WO2005064971A1

WO2005064971A1 - Method, terminal unit and base station unit for providing data communication in a code division multiple access (cdma) telecommunications system

Info

Publication number: WO2005064971A1
Application number: PCT/EP2003/014979
Authority: WO
Inventors: Rinke Terpstra; Haijun Chen
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2003-12-29
Filing date: 2003-12-29
Publication date: 2005-07-14
Also published as: AU2003294970A1

Abstract

The present invention provides a method of providing data communication in a code division multiple access (CDMA) telecommunications system, wherein a physical channel comprising a plurality of transport channels facilitates said data communication. Signalling data signals are transmitted between an originating unit and a receiving unit of said data communications system through at least one of said plurality of transport channels. At least one transmission gap is provided using at least one compressed mode (CPM), said at least one compressed mode comprising the step of providing said least one transmission gap by temporarily scheduling said transmission of said signalling data signals.

Description

Title Method, terminal unit and base station unit for providing data communication in a code division multiple access (CDMA) telecommunications system.

Field of the invention The present invention relates generally to data communication in a code division multiple access (CDMA) telecommunications system, and in particular to a method of providing data communication in a code division multiple access (CDMA) telecommunications system, wherein a physical channel comprising a plurality of transport channels facilitates communication to a receiving unit. The present invention further relates to a terminal unit and a base station unit for use in accordance with such a method.

Background of the Invention In a code division multiple access (CDMA) telecommunications system, data signals between a terminal unit and a receiving unit, such as a base station unit, is performed through a radio access bearer (RAB) established between the terminal unit and the base station unit. This radio access bearer includes a coded composite transport channel, which is comprised of, for instance, two transport channels (TrCH) multiplexed together. Each transport channel comprises its own transport format (TF) , indicating a number of relevant parameters, such as the available data rate on the transport channel. The combined set of transport channels in the coded composite transport channel is indicated by a transport format combination (TFC) . Data signals transmitted through a transport channel are sent in sets of transport blocks of a specific size, as determined by the transport format. In each set, a predetermined maximum number of blocks may be sent, and this maximum number is also determined by the transport format. The transport format further specifies a transmission time interval (TTI), in which interval a single set of transport blocks may be sent through the transport channel. It will be appreciated that the transport block size, the number of blocks per set and the TTI, together determine the data rate of the transport format used for the transport channel. Since a certain maximum data rate is available for a transport channel, by limiting the transport block size (assuming a fixed TTI) the actual data rate of the used transport format may be varied by varying the number of blocks per set or transport block set size. For a given transport channel, a number of different transport formats can be used having a different data rate; the collection of transport formats that may be used for a transport channel is called the transport format set (TFS) . If two transport channels are multiplexed together, in analogy with the description above, since for each transport channel a number of different transport formats is available as indicated in the TFS of a transport channel, an even larger number of transport format combinations is available. Each transport format combination (TFC) is indicated by a transport format combination indicator (TFCI). A coded composite transport channel is therefore characterised by a TFC, which TFC provides an indication of the data rates of the transport channels multiplexed together. The coded composite