Patent Publication Number: US-2005118959-A1

Title: Mobile-unit-assisted modulation management

Description:
TECHNICAL FIELD  
      The present invention generally relates to modulation scheme management in radio communications systems, and in particular to a mobile-unit-assisted modulation scheme management in such systems.  
     BACKGROUND  
      Radio communications systems of today typically employ a modulation scheme, in which an intelligence-bearing signal is superimposed or mixed into a propagating carrier signal.  
      For some communications systems, including a GSM (Global System for Mobile Communications) or GPRS (General Packet Radio Service) system, the sole choice of available modulation scheme has been the GMSK (Gaussian Minimum Shift Keying). GMSK is a kind of constant-envelope phase modulation, where transmitting a zero bit or one bit is represented by changing the phase. Thus, every transmitted symbol represents one bit.  
      Introduction of the EDGE (Enhanced Data rates for GSM Evolution) technology into a GPRS systems provides another modulation scheme to be employable for radio communications, namely 8-PSK (8-state Phase Shift Keying). 8-PSK enables reuse of the channel structure, channel width and the existing mechanisms and functionality of the GMSK-using GPRS system. However, 8-PSK enables higher bit rates per time slot than those available for GMSK. 8-PSK is a linear method that uses phase and amplitude modulation, in which three consecutive bits are mapped onto one symbol. Although the symbol rate remains the same as for GMSK, each symbol now represents three bits instead of one, thus, increasing the raw data rate by a factor of three.  
      An EGPRS (Enhanced GPRS) system having access to both GMSK and 8-PSK modulation can use nine different modulation coding schemes, MCS 1  to MCS 9 . The lower four coding schemes use GMSK whereas the upper five use 8-PSK. These nine MCS use different error correction and, consequently, are adapted for usage under different radio environment conditions. Generally, in good radio environments a more aggressive (less error correction, 8-PSK-associated) coding scheme can be used to provide a higher user data rate, whereas with a poor radio link environment a coding scheme with more error correction (GMSK-associated MCS) and lower user data rate is typically used.  
      The EGPRS system also employs link quality control functionality denoted link adaptation. Link adaptation uses radio link quality measurements from a mobile unit and/or base transceiver station to select the most appropriate modulation coding scheme for downlink and uplink transmission. In particular for a mobile unit, such a measurement report includes only link quality measurements or estimations, e.g. BEP (Bit Error Probability), for the modulation that has been used since a last measurement report. However, since the link quality measurements are dependent on the particular modulation scheme employed, the network has to make an assumption about the relative performance of GMSK modulation and 8-PSK modulation. For example, if the network receives a report with BEP for data received by the mobile unit and modulated by GMSK, the network “maps” this GMSK BEP to a corresponding estimated 8-PSK BEP value.  
      A major problem with this prior art procedure is that a single modulation scheme BEP mapping is used for all mobile units in the system. However, the relative performance of GMSK and 8-PSK modulation is typically different in mobile units from different manufacturers and may also vary from one radio environment to another. Thus, the network may in some instance select a non-optimum modulation coding scheme to use for data transmitted to a mobile unit because of this non-ideal or erroneous BEP modulation mapping.  
     SUMMARY  
      The present invention overcomes these and other drawbacks of the prior art arrangements.  
      It is a general object of the present invention to provide an improved modulation scheme management in communications systems.  
      It is another object of the invention to provide a mobile-unit-assisted management of modulation scheme selection in communications systems.  
      Yet another object of the invention is to provide more accurate decision information used in the selection of modulation scheme for mobile units in communications systems.  
      These and other objects are met by the invention as defined by the accompanying patent claims.  
      Briefly, the present invention involves a mobile-unit-assisted generation of modulation-scheme-dependent link quality data used as a basis for selection of a modulation to use on data transmitted to the mobile unit. In a communications system, in which the invention is applied, a mobile unit has multiple available modulation schemes that are used for modulating data communicated on a communications link between the mobile unit and a base station. Since the performance of the different modulation schemes depends on the radio environment, the selection of a scheme to employ will be based on a link quality measure for the communications link. Such a link quality measure is, though, dependent on the modulation scheme employed for the link.  
      According to the invention, the mobile unit performs signal quality measurements on the communications link, over which data modulated using a first modulation scheme is communicated. The mobile unit then determines a first link quality measure for this first modulation. This first quality measure and/or the measurements of the link quality for the first modulation are used by the mobile unit for estimating a corresponding link quality measure for at least a subset of the other (currently not employed) available modulation schemes. This link quality estimation can then be performed based on the specific capabilities of the mobile unit, in particular based on the specific types and versions of modulation schemes and/or receiver algorithms implemented in the unit. This will result in a much more accurate quality measure estimation than if a central unit in the communications system would perform such estimation on behalf of all connected mobile units, which typically have different modulation capabilities and employ different modulation scheme and receiver algorithm versions. The mobile unit further generates selection information based on this first link quality for the currently used modulation scheme and the second estimated link quality/qualities for the currently not used modulation(s). The selection information is reported to the (central) unit in the communications system performing the selection and decision of modulation schemes for mobile units in the system.  
