OTIC AD-A High Frequency (HF) Automatic Link Establishment (ALE) 91 g II 104 SELECT MAR D. Technical Report 1383 November PDF

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AD-A Technical Report 1383 November 1990 High Frequency (HF) Automatic Link Establishment (ALE) J. P. Rahilly OTIC SELECT MAR D Approved for public release; distribution Is unlimited. 91
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AD-A Technical Report 1383 November 1990 High Frequency (HF) Automatic Link Establishment (ALE) J. P. Rahilly OTIC SELECT MAR D Approved for public release; distribution Is unlimited. 91 g II 104 NAVAL OCEAN SYSTEMS CENTER San Diego, California J. D. FONTANA, CAPT, USN H. R. TALKINGTON, Acting Commander Technical Director ADMINISTRATIVE INFORMATION This work was performed by the Exterior Communications Systems Branch, Code 824, Naval Ocean Systems Center, under the Independent Exploratory Development Program, OCNR-20T, Arlington, VA Released by Under authority of J. B. Rhode, Head R. J. Kochanski, Head Exterior Communications Shipboard Communications Systems Branch Division JG SUMMARY As a result of Independent Exploratory Development (IED) funding of an investigation of High Frequency (HF) Automatic Link Establishment (ALE), the principal investigator on this task has had the opportunity to participate in Federal-level ALE standards development and related test and evaluation planning for proof-of-concept testing of these standards. At the time of Naval Ocean Systems Center's (NOSC) involvement in these activities, there was no Navy, Federal-level participation. Since representatives from virtually all agencies of the U.S. Government participated, it appeared to be an effective starting point for the investigation of HF ALE. As a result of this participation, and the fact that NOSC had earlier purchased two Harris ALE Controllers (RF 7210) designed to meet the ALE Federal-Standard (FED-STD) 1045, the Navy participated in the 1990 FED-STD Over-The-Air test. The new standards, FED-STD 1046 (networking) and 1049 (link protection) were to be tested under the test plan. The Navy was included in the test plan and provided two nodes for the test: one at NOSC San Diego and the second at NOSC Hawaii. During the FED-STD test period, NOSC was also able to conduct, on a noninterference basis, Navy-Only testing over three 16-hour periods. These tests took place on the last days of the test period. The Navy-Only test data have been analyzed and are presented in section 3.0 of this report. KEY FINDINGS FROM NAVY-ONLY TESTING OF FED-STD ALE The FED-STD ALE performed quite well using a double hop HF propagation path over a large Pacific Ocean area. The great circle distance between the two Navy nodes was 2610 miles. A 35-foot whip antenna was used at NOSC Hawaii, and a dual 17-foot whip was used at NOSC San Diego. Both systems used Harris HF transceivers (RF 350 K) with 100-watt output radio frequency (RF) power and RF-382 fast-tuning antenna couplers. Some particularly noteworthy findings from this investigation included the following: A. The FED-STD ALE data transmission modes performed flawlessly at its 62.5 bits-persecond (bps) data rate in both point-to-point and relay modes when links were established. B. Voice reception using ALE frequency/channel selection generally performed poorly at one or the other of the two Navy nodes. However, there were times when both nodes had excellent voice copy. Data analyzed in this report agree with ALE operator experience using voice communications. More sophisticated HF antennas and higher transmitted RF power could have improved this performance. C. Based on the reported results of earlier ALE testing performed by the Joint Interoperability Test Agency plus the Navy-Only test data, it is estimated that over a significant amount of the available test time there were several frequency channels that could support 2400-bps data transmission. Testing is required, using the foregoing communication equipment and a robust data modem to precisely define the actual BER performance. The graphical presentation of the data in this report should assist the reader in obtaining a quantitative assessment regarding channel availability. To achieve a 2400-bps capability, a robust modem such as the Harris RF 3466 or RF 5254C is required. The method to be used in switching the modem from one channel to another to maintain a minimum BER, at this continuous data rate for the longest time, requires a design study. D. The method used in the FED-STD ALE for channel ranking to select the best HF channel, using the composite Link Quality Assessment (LQA) criteria, is flawed. From the test data, it has been determined that several selections using essentially the same LQA can result in instances where the same signal-plus-noise-to-noise ratio (Sinad) existed at both nodes, while at other times Sinad results at each end of the link could have a 13- to 16-dB disparity. However, as will be seen in this report's recommendations regarding ALE use on major combatant ships, this flaw is not of serious concern to the