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TRANSCRIPT
Centrally Controlled Dynamic Spectrum Access forMANETs
(Invited Paper)
Jeffrey Boksiner, Yuriy Posherstnik, Bryan MaySpace and Terrestrial Communications Directorate (S&TCD)
US Army RDECOM CERDEC, Aberdeen Proving Ground, MD, USA
Mark SaltzmanCommunications, Networks & Electronics Division
Scientific Research Corporation, Aberdeen, MD
Sherin KamalSAIC Inc. VA
Abstract—In this paper, we describe an approach to ad-dress increased demand for spectrum access associated withwidespread deployment of Mobile Adhoc Networks (MANETs)in a military environment. Our solution is an approach thatwe call “MANET Real-Time Frequency Management” (MRFM)that uses centralized control to achieve deconfliction with thebackground Electromagnetic Environment (EME) and amongthe mobile MANETs. Our approach automates frequency reuseamong MANETs and automates MANET spectrum sharing withbackground systems using a centralized reasoner and controlmechanism. Our system, which runs as an external application,collects MANET radio state information in real time, appliesspectrum policies, performs spectrum deconfliction and controlsthe frequencies used by the MANET remotely. Our approach doesnot require any modifications to the radio physical, media accessor link layer protocols (the “waveform”). The use of our systemprovides an expedient approach to enable Dynamic SpectrumAccess (DSA) capabilities to MANET radios that currently donot have such capabilities without requiring modifications tothe radio waveform or the radio itself. To validate the MRFMconcept, we implemented MRFM in a prototype system that wassuccessfully demonstrated in several tests.
I. INTRODUCTION
Department of Defense (DoD) policy for the the use of
the electromagnetic spectrum [1] lists several core principles.
These principles include the following:
• Ensure the U.S. warfighter has sufficient spectrum access
to support military capabilities.
• Use the spectrum as efficiently and effectively as practical
to provide the greatest overall benefit to warfighting
capability.
• Pursue spectrum-efficient technologies to support the
increasing warfighter demand for spectrum access and
encourage development of spectrum-dependent systems
that can operate in diverse electromagnetic environments
(EMEs).
Within the context of Army network modernization, key
application of these principles concerns spectrum efficiency
and effectiveness of Mobile Adhoc Networks (MANETs). To
facilitate spectrum access improvement in the near term, it
is desirable to introduce spectrum technology improvements
without waveform modifications, as defined by the DoD
waveform policy [2], or radio hardware changes.
In this paper, we describe one approach to address increased
demand for spectrum access associated with widespread de-
ployment of MANETs in a military environment. Our ap-
proach automates frequency reuse among MANETs and au-
tomates MANET spectrum sharing with background systems
using a centralized reasoner and control mechanism. Our sys-
tem, which runs as an external application, collects MANET
radio state information in real time, applies spectrum policies,
performs spectrum deconfliction and controls the frequencies
used by the MANET remotely. Our approach does not require
any modifications to the radio physical, media access or
link layer protocols (the “waveform”) or radio hardware. The
use of our system provides an expedient approach to enable
Dynamic Spectrum Access (DSA) capabilities to MANET
radios that currently do not have such capabilities without
requiring waveform modifications.
A. MANET Spectrum Considerations
Widespread deployment of any broadband service requires
highly efficient use of spectrum. The most important el-
ements of this efficient spectrum use is spatial frequency
reuse. Just like commercial services, widespread deployment
of MANETs in the military environment to provide voice,
data and situational awareness will require frequency reuse,
however military MANETs face unique spectrum challenges.
• Heterogeneity. Unlike the majority of commercial net-
works that operate on an exclusive use model over a given
geographical area, a variety of military systems must
share the same spectrum within an operating area. This
means that frequencies assigned to MANETs must be
deconflicted against all other military and civilian joint,
coalition and neutral systems (receivers and transmitters)
operating in the environment. The collection of these
background systems generally constitute the EME.
• Mobility. The defining feature of MANETs is mobil-
ity and ad-hoc topology. Unlike commercial networks,
MANETs have no fixed infrastructure (base stations,
2013 IEEE Military Communications Conference
978-0-7695-5124-1/13 $31.00 © 2013 IEEE
DOI 10.1109/MILCOM.2013.115
641
access points, etc.) to anchor the reuse patterns. Also, mil-
itary MANETs are organized hierarchically to correspond
to the organization of the military units. A particular
MANET moves along with the unit it supports. Although
movements are based on maneuver plans, the movement
of MANET nodes are subject to military contingencies
and are not fully predictable.
