KR100902017B1 - Transmitter and method for subcarrier scaling in mobile station of ofdma - Google Patents

Abstract

A transmitter and method for subcarrier scaling in mobile station of OFDMA are provided to adjust the size of subcarrier according to the number of sub-carrier. The transreceiver of the OFDMA terminal are comprised of a modem unit and a radio frequency process part(110). The modem unit comprises a frequency domain processor(120), a controller(130), a sub carrier assignment part(140a, 140b), a size control unit(150), a transmission unit(160) and a receiver(170). The radio frequency process part adjusts the electricity of the transmission signal to a low lever and amplifies it. The sub carrier assignment part(140a) assigns a sub carrier wave to the signal to be transmitted. The sub carrier assignment part(140b) assigns the sub carrier wave to the signal received from the receiver. The size control unit increases the electricity of the signal to be transmitted according to the scaling control value. The transmission unit transmits the signal transformed as analog signal to the radio frequency process part.

Description

Transmission apparatus and method for adjusting subcarrier size in orthogonal frequency division multiple access terminal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to data transmission / reception in a terminal of an orthogonal frequency division multiple access method. In particular, the present invention relates to a transmission apparatus for adjusting the size of subcarriers used in a transmission unit of a modem unit according to the number of subcarriers allocated for uplink data transmission from a base station. And to a method.

In a communication environment of Orthogonal Frequency Division Multiplexing Access (hereinafter, referred to as OFDMA), a base station transmits allocation information of subcarriers for uplink data transmission to each terminal through downlink data. Accordingly, the terminal receiving the downlink data checks the allocation information of the received downlink data, allocates as many subcarriers as the number allocated to the downlink data, and transmits the uplink data. The structure of a transmitting / receiving device in an OFDMA terminal for data transmission / reception is as shown in FIG.

Referring to FIG. 1, a transmitting / receiving apparatus in a terminal includes a modem unit for processing a digital signal and a radio frequency processor (RF unit) 10 for processing an analog signal.

The modem unit includes an OFDM communication transmitter / receiver 20 and 30 for processing digital signals, a carrier processor 41 and 42 and a frequency domain processor 50 for processing data transmitted or received on a subcarrier allocated by a base station. It is composed. The transmitter / receiver 20 and 30 are generally well known and a description of a specific structure will be omitted.

The radio frequency processor 10 includes a power amplifier for amplifying a transmission signal and controls the power amplifier according to a control value P _{Tx_Amp} . Herein, the control value P _{Tx_Amp} is a transmission power value indicated by the base station.

An OFDMA terminal having such a structure has a very variable number of subcarriers allocated from a base station for uplink data transmission, and generates a standardized transmission signal regardless of the number of subcarriers and transmits it to the base station. For example, when the size of the fast Fourier transform (FFT) used for OFDM modulation is 1024, the number of cases in which the base station can allocate subcarriers to each terminal is 1 to 1024. If 840 and 24 of the 1024 subcarriers are allocated, the output signal of the terminal is shown as shown in FIGS. 2A and 2B. 2A and 2B are the 'Inphase' or 'Quadrature' signal among the FFT outputs.

As shown in FIG. 2A, the signal using the 840 subcarriers is distributed between the digital-analog controller (DAC) input / output precursors, but when the signal using the 24 subcarriers is transmitted without adjustment, as shown in FIG. 2B. It can be seen that it is distributed only in about 1/6 intervals. When the DAC bit size used is 10 bits, when transmitting a signal assigned 24 subcarriers, only about 7.5 bits of the 10 bits of the DAC are used, and about 2.5 bits are not used, and thus, the DAC is not fully utilized.

Therefore, in the OFDMA communication environment, even if the number of subcarriers allocated for uplink data transmission from the base station is small, the present invention can use the entire bit interval of the digital-analog controller (DAC) according to the allocated number of subcarriers. An apparatus and method for transmitting a subcarrier are provided.