      The selection information could include determined link quality measures for the different modulations. Alternatively, it includes only one of the quality measures, typically the measure associated with the currently employed modulation, and a quantity derived from the link quality measures. The mobile unit could alternatively perform the modulation scheme selection itself based on the determined quality measures. In such a case, the selection information includes an identification of the selected and, thus, presently most preferred modulation scheme. The selection information could also include a corresponding identification of a presently preferred modulation coding scheme (MCS) associated with the selected modulation.  
      The estimation of the second link quality measure(s) based on the measured and determined first link quality measure can be realized by a quality measure mapping or converting process in the mobile unit. For example, a link quality map or table can be provided in the mobile unit. This table lists different link quality values for the first modulation and the corresponding values for the other modulation scheme(s). The mapping between quality measures is then performed as a table look-up using the determined first quality measure in order to obtain an estimation of the second quality measure(s). Alternatively, a converting function could be used with the first quality measure as input data and then outputting a corresponding quality measure for the currently not employed modulation(s). The table or function is preferably determined based on the particular capabilities and modulation scheme versions of the mobile unit and can be prepared using laboratory measurements and simulations on the mobile unit and/or the modulation hardware/software of the unit.  
      Since the different modulation schemes can be associated with different transmission power levels, the base station transmitting data to the mobile unit preferably reports the power levels, or quantities derived therefrom, to the mobile unit. This power data will then be used in the estimation of the second link quality measure(s) in order to obtain more accurate estimations.  
      The base station could also be configured to intermittently or periodically transmit data modulated with one of the otherwise currently non-employed modulation schemes. This allows the mobile unit to also perform link quality measurements on data modulated with these schemes. These measurements are then used together with the first link quality measure in the estimation of the second link quality measure(s).  
      The mobile unit could be equipped with a link quality enhancing algorithm that is operable on data modulated using a specific modulation scheme, or a specific subset of the available schemes. This enhancing algorithm will then improve the link quality experienced by the mobile unit when data is modulated with the specific modulation scheme(s) but not with other schemes. The mobile unit preferably determines the performance gain (quality enhancement) due to this algorithm. This gain is used in the estimation of the second link quality measure(s) in order to obtain even more accurate estimations.  
      The invention offers the following advantages: 
          Improves the accuracy in estimating link quality measures for both currently employed and currently not employed modulation schemes;     Allows the network to select, at any time instant, the optimal modulation scheme for a mobile unit;     Enhances the user bit rate;     Improves the communications system capacity; and     Facilitates smooth transitions between different modulation schemes.        

      Other advantages offered by the present invention will be appreciated upon reading of the below description of the embodiments of the invention. 
    
    
     SHORT DESCRIPTION OF THE DRAWINGS  
      The invention together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:  
       FIG. 1  is a schematic overview of a portion of a radio communications system, to which the teachings of the present invention can be applied;  
       FIG. 2  is a schematic block diagram illustrating an embodiment of a mobile unit according to the present invention;  
       FIG. 3  is a schematic block diagram illustrating the link quality estimator of  FIG. 2  in more detail;  
       FIG. 4  is a schematic block diagram illustrating another embodiment of a mobile unit according to the present invention;  
       FIG. 5  is a schematic block diagram illustrating yet another embodiment of a mobile unit according to the present invention;  
       FIG. 6  is a schematic block diagram illustrating an embodiment of the link quality enhancement generator of  FIG. 5  in more detail;  
       FIG. 7  is a schematic block diagram illustrating another embodiment of the link quality enhancement generator of  FIG. 5  in more detail;  
       FIG. 8  is a schematic block diagram of a packet control unit according to the present invention;  
       FIG. 9  is a flow diagram illustrating the selection information generating method according to the present invention;  
       FIG. 10  is a flow diagram illustrating the step of estimating link quality of  FIG. 9  in more detail;  
       FIG. 11  is a flow diagram illustrating additional steps of the method of  FIG. 9 ;  
       FIG. 12  is a flow diagram illustrating an additional step of the method of  FIG. 9 ;  
       FIG. 13  is a flow diagram illustrating an embodiment of the step of generating link quality enhancement of  FIG. 12  in more detail;  
       FIG. 14  is a flow diagram illustrating another embodiment of the step of generating link quality enhancement of  FIG. 12  in more detail, and  
       FIG. 15  is a flow diagram illustrating an additional step of the method of  FIG. 9 . 
    
    
     DETAILED DESCRIPTION  
      Throughout the drawings, the same reference characters will be used for corresponding or similar elements.  
      In several radio communications systems of today different modulation schemes or techniques are employed for modulating data transmitted on radio communications links through the systems. In cases of multiple available modulation schemes, the selection of an actual modulation scheme to use is then typically based on the radio quality of the communications link. The present invention relates to performing such a modulation scheme selection.  
      In the following, the invention will be described and disclosed with reference to a radio communications system having access to two possible modulation schemes, GMSK (Gaussian Minimum Shift Keying) and 8-PSK (8-state Phase Shift Keying). However, the invention is not limited to this actual choice of modulation schemes or to communications systems having access to only two different modulation schemes, but can be applied to a general communications system that that can use multiple, i.e. at least two, different modulation schemes for processing data communicated through the system, e.g. a CDMA (Code Division Multiple Access) system using QPSK (Quadrature PSK), 16QAM (16 Quadrature Amplitude Modulation) and 64QAM.  
