KR100438089B1 - A method for allocating OVSF codes in an Uplink Synchronous Transmission Scheme of a mobile communication system - Google Patents

Abstract

In an environment in which Uplink Synchronous Transmission Scheme (USTS) is applied in a mobile communication system, terminals belonging to one base station use one common scrambling code and have the same Orthogonal Variable Spreading Factor (OVSF). A spread code is assigned from a code tree of. In addition, in the uplink, one OVSF code is allocated to each of a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH) so that two OVSF code diagrams can be used. The sign is used. For this reason, the number of OVSF codes is insufficient in the uplink.

The present invention increases the spreading rate of the data channel by one or more steps (4 to 128) when there is room to increase the spreading rate of the data channel in uplink transmission, thereby increasing the number of codes available in the OVSF code tree in the USTS mode. A method for improving the overall cell capacity is presented.

In addition, the present invention enables data transmission by separating and transmitting data having a high spreading rate and having a low data rate into I and Q channels.

Therefore, according to the present invention, the total cell capacity in the USTS mode can be improved by enabling data transmission while increasing the number of codes available in the OVSF code tree.

Description

Method for allocating orthogonal variable spreading rate code in uplink transmission method {A method for allocating OVSF codes in an Uplink Synchronous Transmission Scheme of a mobile communication system}

The present invention relates to a method for allocating an Orthogonal Variable Spreading Factor (OVSF) code for classification of an uplink channel at one base station in a mobile communication system employing an Uplink Synchronous Transmission Scheme (USTS). It is about.

Although many technologies have been developed to improve the performance in the mobile communication system using the CDMA method, there are many obstacles in overcoming the limitations of the wireless environment. As an attempt to increase the channel capacity and improve the channel stability, the Uplink Synchronous Transmission Scheme (USTS) is being discussed as an asynchronous IMT-2000 standard among Korean mobile service companies. Even if international standardization is not performed, the uplink transmission method is considered to be useful and contributes to improving channel stability. Hereinafter, the uplink transmission method (USTS) will be described.

The 3GPP (Asynchronous IMT-2000 Standardization Organization) is currently considering the Uplink Synchronous Transmission Scheme as an additional technology.

In the uplink transmission scheme, data transmitted from all user equipments (UEs) is divided and transmitted by the same scrambling code and different orthogonal codes. At this time, the same signal is transmitted from the base station Node B by the control signal of the base station Node B. This is achieved by a user equipment adjusting the transmission time of a transmission signal to arrive at a time point. This uplink transmission scheme reduces mutual interference by improving orthogonality between signals in a cell covered by a base station. Is an interference cancellation technique.

Timing control for synchronization in a CDMA mobile communication system consists of two steps: initial synchronization and tracking. Initial synchronization is a process of obtaining enough timing synchronization to communicate and tracking maintains the timing obtained from the initial synchronization. It's a process. Normally, initial synchronization occurs during the setup of the call. In some cases, the initial synchronization can be omitted and the tracking process can be performed immediately. The initial synchronization has a tolerance range of approximately ± 1.5 chip hours.

The tracking process for the Uplink Synchronous Transmission Scheme undergoes closed loop timing control, which is similar to a power control loop. The base station Node B transmits a timing alignment bit (TAB) to the terminal UE every 20 ms. If the timing of the received signal is fast, the timing alignment bit is set to 0. The time adjustment bit replaces the 15th (slot # 14) power control bit (TPC) every other frame.

The terminal UE makes a hard decision on a timing alignment bit and combines 20 pieces of information according to 0 or 1 to adjust time timing by a predetermined unit. When tracking using a timing alignment bit, the allowable range of the synchronization is approximately ± 1/8 chip time.

Since TPC bits are typically transmitted in more than two bits, at least two bits are also transmitted in one slot.

Next, an Orthogonal Variable Spreading Factor (OVSF) code related to the present invention will be described.

Asynchronous CDMA Method In an IMT-2000 mobile communication system, an orthogonal variable spreading factor code is used to spread a band of an original signal to have a bandwidth wider than that of the original signal.

