Symbol de-mapping methods in multiple-input multiple-output systems

A method for demapping symbols comprising:

• performing a first quadrature phase shift keying (QPSK) search on a received signal vector that includes multiple elements, wherein the first QPSK search is performed within a first search space and produces an identified QPSK vector;
• transforming the received signal vector to a new origin that corresponds to the identified QPSK vector, resulting in a transformed, received signal vector;
• performing a subsequent QPSK search on the transformed, received signal vector, wherein the subsequent QPSK search is performed within a reduced search space defined by the identified QPSK vector, and wherein the subsequent QPSK search produces a next identified QPSK vector;
• and
• producing search results that include de-mapped bit values corresponding to a QPSK vector identified as a result of a lowest-level search.

A method comprising:

• performing a first quadrature phase shift keying (QPSK) search on a received signal vector, Y, which includes multiple elements, wherein the first QPSK search is performed within a first search space and produces an identified QPSK vector;
• and
• until a reduced search space corresponds to a QPSK constellation,
• canceling higher-order interference based on the identified QPSK vector and scaling the multiple elements within the received signal vector according to
• Y
• ~
• k
• =
• 1
• 2
• ⁢
• (
• Y
• ~
• k
• -
• 1
• -
• x
• ^
• k
• -
• 1
• )
• ,
• where {tilde over (Y)}k is a scaled version of the received signal vector at search level k, and {circumflex over (X)}k is a QPSK vector at search level k, and
• performing a level-k QPSK search according to
• x
• ^
• k
• =
• arg
• ⁢
• ⁢
• min
• QPSK
• ⁢
• ⁢
• vectors
• ⁢
• ⁢
• x
• ⁢
• 
• Y
• ~
• k
• -
• Hx
• 
• 2
• ,
• where is a channel transfer matrix, and x is a transmit signal vector.

A computer-readable medium having computer program instructions stored thereon which, when executed within a multiple-input multiple-output device, results in:

• performing a first quadrature phase shift keying (QPSK) search on a received signal vector that includes multiple elements, wherein the first QPSK search is performed within a first search space and produces an identified QPSK vector;
• transforming the received signal vector to a new origin that corresponds to the identified QPSK vector, resulting in a transformed, received signal vector;
• and
• performing a subsequent QPSK search on the transformed, received signal vector, wherein the subsequent QPSK search is performed within a reduced search space defined by the identified QPSK vector, and wherein the subsequent QPSK search produces a next identified QPSK vector;
• and
• producing search results that include de-mapped bit values corresponding to a QPSK vector identified as a result of a lowest-level search.

An apparatus comprising:

• multiple receive antennas operable to receive multiple received signals;
• and
• a symbol-processing element, operable to
• perform a first quadrature phase shift keying (QPSK) search on a received signal vector that includes multiple elements corresponding to the multiple received signals, wherein the first QPSK search is performed within a first search space and produces an identified QPSK vector;
• transform the received signal vector to a new origin that corresponds to the identified QPSK vector, resulting in a transformed, received signal vector;
• and
• perform a subsequent QPSK search on the transformed, received signal vector, wherein the subsequent QPSK search is performed within a reduced search space defined by the identified QPSK vector, and wherein the subsequent QPSK search produces a next identified QPSK vector.

A multiple-input multiple-output communication device, comprising:

• multiple receive antennas operable to receive multiple received signals;
• and
• a symbol-processing element, operable to
• perform a first quadrature phase shift keying (QPSK) search on a received signal vector that includes multiple elements corresponding to the multiple received signals, wherein the first QPSK search is performed within a first search space and produces an identified QPSK vector;
• transform the received signal vector to a new origin that corresponds to the identified QPSK vector, resulting in a transformed, received signal vector;
• and
• perform a subsequent QPSK search on the transformed, received signal vector, wherein the subsequent QPSK search is performed within a reduced search space defined by the identified QPSK vector, and wherein the subsequent QPSK search produces a next identified QPSK vector.