KR100331876B1 - Allocation Method for channelization code in multi code rate - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a mobile communication system, and in particular, channelization code assignment at a multi-code rate to be suitable for allocating channelization codes that minimize interference when user signals having various chip rates exist on the same carrier frequency. It is about a method. The channelization code allocation method in the multi-code rate according to the present invention is a system in which a user signal having a different chip rate coexists with an orthogonal spreading code in which bit sums of a predetermined period are respectively canceled according to the ratio of chip rates. By assigning a channelization code, the interference between a plurality of user signals having different chip rates can be eliminated and transmitted through one channel.

Description

Allocation Method for Channelization Code in Multi Code Rate

TECHNICAL FIELD The present invention relates to a mobile communication system, in particular at a multi-code rate such that it is suitable for allocating a channelization code that minimizes interference when user signals with various chip rates exist on the same carrier frequency. A channelization code assignment method.

In general, a multiple access communication system transmits / receives several user signals through the same channel. In particular, a communication system using a code division multiple access (CDMA) scheme distinguishes each user signal by an orthogonal code, so that a plurality of user signals can be identified using the same channel. Can be transmitted in time.

To this end, a transmitter of a CDMA communication system multiplies a unique orthogonal code assigned to a corresponding user for each data bit of each user signal and transmits it through one channel, whereas the receiver receives each received data through one channel. Each data bit of the user signal is multiplied by the same orthogonal code at the time of transmission, and then the output bit is integrated for one chip period to extract the user's signal.

This transmission / reception operation can be performed since it assumes that a unique orthogonal code for the user signal received at the receiver of the CDMA communication system is already known.

In this case, a chip rate indicating a transmission rate of the orthogonal code is higher than a bit rate, which is a transmission rate of user data.

Therefore, by dividing the chip rate by the bit rate, the spreading factor (SF) can be obtained. This spread factor SF represents the length of the orthogonalized code that is multiplied by one user data bit.

Meanwhile, in the receiver of the CDMA communication system, since the same orthogonal code is multiplied twice, desired user data can be extracted. However, other data corresponding to interference and error are not removed as components of the orthogonalized code remain in the form of noise. Will remain. This noise is greatly reduced after passing through the receiver's integrator.

Therefore, assuming that time synchronization is performed between each user data and that the chip rates for all user data are the same, the CDMA communication system can eliminate the interference between the user data by orthogonalizing the codes for distinguishing each user. Can be. In this case, if the spread rate SF of the code is applied to each user signal differently, the data rate of each user is different. This code is called an Orthogonal Variable Spreading Factor (OVSF) code.

The spreader provided in the transmitter of the CDMA communication system and the despreader provided in the receiver will now be described in more detail.

1 is a diagram illustrating a spreader provided in a transmitter of a conventional CDMA communication system.

Referring to FIG. 1, b _k (t) is a data signal of user k, and a _k (t) is an orthogonal code signal. Here, the data signal b _k (t) of the user k is _multiplied by the orthogonal code signal a _k (t) and spread and spread all user signals s (t) are multiplexed and transmitted through the same channel.

As such, when a signal transmitted through one same channel is s (t), it may be expressed as Equation 1 below.

In Equation 1, K means the total number of users, Means a carrier frequency.

Here, a _k (t) and b _k (t) can be represented by the following equation.

b _k (t) =

Referring to Equation 2, t is a parameter representing time, and b _{k, m} are m-th data bits of the k-th user and have a value of '1' or '-1'. T _k is the inverse of the data bit rate in the period of the data bit of the k-th user. Here, it is assumed that b _{k, 0} , k = 1,2, ..., K, starts transmission from the moment t = 0. This means that the start time of bit transmission for all users is time synchronized with each other.

On the other hand, a _{k, j} is a j-th chip (chip) of the code assigned to the user k also has a value of '1' or '-1'. The period of a _{k, j} is N _k and satisfies a _{k, j} = a _{k, j + Nk} . Tc is the inverse of the chip rate as the chip period. It is assumed here that the chip periods for all user data are the same. Ψ (t) is a function of the pulse shape of the chip.

2 is a diagram illustrating a despreader provided in a receiver of a conventional CDMA communication system.

Referring to FIG. 2, the input signal r (t) of the receiver can be expressed by Equation 3 below.

r (t) = As (t-τ) + n (t)

Referring to Equation 3, A is distortion occurring through a channel, and n (t) is a noise component.