transport channels are mapped to the physical channel facilitating the data communication with the base station. Each terminal unit communicating with a base station is assigned a unique spreading code which is used by the base station to identify the terminal unit. The length of the spreading code is called the spreading factor, and determines to some degree the maximum data rate available, as will be explained later. Information regarding the transport format combination, the spreading code and the data to be sent, is integrated in a single timeslot and is sent through the physical channel to the base station, where it is processed and forwarded via a radio network controller into the telecommunications system. In CDMA systems, the use of handover procedures, such as inter radio access technology handover (IRATHO), inter radio access technology cell change (IRATCC) and inter-frequency handover (IFHO), are the fundamental /important parts of the system. Handover in CDMA systems is the process in which a terminal unit involved in a data communications process changes a communications mode or in which the terminal unit changes to another base station unit of the system. In order to perform these handovers, the terminal unit has to perform a number of measurements on the telecommunications network, such as intra-frequency measurements, inter-frequency measurements, inter-radio-access-technology (inter-RAT) measurements, traffic volume measurements, quality measurements, internal measurements in the terminal unit itself and/or measurements of the position of the terminal unit. In order to perform these measurements, while at the same time maintaining the data communications, idle periods are to be created during transmission of the data signal, during which idle periods the measurements can be performed by the terminal unit. These idle periods are created using so-called compressed modes (CPM) , using a compressed mode controller (CMC). One type of compresse modes used by the CMC to provide these idle periods or transmission gaps is reduction of the spreading factor (SF) by a factor 2 (abbreviated by SF/2), as will be discussed above. As mentioned above, the maximum available data rate is dependent on the spreading factor used. In CDMA, a single bit sent through the air to the base station unit is "code division multiplexed" by taking the convolution of the bit sent and the spreading code. The length of one bit therefore becomes equal to the length of the spreading factor. A higher spreading factor results in a lower maximum available data rate, and vice versa. In the SF/2 compressed mode, the spreading factor is reduced by a factor 2. The data rate, being linear dependent on the spreading factor, is increased by a factor 2. It then becomes possible to fit an extra time slot in between each of the times! ots containing the data signal to be sent. These extra time slots form the required idle periods or transmission gaps that can be used by the terminal unit to perform the required measurements. The SF/2 compressed mode method is often used for circuit switched (CS) radio access bearers. A disadvantage of the SF/2 compressed mode is that power should be increased at least 3 dB for each radio link in order to maintain the quality of service. If many terminal units are in compressed mode at the same time, this can become problematic. Since power should not be increased above a certain threshold, the network will only support a certain maximum number of terminal units to be in compressed mode. Another disadvantage is that in SF/2 compressed mode, in uplink (UL) mode, i.e. from the terminal unit to the base station, the same scrambling code will always be used (i.e.: in the UL mode the scrambling code will never be changed when SF/2 is performed), but in the downlink (DL) mode, i.e. from the base station to the terminal unit, the same or an alternative scrambling code can be used. The alternative scrambling code is a scrambling code linked to the current scrambling code based on certain rules. Therefore, the SF/2 compressed mode adds to the complexity of code (de) composition and will require more hardware resources of the telecommunications system. Another disadvantage is that SF/2 compressed mode method is complicated and expensive to implement within telecommunications systems.

