Receiver, method for cancelling interference thereof and transmitter for the same

Provided is a method for eliminating an interference operating on a receiver of a transmitter in a communications system, which includes transmitting at least one user signal; changing user phase information to be separated from interference phase information by a preset difference, when receiving the user phase information of the user signal and the interference phase information of an interference signal from at least one receiver; and transmitting at least one other user signal according to the changed user phase information.

TECHNICAL FIELD

The present invention relates to a telecommunication method and apparatus, and more particularly, to a receiver, a method of canceling interference thereof and a transmitter for the same.

BACKGROUND ART

Generally, user signals for a plurality of transceivers exist in communications environment. At this time, the communications system of TDMA (Time Division Multiple Access) or FDMA (Frequency Division Multiple Access) was implemented to assign wireless channel of different time or frequency to transceivers. That is, the communications system separates user signals for each transceiver from each other according to time or frequency.

DISCLOSURE OF INVENTION

Technical Problem

However, in the communications system, rest signals except desired one signal among user signals can operate as an interference signal in a specific receiver. That is, base station is tightly established to increase a frequency reuse factor so as to enhance capacity in the communications system. Hence, a plurality of user signals can exist in a specific wireless channel. Thus, user signals operate as a mutual interference signal so that the reception ability of the receivers can be degraded. Accordingly, it is required to eliminate an interference signal in the communications system.

Solution to Problem

The present invention has been made in view of the above problems, and provides a receiver, a method of canceling interference thereof and a transmitter for the same.

In accordance with an aspect of the present invention, a method for eliminating an interference operating on a receiver of a transmitter in a communications system includes transmitting at least one user signal; changing user phase information to be separated from interference phase information by a preset difference, when receiving the user phase information of the user signal and the interference phase information of an interference signal from at least one receiver; and transmitting at least one other user signal according to the changed user phase information.

In accordance with another aspect of the present invention, a method for eliminating an interference of a receiver in a communications system includes detecting user phase information of user signal and interference phase information of interference signal and feeding back them to a transmitter of the user signal, when receiving the user signal and the interference signal; and eliminating the interference signal by controlling the user phase information and the interference phase information.

In accordance with another aspect of the present invention, a transmitter for eliminating an interference operating on a receiver in a communications system includes a radio frequency unit that transmits at least one user signal, receives user phase information of the user signal and interference phase information of an interference signal; and a rotation unit that controls to change the received user phase information to be separated from the received interference phase information by a preset difference, when receiving the user phase information and the interference phase information, and transmit other user signal according to the changed user phase information.

In accordance with another aspect of the present invention, a transmitter for eliminating an interference of a receiver in a communications system includes a radio frequency unit that receives a user signal and an interference signal; and an interference cancellation unit that detects user phase information of the received user signal and interference phase information of the received interference signal and feeds back them to a transmitter of the user signal, when receiving the user signal and the interference signal, and eliminates the interference signal by controlling the user phase information and the interference phase information.

Therefore, the receiver, the method of canceling interference thereof and a transmitter for the same according to the present invention can suppress the operation of interference signal. That is, transmitter changes phase information of user signal in a complex space, so that receiver can completely eliminate interference signal. Thus, link performance between transmitter and receiver can be improved in communications system. Accordingly, communications quality between transmitter and receiver can be improved in communications system, and the communications range can be extended.

Advantageous Effects of Invention

In the communications system of the present invention, transmitter can suppress the operation of the interference signal in receiver. That is, as transmitter changes phase information of user signal in complex space, receiver can completely eliminate interference signal. Accordingly, the link performance between transmitter and receiver can be improved in the communications system. Accordingly, the communications quality between transmitter and receiver can be improved in the communications system, and the communications range can be extended.

MODE FOR THE INVENTION

In below description, a term “user signal” refers to a signal which is transmitted in a specific transmitter of communications system and is desired to be received in a specific receiver. A term “interference signal” refers to a signal which is transmitted in a specific transmitter of communications system and is not desired to be received in a specific receiver. That is, the interference signal is a signal which is received in a specific receiver while it is a signal which is not desired to be received in a corresponding receiver, and it operates on the user signal of a corresponding receiver as interference. A term “user phase information” refers to location or state related information of user signal, when transmitting a user signal in a specific transmitter of communications system. A term “interference phase information” refers to location or state related information of interference signal, when transmitting an interference signal in another transmitter of communications system. At this time, the user phase information and the interference phase information can be expressed with a complex vector in a complex space which is made of real axis (Re) and imaginary axis (Im).

