KR100438444B1 - Method for allocation frequency band in mobile telecommunication system - Google Patents

Abstract

According to the present invention, a channel frequency allocation apparatus of a transmission apparatus of a wireless communication system includes local oscillators for generating local frequencies for allocating one transmission channel using at least two non-contiguous frequency bands, and the local oscillator. And mixers for mixing the input signals to the corresponding local frequencies, and numbers corresponding to the mixers, respectively, and frequency-converted signals from among the corresponding mixed signals. The filter includes a filter for filtering, an adder for adding the outputs of the filters and outputting the output as a transmission signal, and a switch for distributing the input signals at a period corresponding to the number of the local oscillators and outputting them to the mixers.

Description

Frequency band allocation device and method in wireless communication system {METHOD FOR ALLOCATION FREQUENCY BAND IN MOBILE TELECOMMUNICATION SYSTEM}

The present invention relates to a frequency band allocation apparatus and method of a wireless communication system, and more particularly, to a frequency allocation apparatus and method capable of removing direct current components.

In the conventional wireless communication system, one frequency channel is configured as a continuous frequency band as shown in FIG. 1, and in order to configure N frequency channels, the entire frequency band is divided by N. When the frequency band is allocated as described above, in order to demodulate a signal carried on one channel, the receiver of the wireless communication system performs a frequency down conversion by a carrier frequency to form a baseband signal. Demodulate after making.

In general, a receiver of a communication system uses a frequency converter to frequency down convert a received frequency. The frequency converter includes a heterodyne method and a direct conversion method. The heterodyne method is a method in which a received signal is first lowered to an intermediate frequency band and then converted into a baseband signal through a complex mixer. However, since the heterodyne scheme includes several components for an RF circuit and it is impossible to integrate these components on a single chip, an attempt to integrate all components on a single RF chip using the direct conversion scheme has recently been made. Is being done.

Unlike a heterodyne receiver, a direct conversion receiver converts an RF signal directly into a baseband signal without an intermediate frequency conversion process. Therefore, the receiver using the direct conversion method is also called a zero-IF receiver or a homodyne receiver.

2 shows a configuration of a receiver using the direct conversion method according to the prior art.

Referring to FIG. 2, a preselection filter 211 passes a signal in a frequency band including all frequency channels that can be used by filtering a received signal received through an antenna. The low noise amplifier (LNA) 213 amplifies and outputs the signal from the preselection filter 211. The local oscillator 223 generates a predetermined carrier signal according to a desired frequency channel and a 90 degree phase shifted signal of the carrier. That is, the local oscillator 223 generates a frequency signal for using a predetermined frequency channel. Multipliers 214 and 215 multiply the signal from the low noise amplifier 213 with the carrier and 90 degree phase shifted signals to produce baseband signals of a desired frequency channel. The automatic gain amplifiers 216 and 217 amplify and output the signals from the multipliers 214 and 215 to a predetermined level. Low pass filters (LPFs) 218 and 219 filter out the output signals of the corresponding auto gain amplifiers 218 and 219, respectively, to remove interference other than the desired channel. The analog to digital converters 220 and 221 convert the output signals of the corresponding low pass filters 218 and 219 into digital signals through sampling, quantization, and the like, respectively. A digital signal processor (DSP) 222 demodulates the signals from the analog-to-digital converters 220 and 221 by digital hardware.

As described above, since the direct conversion method does not use an IF frequency, an external IF SAW filter is not required, and since an image frequency does not exist, an image removal filter does not exist. You do not need to use an Image Rejection Filter. As such, external circuits, which prevent the one-chip transceiver of the communication system from being used, are not used, thereby making the circuit of the receiver more compact. And because of this, the price of the equipment can be lowered, making it a factor that has attracted a lot of people now.

However, there are some technical obstacles in implementing such a direct conversion receiver, which include DC offsets, I / Q mismatch, and even-order distortion. Even-order distortion, flicker noise, and LO leakage of local signals. Although many obstacles have been solved among the above obstacles, the DC offset problem is still being studied. That is, when the direct conversion method is used, since the input ports of the local oscillator and the input ports of the mixer and the low noise amplifier are not completely separated, the inputs of the local oscillator are mixed with the other input ports so that the signals of the local oscillator and the inband Self-mixing phenomenon due to in-band interference appears. Thus, an unwanted DC offset occurs in the downconverted baseband signal.

Specifically, the DC offset of the direct conversion receiver is as follows.

First, because the isolation between the local signal LO of the quadrature mixer and the input RF signal is not perfect, a strong local signal LO is also present at the RF input terminal of the mixer. LO Leakage). The local leakage signal (LO Leakage) applied to the RF terminal of the mixer is multiplied by the local signal LO to produce a DC component, which is called a DC offset.

