Synchronizing orthogonal frequency division multiplexed (OFDM) symbols in a receiver

Patent metadata

Field	Value
Publication number	US-9742611-B2
Application number	US-201314061084-A
Country	US
Kind code	B2
Filing date	Oct 23, 2013
Priority date	Oct 23, 2013
Publication date	Aug 22, 2017
Grant date	Aug 22, 2017

Abstract

In an embodiment, an apparatus includes a buffer to store incoming orthogonal frequency division multiplexed (OFDM) samples. This buffer is configured to output the OFDM samples according to a read pointer that can be adjusted by a sum value corresponding to a sum of a length of a symbol and a feedback value, to align the read pointer with the symbol. In addition, the apparatus further includes a feedback circuit coupled to the buffer to receive the output OFDM samples and generate the feedback value based at least in part on the output OFDM samples.

First claim

What is claimed is:

1. An apparatus comprising:
a buffer to store incoming time domain orthogonal frequency division multiplexed (OFDM) samples, the buffer to output the time domain OFDM samples according to a read pointer, wherein the read pointer is adjusted by a sum value corresponding to a sum of a length of a symbol and a feedback value, to align the read pointer with the symbol; and
a feedback circuit coupled between an output of the buffer and a control input of the buffer to receive the output time domain OFDM samples from the buffer and generate the feedback value and provide the sum value to the control input of the buffer based at least in part on the output time domain OFDM samples output by the buffer, the feedback circuit comprising:
a correlation unit to compute a prefix correlation on the output OFDM samples;
a peak detector to detect at least one peak value of the prefix correlation and to output a sample index of the at least one peak value;
a loop filter to filter the sample index; and
a summer to generate the sum value, wherein the summer is to sum the sample index with a predetermined value corresponding to the symbol length to generate the sum value.

2. The apparatus of claim 1 , further comprising a truncation unit to truncate the loop filter output to obtain an integer value.

3. The apparatus of claim 1 , further comprising an integrator coupled to the summer to integrate the sum value.

4. The apparatus of claim 1 , further comprising a carrier frequency offset unit to receive the peak value and to generate a carrier offset value therefrom.

5. The apparatus of claim 4 , further comprising:
a second loop filter to filter the carrier offset value to generate a frequency control signal;
a frequency synthesizer to generate a complex exponential value; and
a multiplier to multiply the incoming OFDM samples with the complex exponential value.

6. The apparatus of claim 1 , wherein the loop filter comprises a second order filter including:
a first path having an integral element;
a second path having a proportional element and a filter element coupled to an output of the integral element; and
a summer coupled to an output of the first and second paths.

7. An apparatus comprising:
a receiver front end to generate a channelized complex signal from an incoming radio frequency (RF) signal including a time domain orthogonal frequency division multiplexed (OFDM) stream;
a synchronization unit coupled to the receiver front end to receive the channelized complex signal and to determine symbol timing and a carrier frequency of the time domain OFDM stream without use of synchronization information within the time domain OFDM stream, wherein the synchronization unit comprises:
a buffer to store samples of the time domain OFDM stream; and
a feedback circuit coupled between an output of the buffer and a control input of the buffer to receive the time domain OFDM samples from the buffer and generate a read pointer for the buffer based at least in part on the time domain OFDM samples, the read pointer dynamically adjustable, wherein the feedback circuit comprises:
a correlation unit to compute a cyclic prefix correlation on the time domain OFDM stream;
a peak detector to detect at least one peak value of the cyclic prefix correlation and to output a sample index of the at least one peak value;
a loop filter to filter the sample index; and
a summer to generate a sum value, wherein the summer is to sum the sample index with a predetermined value corresponding to a symbol length to generate the sum value, the read pointer comprising the sum value; and

the apparatus comprising a tuner to provide an output data stream to a demodulator having substantially zero timing offset and substantially zero frequency offset.

8. The apparatus of claim 7 , wherein the read pointer is to align the transmitted OFDM symbol to a window of a fast Fourier transform (FFT) engine.

9. The apparatus of claim 7 , wherein the loop filter comprises a first path having an integral element, a second path having a proportional element and a filter element coupled to an output of the integral element, and a second summer coupled to an output of the first and second paths.

10. A method comprising:
storing time domain orthogonal frequency division multiplexed (OFDM) samples in a buffer of a receiver;
performing a correlation on a symbol width of the time domain OFDM samples obtained from the buffer;
determining a peak value in the correlation, the peak value corresponding to an index of a peak time domain OFDM sample;
filtering the peak value;
generating a sum value according to a sum of the filtered peak value and a predetermined symbol width corresponding to the symbol width; and
outputting the time domain OFDM samples from the buffer to a signal processing path of the receiver based at least in part on the filtered peak value, including controlling the output of the time domain OFDM samples from the buffer according to a read pointer comprising the sum value generated based on the filtered peak value and the predetermined symbol width.

11. The method of claim 10 , further comprising:
determining a carrier frequency offset using the peak value; and
correcting the time domain OFDM samples output from the buffer based on the carrier frequency offset.

12. The method of claim 10 , further comprising receiving the time domain OFDM samples from a front end circuit of the receiver at a first rate and storing the time domain OFDM samples into the buffer at a second rate.

Assignees

• Silicon Lab Inc

Inventors

• Elenes Javier

Classifications

• H04L27/2662

  Symbol synchronisation · CPC title

• H04L27/2671

  Time domain · CPC title

• H04L27/2678

  using cyclostationarities, e.g. cyclic prefix or postfix · CPC title

• H04L27/2657 Primary

  Carrier synchronisation · CPC title