseband circuits
will be highly integrated, incorporating error-control functions while striving to minimize power
consumption. We will also develop front-end circuits that operate at the microwave or
millimeter-wave carrier frequencies.
We will develop advanced quasi-optical circuit
architectures to develop powerful and efficient transmitters, sensitive receivers, and rapidly
steerable beam control devices. These components can also be useful for millimeter-wave
imaging and radar applications. By exploiting high levels of integration, these components will
be inexpensive to mass produce without sacrificing performance. Our efforts at the device and
component level will develop the hardware that will enable the battlefield communication
network.
Quasi-Optical Circuits
The millimeter-wave frequency band clearly offers the spectrum to accommodate the multitude
of broadband, high-speed services envisioned for the next decade. Achievable transmission
rates are on the order of 5 Gbps – more than 100 times the T3 (45 Mbps) transmission rate. In
fact, this rate is competitive with optical fiber transmission rates, which is currently the
technology of choice to transmit large amounts of information. Millimeter-wave networks not
only provide the necessary bandwidth for high bit rates and wideband modulation schemes,
but the associated short wavelengths also imply smaller antenna and circuit size, resulting in
more compact modules for mobile communications. The increased atmospheric attenuation in
this part of the spectrum is useful for secure satellite crosslinks and high-capacity wireless
local area networks.
A major obstacle in developing millimeter-wave wireless communication systems is the limited
power-handling capability of solid-state devices. Often, a single device is incapable of meeting
the system’s power requirements and the outputs of many devices must be combined. Quasioptical power combining is an attractive and elegant method of achieving this. In a quasioptical combiner, an array of active devices is distributed over a planar radiating surface that
interacts directly with an electromagnetic wave. This approach has a number of advantages.
Power is combined in free space, minimizing conductor losses.
Planar arrays can be
monolithically fabricated; at shorter wavelengths thousands of devices could be integrated onto
a single wafer. The array’s unit cell determines the device’s driving-point impedance, while the
output power is proportional to the number of elements in the array; this allows one to
optimize for gain or low-noise performance through the unit cell and to independently select
the array size to meet the power requirement.
The noise from each device is largely
uncorrelated, so the noise figure of the array will be no worse than that of a single device.
Because of their distributed nature, quasi-optical circuits degrade gracefully; they are
insensitive to the single-point failures that could be catastrophic in rival systems.
The promise of quasi-optical power combining has always been the creation of powerful solidstate millimeter-wave sources. Since the number of devices integrated in the array increases
with the square of the frequency, the benefits become more apparent at higher millimeter-wave
frequencies. An immediate goal would be the long-awaited replacement of vacuum-tube
amplifiers used in medium-power millimeter-wave systems. The long-term goal would be an
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entirely new generation of solid-state radar and communications transmitters that are smaller,
lighter, and less expensive than vacuum-based systems.
Examples of quasi-optical circuits currently under development at the University of Hawaii are
shown in Figs. 1 and 2.
(a)
(b)
Fig 1. Quasi-optical (a) transmission and (b) reflection grid amplifiers.
(a)
(b)
Fig. 2. Examples of three-dimensional grid oscillator configurations: (a) An omnidirectional source
consisting of a 96 transistors, and (b) a self-oscillating mixer consisting of two grids placed on opposite
sides of a photonic crystal.
Secure Communications
Battlefield communication networks depend, in part, on mobility, security, and the ability to
detect and deter unfriendly disruptions and intrusions. Here we discuss two research projects
dealing with secure communications.
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We consider a mobile network based on retrodirective antenna arrays. A retrodirective antenna,
when illuminated by a source signal, has the ability to retransmit a signal directly back to the
source of the initial transmission without any prior knowledge of its location. Applications
include automatic pointing and tracking systems, radar transponders, self-tracking wireless
communication links, and security-sensitive transmissions.
We propose to develop
retrodirective arrays based on self-oscillating mixers, which not only retrodirects the IF signal
back to the source's location, but also radiates a free-running LO in all directions, serving as
an omnidirectional jamming signal to intercepting receivers. The concept is shown in Fig. 3.
Solid Dielectric Core
Incident RF Signal
fo + f
LO Jamming Signal
fo
Retrodirected IF Signal
fo - f
Self-Oscillating
Mixer Grid
Fig. 3. A three-dimensional retrodirective self-oscillating mixer array. An IF signal is retrodirected back to
the RF source while an LO jamming signal is radiated in all directions.
The self-oscillating mixer combines the mixing and LO functions, making a separate LO
unnecessary. A three-dimensional architecture would allow retrodirection of signals over a
greater range of incident angles than planar arrays, which typically can retrodirect signals only
within a 180 degree range. By allowing the RF, IF, and LO signals to operate at very nearly the
same frequency, the omnidirectional LO signal serves as a jamming signal to intercepting
receivers. The RF and IF signals, which are typically low-level in covert communications, are
masked to unwanted observers by the significantly higher-power LO. Frequency hopping of the
RF signal can also be used for thwarting interception of the covert communication. A
reconfigurable aperture for multi-band frequency operation could be achieved by incorporating
MEMS devices into the arrays. These reconfigurable, retrodirective antenna arrays could be
used as the basis for dynamically reconfigurable, secure communication networks.
A second area of research is in channel modeling of the battlefield environment Modeling
would include the effects of varied terrain, foliage, weather, and smoke in the range from 20 100 GHz. Based on these channel models which are likely to correspond to fading
environments, space-time bandwidth efficient coding techniques will be developed to achieve
reliable communications. These new error control techniques, designed across both space and
time, provide jointly coding gains and diversity advantages and therefore, particularly fit such
applications. Another research topic associated with this project is that of security. We propose
to investigate scenarios in which an attacker attempts to cancel the jamming signal based on
the knowledge about the way it is generated.
