Transmitter and method of transmitting and receiver and method of detecting OFDM signals

Abstract

A transmitter transmits payload data using Orthogonal Frequency Division Multiplexed (OFDM) symbols. The first OFDM symbol is a first type having a number of sub-carriers which is less than or equal to the number of sub-carriers of the one or more second OFDM symbols of a second type and a guard interval for the first OFDM symbol is selected in dependence upon the longest possible guard interval of the second OFDM symbol. Accordingly an OFDM communications system can be formed in which data is transmitted using a frame structure in which a guard interval is adapted to allow a mix of different types of OFDM symbols.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority to United Kingdom Application Number 1305799.7, filed 28 Mar. 2013, and European Patent Office Application Number 13170706.9 filed 5 Jun. 2013, the contents of which are incorporated herein by reference in their entirety.FIELD OF THE DISCLOSURE[0002]The present disclosure relates to transmitters and methods of transmitting payload data using Orthogonal Frequency Division Multiplexed (OFDM) symbols.BACKGROUND OF THE DISCLOSURE[0003]There are many examples of radio communication systems in which data is communicated using Orthogonal Frequency Division Multiplexing (OFDM). Systems which have been arranged to operate in accordance with Digital Video Broadcasting (DVB) standards for example, use OFDM. OFDM can be generally described as providing K narrow band sub-carriers (where K is an integer) which are modulated in parallel, each sub-carrier communicating a modulated data symbol such as Quadrature Amp...

AI Technical Summary

Benefits of technology

This patent describes a method for transmitting data using Orthogonal Frequency Division Multiplexed (OFDM) symbols. The method involves forming frames of data, where each frame includes a number of sub-carriers. The first sub-carrier in the frame is dedicated to carrying signalling data, while the second and subsequent sub-carriers are dedicated to carrying payload data. The ratio of sub-carriers used for carrying the signalling data to the sub-carriers used for carrying the payload data is adjusted to improve the likelihood of detecting and recovering the signalling data at the receiver. This results in a more robust communications system that is better able to withstand challenging radio environments.

Problems solved by technology

However, there can also be a reduction in robustness in the sense that it may be more difficult for a receiver to recover data transmitted using a high number of sub-carriers compared to a smaller number of sub-carriers, because for a fixed transmission bandwidth, increasing the number of sub-carriers K also means reducing the bandwidth of each sub-carrier.

A reduction in the separation between sub-carriers can make demodulation of the data from the sub-carriers more difficult for example, in the presence of Doppler frequency shifts.

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