Patent Document ID: 9136925
Application ID: 14281847
Patent Flag: 1

Claim One:
1. A two-path amplify-and-forward relaying method for a bandwidth efficient cognitive radio, comprising the steps of: transmitting PU data from a primary user (PU) transmitter S to a primary user (PU) receiver D in cooperation with a first secondary user (SU) relay R A (SU receiver) and a second secondary user relay R B (SU transmitter), the PU data transmission being divided into first, second, and third timeslots; in the first timeslot transmitting the algebraic subtraction of two successive modulated signals, s 1 and s 2 with total power P s from S to the first secondary user relay R A and the PU receiver D; in the first timeslot transmitting data b 1 with power P B from R B to R A and the PU receiver D, the data b 1 interfering with PU data at R A and D, the received signal at D and R A in the 1 st time slot being characterized by the relations, y D ( 1 ) = P s 2 ⁢ h SD ⁡ ( s 1 - s 2 ) + P B ⁢ h BD ⁢ b 1 + w D ( 1 ) , and y A ( 1 ) = P s 2 ⁢ h SA ⁡ ( s 1 - s 2 ) + P B ⁢ h BA ⁢ b 1 + w A ( 1 ) ; in the second timeslot transmitting the second symbol only s 2 with total power P s to R B and D from S, while R A transmits the previous received data after applying amplify-and-forward (AF) protocol, the second time slot received signals at D and at R B being characterized by the relations, 
 y D (2) =√{square root over ( P s )} h SD s 2 +h AD x A (2) +w D (2) and 
 y B (2) =√{square root over ( P s )} h SB s 2 +h AB x A (2) +w B (2) , where w B and w A are AWGN samples with zero mean and variance σ 2 and x A (2) is the amplified received signal at R A such that x A (2) =β A y A (1) ; in the third timeslot transmitting from R B to R A and D the received signal after removing the interfered SU data b 1 and adding a new fresh version of it but with negative sign −b 1 with power P B , the received signal at D and R A in the third time slot being characterized by the relations, 
 y D (3) =h BD x B (3) −√{square root over ( P B )} h BD b 1 +w D (3) , and 
 y A (3) =h BA x B (3) −√{square root over ( P B )} h BA b 1 +w A (3) , where x B (3) is the amplified received signal at R B after the subtraction of the SU data such that x B (3) =β B (y B (2) −b′ 1 ), where b′ 1 is the modified image of SU data b 1 such that b′ 1 =β A h AB h BA b 1 ; using a maximum likelihood detector (MLD) in the PU and SU to detect the PU and SU data, wherein the MLD estimates a symbol vector {circumflex over (x)} s that gives the minimum Euclidean distance metric at D and R A , independently, the Euclidean distance metric for D and R A being characterized by the relations, μ D =  y D = H D ⁢ x S  2 = ∑ l = 1 L = 3 ⁢  y D ( l ) - h D ( l ) ⁢ x S  2 , and μ A =  y A = H A ⁢ x S  2 = ∑ l = 1 L = 2 ⁢  y A ( l ) - h A ( l ) ⁢ x S  2 , where h D (l) and h A (l) denote the l-th row of H D and H A , respectively, a pairwise-error probability being defined as the probability that the MLD chooses the erroneous data vector c i =(c i1 , c i2 , c i3 ) instead of the transmitted data vector c j =(c j1 , c j2 , c j3 ), where the data symbols c im and c jm are for the m-th user; and controlling SU transmission power and amplifying factors of the two relays R A and R B based on the pairwise-error probability.