WO2005034381A1

WO2005034381A1 - Power control relating to a radio communication system

Info

Publication number: WO2005034381A1
Application number: PCT/SE2003/001581
Authority: WO
Inventors: Stefan Bruhn; Claes Tidestay
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2003-10-09
Filing date: 2003-10-09
Publication date: 2005-04-14
Also published as: AU2003274856A1

Abstract

In a radio communication system a code command transmitted with every second speech frame from an AMR coder indicates the quality of the speech frames received in the opposite link. According to the invention this information can be used by the transmitter to adjust the transmit power.

Description

POWER CONTROL RELATING TO A RADIO COMMUNICATION SYSTEM TECHNICAL FIELD OF THE INVENTION

The present invention generally concerns a method, system and apparatus relating to power control in a radio communication system. Specifically, the present invention relates to fast power control in a mobile AMR codec connection .

DESCRIPTION OF RELATED ART

In an interference limited deployment of a cellular system, a capacity limit is reached when adding more users which would imply that sufficient quality cannot be guaranteed to the users in the system. In such a system, capacity is determined by interference originating from transmissions from other users. To obtain maximum capacity in such a scenario, it is vital not to transmit more power than necessary, since all transmission powers add to the interference level in the system.

An important tool to limit unnecessarily high transmission levels is power control. With power control, the transmitter uses no more transmit power than is necessary to ensure that the receiver experiences adequate quality. At the same time power control is a measure of ensuring that despite varying radio channel conditions the quality of the transmission channel can be maintained such that it does not fall below certain levels.

Since the mobile stations move, and since the traffic distribution might be non-stationary, the transmit power must be continuously updated to compensate for the varying radio conditions that the mobile station experiences. More specifically, the power control should adapt to four time- varying phenomena : • Distance attenuation: the further away the mobile station gets from the base station, the higher transmit power must be used.

• Shadow fading: As the mobile station moves, transmissions can be hindered by large objects, such as trees or buildings .

• Fast fading: The carrier waves may interfere constructively or destructively, depending on the exact location of the mobile station, leading to rapid fluctuations of the received signal strength, (this is not valid for the power control in European Global System for Mobile Communications (GSM) , where the power control is too slow to follow the fast fading) .

• Varying interference: In systems with discontinuous transmission (DTX) , interference will be bursty. During some parts of a conversation, the interference will be high, but during other parts, the interference may be low.

For the uplink power control in prior art, the base station performs measurements of the received quality. The base station then transmits power control commands to the terminal, using radio resources dedicated for power control signaling. The terminal then adjusts its output power according to the power control command.

For the downlink power control in prior art, the terminal estimates the received quality and/or the received power. The terminal then either transmits a measurement report, or a request for a transmit power adjustment to the base station. These transmissions make use of radio resources reserved for power control information. The base station may adjust its output power based on the message received from the terminal . In virtually all power control algorithms, it is required that the receiver measures some entity, upon quantity which a power control decision can be made. The two most common examples are carrier-to-interference (C/I) ratio and the received power. Although the received power is easier to estimate, C/I based power control in general provides much better performance. The receiver then either signals the measured quantity to the transmitter, which adjusts the output power accordingly. Alternatively, the receiver may request or order the transmitter to adjust its output power. These problems are addressed in e.g. US patent application No. 08/845466 which are incorporated by reference herein.

Power control commands can be either absolute or relative. With absolute power control commands, the transmitter is requested to adjust its output power to a specific level. With relative power control commands, the transmitter is requested to either increase or decrease its output power with some specific interval, relative to its current output power. Most often, both the uplink and downlink transmit powers are controlled by the network. The mobile station must obey commands for the uplink traffic. On the other hand, for systems where the mobile station transmits downlink power control commands, the network may choose to ignore them.

Traditionally speech coders in mobile communication systems have been fixed rate coders. That is, the bit rate of the data stream that conveys the speech information is fixed, and so is the amount of redundancy added for channel error protection. A compromise has to be made between the quality of the speech service, the gross bit rate of the radio channel and the degree of channel error protection: On one hand, maximum speech quality requires a high source bit rate and a high gross bit rate. On the other hand, the system resources are limited and the system should be able to accommodate a very large number of users at any given time . This means that the gross bit rate should be kept low, and that the speech service should be robust with respect to interference, which implies heavy channel coding.

The new Adaptive Multi-Rate AMR speech coding system for Global System for Mobile Communications (GSM) overcomes the described problem by being adaptive with respect to the source bit rate, by adapting the speech coder bit rate. For an AMR coder example with 3 modes, the AMR code mode with the highest source bit rate, and thus the highest speech quality under error-free conditions is mode 3, while modes 2 and 1 have lower source bit rates and correspondingly lower quality under error-free conditions. Code mode commands transmitted from the receiver to the transmitter indicate the appropriate codec mode to use.

The power control in GSM system is relatively slow with measurement reporting periods of as much as 480 ms . The ability to combat certain fading effects is thereby very limited. Accordingly, it would be highly desirable to provide a much faster power control to improve system capacity.

SUMMARY OF THE INVENTION

The problem dealt with by the present invention is providing enhanced power control in a radio communication system which eliminates or at least reduces that in a radio communication system the information that indicate a change in the radio link is sent infrequently to the power control, and the uplink or downlink power level is infrequently adjusted accordingly, while at the same time increasing the maximum capacity for the system while a user in the system can be guaranteed to experience sufficient quality.

