KR20000025983A - Transmitter apparatus of code division multiple access system - Google Patents

Abstract

PURPOSE: A transmitter apparatus a CDMA system is provided to be easy to design a high speed circuit by constructing a base band filter suing a simple control circuit, an adder and a shifter. CONSTITUTION: In a transmitter apparatus, a base band filter part(200) includes base band filters(101,103) for filtering I and Q signals of a pilot channel to limit a band width, and base band filters(105,107) for filtering I and Q signals of other channels except for the pilot channel to limit the band width. Multipliers(120,122) multiply a power rate to the I and Q signals of the pilot signal according to the pilot signal, and multipliers(124,126) multiply a power rate to the I and Q signals of other channels except for the pilot channel according to each channel. A first adder(130) adds all I and Q signals, that is, output signals of the multipliers(120,124), and a second adder(132) adds all Q channel signals, that is, output signals of the multipliers(122,126). A first D/A converting part(140) converts an output signal of the first adder(130) into an analog signal, and a second D/A converting part(150) converts an output signal of the second adder(132) into an analog signal.

Description

Transmitter of Code Division Multiple Access System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission apparatus of a code division multiple access (CDMA) mobile communication system. In particular, a baseband filter used to limit the bandwidth of a transmission signal is added to a simple control circuit and an adder. And a transmission apparatus of a code division multiple access system capable of simplifying circuit configuration and reducing power consumption by using a shifter.

The CDMA scheme is proposed by Qualcomm of the United States. The CDMA scheme assigns each subscriber a PN code string having a low cross-correlation coefficient while sharing time and frequency with each user. The signal is spread by using the PN code string and transmitted, and the receiving side generates the same PN code string as that used by the transmitting side to synchronize the signal, and de-spreads the received signal by using the same to restore the original signal. The standard for the CDMA digital mobile communication system is defined in IS-95 (Interim Standard-95) defined by the Telecommunications Industry Association (TIA).

In general, a method for transmitting an information signal in the CDMA method uses a spread spectrum method. This spreading method spreads a band of an information signal to be transmitted by using a spreading signal at a transmitting side, and despreads a received signal by using the same spreading signal as a transmitting side, thereby receiving the original information signal. It is a technique to get.

Since a wireless communication environment for transmitting and receiving data is currently limited in bandwidth, in order for a base station or a terminal of a CDMA system to transmit or receive a predetermined data signal, the bandwidth of the data signal must be limited within a base band. Accordingly, a baseband filter for limiting the bandwidth occupied by the signal at the time of transmission is used in the transmission apparatus of the base station or the terminal of the CDMA system.

1 shows the configuration of a transmission apparatus in a typical CDMA system. As shown, a typical CDMA system transmitter employs multipliers 20 and 22 that multiply the I and Q signals of the pilot channel with the pilot power, i.e., the power ratio of the pilot signal, respectively, and the I and Q signals of the other channel except the pilot channel. And all Q channel signals through the adder 30 and the multipliers 22 and 26, which add all the I channel signals through the multipliers 20 and 24, and multiply the Q signals by the channel power. In addition, the adder 32, the baseband filter 40 for filtering the output signal of the adder 30 to limit the bandwidth, the baseband filter 50 for filtering the output signal of the adder 32 to limit the bandwidth and D / A converters 60 and 70 convert the output signals of the baseband filters 40 and 50 into analog signals, respectively.

In the transmission apparatus of the CDMA system, the data transmitted in each channel are first spread by the PN code, and then the I and Q signals of each channel are multiplied by the power component, i. After multiplication, the I signal is added in adder 30 as the I signal and the Q signal is added in adder 32 as the Q signal.

Thereafter, the I and Q signals added by the adders 30 and 32 are inputted to the baseband filters 40 and 50, respectively, and filtered by the baseband filters 40 and 50, thereby limiting the bandwidth, respectively. 60, 70) is converted into an analog signal and output.

FIG. 2 is a detailed block diagram of the baseband filter used in the transmitter of the CDMA system as described above in FIG. As shown, the baseband filter has a number of shifters (Z ⁻¹ : 42) for delaying and shifting the input signal, and different filter coefficients h ₀ , h ₁ , h ₂ , h ₃ , ..., h _k. And a plurality of adders 46 each of which adds the output signal of the multiplier 44 before the shifter 42 and the output of the multiplier 44 after the shifter, as described above. The I and Q signals input to the baseband filters 40 and 50 are interpolated at predetermined multiples of the chip rate and transmitted to the D / A converters 60 and 70, respectively.