       FIG. 1  is a schematic overview of a portion of a radio communications system  1 , to which the teachings of the invention can be applied. In  FIG. 1 , only units directly involved in the present invention are illustrated in order to simplify the figure. The radio communications system  1  could be a GPRS (General Packet Radio System) system adopting the EDGE (Enhanced Data rates for GSM Evolution) technique or an EGPRS (Enhanced GPRS) system. Generally, the communications system  1  comprises a number of base stations (BS) or base transceiver stations (BTS)  400 ,  420  providing communications links to connected mobile units  100 . These base stations  400 ,  420  are typically connected to and controlled by a base station controller (BSC)  300  or radio network controller (RNC). This BSC  300  in turn includes functionality or units  200  for selecting modulation schemes to use for the communications link  410  to the mobile units based on link quality measurements or estimations from the mobile units  410  and/or the base stations  400 ,  420 . In the figure, this modulation scheme selecting unit is, non-limitedly, represented by a packet control unit (PCU)  200 .  
      During operation, the mobile unit  100  performs signal or link quality measurements for the (downlink) communications link or channel  410  with its associated base station  400 . Based on these measurements a link quality measure is determined or estimated. This determined link quality measure is, however, dependent on the modulation scheme that was used and applied to the data received on the link  410 . Since the selection of modulation scheme to use on a communications link is based on the link quality and this link quality in turn depends on the employed modulation scheme, a corresponding link quality measure for the presently non-employed modulation scheme(s) has to be estimated in order to perform a correct scheme selection.  
      In the prior art systems, this estimation of link quality for the non-employed modulation scheme(s) is performed in the PCU  200 , whereas according to the present invention it is performed in and by the mobile unit  100 . As was discussed in the background section, employing a central PCU-based mapping or conversion between the link qualities for the different modulation schemes may result in a non-optimal choice of modulation scheme for a mobile unit. This is because the relative performances of the different modulation schemes typically differ from different mobile unit types and different manufacturers. By then implementing the determination of the modulation-dependent link qualities in the mobile unit  100 , the particular capabilities of that mobile unit  100 , e.g. the actual performance difference between modulation schemes and receiver algorithms, will be taken into consideration during the link quality mapping. As a result a much more accurate selection of modulation scheme can be performed.  
       FIG. 2  is a schematic block diagram of an embodiment of a mobile unit  100  according to the present invention. The mobile unit  100  includes an input and output (I/O) unit  110  for conducting communication with external units and stations. This I/O unit  110  is in particular configured for receiving radio blocks with modulated data from a base station, to which the mobile unit  100  is connected.  
      The mobile unit  100  further includes a radio link measuring unit or measurer  120  that performs signal measurements on the radio or communications link with the base station. This measuring unit  120  also determines a link quality measure that depends on the modulation scheme presently used for the data received on the link. For example, if GMSK modulation is presently used, the radio link measurer  120  will determine a first GMSK-dependent link quality measure. However, if 8-PSK instead would be used, the radio link measurer  120  would generate a second typically different 8-PSK-dependent link quality measure even though the radio environment would be identical for the two modulation schemes.  
      The radio link measuring unit  120  preferably performs the link measurements on each received burst or radio block and generates the first link quality measure based on these measurements. Alternatively, the measuring unit  120  could be configured for intermittently or periodically performing the signal measurements, e.g. on every second received radio block or every second 100 ms, or some other periodical interval.  
      The first link quality measure for the presently employed modulation scheme could be expressed in terms of bit error probability (BEP) or some other signal or link quality measure used in the art.  
      In a preferred embodiment of the invention, the link quality measure is an average quality measure, e.g. average BEP, over multiple received bursts or over a given period of time. This average quality measure could be a weighted average measure using different weights for different received radio blocks. In such a case, a weight used in the measurements in connection with a recently received radio block is then preferably larger than the corresponding weight for a radio block received earlier. Thus, the weighted average link quality measure should, as accurately as possible, reflect the current radio quality environment and situation for the communications link.  
      Although, the radio link measurer  120  has been described as determining or estimating one link quality measure for a first, presently used, modulation scheme, this measurer  120  could alternatively determine multiple link quality measures associated with this first modulation scheme. For example, the measure could include the average BEP and a coefficient of variation of the BEP, which both will be dependent on the used modulation scheme. Thus, in the present invention, when a modulation-scheme-dependent link quality measure is discussed this also includes multiple related measures associated with the given modulation scheme.  
      In the following it is assumed that the presently employed modulation scheme for the communications link is GMSK so the radio link measurer  120  will determine a GMSK-dependent link quality measure. Thus, the currently non-employed modulation scheme will then be 8-PSK in the present example. However, this should merely be seen as an illustrative example and the invention can also be applied to cases where 8-PSK or some other modulation scheme is currently used for downlink data to the mobile unit  100 .  
      A link quality estimating unit or estimator  130  is provided in the mobile unit  100  for estimating the corresponding link quality measure for the non-employed modulation scheme, i.e. 8-PSK-dependent link quality measure in the present example. This estimator  130  is configured for estimating the 8-PSK-dependent link quality measure based on the GMSK-dependent link quality measure determined by the radio link measurer  120  and/or based on the GMSK-dependent link quality measurement results obtained from this measurer  120 .  
      If the radio communications system can use three or more different modulation schemes, the estimator  130  could then be configured for estimating the modulation-scheme-dependent link quality for at least one of these non-used schemes and preferably for all of those schemes.  
