Patent Application
20140105253
The present invention relates to a two-way relay, a wireless apparatus and a signal processing method thereof. More specifically, the two-way relay of the present invention uses a mapping function to transform signals received from two wireless apparatuses into a relay signal having a relatively low transmit power and broadcasts the relay signal to the two wireless apparatuses.
With development of the modern wireless communications, relays have become indispensable wireless communication apparatuses. Through use of the relays, the communication coverage of the wireless networks gets extended, so ubiquitous and diverse wireless communication services can be provided.
Relay systems currently conceived are mainly classified into the following two kinds of architecture: one-way and two-way. Because two-way relay systems have higher spectrum utilization efficiency than one-way relay systems, two-way relay systems are expected to grow in usage in the future. Currently in a two-way relay system, the two-way relay plays the relaying role through one of the following two commonly used signal processing schemes in the broadcast phase: the Amplify-and-Forward (AF) scheme and the Decoded-and-Forward (DF) scheme. However, the AF scheme has the problem that the transmit power of the two-way relay is high, and the DF scheme has the problem that the two-way relay suffers from a high computational complexity.
Accordingly, an urgent need exists in the art to provide a signal processing scheme that can reduce either the transmit power or the computational complexity of the two-way relay.
An objective of the present invention is to provide a two-way relay, a wireless apparatus and a signal processing method thereof. The present invention in certain embodiments provides a Modulo-and-Forward (MF) signal processing method that can reduce the transmit power necessary for the two-way relay to forward a signal with a low computational complexity. Thereby, the MF signal processing method of certain embodiments of the present invention can reduce the transmit power of the two-way relay as compared with the conventional AF signal processing method, and can reduce the computational complexity as compared with the conventional DF signal processing method.
To this end, the present invention according to certain embodiments discloses a two-way relay for a wireless communication system, which comprises a transceiver and a processor. The transceiver is configured to receive a relay receiving signal. The relay receiving signal comprises a first terminal transmitting signal transmitted by a first wireless apparatus and a second terminal transmitting signal transmitted by a second wireless apparatus. The processor, which is electrically connected to the transceiver, is configured to use a mapping function to transform the relay receiving signal into a relay signal and enable the transceiver to broadcast the relay signal. The mapping function is: fMF(x)=α·c mod(βx+C,B), where α is a transmit power scaling factor, β is a phase rotation factor, x is the relay receiving signal, C is an offset, B is a modulus, and c mod(·) is a complex modulo function and is defined as follows: c mod(xI+jxQ, B)=mod(xI,B)+j mod(xQ, B), where xI is a real component of a complex input signal, xQ, is an imaginary component of the complex input signal, and mod(·) is a modulo function and is defined as follows: mod(A, B)=[(A+B/2)% B]−B/2, where A is an input signal and % is an asymmetric modulo operator defined as follows: p % q=p−└p/q┘q where p and q are any two real numbers and └p/q┘ means taking the largest integer smaller or equal to p/q.
To this end, the present invention according to certain embodiments further discloses a wireless apparatus for the wireless communication system. When the wireless apparatus is the first wireless apparatus, the wireless apparatus is configured to receive a first terminal receiving signal from the two-way relay and, according to a first separated signal function, obtain a second separated signal corresponding to the second terminal transmitting signal, and the first separated signal function is defined as follows: r0=c mod(y0/h0/α−C−βh0x0, B)/β, where r0 is the second separated signal, y0 is the first terminal receiving signal, and x0 is the first terminal transmitting signal. When the wireless apparatus is the second wireless apparatus, the wireless apparatus is configured to receive a second terminal receiving signal corresponding to the relay signal and, according to a second separated signal function, obtain a first separated signal corresponding to the first terminal transmitting signal, and the second separated signal function is defined as follows: r1=c mod(y1/h1/α−C−βh1x1, B)/β, where r1 is the first separated signal, y1 is the second terminal receiving signal, and x1 is the second terminal transmitting signal. The first terminal transmitting signal is transmitted by the first wireless apparatus and is to be transmitted to the second wireless apparatus via the two-way relay, and the second terminal transmitting signal is transmitted by the second wireless apparatus and is to be transmitted to the first wireless apparatus via the two-way relay.
