Abstract:
The invention relates to a method, a device and a system for adapting a communications link based on a quality estimate for a signal transmitted via the communications link. The method comprises receiving and demodulating the transmitted signal, assessing the demodulated signal to derive a first estimate for the signal quality that is to be utilized in a link adaptation scheme, and further processing and decoding the demodulated signal, wherein based on at least one of the further processed, non-decoded signal and information obtained prior to conclusion of decoding a first control signal indicative of the signal quality is generated and utilized to control the link adaptation scheme.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method, a device and a system that are involved in a link adaptation mechanism. More specifically, the invention relates to adapting a communications link between a transmitter and a receiver based on a quality estimate for a signal transmitted via the communications link.  
       BACKGROUND OF THE INVENTION  
       [0002]     Wireless cellular communications is continuing to grow unabated. As wireless applications becomes increasingly widespread, the pressure on network operators to increase the capacity of their networks becomes more intense.  
         [0003]     There are a number of ways of enhancing capacity in a wireless cellular network, including frequency hopping, micro cells, the introduction of adaptive antennas, and link adaptation. Link adaption has thus become an object of increasing interest in recent years.  
         [0004]     In the following, conventional link adaptation mechanisms will be described for an exemplary wideband code division multiple access (WCDMA) scenario. A typical WCDMA scenario including two mobile devices (user equipment, UE), a base station (BS) communicating with the UEs, and a radio network controller (RNC) communicating with the BS is shown in  FIG. 1 . As can be seen from  FIG. 1 , WCDMA downlink transport channels to the UEs include a dedicated channel (DCH) and a high-speed downlink shared channel (HS-DSCH). The HS-DSCH is allocated to an UE on a time-slot by time-slot basis.  
         [0005]     The basic link adaptation mechanisms in the WCDMA standard include power control on the DCH and adaptive coding and modulation on the HS-DSCH. Power control on DCH avoids that more power than is actually required to achieve a certain decoding quality is assigned to individual communications links. Since the total transmit power of the BS is limited, the implementation of such a power control scheme increases the network capacity. Additionally, avoiding excessively high power levels helps to reduce signal interference.  
         [0006]     According to the link adaptation mechanism of adaptive coding and modulation, the transmission rate is adapted to the time-varying channel and interference conditions. In the case of favourable channel conditions for example, a larger modulation format or higher code rate is used to increase the data rate and thus enhance the network capacity.  
         [0007]     A power control scheme in a WCDMA link adaptation context is for example described in H. Schotten and J. Röβler, “System Performance Gain by Interference Cancellation for WCDMA Dedicated and High-Speed Downlink Channels”, VTC 2002, Vancouver. The UE receiver configuration required to implement such a power control based link adaptation mechanism is depicted in  FIG. 2  and will now be described in more detail.  
         [0008]     A signal received from the BS by the UE receiver is demodulated, Rake combined and subjected to an interference cancellation step. Based on the signal that has been subjected to interference cancellation an estimate for the signal-to-interference ratio (SIR) is determined and compared to a SIR target value. Depending on the result of this comparison a power control algorithm generates a power up or a power down command for downlink that is sent in uplink to the BS. Thus, a fast power control loop is established that allows to adjust the power once per slot (at a rate of 1500 slots per second).  
         [0009]     In addition to this fast power control loop an outer power control loop is provided. The outer power control loop adjusts the target SIR setpoint and aims at a constant frame error rate (FER). Outer loop control is based on a check of the cyclic redundancy code (CRC) that is obtained during decoding of a particular data frame. If for example the CRC check indicates that the transmission quality is decreasing, the SIR target may be increased and vice versa.  
         [0010]     As has been mentioned above, adaptive coding and modulation is a further example for an efficient link adaptation mechanism. In  FIG. 6  an approach for adaptive coding and modulation on HS-DSCH known from H. Schotten and J. Röβler, “System Performance Gain by Interference Cancellation for WCDMA Dedicated and High-Speed Downlink Channels”, VTC 2002, Vancouver is depicted. In the scenario of FIG.  6 , the transmission power is kept constant but the transmission rate is adapted to the current channel and interference conditions. A received signal that has been demodulated, Rake combined and subjected to interference cancellation is assessed to generate an estimate for the channel quality. This estimate is then used for channel quality indicator (CQI) signaling in uplink. The CQI signaling determines the modulation format and code rate that is used on downlink. By varying the modulation format and the code rate, the data rate on downlink can be adapted to the time-varying channel and interference conditions.  
