Maximum likelihood rake receiver for use in a code division, multiple access wireless communication system
AssigneeEricsson Inc.
InventorPaul W. Dent
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Abstract
A receiver is disclosed for decoding spread-spectrum coded signals received through a multi-path propagation channel to obtain decided information symbols. The receiver includes a correlator for correlating the numerical signal samples with a despreading code over information symbol periods to obtain complex correlations for different time-alignments, each time-alignment corresponding to a different one of multiple propagation paths. The receiver hypothesizes data symbol sequences, and forms channel estimates for each of the multiple propagation paths as a function of the complex correlations and the hypothesized symbol sequences and selects the most likely of the hypothesized sequences to decode the information symbols.
Claims44
In a receiver for use in a wireless network, said receiver receiving signals carrying symbols over a plurality of channels, said symbols selected from a predefined set of symbols, said receiver having a memory storing a plurality of previously hypothesized sequences of symbols and a plurality of cumulative vectors, each describing one of the sequences of symbols, a method for decoding symbols in the received signal comprising the steps of:
- generating a correlation vector by correlating the received signal over a symbol period using a plurality of time offsets equal to a number of elements of the correlation vector, the plurality of time offsets corresponding to selected ones of said plurality of channels;
- generating a set of new symbol vectors at least in part by multiplying the correlation vector with a new symbol hypothesis selected in turn to be each of the symbols in said set of symbols;
- hypothesizing a plurality of extended sequences of symbols by accumulating each of the set of new symbol vectors with each of the plurality of cumulative vectors;
- and
- determining the most likely extended sequences of symbols by combining the previously hypothesized symbols and one of the set of symbols corresponding to the combined cumulative vectors and new symbol vectors with the longest sum square lengths.
An improved receiver for decoding spread-spectrum coded signals received through multiple propagation channels to obtain decoded information symbols comprising:
- a converter for converting received signals to representative numerical samples;
- a correlator for correlating said numerical signal samples with a despreading code over each of said information symbol periods to obtain, for each symbol period, complex correlations for different time-alignments between said despreading code and said signal samples, each time-alignment corresponding to a different one of said multiple propagation channels;
- hypothesizing means for generating data symbol hypotheses;
- at least one multiplier for combining said data symbol hypotheses with said complex correlations to obtain channel estimates;
- complex vector accumulation means for accumulating said channel estimates corresponding to the same one of said multiple propagation channels for successive symbol hypotheses to obtain cumulative complex vectors for each propagation channel;
- and
- selection means to generate a sum of the square of the lengths of the cumulative complex vectors and to select sequences of symbol hypotheses for which the sum of the squares of the lengths of the cumulative complex vectors is greatest.
A receiver for decoding spread-specturm coded signals received through multiple propagation channels to obtain decoded information symbols, wherein each symbol is encoded in one or more information symbol periods, said receiver comprising:
- converter means for converting received signals to representative numerical samples;
- correlation means for correlating said numerical signal samples with a despreading code over each of said information symbol periods to obtain, for each symbol period, complex correlations for different time-alignments between said despreading code and said signal samples, each time-alignment corresponding to a different one of said multiple propagation channels;
- hypothesizing means for hypothesizing information symbol sequences;
- channel estimation means for forming channel estimates for each of said multiple propagation paths at least in part by multiplying said complex correlations by said hypothesized information symbol sequences;
- decision means to select a most likely of said hypothesized sequences using said channel estimates thereby decoding said information symbols.
A receiver for decoding error-correction coded, interleaved and spread-spectrum modulated signals received through a multiple propagation paths to recover information symbols, wherein the information symbols are each encoded in one modulation interval, said receiver comprising:
- converter means for converting received signals to representative numerical samples;
- correlation means for correlating said numerical signal samples with a despreading code over each of the spread-spectrum modulation intervals to obtain, for each modulation interval, a corresponding set of complex correlations for different time-alignments between said despreading code and said signal samples, each time-alignment corresponding to a different one of said multiple propagation paths;
- information symbol hypothesizing means for hypothesizing sequences of information symbols;
- error-correction coding means for coding said hypothesized symbol sequences to produce coded modulation symbol sequence hypotheses;
- de-interleaving means for selecting ones of said hypothesized modulation symbols from different timeslots for application by the error-correction coding means;
- likelihood estimation means for combining said selected sets of correlations in order to produce a likelihood indication for each of said hypothesized information symbol sequences;
- and
- selection means for selecting an information symbol sequence having a greatest likelihood indication.
A method for decoding spread-spectrum modulated symbols received by multi-path propagation, each symbol being modulated during one modulation interval, said symbols including known symbols interspersed with unknown data symbol, said method comprising:
- converting received signals to representative numerical signal samples;
- correlating said numerical signal samples with a despreading code over each of the spread-spectrum modulation symbol intervals to obtain, for each modulation interval, a corresponding set of complex correlations for different time-alignments between said despreading code and said signal samples, each time-alignment corresponding to a different one of said multiple propagation paths;
- initiating a Maximum Likelihood Sequence Estimator to a single starting state including a likelihood indication using sets of correlations corresponding to known pilot symbols interspersed before unknown data symbols;
- information symbol hypothesizing means for hypothesizing sequences of information symbols;
- successively hypothesizing unknown data symbols within said Maximum Likelihood Sequence Estimator and multiplying each new data symbol hypothesis by a corresponding set of correlations and combining with one or more of the previous states to obtain an expanded number of states, each corresponding to hypothesized sequences extended by one more unknown data symbol each having an associated likelihood indication;
- selecting sequences having highest likelihood indications in order to keep the number of states at or below a maximum allowed number of states;
- combining sets of correlations corresponding to pilot symbols interspersed after said unknown data symbols with the previous state or states in order to obtain an contracted number of states corresponding to a reduced number of hypothesized symbol sequences;
- and
- selecting from the reduced number of symbol sequences the hypothesized symbol sequence having the indication of highest likelihood thereby decoding said unknown symbols.
Dependencies are inferred from the claim text.