Navy. E. The most significant finding in the testing of the FED-STD ALE relates to its use of a single HF frequency for point-to-point linking between nodes. This is a serious limitation in the employment of the FED-STD ALE aboard major combatant surface ships of the Navy. On these ships, the shipboard electromagnetic interference (EMI) environment is such that the ALE will be constrained to use limited reception regions in the HF spectrum. This limits the number of receive frequencies available for LQA and linking. Outside of these receive regions, the node-to-node three-way handshaking, used for the exchange of Sinad and PBER data needed for ALE LQA matrix construction, would be significantly degraded by high shipboard EMI levels. On the other hand, because of lower EMI levels at a shore node, the HF frequencies that a shore node might like to receive will cover a much larger unrestricted spectral portion of the 2- to 30-MHz HF band. The ship may not be troubled in transmitting to the shore station at any of these desired shorereceive frequencies. The conclusion is clear: the Navy requires a two-frequency ALE that will allow receive frequency flexibility needed to accommodate its shipboard EMI environment and one that will not penalize shore reception capability. With the two-frequency ALE concept, the present difficulties cited earlier disappear, relative to the Sinad disparity that can exist between both nodes for a given LQA. Instead, each node will seek receive frequencies that will maximize the measured Sinad and, thus, minimize the BER levels in received data. Additionally, with a two-frequency ALE system, a capability for full duplex data communications also would be pssible. A separate HF receiver and transmitter would be the HF radio equipment configuration if full duplex operation is to be used. HF transceivers that have transmit and receive frequencies remotely controlled by the ALE controller could operate in a dual-frequency half-duplex mode. More will be said on this subject in the next part of this report. ILLUSTRATION OF POSSIBLE FUTURE ADVANCED TWO-FREQUENCY ALE CONCEPT An ideal point-to-point, two-frequency ALE configuration would use the ALE to control the transceiver's receive and transmit frequencies in a dual frequency time division multiplex (TDM) mode. The transceiver at each node would be performing in a TDM-programmed two-way sounder operation over the HF band (except for transmit frequency exclusions). During each node's transmit frequency slot, it would advise the other node of the Sinad value of the HF frequency received in its previous receive frequency TDM slot. The data exchange would allow each node to rank the transmit frequencies based on the receive node's Sinad data. When a two-frequency ALE is to be performed for the purpose of verifying the link quality using the two frequencies or for the transmission of voice or data, this could be done automatically using a two-frequency instead of a single-frequency ALE/ LQA matrix. At the next more sophisticated level, after a link quality verification of the selected frequencies, the best set could be handed over to the transmitter and receiver at each node that is to be used for full-duplex, high-speed data communication. The advent of broadband HF transmitting systems, such as the AN/URC 109 or the Harris RF 1170, appears to allow an ALE transceiver's RF transmission over the HF band to go on concurrently with the HF transmission of 2400-bps data. If this simultaneous transmission can be properly achieved over the HF band, an ALE update of the transmitter and receiver to the best HF frequencies could be performed in near-real-time. The purpose of the update being to maintain continuous 2400-bps data reception at the lowest possible BER. ii CONTENTS 1.0 INTRODUCTION I 1.1 General Comments on Benefits from IED Project Background and Objectives TECHNICAL DISCUSSION OF AUTOMATIC LINK ESTABLISHMENT FED-STD ALE FED-STD Architecture and Protocols Implementation of FED-STD ALE Single HF Frequency Point-to-Point ALE ALE POINT-TO-POINT NAVY TEST RESULTS Navy Test Scenario Overview of Navy Test Findings Results of Test Data Analysis Total Channel Availability at Specific LQA/Sinad Levels Versus T im e Channel/Frequency Support of DTM and Voice Communications Versus Time, Over Three Test Periods Channel Support for DTM and 2400-bps Data Transfer Channel Support of Good Quality Voice Communications CONCLUSIONS AND RECOMMENDATIONS Conclusions-General Conclusions Regarding Navy Operational Use of FED-STD ALE Operational Support Possibilities for High Data Rate Communication-2400 bps Using FED-STD ALE Application of FED-STD ALE in the Navy Shipboard Electromagnetic Interference Environment Recom m endations G LO SSA RY REFEREN CES FIGURES 3-1. Test nodes and HF frequencies for FED-STD over-the-air testing Printout of ALE data logger output HF radio equipment plus ALE controller used for testing Plot of FED-STD ALE LQA versus Sinad Number of available channels versus time 17/18 Sept Number of available channels versus time 18/19 Sept Number of available