Patent Publication Number: US-8976840-B2

Title: Radio receiver for detecting an additive white Gaussian noise channel

Description:
RELATED APPLICATION 
     This application claims priority to European Application No. 13170134.4, filed 31 May 2013, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Embodiments disclosed herein relate to a radio receiver and a method therein. In particular, embodiments disclosed herein relate to detecting an Additive White Gaussian Noise, AWGN, channel. 
     BACKGROUND 
     Communication devices, such as wireless devices, are enabled to communicate wirelessly in a radio communications system, sometimes also referred to as a radio communications network, a mobile communication system, a wireless communications network, a wireless communication system, a cellular radio system, or a cellular system. The communication may be performed via a radio channel, e.g., between two wireless devices, between a wireless device and a regular telephone, and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network. 
     A cellular radio system covers a geographical area which is divided into cell areas, wherein each cell area is served by a network node such as a Base Station (BS), e.g., a Radio Base Station (RBS), which sometimes may be referred to as, e.g., eNB, eNodeB, NodeB, or BTS (Base Transceiver Station), depending on the technology and terminology used. A cell is the geographical area where radio coverage is provided by the base station at a base station site. 
     Wireless devices are also known as, e.g., user equipments, mobile terminals, wireless terminals and/or mobile stations, mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data with another entity. 
     Code Division Multiple Access (CDMA) is a radio channel access method used by various radio communication technologies, such as, for example, Wideband Code Division Multiple Access (WCDMA). WCDMA is a mobile phone standard used in various mobile phone systems, such as for example the Universal Mobile Telecommunications System (UMTS). 
     Wireless devices require a lot of processing power. For example, these devices make use of energy consuming receivers such as, e.g., a computational-intensive rake receiver. A rake receiver is a receiver designed to counter the effects of multipath propagation, such as multipath fading. It does this by using several “sub-receivers” called fingers. The fingers are correlators, each of which is assigned to a different multipath component. Each finger independently decodes a single multipath component. At a later stage, the contribution of all fingers is combined in order to make the most use of the different transmission characteristics of each transmission path. 
     The multipath channel through which a radio wave transmits can be viewed as transmitting the original, i.e., line of sight, wave pulse through a number of multipath components. Multipath components are delayed copies of the original transmitted wave traveling through a different echo path, each with a different magnitude and time-of-arrival at the receiver. Since each component contains the original information, if the magnitude and time-of-arrival (phase) of each component is computed at the receiver, through a process called channel estimation, then all the components can be added coherently to improve the information reliability. 
     Moreover, wireless devices may use sophisticated Forward Error Correction (FEC) decoders, like turbo decoders, which also consume a lot of energy. A turbo decoder decodes the output signal from the rake receiver. The turbo decoder is constructed from two decoders: an interleaver and a deinterleaver. The turbo decoding algorithm may run multiple times on the same data to improve the output of the turbo decoder. A turbo decoder has a better performance than a conventional decoder due to this iterative algorithm. However, the power consumption also increases as the number of iterations increases. 
     To achieve an acceptable usage time before the battery is empty, an energy-efficient architecture is a vital requirement. Low power hardware is a first requirement to achieve an energy efficient architecture. Additionally, optimal control of this low power hardware is needed to save energy consumption. Furthermore, an adequate quality of a wireless link between the wireless device and a second radio node, such as a base station, is desired. This is not trivial due to the changing conditions of the external environment. 
     SUMMARY 
     An object of embodiments herein is to provide a way of improving the performance of a radio receiver. 
     According to a first aspect of embodiments herein, the object is achieved by a method in a radio receiver for detecting an Additive White Gaussian Noise, AWGN, channel. The radio receiver comprises a rake receiver. The method comprises the radio receiver receiving signals transmitted via a propagation channel from a transmitter and measuring a power profile of the propagation channel based on the received signals. The method further comprises calculating a plurality of normalized power templates of an AWGN channel based on rake finger positions within the rake receiver, wherein each of the normalized power templates corresponds to a different predetermined sampling timing shift. For each of the normalized power templates, the method further comprises calculating a metric relating to a difference between a normalized measured power profile of the propagation channel and the corresponding normalized power template. The method further comprises determining a minimum value of the calculated metrics, filtering the minimum value of the calculated metrics, and determining that the propagation channel comprises an AWGN channel when the filtered minimum value of the calculated metrics is lower than a threshold value. 
     According to a second aspect of embodiments herein, the object is achieved by a radio receiver for detecting an Additive White Gaussian Noise, AWGN, channel. The radio receiver comprises a rake receiver, a calculation circuit, and a determining circuit. The calculation circuit is configured to measure a power profile of the propagation channel based on the received signals, and calculate a plurality of normalized power templates of an AWGN channel based on rake finger positions within the rake receiver, wherein each of the normalized power templates corresponds to a different predetermined sampling timing shift. For each of the normalized power templates, the calculation circuit calculates a metric relating to a difference between a normalized measured power profile of the propagation channel and the corresponding normalized power template. The calculation circuit is further configured to determine a minimum value of the calculated metrics and filter the minimum value of the calculated metrics. The determining circuit is configured to determine that a propagation channel comprises an AWGN channel when the filtered version of the minimum value of the calculated metrics is lower than a threshold value. 
     According to another aspect of embodiments herein, the object is achieved by a method in a radio receiver comprising a rake receiver for determining whether a propagation channel through which signals are received comprises an AWGN channel. The method comprises receiving signals via the propagation channel from a transmitter, and identifying a central rake finger position corresponding to a maximum signal strength of the received signals. The method further comprises measuring a power profile of the received signals using a first number of rake fingers centered on the identified central rake finger and normalizing the measured power profile. The method further comprises obtaining a normalized power template for a hypothetical signal received via an AWGN channel based on the same rake fingers and centered on the identified central rake finger, and obtaining an additional normalized template for each of a plurality of predetermined time shifts relative to the identified rake finger position based on the hypothetical signal as shifted by the corresponding predetermined time shift. For each of the normalized power templates, the method comprises determining a metric based on a difference between that normalized power template and the normalized measured power profile, and filtering a minimum value of the calculated metrics to determine a filtered metric. If the filtered metric is less than a threshold, the method comprises characterizing the propagation channel as an AWGN channel. 
     Because the radio receiver is able to determine that a propagation channel is an AWGN channel, the radio receiver is able to set itself in a mode dedicated to receive signals transmitted via AWGN channels. This ability makes it possible to reduce the number of rake fingers in the rake receiver, the number of turbo iterations in the turbo decoder, and/or the number of receiving antennas if more than one receiving antenna is used. It is also possible to correct for a sampling timing error, e.g., in an analog-to-digital converter. In this way the performance of the radio receiver is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of embodiments herein are described in more detail with reference to attached drawings in which: 
         FIG. 1  shows a schematic block diagram illustrating a first scenario of radio transmission between two radio nodes. 
         FIG. 2  shows a schematic block diagram illustrating a second scenario of radio transmission between two radio nodes. 
         FIG. 3  shows a schematic block diagram illustrating details in embodiments of a radio receiver. 
         FIG. 4  shows a flowchart depicting embodiments of a method in a radio receiver. 
     
