(19)
(11)EP 1 788 726 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
31.05.2017 Bulletin 2017/22

(21)Application number: 07103008.4

(22)Date of filing:  05.10.1999
(51)International Patent Classification (IPC): 
H04B 7/26(2006.01)
H04J 11/00(2006.01)

(54)

Method and stations for encoding data with scrambling codes in a CDMA slotted system

Verfahren und Vorrichtungen zur Datenkodierung mit Verwürfelungskodes in einem CDMA-slotted-System

Procédé et dispositifs pour le codage de données avec des codes de brouillage dans un système CDMA à intervalles


(84)Designated Contracting States:
DE FR GB IT

(30)Priority: 29.10.1998 GB 9823605

(43)Date of publication of application:
23.05.2007 Bulletin 2007/21

(62)Application number of the earlier application in accordance with Art. 76 EPC:
99952529.8 / 1044519

(73)Proprietor: Koninklijke Philips N.V.
5656 AE Eindhoven (NL)

(72)Inventor:
  • Moulsley, Timothy J.
    5656 AA Eindhoven (NL)

(74)Representative: Roche, Denis et al
Société Civile SPID Philips IP&S 33, rue de Verdun BP 313
92156 Suresnes Cedex
92156 Suresnes Cedex (FR)


(56)References cited: : 
EP-A- 0 957 604
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Technical Field



    [0001] The present invention relates to a method of operating a radio communication system, and further relates to such a system and to primary and secondary stations for use in such a system. While the present specification describes a system with particular reference to the emerging Universal Mobile Telecommunication System (UMTS), it is to be understood that such techniques are equally applicable to use in other mobile radio systems.

    Background Art



    [0002] A number of radio communication systems, both existing and emerging, use Code Division Multiple Access (CDMA) techniques, one example being UMTS when operating in a wide band Code Division Multiple Access (CDMA) frequency division duplex mode. Such systems are typically cellular, with a Base Station (BS) servicing a plurality of Mobile Stations (MS) in a cell.

    [0003] Figure 1 is a block schematic diagram of a radio communication system using CDMA, comprising a primary station (BS) 100 and a plurality of secondary stations (MS) 110. The BS 100 comprises a microcontroller (µC) 102, transceiver means 104 connected to radio transmission means 106, and connection means 108 for connection to the PSTN or a private network. Each MS 110 comprises a microcontroller (µC) 112 and transceiver means 114 connected to radio transmission means 116. Communication from BS 100 to MS 110 takes place on a downlink channel 122, while communication from MS 110 to BS 100 takes place on an uplink channel 124.

    [0004] Figure 2 shows an example of a known arrangement for spreading and scrambling using Quadrature Phase Shift Keying (QPSK) modulation. Data is supplied on input line 202 to a serial to parallel converter 204, which maps each pair of data bits to I and Q branches respectively. A channelisation code 210 is supplied to mixers 206, 208 in the I and Q branches to spread the data to the chip rate. The data is then scrambled by a BS-specific scrambling code 216 supplied to I and Q mixers 212, 214. The resultant data is used to modulate a cosine carrier 220 by an I mixer 218, and a sine carrier 224 by a Q mixer 222. The I and Q branches are then combined by a combiner 226 before being passed to radio broadcast means 228 for transmission as a QPSK signal.

    [0005] If a BS supports more than one cell (for example in a sectorised transmission arrangement), the scrambling code 216 could be cell-specific instead of BS-specific.

    [0006] Different physical channels use different channelisation codes (usually orthogonal), while the scrambling code is the same for all physical channels in one cell.

    [0007] On the downlink channel 122 a number of channelisation codes (usually orthogonal) are used to separate transmissions intended for different users, and an additional scrambling code is applied to distinguish the transmitting BS 100. Hence, to decode a message intended for it a MS 110 has to know both the code for the BS 100 sending the data and the code for its channel.

    [0008] Similarly on the uplink channel 124 a channelisation code is used to select the channel on which the MS 110 is to transmit and a scrambling code, specific to the MS 110, is used.

    [0009] A problem with this arrangement is the possible lack of channelisation codes for the downlink 122 since codes which have been allocated to one user, but are not currently in use, may not be available for another user. One possibility for relieving this shortage is to use more than one scrambling code per cell. However, this has the disadvantage that signals transmitted to one user with one scrambling code will not be orthogonal to signals transmitted to a different user with a different scrambling code, resulting in increased interference.

    [0010] WO 94 29981 discloses a method of introducing discontinuous transmission in CDMA communication techniques by using a lower spreading ratio whereby the spread information fills only part of a time frame. However, such a scheme increases the number of spreading codes in use, which may result in a shortage of such codes.

    Disclosure of Invention



    [0011] An object of the present invention is to reduce the problems caused by the use of more than one scrambling code in a cell.