The OVSF code ensures orthogonality not only between different codes of the same length but also between different codes of different lengths. For this purpose, the generation of the sign follows the scheme shown in FIG. In C _{ch, SF, k} in the form of sign, C means OVSF code, ch means code used for spreading, SF means spreading rate, and k is the k-th code among the SF branches. Indicates that

Referring to FIG. 1, the code tree starts from the first code C _{ch, 1,0} = 1 having a diffusion rate of 1. The second symbols with a diffusion rate of 2 are generated by combining C _{ch, 1,0} . C _{ch, 2,0} = {C _{ch, 1,0} C _{ch, 1,0} } = {1, 1} C _{ch, 2,1} = {C _{ch, 1,0} -C _{ch, 1,0} } = {1, -1} and the branches below are generated in the same way.

FIG. 2 shows an orthogonal variable spreading factor code thus generated in a code tree.

In FIG. 2, only the symbols having a diffusion rate of 8 are displayed and the branches having a diffusion rate of 16 are displayed, but no symbols are shown. By subdividing branches in the same way, an Orthogonal Variable Spreading Factor code with a code length of 256 can be generated. On the other hand, in order to have orthogonality between each spreading rate code _, a parent code existing between a certain code and the root (C _{ch, 1,0} = 1) cannot be used with the code.

For example, in FIG. 2, C _{ch, 8,0} cannot be used together with C _{ch, 2,0} or C _{ch, 4,0} , but C _{ch, 2,1} or C _{ch, 4,1} or C _{ch. , 8,1} can be used together.

Next, a dedicated physical channel to which an Orthogonal Variable Spreading Factor (OVSF) code according to the present invention is applied will be described.

Dedicated Physical Data Channel (DPDCH) is a physical channel of an asynchronous CDMA IMT-2000 mobile communication system. A radio frame is composed of 15 time slots in 10 ms units. It is used to transmit user data.

Spreading factor takes one of 4, 8, 16, 32, 64, 128 and 256 in the uplink. At a low data rate, only one dedicated physical data channel (DPDCH) is used, and as the data rate increases, up to six can be supported. At a low data rate, only one dedicated physical data channel (DPDCH) is sufficient, and as the data rate increases, up to six channels (all channels use SF = 4) can be used. (See Figure 3)

Dedicated Physical Control Channel (DPCCH) is a physical channel of asynchronous CDMA IMT-2000 mobile communication system like DPDCH, and one radio frame is every 15 ms. It consists of two time slots and transmits control information for transmission of a dedicated physical data channel (DPDCH). Spreading factor is always 256 in the uplink.

The spreading through mapping of the dedicated physical data channel (DPDCH) and the dedicated physical control channel (DPCCH) to I and Q is as follows.

When the data rate is low, only one dedicated physical data channel (DPDCH) is used. The dedicated physical data channel (DPDCH) is an I channel (normal phase channel). And a dedicated physical control channel (DPCCH) transmitted on a Q channel (orthogonal phase channel), are spread through a 0 th OVSF code having a spreading factor of 256. When two or more dedicated physical data channels (DPDCHs) are used because the data rate is high, the spreading factor 4 is used for all dedicated physical data channels (DPDCHs). The low diffusion coefficient here means that many data can be transmitted in the same band. There are four OVSF codes with a spreading factor of four. For the first and second dedicated physical data channels (DPDCH), C _{ch, 4,1} in Figure 1 is assigned to the third and fourth dedicated physical data channels (DPDCH). For C _{ch, 4,3,5th} and 6th dedicated physical data channels (DPDCH) _{, Cch, 4,2} codes are used.

Mapping of the dedicated physical data channel DPDCH and the dedicated physical control channel DPCCH to the I and Q channels is shown in FIG. 3. Since the 0 th OVSF code C _{ch, 256,0} of the spreading factor 256 used by the dedicated physical control channel (DPCCH) is at the _branch of the C _{ch, 4,0} code, The parent code C _{ch, 4,0} code cannot be used.

That is, the OVSF code is assigned first as the spreading factor for the dedicated physical control channel (DPCCH) before the OVSF code is assigned as the spreading factor for the dedicated physical data channel (DPDCH).

In the prior art, since all terminals have different scrambling codes when the uplink transmission method (USTS) is not used, there is no problem because each terminal has an OVSF code tree and separately assigns OVSF codes. . That is, since the conventional scrambling code is used as a different one, even if the same spreading code is used as other terminals, there is no big problem in distinguishing channels.

However, in the case of using the uplink transmission method (USTS), since the terminals in the base station have a common scrambling code, since the OVSF codes allocated to the uplink channel in one OVSF code tree must be orthogonal to and different from each other, the limited OVSF Due to the number of codes, an OVSF code shortage phenomenon occurs.