channels versus time 19/20 Sept Number of available channels versus time 17/18 Sept 1990; LQA 48, L Q A iii CONTENTS (Continued) 3-9. Number of available channels versus time 18/19 Sept 1990; LQA 48, L Q A Number of available channels versus time 19/20 Sept 1990; LQA 48, L Q A Sinad on channel 5 versus time 17/18 Sept Sinad on channel 5 versus time 18/19 Sept Sinad on channel 5 versus time 19/20 Sept Sinad on channel 5 versus time 17/18 Sept 1990 Hawaii signal measured in San D iego Sinad on channel 5 versus time 18/19 Sept 1990 Hawaii signal measured in San D iego Sinad on channel 5 versus time 19/20 Sept 1990 Hawaii signal measured in San D iego Available channels with LQA 48 versus time 17/18 Sept Available channels with LQA 48 versus time 18/19 Sept Available channels with LQA 48 versus time 19/20 Sept Available channels with LQA 80 versus time 17/18 Sept Available channels with LQA 80 versus time 18/19 Sept Available channels with LQA 80 versus time 19/20 Sept TABLE 3-1. LQA versus Sinad comparisons... 8 Accession For N-TI S GRA&I DTIC TAB 03 Unannounced Justification 0 BY Distribution/ Availability Codes Avail and/or IN Dist Speold. 3 i iv 1.0 INTRODUCTION This report presents the findings developed as a result of a Navy-funded Independent Exploratory Development (IED) investigation. This investigation allowed the testing of a new processor-based communication technology created to improve high frequency (HF) communications. The new HF communication technology that was examined is called Automatic Link Establishment (ALE) and is in accordance with Federal Standard (FED-STD) 1045 and Military Standard (MIL-STD) A. This report does not provide a complete textbook treatment of this subject. What is presented is a discussion of aspects of the subject necessary for an understanding of the study findings and use of this technology on Navy combatant warships to meet general command, control, communications, intelligence (C 3 I) requirements. Because this report is unclassified, special C 3 1 requirements that might be of interest in the use of non-fed-std HF ALE techniques are not discussed. The first part of this report is an introductory technical discussion of various aspects of HF FED- STD ALE. The last part addresses the test data analysis and results. Test data were obtained by Naval Ocean Systems Center (NOSC) during a Navy-Only test phase performed in conjunction with Navy support of a FED-STD Over-The-Air testing. During the Navy-Only test, both NOSC San Diego and NOSC Hawaii were active as data collection test nodes, and they used the same ALE/networking/ protection protocol and equipment as when they were part of the FED-STD test network. This report attempts to assess the new HF ALE capability that satisfies FED-STDs 1045, 1046, and 1049 requirements in terms of its strengths and weaknesses for Navy communications. 1.1 GENERAL COMMENTS ON BENEFITS FROM IED PROJECT Prior to presenting the details of this investigation, it is appropriate to comment on the overall benefit derived from the Navy IED program that funded this investigation of HF ALE. The funding of this IED task has permitted the following: A. NOSC Principal Investigator (PI), James P. Rahilly, to participate and become a member of both Government-wide Federal Standards Development and Test and Evaluation Working Groups. The principal concern of these working groups to date has been the development and testing of FED-STDs 1045, 1046, and B. Meeting and exchanging technical information with Naval Research Laboratory (NRL) engineering personnel who are known for their expertise in HF communications. This exchange established a working relationship between NRL and NOSC to improve Navy HF communication by the possible use of HF ALE. C. Travel and technical discussions with contractors (CNR and Harris Corp) to determine in what way HF ALE techniques might be used to improve Navy HF C3I communications. D. Access to FED-STD ALE documentation and test reports to become better acquainted with the background and state of FED-STD HF/ALE. E. A working relationship with FED-STD participants has led to NOSC being accepted as a member and asked to provide test nodes for Over-The-Air FED-STD Proof-Of-Concept (POC) testing. F. Obtaining ALE test data and Navy test results, which show the HF/ALE performance over a 2610-mile ocean path. These results (section 3.0) were obtained by NOSC during the FED-STD testing period on a noninterference basis using IED funding. G. Development of concepts for integrating the benefits of the FED-STD ALE with the capabilities of high-performance modems, sturh as the Harris 3466 or 5254C. Because development in this area may allow a significant improvement for the Navy in the availability of HF High data rate (2400 bps) communication capabilities, this has been recommended for future IED funding. 