Briefly, the present invention solves said problem, according to one aspect of the invention, by a method, system and apparatus wherein the information from the coded mode command is used, which indicate a change in the radio link faster, to more frequently control either the uplink power or the downlink power level.

The problem is solved by method according to claim 1, system according to claim 21, and apparatus according to claim 26.

One object of the invention is to enable fast power control without any additional signaling.

Yet another object of the invention is to provide more accurate adaptation to the environment with frequent transmit power updates.

Still another object of the invention is to increase the system capacity with fast power control.

An advantage afforded by the invention is reduced interference level in a radio communication system and thus an increased capacity.

Yet another advantage of the invention is higher capacity in a radio communication system with simple means, i.e. no added equipment or new functions.

Still another advantage of the invention is to decrease battery drain in mobile stations and thus to extend talktime.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a curve chart illustrating speech quality of different AMR modes and the principle of mode adaptation. FIG. 2 is a curve chart illustrating speech quality of MR515 and MR102 AMR modes.

FIG. 3 is a curve chart illustrating C/I ratio distribution for mobile stations in a radio communication system.

FIG. 4 is a schematic diagram of a cell in a radio communication system comprising a base station and mobile stations .

FIG. 5 is a block diagram illustrating the overall Adaptive Multi-rate AMR system for uplink and downlink according to the invention.

FIG. 6 is a flow chart illustrating a power control technique according to a first embodiment of the invention

DESCRIPTION OF PREFERRED EMBODIMENTS

Adapting the source coding rate is called codec mode adaptation and allows adapting the degree of error protection. At a given fixed gross bit rate (speech+channel coding) , this mechanism varies the partitioning between source bit rate and the redundancy added for channel error protection.

The Adaptive Multi-Rate AMR speech coding system for Global System for Mobile Communications (GSM) consists of a number of codec modes with different source bit rates. For each of these codec modes, there exist corresponding channel codecs, which perform the mapping between the source bits and the fixed number of transmitted gross bits. FIG. 1 displays a principle sketch of speech quality as a function of the channel quality for an example AMR codec with 3 modes. In this example, mode 3 has the highest source bit rate and thus the highest speech quality under error-free conditions. Modes 2 and 1 have lower source bit rates and correspondingly lower quality under error-free conditions. However, due to its relatively low error protection, codec mode 3 is sensitive to channel errors and breaks down in channel conditions for which mode 2 and, particularly, mode 1 still exhibit robust operation. Codec mode 1 is the most robust mode and can operate under channel conditions where the other modes have already broken down.

TAB.

For a given gross bit rate (speech+channel coding) different quality curves can be obtained by changing the partitioning between speech and channel coding. The idea with Adaptive Multi-Rate AMR is to use a multi mode speech coder and to change the speech coder mode based on channel quality measurements to always use the optimal speech coder mode. Ideally, this allows for achieving a speech quality curve of the AMR codec that corresponds to the envelope of the quality curves of the individual codec modes. This is illustrated in FIG. 1 by the dashed line. TAB. 1 shows the bit rate of the eight AMR speech coder modes. In the prior art GSM system there is a function called power control. The purpose of the power control is to increase the transmitting power for the users that have a poor carrier- to-interference C/I ratio and decrease it for the users that have a too good C/I.

Ideally the power control would make all users experience the same C/I, see the ideal distribution curve in FIG. 3. In reality this is far from true, see the real distribution curve in FIG. 3, and there are several reasons for this. First of all, there is a maximum possible output power. One other issue with power control is that it unlike Adaptive Multi-Rate AMR affects other users. A power change will not only change the C/I ratio for the controlled link but it also change the C/I ratio for other links since it changes the interference level. This means that even in systems with power control, different users will experience different C/I ratios. Ideally no mobile stations will obtain a C/I ratio below point 301 in FIG. 3, see the dashed area. For a mobile station with a certain AMR coded mode, e.g. AMR515, an optimal C/I ratio 210 can be obtained, this optimal C/I ratio 210 is normally just before the AMR coded mode curve is straightening, see point 212 for AMR515 in FIG. 2. The C/I ratio point 230 illustrate the point 232 where an optimal C/I ratio is obtained for the higher AMR coded mode AMR102. At C/I point 220,222 in FIG. 2 the curve starts straightening, and between that C/I point 220,222 and a C/I point 230,223, the speech quality 221 is at the same level.

The target C/I ratio for the power control is set to a level that gives the desired speech quality, see FIG. 2. For this C/I target one of the AMR modes is the optimal.

The principle operation of AMR codec mode adaptation is as follows. Incoming speech is source and channel encoded, applying the currently selected codec and channel modes. The resulting payload gross bits are transmitted over the air interface together with adaptation data from codec mode adaptation. Codec mode adaptation data consists either of link measurement data, i.e. any data reflecting the estimated channel quality/capacity or of a codec mode request informing the sending side about the codec mode it should select. The receiving side detects the codec mode used and applies it for channel and source decoding of the received speech payload data. The received link measurement data or codec mode request is used for choosing the codec mode for the outgoing link. Moreover, the receiving side performs measurements on the incoming link, which leads to link measurement data or a codec mode request for that link.

Link measurement data is generated by a link measurement device in the receiving side. It is indicative of the measured quality of the incoming link. This data can - after suitable quantization - be directly transmitted to the sending side or it can first be fed into an adaptor device. The adaptor generates a codec mode request or a command in response to the measurement data, which is an indication of the codec mode to be used by the sending side. If this adaptor is located on the receiving side, the corresponding codec mode request/command is sent to the sending side instead of the original measurement data. However, if the adaptor is located at the sending side, the measurement data has to be transmitted to that side. A binding codec mode request is usually referred to as "codec mode command" whereas if this is merely the indication of the preferred mode and the sending side has the authority to override it, it is referred to as "codec mode request" . This distinction is of minor relevance in the context of the invention; in the following the acronym CMR will be used for both of them.