Since the channel cannot be allocated due to the lack of the OVSF code, it is not possible to maximize the uplink transmission scheme (USTS) gain for the purpose of increasing cell capacity. In other words, in uplink, a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH) are transmitted by dividing the channels.

Therefore, in the uplink transmission method (USTS) using the scrambling code as the same, a spreading code of at least the number of terminals x 2 is required because a different spreading code must be used.

In view of the above problem, the present invention provides a number of codes that can be used in an OVSF code tree by increasing the spread rate of the data channel by one or more steps (4 to 128) when there is room for increasing the spread rate of the data channel in uplink transmission. We propose a method to improve the total cell capacity in the USTS mode by increasing.

1 is a view showing a conventional OVSF code generation method

2 is a view showing a conventional OVSF code tree structure

3 is a diagram illustrating spread of a dedicated physical channel of a conventional uplink;

4 illustrates an OVSF code allocation method of the present invention.

5 is a diagram showing spreading of an uplink dedicated physical channel of the present invention;

6 is a diagram showing an increase in usable code due to OVSF code assignment of the present invention.

The present invention is a method of increasing the number of codes that can be used in the OVSF code tree for the data channel in the uplink transmission of the uplink transmission method (USTS) by dividing the data into two for the dedicated physical data channel (DPDCH), OVSF code In the code tree, creating a OVSF code with double the code length by adding one pruning from the OVSF code to be allocated before splitting, and using this OVSF code as a new spreading code and using the code length as a spreading factor. It features.

In addition, since the spreading factor is doubled in the present invention, the same data must be doubled in order to transmit the same data at the same time. Thus, the divided data is divided into I, Q channels (phase and orthogonal channels). It is characterized by maintaining the same band by distributed transmission.

In addition, in the present invention, two OVSF codes having a double code length are generated by adding a pruning from the OVSF code to be allocated before the division, and one of them is used as a new spreading code of the other terminal.

Other objects and features of the present invention will become apparent from the detailed description of the embodiments with reference to the accompanying drawings. Hereinafter, an OVSF code allocation method of an uplink transmission method (USTS) according to the present invention will be described with reference to the accompanying drawings.

First, a general description of the present invention will be given.

First, in the case of not considering the uplink transmission scheme (USTS), the spreading rate is first obtained to obtain an OVSF code to be allocated to one dedicated physical data channel (DPDCH).

The diffusion rate can be obtained according to Equation 1 below.

Data Rate x Spreading Factor = Chip rate (3.84 Mcps)

Here, 3.84 Mcps is a chip rate in an asynchronous CDMA IMT-2000 mobile communication system and is usually fixed unless a variable chip rate is used. When a data rate of data to be transmitted on a dedicated physical data channel (DPDCH) is determined, its spread rate can be determined.

After the spreading rate is determined, an OVSF code having a spreading rate orthogonal to and estimated from an existing code is selected from an OVSF code tree.

Now, considering the application of the uplink transmission method (USTS), the data is divided into two, and in the OVSF code tree, the pruning is performed once again on the branch of the OVSF code to be allocated to the dedicated physical data channel (DPDCH) before the division. Two OVSF codes having a double code length are generated and one of the two codes is used as a spreading code for spreading the data divided into the two.

In this case, since the spreading factor has been doubled, in order to transmit the same data at the same time, the band should be doubled. Therefore, the same band can be obtained by transmitting the divided data in I and Q channels. have.

That is, the data rate of each channel is halved.

The other one of the two OVSF codes having the double code length generated as described above may be used as a spreading code for spreading data of another terminal.

4 illustrates such an effect. In the portion of the OVSF code tree of FIG. 4, the number of SFs having a Spreading Factor (SF) is SF. Here, k (k is one of 0, 1, ..., SF-1) denotes C _{ch, SF, k} .

Hereinafter, the method of the present invention will be described by way of example.

For example, when there are n-1 terminals of uplink transmission method (USTS) in a cell, a procedure of allocating an OVSF code to terminals of a new uplink transmission method (USTS) is as follows.

1. Allocate and spread C _{ch, 256, n-1} for the dedicated physical control channel (DPCCH) of the terminal. Here, before assigning the OVSF code as the spreading code for the dedicated physical data channel (DPDCH), the OVSF code is first assigned as the spreading factor for the dedicated physical control channel (DPCCH).

