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Real-time Compression for Acoustic Array Time-Domain Data


TECHNOLOGY AREA(S): Sensors, Electronics, Battlespace 

OBJECTIVE: Create innovative algorithms and software for commercial off-the-shelf (COTS) general-purpose computers and Digital Signal Processing (DSP) equipment capable of converting time-domain data from a passive acoustic array into a compressed data stream that can be transmitted via satellite communications (SATCOM) and rebuilt into a replica of the original data. 

DESCRIPTION: The Navy is seeking solutions to enable data from acoustic arrays to be transmitted in real-time without degradation to shore facilities for processing by specialists. Such transmission solutions would reduce the need for installation of expensive data processing and display systems on ships and the requisite specially trained crewmembers on-board to perform real-time data analysis. Since the capability sought is expected to be fielded as software that can be integrated into the shipboard array processor system, the recurring cost to field the capability would be minimal. Current surface Anti-Submarine Warfare (ASW) practice for Surveillance Towed Array Sensor System (SURTASS) ships requires installation of an expensive, custom-built data processing system on each ASW ship, because the data from the arrays is too large to be transmitted to shore in real-time via Navy satellite communications (SATCOM). The quantity of data expected to be created by next-generation arrays is even greater and available satellite data bandwidth is not expected to grow from its present size. Therefore, current and future ASW platforms need a lossless data compression capability that enables raw time-domain data from each element of the array (up to 256 channels simultaneously) to be transmitted to shore and reconstructed as an exact replica to enable accurate data processing and precise target localization. A unique solution to acoustic data compression is required for this application. Unlike consumer audio applications in which psychoacoustic phenomena are leveraged and much of the inaudible data is selectively removed, the compression scheme must preserve the time-domain waveform precisely in both amplitude and time across all sensor channels in order for the array beamforming performance to be fully exploited by the DSP system. Additionally, unlike commercial audio applications, all sensor channels are receiving data from a common real-world physical source (e.g., there is not a guitar on one channel and a vocal on another); therefore, each channel is processing the same acoustic data, but with variations in amplitude and time among the channels. It may be assumed that the configuration of the sensors, including their spacing and bandwidth, is provided to the compression and decompression algorithm. Sampling rates may vary among sensor channels. It should be noted that ambient noise needs to be preserved in the compression, and electronically induced sensor noise can be assumed less than ambient noise (and therefore inconsequential). The product for this effort is software source code that can be integrated into the Navy’s common processor system, which is based upon the Intel x86-64 platform and the Linux operating system. (Previously other SBIR-sponsored software projects have been integrated into this common processor system, and appropriate safeguards to protect the contributors’ intellectual property have been put in place.) A COTS DSP device may be used if required, but it will need to be integrated into the processor system. It is acceptable to leverage available open-source code. The objective ratio of compression is 80% compared to the raw array data stream with an input/output latency of less than one minute. In summary, the capability includes the following characteristics that are not available in today’s lossless compression/de-coding schemes: 1. Input has user-variable number of channels up to 256 2. Output incorporates forward error correction (FEC) with automatic negotiation capable of supporting radio/satellite data links with a bit error rate of 0.01, end-to-end latency of two seconds, and data block outages of up to two seconds 3. Including FEC, output is single data stream composed of 80% of the data volume compared to raw data 4. Sample rates can be selected by the user in 1Hz intervals up to at least 96kHz 5. Sample rates can vary among channels, but will be in integer multiples of each other 6. After coding and de-coding, the time domain waveform shall be visually identical to the original with objective performance of true effective 16-bit resolution (96dB dynamic range), < 0.05% Total Harmonic Distortion (THD), frequency response accuracy +/- 0.1dB, and phase accuracy between channels of +/- 1 degree at 0.9*(Nyquist frequency/2) 7. Coding and de-coding processing latency not to exceed one minute Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. Owned and Operated with no Foreign Influence as defined by DOD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Security Service (DSS). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DSS and NAVSEA in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advance phases of this contract. 

PHASE I: Develop a concept for real-time lossless compression for acoustic array time-domain data implementation and perform analysis, modeling, and/or a demonstration to support the technical recommendation. The Phase I Option, if awarded, will include the initial design specifications and capabilities description to build a prototype solution in Phase II. Develop a Phase II plan. 

PHASE II: Using the requirements and concept of Phase I and the Phase II Statement of Work (SOW), develop and deliver a prototype for a complete implementation of the data compression and decoding capability. Demonstrate the prototype’s performance in a lab using real-life array data that will be supplied by the Navy. (Since this data is classified, this demonstration can be performed on accredited classified equipment in the performer’s facility or at a Navy facility.) Support a temporary installation of the compression capability aboard a Navy ship to demonstrate the performance of its design in an operational environment; support the installation of the decoding capability at a Navy shore site; and provide operational testing technical support and performance analysis. In preparation for a potential Phase III, provide an estimate of schedule, non-recurring cost, and product cost to support integration of the capability into the Navy processor system. It is probable that the work under this effort will be classified under Phase II (see Description section for details). 

PHASE III: Support the Navy in transitioning the technology to Navy use. Work with the Navy’s integrator to support the integration and testing of the capability into the Navy processing equipment on-board an operational SURTASS ship. Tasks may include software development, software quality assurance, cybersecurity support, development of documentation, and test support on shore and at-sea. Deliver future software/hardware builds of the processor system with the SBIR-developed integrated compression and de-coding capability. Passive acoustic arrays are used in the oil industry and this data compression capability would have direct application for data storage or transmission via radio. As an example of a business case, this data compression capability could be used to decrease deployment costs significantly by enabling the use of a relatively inexpensive unmanned vessel to collect acoustic data rather than a ship with crew ($50k-100k/day). 


1: Johnson, M., Partan, J., and Hurst, T. "Low Complexity Lossless Compression of Underwater Sound Recordings." J. Acoust. Soc. Am., March 2013, Vol 133, No. 3, pp. 1387-1398.

2:  Liebchen, Tilman. "MPEG-4 ALS – The Standard for Lossless Audio Coding." The Journal of the Acoustic Society of Korea, October 2009, vol. 28, no. 7.

KEYWORDS: Audio; Lossless Compression; Acoustic Data Compression; Real-time Data Compression; Lossless Compression/De-coding Schemes; Data Compression; Communications In A Battlespace Environment 


Mandeep Nehra 

(401) 832-9174 

Mary Johnson 

(401) 832-3840 

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