In order to achieve the above object of the present invention, a transmission apparatus for subcarrier size adjustment in an orthogonal frequency division multiple access type terminal includes: a control value and a size control value of a subcarrier according to the number of subcarriers to be allocated to a signal to be transmitted; A modem unit for obtaining a correction control value according to the control unit, adjusting a size of a subcarrier allocated to the signal to be transmitted according to the scaling control value, and outputting a transmission signal to which the adjusted subcarrier is allocated; And a radio frequency processing unit for adjusting the power magnitude of the output transmission signal by the correction control value, amplifying the transmission signal with the adjusted power magnitude, and transmitting the amplified transmission signal to a base station.

In addition, the transmitter for subcarrier size adjustment in the orthogonal frequency division multiple access method terminal for achieving the objects of the present invention, obtains the size control value of the subcarrier according to the number of subcarriers to be allocated to the transmission signal, A control unit for obtaining a correction control value according to the scaling control value; A scaler for adjusting a size of a subcarrier allocated to the signal to be transmitted according to the scale control value; A transmitter for digitally processing a signal to which the adjusted subcarrier is allocated and outputting the digital signal as an analog transmission signal; And a radio frequency processing unit for adjusting the power magnitude of the transmission signal output from the transmission unit by the correction control value, amplifying the transmission signal with the adjusted power magnitude, and transmitting the amplified signal to the base station.

On the other hand, in the orthogonal frequency division multiple access method terminal for adjusting the subcarrier size in order to achieve the objects of the present invention, (a) the signal to be transmitted according to the maximum number of subcarriers retrieved using the allocation information received from the base station Allocating the subcarriers to; obtaining a correction control value of the subcarrier and a correction control value according to the scaling control value according to the found maximum number of subcarriers; (c) adjusting a size of a subcarrier allocated to the signal to be transmitted according to the scaling control value; (d) digitally processing the signal to which the scaled subcarrier is assigned and outputting the analog signal as a transmission signal; (e) adjusting a power magnitude of the transmission signal output from the transmitter by the correction control value; And (f) amplifying the transmission signal at the adjusted power level and transmitting the amplified signal to a base station.

Therefore, the present invention can reduce the power amplification of the radio frequency processing unit of the analog stage by increasing the power of the transmission signal by scaling in the modem which is the digital signal stage in the transmitting device in the OFDMA terminal, that is, increasing the amplitude. When a smaller subcarrier is used compared to the available subcarriers, the amplitude of the uplink signal may be solved relatively, and the power consumption of the analog stage, which consumes a large amount of power consumption, may be reduced.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, if it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In the embodiment of the present invention will be described by applying the terminal in the OFDMA communication environment, the terminal is assigned the number of subcarriers from the base station, the subcarrier size in the general transmitter to adjust the size of the subcarriers according to the assigned number of subcarriers Includes a transmitter with a new structure that adds functionality for coordination. In the embodiment of the present invention, the transmission apparatus of the new structure will be described mainly, and the reception apparatus of the terminal does not belong to the scope of the present invention, but for convenience of description of the transmission apparatus, a general OFDMA receiver is applied. It will be briefly described.

Next, a structure of a transmitting / receiving device in a terminal according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a diagram illustrating a structure of a transmitting / receiving device in an OFDMA terminal according to an embodiment of the present invention.

Referring to FIG. 3, the transmission / reception apparatus may be largely divided into a modem unit and a radio frequency processor 110.

The modem unit may include a frequency domain processor 120, a controller 130, a subcarrier allocator 140a and 140b, a size adjuster 150, a transmitter 160, and a receiver 170. The control unit 130 may be included in the modem unit to perform overall control, or may be formed outside the modem unit to perform overall control of the modem unit.

The radio frequency processor 110 includes a power amplifier, and amplifies by adjusting the power of the transmission signal output from the modem unit according to the correction control value received from the controller 130. That is, the radio frequency processor 110 amplifies the power of the transmission signal by lowering the size of the subcarrier increased by the size adjusting unit 150.

