KR100511668B1 - Apparatus and method for OVSF code search in mobile communication system - Google Patents

Abstract

The present invention provides an apparatus and method for OVSF search of a mobile communication system, comprising: a front end portion of a receiver for transmitting a signal processed by a base station through an antenna; Including the OVSF search unit to find the re-spread power level in the transmission signal of the front end unit to search for the user's OVSF to perform the re-spreading, the receiving end of the base station using the user's own re-spread power level of the transmission signal The spreading factor and channel number of the OVSF that is used can be found and respreaded.

Description

Apparatus and method for OVSF code search in mobile communication system

The present invention relates to an orthogonal variable spreading factor (OVSF) code retrieval apparatus and a method thereof of a mobile communication system. In particular, a spreading factor of an OVSF used by a user by using a re-spreading power level of a transmission signal in a receiving end of a base station. The present invention relates to an OVSF code retrieval apparatus and method for mobile communication system suitable for finding and reproducing a channel number.

In general, a mobile communication system is a communication system that targets mobile devices such as people, cars, ships, trains, and airplanes, which includes key phone systems, mobile phones (mobile phones, vehicle phones), port phones, aircraft phones, and mobile phones. Trains, cruise ships, express buses), radio calling, radiotelephony, satellite mobile communication, amateur radio, and fishing service ships.

The mobile communication system includes an AMPS (Advanced Mobile Phone Service) system using an analog method, a Code Division Multiple Access (CDMA) system using a digital method, a Wideband Code Division Multiple Access (WCDMA), and a TDMA (Time). Division Multiple Access, Time Division Multiple Access (FDMA) system, Frequency Division Multiple Access (FDMA) system, Wireless Local Loop (WLL), CDMA2000-1x, IMT-2000 (International Mobile Telecommunication in the year 2000 , Global mobile communications) systems.

1 is a block diagram of a general mobile communication system.

As shown therein, a wireless operation apparatus (Base Station Manager, BSM) 10 for performing wireless operation of the mobile communication system; A network management device (Network Management System, NMS) 20 connected with the wireless operation device 10 to manage a mobile communication system; A base station controller (BSC) 30 which is connected to the radio operation apparatus 10 and controls a radio link and a wire link and performs a handoff function for maintaining a continuity of a call even when a subscriber is moving; It is connected to the wireless operation device 10, and comprises a base station (Base Transceiver Station, BTS) 40 for performing communication using a protocol in a wireless section with the terminal.

2 is a block diagram of a base station of a conventional mobile communication system.

As shown therein, the modem 41 receives and modulates a signal from the base station controller 30; A transceiver (42) connected to the modem (41) to perform signal transmission / reception processing; A power amplifier 43 connected to the transceiver 42 to amplify the power of the received signal; It is composed of a front end (44) so that the signal amplified by the power amplifier 43 is transmitted through an antenna.

On the other hand, in a CDMA system or the like, multiple users may be connected by using a specific spreading code to spread the bandwidth of the original information bit. In IS-95 (PCS, cellular), a spread called PN-code (Pseudo Noise code) was used. In the asynchronous IMT-2000 system, a code called OVSF is used to spread the original information bits. This use of OVSF is defined in the 3rd Generation Partnership Project (3GPP) Specification.

Therefore, conventionally, the receiving end performs a normal despreading process using the information of the OVSF code provided by the transmitting end.

However, the technique using the OVSF code provided to the conventional transmitter has the following problems.

That is, due to the characteristics of the OVSF code, the retransmission signal is also detected in another OVSF code located in the lower SF (Spreading Factor) or the upper SF of the OVSF branch where the specific OVSF code assigned to the user exists. If you do not use the exact information of the OVSF provided by, it is difficult to determine the OVSF code that the actual user is using, so the correct respreading process cannot be performed.

Therefore, there was a difficulty in that the transmitting end had to provide accurate OVSF information to the receiving end.

