Finger assignment in a CDMA rake receiver

A method of assigning finger processing elements in a rake receiver for use in a CDMA communications system, comprising the steps of:

• receiving a spread-spectrum radio-frequency (RF) signal having a plurality of multipath signal components forming a multipath profile;
• measuring the multipath profile of the RF signal to obtain a sequence of measurements, wherein adjacent measurements within the sequence are separated by a predetermined timing resolution, and each measurement has an amplitude indicative of signal strength;
• identifying the best candidate path of the RF signal to demodulate by determining which measurement within the sequence of measurements has the highest signal strength;
• and
• determining whether a finger processing element is available and, if so, deriving a timing offset for the best candidate path as a function of at least the measurement for the best candidate path and the measurements adjacent thereto, the resolution of the derived timing offset being higher than the predetermined timing resolution, and assigning the available finger processing element to the best candidate path using the derived timing offset.

A rake receiver for use in a CDMA communications system, comprising:

• an antenna for receiving a spread-spectrum radio-frequency (RF) signal having a plurality of multipath components forming a multipath profile;
• a plurality of finger processing elements coupled to the antenna, each finger processing element being configured to be assigned to a particular propagation path of the RF signal, and to demodulate the assigned propagation path of the RF signal to generate a demodulated signal;
• a searcher unit coupled to the antenna and configured to measure the multipath profile of the RF signal to obtain sequences of measurements, the searcher unit having a predetermined timing resolution which separates adjacent measurements within the sequences of measurements, and each measurement having an amplitude indicative of signal strength;
• a finger assignment and control unit coupled to the searcher unit and the plurality of finger processing elements and configured to read the sequences of measurements, to identify the best candidate paths of the RF signal to demodulate by determining which measurements within the sequences have the highest signal strengths, to derive timing offsets for the best candidate paths as a function of at least the measurements for the best candidate paths and the measurements adjacent thereto, wherein the derived timing offsets have resolutions higher than the predetermined timing resolution of the searcher unit, and to assign the finger processing elements to the best candidate paths using at least the derived timing offsets;
• and
• a combiner coupled to the plurality of finger processing elements and configured to combine the demodulated signals from each of the finger processing elements to generate an output signal from the rake receiver.

A method of adjusting finger processing elements in a rake receiver for use in a CDMA communication system, comprising the steps of:

• receiving a spread-spectrum radio-frequency (RF) signal having a plurality of multipath signal components forming a multipath profile;
• sampling one of the multipath signal components of the spread-spectrum RF signal to obtain early, on-time and late samples using a finger processing element;
• deriving a timing offset for the on-time sample as a function of at least the early, on-time and late samples of the sampled multipath signal component;
• defining a quadratic which passes substantially through the early, on-time and late samples, and solving for a peak of the quadratic to estimate the timing offset for the one-time sample;
• generating a correction factor and applying the correction factor to the estimated timing offset from the quadratic;
• and
• adjusting the finger processing element to track the timing of the on-time sample of the sampled multipath signal component using the derived timing offset.