Cell site demodulation architecture for a spread spectrum multiple access communication systems
AssigneeQUALCOMM Incorporated
InventorsJeffrey A. Levin, David E. Werner, Kenneth D. Easton
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Abstract
An integrated demodulation processor used in a modem for a spread spectrum communications system despreads multipath receive signals then uses a time sliced transform processor to process the multiple signals in to a single series of soft decision results. The demodulation processor uses a single transform engine which operates on a time slice basis. The output of the processor engine cascade through a pipeline processor which, on a time slice basis, operates on signals corresponding to each multipath receive signal. The processed results are dual maxima decoded to provide soft decision data.
Claims94
A pipelined demodulation processor receiving an antenna signal comprised of a group of spread spectrum modulated call signals sharing a common frequency band and processing an active call signal within said group of spread spectrum modulated call signals, said active call signal originating from a remote transmitting unit, said pipelined demodulation processor comprising:
- a plurality of demodulation element front ends for receiving data samples of said group of spread spectrum modulated call signals wherein each of said spread spectrum modulated call signals comprises a series of bits encoded in groups of a fixed length into a series of symbols comprised of a series of code chips having a transmission rate and wherein said data samples are received at a rate corresponding to said transmission rate, and for providing despread code chips;
- a chip buffer for receiving said despread code chips from each of said plurality of demodulation element front ends and storing a limited number of said despread code chips to collect a set of said despread code chips to create a first element symbol from a first one of said plurality of demodulation element front ends and corresponding to a first transmitted symbol;
- a transform processor engine for receiving from said chip buffer said first element symbol and decoding said first element symbol to produce a first series of estimates wherein said first series of estimates comprises an energy level corresponding to each possible code sequence of said corresponding series of bits wherein said transform processor engine decodes said first element symbol at a rate higher than said transmission rate;
- a combiner for receiving and storing said first series of estimates;
- a maximum detector for receiving said first series of estimates and determining a maximum energy level and corresponding code sequence of said first series of estimates;
- and
- a time tracking block for receiving an indication of said code sequence corresponding to said maximum energy level and for providing an advance or retard indication to said first one of said demodulation element front ends.
A method of demodulating a signal received in a group of signals, wherein said signal is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time, said method of demodulating comprising the steps of:
- despreading a first fixed length set of samples of said signal with said PN sequence offset in time by a first amount from said transmission time to produce at said symbol rate a first series of symbol estimates;
- despreading a second fixed length set of samples of said signal with said PN sequence offset from said first amount by an early factor to produce a first early series of symbol estimates;
- despreading a third fixed length set of samples of said signal with said PN sequence offset from said first amount by a late factor to produce a first late series of symbol estimates;
- decoding during a first time slice a first symbol estimate of said first series of symbol estimates to produce a first set of index estimates, said first set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to a first transmitted symbol;
- determining during a second time slice a maximum energy value of said first set of index estimates;
- storing during said second time slice said first set of index estimates to produce a stored set of index estimates;
- uncovering during a third time slice an early energy value by correlating said first early series of symbol estimates with said symbol value corresponding to said maximum energy value;
- uncovering during said third time slice a late energy value by correlating said first late series of symbol estimates with said symbol value corresponding to said maximum energy value;
- summing during a fourth time slice a difference between said early energy value and said late energy value to a stored timing value;
- despreading a fourth fixed length set of samples of said signal with said PN sequence offset in time by a second amount from said transmission time to produce at said symbol rate a second series of symbol estimates;
- despreading a fifth fixed length set of samples of said signal with said PN sequence offset from said second amount by said early factor to produce a second early series of symbol estimates;
- despreading a sixth fixed length set of samples of said signal with said PN sequence offset from said second amount by said late factor to produce a second late series of symbol estimates;
- decoding during a fifth time slice a second symbol estimate of said second series of symbol estimates to produce a second set of index estimates, said second set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to said first transmitted symbol;
- determining during a sixth time slice a maximum energy value of said second set of index estimates;
- adding during said sixth time slice said second set of index estimates to said stored set of index estimates according to like corresponding symbol value to produce a summed set of index estimates;
- uncovering during a seventh time slice a second early energy value by correlating said second early series of symbol estimates with said symbol value corresponding to said maximum energy value of said second set of index estimates;
- uncovering during said seventh time slice a second late energy value by correlating said second late series of symbol estimates with said symbol value corresponding to said maximum energy value of said second set of index estimates;
- summing during an eighth time slice a difference between said second early energy value and said second late energy value to a second stored timing value;
- and
- dual maxima processing during a tenth time slice said summed set of index estimates to produce soft decision data.