Accordingly, the present invention has been proposed to solve the above conventional problems, and an object of the present invention is to use a spreading factor of the OVSF that is used by a user by using a respread power level of a transmission signal at a receiving end of a base station. An object of the present invention is to provide an apparatus and method for OVSF code retrieval in a mobile communication system capable of finding a channel number and performing respreading.

In order to achieve the above object, an OVSF code search apparatus of a mobile communication system according to an embodiment of the present invention,

An analog / digital converter for converting an output signal of the base station into a digital signal; a descrambler for descrambling the digital signal; Technical features of the present invention include an OVSF processing unit for searching the entire OVSF code for the descrambled signal and calculating an assigned OVSF code.

In order to achieve the above object, an OVSF code search method of a mobile communication system according to an embodiment of the present invention,

 Converting a transmission signal of the base station into a digital signal; Descrambling the digital signal; And a third step of calculating an assigned OVSF code by searching an OVSF code for the descrambled signal, wherein the third step comprises: selecting a OVSF code to be searched again; Calculating a re-spread symbol power using the selected OVSF code; And a third step of calculating an allocated OVSF code using the calculated re-spread symbol power.

Hereinafter, an embodiment according to the present invention, the OVSF code retrieval apparatus of the mobile communication system and the method configured as described above will be described in detail with reference to the accompanying drawings.

3 is a block diagram of an OVSF search apparatus of a mobile communication system according to the present invention.

As shown here, the front end portion 44 of the receiving end for transmitting a signal processed by the base station through the antenna; The OVSF search unit 50 is configured to search for a user's OVSF by searching for a respread power level in the transmission signal of the front end unit 44 and perform respreading.

The OVSF search unit 50 includes an analog / digital converter 51 for converting a transmission signal, which is an analog signal of the front end unit 44, into a digital signal; A descrambler (52) for descrambling the digital signal converted by the analog / digital converter (51); And an OVSF processing unit 53 for searching the entire OVSF code for the descrambled signal and calculating an assigned OVSF code.

4 is a flowchart illustrating an OVSF search method of a mobile communication system according to the present invention.

First of all, the OVSF code retrieval method of the mobile communication system according to the present invention includes: a first step of converting a transmission signal of a base station into a digital signal; Descrambling the digital signal; And a third step of searching for an OVSF code for the descrambled signal and calculating an assigned OVSF code. Referring to FIG. 4 in detail, the OVSF for measuring a level of respread symbol power is measured. Determining (ST11); Performing OVSF respreading after this step to measure respread symbol power and filter the respread symbols (ST13 to ST14); If this step is performed, the step of calculating the level of the re-spread symbol power is performed to perform case determination according to the calculated symbol power level (ST15).

In the case determination step, in case determination, SF is M, CH is N, OVSF (a, b) is an OVSF code having SF = a and channel number = b, and pow_lev (a, b) is When implying the number of respread symbol power levels for OVSF (a, b),

[pow_lev (M, N) <pow_lev (2M, 2N)] or [pow_lev (M, N) <pow_lev (2M, 2N + 1)]

If a case determination is made, then the assigned OVSF is OVSF (M, N).

In the case determination step, at the time of case determination,

[pow_lev (M, N)> = pow_lev (2M, 2N)] or [pow_lev (2M, 2N + 1) = 0]

When the case decision is made as shown in FIG. 2, the upper tree of the OVSF (2M, 2N) is searched to search the allocated OVSF.

In the case determination step, at the time of case determination,

[pow_lev (M, N)> = pow_lev (2M, 2N + 1)] or [pow_lev (2M, 2N + 1) = 0]

When the case decision is made as follows, the upper tree of OVSF (2M, 2N + 1) is searched to search the allocated OVSF.

In the case determination step, at the time of case determination,

[pow_lev (M, N)> = pow_lev (2M, 2N)] or [pow_lev (M, N)> = pow_lev (2M, 2N + 1)]

When the case decision is made as shown in FIG. 2, the upper tree of each of OVSF (2M, 2N) and OVSF (2M, 2N + 1) is searched.

The operation of the OVSF code retrieval apparatus and method of the mobile communication system according to the present invention configured as described above will be described in detail with reference to the accompanying drawings.

