Methods and apparatus for resovling frequency errors during transistion between communication networks

A mobile device operable for communication in at least first and second communication networks, the device comprising:

• a transceiver configured to receive a first channel from the second communication network, the first channel having at least one known characteristic;
• a decoder configured to initially decode the first channel for a prescribed period;
• a frequency error calculation unit configured to calculate an initial frequency error value based on the decoded first channel from the decoder;
• a frequency rotator configured to receive the initial frequency error value calculated by the frequency error calculation unit and adjust the frequency of a second channel received by the transceiver by an amount based on the determined initial frequency error value for decoding of the second channel by the decoder, and
• a processor configured to:
• determine when a decoding failure of the second channel by the decoder occurs, and to determine when a received signal strength of the second channel crosses a predetermined signal strength threshold;
• and
• initiate repeat decoding of the first channel by the decoder for the prescribed period, and determination of a subsequent frequency error value by the frequency error calculation unit to cause the digital rotator to rotate the based on the subsequent frequency error value when a decoding failure of the second channel has occurred and the received signal strength has crossed the predetermined signal strength threshold;
• wherein the first channel is a frequency correction channel (FCCH) and second channel is a synchronization channel.

An apparatus for resolving frequency errors in a wireless device transitioning from a first communication network to a second communication network comprising:

• means for receiving a first channel from the second communication network, the first channel having at least one known characteristic;
• means for decoding the first channel for a prescribed period;
• means for determining an initial frequency error value based on the decoding of the first channel for the prescribed period;
• means for adjusting a digital frequency rotator used to decode a second channel received from the second communication network by an amount based on the determined initial frequency error value;
• and
• means for continuously decoding the second channel using the digital frequency rotator adjusted based on the initial frequency error value;
• means for determining when a decoding failure of the second channel decoding occurs, and a received signal strength of the second channel crosses a predetermined signal strength threshold;
• and
• means for repeating decoding of the first channel for the prescribed period, determining a subsequent frequency error value, and adjusting the digital rotator based on the subsequent frequency error value when a decoding failure has occurred and the received signal strength has crossed the predetermined signal strength threshold;
• wherein the first channel is a frequency correction channel (FCH) and the second channel is a synchronization channel (SCH).

A computer program product, comprising:

• a computer-readable medium physically embodied with computer-readable program code for:
• causing a computer to receive a first channel from a communication network, the first channel having at least one known characteristic;
• causing a computer to decode the first channel for a prescribed period;
• causing a computer to determine an initial frequency error value based on the decoding of the first channel for the prescribed period;
• causing a computer to adjust a digital frequency rotator used to decode a second channel received from a communication network by an amount based on the determined initial frequency error value;
• causing a computer to continuously decode the second channel using the digital frequency rotator adjusted based on the initial frequency error value;
• causing a computer to determine when a decoding failure of the second channel decoding occurs, and a received signal strength of the second channel crosses a predetermined signal strength threshold;
• and
• causing a computer to repeat decoding of the first channel for the prescribed period,
• determine a subsequent frequency error value, and adjust the digital rotator based on the subsequent frequency error value when a decoding failure has occurred and the received signal strength has crossed the predetermined signal strength threshold;
• wherein the first channel is a frequency correction channel (FCCH) and second channel is a synchronization channel (SCH).

A processor programmed to execute a method for resolving frequency errors in a wireless device transitioning from a first communication network to a second communication network, the method comprising:

• decoding the first channel for a prescribed period;
• determining an initial frequency error value based on the decoding of the first channel for the prescribed period;
• adjusting a digital frequency rotator used to decode a second channel received from the second communication network by an amount based on the determined initial frequency error value;
• continuously decoding the second channel using the digital frequency rotator adjusted based on the initial frequency error value;
• determining when a decoding failure of the second channel decoding occurs, and a received signal strength of the second channel crosses a predetermined signal strength threshold;
• and
• repeating decoding of the first channel for the prescribed period, determining a subsequent frequency error value, and adjusting the digital rotator based on the subsequent frequency error value when a decoding failure has occurred and the received signal strength has crossed the predetermined signal strength threshold;
• wherein the first channel is a frequency correction channel (FCCH) and second channel is a synchronization channel (SCH).