WO2001035541A2

WO2001035541A2 - Method for decoding a spread-coded signal and corresponding decoding device

Info

Publication number: WO2001035541A2
Application number: PCT/DE2000/003893
Authority: WO
Inventors: Jürgen MICHEL; Bernhard Raaf
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-11-11
Filing date: 2000-11-07
Publication date: 2001-05-17
Also published as: WO2001035541A3

Abstract

The invention relates to a method for decoding a spread-coded signal. The aim of the invention is to decode a received bit sequence (s(t)) of a first transmission channel (A) which is based on a spread code of a data sequence (di(t)). To this end, said data sequence is correlated with a truncated de-spreading sequence (c'i(t)) derived from the first spread sequence (ci(t)) and then integrated. Additionally, a correction is carried out to compensate for the influence of the second transmission channel (B) on the first transmission channel (A) depending on the knowledge of at least one second transmission channel (B) via which bits are transmitted that are encoded by a second spread sequence that is complementary to the first spread sequence (ci(t)).

Description

description

Method for decoding a spread-coded signal and corresponding decoding device

The present invention relates to a method for decoding a spread-coded signal according to the preamble of claim 1 and a corresponding decoding device, in particular for use in a mobile radio receiver, according to the preamble of claim 13.

In transmission systems operated according to the principle of band spreading technology (DS-CDMA, "Direct Sequence Code Division Multiple Access"), the data symbols to be transmitted are keyed by a fast spreading sequence of length T = N - T _C. T denotes the duration of a data symbol to be transmitted, while T _c denotes the so-called chip duration of the spreading sequence. The chip duration T _c is significantly shorter than the symbol duration T, so that an ideally white broadband is used due to the spread coding

Transmitted signal is obtained, which is transmitted to a receiver via a multi-way channel and detected there.

So that several participants can use the transmission system at the same time, orthogonal spreading sequences or spreading codes, which are also referred to as channelization codes, are used for spreading the data symbols to be transmitted. A specific spreading sequence is assigned to each participant.

2 shows a code tree used in accordance with the UMTS mobile radio standard ("Universal Mobile Telecommunication System"), the orthogonal spreading sequences or spreading codes c _SF , n to be used for each spreading factor SF having n = 0 ... SF-1 are shown. ) ω w M l- ¹ P ¹

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desired transmission signal impaired or even impossible. If, for example, a transmission signal of a transmission channel to which the spreading sequence c _S F, 2n (n = 0 ... SF / 2-1) is assigned is despread in the receiver with the spreading sequence shortened by half, this transmission signal cannot be removed in the receiver a transmission signal can be distinguished, which has been transmitted via a transmission channel to which the spreading sequence c _S F, 2n ₊ ι is assigned (cf. the code tree shown in FIG. 2).

To distinguish a transmission channel with the spreading sequence c _S F, 2n of length SF (n = 0 ... SF / 2-1) from a transmission channel with the spreading sequence c _SF , 2 _{n +} ι z, detection has so far been used in conventional mobile radio systems performed with the non-shortened spreading sequence. This also applies in particular if one of the two transmission channels is used in the corresponding mobile radio system, for example as a so-called pilot channel, via which symbols are transmitted continuously in unmodulated form or modulated with known data. In addition, according to the current state of UMTS standardization, for example, a fixed spreading sequence, ie a fixed channelization code, is provided for the paging channel.

The present invention has for its object to provide an improved method for decoding spread-coded signals and a corresponding decoding device, with the help of which the effort in despreading can be reduced by the effective use of shortened (de) spreading sequences.

This object is achieved according to the invention by a method with the features of claim 1 or a decoding device with the features of claim 13. The

Subclaims define advantageous and preferred embodiments of the present invention. The present invention assumes that a continuously transmitted transmission channel, for example a pilot channel, is present, via which a data sequence spread with a fixed spreading sequence or a fixed channelization code is transmitted, which is preferably known. In UMTS mobile radio systems, this transmission channel can be formed by the CPICH channel ("Common Pilot Indicator Channel").

