Method and apparatus for transmitting and receiving digital data over a bandpass channel

A method of reconstructing acquired digital data received over a bandpass channel comprising the steps of:

• receiving an analog quadrature amplitude modulated waveform transmitted over a bandpass channel at a carrier frequency;
• converting the analog quadrature amplitude modulated waveform into digital sampled waveform sums;
• demodulating the digital sampled waveform sums at a sample rate using orthogonal carrier signals at the carrier frequency to form x and y coordinate streams;
• decoding the x and y coordinate streams into a series of symbols at a symbol rate where the sample rate is an integer multiple of the symbol rate and an integer multiple of the carrier frequency;
• and
• mapping the series of symbols where each symbol represents a sequence of digital bits to produce a digital data stream representative of the acquired digital data.

A method of transmitting digital data acquired in an oil well logging operation from the downhole logging instrumentation to the surface over a logging cable, comprising the steps of:

• acquiring the digital data downhole from one or more downhole logging instruments at a symbol rate;
• modulating an analog carrier waveform with the acquired digital data using a quadrature amplitude modulation technique comprising the substeps of:
• mapping the acquired digital data as a series of symbols at a symbol rate where a unique sequence of digital bits is represented by a symbol and each symbol is indicative of a point in signal space,
• outputting the symbols as two streams at a sample rate representing the x and y coordinates in signal space of the symbols, the sample rate being an integer multiple of the symbol rate,
• multiplying a first carrier signal by the x coordinate stream to obtain a first product,
• multiplying a second carrier signal, orthogonal to the first carrier signal, by the y coordinate stream to obtain a second product, and
• adding the first and second products to produce a sampled waveform;
• converting the sampled waveform to an analog QAM waveform;
• transmitting the analog QAM waveform over the logging cable to a surface receiver;
• and wherein the first and second carrier signal are digital samples of orthogonal signals that occur at the same frequency and the modulating step further comprises outputting the x and y coordinate streams at a sample rate which is an integer multiple of the signal rate.

A method for transmitting acquired digital data over a bandpass channel as a quadrature amplitude modulated waveform and receiving the modulated data and constructing a representation of the acquired digital data, comprising the steps of:

• modulating an analog carrier signal with the acquired digital data using a quadrature amplitude modulation technique comprising the substeps of
• mapping the acquired digital data as a series of symbols where a unique sequence of digital bits is represented by a symbol and each symbol is indicative of a point in signal space,
• outputting the symbols at a sample rate as two streams representing the x and y coordinates in signal space of the symbols,
• multiplying a sample of a first carrier signal representation by the x coordinate stream to obtain a first product, the sample rate being an integer multiple of the carrier signal frequency,
• multiplying a sample of a second carrier signal representation, orthogonal to the first carrier signal, by the y coordinate stream to obtain a second product, and
• adding the first and second products to produce a sampled waveform;
• converting the sampled waveform to an analog QAM signal;
• transmitting the analog QAM signal over a bandpass channel;
• receiving the transmitted analog QAM signal;
• converting the analog QAM signal into a digital sampled waveform;
• demodulating the digital sampled waveform into two coordinate streams using a quadrature amplitude demodulation technique;
• and
• decoding the two coordinate streams into a representation of the acquired digital data.

A transmitter for acquiring digital input data and modulating the data onto an analog transmission carrier signal, comprising:

• means for acquiring the digital input data;
• mapping means coupled to the acquiring means for mapping the digital input data into a series of symbols representing points in signal space, and for outputting the location of the points as two coordinate streams representing the x and y coordinates of the points;
• modulation means for quadrature amplitude modulating the x and y coordinate streams to orthogonal carrier signals and combining the orthogonal carrier signals to form the analog transmission carrier signal, the modulation means including
• means for outputting a sampled waveform derived from multiplying the x and y coordinate streams by digital samples of respective orthogonal carrier signals, and adding the x and y product streams to form the sampled waveform,
• the rate of sampling the carrier signals being an integer multiple of the carrier signal frequency;
• digital to analog converter means, for converting the sampled waveform sums into an analog transmission carrier signal.

A system for transmitting acquired digital input data as a quadrature amplitude modulated waveform and for receiving the waveform and demodulating the waveform to construct a representation of the input data, comprising:

• means for acquiring the digital input data;
• mapping means coupled to the acquiring means for mapping the digital input data into a series of symbols representing points in signal space, and for outputting the location of the points as two coordinate streams representing the x and y coordinates of the points;
• modulation means for quadrature amplitude modulating the x and y coordinate streams to orthogonal carrier signals and combining the orthogonal carrier signals to form a sampled waveform,
• the modulation means being operable for multiplying the x and y coordinate streams by samples of the carrier signals to form x and y sampled product values where the rate of sampling the carrier signals is four times the carrier frequency, and for adding the x and y product values to form sampled waveform sums;
• digital to analog converter means for converting the sampled waveform sums into an analog quadrature amplitude modulated waveform for transmission over a bandpass channel;
• analog to digital converter means for converting the analog quadrature amplitude modulated waveform received from the bandpass channel into received digital sampled waveform sums;
• demodulation means for receiving the digital sampled waveform sums at the sample rate and dividing by representations of the orthogonal carrier signals to form received x and y coordinate streams;
• and
• decoding means for constructing a representation of the input data using the x and y coordinate streams.