US 5,488,632 A · Transmission and reception in a hostile interference environment

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.

Claims25

Dependent claims

Apparatus for receiving an orthogonal frequency division multiplex (OFDM) signal transmitted at low power in a frequency band subject to interference from other transmissions, said OFDM signal comprising a plurality of OFDM carriers modulated by a block of samples, comprising:

means for demodulating the received OFDM carriers so as to produce a block of values representing the block of samples modulating said OFDM carriers;
means for decoding information contained in said sample values, the decoding means excluding from the decoding process sample values demodulated from OFDM carriers at frequencies likely to experience interference from said other transmissions;
and
means for outputting said decoded information.

1 more element

Apparatus for transmitting and receiving information in a frequency band subject to interference from other transmissions, comprising:

a transmitter, comprising:
means for inputting, in the form of blocks of digital data, the information to be transmitted;
means for coding each of the data samples in a block into one of a plurality of allowed values;
means for modulating a set of orthogonal frequency division multiplex (OFDM) carriers with the coded data sample values such that a data sample located in the block at a position corresponding to an OFDM carrier having a frequency identified as likely to experience interference is at least one of omitted and translated and duplicated to another location in the block, whereby another OFDM carrier having a frequency which is not identified as likely to experience is modulated;
and
means for transmitting a plurality of OFDM carriers modulated with the block of samples at a power which is low compared with the power of said other transmissions;
and
a receiver, comprising:
means for receiving the modulated OFDM carriers;
means for demodulating the received OFDM carriers so as to produce a block of values representing the block of samples modulating said OFDM carriers;
means for decoding information contained in said sample values, the decoding means excluding from the decoding process sample values demodulated from OFDM carriers at frequencies likely to experience interference from said other transmissions;
and
means for outputting said decoded information.

10 more elements

Apparatus for transmitting information in a frequency band subject to interference from other transmissions, comprising:

a transmitter, comprising:
means for inputting, in the form of blocks of digital data, the information to be transmitted;
means for coding each of the data samples in a block into one of a plurality of allowed values;
means for modulating a set of orthogonal frequency division multiplex (OFDM) carriers with the coded data sample values such that a data sample located in the block at a position corresponding to an OFDM carrier having a frequency identified as likely to experience interference is at least one of omitted and translated and duplicated to another location in the block, whereby another OFDM carrier having a frequency which is not identified as likely to experience is modulated;
and
means for transmitting a plurality of OFDM carriers modulated with the block of samples at a power which is low compared with the power of said other transmissions.

3 more elements

Dependencies are inferred from the claim text.

Transmission and reception in a hostile interference environment

Life of this patent

Transmission and reception in a hostile interference environment

Life of this patent

Abstract

Claims25