WO2005064972A1

WO2005064972A1 - Method, terminal unit and base station unit for providing data communication in a code division multiple access (cdma) telecommunications system

Info

Publication number: WO2005064972A1
Application number: PCT/EP2003/014980
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: AU2003296750A1

Abstract

The present invention relates 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 said data communication. Each of said transport channels has a transport format (TF) indicating a data rate of said transport channel. A data signal is transmitted between an originating unit and a receiving unit through at least one of said plurality of transport channels, and at least one transmission gap is provided using at least one compressed mode (CPM). The compressed mode comprises the step of providing at least one transmission gap using spare transmission capacity between the available data rate of said at least one transport channel and the required data rate by said data signal.

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 times! ot 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). In practice, two compressed modes may be used by the CMC to provide these idle periods or transmission gaps; i.e. reduction of the spreading factor (SF) by a factor 2 (abbreviated by SF/2), and higher layer scheduling (HLS) . These compressed modes, which are known to the skilled person, are describer briefly herein below. 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 timeslot in between each of the timeslots containing the data signal to be sent. These extra timeslots 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. In the higher layer scheduling (HLS) compressed mode, restrictions are set to the transport format combinations (TFC) that may be used in a compressed frame. Due these restrictions, the maximum data rate actually used by the coded composite transport channel is known and a transmission gap may be created based on this knowledge. Higher layer scheduling is often used for packet switched (PS) radio access bearers. A disadvantage of higher layer scheduling is that the terminal unit should not receive/sent information in certain slots, because in HLS it is scheduled that no data will be transmitted/received during these slots. Therefore, higher layer scheduling is considered to be used for non-real time (NRT) traffic only, since the HLS method will introduce delay and reduce the throughput of the channel.

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, without using more code and hardware resources, and without introducing delays and reducing the transmission throughput. 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, each of said transport channels having a transport format (TF) indicating a data rate of said transport channel, wherein a data signal is transmitted between an originating unit and a receiving unit 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 at least one transmission gap using spare transmission capacity between the available data rate of said at least one transport channel and the required data rate by said data signal. The benefits of the invention will be appreciated, in that by using spare transmission capacity between the available data rate of said at least one transport channel and the required data rate by said data signal, 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 and the compressed mode may be applied to both real time (RT) and non-real time (NRT) traffic. Note that especially in the case of (circuit switched) voice traffic, often only a small part of the available data rate is used for sending the data signal and there may be more than sufficient spare transmission capacity within the transport channel. In an embodiment of the present invention, providing said transmission gap further comprises a step of changing the current transport format of said at least one transport channel to an alternative transport format having a higher data rate than said current transport format. It will be appreciated that in cases wherein the spare capacity (if any) within the transport channel is insufficient for creating transmission gaps, it is also possible to select a different transport format from the available transport formats in the transport format set (TFS) at a higher data rate. The difference between the higher data rate of the alternative transport format and the data rate actually required by the data signal may then be used for creating the transmission gaps. In another embodiment a plurality of empty blocks of data within said data signal constitute said spare transmission capacity, and providing said transmission gap further comprises a step of shifting said empty blocks of data together in time forming said transmission gap. In some cases, the data signal may comprise empty blocks comprising no data or no data of interest. Said empty blocks of data may be shifted in time such that together, these empty blocks constitute a transmission gap. In particular, a data signal mapped onto a transport channel may be 'stretched' using a rate matching method (e.g. adding extra bits). This 'stretched' data may contain empty blocks (of one or more bits of length) that can be shifted such that they are adjacent to each other, forming a transmission gap. In an embodiment of the invention, said transport channel comprises a plurality of subsequent frames, and each frame comprises one or more transport blocks arranged ^"for comprising said data signal. If, in accordance with another embodiment, each frame comprises a plurality of transport blocks, said transport blocks may be integrated in said frame using at least one of a group comprising time division multiplexing, frequency division multiplexing and code division multiplexing. It will be appreciated that any of these multiplexing techniques may be suitable for increasing the amount of available capacity in a transport channel and thereby creating spare capacity. 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 ( -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 applicabil ty 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, such as higher layer scheduling, reduced spreading factor 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, said terminal unit comprising means for selecting at least one transport channel from a plurality of transport channels comprised by a physical channel arranged for facilitating data communications, wherein each of said plurality of transport channels comprises a transport format (TF) indicating a data rate of said transport channel, further comprising means for transmitting a data signal between said terminal unit and a receiving unit through said at least one transport channel, 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 at least one transmission gap using spare transmission capacity between the available data rate of said at least one transport channel and the required data rate by said data signal. 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, wherein each of said plurality of transport channels comprises a transport format (TF) indicating a data rate of said transport channel , further comprising means for transmitting a data signal between said base station unit and a receiving unit through at least one transport channel and which means are arranged for maintaining said communication on different transport formats. 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 3 schematically illustrates a transport channel, using a method according to the present invention; figure 4 schematically illustrates another transport channel using a method according to the present invention; figures 5A and 5B respectively schematically illustrate a normal mode and a compressed mode in a transport channel, in accordance with another embodiment of the invention;