      In a first embodiment, the link quality estimator  130  is configured for generating a corresponding link quality measure for the 8-PSK modulation as the measurer  120  has done for the GMSK modulation. This means that if the GMSK-dependent measure is represented as BEP, the estimator generates an 8-PSK-dependent BEP value based on the GMSK-measure. Correspondingly, if the GMSK measure instead is represented as average BEP and coefficient of variation, the estimator  130  generates an 8-PSK-dependent average BEP and coefficient of variation.  
      In an alternative embodiment, the base station, to which the mobile unit  100  is connected, is caused to intermittently or periodically transmit radio blocks or data modulated using 8-PSK even though GMSK should presently be used, and vice versa. However, if the present modulation is GMSK, intermittently transmitting 8-PSK blocks, which has a higher probability of getting lost than corresponding GMSK blocks, might result in that the mobile unit ( 100 ) will not detect these 8-PSK blocks. This problem may be lessened by the base station choosing the most appropriate modulation coding scheme (MCS) associated with 8-PSK, e.g. MCS 5  having a lower loss probability than the remaining 8-PSK-associated MCS (MCS 6 - 9 ).  
      By then providing some 8-PSK modulated data, 8-PSK-dependent measurements can be performed thereon by the measurer  120 , which then forwards such measurement results to the estimator  130 . This link quality measurer  130  then uses these 8-PSK-measurements in addition to the GMSK-dependent link quality data from the measurer  120  in the process of determining a corresponding 8-PSK-dependent link quality measure. Thus, basing this link quality estimation on actual measurement results for the given modulation scheme typically provides a more accurate estimation than by only using measurements for other modulation schemes. This inclusion of radio blocks modulated with a currently non-optimal modulation scheme for the purpose of producing more accurate link quality measurements can be straightforwardly implemented for downlink communications. For example, in cases where GPRS and EGPRS are mixed, transmission with GMSK is already normally used every Xth block, where X is a positive number larger than one, e.g. four, even when 8-PSK is used in order to enable uplink state flag (USF) decoding by the mobile unit.  
      In yet another embodiment, the link quality estimator  130  is configured for generating a less detailed measure for the non-used 8-PSK link quality than the presently used GMSK modulation. For example, if the GMSK link quality measure from the radio link measurer  120  is represented as average BEP and coefficient of variance, the corresponding 8-PSK measure could simply be a BEP value. Alternatively, a single 8-PSK-dependent value could be used to represent an interval of GMSK link quality values. For example, if the is determined GMSK-dependent measure is within the interval X 1 &lt;GMSK-measure&lt;X 2 , X 1 &lt;X 2  are real numbers, the corresponding estimated 8-PSK-dependent measure should be Y 1 , whereas if X 2 &lt;GMSK-measure&lt;X 3  Y 2  should be selected as 8-PSK-dependent measure, Y 1 , Y 2  are real numbers.  
      In some communications systems, different maximum transmission power levels may be used for GMSK-modulated radio blocks than for 8-PSK-modulated blocks. A reason could be that the power amplifier non-linearities in the base station transmitter are typically more servere for 8-PSK. The base station could then report the used power levels for GMSK and the corresponding level for 8-PSK to the mobile unit  100 . Alternatively, a power quantity derived from these power levels, such as ratio between the GMSK power level and the 8-PSK power level, a difference therebetween or some other quantity derived therefrom, could be communicated to the mobile unit  100 . The link quality estimator  130  is then configured for using the received power data or quantity in the estimation of the 8-PSK-dependent link quality measure, which will result in a more accurate estimation value.  
      The GMSK-dependent link quality measure from the radio link measurer  120  and the corresponding 8-PSK-dependent link quality measure from the link quality estimator  130  are then forwarded to a selection information generating unit or generator  140 . This unit  140  generates selection information based on these received quality measures. This information will form basis for the selection or decision of which modulation scheme to use for the downlink to the mobile unit  100 .  
      If each received modulation-scheme-dependent link quality measure basically includes multiple values, e.g. an average and a variance value, the generator  140  could be configured to consider all such values or only one or a subset thereof, e.g. the average BEP value of respective modulation scheme, in the information generation.  
      The selection information can then include the (two) determined modulation-scheme-dependent link quality measures from the measurer  120  and the estimator  130 . Alternatively, the information includes the link quality measure for the presently employed modulation scheme (from the measurer  120 ) and a quantity derived from the link quality measures, e.g. a difference between or a ratio of the GMSK measure and the 8-PSK measure, or some other quantity that allows determination of the 8-PSK measure using the GMSK measure in the selection information.  
      The generated selection information is then preferably transmitted using the I/O unit  110  to an external unit in the communications system that performs the selection of modulation scheme on behalf of connected mobile units, e.g. the PCU of  FIG. 1 . The selection information, thus, forms basis for this decision and selection process in the external unit.  
      As is well known in the art, the two modulation schemes 8-PSK and GMSK are each associated with different modulation and coding schemes (MCS) used for coding the data transmitted over air in the system. As for selection of modulation scheme, the actual choice of a suitable MCS is typically dependent on radio link quality measurements. This means that the selection information can also, or alternatively, be used for selection of an appropriate MCS to use on the downlink to the mobile unit  100 .  
      The selection information generator  140  could be configured for intermittently or periodically transmit the information via the I/O unit  110  to the external unit (PCU). Alternatively, or in addition, the selection information could be reported to the PCU upon reception of a report request therefrom.  