         [0011]     As has become apparent from the above, efficient link adaptation requires a sufficiently accurate estimation of the quality of the received signal on the one hand and, to closely track channel and interference conditions, a low estimation and reporting delay of the signal quality on the other hand. Obviously, these requirements are contradictory because depending on the implementation details of the receiver, a fast estimation of signal quality and a low reporting delay do often not allow a sufficiently accurate signal quality estimation.  
         [0012]     There is thus a need for a method, a device and a system that enable a more efficient link adaptation based on a signal quality estimate.  
       SUMMARY OF THE INVENTION  
       [0013]     As regards a method, the need for efficiently adapting a communications link between a transmitter and a receiver based on a quality estimate for a signal transmitted via the communications link is satisfied by a link adaptation approach comprising receiving and demodulating the transmitted signal, assessing the demodulated signal to derive a first estimate for the signal quality that is to be utilized in a link adaptation scheme, and further processing and decoding the demodulated signal. Based on at least one of the further processed, non-decoded signal and information obtained prior to conclusion of decoding, a first control signal indicative of the signal quality is generated and utilized to control the link adaptation scheme.  
         [0014]     Control of the link adaptation scheme by means of the first control signal prior to completion of the decoding operation allows an improved link adaptation with respect to the tracking speed and tracking accuracy of time-varying channel and interference conditions. Moreover, based on the first control signal it is possible to implement signal quality estimation as a two-step or multiple-step procedure. Thus signal quality estimation becomes more robust.  
         [0015]     The further processing that is performed between demodulation and decoding preferably includes at least one of Rake combining, de-interleaving and advanced receiver techniques like interference cancellation. It is particularly advantageous to derive the first estimate for the signal quality from the demodulated signal prior to subjecting the demodulated signal to an advanced receiver technique and to generate the first control signal generated on the basis of a signal that has been subjected to an advanced receiver technique. Generation of the first estimate prior to performing an advanced receiver technique ensures that an additional processing delay associated with the advanced receiver technique does not result in a link adaptation delay. Additionally, controlling the link adaptation scheme by means of the first control signal after the advanced receiver technique has been performed allows (prior to conclusion of demodulation) the taking into account of signal enhancement effects that resulted from the advanced receiver technique and that would not be or only difficultly be predictable prior to applying the advanced receiver technique to the demodulated signal.  
         [0016]     The first control signal may be generated on the basis of a second estimate for the signal quality or may form the basis for generating the second estimate. The first estimate and the second estimate for the signal quality are preferably derived from the demodulated signal at different processing stages. This means that the demodulated signal from which the second estimate is derived might have been processed further compared to the demodulated signal that formed the basis for deriving the first estimate. Thus, the second estimate will in general be more accurate than the first estimate but will become available at a later point in time. The second estimate, although being more accurate, will therefore be associated with a larger processing delay  
         [0017]     At least one of the first control signal and the second estimate may be generated based on metrics information obtained during further processing or decoding. Thus, metrics information derived anyway in the receiver may be utilized to control the link adaptation scheme.  
         [0018]     Various link adaptation schemes can be implemented. According to a preferred variant of the invention the link adaptation scheme includes an association between the first estimate and an adaptation signal controlling the counterpart of the receiver, i.e. the transmitter. Such an association may for example be defined by a mapping mechanism or any other mechanism that allows to generate an adaptation signal from the first estimate in a replicable manner. The adaptation signal may for example be a power up command, a power down command or a command that is used in context with CQI signalling.  
