Abstract: A half duplex radio transceiver comprises a transmitter (100) and a low IF receiver (200). The difference between the transmit frequency and the receive frequency is equal to the low IF. A common frequency generator (300) is shared between the transmitter and receiver without needing to be retuned. An upconversion signal at the transmit frequency is used for down conversion in the receiver. Transceivers at opposite ends of a communication link, such as in a master/slave network, have their transmit and receive frequencies interchanged. Optionally a transceiver may be configurable to either form e.g. as either a master of a slave station. Channel sensing for Carrier Sense Multiple Access (CSMA) may be performed on the transmit frequency without retuning the receiver.

Abstract: A communications system comprises a beacon and at least one portable device for receiving data from the beacon. The beacon broadcasts messages using a first protocol which provides a series of inquiry messages which hop frequencies (such as Bluetooth). Additional data is broadcast using a spread spectrum transmission technique. These two modes enable the spread spectrum transmission technique to be used to enable an unsynchronized receiver to establish communication in a short time, so that data can be sent to the receiver as quickly as possible. The frequency hopping technique may require a longer call set-up procedure, but provides a more appropriate communications protocol for bi-directional transfer of larger quantities of data.

Abstract: A method of powering-up a battery powered equipment by a phased activation of a function, for example the gain of a power amplifier (44), to increase the current consumption in a manner which avoids an excessive transitory drop in the supply voltage from the battery (42). Such a transitory drop may inhibit the powering-up operation and also may cause the battery to be exchanged prematurely because it appears that the battery is no longer usable. The phased activation of the function may be effected in a pre-planned phase sequence or by using a control loop monitoring the supply voltage.

Abstract: A transceiver for use in a time division radio system comprises a transmitter (104) and a receiver (106), each coupled to a different port of an antenna (102). By suitable switching of low impedances between antenna ports and ground, signals can be routed as required between the transmitter, receiver and antenna. In one embodiment the antenna (102) is a folded monopole which is fed at one end while the other end is grounded by switching the appropriate circuitry (114,112) to a low impedance state. In a modification of this embodiment one switch (114) connects the antenna (102) to a DC supply (Vc) which provides power for the transmitter when the transceiver is functioning as a transmitter.

Abstract: A method of determining the position of a mobile unit (MS1) having a GPS receiver (24) is disclosed. The method comprising the steps of measuring mobile unit pseudoranges at the mobile unit (MS1) using the GPS receiver (24); providing reference pseudoranges corresponding to a reference location situated remote from the mobile unit (BS1); and determining the position of the mobile unit (MS1) relative to the reference location (BS1) as a function of both the reference pseudoranges and the mobile unit pseudoranges.

Abstract: A system for communicating digital data comprises a splitting device (38) for separating an input digital data word, which may be provided by a speech coding arrangement (34,36), into most significant bits and less significant bits. The most significant bit(s) of the digital data word are encoded (40) using a robust signalling alphabet and less significant bit(s) are encoded (42,44) using progressively less robust signalling alphabets. All of the symbols resulting from the encoding are combined (46) and transmitted (48). On reception (50) the received signal is split (52) and demodulated (54,56,58) to provide respective portions of a received data word to a combining means (60). Where the data word was originally provided by speech coding arrangement the received data word may be provided to a resynthesising arrangement (62,64). The signalling alphabets may comprise 2-level modulation, 3,4 and 8-level modulation and/or phase modulation of various degrees.

Abstract: A system for communicating digital data comprises a splitting device (38) for separating an input digital data word, which may be provided by a speech coding arrangement (34,36), into most significant bits and less significant bits. The most significant bit(s) of the digital data word are encoded (40) using a robust signalling alphabet and less significant bit(s) are encoded (42,44) using progressively less robust signalling alphabets. All of the symbols resulting from the encoding are combined (46) and transmitted (48). On reception (50) the received signal is split (52) and demodulated (54,56,58) to provide respective portions of a received data word to a combining means (60). Where the data word was originally provided by speech coding arrangement the received data word may be provided to a resynthesising arrangement (62,64). The signalling alphabets may comprise 2-level modulation, 3,4 and 8-level modulation and/or phase modulation of various degrees.

Abstract: In an arithmetic apparatus operands are represented as powers of a generator so that multiplications can be performed as simple additions. However this makes actual addition difficult. Additions are therefore performed by means of a subtractor circuit (1), a Zech table (2) and an adder circuit (3). In order to perform these additions when each power is in plural residue form (x.sub.1, x.sub.2 and y.sub.1, y.sub.2) and give the result power also in plural residue form (i.sub.1, i.sub.2), the subtractor circuit comprises subtractor subcircuits (1A, 1B), the adder circuit comprises adder subcircuits (3A, 3B) and the Zech table is arranged to produced its output also in plural residue form (j.sub.i, j.sub.2). In order to obtain the correct result even when the power representation y.sub.1, y.sub.2 represents an operand value of zero the apparatus also includes a detector (58) for this condition, this controlling a multiplexer (61) which then conducts the other operand (x.sub.1, y.sub.

