Spread spectrum or inversely spread device especially for transmission in cellular mobile radio system of code division multiple access

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention generally applies spread spectrum to a spread spectrum communication system, that is, a sequence of data to be transmitted using a spread code on the transmitting side, and conversely performs despreading on the receiving side to obtain the original sequence. Regarding the system.

【0002】

[Conventional technology]

The input data sequence of N symbols represented by (d1, d2, ..., dN) is c._QSpreading using the code of length (or spreading factor) Q represented by = (c1, c2, ..., cQ) produces a sequence of lengths Q · N, which is (d1 · It can be expressed as c1, d1 c2, ..., d1 cQ, d2 c1, d2 c2, ..., dN cQ), where d1 c1 represents the multiplication of d1 and c1. ..

【0003】

An alternative representation of the diffusion sequence of length Q · N is (d1 · c_Q, d2 c_Q, ... dN c_Q), And here d1 · c_QIs the spread code c to symbol d1_QRepresents the product multiplied by.

【0004】

A more common spreading technique is to have a different spreading code for each symbol of the input sequence, in which case the resulting spreading sequence will be (d1 · c)._Q⁽¹⁾, d2 c_Q⁽²⁾, ..., dN c_Q^(N)) Can be expressed, c_Q⁽¹⁾Is the spread code associated with symbol d1. It is preferred that all spreading cords have the same length Q so that the resulting spreading sequence has lengths Q · N.

【0005】

FIG. 1 is a schematic representation of the principle of diffusion, where Ts indicates the basic period (or symbol period) of the non-diffusion sequence, Tc indicates the basic period (or "chip" period) of the diffusion sequence, and Ts and Tc. Is in the relation of the formula Ts = Q · Tc. In this figure, dn and dn + 1 correspond to two consecutive symbols in a non-spreading incoming sequence, and d'l and d'l + 1 are two consecutive basic symbols of the same spreading symbol in this incoming sequence. Corresponds to (or "chip").

【0006】

One advantage of the above system is that multiple users can share the same frequency band by assigning different codes to each user.

【0007】

One important application area is code division multiple access (CDMA) cellular mobile radio systems.

【0008】

In these systems, spreading sequences are generally scrambled code (or) before being transmitted, for a variety of reasons, including improved protection from interference, or to ensure the confidentiality of the information transmitted. Scrambled using sequence).

【0009】

The incoming sequence of L basic symbols or "chips" represented by (d'1, d'2, ..., d'L) is represented by (v1, v2, ..., vL). Scramble using a length L scramble sequence produces a length L sequence that can be represented by (d'1 · v1, d'2 · v2, ..., d'L · vL). ..

【0010】

This scrambled sequence can be a very long, usually pseudo-random sequence. Sequences of this type can be protected from interference signals by randomizing them, at least for the duration of the scrambled sequence.

【0011】

This scrambled sequence can also be a short sequence of length L, which is usually equal to (or an integral multiple of) the length Q of the spreading code, as shown in FIG. In Figure 2, using the same type of representation as in Figure 1, d l and d l + 1 represent two consecutive basic symbols (or chips ) of the same diffuse / scramble symbol in this incoming sequence. .. By assigning different scramble sequences to cells that reuse the same spread code, this specifically reduces interference between cells. One advantage of these short sequences is that they generate cyclostationary transmission signals with a period proportional to L, allowing the efficient use of certain classes of algorithms, as described below. Is. A description of cyclostationary signals can be found, for example, in the literature "Exploitation of Spectral Redundancyin Cyclostationary Signals", IEEE Signal Processing Magazine, April 1991, pp. 14-36.

【0012】

Interference between users in the same cell uses a decoding algorithm on the receiving side to identify the interfering signals as interfering signals and thereby reject them, especially based on their knowledge of the received signal and the codes of the various users. By doing so, it can be lowered. Examples of such decoding algorithms are so-called subtractive detection algorithms or joint detection algorithms. Algorithms that take advantage of their cyclical properties can be used, especially if all cyclical stationery signals have the same short period. Such algorithms are described, for example, in the literature "Interference Rejection in Digital Wireless Communications", IEEE Signal Processing Magazine, May 1997, pp. 37-62.