Summary of the Invention It is an object of the present invention to provide a mechanism of creating transmission gaps, without changing the spreading factor, without increasing the power, and without using more code and hardware resources. These and other objects are achieved by the present invention, in that there is provided a. method of providing data communication in a code division multiple access (CDMA) telecommunications system, wherein a physical channel comprising a plurality of transport channels facilitates said data communication, wherein signalling data signals are transmitted between an originating unit and a receiving unit of said data communications system through at least one of said plurality of transport channels, and wherein at least one transmission gap is provided using at least one compressed mode (CPM), said at least one compressed mode comprising the step of providing said least one transmission gap by temporarily scheduling said transmission of said signalling data signals. The benefits of the invention will be appreciated, in that by temporarily scheduling said transmission of said signalling data signals, a transmission gap can be easily created within the existing radio access bearer and coded composite transport channel. The spreading factor can be left unaltered, there will be no requirement for increasing the power, and since the required data rate for the data signal can be guaranteed, no delay will be introduced by the compressed mode suggested. Therefor, the throughput is guaranteed. The method of the present invention provides an alternative compressed mode that may be applied to, for instance, circuit switched traffic where conventionally the SF/2 compressed mode is used for this type of traffic. In an embodiment of the present invention, said transmission gap is provided by temporarily suspending transmission of said signalling data signals. It will be appreciated that transmission gaps can be readily created by suspending the signalling traffic temporarily. In another embodiment of the present invention, said transmission gaps are used by any of said originating unit and said receiving unit for performing one or more measurements related to said transmission of said data signal. In particular, said measurements may be related to a handover process in said telecommunications system. In accordance with some specific embodiments, said measurements may comprise at least one of a group comprising intra- frequency measurements, inter-frequency measurements, inter-radio-access- technology (inter-RAT) measurements, traffic volume measurements, quality measurements, internal measurements of said originating unit, measurements of a position of said originating unit. The different types of measurements are related to measurements performed in handover processes in CDMA systems, such as wideband code division multiple access (W-CDMA) systems. Note that various different handover processes may be used by the terminal unit, which are know to the person skilled in the art, such as hard handovers, soft handovers and softer handovers. In accordance with an embodiment of the present invention, a plurality of measurements are performed simultaneously by said originating unit during said at least one transmission gap. It will be appreciated that by performing a number of measurements simultaneously, less transmission gaps need to be created, which provides benefits in that also less spare transmission capacity is required in order to be able to perform the method of the present invention. In a preferred embodiment, the method of the present invention comprises at least one alternative compressed mode for providing at least one transmission gap in said at least one transport channel. By providing alternative compressed modes, it becomes possible to use different compressed modes in different situations. The applicability of this embodiment is increased if said method comprises a step of selecting a particular compressed mode for providing said transmission gap. It then becomes possible to switch between different compressed modes. The method of the present invention may applied in combination with different types of radio access bearers, such as circuit switched radio access bearers and packet switched radio access bearers. In another embodiment of the present invention, said compressed mode is selected dependent on said type of radio access bearer. It will be appreciated that different types of radio access bearers (CS / PS) may be especially suitable for use with different kinds of compressed modes, e.g. said reduced spreading factor mode or any other compressed mode, such as the compressed mode described above. Said data signal may be of a type comprising at least one of a group including digital ised voice type data, messaging type data, internet protocol type data and multimedia type data. It will be appreciated that, in accordance with another embodiment, said compressed mode is selected dependent on said type of data signal. The originating and receiving units may be any unit that is arranged for performing data communication in a code division multiple access telecommunication system, such as terminal units (mobile phones, wireless modems, etc.), base stations, radio network controllers, switches, etc. According to a second aspect of the present invention, there is provided a terminal unit, such as a mobile phone, arranged for performing data communications in a code division multiple access (CDMA) telecommunications system having a plurality of transport channels comprised by a physical channel arranged for facilitating said data communications, said terminal unit comprising means for transmitting signalling data signals between said terminal unit and a receiving unit through at least one of said plurality of transport channels, and means for providing at least one transmission gap using a compressed mode (CPM), wherein said means for providing said transmission gap are arranged for providing said at least one transmission gap by temporarily scheduling transmission of said signalling data signals. According to a third aspect of the present invention, there is provided a base station unit arranged for performing data communications in a code division multiple access (CDMA) telecommunications system, said base station unit comprises means for performing said communication on at least one transport channel of a plurality of transport channel comprised by a physical channel arranged for facilitating data communication, further comprising means for processing scheduled signalling data signals received by said base station unit through at least one transport channel. The present invention will now be further elucidated in the following description of a preferred embodiment thereof, with reference to the enclosed drawings and the reference signs incorporated therein. Brief description of the Drawings Figure 1 schematically illustrates a UMTS Terrestrial Radio Access Network (UTRAN); figure 2 schematically illustrates a Radio Interface Protocol Structure for Wideband Code Division Multiple Access (W-CDMA); figure 3A schematically illustrates a transport channel carrying signalling data traffic ; figure 3B schematically illustrates the transport channel of figure 3A, wherein a compressed mode according to a method according to the present invention is used.

