KR100379698B1 - A method for determining reference time of scrambling code to support USTS in W-CDMA system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a reference time point of a reverse scrambling code in a base station when a reverse synchronization scheme from a mobile station to a base station is applied in an asynchronous wideband code division multiple access (W-CDMA) mobile communication wireless network. The reference time point is 'n × 256 chip + Tref, (n = 0 to 149)' from the boundary 31 of the P-CCPCH frame (Tref is a parameter value for compensating for the time delay between the base station and the mobile station in the USTS). By setting it to a later point of view, it is possible to minimize the amount of offset information of the corresponding scrambling code provided from the base station to the mobile station, and to make the boundary of the scrambling code and the channel code boundary coincide with each other to implement optimal backward synchronization.

Description

A method for determining reference time of scrambling code to support USTS in W-CDMA system

The present invention relates to a method for determining a scrambling code reference time point in a wideband code division multiple access system using a reverse synchronous transmission scheme. More particularly, the present invention relates to a mobile station in an asynchronous wideband code division multiple access (W-CDMA) mobile communication network. The present invention relates to a method of determining a reference time point of a reverse scrambling code at a base station and a scrambling code offset at each mobile station according to the case in which a reverse synchronization scheme from a base station to a base station is applied.

In a conventional code division multiple access mobile communication network, a call path generated between a mobile station and a base station includes a forward channel and a reverse channel. In the case of a forward channel transmitted from a base station to a mobile station, a plurality of channels existing in one base station are synchronized with each other, thereby significantly reducing inter-channel interference during decoding by using an orthogonal code having an orthogonality characteristic between each channel. You can. However, in the case of the reverse channel transmitted from the mobile station to the base station, the mobile station operates in an asynchronous form because the location and the transmission time point of the mobile station are different. As the channel of the mobile station increases, the interference in the reverse direction increases and the capacity is limited.

In the case of the reverse direction, the transmission time at the mobile station is adjusted to synchronize between the reverse channels, and multiple mobile stations use the same scrambling code and the division of the channels is orthogonal code to minimize the interference between the channels and the capacity. This method is called Uplink Synchronous Transmission Scheme (USTS).

In the USTS technology, in order to guarantee orthogonality between channel codes when multiple mobile stations use the same scrambling code in a reverse channel, a reference time point of this scrambling code must be promised at a base station, and based on this, an offset between a scrambling code and a transmission frame at the mobile station is used. This is determined.

In general, USTS refers to maximizing orthogonality between reverse channels in accordance with a reference time managed by a corresponding base station Node B for transmitting time points of a plurality of mobile stations UE in one base station cell. Is as follows.

The mobile station in the base station cell attempts a call connection using a reverse channel, and the base station measures a round trip propagation delay of the signal to obtain a time difference between the reference time and the frame start time of the mobile station that attempted the call connection. When the mobile station arrives at the mobile station, the base station informs the time difference from the reference time by calculation. By informing the time offset information from the base station to the mobile station using the control channel, the mobile station adjusts the frame transmission timing in the transmission channel so that the mobile station is received by the base station at the reference time held by the base station. The time of arrival of the signal from the mobile station to the base station is adjusted to the reference time by measuring the continuous time offset during the call, and transmitting to the mobile station and adjusting the transmission time at the mobile station. Other mobile stations attempting a call within the same base station are also informed of the time difference compared to the unique reference time held by the base station in the same manner to adjust the frame reference time to the base station's reference time.

This USTS is currently being considered in the standardization work for the next generation asynchronous mobile communication system, i.e., an asynchronous W-CDMA system. As described above, the USTS sets the reception timing at the base station receiver for the reverse link from the mobile station to the base station. It is a technique of adjusting the signal transmission timing in a mobile station as a reference. In other words, the mobile stations irregularly located in a single cell have different distances from the corresponding base station, so that the propagation delay of the signal is also different. It is possible to increase, and the technique applied to the reverse link in consideration of this is USTS. Further adjustment of the data transmission time at each mobile station by the propagation delay for the reverse link enables synchronization of the timing at which the signal is received at the base station receiver, thus maximizing the orthogonality of the code.

When USTS is applied in an asynchronous W-CDMA system, a mobile station and a base station use two codes, a scrambling code and a channel code. A scrambling code is used to distinguish between neighboring base stations and a channel code is used to distinguish a channel between mobile stations. Mobile stations used for the same scrambling code are canceled by the orthogonality of the channel code.