    
    
     DETAILED DESCRIPTION 
     As part of developing embodiments herein, a problem will first be identified and discussed below. 
     Power consumption is one of the most important key performance indicators for wireless device differentiation. For equipment intended for use with CDMA the key factors affecting the power consumption is the number of rake fingers used for dispreading and combining in the rake receiver and the number of iterations in the turbo decoder. 
     According to prior art EP1719258 B1 the number of rake fingers may be reduced according to information in a Root-Mean-Square (RMS) delay spread. I.e., if the fading path has a low dispersion, the number of rake fingers may be reduced. However, the reduction of the number of rake fingers or turbo iterations in the turbo decoder degrades the receiver performance, e.g., by a lower downlink data throughput. Prior art EP1314254 B1 presents a method to dynamically terminate the number of iterations in a turbo decoder. However, the number of rake fingers may not be reduced and the dynamic termination requires additional calculations after each iteration. Therefore it is important to be able to reduce the number of rake fingers and/or iterations in the turbo decoder without any performance loss. 
     Embodiments herein address the problem of lowering the power consumption in a radio receiver without degrading the performance of the radio receiver. 
     According to embodiments herein, the objective is achieved by determining that a propagation channel, i.e., the path between a transmitter and a receiver, is an Additive White Gaussian Noise (AWGN) channel. An AWGN channel is a model channel in which the only impairment to communication is a linear addition of wideband or white noise with a constant spectral density and a Gaussian distribution of amplitude. The model does not account for multipath transmission. A propagation channel seen by a motionless radio receiver connected to a small cell may, for example, often be treated as an AWGN channel. Today, as more and more small cells are deployed, more and more of the radio channels in the small cells may be treated as AWGN channels. By determining that the channel carrying the received signals, i.e., the propagation channel, is an AWGN channel, both the number of iterations, for example the maximum number of iterations, in the turbo decoder and the number of rake fingers may be reduced without any performance loss. In addition, if the receiver has two or more receiving antennas, used for receiver diversity or spatial multiplexing, only the necessary antennas may be activated. This leads to a large reduction of the power consumption in the radio receiver without any performance degradation. 
     Further advantages of embodiments herein are that the radio receiver may correct for a sampling timing error and that the determination of an AWGN channel requires a low computational complexity, i.e., a low number of Million Instructions Per Second (MIPS) is required. 
       FIG. 1  depicts a first scenario of radio transmission between a radio transmitter  110  and a radio receiver  120  according to embodiments herein. The radio receiver  120  may be comprised in a radio node  121 . The radio node may for example be one of the wireless device types mentioned above. The radio transmitter  110  communicates with the radio receiver  120  by transmitting coded data, e.g. by utilizing CDMA-based technology. In a first scenario many copies of the coded data transmitted from the radio transmitter  110  may arrive at the radio receiver  120  due to for example reflections from obstacles, such as a building  130  and/or a mountain  140 . These copies may have different amplitudes, phases and delays due to the different transmission paths. In  FIG. 1  the propagation channel is determined not to be an AWGN channel due to the multiple copies of the transmitted coded data. 
       FIG. 2  depicts a second scenario of radio transmission between the radio transmitter  110  and the radio receiver  120  according to embodiments herein. Here there is only one transmission path for the transmitted coded data and hence only one copy of the transmitted data arrives at the radio transmitter  110 . The propagation channel is determined to be an AWGN channel in  FIG. 2 . 
