A method of operating a radio communication system uses a code division multiple access (CDMA) technique. multiple scrambling codes may be used in a single cell to alleviate the shortage of channelisation codes available for downlink channels from a primary station. To minimise interference caused by the presence of non-orthogonal signals, signals to a single secondary station may be transmitted as a plurality of parts encoded with different scrambling codes.
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10. A secondary station for use in a radio communication system employing a code division multiple access technique,
the secondary station comprising
means for receiving spreaded data from a single primary station, the data encoded in separate and distinct portions by using at least one of a primary scrambling code and or a secondary scrambling code, wherein said data includes a slotted mode signal having a first portion encoded with the primary scrambling code and a second portion encoded with the secondary scrambling code, both portions being transmitted contemporaneously;
wherein the data is transmitted in slotted frames and non-slotted frames.
0. 22. A primary station for use in a radio communication system employing a code division multiple access technique, the primary station comprising:
a transceiver for transmitting data to a plurality of secondary stations in slotted frames and non-slotted frames;
wherein the data in the non-slotted frames is encoded with a first scrambling code and at least a portion of the data in the slotted frames is encoded with a different scrambling code.
0. 20. 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 from a single primary station data in slotted frames and non-slotted frames;
means for receiving in the non-slotted frames data encoded with a first scrambling code; and
means for receiving data in the slotted frames at least a portion of which is encoded with a different scrambling code.
0. 24. A secondary station for use in a radio communication system employing a code division multiple access technique, the secondary station comprising:
a transceiver for receiving data from a single primary station data in slotted frames and non-slotted frames;
wherein in the non-slotted frames the transceiver receives data encoded with a first scrambling code and in the slotted frames the transceiver receives data at least a portion of which is encoded with a different scrambling code.
0. 18. A primary station for use in a radio communication system employing a code division multiple access technique, the primary station comprising:
means for transmitting to a plurality of secondary stations;
means for transmitting to a secondary station data in slotted frames and non-slotted frames; and
means for encoding data in the non-slotted frames with a first scrambling code and means for encoding at least a portion of the data in the slotted frames with a different scrambling code.
0. 16. A method of operating a radio communication system employing a code division multiple access technique, the method comprising:
enabling a primary station to transmit to a plurality of secondary stations, the primary station transmitting to a secondary station of the plurality of secondary stations data in slotted frames and non-slotted frames;
wherein data in the non-slotted frames is encoded with a first scrambling code, and at least a portion of the data is encoded in the slotted frames with a different scrambling code.
1. A method of operating a radio communication system employing a code division multiple access technique, comprising
a primary station transmitting data to a plurality of secondary stations,
the primary station encoding different separate and distinct portions of said data with different scrambling codes after spreading of said data, using at least one of a primary scrambling code and or a secondary scrambling code to encode the separate and distinct portions of said data for transmission to a secondary station, and transmitting a slotted mode signal to the secondary station using a primary scrambling code for a first portion of the data and a secondary scrambling code for the remainder of the data, both portions being transmitted contemporaneously;
wherein the data is transmitted in slotted frames and non-slotted frames.
6. A primary station for use in a radio communication system employing a code division multiple access technique,
the primary station having:
means for transmission of data to the secondary stations and;
means for encoding different separate and distinct portions of said data with different scrambling codes after spreading of said data, and
means for using at least one of a primary scrambling code and or a secondary scrambling code to encode the separate and distinct portions of said data for transmission to a secondary station, and means for transmitting a slotted mode signal to the secondary station using the primary scrambling code for a first portion of the data and the secondary scrambling code for the remainder of the data, both portions being transmitted contemporaneously;
wherein the data is transmitted in slotted frames and non-slotted frames.
5. A radio communication system employing a code division multiple access technique comprising:
a primary station and a plurality of secondary stations,
the primary station having:
means for transmission of data to the secondary stations and;
means for encoding different separate and distinct portions of said data with different scrambling codes after spreading of said data, and
means for using at least one of a primary scrambling code and or a secondary scrambling code to encode the separate and distinct portions of said data for transmission to a secondary station, and means for transmitting a slotted mode signal to the secondary station using the primary scrambling code for a first portion of the data and the secondary scrambling code for the remainder of the data, both portions being transmitted contemporaneously;
wherein the data is transmitted in slotted frames and non-slotted frames.