FIG. 1is a block diagram illustrating a schematic configuration of a communications system according to an exemplary embodiment of the present invention.

Referring toFIG. 1, the communications system of the present embodiment includes at least one receiver100and transmitters200,300.

The receiver100receives user signal of a specific wireless channel. At this time, the receiver100receives not only user signal but also interference signal, when interference signal exists together with user signal in a corresponding wireless channel. After removing interference signal, the receiver100processes user signal. That is, the receiver100can detect user phase information of user signal and interference phase information of interference signal. Moreover, the receiver100rotates user phase information and interference phase information in a complex space to eliminate interference signal. Transmitters200,300transmit user signal or interference signal through a specific wireless channel. That is, in the receiver100, a specific transmitter200transmits user signal and another transmitter300transmits interference signal. At this time, the transmitter200changes user signal and transmits it so as to efficiently eliminate interference signal in the receiver100. Here, the transmitter100changes user phase information of user signal and transmits it. The receiver100in the communications system is illustrated in detail in below.

FIG. 2is a block diagram illustrating an internal configuration of a receiver inFIG. 1, andFIG. 3is a drawing illustrating interference cancellation ofFIG. 2.

Referring toFIG. 2, the receiver100of the embodiment includes a radio frequency unit (RF unit)110and a single antenna interference cancellation processor (SAIC processor)120. The RF unit110performs a communication function of the receiver100. In a predefined wireless channel, this RF unit110receives user signal (Signal) and interference signal (Interference). The SAIC processor120performs a function for improving the communications performance of the receiver100. This SAIC processor120detects user phase information and interference phase information and classifies the user signal and the interference signal. The SAIC processor120feeds back the user phase information and the interference phase information to the transmitter200through the RF unit110. Moreover, the SAIC processor120eliminates the interference signal. That is, the SAIC processor120amplifies user signal or damps the interference signal, thereby relatively eliminating the interference signal. For example, as shown inFIG. 3(a), the SAIC processor120can detect the user phase information of user signal and the interference phase information of interference signal in the complex space. That is, the SAIC processor120can detect the size of the user signal as ‘S’, and detect the size of the interference signal as ‘R’. And the SAIC processor120can detect the phase difference of the user phase information and the interference phase information as ‘θ’. At this time, the Signal-to-Interference-plus-Noise Ratio (SINR) can be determined like Math Figure 1.

Here, SINRiindicates the ratio of the user signal and the interference signal inputted to the SAIC processor120, and N indicates the size of white noise. As shown inFIG. 3(b), the SAIC processor120can rotate the user phase information to contact to real axis in the complex space. The SAIC processor120can rotate the interference phase information together with the user phase information. At this time, the SAIC processor120maintains the phase difference of the user phase information and the interference phase information as ‘θ’. That is, the SAIC processor120maintains the size of the user signal as ‘S’, while damping the size of the interference signal as ‘R cos θ’. At this time, the SAIC processor120can control the Signal-to-Interference-plus-Noise Ratio like Math Figure 2.

Here, SINRoindicates the ratio of the user signal and the interference signal outputted from the SAIC processor120. Alternatively, as shown inFIG. 3(c), the SAIC processor120can rotate the interference phase information to contact to imaginary axis in the complex space. The SAIC processor120can rotate the user phase information together with the interference phase information. At this time, the SAIC processor120maintains the phase difference of the user phase information and the interference phase information as ‘θ’. That is, the SAIC processor120damps the size of the user signal as ‘S sin θ’, while completely eliminating the size of the interference signal. At this time, the SAIC processor120can control the Signal-to-Interference-plus-Noise Ratio like Math Figure 3.

At this time, if the phase difference of the user phase information and the interference phase information is 90°, the SAIC processor120maintains the size of the user signal as ‘S’, while completely eliminating the size of the interference signal, because if the SAIC processor120rotates the user phase information to contact to real axis, the interference phase information can contact to imaginary axis. Alternatively, if the SAIC processor120rotates the interference phase information to contact to imaginary axis, the user phase information can contact to real axis. Here, the phase difference of the user phase information and the interference phase information is 90°, the SAIC processor120can control the Signal-to-Interference-plus-Noise Ratio like Math Figure 4.

In below description, the transmitter200in the communications system is illustrated in detail.