    [0012] According to a first aspect of the present invention there is provided a method of operating a radio communication system employing a code division multiple access technique, comprising a primary station transmitting different data signals simultaneously, wherein the different data signals are encoded with different spreading codes and common scrambling code,
    characterised in that the required data bit rate is variable, and by, when the required data bit rate exceeds what is possible with the available spreading codes, providing additional data capacity by encoding the excess data with an already-used spreading code and a different scrambling code.

    [0013] According to a second aspect of the present invention there is provided a primary station for use in a radio communication system employing a code division multiple access technique, comprising means for transmitting different data signals simultaneously, wherein the different data signals are encoded with different spreading codes and common scrambling code,
    characterised in that the required data bit rate is variable, and by means adapted to, when the required data bit rate exceeds what is possible with the available spreading codes, provide additional data capacity by encoding the excess data with an already-used spreading code and a different scrambling code.

    [0014] According to a third aspect of the present invention there is provided a secondary station for use in a radio communication system employing a code division multiple access technique, the secondary station comprising means for receiving data encoded with a first scrambling code, characterised by means for receiving simultaneously data encoded with a different scrambling code.

    [0015] The present invention is based on the recognition, not present in the prior art, that a plurality of scrambling codes can be allocated for transmissions from one BS to a single MS.

    Brief Description of Drawings



    [0016] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein:Figure 1 is a block schematic diagram of a radio communication system, as described above;

    Figure 2 is a block schematic diagram of part of a transmitter, as described above;

    Figure 3 illustrates a downlink slotted mode using a secondary scrambling code;

    Figure 4 illustrates a downlink slotted mode using primary and secondary scrambling codes; and

    Figure 5 illustrates a variable rate multicode transmission using primary and secondary scrambling codes.



    [0017] In the drawings the same reference numerals have been used to indicate corresponding features.

    Modes for Carrying Out the invention



    [0018] A first illustrative embodiment of the present invention is the implementation of downlink slotted mode shown in Figure 3. Slotted mode is required in order to introduce gaps in the transmission during which the MS 110, which may have only one receiver, can make measurements on other carriers, for example to prepare for handover. A succession of frames 302 is transmitted on a downlink channel 122, each of length 10ms in UMTS. In one frame the data is transmitted during two active parts 304 of the frame, the remainder of the frame being an idle period 306 during which the required measurements can be made.

    [0019] The consequence of this is that the bit rate and transmission power both need to be increased during the active part of the frame. The bit rate can be increased by reducing the spreading factor (for example by a factor of two for the 50% idle period 306 illustrated). However, this requires the allocation of another channelisation code, that is the provision of a second channel for the MS 110. This is an inefficient use of codes, since the extra resource is only required during the slotted frame.

    [0020] One option in accordance with the present invention, as illustrated in Figure 3, is to use a primary scrambling code for all the non-slotted frames 302, while using a secondary scrambling code for the slotted frame 304.

    [0021] A preferred option is illustrated in Figure 4. Here a first part 402 of the active part of the slotted frame is transmitted using the primary scrambling code, while a second part 404 of the slotted frame is transmitted using the secondary scrambling code. This alternative has the advantage of minimising the amount of "non-orthogonal" energy transmitted.

    [0022] In general, for any transmission scheme using two or more scrambling codes for one MS 110 it is preferable to designate one code as the primary code and to transmit as much data as possible using this code (thereby maximising the power transmitted using this code), while minimising the power transmitted using the secondary codes. Hence the secondary code should be used to carry traffic with a low average data rate (which includes a high data rate with a low duty cycle, as in the slotted mode example).

    [0023] A second illustrative embodiment of the present invention is the implementation of variable rate multi-code transmissions shown in Figure 5. When the required bit rate exceeds what is possible with a single channelisation code, multiple codes can be used, corresponding to multiple physical channels. The figure shows a first physical channel 502, comprising a succession of frames 302, a second physical channel 504 and an nth physical channel 506.

    [0024] For any particular instantaneous data rate, the data can be organised to minimise the number of codes used, allocating some of the least used channelisation codes to the secondary scrambling code. For example, in Figure 5 the first and second channels 502, 504 could be transmitted using the primary scrambling code, while the nth channel 506 could be transmitted using the secondary scrambling code. In general as many channels as possible should be transmitted using the primary scrambling code, consistent with efficient use of channelisation codes.

    [0025] Use of this scheme will save channelisation codes while minimising the resulting interference.

    [0026] Other possible uses for secondary scrambling codes are packet transmissions, rare but urgent signalling (for example packet acknowledgements), and uplink power control where there is little or no downlink data.

    [0027] From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in radio communication systems and component parts thereof, and which may be used instead of or in addition to features already described herein.

    [0028] In the present specification and claims the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, the word "comprising" does not exclude the presence of other elements or steps than those listed.

    Industrial Applicability



    [0029] The present invention is applicable to a range of radio communication systems, for example UMTS.


