Ntia special Publication 94-30 a technical Report to the Secretary of Transportation on a National Approach to Augmented gps services

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Security.  The system provides the same level of user safety and security as current marine radionavigation aids. The system does not employ encryption or any other user screening or security features.
Infrastructure Cost.  The total cost for establishing the operational system of 61 sites is $14.2M. The annual cost for operations and maintenance (O&M) is $4.2M. The total life cycle cost over 20 years is $14.2M + 20($4.2M) = $98.2M.

User Cost.  Users of the system require a LF/MF radio coupled with a DGPS-capable receiver. Current cost for low-end equipment is less than $1,000.
Data Link Characteristics.  The system adds a digitally modulated minimum shift keying (MSK) subcarrier to transmissions from marine radio beacons operating in the 283.5 to 325 kHz (LF/MF) band. The LF/MF signal propagates in the groundwave mode. The signal can be received at ranges which are well beyond line of sight.
Data Format.  The system broadcasts using the RTCM SC-104 format, Version 2.1. Type 9 messages are used for the GPS differential corrections. This format is supported by numerous GPS equipment manufactur­ers and service providers. The RTCM format has been designated for international maritime use by the International Telecommunication Union (ITU).
Time Frame of Availability.  At least 12 prototype sites are operating, with a total of 61 planned to be fully operational by January 1996.

3.3.2  USCG LF/MF Radiobeacon System Expanded
With the addition of 20 to 50 beacon sites to provide nationwide coverage, this system is a nationwide expansion of the system described in Section 3.3.1. All factors described in Section 3.3.1 are identical except coverage area, infrastructure cost, and time frame of availability.
Coverage Area.  The USCG Expanded (USCG(E)) System is designed to provide nationwide coverage including harbor/harbor approach areas and other critical waterways for which the USCG provides aids to navigation. Figure 3-3 shows the predicted coverage area for 41 additional beacon sites, and Figure 3-4 shows the predicted composite coverage for the original 61 beacon sites plus the 41 additional sites. Inland coverage depends on ground conductivity and the actual number of sites to achieve nationwide coverage can only be estimated at this time. Appendix H describes the expected coverage and availability of an LF/MF radiobeacon system.
Infrastructure Cost.  The total cost for establishing the additional 20-50 sites is $3M to $8M. The additional annual cost for operations and maintenance (O&M) is $1M to $2M. The maximum total life cycle cost over 20 years for the USCG(E) system would be $146M.
Time Frame of Availability.  It is expected that the additional 20 to 50 sites will require a total of 1 to 2 years deployment time.

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