Currently, the structure of a downlink dedicated channel used in a general asynchronous W-CDMA system is as shown in FIG. 1, as shown in the figure. In the dedicated channel of the W-CDMA system, a system frame for each radio frame is shown. System Frame Number (SFN) (Frame n-1, Frame n, Frame n + 1, Frame n + 2) is repeated in units of 0 to 4096 chips and correspondingly, Connection Frame Nember: Hereinafter, CFN) is repeated in 256 chip units, and the interval between each SFN (or CFN), that is, the length of one radio frame is 10ms, and the network and the terminal are synchronized based on the SFN.

That is, since the length of one radio frame is 10ms in the forward (or downlink) downlink DPCH, it is composed of 15 sub slots (slot # 0 to slot # 14). In order to apply the USTS scheme in a dedicated channel structure of a W-CDMA system, Time Alignment Bit (TAB) information as a time offset information for timing adaptation of the USTS every 20ms (ie, one per two radio frames) is used. Is transmitted by puncturing instead of a transmit power control (TPC) bit carried in a corresponding radio frame.

The mobile station, which has received the TAB information, maintains synchronization with the reverse direction by performing timing adaptation based on the received TAB information. For example, if the TAB bit is "0", the uplink transmission from the mobile station is delayed by 1/4 chip. If the TAB bit is "1", the reverse link transmission is 1/4. The chip is sent as soon as possible. This procedure is called timing tracking.

On the other hand, in order to use the orthogonal characteristics of the channel code in the asynchronous W-CDMA system to which USTS is applied, the synchronization of the scrambling code repeated in the 38400 chip period (10 ms) as well as the channel code repeated in the 256 chip period must match. That is, at the moment the reverse link signal reaches the base station receiver, the scrambling codes of the reverse link signals of all mobile stations in the same cell must be identical and aligned on the time axis.

To this end, in consideration of the propagation delay between the base station and the mobile station as well as the time of transmission of the forward channel, the mobile station should be able to calculate the prediction and the offset of the scrambling code for the time when the signal to reach the base station receiver.

FIG. 2 shows an example of a reception timing diagram of a reverse signal received from two mobile stations UE1 and UE2 at a base station receiver when the USTS technique is applied. In FIG. 2, a dedicated channel (1) of a first mobile station UE1 is shown. Between the DPCH1 and the dedicated channel DPCH2 of the second mobile station UE2, the first channel codes a0 to a255 and the second channel codes b0 to b255 repeated in 256 chip cycles are used for the initial timing setting process and TAB. It can be seen that timing tracking is performed to synchronize at time points a0 and b0. However, the scrambling codes S0 to S38399 repeated in units of 38400 chips are shifted by 256x20 chips and offsets are generated.

As described above, even when timing adjustment is performed by the TAB, the offset of the reverse scrambling code is present. Therefore, the offset of the scrambling code received from the base station receiver in the cell is required in order to fully synchronize the reverse link in order to maximize the orthogonality of the code. The same must be adjusted for all mobile stations, for which it is necessary to be able to calculate the offset of the scrambling code, and to calculate the offset of the scrambling code, a setting for an arbitrary reference time point for the scrambling code is required.

That is, the offset of the scrambling code indicates the difference between the start boundary of the scrambling code and the start point of the reverse channel frame. The offset of the scrambling code is different depending on the reference time point of the scrambling code. Since it can be set to an appropriate arbitrary value, when applying the USTS technology to the asynchronous W-CDMA system, a method of determining the optimal time point of the scrambling code for calculating the offset of the scrambling code for the synchronization of the scrambling code is required.

SUMMARY OF THE INVENTION The present invention has been made in accordance with the above requirements, and an object thereof is to provide an optimal method for determining a reference time point of a scrambling code in an asynchronous W-CDMA system to which USUS is applied. It is an object of the present invention to provide a method for determining a scrambling code reference time point in a wideband code division multiple access system to which a reverse synchronous transmission scheme is applied to minimize the amount of offset information of a corresponding scrambling code.

1 is a structural diagram of a forward link dedicated channel used in an asynchronous W-CDMA system,

2 illustrates an example of a reception timing diagram of a reverse signal received from two mobile terminals at a base station receiver;

3 is a timing diagram illustrating a method of determining a scrambling code reference time point in a wideband code division multiple access system to which a reverse synchronous transmission scheme is applied according to an embodiment of the present invention. Is a diagram showing the time relationship between

4 is a diagram illustrating a relationship between a scrambling code offset and a time point at which a scrambling code is restarted according to the present invention.

※ Explanation of code for main part of drawing

31: boundary of primary common control physical channel frame

32: Forward dedicated channel frame

33: reverse dedicated channel frame

In order to achieve the above object, the scrambling code reference timing determination method in the wideband code division multiple access system to which the reverse synchronous transmission method is applied according to the present invention is provided. A method of determining a reference time point of a code, comprising: a first step of setting a frame boundary of a forward common channel as a first reference point; And taking the integer multiple of the repetition period value of the channel code from the set first reference point and adding a predetermined chip value to compensate for the time delay between the base station and the mobile station, and setting the second reference point as the second reference point. And a second step of determining the reference time point of the scrambling code for the corresponding mobile station.

