Abstract: A method of transferring secure data in a remote control system including a remote controller (12) and an apparatus (10) which is operable in response to commands relayed by way of the remote controller. The apparatus has a receiver (38) for receiving transmissions from the remote controller (12), the information from the transmissions being stored in a storage device (42). The remote controller has a transmitter (26), a memory (22) for storing secure data and commands and a keypad (24). The transmitter (26) is controlled so that in response to a user wishing to transfer secure data to the user apparatus (10), it transmits this data at a power level lower than that which is normally used for sending other commands. The link between the remote controller (12) and the user apparatus (10) may be wireless or infra-red.

Abstract: A method of transmitting messages in an answer-back paging system in which a primary station (10,14,16) transmits a series of messages addressed to respective secondary stations (20) on a down-link. The primary station then invites the secondary stations to transmit their responses, for example as CDMA signals, on an up-link. On receipt the primary station analyses those responses which are deemed to be intelligible, matches them to the originally transmitted messages and transmits acknowledgements to the relevant secondary stations. The primary station then issues another invitation to those stations whose responses had not been detected requesting them to reply on the up-link. Those responses which are deemed intelligible are processed as before and acknowledgements are transmitted together with another invitation on the down-link. The cycle of operations is repeated until either a predetermined number of cycles have elapsed or it is considered that all the intelligible responses have been received.

Abstract: For battery economizing in a receiving station (CU) having a radio identity code (RIC) consisting of M bits, a base station (MIU) transmits a wake-up message consisting of at least two repetitions of a wake-up sequence having N concatenated parts. Each of the N parts includes a sync code word and a different fraction M/N of bits of a radio identity code (RIC). The receiving station is energized intermittently in order to detect carrier and at least one of the N parts. In response to detecting that one of the N parts is received, the receiving station remains energized and analyzes at least the detected one of the N parts. If the received bits of the transmitted radio identity code do not correspond to the corresponding bits of the receiving station's radio identity code, the receiving station reverts to intermittent energization, otherwise it remains energized to receive a message appended to the transmitted radio identity code.

Abstract: A message transmission system includes at least one primary station arranged for making transmissions on a down-link and a plurality of secondary stations arranged for making transmissions on an up-link, each of the secondary stations having its own address which is transmitted as part of the down-link message. Each of the secondary stations is configured for generating responses to messages as pseudo-random data sequences, the pseudo-random data sequence being generated by a secondary station at any one time being dependent on at least the address assigned to the secondary station and/or information contained in the message.

Abstract: A communications system including a primary station and at least one or more secondary stations. The secondary station transmits signals as spread spectrum signals and a receiver in the primary station receives and decodes the spread signals. Frequency offsets in the received spread spectrum signals are dealt with by digitizing the received signals to produce raw data samples which are despread, frequency analyzed and the spectrums derived are scanned for peaks exceeding a predetermined threshold and the outputs indicate the presence or absence of codes.

Abstract: A method of reducing computation in spread spectrum signals in which a spread spectrum signal sent by a transmitting station (SS1) includes a group and an individual identity code. A receiver (10, 12) stores the received signals based on their group codes and analyses the stored signals on a group by group basis. This greatly reduces this computation required when recovering individual messages from a number of simultaneously transmitted spread spectrum signals. Optionally the transmitting station may send the group and individual identity code signals simultaneously as quadrature signals.

Abstract: A selective call system including a system controller, a base station transceiver and a plurality of secondary stations with receivers and low powered transmitters capable of sending spread spectrum signals. Invitations are issued to the secondary stations by the system controller at varying power levels. Only those secondary stations receiving the invitation signal are able to respond. Those secondary stations too far away cannot respond to a low power invitation, and since each secondary station can only respond once, upon a received invitation of increased power, such outer lying secondary stations can respond without interference from closer lying secondary stations.

Abstract: A data receiver in which the phase of the carrier signal is controlled so that the threshold levels used for coherent demodulation occur at the quarter points, that is 0.degree., 90.degree., 180.degree. and 270.degree.. An input signal is mixed with a local oscillator signal in a pair of mixers and the outputs therefrom are low pass filtered and subsequently demodulated. Any phase errors between the local oscillator signal and the input carrier signal are corrected by a correction loop. The carrier phase error is corrected after (or downstream of) the low pass filters, so that the phase can be corrected rapidly without the risk of instability.

Abstract: A data demodulator for digital signals in which the times of the zero crossings in hard limited signals in the orthogonal outputs (I and Q) of a direct demodulation receiver are used to recover the carrier and clock signals.

Abstract: A multi-tone sequential call signal detector in which a microcomputer is used to detect the tones of a received signal by simulating digitally the response of analogue tuned circuits. The detector includes a limiter for producing a square wave signal from a tone signal, a differentiator for producing interrupt pulses, and a microcomputer which responds to the interrupt pulses to activate a visual display and a call lamp of an output circuit when it detects all the received tones of the signal. The microcomputer performs an algorithm by which it measures the period between successive interrupt pulses, determines which tone frequency has this period, starts a number count which represents the "rise" response of a tuned circuit for that tone frequency, and determines when the number count reaches a threshold number which represents the resonant condition of the tuned circuit.

Abstract: Automatic frequency control (afc) particularly for single sideband (SSB) receiving systems.In a SSB receiving system, fine tuning is carried out using an afc loop. In one embodiment the loop includes a frequency discriminator for measuring the frequency of a composite i.f. signal (pilot carrier and modulating signal) and producing a waveform having an amplitude corresponding to the measured frequency. The amplitude waveform comprises the pilot carrier interspersed by the modulating signal. The frequency of the pilot carrier is measured using a peak detecting circuit and this measurement is used to automatically fine tune the receiver.