Furthermore, the present invention is based on the fact that the data of a further transmission channel, for example a broadcast control channel (BCCH) or a paging channel, are spread with a spreading sequence which has the same spreading factor as the spreading sequence of the first-mentioned continuously transmitted transmission channel and about this spreading sequence is complementary. This additional transmission channel can then be decoded in the receiver by multiplication or correlation with the corresponding shortened spreading sequence and subsequent integration. In order to compensate for the influence of the first-mentioned continuously transmitted transmission channel on the further transmission channel, a corresponding correction is carried out in the receiver using the previous knowledge via the first-mentioned transmission channel, with in particular knowledge of the known data sequence of the continuously transmitted transmission channel and the transmission power ratio between the two both transmission channels is used.

In this way, the use of the shortened (de) spreading sequence can significantly reduce the effort involved in despreading a received signal, so that in particular in the sleep mode of a mobile station when decoding one or more transmission channels with a preferably constant spreading factor, such as, for example, in UMTS, broadcast control - or the paging channel, the power consumption reduced and the efficiency can be increased. The power saving is particularly important in the paging mode of a mobile station, since it contributes directly to the extension of the standby time of the mobile station. The problems occurring with the prior art described at the beginning of using shortened (un) spreading sequences can be eliminated or at least significantly reduced by the compensation carried out according to the invention.

The present invention is particularly suitable for decoding downlink channels, i.e. of transmission channels which are directed from a base station to a mobile station in DS-CDMA ("Direct Sequence Code Division Multiple Access") mobile radio systems, such as, for example, a UMTS mobile radio system.

The invention is explained in more detail below with reference to the accompanying drawing using a preferred exemplary embodiment.

Fig. 1 shows a simplified block diagram of a transmitter and a receiver of a DS-CDMA mobile radio system according to the invention, and

2 shows a code tree for DS-CDMA mobile radio systems, in which the usable orthogonal spreading sequences are given for different spreading factors.

1 schematically shows the structure of the section of a section which contributes to the coding or spreading of transmission data

Transmitter 1 shown in a DS-CDMA mobile radio system, which is in particular the transmitter of a base station.

In DS-CDMA mobile radio systems, the data sequence or

Data sequence d (t) of a transmission channel directly in a unit 2 with a channel-specific spreading sequence or multiplied by a channel-specific spreading / channeling code Ci (t). The channel-specific spreading sequence d (t) is generated by a corresponding code generator 3. The so-called chips of the spreading sequence Cι (t) have a significantly shorter duration T _c than the individual transmission symbols with the symbol duration T, the relationship T = N - T _C in particular. Multiplication by the spreading sequence results in a band-spread, ie broadband, transmission signal S _ι (t) which is modulated onto a carrier signal cos (ω _D t) by a modulator 4. After the spreading and modulation, filtering is carried out with the aid of a bandpass filter 5 and the transmission power is adjusted with the aid of a power amplifier 6. The transmission signal is then transmitted to a receiver 7.

1 schematically shows the structure of the section of the receiver 7 of a DS-CDMA mobile station that contributes to decoding or despreading.

A bandpass filter 8 for selection and noise reduction is initially located at the receiver input. The bandpass filter 8 is followed by a de odulator 9 which transforms the received signal s (t) back into the baseband. Depending on the modulation method, this may require a synchronous regeneration of the carrier signal cos (ω _D t), which is usually implemented with a phase locked loop 10 ("phase locked loop", PLL). After the signal is back in the baseband, the de-spreading takes place.

