Abstract: A method of pre-emphasising a signal comprises the steps of a) receiving the signal as an input; b) applying the input signal to a processing system comprising a pair of parallel signal processing paths each comprising a non-linear phase filter and a non-linearity, and a further parallel path, wherein the filters in the pair of processing paths have equal but opposite phase responses and substantially equal magnitude responses, and wherein the outputs of the parallel processing paths are combined to produce the raw pre-emphasised signal; whereby the input signal is subjected to a non-linear dynamic range compression which is phase linear. Alternatively or additionally the input signal is split into at least three different frequency bands for non-linear processing. Preferably the pre-emphasised signal is pre-corrected using an iterative system. Complementary de-emphasis systems are also described, as well as pre-emphasis and de-emphasis apparatus.

Abstract: A low power OFDM signal may be transmitted in an environment where it is subject to interference from other transmissions, e.g. broadcast television services. In a receiver interference is reduced by ignoring information modulating OFDM carriers at the frequencies corresponding to the carriers of the interfering transmissions; adjacent channel interference is reduced by ignoring data on OFDM carriers at the band edges and interference from third order intermodulation products is reduced by the ignoring OFDM carriers affected. Image channel interference is reduced by using an intermediate frequency for a first mixing process in the receiver such that the image channel interference affects OFDM carriers at frequencies which are already being ignored by the receiver. Preferably no data is modulated onto OFDM carriers which are to be ignored by the receiver. Preferably the modulation of the OFDM carriers is arranged so as to produce a real baseband representation of the OFDM signal.

Abstract: Digital data, in the form of blocks delimited by end-of-block words, that is to be coded into variable length codewords, is protected against errors occurring within a block, as well as errors crossing block boundaries, by modulating the respective end-of-block words with a bit, or bits, of a larger reference pattern which bit, or bits, have been conditioned to carry information on the content of VLC codewords coding a corresponding (eg. preceding) data block. The "modulation" may be by means of selecting between different possible end-of-block words dependent upon the value of the conditioned reference pattern bit, or bits, or by means of appending the conditioned bit(s) to the end-of-block word. The reference pattern may be a repeated pseudo-random sequence.

Abstract: In an OFDM signal individual OFDM carriers are modulated by samples of signals which can only take a limited range of allowed values and a block of samples modulates the group of carriers during a time period T. In a receiver, the signal modulating an individual OFDM carrier may be demodulated by estimating the position of reference axes serving as the frame of reference against which the allowed modulating values are defined, and multiplying the value of the demodulated samples by the complex conjugate of a point on one of the estimated reference axes. The spread of the groups of samples demodulated from each OFDM carrier gives an indication of whether the receiver is synchronised to the block boundaries. Preferably spread of the complex samples is evaluated in the radial direction only and used to steer the sample clock frequency. Phase drift of the demodulated samples from one block to the next indicates the degree of local oscillator frequency error.

Abstract: In a high definition multiplexed analog component system, a high definition signal is processed by splitting it into high and low frequency components and pre-emphasizing the high frequency component with a non-linear characteristic and at the receiver a complementary de-emphasis process is applied to produce a noise-reduced high definition signal compatible with existing conventional receivers. A processor of a pre-connector for the high definition signal can be used for intersample interference due to non-compatibility between the pre and de-emphasis characteristics in a digital implementation of the system.