Reception device
It is possible to demodulate a plurality of modulated signals transmitted from a plurality of antennas by using a comparatively small-size circuit with a preferable error ratio characteristic. Partial bit judgment units ( 509, 512 ) demodulates partial bits of the 64 QAM-modulated signal by modifying which of the bits in the 6-bit strings constituting a symbol is to be demodulated depending on in which region of the IQ plane the reception signal point exists. This improves the partial bit error characteristic judged by the partial bit judgment units ( 509, 512 ), which in turn improves reliability of the reduced candidate signal point for use by a likelihood detection unit ( 518 ). As a result, it is possible to improve the error ratio characteristic of the final reception digital signals ( 322, 323 ).
1. A receiving apparatus that receives a modulated signal transmitted from a transmitting apparatus, said receiving apparatus comprising:
a channel fluctuation estimation section that finds a channel estimate of each modulated signal; and
a Euclidian distance calculation section that has said channel estimate and said received signal as input, finds a candidate signal point from said channel estimate, and calculates an approximation of a Euclidian distance between said candidate signal point and said received signal using a bit shift and an adder, wherein:
said Euclidian distance calculation section:
outputs a Euclidian distance approximation as |y| when a size relationship of an I-direction distance x and Q-direction distance y for said candidate signal point and said reception signal point on an IQ plane is |x|<|y| and is also 0<|x|<|y|×(¼+⅛),
outputs a Euclidian distance approximation as |y|×(1+⅛) when said size relationship is |x|<|y| and is also|y|×(¼+⅛)<|x|<|y|×(½+⅛),
outputs a Euclidian distance approximation as |y|×(1+¼) when said size relationship is |x|<|y| and is also |y|×(½+⅛)<|x|<|y|×(½+¼+⅛), and
outputs a Euclidian distance approximation as |y|×(1+¼+⅛) when said size relationship is |x|<|y| and is also |y|×(½+¼+⅛)<|x|.
2. A receiving apparatus that receives a modulated signal transmitted from a transmitting apparatus, said receiving apparatus comprising:
a channel fluctuation estimation section that finds a channel estimate of each modulated signal; and
a Euclidian distance calculation section that has said channel estimate and said received signal as input, finds a candidate signal point from said channel estimate, and calculates an approximation of a Euclidian distance between said candidate signal point and said received signal using a bit shift and an adder, wherein:
said Euclidian distance calculation section:
outputs a Euclidian distance approximation as |x| when a size relationship of an I-direction distance x and Q-direction distance y for said candidate signal point and said reception signal point on an IQ plane is |x|>y| and is also 0<|y|<|x|×(¼+⅛),
outputs a Euclidian distance approximation as |x|×(1+⅛)when said size relationship is |x|>|y| and is also |x|×(¼+⅛)<|y|<|x|×(½+⅛),
outputs a Euclidian distance approximation as |x|×(1+¼) when said size relationship is |x|>|y| and is also |x|×(½+⅛)<|y|<|x|×(½+¼+⅛), and
outputs a Euclidian distance approximation as |x|×(1+¼+⅛) when said size relationship is |x|>|y| and is also |x|×(½+¼+⅛)<|y|.
3. A receiving apparatus that receives modulated signals transmitted from a transmitting apparatus that transmits different modulated signals from a plurality of antennas, said receiving apparatus comprising:
a channel fluctuation estimation section that finds a channel estimate of each modulated signal;
a partial bit demodulation section that demodulates only some bits of said modulated signal using a detection method different from likelihood detection;
a signal point reduction section that reduces candidate signal points using demodulated partial bits and said channel estimate; and
a likelihood detection section that performs likelihood detection using reduced said candidate signal points and a received baseband signal,
wherein said likelihood detection section:
performs likelihood detection based on a Manhattan distance between said candidate signal point and a reception signal point of said received baseband signal;
performs likelihood detection,
taking a Euclidian distance approximation to be |y| when a size relationship of an I-direction distance x and Q-direction distance y for said candidate signal point and said reception signal point on an IQ plane is |x|<|y| and is also 0<|x|<|y|×(¼+⅛),
taking a Euclidian distance approximation to be |y|×(1+⅛) when said size relationship is |x|<|y| and is also |y|×(¼+⅛)<|x|<|y|×(½+⅛),
taking a Euclidian distance approximation to be |y|×(1+¼) when said size relationship is |x|<|y| and is also |y|×(½+⅛)<|x|<|y|×(½+¼+⅛), and
taking a Euclidian distance approximation to be |y|×(1+¼+⅛) when said size relationship is |x|<|y| and is also |y|×(½+¼+⅛)<|x|; and
performs likelihood detection,
taking a Euclidian distance approximation to be |x| when a size relationship of an I-direction distance x and Q-direction distance y for said candidate signal point and said reception signal point on an IQ plane is |x|>|y| and is also 0<|y|<|x|×(¼+⅛),
taking a Euclidian distance approximation to be |x|×(1+⅛) when said size relationship is |x|>|y| and is also |x|×(¼+⅛)<|y|<|x|×(½+⅛),
taking a Euclidian distance approximation to be |x|×(1+¼) when said size relationship is |x|>|y| and is also |x|×(½+⅛)<|y|<|x|×(½+¼+⅛), and
taking a Euclidian distance approximation to be |x|×(1+¼+⅛) when said size relationship is |x|>|y| and is also |x|×(½+¼+⅛)<|y|.