First, the present invention seeks to perform respreading by finding a spreading factor and channel number of an OVSF used by a user at a receiving end of a base station.

Thus, the present invention does not require the receiving end to use the OVSF information for each user possessed at the transmitting end. That is, the receiver may search for the OVSF code by using the number of respread power levels of the transmission signal to perform the normal respreading process by itself. Therefore, each user's OVSF-related information necessary for the re-spreading process for signal recovery is retrieved by itself.

In addition, if noise with a large variation is added to the transmission signal, the performance of the search algorithm greatly affects performance. Therefore, an additional noise cancellation technique is required. Otherwise, it is used for self-verification of the transmitter. It is suitable to be used as an independent module or device.

Referring to Figure 4 describes the operation of the present invention in detail as follows.

First, the OVSF to measure the level of respread symbol power is determined. At this time, there may be a plurality of OVSF. The search point is set to include a spreading factor (SF), a channel number, a repetition number, and the like.

The respread process is performed using the determined OVSF, and the respread symbol power is measured.

Since the power of the re-spread symbol is calculated in the unit of float, and countless power levels are generated, the power value is filtered to an appropriate level by using related parameters for efficient operation of the algorithm.

In order to calculate the number of power levels, it is necessary to measure the re-spreading symbol by an appropriate period. If it is assumed to be 1 slot, it is necessary to measure as much as 2560 chips.

Therefore, repeat iteration is set to repeat 2560 times in case of 1 slot. Here, 2560 chips per slot is a standard defined in the asynchronous IMT-2000 specification. When a transmitter transmits a signal, it transmits in units of one slot. In this case, one slot corresponds to a 0.667 msec interval, and the number of chips included is 2560. That is, the number of chips transmitted in one slot is 2560.

The respread symbol power level is then calculated.

By this calculation, the number of symbol power levels can be determined, and the case determination is performed accordingly.

Thus, if it is confirmed that the allocated OVSF is correct and that the allocated OVSF is found, that is, if an OVSF code having the minimum number of symbol power levels is found, the code is determined as the assigned OVSF code and the OVSF having the lower SF of the same branch is determined. The search stops.

On the other hand, the core idea of the present invention is that the number of respread power levels of the OVSF allocated to the user at the transmitting end is small compared with other OVSFs in the same branch. In other words, search for the OVSF having the minimum number of respread power levels while searching from the smallest OVSF in the branch.

Here, the number of power levels means the number of levels during a specific period (for example, 1 slot = 2560 chips) with respect to the result obtained when the transmitted signal input in the chip unit is re-spread and converted into the bit unit by the specific OVSF. Say.

1. Assigned OVSF

The number of power levels that can be obtained in the case of re-diffusion is 1 (A ^ 2) without DTX (Discontinuous Transmission), and 2 (0, A ^ 2) with DTX. Have. That is, the number of power levels in the code allocated in the branch will have a minimum value.

If there is no information bit to be transmitted, a specific bit is randomly generated and not sent in succession. That is, when the magnitude value is viewed, it is 0 [mv]. So 1 means power level A ^ 2, and 2 means 0 and A ^ 2. In addition, if there is no DTX, it means that it has a magnitude value in all sections, so taking the square of the magnitude value is a power value, so if the magnitude value is A, it will have A ^ 2. Since the magnitude value is 0 in the interval, it has A ^ 2 and 0.

2. OVSF with SF lower than OVSF allocated in the same branch

2.1 Single user per a branch

This will have the same power level number as the assigned code. This is because if the symbols spread using the assigned code are respread to smaller SFs, only one symbol is divided into a plurality of identical symbols, and since the respreading period is reduced by the corresponding SFs, the power levels will be the same. to be.

2.2 Multiple user per a branch

It will have a power level number equal to or greater than the assigned code. This is because a plurality of OVSFs may be assigned to the same branch and thus may have random power levels.