【0013】

These cellular mobile radio systems provide protection from transmission errors, especially when the user's own bit transfer speed changes (eg when transmitting multimedia type data) or depending on the propagation state of the radio signal. In order to increase or decrease the degree, it is necessary to increase or decrease the redundancy introduced into the data to be transmitted, so that it is necessary to be able to transmit data at various bit transfer speeds.

【0014】

Multiple length Qm when the capacity of a single code of length Qm is exceeded in order to increase the bit transfer rate of the data transmitted by the user for the same allocated frequency band (ie, same duration Tc). Assigning the code to a user is known in itself.

【0015】

Techniques such as those described above have the specific drawback of being somewhat complicated to implement.

【0016】

Another technique known in itself that avoids the above drawbacks is to reduce the length of the code assigned to the user, allowing the user to continue transmitting with only one code, and the same assigned frequency band (ie). For the same duration Tc), it increases the bit transfer rate of the data transmitted by the user. Figure 3 outlines the principles of this type of technology, where the three consecutive symbols dn, dn + 1, and dn + 2 in the incoming sequence in this example are identified by the subscripts 1 and 2, respectively. It uses the same type of representation as in Figures 1 and 2, except that it has bit transfer rates for two different incoming sequences, and the symbol period corresponds to Ts1 for symbol dn, symbols dn + 1 and dn. +2 corresponds to Ts2, the code length corresponds to Q1 for the symbol dn, and corresponds to Q2 for the symbols dn + 1 and dn + 2.

【0017】

In this case, it may be necessary for the cellular mobile radio system to simultaneously manage multiple users whose instantaneous bit transfer rates, and thus the spreading codes, may differ and they may take different values over time. Problems arise because of the nature. The problem is that some algorithms, specifically the decoding algorithms, especially the decoding algorithms referenced above, cannot accept code of different lengths (simultaneously or separately) for each user without modification. Is.

【0018】

The same kind of problem will occur when assigning multiple codes of various lengths to the same user.

【0019】

The same kind of problem will occur when assigning variable length code to users.

【0020】

[Problems to be Solved by the Invention]

A particular object of the present invention is to provide a solution to this problem so that they can accept different lengths of code without modifying such algorithms.

【0021】

[Means for solving problems]

Thus, in one embodiment, the invention is in a spectrum spreading or despreading device, especially for transmission in a cellular mobile radio system with code split multiple connections, which device uses a spread code of length Q to sequence incoming calls. To spread or despread each subsequence, use a means to distribute the data symbol of the incoming sequence into various subsequences and a spread code of length Q0, which is a multiple of length Q, to spread or despread each subsequence. The subsequence, and the diffusion code of length Q0 applied thereto, including means of despreading, are such that the sequence obtained by superimposing the diffusion or dediffusion subsequences thus obtained is of length Q. It is determined to be the same as the sequence obtained by using a code to spread or despread the incoming sequence.

【0022】

In another aspect, the invention is in a device that despreads an incoming sequence using each of the K spread codes of length Qk (1 k K), which device is of length Qk (1). A means of distributing the data symbol of an incoming sequence into various subsequences and a length Q0, which is a multiple of the length Qk, in order to despread the incoming sequence using each spreading code of kK). The subsequence, and the spread code of length Q0 applied to them, includes a means of despreading each of these subsequences using a spread code, which superimposes the backspread subsequence thus obtained. The sequence obtained by is determined to be the same as the sequence obtained by despreading the incoming sequence using a code of length Qk, the length Q0 being common to the K codes.

【0023】

In another aspect, the invention is in a device that spreads K incoming sequences using each of the K spread codes of length Qk (1 k K), which device is of length Qk. A means of distributing the data symbol of the incoming sequence into various subsequences and a multiple of the code length Q in order to spread the kth incoming sequence using the spreading code of (1 k K). The subsequences, and the spread code of length Q0 applied to them, include the means for spreading each of these subsequences using a spread code of length Q0, and the various spread subsequences thus obtained. The sequence obtained by superimposing the sequences is determined to be the same as the sequence obtained by spreading the incoming sequence using the code of length Qk, and the length Q0 is common to the K codes. is there.

