Matsushita Communication Industrial Corporation of America

Matsushita Communications Industrial Corporation

Mark A Ruff

Earl Anthony Daughtry

Richard M Stone

Christopher S Quire

A method for determining the integrity of a received signal in a frequency tracking environment so that a determination can be made whether Automatic Frequency Control (AFC) can be utilized. Several samples of the frequency are taken (205). At least one statistic based on these frequency samples is calculated for use in determining whether the received signal may be used for AFC operation. These statistics may include, for example, the mean, the mean deviation, the standard deviation, and the variance of the measured frequency. A strong signal limit and a weak signal limit are used to determine whether AFC operation should be disabled. If the calculated statistic is less than the strong signal limit (210) then AFC operation is enabled. If the calculated statistic is also greater than the weak signal limit (220) then AFC operation is disabled (225). This allows the receiver to continue AFC operation until the signal level is so weak as to cause erroneous frequency measurements. If the calculated statistic is between the strong signal limit (210) and the weak signal limit (220) then the signal strength is tested (230). If the signal strength is below a minimum value then AFC operation is enabled but if the signal strength is above this minimum value then AFC operation is disabled because a strong interfering signal may be present.

Method and system for determining the integrity of a received signal

A method and an apparatus for compensating for aging and temperature of the crystal in a crystal oscillator. An RF signal which is transmitted by a mobile telephone switching office (MTSO) (108) and received by the antenna (118). The signal transmitted by the MTSO (108) serves as an external reference. A crystal-controlled main oscillator/time base generator (134) provides a local reference frequency to the converters (120) and provides a time base signal to a counter (136). A controller (112) reads an aging correction value from a memory and provides a frequency control signal to the main oscillator (134). The converters (120) convert the received RF signal to an IF frequency. A limiter (122) provides a limited IF signal to the counter (136). Counter (136) counts the number of cycles of the limited IF signal that appear in a cycle of the time base signal. A controller (112) compares this measured count to a reference count and the count error is determined. The count error is compared to an allowable count error. If the count error is excessive then the controller (112) adjusts the frequency control signal provided to the main oscillator (134) so as to change the frequency of the main oscillator (134). Once the controller (112) has shifted the frequency so that the count error is not excessive then the controller (112) stores the new aging correction value. The measured count is therefore depends upon the frequency of the main oscillator (134) and the frequency of the received signal. This process automatically compensates for the frequency of the main oscillator (134) and, therefore, for aging of the crystal. The frequency of oscillation of the main oscillator (134) is therefore as accurate as the external reference, typically the highly accurate MTSO (108). A high precision oscillator (134) has thus been obtained using an external reference (MTSO 108) and an aging correction value.

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Cumming, GA, United States of America

Mark A Ruff