Further, the present invention according to certain embodiments discloses a signal processing method for a two-way relay. The two-way relay comprises a transceiver and a processor. The signal processing method is executed by the processor and comprises the following steps of: (a) receiving a relay receiving signal via the transceiver, wherein the relay receiving signal comprises a first terminal transmitting signal transmitted by a first wireless apparatus and a second terminal transmitting signal transmitted by a second wireless apparatus; (b) using a mapping function to transform the relay receiving signal into a relay signal; and (c) enabling the transceiver to broadcast the relay signal. The mapping function is: fMF(x)=α·c mod(βx+C,B), where α is a transmit power scaling factor, β is a phase rotation factor, x is the relay receiving signal, C is an offset, B is a modulus, and c mod(·) is a complex modulo function and is defined as follows: c mod(xI+jxQ, B)=mod(xI,B)+j mod(xQ, B), where xI is a real component of a complex input signal, xQ, is an imaginary component of the complex input signal, and mod(·) is a modulo function and is defined as follows: mod(A, B)=[(A+B/2)% B]−B/2, where A is an input signal and % is an asymmetric modulo operator defined as follows: p % q=p−└P/q┘q where p and q are any two real numbers and └p/q┘ means taking the largest integer smaller or equal to p/q.
The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention.
In the following description, the present invention will be explained with reference to example embodiments thereof. However, these example embodiments are not intended to limit the present invention to any specific examples, embodiments, environment, applications or particular implementations described in these example embodiments. Therefore, description of these embodiments is only for purpose of illustration rather than to limit the present invention, and the scope of this application shall be governed by the claims. It should be appreciated that, in the following embodiments and the attached drawings, elements unrelated to the present invention are omitted from depiction; and dimensional relationships among individual elements in the attached drawings are illustrated only for ease of understanding, but not to limit the actual scale.
A first embodiment of the present invention is shown in
The first wireless apparatus T0 comprises a transceiver 21 and a processor 23 electrically connected with the transceiver 21. The second wireless apparatus T1 comprises a transceiver 31 and a processor 33 electrically connected with the transceiver 31. The first wireless apparatus T0 and the second wireless apparatus T1 communicate with each other via the two-way relay R.
The two-way relay R comprises a transceiver 11 and a processor 13 electrically connected with the transceiver 11. In a multiple access (MAC) phase, the first wireless apparatus T0 transmits a first terminal transmitting signal x0 and, at the same time, the second wireless apparatus T1 transmits a second terminal transmitting signal x1.
Then, a relay receiving signal x is received by the two-way relay R. The relay receiving signal x may be represented by x=x0·h0+x1·h1+zR, where h0 is a first channel coefficient associated with the first terminal transmitting signal x0, h1 is a second channel coefficient associated with the second terminal transmitting signal xI, and zR is the additive noise at the two-way relay R.
Next, the Modulo-and-Forward (MF) signal processing method of the present invention will be described. After having received the relay receiving signal x, the processor 13 uses a mapping function to transform the relay receiving signal x into a relay signal 102. The mapping function is represented by the following Equation 1:
f
MF(x)=α·c mod(βx+C,B) (1)
where, x is an input signal (here, the relay receiving signal) of the function, α is a transmit power scaling factor, β is a phase rotation factor, C is an offset, B is a modulus, and c mod(·) is a complex modulo function and is defined by the following Equation 2:
c mod(xI+jxQ,B)=mod(xI,B)+j mod(xQ,B) (2)
where xI is a real component of a complex input signal (here, the relay receiving signal), x is an imaginary component of the complex input signal, and mod(·) is a modulo function and is defined by the following Equation 3:
mod(A,B)=[(A+B/2)% B]−B/2 (3)
where A is an input signal, and % is an asymmetric modulo operator defined as follows: p % q=p−└p/q┘q where p and q are any two real numbers and └p/q┘ means taking the largest integer smaller or equal to p/q. After the relay receiving signal x has been transformed into the relay signal 102 by use of the mapping function, the processor 13 enables the transceiver 11 to broadcast the relay signal 102 to the first wireless apparatus T0 and the second wireless apparatus T1 in a broadcast (BC) phase.
Similarly, the relay signal 102 is liable to influence of the channel effect between the relay station R and the first and the second wireless apparatuses T0 and T1 during transmission. Therefore, a first terminal receiving signal y0 received by the first wireless apparatus T0 may be represented by y0=h0·fMF(x) zT0 and a second terminal receiving signal y1 received by the second wireless apparatus T1 may be represented by y1=h1·fMF(x)+zT1 where zT0 is an additive noise and zT1 is also an additive noise.