Detailed description of the Drawings Figure 1 schematically illustrates a UMTS Terrestrial Radio

Access Network 1, wherein a plurality of terminal units or user equipment units (UE) 2, 3 and 4 are connected to a plurality of base station units or nodes 5, 6, 7 through wireless connections 15, 16, 17. Base station units 5, 6 and 7 are connected to one or more radio network controllers (RNC) 10 and 11, through connections 18, 19 and 20. Radio network controllers (RNCs) 10 and 11 are connected to a core network (CN) 12, through connections 22 and 23. The connections 15, 16 and 17 between UE 2, 3 and 4 and base station units 5, 6 and 7 respectively, may be comprised of one or more physical channels comprising a plurality of transport channels. Said transport channels may be combined in sets or combinations of transport channels, each transport channel combination characterized by a transport format combination (TFC), which indicates the transport formats (TF) of the transport channels in the combination. Such a combination may be referred to as a coded composite transport channel. Figure 2 schematically shows a radio interface protocol structure. A number of channels 25 and 26 is mapped to a physical channel 43. The channels 25 and 26 may be divided in C-plane channels 25, primarily used for signalling purposes, and U-plane channels 26, primarily used for user data (voice, messaging, Internet protocol, etc.). A radio resource control (RRC) 27 forms a sublayer which exists in the control plane (C-plane) only, and is responsible for controlling the configuration of lower layers in the protocol structure. The radio resource control (RRC) 27 provides a signalling data signal through radio access bearers 28. Radio link control units (RLC) 30 and 31 map the data signals in radio access bearers 28 and 29 to logical channels 34 and 35. In medium access control (MAC) 37, the logical channels 34 and 35 are mapped onto a plurality of transport channels 40. Said transport channels 40 are mapped onto the physical channel 43 in physical layer 38. The mapping of logical channels 34 and 35 onto transport channel 40 is controlled by radio resource control (RRC) 27 using control connection 41. Also the mapping of transport channels 40 onto physical channel 43 is controlled by the RRC 27 using control connection 42. The protocol structure illustrated in figure 2 may be a typical protocol structure used in a W-CDMA telecommunications system. As described above, transport channels 40 may be multiplexed together forming coded composite transport channels. In a coded composite transport channel, a plurality of transport channels comprising different transport formats (TF) are multiplexed together. Data signals transmitted through a transport channel are sent in sets of transport blocks of a specific size, as determined by the transport format. In each set of transport blocks, a predetermined maximum number of blocks may be sent, as determined by the transport format. The transport format also specifies a transmission time interval (TTI), specifying the time interval wherein a single set of transport blocks may be sent subsequently through the transport channel. A schematic illustration of a transport channel is provided in figures 3A and 3B, wherein figure 3A indicates a regular (uncompressed) communication mode of the transport channel and wherein figure 3B illustrates the same transport channel as in figure 3A operating in a compressed mode (CPM) in accordance with a method of the present invention. As schematically illustrated, the time passes in the direction indicated by arrow 49 in figure 3A. The transport channel is divided in time slots, such as time slot 61, characterized by a transmission time interval (TTI) schematically indicated by double arrow 60 in figures 3A and 3B. In each time slot, a transport block set 50, 51, 52, 53, 54, 55 may be sent through the transport channel. Each transport block set is comprised of a plurality of transport blocks, such as transport blocks 57, 58 and 59 in transport block set 50. The total number of transport blocks that may be comprised by the transport block set will be determined by the maximum data rate available for that transport channel. The actual data rate used in the transport channel is determined by the transport block size, the transmission time interval 60 and the transport block set size, i.e. the number of transport blocks per set (in the present example: 3). Assuming a fixed TTI (e.g. 40 ms) and a fixed transport block size (e.g. 320 bit), it will be appreciated that the actual data rate used in the transport channel is linear dependent on the transport block set size of the transport channel. Suppose the maximum available data rate in the transport channel corresponds to a maximum set size of five transport blocks, then the transport block set size may accordingly may be varied between 0 and 5 transport blocks per set. The transport block set size may therefor be indicated by a integer. Assume that two transport channels are multiplexed together having a fixed transport block size, e.g. 320 bit, and a fixed transmission time interval, e.g. 40 ms. The transport block set size of the first of the two transport channels may be varied between 0 and 1 block, while the transport block set size of the second of the two transport channels may be varied between 0 and 4 transport blocks. The coded composite