In the despreader, the input signal r (t) shown in Equation 3 is multiplied by the same code a _i (t) and the orthogonalized code multiplied by the spreader, and the output bits are integrated for one period. Then, all user data signals other than a _i (t) code are canceled and only the data signal of the desired user is extracted.

For the sake of simplicity, the output signal Z _i (T), T = q * T _i, of the despreader is represented by the following equation: distortion A = 1 and noise n (t) = 0. It can be expressed as 4. Where i represents the number of the user signal to be received.

Z _i (T) = b _{i, q} + I _{k, i} (T)

Here, the interference signal I _{k, i} (T) can be expressed as follows.

T _{i ≤} T _k

T _i ＞ T _k

Wherein round_down (x) is a function representing the maximum value among integer that is less than x, or, regardless of the user data bit b _{k, m} transmitted interference signal I _{k, i} (T) in order to have a zero value R _{k , i} (m), m = α _{k, i} (T), ....., β _{k, i} (T) should be '0'. The code that satisfies this is the OVSF code.

This OVSF code, C _{SF, n,} n = 1, 2, ..., SF, can be generated as shown in Figure 3 (Reference: 3GPP RAN 25.213, V2.1.0 (1999-04), Spreading and modulation (FDD)

At this time, c _1,1 is the beginning of the code tree, the code c _2,1 and c _2,2 corresponding to the stem of the two strands split from c _1,1 .

That is, the code c _2,1 connects two codes of c _1,1 to each other, and c _2,2 connects c _1,1 and c _1,1 to the product of (-1).

From code c _2,1 and code c _2,2 , the trunk of the two strands is split by using the same procedure as the above method to draw a code tree.

At this time, user k's code a _{k, j} is selected and used among _{SF, N} , n = 1, 2, ... SF, where SF = N _k , starting from the code OVSF to be used. the roots of c OVSF code in the trunk split out from the OVSF code to use _1,1 OVSF code in the trunk and must not be used to go from the current system.

However, in the conventional OVSF code, a generation and allocation method for signals having the same chip rate may be implemented as described above, but considering the case where signals having different chip rates are mixed on the same carrier frequency Until now, no method of allocating OVSF codes for multi-code chip rates is presented.

Therefore, when randomly assigning OVSF codes to various signals having different chip rates according to the conventional OVSF code generation and assignment, there is a problem in that orthogonality between codes cannot be achieved and interference occurs between user signals.

Accordingly, an object of the present invention has been devised in view of the above-described problems of the prior art, and channelizes an orthogonal spreading code capable of distinguishing each user without interfering with each other for each user signal having a different code chip rate. An object of the present invention is to provide a channelization code allocation method at a multi-code rate of code allocation.

Another object of the present invention is to provide a channelization code allocation method at a multi-code rate for allocating orthogonal spreading codes that do not interfere with each other according to pulse types of chips for each signal having different chip rates. .

According to an aspect of the present invention for achieving the above object, the channelization code allocation method in the multi-code rate is a chip different from each other in the orthogonal spreading code, each bit offset of a predetermined period determined by the ratio of the chip rate This is done by assigning a channelization code of a system in which a user signal having a rate coexists.

Preferably, the channelization code uses an orthogonal spreading code in which bits of a predetermined period determined in accordance with the ratio of the chip rate are point-symmetric with respect to the pulse shape of the chip.

1 is a diagram illustrating a spreader provided in a transmitter of a conventional CDMA communication system.

2 illustrates a despreader provided in a receiver of a conventional CDMA communication system.

3 is a view for explaining a method of generating a conventional OVSF code.

4 illustrates an example of an OVSF code that can be allocated to a user signal having a chip rate twice the reference chip rate according to the channel code allocation method of the present invention.

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

The present invention proposes a channelization code allocation method in a multi-code rate for finding and allocating OVSF codes that do not interfere with user signals having different chip rates among all orthogonal spreading codes, that is, OVSF codes.

In addition, since the OVSF code is affected by the pulse type of the chip, that is, whether the chip pulse is a rectangular wave or a symmetrical wave, the channelized code allocation method is used at the multi-code rate for finding and assigning the OVSF code for each pulse type. Suggest.

Hereinafter, a channelization code allocation method according to the present invention will be described in detail.

