Abstract: In a frame sync method, a receiver searches for the presence of an N-symbol long unique word pattern. For each possible frame sync detected, the receiver proceeds to demodulation and FEC processing. After each iteration of the FEC decoder, the detected unique word pattern is compared to the expected one and the frame sync is detected if the number of unique word errors has decreased.

Abstract: In a wireless communications system, transceivers transmit short bursts to a base station, which determines timing corrections from the time of receipt of the burst and transmits the timing corrections to the respective transceivers. In one aspect, the base station indicates to the transceivers a plurality of time slots, each transceiver selects one of the time slots at random, formats a burst including an indicator of the selected time slot and transmits the burst in that slot. In another aspect, the base station transmits to each transceiver a timing uncertainty value, which determines how the timing correction will be modified by the tranceiver as the interval since last receiving a timing correction increases. Data bursts are transmitted in a format comprising a first unique word, a content field and a second unique word, in that order. The bursts are transmitted in a TDMA channel format which can accommodate both short and long bursts in a block format of constant periodicity.

Abstract: In a wireless communications system, transceivers transmit short bursts to a base station, which determines timing corrections from the time of receipt of the burst and transmits the timing corrections to the respective transceivers. In one aspect, the base station indicates to the transceivers a plurality of time slots, each transceiver selects one of the time slots at random, formats a burst including an Indicator of the selected time slot and transmits the burst in that slot. In another aspect, the base station transmits to each transceiver a timing uncertainty value, which determines how the timing correction will be modified by the tranceiver as the interval since last receiving a timing correction increases. Data bursts are transmitted in a format comprising a first unique word, a content field and a second unique word, in that order. The bursts are transmitted in a TDMA channel format which can accommodate both short and long bursts in a block format of constant periodicity.

Abstract: A mobile satellite communications terminal (2) comprises a portable computer (68), an interface card (8) containing intermediate frequency (IF) conversion circuitry (28, 52), and an antenna assembly (10) including RF conversion circuitry (34, 50) and an antenna (44). The interface card (8) is connected to the antenna assembly (10) by a detachable cable (32), which carries IF signals. This arrangement reduces RF power losses and interference. The antenna (44) is manually steerable towards a geostationary or quasi-geostationary satellite (12). A navigation signal antenna (56) is mounted on the antenna assembly (10) and is steerable independently of the antenna (44) so as to be vertically aligned, which is the optimum position for receiving navigation signals. The antenna assembly (10) includes orientation sensors (70, 75) which allow the difference between the current and the correct orientation of the antenna (44) to be calculated.

Abstract: Data is transmitted in a signal comprising a data signal D.sub.m at a frequency within a range B of discrete frequency tones D.sub.0 to D.sub.m-1 representing a predetermined range of digital values, and a pilot signal (36, 37). The signal is received by a circuit comprising a transformer (44 to 54) which transforms the received signal into a set of frequency samples of the pilot signal and a set of frequency samples of the data signal. The samples are input to a correlator (58) which correlates the set of frequency samples of the pilot signal with the set of frequency samples of the data signal at each of the discrete frequency tones in order to identify the discrete frequency tone to which the frequency of the data signal corresponds. In this way, the digital value represented by the data signal can be identified. The circuit is suitable for use in a radio pager for receiving data signal transmissions from a distant source which may be transmitted from a satellite.