Advanced Communication Systems

image of four-channel WCDMA (wideband code division multiple access) signal, one of the 3G standards, with and without digital predistortion. The WCDMA signal is wideband code division multiple access, one of the 3G standards

Four-channel WCDMA (wideband code division multiple access) signal, one of the 3G standards, with and without digital predistortion.

image of software-defined radio on a CD demo system–UHF radio using OSSIE SCA (open source SCA implementation: embedded), FSK/PSK/MSK modem, standard laptop, and USB-based RF interface devices

Software-defined radio on a CD demo system – UHF radio using OSSIE SCA (open source SCA implementation: embedded), FSK/PSK/MSK modem, standard laptop, and USB-based RF interface devices.

Image of Specialty antenna: tapered-aperture small-helix antenna

Specialty antenna: tapered-aperture small-helix antenna.

image of transceiver trade space analysis tool

Transceiver trade space analysis tool.

Image of example custom protocol simulation scenario

Click image for enlarged view 
Example custom protocol simulation scenario.

Image of custom protocol implementation hardware timing results

Click image for enlarged view 
Custom protocol implementation hardware timing results.

During the last decade, programmable digital radio systems have been replacing fixed analog radio systems as programmable hardware components have become more capable, inexpensive and available, and wireless communications applications have demanded reusable, reconfigurable and flexible radios.

Engineers at Southwest Research Institute (SwRI) have extensive experience in research and development projects involving flexible communications systems and software-defined radio for commercial, military, and other government agencies. SwRI has demonstrated the viability of this technology through system simulations and hardware demonstrations.

Software-Defined Radio Architecture

SwRI has conducted software-defined radio research for implementation of software architectures on general purpose processors and other programmable hardware components. In addition, engineers have researched and developed architectures for specialty applications such as:

  • New military radios that require quick-boot software component architecture
  • Software-defined radios that require compliance with the Joint Tactical Radio System
  • Software-defined radios for application in the space exploration domain

Model-Based Design Systems

Model-based design tools for software-defined radio and other radio systems have also been developed at SwRI. One set of models describes:

  • Communications and processing requirements
  • Available hardware
  • Relevant properties of the alternative software architectures

This model-based design tool allows the design space to be quickly searched and incrementally refined in higher payoff regions.

Miniature Software-Defined Radio Satellite Terminal

Engineers designed and implemented a reconfigurable satellite terminal that was compatible with an existing satellite network, and transmitted small data packets over a low-bit rate channel to the network. The terminal was extremely small and built with commercially available parts. Engineers developed a waveform that was compatible with the network and implemented the waveform firmware and integrated it with other devices and an RF module to create a small low-power satellite terminal. In order to successfully integrate with the existing satellite network, and due to poor documentation of the system, the SwRI team had to employ complex and sophisticated reverse engineering techniques.

Digital Predistortion

Digital predistortion is an important enabling technology for software-defined radio because it:

  • Improves spectrum control and efficiency
  • Can support more flexible radio frequency (RF) hardware

Internal research at SwRI has produced a set of algorithms for digital predistortion, including:

  • Linear and non-linear compensation
  • Memory effects compensation
  • Crest-factor reduction

Engineers have also developed proof-of-concept subsystems for digital predistortion in third-generation (3G) cellular, television, and other broadcast systems.

Smart Antennas

Smart antenna systems can adaptively point the main antenna beam in the direction of a desirable transceiver and can be made to resonate at different frequencies. Engineers have extensive experience in developing smart antennas. Areas of study in specialty antenna research include:

  • Broadband antennas
  • Electrically small antennas
  • Low-observable antennas
  • Phased-array radar systems
  • Antennas with other special attributes

Software-Defined Radio on CD

The SwRI-developed demonstration software-defined radio is Joint Tactical Radio System-compliant and is built on a standard laptop that implements the base-band waveform processing ,and an IF/RF module that plugs into the laptop USB and provides a base-band digital to RF interface. The laptop is booted from a compact disc that includes:

  • All of the waveform processing software
  • The software component architecture operating environment
  • The xml domain profiles
  • A simple user interface

Reconfigurable Space Transceiver

image of a prototype software-defined radio

SwRI teamed with NASA's Johnson Space Center to design and build a prototype software-defined radio that is compatible with the Space-to-Space Communications System, a wireless communications system used to carry voice and telemetry data between the space shuttle, the international space station, and the extravehicular mobility unit. SwRI demonstrated integrated operation of the software-defined radio with a network of Space-to-Space Communications System flight radios.

In a project for a major aerospace company, SwRI built a tool for analyzing the tradeoffs between costs (size, weight, power, and development time) as variations occur in:

  • Waveform algorithm
  • Performance
  • Hardware platform
  • Operating environment
  • Software vs. hardware allocation

This tool supported a trade space analysis for space-borne communications systems, utilizing FPGA hardware and leveraging standard communications architectures such as the Joint Tactical Radio System software component architecture.

Custom Protocol Development

SwRI developed a technique for leveraging the investment in standards, such as 802.11, to develop highly customized wireless protocols for applications with vastly different signal environments than that for which the standard was developed. The objective was to develop a demonstration system that leverages 802.11 electronics in a target environment with long distances (up to 150 nautical miles) and high closing speed between the radios (high Doppler effect). The approach utilizes the physical layer electronics developed to support the 802.11 standard, but replaces the collision avoidance-based Media Access (MAC) and link layer with a custom, scheduled protocol with deterministic behavior.

Benefiting government, industry and the public through innovative science and technology
Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.