The controller 130 searches for the number of subcarriers to be transmitted for each OFDMA symbol within a transmission time allocated to the terminal by referring to the allocation information of the subcarriers received from the base station. After retrieving the maximum number of subcarriers to be allocated to the signal to be transmitted, related allocation information is transmitted to the subcarrier assignment unit 140a to allocate the maximum number of subcarriers to the signal. The controller 130 obtains a scaling control value according to the number of subcarriers to be allocated to the signal to be transmitted by referring to a preset lookup table, obtains a correction control value according to the scaling value, and transmits it to the radio frequency processor 110. Is authorized. The correction control value is a value for controlling power amplification of the transmission signal, and a detailed calculation method will be described later. The scaling control value may be a multiplication value multiplied by a complex value of the subcarrier or a shift value for moving the subcarrier in units of bits.

The subcarrier allocator 140a allocates a subcarrier to the signal to be transmitted according to allocation information received from the control unit 130, that is, the maximum number of subcarriers retrieved from the transmitting side, and the subcarrier allocator 140b receives the receiver 170. Assigns a subcarrier to the received signal.

The size adjusting unit 150 is formed between the subcarrier allocating unit 140a and the transmitting unit 160, and receives the size control value from the control unit 130 to allocate the size of the subcarrier allocated by the subcarrier allocating unit 140a. Is adjusted according to the received scaling control value to increase the power of the signal to be transmitted. The scaler 150 is formed of a multiplier when receiving a multiplication value using the scale control value and using a multiplication method, and is configured as a shifter when receiving a shift value using the scale value and using a shift method. Can be. Such a multiplication method and a moving method will be described in detail below.

The transmitter 160 includes a fast inverse Fourier transformer 161, a parallel / serializer 162, a cyclic prefix (CP) adder 163, a time domain processor 164, and a digital-to-analog converter (DAC) 165. And converts the digital signal into an analog signal by processing the signal output from the scale adjusting unit 150 and converting the digital signal into an analog signal, and then transmitting the converted analog transmission signal to the radio frequency processing unit 110.

The receiver 170 may include a fast Fourier transformer 171, a parallel / serializer 172, a cyclic prefix remover 173, a time domain processor 174, and an analog-to-digital converter (ADC) 175. And digitally process the signal received from the radio frequency processing unit 110 and transmit the digital received signal to the subcarrier allocation unit 140b.

In order to transmit a base station by adjusting the size of a transmission signal in a transmitting / receiving apparatus in an OFDMA terminal having such a structure, it is necessary to calculate a scaling value for the number of subcarriers used as shown in Table 1 below. Table 1 shows an example of using a subcarrier in multiples of 24. Table 1 below calculates the total power of OFDMA symbols for each multiple, and shows the difference when the number of subcarriers to which the symbol power can be allocated is maximum compared to the total power of OFDMA symbols used.

Referring to Table 1, OFDMA power using 24 subcarriers is -15.44 [dB] smaller than OFDMA power using 840 subcarriers. Therefore, the transmitted signal also becomes small. Accordingly, when the value transmitted to the subcarrier, that is, the optimizing scaling value is about 5.9 times, the signal power is increased to use the entire bit section of the DAC 165.

In Table 1, the controller 130 controls the number of subcarriers in the first column and the scaling value in the case of moving in the unit of an optimal scaling value or a bit unit of the fifth column. Approximated scaling value can be set in the lookup table in advance. Using the preset values, the scaling power value and the relative difference value of amplitude are small. Able to know.

In Table 1, when the first column and the fourth column are used as a lookup table, a method of multiplying a scaling control value may be applied.

For example, when the output of the subcarrier processing unit 140a is X _k = X _{k , I} + X _{k , Q} , and the scaling control value is a multiplication value a, the control unit 130 performs the a < Resize by multiplying real and imaginary parts as in 1>.

X _{k , adj} = aX _{k , I} + jaX _{k , Q}

In the <Equation 1> k is the value of the sub-carrier index (index), and, X _k, X _k and _{I, Q} is a complex value a real part (or Inphase) and the imaginary part _k of X (or Quadrature).

Meanwhile, when using the first column and the fifth column as the lookup table in Table 1, a method of moving bit by bit may be applied. This method can achieve the same effect as the multiplication of the exponents of two.

Table 2 below shows increased power when left shifted by 1 to 3 bits, which is a multiple of about 6 [dB]. Therefore, simply resizing can be approximated by moving left as shown in Equation 2 below.

