A transmitter transmits payload data using Orthogonal Frequency Division Multiplexed (OFDM) symbols, the transmitter including a frame builder to receive the payload data and to receive signalling data for use in detecting and recovering the payload data at a receiver, and to form the payload data into data-units for transmission. A modulator modulates plural sub-carriers of one or more OFDM symbols with the signalling data and the payload data in accordance with a modulation scheme to provide for each of plural sub-carriers a modulation symbol, a prefixing circuit prefixes a guard interval to the one or more OFDM symbols, and a transmission circuit transmits the one or more OFDM symbols. The modulator includes an I/Q interleaver to receive a real component of the modulation symbol of each of the one or more sub-carriers and to interleave the real component of the modulation symbols differently to the imaginary component.

Techniques for detecting and demodulating a signal/transmission are described. Signal detection is performed in multiple stages using different types of signal processing, e.g., using time-domain correlation for a first stage, frequency-domain processing for a second stage, and time-domain processing for a third stage. For the first stage, products of symbols are generated for at least two different delays, correlation between the products for each delay and known values is performed, and correlation results for all delays are combined and used to declare the presence of a signal. For demodulation, the timing of input samples is adjusted to obtain timing-adjusted samples. A frequency offset is estimated and removed from the timing-adjusted samples to obtain frequency-corrected samples, which are processed with a channel estimate to obtain detected symbols. The phases of the detected symbols are corrected to obtain phase-corrected symbols, which are demodulated, deinterleaved, and decoded.

A robust frequency drift tracking receiver. The received signal is translated to an intermediate frequency in the RF stage by a quadrature demodulator, and is then brought into the base band by a digital mixer made by a CORDIC. A base band processing, stage allows for a synchronisation of the receiver relative to the data frame, to estimate data and to output a counter-reaction signal to the CORDIC, obtained by integration of successive frequency corrections with a predetermined step.

Systems and methods pertain to a receiver configured to receive and detect convolutionally coded Gaussian frequency-shift keying (GFSK) signals comprising a trellis of branches. The receiver implements a Per-Survivor Processing (PSP) algorithm to generate frequency estimate, phase estimate, and branch metric increment for each branch of a trellis. A Viterbi Algorithm is applied to the trellis for Maximum Likelihood Sequence Estimation (MLSE) of information bits. The receiver includes a PSP block comprising a number of blocks equal to the number of branches of the trellis. Each block includes a Phase Corrector, Decision Feedback Demodulator (DFD), and a Frequency Tracking Loop (FTL) to update the PSP variables.

A radio transmitter (4) comprises an encoder (5) that receives one or more variable message bits, and encodes each message bit that has a first value as a predetermined first binary chip sequence and encodes each message bit that has the opposite value as a predetermined second binary chip sequence. The radio transmitter (4) transmits data packets, each comprising (i) a predetermined synchronisation portion, comprising one or more instances of the first binary chip sequence, and (ii) a variable data portion, comprising one or more encoded message bits output by the encoder. A radio receiver (9) receives such data packets. It uses the synchronisation portion of a received data packet to perform a frequency and/or timing synchronisation operation, and then decodes message bits from the data portion of the data packet.