US 8,009,775 B2 · Automatic frequency control for a wireless communication system with multiple subcarriers

Abstract

Techniques for performing frequency control in an OFDM system are described. In one aspect, frequency acquisition is performed based on a received pilot, and frequency tracking is performed based on received OFDM symbols. For frequency acquisition, an initial frequency error estimate may be derived based on the received pilot, and an automatic frequency control (AFC) loop may be initialized with the initial frequency error estimate. For frequency tracking, a frequency error estimate may be derived for each received OFDM symbol, and the AFC loop may be updated with the frequency error estimate. Frequency error in input samples is corrected by the AFC loop with the initial frequency error estimate as well as the frequency error estimate for each received OFDM symbol. In another aspect, a variable number of samples of a received OFDM symbol are selected, e.g., based on the received OFDM symbol timing, for use for frequency error estimation.

Claims40

Dependent claims

An apparatus, comprising:

at least one processor configured to perform frequency acquisition based on a time division multiplexed (TDM) received pilot and to perform frequency tracking based on received Orthogonal Frequency Division Multiplex (OFDM) symbols;
a memory coupled to the at least one processor;
and
wherein the at least one processor is further configured to process the TDM received pilot by:
providing a plurality of input samples to a delay line that delays each input sample by a plurality of sample periods corresponding to a length of a pilot sequence;
producing a complex conjugate of each delayed sample from the delay line;
multiplying each delayed sample with the complex conjugate;
peak detecting an output of the multiplying to detect the TDM received pilot and to provide a sample index for a start of a first pilot sequence;
and
accumulating the output of the multiplying over the plurality of sample periods corresponding to the length of the pilot sequence to provide a correlation result for each pilot sequence based on the sample index provided by the peak detecting.

7 more elements

A processor, comprising:

a first processing unit configured to perform frequency acquisition based on a time division multiplexed (TDM) received pilot;
a second processing unit configured to perform frequency tracking based on received Orthogonal Frequency Division Multiplex (OFDM) symbols;
and
wherein the first processing unit is further configured to process the TDM received pilot by:
providing a plurality of input samples to a delay line that delays each input sample by a plurality of sample periods corresponding to a length of a pilot sequence;
producing a complex conjugate of each delayed sample from the delay line;
multiplying each delayed sample with the complex conjugate;
peak detecting an output of the multiplying to detect the TDM received pilot and to provide a sample index for a start of a first pilot sequence;
and
accumulating the output of the multiplying over the plurality of sample periods corresponding to the length of the pilot sequence to provide a correlation result for each pilot sequence based on the sample index provided by the peak detecting.

7 more elements

A computer-readable medium encoded with a computer program, comprising:

at least one code executable by a computer to perform frequency acquisition based on a time division multiplexed (TDM) received pilot including:
at least one code executable by the computer to provide a plurality of input samples to a delay line that delays each input sample by a plurality of sample periods corresponding to a length of a pilot sequence;
at least one code executable by the computer to produce a complex conjugate of each delayed sample from the delay line;
at least one code executable by the computer to multiply each delayed sample with the complex conjugate;
at least one code executable by the computer to peak detect an output of the multiplying to detect the TDM pilot and to provide a sample index for a start of a first pilot sequence;
and
at least one code executable by the computer to accumulate the output of the multiplying over the plurality of sample periods corresponding to the length of the pilot sequence to provide a correlation result for each pilot sequence based on the sample index provided by the peak detecting;
and
at least one code executable by the computer to perform frequency tracking based on received Orthogonal Frequency Division Multiplex (OFDM) symbols.

6 more elements

Dependencies are inferred from the claim text.

Automatic frequency control for a wireless communication system with multiple subcarriers

Life of this patent

Automatic frequency control for a wireless communication system with multiple subcarriers

Life of this patent

Abstract

Claims40