CMRs are generated by the codec mode adaptation device based on an estimate of the channel quality. This operation is a mapping of the measurement to the CMR. This may involve the comparison of the measurement values with certain thresholds. The measurements can be any channel quality estimate. Usually, as it is specified in GSM 05.09, CMRs are generated by comparing a filtered C/I measurement value with some thresholds .

Filtering of measurement values is usually done with a filter having memory since instantaneous measurements taken from only one TDMA burst or one frame usually are too strongly fluctuating. The purpose of the filtering is to generate a measurement value which deviates less from the expectation of the true value than the instantaneous measurements. Typical filters are linear smoothing and prediction filters having a length of 500 ms . Examples for such filters are given in GSM 05.09: Link Adaptation.

The Adaptive Multi-Rate AMR speech coding standard comprises of 8 different modes. Thus, if the CMRs are transmitted using a block code, the code could comprise 8 different code words which would allow to directly signal any of the modes. However, in order to improve channel error robustness, the block code specified in GSM 05.03 merely comprises 4 code words meaning that only up to 4 modes out of a so-called Active Codec Set ACS can directly be signaled. The Active Codec Set (ACS) is defined during call setup and/or handover by layer 3 signalling, as specified in GSM 04.08, or by using the RATSCCH protocol (Robust AMR Traffic Synchronized Control Channel), as specified in GSM 05.09. The available protocol elements for Active Codec Set (ACS) definition allow the Active Codec Set (ACS) to contain up to 4 arbitrary though mutually exclusive modes.

However, one skilled in the art will recognize that other coders such as e.g. audio, video or speech coders with the same/similar characteristics as the AMR speech coder may be used in the f ture . Fig. 5 presents a general block diagram of the overall Adaptive Multi-Rate AMR system for uplink and downlink over the same radio interface with the new units 512, 522 according to the invention. The system consists of the major components Transcoding and Rate Adaptor Unit TRAU and Base Tranceiver Station BTS on the network side and the Mobile Station MS. On the network side, speech encoder SPE1 and channel encoder CHEl as well as channel decoder CHD1 and speech decoder SPDl are connected via the serial A-bis interface. For each link, quality information is derived by estimating the current channel state. Based on the channel state, and also taking into consideration possible constraints from network control, the codec mode control, which is located on the network side, selects the codec modes to be applied.

The channel mode to use (TCH/AFS, TCH/AHS, O-TCH/AHS, TCH/WFS, O-TCH/WFS or O-TCH/WHS) is controlled by the network. Uplink and downlink always apply the same channel mode.

For codec mode adaptation the receiving side 511,521 performs link quality measurements of the incoming link. The measurements are processed yielding a Quality Indicator. For uplink adaptation, the Quality Indicator is directly fed into the UL mode control unit. This unit compares the Quality Indicator with certain thresholds and generates, also considering possible constraints from network control, a Codec Mode Command CMR indicating the codec mode to be used on the uplink (radio signals transmitted from the second transmitting end 520 to the first receiving end 511) . The Codec Mode Command CMR is then transmitted inband to the mobile MS side (from the first transmitting end 510 to the second receiving end 521) and according to the invention in control unit 522 the Codec Mode Command CMR is used to adjust the transmission power level at the amplifier AMP2 for the radio signals to be transmitted from the second transmitting end 520 to the first receiving end 511, in accordance with a given algorithm with the Codec Mode Command CMR received as a parameter in the algorithm. In accordance with the invention is further in control unit 522 a codec mode applied for the radio signals to be transmitted from the second transmitting end 520 to the first receiving end 511, in accordance with a given algorithm with the CMR received as a parameter in the algorithm. Thus the incoming speech signal is encoded in the applied codec mode. For downlink adaptation, the DL Mode Request Generator within the mobile compares the DL Quality indicator with certain thresholds and generates a Codec Mode Request CMR indicating the preferred codec mode for the downlink (radio signals transmitted from the first transmitting end 510 to the second receiving end 521) . The Codec Mode Request CMR is transmitted inband to the network side where it is fed into the DL Mode Control unit. This unit generally grants the requested mode. However, considering possible constraints from network control, it may also override the request. The DL Mode Control unit includes according to the invention a control unit 512 where the Codec Mode Request CMR is used to adjust the transmission power level at the amplifier AMPl for the radio signals to be transmitted from the first transmitting end 510 to the second receiving end 521, in accordance with a given algorithm with the Codec Mode

Request CMR received as a parameter in the algorithm. In accordance with the invention is further in control unit 512 a codec mode applied for the radio signals to be transmitted from the first transmitting end 510 to the second receiving end 521, in accordance with a given algorithm with the CMR received as a parameter in the algorithm. Thus the resulting codec mode is applied for encoding of the incoming speech signal in downlink direction. Both for uplink and downlink, the presently applied codec mode is transmitted inband as Codec Mode Indication together with the coded speech data. At the decoder, the Codec Mode Indication is decoded and applied for decoding of the received speech data.

However, one skilled in the art will recognize that the control units 512,522 may be placed anywhere in the Base Tranceiver Station BTS or Mobile Station MS, as long as the result from the algorithm with the CMR as input result in a codec mode to be applied by the speech encoder SPl,SP2 and CHE1,CH2 and result in an adjustment of the transmission power level at the amplifier AMPl,AMP2.

