N241-059 TITLE: Wideband Interference Suppression

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Sensing and Cyber; Microelectronics

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Define, develop, and demonstrate a microelectronics made interference suppression system for use in a single antenna system that can operate simultaneously over a wide spectral bandwidth that contains multiple independent and uncooperative loud signals as well as many small signals which are both of significant interest (SOI) and of low interest (NSOI) categories.

DESCRIPTION: The radio frequency spectrum has become increasingly crowded due to the rapid expansion of wireless networks and growth of the expectation, even in the military, that discussion of alternative response behaviors will occur during decision making. The proximity and overlapping frequency allocations of multiple wireless systems inevitably lead to communication interference. Military environments, both on land and at sea, face additional challenges with constantly shifting transmitters that change location, transmission direction, and frequency. The move toward every platform doing many operations simultaneously drives up the number of functionalities each platform engages in and each has its own transmitter. The resulting electromagnetic environment is complex and carries a significant risk of unintentional interference, especially given the likelihood of signal reflections from neighboring platforms within the battle group. Design and placement of antennas alone cannot sufficiently address the issue.

While digital signal processing techniques have made great advances in enhancing modern electronic warfare, communications, and radar systems, the most efficient approach to interference mitigation is to protect the receiver from exposure to interferers. This requires hardware that can suppress interference as close to the receive antenna as possible, typically at the front end. And as future receivers aim to eliminate analog down-conversion stages and ingest wider bandwidths for direct digitization, the demand for front-end filtering becomes even more critical. Meanwhile the pace of battle has accelerated and the sheer bulk of signals needing attention drives the priority of shrinking the time it takes to respond to any one scenario. Speed of adaptation becomes a critical system parameter.

One possible solution is provision of a number of fast tuning, analog filters. Individually they need to possess steep band edges, highly attenuating stop bands, and low insertion loss. All proposals should quantify their expectations regarding these parameters. Static filters are a well-established and reliable technology. They would be sufficient if the interferers’ frequency, spectral width, and power were known and consistent, which unfortunately is no longer the case. Effectively addressing the challenges posed by today’s electromagnetic environments demands the use of multiple fast tuning or self-generated notch filters. These filters should be generated independently (in linear fashion) and adjusted in terms of center frequency. A mechanism should be defined to control the bandwidth and depth, which may be interdependent parameters. If active control is required, the same control parameters must produce the same response independent of the previous control settings (i.e., no history effects). The time between the arrival of a new interfering signal and the beginning of its suppression within the total signal needs to be less than a microsecond and ideally less than 1 nanosecond. Additionally, the passband of the total filter should exhibit transmission losses of << 1dB when on and less when parked/inactive/off. The technology selected for demonstrations should imply the net total device insertion loss upon signal Input/Output (I/O) should not dominate the system behavior. Furthermore, the filters need to demonstrate characteristics such as reliability, environmental temperature stability, and resistance to mechanical vibration. To succeed as a product, a high level of as fabricated device-to-device repeatability is needed, or testing and calibration costs can balloon.

Both innovation of the proposed notch filtering mechanism and a lack of distortion of acceptable amplitude signals are sought. Device concepts requiring a reference signal for the signal to be removed must describe how to obtain same for uncooperative transmitters. Systems requiring signals analysis to determine the frequencies at which filters should be tuned need to include that processing time in their turn on/off time estimates. The production of out of signal band interference is not an acceptable byproduct.

The solutions proposed will also be judged on the processing latency they introduce and their design complexity and Size, Weight and Power (SwaP) when the functional instantaneous bandwidth (IBW) contains hundreds of simultaneous signals of interest and there is only one antenna available. The ultimate IBW will exceed 20 GHz. Photonic approaches are acceptable but not required. Such proposals should indicate the expected required optical power of the photonic carrier. All proposals should be careful to define the acceptable range of Radio Frequency (RF) carrier frequencies, estimate wall plug power costs of implementation, describe all during operation circuit trimming required, and provide a discussion of the individual contributions to the system's overall noise figure in a technical risks section.

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 32 U.S.C. § 2004.20 et seq., National Industrial Security Program Executive Agent and Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence and Security Agency (DCSA) formerly Defense Security Service (DSS). The selected contractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances. This will allow contractor personnel to perform on advanced phases of this project as set forth by DCSA and ONR 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 during the advanced phases of this contract IAW the National Industrial Security Program Operating Manual (NISPOM), which can be found at Title 32, Part 2004.20 of the Code of Federal Regulations. Reference: National Industrial Security Program Executive Agent and Operating Manual (NISP), 32 U.S.C. § 2004.20 et seq. (1993). https://www.ecfr.gov/current/title-32/subtitle-B/chapter-XX/part-2004

PHASE I: In the base, develop the approach, as outlined in the Description, toward the ultimate demonstration for more than two interferers of different bandwidths, including spread spectrum noise like signals, and both narrow and wide band desired signals spread over the entire proposed input IBW simultaneously. The initial demonstration of a multi-notch filtering system should focus on the 3 MHz to 6 GHz communications dominated band, and provide up to 10 independent notches, tunable across the entire band with > 40 dB stop-band rejection and 3-dB bandwidth of < 1 MHz per notch, self or externally adjustable up to > 20 MHz. The Phase I base period should include sufficient performance measurements to allow estimation of the performance expected if the Phase II preliminary plan is accepted. In the Phase I option period, if exercised, further optimize the circuit design and test the prototype more completely with all kinds of signals of interest and interferers.

PHASE II: Review whether the Phase I choices of materials and approach is optimal for wide band ingest performance. If not, consult with the government sponsor whether a change in materials is warranted and if yes, develop a new brass board demonstrator. If not, proceed toward a full IBW demonstration aiming for minimum size, weight and power while including additional C(G)OTS components to be named by government. If the Phase II Option is exercised, continue progress toward integrating this circuit with other required parts in a system.

Work in Phase II may become classified. Please see note in Description paragraph.

PHASE III DUAL USE APPLICATIONS: The successful result of this SBIR topic will be an enabling technology. Interference suppression is necessitated by the common issue of co-site interference when many transmit antennas are closely collocated with receive antennas without sufficient free space isolation for Simultaneous Transmit And Receive (STAR) to be possible. Moreover, many commercial base-stations have the antennas of many vendors collocated on the same tower and are increasingly bothered by co-site interference.

REFERENCES:

1. Interference Suppression - an overview | ScienceDirect Topics https://www.sciencedirect.com/topics/computer-science/interference-suppression
2. Poor, H.V. "Adaptive Interference Suppression for Wireless Multiple-Access Communication Systems."Circuits and Systems for Wireless Communications In: Helfenstein, M., Moschytz, G.S. (eds). Springer, Boston, MA, 2002. https://doi.org/10.1007/0-306-47303-8_27

KEYWORDS: Co-site interference; photonic interference cancellation; actively tuned filters; RF isolation; ultra-wide instantaneous bandwidth reception; spurs; intermodulation distortion

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