    Claims

    1. A method of operating a UMTS system employing a code division multiple access technique, comprising a primary station (100) transmitting different data signals simultaneously, wherein the different data signals are encoded with a first channelization code of a predetermined set of different channelization codes and a common scrambling code, characterised in that the required data bit rate is variable, and by, when the required data bit rate exceeds what is possible with the first channelization code, providing additional data capacity by encoding the excess data with at least one further channelization codes of the predetermined set of different channelization codes with the common scrambling code and with a different scrambling code in combination with at least one of the already-used channelization codes.
     
    2. A UMTS primary station (100) comprising means for operating in a UMTS system employing a code division multiple access technique, the UMTS primary station comprising means (104) for transmitting different data signals simultaneously, wherein the different data signals are encoded with a first channelization code of a predetermined set of different channelization codes and a common scrambling code,
    characterised in that the required data bit rate is variable, and by means (102) adapted to, when the required data bit rate exceeds what is possible with the first channelization code, provide additional data capacity by encoding the excess data with at least one further channelization code of the predetermined set of channelization codes with the common scrambling code and a with a different scrambling code in combination with at least one of the already-used channelization codes.
     


    Ansprüche

    1. Verfahren zum Betreiben eines UMTS-Systems unter Anwendung einer Codemultiplexverfahrens- (Code Division Multiple Access) Technik, mit einer Primärstation (100), die verschiedene Datensignale gleichzeitig übermittelt, wobei die verschiedenen Datensignale mit einem ersten Kanalisierungscode eines vorher festgelegten Satzes von verschiedenen Kanalisierungscodes und einem gemeinsamen Scrambling-Code codiert werden,
    dadurch gekennzeichnet, dass die erforderliche Datenbitrate variabel ist, und dass, wenn die erforderliche Datenbitrate größer ist, was bei dem ersten Kanalisierungscode möglich ist, zusätzliche Datenkapazität durch Codieren der Überschussdaten mit mindestens einem weiteren Kanalisierungscode des vorher festgelegten Satzes von verschiedenen Kanalisierungscodes mit dem gemeinsamen Scrambling-Code und mit einem anderen Scrambling Code in Kombination mit mindestens einem der bereits verwendeten Kanalisierungscodes bereitgestellt wird.
     
    2. UMTS-Primärstation (100) mit Mitteln zum Betrieb in einem UMTS-System unter Anwendung einer Codemultiplexverfahrens-Technik, wobei die UMTS-Primärstation Mittel (104) zur gleichzeitigen Übertragung verschiedener Datensignale umfasst, wobei die verschiedenen Datensignale mit einem ersten Kanalisierungscode eines vorher festgelegten Satzes von verschiedenen Kanalisierungscodes und einem gemeinsamen Scrambling-Code codiert sind,
    dadurch gekennzeichnet, dass die erforderliche Datenbitrate variabel ist, sowie durch Mittel (102), die so eingerichtet sind, dass sie, wenn die erforderliche Datenbitrate größer ist, was bei dem ersten Kanalisierungscode möglich ist, zusätzliche Datenkapazität durch Codieren der Überschussdaten mit mindestens einem weiteren Kanalisierungscode des vorher festgelegten Satzes von Kanalisierungscodes mit dem gemeinsamen Scrambling-Code und mit einem anderen Scrambling Code in Kombination mit mindestens einem der bereits verwendeten Kanalisierungscodes bereitstellen.
     


    Revendications

    1. Procédé de fonctionnement d'un système UMTS employant une technique d'accès multiples par répartition de code, comprenant une station primaire (100) transmettant simultanément différents signaux de données, dans lequel les différents signaux de données sont codés avec un premier code de canalisation d'un ensemble prédéterminé de différents codes de canalisation et un code de brouillage commun,
    caractérisé en ce que le débit binaire de données nécessaire est variable et par, lorsque le débit binaire de données nécessaire dépasse ce qui est possible avec le premier code de canalisation, la fourniture d'une capacité de données supplémentaire par le codage de l'excédent de données avec au moins un autre code de canalisation de l'ensemble prédéterminé de différents codes de canalisation avec le code de brouillage commun et avec un code de brouillage différent en combinaison avec au moins l'un des codes de canalisation déjà utilisés.
     
    2. Station primaire UMTS (100) comprenant des moyens de fonctionnement dans un système UMTS employant une technique d'accès multiples par répartition de code, la station primaire UMTS comprenant des moyens (104) pour transmettre simultanément différents signaux de données, dans laquelle les différents signaux de données sont codés avec un premier code de canalisation d'un ensemble prédéterminé de différents codes de canalisation et un code de brouillage commun,
    caractérisée en ce que le débit binaire de données nécessaire est variable et par des moyens (102) aptes à effectuer, lorsque le débit binaire de données nécessaire dépasse ce qui est possible avec le premier code de canalisation, la fourniture d'une capacité de données supplémentaire par le codage de l'excédent de données avec au moins un autre code de canalisation de l'ensemble prédéterminé de codes de canalisation avec le code de brouillage commun et avec un code de brouillage différent en combinaison avec au moins l'un des codes de canalisation déjà utilisés.
     




    Drawing











    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description