KR100486530B1 - Generation method of othogonal variable spreading factor codes - Google Patents

Abstract

The present invention relates to a method for generating an Orthogonal Variable Spreading Factor (OVSF) code. Particularly, the present invention relates to a time division duplex (TDD) standard through a Transport Format Combination Indicator (TFCI). The present invention relates to a method for easily generating an orthogonal variable diffusion coefficient. In the related art, a delay occurs because a code tree needs to be generated up to a desired code length in order to obtain an OVSF code defined in the TDD standard, and there is a problem in that an additional memory is required when storing the code tree. In view of the above problems, the present invention obtains information bits for a predetermined TFCI operation according to a spreading coefficient (SF (Q)) and a sequence index (k) representing a desired OVSF code, and then uses the same TFCI calculation method. Substituting to calculate the TFCI code that regularly corresponds to the OVSF code and simply converting it to generate the OVSF code, to obtain a complex and delayed code tree to obtain the OVSF, or to add additional devices There is no need to do this, which can reduce hardware complexity and increase efficiency.

Description

Orthogonal Variable Diffusion Coefficient Code Generation Method {GENERATION METHOD OF OTHOGONAL VARIABLE SPREADING FACTOR CODES}

The present invention relates to a method for generating an Orthogonal Variable Spreading Factor (OVSF) code. Particularly, the present invention relates to a time division duplex (TDD) standard through a transport format combination indicator (TFCI). The present invention relates to a method for easily generating an orthogonal variable diffusion coefficient.

Wideband code division multiple access (Wideband CDMA) supports the various transmission speeds in the 3rd generation mobile communication. Since the bandwidth of the spread signal is constant regardless of the transmission speed, it is necessary to provide various spreading factors (SF). Therefore, an Orthogonal Variable Spreading Factor (OVSF) code having orthogonality among all the diffusion coefficients is used. This OVSF code must be provided to generate a channelization code.

The broadband code division multiple access schemes include time division duplex (TDD) and frequency division duplex (FDD). Among them, in the case of frequency division duplex, an OVSF code having a spreading factor of 256 is used. In the case of time division redundancy, OVSF codes having spread coefficients (code lengths) of 1, 2, 4, 8, and 16 are used. However, even if the spreading coefficient is up to 16, a lot of calculation is required to calculate the OVSF code, and if it is stored in the memory, a large amount of capacity is required.

Now, a method of calculating a general OVSF code will be described with reference to FIG. 1.

1 illustrates a general method of calculating an OVSF code in a tree structure, where Q is a spreading factor and k is a sequence index. The spreading factor Q means the length of the code.

As shown, when the diffusion coefficient Q is 1, the sequence index k is 1, and the code value at this time is (1). When the spreading factor Q is 2, spreading occurs in two ways, where the sequence index k becomes 1 and 2 to distinguish each code value ((1,1), (1, -1)). . In this way, the OVSF code until the spreading factor Q is 16 is obtained. That is, in order to obtain an OVSF code having a length of 16, a code tree must be generated in order from an OVSF code having a code length of 1. Thus, a large amount of computation is required to generate an OVSF code of length 16. The OVSF code acquisition scheme is specified in the 3rd generation communication standard (3G TS 25.223).

However, there is a significant delay in computing the OVSF code in this way, and there is no delay if you store the code tree, but a lot of memory is required. In some cases, additional circuits may be configured to generate OVSF code quickly, but there are hardware requirements.

As described above, since a code tree must be generated to a desired code length in order to obtain an OVSF code defined in the TDD standard, there is a problem that additional memory is required when storing the code tree.

In view of the above problems, the present invention easily obtains OVSF code without a separate complicated process or memory by using a basic sequence and a TFCI generation process for a transport format combination indicator (TFCI). The purpose of the present invention is to provide a method for generating orthogonal variable diffusion coefficient codes.

In order to achieve the above object, the present invention provides a method for generating an Orthogonal Variable Diffusion Coefficient (OVSF) code for use in time division duplex (TDD) communication. Obtaining an information bit for generating an identifier (TFCI) code; Calculating a TFCI code using the known basic sequences (Table 1) for the information bit and the TFCI code; And generating an OVSF code by mapping certain elements of the calculated TFCI code to OVSF code values.

The acquiring of the information bits may include: temporarily setting a value obtained by subtracting 1 from a sequence index to a binary value of a length obtained by subtracting 1 from a spreading coefficient; And reordering in the reverse order such that the most significant bit of the binary value becomes the least significant bit and the least significant bit becomes the most significant bit, and then padding the data into five bits.

The generating of the OVSF code may further include generating an OVSF code by mapping an element of the calculated TFCI code to 0 and 1 to -1.