As been described above the CMR transmitted with every second speech frame from an AMR coder indicates the quality of the speech frames received in the opposite link. According to the invention this information can be used by the transmitter to adjust the transmit power. In FIG. 6 a first step 601, a first transmitting end 510 (second transmitting end 520) sending radio signals on a traffic channel in a codec mode to a second receiving end 521 (first receiving end 511), and a second transmitting end 520 (first transmitting end 510) sending radio signals on a traffic channel in a codec mode to a first receiving end 511 (second receiving end 521) . In a second step 602 a CMR is transmitted from first transmitting end 510 (second transmitting end 520) to a second receiving end 521 (first receiving end 511) , which indicate the codec mode to be used by the second transmitting end 520 (first transmitting end 510) . Further in step 603 the CMR is received at the second receiving end 521 (first receiving end 511) . CMR is used as a parameter in step 604, in an algorithm to apply a codec mode and adjust a transmission power level for the radio signals to be transmitted from the second transmitting end 520 (fist transmitting end 510) to the first receiving end 511 (second receiving end 521) . In parenthesis the opposite direction is described. Assume that the power control tries to adjust the transmit power, so that the receiver experiences a given quality. For conventional power control algorithms, this usually translates into maintaining a target C/I. This target C/I corresponds to a specific AMR codec mode with a corresponding quality. The higher the target C/I, the higher the AMR codec mode. Thus, the transmitter could just as well try to adjust its output power to maintain a given AMR codec mode, e.g. MR74. In a first embodiment of the invention, the receiver 511,521 interprets the CMR before passing it to the speech coder SPDl,SPD2. The transmitter 510,520 including the amplifier AMP1,AMP2 then adjusts its output power to make the C/I at the receiver fall into the C/I range of a target AMR codec mode. In an example of the first embodiment, if the desired AMR codec mode is MR74, the transmitter 510,520 would increase the output power on any request by the receiver 511,521 for an AMR mode lower than MR74. Also, any request for an AMR codec mode higher than MR74 would trigger the transmitter 510,520 to lower its output power. The first embodiment of the invention as described above allows Fast Power Control FPC on the downlink without modifying the standard. The CMRs received from the Mobile Station MS are interpreted as Fast Power Control FPC commands, which is in addition to their original meaning as pure codec mode requests or commands. The CMR is used as a parameter in an algorithm to adjust the transmission power level for the radio signals to be transmitted from the transmitting end 510,520 to the receiving end 511,521. An example of the first embodiment, a received target C/I range for all the radio signals to be transmitted is determined. By comparing a codec mode corresponding to the target C/I range with the codec mode as indicated by the received CMR the transmission power level can be decided. Applying the codec mode as indicated by the received CMR to the radio signals transmitted from the second transmitting end 520 to the first receiving end 511 (this apply for the opposite direction) , and increase the transmission power level if the codec mode applied being more robust than a codec mode corresponding to the C/I range, while decrease the transmission power level if the codec mode applied being less robust than a codec mode corresponding to the C/I range. There are, however, problems with this solution: One problem is codec mode toggling as consequence of Fast Power Control FPC. This problem will be illustrated with an example. Assume that the Active Codec Set (ACS) comprises 2 modes, e.g., MR122 and MR74. Further, in a second embodiment of the invention, assume that receiving ' CODEC_MODE_l ' (a CMR comprising a code word having ' CODEC_MODE_l ' as a value) as CMR would mean to select the more robust of both modes, i.e. MR74. At the same time this would be interpreted as command to increase the TX power. Receiving ' C0DEC_M0DE_2 ' (a CMR comprising a code word having ' C0DEC_M0DE_2 ' as a value) would mean to select MR122 and to decrease the TX power. Assuming that Fast Power Control FPC is in a steady state, this means that the C/I at the receiver 511,521 toggles around the control target and the Fast Power Control FPC commands alternate between raising and lowering the TX power. Consequently, the selected codec mode would toggle between MR74 and MR122. The codec mode toggling is an undesirable situation since the speech quality can never be at the same level as if the higher-rate mode of both modes MR122 was used permanently. A solution to this problem, according to a third embodiment of the invention, is that the received CMRs are not used as direct requests or commands of the codec mode to be used on the outgoing link. Rather, an additional unit (the control units 512,522) generates the codec mode to be used in response of the receiving CMRs according to some algorithm. This algorithm can simply be a re-mapping of CMRs, as shown in TAB. 2.

TAB .

