Dual mode satellite/cellular terminal

DETAILED DESCRIPTION OF THE DISCLOSURE FIG.
1 illustrates the allocations of frequencies for Personal Satellite Communications services in world regions R1, R2 and R3 compared to FCC proposals for new frequencies to be offered by auction for new landbased Personal Communications Services.
It can be seen that the PCS bands marked DEFG conflict with the satellite PSC bands.
However, the FCC has at the present time abandoned plans to allocate frequency bands DEFG to PCS, and the planned frequency auction is restricted to bands marked A,B and C.
The separate A, B and C groups represent up- and downlink bands for directions from mobile to base and from base to mobile, respectively, and the 80 MHz separation is known as the duplex spacing.
In between the up- and downlink bands, the frequencies will be offered on an unlicensed and largely unregulated basis.
The unregulated band has no envisaged frequency duplex spacing and is only suitable for simplex, half-duplex or press-to-talk systems, or systems which use same-frequency time-duplex operation such as the Digital European Cordless Telephone Standard (DECT).
The duplex spacing between satellite uplink and downlink bands is seen to be somewhat larger.
While this facilitates the construction of small, low-loss duplexers that would permit transmission and reception through the same antennas simultaneously, duplexers are still components that are preferably avoided by using the time-duplex method at least in the portable telephone terminal.
Avoiding such highly frequency-selective components also facilitates the construction of a receiver that would embrace both the PCS receive band 1930-1970 MHz as well as the PSC receive band.
The present invention includes, but is not restricted to, the construction of dual-mode PCS/PSC terminals in the bands illustrated in FIG.
1.
The present invention can alternatively be applied to dual-mode terminals in which the cellular band is in the 900 MHz range, or indeed in which the satellite and cellular frequency bands lie in any frequency range