초록 ▼

A frequency error calibration, estimation and compensation device and method for direct sequence spread spectrum systems, such as digital cordless telephones having a handset and a base station. Initial frequency calibration occurs when the handset is physically coupled to the base station. The allo

A frequency error calibration, estimation and compensation device and method for direct sequence spread spectrum systems, such as digital cordless telephones having a handset and a base station. Initial frequency calibration occurs when the handset is physically coupled to the base station. The allowable frequency error range is divided into a plurality of frequency bins. Both the handset and base station transmit and receive messages using a predetermined frequency offset bin as an estimate of the frequency error. A signal quality value is determined and then a next bin is selected and a next signal quality value is determined. Once a signal quality value has been determined for each frequency bin, a communications link is established between the handset and the base station to allow automatic frequency control tracking to fine tune the frequency offset value. If the signal quality is not above a threshold value, the procedure is repeated. After system calibration, frequency error estimation is performed by cross product demodulation of the received in-phase and quadrature signals. The cross product output is limited and filtered. A phase rotator performs frequency compensation by multiplying the received in-phase and quadrature signals by (cos.phi.(t)+jsin.phi.(t)) where .phi.(t) is the sum of the current phase value and the limited and filtered cross product value.

대표청구항 ▼

[ What is claimed is:] [1.] In a direct sequence spread spectrum communications system, a frequency error estimation and compensation circuit to correct frequency error in received in-phase (I) and quadrature (Q) signals comprising:matched filter means for removing a spreading code from the received

[ What is claimed is:] [1.] In a direct sequence spread spectrum communications system, a frequency error estimation and compensation circuit to correct frequency error in received in-phase (I) and quadrature (Q) signals comprising:matched filter means for removing a spreading code from the received I and Q signals;phase rotator means for multiplying the received I and Q signals by (cos.phi.(t)+jsin.phi.(t)) before providing the received I and Q signals to the matched filter means, wherein .phi.(t) is a phase value representing the estimated frequency error in the received I and Q signals and wherein an initial phase value .phi.(t) for the phase rotator means is determined by a frequency calibration bin search;cross product determining means for calculating a cross product of the received I and Q signals, the cross product an estimate of the frequency error in the received I and Q signals; andfiltering means for filtering and limiting the cross product, and determining a phase error value based on the filtered and limited cross product, the phase error value being used to modify the phase value .phi.(t);wherein the phase rotator means adjusts the phase of the received I and Q signals based on an updated phase value .phi.(t) determined by adding a previous value .phi.(t) with the phase error value determined by the filtering means.