Iterative rake receiver and corresponding reception process

A process for receiving CDMA radiocommunication signals obtained from spectrum symbols spread using pseudo-random sequences and having been propagated along a number of paths, said process comprising:

• restoring for each symbol, L unspread signals corresponding to L different paths;
• calculating L estimates of the L different paths;
• demodulating each of the L unspread signals using the corresponding L estimates to obtain L contributions of the paths;
• forming a sum of said L contributions, which gives an estimate of a received symbol;
• making a decision about a value of the received symbol based on a value of the estimate of the received symbol;
• processing blocks of N symbols, each block comprising data symbols and control symbols, each symbol being identified by a rank k that it occupies within the block, where k varies from 0 to N−1;
• considering for each path, identified by an index l where l varies from 0 to L−1, and for each block, a vector Cl with N components, which characterizes the path during the block;
• and
• considering a matrix E [ClCl*T] which has N eigenvectors denoted Bk using said N eigenvectors Bk as a base, and decomposing each vector Cl in said base, where decomposition coefficients denoted Glk form independent Gaussian random variables,
• wherein the decomposition coefficients Glk define a vector Gl with N components for each path, and each vector Gl is estimated using an iterative process based on an estimation-maximization (EM) algorithm based on a maximum a posteriori probability criterion.

A CDMA radiocommunication signals receiver for receiving signals obtained from spectrum symbols spread using pseudo-random sequences and having been propagated along a number of paths, said receiver comprising:

• a filter configured to restore L unspread signals for each symbol, corresponding to L different paths;
• a calculating circuit configured to calculate L estimates of the L different paths;
• a demodulator configured to process each of the L unspread signals using the corresponding L estimates to obtain L path contributions;
• an adder configured to form a sum of said L path contributions and for outputting an estimate of a received symbol;
• a decision circuit configured to make a decision about a value of the received symbol based on a value of the estimate of the received symbol output by the adder,
• wherein
• the receiver processes blocks of N symbols, each block comprising data symbols and control symbols, each symbol being identified by a rank k that it occupies in the block, where k varies from 0 to N−1,
• for each path identified by an index l, where l varies from 0 to L−1, and for each block, the receiver considers a vector Cl with N components that characterizes the path during the block,
• the receiver defines a vector base BK, vectors of the vector base BK being N eigenvectors of the matrix E [ClCl*T], each vector Cl being decomposed in said vector base, where decomposition coefficients denoted GlK form independent random Gaussian variables, and
• wherein coefficients GlK, define a vector Gl with N components for each path l, and the calculating circuit estimates each vector Gl, using an iterative process based on EM estimation-maximization algorithm based on a maximum a posteriori probability criterion.