Data detection in communication system

A radio receiver utilizing a rake receiver, the radio receiver comprising:

• a communication interface for receiving a signal comprising a plurality of symbols, wherein at least one symbol is modulated with a different spreading code sequence;
• and
• a control unit configured to adapt rake receiver fingers to properties of a radio channel related to a symbol of at least one spreading code;
• despread the signal with at least one spreading code sequence in order to form despread symbols;
• calculate, from a despread symbol of a first spreading code, a reliability metric for at least one possibly transmitted symbol by comparing the at least one possibly transmitted symbol with at least one rake receiver finger related to the at least one symbol at a time;
• select, based on reliability metrics, a number of most probable candidates for the at least one possibly transmitted symbol for further processing;
• calculate recursively reliability metrics from a despread symbol of the at least one spreading code by taking into account reliability metrics calculated for the most probable candidates preceding the at least one symbol currently being processed and by comparing the at least one possibly transmitted symbol with the at least one rake receiver finger related to the at least one symbol at a time, the reliability metric comprising more information on cross-correlation properties between spreading codes after every calculation of the reliability metric, and
• select, after calculating the reliability metrics for the at least one possibly transmitted symbol, the number of most probable candidates for a transmitted symbol sequence based on the reliability metrics.

A radio receiver utilizing a rake reception mechanism, the radio receiver comprising:

• communication means for receiving a signal comprising a plurality of symbols, wherein at least one symbol is modulated with a different spreading code sequence;
• adapting means for adapting rake receiver fingers to properties of a radio channel related to a symbol of at least one spreading code;
• dispreading means for despreading the signal with at least one spreading code sequence in order to form despread symbols;
• first calculating means for calculating, from a despread symbol of a first spreading code, a reliability metric for at least one possibly transmitted symbol by comparing the at least one possibly transmitted symbol with at least one rake receiver finger related to the at least one symbol at a time;
• first selecting means for selecting, based on reliability metrics, a number of most probable candidates for the at least one possibly transmitted symbol for further processing;
• second calculating means for calculating recursively reliability metrics from a despread symbol of the at least one spreading code by taking into account reliability metrics calculated for the most probable candidates preceding the at least one symbol currently being processed and by comparing the at least one possibly transmitted symbol with the at least one rake receiver finger related to the at least one symbol at a time, the reliability metric comprising more information on cross-correlation properties between spreading codes after every calculation of the reliability metric, and
• second selecting means for selecting, after calculating the reliability metrics for the at least one possibly transmitted symbol, the number of most probable candidates for a transmitted symbol sequence based on the reliability metrics.

A computer program embodied on a computer-readable medium, the computer program including instructions for controlling a computer process of symbol detection in a radio receiver utilizing a rake receiver to perform the steps of:

• receiving a signal comprising a plurality of symbols, wherein at least one symbol is modulated with a different spreading code sequence;
• adapting rake receiver fingers to properties of a radio channel related to a symbol of at least one spreading code;
• despreading the signal with at least one spreading code sequence in order to form despread symbols;
• calculating, from a despread symbol of a first spreading code, a reliability metric for at least one possibly transmitted symbol by comparing the at least one possibly transmitted symbol with at least one rake receiver finger related to the at least one symbol at a time;
• selecting, based on reliability metrics, a number of most probable candidates for the at least one possibly transmitted symbol for further processing;
• calculating recursively reliability metrics from a despread symbol of the at least one spreading code by taking into account the reliability metrics calculated for the most probable candidates preceding the at least one symbol currently being processed and by comparing at least one possibly transmitted symbol with the at least one rake receiver finger related to the received at least one symbol at a time, the reliability metric comprising more information on cross-correlation properties between the at least one spreading code after every calculation of the reliability metric, and
• selecting, after calculating the reliability metrics for the at least one possibly transmitted symbol, the number of most probable candidates for a transmitted symbol sequence based on the reliability metrics.

A computer program distribution medium readable by a computer and encoding a computer program of instructions for executing a computer process of symbol detection in a radio receiver utilizing a rake receiver, the process comprising:

• receiving a signal comprising a plurality of symbols, wherein at least one symbol is modulated with a different spreading code sequence;
• adapting rake receiver fingers to properties of a radio channel related to a symbol of at least one spreading code;
• despreading the signal with at least one spreading code sequence in order to form despread symbols;
• calculating, from a despread symbol of a first spreading code, a reliability metric for at least one possibly transmitted symbol by comparing the at least one possibly transmitted symbol with at least one rake receiver finger related to the at least one symbol at a time;
• selecting, based on reliability metrics, a number of most probable candidates for the at least one possibly transmitted symbol for further processing;
• calculating recursively reliability metrics from a despread symbol of the at least one spreading code by taking into account the reliability metrics calculated for the most probable candidates preceding the at least one symbol currently being processed and by comparing the at least one possibly transmitted symbol with the at least one rake receiver finger related to the at least one symbol at a time, the reliability metric comprising more information on cross-correlation properties between the at least one spreading code after every calculation of the reliability metric, and
• selecting, after calculating the reliability metrics for the at least one possibly transmitted symbol, the number of most probable candidates for a transmitted symbol sequence based on the reliability metrics.