         [0019]     If a link adaptation scheme defining an association between the first estimate and an adaptation signal is implemented, the first control signal may be used to control (e.g. change) this association. If for example a mapping mechanism between the first estimate and a corresponding adaptation signal is defined, the first control signal may be used to adjust this mapping mechanism to thereby improve link adaptation, e.g. improve at least one of transmit power control, adaptive coding and adaptive modulation.  
         [0020]     The decoded signal or information like the CRC obtained as a decoding result may be assessed to generate a second control signal for e.g. additionally controlling the link adaptation scheme or for triggering re-transmission. The second control signal will however not be based on an estimate for the signal quality but on a “hard figure” like the CRC or on the decoded signal. The second control signal allows implementation of a two-step control of the link adaptation scheme, namely a faster but less accurate control step on the basis of the first control signal and a slower but more accurate control step on the basis of the second control signal.  
         [0021]     According to a further aspect of the invention in context with the link adaptation schemes of adaptive coding, adaptive modulation or a combination thereof, a first estimate for the signal quality that is to be utilized in the particular link adaptation scheme is derived from the demodulated signal prior to decoding thereof. Based on the decoded signal or on information that has become available only after decoding (like the CRC) a control signal indicative of the signal quality may be generated and utilized to control at least one of adaptive coding and adaptive modulation. The first control signal is preferably generated on the basis of an assessment of the CRC.  
         [0022]     The invention can be implemented as a hardware solution or as a computer program product comprising program code portions for performing the steps of the invention when the computer program product is run on a computing device. The computer program product may be stored on a computer-readable recording medium like a data carrier that is for example in fixed association with or removable from the computing device.  
         [0023]     As regards the hardware solution, the invention is directed to a receiver that is configured to be coupled by an adaptable communications link to a transmitter, wherein link adaptation is performed based on an estimate of the signal transmitted via the communications link to the receiver. The receiver comprises a demodulator for demodulating the received signal, at least one processing component the further processing the demodulated signal, and a decoder for decoding the further processed signal. A first signal branch of the receiver is coupled to a first node between the demodulator and the at least one processing component. The first branch includes a first estimating component for deriving a first estimate for the signal quality that is to be utilized in a link adaptation scheme. A second signal branch of the receiver is coupled to at least one of the processing component, the decoder and a second node between a processing component and the decoder. The second signal branch is configured to transmit a first control signal that is indicative of the signal quality and that controls the link adaptation scheme. The processing component preferably performs at least one of Rake combining, de-interleaving and one or more advanced receiver techniques like interference cancellation.  
         [0024]     In the second signal branch a second estimating component can be arranged for deriving a second estimate for the signal quality based on which the first control signal may be generated. In addition to the first and the second signal branch a third signal branch may be provided. The third signal branch can be coupled to a third node arranged in a signal path after the decoder and may include an assessment unit that generates a second control signal for controlling the link adaptation scheme.  
         [0025]     According to further aspect of the invention, the invention is directed to a receiver for demodulating a received signal, a decoder for decoding the demodulated signal, a first signal branch coupled to a first node between the demodulator and the decoder and a second signal branch coupled to the decoder or a second node in a signal path behind the decoder. The first signal branch includes a first estimating component for deriving a first estimate for the signal quality that is to be utilized in a link adaptation scheme relating to at least one of adaptive coding and adaptive modulation. The second signal branch is configured to transmit a control signal which is Indicative of the signal quality and controls the link adaptation scheme.  
         [0026]     The receivers discussed above may be included in a mobile terminal like a UE. Alternatively or additionally, the receivers may be incorporated in a non-mobile device like a BS.  
         [0027]     According to still a further aspect, the invention is directed to a wireless communications system including a transmitter, a receiver and an adaptable communications link between the transmitter and the receiver. The system comprises on a receiver side a demodulator for demodulating the transmitted signal, at least one processing component for further processing the demodulated signal, and a decoder for decoding the further processed signal. The system further comprises a first control loop stretching between the transmitter and the receiver, the first control loop including a first node arranged between the demodulator and the at least one processing component and further including a first estimating component for deriving a first estimate for the signal quality that is to be utilized in a link adaptation scheme. The estimating component may be part of the transmitter or of the receiver. The system further comprises a control branch including at least one of the processing component, the decoder and a second node between the processing component and the decoder. The control branch is configured to transmit a first control signal. The first control signal is indicative of the signal quality and controls the link adaptation scheme.  