The DC offset not only lowers the signal to noise ratio (SNR) of the signal by operating the DC value itself as noise, but also saturates the baseband amplifier. have. In this case, since the gain of the amplifier drops considerably, the received signal is not amplified to a sufficient level, which in turn increases the error rate of the signal.

Another representative DC offset is the DC offset caused by the interference applied to the receiver. When a strong jam is applied to the mixer input terminal of the receiver, the signal magnitude coupled to the LO port of the mixer may generate a significant DC component at the IF stage after frequency mixing. .

3A and 3B are diagrams for explaining generation of DC offset in the two cases described above. FIG. 3A is a diagram for explaining DC offset generated by a local signal, and FIG. 3B is generated by strong interference. It is a figure for demonstrating DC offset. The process of generating DC offset will be examined through the formula.

First, referring to FIG. 3A, the RF receiver 111 receives an RF signal input through an antenna, and the amplifier 113 amplifies the weak received RF signal. The mixer 115 mixes the amplified RF signal and the local signal generated by the local oscillator 121, and the filter 117 outputs the down-converted signal by low-pass filtering the baseband signal from the mixed signal.

In this case, when the self-mixing DC offset of the local signal LO is expanded, the local signal LO generated by the local oscillator 121 may be substituted. The local leakage signal (LO leakage) input to the RF terminal of mixer 115 is If possible, the output of the mixer 115 can be expressed as Equation 1 below.

In Equation 1 Is the DC component and remains at the output of filter 117 to operate as noise.

Secondly, referring to FIG. 3B, in the case of a self-mixing DC offset caused by a strong interferer input through an antenna, the interference at the input terminal of the mixer 115 may be considered. The local signal LO is coupled to the local oscillator 121. In this case, the output of the possible mixer 115 can be expressed as Equation 2 below.

In Equation 2 Is a DC component (DC term) and remains after LPF to operate as noise.

As described above, the most economical method for the frequency down conversion in the receiver of the wireless communication system is a direct conversion method. However, when the frequency down conversion is performed on the channel of the frequency band allocated by the method as shown in FIG. 1 using the direct conversion method, as shown in FIGS. 3A and 3B, a local oscillator and an in-band interferer A self-mixing phenomenon occurs due to an in-band interferer, and a DC offset is generated in the frequency down-converted signal. Such a DC offset increases the magnitude of the desired signal and detracts from the linear religion of the device, resulting in poor final demodulation performance. Therefore, it is possible to consider notch filtering which removes the DC component immediately after down conversion. In general, modulation schemes are difficult to apply because they contain the most information at the position where the DC component occurs.

In order to prevent such a phenomenon, a frequency spectrum as shown in FIG. 4 is formed by using a modulation scheme that removes a DC component such as frequency shift keying (FSK) or quadrature-amplitude modulation (QAM). There is also. In this case, since the notch filtering may be performed to remove the DC component after the direct conversion, the problem caused by the DC offset may be solved. However, because the frequency offset occurs in the receiver, the original frequency spectrum is distorted after notch filtering. In other words, when the frequency band is allocated as shown in FIG. 4, the DC component may be DC-free if there is no frequency offset in the receiver. However, in practice, the frequency offset always occurs, so when using the direct conversion method, the DC offset occurs. Therefore, in order to remove the DC offset as described above, a certain amount of margin may be provided in the DC portion in advance so that signal distortion does not appear after notch filtering even if a certain frequency offset occurs. do.

Accordingly, an object of the present invention is to provide an apparatus and method for frequency upconverting a transmission signal modulated by a transmitter so that a DC component can be removed during frequency downconversion in a receiver of a wireless communication system.

Another object of the present invention is to provide an apparatus and method for allocating one frequency channel using two non-contiguous frequency bands in a wireless communication system.

In order to achieve the above object, a channel frequency allocation apparatus of a transmission apparatus of a wireless communication system according to an embodiment of the present invention generates local frequencies for allocating one transmission channel using at least two non-contiguous frequency bands. Local oscillators, mixers each having a number corresponding to each of the local oscillators, and mixers each mixing an input signal with the corresponding local frequency, and mixers having a number corresponding to each of the mixers, respectively, and a corresponding mixed signal, respectively. Among them, a filter for filtering a frequency up-converted signal, an adder for adding the output of the filter and outputting it as a transmission signal, and a signal input at a period corresponding to the number of local oscillators are divided and output to the mixers, respectively. It is characterized by consisting of a switch to.

1 is a diagram illustrating a method for allocating a frequency band in a conventional wireless communication system.

2 is a view showing the configuration of a receiver using a direct conversion method according to the prior art.