【0024】

According to another feature, the K diffusion cords have a predetermined maximum length Qmax or less, and the length Q0 is Qmax or less.

【0025】

According to another feature, the device further includes processor means for receiving the spreading or despreading subsequences obtained for K codes.

【0026】

According to another feature, said means of processing the despread subsequence thus obtained for K codes includes means of performing a joint detection algorithm.

【0027】

The present invention also aims at entities for cellular mobile radio communication systems, particularly base transceiver stations, including mobile stations (or mobile terminals) and the above types of spreading or despreading devices.

【0028】

Other objects and features of the present invention will become apparent by reading the description of one embodiment given in connection with the accompanying drawings.

【0029】

BEST MODE FOR CARRYING OUT THE INVENTION

The transmitter shown in FIG. 4 uses K incoming data sequences ST1 to STK, and each spread code c._Q₁⁽¹⁾From c_QK^(K)Scramble code c for means 2 to spread using and K data sequences ST'1 to ST'K from means 2._EMeans 3 to scramble using, and a modulator means 4 that receives various sequences ST "1 to ST" K from means 3, and a transmitter that receives a modulated signal from means 4 and supplies a corresponding radio signal. Including means 5 and.

【0030】

The receiver shown in FIG. 5 uses the scramble code c for the receiver means 6, the demodulator means 7, and the data sequence SR from the means 7._EDescrambling means 8 and the data sequence SR'from means 8 using K, respectively, the spreading code c_Q1⁽¹⁾From c_QK^(K)Includes means 9 for supplying SRKs from the K despreading sequences SR1 used by the decoding algorithm of the type described above in processing means 10 to backdiffuse and supply the received data sequence SR.

【0031】

The device according to the present invention shown in FIG. 6 is a means for dividing the data symbol of the incoming sequence from the subsequence S1 to Sp in order to spread or despread the incoming sequence S using the spread code C of length Q 20. And 21 (211 to 21p) means of spreading or despreading each of these subsequences using a spread code of length Q0 (Q0 / Q equals p), which is a multiple of length Q. The various codes of length Q0 applied to the various subsequences are represented by C1 to Cp, respectively.

【0032】

The subsequences S1 to Sp, and the codes C1 to Cp, are sequences obtained by superimposing the various spreading or despreading subsequences thus obtained, using code C of length Q to spread or spread the incoming sequence. It is determined to be the same as the sequence obtained by backdiffusion.

【0033】

FIG. 7 is a diagram showing an example of the operation of the above-mentioned type of device.

【0034】

The incoming sequence S is a symbol It is formed from d1, ..., dp, ... d2p, ... and so on.

【0035】

In the example shown in Figure 7, sequence S1 is a symbol. Formed from d1, dp + 1, d2p + 1, ..., etc., sequence S2 is a symbol Formed from d2, dp + 2, d2p + 2, ... etc, ... Sequence Sp is a symbol It is formed from dp, d2p, d3p, ... and so on.

【0036】

The code C in question is C = (c1, c2, ... cQ).

【0037】

In the example shown in Figure 7, the codes C1, ..., Cp are C1 = (c1, c2, ... cQ, 0, ..................................... ............ 0), C2 = (0, .................. 0, c1, c2, ... cQ, 0, .............. .... 0), ... Cp = (0, ....................................................... ... 0, c1, c2, ... cQ).

【0038】

For clarity, Figure 7 shows the various codes C1, ..., Cp facing the various subsequences S1, ..., Sp to which they apply.

【0039】

In this example, the sequence obtained by superimposing the various spreading or despreading subsequences thus obtained is the same as the sequence obtained by spreading or despreading the incoming sequence using a code of length Q. Demonstrate that.

【0040】

Other examples are of course possible, and it is clearly impossible to describe them all herein.