After the first terminal receiving signal y0 is received by the transceiver 21 of the first wireless apparatus T0, the processor 23 calculates a second separated signal corresponding to the second terminal transmitting signal from the first terminal receiving signal y0 according to a first separated signal function, where the first separated signal function is defined as the following Equation 4:
r
0
=c mod(y0/h0/α−C−βh0x0,B)/β (4)
where, r0 is the second separated signal, and y0 is the first terminal receiving signal. It shall be particularly appreciated that, as will be understood by those of ordinary skill in the art, the second separated signal r0 is equal to the second terminal transmitting signal x1 if the influence of noises is not taken into account and if it is assumed that the channel effect can be ideally compensated.
Similarly, after the second terminal receiving signal y1 is received by the transceiver 31 of the first wireless apparatus T1, the processor 33 calculates a first separated signal corresponding to the first terminal transmitting signal from the second terminal receiving signal y1 according to a second separated signal function, where the second separated signal function is defined as the following Equation 5:
r
1
=c mod(y1/h1/α−C−βh1x1,B)/β (5)
where, r1 is the first separated signal, and y1 is the first terminal receiving signal. It shall be particularly appreciated that, as will be understood by those of ordinary skill in the art, the first separated signal r1 is equal to the first terminal transmitting signal x0 if the influence of noises is not taken into account and if it is assumed that the channel effect can be ideally compensated.
A second embodiment of the present invention is shown also in
When the first terminal transmitting signal x0, the second terminal transmitting signal x1 and the relay receiving signal x are pulse amplitude modulation (PAM) signals, the phase rotation factor β is 1, and the imaginary component xQ, of each of the signals is 0. In this case, let the modulus B be as shown by the following Equation 6:
B=2·max(a0M0|h0|,α1M1|h1|) (6)
where, a0 and a1 are signal scaling factors, M0 is a PAM modulation order of the first terminal transmitting signal x0, and M1 is a PAM modulation order of the second terminal transmitting signal x1.
An example is provided below to illustrate the ability of this invention to reduce the transmit power of the relay station in the relaying of PAM signals, as compared to the present art. For ease of description, the comparison will be made in terms of peak transmit power. It will be understood by those skilled in the art that, in addition to the peak transmit power, the average transmit power of the relay station is also reduced by this invention.
For this example, a case where the first terminal transmitting signal x0 and the second terminal transmitting signal x1 are 4-PAM signals (the PAM modulation order M0 of the first terminal transmitting signal x0 and the PAM modulation order M1 of the second terminal transmitting signal x1 are both 4) and the possible signal values thereof are −3a, −1a, 1a or 3a, with a0 and a1 both equal to a, will be described. When the signal scaling factor a is 1, the transmit power scaling factor α is 1, and the first channel coefficient h0 and the second channel coefficient h1 are both 1, the modulus B calculated from Equation 6 is 8.
Then, in a case where the offset is not taken into account (i.e., the offset C is 0), the possible signal values of the first terminal transmitting signal x0 and the second terminal transmitting signal x1 are both +3, +1, −1, and −3, and the noise in each receiving signal is assumed to be 0, the maximum possible amplitude of the relay signal 102 obtained from Equation 1 is 4 and the peak transmit power thereof is 16 (a square of 4). As can be seen, the peak transmit power of the relay station for the relay signal 102 can be decreased from 36 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6) to 16 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme. Furthermore, a second separated signal r0 of value equal to x1 can be obtained by substituting the first terminal receiving signal y0 into the first separated signal function (i.e., Equation 4). Similarly, a first separated signal r1 of value equal to x0 can be obtained by substituting the second terminal receiving signal y1 into the second separated signal function (i.e., Equation 5).
Further in a case where the offset C is 1 (i.e., the offset C=B/2Mi, where i=arg max(aiMi|hi|, i=0 or 1)), the maximum possible amplitude of the relay signal 102 obtained from Equation 1 is 3 and the peak transmit power thereof is 9 (a square of 3). Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 36 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6) to 9 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme. Similarly, a second separated signal r0 of value equal to x1 can be obtained by substituting the first terminal receiving signal y0 into the first separated signal function (i.e., Equation 4); and a first separated signal r1 of value equal to x0 can be obtained by substituting the second terminal receiving signal y1 into the second separated signal function (i.e., Equation 5).
A third embodiment of the present invention is shown also in
Let the modulus B be as shown by the following Equation 7:
B=2·max{a0M0|h0|sec(mod(θ0θ,π/2)),a1M1|h1|sec(mod(θ1+θ,π/2))} (7)
where, a0 and a1 are signal scaling factors, M0 is a root value of a QAM modulation order of the first terminal transmitting signal x1, θ0 is a first channel phase angle of the first channel coefficient, M1 is a root value of a QAM modulation order of the second terminal transmitting signal x1, and θ1 is a second channel phase angle of the second channel coefficient. In addition, θ is a phase angle whose value is greater than or equal to −π/4 and smaller than π/4, and the phase rotation factor is ejθ.
