KR20000073314A - A Preamble receiver for CDMA system - Google Patents

Abstract

PURPOSE: A preamble receiver of a code division multiple access(CDMA) system, is provided to efficiently receive a preamble of an access channel by using a signature where 0(zero) is inserted and a correlation bank having correlators, so that system performance can be improved. CONSTITUTION: A code division multiple access(CDMA) system receives a predetermined preamble through a random access channel of a reverse link, when propagation delay exists between a base station configuring an optional cell and a terminal in the cell area. A signature generator generates a predetermined signature symbol and a signature symbol having added 0(zero) from 1(one) to (N-1), by referring to wave delay. A signature correlation bank(30) has N of signature correlators. Each of the signature correlators multiplies interface-filtered receiving signals by the signature symbol or the zero-added signature symbol, to output a correlation signal. N accumulation banks(40-1/40-N) respectively receive and accumulate outputs of the signature correlators. A decider(50) receives outputs of the accumulation banks and selects a maximum value. And the decider(50) compares the maximum value with a predetermined threshold, to decide whether receiving is successful.

Description

Preamble receiver for code division multiple access system {A Preamble receiver for CDMA system}

The present invention relates to a preamble receiver for receiving a preamble for random access in a code division multiple access (CDMA) system applied to a next generation mobile communication system (IMT-2000).

In recent years, the International Telecommunication Union (ITU-R) has recommended several features that the International Mobile Telecommunication-2000 (IMT-2000) system should have as a global standard for mobile communication. It is becoming. As such, the systems proposed as IMT-2000 system are largely using synchronous CDMA technology and asynchronous CDMA technology. Synchronous and asynchronous CDMA systems use direct sequence spread band method as a wireless access method, and use voice and non-voice. Can provide services.

In the IMT-2000 system, the radio access standard has a hierarchical structure. The channel structure of the physical layer is independently used by the common channel and the terminal unit commonly used between the forward channel and the reverse channel, and the base station and the terminal station. It is divided into dedicated channels. For example, in the synchronous CDMA system, in the forward link, a pilot channel for fast synchronization acquisition and tracking by providing time and phase and signal strength information, a synchronization channel for initially acquiring time synchronization, and independent of all information and terminals of the system There are a paging channel, a signal channel, a traffic channel, etc. for transmitting the information transferred to the reverse link, and in the reverse link, there are a pilot channel, a signal channel, a traffic channel, etc., which are used independently from an access channel commonly used. In this case, the access channel transmits various response signals by performing a function corresponding to the paging channel in the forward direction, and is used for channel setup, that is, call setup of the terminal and the base station.

Asynchronous CDMA systems also have multiple channels on the forward and reverse links. In particular, it is necessary to accurately receive preambles received through a random access channel (RACH) on the reverse link. That is, in a mobile communication network composed of a plurality of cells, the base station apparatus does not know the location of the terminals belonging to its own cell. Therefore, the preamble receiver should be designed in consideration of the delay according to the cell size.

Accordingly, the present invention has been proposed to meet the above necessity, and an object thereof is to provide a preamble receiver capable of accurately receiving a preamble in consideration of propagation delay time.

In order to achieve the above object, the apparatus of the present invention is divided into a plurality of cell regions, and when there is a propagation delay time of Tp between a base station constituting an arbitrary cell and a terminal located in the cell region, In a CDMA system capable of receiving a predetermined preamble through a random access channel,

Signature symbol generating means for generating a predetermined signature symbol and a signature symbol having zeros added from 0 to N-1 in consideration of propagation delay; A signature correlation bank comprising N signature correlators, each signature correlator multiplying a matched filtered reception signal with the signature symbol or a zero-signed signature symbol to output a correlation signal; N cumulative banks receiving and accumulating the outputs of the signature correlators; And determining means for receiving the output of the cumulative bank, selecting a maximum value, and then determining whether the reception is successful by comparing with a predetermined threshold value.

As described above, the present invention calculates the output of the 256-tap matching filter using in-phase components and quadrature components to form a signature correlation bank, and the correlation value is calculated for a predetermined preamble time (1 ms) in the cumulative bank. Accumulate can receive the preamble efficiently.