FIG. 4is a block diagram illustrating an internal configuration of a transmitter inFIG. 1, andFIG. 5is a drawing illustrating the interference cancellation ofFIG. 4.

Referring toFIG. 4, the transmitter200of the embodiment includes a modulator210, a RF unit220, a phase controller230and a phase rotator240. The modulator210performs a function of generating a user signal. At this time, the modulator210modulates the user signal with the Gaussian minimum shift keying (GMSK). The RF unit220performs the telecommunication function of the transmitter200. This RF unit220transmits user signal through a predefined wireless channel. And the RF unit220receives user phase information and interference phase information from the receiver100. The phase controller230calculates rotation value for separating user phase information from interference phase information by a preset difference. At this time, the difference may be 90°, and the phase controller230can calculate rotation value for controlling the phase difference of the user phase information and the interference phase information to be 90° in the complex space like MathFIG. 5.

The phase rotator240changes user phase information. That is, the phase rotator240rotates user phase information in the complex space as much as rotation value. The phase rotator240controls the RF unit220to transmit user signal according to user phase information.

For instance, when the receiver100receives user phase information and interference phase information, the transmitter200, as shown inFIG. 5(a), rotates user phase information and transmits user signal. When receiving user signal, as shown inFIG. 5(b), the receiver100rotates user phase information and interference phase information and eliminates interference signal. At this time, since the phase difference of the user phase information and the interference phase information is 90°, the receiver100maintains the size of user signal as ‘S’, while completely eliminating the size of interference signal. The interference cancellation procedure performed in the communications system having such configuration is illustrated.

FIG. 6is a flowchart illustrating an interference cancellation procedure in a communications system according to an exemplary embodiment of the present invention.

Referring toFIG. 6, in the interference cancellation procedure of the embodiment, the transmitter200determines user phase information (411). The transmitter200transmits user signal through user phase information (413). When receiving user signal, the receiver100detects user phase information of user signal (415). Here, although not illustrated, the receiver100can receive the interference signal of other transmitter300independently of user signal. At this time, when receiving the interference signal, the receiver100detects the interference phase information of the interference signal at step415. Moreover, the receiver100transmits a feedback signal including the user phase information and the interference phase information (417).

Next, when receiving a feedback signal, the transmitter200calculates rotation value for separating user phase information from interference phase information by a preset difference (419). At this time, the difference may be 90°, and the transmitter200can calculate rotation value for controlling the phase difference of the user phase information and the interference phase information to be 90° in the complex space. The transmitter200changes user phase information by using rotation value (421). That is, the transmitter200rotates user phase information in the complex space as much as rotation value. In addition, the transmitter200transmits user signal according to user phase information (423). Then, when receiving a user signal, the receiver100eliminates interference (425). At this time, the receiver100rotates user phase information and interference phase information and eliminates interference. Here, since the phase difference of the user phase information and the interference phase information and is 90°, the receiver100can completely eliminate the size of the interference signal while maintaining the size of user signal. In the meantime, it was illustrated that a transmitter of communications system of the above-described embodiment transmits a user signal for a single receiver, but it is not limitative. That is, the present invention can be implementation even when a transmitter transmits a plurality of user signals for a plurality of receivers through a specific wireless channel in a communications system.

FIG. 7illustrates such an example, andFIG. 7is a block diagram illustrating a schematic configuration of a communications system according to another exemplary embodiment of the present invention. At this time, transmitter can transmit user signals through a Multi-User Reusing One Slot (MUROS) technique.

Referring toFIG. 7, the communications system of the embodiment includes a plurality of receivers500,600and transmitters700,800. Receivers500,600receive the user signal of a specific wireless channel. At this time, receivers500,600can receive each user signal in the same wireless channel. Receivers500,600receive not only each user signal but also interference signal, when interference signal exists with user signal in a corresponding wireless channel.

After eliminating interference signal, receivers500,600process each user signal. That is, receivers500,600can detect the user phase information of user signal and the interference phase information of interference signal. Moreover, receivers500,600can rotate user phase information and interference phase information in a complex space, and eliminate interference signal. Transmitters700,800transmit user signal or interference signal through a specific wireless channel. That is, in the receivers500,600, a specific transmitter700transmits user signal, and other transmitter800transmits interference signal. At this time, the transmitter700transmits user signal to the receivers500,600through a specific wireless channel while transmitting user signal through user phase information which is different for respective receivers500,600.

