KR20000046189A - Method for selecting valid bit - Google Patents

Abstract

PURPOSE: A method for selecting a valid bit is provided to improve a receiving performance of an entire receiving system by selecting an optimum valid bit according to an error rate of a decoded bit. CONSTITUTION: An OVSF bit selecting unit(310) selects a valid bit according to an OVSF. A most significant bit inputted from an integrating unit(20) is used in a bit selection/truncation unit. The bit selection/truncation unit selects valid bits with 2 bits according to a bit error rate and transmits 3 bits to a viterbi decoder(40). If a signal with N bits is transmitted to an inverse diffusion unit(10), the inverse diffusion unit(10) multiplies the received signal with N bits by a PN-code and a Walsh code for recovering the received signal as an original signal.

Description

Valid bit selection method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CDMA receiver, and more particularly, to improve the decoding efficiency of a Viterbi decoder in a CDMA receiver using an Orthogonal Variable Spreading Vector (OVSF) code, such as the next generation mobile communication system (IMT-2000). A method of selecting valid bits from a despreaded result value.

In general, the CDMA receiver integrates the despreaded result value and selects the most significant bit of the 3 bits. When the selected most significant bit 3 bits are delivered, the Viterbi decoder 40 uses the soft decision to make a soft decision. To perform.

However, the conventional CDMA receiving apparatus does not use an orthogonal variable spreading factor (hereinafter, abbreviated as OVSF), so there is no bit selection function according to OVSF.

1 is a block diagram showing a part of a general CDMA receiving apparatus.

Referring to FIG. 1, the despreader 10 despreads a received signal into a PN-code and a Walsh code in the CDMA receiver, and the despreaded signal is an integrator 20. Is integrated over a 64-chip period.

The bit selector 30 selects three bits to be transmitted to the Viterbi decoder 40 from the N bits of data integrated by the integrator 20.

Here, since the data of the integrator 20 outputs more bits than 3 bits, the bit selector 30 selects only the most significant bit 3 bits and transmits the bit to the Viterbi decoder 40.

The Viterbi decoder 40 performs a soft decision to increase the decoding efficiency of the received signal.

In addition, the controller 50 controls each of these blocks.

However, since the OVSF is not considered in the CDMA receiving apparatus according to the prior art, it is not possible to select a valid bit of the integral result value according to the OVSF.

Therefore, there is a disadvantage in that the valid bit cannot be selected according to the channel state.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and in contrast to the case of using OVSF as in next-generation mobile communication, selecting an optimal valid bit according to a channel state, that is, an error rate of a bit to be decoded. An effective bit selection method is provided.

According to an aspect of the present invention for achieving the above object, the effective bit selection method, the method comprising: integrating the despread received signal by an arbitrary symbol length, determining the most significant bit of the integrated signal; And sequentially searching the remaining bits except the most significant bit of the integrated signal, and selecting any valid bit according to the search result.

Preferably, the searching step sequentially searches the remaining bits to be decoded from the next bit of the determined most significant bit to the least significant bit side using the search window.

In addition, the selecting of the valid bits decodes the searched remaining bits and selects an optimal valid bit according to a bit error rate, wherein the optimal valid bit places the remaining bits except the most significant bit toward the least significant bit side. This is a valid bit having a minimum bit error rate selected by sequentially decoding bit by bit.

In the step of selecting the valid bit in the present invention, when the most significant bit represents a negative value, the bit value between the most significant bit and the selected valid bit must be all "1", and if there is a bit of "0" Has all selected valid bits set to "0", and when the most significant bit represents a positive value, the bit value between the most significant bit and the selected valid bit must all be "0", and if there is a bit of "1", All valid bits are set to "11".

1 is a block diagram showing a part of a general CDMA receiver.

2 is a block diagram showing a configuration of a bit selector for explaining a valid bit selection method according to the present invention;

* Description of the symbols for the main parts of the drawings *

10: despreader 20: integrator

30: bit selector 40: Viterbi decoder

50: control unit 310: OVSF bit selection unit

320: bit select / remove section

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

The configuration of the CDMA receiving apparatus for explaining the effective bit selection method according to the present invention is similar to that of FIG.

Therefore, first, the operation of each block according to the present invention will be briefly described with reference to FIG. 1, and the basic operations of the despreader 10, the integrator 20 and the Viterbi decoder 40 are the same as in the related art. The control unit 50 controls not only to select the significant digit of the integral result value according to the OVSF but also to select the significant digit according to the channel state. More specific points can be seen in the internal configuration of the bit selector 300 according to the present invention.

2 is a block diagram illustrating a configuration of a bit selector for explaining a valid bit selection method according to the present invention.

1 and 2, the OVSF bit selector 310 selects a valid bit according to the OVSF, and the most significant bit input from the integrator 20 remains unchanged in the bit selection / truncation. use.

The bit selection / truncation according to the bit error rate BER selects two valid bits according to the bit error rate, and transfers all three bits to the Viterbi decoder 40.

When the N-bit signal is transmitted to the despreader 10, as in the currently commercially available CDMA receiver, the despreader 10 receives the P-code and Walsh code by N-bit. The signal is multiplied and restored to the original signal.

However, since a signal spread and transmitted by the CDMA transmission apparatus is distorted by noise or the like through the wireless space, a case where the original signal cannot be restored is generated.

In order to prevent this from being restored to the original signal, the receiving apparatus has a function of integrating the despread signal by the symbol length to restore the original signal stably.

However, when OVSF is used as in the present invention, since the number of chips per symbol varies variably, that is, the number of chips per symbol varies as the OVSF varies to 16, 32, 64, 128, 256, and the like. The integration time of the part 20 will vary accordingly. This means that the value output from the integrating unit 20 increases or decreases according to OVSF.