A method of demodulating a signal received in a group of signals, wherein said signal is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time, said method of demodulating comprising the steps of:
- despreading a first fixed length set of samples of said signal with said PN sequence offset in time by a first amount from said transmission time to produce at said symbol rate a first series of symbol estimates;
- despreading a second fixed length set of samples of said signal with said PN sequence offset from said first amount by an early factor to produce a first early series of symbol estimates;
- despreading a third fixed length set of samples of said signal with said PN sequence offset from said first amount by a late factor to produce a first late series of symbol estimates;
- decoding during a first time slice a first symbol estimate of said first series of symbol estimates to produce a first set of index estimates, said first set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to a first transmitted symbol;
- determining during a second time slice a maximum energy value of said first set of index estimates;
- storing during said second time slice said first set of index estimates to produce a stored set of index estimates;
- uncovering during a third time slice an early energy value by correlating said first early series of symbol estimates with said symbol value corresponding to said maximum energy value;
- uncovering during said third time slice a late energy value by correlating said first late series of symbol estimates with said symbol value corresponding to said maximum energy value;
- summing during a fourth time slice a difference between said early energy value and said late energy value to a stored timing value;
- despreading a fourth fixed length set of samples of said signal with said PN sequence offset in time by a second amount from said transmission time to produce at said symbol rate a second series of symbol estimates;
- despreading a fifth fixed length set of samples of said signal with said PN sequence offset from said second amount by said early factor to produce a second early series of symbol estimates;
- despreading a sixth fixed length set of samples of said signal with said PN sequence offset from said second amount by said late factor to produce a second late series of symbol estimates;
- decoding during a fifth time slice a second symbol estimate of said second series of symbol estimates to produce a second set of index estimates, said second set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to said first transmitted symbol;
- determining during a sixth time slice a maximum energy value of said second set of index estimates;
- adding during said sixth time slice said second set of index estimates to said stored set of index estimates according to like corresponding symbol value to produce a summed set of index estimates;
- uncovering during a seventh time slice a second early energy value by correlating said second early series of symbol estimates with said symbol value corresponding to said maximum energy value of said second set of index estimates;
- uncovering during said seventh time slice a second late energy value by correlating said second late series of symbol estimates with said symbol value corresponding to said maximum energy value of said second set of index estimates;
- and
- summing during an eighth time slice a difference between said second early energy value and said second late energy value to a second stored timing value.
A communication system comprising a first unit generating a signal which is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time wherein said system further comprises a second station comprising:
- a first demodulation and storage element for receiving in real time a set of samples of said signal and producing at said symbol rate a series of first element symbols which are estimates of said series of symbols wherein said series of first element symbols includes a first element symbol;
- a shared transform processor for receiving said series of first element symbols from said first demodulation and storage element and producing at a rate higher than said symbol rate a series of estimates of said series of data bits wherein said series of estimates includes a first series of estimates corresponding to said first element symbol;
- and
- a combiner for receiving and storing said first series of estimates;
- a maximum detector for receiving said first series of estimates and determining a maximum energy level and corresponding symbol value of said first series of estimates;
- and
- a time tracking block for receiving an indication of a symbol value corresponding to said maximum energy level and for providing a timing advance or retard indication to said first demodulation element.
A communication system comprising a first unit generating a signal which is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time wherein said system further comprises a second station comprising:
- a first demodulation and storage element for receiving in real time a set of samples of said signal and producing at said symbol rate a series of first element symbols which are estimates of said series of symbols wherein said series of first element symbols includes a first element symbol;
- a shared transform processor for receiving said series of first element symbols from said first demodulation and storage element and producing at a rate higher than said symbol rate a series of estimates of said series of data bits wherein said series of estimates includes a first series of estimates corresponding to said first element symbol;
- and
- an integrated search processor for receiving said signal, and for providing a first search symbol and wherein said shared transform processor is further for receiving from said integrated search processor said first search symbol and producing a first search series of estimates.
A communication system comprising a first unit generating a signal which is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time wherein said system further comprises a second station comprising:
- a first demodulation and storage element for receiving in real time a set of samples of said signal and producing at said symbol rate a series of first element symbols which are estimates of said series of symbols wherein said series of first element symbols includes a first element symbol;
- a shared transform processor for receiving said series of first element symbols from said first demodulation and storage element and producing at a rate higher than said symbol rate a series of estimates of said series of data bits wherein said series of estimates includes a first series of estimates corresponding to said first element symbol;
- and
- wherein said communication system further comprises a queuing arbiter for controlling transfer of data from said first demodulation and storage element to said shared transform processor engine.
