BACKGROUND OF THE INVENTION Generally, in a wireless telecommunication network communication is established between a respective user's terminal device as a first type transceiver device (mobile station MS) and a respective second type transceiver device (base transceiver station BTS). Each second type transceiver device is controlled by a network control device such as a base station controller BSC (a plurality of which, in turn, is under control of a mobile switching service center MSC), and a transcoder unit TC (also referred to as transcoder rate adaptation unit TRAU) performing channel coding (and channel decoding) is associated thereto.

Each of the above mentioned first and second transceiver devices is provided with a sending/receiving coding/decoding means for effecting a transmission of data (for example speech data) between the first and second transceiver devices, which will be briefly explained below.

Data such as speech data to be transmitted from a terminal device, i. e. a mobile station MS, to said base transceiver station BTS (in uplink direction) are generated and converted to digital data at the terminal device side.

Then, the speech data are prepared for being transmitted by coding the data using a speech codec as a data related part of the codec means. The speech codec performs a coding of the data to achieve data compression and removal of redundancy in the data. Subsequently, the thus encoded data are supplied to a channel codec as a channel related part of the codec means. The channel codec performs a coding of the data for transmission via a transmission channel to the base transceiver station BTS. In particular, the channel codec is adapted to perform a channel coding which is suitable to detect and/or correct transmission errors in the transmitted data. Finally, the thus (twice) encoded data are transmitted from the mobile station MS to the base transceiver station BTS.

At the receiving side, i. e. at the base transceiver station BTS, a similar processing is conducted in reverse order, while the aforementioned coding operation is replaced by the corresponding decoding operation, to complete uplink transmission.

Similarly, downlink transmission from the base transceiver station BTS to the terminal device MS is effected.

In wireless telecommunication networks such as radio telecommunication networks, examples for the speech coding are the commonly used LPC-RPE coding and/or LTP coding, while examples for the channel coding are the commonly used block coding and/or convolutional coding. Each of such coding/decoding schemes or methods, respectively, corresponds to a respective operating mode of the codec and

is defined by corresponding operation parameters for said codec. In particular, each codec mode has some different characteristics as compared to other modes.

As regards the transmission channel, also the transmission channel can be operated in different codes, which are for example distinguished by the possible transmission data rate. In current telecommunication networks such as radio telecommunication networks, it is distinguished between two channel modes: a full rate mode and a half rate mode, which differ by a factor of two in terms of transmission data rate. within each of such channel modes, above mentioned codec modes may be activated.

The choice as to which channel mode is activated is taken by the network control device such as the base station controller BSC. The selection in this regard depends on quality and/or capacity optimization as a part of the network planning in terms of overall range/capacity/quality effected by the network operator.

The choice as to which codec operating mode is to be selected depends on the intention to maximize the speech quality or data transmission quality, respectively. In this connection, a compromise has to be found between the amount of data coding (speech coding) and channel coding and a corresponding control signaling will be required.

However, in currently adopted telecommunication network infrastructure arrangements, channel codecs and (speech) data codecs constituting a codec means are located in separate network elements. Additionally, a radio resource management functionality as a part of a network control device is located in a still other network device.

Within such a conventional network structure there is currently no signaling agreed on for implementing the new functionalities. Moreover, an exact method for determining a codec mode adaptation has not been defined, while also a corresponding control device and its location within the network has not been defined.

SUMMARY OF THE INVENTION Hence, it is an object of the present invention to overcome the above mentioned lack of definitions and to propose a corresponding definition of the method for codec mode selection and the corresponding control means, as well as to define the location of such control means within the network and to propose suitable signaling schemes applicable thereto. Moreover, the present invention aims to suggest correspondingly adapted network devices such as terminal stations, base transceiver stations etc., which are adapted to implement the proposed method and to handle the necessary signaling.

According to the present invention, this object is achieved by a method for adapting an operating mode of a coding/decoding means of a transceiver device, the coding/decoding means being adapted to be operated in a plurality of operating modes, the method comprising the steps of: detecting channel conditions of a transmission channel, judging, whether said detected channel conditions satisfy a predetermined condition, and instructing to modify a current operating mode of said coding/decoding means to a new operating mode of said plurality of operating modes, if the presence of said predetermined condition has been judged.

Furthermore, this object is achieved by a first type of transceiver device operated in a telecommunication network comprising at least one transceiver device of a second type and at least one network control device, said first type transceiver device comprising: processing means adapted to carry out the above method, and issuing an instruction to modify said operating mode, informing means adapted to inform at least one of said network devices of said instruction to modify said operating mode, and mode changing means being responsive to a command to change said mode.

