Jim Marshall

Shipboard experiments for a multihop 802.11 communications system-RF channel characterization and MAC performance measurement

Wireless relays offer one approach to providing communications among small teams operating below-decks on neutral or hostile ships. Two sets of experiments were conducted aboard a container ship to determine the viability of this approach. In the first set of experiments, RF propagation loss and coherence bandwidth were assessed in both the 2.4 GHz and 5.8 GHz ISM bands. In the second set, packet latency and throughput were assessed for 802.11a and 802.11b networks operating in multihop configurations with hidden nodes. On the basis of these experiments, it is concluded that the wireless relay concept is workable in the shipboard environment using 802.11 wireless networks. The 802.11 variants offer different trades among data rate, relay separation, and supporting hardware requirements

Non-homogeneous gain state optimization for transponding satellite communications

Recent advances in the design of transponding communications satellites the ability to switch transponder sub-bands among multiple up-link and down-link antennas. This feature increases the flexibility of traffic routing and improves spectral re-use characteristics. A side benefit of such a new system is the capability of applying different transponder gains to carriers in different sub-channels within a given transponder. Recently, techniques have been developed for analyzing link supportability and the transponder loading with these non-homogeneous gain states. However, these new analysis techniques require that the gains be known a-priori. to complement these analysis techniques a method is needed for selecting the best gains to be used in each sub-channel. This paper presents such a method for selecting transponder gains. We define the constraining equations, which ensure that each link can be supported, and propose a optimization metric that maximizes the overall supportability. We the suggest an optimization approach that can be sued to select the gains for each sub-channel and the overall transponder operating point. The approach described includes a means of selecting the starting point for the optimization. A numerical example is provided.

A communications analysis tool set that accounts for the attenuation due to foliage, buildings, and ground effects

The purpose of this paper is to describe a communications analysis tool, referred to as OPAR, that can be used in support of both in-field demonstrations and large-scale simulation activities. Using overhead imagery as a backdrop, OPAR provides a graphical user interface that allows the user to quantify the source/destination path attenuation in a mobile, ad-hoc communications network, taking into account obstructions due to foliage and buildings.

COMMUNICATIONS CONCEPTS TO SUPPORT EARLY IMPLEMENTATION OF IVHS IN NORTH AMERICA

ABSTRACT The most critical element of Intelligent Vehicle Highway Systems (IVHS) will be the communication system that links the highway infrastructure and mobile vehicles. Not only must it be designed to allow users who purchase systems in one city to travel or permanently move to another, but also it must support robust, relatively high-capacity data communications, at least in the infrastructure-to-vehicle (ITV) direction, and have a cost that is in balance with the perceived benefits that the overall IVHS system provides to users. The availability of ITV communications, in particular, is essential to the implementation of nearly all other aspects of IVHS. As a result, a need exists to expedite the definition, development and implementation of this subsystem. It is in fact more important to provide an early ITV communications capability in order to support other IVHS developments than it is to ensure that the first ventures into this area are the “best” solutions to long-term IVHS needs. This paper dis...

Algorithms for MUOS Capacity Analysis

The Mobile User Objective System (MUOS) for satellite communications (SATCOM) is being developed to provide important beyond line-of-sight (BLOS) communications for tactical military users. There is a keen interest in the MUOS data rate capacity as it relates to the available system bandwidth. A set of wide-band code-division multiple access (WCDMA) waveforms will be used to share bandwidth among users and so multiple access interference (MAI) must be considered in evaluating system capacity. In addition, frequency reuse is accomplished based on the employment of multiple satellite beams. While this improves the system capacity, it complicates the supportability analysis because adjacent beam interference can increase the MAI and, as a result, can impact system capacity. The purpose of this paper is to develop algorithms that determine supportability for a given set of links in the MUOS system. These algorithms will be useful in determining system capacity for heterogeneous sets of links. The algorithms take into account the MAI impact of other beams using the same carrier from the same and adjacent satellites. Furthermore, these algorithms have been designed to significantly reduce the dimensionality of the problem and, hence, ease the computational burden required for link supportability calculations. An example capacity calculation is shown for a homogeneous set of users.