      The link quality estimator  130  and the selection information generator  140  and possibly the radio link measurer  120  can be implemented in a information generating unit  190  that is adapted for arrangement and operation in the mobile unit.  
      The units  110  to  140  of the mobile unit  100  may be implemented as software, hardware or a combination thereof.  
      This, mobile-unit-assisted modulation scheme selection helps the communications network in selecting, at any time instant, the optimal modulation scheme, and hence improve the user bit rate and the system capacity. This embodiment of the invention that reports both 8-PSK-dependent link quality and GMSK-dependent link quality even although only one of the modulation schemes have been used between information-reporting events, also facilitates a more smooth transition between modulation schemes.  
       FIG. 3  is a schematic block diagram of an embodiment of the link quality estimator  130  of  FIG. 2 . This estimator  130  includes a link quality map or table  134  that lists different 8-PSK and GMSK link quality values Such a table  134  then allows mapping or conversion between different modulation-dependent quality values. Thus, for a given GMSK quality value the table  134  includes a corresponding 8-PSK value, and vice versa. This means that when a link quality map processor  132  in the estimator  130  receives a measured and determined GMSK link quality measure from the radio link measurer, the processor  132  performs a look-up in the table  134  and retrieves the corresponding 8-PSK link quality measure.  
      The table  134  could be implemented to include equally detailed quality measures for the two modulation schemes, e.g. if an average BEP and variance thereof is used for retrieving corresponding 8-PSK measures, an average 8-PSK-dependent BEP and variance may be obtained from the table  134 . Alternatively, a less detailed value could be retrieved, e.g. only a single BEP compared to average and variance values. In the case of more than two available modulation scheme, several tables  134  could be implemented in the estimator  130  or a single  134  could list the different link quality values for all of the schemes.  
      Alternatively, the table  134  is omitted and the processor  132  instead employs a link quality mapping or converting algorithm or function. Such a function then has the GMSK-dependent link quality or GMSK-dependent measurements from the radio link measurer as input parameter and outputs a corresponding 8-PSK-dependent quality measure. Other input parameters, such as 8-PSK measurement results on intermittently received radio blocks and/or power level data from the base station, could also be used in the function in order to obtain a more accurate estimated 8-PSK measure. If the GMSK measure is represented by two values, the function could output a single or two 8-PSK values. It could be possible that one and the same function could be used for both converting GMSK values into 8-PSK values and vice versa. Alternatively, and also if more than two modulation schemes are possible, several different converting functions can be implemented in the processor  132 .  
      The mapping table  134  and/or the function is preferably generated based on the capabilities of the mobile unit, in particular based on the specific version and types of modulation schemes and the receiver algorithm(s) employable in the mobile unit. Such a table or function can be produced based on standard laboratory measurements and/or simulations on the mobile unit or the modulation software and/or hardware implemented in the unit. Having such a mobile-unit-adapted link quality conversion for different modulation schemes enhances the link quality estimation and results in a more accurate selection information than by using a central mapping functionality in network for all types of mobile units.  
      Thus, the processor  132  is configured for receiving the GMSK measure and possibly other input data, such as 8-PSK measurement results and power level quantity, from other units in the mobile unit or from external unit, and uses them in the generation of the estimated 8-PSK link quality measure.  
      In a first embodiment of the invention, the table  134  or function is configured for considering the possibly different transmission power levels of GMSK and 8-PSK modulation. This means that the table  134  could for each GMSK value list several 8-PSK values but for different values of the power level quantity Alternatively, the processor  132  could, once an 8-PSK value has been retrieved from the table  134 , modify this value based on the power level quantity.  
      The unit  132  of the link quality estimator  130  may be implemented as software, hardware or a combination thereof. The unit  132  and table  134  may all be implemented in the estimator  130 . However, a distributed implementation is also possible, with the unit  132  and/or table  134  provided in elsewhere in the mobile unit.  
       FIG. 4  is a schematic block diagram illustrating another embodiment of a mobile unit  100  according to the present invention. The I/O unit  110 , radio link measurer  120  and link quality estimator  130  are similar to the corresponding units in  FIG. 2  and are not further discussed herein.  
      The mobile unit  100  includes a link quality comparing unit or comparator  150  that receives the GMSK-dependent link quality measure from the measurer  120  and the corresponding estimated 8-PSK-dependent measure from the estimator  130 . A modulation scheme selector  160  then selects one of these modulation schemes based on the comparison. This selector  160  typically selects the modulation scheme giving rise to a best link quality for the communications link based on the comparison performed by the comparator  150 . The selector  160  also generates a notification or identification of the selected modulation scheme. In cases with only two possible schemes, such as GMSK and 8-PSK, a single bit can be used to represent the selected and presently preferred modulation. However, if more than two modulations are accessible for the mobile unit  100 , more than one bit may have to be used for the identification of the selected modulation.  
      Furthermore, the selector  160  could also be configured for selecting, in addition to a suitable modulation scheme, a modulation and coding scheme to use on the communications link. Also this selection is based on the operation of the comparator  150  on the input link quality measures. The selector  160  can then, or in addition, generate a notification or identification of the selected MCS.  
