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Next Generation Satellite Transponder using Low-Cost Adaptive HPA Linearization Technologies

Description:

TECHNOLOGY AREA(S): Space Platforms 

OBJECTIVE: Develop and demonstrate low-cost advanced adaptive linearization technologies for next generation military satellite transponder to adaptively suppress the amplitude modulation-to-amplitude modulation (AM-AM) and amplitude modulation-to-phase modulation (AM-PM) effects caused by the High Power Amplifier (HPA) in the presence of nonlinear interferences and smart jammers. 

DESCRIPTION: The military protected tactical satellite (MPTS) system represents the future of advanced military satellite communications (SATCOM) by increasing connectivity, data rates and anti-jamming capabilities of aerial and ground forces in contested environments. Simple non-processing or turn-around transponder satellite architecture operating in multi-carrier modes is currently adopted in the MPTS system design. However, when satellite HPAs operate in saturation regions, particularly in the presence of inter-symbol interferences, adjacent channel interferences, and jammers (uplink or downlink or both), the SATCOM links suffer from nonlinear distortion, commonly characterized by the AM-AM and AM-PM effects. These nonlinear distortions degrade communication performance in terms of larger bit error rates (BER) and more required carrier-to-noise power spectral density ratios (C/N). Practical progress towards mitigating potential nonlinearities of transponders has been made with the deployment of digital adaptive signal predistortion, which employs an approximate inverse non-linearity ahead of HPAs. With the emergence of radio interferences and smart jammers (i.e., smart jammers monitor and attack potential weaknesses of a SATCOM system causing a wide range of disruption from “Un-noticeable” to “Noticeable” Disruption to a single SATCOM user or multiple SATCOM users), the Air Force seeks innovative design alternatives to adaptively linearize the satellite HPAs, including Traveling Wave Tube Amplifiers (TWTAs) and/or Solid State Power Amplifiers (SSPAs) to manage the technical risks; e.g., AM-AM and AM-PM effects. Existing predistortion concepts employing Extended Saleh’s Model, Modified Linear-Log Model, data and signal predistortion via polynomials or look-up tables, channel inversion, etc. may be implemented using linear programming, which are appropriate and thereby, sufficient for linearizing the HPA nonlinearity in the absence of onboard multiple carrier amplification. Due to dynamic nature of a smart jammer, it may rather require advanced non-linear programming techniques as well as indirect/direct parameter estimation and/or direct learning for the linearization of the satellite HPA. Prospective proposers can develop and demonstrate low-cost advanced adaptive linearization technologies using non-linear programming techniques. Thus, testing with high fidelity simulation or emulation environments can significantly reduce the costs associated with actual field-testing and allow for fast prototyping of the proposed adaptive linearization technologies. This SBIR topic is soliciting innovations benefiting the next generation MPTS to suppress HPA distortion caused by AM-AM/AM-PM effects in the presence of multicarrier nonlinear interferences and smart jammers. In evaluating the performance of the proposed adaptive linearization technologies, prospective proposers are expected to consider the existing and future MPTS configurations, including low resolution processors, analog to digital converters (ADCs) and digital to analog converters (DACs) onboard for implementing digital predistortion to adequately address size, weight, power and cost (SWAP-C) constraints and to implement hardware based engineering development unit for testing and evaluating potential effects of lowering resolution for ADCs, DACs, and onboard processors on bit-error-rate performance when digital predistortion is performed. 

PHASE I: Identify a proof of concept of the adaptive linearization model. Capture potential key areas where new development is needed and suggest appropriate methods to realize adaptive linearization technologies. Incorporate satellite transponder imperfections during design development. Evaluate potential impacts of nonlinear interferences and smart jammers on the linearized satellite transponder. 

PHASE II: Optimize the Phase I results to include potential effects of input and output multiplexer filters as well as input and output backoff. Build an engineering development unit to demonstrate potential transmission performance increase (e.g., low output power backoff and low carrier spacing). Develop a path toward for optimizing SWAP-C and demonstrate new capability with total cost assessment. Integrate the tech solution with distributed predistortion, nonlinear equalization on return links, and use in time-frequency packing. 

PHASE III: DUAL USE APPLICATIONS: Demonstrate an adaptive linearized transponder satellite system in relevant environment for commercial or dual use. Partner with DoD primes and communication providers to integrate the technology into their offerings. 

REFERENCES: 

1: "Advantages of Using Dynamic Predistortion with the CDM-760", http://www.comtechefdata.com/files/articles_papers/WP-Advantages-of-Using-Dynamic-Predistortion-with-the-CDM760.pdf

2:  Allen Katz, "TWTA Linearization", http://www.lintech.com/PDF/twta_lin.pdf

3:  M. Kojima, et. al., "Study on Transmission Performance over SSPA for Satellite and Using Equalization at Receiver," 34th AIAA Int'l Communications Satellite Systems Conference, AIAA 2016-5761, 2016

4:  R. Piazza, M. R. B. Shankar, B. Ottersten, "Data Predistortion for Multicarrier Satellite Channels based on Direct Learning," IEEE Transactions on Signal Processing, Vol. 62, No. 22, pp. 5868-5880, 2014

KEYWORDS: MILSATCOM, MPTS, High Power Amplifier, Linearized Satellite Transponder, SWAP-C, MODCOD, AM-AM, AM-PM, Linearization, Non-linear Programming, Classical Jammer, Smart Jammer, Saleh’s Model, Linear Log-model 

CONTACT(S): 

Khanh Pham 

(505) 846-4823 

khanh.pham.1@us.af.mil 

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