Moreover, this object is achieved by a second type of transceiver device operated in a telecommunication network comprising at least one transceiver device of a first type and at least one network control device, said second type transceiver device comprising: processing means adapted to carry out the above method, and issuing an instruction to modify said operating mode, informing means adapted to inform at least one of said network control devices of said instruction to modify said operating mode, and mode changing means being responsive to a command to change said mode.

Still further, the present invention also proposes a network control device adapted to control a telecommunication network comprising at least one transceiver device of a first and a second type, respectively, said network control device comprising a mode information receiving means adapted to receive a mode request or mode command from said first or second type transceiver devices, and mode changing means adapted to change said mode upon receipt of said mode request or mode command.

Advantageous further developments of the present invention are defined in the respective subordinated claims.

Accordingly, with the present invention it is possible to define an exact method for codec mode adaptation and location of a correspondingly adapted control device.

Moreover, a codec mode adaptation can be effected independently for the uplink and the downlink transmission direction.

Depending on the chosen particularities of the mode adaptation method, the mode selection for adaptation may be performed with least possible delay or, when taking a certain delay into account, with least possible faulty or unnecessary adaptation operations.

Similarly, a delay in mode adaptation can be optimized by properly selecting the location of the correspondingly adapted processing means for deciding the mode adaptation.

Also, in such a scenario, less complex signaling can be realized. Also, in particular signaling scenarios, radio resource management (RRM) related information can be used in the signaling.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more readily understood when referring to the enclosed drawings, in which: Fig. 1 illustrates a flow chart of the method for adapting an operating mode of a coding/decoding means of a transceiver device; Fig. 2 shows a diagram of the detected or measured bit error rate as a channel condition over time and the

respectively initiated actions in dependence on a current channel condition; Fig. 3 depicts a table of codec operating modes which are defined by code parameters for a channel codec part and a data (speech) codec part, with such a table being for example implemented as a look up table LUT; Fig. 4A through 4C illustrate schematically mode selection signaling scenarios in downlink transmission; and Fig. 5A through 5C illustrate schematically mode selection signaling scenarios in uplink transmission.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The present invention will subsequently be described in detail with reference to the drawings.

According to the present invention, the amount of channel coding is reduced, if the channel conditions are good. In addition, in such a case the speech coding bit rate can be increased. Conversely, if the channel conditions are poor which manifests for example in an increase in the bit error rate, the amount of channel coding is increased and the speech coding rate is decreased. All this, of course, is effected within the limits of available data (e. g. speech) and channel coding modes. Stated in other words, increasing and decreasing respective modes resides in a switching over between respective predetermined modes which are defined by respective code parameters. Such code parameters may be present in a prestored addressable look up table LUT, with the contents at an address thereof representing a respective code to be selected. In such a case, increasing /decreasing a code may be deemed to correspond to an

increase/decrease of the respective address denoting the corresponding code.

According to the present invention, codec mode adaptation and/or selection is performed based on a channel quality estimation. To this end, the decision as to whether and/or which codec operating mode is to be selected can be based on the bit error rate of the channel measured (detected) by the channel decoder of the respective receiving side.

Alternatively, parameters exchanged between a terminal device MS and a base transceiver station BTS on a control channel such as the SACCH (slow associated control channel) in a so-called measurement report can be used as a basis for decision. In particular, the parameters RX_qual (corresponding to a bit error rate) or RX_lev (describing the reception level, i. e. signal strength of a received signal) can suitably be used. Furthermore, also the prevailing traffic load can be used as a basis for the decision.

The following description, however, focuses on the bit error rate as an example of the measured and/or detected channel condition used for the decision. Various methods for defining the bit error rate or pseudo bit error rate can be adopted. One possible known method is briefly presented as an example here. This known method resides in storing the received encoded data bits, performing decoding, re-encoding the data and then comparing the result with the stored encoded data bits.

The thus detected channel condition is evaluated by judging whether a predetermined condition is satisfied. The predetermined condition may be defined by at least one threshold value. Preferably, two threshold values TH1 and TH2 are selected which define a margin there between. The

thresholds can be selected dependent on speech codec characteristics.

In a modification, also multiple thresholds such as two lower thresholds and two upper thresholds can be defined.

Then, a codec mode adaptation is effected in a more severe way when the channel condition exceeds/is below both upper/lower thresholds as compared to the case when the channel condition exceeds/is below only one of the upper/lower thresholds. A"severe"adaptation means that a codec mode is changed to a larger extent at a time than otherwise.