In addition, the forward common channel is a primary common control physical channel (P-CCPCH), the repetition period of the channel code is 256 chips, the repetition period of the scrambling code is 38400 chips, the integer Is a number greater than or equal to 0 and less than or equal to 149.

Hereinafter, a method of determining a scrambling code reference time point in a wideband code division multiple access system to which a reverse synchronous transmission scheme according to a preferred embodiment of the present invention is applied will be described in detail with reference to the accompanying drawings.

First, although described above in the background of the present invention, once again describing the USTS technology, USTS is used as orthogonality between each reverse channel in accordance with a reference time managed by a base station for transmission of a plurality of mobile stations in one base station. In this case, the first mobile station in the base station cell attempts a call connection using a reverse channel, and the Node B of the base station measures a round trip propagation delay of the signal to determine the time between the reference time and the frame start time of the mobile station that attempted the call connection. Find the difference. By providing information on the time difference from the base station to the mobile station using the control channel, the mobile station adjusts the frame reference time in the transmission channel to the reference time held by the base station. Even during a call, the time difference is continuously measured and transmitted to the mobile station, and the mobile station adjusts the transmission time point accordingly so that the base station arrival time of the mobile station matches the reference time. At this time, the mobile station and the base station use two codes, a scrambling code and a channel code. The channel code is used to distinguish the mobile station from the channel, and mobile stations using the same scrambling code are eliminated by the orthogonality of the channel code. However, even in this case, the uplink scrambling code must be synchronized with the base station to ensure orthogonality. In the case of USTS, since the boundary of the uplink channel frame is a multiple of 256 chips among the mobile stations, the uplink scrambling code and the scrambling in each mobile station are eventually used. There is an offset between the scrambling code boundaries. The offset depends on how the base station sets the reference time of the scrambling code, and by defining the effective time, information about the scrambling code offset can be managed more efficiently.

On the other hand, in the general asynchronous W-CDMA to which USTS is not applied, each mobile station has its own scrambling code, and this scrambling code coincides with a frame boundary of 10 ms so that the above-described offset of the scrambling code does not occur.

3 is a timing diagram illustrating a method of determining a scrambling code reference time point in a wideband code division multiple access system to which a reverse synchronous transmission scheme is applied according to an embodiment of the present invention. A diagram showing the time relationship between them.

Referring to the figure, the base station has a Primary Common Control Physical Channel (P-CCPCH), which is one of the forward common channels, and this channel defines the reference time of the base station.

For a DL DPCH frame 32, the frame 32 starts after τ _{DPCH, n} (n represents a channel for each mobile station) relative to the boundary 31 of the P-CCPCH frame. Τ _{DPCH, n} is set differently for each mobile station in units of 256 chips. That is, the τ _{DPCH, n} value represents a difference between the time point of the boundary 31 of the P-CCPCH frame and the time of transmission of the forward dedicated channel frame 32.

In the case of a UL DPCH frame 33, a mobile station transmits data according to a predetermined reference time point to operate as a USTS. The start time point of the reverse dedicated channel frame 33 is the P-CCPCH from a base station point of view. From the boundary 31 of the frame comes after 'T0 + Tref + τ _{DPCH, n} '. Here, T0 is a nominal time difference between the forward channel reception and the reverse channel transmission of the mobile station in the conventional scheme, and is set to 1024 chips, and Tref is a parameter value to compensate for the time delay between the base station and the mobile station in the USTS. One base station has one value.

Therefore, since the T0 and the Tref value are fixed values, the start time of the reverse dedicated channel frame 33 is different for each mobile station according to the variable τ _{DPCH, n} value, and 256 chip intervals are provided for each mobile station, that is, each channel. Have. This means that since the maximum length of the channel code used in the reverse channel is 256 chips (the channel code is repeated in 256 chip cycles), there is no problem in satisfying the channel orthogonality between each reverse dedicated channel frame.

The reverse scrambling code is repeated with a period of 10 ms (= 38400 chips). In order to obtain orthogonal effects in the reverse direction, each mobile station must use the same scrambling code, and from the base station perspective, the scrambling code of the reverse dedicated channel frame received from each mobile station must be started at the same time.

However, as described above, the dedicated channel of each mobile station, that is, the forward dedicated channel frame 32 is delayed by τ _{DPCH, n} from the P-CCPCH boundary 31, so that the reverse dedicated channel frame received at the base station ( 33 The boundary is also different by multiples of 256 chips between mobile stations.