transport channel of these two transport channels may therefor comprise a total of ten different transport format combinations, in this case being (0,0), (1,0), (2,0), (3,0), (4,0), (0,1), (1,1), (2,1), (3,1), and (4,1). The various transport format combinations that may be comprised by the coded composite transport channel may be indicated by a transport format combination indicator (TFCI), which may be an integer number providing a label to each possible transport format combination (TFC). In the transport channel of figures 3A and 3B, sets of three blocks are sent onto the transport channel each time interval. The actual amount of data to be sent in these data blocks may vary, and in figures 3A and 3B, a filled transport block comprising data to be sent onto the network, is indicated by a shaded block, such as block 57 of transport block set 50. If the transport channel is used for carrying signalling data traffic, not all of the transport block sets 50, 51, 52, 53, 54 and 55 in the may be used for carrying data. Especially in cases wherein the data signal is bursty, some of the transport block sets may be completely filled, while others may be empty. Referring to figure 3A, in the present case, in uncompressed mode, transport blocks 57, 62, 63, 64, 65 and 68 of transport block sets 50, 51, 53, 54 and 55 contain data, while the other transport blocks are empty. As described above, in CDMA systems, the use of handover procedures are fundamental and important parts of the system. Handover in CDMA systems is the process in which a UE involved in a data communications process changes a communications mode or changes to another base station unit of the system. In order to perform the handovers, the UE has to perform a number of measurements in the telecommunications network. These measurements have to be performed during the data communications, and in order to perform these measurements, transmission capacity needs to be created within the transport channels. This is performed by using a, so called, compressed mode (CPM), and using said CPM to provide transmission gaps. In accordance with the present invention, in compressed mode (CPM) as illustrated in figure 3B, the signalling data traffic in the transport channel is scheduled in order to provide transmission gaps. Therefore, the data sent in block 62 of figure 3A may (if possible) be sent in transport block 58 of transport block set 50 in figure 3B. If it is not possible to send the contents of a transport block in an earlier transport block set, then alternatively transmission of the data in that transport block may be postponed and sent in a later transport block set. The latter is done for instance with the contents of transport blocks 63 and 64 in time slot 53 of figure 3A. In the compressed mode of figure 3B, the contents of these two transport blocks is sent in transport block set 54, which is then completely utilised. By scheduling the data to different transport blocks, it becomes possible to create a transmission gap that is large enough to carry out handover measurements, such as intra-frequency measurements, inter-frequency measurements, inter-radio- access-technology (inter-RAT) measurements, traffic volume measurements, quality measurements, internal measurements in the UE itself and/or measurements of the (geographic) position of the UE, or other tasks for which CPM is required. Note that blocks 51, 52 and 53 in figure 3B are reserved for carrying out the tasks mentioned and may therefore not be used to carry any other traffic, as indicated by the dotted circumference of the blocks. Note that the methods of the present invention may be used in connection with uplink (UL) and downlink (DL) . Therefor the method of the present invention may be implemented in user equipment units (UE) as well as base station units. The transmission gaps created by using CPM may be used by performing a plurality of measurements simultaneously. This may of course be dependent on the spare capacity available in the transport channel. The UE or base station may decide to use any of the compressed mode (CPM) described above. In addition, according to another embodiment of the present invention, the UE or the base station may select a compressed mode from a number of available alternative compressed modes, amongst which for instance a compressed mode according to the present invention as described above. As the person skilled in the art will appreciate, in addition to the compressed modes described above, the UE or the base station may also use another compressed mode, such as the reduced spreading factor compressed mode, known in the art. In fact the telecommunications unit using the compressed mode may, prior to operating in compressed mode, select the most suitable compressed mode from a number of alternative compressed modes available. It will be appreciated, that each type of compressed mode may have benefits for some kind of traffic. In particular the compressed mode may either be selected dependent on the type of radio accessed bearer (e.g. CS or PS) used in the communications, or alternatively, the type of data signal to be transmitted. For the purpose of comprehensiveness, it is noted here that numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefor understood that, within the scope of the appended claims, the invention may be practised otherwise than as specifically described herein.