3A and 3B are views for explaining an operation in which a DC component is generated during a frequency down conversion in a wireless communication system using the frequency band allocation method as shown in FIG.

4 is a view for explaining a frequency band allocation method for removing a DC component in a conventional wireless communication system,

5 is a view for explaining a method of allocating a frequency band in a wireless communication system according to an embodiment of the present invention;

6 is a diagram illustrating a frequency spectrum of a channel according to a frequency allocation method in a wireless communication system according to an embodiment of the present invention;

7 is a diagram showing the configuration of a transmitting apparatus of a wireless communication system to which a frequency band is allocated according to an embodiment of the present invention;

8 is a diagram showing another configuration of a transmitter of a wireless communication system to which a frequency band is allocated according to an embodiment of the present invention.

9 is a block diagram of a receiving apparatus of a wireless communication system according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be noted that the same components in the figures represent the same numerals wherever possible.

The embodiment of the present invention completely removes the DC component from the modulated signal by configuring one channel with two non-contiguous frequency bands in the wireless communication system, and thus, the frequency downconversion using the direct conversion method. The receiver can be economically configured.

To this end, an embodiment of the present invention allocates a frequency band as shown in FIG. That is, in the embodiment of the present invention, in order to configure N channels, the entire frequency band is divided into 2N channels, and the two channels are collected to form one channel. Therefore, when the frequency band is allocated as shown in FIG. 5, one channel is composed of two frequency bands as shown in FIG. 6 is a diagram illustrating a channel frequency spectrum in a transmitter using a frequency band allocation method according to an embodiment of the present invention.

In order to generate the frequency spectrum as shown in FIG. 6, two independent spectra are generated by a general modulation method, and each of them is up-converted into an intermediate frequency band, and then the image is filtered. To remove the desired spectrum. In this case, since another channel may enter the middle empty frequency band of FIG. 6, the transmitter should use a bandpass filter (BFP) that outputs only a desired band and attenuates a high frequency band and a low frequency band.

FIG. 7 illustrates a configuration of a transmitter for generating a transmission signal having a channel frequency spectrum as shown in FIG.

Referring to FIG. 7, the coded data from the encoder is applied to the switch 610 and distributed to the first modulator 621 and the second modulator 631, respectively. In this case, the unit of the encoded data to be distributed may be set as necessary. The switch 610 may be implemented as a demultiplexer or a serial-to-parallel converter. The first modulator 621 modulates the coded data switched by the switch 610 and outputs the modulated data as shown in 651. The first mixer 623 mixes the output of the first modulator 621 with the first local signal output from the first local oscillator 627. The first local signal is a local signal for generating a frequency signal of channel1. Accordingly, the first mixer 623 mixes the first modulated signal and the first local signal to generate a signal such as 653. Occurs. Then, the first filter 625, which is a band filter, filters the band of the first modulated signal + the first local signal for up-converting the frequency in the frequency signal as shown in 653 and outputs the same as 655.

In addition, the second modulator 631 modulates the coded data switched by the switch 610 and outputs the modulated data as shown in FIG. 661. The second mixer 633 mixes and outputs the output of the second modulator 631 with the second local signal output from the second local oscillator 637. The second local signal is a local signal for generating a frequency signal of channel1. Accordingly, the second mixer 633 mixes the second modulated signal and the second local signal to generate a signal such as 663. Occurs. Then, the second filter 635, which is a band filter, filters the band of the second modulated signal + the second local signal for up-converting the frequency in the frequency signal of 663 and outputs the same as 665.

At this time, the first local frequency and the second local frequency are set to have a channel frequency spectrum as shown in FIG. Therefore, the signal mixed up in the first mixer 623 and the second mixer 633 has a frequency difference between the channel 1 and the channel 2, and the first filter 625 and the second filter 635 connected to the corresponding mixer respectively correspond. The frequencies of the upper band are filtered by the mixed signals output from the mixers 623 and 633. Therefore, the transmission signal finally output through the adder 640 has a channel frequency spectrum such as 670.

As described above, the transmission apparatus of the wireless communication system configures and transmits one transmission channel by using two or more frequency bands that are not continuous.

FIG. 8 shows another configuration of a transmitter for generating a transmission signal having a channel frequency spectrum as shown in FIG. FIG. 8 has a structure in which the first modulator 621 and the second modulator 631 connected to the rear end of the switch 610 are configured as one modulator 670, and the switch 610 is connected to the rear end of the modulator 610. . Operation of the transmitter having the configuration as shown in FIG. 8 proceeds similarly to FIG.