The combination of the need to locally deconflict against the
background EME and to support frequency reuse for mobile
networks with no fixed infrastructure presents a formidable
challenge to MANET spectrum management. One solution
is to assign frequencies to each MANET using pre-mission
spectrum planning tools, such as the Coalition Joint Spectrum
Management Planning Tool (CJSMPT) [3], While effective,
this approach is suboptimal, since the spectrum plan must
allow for a variety of contingencies and various deviations
from the maneuver plans. Another approach is Policy-Based
Radio (PBR) with sensing-based Dynamic Spectrum Access.
While sensing-based DSA should provide efficient spectrum
use, it’s implementation requires considerable change to the
radio protocols and the supporting spectrum management
infrastructure. Our goal is to enable PBR and DSA features in
current non-DSA MANET networks without modifying the in-
trinsic MANET protocols. Our solution described in this paper
is an approach that we call “MANET Real-Time Frequency
Management” (MRFM) that uses centralized control to achieve
deconfliction with the background EME and among the mobile
MANETs. In this paper we describe MRFM and a system we
have developed to implement and demonstrate MRFM.
B. Organization
The remainder of the paper is organized as follows:
• Sec II describes the basic principles and the algorithms
of MRFM.
• Sec III provides the MRFM system description.
• Sec IV describes the results of MRFM implementation
and demonstration.
• Sec V is the conclusion section.
II. MRFM PRINCIPLES AND ALGORITHMS
We assume that a number of MANET networks are required
to operate within a commanders Area of Interest (AoI). Also,
we assume that an enterprise frequency management process
exists that assigns frequencies to fixed and mobile emitters
and that these assignments and the appropriate equipment
characteristics are stored in a spectrum database, such as
the Spectrum Knowledge Repository (SKR) that is contained
within CJSMPT mentioned in refsec:challenges. This assump-
tion is consistent with the architecture proposed for policy-
based spectrum management [4]. The MANETs are allotted a
number of frequencies in the AoI such that
• The number of MANETs exceeds the number of allotted
frequencies requiring frequency reuse, and
• One or more MANET AoI-wide frequencies overlap
frequencies assigned to background systems requiring
local EME deconfliction.
Fundamentally, MRFM operation consists of the following
two steps:
1) Development of the digital spectrum policy for the
MANET AoI, and
2) Execution of the spectrum policy and a simultaneous
real-time frequency deconfliction among MANETs
The advantage of developing the spectrum policy first is that
the process of reasoning against this policy, which consists
of a policy query, is considerably faster that computation
of the interference between MANET and background EME.
However, the conversion of the background EME into policy
introduces a slight loss of fidelity, so that in cases where the
background EME is small, it is advantageous to skip the policy
step and perform all deconfliction in real-time.
A. Interference Determination
The spectrum policies and the real-time deconfliction are
based on evaluation the interference equation, which represents
the link budget equation applied to the interfering signal. The
equation using dB units is
PRFI = PTD − Ll, (1a)
Ll = LO + LS(p)−GTD(φ, θ)−GRP (φ, θ), (1b)
where
PRFI is the received power of the potential interferer,
PTD is the transmitter power of the potential transmitter,
Ll is the total loss ,
GTD is the directional antenna gain of the interferer,
GRP is the directional antenna gain of the receiver,
LS is the propagation loss that is exceeded for a percent-
age of time (probability) p, and
LO represents the sum of other possible losses, such as
line loss, cross-polarization loss, etc.
To evaluate interference over a given frequency range we
need to determine the interference power that propagates to
the receiver detector PI by subtracting the losses due to the
receiver filters. We calculate this extra loss using Frequency
Dependent Rejection (FDR) as follows [5]:
PI = PRFI − FDR(Δf). (2)
FDR represents the power loss due to receiver filtering and is
given by
FDR(Δf) =
∫∞−∞ df S(f)
∫∞−∞ df S(f)R(f+Δf)
, (3)
where
S(f) is the transmitter power spectral density assuming
the signal is uninterrupted,
R(f) is the receiver selectivity with the receiver tuned to
the transmitter frequency, and
Δf is the frequency separation between the interferer and
victim.
We evaluate the presence of interference by comparing PI to
an interference threshold, known as the Interference Protection
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Criterion (IPC) α. Unacceptable interference is deemed to
occur if PI > α. The most reliable way to determine the IPC
is by direct laboratory measurement. An alternative is to use
a signal-to-interference (SIR) or interference-to-noise (INR)
criterion defined by
α = N + INR, (4)
where N is the noise power at the receiver detector. Typically,
it is common to use INR = −6 dB.
