US 5,732,113 A · Timing and frequency synchronization of OFDM signals

Abstract

A method and apparatus achieves rapid timing synchronization, carrier frequency synchronization, and sampling rate synchronization of a receiver to an orthogonal frequency division multiplexed (OFDM) signal. The method uses two OFDM training symbols to obtain full synchronization in less than two data frames. A first OFDM training symbol has only even-numbered sub-carriers, and substantially no odd-numbered sub-carriers, an arrangement that results in half-symbol symmetry. A second OFDM training symbol has even-numbered sub-carriers differentially modulated relative to those of the first OFDM training symbol by a predetermined sequence. Synchronization is achieved by computing metrics which utilize the unique properties of these two OFDM training symbols. Timing synchronization is determined by computing a timing metric which recognizes the half-symbol symmetry of the first OPDM training symbol. Carrier frequency offset estimation is performed in using the timing metric as well as a carrier frequency offset metric which peaks at the correct value of carrier frequency offset. Sampling rate offset estimation is performed by evaluating the slope of the locus of points of phase rotation due to sampling rate offset as a function of sub-carrier frequency number.

Claims26

Dependent claims

A method for synchronizing a receiver to an OFDM signal, said OFDM signal comprising a first OFDM training symbol exhibiting a half-symbol symmetry, the method comprising the steps of:

a) coupling said OFDM signal into said receiver;
b) performing an analog-to-digital conversion of said OFDM signal to obtain samples of said OFDM signal;
and
c) performing calculations on said samples to evaluate a timing metric, said timing metric utilizing the half-symbol symmetry of said first OFDM training symbol such that said timing metric indicates the correct symbol/frame timing point;
whereby said receiver can achieve timing synchronization with said OFDM signal, enabling said receiver to demodulate said OFDM signal in order to recover data encoded thereon.

2 more elements

A method for synchronizing a receiver to an OFDM signal, said OFDM signal comprising a first OFDM training symbol having half-symbol symmetry;

the method comprising the steps of:
a) determining a correct timing synchronization of a received OFDM signal such that a timing index d.sub.opt is determined which indicates a position of a first sample of said first OFDM training symbol within said OFDM signal;
b) computing a sum ##EQU13## and c) computing an angle, .phi., of said sum such that .phi.(.pi..multidot.T.sub.s) is an estimate of a carrier frequency offset of the received OFDM signal, where T.sub.s is a symbol interval;
whereby said receiver can estimate said carrier frequency offset to a maximum of .+-.1/T.sub.s, the estimate enabling said receiver to synchronize to the frequencies of the OFDM sub-carriers and thereby minimize ICI.

1 more element

An apparatus for synchronizing a receiver to an OFDM signal, said OFDM signal comprising a first OFDM training symbol having half-symbol symmetry, said synchronizing apparatus comprising:

a) storage means for storing digital samples, r.sub.i, of said OFDM signal and results of computations performed thereon;
and
b) computing means for performing computations on said samples in order to evaluate a timing metric, said timing metric indicating a correct timing point by utilizing the half-symbol symmetry of said first OFDM training symbol;
whereby said receiver can achieve timing synchronization to said OFDM signal, enabling said receiver to demodulate said OFDM signal in order to recover data encoded thereon.

1 more element

Dependencies are inferred from the claim text.

Timing and frequency synchronization of OFDM signals

Life of this patent

Timing and frequency synchronization of OFDM signals

Life of this patent

Abstract

Claims26