Abstract: In a modulo p arithmetic apparatus operands are represented as powers of a generator so that multiplications can be performed as simple additions. However, this makes actual addition difficult. Additions are therefore performed by means of a modulo (p-1) subtractor circuit (1), a Zech table (2) and a modulo (p-1) adder circuit (3). In order to reduce the size of the Zech table which would otherwise be required, specific values of the output of the subtractor circuit are converted to their negatives modulo (p-1) by means of a converter circuit (15) prior to their application to the Zech table, making use of the fact that each negative modulo (p-1) maps directly to a unique positive number which is often different from the number which was originally converted.

Abstract: A radio transmission system a base station comprises a plurality of transmitters arranged to transmit from the same site and having substantially the same output power, each transmitting on an individual channel within a dedicated block of contiguous channels. Receivers tuned to channels within said block of channels therefore require a limited image and adjacent channel rejection, of the order of 30 db. The receiver is preferably a direct conversion phasing receiver which has a local oscillator which can be tuned to a frequency within the block such that an image of any channel also falls within the block of channels. The system is suitable for local area radio systems such as paging or cordless telephones.

Abstract: A signal channel system which is particularly suitable for the employment of direct conversion receivers has a block of adjacent transmission frequency bands allocated to it. Each signal channel is split into two sub-channels or parts occupying mutually different frequency bands for transmission and the bands occupied by the sub-channels of the various channels are interleaved. In the receiver the local oscillator is tuned midway between the bands corresponding to the sub-channels of the wanted channel and the corresponding signals are recovered by bandpass filtering, phase-shifting, summing and differencing, demodulating and combining the frequency down-converted outputs of quadrature related mixers to which the received and the local oscillator signals are applied. Although d.c.

Abstract: An active polyphase filter arrangement in which asymmetric poles and zeros are obtained using feedback. In implementing the active polyphase filter arrangement there is provided a feedforward path comprising a first polyphase filter and a feedback path comprising a second polyphase filter. Both filters are preferably two phase filters. In operating the polyphase filter arrangement the loop gain at the unwanted "image" frequency can either be made much greater than unity thereby making the feed forward path insensitive to mismatching or be made much less than unity thereby making the feedback path insensitive to mismatching.

Abstract: A d.c. block capacitor circuit suitable as an integrated circuit in that it requires only one pin for the connection of an external capacitor. The circuit has particular, but not exclusive, application to direct conversion receivers. The circuit comprises an operational amplifier (10) having an inverting and a non-inverting input and an output. A pair of resistors (12, 14) having values R1, R1', respectively, connect the respective amplifier inputs to a signal input (16). The amplifier has a feedback resistor (18) having a value R2 connected between the inverting input and the output. Another resistor (20) having a value R2'and a capacitor (22) are connected between the non-inverting input and either and same or different voltage reference point(s). The values of the resistors (12, 14, 18, 20) are selected so that the ratio of R2':R1' equals the ratio R2:R1. Any d.c.

Abstract: A radio frequency tuning circuit, for use in a transmitter or receiver, which rejects image frequencies of the frequency band of a supplied RF signal to which it is tuned. The circuit comprises an N-path filter and a feedback loop connecting the output of such filter to the input of an RF amplifier to which the RF signal is applied. The filter includes a tunable local oscillator and a pair of quadrature related signal paths including mixers therein driven by such oscillator, the outputs of such paths being combined by a summing amplifier which produces the output RF signal. The output of the summing amplifier is also supplied to the feedback path, causing the center frequency of the transfer characteristic of the N-path filter to be displaced from the local oscillator frequency. The RF output signal thereby includes substantially only single sideband of the signals produced by the two signal paths.

Abstract: An FM data receiver of the offset type, in which the local oscillator frequency is located between the two frequency-shift-keyed signalling frequencies. To counter the effects of drift in the local oscillator, a simple AFC system mixes the signalling tone signals with delayed signals to provide a frequency control signal.

Abstract: A direct modulation FM data receiver including a mixer (14) having a first input for receiving a directly modulated FM signal (f.sub.c .+-..DELTA.f), where .DELTA.f is the deviation and f.sub.c the carrier, and a second input for a local oscillator (20) signal (f.sub.L) having a frequency within the signal channel but offset from the input signal carrier (f.sub.c) by an amount (.delta.f). Demodulating circuits (22 to 30) distinguish between the signalling tones (.DELTA.f+.delta.f) and (.DELTA.f-.delta.f) and derive a data output signal therefrom.

Abstract: An FM demodulator in which an incoming FM signal (2a sin(.omega.+.delta..omega.)t) is demodulated to baseband (.delta..omega.) by applying it to first and second mixers (12, 14). The output (b sin .omega. t) of a local oscillator (16) is applied to one (14) of the mixers and is also applied to the other (12) of the mixers via a 90.degree. phase shifter (18). The phase of the output of one of the mixers is shifted so as to be in phase or in antiphase to the other and is applied together with the output of the other of the mixers to a signal divider (22), the output of which comprises the baseband signal which is substantially independent of fading.