Dennis J. Baker

A design concept for reliable mobile radio networks with frequency hopping signaling

The design of a packet radio network must reflect the operational requirements and environmental constraints to which it is subject. In this paper, we outline those features that distinguish the High Frequency (HF) Intra Task Force (ITF) Network from other packet radio networks, and we present a design concept for this network that encompasses organizational structure, waveform design, and channel access. Network survivability is achieved through the use of distributed network control and frequency hopping spread-spectrum signaling. We demonstrate how the execution of the fully distributed Linked Cluster Algorithm can enable a network to reconfigure itself when it is affected by connectivity changes such as those resulting from jamming. Additional resistance against jamming is provided by frequency hopping, which leads naturally to the use of code division mutiple access (CDMA) techniques that permit the simultaneous successful transmission by several users. Distributed algorithms that exploit CDMA properties have been developed to schedule contention-free transmissions for much of the channel access in this network. Contention-based channel access protocols can also be implemented in conjunction with the Linked Cluster network structure. The design concept presented in this paper provides a high degree of survivability and flexibility, to accommodate changing environmental conditions and user demands.

The Design and Simulation of a Mobile Radio Network with Distributed Control

A new architecture for mobile radio networks, called the linked cluster architecture, is described, and methods for implementing this architecture using distributed control techniques are presented. We illustrate how fully distributed control methods can be combined with hierarchical control to create a network that is robust with respect to both node loss and connectivity changes. Two distributed algorithms are presented that deal with the formation and linkage of clusters and the activation of the network links. To study the performance of our network structuring algorithms, a simulation model was developed. The use of Simula to construct, software simulation tools is illustrated. Simulation results are shown for the example of a high frequency (HF) intratask force (ITF) communication network.

A distributed simulation and prototyping testbed for radio communication networks

The authors discuss the development of a testbed, called the distributed simulation and prototyping testbed (DSPT), to model variable-connectivity radio networks. The DSPT constitutes a software environment in which distributed simulation and prototyping models of radio communication and command and control systems can easily be built. The environment consists of four separate software packages: communication simulation, communication monitor, scenario update/controller, and prototype node. These four packages work together to form a single distributed simulation and prototyping facility for communication network studies. They relieve the user from the need to consider many of the details that must be handled to implement a distributed testbed. Each package is easily extensible and can be tailored to specific networks, scenarios, monitor views, and prototyping needs. >

Distributed Network Reconfiguration in Response to Jamming at HF

The use of relays is known to increase the resistance of communication links to interference. In a multi-user network it is necessary to establish robust management techniques that allow the users to take advantage of the relaying power a network inherently possesses. In this paper we consider an Intra Task Force (ITF) Network that operates at HF. We employ a network architecture that provides for the automated selection of relay nodes without the need for a central controller. Under this architecture the network reorganizes itself in response to topology changes such as those that result from jamming. Communication range models suitable for a jammed HF channel are presented. We demonstrate that the combination of spread spectrum signaling, error correcting coding, path redundancy through frequency diversity, and adaptive relaying using automated network restructuring provide this network with a strong defense against jamming.

Comparison of two transmission strategies for use in survivable radio networks

The authors describe work examining two architectures for use with dynamically changing broadcast networks. The first architecture is a single channel network with a single transmitter and a single receiver per communication node. The second architecture allows the utilization of many frequencies and requires one transmitter and five receivers per node. Using both Monte Carlo techniques and topological analysis, throughput performance of the two architectures is characterized across several structural variables. The sensitivity of the performance to these variables is examined and explained for both architectures, as well as the significance of these sensitivities for realistic military environments. It is shown that using an equivalent equipment comparison between the architectures the multichannel system has better throughput performance than the single channel system across all topologies. In addition, since global connectivity information is not required for efficient operation in the multichannel architecture, it should be able to respond more quickly to changing conditions.<<ETX>>

Prototyping communication system software with the Distributed Simulation and Prototyping Testbed

The authors describe the Distributed Simulation and Prototyping Testbed (DSPT) and show how it is used to develop prototype software. The ability to prototype software offers significant advantages to the successful development of C/sup 3/ systems, which are typically distributed, complex, and hard to test. The DSPT itself is a distributed system. However, its distributed nature is transparent to the user since interprocess communication and synchronization are handled automatically. The DSPT also provides detailed models of physical layer objects, platforms, transmitters, receivers, etc., via a well-defined interface. This interface provides the context for developing models of higher layer protocols. The use of DSPT tools to develop prototype software for the US Navys Unified Network Technology is considered.<<ETX>>

Design, implementation, and use of a real-time distributed simulation testbed for mobile communication networks

There is a need to design, develop, and test new mobile communication networks for military applications. The hardware cost to outfit a single node may be quite high. Much of the cost is in rf hardware, modems, and encryption devices. Replicating such costs over several nodes and adding the cost of maintaining a field site can quickly lead to unacceptable budget levels. One solution to this problem is, in the initial development and testing phase, to develop network communication systems that can operate with either real or simulated transmitters, receivers, modems, etc. This paper describes how we accomplished this task for the development of a high frequency, data/voice (D/V) mobile network. The underlying, distributed, real-time simulation software evolved from Sim++2. On top of this we built a simulation package to model mobile communication networks. Software for the SubNet Controller (SNC) of the hf D/V Network was developed to work with these simulation packages as well as to work with real rf equipment. The SNC software was tested in a 6-node network in which some of the rf equipment was simulated and some was real. The resultant system provides a testbed for examining the performance of command and control systems that must operate over mobile rf communication systems.

The use of multiple protocols in multi-hop radio networks

The authors introduce the idea of multiple protocols and illustrate its validity by considering the problem of routing in multihop radio networks. A continuing, simulation-based performance evaluation at Naval Research Laboratorys (NRL) Distributed Simulation and Prototyping facility shows that overall network performance improves significantly when multiple protocols are switched in response to changing environmental conditions rather than using a single routing protocol. Dynamic conditions illustrated in the simulations are implemented as changes in topological connectivity. Important new issues that arise when multiple protocols are employed are identified for further research.<<ETX>>

The design of a flexible distributed testbed for communication systems

The structure and design of a simulation testbed for communication systems are described. The testbed, which is called the Distributed Simulation and Prototyping Testbed (DSPT), models the physical-layer activities of communication networks with a design that facilitates the addition of higher-layer protocols either as part of the simulation program itself or as prototype software that can execute concurrently with the simulation on a separate machine. As is typical of R&D systems, the DSPT requirements have evolved with the projects that it supports. The author shows some of the benefits of developing software using the object-oriented methodology in the dynamic R&D environment. The design involves extensions to the Simula programming language, which are easily implemented using Simulas class inheritance capability. The author explores these extensions and discusses further needs of the Simula language that appeared during the implementation of DPST.<<ETX>>