Final Report: 03-LW-005 Space-Time Secure Communications for Hostile Environments
The development of communications for highly reverberative environments is a major concern for both the private and military sectors whether the application is aimed at the securing a stock order or stalking hostile in a tunnel or cave. Other such environments can range from a hostile urban setting populated with a multitude of buildings and vehicles to the simple complexity of a large number of sound sources that are common in the stock exchange, or military operations in an environment with a topographic features hills, valleys, mountains or even a maze of buried water pipes attempting to transmit information about any chemical anomalies in the water system servicing a city or town. These inherent obstructions cause transmitted signals to reflect, refract and disperse in a multitude of directions distorting both their shape and arrival times at network receiver locations. Imagine troops attempting to communicate on missions in underground caves consisting of a maze of chambers causing multiple echoes with the platoon leader trying to issue timely commands to neutralize terrorists. This is the problem with transmitting information in a complex environment. Waves are susceptible to multiple paths and distortions created by a variety of possible obstructions, which may exist in the particular propagation medium. This is precisely the communications problem we solve using the physics of wave propagation to not only mitigate the noxious effects created by the hostile medium, but also to utilize it in a constructive manner enabling a huge benefit in communications. We employ time-reversal (T/R) communications to accomplish this task. This project is concerned with the development of secure communications techniques that can operate even in the most extreme conditions while maintaining a secure link between host and client stations. We developed an approach based on the concept of time-reversal (T/R) signal processing. In fact, the development of T/R communication systems is a recent signal processing research area dominated by applying these techniques to communicate in hostile environments. The fundamental concept is based on time-reversing the impulse response or Green's function characterizing the uncertain communications channel to mitigate deleterious dispersion and multipath effects. In this project, we have performed proof-of-principle experiments to demonstrate point-to-point and array-to-point communications by first establishing the basic theory to define and solve the underlying multi-channel communications problem and then developing various realizations of the resulting T/R receivers. We showed that not only do these receivers perform well in a hostile environment, but they also can be implemented with a ''1-bit'' analog-to-digital (A/D) converter design structure. We validated these results by performing the proof-of-principle acoustic communications simulations and experiments in air as well as electromagnetic (EM) simulation/experiments. It was shown that the resulting T/R receivers are capable of extracting the transmitted coded sequence from noisy microphone array measurements with zero (bit) error. We chose to perform the bulk of our work in the acoustics medium for simplicity in implementation and cost compared to the EM modality. However, we did perform some simple simulations and experiments using the LLNL micro-impulse transceiver system.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 900171
- Report Number(s):
- UCRL-TR-218332; TRN: US200709%%564
- Country of Publication:
- United States
- Language:
- English
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