In TAB. 2 is described what actions to be taken when receiving one of the two code words in a two-mode Active Codec Set (ACS), and the target is the MR122 mode. Note that the CMRs are re-mapped before being passed to the speech coder. According to the described example of the third embodiment of the invention there would be no codec mode adaptation any longer since the CMRs are merely interpreted as Fast Power Control FPC commands and mode MR122 is used permanently. An example of how to realize the third embodiment is by using the value of the CMR word in CMR, e.g. C0DEC_M0DE_1 and C0DEC_M0DE_2 received at the receiving end 521,511 from the transmitting end 510,520 and using the values as parameters in the algorithm to get a codec mode and a power control command to be applied, when transmitting radio signals at the transmitting end 520,510. A first example of how the algorithm could be working is by using the value of the CMR word in CMR, e.g. C0DEC_M0DE_1 and C0DEC_M0DE_2 received at the receiving end 521,511 and having a corresponding power control command for each CMR value. Each value e.g. C0DEC_M0DE_1 and C0DEC_M0DE_2 indicate a power control command e.g. to raise the power level or to lower the power level . How much the power level is raised or lowered can be decided by a certain step that can e.g. be varied, etc. A second example of how the algorithm could be working is by using the ACS table and in that ACS table mapping the CMR value e.g. CODEC_MODE_l and CODEC_MODE_2 in accordance with the corresponding row in the ACS table, see e.g. TAB. 2 where CODEC_MODE_l is indicated by command 'Raise TX power' and CODEC_MODE_2 is indicated by command 'Lower TX power'. A third example of how the algorithm could be working is by using the CMR value e.g. CODEC_MODE_l and CODEC_MODE_2 and adapting the CMR value e.g. CODEC_MODE_l and CODEC_MODE_2 by first mapping the CODEC_MODE_l and CODEC_M0DE_2 in accordance with the codec mode corresponding to the target C/I range, and applying the mapped codec mode for the radio signals to be transmitted from the second transmitting end to the first receiving end. The target C/I range is the received target C/I range for all the radio signals to be transmitted. However, it is beneficial to keep the possibility of codec mode adaptation for the case that Fast Power Control FPC reaches its transmission power limits and increased robustness can only be achieved by selecting a more robust codec mode. This can simply be achieved, according to a fourth embodiment of the invention, by including additional more robust modes in the Active Codec Set (ACS), e.g. MR515 and MR67. A possible mapping from received CMR code words to actually applied codec modes (and Fast Power Control FPC commands) is given in TAB . 3.

TAB.

In TAB. 3 is described an example of the fourth embodiment of the invention, what actions to be taken when receiving one of the code words in a four-mode Active Codec Set (ACS) , and the target is the MR122 mode. The Active Codec Set (ACS) table as seen in TAB. 3 can interpreted as the algorithm to adjust the transmission power level, by using the ACS table and in that ACS table mapping the CMR value e.g. CODEC_MODE_l-4 in accordance with the corresponding row in the ACS table, see e.g. TAB. 3 where CODEC_MODE_l is indicated by command 'Raise TX power' and C0DEC_M0DE_4 is indicated by command 'Lower TX power'. Further the TAB. 3 can be interpreted as being used to map the CMR value e.g. CODEC_MODE_l-4 in accordance with the corresponding row in the ACS table, where e.g. CODEC_MODE_l indicates in accordance with corresponding row the codec mode MR515 to be applied and CODEC_MODE_2 indicates in accordance with corresponding row the codec mode MR74 to be applied. Third column in TAB. 3 can be seen as the coded mode used before applying FPC and fourth column as the new column with the corresponding codec modes for each CMR value. It can also be interpreted as the CMRs are re-mapped before being passed to the speech coder. Another similar solution, according to a fifth embodiment of the invention, is that the meaning of the received CMR code words is not any longer directly related to any codec mode. Rather, it would be a mere report of the presently measured C/I at the receiver. E.g., CODEC_MODE_l means C/I <= 4 dB, CODEC_MODE_2 means 4 dB < C/I <= 7 dB, CODEC_MODE_3 means 7 dB < C/I <= 10 dB, and CODEC_MODE_4means C/I > 10 dB. It is then up to the transmitting end to assign Fast Power Control FPC commands and CMRs in response to the received C/I measurements. All these solutions are possible without any changes to the standard for the downlink, since the standard allows the network to override CMRs received from the Mobile Station MS. However, the solutions are problematic in a conceptual sense (dirty solutions) since the transmitting end does not get its codec mode requests granted. More severe, for the uplink these solutions cannot directly be applied without changes to the standard since the CMRs received from the network are binding for the Mobile Station MS. Hence, a solution is desirable which is conceptually clean and merely requires minor changes to the standard and which is interoperable with the present standard. Such a solution, according to a sixth embodiment of the invention, is to setup the Active Codec Set (ACS) in a way that it contains more than one instance of the same codec mode. This allows for signaling different CMR code words for the same codec mode, where the only difference between them is their meaning for Fast Power Control FPC. In an example of the sixth embodiment of the invention, the Active Codec Set (ACS) could comprise two instances of the MR122 mode, where one of the CMR code words ' CODEC_MODE_l ' would be a signal to raise the TX power and the other CMR code word ' C0DEC_M0DE_2 ' would be a signal to lower the TX power. ' C0DEC_M0DE_1 ' would be sent if the measured C/I is below some threshold of, e.g. 15 dB, ' C0DEC_M0DE_2 ' would be sent if the measured C/I is above that threshold. This example is illustrated in TAB. 4. Here, only Fast Power Control FPC and no codec mode adaptation are provided.

TAB.

In TAB. 4 is described what actions to be taken when receiving one of the two code words in a two-mode Active Codec Set (ACS), and the target is C/I=15 dB. In this case, no re-mapping of the code-words are necessary. An example of how TAB . 4 can be interpreted by mapping the CMR value e.g. CODEC_MODE_l-2 in accordance with the corresponding row in the ACS table, where e.g. CODEC_MODE_l indicates in accordance with corresponding row the codec mode MR122 to be applied and CODEC_MODE_2 indicates in accordance with corresponding row the codec mode MR122 to be applied. Again, according to a seventh embodiment of the invention, it is easy to include codec mode adaptation functionality for the event that Fast Power Control FPC reaches its TX power limits. As an example, it would be possible to include two more robust modes MR515 and MR74. This example is illustrated in TAB. 5.

TAB.

