Battery operated radio receivers having power save by reducing active reception time

#Communication systems between a remote (base) station, and a mobile station or terminal, such as cellular phones and pagers, commonly include a current-saving mode, usually called an Idle or Standby mode, in order to save battery power in the mobile terminals. In these terminals, the Standby mode consists of a relatively long “sleep” interval in which most of the terminal blocks of the mobile station are deactivated, and a relatively short “reception” interval in which the terminal is enabled to receive from the base station transmitted data, usually a paging or a broadcast message, which may be intended for the terminal. The mobile station checks whether this message is intended for itself, and according to its contents, decides on further actions, like going to the sleep phase, continuing the reception phase, etc. Prior to the data detection in the reception phase, there is a pre-conditioning or synchronization period in which the receiver pre-conditions the receive path for data detection, e.g., synchronizes to the correct gain, frequency, DC offset, timing, and/or to other parameters the receiver may need. Examples for such parameters are equalizer tap gains when an equalizer is employed, or “fingers” gains and delays when a “RAKE” receiver is employed.

#In the present systems of the foregoing type, the batteries provided in the receivers are generally capable of operating the receiver for a total Standby time of approximately 200 hours, and a total Talk time of approximately 2 hours before battery-recharging is required. It would be very desirable to increase this Standby time by decreasing the current drawings on the battery during this time.

#Various techniques have been developed for reducing current drain in battery-operated receivers, as described, for example, in U.S. Pat. Nos. 5,708,971 and 5,737,322, but there is still a need to further decrease current drain particularly during the long “Standby” period.

#The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

#FIG. 1 is a schematic illustration of a prior art CDMA mobile station receiver;

#FIG. 2 is a timing diagram of the Standby period in the prior art receiver of FIG. 1;

#FIG. 1 is a schematic. block diagram of a typical mobile station direct sequence (CDMA) receiver 100 in accordance with the prior art. RF signals are received by an antenna 101, filtered, amplified and downconverted to an intermediate frequency (IF) by a downconverter 102, amplified by a first automatic gain control (AGC) circuit 103, filtered by a bandpass filter 104, typically a surface acoustic wave (SAW) filter, to eliminate signals outside the required bandwidth, and amplified by a second automatic gain control (AGC) circuit 106.

#The amplified IF signals are multiplied by two IF sinusoidal signals generated by a synthesizer 130, and shifted by 90° relative to each other by a phase splitter 132, to produce an in-phase signal I and a quadrature signal Q. The in-phase signal I is multiplied by a mixer 108, filtered by a low-pass filter 110 and digitized by an A/D converter 112. Similarly, the quadrature signal Q is multiplied by a mixer 109, filtered by a low-pass filter 111 and digitized by an A/D converter 113. An AGC 126 is coupled to a power estimator 124 and to the first and second AGC circuits.

#A searcher 120 performs the correlations needed to determine the various multipath delays τ inside the target window. The digitized signals are correlated, at the delays determined by searcher 120, by the correlators of a de-spreader bank 114, whose outputs are transferred to the searcher 120. The outputs of de-spreader bank 114 are combined, in a maximal ratio sense, in a rake combiner 116 and fed to the data detection unit 118 that performs de-interleaving and FEC decoding to produce the final output signal.