1 illustrates a structure of a random access channel of a CDMA system to which the present invention is applied;

FIG. 2 illustrates a procedure of transmitting a preamble unit and a message unit from a random access channel of FIG. 1 to a terminal;

3 is a view illustrating a detailed structure of a preamble part;

4 is a diagram illustrating timing of a random access procedure;

5 is a block diagram illustrating a random access channel preamble receiver of the present invention;

6 is a detailed block diagram of the cumulative bank i shown in FIG. 5;

FIG. 7 is a detailed block diagram of the determining unit illustrated in FIG. 5.

* Explanation of symbols for main parts of the drawings

10: matching filter 20: adder

30: Signature Correlation Bank 32-1 ~ 32-N: Signature Correlator

40-1 to 40-N: Cumulative bank 42: Adder

44: delay line 50: determination unit

52: maximum selector 54: comparator

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As described above, in the IMT-2000 system, which is deciding a standard as a third generation mobile communication technology, a random access channel (RACH) exists from a terminal to a base station in order to establish a communication channel in the reverse direction. As shown in FIG. 1, the random access channel transmission structure is largely divided into a preamble part and a message part. When the preamble spreading code is 256 chip periods and the chip rate is 4.096 Mcps, the preamble part of FIG. 1 is defined to have a length of 1 ms, and the message part is defined to have a length of 10 ms.

2 is a diagram illustrating a procedure of transmitting a preamble unit and a message unit from a terminal to a base station. Referring to FIG. 2, a preamble and a message are transmitted on an access channel of a reverse link, and an Acquisition Indication is transmitted on a forward link. In addition, the size of the preamble unit indicates the relative power level. At first, the preamble part transmits with a low power but gradually increases the power when there is no response. That is, the terminal repeatedly transmits a preamble of 1 ms until a signal indicating Acquisition Indication (AI) has been successfully received at the base station. When the terminal receives the AI signal, it transmits a message unit necessary for access.

3 shows a preamble structure of 1 ms. The preamble unit is divided into 16 kinds of preamble signatures (signatures hereinafter, simply referred to as signatures) as shown in Table 1 below, and each signature includes 16 preamble symbols as shown in FIG. 3. Each preamble symbol is composed of a preamble spreading code of 256 chip periods.

Preamble symbols Signature P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 One A A A -A -A -A A -A -A A A -A A -A A A 2 -A A -A -A A A A -A A A A -A -A A -A A 3 A -A A A A -A A A -A A A A -A A -A A 4 -A A -A A -A -A -A -A -A A -A A -A A A A 5 A -A -A -A -A A A -A -A -A -A A -A -A -A A 6 -A -A A -A A -A A -A A -A -A A A A A A 7 -A A A A -A -A A A A -A -A -A -A -A -A A 8 A A -A -A -A -A -A A A -A A A A A -A A 9 A -A A -A -A A -A A A A -A -A -A A A A 10 -A A A -A A A -A A -A -A A A -A -A A A 11 A A A A A A -A -A A A -A A A -A -A A 12 A A -A A A A A A -A -A -A -A A A A A 13 A -A -A A A -A -A -A A -A A -A -A -A A A 14 -A -A -A A -A A A A A A A A A -A A A 15 -A -A -A -A A -A -A A -A A -A -A A -A -A A 16 -A -A A A -A A -A -A -A -A A -A A A -A A

Referring to Table 1, there are 16 preamble signatures and each signature consists of 16 preamble symbols. In Table 1, A represents "1 + j", and the preamble diffusion code uses a gold code having a 256 chip period. At this time, there are 16 signatures for distinguishing when multiple users access the system at the same time. Each signature is orthogonal to each other.

FIG. 3 shows a preamble configuration when the i-th signature is used, and each preamble signature sequence Pi, j (j = 1, ..., 16) has a 256-chip period free. The preamble is 1ms long because it is spread by the symbol diffusion code, and in the embodiment of the present invention, the chip rate is 4.096 Mcps.