Here, the transmitter700can transmit user signal by controlling the phase difference of user phase information for respective receivers500,600to be 90°. The transmitter700changes user signal to efficiently eliminate interference signal in the receivers500,600and transmits it. At this time, the transmitter700changes the user phase information of user signal and transmits it. Here, the transmitter700maintains the phase difference of user phase information for respective receivers500,600as 90°. At this time, receivers500,600in the communications system are illustrated in detail.

FIG. 8is a block diagram illustrating an internal configuration of a receiver inFIG. 7, andFIG. 9is a drawing illustrating the interference cancellation ofFIG. 8.

Referring toFIG. 8, a first receiver500of the embodiment includes a RF unit510and a single antenna interference cancellation processor (SAIC processor)520. The RF unit510performs a telecommunication function of a first receiver500. Such RF unit510receives a first user signal i.e., Orthogonal Sub-Channel signal1(OSC1) and a first interference signal (I1) in a predefined wireless channel. At this time, the RF unit510can more receive a second user signal i.e., Orthogonal Sub-Channel signal2(OSC2) in a corresponding wireless channel.

The SAIC processor520performs a function for improving the communications performance of the receiver500. This SAIC processor520can detect first user phase information and first interference phase information, and classify the OSC1and the first interference signal. At this time, the SAIC processor520can detect second user phase information, and classify the OSC1, the first interference signal, and the OSC2. The SAIC processor520feeds back first user phase information and first interference phase information to the transmitter700through the RF unit510. Moreover, the SAIC processor520eliminates the first interference signal. At this time, the SAIC processor520can more eliminate the OSC2. That is, the SAIC processor520amplifies the OSC1or damps the first interference signal, thereby relatively eliminating the first interference signal. For instance, as shown inFIG. 9(a), the SAIC processor520can detect the first user phase information of OSC1and the first interference phase information of first interference signal in a complex space. At this time, the SAIC processor520can more detect the second user phase information of OSC2. That is, the SAIC processor520can detect the size of the OSC1as ‘S1’, detect the size of the first interference signal as ‘R1’, and detect the size of the OSC2as ‘S2’. In addition, the SAIC processor520can detect the phase difference of the first user phase information and the first interference phase information as ‘θ’. At this time, the ratio of the size of the OSC1to the first interference signal and the OSC2is determined like Math Figure 6.

Here, SINRi1indicates the ratio of the user signal and the interference signal inputted from the first receiver500to the SAIC processor520, and N1indicates the size of white noise in the first receiver500. As shown inFIG. 9(b), the SAIC processor520can rotate the first user phase information to contact to real axis in a complex space. The SAIC processor520can rotate the first interference phase information and the second user phase information together with the first user phase information.

At this time, the SAIC processor520maintains the phase difference of the first user phase information and the first interference phase information as ‘θ’. Moreover, the SAIC processor520maintains the phase difference of the first user phase information and the second user phase information as ‘90°’. That is, the SAIC processor520maintains the size of the first user signal as ‘S1’, while damping the size of the first interference signal as ‘R1cos θ’. Moreover, since the second user phase information contacts to imaginary axis, the SAIC processor520completely eliminates the size of the OSC2, so that the OSC2and the first interference signal can be prevented from being operated as interference. At this time, the SAIC processor520can control the ratio of the size of OSC1to the size of the first interference signal and the OSC2like Math Figure 7.

Here, SINRo1indicates the ratio of the user signal and the interference signal outputted from the SAIC processor520.

Alternatively, as shown inFIG. 9(c), the SAIC processor520can rotate the first interference phase information to contact to imaginary axis in an imaginary space. The SAIC processor520can rotate the first user phase information and the second user phase information together with the first interference phase information. At this time, the SAIC processor520maintains the phase difference of the first user phase information and the first interference phase information as ‘θ’. Moreover, the SAIC processor520maintains the phase difference of the first user phase information and the second user phase information as ‘90°’. That is, the SAIC processor520damps the size of the first user signal as ‘S1sin θ’, while completely eliminating the size of the first interference signal. Moreover, since the second user phase information contacts to imaginary axis, the SAIC processor520completely eliminates the size of the OSC2, so that the OSC2and the first interference signal can be prevented from being operated as interference. At this time, the SAIC processor520can control the ratio of the size of OSC1to the size of the first interference signal and the OSC2like Math Figure 8.