In generating the OVSF code, the present invention is to generate the OVSF code through the TFCI code rather than generating the conventional code tree or looking up the internal memory, and generates the TFCI code which is basically used in the CDMA TDD scheme. It should be noted that the process is used as is. The present invention will allow the TFCI code to be properly generated to correspond with regularity with the OVSF code.

First, the TFCI code to be used in the present invention will be mentioned. However, since the TFCI code is not used for communication control but is used to generate the OVSF, the description will be focused on the part used in the present invention.

In general, according to the radio access network standard of the Third Generation Partnership Project (3GPP), a predetermined TFCI bit is coded and inserted into a dedicated physical control channel that provides control information for each time slot constituting a radio frame. . That is, the transmission format information is coded and inserted into each radio frame.

According to the above-mentioned 3GPP standard, the TFCI bit is varied from a minimum of 1 bit to a maximum of 10 bits, and the number of bits is determined at the point where the call starts by signal processing of a higher layer. The TFCI is provided with a different coding scheme according to the determined number of bits. Since the present invention uses 16 × 5 TFCI, only the first lead-muller coding used in the case of 5 bits will be described. The first lead-muller coding is bi-orthogonal coding and converts TFCI determined through the orthogonal coding into a TFCI codeword.

The TDD standard defines a base sequence of TFCI for the quadrature coding. The base sequence defined for 16 × 5 TFCI is shown in Table 1 below. I is a sequence number, and M _{i, n} (n = 0,1,2,3,4) represents a sequence sequence.

i M _{i, 0} M _{i, 1} M _{i, 2} M _{i, 3} M _{i, 4} 0 One 0 0 0 One One 0 One 0 0 One 2 One One 0 0 One 3 0 0 One 0 One 4 One 0 One 0 One 5 0 One One 0 One 6 One One One 0 One 7 0 0 0 One One 8 One 0 0 One One 9 0 One 0 One One 10 One One 0 One One 11 0 0 One One One 12 One 0 One One One 13 0 One One One One 14 One One One One One 15 0 0 0 0 One

Table 1 shows a basic sequence for generating a 16 × 5 TFCI code, with a slight modification of the first-order read-muller coding, to generate a TFCI code (b ₀ , b ₁ , ..., b ₁₅ ). To use the following equation (1). This is the content defined in 3GPP (3G TS 25.222).

Here, b _i denotes a TFCI code, a _n denotes an information bit, and M _{i, n} denotes a basic sequence of 16 × 5 TFCI.

The information bit (a _n ) means an information bit determined to generate an appropriate TFCI code, and the present invention provides a method for easily identifying an information bit so that the generated TFCI code regularly corresponds to the OVSF code. will be.

As described above, it should be noted that the third generation communication method uses the TFCI code generation process already in use.

Now, let's look again at the 16 × 5 TFCI basic sequence in Table 1 above. It will be readily appreciated that the base sequence is a modification of the primary read-muller code. To change this to the base sequence (sequence) of the primary Reed-Muller code, the values with sequence number i of 15 must be in the first sequence number. Therefore, in the present invention, when the TFCI code is calculated, the TFCI codewords are generated in the order of b ₁₅ , b ₀ , b ₁ , ... b ₁₄ .

Now, in order to realize the present invention, a process of generating a TFCI code for generating a corresponding OVSF code when the spreading coefficient SF (= Q) and the sequence index k are determined will be described in detail. To this end, some of the relationship between the spreading coefficient SF, the sequence index k, the information bits a _n , and the calculated TFCI code are shown in Table 2.

As shown in Table 2, an information bit for determining a corresponding TFCI code based on a spreading factor (SF) and a sequence index (k) necessary to determine an OVSF code, and a TFCI obtained by applying the same to Equation 1 The signs are listed in order.

The TFCI code is to begin with a ₁₅ b as described above, and then _{b 15 b 0 b 1, ...} , the operation in the order of _{b-Q 2} will lists them, this is because the obtained TFCI for determining the OVSF code Only the number of diffusion coefficients (SF) determined is needed. That is, if the diffusion coefficient (SF) is 2, since the OVSF code has two elements, the TFCI for generating it needs only two elements. That is, b ₁₅ and b ₀ can be found.

Now, let's examine the correlation between the TFCI and OVSF codes obtained as above. If SF (Q) is 2 and index k is 2, the TFCI obtained in Table 2 is 01. If this corresponds to 0 as 1 and 1 as -1, the value becomes the OVSF code (1, -1), which can be seen through FIG.

If SF (Q) is 4 and index k is 3, the TFCI obtained in Table 2 is 0101. If this corresponds to 0 as 1 and 1 as -1, the value becomes the OVSF code (1, -1,1, -1), which can be seen through FIG.