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 figure 3. In figure 3, the time passes in the direction indicated by arrow 49. 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 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 and the transport block set size, i.e. the number of transport blocks per set. Assuming a fixed TTI (e.g. 40 ms) and a fixed transport block size (e.g. 128 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 figure 3, 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 figure 3, 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. In practise, not all the transport blocks in each set may be used for sending the data signal onto the network. As indicated in figure 3 each of the transport blocks sets 50, 51, 52, 53, 54, 55 comprises at least one free transport block, such as transport block 59. It will be appreciated that voice traffic will often use only a small part of the available data rate. 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 the transport channel schematically indicated in figure 3, a compressed mode may be facilitated by reserving the unused blocks 63, 64 and 65 of the subsequent transport block sets 53, 54 and 55. Note that the arrow indicated by 66 corresponds to the time wherein the UE operates in a compressed mode (CPM). By using the unused blocks in each transport block set, the UE is enabled to create transmission gaps and to perform the measurements required for the handover procedure, 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. Blocks 63, 64 and 65 (and the corresponding blocks in the subsequent (not shown) transport blocks) are reserved for the compressed mode (CPM), and cannot be used for sending the data signal. Note that the dotted circumference of the blocks indicates that the blocks are reserved for compressed mode and cannot be used for other traffic. Figure 4 shows an alternative to the present invention, that may be used when (before operating in Compressed Mode) the available data rate in the transport channel is highly utilized. Note that transport block sets 70, 71 and 72 only occasionally provide an unused block, such as transport block 76. A compressed mode cannot be facilitated by using the unused transport blocks, since there are insufficient unused transport blocks to perform the required measurements. In this case an alternative compressed mode, in accordance with the present invention, can be used. Note that, as indicated by arrow 84, from transport block set 73 onwards (transport block set 73, 74 and 75), the UE operates in compressed mode. Transmission gaps or idle periods are created by creating unused blocks 78, 79 and 80 by temporarily changing the transport format to a higher data rate available in the transport channel. The spare capacity created by increasing the available data rate of the transport channel is used to create transmission gaps for performing handover measurements. Figures 5A and 5B respectively illustrate another embodiment of the present invention, wherein figure 5A schematically shows a normal mode in a transport channel and figure 5B shows a compressed mode for said transport channel. Time passes in the direction indicated by arrow 100. Double arrow 102 indicates a transmission time interval (TTI), and within each transmission interval (between two subsequent dotted lines), a single frame 101 of data is sent through said transport channel. Each frame consists of a same number of bits, in this case, each frame comprises 10 bits of data, as indicated in the figure. The data in said frame 101 is comprised by one or more integrated transport blocks, as described below. In figure 5A, a block of data 103, consisting of 9 bits of data, is fitted in a single frame comprised of 10 bits using a rate matching method. Here, the rate matching method used adds an extra bit 104 to the block 103, and integrates the 10 bits of block 103 and bit 104 together in frame 101 as a transport block 110. Same is done for the subsequent frames, such that each frame comprises a single transport block, such as transport blocks 110, 111, 112, 113, 114, 115, 116, 117, 118 and 119. A total of 90 bits has been sent through the transport channel using 10 frames. Note that each of the transport blocks comprises at least one bit, such as bit 104, which is added to the actual payload of that transport block only because of rate matching, and may be considered spare capacity as it does not contain any valuable information. A transport block, such as transport block 115, therefore consists of a first part 115A containing the actual data to be sent, and a second part 115B containing the extra 'rate matching' bit, both parts 115A and 115B integrated in a single transport block 115. Note further that, although each of the transport blocks 110, 111, 112, 113, 114, 115, 116, 117, 118 and 119 comprise a single block of data, such as block 103, the transport blocks may be comprised of more than one block of data. In figure 5B, a similar transport channel is shown operating in a compressed mode in accordance with the present invention. Here, blocks of data, such as block 120, are sent through the transport channel in frames 140, 141, 142, 143, 144, 145, 146, 147 and 148. However, instead of adding extra bits for rate matching purposes, bits of a following block have been added to each of the transport blocks in the frames. As a result, the transport blocks 130, 131, 132, 133, 134, 135, 136, 137, 138 and 139, are shifted one against the other in frames 140, 141, 142, 143, 144, 145, 146, 147 and 148. Therefore, 90 bits of data have been sent through the transport channel in 9 frames, and the 10^th frame 149 may be used for other purposes, thereby forming a transmission gap 150. This transmission gap may be used for performing handover measurements. As an alternative, spare capacity may also be created by changing the transport format to another data rate, such that each frame may comprise more bits, e.g. 11 bits per frame while the payload for each transport block only consists of 9 bits of data. By shifting the data blocks as indicated in relation to figures 5A and 5B, transmission gaps may be created. 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 the reduced spreading factor compressed mode or the higher layer scheduling 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, each of said transport channels having a transport format (TF) indicating a data rate of said transport channel, wherein a data signal is transmitted between an originating unit and a receiving unit 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 at least one transmission gap using spare transmission capacity between the available data rate of said at least one transport channel and the required data rate by said data signal.