At this time, if the phase difference of the first user phase information and the first interference phase information is 90°, the SAIC processor520maintains the size of the OSC1as ‘S1’, while completely eliminating the size of the first interference signal and the OSC2, because if the SAIC processor520rotates the first user phase information to contact to real axis, the first interference phase information and the second user phase information can contact to imaginary axis. Alternatively, if the SAIC processor520rotates the first interference phase information to contact to imaginary axis, the first user phase information can contact to real axis and the second user phase information can contact to imaginary axis. Here, the phase difference of the first user phase information and the first interference phase information is 90°, the SAIC processor520can control the ratio of the size of OSC1to the size of first interference signal and OSC2like Math Figure 9.

In the meantime, since the basic configuration of the second receiver600of the embodiment is similar to a corresponding configuration of the first receiver500, the detailed description is omitted. However, the second receiver600operates to eliminate the size of the second interference signal, i.e., ‘R2’, and the size of the OSC1i.e., ‘S1’. For example, the second receiver600operates to maintain the size of the OSC2as ‘S2’, while completely eliminating the size of the second interference signal, i.e., ‘R2’, and the size of the OSC1i.e., ‘S1’. The transmitter700of the communications system is illustrated in detail.

FIG. 10is a block diagram illustrating an internal configuration of the transmitter inFIG. 7.FIG. 11is a drawing illustrating the interference cancellation ofFIG. 10.

Referring toFIG. 10, the transmitter700of the embodiment includes a first modulator710, a second modulator720, a phase shifter730, a signal adder740, a RF unit750, a phase controller760, and a phase rotator770. The first modulator710performs a function of generating OSC1for a first receiver500. At this time, the first modulator710modulates the OSC1with the Gaussian minimum shift keying (GMSK). The second modulator720performs a function of generating OSC2for a second receiver600. At this time, the second modulator720modulates the OSC2with the Gaussian minimum shift keying (GMSK). The phase shifter730controls second user phase information of the OSC2. That is, the phase shifter730controls second user phase information in order to be separated from the first user phase information by 90° in complex space. The signal adder740adds the OSC1and the OSC2to a predefined wireless channel. The RF unit750performs a communication function of the transmitter700. This RF unit750transmits the OSC1and the OSC2. Moreover, the RF unit750receives first user phase information, first interference phase information, second user phase information, and second interference phase information from receivers500,600.

The phase controller760calculates a rotation value for separating the first user phase information and the second user the phase information from the first interference phase information or the second interference phase information by a preset difference. At this time, the difference can be 90°, and the phase controller760calculates a rotation value for controlling the phase difference of the first user phase information and the second user phase information to be maintained by 90°. And the phase controller760calculates a rotation value for controlling the phase difference of the first user phase information and the first interference phase information and the phase difference of the second user phase information and the second interference phase information to be approximate 90°. That is, the phase controller760calculates a rotation value by comparing first interference phase information with second interference phase information, after normalizing the first user phase information and the second user phase information into a single value.

For instance, if the first interference phase information and the second interference phase information are similar, as shown inFIG. 11(a), the phase controller760calculates a rotation value for controlling the phase difference of the first user phase information and the first interference phase information to be 90° in complex space. Alternatively, the phase controller760calculates a rotation value for controlling the phase difference of the second user phase information and the second interference phase information to be 90° in complex space. At this time, if the separation value of the first interference phase information and the second interference phase information is a preset critical value or less, the phase controller760can determine that the first interference phase information and the second interference phase information are similar. And the phase controller760can calculate a rotation value like Math Figure 10.

Alternatively, if the first interference phase information and the second interference phase information are different, as shown inFIG. 11(b), the phase controller760calculates a median of the first interference phase information and the second interference phase information. And the phase controller760calculates a rotation value for controlling the phase difference of the first user phase information and the median to be 90° in complex space. Alternatively, the phase controller760calculates a rotation value for controlling the phase difference of the second user phase information and the median to be 90° in complex space. At this time, if the separation value of the first interference phase information and the second interference phase information exceeds a preset critical value, the phase controller760can determine that the first interference phase information and the second interference phase information are different. And the phase controller760can calculate a rotation value like Math Figure 11.

Here, β indicates the phase difference of the first interference phase information or the second interference phase information and the median. For instance, if the phase difference of the first interference phase information and the second interference phase information is 90°, as shown inFIG. 11(c), the phase controller760calculates the median of the first interference phase information and the second interference phase information. That is, the phase controller760calculates the median having a phase difference 45° with the first interference phase information or the second interference phase information. And the phase controller760calculates a rotation value for controlling the phase difference of the first user phase information to be 90° in complex space. Alternatively, the phase controller760calculates a rotation value for controlling the phase difference of the second user phase information and the median to be 90° in complex space. At this time, the phase controller760can calculate a rotation value like Math Figure 12.