      This identification (or identifications) is then brought to the selection information generator  140 . Thus, in this embodiment of the invention the mobile unit  100  itself performs the selection of modulation scheme and/or MCS to use and the selection information transmitted to the PCU then includes the result from this selection, i.e. the identification(s). The PCU could choose to use the proposed modulation scheme and/or MCS in the received report from the mobile unit  100  for the communications link between the unit  100  and the base station.  
      In addition, the selection information could also include the link quality measures as discussed above in connection to  FIG. 2 . The unit (PCU) receiving the report with the selection information could then optionally perform a similar link quality comparison and modulation scheme and MCS selection. It might be possible that the PCU proposes another selection of modulation scheme and/or MCS than the mobile unit  100 . This may be due to that the PCU have access to additional input data, e.g. power level data, that is not accessible for the mobile unit  100  so that the PCU can perform a more accurate selection.  
      The information generating unit  100  can in this embodiment, thus, include the link quality comparator  150  and the modulation scheme selector  160  in addition to the link quality estimator  130 , the selection information generator  140  and possibly the radio link measurer  120 .  
      The units  110  to  160  of the mobile unit  100  may be implemented as software, hardware or a combination thereof.  
       FIG. 5  is a schematic block diagram of yet another embodiment of a mobile unit  100  according to the present invention. The I/O unit  110 , radio link measurer  120  and link quality estimator  130  are similar to the corresponding units in  FIG. 2  and are not further discussed herein.  
      This mobile unit  100  embodiment has access to a link quality enhancing algorithm or unit  170  that is applicable for data modulated using a subset of the available modulation schemes. For example, the link quality enhancing algorithm  170  could only be operational on GMSK-modulated data but not 8-PSK-modulated data. Typically, such an enhancing algorithm  170  allows usage of a given modulation scheme even under radio conditions that otherwise would not be possible due to a too low link quality. This means that the algorithm  170  is able to enhance the link quality on the communications link experienced by the mobile unit  100  during usage of one or a subset of the modulation schemes. For example, the enhancing unit  170  could have interference suppressing capability or some other functionality for link quality enhancement.  
      Since the quality enhancing algorithm  170  is applicable only to a subset of the available modulation schemes, it will affect the link quality measures for this/these modulation scheme(s) but typically not for other modulations. This means that if the obtained link quality enhancement is not considered in the modulation selection process a non-optimal modulation could be selected.  
      Furthermore, the gain or performance of the enhancing algorithm  170  could also be dependent on the actual radio environment, e.g. on the number and relative strength of interfering signals, and/or traffic load. This means that the selection will be even more insecure if the current link quality gain or enhancement is not used.  
      Non-limiting examples of such link quality enhancing algorithms  170  that can be applicable according to the invention are Single Antenna Interference Cancellation (SAIC) and Single Antenna Interference Rejection (SAIR).  
      For example, the current SAIC algorithms only give performance gains when the carrier or link is GMSK modulated. Furthermore, the gain from SAIC depends strongly on the number and relative strengths of the interfering signals. This means that some SAIC algorithms presently may improve the GMSK performance by anything between 0 and 9 dB depending on the radio environment and the SAIC algorithm version employed. Thus, the relative performance between GMSK and 8-PSK is uncertain by up to 9 dB if SAIC gain is not used in the selection process. Therefore, it will be very difficult to conduct an accurate modulation scheme selection without knowledge of the SAIC performance.  
      As an example of the potential problem, consider downlink transmission where the currently selected MCS is GMSK-modulated. Further assume that the radio environment is suitable for SAIC and that the C/I is high enough to give link quality reports from the mobile unit indicating very good quality, i.e. very low GMSK BEP is reported to the network or PCU. The PCU, which does not know that SAIC is an important reason for the low GMSK BEP will switch to 8-PSK. Since SAIC does not give gains with 8-PSK modulation, there will be many block errors and many blocks may be lost before the PCU receives a new link quality report from the mobile unit and realizes this and switches back to GMSK modulation. There may then be extensive switching back and forth between the modulations (ping-pong effect), in the worst case resulting in about 50% of the blocks being retransmitted.  
      Thus, a link quality enhancement generator or generating unit  180  is preferably implemented in the mobile unit  100  for determining the quality enhancement caused by operation of the algorithm  170 . The generator  180  typically determines such an enhancement as the obtained performance gain.  
      This could be the average gain over multiple radio blocks or over a certain period of time, e.g. average gain since a last measurement report was generated and transmitted to the PCU. Since the enhancement algorithm  170  is typically activated in some bursts and deactivated in other bursts, the mobile unit  100  can choose simply to estimate link quality with enhancement gain from all received bursts modulated with the modulation scheme associated with the algorithm and link quality without the enhancement gain from only these bursts where the algorithm is deactivated. These two link qualities can then be used to determine the performance gain of the algorithm  170 .  
      The selection information determined by the generator  140  is determined based on this link quality enhancement value and/or the enhancement value is basically included in the information. For example, the selection information could then include the 8-PSK-dependent link quality measure, the GMSK-dependent link quality measure as determined with activation of the link quality enhancing algorithm  170  and the generated enhancement value. Alternatively, the information includes the 8-PSK-dependent link quality measure, the GMSK-dependent link quality measure as determined with activation of the link quality enhancing algorithm  170  and the GMSK-dependent link quality measure as determined without usage of the link quality enhancing algorithm  170 .  