In the conventional channelization code allocation method for each user signal having the same chip rate, the interference between each user signal is eliminated by using the OVSF code as a code for distinguishing each user when each user signal is time synchronized with each other. .

In the present invention, as in the prior art, it is assumed that time synchronization is performed between the respective user signals. At this time, it is assumed that the user signals have different chip rates.

Here, the different chip rates of each user signal are limited. That is, the lowest chip rate among the chip rates of the user signal is R₀In this case, the other chip rate is R₀* (y = 1, 2, 3, ...)

At this time, the method of allocating an OVSF code for a user signal having a chip rate of R ₀ is performed according to the same process as in the related art.

However, R ₀ * An OVSF code that assigns to a user signal with a chip rate of (y = 1, 2, 3, ...) allocates only a portion of the entire OVSF code.

Hereinafter, the channelization code allocation method according to the chip rate of the present invention will be described by applying to a transmitter and a receiver of an actual CDMA communication system.

The transmitter and receiver of the communication system used in the present invention have the same structure as the prior art.

Here, the data signal b _k (t) of the user k is as shown in Equation 2, but the code signal is as shown in Equation 5 below.

Where a _{k, j} is the value of the jth chip of the code assigned to the kth user and has a value of '1' or '-1'. And T _c , _k is the inverse of the chip rate in the chip period of the k-th user. The chip period can be represented by T _{c, k} = M _k T _f , M _k = 1,2,4,8 ....., and T _f = 1 / R ₀ .

Ψ _k (t) is a function representing the chip pulse shape of the k-th user.

Therefore, the data signal b _k (t) of the user k is multiplied by the code signal a _k (t), and all the spread user signals are transmitted through the same channel. The transmission signal s (t) sent through the channel is the same as Equation 3.

In addition, the receiver used in the present invention is the same as in the prior art, the interference signal I _{k, i} (T) of the output signal Z _i (T), T = q * T _i of the _despreader is the following equation 6.

T _i ≤ T _k

T _i ＞ T _k

Here, α _{k, i} (T) and β _{k, i} (T) are the same as in Equation 4, respectively.

Therefore, in order for the interference signal I _{k, i} (T) to have a zero value regardless of the data bits b _{k, m} of the transmitted user signal _, R _{k, i} (m) (m = α _{k, i} (T), It can be seen that the value of ....., β _{k, i} (T)) should be '0'.

In addition, in order to satisfy the above equation, the conditions for the chip pulse function must be considered together with the conditions for the a _{k and i} codes.

Therefore, in the present invention, the case where the chip pulse function is a square wave or the sine file whose left and right are symmetric with respect to the center of the pulse is considered. First, the method of allocating an OVSF code when the chip pulse is a square file is described.

If the chip pulse is a square wave, it has a value of '1' in a specific range. That is, Equation 6 is simple as in Equation 7 since Ψ _k (t) has a value of '1' in a section where t = [0, T _{c, k} ] and a value of '0' in other sections. Can be represented.

T _i ≤ T _k

T _i ＞ T _k

Equation 7 is the correlation between two codes a _{k, j} and a _{i, n} .

Therefore, a signal having a short chip period (i.e., a signal having a high chip rate) among the two codes is called a _{i, n} and a signal having a long chip period is a _{k, j , where} the chip period T _{c, The} relation shown in Equation 8 is established between _k and the chip period T _{c, i} of the code a _{i, n} .

T _{c, k} = T _{c, i} * P _{k, i}

P _{k, i} = T _{c, k} / T _{c, i} = M _k / M _i

At this time, the code a _{i, n} changes P _{k, i} times while the code a _{k, j} changes its value once for a certain period of T _{c, k} . Therefore, Equation 7 changes as in Equation 9 below.

T _i ≤ T _k

T _i ＞ T _k

At this time, the condition that Equation 9 has a value of '0' for any a _{k, r} is a condition that the sum of the code values is '0' while the code a _{i, s} changes P _{k, i} times.

Therefore, the following equation 10 must be satisfied for all other user indexes k having a chip rate smaller than user i.

r = 0,1, ....., N _i / P _{k, i} -1

For example, in systems where there are signals of all chip rates, i.e., R ₀ , 2 * R ₀ , 4 * R ₀ ....., the assignment of the OVSF code first, the signal with chip rate R ₀ is conventional Create and assign OVSF code in the same way as

However, for a signal with a chip rate of 2 * R ₀ , an OVSF code shown in FIG. 4 is generated from the OVSF code shown in FIG. 3 and an arbitrary one of them is allocated.