In FIG. 2, if the branch is _pressed five times to the right side from SF = 8, a code having a length of 256 having SF = 256 is _obtained, and is sequentially allocated from C _{ch, 256,0} which is the sign of the uppermost branch. In general, dividends can be paid at the tributaries of the C _{ch, 4,0} codes.

2. SF _old (= SF) for the dedicated physical data channel (DPDCH) is determined according to the data size to be transmitted. If the data rate is determined according to the needs of the upper layer, the spreading rate (SF) is determined accordingly. In uplink transmission, a single terminal may occupy all six dedicated physical data channels (DPDCH).

The present invention is applicable to any terminal that will use only the I channel if the data rate is low and the present invention is not applied. If the SF applied to the terminal is 256, the present invention cannot be implemented.

3. When the present invention is not applied, if there is one dedicated physical data channel (DPDCH) to be transmitted and SF _old is 4 or more and 128 or less, SF _old is doubled to determine a new SF _new (= 2SF).

4. Divide the data to be sent into two data sets.

5. The two divided data sets are allocated to C _{ch, 2SF, 2k} in FIG. 4 according to the newly determined SF _new and spread. Of course _, you can also assign C _{ch, 2SF, 2k + 1} .

The new SF _new is applied to both of the divided half-size data. Then, C _{ch, 2SF, 2k} branches become new SF _new in C _{ch, SF, k} stems, and other branches C _{ch, 2SF, 2k + 1} can be used for other terminals.

6. The two spread data sets correspond to the first dedicated physical data channel DPDCH1 and the second dedicated physical data channel DPDCH2, respectively.

7. The first dedicated physical data channel DPDCH1 maps to the I channel, and the second dedicated physical data channel DPDCH2 and the dedicated physical control channel DPCCH map to the Q channel for transmission.

8. The C _{ch, 2SF, 2k + 1} code is allocated to the next terminal requesting the spread of SF.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments.

In addition, the present invention can also be used in other CDMA mobile communication system that distinguishes channels using OVSF codes. In the case of a system in which a terminal precisely adjusts an uplink signal arrival time and a system in which spreading codes are used as a division of a terminal, the method of the present invention can be applied.

Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

If a given transmission band is W, a transmission rate of transmission data of a k-th terminal in a cell is B _k , and a SF (Spreading Factor) required for transmitting transmission data is SF _{req, k} , the following relationship is established.

W = B _k SF _{req, k}

If the SF is used to confirm the method presented in this invention is defined as SF _{USTS, k,} between said _{req SF, k} and SF _{USTS, k} is as follows.

SF _{USTS, k} = 2SF _{req, k}

Here, DPDCH1 corresponds to I channel and DPDCH2 corresponds to Q channel.

In this way, when casting by diffusion in a given bandwidth W data B _k, which want to send, an OVSF code with the way that by dividing the data into two parts sent to the I, Q C _{ch, SF, k} from the C _{ch, 2SF, 2k} By separating C _{ch, 2SF, and 2k + 1} and using only one of them, the number of codes that can be used for a dedicated physical data channel (DPDCH) can be doubled as much as possible.

That is, the number of OVSF codes required to transmit data of the same size in the same bandwidth is reduced.

Therefore, according to the present invention, the total cell capacity in the USTS mode can be improved by enabling data transmission while increasing the number of codes available in the OVSF code tree.

Claims (5)

In a code division multiplexing mobile communication system for synchronizing the arrival time of an uplink signal, Determining a spreading rate based on a data rate required from a higher layer; Determining an orthogonal variable spreading code having a code length equal to the spreading rate in a code system of an orthogonal variable spreading code; Determining an orthogonal variable spreading code having a code length doubled from the predetermined orthogonal variable spreading code in the code system of the orthogonal variable spreading code; And assigning the predetermined code to the spread of the data. 4. The method of claim 1, wherein the data is divided and distributed in the in-phase and quadrature channels of quadrature phase modulation and transmitted. 2. The uplink transmission method according to claim 1, wherein in the step of determining an orthogonal variable spreading code having a double code length, one of the two codes is defined as an orthogonal variable spreading code of another terminal having the same data rate. Of Orthogonal Variable Spread Codes The method of claim 1, wherein the mobile communication system is a mobile communication terminal. The method of claim 1, wherein the spreading rate determined based on the data rate required from the upper layer is 4 or more and 128 or less.