         [0028]     A second control loop can be provided that includes the decoder or a third node arranged in a signal path after the decoder. The second control loop may additionally comprise an assessment unit for generating a second control signal for controlling the link adaptation scheme or for triggering re-transmission. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     In the following the invention will be described with reference to exemplary embodiments illustrated in the figures, in which:  
         [0030]      FIG. 1  is a schematic block diagram of a WCDMA wireless communications system;  
         [0031]      FIG. 2  is a schematic block diagram of a prior art link adaptation mechanism based on power control;  
         [0032]      FIG. 3  is a first embodiment of the invention of a link adaptation mechanism based on power control;  
         [0033]      FIG. 4  is a second embodiment of the invention of a link adaptation mechanism based on power control;  
         [0034]      FIG. 5  is a third embodiment of the invention of a link adaptation mechanism based on power control;  
         [0035]      FIG. 6  is a schematic block diagram of a prior art link adaptation mechanism based on adaptive coding and modulation;  
         [0036]      FIG. 7  is a schematic block diagram of a fourth embodiment of the invention based on adaptive coding and modulation; and  
         [0037]      FIG. 8  is a schematic block diagram of a fifth embodiment of the invention based on adaptive coding and modulation. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0038]     In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular embodiments, circuits, signal formats etc. in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In particular, while the different embodiments are described herein below incorporated in a WCDMA system, the present invention is not limited to such an implementation, but for example can be utilized in any transmission environment that requires link adaptation. Moreover, those skilled in the art will appreciate that the functions explained herein below may be implemented using individual hardware circuitry, using software functioning in conjunction with a programmed microprocessor or general purpose computer, using an application specific integrated circuit (ASIC), and/or using one or more digital signal processors (DSPs).  
         [0039]     In  FIG. 1 a  wireless communications system  10  according to the WCDMA standard in which the invention can be practiced is shown. As has been mentioned before, the system  10  includes an RNC  12 , a BS  14 , a first UE communicating with the BS  14  on DCH and a second UE  18  receiving information from the BS  14  on HS-DSCH.  
         [0040]     In  FIG. 3 a  schematic block diagram of a UE receiver  20  according to a first embodiment of the invention as implemented in the UE  16  depicted in  FIG. 1  is shown. The receiver  20  of  FIG. 3  is configured to communicate via an adaptable communications link  22  with a transmitter in the form of the BS  14  depicted in  FIG. 1 . In the present embodiment the adaptable communications link  22  is the power-controlled DCH.  
         [0041]     The receiver  20  of  FIG. 3  comprises a receiver path  24  with a demodulator  26  for demodulating a received signal, a processing component  28  for performing the processing operation of Rake combining, a further processing component  29  for performing interference cancellation, and a decoder  30  which additionally performs deinterleaving. It should be noted that interference cancellation need not necessarily be performed immediately after Rake combining. It could alternatively be performed after deinterleaving and prior to decoding.  
         [0042]     The receiver  20  further comprises three signal branches  30 ,  32 ,  34 . A first signal branch  30  is coupled to a node  40  between the demodulator  26  and the processing component  28 . The first signal branch  30  includes a first estimating component  42  that is configured to determine a first quality estimate like a first SIR related value (e.g. the SIR value, a parameter required to determine the SIR value or a parameter derived from the SIR value) on the basis of an output signal of the demodulator  26 . Alternatively, the first signal branch  30  could be coupled between the processing component  28  for Rake combining and the processing component  29  for interference cancellation.  
         [0043]     A second signal branch  32  is coupled to a second node  44  between the processing component  29  for interference cancellation and the decoder  30 . The second signal branch  32  includes a second estimating component  46  that determines a second quality estimate (e.g. a second SIR related value) on the basis of an output signal of the processing component  29 , i.e. on the basis of a demodulated signal that has been subjected to the advanced receiver techniques of Rake combining and interference cancellation.  
