Patent ID: 7042954

Claim:
A 64-ary QAM (Quadrature Amplitude Modulation) demodulation apparatus for receiving an input signal R k (X k ,Y k ) comprised of a k th quadrature-phase signal Y k and a k th in-phase signal X k , and for generating soft decision values Λ(s k,5 ), Λ(s k,4 ), Λ(s k,3 ), Λ(s k,2 ), Λ(s k,1 ) and Λ(s k,0 ) for the input signal R k (X k , Y k ) by a soft decision means, comprising: a first soft decision value generator, adapted to receive the quadrature-phase signal Y k of the received signal R k and a distance value 2a between six demodulated symbols on the same axis, and to generate soft decision values Λ(s k,5 ), Λ(s k,4 ) and Λ(s k,3 ) for sixth, fifth and fourth demodulated symbols using the following equations, Z 1k =|Y k |−4 a Z 2k =|Z 1k |−2 a Λ ⁢ ( s k , 5 ) = Y k + c ⁢ ( α · Z 1 ⁢ k + β · Z 2 ⁢ k ) , where α = { 3 if ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ) = 0 0 if ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ) = 1 ⁢ ⁢ β = { 0 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ) = 0 - 1 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ) = 1 ⁢ ⁢ and ⁢ ⁢ c = { 1 if ⁢ ⁢ MSB ⁡ ( Y k ) = 0 - 1 if ⁢ ⁢ MSB ⁡ ( Y k ) = 1 ⁢ ⁢ Λ ⁡ ( s k , 4 ) = Z 1 ⁢ k + γ · Z 2 ⁢ k , where ⁢ ⁢ γ = { 0 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ) = 1 1 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ) = 0 ⁢ ⁢ and ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ) = 0 - 1 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ) = 0 ⁢ ⁢ and ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ) = 1 Λ( s k,3 )= Z 2k where Λ(s k,5 ) indicates the soft decision value for the sixth modulated symbol, Λ(s k,4 ) indicates the soft decision value for the fifth modulated symbol, and Λ(s k,3 ) indicates the soft decision value for the fourth modulated symbol; and a second soft decision value generator, adapted to receive the in-phase signal X k of the received signal R k and the distance value 2a between the six demodulated symbols on the same axis, and generating soft decision values Λ(s k,2 ), Λ(s k,1 ) and Λ(s k,0 ) for third, second and first demodulated symbols using the following equations, Z′ 1k =|X k |−4 a Z′ 2k =|Z′ 1k |−2 a Λ ⁢ ( s k , 2 ) = X k + c ′ ⁢ ( α ′ · Z 1 ⁢ k ′ + β ′ · Z 2 ⁢ k ′ ) , where α ′ = { 3 if ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ′ ) = 0 0 if ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ′ ) = 1 ⁢ ⁢ β ′ = { 0 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ′ ) = 0 - 1 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ′ ) = 1 ⁢ ⁢ and ⁢ ⁢ c ′ = { 1 if ⁢ ⁢ MSB ⁡ ( X k ) = 0 - 1 if ⁢ ⁢ MSB ⁡ ( X k ) = 1 ⁢ ⁢ Λ ⁡ ( s k , 1 ) = Z 1 ⁢ k ′ + γ ′ · Z 2 ⁢ k ′ , where ⁢ ⁢ γ ′ = { 0 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ′ ) = 1 1 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ′ ) = 0 ⁢ ⁢ and ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ′ ) = 0 - 1 if ⁢ ⁢ MSB ⁡ ( Z 2 ⁢ k ′ ) = 0 ⁢ ⁢ and ⁢ ⁢ MSB ⁡ ( Z 1 ⁢ k ′ ) = 1 Λ( s k,0 )= Z′ 2k where Λ(s k,2 ) indicates the soft decision value for the third modulated symbol, Λ(s k,1 ) indicates the soft decision value for the second modulated symbol, and Λ(s k,0 ) indicates the soft decision value for the first modulated symbol and the “MSB” means the most significant bit and the “a” means a distance value on the same axis.