9 is a block diagram of a receiving apparatus of a wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 9, a preselection filter 911 passes a signal of a frequency band including all frequency channels that can be used by filtering a received signal received through an antenna. The low noise amplifier (LNA) 913 amplifies and outputs a signal from the preselection filter 911. The local oscillator 925 generates a predetermined carrier signal according to a desired frequency channel and a 90 degree phase shifted signal of the carrier. Multipliers 914 and 915 multiply the signal from the low noise amplifier 913 with the carrier and 90 degree phase shifted signals to generate a baseband signal of a desired frequency channel. That is, it generates one channel signal consisting of two frequency bands according to the present invention. Nach filters 916 and 917 notch the DC offset by self-mixing with the DC portion, which is the other channel component in the center, from the corresponding multipliers 914 and 915, respectively. filter and remove it. The automatic gain amplifiers 918 and 919 amplify and output the signals from the corresponding elimination filters 914 and 915 to a predetermined level, respectively. Low pass filters (LPFs) 920 and 921 filter out the output signals of the corresponding auto gain amplifiers 918 and 919, respectively, to remove interference other than the desired channel. Analog to Digital Converters (ADCs) 922 and 923 convert the output signals of the corresponding low pass filters 920 and 921 into digital signals through sampling, quantization, and the like, respectively. A digital signal processor (DSP) 924 performs digital demodulation by processing signals from the analog-to-digital converters 922 and 923 with digital hardware.

As described above, the receiving apparatus down-converts a frequency by a direct conversion method in order to demodulate a modulated channel according to the present invention, and then removes a DC portion, which is another channel component in the center, by simple AC coupling. Baseband signal processing is possible.

As described above, the transmitting apparatus of the wireless communication system constitutes one transmitting channel composed of two or more frequency bands which are not continuous, and the receiving apparatus lowers the frequency by a direct conversion method in order to demodulate the modulated channel in the transmitting apparatus. After removing the DC part, which is another channel component in the middle, by AC coupling method, baseband signal processing is performed. Therefore, the frequency band allocation as described above makes it very easy to apply the frequency down converter to the receiver by the direct conversion method, so that the RF circuit can be configured very simply, thereby making it possible to construct an economical receiver.

Claims (8)

In the channel frequency allocation apparatus of the transmitter of the wireless communication system, Local oscillators generating local frequencies for allocating one transmission channel using at least two non-contiguous frequency bands, Mixers each provided with a number corresponding to the local oscillators, each mixing an input signal with the corresponding local frequency; Filters provided with a number corresponding to the mixers, respectively, and filter the frequency-converted signal among the corresponding mixed signals; An adder for adding the outputs of the filters and outputting them as a transmission signal; And a switch for distributing an input signal at a period corresponding to the number of the local oscillators and outputting the signals to the mixers, respectively. In the channel frequency allocation apparatus of the transmitter of the wireless communication system, Local oscillators for generating first and second local frequencies for allocating one transmission channel using non-contiguous first and second frequency bands; First and second mixers for mixing an input signal into the corresponding first and second local frequencies, respectively; First and second filters for filtering a frequency up-converted signal during the output of the first and second mixers, respectively; An adder for adding the outputs of the first and second filters and outputting them as a transmission signal; And a switch for distributing the signal and outputting the signal to the first and second mixers, respectively. 3. The apparatus as claimed in claim 2, further comprising first and second modulators for modulating the switched transmission signal respectively connected to the front end of the mixer. 3. The apparatus as claimed in claim 2, further comprising a modulator connected to the front end of the switch to modulate the input signal. A channel frequency allocation method of a transmitting apparatus of a wireless communication system having local oscillators for generating local frequencies for allocating one transmission channel using at least two non-contiguous frequency bands, Distributing a signal input at a period corresponding to the number of local oscillators; Mixing the divided input signals into corresponding local frequencies, respectively; Filtering the frequency up-converted signal among the mixed signals, And adding the frequency up-converted signal and outputting the signal as a transmission signal. In the transmitter of a wireless communication system, To divide the total number of available frequency bands into 2N to form N frequency channels, to allocate at least two non-contiguous frequency bands to one frequency channel, to use a given one of the frequency channels A local oscillator for generating a frequency signal, A mixer for mixing a transmit baseband signal and the frequency signal from the local oscillator; And an adder for outputting the mixed signal from the mixer as a transmission signal. In the receiving apparatus of the wireless communication system for dividing the total available frequency band into 2N to configure N frequency channels, and using at least two non-contiguous frequency bands as one frequency channel, A local oscillator for generating a frequency signal for demodulating a given one of said frequency channels; A mixer for mixing a received radio frequency signal with the frequency signal from the local oscillator to generate a received baseband signal; And a notch filter for removing a direct current component existing between two frequency bands constituting the given frequency channel in the baseband signal from the mixer and a direct current offset due to self-mixing. Device. delete