Abstract: A method of estimating a digitized data signal transmitted as a sequence of data symbols. The received signal is generally distorted by transmission through a dispersive communications channel. The received symbols can exist in a plurality of different states depending on the number of symbols in the data alphabet and the extent of intersymbol interference. In the present method a near-instaneous soft decision is made (without the need for memory storage) for each estimated symbol using the following main steps. 1) Determine for each state at a given time increment k the respective partial path metric (M.sub.A) in respect of the state transition corresponding to the transmission of a first symbol type (A). 2) Determine for each state at the same time increment k the respective partial path metric (M.sub.B) in respect of the state transition corresponding to the transmission of a second symbol type (B). 3) Select the maximum value (M.sub.Amax and M.sub.

Abstract: A radio receiver includes apparatus for correcting phase and frequency offsets in a digitally modulated carrier signal. The receiver includes processing circuitry which outputs a baseband signal at point. The circuitry includes a local oscillator generating a signal intended to have a phase and frequency related (e.g. substantially equal) to the carrier signal. The baseband signal from the circuitry is input to a demodulator which generates a signal in the form of a sequence of digits corresponding to the original carrier signal. The baseband signal is sampled by a sampler and the demodulated signal is sampled by a sampler. Processing circuitry calculates the correlation function of the two sample signals and determines the value of the phase .PHI..sub.x at a time when the correlation function is a maximum. A control signal V.sub.c indicative of the phase .PHI..sub.

Abstract: A levelling control arrangement for an RF transmitter circuit which additionally compensates for filter ripple, i.e. frequency dependant power variations caused by the filter disposed between a transmitter amplifier and an antenna. The forward and reflected power is sampled by a dual directional coupler between the amplifier and the filter. Signals V.sub.fwd and V.sub.rev are thus obtained indicative of the forward and reflected power levels respectively. The reflected signal V.sub.rev is subtracted from the forward signal V.sub.fwd at comparator and the difference signal V.sub.diff is compared with a reference signal Vref at comparator to produce a signal V.sub.c which is used to control the gain of the amplifier in such manner that the power developed by the amplifier increases as the signal V.sub.rev increases and vice versa. To protect against excessive reflected power levels a limiter may be included which causes the power developed by the amplifier to be reduced only if V.sub.