2. Method according to claim 1, wherein providing said transmission gap further comprises a step of changing the current transport format of said at least one transport channel to an alternative transport format having a higher data rate than said current transport format.

3. Method according to any of the previous claims, wherein a plurality of empty blocks of data within said data signal constitute said spare transmission capacity, and wherein providing said transmission gap further comprises a step of shifting said empty blocks of data together in time forming said transmission gap.

4. Method according to any of the previous claims, wherein said transport channel comprises a plurality of subsequent frames, and wherein each frame comprises one or more transport blocks arranged for comprising said data signal.

5. Method according to claim 4, wherein each frame comprises a plurality of transport blocks, wherein said transport blocks are integrated in said frame using at least one of a group comprising time division multiplexing, frequency division multiplexing and code division multiplexing.

6. Method according to any of the previous claims, wherei 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.

7. Method according to claim 6, wherein said measurements are related to a handover process in said telecommunications system.

8. Method according to claim 7, 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.

9. Method according to any of the claims 6-8, wherein a plurality of measurements are performed simultaneously by said originating unit during said at least one transmission gap.

10. 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.

11. Method according to claim 10, further comprising a step of selecting a particular compressed mode for providing said transmission gap.

12. 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.

13. Method according to claim 12 in dependence of claim 11, wherein said compressed mode is selected dependent on said type of radio access bearer.

14. 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 ised voice type data, messaging type data, internet protocol type data and multimedia type data.

15. Method according to claim 14 in dependence of claim 11, wherein said compressed mode is selected dependent on said type of data signal.

16. Method according to any of the previous claims, wherein said originating unit is a terminal unit, such as a mobile phone.

17. Method according to any of the previous claims, wherein said receiving unit is base station unit, arranged for receiving data signals from a plurality of originating units.

18. Terminal unit, such as a mobile phone, arranged for performing data communications in a code division multiple access (CDMA) telecommunications system, said terminal unit comprising means for selecting at least one transport channel from a plurality of transport channels comprised by a physical channel arranged for facilitating data communications, wherein each of said plurality of transport channels comprises a transport format (TF) indicating a data rate of said transport channel, further comprising means for transmitting a data signal between said terminal unit and a receiving unit through said at least one transport channel, 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 at least one transmission gap using spare transmission capacity between the available data rate of said at least one transport channel and the required data rate by said data signal.

19. Terminal unit according to claim 18, wherein said means for providing a transmission gap further comprises means for changing a current transport format of said at least one transport channel to an alternative transport format having a higher data rate than said original transport format.

20. Terminal unit according to any of the claims 18 or 19, further comprising means for shifting a plurality of empty blocks of data within said data signal together in time forming said transmission gap.

21. Terminal unit according to any of the claims 18-20, comprising means for integrating said plurality of transport blocks in at least one frame comprised by said transport channel, wherein said means for integrating said transport blocks are arranged for performing at least one of a group comprising time division multiplexing, frequency division multiplexing and code division multiplexing.

22. Terminal unit according to any of the claims 18-21, further comprising means for performing one or more measurements related to said data communications.

23. Terminal unit according to claim 22, 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.

24. Terminal unit according to any of the claim 23, wherein said means for performing measurements is arranged for performing a plurality of measurements simultaneously during said at least one transmission gap.

25. Terminal unit according to any of the claims 18-24, wherein said means for providing a transmission gap further comprises means for selecting a compressed mode from a plurality of alternative compressed modes.

26. Terminal unit according to any of the claims 18-25, 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.

27. Terminal unit according to claim 26 in dependence of claim 25, wherein said means for selecting a compressed mode is arranged for selecting said compressed mode dependent on said type of radio access bearer.

28. Terminal unit according to any of the claims 18-27, said terminal unit being arranged for transmitting a data signal of a type comprising at least one of a group comprising digital ised voice type data, messaging type data and internet protocol type data, multimedia type data.

29. 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, wherein each of said plurality of transport channels comprises a transport format (TF) indicating a data rate of said transport channel, further comprising means for transmitting a data signal between said base station unit and a receiving unit through at least one transport channel and which means are arranged for maintaining said communication on different transport formats.