Left shift [bit] Increased power [dB] One 6.020599913 2 12.04119983 3 18.06179974

X _{k , adj} = (X _{k , I} << b) + j (X _{k , Q} << b)

In Equation 2, A << b means an operation of bit shifting the complex value A to the left by the shift value (b bit). Therefore, the controller 130 adjusts the power level of the signal by moving the complex values X _{k, I} , X _{k, and Q} of the output of the subcarrier allocation unit 140a by b, respectively.

Next, a method for adjusting the size of a signal to be transmitted to a base station using such a multiplication or moving method will be described in detail with reference to the accompanying drawings.

4 is a diagram illustrating a method for scaling in an OFDMA terminal according to an embodiment of the present invention.

Referring to FIG. 4, in step 210, the terminal searches for the maximum number of subcarriers using the allocation information received from the base station through the control unit 130 of the transmitting apparatus, and searches for the maximum subcarrier found through the subcarrier allocation unit 140a. The subcarriers are allocated to the transmitted signal according to the number.

In step 220, the terminal obtains a correction control value of the subcarrier and a correction control value according to the scaling control value according to the maximum number of subcarriers found through the controller 130. The scale control value and the correction control value calculation will be described in detail below.

Thereafter, in step 230, the terminal adjusts the size of the subcarrier allocated to the signal to be transmitted through the size adjusting unit 150 according to the obtained size control value, and then transmits the signal to which the sized subcarrier is allocated. To send).

Accordingly, in step 240, the terminal processes the signal transmitted from the size adjusting unit 150 as a digital signal and outputs the analog signal as a transmission signal. That is, the transmitter 160 inversely transforms the signal by the fast inverse Fourier transformer 161 and then converts the signal into a serial signal by the parallel / serial converter 162. Then, the transmitter 160 adds a CP to the converted serial signal through the CP adder 163, converts the time domain processor 164 into the time domain, and finally converts the analog signal from the DAC 165 into an analog signal. The converted signal is transmitted to the RF processor 110 as a transmission signal.

Then, in step 250, the terminal receives an analog transmission signal from the transmitter 160 in the RF processor 110 and adjusts the power level of the transmission signal to be lower by the correction control value received from the controller.

In step 260, the terminal amplifies the transmission signal with the adjusted power level through the radio frequency processor 110 and transmits the amplified signal to the base station. At this time, the power of the transmission signal output from the antenna of the radio frequency processor 110 should be in accordance with the value indicated by the base station regardless of the size adjustment. That is, the transmission signal can be seen that the increased power in the modem unit is the power level is lowered again in accordance with the correction control value in the radio frequency processing unit 110 will eventually follow the value indicated by the base station.

In the method of adjusting the size of the subcarrier, a control unit operation of the transmitter for obtaining the scaling control value and the correction control value will be described in more detail with reference to the accompanying drawings.

5 is a diagram illustrating an operation of a controller of a transmitting apparatus according to an exemplary embodiment of the present invention.

Referring to FIG. 5, in step 310, the controller 130 of the transmitter of the terminal receives carrier allocation information from the base station, and in step 320, the controller 130 searches for the maximum number of subcarriers by referring to the subcarrier allocation information. Then, the allocation information related to the maximum number of subcarriers retrieved is transmitted to the subcarrier allocation unit 140a.

Then, in step 330, the controller 130 obtains a scaling control value using a preset lookup table, obtains a correction control value for controlling a power amplifier (not shown) of the radio frequency processing unit 110, and the radio frequency. Application to the processing unit 110. In this case, the scaling control value may be calculated using the multiplication or movement method, and thus values as shown in Table 1 may be obtained. In addition, the correction control value may be calculated using Equation 3 below.