Claims

1. Method of providing data communication in a code division multiple access (CDMA) telecommunications system, wherein a physical channel comprising a plurality of transport channels facilitates said data communication, wherein signalling data signals are transmitted between an originating unit and a receiving unit of said data communications system through at least one of said plurality of transport channels, and wherein at least one transmission gap is provided using at least one compressed mode (CPM), said at least one compressed mode comprising the step of providing said least one transmission gap by temporarily scheduling said transmission of said signalling data signals.

2. Method according to claim 1, wherein said transmission gap is provided by temporarily suspending transmission of said signalling data signals.

3. Method according to any of the previous claims, wherein said transmission gaps are used by any of said originating unit and said receiving unit for performing one or more measurements related to said transmission of said data signal.

4. Method according to claim 3, wherein said measurements are related to a handover process in said telecommunications system.

5. Method according to claim 4, wherein said measurements comprise at least one of a group comprising intra-frequency measurements, inter-frequency measurements, inter-radio-access-technology (inter-RAT) measurements, traffic volume measurements, quality measurements, internal measurements of said originating unit, measurements of a position of said originating unit.

6. Method according to any of the claims 3-5, wherein a plurality of measurements are performed simultaneously by said originating unit during said at least one transmission gap.

7. Method according to any of the previous claims, comprising at least one alternative compressed mode for providing at least one transmission gap in said at least one transport channel.

8. Method according to claim 7, further comprising a step of selecting a particular compressed mode for providing said transmission gap.

9. Method according to any of the previous claims, wherein a radio access bearer comprises said at least one transport channel, wherein said radio access bearer is of a type comprising at least one of a group comprising circuit switched radio access bearers and packet switched radio access bearers.

10. Method according to claim 9 in dependence of claim 8, wherein said compressed mode is selected dependent on said type of radio access bearer.

11. Method according to any of the previous claims wherein a said data signal is of a type comprising at least one of a group including digital i sed voice type data, messaging type data, internet protocol type data and multimedia type data.

12. Method according to claim 11 in dependence of claim 8, wherein said compressed mode is selected dependent on said type of data signal .

13. Method according to any of the previous claims, wherein either one or more of said originating unit or said receiving unit is a terminal unit, such as a mobile phone.

14. Method according to any of the previous claims, wherein either one or more of said originating unit or said receiving unit is a base station unit, arranged for transmitting and receiving data signals to and from a plurality of terminal units.

15. Terminal unit, such as a mobile phone, arranged for performing data communications in a code division multiple access (CDMA) telecommunications system having a plurality of transport channels comprised by a physical channel arranged for facilitating said data communications, said terminal unit comprising means for transmitting signalling data signals between said terminal unit and a receiving unit through at least one of said plurality of transport channels, and means for providing at least one transmission gap using a compressed mode (CPM), wherein said means for providing said transmission gap are arranged for providing said at least one transmission gap by temporarily scheduling transmission of said signalling data signals.

16. Terminal unit according to claim 15, wherein said means for providing said at least one transmission gap further comprises means for temporarily suspending transmission of said signalling data signals.

17. Terminal unit according to any of the claims 15 and 16, further comprising means for performing one or more measurements related to said data communications.

18. Terminal unit according to claim 17, wherein said means for performing measurements is arranged for performing measurements comprised by a group comprising intra-frequency measurements, inter-frequency measurements, inter-radio-access-technology (inter-RAT) measurements, traffic volume measurements, quality measurements, internal measurements of said originating unit, measurements of a position of said terminal unit.

19. Terminal unit according to any of the claim 18, wherein said means for performing measurements is arranged for performing a plurality of measurements simultaneously during said at least one transmission gap.

20. Terminal unit according to any of the claims 15-19, wherein said means for providing a transmission gap further comprises means for selecting a compressed mode from a plurality of alternative compressed modes.

21. Terminal unit according to any of the claims 15-20, wherein said means for transmitting a data signal is arranged for setting up a radio access bearer comprising said at least one transport channel, wherein said radio access bearer is of a type comprising at least one of a group comprising circuit switched radio access bearers and packet switched radio access bearers.

22. Terminal unit according to claim 21 in dependence of claim 20, wherein said means for selecting a compressed mode is arranged for selecting said compressed mode dependent on said type of radio access bearer.

23. Terminal unit according to any of the claims 15-22, wherein said terminal unit is arranged for transmitting a data signal of a type comprising at least one of a group comprising digitali sed voice type data, messaging type data and internet protocol type data, multimedia type data.

24. Base station unit arranged for performing data communications in a code division multiple access (CDMA) telecommunications system, said base station unit comprises means for performing said communication on at least one transport channel of a plurality of transport channel comprised by a physical channel arranged for facilitating data communication, further comprising means for processing scheduled signalling data signals received by said base station unit through at least one transport channel.