In TAB. 5 is described what actions taken when receiving one of the four code words in a four-mode Active Codec Set (ACS) , and the target is C/I=15 dB. No re-mapping of CMRs are necessary, i.e. mapping the CMR value e.g. CODEC_MODE_l- 4 in accordance with the corresponding row in the ACS table, where e.g. CODEC_MODE_l indicates in accordance with corresponding row the codec mode MR515 to be applied and CODEC_MODE_4 indicates in accordance with corresponding row the codec mode MR122 to be applied for transmission of radio signals. It is important to point out that unlike the other solutions provided above, setting up the Active Codec Set (ACS) such that it comprises several instances of one codec mode avoids the need to re-map the received CMRs . The benefit is that they really reference the codec mode which should be used. The described solution merely requires a minor modification of the standard since today the standard does not explicitly exclude the Active Codec Set (ACS) to comprise several instances of the same codec mode. It merely does not provide the corresponding signaling elements for defining such Active Codec Sets (ACSs) . Hence, according to an eight embodiment of the invention, the only required change is to add such signaling elements to layer 3 signaling, specified in GSM 04.08 and to the RATSCCH protocol. Such new signaling elements would not conflict with older equipment, such as e.g. Mobile Stations MSs not supporting them. Such equipment would simply signal back an 'UNKNOWN' message telling that the feature is not supported. Regular codec mode adaptation operation without Fast Power Control FPC would be the consequence. In order to enable Fast Power Control FPC operation, according to the eighth embodiment of the invention, it is possible to add corresponding explicit signaling elements to layer 3 and RATSCCH signaling. However, another possibility is implicit signaling, a ninth embodiment of the invention. That is, whenever the Active Codec Set (ACS) comprises more than one instances of the same codec mode Fast Power Control FPC is enabled. The transmission power level e.g. is only adjusted if the value of the CMR word in CMR indicate the same codec mode. The instance associated with a higher measured C/I value causes the TX power to be reduced, that one associated with a lower measured C/I value causes the TX power to be augmented. According to a tenth embodiment of the invention, if there are three instances of the same codec mode, that instance associated with a middle measured C/I value means to keep the TX power unchanged. There may be the need to adjust the Fast Power Control FPC target during a call. This may for instance happen if the original Fast Power Control FPC target cannot be met. Taking the examples illustrated in tables 3 and 5, such a condition could be detected if, according to a eleventh embodiment of an invention, continuously for some predetermined length of time, CMRs are transmitted indicating the request of a more robust codec mode or the Fast Power Control FPC command to raise the TX power. The RATSCCH protocol, specified in GSM 05.09, with additional signaling elements according to the invention provides means for changing the Fast Power Control FPC target during a call. Conversely, continuous CMRs indicating the request to lower the TX power or to select a less robust codec mode can be a signal, according to the eleventh embodiment of the invention, to adjust to Fast Power Control FPC target upwards. Fast Power Control FPC targets can also be adjusted by network control, e.g., in response of traffic load. During times of high traffic load lower Fast Power Control FPC targets could be used than during times of low traffic. An example of how to realize the eleventh embodiment is to update the ACS table often, e.g. during call setup and/or handover by layer 3 signalling, as specified in GSM 04.08, or by using the RATSCCH protocol (Robust AMR Traffic Synchronized Control Channel) to adjust by network control, e.g., in response of traffic load.

In order to achieve good performance of the Fast Power Control FPC it is important to be able to react fast on changes of the C/I level at the receiver. The filters usually taken for codec mode adaptation are not optimal for Fast Power Control FPC since the effective Fast Power Control FPC control loop delay is lower that the codec mode adaptation delay. These delays are defined as the length of time from the event of a changed channel condition to the event of the corresponding adaptation action (i.e. modifying the TX power for Fast Power Control FPC or applying a suitable codec mode in case of codec mode adaptation) . For codec mode adaptation this delay is in the order of 100 to 140 ms or even more, while for Fast Power Control FPC this delay is in the order of 50 to 90 ms . As a solution, according to a twelfth embodiment of the invention, it is proposed to apply a second measurement filter for Fast Power Control FPC, which has a shorter length. Provided that the CMR generated by using the original measurement filter does not indicate to request a much more robust mode, the Fast Power Control FPC command is generated based on the second filter. Today, the Active Codec Set (ACS) comprises four modes. This is sufficient for Adaptive Multi-Rate AMR to provide good speech quality. However, this code set may not be sufficient to provide fine enough granularity to enable accurate power control, since the power can be regulated within a quite large span. This limitation can be circumvented with a larger Active Codec Set (ACS) .

According to a thirteenth embodiment of the invention, the CMRs may be interpreted as absolute or as relative PC commands. As CMR transmission is as frequent as every 40 ms, it may however be preferable to interpret them as relative commands, for instance, as either to raise or to lower the TX power by a certain step size. This step size can either be fixed or adaptive .