A communication system comprising a first unit generating a signal which is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time wherein said system further comprises a second station comprising:
- a first demodulation and storage element for receiving in real time a set of samples of said signal and producing at said symbol rate a series of first element symbols which are estimates of said series of symbols wherein said series of first element symbols includes a first element symbol;
- a shared transform processor for receiving said series of first element symbols from said first demodulation and storage element and producing at a rate higher than said symbol rate a series of estimates of said series of data bits wherein said series of estimates includes a first series of estimates corresponding to said first element symbol;
- and
- wherein said first demodulation element comprises:
- a pseudonoise (PN) sequence generator for producing a sequence of PN data chips wherein said sequence of PN data chips corresponds to said PN sequence used to modulate said signal in said first unit, wherein first demodulation and storage element produces said sequence of PN data chips at an offset in time from said transmission time;
- a decimation multiplexer for receiving data samples of said signal and selecting a portion of said data samples;
- a despreader for correlating said portion of said data samples with said sequence of PN data chips and for producing correlated output bits;
- and
- a timing generation register for controlling said offset in time of said sequence of PN data chips and said selecting of said portion of said data samples.
An communication system comprising a first unit generating a signal which is comprised of a series of data bits encoded in fixed length groups into a series of symbols comprised of a series of code chips wherein said series of symbols are transmitted at a symbol rate, said communication system further comprising a second station comprising:
- a first demodulation circuit portion having an input receiving samples of said signal and having an output, said first demodulation circuit portion accumulating energy once per code chip in real time;
- a second demodulation circuit portion having an input receiving said samples of said signal and having an output, said second demodulation circuit portion accumulating energy once per code chip in real time;
- a shared transform processor coupled to said output of said first and second demodulation circuit portions and having an output, wherein said shared transform processor transforms sets of said accumulated energies once per symbol from each of said first and second demodulation circuit portion in succession;
- and
- a pipelined processor coupled to said output of said shared transform processor for assigning a symbol weighting metric once per symbol for each of said first and second demodulation circuit portion in succession.
A system for demodulating a signal received in a group of signals, wherein said signal is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time, said system comprising:
- a first demodulation element means for despreading a first fixed length set of samples of said signal with said PN sequence offset in time by a first amount from said transmission time to produce at said symbol rate a first series of symbol estimates;
- a shared transform means for decoding during a first time slice a first symbol estimate of said first series of symbol estimates to produce a first set of index estimates, said first set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to a first transmitted symbol;
- a maximum detection means for determining during a second time slice a maximum energy value and corresponding symbol value of said first set of index estimates;
- a combining means for storing during said second time slice said first set of index estimates to produce a stored set of index estimates;
- a second demodulation element means for despreading a fourth fixed length set of samples of said signal with said PN sequence offset in time by a second amount from said transmission time to produce at said symbol rate a second series of symbol estimates;
- wherein said shared transformer is further for decoding during a fifth time slice a second symbol estimate of said second series of symbol estimates to produce a second set of index estimates, said second set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to said first transmitted symbol;
- wherein said maximum detection means is further for determining during a sixth time slice a maximum energy value and corresponding symbol value of said second set of index estimates;
- and
- wherein said combining means is further for adding during said sixth time slice said second set of index estimates to said stored set of index estimates according to like corresponding symbol value to produce a summed set of index estimates.
A method of demodulating a signal received in a group of signals, wherein said signal is comprised of a series of data bits encoded in fixed length groups into a series of symbols wherein said series of symbols are transmitted at a symbol rate, and wherein said signal is spread spectrum modulated with a pseudonoise (PN) sequence aligned to a transmission time, said method of demodulating comprising the steps of:
- despreading a first fixed length set of samples of said signal with said PN sequence offset in time by a first amount from said transmission time to produce at said symbol rate a first series of symbol estimates;
- decoding during a first time slice a first symbol estimate of said first series of symbol estimates to produce a first set of index estimates, said first set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to a first transmitted symbol;
- determining during a second time slice a maximum energy value of said first set of index estimates;
- storing during said second time slice said first set of index estimates to produce a stored set of index estimates;
- despreading a fourth fixed length set of samples of said signal with said PN sequence offset in time by a second amount from said transmission time to produce at said symbol rate a second series of symbol estimates;
- decoding during a fifth time slice a second symbol estimate of said second series of symbol estimates to produce a second set of index estimates, said second set of index estimates comprising an energy value corresponding to each possible symbol value corresponding to said first transmitted symbol;
- determining during a sixth time slice a maximum energy value of said second set of index estimates;
- and
- adding during said sixth time slice said second set of index estimates to said stored set of index estimates according to like corresponding symbol value to produce a summed set of index estimates.
Dependencies are inferred from the claim text.