         [0044]     A third signal branch  34  is coupled to a third node  50  which is located in the receiver path  24  behind the decoder  30 . The third signal branch  34  includes a component  52  that evaluates a parameter which is indicative of the quality of the decoded signal. For example, the bit error rate (BER) or the frame error rate (FER) allow a reliable assessment of the signal quality. In the embodiment depicted in  FIG. 3 , a frame reliability indicator, namely the CRC check result obtained as a result of decoding a particular user data frame, is assessed to determine information relating to the quality of the decoded signal. To that end, the component  52  is configured as a CRC checker.  
         [0045]     The receiver  20  of  FIG. 3  further comprises two components  54 ,  56  that allow to implement and control the specific link adaptation mechanism of power control used in the first embodiment. More specifically, the receiver  20  includes a link adaptation unit  54  and a link adaptation controller  56 . The link adaptation unit  54  is located in both the first signal branch  30  and the second signal branch  32 . It may optionally also be included in the third signal branch  34 . The link adaptation controller  56  is included in the third signal branch  34  only.  
         [0046]     Both the link adaptation unit  54  and the link adaptation controller  56  are configured to communicate on uplink with the BS  14  or, via the BS  14 , with the RNC  12  shown in  FIG. 1 . As becomes apparent from  FIGS. 1 and 3 , the three signal, branches  30 ,  32 ,  34  are part of different control loops that stretch between the receiver  20  of the UE  16  on the one hand and at least one of the BS  14  and the RNC on the other hand and that include the adaptable communications link  22  on downlink as well as a plurality of control links  60  that will be discussed in more detail below.  
         [0047]     Now the link adaptation mechanism performed during operation of the receiver  20  depicted in  FIG. 3  will be explained.  
         [0048]     A signal received by the receiver  20  via the communications link  22  is demodulated by the demodulator  26 . Additionally, de-spreading in each Rake finger can be performed either in the demodulator  26  or in a subsequent processing component. The demodulated signal is input to both the processing component  28  included in the receiver path  24  and the first estimating component  42  included in the first signal branch  30 . Based on the demodulated input signal the first estimating component  42  derives a first signal quality estimate that is fed to the link adaptation unit  54 .  
         [0049]     The link adaptation unit  54  can implement various power control schemes. According to a first power control scheme, the adaptation unit  54  includes a mapping mechanism for mapping the first signal estimate received from the first estimating component  42  on a signal quality parameter that constitutes or can be translated into an adaptation signal in the form of a power control command. This power control command is then transmitted via one of the control links  60  on uplink to the BS. In accordance with the received adaptation signal the BS controls transmit power on the downlink communications link  22 . Thus, a fast power control loop may be established because the received signal is input into the first estimation component  42  with a comparatively low processing delay. However, since the first signal quality estimate has been generated by the first estimating component  42  on the basis of a received signal that has only slightly been processed, the first estimate of the signal quality (here a first SIR related value) is not very accurate.  
         [0050]     According to a second power control scheme that can be implemented by the link adaptation unit  54 , the first signal quality estimate in the form of the first SIR related value is compared with a target value received via one of the control links  60  and via the BS from the RNC. If the first SIR related value received from the first estimating unit  42  is higher than the target value, a power control command is generated that commands the BS to lower the transmit power on the communications link  22 . If the estimated first SIR related value is too low, an adaptation signal in the form of a power up command is sent to the BS.  
         [0051]     As has been mentioned above, the demodulated signal is not only input to the first estimating component  42  but simultaneously to the processing component  28  that performs Rake combination. The Rake combined signal is then subjected to interference cancellation. Interference cancellation constitutes an advanced receiver technique that allows to reduce the transmit power on the communications link  22  and thus enhances network capacity. Due to the complex mechanisms involved in interference cancellation, the processing component  29  is associated with a considerable processing delay.  
