STARSHINE FREQUENCY COORDINATION REQUEST by WB4APR ------------------------------------------------------------------------ 18 Feb 02 The mission of STARSHINE and the other APRS Satellites is unique in the Amateur Satellite Service as they are designed to support the text messaging and position tracking needs of Schools, mobiles and handhelds only and links into the terrestrial internet system. As such, the link margins to user OMNI antennas require downlinks in the 2 meter band. For international operation, 145.825 will be shared with other existing AX.25 packet satellites which all agree to a low dutycycle downlink making channel sharing possible. The following design summary should provides the background. UPLINKS AND RECEIVE GAINS: User up&downlinks fall into several different classes based on ERP and receiver antenna gain as shown below. The column labeled Standby-receive gain is for the user who is not aware of, nor optimized for satellite reception. For example, an HT in a pocket, or a mobile parked under trees. ERP ERP Rcv Rcv Rcv UHF VHF UHF VHF STBY USERS (W) (W) dBi dBi dBi Applications --------- --- ---- --- --- --- ------------------------------ HANDHELDS 3 5 3 3 -6 Sailboats, Hikers, Wilderness MOBILES 70 100 5 5 -6 Boats, Remote Travelers HOME STNS 700 1000 13 13 Not intended for PCsat NETWORK IGATE RCV 7 5 Omni Internet receive site MSG NODE 70 100 Internet to user UPLINK site COMMAND 700 1000 13 13 US Naval Acadmy Ground Station MISSIONS: Since several other amateur satellties have provided imaging and file store- and-forward for the last several years, the APRS satellite mission concentrates on the current trend towards personal real-time wireless messaging using UI digipeating. In this context, the following list prioritizes these needs. 1) Handheld/Mobile message uplink to Internet (emergency and routine) 2) Handheld/Mobile message downlink delivery from Internet 3) Handheld/Mobile to Handheld/Mobile real-time communications 4) Nationwide Bulletin delivery to all users 5) Handheld/Mobile GPS position tracking to internet 6) GPS tracking of buoys, telemetry devices, wildlife, expeditions 7) Other UI digipeating applications (TBD) 8) Message Store-n-forward (limited special applications only) FUNDAMENTAL ASUMPTIONS: 1) Optimum ALOHA CSMA channel effeciency is about 18% due to collisions 2) VHF links have a 9 dB advantage over UHF links (omni to omni) 3) 1200 baud AFSK has a 7 dB advantage (measured) over 9600 baud FSK 4) T/R delays render 9600 only twice as fast as 1200 for short bursts 5) UHF uplinks require wide bandwith to avoid doppler (- 4 dB) 6) UHF downlinks require user tuning throughout pass (not desired) 7) There are available off-the-shelf handheld and mobile radios now that can serve as stand-alone digital satellite transceivers REQUIREMENTS/CONSTRAINTS Design Drivers: The following are some of the obvious first-order alignments of requirements to hardware and frequencies. From these, then, we determined the optimum trade-offs to arrive at our final design and frequency requirement on the 2 meter band. 1) MSG delivery to HT in Standby requires best possible downlink (1200 baud VHF). Igate uplink is relatively unconstrained. 2) MSG receipt from HT requires best possible uplink (1200 baud VHF). Downlink to internet is relatively unconstrained. 3) Continent wide Bulletin Delivery requires downlink on existing dedicated terrestrial APRS frequencies (144.39 in USA and 144.8 in Europe (both 1200 baud). 4) HT/Mobile real-time messaging requires same up/downlink baudrate 5) GPS HT/Mobile tracking is relatively unconstrained. 6) Low power GPS tracking devices requires best uplink (1200 baud VHF) and the uplink must not be used by any other satellite uplink to avoid unintentional interference to other systems. 7) Other UI digipeating applications should be crossband full duplex and should use same up/downlink baud rates 8) Store-n-forward (rare) is unconstrained with equal baud rates 9) Spread of applications among multiple receivers to minimize collisions is desired. 10) Reundancy and Backups are desired. 11) UHF downlinks are of little value due to poor link budget and doppler 12) UHF Uplinks can work without doppler tuing with a 30Khz Satellite RCVR 13) KISS applies (Keep it Simple, Stupid) HARDWARE ALIGNMENT: Using the above as the basis, we chose a dual-port KPC-9612 TNC to satisfy as many of the above requirements as possible. The KPC-9612 can cross relay from either of its two inputs to its two outputs. Since we only have one transmitter on VHF for best downlink, we output both the 1200 and 9600 baud data to the same transmitter (with appropriate PTT/DCD cross strapping). USERS UPLINK TNC DOWNLINK ---------------- ------- ------------ -------- STARSHINE KPC-9612 #1 HT-to-HT 145.825 ------> 1200 Baud -*-----> 145.825 GPS---> \ / | / \ | Mobile-to-Mobile 435.250 ------> 9600 Baud -* STARSHINE KPC-9612 #2 Ht-to-HT 145.825 ------> 1200 Baud ------> 145.825 Notice that the Igates monitor both downlinks to capture every packet heard and feed to the worldwide APRServe internet linked network. Our AMSAT/ITU Frequency request is: 1) to share 145.825 with other low dutycycle AX.25 packet Satellites. 2) To share 435.250 for all 9600 baud 50w mobiles. Bob Bruninga, WB4APR@amsat.org