In the conventional W-CDMA scheme, since the reverse channel operated asynchronously, the period of the frame and the scrambling code of the reverse channel were coincident, but in the USTS, the offset must be able to be calculated so that a mobile station-specific offset is generated between the two. This offset can be obtained according to how the reference time point of the scrambling code is determined.

Therefore, in the present invention, the reference time point of the scrambling code is defined as the boundary 31 of the P-CCPCH frame or 'n × 256 chips + Tref, (n = 0 to 149) from the boundary 31 of the P-CCPCH frame. Set to the point later.

In FIG. 3, D1 is a scrambling code offset when the reference time point of the scrambling code for one terminal in the base station is set to 'T0 + Tref' (that is, in the case of n = 4). In this case, the scrambling code offset of the corresponding mobile station is τ _{DPCH, n} (= D1), and this value is informed to the mobile station from the base station when the call is set up. There is no need to inform separately.

However, in the case of soft handoff, it is necessary to inform the new base station of this value. In this case, only 8 bits of information can transmit the scrambling code offset of the corresponding mobile station. In addition, since τ _{DPCH, n} is a multiple of 256 chips, the boundary of the reverse dedicated channel frame and the scrambling code are all different by a multiple of 256 chips, so that the boundary of the scrambling code and the boundary of the channel code coincide with each other. Done.

Meanwhile, the scrambling code offset is determined only by τ _{DPCH, n} even when the reference time point of the scrambling code is not equal to n = 4 as in the above-described example, so the above description is applied as it is.

In Fig. 3, D2 does not consider the Tref value as in the example of the present invention described above in determining the reference time point of the scrambling code (i.e., 'n × 256 chips + Tref, (n = from the boundary of the P-CCPCH frame). inde scrambling code offset in the case 0-149) jeonghaejun only "frame boundary 31 of the value without determining a reference point of a scrambling code to the point) P-CCPCH in the back by the offset in this case, the scrambling code is Tref and τ _{DPCH, Since} it is determined by two parameters, a larger amount of bits are needed to inform the scrambling code offset information from the base station to the mobile station.

Therefore, in the present invention, in order to reduce the amount of information transmitted between the base station and the mobile station, the former method, i.e., 'n × 256 chips + Tref, (n = 0 to 149)' from the boundary of the P-CCPCH frame The reference time point of the scrambling code is determined by the time point of.

4, a reference time point of the scrambling code as described with reference to FIG. 3 is a time point 'n0256 chip + Tref (n = 4)' from the boundary of the P-CCPCH frame, that is, 'T0 + Tref'. When the scrambling code offset and the scrambling code is restarted is shown.

In the figure, the reverse channel frame (UL DPCH frame) 42 starts with a delay of the scrambling code offset τ _{DPCH, n} from the boundary 41a of the scrambling code 41, and there is 38400 chips in one frame, so scrambling The reset point 43 of the code restart is '38400 chip-scrambling code offset', that is, '38400 chip-τ _{DPCH, n} '. Therefore, according to the present invention, it can be seen that the restart time of the scrambling code in the mobile station is also determined only by τ _{DPCH, n} .

As described in detail above, according to the method of determining a scrambling code reference time point in a wideband code division multiple access system to which a reverse synchronous transmission method according to the present invention is applied, an optimal time point for a scrambling code reference time point in an asynchronous W-CDMA system to which USTS is applied In addition, it provides a method of determining the size of the scrambling code, and in particular, minimizes the amount of offset information of the corresponding scrambling code provided from the base station to the mobile station, and allows the boundary of the scrambling code and the channel code to coincide with each other, thereby implementing an optimal backward synchronization. Created.

Claims (3)

A method of determining a reference time of a scrambling code in a wideband code division multiple access system base station to which a reverse synchronous transmission scheme is applied, A first step of setting a frame boundary of the forward common channel as the first reference point; And From the set first reference point, an integer multiple of the repetition period value of the channel code is added to the second reference point after the sum of the preset chip values in order to compensate for the time delay between the base station and the mobile station. And a second step of determining the reference time point of the scrambling code for the mobile station. The method of claim 1, The forward common channel is a primary common control physical channel (P-CCPCH), characterized in that the scrambling code reference time determination method in a wideband code division multiple access system to which the reverse synchronization transmission method is applied. The method according to claim 1 or 2, The repetition period of the channel code is 256 chips, the repetition period of the scrambling code is 38400 chips, and the integer is a number from 0 to 149, the scrambling in the wideband code division multiple access system to which the reverse synchronization transmission method is applied. How to determine the code baseline.