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Research and Development Technical Report CECOM-TR-91-3

Tactical Line-of-Sight Radio Propagation ReliabilityKenneth H. Brockel, CECOM C3 Systems Directorate William T. Barnett, Telos Corporation

Kenneth D. Chaney, OPM Mobile Subscriber Equipment Joseph R. Inserra, CECOM C3 Systems DirectorateRobert J. Locher, OPM Mobile Subscriber Equipment Francis G. Loso, CECOM C3 Systems Directorate Victor J. Procoplo, CECOM C3 Systems Directorate Arvids Vigants, Telos Corporation

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2 0. 9_2OCT 2 01932

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October 1991Second Printing

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92 U'~DISTRIBUTION STATEMENTV Approved for public release. Distribution is unlimited.

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U.S. Army Communications-Electronics Command Command, Control and Communications Systems Directorate Fort Monmouth, New Jersey 07703-5203

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I I INOTICES

DisclaimerThe findings in this report are not to be construed as an official Department of the Army position, unless so designated by

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other authorized documents.The citation of trade names and names of manufacturers in this report is not to be construed as official Government endorsement or approval of commercial products or services referenced herein.

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Destruction Notice Destroy this report when it is no longer needed. Do not return

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it to the originator.Second Printing July 1992 This edition corrects typographical errors and terminology.

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OMU No.074-188ucuowa. W asg .is - Ida otajm d"i',w

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Kenneth H. Brockel, William T. Barnett, Kenneth D. Chaney, Joseph R. Inserra, Robert J. Lecher, Francis G. Loso, Arvids ViRants Victor J. Proco1io1 4. PIERFOMING ORGANIZATION NAME(S) AND ADSRESS(ES) .S. Army Coimnunications-Electronics Command Command, Cont-rol and Communications Systems Directorate

= 3. PERFORMING ORGANIZATION REPORT NUMnER CECOM-TR-91-3

AMSEL-RD-C3-EM (V.J. Procopio) ATTN: Fort Monmouth, NJ 07703-5203 9. SPONSORING/IMONITORING AGENCY NAMES) AND ADDRESS(ES) 10. SPONSORNG/MONITORINGAGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTIONIAVAILABiLITY STATEMENT Approved for public release. Distribution is unlimited.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 wods)

Recent deployment to Southwest Asia (SWA) of tactical Line-of-Sight (LOS) radio links, such as those used with Mobile Subscriber Equipment (MSE) and other Tri-Service Tactical Communications (TRI-TAC) systems, and user feedback indicating time-varying The climate encountered in performance have raised the question of link reliability. SWA (desert terrain in proximity to bodies of water) is known to be very difficult for LOS radio because it causes frequent and large reductions in received signal This report provides predictions of strength, referred to as time-varying fading. performance for the systems fielded based on the latest technical literapropagation The ture and validates them with current information collected from system users. Particular conditions that cause time-variant fades on LOS paths are also addressed. focus will be directed at the tactical environment and the unique challenge that exists to achieve highly reliable links with the limited antenna gains and terrain This report also addresses future work that clearances present in the tactical world. should be accomplished to ensure that LOS operators and planners have the latest data available to optimize the effectiveness oi their current LOS capability.14. SUBJECT TERMS 15. NUMBER OF PAGFS

Army Tactical Radio, Propagation, Line-of-Sight Links, Fading, Multipath Fading, Propagation Reliability, Climate Effects17. SECURITY CiASSIFICATION

8216. PRICE CODE20. UMITATION OF ABSTRACT

OF REPORT Unclassified

11. SECURITY CLASSIFICATION

19. SECURITY CLASSIFICATION

OF THIS PAGE Unclassified

OF ABSTRACT Unclassified

ULStandard Form 298 (Rev. 2-89)Prr,urihd by ANSI Std 293Z39-.1

NSN 7540-01-280-5500

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FOREWORDThe Mission of the LOS ProDagatLon Reliability Workina GrouR o Enhance Army Tactical Line-of-Sight (LOS) Radio per-

formance.o Incraase soldiezs' ments. o Assist acquisition managers in fielding highly reliable capabilitieE to successfully deploy

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Tactical LOS Radio ini difficult propagation environ-

transmission systems.