1.2 BACKGROUND AND OBJECTIVES Because establishing and maintaining HF long-haul communication links by the Navy currently requires the expenditure of much time and effort by skilled Navy manpower, due to the vagaries of HF propagation, the arrival of satellite communication has been generally viewed as a welcome communication alternative. The advantages in using satellite communication for long-haul communications has, over the years, caused a decrease in Navy interest in HF communications. Consequently, there is a Navy reluctance to stress training of HF communicators to develop and improve operator proficiency. The resultant reduction in operator HF proficiency has caused even less interest in using HF for long-haul communication. HF ALE technology offers a promise for providing a solution to the above Navy difficulties in using HF. As the name implies, the process of providing a two-way path or link for HF communications is implemented in a fully automatic manner. No operator is needed to select HF frequencies and establish an HF link between the two nodes. This is achieved in the ALE system by its performing a real-time HF signal reception assessment at each node. This assessment includes the quality of HF propagation and HF receiver noise/interference when HF communications is to take place. As a result of the exchanges of information between two nodes, usable communication links can automatically be established. With these assessments, the FED-STD ALE equipment can identify, from a set of allowed HF transmit frequencies in a point-to-point (PTP) situation, the most desirable frequency channels to use. In accordance with the FED-STD 1045, or its military version MIL-STD A, the ALE uses the Link Quality Assessment (LQA) as a method for ranking the allowed frequencies/channels. A three-way handshake between the two nodes allows the exchange of measured signal-plus-noise-to-noise (Sinad) and pseudo-bit-error-rate (PBER) measurements. Using these measured values, a single composite LQA value is developed that ranks the performance of the point-to-point (PTP) link between the two nodes, at each of the available usable channel/frequencies. More will be said on this subject later in this report. What is now the ALE standard (FED-STD 1045) began development in The FED-STD Test and Evaluation working group has been chaired by a representative from the Defense Communication Agency. The chairman directed in 1988 that a series of POC Over-The-Air tests be performed to validate the FED-STD 1045 ALE standard. These tests were done by the Joint Interoperability Test Center (JITC), at Fort Huachuca, AZ. The tests used an ALE system produced by the Harris Corp in accordance with the FED-STD 1045 ALE standard. This equipment was used for POC testing, and the results were reported by the U.S. Department of Commerce (1988). Prior to the Over-The-Air testing, laboratory simulations were conducted at the Institute of Telecommunications Sciences (ITS), Department of Commerce Laboratories in Boulder, Colorado. These and other tests were performed between competing ALE approaches (Mitre and Rockwell/Collins ACP). Later, simulation tests were made on the final ALE configuration prior to the 1988 Over-The-Air testing. Because the ALE system uses a digital processor for its various functions, it therefore possessed a capability for extensive addressing and special calls for network operation employing up to 15 nodes. FED-STD networking protocols were later defined in a new networking standard, FED-STD The HF FED-STD ALE is intended to serve virtually all Federal agencies including Department of Defense (MIL-STD A), the Justice Department, U.S. Coast Guard, and the Central Intelligence Agency. It is, therefore, necessary that the Link Protection modules, provided by National Security Agency, be used to prevent unauthorized access or spoofing of operational links. This requirement has been addressed in the FED-STD 1049, the Link Protection Standard. 2 The incorporation of the new protocol for FED-STDs 1046 and 1049 into the POC ALE controller has been completed recently by the Harris Corporation. These two new FED-STD areas, as well as certain previously untested ALE areas of FED-STD 1045, were tested during August 1990 in laboratory simulation tests at ITS Boulder, CO. This was followed by Over-The-Air tests of these new standards during September. Since NOSC already had procured two RF 7210 ALE controllers, designed to FED-STD 1045, the Center proposed to participate and support the new FED-STD Over-The-Air tests by providing two Navy test nodes. One of these nodes was at NOSC San Diego and the second was at NOSC Hawaii. The Navy objectives were, first, to be represented in these Federal tests and, second, to determine how FED-STD 1045 ALE developments could support Navy HF communication needs. The Navy- Only tests were conducted to satisfy the second objective. The results of the Navy-Only part of this testing is contained in section 3.0 of this report. 2.1 FED-STD ALE 2.0 TECHNICAL DISCUSSION OF AUTOMATIC LINK ESTABLISHMENT The FED-STD ALE belongs in the category of Non-Frequency Hopped ALE. In this ALE, the basis for the decision to use a particular HF frequency is determined from its LQA values. The LQA values are assigned t
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