Link Analysis of Commercial and Wideband Gapfiller Satellite (WGS) Satellites Using DVB-S2 with Variable Coding and Modulation (VCM)

A link analysis was performed of the digital video broadcast-satellite (DVB-S) second generation waveform (DVB-S2) using a commercial (Ku band) and the wideband gapfiller satellite (WGS) satellite at X-band and Ka-band. The analysis is for the CENTCOM VSAT network (also known as the global war on terrorism [GWOT] network) that uses the EUTELSAT W6 satellite (21.5deg east) and supports both forward (DVB-S) and return traffic [DVB-return channel by satellite (RCS)] traffic in the same 72 MHz transponder. The forward traffic consists of nominal DVB-S broadcasts to receive-only terminals (1 m) as well as duplex 1.8 m and 2.4 m terminals. The return traffic consists of constant-rate, tactical, video feeds (from the 2.4m terminals) along with SIPRNET Internet protocol (IP) interactive traffic (from the 1.8 m terminals). The hub is located at Landstuhl, Germany. The paper considers 3 cases. First, the capacity of the Eutelsat W6 transponder is computed for the forward and return traffic sharing the same transponder. Next, the capacity is computed for DVB-S2 using constant coding and modulation (CCM) and variable coding and modulation (VCM) over the baseline GWOT network. Finally, the system capacity is computed using WGS (at 60deg east) again using DVB-S2 with CCM and VCM and DVB-RCS

Approaches and requirements for tactical SATCOM ATM integration

Military procurement philosophy is currently evolving toward the use of commercial off-the-shelf (COTS) products to reduce cost to the taxpayer and to provide military users with advanced technology. Meanwhile, commercial asynchronous transfer mode (ATM) products are being developed and implemented in commercial communications networks. This commercial technology is rapidly progressing toward international standardization. Furthermore, with promises to offer multimedia services and potential interoperation among different communications networks by multiplexing all offered traffic statistically, ATM could provide a significant enhancement to tactical communications services and improve satellite resource utilization efficiency. This paper develops and compares several approaches for integrating ATM technology into the tactical SATCOM networks. The paper also identifies requirements including forward error correction, automatic repeat requests (ARQ) and congestion controls for the integrated tactical SATCOM ATM (TSA) network.

Mixed channel resource allocation analysis

Concepts of operation for SHF DSCS MILSATCOM are currently evolving to allow a mix of ECCM, FDMA and TDMA/DAMA traffic in the same transponder. Techniques for analyzing supportability for scenarios with a mix of ECCM and FDMA traffic have been developed. However, to support DAMA operation, techniques are needed for allowing quick allocation of satellite resources in mixed channel scenarios, with hierarchical arbitration and guaranteed supportability. This paper analyzes the hierarchical resource allocation problem in mixed channel scenarios for the case where all time slots in any TDMA waveform have approximately the same amplitude. The paper determines the parameters needed by the central controller in making allocation decisions and the resources that need to be allocated. The relationship between the level of allocation of these resources and network supportability are also determined along with the required uplink EIRP for each transmission. The hierarchical allocation of resources for DAMA operation in mixed channel scenarios is possible using the techniques described in this paper.<<ETX>>

WGS Capacity using the DoD Joint IP Modem (DVB-S2, RCS)

The DoD joint internet protocol modem is based on the digital video broadcast (DVB) standard. In a star network topology the forward traffic is DVB-Satellite 2 (DVB-S2) and the return traffic is DVB-return channel by satellite (DVB-RCS). The joint modem adds an embedded TRANSEC capability and a mesh overlay allowing user terminals to communicate without passing through the hub. The analysis will take advantage of the variable coding and modulation (VCM) feature [as well as the constant coding and modulation (CCM) feature of DVB-S]. First, the DVB-S2 capacity will be determined for wideband gapfiller satellite (WGS) located at 175deg east using a set of reference links located in Korea using CCM and VCM in the forward direction. Then the capacity of WGS will be determined in the return direction using DVB-RCS. Finally, the mesh capacity will be determined using WGS with VSAT terminals (1m) in Korea for voice over internet protocol (VoIP) traffic

The communications resource planning tool

In tactical environments where radio communications is critical to operational missions, the ability to predict connectivity is of primary importance. Success in closing radio links in these scenarios depends to a great degree on degradations to the link including obstructions that might obscure line of sight between transmitters and receivers. Jammers can also severely degrade communications performance. The effects of these factors must be taken into consideration in the planning and performance prediction of tactical wireless links. This paper describes a tool that can be used to plan communications links in the presence of degradations such as path obstructions or the effects of jammers. We describe the tool and its features. The equations for determining the impact of jammers are provided and an example is shown.