3. OVSF with SF greater than OVSF allocated in the same branch

Since the OVSF has a different amplitude value according to the amplitude combination (even_bit-odd_bit pair) in the OVSF which is SF / 2, the number of power levels is further increased.

This is because the amplitude level pattern of the symbols that attempt to despread from the OVSF allocated by the transmitter is despread to the assigned "OVSF with twice the SF of the OVSF". )). In other words, "the OVSF in the same tree where SF is twice as large as the assigned OVSF" is different from the allocated OVSF and the code itself is the same but twice the period. Therefore, if you average the two amplitude level patterns obtained by respreading with an "assigned" OVSF, you can obtain them by respreading them as "OVSF with twice as much SF as the assigned OVSF," depending on how much the two amplitude values are. The amplitude level pattern is wrong.

5 is a graph showing a power level distribution according to SF in a branch in which an allocated OVSF used in the present invention exists.

So, based on the amplitude level obtained by re-spreading using the assigned OVSF, if you re-spread using the OVSF with the smaller SF among the OVSFs in the same OVSF tree, you can get the same or more number of amplitude levels. If we re-spread using OVSF with large SF, we can get more amplitude level.

FIG. 6 is a state diagram illustrating a relationship between an allocated OVSF, an OVSF having a low SF, and an OVSF having a high SF, which are used in the present invention. FIG. 7 is a diagram illustrating an example of a power level measurement of each OVSF in FIG. 6.

6 and 7 show different periods when the input signal is fixed and then respread using OVSF having 1/2 times SF and OVSF having 2 times SF in the tree to which the allocated OVSF belongs. Here is an example that illustrates the incorrect number of power values.

Therefore, FIGS. 6 and 7 simply show examples of power levels measured in the OVSF code in the same branch as the corresponding OVSF code when a user uses a specific OVSF code. The power level distribution as shown in FIG. It can be seen that.

FIG. 8 is a block diagram illustrating a case determination operation of FIG. 4.

So SF is M, CH is N, OVSF (a, b) is an OVSF code with SF = a and channel number = b, and pow_lev (a, b) is a respread symbol for OVSF (a, b) In terms of the number of power levels, there are four cases:

1.Case 1: [pow_lev (M, N) <pow_lev (2M, 2N)] or [pow_lev (M, N) <pow_lev (2M, 2N + 1)]

In this case, the assigned OVSF is OVSF (M, N).

There is no need to search for the lower branches of OVSF (2M, 2N) and OVSF (2M, 2N + 1). This is because the OVSF code cannot assign to OVSFs that depend on the assigned OVSF.

2. Case 2: [pow_lev (M, N)> = pow_lev (2M, 2N)] or [pow_lev (2M, 2N + 1) = 0]

This case means that the assigned OVSF is in the OVSF with the upper SF in the same branch.

In order to search the assigned OVSF, the search is performed in the same manner with respect to the upper tree of OVSF (2M, 2N).

There is no need to search the upper tree of OVSF (2M, 2N + 1).

3. Case 3: [pow_lev (M, N)> = pow_lev (2M, 2N + 1)] or [pow_lev (2M, 2N + 1) = 0]

This is similar to Case 2, replacing OVSF (2M, 2N) with OVSF (2M, 2N + 1).

4. Case 4: [pow_lev (M, N)> = pow_lev (2M, 2N)] or [pow_lev (M, N)> = pow_lev (2M, 2N + 1)]

This makes a search for each higher tree of OVSF (2M, 2N) and OVSF (2M, 2N + 1).

Applying this invention can be performed as follows.

The base station used in WCDMA needs to check whether the power specified for each user is properly applied and transmitted.

To check this, measurement equipment capable of measuring transmit power per user may be used, or a self-diagnostic board may be used in the base station.

Either way, there is a common problem that the base station must know the assigned OVSF code when the base station assures each user's signal. In this case, if the information on the allocated OVSF code is impossible or cannot be received by the base station, if it is found through its own search, completely independent modularization is possible.

As described above, the present invention performs respreading by finding the spreading factor and channel number of the OVSF used by the user by using the number of respread power levels of the transmission signal by the receiving end of the base station.