However, the baseband filter 40 as shown in FIG. 2 uses a plurality of multipliers, which generally increase the amount of logic circuits required in an integrated circuit configuration, and at least the chip rate ( It should be composed of a high speed multiplication circuit (at least 16MHz when the chip rate is about 4MHz) operating at more than four times the chip rate.Therefore, there is a difficulty in practical implementation, and the size of the entire circuit is very large and power consumption is increased. There was a problem.

Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to use a simple control circuit, an adder, and a shift without using a multiplier in configuring a transmission apparatus of a CDMA system. The present invention provides a transmission apparatus of a CDMA system to simplify the configuration and reduce power consumption.

According to a preferred embodiment of the present invention for achieving the above object, the transmission apparatus used in the CDMA mobile communication system, outputs by limiting the bandwidth by filtering the I and Q signals of the pilot channel and the I and Q signals of other channels A signal provided from a baseband filter comprising a number of baseband filters corresponding to the number of channels, and a baseband filter filtering I and Q signals of a pilot signal among the baseband filters constituting the baseband filter; Two multipliers for multiplying and outputting a power ratio according to a pilot signal, and a plurality of baseband filters for filtering I and Q signals of all other channels except for the pilot channel signal among the baseband filters constituting the baseband filter unit Multiple multiplications by outputting the signal provided from A first adder for summing and outputting signals of all I channels among the output signals of the multipliers, a second adder for summing and outputting signals of all Q channels among the output signals of the multipliers, and the first adder And a second D / A converter for converting the output signal of the digital signal into an analog signal, and a second D / A converter for converting the output signal of the second adder to an analog signal.

1 is a block diagram showing a transmission apparatus of a conventional code division multiple access system;

2 is a detailed block diagram of a baseband filter constituting a transmitter of the conventional code division multiple access system shown in FIG. 1;

3 is a block diagram showing a transmission apparatus of a code division multiple access system according to an embodiment of the present invention;

4 is a detailed configuration diagram of a baseband filter constituting a transmitter of a code division multiple access system according to the present invention shown in FIG.

5A and 5B are diagrams illustrating signals input to a baseband filter and output waveform diagrams thereof according to the prior art, respectively;

6A and 6B are diagrams illustrating signals input to the baseband filter and output waveform diagrams thereof according to the present invention, respectively;

Figure 7 is a graph comparing the absolute difference in output between the baseband filter according to the prior art and the present invention.

<Description of the code | symbol about the principal part of drawing>

101, 103, 105, 107: baseband filter

102, 104, 106, 108: MUX and controller 110: control unit

111, 113, 115: Shifters 112, 114, 116, 130, 132: Adder

120, 122, 124, 126: Multiplier 125: Delay & Adder

140, 150: D / A conversion unit 200: baseband filter unit

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram showing the configuration of a transmission apparatus of a CDMA system according to a preferred embodiment of the present invention.

First, as shown in FIG. 3, the transmitting apparatus of the CDMA system according to the present invention filters the I and Q signals of the pilot channel, respectively, the baseband filters 101 and 103 for limiting the bandwidth and all other except the pilot channel. A baseband filter unit 200 consisting of baseband filters 105 and 107 for limiting bandwidth by filtering the I and Q signals of the channel, respectively, and the I and Q signals of the pilot channel among the output signals of the baseband filter unit 200. Multipliers (120, 122) multiplying the power ratio according to the pilot signal, and multipliers (124, multiplying the I and Q signals of all other channels except the pilot channel among the output signals of the baseband filter unit 200 by the power ratio for each channel. 126, a first adder 130 that adds the output signals of the multipliers 120 and 124, that is, all I channel signals, and a second adder that adds the output signals of the multipliers 122 and 126, that is, all Q channel signals. Adder 132, First Adder 130 A first D / A converter 140 for converting an output signal into an analog signal and outputting the analog signal, and a second D / A converter 150 for converting the output signal of the second adder 132 into an analog signal and outputting the analog signal; do.

In the baseband filter unit 200 composed of a plurality of baseband filters 101, 103, 105, and 107, a pair of baseband filters 101 and 103 may receive I and Q signals of a pilot channel input for data transmission. While filtering by outputting each channel to limit the bandwidth, the pair of baseband filters 105 and 107 respectively filter the I and Q signals of all channels except the pilot channel to output the bandwidth. At this time, the baseband filter (101, 103) for filtering the I and Q signal of the pilot channel signal, but the filter for filtering the I and Q signals of the other channels except the pilot channel is the number of channels other than the pilot channel Depending on the number is variable. That is, since one channel signal includes the I and Q signals, respectively, it is usually composed of twice the number of channels. In other words, the baseband filter 105 and the baseband filter 107 are each formed in the same number as the number of channels other than the pilot channel.