An example is provided below to illustrate the ability of this invention to reduce the transmit power of the relay station in the relaying of QAM signals, as compared to the present art. For ease of description, the comparison will be made in terms of peak transmit power. It will be understood by those skilled in the art that, in addition to the peak transmit power, the average transmit power of the relay station is also reduced by this invention.
For this example, a case where the first terminal transmitting signal x0 and the second terminal transmitting signal x1 are 16-QAM signals, and possible signal values of a real component and an imaginary component of the first terminal transmitting signal x0 and the second terminal transmitting signal x1 are −3a, −1a, 1a or 3a, with a0 and a1 both equal to a, will be described. If the signal scaling factor a is 1, the transmit power scaling factor α is 1, the first channel coefficient h0 is 1, the second channel coefficient h1 is 1, the first channel phase angle θ0 is 0, the second channel phase angle θ1 is 0, the QAM modulation order of the first terminal transmitting signal x0 is 16 (i.e., M0=4), the QAM modulation order of the second terminal transmitting signal x1 is also 16 (i.e., M1=4), and zR is 0, then the maximum possible amplitude of the relay receiving signal x is 6√{square root over (2)}.
The modulus B is calculated to be 8 according to Equation 7 if the phase rotation is not taken into account (i.e., the phase rotation factor β is 1, and θ is 0). Additionally, if the offset is not taken into account (i.e., the offset C is 0), then, by substituting the transmit power scaling factor α, the phase rotation factor β, the relay receiving signal x, the offset C and the modulus B into the mapping function (i.e., Equation 1), the maximum possible amplitude of the relay signal 102 will be calculated to be 4√{square root over (2)}, and the peak transmit power thereof is 32. Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 72 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6√{square root over (2)}) to 32 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme.
Additionally, if the phase rotation is not taken into account (i.e., the phase rotation factor β is 1, and θ is 0) but the offset is taken into account and be such that C=(B/2Mi)+j(B/2Mi), where i=arg max{aiMi|hi|sec(mod(θi+θ,π/2)), i=0 or 1}, then C is 1+j. Then, by substituting the transmit power scaling factor α, the phase rotation factor β, the relay receiving signal x, the offset C and the modulus B into the mapping function (i.e., Equation 1), the maximum possible amplitude of the relay signal 102 will be calculated to be 3√{square root over (2)}, and the peak transmit power thereof is 18. Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 72 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6√{square root over (2)}) to 18 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme.
Next, the first wireless apparatus T0 calculates the second separated signal r0 according to the first separated signal function (i.e., Equation 4), and the second wireless apparatus T1 calculates the first separated signal r1 according to the second separated signal function (i.e., Equation 5).
A fourth embodiment of the present invention is shown also in
An example is provided below to illustrate the ability of this invention to reduce the transmit power of the relay station in the relaying of QAM signals, as compared to the present art. For ease of description, the comparison will be made in terms of peak transmit power. It will be understood by those skilled in the art that, in addition to the peak transmit power, the average transmit power of the relay station is also reduced by this invention.
For this example, a case where the first terminal transmitting signal x0 and the second terminal transmitting signal x1 are 16-QAM signals, and possible signal values of a real component and an imaginary component of the first terminal transmitting signal x0 and the second terminal transmitting signal x1 are −3a, −1a, 1a or 3a, with a0 and a1 both equal to a, will be described. If the signal scaling factor a is 1, the transmit power scaling factor α is 1, the first channel coefficient h0 is ejπ/4, the second channel coefficient h1 is e−jπ/4, the first channel phase angle θ0 is π/4, the second channel phase angle θ1 is −π/4, the QAM modulation order of the first terminal transmitting signal x0 is 16 (i.e., M0=4), the QAM modulation order of the second terminal transmitting signal x1 is also 16 (i.e., M1=4), and zR is 0, then the maximum possible amplitude of the relay receiving signal x is 6√{square root over (2)}.
Additionally, the modulus calculated according to Equation 7 is 8√{square root over (2)} if the offset and the phase rotation are not taken into account (i.e., the offset C is 0, the phase rotation factor β is 1, and θ is 0). Then, by substituting the transmit power scaling factor α, the phase rotation factor β, the relay receiving signal x, the offset C and the modulus B into the mapping function (i.e., Equation 1), the maximum possible amplitude of the relay signal 102 will be calculated to be √{square root over (40)}, and the peak transmit power thereof is 40. Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 72 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6√{square root over (2)}) to 40 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme.