Discontinuous transmission (DTX) is a technique essentially turning off transmission during periods of speech inactivity. The purpose of discontinuous transmission (DTX) is to reduce the interference level in a radio network and thus to increase capacity. Furthermore, discontinuous transmission (DTX) helps to decrease battery drain in Mobile Stations and thus to extend talktime. Discontinuous transmission (DTX) does not totally turn off transmission during speech inactivity. Rather, so-called Silence Descriptor SID frames conveying a description of the background noise characteristics are transmitted to the receiver enabling it to generate a comfort noise signal. In GSM AMR, Silence Descriptor SID frames are transmitted at a rate of once per 8 frames (160 ms) specified in GSM 06.93. AMR Silence Descriptor SID frames do not only convey comfort noise parameters. In addition, they comprise coded mode adaptation data, which, apart from other data, are the CMRs for the other link. These CMRs are encoded using a 16 bit block code specified in GSM 05.03. In case of discontinuous transmission (DTX) , the CMR transmission rate is lower, namely, it is identical to the transmission rate of the Silence Descriptor SID frames. For that reason, it can be advisable to apply a larger step size than during regular operation. There also exist other ways to improve Fast Power Control FPC performance in discontinuous transmission (DTX) . One possibility, according to a fourteenth embodiment of the invention, is to deviate from transmitting Silence Descriptor SID frames at a fixed rate of e.g. once every 8 frames. Rather, immediate Silence Descriptor SID frame transmission could be allowed whenever a significant deviation of the measured C/I from the target C/I is detected. Even though this compromises the DTX gain by slightly increasing the channel activity, this loss is more than compensated by the gain of more efficient Fast Power Control FPC. A further possibility, according to a fifteenth embodiment of the invention, is to modify the 16 bit block code used for CMR transmission during discontinuous transmission (DTX) . As this is a very strong code, sufficient channel error robustness can be achieved only using the 8 bit block code, which is used for CMR transmission during regular operation (on a FR speech traffic channel) . Note in particular, that due to PC extremely poor radio channel condition can basically be avoided such that 8 bit block codes provide sufficient robustness. The remaining 8 bits are now free for transmission of a high-resolution PC command, which, e.g., also makes use of the same 8 bit block code comprising 4 code words. This PC command can thus encode different step sizes (or absolute TX power levels) by which (or to which) the TX power has to be adjusted. As a person skilled in the art appreciates, application of the invention is in no way limited to only cellular radio communication networks conforming to the GSM specification. The AMR speech coder is also specified for Universal Mobile Telecommunications Service UMTS even though a link adaptation system similar to GSM is not specified. The same basic principle is however applicable to UMTS regardless of how the AMR mode is selected on the two radio links in a UMTS mobile to mobile call. Thus the invention is also applicable in other Code Division Multiple Access CDMA based cellular communication system, e.g. cellular networks adhering to the IS-95, and the CDMA-2000 specifications.

As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed.

Claims

1. A fast power controlling method in a radio communication system, the system comprising: a first transmitting end transmitting radio signals to a second receiving end on a traffic channel associated with a codec mode; a second transmitting end transmitting radio signals to a first receiving end on a traffic channel associated with a codec mode; the first transmitting end transmitting a CMR to the second receiving end, indicating the codec mode to be used by the second transmitting end; c h a r a c t e r i s e d in that the method comprises the steps of: in response to the CMR received at the second receiving end, applying a codec mode and adjusting a transmission power level for the radio signals to be transmitted from the second transmitting end to the first receiving end, in accordance with a given algorithm with the CMR received as a parameter in the algorithm.

2. A method according to claim 1, comprising the further steps: determining a received target C/I range for all the radio signals to be transmitted; in response to the CMR received at the second receiving end, applying a codec mode for the radio signals to be transmitted from the second transmitting end to the first receiving end, by using a codec mode as indicated by the received CMR, and if the codec mode applied being more robust than a codec mode corresponding to the target C/I range, increasing the transmission power level, while if the codec mode applied being less robust than the codec mode corresponding to the target C/I range, decreasing the transmission power level, for the radio signals to be transmitted from the second transmitting end to the first receiving end.

3. A method according to claim 1, wherein the CMR comprising a CMR word having at least a first and a second CMR value; the method comprising the further steps: in response to the first CMR value received at the second receiving end, applying a codec mode by using the received first CMR value in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, and applying a power control command in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, for the radio signals to be transmitted from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, applying a codec mode by using the received second CMR value in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, and applying a power control command in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, for the radio signals to be transmitted from the second transmitting end to the first receiving end.

4. A method according to claim 3, wherein the algorithm comprising: in response to the first CMR value received at the second receiving end, applying a codec mode by using the received first CMR value in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, and increasing the transmission power level for the radio signals to be transmitted from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, applying a codec mode by using the received second CMR value in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, and decreasing the transmission power level for the radio signals to be transmitted from the second transmitting end to the first receiving end.

5. A method according to claims 3-4, wherein the algorithm comprising: in response to the first CMR value received at the second receiving end, applying a codec mode as indicated by the received first CMR value in accordance with the corresponding row in the ACS table, for the radio signals to be transmitted from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, applying a codec mode as indicated by the received second CMR value in accordance with the corresponding row in the ACS table, for the radio signals to be transmitted from the second transmitting end to the first receiving end.

6. A method according to claims 3 and 5, wherein the algorithm comprising: in response to the first CMR value received at the second receiving end, applying a power control command as indicated by the received first CMR value in accordance with the corresponding row in the ACS table, for the radio signals to be transmitted from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, applying a power control command as indicated by the received second CMR value in accordance with the corresponding row in the ACS table, for the radio signals to be transmitted from the second transmitting end to the first receiving end.

7. A method according to claims 3, 4 and 6, wherein the algorithm comprising: determining a target C/I range for all the radio signals to be transmitted; adapting the codec mode as indicated by the received first or second CMR value by first mapping the codec mode indicated by the received first or second CMR value in accordance with the codec mode corresponding to the target C/I range, and applying the mapped codec mode for the radio signals to be transmitted from the second transmitting end to the first receiving end.

8. A method according to claim 3, wherein applying a power control command for the radio signals to be transmitted from the second transmitting end to the first receiving end only if the first or second CMR value indicate the same codec mode.