The preceding analysis technique assumes that the inter-
ference determination is determined by considering a single
dominant interferer. This is reasonable on heuristic grounds
since each MANET operates on time-division basis, so we
expect that the single dominant interference event will control
interference determination. The survey of interference analysis
techniques in ref [6] observes that the literature has shown that
the “single dominant interferer” approach is effective approach
under a high (∼ 4) path loss exponent. Since a high path loss
exponent is generally associated with ground networks, and
the overall number of networks is relatively small, we expect
that our approach provides a sound solution.
B. Digital Spectrum Policies
Spectrum policies represent a variety of rules that control
how a DSA system uses spectrum. In MRFM, we primarily
develop spatial policies. Spatial policies define spatial restric-
tions on the use of frequencies by the MANET. The restrictions
are based on the protection of the background receivers from
interference by the MANET and protection of the MANET
nodes from interference by the background emitters. The
restrictions are defined for co-channel and adjacent channel
operation. The concept of the spatial policy is similar to the
protection areas commonly used in spectrum management.
1) Fixed Systems: Calculation of a protection policy for
fixed background systems is straight-forward. Since we know
the relevant technical parameters of each receiver from the
spectrum database, it is possible to calculate a detailed pro-
tection contour using eq. 1. In general, the protection contour
may be disconnected due to terrain effects. Since determining
location with respect to an arbitrary contour is computationally
expensive, the exact contour may be replaced with simpler
shapes that envelop the actual contours. Queries with respect to
a rectangle or a circle are simpler and can be used to represent
the contours. Fig. 1 shows the notional representation of exact
and simplified protection contours.
The dimensions of the protection contour are a function of
frequency separation between the receiver and the interferer.
2) Mobile Systems: The extension to the case of mobile
background systems is also straight-forward if their Area of
Operation (AoO) is in the spectrum database. We suggest three
basic approaches:
• Monte-Carlo simulation that calculate interference from
a random sample of locations. This is the most thorough
approach, but is also the most resource and time intensive.
• An approach that calculates the protection contour from
the boundary of the AoO. This is a conservative approach,
Fig. 1. Illustration of the concept of spatial prohibitive policy. Solid linesrepresent exact contours for prohibitive policy for co-channel (CC) systems,while the dashed line represent the contour for an adjacent channel system.DSA systems operating inside the contour apply the prohibitive policy andare not allowed to operate at the frequencies specified by the policy.
since most of the time, the mobile nodes are inside
the boundary. Also, this approach may miss interference
regions from points at high elevation inside the AoO.
• A hybrid approach that calculates the protection contour
on the basis of points at the boundary and high-elevation
points inside the AoO. This approach is less intensive
than full Monte-Carlo simulation. We selected this ap-
proach for our systems.
C. Deconfliction
Once the policies are established, the remaining key al-
gorithm concerns deconfliction of the MANET frequencies.
There are two steps to the deconfliction algorithm:
1) Computing the adjacency matrix that indicates what nets
can interfere with one another, and
2) Frequency selection using a graph coloring algorithm.
We describe these two steps in the following.1) Adjacency Matrix: The adjacency matrix is the graph-
theoretic representation of interference relationship among
nets. If each network is represented by a vertex, the adja-
cency matrix identifies the edges between the vertexes, where
each edge indicates a potential of the interference between
the networks. When two networks have potential for mutual
interference we call such networks coupled.
We compute the adjacency matrix by evaluating the interfer-
ence equation described in Sec. II-A between each node in one
MANET against every other node in all other MANETs. Also
we treat all relevant background systems as additional vertexes
in the adjacency matrix. We evaluate the coupling between
MANET nets and background systems either by evaluating
interference directly or by checking if any MANET network
members are within the prohibited policy contour associated
with the background system.
Fig. 2 shows an example of an adjacency matrix. In our
format, the matrix is formatted to contain 2 digit integers
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Fig. 2. An example of an adjacency matrix. The matrix is formatted to contain2 digit integers indicating the maximum interference dB above threshold thatany given node in a subnet was calculated to receive from a transmittingsubnet. The background systems are denoted in the matrix with a capital F.
indicating the maximum interference dB above threshold that
any given node in a subnet was calculated to receive from
a transmitting subnet. Any number in the matrix above 0
indicates the subnets are coupled, and will interfere with
each other on a given frequency. The matrix also contains
information regarding background systems (fixed frequency),
to ensure the background emitters are protected and their
frequencies do not get reused if an MRFM subnet would be
coupled to the background emitter. The fixed frequencies are
denoted in the matrix with a capital F.2) Frequency Selection: The Frequency Selection Algo-
rithm (FSA) is based on the well-known equivalence between
the problem of assigning non-interfering frequencies and ver-
tex graph coloring [7]–[10]. Our algorithm uses the sequential
graph coloring algorithm [10]. While, this algorithm is known
not to be optimum, it is simple and executes quickly.