      As was discussed above, once the selection information is determined by the generator  140  it is included in a measurement report transmitted by the I/O unit  110  to the PCU. The teachings of this embodiment of the mobile unit  100  may also be combined with the embodiment of the mobile unit discussed in connection with  FIG. 4 . Thus, the mobile unit  100  selects a suitable modulation scheme based on the measured and estimated link quality measures and the determined link quality enhancement.  
      In this embodiment, the information generating unit  190  includes the link quality enhancing algorithm  170 , the link quality enhancement generator  180  in addition to the link quality estimator  130 , the selection information generator  140  and possibly the radio link measurer  120 .  
      The units  110  to  140  and  170  to  180  of the mobile unit  100  may be implemented as software, hardware or a combination thereof.  
       FIG. 6  is a schematic block diagram of an embodiment of the link quality enhancement generator  180  of  FIG. 5 . In this embodiment, the link quality for the modulation scheme(s), to which the enhancing algorithm can be applied, is determined both without activation of the algorithm and with operation of the algorithm. This means that for this/these modulation scheme(s) generally two link quality measures are determined, where the one determined with activation of the algorithm typically is the better one, i.e. smaller if the measure is represented as BEP. A link quality comparator or comparing unit  182  is implemented in the enhancement generator  180  for comparing these two link quality measures for a modulation scheme. The link quality enhancement could be expressed as a difference between the quality measures or as a ratio of them.  
      The unit  182  of the link quality enhancement generator  180  may be implemented as software, hardware or a combination thereof. The unit  182  may be implemented in the generator  180 . However, a distributed implementation is also possible, with the unit  182  provided in elsewhere in the mobile unit.  
       FIG. 7  is a schematic block diagram of another embodiment of the link quality enhancement generator  180  of  FIG. 5 . This embodiment includes an algorithm activation counter  184 . As was discussed above, the link quality enhancing algorithm is typically activated for some received bursts or radio blocks but not for others. For example, SAIC can potentially be activated for all received GMSK-modulated radio blocks. However, due to external radio environmental conditions SAIC is typically deactivated in situations where it would not result in any performance enhancement or would worsen the link quality. By counting the number of potential radio blocks for which the algorithm is activated, the counter  184  can determine an activation ratio.  
      Such a ratio could e.g. be defined as the number of radio blocks for which the algorithm was activated divided by the total number of blocks for which the algorithm actually could have been activated, i.e. all received GMSK blocks in the case of SAIC. Such an activation ratio could be an (rough) indication of the link quality enhancement caused by the algorithm. The activation ratio can also optionally be supplemented with data of the average performance gain obtained by the operation of the algorithm in order to define a more accurate quality enhancement. Alternatively, laboratory measurements can have been performed to determine, on average, what performance gain a certain activation ratio corresponds to. For example, an activation ratio of 75% could be used to represent a gain of 7 dB, or a given average gain, e.g. 7 dB could be represented by an interval of activation ratio, e.g. 100-75%. This means that if the counter  184  determines the ratio to be 83%, the algorithm results in a link quality enhancement of 7 dB in this illustrative example.  
      The unit  184  of the link quality enhancement generator  180  may be implemented as software, hardware or a combination thereof. The unit  184  may be implemented in the generator  180 . However, a distributed implementation is also possible, with the unit  184  provided in elsewhere in the mobile unit.  
       FIG. 8  is a schematic block diagram of a unit performing the selection of modulation schemes on behalf of mobile units in the network. In the figure this unit is, non-limitedly, represented by a packet control unit  200 . The PCU  200  includes an I/O unit  210  for conducting communications with external units. The I/O unit  210  is in particular configured for receiving link quality measurement reports from mobile units connected to the communications system. Furthermore, the I/O unit  210  could also transmit requests for such reports to mobile units, unless the mobile units are not configured for automatically transmitting such reports.  
      An optional measurement request generator  220  is implemented in the PCU  200  for generating the request messages that the I/O unit  210  transmits to mobile units, possible via base stations. The generator  220  could be configured for intermittently or periodically generating these reports. However, if the mobile units automatically transmit such reports to the PCU  200 , without the need of received requests, this generator  220  could be omitted from the PCU  200 .  
      The PCU  200  also includes a modulation scheme selector  230  that selects a modulation scheme to use on the (downlink) channel to a mobile unit based on selection information from the mobile unit. Thus, the received selection information constitutes basis for selection, which the selector  230  uses in its decision process. As was discussed in the foregoing, the selection information could include: 1) GMSK and 8-PSK link quality; 2) one of GMSK and 8-PSK link quality plus a quantity derived from the GMSK and 8-PSK link quality; 3) in case of more than two possible modulation schemes, the link quality for at least two of the schemes and preferably from all of the available schemes; 4) the data according to any of 1) to 3) plus a link quality enhancement; 5) the data according to any of 1) to 3) plus an activation ratio for an link quality enhancing algorithm; 6) indication of a preferred modulation scheme; 7) indication of a preferred MCS; 8) indication of a preferred modulation scheme and MCS; or 9) a combination of any of the data according to 1) to 8).  
      The selector  230  could also be configured for selecting a MCS based on the selection information.  
      If the received selection information has not been generated by the mobile unit based on power level considerations, i.e. the fact that the transmission power levels of the base station could differ for different modulation schemes, the selector  230  could use such power data in the selection process. An optional power command generator  240  transmits a power level request to the base station communicating with the mobile unit. This request urges the base station to return power level data to the PCU  200 . The selector  230  could then modify the link quality measures from the mobile unit based on such received power data in order to obtain even more accurate quality measures that, thus, enable a more accurate modulation scheme selection.  