       FIG. 3  depicts the radio receiver  120  in the radio node  121  in more detail according to embodiments herein. As mentioned above the radio receiver  120  may comprise more than one receiving antenna. For simplicity, embodiments herein are described having two antennas, but the concept is valid also for more than two antennas. Thus, the radio receiver  120  may comprise a first receiving antenna  311  and a second receiving antenna  312 . The radio receiver  120  further comprises an A/D converter  330 , a rake receiver  340 , and a turbo decoder  350 . Before coded data is decoded, the data may be converted from analogue to digital domain in the A/D converter  330 . In order to increase a signal-to-noise ratio, the radio receiver  120  comprises the rake receiver  340 . The rake receiver  340  has multiple rake fingers  341 ,  342  to correlate the received coded data from different transmission paths. The rake receiver  340  then combines the results of the different transmission paths to construct one output signal from the rake receiver  340 . The output signal from the rake receiver  340  is then decoded in the turbo decoder  350 . 
     Examples of embodiments of a method in the radio receiver  120  for detecting an AWGN channel will now be described with reference to a schematic flowchart depicted in  FIG. 4 . The method comprises the following actions, which actions may be taken in any suitable order. Dashed lines of some boxes in  FIG. 4  indicate that this action is not mandatory. 
     As mentioned above, the radio receiver  120  comprises the rake receiver  340  depicted in  FIG. 3 . The rake receiver  340  comprises multiple rake fingers  341 ,  342  to correlate the received coded data from different transmission paths. 
     Action  401   
     The radio receiver  120 , which may be comprised in the radio node  121 , receives signals transmitted via a propagation channel from the radio transmitter  110 . The signals received via the propagation channel are demodulated and then sampled in the A/D converter  330  before being sent into the rake receiver  340 . In the rake receiver  340 , the magnitude and time-of-arrival of each component of the propagation channel signals are computed through channel estimation. The information obtained from the channel estimation will be used in the coming actions to determine whether a channel is an AWGN channel. 
     Action  402   
     The radio receiver  120  may estimate the velocity and the path dispersion of the propagation channel in order to narrow down the number of channels that may be considered to be an AWGN channel. In this way, computation time and power consumption is kept low. The propagation channels with a low velocity and low path dispersion may be considered as candidates for an AWGN channel. 
     Action  403   
     In order for the radio receiver  120  to be able to determine that the propagation channel carrying the received signals is an AWGN channel the radio receiver  120  may first obtain a metric, M, relating to a difference between the power profile of the sampled propagation channel and the power profile of an AWGN model. More specifically, the metric for a specific sampling timing shift relates to a difference between a normalized measured power profile of the propagation channel and a normalized power template determined for the sampling timing shift. The normalized power template describes the normalized power profile of an AWGN channel model for that sampling timing shift. 
     The metric may be obtained according to the sub-actions  403   a - 403   e  below, which may be performed in any suitable order. 
     Action  403   a    
     In action  403   a  the radio receiver  120  obtains the normalized power templates for each of N sampling timing shift mentioned above in action  403 . The normalized power template comprises a Raised Cosine filter (RC). The filter coefficients (i, f) are pre-calculated, e.g., according to: 
               RC   ⁡     (     i   ,   f     )       =         sin   ⁢       π   ⁡     (       t   f     +     τ   i       )         T   c             π   ⁡     (       t   f     +     τ   i       )         T   c         ⁢       cos   ⁢       α   ⁢           ⁢     π   ⁡     (       t   f     +     τ   i       )           T   c           1   -       (       απ   ⁡     (       t   f     +     τ   i       )         T   c       )     2                         i   =   1     ,   …   ⁢           ,     N   ;     f   =   1       ,   …   ⁢           ,   F         
where i represents the index of sampling timing shift, when matching the raised cosine filter coefficient to the measured power profile, f represents the rake finger  341 ,  342  position within the rake receiver  340 , F represents the number of rake fingers, N represents the number of sampling timing shifts, τ i  represents the sampling timing shift when matching the RC filter coefficient to the measured power profile, t f  corresponds to the sampling time at the rake finger  341 ,  342  position, f, T c  represents the chip spacing, and α represents the roll-off factor. For example, the number of rake fingers  341 ,  342 , F, may be set to 5 and t f  may be set to −T c , −½T c , 0, ½T c , and T c . Further, N may be set to 7, and τ i  may be set to −⅜T c , − 2/8T c , −⅛T c , 0, ⅛T c , 2/8T c , and ⅜T c , and α=0.22. The raised cosine filter coefficients are normalized using the L2 norm.
 