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

As described above, the OVSF retrieval apparatus and method of the mobile communication system according to the present invention has the effect that the receiving end does not have to use the OVSF information for each user having the transmitting end. That is, the receiver may search for the OVSF code by using the respread power level of the transmission signal to perform the normal respreading process. Therefore, each user's OVSF-related information necessary for the re-spreading process for signal recovery is retrieved by itself.

1 is a block diagram of a general mobile communication system,

2 is a block diagram of a base station of a conventional mobile communication system,

3 is a block diagram of an OVSF search apparatus of a mobile communication system according to the present invention;

4 is a flowchart illustrating an OVSF search method of a mobile communication system according to the present invention;

5 is a graph showing power level distribution according to SF in a branch in which an allocated OVSF used in the present invention exists.

6 is a state diagram showing the relationship between the assigned OVSF used in the invention, the OVSF having a low SF and the OVSF having a high SF,

FIG. 7 is a diagram illustrating an example of power level measurement of each OVSF in FIG. 6.

FIG. 8 is a block diagram illustrating a case determination operation of FIG. 4.

Explanation of symbols on the main parts of the drawings

10: Wireless operation device (BSM) 20: Network management device (NMS)

30: base station controller (BSC) 40: base station (BTS)

41: modem 42: transceiver

43: power amplifier 44: front end

50: OVSF search unit 51: analog / digital conversion unit

52: descrambler 53: OVSF processing unit

Claims (7)

An analog / digital converter for converting an output signal of the base station into a digital signal; A descrambler for descrambling the digital signal; And an OVSF processing unit configured to search the entire OVSF code for the descrambled signal and calculate an allocated OVSF code using the number of respread symbol power levels. delete        Selecting a OVSF code to search for;        Calculating a re-spread symbol power using the selected OVSF code;        And calculating a allocated OVSF code using the calculated number of respread symbol power levels. The method of claim 3, wherein the third step, In case determination, SF is M, CH is N, OVSF (a, b) is an OVSF code with SF = a and channel number = b, and pow_lev (a, b) for OVSF (a, b). When we mean the number of respread symbol power levels, [pow_lev (M, N) <pow_lev (2M, 2N)] or [pow_lev (M, N) <pow_lev (2M, 2N + 1)] When the case determination is made, such that the assigned OVSF is OVSF (M, N) characterized in that the mobile communication system OVSF code search method. The method of claim 3, wherein the third step, In case determination, SF is M, CH is N, OVSF (a, b) is an OVSF code with SF = a and channel number = b, and pow_lev (a, b) for OVSF (a, b). When we mean the number of respread symbol power levels, [pow_lev (M, N)> = pow_lev (2M, 2N)] or [pow_lev (2M, 2N + 1) = 0] When the case determination is made as follows, the OVSF code search method of the mobile communication system, characterized in that for searching the upper tree of the OVSF (2M, 2N) to search the assigned OVSF. The method of claim 3, wherein the third step, In case determination, SF is M, CH is N, OVSF (a, b) is an OVSF code with SF = a and channel number = b, and pow_lev (a, b) for OVSF (a, b). When we mean the number of respread symbol power levels, [pow_lev (M, N)> = pow_lev (2M, 2N + 1)] or [pow_lev (2M, 2N + 1) = 0] When the case determination is made as follows, the OVSF code search method of the mobile communication system, characterized in that for searching the upper tree of the OVSF (2M, 2N + 1) to search the assigned OVSF. The method of claim 3, wherein the third step, In case determination, SF is M, CH is N, OVSF (a, b) is an OVSF code with SF = a and channel number = b, and pow_lev (a, b) for OVSF (a, b). When we mean the number of respread symbol power levels, [pow_lev (M, N)> = pow_lev (2M, 2N)] or [pow_lev (M, N)> = pow_lev (2M, 2N + 1)] When the case determination is made, the OVSF code search method of the mobile communication system, characterized in that for searching the upper tree of each of the OVSF (2M, 2N) and OVSF (2M, 2N + 1).