The code shown in Fig. 4 is found as follows. First, in the case of a chip rate of 2 * R _{0, since} the chip rate is doubled compared to the chip rate of R ₀ , the code bits are grouped by two and added to find a code that becomes '0'. Then c _2,2 = (1, -1), c _4,3 = (1, -1, 1, -1), c _4,4 = (1, -1, -1, 1) ... This is equivalent to code.

For the 4 * R ₀ signal, the chip rate is doubled compared to the 2 * R ₀ chip rate, so the code bits are grouped together to find the code that becomes '0'. Since the chip rate is increased four times as compared to the chip rate of R ₀ , four code bits are bundled and added to find a code that becomes '0'.

In addition, an OVSF code can be generated according to the above-described method even for a signal having a chip rate higher than 4 * R0.

Then, the method of allocating the found OVSF code according to the above process is performed in the same manner as the conventional method. That is, the code of the stem starting from the OVSF code to be allocated to the root code and the code splitting from the code to be allocated should not be used for the same chip rate signal.

This section describes how to generate and assign an OVSF code in the case of a sine file whose chip pulses are symmetrical left and right about the center of the pulse.

Ψ _k (t-T _{c, k} / 2-d) = Ψ _k (tT _{c, k} / 2 + d), where d≥0, R _{k, i} (m) in Equation 6 returns the value of '0' The condition of having the following expression 11 must be satisfied for all other user indexes k having a chip rate smaller than the codes a _{i, n} .

d = 0,1 ...., N _i / P _ki -1

Therefore, if Expression 11 is satisfied, Expression 12 below must be satisfied.

a _{i, r} p _{k, i} + p _{k, i} / 2-ｅ = -a _{i, r} p _{k, i} + p _{k, i} / 2-1 + ｅ

r = 0,1, ..... N _i / P _{k, i} -1, ｅ = 1, 2, ....., P _{k, i} / 2

That is, when the chip pulse is a symmetrical file, the OVSF codes satisfying Equations 10 and 12 are found and assigned.

This means that when the chip rate is 2 * R ₀ , two bundles are set to '0' and at the same time, OVSF codes that are point symmetrical are found and allocated. Here, point symmetry refers to codes in which different code bits are arranged when the first half and the second half of the even-numbered code bits are divided in order from the middle point to the middle point.

Therefore, the chip rate R ₀ and 4 * R ₀ of the chip rate only when the system chip pulse is symmetrical file from coexisting code that can be applied is c = _4,2 made of the point symmetry (1, 1, -1, -1), c _4,3 = (1, -1, 1, -1), c _8,3 = (1, 1, -1, -1, 1, 1, -1, -1), c _{8 , 5} = (1, -1, 1, -1, 1, -1, 1, -1), ...

As described above, the channelization code allocation method in the multi-code rate of the present invention can spread and transmit a plurality of user signals having different chip rates, thereby eliminating interference between signals having different chip rates. This has the effect of improving performance.

Claims (7)

In a code division multiplex wireless communication system in which a plurality of data signals divided into different spreading codes are transmitted in one spreading frequency band, Allocating a plurality of chip rates to the plurality of data signals; Allocating a first spreading code to a first data signal to which a minimum chip rate of the chip rate is applied; When code bits are sequentially selected from the orthogonal code group in the unit of the constant multiple in a second data signal having a chip rate that is a constant multiple of the minimum chip rate, a second spread is selected by selecting codes having the same number of different code bits. Spreading code assignment method comprising the step of assigning to a code. Claim 2 has been deleted. Claim 3 has been deleted. 2. The method of claim 1, wherein the constant multiple is a positive integer square of two. 5. The method of claim 4, wherein the orthogonal code group is an orthogonal variable spreading factor (OVSF) code group. 6. The method of claim 5, wherein the second spreading code divides an even number of code bits among the codes of the orthogonal variable spreading factor (OVSF) code group into a first half and a second half, and compares them with each other in an order from the midpoint to the midpoint. The spreading code allocation method in a code division multiple access wireless communication system, characterized in that the code is arranged in a different code bits. The spreading code allocation method of claim 1, wherein the spreading code is a channelization code for distinguishing a wireless communication channel.