50 may be useful, which means a total of 2150 * 80 = 172 000 voice links are available through the Iridium system. Some of these links may be used for data communication which reduces the overall voice capacity. Guard band 41.67 kHz CH 239 CH 240 1616 MHz 1626.5 MHz Figure 11.12 Iridium frequency spectrum usage Broadband Telecommunications Technologies and Management Figure 11.13 Iridium frequency spectrum reuse Clearly the limited spectrum made available to the Iridium system limits the overall system capacity. Iridium is also planning on launching new services using spectrum in the K band in order to provide up to 8 Mbps data communications services [14, 15, 16]. Case Study 11.1: Iridium and Globalstar Using satellites to provide mobile connectivity gained currency in the late 1980s as the first generation of mobile telephony systems were rolled out. At the time the mobile service coverage was patchy and confined mainly to large metropolitan areas. Even within these cities the coverage was not perfect and calls would regularly drop out. Moreover many countries did not have a mobile phone service, and no coverage existed outside populated areas. Furthermore, mobile phones were expensive with handset prices of more than $2000 and phone call rates of more than $3 per minute. There was a business opportunity to improve the cost/performance of these systems. One response was the development of mobile telecommunications using GEO satellites, however these systems were generally intended for trucks and trains where large antennas could be installed to meet the required link budget. Mobile communications using a constellation of LEO satellites solved the problem of large antennas as the path loss could be reduced by more than 30 dB. Three LEO mobile satellite projects were launched in the early 1990s, Teledesic was primarily funded by Microsoft, Globalstar was funded by Qualcomm, and Iridium by Motorola. Of the three, Teledesic was the most ambitious with plans to launch some 840 satellites and provide transmission rat