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Accesion ForNTIS S(UTIC CRA&W 1A1 U:i4niaouticed J'Jastiicatio By .............Di~t. ibution

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IEXECUTIVE SUMMARY m This report will focus on Army Tactical Line-of Sight (LOS) Radio and the significant threat posed by the propagation environment to highly reliable communications. Anecdotal reports from LOS operators indicated that large performance-affecting variations

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in received signal strength on many of their radio links were adaily problem during recent Southwest Asia (SWA) operations. The

climate in SWA is known to be difficuli for LOS radio propagation because it causes large and frequent reductions in received signal strength, referred to as time-varying fading. The LOS Propagation Reliability Working Group was established to investigate the problem of degraded link reliability due to time-varying fading and other related propagation issues. A key element of our effort is user feedback from the soldiers. Data corroborating the existence of significant link propagatiorn problems and degrdded link reliability were obtained during visits to the 35th Signal Brigade at Fort Bragg, North Carolina, and the 57th Signal Battalion at Fort Hood, Texas. Frequency management issues and the related radio frequency interference problems were identified. It was evident that the soldiers were

not adequately Lrained with regard to either time-varying propa&gation or the fragility of digital transmission systems. This, in part, aggravated the link reliability problems encountered in SWA. Satisfactory reliability, however, was achieved on the overall radio network by employing extensive link level redundancies. Due to the success of the overall network, .ifter-action reports often failed to mention single-link reliability problems. Such redundancies may not always be feasible in future applications such as the nonlinear battlefield of AirLand OperaLions

(ALO).

The users also identified a need for Mobile Subscriber

Equipment (MSE) link reliabilities much greater than the current 90-percent design point. For single-thread links, a reliability approaching 100 percent was requested.

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This report baselines the key Army LOS radio specificatinns end develops the maximi, 1 possible equipment fade margins a a prelude The operating fade marqin to assessing the envirounmental threat. is defined as the difference in the average receivsd signal power and that requir(d for operation at a Bit Error Rate of 10-5. Tactical frequency ranges .nvestigated included the UHF bands of 220 to 400 MHz and 1350 to 1850 MHz and the SHF band of 4.4 to The evaluation of Army LOS link engineering methods for 5.0 GHz. MSE found that small and fixed fade margins Gf 4 to 6 dB (Bullington, 1957) are allocated for signal strength variations due to fading. We find this margin value toc small in view of urrent LOS link engineering methodology, which includes parameters for climate, location, fraquency, and path length. A major contribution of our effort is the development of a multiLOS model suitable for Army tatical path fading reliability This model accounts for frequency, path length, and .eadio. climate, and provides fade margin requirements for any needed Application graphs and tables are derived and reliability. This model is primarily based on the provided in this report. extensive radio systems work done at AT&T Bell Laboratories in and on results repoited in a recent paper the last 20 years We found, for example, that a radio operat(Olsen-Segal, 1991). ing at 1600 MHz on a 20-km path in a SWA climate would require an operating fade margin of 17 dB for 99.9-percent reliability (15 At 40 km, the operating fade minutes/day of fading outage). Clearly, high reliabilmargin required would increase to 28 dB. ity IUnks require substantial. fade margins. The amount of fade margin available for allocation to other threats and equipment degradations is the difference in the ideal maximum fade margin, obtained when all the equipment is working at its baseline specification with the antennas completely unobA or trees, and the required fade margin. structed by hills

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value of 0 dB fo1 the available fade margin determines the maximum possible path length for a given reliability requirement. For 99.9-percent link reliability and a difficult propagation climate such as SWA, the maximum possible link path lengths range from 35 to 45 km for the radios considured. These results indicate that the radios have the capability to meet their applica-

tion requirements,

but only if

the required fade margins are

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realized in practice. This capability may be diminished by such effects as misaligned antennas or reduced link clearance, which can easily cost 10 dB or more of margin. For example, a net 3 dB

of degradation would reduce the maximum path lengths by about 5km. Our principal conclusion is that the environmental threat imposed