The despreading is started as soon as a bit or symbol with the chip length M-T _c (M <N) transmitted using the DS-CDMA band spreading technique has been received. If the signal-to-noise ratio is sufficient, the original transmission sequence d _t () can be obtained in a unit 11 by correlation with the shortened channel-specific spreading sequence c'i (t) provided by a spreading code generator 12, which has the length M-T _c. t) complete again ) cυ r M t->P>

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Transmission channel to which the spreading sequence c _S F, 2n (n = 0 ... SF / 2-1) is assigned, with the spreading sequence shortened by half, does not despread this transmission signal in the receiver from a transmission signal which is transmitted via a Transmission channel has been transmitted to which the spreading sequence c _S F, ₂ n + ι is assigned (cf. the code tree shown in FIG. 2).

This problem is solved according to the invention in that in the receiver 7, with the aid of an appropriate device, the bit sequence output by the integrator 13 is corrected in order to compensate for the influence of a transmission channel which is complementary to the respective transmission channel.

To explain the principle according to the invention, it is assumed below that at least one continuously transmitted transmission channel B is present, for example the pilot channel of a base station transmitted via a downlink, the data sequence of which is known and which is spread with a fixed spreading sequence. The data sequence of this transmission channel B can be transmitted, for example, with a transmitter 1 of the type shown in FIG. 1.

If a spreading sequence c _± (t) is used for a further transmission channel A for spreading, which is complementary to the spreading sequence used for the previously described transmission channel B, the de-spreading of this transmission channel A in a receiver 7 of the type shown in FIG. 1 can be effective through the correlation with the shortened spreading sequence c'i (t) and subsequent integration if the influence of the transmission channel B complementary and continuously transmitted to the transmission channel A is compensated in the receiver 7 with the aid of a compensation unit 14. The compensation is particularly dependent on the Previous knowledge of the known data sequence transmitted via the transmission channel B and the known power ratio between the transmission channels A and B are carried out. Depending on this information, a corresponding value can be added to or subtracted from the output signal of the integrator 13 in the compensation unit 14. The mode of action of

Compensation unit 14 is always such that the influence of the complementary transmission channel B can be minimized or even completely eliminated.

According to the nomenclature of the UMTS specification, the spreading sequence c _S F, 2n + ι is the spreading sequence complementary to the spreading sequence c _SF , 2n (n = 0 ... SF / 2-1). This relationship also applies in reverse, ie the spreading sequence c _SF , 2n is the spreading sequence complementary to the spreading sequence C _S F, 2Π + I.

The principle described above is advantageous, for example, for the despreading and decoding of transmission channels A which have a constant transmission power ratio to the continuously transmitted transmission channel B. In particular, the invention is advantageously applicable for the despreading and decoding of broadcast and paging channels. A signal from a base station is transmitted via these channels to several mobile stations located in one and the same radio cell. To ensure that this signal can be received by all mobile stations, it must be transmitted by the base station at a relatively high power. However, most mobile stations are in a more favorable position and can use the method described above. Power saving is particularly important in paging mode because it directly increases the standby time. The result of this is that an A / D converter on the receiving side (not shown in FIG. 1) and the correlators 11 required for despreading are intermittent in the receiver CO CO tr P ¹ P ¹ no Cn o cn σ Cn

an example of the corresponding channel in a UMTS mobile radio system is given.

To de-spread channel B, taking into account the power ratio between the two channels A and B and knowledge of the data sequence transmitted via channel A in receiver 7, the correlation with the partial sequence +1 +1 instead of the complete spread sequence +1 +1 -1 is sufficient. 1.

Claims

claims

1. A method for decoding a spread-coded signal, wherein a receive bit sequence (s (t)) of a first transmission channel (A), which is based on spread coding a data sequence (d _x (t)) with a first spread sequence (C _ι (t)) , correlated with a shortened despreading sequence (c'xtt)) derived from the first spreading sequence (C _ι (t)) and then integrated in order to recover the original data sequence (d _x (t)), characterized in that after the correlation with the shortened despreading sequence (c ' _x ft)) and the integration, a correction of the resulting bit sequence is carried out in order to recover the original data sequence (d _x (t)), the correction being carried out as a function of knowledge of at least one second transmission channel (B) via which a bit sequence is transmitted continuously, which is spread-coded with a second spreading sequence complementary to the first spreading sequence (Cj. (t)) order to compensate for the influence of the second transmission channel (B) on the first transmission channel (A).