FIG. 4 is a timing diagram illustrating a procedure of transmitting and receiving a preamble unit, a response signal AI, and a message described with reference to FIG. 2. Referring to FIG. 4, the access slot timing of the base station and the access slot timing of the terminal are separated by a propagation delay time "Tp". This propagation delay time (Tp) is approximate when the cell radius is 30 km. to be. The base station receives the preamble after 2Tp time (called a round trip delay) from the access slot timing of the base station. That is, the 2Tp time is proportional to the distance between the base station and the terminal. Since the base station does not know the position of the terminal, this propagation delay time should be considered when designing the preamble receiver.

5 is a block diagram illustrating a preamble receiver of a random access channel in consideration of propagation delay time according to the present invention. As shown in FIG. 5, the preamble receiver of the present invention includes a 256-tap matching filter 10, an adder 20, a signature correlation bank 30, N cumulative banks 40-1 to 40-N, It is composed of the decision unit 50, the signature correlation bank 30 is composed of N correlators (32-1 ~ 32-N). In the embodiment of the present invention, the period of the spreading code is 256 chips, N is a terminal having a propagation delay Tp value (unit: sec) at the cell boundary area, the maximum length of one chip is Tc, and a preamble is one preamble. In the case where the symbol of k consists of k chips, an integer closest to 2Tp / (Tc × k) is determined.

Referring to FIG. 5, the received signal of the random access channel is applied to a matched filter 10 of 256 taps. The matched filter 10 outputs a correlation value for the 256 chips of the preamble spreading code, and unlike the correlator, the correlation value is output for each chip.

The adder 20 performs an operation as shown in Equation 5 to be described below so that only the cosine and the sinusoid remain in the in-phase (I) component and the quadrature (Q) component, respectively. The output computed in the adder 20 is applied to a signature correlation bank 30.

The signature correlation bank 30 includes a round trip delay (2Tp) as described above and a signature correlator corresponding to the number (N) determined according to the number of symbols. For example, if the chip rate is 4.096 Mcps, the length of one chip is The length of one symbol Becomes So assuming a 30km cell, the round trip delay (2Tp) Becomes the signature correlation bank 30 It should consist of three signature correlators. In this case, the first signature correlator 32-1 is multiplied with the signature sequence as it is, and the second signature correlator 32-2 has one zero in front of the signature sequence. The signature sequence inserted with the symbol is multiplied, and the Nth signature correlator 32-N is multiplied with the signature sequence with N-1 zero symbols inserted. That is, the signature input to each of the correlators 32-1 to 32-N is any one of 16 signatures, and at least in consideration of a signature for receiving a preamble when there is no propagation delay and a propagation delay, A signature with one or more zero symbols added is generated in a signature generator (not shown). Therefore, the receiver of the base station needs to have at least 16 preamble receivers in order to receive all 16 signatures. At this time, the signature with one additional zero is for receiving a preamble when the propagation delay is within 256 chips (ie, one cycle of the spreading code), and the signature with two zeros is 256 ×. It is for receiving a preamble in the case of two chips or less. In the same way, the N-1 zero-signature is for receiving the preamble transmitted at the maximum delay point of the cell radius. Thus, the receiver of the present invention transmits the terminal at any point within the cell radius. One preamble can be correctly received.

The output from the signature correlation bank 30 is applied to each cumulative bank 40-1 to 40-N and accumulates by the number of symbols (16 times) to obtain a correlation value for the 1 ms preamble. Accumulate. A detailed configuration of the i-th accumulation bank is shown in FIG. 6.

Referring to FIG. 6, each cumulative bank 40-i (i is 1 to N) is a sum adder 42 operating at 1 / Tc speed, and a relay line for delaying 256 samples and outputting them in parallel (256 sample). Delay line: 44, when the value calculated in units of chips from the signature correlation bank 30 is processed in the adder 42 and the delay line 44 at a rate of 1 / Tc, 1ms pre When the reception of the emblem is completed, 256 parallel data are output to the determination unit 50. That is, when 256 x N correlation values for the 1 ms preamble are obtained, they are provided to the decision circuit 50. Where Tc is the length of the chip and in the embodiment of the present invention Tc is 1 / 4.096 Mcps (about 244 kV).

