Abstract: An emergency call capable system is disclosed. The system comprises a processing means configured to: instruct a communications apparatus to initiate a call to a remote system in response to a trigger event; determine whether the call satisfies a condition comprising at least one of: (a) the call passes a call duration test; and (b) that data transferred from the remote system after initiating the call passes a human voice test; and instruct the communications apparatus to initiate a further call to the remote system in response to failing to satisfy the condition. Also disclosed is a computer-implemented method of operating an emergency call capable system.

Abstract: For combining diversity path signals comprising symbols each modulated in accordance with one of a plurality of orthogonal (e.g. Walsh) functions, a diversity combiner includes, for each path, a demodulator to demodulate each modulated signal symbol in accordance with a selected one of the orthogonal functions, a phase estimator to estimate a phase rotation and amplitude of the diversity path signal from the demodulated signal, and a complex signal multiplier to derotate the phase and weight the amplitude of the diversity path modulated signal in dependence upon the estimated phase rotation and amplitude. The combiner sums real parts of the phase-derotated and weighted modulated signals of the diversity paths, demodulates the combined signal in accordance with all of the orthogonal functions, and selects the maximum demodulated signal for each symbol thereby to determine for the symbol the selected one of the orthogonal functions.

Abstract: A method of encoding a digital signal comprising a sequence of digital words, each comprising a first portion and a second portion, comprises the steps of successively encoding respective first portions using a trellis code to produce a corresponding sequence of trellis-encoded words, using each of the trellis-coded words to select one of a plurality of subcodes of a block code, and using the selected subcode to encode the corresponding second portion of the digital word corresponding sequentially to the trellis-coded word used to select the subcode, thereby providing a sequence of codewords corresponding to the sequence of digital words.

Abstract: A code division multiple access (CDMA) communications system comprises a plurality of CDMA transmitters and at least one reception station coupled together by a communications channel. Each CDMA transmitter encodes a digital signal with a spreading code, each bit of the digital signal being encoded by a spreading code segment comprising a multiplicity of chips. All of the transmitters transmit their respective encoded signals to the reception station asynchronously via the communications channel so as to occupy the same bandwidth. Each receiver receives the combined signals of all of the transmitters and correlates it with a selected one of the spreading code segments to detect the digital signal from the corresponding transmitter. Each receiver uses also the signal-to-noise ratios of detected signals other than its own, with respect to chip delays relative to a reference one of the signals, to suppress multiple access interference (MAI) caused by such other detected signals.

Abstract: A surface wave device, for use in differential coherent detection in a commutation signaling communications system using N predetermined M-bit codewords, propagates surface waves for each codeword to a first coded output IDT (inter-digital transducer) comprising M parallel taps with a pitch t=T/M, the taps having phases representing bits of the respective codeword, and to a second output IDT which is at a distance from an input IDT greater by T than the first coded output IDT, to provide an additional delay of one information symbol. The input IDT, or each tap of each coded output IDT, has a length equal to t. The second output IDT can comprise a coded IDT, or a delay tap responsive to the surface wave propagated via the first coded output IDT.