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the compensation is carried out depending on knowledge of the known bit sequence transmitted continuously via the second transmission channel (B).

3. The method according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the correction is carried out depending on knowledge of the relationship between the transmission power of the first transmission channel (A) and the transmission power of the second transmission channel (B).

4. The method according to any one of the preceding claims, characterized in that the length of the shortened despreading sequence (c ' ₁ (t)) used to despread the received bit sequence (s (t)) transmitted via the first transmission channel (A) is set as a function of the transmission quality of the first transmission channel (A).

5. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that to de-spread the over the first

The received despreading sequence (s (t)) transmitted transmission channel (A) uses the shortened despreading sequence (c ' ₁ (t)) half as long as the spreading sequence (d (t)) used for spreading the first transmission channel (A).

6. The method as claimed in one of the preceding claims, that a transmission channel is selected as the first transmission channel (A) which has a transmission power ratio which is approximately constant over time with the second transmission channel (B).

7. The method according to any one of the preceding claims, characterized in that the spreading sequence used for the spreading coding of the first transmission channel (A) (d (t)) corresponds to the spreading code c _S F _/ 2n in a corresponding spreading code tree system, and that for spreading coding of the second transmission channel (B) the spreading sequence used in a corresponding code tree system corresponds to the spreading code c _S F 2n + ι, where SF denotes the determined spreading factor and n one

SF represents an integer value between 0 and 1.

2

8. The method according to any one of claims 1-6, characterized in that the spreading sequence (c (t)) used for spreading coding of the first transmission channel (A) corresponds to the spreading code CsFf ₂ n + ι in a corresponding spreading code tree system, and that the spreading sequence used for spreading coding of the second transmission channel (B) corresponds to the spreading code in a corresponding code tree system CS corresponds to _J∑ Π, where SF denotes the specific spreading factor and n one

SF represents an integer value between 0 and -—- 1.

9. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the first transmission channel (A) is a broadcast control channel of a mobile radio system.

10. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the first transmission channel (A) is a paging channel of a mobile radio system.

11. The method according to claim 9 and claim 10, characterized in that the broadcast control channel is selected from a base station of a mobile radio system for the first transmission channel (A), and that the paging channel is selected by the base station of the mobile radio system for the first transmission channel (A) if there is no broadcast control channel in the radio cell of the mobile radio system assigned to the base station.

12. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the second transmission channel (B) is a pilot channel of a mobile radio system.

13. decoding device for decoding a spread-coded signal, with correlation means (11) for correlating a received bit sequence (s (t)) transmitted over a first transmission channel (A), which is based on spread coding a data sequence (d _x (t)) with a first spread sequence (d (t)) a shortened despreading sequence (c ' _x (t)) derived from the first spreading sequence (d (t)), and with integrating means (13) for integrating via the despread received bit sequence (s (t)) output by the correlation means (11) recovering the original data sequence (dχ (t)), characterized in that the integration means (13) are followed by correction means (14) which correct the bit sequence output by the integration means (13) depending on knowledge of at least one second transmission channel (B), in order to recover the original data sequence (d _x (t)) and to compensate for the influence of the second transmission channel (B) on the first transmission channel (A), the second Ub transmission channel (B) is a transmission channel via which a bit sequence is transmitted continuously, which is spread-coded with a second spreading sequence complementary to the first spreading sequence (d (t)).

14. Decoding device according to claim 13, so that the decoding device is designed to carry out the method according to one of claims 1 to 12.

15. Decoding device according to claim 13 or 14, so that the decoding device is used in a mobile radio receiver, in particular in a mobile station.

16. Decoding device according to claim 15, characterized in that the mobile radio receiver is operated in accordance with the UMTS mobile radio standard.