As shown in FIG. 7, the decision unit 50 includes a maximum selector 52 and a comparator 54. The maximum selector 52 is 256 x from the cumulative banks 40-1 to 40 -N. The N cumulative values are applied as decision variables to select a double maximum value, and the comparator 54 compares the maximum value with a preset threshold, and when the maximum value exceeds the threshold, the preamble Outputs a reception success signal (e.g., a high level signal) indicating successful reception. The base station apparatus transmits a response message AI to the terminal according to the reception success signal of the preamble receiver.

The mathematical interpretation of such a preamble receiver is as follows.

First, i-th signature When expressed as, 1ms preamble transmission signal Is equal to the following Equation 1.

here Is the preamble spreading code of 256 chip period, Is the size , The length It is a rectangular function.

And received signal Is as shown in Equation 2 below.

here , , Represents the attenuation factor, phase, and additive white Gaussian noise (AWGN) of each channel, Wow Is the received signal Denotes the in-phase and quadrature components of. In this case, it is assumed that there is no delay caused by the channel. For convenience, the AWGN component is removed and the equation is expanded as shown in Equation 3 below.

Meanwhile, 256-tap matched filter output of the preamble receiver Is as shown in Equation 4 below.

here ,

ego, to be.

The reminder after going through the adder 20 Is as shown in Equation 5 below.

In addition, the output of the cumulative banks 40-1 to 40-N Is as shown in Equation 6 below.

here, to be.

And a decision variable that is input to the decision unit 50. Equation 7 is as follows.

As described above, the preamble receiver of the present invention is implemented in the receiving portion of the base station apparatus so that the terminal in the corresponding cell of the base station can efficiently receive the preamble transmitted through the random access channel and send a response signal.

As described above, according to the present invention, a preamble of an access channel is propagated in a CDMA communication system in a wireless environment, which is divided into cells by using a zero-signed signature and a correlation bank having a plurality of correlators in consideration of propagation delay. It is possible to improve the performance of the communication system by accurately receiving in consideration of the delay.

Claims (5)

A CDMA system partitioned into a plurality of cell regions and capable of receiving a predetermined preamble through a random access channel when there is a propagation delay time of Tp between a base station constituting an arbitrary cell and a terminal located in the cell region. To Signature symbol generating means for generating a predetermined signature symbol and a signature symbol having zeros added from 1 to N-1 in consideration of propagation delay; A signature correlation bank comprising N signature correlators, each signature correlator multiplying a matched filtered reception signal with the signature symbol or a zero-signed signature symbol to output a correlation signal; N cumulative banks each receiving an output of each of the signature correlators and accumulating each other; And And a determining means for receiving the output of the cumulative bank, selecting a maximum value, and comparing the predetermined threshold with a predetermined threshold to determine whether the reception is successful. 2. The N symbol of claim 1, wherein the terminal is located at a cell boundary area, has a maximum Tp value (unit μsec), a time length of one chip is Tc μsec, and a symbol of one preamble includes k chips. The preamble receiver of the code division multiple access system, characterized in that the case is an integer closest to 2 Tp / (Tc × k). The preamble receiver of claim 1, wherein the preamble receiver further comprises an adder for separating in-phase components and quadrature components from the output of the matched filter at the front end of the correlation bank. The accumulator bank of claim 1, wherein the accumulator bank is operated at a 1 / chip length (Tc) speed, and the output of the adder is delayed to the adder while operating at a 1 / chip length (Tc) speed to receive the preamble. A preamble receiver of a code division multiple access system, comprising: a predetermined number of delay lines output in parallel upon completion. 2. The code division according to claim 1, wherein the determining means comprises a maximum value selector which receives the output of the cumulative bank and selects a maximum value, and a comparator which compares the output of the maximum value selector with a predetermined threshold value. Preamble receiver in a multiple access system.