         [0052]     The output signal of the processing component  29  is fed to both the decoder  30  and the second estimating component  56  in the second signal branch  32 . The second estimating component  46  assesses the signal received from the processing component  29  and generates a second a signal quality estimate in the form of a second SIR related value. Since this assessment is performed on the basis of a signal that has been demodulated, Rake combined and subjected to interference cancellation, the accuracy of the second signal quality estimate is much higher than the accuracy of the first signal quality estimate generated by the first estimation component  42 . However, the second signal quality estimate is generated with a significantly higher processing delay.  
         [0053]     The second signal quality estimate is output by the second estimation component  46  and fed to the link adaptation unit  54 . In the link adaptation unit  54  the second signal quality estimate is used to adjust the mapping rule for the first signal quality estimate.  
         [0054]     If the link adaptation unit  54  implements the link adaptation scheme associated with a target value, the second estimate for the SIR related value received from the second estimating component  46  may be used to change the target value appropriately. For example in the case the second signal quality estimate (estimated second SIR related value) is higher than the first signal quality estimate (estimated first for the SIR related value), the link adaption unit  54  may control the link adaptation scheme such that the target value is lowered and vice versa.  
         [0055]     Thus, the output signal of the second estimating component  46  is used to control the link adaptation scheme implemented by the link adaptation unit  54 . It can be seen that the fast link adaptation loop includes a two-step signal quality estimation using a less accurate first signal quality estimate that is available with low processing delay and a more accurate second signal quality estimate that is obtained with a higher processing delay. In sum a fast and accurate signal quality estimation is achieved. It should be noted here that in principle the link adaptation unit  54  could also be moved from the receiver  20  to the base station  14  of  FIG. 1  without loosing the benefits provided by the invention.  
         [0056]     In addition to the fast link adaptation loop described above an outer power control loop is provided. The outer power control loop includes the third signal branch  34  with the CRC checker  52  and the link adaptation controller  56  and operates as follows. The CRC obtained as a result of decoding of a particular user data frame is checked by the CRC checker  52  and a corresponding check result is output as a frame quality indicator to the link adaptation controller  56 . The link adaptation controller  56  assesses the frame quality indicator and generates a control signal for controlling the link adaptation scheme. The link adaptation scheme might be controlled either directly, i.e. via a direct link between the link adaptation controller  56  and the link adaptation unit  54  (dashed line), or indirectly via the BS and the RNC. In the case of an indirect control the link adaptation controller  56  sends an adaptation control signal via one of the control links  60  and via the BS to the RNC and the RNC controls the link adaptation unit  54 , which may either be part of the receiver  20  or of the BS as has been mentioned above. In principle the link adaptation controller  56  may also be moved to the RNC or the BS.  
         [0057]     Depending on the outcome of the assessment that is performed within the link adaptation controller  56 , the link adaptation scheme is controlled. Should for example the CRC check result indicate that the transmission quality is changing, the mapping mechanism or the target value applied by the link adaptation unit  54  may be changed upon receipt of a corresponding control signal from the link adaptation controller  56 . The link adaptation controller  56  thus performs a similar task like the second estimating component  46 . However, while the task of the second estimating component  46  is based on a mere estimate of the signal quality, the task of the link adaptation controller  56  is based on a statistics of a plurality of “hard” CRC check results.  
         [0058]     While the control of the link adaptation scheme by the link adaptation controller  56  is thus more accurate than the corresponding control by the second estimating component  46 , the control by the second estimating component  46  is associated with a much lower processing delay. This is due to the fact that the second signal branch  32  including the second estimating component  46  taps the receiver path  24  prior to de-interleaving and decoding, whereas the third signal branch  34  including the link adaptation controller  56  taps the receiver path  24  after de-interleaving and decoding. By means of the second estimating unit  46  and the link adaptation controller  56  a two-step link adaptation scheme control is implemented.  
         [0059]     It should additionally be noted that the embodiment depicted in  FIG. 3  allows to get larger performance or link gain from the implementation of advanced receiver structures like interference cancellation components because by means of the second estimating component  46  the signal enhancements are modelled more accurately. Simultaneously, the first signal estimating component  42  allows a fast link adaptation that is not effected by the processing delay associated with interference cancellation. In  FIGS. 4 and 5 , two further embodiments of receivers  20  according to the present invention are depicted. Since the embodiments are to a large extent similar to the first embodiment discussed above, only the differences to the first embodiment will be explained in more detail.  