The multiplier 120 multiplies the output signal of the baseband filter 101 which filters the I signal of the pilot channel by the pilot power, that is, the power ratio of the pilot channel, and the multiplier 122 filters the Q signal of the pilot channel. The output signal of the baseband filter 103 is multiplied by the power ratio of the pilot channel and output.

The multiplier 124 multiplies the output signal of the baseband filter 105 for filtering the I signal of another channel other than the pilot channel signal by outputting the power ratio of the channel, and the multiplier 126 outputs the output signal of the channel other than the pilot channel signal. The output signal of the baseband filter 107 filtering the Q signal is multiplied by the power ratio of the channel and output. In this case, the multipliers 124 and 126 have the same number as the number of baseband filters 105 and 107, respectively.

Meanwhile, the first adder 130 adds the output signals of the multipliers 120 and 124, that is, all I channel signals, and outputs them to the first D / A converter 140, and the second adder 132 is a multiplier ( All Q channel signals that are output signals of the 122 and 126 are added and output to the second D / A converter 150.

The first D / A converter 140 converts the output signal of the first adder 130 into an analog signal and outputs the analog signal, and the second D / A converter 150 outputs the second adder 132. The signal is converted into an analog signal and output.

4 is a detailed block diagram showing the configuration of each baseband filter shown in FIG.

As shown in FIG. 4, each of the baseband filters 101, 103, 105, and 107 constituting the baseband filter unit 200 determines an input signal and selects and outputs a predetermined signal according to the determination result. Shifts and delays the signals output from the control unit 110, which is composed of a plurality of MUX / controllers 102, 104, 106, 108, and the MUX / controllers 102, 104, 106, 108 of the control unit 110, respectively. Adders 112, 114, and 116 that add the signals delayed by the plurality of shifters 111, 113, 115 and the respective shifters 111, 113, 115 and the output signals of the MUX / controllers 104, 106, 108, respectively. Delay / adder 125 is formed.

According to the present invention, in order to configure the baseband filter as shown in FIG. 4, the characteristics of the conventional baseband filter shown in FIG. 2 should be considered. Hereinafter, the configuration of FIG. 4 will be described in detail with reference to FIG. 2. do.

The power ratio of each channel (1, ..., k) is a ₁ , a ₂ , a ₃ , ...., a _k , and the input signal for I or Q of each channel is x ₁ (n), x ₂ (n), ..., x _k (n) 1 and 2, the outputs of the baseband filters 40 and 50 that pass through the adders 30 and 32 may be represented by Equation 1 below.

h (n) ⊗ (a ₁ x ₁ (n) + a ₂ x ₂ (n) + ... + a _k x _k (n))

At this time, the filter structure as shown in FIG. silver (a ₁ x ₁ (n) + a ₂ x ₂ (n) + ... + a _k x _k (n)) Is interpolated by J times, that is, (J-1) zeros ("0") are inserted.

In summary, Equation 1 described above may be represented by Equation 2 below.

a ₁ (h (n) ⊗x ₁ (n)) + a ₂ (h (n) ⊗x ₂ (n)) + .... + a _k (h (n) ⊗x _k (n))

Accordingly, the transmitter structure of FIG. 3 according to the present invention represented by Equation 2 may be derived from the transmitter structure of FIG. 1 represented by Equation 1.

Also, signal input sampled at a given chip rate x (n) The output y (n) of the baseband filters 101, 103, 105, and 107 for the given baseband filter coefficient h (k) is defined as in Equation 3 below.

Where input to the filter Is the input data to the transmitter x (n) Is interpolated at J times the chip rate. That is, J-1 '0' is inserted into the input data. x (n) , 0, 0, ..., 0). In addition, the sampling time k of the baseband filter becomes J times the chip rate. Input signal in x (n) Is a binary (ie, +1 or -1) and the rest is 0, the structure of the baseband filter of FIG. 2 may be changed to the structure of FIG. 4.

Assuming I = K / J, (K: total number of filter coefficients, J: sampling rate per chip), the interpolated Wow x (ni) The relationship of J may be as follows.

Case 1:

The input signal is composed of I different input signal groups s (1, ni) as in the case 1 described above, and the filter coefficients for the different input signal groups are each signal group i = 0, The filter coefficients corresponding to j = 0 in 1, ..., I-1.

Case 2:

The input signal is composed of I + 1 different input signal groups s (1, ni) as in the case 2 described above, and the filter coefficients for the different input signal groups are i = 0 as shown in Equation 5 below. 0 and filter coefficients corresponding to j = 0 in each signal group i = 1, ..., I.

Case 3:

The input signal is composed of I + 1 different input signal groups s (1, ni) as in the case 3 described above, and the filter coefficients for the different input signal groups are 0 when i = 0 as shown in Equation 6 below. And filter coefficients corresponding to j = 0 in each signal group i = 1, ..., I.