In Equation 3, P _{Tx _ Amp} is a control value for controlling the power amplifier when the size of the subcarrier is not adjusted, and P _{Tx _ Amp , adj} is a control value for adjusting the size of the subcarrier. The control value that is controlled, that is, the correction control value, and the value P _s is a value obtained by multiplying -1 by a value corresponding to the third column of the <Table 1> when the multiplication method is applied, and when the shift method is applied, the < This is the value for column 6 in Table 1>. For example, when 24 subcarriers are used, a 15.44 [dB] signal is generated than when 840 subcarriers are used. Thus, the modem unit increases the magnitude of 'Inphase' and 'Quadrature' signal of each of 24 subcarriers by 5.9 times. This means that the modem unit amplified 15.44 [dB] in the transmission signal, so the 15.44 [dB] should be lowered in the amplification degree of radio frequency. Therefore, the correction control value (P _{Tx_Amp, adj)} is a _{P Tx _ Amp -15.44 [dB]} .

In operation 340, the controller 130 transmits the obtained scaling control value to the size adjusting unit 150. Accordingly, the scaler 150 increases the size of the subcarrier by the scale control value by applying the scale control value to the complex value of the subcarrier input from the subcarrier allocator 140a.

In step 350, the controller 130 applies the obtained correction control value to the radio frequency processor 110. Accordingly, the radio frequency processor 110 amplifies the output analog signal, that is, the transmission signal, and transmits the amplified signal to the base station. In this case, the RF processor 110 subtracts and amplifies the power of the transmission signal by the correction control value received from the controller 130.

When adjusting the size of the subcarrier of the signal to be transmitted to the base station through this process, the output of the FFT of the receiver is as shown in Figure 6c. This is the same as FIG. 6B attached, and looks the same when compared to the case where no scaling is performed as shown in FIGS. 6A and 6B. To be precise, the use of small subcarriers improves the signal quality, but the signal-to-noise ratio (SNR) of less than 35dB has little effect in a typical wireless communication environment. This is because the noise power is relatively larger than the improvement. 6A and 6B illustrate an FFT output of a receiver when transmitting a signal using 840 and 24 subcarriers after 10-bit DAC conversion.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

1 is a diagram showing the structure of a transmitting / receiving device in a typical OFDMA terminal;

2A and 2B illustrate signals generated in a time domain processor based on the number of subcarriers allocated by a general terminal;

3 is a diagram illustrating a structure of a transmitting / receiving apparatus in an OFDMA terminal according to an embodiment of the present invention;

4 is a diagram illustrating a method for scaling in an OFDMA terminal according to an embodiment of the present invention;

5 is a view illustrating an operation of a control unit of a transmitting device according to an embodiment of the present invention;

6A and 6B illustrate an FFT output of a receiving side when a signal using a subcarrier is not scaled;

6C is a diagram illustrating an FFT output of a receiving side when a signal using a subcarrier is scaled according to an embodiment of the present invention.

Claims (17)