As described above, by calculating Equation 1 from the base sequence number 15 using the appropriate information bits, the TFCI can be simply converted to the OVSF code. To this end, a method of inferring the appropriate information bits will be described in detail.

Although the information bits listed in Table 2 can be stored in memory, this method is not used because additional memory is required. Note that the bits of information can be obtained through simple operations, and the actual implementation is very simple, even though the details are longer.

First, look at the information bit string of Table 2 and the corresponding information bit decimal string, it does not exactly match. However, looking again, taking into account the spreading factor SF (Q) and the index k, it separates the lower bits as many as the spreading factor SF-1 of each information bit (a, b, c in Table 2). If you look at the most significant bit of these as the least significant bit, you can see that it is the same as the information bit decimal value. It will also be appreciated that the information bit decimal value is the index (k) value-1.

By looking at the information bits, we actually apply what we have checked to get the desired OVSF code using only the spreading factor (SF (Q)) and the sequence index (k). This will be described with reference to the flowchart of FIG. 2.

2 shows a method of generating an OVSF code through the determination of the spreading coefficient SF (Q) and the sequence index k, and using the spreading coefficient SF (Q) and the sequence index k. Obtaining an information bit for generating a 5 TFCI code; Calculating a TFCI code using the information bits and basic sequences of a 16x5 TFCI code; And generating an OVSF code by mapping predetermined elements of the calculated TFCI code to OVSF code values.

First, when the spreading coefficient SF (Q) and the sequence index k are determined, the value of the sequence index k-1 is regarded as an information bit decimal value. The information bit decimal value is made into the digit binary number of the spreading factor Q-1, and then rearranged with the most significant bit into the least significant bit and the least significant bit into the most significant bit. Then, padding is padded with zeros from the most significant bit to fit the information bits consisting of 5 bits to obtain the information bits for generating 16 × 5 TFCI codes.

The TFCI code is calculated using the obtained information bits and Equation 1, and only the number of diffusion coefficients Q is required in order of b ₁₅ b ₀ b ₁ ,..., B ₁₄ . That is, if Q = 2, b ₁₅ b ₀ is calculated, and if Q = 4, b ₁₅ b ₀ b ₁ b ₂ is calculated.

The TFCI obtained by this method has the same elements as the diffusion coefficient, and each element is mapped to 0 by 1 and 1 by -1 to generate an OVSF code.

Therefore, the information bits needed to calculate the TFCI having a regular correlation with the OVSF code can be obtained by simple conversion. Therefore, if the TFCI calculation method being used is used as it is, the spreading factor (SF (Q)) representing the desired code among the OVSF codes ) And the OVSF code can be obtained quickly according to the sequence index (k).

As described above, the present invention obtains information bits for a predetermined TFCI operation according to a spreading coefficient (SF (Q)) and a sequence index (k) representing a desired OVSF code, and then substitutes them into a conventional TFCI calculation method. By calculating the TFCI code that regularly corresponds to the corresponding OVSF code and simply converting it to generate the corresponding OVSF code, it is possible to obtain a complex and delayed code tree or add additional devices to obtain the OVSF. There is no need to reduce hardware complexity and increase efficiency.

1 is a part of a code tree for generating a general orthogonal variable diffusion coefficient code.

2 is a flowchart illustrating a method for generating an orthogonal variable diffusion coefficient code according to the present invention.

Claims (4)

A method of generating an orthogonal variable spreading factor (OVSF) code used for time division duplex (TDD) communication, If a spreading coefficient and a sequence index are determined, obtaining information bits for generating a transport format combination identifier (TFCI) code using the same; Calculating a TFCI code using the known basic sequences (Table 1) for the information bit and the TFCI code; And generating an OVSF code by mapping predetermined elements of the calculated TFCI code to an OVSF code value. 2. The method of claim 1, wherein the acquiring of the information bits comprises: temporarily setting a value obtained by subtracting 1 from a sequence index to a binary value of a length subtracted from a spreading factor; And arranging in the reverse order such that the most significant bit of the binary value becomes the least significant bit and the least significant bit becomes the most significant bit, and then padding the data with five bits. The method of claim 1, wherein the calculating of the TFCI code comprises the following equation: (b _i is the TFCI code, a _n is the information bit, M _{i, n} is the basic sequence of 16 × 5 TFCI code) And calculating a TFCI code by a spreading coefficient in the order of b ₁₅ , b ₀ , b ₁ ... b ₁₄ . The orthogonal method of claim 1, wherein the generating of the OVSF code further comprises generating an OVSF code by mapping 0 of the elements of the calculated TFCI code to 1 and 1 to −1. Variable diffusion coefficient code generation method.