Methods and apparatus for use in obtaining frame synchronization in an OFDM communication system

A method for use in obtaining frame synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, the OFDM communication system including a base unit which transmits a plurality of pilot tones having a first predetermined pattern in one or more time slots of a plurality of time slots, thereby defining a second predetermined pattern of one or more time slots having the first predetermined pattern and one or more other time slots not having the first predetermined pattern, the method comprising:

• receiving OFDM signals within a time slot;
• determining a signal level in the OFDM signals at each frequency of a plurality of pilot tone frequencies;
• comparing the signal levels in the OFDM signals with the first predetermined pattern;
• detecting whether a match exists between the signal levels in the OFDM signals and the first predetermined pattern;
• storing a detection result;
• repeating the receiving, determining, comparing, detecting, and storing for each time slot of a plurality of time slots, to thereby produce a plurality of detection results;
• comparing the plurality of detection results and the second predetermined pattern;
• and
• identifying a boundary of a message slot based on results of the comparing.

A method for use in obtaining frame synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, the OFDM communication system including a plurality of base units which simultaneously transmit a plurality of pilot tones in a predetermined pilot tone pattern during some of a plurality of time slots of a message slot but do not simultaneously transmit the predetermined pilot tone pattern during some of the other time slots in the message slot, the method comprising:

• receiving OFDM signals within a time slot;
• determining a signal level in the OFDM signals at each frequency of a plurality of pilot tone frequencies;
• performing a correlation between the signal levels and the predetermined pilot tone pattern;
• generating and storing a pattern detection value based on performing the correlation;
• repeating the receiving, determining, performing, generating and storing for each time slot of the plurality of time slots;
• repeating, for a plurality of message frame durations, the above steps of repeated receiving, determining, performing, and generating to produce a plurality of averaged pattern detection values;
• and
• performing a correlation between the plurality of averaged pattern detection values and a predetermined message frame pattern;
• and
• detecting a boundary of a message slot based on performing the correlation.

A method for use in obtaining frame synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) communication system having a plurality of base units, each base unit taking a turn in transmitting a plurality of pilot tone signals over a plurality of message frames, the method comprising:

• receiving OFDM signals within a message frame;
• determining a signal level of a plurality of pilot tones in the OFDM signals;
• repeating the receiving and determining for each message frame of a plurality of message frames to produce a plurality of signal levels associated with the plurality of base units;
• identifying a maximum signal level from the plurality of signal levels;
• and
• selecting a message frame for decoding messages based on the identified maximum signal level.

A method for use in obtaining frame synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) communication system including a plurality of base units, each base unit taking a turn in transmitting a plurality of pilot tone signals over a plurality of message frames, the method comprising:

• receiving OFDM signals within a message frame;
• determining a signal level of a plurality of pilot tones in the OFDM signals;
• repeating the receiving and determining for each message frame of a plurality of message frames to produce a plurality of signal levels;
• generating a rank of the plurality of base units in accordance with the signal levels;
• repeating the following steps if necessary until a serving base unit is confirmed:
• selecting a candidate base unit from the rank;
• decoding a message within the message frame associated with the selected candidate base unit;
• comparing a base unit identifier in the message and a prestored base unit identifier;
• and
• confirming that the candidate base unit is the serving base unit based on a match between the base unit identifier and the prestored base unit identifier.

A method for use in obtaining frame synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, the OFDM communication system having a plurality of base units which simultaneously broadcast a plurality of pilot tones in a predetermined pilot tone pattern during one or more time slots of a plurality of time slots, the plurality of time slots defining boundaries of a message slot, a plurality of message slots defining boundaries of a message frame, each base unit taking a turn on a message frame by message frame basis to transmit all of the plurality of pilot tones during the other time slots of the plurality of time slots, the method comprising:

• receiving OFDM signals within a time slot;
• determining a signal level in the OFDM signals at each frequency of a plurality of pilot tone frequencies;
• performing a correlation between the signal levels and the predetermined pilot tone pattern;
• generating and storing a pattern detection value based on performing the correlation;
• repeating the receiving, determining, performing, and generating and storing for each time slot of a plurality of time slots over a message slot duration;
• repeating, for a plurality of message frame durations, the above steps of repeated receiving, determining, performing, and generating to produce a plurality of averaged pattern detection values;
• performing a correlation between the plurality of averaged pattern detection values and a predetermined message frame pattern;
• detecting a boundary of a message slot based on performing the correlation;
• receiving OFDM signals within one of the other time slots;
• determining a signal level of a plurality of pilot tones in the OFDM signals;
• repeating the receiving and determining for each of the other time slots within the message frame to produce a plurality of signal levels;
• generating a rank of the plurality of base units in accordance with the plurality of signal levels;
• repeating the following steps if necessary until a serving base unit is confirmed:
• selecting a candidate base unit from the rank based on its associated signal level;
• decoding a message within a message frame associated with the selected candidate base unit;
• comparing a base unit identifier in the message and a prestored base unit identifier;
• and
• confirming that the candidate base unit is the serving base unit based on a match between the base unit identifier and the prestored base unit identifier.