Obtaining a scaling control value of the subcarrier and a correction control value according to the scaling control value according to the number of subcarriers to be allocated to the signal to be transmitted, adjusting the size of the subcarrier allocated to the transmission signal according to the scaling control value, A modem unit for outputting a transmission signal to which the adjusted subcarrier is allocated; And And a radio frequency processor for adjusting the power magnitude of the output transmission signal by the correction control value, amplifying the transmission signal with the adjusted power magnitude, and transmitting the amplified transmission signal to a base station. The size of the subcarrier means an amplitude, the transmitting device for adjusting the size of the subcarrier in the orthogonal frequency division multiple access method terminal. The method of claim 1, When the modem unit retrieves the maximum number of subcarriers using the allocation information received from the base station, the modem allocates the subcarriers to the transmitted signal by the maximum number of subcarriers found and obtains the size control value using a preset lookup table. Transmitter for subcarrier size adjustment in orthogonal frequency division multiple access method terminal, characterized in that. The method of claim 2, The modem unit obtains the scaling control value so that the transmission signal uses the entire bit section during digital-to-analog conversion, and increases the power of the transmission signal by adjusting the size of the allocated subcarrier according to the scaling control value. Transmitter for subcarrier size adjustment in orthogonal frequency division multiple access method terminal characterized in that the. The method of claim 2, The modem unit uses the scaling control value as a multiplication value, and multiplies the multiplication value by the real part and the imaginary part of the complex value of the assigned subcarrier to adjust the size of the subcarrier. Transmitter for subcarrier size adjustment in access terminal. The method of claim 2 The modem unit uses the scaling control value as a shift value in units of bits, and adjusts the size of the subcarrier by moving the complex value of the assigned subcarrier by the shift value. Transmitter for subcarrier size adjustment A control unit obtaining a scaling control value of the subcarrier according to the number of subcarriers to be allocated to a signal to be transmitted, and obtaining a correction control value according to the scaling control value; A scaler for adjusting a size of a subcarrier allocated to the signal to be transmitted according to the scale control value; A transmitter for converting a signal to which the adjusted subcarrier is allocated to an analog signal and outputting an analog transmission signal; And And a radio frequency processor for adjusting the power magnitude of the transmission signal output from the transmitter by the correction control value, amplifying the transmission signal with the adjusted power magnitude, and transmitting the amplified signal to a base station. The size of the subcarrier means an amplitude, the transmitting device for adjusting the size of the subcarrier in the orthogonal frequency division multiple access method terminal. The method of claim 6, Or a subcarrier assignment unit for allocating the subcarriers to the transmitted signal by the maximum number of subcarriers when the maximum number of subcarriers is searched by using the allocation information received from the base station. Transmission apparatus for adjusting subcarrier size in a mobile terminal. The method of claim 6, The size adjusting unit adjusts the size of the subcarrier by the size control value to increase the power of the signal to which the subcarrier is allocated to use the entire bit section during digital-to-analog conversion. Transmitter for subcarrier size adjustment The method of claim 6, The scaling unit is an orthogonal frequency division multiplexing unit which receives a multiplication value from the control unit by the scaling control value and multiplies the real part and the imaginary part of the complex value of the assigned subcarrier to adjust the size of the subcarrier. Transmitter for subcarrier size adjustment in access terminal. The method of claim 6 The size adjusting unit is a orthogonal frequency division multiple access method, characterized in that the mobile unit receives a shift value in units of bits as the scaling control value and adjusts the size of the subcarrier by moving the complex value of the assigned subcarrier by the shift value. Transmitter for subcarrier size adjustment in terminal. The method according to claim 1 or 6, The correction control value is a control value for controlling the power amplification of the transmission signal subtracted from the increased power value according to the size adjustment of the subcarrier for the subcarrier size adjustment in the orthogonal frequency division multiple access method terminal. Transmitting device. (a) allocating subcarriers to a signal to be transmitted according to the maximum number of subcarriers retrieved using the allocation information received from the base station; obtaining a correction control value of the subcarrier and a correction control value according to the scaling control value according to the found maximum number of subcarriers; (c) adjusting a size of a subcarrier allocated to the signal to be transmitted according to the scaling control value; (d) converting the signal to which the scaled subcarrier is allocated to an analog signal and outputting an analog transmission signal; (e) adjusting the power magnitude of the transmission signal output from the transmitter by the correction control value; And (f) amplifying and transmitting the transmission signal to the base station at the adjusted power level, The size of the subcarrier means an amplitude, characterized in that for the subcarrier size adjustment in the orthogonal frequency division multiple access method terminal. The method of claim 12, The scaling control value is obtained by using a preset lookup table and is a multiplication value of a subcarrier in an orthogonal frequency division multiple access type terminal, wherein the multiplication value is multiplied by the real part and the imaginary part of the complex value of the assigned subcarrier. Way for you. The method of claim 12, The scaling control value is obtained using a preset lookup table and is a shift value for shifting a complex value of the allocated subcarrier in units of bits. . The method of claim 12, The correction control value is a control value for controlling the power amplification of the transmission signal subtracted from the increased power value according to the size adjustment of the subcarrier for the subcarrier size adjustment in the orthogonal frequency division multiple access method terminal. Way. The method of claim 12, wherein step (c) comprises: Receiving a multiplication value with the scaling control value; And adjusting the size of the subcarrier by multiplying the received multiplication value by the real part and the imaginary part of the complex value of the assigned subcarrier, respectively. For sending. The method of claim 12, wherein step (c) comprises: Receiving a shift value in bits as the scaling control value; And And adjusting the size of the subcarriers by moving the allocated subcarriers by the received movement value.

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