US 9,866,368 B1Granted

Method and apparatus for time tracking in OFDM wireless communication systems

AssigneeMbit Wireless, Inc.

InventorBhaskar Patel

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Abstract

In a mobile wireless communication system a client terminal needs to continuously maintain its receive and transmit operations in time alignment with the serving base station timing. A client terminal may initially achieve the timing alignment with the serving base station through the cell search procedure. Subsequently, as a client terminal may move toward or away from a serving base station, it may need to continuously track its timing to remain time aligned with the serving base station. In Orthogonal Frequency Division Multiplexing (OFDM) systems, one of the commonly used methods for time tracking may be the Cyclic Prefix (CP) correlation. When the length of the CP is small, the reliability of the CP correlation may be low, especially when the signal quality is poor. A method and apparatus are disclosed that use the initial synchronization signals for time tracking for improved performance and reduced complexity.

Claims20

Dependent claims

A method for time tracking at a client device being served by a base station in an Orthogonal Frequency Division Multiplexing (OFDM) wireless communication system, the method comprising:

controlling, by a processing device, for each of at least one interval of a received signal,
filtering the received signal to obtain a filtered signal having a bandwidth corresponding to a predetermined central bandwidth,
in which the filtered signal corresponds to a bandwidth of a Primary Synchronization Signal (PSS) and a bandwidth of a Secondary Synchronization Signal (SSS) of the received signal, and
in which a sampling rate of the filtered signal is according to a bandwidth of the received signal, a sampling rate of the received signal and a predetermined estimation accuracy for timing error;
first cross-correlation processing of the filtered signal and a time domain replica of the PSS of the serving base station having a sampling rate of the received signal, to obtain a first cross-correlation output signal;
second cross-correlation processing of the filtered signal and a time domain replica of a SSS of the serving base station having the sampling rate of the received signal, to obtain a second cross-correlation output signal;
combining the first and second cross-correlation output signals to obtain a plurality of combined cross-correlation values;
and
when the bandwidth of the received signal is not less than a predetermined bandwidth, estimating a timing error from a position of a maximum of the combined cross-correlation values, and
when the bandwidth of the received signal is less than a predetermined bandwidth, performing interpolation on the combined cross-correlation values to obtain interpolated cross-correlation values and estimating the timing error from a position of a maximum of the combined cross-correlation values and the interpolated cross-correlation values.

7 more elements

An apparatus for time tracking at a client device being served by a base station in an Orthogonal Frequency Division Multiplexing (OFDM) wireless communication system, the apparatus comprising:

circuitry configured to control, for each of at least one interval of a received signal,
filtering the received signal to obtain a filtered signal having a bandwidth corresponding to a predetermined central bandwidth,
in which the filtered signal corresponds to a bandwidth of a Primary Synchronization Signal (PSS) and a bandwidth of a Secondary Synchronization Signal (SSS) of the received signal, and
in which a sampling rate of the filtered signal is according to a bandwidth of the received signal, a sampling rate of the received signal and a predetermined estimation accuracy for timing error;
first cross-correlation processing of the filtered signal and a time domain replica of the PSS of the serving base station having a sampling rate of the received signal, to obtain a first cross-correlation output signal;
second cross-correlation processing of the filtered signal and a time domain replica of a SSS of the serving base station having the sampling rate of the received signal, to obtain a second cross-correlation output signal;
combining the first and second cross-correlation output signals to obtain a plurality of combined cross-correlation values;
and
when the bandwidth of the received signal is not less than a predetermined bandwidth, estimating a timing error from a position of a maximum of the combined cross-correlation values, and
when the bandwidth of the received signal is less than a predetermined bandwidth, performing interpolation on the combined cross-correlation values to obtain interpolated cross-correlation values and estimating the timing error from a position of a maximum of the combined cross-correlation values and the interpolated cross-correlation values.

7 more elements

Dependencies are inferred from the claim text.

Facts

Application: 15/059,437Filed 3 Mar 2016
Granted: 9 Jan 2018
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

H04L 5/0007
Time-frequency: the frequencies being orthogonal, e.g. OFDM or DMT
H04L 27/26
Modulated-carrier systems: systems using multi-frequency codes
H04L 27/2656
Synchronisation arrangements: frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe…
H04L 27/2666
Synchronisation arrangements: acquisition of further OFDM parameters, e.g. bandwidth, subcarrier spacing, or guard interval length