In some cases, there may not be enough available fre-
quencies to ensure deconfliction between all the subnets. If
the case occurs, the FSA will start to decouple subnets to
gain assignable frequencies. The decoupling will be based
on the adjacency matrix from SAM, with the lowest priority
subnet being decoupled first. The lowest priority subnet will
always be decoupled first with the next subnet that contains the
lowest calculated interference above threshold. This ensures
the algorithm always provides a solution, and the subnets
always have a frequency assignment. However, in a scenario
where the spectrum requirement at a given time is greater than
the available spectrum, subnets may experience interference.
Once additional spectrum becomes available again, SAM will
produce a new adjacency matrix and the FSA will reassign
frequencies to ensure deconfliction on a non-interference basis.
III. MRFM SYSTEM DESCRIPTION
The MRFM system consists of the following components:
• Spectrum Database
• MANET Electromagnetic Environment Map (MEEM)
• Mission Thread Template (MTT)
• Electromagnetic (EM) Proxy
• Spectrum Analysis Module (SAM)
• Reasoner
• Communications Server
• Graphical User Interface (GUI)
Fig. 3. An example of graph coloring on an adjacency matrix. Each vertexrepresent a MANET network and edges represent possible interference. Dif-ferent vertex colors correspond to different frequencies separated sufficientlyto avoid adjacent channel interference.
Fig. 4. The MRFM system description.
• Radio Control Toolbox Module (RCTM).
The following sections describe each of these components.
Fig. 4 shows the MRFM system as we implemented it for our
demonstration.
A. Mission Thread Template (MTT)
The MTT requires the user to gather the requirements and
specifications about the non-DSA subnets being controlled by
the MRFM. This information includes: Network ID, Radio
ID, Transmit Power, frequency pool, net force structure, and
equipment characteristics. The MTT is provided as an input
to the Proxy, which then queries the Spectrum Database based
on the data provided by the MTT. The MTT is also provided
as input to the GUI to enable the visualization of the available
frequency pool and the net force structure.
The mission scenario AoI is contained within the MTT. The
MTT also contains the pieces of equipment to be used, and the
net force structure to identify which piece of equipment is in
which net. The user loads the MTT using the GUI, which
provides all that information to the 3D GUI visualizer, as
well as to the Proxy. The GUI displays the frequency pool, as
well as the real-time location and operating frequency of all
subnets. The Proxy uses the AoI coordinates provided in the
MTT to query the spectrum database, gather the background
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emitter records, and to obtain equipment characteristics for the
systems operational within the AoI. The Proxy then formats
the database query results into a standardized XML format
which can then be read by SAM.
B. Spectrum Database
A spectrum database is a relational collection of information
necessary to perform spectrum analysis calculations and fre-
quency deconfliction. The database must contain information
such as the required transmitter and receiver characteristics
of any system that has received a frequency assignment. The
database provides information through the Proxy to be used
as input by the Spectrum Analysis Module.
C. MANET Electromagnetic Environment Map (MEEM)
The MEEM is an entity containing all the relevant radio
information that may be used by one or more of the system
components within the MRFM. The MEEM includes infor-
mation such as: Lat/Long of each node in each subnet, the
frequency setting of each node in each subnet, and the radio
state of each node in each subnet. The MEEM is implemented
as a local multicast group, enabling any of the components to
join the group and subscribe to receive updates in real time.
The interface is defined using XML messages.
D. EM Proxy
The EM Proxy is the central interface between the different
components of the MRFM. The Proxy queries the spectrum
database to obtain background spectrum assignments for the
AoI for a given mission scenario. The database query also
contains equipment characteristics, to provide information
such as TX power, receiver sensitivity, transmitter emission
masks, receiver selectivity curve, etc. Once the Proxy receives
the results from the database query, it must transform it into
an XML format that is understood by SAM.
In addition, the Proxy also provides information to the
GUI to enable visualization of real-time movement, operating
frequency, and radio status.
E. Spectrum Analysis Module (SAM)
SAM is the computational brain of the MRFM system. SAM
implements the interference analysis, including FDR, propaga-
tion analysis, and policy generation described in Sec. II-A and
II-B. SAM is capable of generating spatial digital spectrum
policy in machine-readable OWL format [11], [12], where the
operational frequencies of the background nets are prohibited
from use by any other nets within the protective contour. SAM
is also capable of producing protective grids, as shown in Fig.
3. Finally, SAM computes the adjacency matrix based on net
to net interference calculations.
