Method and apparatus for determining signal strength in a variable data rate system

DETAILED DESCRIPTION The present invention determines signal strength in a variable rate communication system in a rate independent manner.
In the preferred embodiment of the present invention data is grouped in symbols called power control groups.
The power control groups are transmitted at various positions within a data frame utilizing a pseudo-random distribution method.
By utilizing a subset of power control groups designated as active power control groups, the accuracy of signal strength measurement is greatly improved.
The active power control groups define time intervals during which a power control group is always transmitted.
A receiver using the signal energy of only the active power control groups can make an accurate signal strength measurement.
In the preferred embodiment using CDMA, the active power control groups include all power control groups transmitted during the lowest data rate.
The time intervals containing power control groups present the lowest data rate also contain power control groups at all higher data rates.
The lowest data rate in the preferred embodiment is one-eighth the full transmission rate.
The system operation begins with a reset upon startup or when a demodulator element is assigned to a new input signal.
After reset, signal energy levels are collected in the time intervals corresponding to active power control groups.
The higher the energy level of a signal the stronger the signal.
The energy levels are stored in one or more memory elements and summed over time to obtain average signal strength measurements.
Typically, the memory storage elements containing the oldest measurements are cleared and reused for new energy measurements through a process called aging.
Energy measurements are summed and compared with several threshold levels arranged to create hysteresis.
A first predetermined threshold level represents the energy level a signal should have before further signal processing occurs.
Signal processing occurs when the summed energy levels meet or exceed the first predetermined threshold