The channel condition is measured or detected periodically.

Each such periodically obtained measurement value can be evaluated in terms of whether the predetermined condition is met. However, as an alternative, it is conceivable to evaluate only the average value of P periodically obtained measurement values in terms of whether the predetermined condition is met. As a still further alternative, it is also conceivable to judge the presence of the predetermined condition, if N out of P of such periodically obtained measurement values satisfy the predetermined condition.

These two alternatives mentioned, though somewhat causing a delay in the mode adaptation, may advantageously prevent an unnecessary or faulty adaptation, thereby stabilizing the proposed method.

Fig. 1 illustrates a flow chart of the method for adapting an operating mode of a coding/decoding means of a transceiver device. That is, the proposed method as illustrated in the flowchart can be implemented in a processing means (not shown) of a mobile station MS transceiver device as well as in a base transceiver station BTS transceiver device.

In a step S10, the method as exemplified in the following description starts with a measurement of the pseudo bit error rate BER as a detecting step of a channel condition.

In subsequent steps S11-S14, it is judged whether the detected/measured bit error rate satisfies a predetermined condition.

Namely, in step S11, the bit error rate is compared with a (lower) first threshold value TH1. If the bit error rate is not below said first threshold value TH1 (NO in step S11), the flow advances to step S12. In step S12, the measured bit error rate is compared with a (higher) second threshold value TH2. If said bit error rate is below said second threshold value TH2 (YES in step S12), it is judged that the bit error rate is within an error rate margin defined by said two thresholds TH1, TH2, and the method proceeds to step S17. In step S17, no change is effected since the bit error rate has been judged to be within an admissible margin that does not require a codec mode adaptation, and the method returns to step S10.

If, however, in step S12 the comparison yielded that the bit error rate is not below the second threshold TH2 but exceeds the threshold TH2 (NO in step S12), the method advances to step S14. In step S14, it is checked whether the present channel codec mode corresponds to the strongest channel code of a plurality of codes according to which the codec means can be operated.

Here, it should be noted that the expression"strongest" channel code means the channel code used by the codec means which has the best or strongest capability to correct transmission errors in the data transmitted via the

channel. Likewise, an expression @weakesttt channel code (to be referred to later) means the channel code used by the codec means which has the least or weakest capability to correct transmission errors in the data transmitted via the channel. Stated in other words, a channel codec operated according to a stronger channel code has the capability to correct and/or detect a larger number of bit errors. This is achieved through a larger number of added redundant bits. A result is that within the constraints of the total channel data rate, the remaining space or transmission capacity for data (e. g. speech) is reduced. Therefore, a speech code with lower bit rate ("weaker"speech codec mode) must be used, thus effecting lower fidelity to the original speech. The opposite holds similarly for a channel codec operated according to a weaker channel code.

If it is determined in step S14, that the currently used channel code is the strongest available one (YES in step S14), the flow returns via step S17 where no change is effected to the initial step S10.

However, in case step S14 resulted in that the currently used channel code is not the strongest available one (NO in step S14), the method advances to step S16.

In step S16, an instruction to modify the channel code is obtained. More precisely, in this condition, the channel code is instructed to be increased by one step. As mentioned herein above, such an increase by one step may correspond to a selection of a code which is specified by the parameters stored at an address of a corresponding look up table LUT, which address differs by one from the address specifying the currently used code. After the channel code has thus been increased to a stronger one, the flow returns from step S16 to step S10.

Now, returning to step S11, if it is judged in step S11 that the measured bit error rate is below said first threshold TH1 (YES in step S11) and thus below the admissible bit error rate margin, the flow proceeds to step S13.

In step S13, it is checked whether the currently used channel code is the weakest available one (weakest in the sense of the least error correction capability as explained before), and if so (YES in step S13), the flow returns via step S17 where no change is effected to the initial step S10.

However, in case step S13 resulted in that the currently used channel code is not the weakest available one (NO in step S13), the method advances to step S15.

Also in step S15, an instruction to modify the channel code is obtained. More precisely, in this condition, the channel code is instructed to be decreased (reduced) by one step.

As mentioned herein above, such a decrease by one step may correspond to a selection of a code which is specified by the parameters stored at an address of a corresponding look up table LUT, which address differs by one from the address specifying the currently used code. After the channel code has thus been decreased to a weaker one, the flow returns from step S15 to step S10.