2. A The method as claimed in
3. A The method as claimed in
4. A The method as claimed in
7. A The primary station as claimed in
8. A The primary station as claimed in
9. A The primary station as claimed in
0. 11. A communication station comprising:
a transmitter for transmitting transmit data to a terminal; and
a receiver for receiving receive data from said terminal;
wherein one of said transmit data and receive data has a first portion and a second portion, said first portion being encoded with a primary scrambling code and said second portion being encoded with a secondary scrambling code; and
wherein said communication station is configured to one of transmit and receive both said first portion and said second portion contemporaneously.
0. 12. The method as claimed in claim 1, further comprising the step of transmitting a slotted mode signal to the secondary station using a primary scrambling code for a first portion of the data and a secondary scrambling code for the remainder of the data, both portions being transmitted contemporaneously.
0. 13. The primary station as claimed in claim 6, further comprising means for transmitting a slotted mode signal to the secondary station using the primary scrambling code for a first portion of the data and a secondary scrambling code for the remainder of the data, both portions being transmitted contemporaneously.
0. 14. The radio communication system as claimed in claim 5, further comprising means for transmitting a slotted mode signal to the secondary station using the primary scrambling code for a first portion of the data and the secondary scrambling code for the remainder of the data, both portions being transmitted contemporaneously.
0. 15. The secondary station as claimed in claim 10, wherein said data includes a slotted mode signal having a first portion encoded with the primary scrambling code and a second portion encoded with the secondary scrambling code, both portions being transmitted contemporaneously.
0. 17. The method as claimed in claim 16, wherein in the slotted frames a first portion of the data is encoded with the first scrambling code and a second portion of the data is encoded with the different scrambling code, both portions being transmitted contemporaneously.
0. 19. The primary station as claimed in claim 18, further comprising means for encoding a first portion of the data in the slotted frames with the first scrambling code and a second portion of the data in the slotted frames with the different scrambling code, both portions being transmitted contemporaneously.
0. 21. The secondary station as claimed in claim 20, further comprising means for receiving a first portion of the data in the slotted frames encoded with the first scrambling code and a second portion of the data in the slotted frames encoded with the different scrambling code, both portions being transmitted contemporaneously.
0. 23. The primary station as claimed in claim 22, wherein a first portion of the data in the slotted frames is encoded with the first scrambling code and wherein a second portion of the data in the slotted frames is encoded with the different scrambling code, both portions being transmitted contemporaneously.
0. 25. The secondary station as claimed in claim 24, wherein a first portion of the data in the slotted frames is encoded with the first scrambling code and a second portion of the data in the slotted frames is encoded with the different scrambling code, both portions being transmitted contemporaneously and received by the transceiver.
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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.
A number 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.
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.
Different physical channels use different channelisation codes (usually orthogonal), while the scrambling code is the same for all physical channels in one cell.
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.
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.
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.
An object of the present invention is to reduce the problems caused by the use of more than one scrambling code in a cell.
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 data to a plurality of secondary stations, the primary station encoding different portions of said data with different scrambling codes, characterised by using a primary and a secondary scrambling code to encode data for transmission to a single secondary station.
According to a second aspect of the present invention there is provided a radio communication system employing a code division multiple access technique comprising a primary station and a plurality of secondary stations, the primary station having means for transmission of data to the secondary stations and means for encoding different portions of said data with different scrambling codes, characterised in that the primary station has means for using a primary and a secondary scrambling code to encode data for transmission to a single secondary station.
According to a third 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, the primary station having means for transmission of data to the secondary stations and means for encoding different portions of said data with different scrambling codes, characterised in that the primary station has means for using a primary and a secondary scrambling code to encode data for transmission to a single secondary station.
According to a fourth 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, characterised in that the secondary station has means for receiving data from a single primary station encoded using a primary and a secondary scrambling code.
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.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein:
In the drawings the same reference numerals have been used to indicate corresponding features.
A first illustrative embodiment of the present invention is the implementation of downlink slotted mode shown in
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.
One option in accordance with the present invention, as illustrated in
A preferred option is illustrated in
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).
A second illustrative embodiment of the present invention is the implementation of variable rate multi-code transmissions shown in
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
Use of this scheme will save channelisation codes while minimising the resulting interference.
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.
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.
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.
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