Furthermore, these techniques can be derived in conjunction with unequal error protection
(UEP), a scheme in which a certain percentage of critical information is always more protected
than the remaining part. As a result, a UEP coding scheme guarantees that the critical
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information is always retrieved at the receiver, while the remaining part can be lost in case of
unfavorable transmission conditions. A typical UEP scenario for the battlefield environment is
depicted in Fig. 4. In this figure, transmitter (a) attempts to send information to both base (b)
and base (c). The transmission between (a) and (b) is clear, so that all information is retrieved
without too much effort. On the other hand, the transmission between (a) and (c) is severely
distorted and any attempt to retrieve the entire information would fail. However, a UEP coding
scheme allows to reconstructed the critical information part with much more effectiveness
than the straightforward time sharing approach composed of two codes: one powerful code
associated with the critical information and one less powerful code associated with the
remaining information.
Fig. 4.
Mobile Wireless Networks
On the battlefield, many of the communications systems will consist of a number of hand-held
devices that must be effectively connected in a network. The networks will be mobile which
results in changing network topologies (ad-hoc networks). The ad-hoc networks must operate
effectively in a wide range of different environmental conditions and terrain changes. The
networks must also be able to transmit a variety of information sources over the mobile links.
We will address networking problems, communications systems design problems, and
efficiently transmission of multimedia traffic.
Network control will be distributed resulting in peer to peer architectures that are self
organizing and have adaptive capabilities. The ad-hoc networks will require new forms of
network protocols and management. The mobile and changing environments require accurate
channel propagation models. Satellite navigation systems such as the Global Positioning
System (GPS) will be used to locate the hand held devices. With these models in place a
performance analysis will be conducted to assess Quality of Service (QoS) guarantees. We will
study different signaling schemes for sending and receiving information streams in mobile
environments. This involves using coding, modulation, equalization, and detection algorithms
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to transmit different sources of information. Because transmitters and receivers are mobile
and environmental conditions change, many of the algorithms that will be deployed will be
adaptive. One class of algorithms that will be studied are blind source separation algorithms
where adaptive algorithms can be run without training sequences.
The hand-held devices will only be able to transmit and receive information at moderate data
rates. In order to successfully transmit and receive video data sophisticated compression
algorithms will be used. We will study traffic behavior and use source coding methods such as
wavelet transforms to send low bit rate video to and from mobile hand-held devices.
Strategic Strengths of the University of Hawaii
The University of Hawaii’s College of Engineering was one of the pioneers in wireless
communication technologies, having developed the first wireless packet radio system using the
ALOHA protocol some 30 years ago. The ideas used in this protocol strongly influenced the
development of the CSMA/CD access protocol used in the Ethernet, the network model most
widely used in the world for computer communications. More recently, faculty members have
developed error-control protocols that are currently used in telecommunication satellites for
NASA and Europe's Global Satellite Mobile (GSM) system as an international standard for
reliable data transmission.
To carry on this legacy, the College of Engineering recently formed the Center for Advanced
Communications to focus on next-generation wireless technologies. Over a dozen faculty
members in diverse research areas are jointly working together to develop a world-class
research and training center for wireless communications. The establishment of the Center for
Advanced Communications benefits both the State and the Nation:

State of Hawaii: Hawaii is in its ninth year of economic depression, primarily due
to its over-dependence on tourism as its major industry. Realizing the tremendous
economic potential of wireless communications, Hawaii Governor Benjamin
Cayetano recently approved $1 million in start-up funds for the Center, intending it
to provide a stimulus for a high-tech wireless industry in Hawaii.

United States: The Pacific Rim is anticipated to witness an economic boom, with
China expecting to make a large impact on the 21st century economy. Hawaii’s
strategic location between the mainland U.S. and Asia, as well as its central timezone position, means that it can play a pivotal role for the developing
telecommunications infrastructure in Asia. For example, U.S. companies can use
Hawaii as a staging ground for launching commercial ventures, drawing on UH
graduates who are not only trained in wireless communications, but who are also
well-versed in Asian language and culture.
The most important beneficiaries of a university research center is its students, and the Center
for Advanced Communications is dedicated to equipping its students with the research skills
necessary for maintaining our Nation’s leadership in wireless communications. Table I
summarizes the number and type of personnel who will be involved with the proposed
research.
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Fig. 4. The proposed research will be carried out in several areas within the UH Center for
Advanced Communications.
TABLE I: PERSONNEL WITH DIRECT ACCESS TO THE PROPOSED INSTRUMENTATION
Personnel
Faculty
Postdoctoral fellows
Graduate research assistants
Undergraduate students
Number
5
3
20
20
Recent Research Projects of the Wireless Center
Members of the Wireless Center have been involved in a number of projects in recent years:
PROJECT
Quasi-Optical Power Combining
(ARO)
Active and Reconfigurable Photonic
Bandgap Structures (DARPA/ARO)
Millimeter-Wave Systems for
Wireless Communication Systems
(NSF)
FUNDING
$X
1997 – 2002
$395,785
1998 – 2000
$399,952
1999 - 2003
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OBJECTIVE
Develop innovative circuit architectures
for combining solid-state devices
Develop advanced electromagnetic and
microelectromechanical structures
Develop novel devices, circuits, and
subsystems for millimeter-wave
wireless communications