Occation l (only, l ≥2)

When the input signal is described above l It is composed of I + 1 different input signal group s (1, ni), and the filter coefficient for each different input signal group is 0 when i = 0 as shown in Equation 7 and each signal group i The filter coefficients corresponding to j = 0 at = 1, ..., I.

Case J:

The input signal is composed of I + 1 different input signal groups s (1, ni), such as J, and the filter coefficients for the different input signal groups are i = 0 as shown in Equation 8 below. 0 and filter coefficients corresponding to j = 0 in each signal group i = 1, ..., I.

That is, as described above, the filter coefficients of the respective MUXs and the controllers 102, 104, 106, and 108 constituting the baseband filter according to the present invention are obtained from the filter coefficients of the conventional baseband filter shown in FIG. Thus, each MUX and controller 102, 104, 106, 108 may be implemented according to the obtained filter coefficients.

Chip rate input signal according to the MUX and the controllers 102, 104, 106, and 108 configured as described above x (n) With respect to J outputs are made from the control unit 110, which is comprised of respective MUXs and controllers 102, 104, 106 and 108. Therefore, the controller 110 composed of the MUX and the controllers 102, 104, 106, and 108 operates at J times the chip rate.

Also, if If 1, the filter coefficients c (l, i) are output as they are. If -1, the filter coefficient c (l, i) is replaced with -c (l, i) and output. In this case, the filter coefficients are selected by the MUX and the controllers 102, 104, 106, and 108 in the order of idx1 of the filter coefficients c (idx1, idx2) of 2, 3, 4,. Make sure to output as is and repeat this for all input signals. In addition, the I and Q signals of the respective channels passing through the respective baseband filters 101, 103, 105, and 107 become interpolated signals at J times the chip rate, so that each of the multipliers 120, 122, 124, and 126 is used. After the power ratio of the channel is multiplied, all of the I signals are added to the first adder 130 and then provided to the first D / A converter 140, and all of the Q signals are added to the second adder 132 and then to the first. 2 D / A converter 150 is provided.

5A and 5B are signals input to a baseband filter and output waveforms thereof according to the prior art, respectively, and the input signal shown in FIG. 5A is input to the baseband filter 40 or 50 of the prior art. Is a signal input through a pilot channel or other channel, multiplied by a power ratio at a multiplier (20, 22) or (24, 26), and then the real (I and Q signals) are added at the adder (30) or (32). real signal, and FIG. 5B illustrates an output result of filtering the input signal shown in FIG. 5A.

6A and 6B are signals inputted to the baseband filter according to the present invention and their output waveforms, respectively, and each input signal shown in FIG. 6A is a pilot channel and its different from the above-described conventional input signals. Examples of binary input signals that may be input through other channels are illustrated, and FIG. 6B illustrates an output result of filtering each input signal illustrated in FIG. 6A.

5b and 6b, it can be seen that the output between the baseband filter according to the prior art and the present invention is output in almost the same form, and the absolute difference between them is at most 1 × 10 ⁻ as illustrated in FIG. 7. It can be seen that there is only a difference of about ¹⁵ .

As described above, the present invention can reduce the size of a circuit by using a simple control circuit, an adder and a shifter, without using a multiplier used in a baseband filter. In a system with fewer channels, the power consumption is reduced by reducing the size of the circuit, and there are various effects such as being easy to design a high-speed circuit.

Claims (2)

A data transmission apparatus of a code division multiple access (CDMA) mobile communication system, A baseband filter comprising a number of baseband filters corresponding to the number of channels outputting a limited bandwidth by filtering I and Q signals of a pilot channel and I and Q signals of other channels; Two multipliers for multiplying a power ratio according to a pilot signal to a signal provided from a baseband filter for filtering I and Q signals of a pilot signal among the baseband filters constituting the baseband filter unit; A plurality of multipliers for multiplying the power ratio of each channel by the signal provided from a plurality of baseband filters for filtering the I and Q signals of all other channels except the pilot channel signal of the baseband filters constituting the baseband filter unit ; A first adder for adding up and outputting signals of all I channels among the output signals of the multipliers; A second adder for adding up and outputting signals of all Q channels among the output signals of the multipliers; A first D / A converter converting an output signal of the first adder into an analog signal; And a second D / A converter for converting the output signal of the second adder into an analog signal. The method of claim 1, Each baseband filter constituting the baseband filter unit, A controller comprising a plurality of MUX / controllers for determining an input signal and selecting and outputting a predetermined signal accordingly; And a delay / adder comprising a plurality of shifters for delaying and shifting the output signal of the controller and an adder for adding the shifted signals from the shifter and the output signals of the MUX and the controller, respectively. Transmission device.