In connection with Fig. 1, a description has been given under the assumption that each measurement result is evaluated in steps Sll, S12. Nevertheless, as mentioned above, also an average value of P consecutively obtained measurement results can be made the subject of these comparison and/or judgment steps. Also, as previously

explained, in these steps a judgment may be validated only, if N out of P measurement results fulfill the indicated condition. For example, N can be set to be greater or equal to P/2.

Additionally, in steps S15, S16 a channel code has been modified (increased/decreased) by one step only.

Nevertheless, a change by more than one step is conceivable to thereby effect a codec mode adaptation in a more severe way. According to such a modification, the amount of modification (one or more than one steps) could be rendered dependent on the amount the measured bit error rate exceeds or is below a certain threshold TH2, TH1. To this end, a respective second upper/lower threshold could be defined.

Then, if the bit error rate is only below TH1 (step S11) and the weakest channel code is not active, a reduction by one step is effected, while if the bit error rate is below TH1 (step Sll) and below an additional threshold THla (THla < TH1), a reduction by for example two steps could be effected, if the second weakest or weakest code is not active.

Fig. 2 shows a diagram of the detected or measured bit error rate as a channel condition over time and the respectively initiated actions in dependence on a current channel condition.

The figure shows an example of the variation of the measured or calculated bit error rate with time. In case the bit error rate is within an admissible bit error rate margin defined between the two thresholds TH2, TH1, no change in the channel code (coding parameters) is initiated. If the bit error rate is out of said margin and exceeds the upper threshold TH2, this means that the channel conditions are not good since the bit error rate is

too high, and the channel code is increased. This means that a stronger channel code is activated, the characteristics of which are more suitable to correct transmission errors due to the"bad"channel.

If the measured bit error rate is out of said margin and is below the lower threshold TH1, this indicates that the channel is in a"good"condition since only few transmission errors occur. Then, the channel code is reduced, which means that a channel code is activated the characteristics of which are less suitable to correct transmission errors, which is no longer so much required since the channel condition is good.

Accompanying a change of the channel codec mode is a change in the (speech) data codec mode. Namely, if the channel codec mode is selected to be"stronger"in the sense that a better error correction capability of the code is selected, then the data codec mode is in parallel selected such that a speech code with lower bit rate must be used for the data codec (referred to as a"weaker"data code). Similarly, if the channel codec mode is selected to be"weaker"in the sense that a reduced error correction capability of the code is selected, then the data codec mode is in parallel selected such that a speech code with higher bit rate is to be used (referred to as a"stronger"data code).

Fig. 3 depicts a table of codec operating modes which are defined by code parameters for a channel codec part and a data (speech) codec part, with such a table being for example implemented as a look up table LUT. Fig. 3 summarized the above explained interdependencies.

The address of the look up table LUT is denoted as the codec mode number (in the illustrated example, four modes

with addresses or codec mode numbers 1 to 4 are shown).

Associated to each such address are the parameters for a code to be used by a channel codec part and a data codec part. At address"4", the"strongest"channel code parameters are assumed to be stored together with the "weakest"data code parameters, while at address"1"the "weakest"channel code parameters are assumed to be stored together with the"strongest"data code parameters. At addresses"2"and"3"codes or code parameters of intermediate strength and/or weakness are stored.

Fig. 4A through 4C illustrate schematically mode selection signaling scenarios in downlink transmission.

Donwlink transmission means that the data (speech) are transmitted from the network side, i. e. the base transceiver station BTS, to the terminal device or mobile station MS. Thus, the received data are processed at the mobile station, and a processing device adapted to substantially perform the above described processing is located at the mobile station.

Thus, as indicated in Fig. 4A, there is a signaling scenario I according to which the mobile station MS performs the entire mode selection. Accordingly, the mobile station MS detects or calculates the bit error rate and comprises a processing means (not shown) which is adapted to perform the processing illustrated in Fig. 1. At an output of the processing means, an instruction regarding the modification of the current codec mode is output to an informing means (not shown).

If the mobile station MS performs the mode selection, the informing means generates a corresponding mode command which is forwarded to the network devices BTS, TC where it

is read and validated in that the network devices change the codec mode accordingly. Also, the mode command is validated in the mobile station itself in that mode changing means (not shown) which is responsive to said command changes said mode.

According to this signaling scenario I, advantageously the least delay in taking the mode decision is caused.

Alternatively, in a scenario II in Fig. 4A, the base transceiver station BTS performs the mode selection. Also according to this scenario, at the mobile station MS side, an instruction regarding the modification of the current codec mode is output from the processing means (not shown) to an informing means (not shown).