         [0060]     Referring to  FIG. 4  it can be seen that the first signal branch  30  including the first estimating component  42  has been attached to the node  44  between the processing component  29  and the decoder  30 . The second signal branch  32  has directly been attached to the decoder  30 . Thus, the first signal quality estimate, i.e. the first SIR related value, is derived from the received signal after interference cancellation and the second signal quality estimate is derived based on metrics obtained during decoding.  
         [0061]     In the third embodiment depicted in  FIG. 5  the link adaptation unit  54  is attached to the output of the decoder  30  via a fourth signal branch  59 . Thus, additional parameters for controlling the link adaptation scheme applied by the link adaptation unit  54  are provided.  
         [0062]     In  FIG. 7 a  fourth embodiment of a receiver  20  according to the invention is shown. This receiver  20  is part of the UE  18  which in  FIG. 1  is attached to the BS  14  on HS-DSCH.  
         [0063]     The fourth embodiment is based on the link adaptation mechanism of adaptive coding and modulation. As can be seen from  FIG. 7 , the receiver  20  includes in a receiver path  24  a demodulator  62  that additionally performs Rake combining, a processing component  64  performing interference cancellation, and a decoder  66  additionally performing de-interleaving. In a first signal branch  68  coupled to a node  70  between the decoder  68  and the processing component  64  an estimating component  72  for performing channel quality estimation is arranged. A second signal branch  74  is coupled to the decoder  66  and transmits a first control signal, that has been generated based on metrics information obtained during decoding, to the estimating component  72 . A third signal branch  76  is coupled to a third node  80  arranged in the receiver path  24  behind the decoder  66 . An assessment unit in the form of a CRC checker  82  is included in the third signal branch.  
         [0064]     Now the operation of the receiver  20  depicted in  FIG. 7  will be described in more detail.  
         [0065]     A signal received by the receiver  20  via the adaptable communications link  22  is subjected to demodulation and Rake combination in the demodulator  62  and to interference cancellation in the processing unit  64 . The estimating component  72  assesses the demodulated signal output by the processing component  64  and derives an estimate for the signal quality in the form of a channel quality parameter. This channel quality parameter is used in an uplink CQI signalling context to control the modulation scheme or data rate used on the communications link  22  (fast control loop). The operations performed by the estimating component  72  can be similar to the mapping mechanism or the comparison of an estimate of an SIR related value with a target value as explained above with reference to the receiver structure of the first embodiment.  
         [0066]     A control signal in the form of metrics information obtained during decoding is fed via the second signal branch  74  to the estimating component  72  to control the channel quality estimation performed by the estimating component  72  and to thus control the link adaptation scheme.  
         [0067]     As can be gathered from  FIG. 7 , an outer control loop including the third signal branch  76  and the CRC checker  82  is additionally provided. The CRC checker  82  is configured to trigger re-transmission of a particular frame in the case the CRC check for this frame has failed.  
         [0068]     In  FIG. 8 a  fifth embodiment of a receiver  20  according to the invention is shown. The fifth embodiment is similar to the fourth embodiment described above with reference to  FIG. 7 .  
         [0069]     Again, the first signal branch  68  including the estimating component  72  is coupled between the demodulator  90  (which in the fifth embodiment is integral with the processing component for performing interference cancellation) and the decoder  66 . A second signal branch  92  is coupled from the node  80  behind the decoder  66  via the CR checker  82  to the estimating component. A control signal in the form of the CRC check result may thus be input via the second signal branch  92  to the estimating component  72  controlling the link adaptation scheme, i.e. the modulation and code rate settings, by adjusting the parameters used during channel quality estimation.  
         [0070]     While the present invention has been described with respect to particular embodiments, those skilled in the art will recognize that the present invention is not limited to the specific embodiments described and illustrated herein. Therefore, while the present invention has been described in relation to its preferred embodiments, it is to be understood that this disclosure is only illustrative. Accordingly, it is intended that the invention be limited only by the scope of the claims appended hereto.