F. Reasoner
The Reasoner receives Position Location Information (PLI)
from each MANET node (accessed through the MEEM), as
well as the adjacency matrix created by SAM. The FSA,
contained within the Reasoner, uses the matrix as an input, and
identifies the optimum frequency reuse for the given locations
(a) (b)
Fig. 5. Illustration of notional protection contours for a passive receiver.Solid lines represent exact contours that would be calculated at a particularfrequency for a particular probability of interference.
of each MANET node at a given time. Once all acceptable
frequencies are assigned, the Reasoner provides a list of each
subnet with its proper corresponding frequency assignment to
the Communications Server.
While the module is referred to as a Reasoner, it may not
necessarily be doing any reasoning on digital policies or other
cognitive reasoning, as a Computer Science definition would
imply. The functionality of the Reasoner depends on the mode
of operation for SAM, as well as on the native capabilities of
the radio hardware being used.
G. Communication Server
The MRFM relies on the Simple Network Management
Protocol (SNMP), an Internet-standard protocol for managing
devices on an IP network to enable control of the communi-
cation systems from the Communications Server.
The Communications Server provides the interface between
the software and the MRFM-enabled network. The Server
receives the PLI, decodes the PLI, converts it to degrees lati-
tude and longitude, and provides the locations to the MEEM.
Once SAM calculates an adjacency matrix, the Reasoner de-
termines which frequency preset must be used on each subnet.
The Communications Server then sends out an SNMP “set”
command to the local multicast group. A similar component,
RCTM, also exists on each End User Device (EUD) attached
to every MRFM radio node. When the Communications Server
sends out the multicast SNMP command, each RCTM running
on the EUD in that group receives the command, and executes
the frequency preset change on the respective local radio node.
H. Graphical User Interface (GUI)
The GUI serves the function of providing an interface
and visualization of the operational scenario for the user.
The GUI consists of the NASA World Wind 3D mapping
and visualization suite. The GUI also uses the MEEM to
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Fig. 6. The screen capture of the MRFM user interface.
obtain the PLI for all nodes, with each PLI then displayed
on the map. Background emitters, which are queried from the
spectrum database by the Proxy and provided to the GUI, are
also displayed using the military standard icons MIL-STD-
2525C [13]. The MTT provides the list of available frequency
channels from the frequency pool, which is then displayed in
a table. The table also indicates which net is operating on
which frequency. This information is not vital, but is useful
in providing situational awareness for the user. Fig. 6 shows
a screen capture of the user interface.
I. Radio Control Toolbox Module (RCTM)
The RCTM is a key component of the MRFM, allowing for
the real-time frequency management of the MRFM-enabled
radio nodes. The RCTM resides on an Android-based device or
within the operating system of the radio, if available. The mod-
ule is responsible for polling and aggregating PLI data from all
the radio nodes. The polling is to ensure connectivity between
the Communications Server and the RCTM. The aggregate PLI
is used within the MRFM to discover the network hierarchy,
since it provides additional information such as node identifier
and minimizes the network overhead by reducing the amount
of messages passed between the Communications Server and
each radio node’s RCTM. The PLI is crucial information for
SAM, because the spectrum analysis calculations are based
on each node n real-time location. The RCTM also receives
frequency change commands from the Communications Server
and executes those changes on the local radio nodes.
IV. IMPLEMENTATION AND DEMONSTRATION
We implemented the MRFM in a demonstration system. The
hardware used for implementation included one laptop running
the software, several Android devices, and several radios. The
spectrum database used for the implementation was the SKR
contained within CJSMPT mentioned in Sec I-A.
The implementation of the RTFM was performed in sev-
eral phases. The first phase was a proof of concept, where
one MANET subnet was deconflicted with many background
emitters, and a grid-based digital spectrum policy was used
by the RCTM to ensure non-interference during real-time
frequency management of other MANET systems. The proof
of concept was successfully demonstrated at a series of field
experiments. The second phase was a developmental product
where multiple subnets are deconflicted with each other, as
well as with background emitters. The deconfliction ensures
non-interference, while the frequency selection algorithm pro-
vides greatly increased spectral efficiency and spectrum reuse.
This capability was also successfully demonstrated in several
outdoor tests.
V. CONCLUSION
We have developed a novel approach for providing DSA
capabilities to non-DSA MANETs through centralized control.
While the initial application of this technology is to improve
effectiveness of the MANET spectrum use, this capability can
be extended to support other applications, such as spectrum
sharing between military and commercial communication sys-
tems. Centralized MANET control could facilitate MANET
operation as either a primary or secondary user in bands
shared with commercial wireless systems. We believe that the
use of centralized control offers many possibilities for future
MANET capabilities and research.
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