Process for decoding alamouti block code in an ofdm system, and receiver for the same

A process for decoding a signal being representative of a Space Time Block coding (STBC) or Space Frequency Block coding (SFBC) based on a transmission, firstly, of a pair of finite-alphabet complex symbols x1 and x2, and secondly, of symbols −x2* and x1*, wherein * is a conjugate operation, during two parallel channels (SFBC), wherein the process comprises:

• receiving an OFDM signal, from at least one antenna, by a receiver comprising one single antenna;
• performing an OFDM demodulation in order to generate N frequency domain representations of the received OFDM signal, each N frequency domain representation being associated to one carrier;
• performing a decoding process applied on the demodulated OFDM signal, in order to group the received OFDM signal in word code, Y=(y1, y2), being representative of the received OFDM signal received during two signaling periods (STBC) or two parallel channels (SFBC);
• decoding the word code, Y=(y1, y2), in order to compute transmitted symbols x1 and x2 in accordance with a formulation,
• [
• y
• 1
• y
• 2
• *
• ]
• =
• [
• h
• 1
• h
• 2
• h
• ~
• 2
• *
• -
• h
• ~
• 1
• *
• ]
• 
• [
• x
• 1
• x
• 2
• ]
• +
• [
• n
• 1
• n
• 2
• *
• ]
• Or
• y
• =
• Hx
• +
• n
• wherein H is a matrix, h1 and h2 are representative of the channel applicable to the transmission of x1 and x2 while {tilde over (h)}1′ and {tilde over (h)}2 are representative of the channel applicable to the transmission of −x2* and x1*, and wherein n1 and n2 are noise,
• wherein decoding the word code comprises:
• applying a lattice reduction algorithm on the matrix H, H=(b1, b2), in order to transform the matrix H into a reduced matrix Hred=(b′1, b′2) comprising vectors that are substantially orthogonal, wherein the lattice reduction algorithm on each carrier k is based on an iterative algorithm that was initialized based on values (b1k-1, b2k-2) computed at a preceding iteration;
• and
• performing a detection process on the reduced matrix Hred in order to minimize noise and interference immunity.

A receiver for decoding a signal being representative of a Space Time or Frequency Block coding based on a transmission, firstly, of a pair of finite-alphabet complex symbols x1 and x2 with, secondly, the symbols −x2* and x1* (*being the conjugate operation) during two signaling periods (STBC) or two parallel channels (SFBC), the receiver comprising:

• one antenna;
• a receive RF front end circuit adapted to receive an OFDM signal via the one antenna;
• an OFDM demodulator adapted to generate a demodulated OFDM signal comprising N frequency domain representations of the received OFDM signal, wherein each N frequency domain representation is associated to one carrier;
• a decoder adapted to perform a decoding process on the demodulated OFDM signal, wherein the decoding process groups the received demodulated OFDM signal in word code, Y=(y1, y2), being representative of the received OFDM signal during two signaling periods (STBC) or two parallel channels (SFBC);
• wherein the decoder is further adapted to decode the word code, Y=(y1, y2), in order to compute the transmitted symbols x1 and x2 in accordance with a formulation,
• [
• y
• 1
• y
• 2
• *
• ]
• =
• [
• h
• 1
• h
• 2
• h
• ~
• 2
• *
• -
• h
• ~
• 1
• *
• ]
• 
• [
• x
• 1
• x
• 2
• ]
• +
• [
• n
• 1
• n
• 2
• *
• ]
• Or
• y
• =
• Hx
• +
• n
• where H is a matrix, h1 and h2 are representative of the channel applicable to the transmission of x1 and x2 while {tilde over (h)}1′ and {tilde over (h)}2 are representative of the channel applicable to the transmission of −x2* and x1*, and wherein n1 and n2 are noise;
• wherein the decoder is further adapted to apply a lattice reduction algorithm on said matrix H, H=(b1, b2), in order to transform said matrix H in a reduced matrix Hred, Hred=(b′1, b′2), comprising vectors that are substantially orthogonal, wherein the lattice reduction algorithm on each carrier k is based on an iterative algorithm that was initialized based on values (b1k-1, b2k-2) computed at a preceding iteration;
• and
• a detector adapted to detect received symbols using the reduced matrix Hred.