Channel probe observations of propagation conditions along a 1294‐km transauroral path between Sondrestrom, Greenland, and Keflavik, Iceland, were made during the period from March 13 to April 2, 1992. The midpoint of this path was located at a corrected geomagnetic latitude of 72°. The objective of these measurements was to supplement the existing data base describing propagation conditions on the HF transauroral channel with data pertaining to a period around the time of solar maximum. Received signals for this path fell into three distinct groups depending on their amplitude and delay and Doppler spread characteristics. These are (1) strong, specularly reflected ionospheric returns characteristic of a quiescent daytime ionospheric channel during magnetically quiet conditions; (2) strong specular multipath signals reflected from horizontal gradients of electron density and regularly encountered at night; and (3) weak scatter returns that are also a persistent nighttime phenomenon. The scatter returns are usually observed at delays exceeding those anticipated for the one‐hop return and, very often, at frequencies that are well above the MUF for the great circle propagation path. The multipath and scatter returns exhibit large delay and Doppler spreads indicative of spatially extensive distributions of drifting and randomly moving irregularities. Two measurement events are discussed which illustrate these conclusions: a noontime measurement with Kp = 3, and a midnight measurement with Kp = 2. The noontime measurement exhibited a scatter return from an isolated irregularity region in addition to the usual ionospheric reflected signals. A simple irregularity drift model produced delay and Doppler shift curves that were consistent with those observed for the scatter component of the received signal and supported a hypothesis of an irregularity region drift speed of 1200 m s−1 parallel to the great circle propagation path.

Hybrid communication systems exploit channel diversity to improve network performance. One such example is hybrid Free Space Optical (FSO)/Radio Frequency (RF) systems. These networks aim to merge the high capacity of FSO links with the high availability of RF links to form resilient high-bandwidth communications. When used for wireless communications, the main challenge is the dynamic response to variations in the atmospheric channel in adverse weather conditions. In this paper we simulate adaptive hard-switched transmission algorithms on a practical prototype hybrid system. FSO channel scenarios are formed based on climate data, and are emulated on the prototype system to compare the performance of the hybrid system to each solo carrier respectively.

Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. This report describes the development and test of processing and transponding payload configurations for the High Altitude Relay and Router (HARR) project. This work was performed by the U.S. Naval Research Laboratory (NRL) to support a viable long-range end-to-end mobile ad hoc wireless network in a tactical environment. HARR has the potential to provide closed network communications and other tactical capabilities between nodes separated by up to 200 miles at a reduced cost as compared to other existing technologies. HARR achieves these results by flying its payloads in untethered balloons at near-space altitudes around 20,000 m (approximately 65,000 ft), providing a relay capability over a substantial area of operation. The report describes the design and integration of the airborne and ground node systems that make up this network, and analyzes test data collected using unicast and multicast transport protocols in an IP-based environment. The field test data discussed in this report was collected at Lubbock, Texas, in June 2006. Additional followup testing was conducted through the summer and fall of 2006 at NRL in Washington, DC. REPORT TYPE 1. REPORT DATE (DD-MM-YYYY) TITLE AND SUBTITLE AUTHOR(S) PERFORMING ORGANIZATION REPORT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S ACRONYM(S) 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S REPORT NUMBER(S) Network relay RF communicationsTransponder 802.11b

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No abstract