9. A method according to claims 1-8, wherein the CMR value is corresponding to an AMR encoding mode, being associated with a C/I range.

10. A method according to claim 9, wherein the CMR value is further corresponding to a power control command.

11. A method according to claim 10, wherein the CMR value and its corresponding AMR encoding mode and power control command are set in an ACS table.

12. A method according to claim 11, wherein the corresponding AMR encoding mode and power control command are being updated in the ACS table.

13. A method according to claim 9, wherein at least a first CMR value corresponding to a first AMR encoding mode and at least a second CMR value corresponding said first AMR encoding mode in an ACS table.

14. A method according to claims 3, 6 and 10-12, wherein the power control command comprising a command to increase or decrease the transmission power level by certain step sizes.

15. A method according to claims 1-2 and 5, wherein the transmission power level is increased or decreased by certain step sizes.

16. A method according to claims 14-15, wherein a step size can be fixed or adaptive.

17. A method according any one of claims 5-6, and 11-13, wherein the ACS table is transmitted in a RATSCCH message from a base station or a mobile station.

18. A method according to claim 17, wherein the RATSCCH message is transported in a layer 3 RTSCCH_DATA message.

19. A method according to claim 17, wherein the RATSCCH message is transported in a layer 3 as signaling elements in a RATSCCH protocol.

20. A method according to claims 1-19, wherein the CMR is signaled by layer 3 signaling.

21. A radio communication system comprising: a first transmitting end having means for transmitting radio signals to a second receiving end on a traffic channel associated with a codec mode, a second transmitting end having means for transmitting radio signals to a first receiving end on a traffic channel associated with a codec mode, the first transmitting end having means for transmitting a CMR to the second receiving end, an indication of the second codec mode to be used by the second transmitting end; c h a r a c t e r i s e d in that said radio communication system comprises: means at the second receiving end for receiving a CMR; means for applying a codec mode and means for adjusting a transmission power level, in accordance with a given algorithm with the CMR received as a parameter in the algorithm; means for transmitting at the second transmitting end the codec mode applied and power level adjusted radio signals to the first receiving end.

22. A radio communication system according to claim 23, wherein the CMR comprising CMR word having at least a first and a second CMR value; the system comprising: means at the second receiving end for receiving the first CMR value, means for applying a codec mode by using the received first CMR value in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, and means for applying a power control command in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, a transmitting means for transmitting the radio signals from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, means for applying a codec mode by using the received second CMR value in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, and means for applying a power control command in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, a transmitting means for transmitting the radio signals from the second transmitting end to the first receiving end.

23. A radio communication system according to claim 22, the system comprising: means at the second receiving end for receiving the first CMR value, means for applying a codec mode, and a power control command, as indicated by the received first CMR value in accordance with the corresponding row in the ACS table, means for transmitting the radio signals from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, means for applying a codec mode, and a power control command, as indicated by the received second CMR value in accordance with the corresponding row in the ACS table, means for transmitting the radio signals from the second transmitting end to the first receiving end.

24. A radio communication system according to claims 21-23, wherein first transmitting end and first receiving end are placed in a Base Transceiver Station (BTS) , and a second transmitting end and second receiving end are placed in a Mobile Station (MS) .

25. A radio communication system according to claims 21-23, wherein first transmitting end and first receiving end are placed in a Mobile Station (MS) , and a second transmitting end and second receiving end are placed in a Base Transceiver Station (BTS) .

26. A node in a radio communication system, the node comprising: a first transmitting end having means for transmitting radio signals to a second receiving end on a traffic channel associated with a codec mode, a first receiving end having means for receiving radio signals from a second transmitting end on a traffic channel associated with a codec mode, c h a r a c t e r i s e d in that the node comprises: means at the first receiving end for receiving a CMR from a second transmitting end, an indication of the codec mode to be used by the first transmitting end; means for applying a codec mode and means for adjusting a transmission power level, in accordance with a given algorithm with the CMR received as a parameter in the algorithm; means for transmitting at the first transmitting end the codec mode applied and power level adjusted radio signals to the second receiving end.

27. A node according to claim 26, wherein the CMR comprising CMR word having at least a first and a second CMR value; the node comprising: means for receiving the first CMR value transmitted from a second transmitting end, means for applying a codec mode by using the received first CMR value in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, and means for applying a power control command in accordance with a given algorithm with the first CMR value received as a parameter in the algorithm, a transmitting means for transmitting the radio signals from the second transmitting end to the first receiving end; and in response to the second CMR value received at the second receiving end, means for applying a codec mode by using the received second CMR value in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, and means for applying a power control command in accordance with a given algorithm with the second CMR value received as a parameter in the algorithm, a transmitting means for transmitting the radio signals from the second transmitting end to the first receiving end.

28. A node according to claim 27, the node comprising: means for receiving the first CMR value at ther first receiving end, means for applying a codec mode, and a power control command, as indicated by the received first CMR value in accordance with the corresponding row in the ACS table, means for transmitting the radio signals at the first transmitting end to the second receiving end; and means for receiving the second CMR value at the first receiving end, means for applying a codec mode, and a power control command, as indicated by the received second CMR value in accordance with the corresponding row in the ACS table, means for transmitting at the first transmitting end the radio signals to the second receiving end.

29. A node according to claims 26-28, wherein the node is a mobile station (MS) or Base Tranceiver Station (BTS) .

0. A method according to claims 1-20, wherein the Silence Descriptor SID frames conveying the CMR for the second transmitting end to the first receiving end.