N121-097 TITLE: Improved High Frequency Communications

TECHNOLOGY AREAS: Information Systems

ACQUISITION PROGRAM: MARCORSYSCOM PRC-150; and Marine Expeditionary Rifle Squad

OBJECTIVE: Improve reliability and predictability of time-of-day dependent high-frequency (HF) channels by providing high-throughput ionospheric skywave or Near-Vertical Incidence Skywave HF (e.g., 2-30 MHz frequency band) communications with a throughput of at least 100 kb/s.

DESCRIPTION: HF communications technologies have not been actively developed or improved in recent years with the exception of NATO STANAG (ref. 1) and commercial activities working with a 24-kHz channel as opposed to the standard 3-kHz channel. Recent military operations have demonstrated a shortfall in long-range tactical communications in complex terrain environments that HF communications are filling. However, due to the HF channel variations, poor signal-to-noise ratio (SNR), and interference (ref. 2, 3), attempts to improve the channel capacity, spectral efficiency, or link have met with little success using traditional approaches. If the SNR can be increased and stabilized, higher-order modulations can increase spectral efficiency (ref. 4). Local coverage (e.g., 0 to 10 miles) may also be increased by multiple-input, multiple-output (MIMO) (ref. 5, 6) and opens the possibility for an HF local area network (LAN) (ref. 7). Local to medium-range coverage (e.g., 0 to 300 miles) may be increased by exploiting the Near-Vertical Incidence Skywave (NVIS) (ref. 8). Some of the limitations in the tactical NVIS radios may be overcome by exploiting the multipath bundles in the NVIS, the launch angles (e.g., low-angle main beam for long-haul, high angle for local and medium haul), and polarizations diversities.

Overall goals and possible approaches include the following:
1. Exceeding the performance of existing wide-channel HF radios by at least 25%
2. Using NVIS as an MIMO option (two-channel)
3. Porting the HF networking and beamforming that currently exists on ships (3kHz band) to the Marine operations
4. Designing HF networking to increase link coverage

Performance gains that can be realized through tradeoffs of HF waveforms, polarizations, and antenna design are of particular interest.

PHASE I: Develop a technical description and system design, supported by modeling, to show predicted performance gains. Include a high-level methodology for attaining Federal Communications Commission (FCC) and International Telecommunications Union (ITU) approval.

PHASE II: Complete a breadboard implementation to validate the model in laboratory and provide over-the-air demonstrations.

PHASE III: Develop a TRL7 prototype for demonstration at NVIS or skywave distances showing a data throughput of more than 100 kb/s.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Ham radio operators supporting natural disasters and governmental and non-governmental agencies performing human assistance/disaster relief missions can use infrastructure-free over-the-horizon communications capabilities that can transmit images and low-quality video.

REFERENCES:
1. Kariyawasam, S. R.; Heravi, B. M.; Honary, B.; Barclay, L.; Vongas, G. [2009] HF-IP: Propagation analysis, 11th International Conference on Ionospheric Radio Systems and Techniques, IRST 2009.

2. Harris, T.J.; Scholz, M.L. [2006] Characterisation of Narrowband HF Channels in the Mid- and Low- Latitude Ionosphere, Proceedings RTO-MP-IST-056, Paper 17. Neuilly-sur-Seine, France: RTO. Available from: http://www.rto.nato.int/abstracts.asp.

3. Bark, G. [1999] Performance comparison of spread-spectrum methods on an interference-limited HF channel, IEE Proc.-Commun 146(1).

4. Jorgenson, M.B.; Johnson, R.W.; Blocksome, R.; Nelson, R.W.; Harris, D.; Boesdorfer, G. [2010] Implementation and on-air testing of a 64 kbps wideband HF data waveform, Military Communications Conference, MilCom-2010.

5. Abbasi, N. and Gunashekar, S. D. and Warrington, E. M. and Salous, S. and Feeney, S. M. and Bertel, L. and Lemur, D. and Oger, M. [2009] Capacity estimation of HF-MIMO systems, 11th International Conference on Ionospheric Radio Systems and Techniques, IRST 2009.

6. Feeney, S.M.; Salous, S.; Warrington, E.M.; Gunashekar, S.D.; Abbasi, N.; Bertel, L.; Lemur, D.; Oger, M. [2009] Compact antenna arrays for HF MIMO applications,11th International Conference on Ionospheric Radio Systems and Techniques, IRST 2009.

7. Jonathan Chan, Jose Ramos [2010] Wideband High-Frequency Internet Protocol Test Results 17 November 2010, SPAWAR Presentation 17-NOV-2010.

8. S. Antoniou, L. Christofi, P.R. Green and G.F. Gott [2006] High rate data transmission in the mid-latitude NVIS HF channel, IEEE Proceedings online no. 20050124.

KEYWORDS: High frequency; over-the-horizon; near-vertical incidence skywave (NVIS), ionospheric skywave; skywave; MIMO

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