In addition, considering that the bits that can be received for the soft decision in the Viterbi decoder 40 are 3 bits, if the valid bit is not properly selected, the hard decision may not be much different from that of the hard decision. .

Therefore, in the present invention, the bit selector 300 according to the present invention of FIG. 2 is provided with a function of selecting a valid bit from the output value of the integrator 20 according to the OVSF.

In more detail, when the integrated output signal is N bits, the second, third, fourth, ... N _ST bits from the most significant bits become meaningless bits according to OVSF.

When the number of signal bits input to the CDMA receiver is 4 bits, assuming that the despread values have only +7 and -8, the output of the integrator 20 according to OVSF is shown in Table 1 below.

OVSF Integrator Output Integrator Output Valid Bits Integrator Output Bits (All OVSF Considered) 16 70h / 80h 8 12 32 E0h / 100h 9 12 64 1C0h / 200h 10 12 128 380h / 400h 11 12 256 700h / 800h 12 12

As shown in Table 1, the integrated output bits are 12 bits, while the actual meaningful bits are 8, 9, 10, 11, 12 bits from the least significant bit according to OVSF.

Therefore, an appropriate input can be given to the Viterbi decoder 40 only by selecting a valid bit according to the OVSF.

Such a function is realized by the bit selector 300 according to the present invention shown in FIG.

Table 1 is based on the assumption that the despread value is +7 or -8. In practice, however, the effective bit selected must depend on the state of the channel.

In order to overcome this problem, in the present invention, a bit selection / removing unit 320 according to a bit error rate is provided.

The OVSF bit selector 310 selects a valid bit and inputs the selected bit to the Viterbi decoder 40 to measure the bit error rate.

After that, measure a new bit error rate by moving one bit toward the least significant bit, and if the newly measured bit error rate is a better result, move another bit error rate by one bit toward the least significant bit.

In this case, if the newly measured bit error rate is better than the previous bit error rate result, the bit error rate is continuously measured toward the least significant bit. However, if the new bit error rate is worse than the previous bit error rate result, the bit error rate is moved to the previous bit to stop. That is, it stops after returning 1 bit to the most significant bit.

When the search window is fixed after the optimal valid bit is selected as described above, when the signal input to the bit select / remove unit 320 is out of the window due to a bit error, the bit value of the search window is adjusted as follows. This reduces the error for bit errors.

First, when there is a valid bit between the most significant bit of "1" and the bit value of the search window, all bit values of the search window are set to "0". That is, all valid bits are set to "0".

On the contrary, when there is a valid bit between the most significant bit of "0" and the bit value of the search window, all bit values of the search window are set to "1". In other words, all valid bits are set to "1".

An example of this is as follows.

If the sign bit is "1", the bits between the search window and the sign bit should all be "1". If there is a valid bit "0" as shown below, all the values in the search window are read as "0". Becomes smaller.

Sign bit window One 1 0 1 0 1 0 1 1 0 0 0

That is, as shown above, when the sign bit is "1", all bits between the search window and the sign bit should be "1". Since the second bit is "0", the bit value of the search window " Read 01 "as" 00 ".

This is because "10101" is negative because the sign bit is negative ₍ since 2's complement of = 10101 is 01011). Therefore, the 3-bit "101" decoded including the valid bit selected in the search window is "-3 ₍₁₀₎ (since 2's complement of = 101 is 011)", but in the present invention, since the 3 bits to be decoded is "100", "-4 ₍₁₀₎ (because two's complement of = 100 is 100)", and as a result, the error from the original value "-10" is reduced.

Another example according to the present invention will be described.

If the sign bit is "0", the bits between the search window and the sign bit should all be "0". If there is "1" as shown below, if all the values in the search window are read as "1", the error is small. Lose.

Sign bit window 0 0 0 1 0 1 0 1 1 0 0 0

That is, as shown in the above example, when the sign bit is "0", all bits between the search window and the sign bit should be "0". Since the third bit is "1", the bit value of the search window Read "01" as "11".

This is because "00101" is "5 ₍₁₀₎ " because the sign bit is a positive value. Therefore, the three bits "1" to be decoded including the valid bit selected in the search window are "1 ₍₁₀₎ ", but in the present invention, since the three bits to be decoded are "11", the result is "3 ₍₁₀₎ ", resulting in the original. The error with the value "5" is reduced.

As described above, the present invention selects an optimal valid bit according to a channel state, that is, an error rate of a bit to be decoded, in order to use OVSF as in next-generation mobile communication, thereby increasing the decoding efficiency of the decoder and The reception performance is improved.

Claims (6)

Integrating the despread received signal by any symbol length; Determining the most significant bit of the integrated signal; Sequentially searching for bits other than the most significant bit of the integrated signal; And selecting an arbitrary valid bit according to the search result. 2. The method of claim 1, wherein the searching step sequentially searches the remaining bits to be decoded from the next bit of the determined most significant bit to the least significant bit side using a search window. The method of claim 1, wherein the selecting of the valid bits comprises decoding the remaining bits found and selecting an optimal valid bit according to a bit error rate. 4. The valid bit selection method of claim 3, wherein the optimal valid bit is a valid bit having a minimum bit error rate selected by sequentially decoding two bits except the most significant bit to the least significant bit side. The bit value between the most significant bit and the selected valid bit must be "1" when the most significant bit represents a negative value. If there is, valid bit selection method characterized in that all selected valid bits to "0". The bit value between the most significant bit and the selected valid bit should all be "0" when the most significant bit represents a positive value. If present, all selected valid bits are " 11 ".