However, differing from scenario I, the informing means generates a corresponding mode request which is forwarded to a network device, here the base transceiver station BTS, where it is read and validated in that the network device BTS decides the change in the codec mode and changes the mode accordingly, and generates a corresponding mode command. The mode command is signaled to the mobile station MS as well as to another network device TC and respectively validated in the mobile station and the network device TC in that mode changing means (not shown) which are responsive to said command, change the codec operating mode.

Fig. 4B shows a further alternative downlink signaling scenario III according to which the base station controller device BSC as a network control device takes the final decision regarding the adaptation or changing of the codec operating mode. The difference to scenario II merely resides in that the mode request is forwarded from the

mobile station to the base station controller device BSC, which controller forwards then the mode command to the mode changing means of the base transceiver station BTS, the mobile station MS and the transcoder device TC where the mode is respectively changed.

This scenario III is advantageous in that it is possible to use RRM related information in taking the decision, without the need to make this information available to other network devices besides the base station controller device BSC.

Fig. 4C illustrates a fourth possible scenario for a mode selection signaling in downlink. The adopted signaling scheme is similar to the third one (III). The difference resides merely in that the transcoder device TC now receives the mode request from the mobile station MS, takes the final decision on the mode change, changes the mode accordingly and forwards the corresponding mode command via the base station controller device BSC to the base transceiver device BTS and the mobile station MS. The base transceiver station BTS and the mobile station MS in response to said command, change the codec mode accordingly.

Fig. 5A through 5C illustrate schematically mode selection signaling scenarios in uplink transmission. The most significant difference as compared to the downlink scenarios resides in that in uplink the base transceiver station BTS receives the data and is adapted to perform the method illustrated in Fig. 1.

In detail, Fig. 5A depicts a first uplink mode selection signaling scenario (I), according to which the base transceiver station BTS decides the codec mode adaptation,

changes the codec mode of the codec provided in the base transceiver station BTS and commands the mobile station and the transcoder TC by a respective mode command to change the codec mode accordingly. (This scenario is to a certain extent comparable to scenario I of Fig. 4A, so that a fully detailed description thereof is considered to be not required, since the explanations as given with respect to Fig. 4A, I, are considered to be likewise applicable to the present case of uplink transmission).

This option I is beneficial in terms of a lower delay and less signaling amount to be exchanged between network elements.

Fig. 5B shows a second scenario II for uplink signaling according to which the base station controller device BSC takes the final decision concerning the mode change.

Thus, as illustrated, the base station controller device BSC receives the mode request from the base transceiver station BTS, while the following processing and signaling is similar to the case illustrated in Fig. 4B (third downlink scenario) so that a repeated description thereof is deemed to be dispensable.

Analogously to the downlink scenario, this second option (II) in uplink has the advantage that RRM related information can be used for taking the decision, without the need to make this information available to other network elements apart from the base station controller device BSC.

Additionally, Fig. 5C shows a third uplink signaling scenario, according to which the transcoder device takes

the final decision regarding the mode change or mode adaptation.

Thus, as illustrated, the transcoder device TC receives the mode request from the base transceiver station BTS, while the following processing and signaling is similar to the case illustrated in Fig. 4C (fourth downlink scenario) so that a repeated description thereof is deemed to be dispensable.

As regards the signaling between the network elements, the signaling can be adapted to take place in-band between the speech data/channel codec means. In-band signaling means that no dedicated signaling channel needs to be reserved.

Instead, signaling bits are multiplexed with the speech coding bits, i. e. the coded speech data bits. For the above explanation purposes, however, an in-band signaling has been assumed which is reflected in the drawings by the signaling step of reading the IB signaling.

Accordingly, as described above, the present invention proposes a method for adapting an operating mode of a coding/decoding means of a transceiver device, the coding/decoding means being adapted to be operated in a plurality of operating modes, the method comprising the steps of: detecting channel conditions of a transmission channel, judging, whether said detected channel conditions satisfy a predetermined condition, and instructing to modify a current operating mode of said coding/decoding means to a new operating mode of said plurality of operating modes, if the presence of said predetermined condition has been judged. Also, the present invention proposes network elements correspondingly adapted to carry out the proposed method, such as terminal devices, base transceiver stations and network control devices. Suitable

signaling scenarios for corresponding signaling between the network elements are presented and discussed in regard of their particular advantages.

It should be understood that the above description and accompanying figures are merely intended to illustrate the present invention by way of example only. The preferred embodiments of the present invention may thus vary within the scope of the attached claims.