If the phase rotation is further taken into account (i.e., the value of the phase angle θ is greater than or equal to −π/4 and smaller than π/4, and the phase rotation factor β is ejθ) but the offset is still not taken into account (i.e., the offset C is 0), the modulus is calculated to be 8 according to Equation 7, where let θ=−π/4. Then, by substituting the transmit power scaling factor α, the phase rotation factor β, the relay receiving signal x, the offset C and the modulus B into the mapping function (i.e., Equation 1), the maximum possible amplitude of the relay signal 102 will be calculated to be 4√{square root over (2)}, and the peak transmit power thereof is 32. Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 72 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6√{square root over (2)}) to 32 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme.
Furthermore, if the phase rotation is taken into account (i.e., the value of the phase angle θ is greater than or equal to −π/4 and smaller than π/4, and the phase rotation factor β is ejθ) but the offset is still not taken into account (i.e., the offset C is 0) and the phase angle θ is let to be as shown by the following Equation 8:
where θt is a variable, and the output value obtained from the function
is the phase angle θ. The modulus is calculated to be 8 according to Equation 7, where the phase angle yielding this modulus is calculated to be θ=−π/4 according to Equation 8. Then, by substituting the transmit power scaling factor α, the phase rotation factor β, the relay receiving signal x, the offset C and the modulus B into the mapping function (i.e., Equation 1), the maximum possible amplitude of the relay signal 102 will be calculated to be 4√{square root over (2)}, and the peak transmit power thereof is 32. Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 72 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6√{square root over (2)}) to 32 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme.
Yet furthermore, if the phase rotation is taken into account (i.e., the value of the phase angle θ is greater than or equal to −π/4 and smaller than π/4, and the phase rotation factor β is ejθ), and the offset is also taken into account and be such that C=(B/2Mi)+j(B/2Mi), where i=arg max{aiMi|hi|sec(mod(θi+θ,π/2)), i=0 or 1}), then the modulus B is calculated to be 8 according to Equation 7, where the phase angle yielding this modulus is calculated to be θ=−π/4 according to Equation 8, and C is 1+j. Then, by substituting the transmit power scaling factor α, the phase rotation factor β, the relay receiving signal x, the offset C and the modulus B into the mapping function (i.e., Equation 1), the maximum possible amplitude of the relay signal 102 will be calculated to be 3√{square root over (2)}, and the peak transmit power thereof is 18. Accordingly, the peak transmit power of the relay station for the relay signal 102 can be decreased from 72 (a square of the maximum possible amplitude of the relay receiving signal x, i.e., a square of 6√{square root over (2)}) to 18 as compared with the conventional Amplify-and-Forward (AF) signal processing scheme.
Next, the first wireless apparatus T0 calculates the second separated signal r0 according to the first separated signal function (i.e., Equation 4), and the second wireless apparatus T1 calculates the first separated signal r1 according to the second separated signal function (i.e., Equation 5).
A fifth embodiment of the present invention is shown in
Firstly, a relay receiving signal is received via the transceiver in step S100. The relay receiving signal comprises a first terminal transmitting signal transmitted by a first wireless apparatus and a second terminal transmitting signal transmitted by a second wireless apparatus. Then, the relay receiving signal is transformed into a relay signal by use of a mapping function in step S110. Finally, the transceiver is enabled to broadcast the relay signal in step S120.
It shall be appreciated that, the mapping function is as shown in Equation 1, and the complex modulo function and the modulo function defined in the mapping function are as defined in the first embodiment, so no further description will be made thereon herein.
In addition to the aforesaid steps, the signal processing method of the fifth embodiment can also execute all the operations and functions set forth in the first embodiment to the fourth embodiment. How the signal processing method of the fifth embodiment executes these operations and functions will be readily appreciated by those of ordinary skill in the art based on the explanation of the first embodiment to the fourth embodiment, and thus will not be further described herein.
According to the above descriptions, the two-way relay of the present invention plays the relaying role through Modulo-and-Forward (MF) signal processing to reduce the relay transmit power of the two-way relay. Thereby, the MF signal processing method of the present invention can reduce the transmit power of the two-way relay as compared with the conventional AF signal processing method, and can reduce the computational complexity as compared with the conventional DF signal processing method.
The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/712,814 filed on Oct. 12, 2012, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61712814 | Oct 2012 | US |
