Communication system using OFDM

A method of communicating over a wireless network using an OFDM communication system comprising the steps of;

• in each transmitter,
• providing a stream of data,
• arranging the data into packets,
• appending a pilot symbol comprising a repeated pseudo random binary sequence to the start of each data packet,
• multiplexing the packets to convert the data from serial to parallel,
• performing an inverse fast Fourier transform on the data to convert the multiplexed data from the frequency domain to the time domain,
• converting the data from digital data to analogue data, and
• using the data to modulate an RF carrier thereby frequency shifting the data to a higher frequency band for transmission,
• in each receiver,
• demodulating an RF carrier from the received data thereby shifting the data to baseband,
• converting the demodulated analogue signal into a stream of digital data,
• detecting the start of a packet of the down-sampled data by searching for significant correlations with the pilot symbol within the data stream,
• making an estimate of at least one signal parameter, removing the estimated frequency-offset and phase-offset using a digital phase locked loop,
• transforming the data using a fast Fourier transform from time domain data to frequency domain data,
• assigning each bit of the transformed data to an allowable data point to produce noise free data, and
• demultiplexing the noise free data from parallel data to serial data.

A method of transmitting data over a wireless network using an OFDM communication system comprising the steps of;

• providing the transmitter with a stream of data,
• arranging the data into packets,
• appending a pilot symbol comprising a repeated pseudo random binary sequence to the start of each data packet,
• multiplexing the packets to convert the data from serial to parallel,
• performing an inverse fast Fourier transform on the data to convert the multiplexed data from the frequency domain to the time domain,
• converting the data from digital data to analogue data, and
• using the data to modulate an RF carrier thereby frequency shifting the data to a higher frequency band for transmission.

A method of receiving data over a wireless network using an OFDM communication system comprising the steps of;

• demodulating an RF carrier from the received data thereby shifting the data to baseband,
• converting the demodulated analogue signal into a stream of digital data,
• detecting the start of a packet of the down-sampled data by searching for significant correlations with the pilot symbol within the data stream where the pilot symbol is a repeated pseudo random binary sequence,
• making an estimate of at least one signal parameter, removing the estimated frequency-offset and phase-offset using a digital phase locked loop,
• transforming the data using a fast Fourier transform from time domain data to frequency domain data,
• assigning each bit of the transformed data to an allowable data point to produce noise free data, and
• demultiplexing the noise free data from parallel data to serial data.

An OFDM communications system for wireless networks including at least one transmitter and at least one receiver;

• each transmitter including,
• a signal source arranged to provide data,
• a transmit modulator arranged to arrange the data into data packets and append a pilot symbol to the start of each data packet,
• a multiplexer arranged to convert the data packets from serial data to parallel data,
• an inverse fast Fourier transform operator arranged to convert the multiplexed data from the frequency domain to the time domain,
• an up-sampler arranged to sample the time domain data at a rate greater than the nominal data rate,
• a digital low pass filter arranged to remove out-of-band noise from the sampled data,
• a digital to analogue converter arranged to convert digital data to analogue data, and
• an RF module arranged to modulate an RF carrier with the transformed data thereby transforming the data to a higher frequency band for transmission,
• each receiver including,
• an RF module arranged to demodulate an RF carrier from the received signal thereby transforming the data to a lower frequency band,
• an analogue to digital converter arranged to convert analogue data to digital data and further arranged to sample the data at a rate greater than the nominal data rate,
• a digital low pass filter arranged to remove out-of-band noise,
• a down-sampler (decimator) arranged to reduce the sample rate to the nominal data rate,
• a frame detector arranged to search for significant pilot symbol correlations within the digital data stream and make initial estimates of at least one signal parameter,
• a digital phase locked loop arranged to remove estimated frequency- and phase-offsets from the low pass signal,
• a fast Fourier transform operator arranged to transform the data outputted from the phase locked-loop from the time domain to the frequency domain,
• a linear phase corrector arranged to remove estimated sub-sample timing errors from the Fourier transformed data stream,
• a decision block arranged to decide to which allowable data point each bit in the transformed data is assigned to produce noise free data, and
• a demultiplexer arranged to convert the noise free data from parallel data to serial data, and
• wherein the pilot symbol is a repeated pseudo random binary sequence.

An OFDM communications system for wireless networks including at least one transmitter and at least one receiver;

• each transmitter including,
• a signal source arranged to provide data,
• a transmit modulator arranged to arrange the data into data packets and append a pilot symbol comprising a repeated pseudo random binary sequence to the start of each data packet,
• a multiplexer arranged to convert the data packets from serial data to parallel data,
• a Fourier transform operator arranged to convert the multiplexed data from the frequency domain to the time domain,
• a digital to analogue converter arranged to convert digital data to analogue data, and
• an RF module arranged to modulate an RF carrier with the transformed data thereby transforming the data to a higher frequency band for transmission,
• each receiver including,
• an RF module arranged to demodulate an RF carrier from the received signal thereby transforming the data to a lower frequency band,
• an analogue to digital converter arranged to convert analogue data to digital data,
• a frame detector arranged to search for significant pilot symbol correlations within the digital data stream and make initial estimates of at least one signal parameter,
• a digital phase locked loop arranged to remove estimated frequency- and phase-offsets from the low pass signal,
• a Fourier transform operator arranged to transform the data outputted from the phase locked-loop from the time domain to the frequency domain,
• a decision block arranged to decide to which allowable data point each bit in the transformed data is assigned to produce noise free data, and
• a demultiplexer arranged to convert the noise free data from parallel data to serial data.

A transmitter for an OFDM communications system including

• a signal source arranged to provide data,
• a transmit modulator arranged to arrange the data into data packets and append a pilot symbol comprising a repeated pseudo random binary sequence to the start of each data packet,
• a multiplexer arranged to convert the data packets from serial data to parallel data,
• a Fourier transform operator arranged to convert the multiplexed data from the frequency domain to the time domain,
• a digital to analogue converter arranged to convert digital data to analogue data, and
• an RF module arranged to modulate an RF carrier with the transformed data thereby transforming the data to a higher frequency band for transmission.

A receiver for an OFDM communications system including,

• an RF module arranged to demodulate an RF carrier from the received signal thereby transforming the data to a lower frequency band,
• an analogue to digital converter arranged to convert analogue data to digital data,
• a frame detector arranged to search for significant pilot symbol correlations within the digital data stream and make initial estimates of at least one signal parameter where the pilot symbol is a repeated pseudo random binary sequence,
• a digital phase locked loop arranged to remove estimated frequency- and phase-offsets from the low pass signal,
• a Fourier transform operator arranged to transform the data outputted from the phase locked-loop from the time domain to the frequency domain,
• a decision block arranged to decide to which allowable data point each bit in the transformed data is assigned to produce noise free data, and
• a demultiplexer arranged to convert the noise free data from parallel data to serial data.