Glonass

The GLONASS system, developed by the former Soviet Union for military application, was inaugurated in 1982. There are a number of similarities in these systems. Table 10.2 compares their main orbital parameters. The full constellation comprises 21 satellites with three in orbit spares at an altitude of 25,510 km inclined at 64.8*. Satellites transmit on two frequencies, at about the same level as GPS satellites, but use the frequency hopped spread spectrum technique. For civil applications, a single 511 bit code, repeating every I ms, is used with differential coding in an RZ format at 50 bps (Daly, 1993; Dale et al., 1989); the military code operates at 10 times the civilian code rate. Frequencies lie in 1,240 1,260 and 1,597 1,617 MHz, the channel spacing for these two bands is respectively 0.4375 and 0.5625 MHz, and the number of channels is 24 in each case. A BPSK modulation scheme is used with a bandwidth of 1 MHz for civilian applications and 10 MHz for military applications. Navigation data and the principle of positionfixing are similar to GPS. However, there are a number of differences which cause difficulty in integrating them, but nevertheless integration is technically feasible. Some notable comparative system features include:

The GPS system is well maintained with reliable satellites; the GLONASS constellation is not well maintained at present due to lack of financial resources, there were only nine satellites functioning in the first quarter of 1999, degrading system performance, and therefore not many receivers are being manufactured and sold.

There is a large degree of compatibility in orbital geometry.

While GPS satellites can be monitored continuously through a network of ground stations, GLONASS satellites can be monitored only within the former Soviet Union territory.