      The power command generator  240  could also, or alternatively, transmit power commands to the base station and urging the station to report the power level data to the mobile unit instead of or as a complement to reporting the data to the PCU  200 .  
      An optional unit  250  for generating modulation scheme exchange commands could also be implemented in the PCU  200 . This unit  250  intermittently or periodically transmits exchange commands to a base station, urging the station to intermittently or periodically transmit data to a mobile unit, which data is modulated with a presently not employed modulation scheme. This temporary modulation scheme exchange allows the mobile unit to perform link quality measurements on data modulated using an otherwise currently not employed modulation and, thus, allows a more accurate estimation of the link quality for that modulation.  
      The units  210  to  250  of the PCU  200  may be implemented as software, hardware or a combination thereof. The units  210  to  250  may all be implemented in the PCU  200  in a single network node in the communications system. However, a distributed implementation is also possible, with the units  210  to  250  provided in different network nodes. For example, the functionalities of the generators  240  and  250  could be implemented in different base stations.  
       FIG. 9  is a flow diagram illustrating a method of generating decision or selection information for selection of a modulation scheme for a mobile unit. The method starts in step S 1 , where the mobile unit performs modulation-scheme-dependent signal or link quality measurements on radio blocks or bursts received on a communications link from a base station. Based on these measurements a link quality measure for the currently employed modulation scheme (modulation scheme  1 ) is determined. In a next step S 2 , a corresponding link quality measure is estimated for the other available but currently non-employed modulation scheme(s) (modulation scheme  2 ). This estimation is performed based on the determined link quality for the current modulation and/or from the measurement results for that modulation. Finally, in step S 3 , selection information is generated based on the determined and estimated link quality measures. This information will be used for selection of a suitable modulation scheme and/or MCS to use for the mobile unit. The method then ends.  
       FIG. 10  is a flow diagram illustrating an embodiment of the estimation step of  FIG. 9  in more detail. The method continues from step S 1 . In a next step S 10 , the mobile unit receives transmission power level data from the base station communicating with the mobile unit. The mobile unit can now determine a respective power associated with the different modulations based on this power data. Such power information is used in the process for the determination of the modulation-dependent link quality measures. The mobile unit further intermittently or periodically receives data/blocks modulated with the currently not employed (or optimal) modulation scheme(s) in step S 11 . This allows the mobile unit to perform actual measurements also for this/these modulation(s) and thereby increases the accuracy of the link quality estimation for such modulation(s). This means that both the link quality measure for the currently employed modulation and these measurements, and optional power data, can be used in the estimation. In the next step S 12 , a look-up table is used with the measured and determined link quality measure for the currently employed modulation as input. Such a table includes a list of measures for the first modulation and corresponding values for the second modulations. Alternatively, one or several converting functions could be used with the measure of the first modulation as input and outputs an estimated link quality value for the second modulation. The table and function can be adapted for the functionalities and capabilities of the particular mobile unit. The method then continues to step S 3  of  FIG. 9 .  
       FIG. 11  is a flow diagram illustrating additional steps of the method of  FIG. 9 . The method continues from step S 2 . In step S 20  the link quality measures for the different modulations are compared in order to determine a best link quality and associated modulation. The currently best or most optimal modulation scheme is then selected in step S 21  based on the comparison. In case the measures are BEPs, the modulation associated with a lowest BEP is typically selected in this step. In the optional step S 22 , a corresponding MCS for this selected modulation scheme is selected. Identification of the selected modulation and/or MCS is included in the selection information as the method continues to step S 3 .  
       FIG. 12  is a flow diagram illustrating an additional step of the method of  FIG. 9 . The method continues from step S 1 . In step S 30 , a link quality enhancement is generated for the quality enhancing algorithm operational on data modulated using a subset, e.g. one of, the available modulation schemes. This quality enhancement is used further in the estimation process of the next step S 2  and/or is included in the selection information.  
       FIG. 13  is a flow diagram illustrating an embodiment the enhancement generating step of  FIG. 12 . The method continues from step S 1 . In a next step S 40 , the link quality for the modulation scheme(s) associated with the enhancing algorithm is determined without activation of the algorithm. Step S 41  compares this non-activated link quality with a corresponding link quality measure for the same modulation but with operation of the algorithm. The link quality enhancing gain can now be determined based on these two link quality measures. The method then continues to step S 2 .  
       FIG. 14  is a flow diagram illustrating another embodiment the enhancement generating step of  FIG. 12 . The method continues from step S 1 . In a next step S 50 , the activation ratio of the enhancing algorithm is determined. This ratio is typically expressed as the number of burst during which the algorithm was activated divided y the total number of burst during which the algorithm could potential have been activated. The link quality enhancement can, at least, be estimated based on such activation ratio, and possible other data such as average enhancing gain for the algorithm.  
       FIG. 15  is a flow diagram illustrating an additional step of the method of  FIG. 9 . The method continues from step S 3 . In a next step S 60 , the generated selection information is reported to a unit in the communications network performing the modulation selection, e.g. the PCU. This report could be intermittently or periodically transmitted to the PCU. Alternatively, or in addition, the report could be transmitted upon reception of a request from the PCU.  
      It will be understood by a person skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.