Truncated maximum likelihood sequence estimator

A wireless digital unit, comprising:

• an antenna that transmits and receives an RF waveform including a modulated symbol stream;
• a transmitter coupled to the antenna, that receives a mapped data stream from a modem, that modulates the mapped data stream to provide the modulated symbol stream and that converts the modulated symbol stream into the RF waveform;
• a receiver coupled to the antenna, that receives the RF waveform from the antenna, that converts the RF waveform to a demodulated symbol stream and that samples the demodulated symbol stream to provide samples of the demodulated symbol stream;
• a modem that maps digital information into the mapped data stream and that unmaps the samples of the demodulated symbol stream to provide a best estimate of the symbol stream, the modem including a truncated maximum likelihood sequence estimator, including:
• a memory containing a lookup table including a plurality of threshold values, each threshold value being a function of a next sample of a received signal, a first decision made on a first previous sample of the received signal and a second decision made on a second previous sample of the received signal, and providing at an output at least one threshold value from an addressed location within the lookup table identified by the next sample of the received signal, the first decision made on the first previous sample and the second decision made on the second previous sample;
• and
• a comparator, coupled to the lookup table and responsive to the at least one threshold value provided by the lookup table and a current sample of the received signal, comparing the current sample of the received signal with the at least one threshold value and providing as an output the best estimate of the symbol stream.

A wireless local area network, comprising:

• a first computer interfaced to a first wireless digital unit;
• a processor interfaced to a second wireless digital unit so that the computer communicates wirelessly with the processor via the wireless units, wherein the first wireless unit and the second wireless unit each include:
• a memory containing a lookup table including a plurality of threshold values, each threshold value being a function of a next sample of a received signal, a first decision made on a first previous sample of the received signal and a second decision made on a second previous sample of the received signal, and providing at an output at least one threshold value from an addressed location within the lookup table identified by the next sample of the received signal, the first decision made on the first previous sample and the second decision made on the second previous sample;
• and;
• a comparator, coupled to the output of the lookup table and responsive to the at least one threshold value provided by the lookup table and a current sample of the received signal, comparing the current sample of the received signal with the at least one threshold value and that outputs a best estimate of the current sample of the received signal.

A method for calibrating a wireless digital unit including a truncated maximum likelihood sequence estimator that provides a best estimate of a transmitted symbol and that includes a memory containing a lookup table including a plurality of threshold values, each of the threshold values stored in the lookup table being a function at least a next sample of a received signal, a first decision made on a first previous sample of the receive signal and a second decision made on a second previous sample of the received signal, and a comparator, coupled to an output of the lookup table and responsive to at least one threshold value output from the lookup table and a current sample of the received signal, that compares the current sample of the received signal with the at least one threshold value and that provides the best estimate of the transmitted symbol, the method comprising the steps of:

• generating a known data sequence;
• modulating a carrier signal with the known data sequence to provide a modulated RF waveform;
• transmitting the modulated RF waveform to the wireless digital unit;
• receiving the modulated RF waveform with the wireless digital unit and sampling the modulated RF waveform to yield samples of the modulated RF waveform;
• and
• calculating the at least one threshold value for the address location from the known data and the samples of the RF waveform.