【0041】

The apparatus according to the present invention is particularly used in the reverse diffusion means 9 of FIG. In this case, the device according to the invention is used in a base transceiver station or mobile terminal and has a spreading code (or code) assigned to a given user to use a decoding algorithm such as the algorithm described above. Incoming calls using not only the code assigned to that user, if assigned), but also the code assigned to another user (and perhaps the other code assigned to that user). The data sequence can be despread.

【0042】

In the above-mentioned fields of application, a device that reverse-spreads an incoming sequence using each K spread code of length Qk (1 k K) is a device that reverse-spreads an incoming sequence with each K spread code, as shown in FIG. Means 20 to reverse spread the incoming sequence using₁From 20_KMeans and means to distribute the data symbols of the incoming sequence to various subsequences, such as Means 21₁(211₁From 21p₁) To 21_KIncludes means to despread each of these subsequences using a spread code of length Q0, which is a multiple of the corresponding code length (Q1 to QK, etc.).

【0043】

For each value of k (1 k K), the subsequence, and the diffusion code applied thereto, is a code of length Qk obtained by superimposing the reverse diffusion subsequences thus obtained. Is determined to be the same as the sequence obtained by despreading the incoming sequence using, and the length Q0 is common to the K codes.

【0044】

As shown above, this results in means 21₁From 21_KIt is no longer necessary to modify the decoding algorithm used in means 22 to receive subsequences from such means so that it accepts codes of various lengths.

【0045】

The device according to the invention used on the transmitting side, especially on the transmitting side in a code division multiple access cellular mobile radio system, can be used in the spreading means 2 of FIG. In this case, the device according to the invention can be used in a base transceiver station to spread different incoming data sequences for different users served by the base transceiver station. It can also be used on mobile terminals by assigning various spread codes to the user.

【0046】

In the above types of application fields, a device that spreads K incoming sequences such as S1 to SK using each K spreading code of length Qk (1 k K) is shown in FIG. To, means 200₁From 200_KAnd so on, the means to distribute the data symbols of the incoming sequence such as S1 to SK added to it to various subsequences, and for each value of k (1 k K), the subsequence and applied to them. The spreading code is determined so that the sequence obtained by superimposing the spreading subsequences thus obtained is the same as the sequence obtained by spreading the incoming sequence using a code of length Qk. The length Q0 is common to K cords.

【0047】

As a result, again, means 210₁From 210_KAny coding algorithm used in means 220 that receives subsequences from such means does not need to be modified to accept codes of various lengths.

【0048】

One of ordinary skill in the art will not be aware of any particular problem in implementing the various means of constructing the block diagrams of FIGS. 6, 8, and 9. Therefore, it is not necessary to describe these means in more detail than referring to their functions.

【0049】

Although these figures are theoretical figures, in practice, the structure can obviously vary, specifically, the various components of these figures into a common signal processor means. Note that it can be summarized.

【0050】

It should also be noted that the description can be varied, specifically, the spread code can be varied for each of the various symbols of the data sequence to which it is applied to improve efficiency. I want to.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the spread spectrum of an incoming sequence.

[Figure 2]

It is a figure which shows the spread spectrum and scrambling of an incoming sequence.

[Fig. 3]

It is a figure which shows the spread spectrum in the case of a variable length spread code.

[Fig. 4]

It is a block diagram which shows an example of the transmitter for the cellular mobile radio system of code division multiple access to which this invention can apply.

[Fig. 5]

It is a block diagram which shows an example of the receiver for the cellular mobile radio system of code division multiple access which can apply this invention.

[Fig. 6]

It is a block diagram which shows an example of the apparatus by this invention.

[Fig. 7]

It is a figure which shows the operation of the above-mentioned type of apparatus.

[Fig. 8]

In particular, it is a block diagram which shows an example of the apparatus by this invention used on the transmitting side in a cellular mobile radio system of code division multiple access.

[Fig. 9]

In particular, it is a block diagram which shows an example of the apparatus by this invention used on the receiving side in a cellular mobile radio system of code division multiple access.

[Explanation of symbols]

2 Diffusion means 3 Scramble means 4 Modulator means 5 Transmitter means