The interference cancellation procedure performed in the communications system having such configuration is illustrated.

FIG. 12is a flowchart illustrating a interference cancellation procedure in a communications system according to another exemplary embodiment of the present invention.

Referring toFIG. 12, in the interference cancellation procedure of the present embodiment, the transmitter700determines user phase information (911). The transmitter transmits a user signal through the user phase information (913). At this time, the transmitter700transmits OSC1for the first receiver500through the first user phase information. Moreover, the transmitter700transmits OSC2for the second receiver600through the second user phase information. That is, the transmitter700controls the phase difference of the first user phase information and the second user phase information to be 90°, and transmits the OSC1and the OSC2. Thereafter, when receiving the OSC1, the first receiver500detects the first user phase information of the OSC1(915). Here, although not shown, the first receiver500can receive the OSC2, independently of the OSC1, and can receive the first interference signal of other transmitter800. At this time, when receiving the first interference signal, the first receiver500detects the first interference phase information of the first interference signal at step915. Similarly, when receiving the OSC2, the second receiver600detects the second user phase information of the OSC2(917). Here, although not shown, the second receiver600can receive the OSC1, independently of the OSC2, and can receive the second interference signal of other transmitter800. At this time, when receiving the second interference signal, the second receiver600detects the second interference phase information of the second interference signal at step917. Then, the first receiver500and the second receiver600individually transmit a feedback signal that respectively includes the first user phase information, the first interference phase information, and the second user phase information, the second interference phase information (919). And then, when receiving a feedback signal, the transmitter700normalizes user phase information (921). That is, the transmitter700normalizes the first user phase information and the second user phase information into a single value. The transmitter700calculates a rotation value for separating the user phase information from the median of the first interference phase information and the second interference phase information by a preset difference (923). At this time, the transmitter700calculates a rotation value for controlling the phase difference of the user phase information, i.e., the first user phase information or the second user phase information and the median to be 90° in complex space. The transmitter700changes the first user phase information and the second user phase information by using a rotation value (925). That is, the transmitter700respectively rotates the first user phase information and the second user phase information in complex space by rotation value. Moreover, the transmitter700transmits the OSC1according to the first user phase information, transmits the OSC2according to the second user phase information (927). Finally, when receiving the OSC1, the first receiver500eliminates interference (929). That is, the first receiver500can eliminate the first interference signal, and can eliminate the OSC2. At this time, the first receiver500rotates the first user phase information, the second user phase information, and the first interference phase information to eliminate interference. Here, since the phase difference of the first user phase information and the first interference phase information, and the first user phase information and the second user phase information are 90° respectively, the first receiver500can completely eliminate the size of the first interference signal and the OSC2while maintaining the size of the OSC1.

And, when receiving the OSC2, the second receiver600eliminates interference (931). That is, the second receiver600can eliminate the second interference signal, and can eliminate the OSC1. At this time, the second receiver600rotates the first user phase information, the second user phase information, and the second interference phase information to eliminate interference. Here, since the phase difference of the second user phase information and the second interference phase information, and the second user phase information and the first user phase information are 90° respectively, the second receiver600can completely eliminate the size of the second interference signal and the OSC1while maintaining the size of the OSC2. In the meantime, in the above-described embodiments, it was illustrated that transmitter uses a feedback signal of receiver to change user phase information. However, it is not limitative. That is, even when transmitter does not use a feedback signal, the present invention can be implemented. Therefore, transmitter does not need to receive user phase information and interference phase information through feedback signal in receiver. For instance, transmitter obtains an arbitrary rotation value in every TDMA frame, so that it can rotate user phase information by rotation value in complex space. In other words, transmitter randomizes the phase difference of the user phase information and the interference phase information, so that it can suppress the operation of the interference signal in receiver.

According to the present invention, in the communications system, transmitter can suppress the operation of the interference signal in receiver. That is, as transmitter changes phase information of user signal in complex space, receiver can completely eliminate interference signal. Accordingly, the link performance between transmitter and receiver can be improved in the communications system. Accordingly, the communications quality between transmitter and receiver can be improved in the communications system, and the communications range can be extended.