     The normalized power templates will be used to perform matching with the normalized measured power profile of the propagation channel. For each sampling timing shift τ i  (where i=1, . . . , N), a matching will be performed. Thus, the matching with the normalized measured power profile will be performed N times. It will be appreciated that the values of the sampling timing shifts are predetermined. Different sampling timing shifts are introduced in the matching procedure to find the sampling timing error for the best matching template, as described in further detail in the following actions. 
     Action  403   b    
     In action  403   b  the radio receiver  120  obtains the normalized measured power profile of the propagation channel mentioned above in action  403 . 
     The radio receiver  120  obtains F normalized measured power profiles, P(f), for the same rake finger  341 ,  342  positions f as the normalized power template above. The normalized measured power profiles are obtained by taking the square of the absolute value of the measured channel estimates, h ch (f), and normalizing it with the L2 norm, e.g., according to: 
     
       
         
           
             
               
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     The channel estimates are calculated from the received despread propagation channel symbols. For example, the estimation may be done based on the received pilot symbols transmitted on a standard defined channel used for the channel estimation, such as for example a Common Pilot Channel (CPICH) and/or a Common Packet Channel (CPCH) in WCDMA. 
     In the case of the above example, the radio receiver  120  calculates P(f) from the finger positions c−T c , c−½T c , c, c+½T c , and c+T c , where c corresponds to the maximum peak position of a monitored path delay. When performing the matching, c may be set to zero. 
     Action  403   c    
     In this action the radio receiver  120  obtains the metric for each of the i=1, . . . , N sampling timing shifts. The radio receiver  120  may obtain the metric for the i th  sampling timing shift by taking the square root of the sum of the absolute square of the differences of the normalized measured power profile and the normalized power template calculated for the i th  sampling timing shift according to: 
                 M   ⁡     (   i   )       =         ∑     f   =   1     F     ⁢              P   ⁡     (   f   )       -   bias   -     RC   ⁡     (     i   ,   f     )              2           ,         
for each i=1 . . . N,
 
where the summation is performed for the different rake finger  341 ,  342  positions, and where bias represents a finite noise floor power. For each sampling timing shift index i ranging from 1 to the number N of sampling timing shift values, a value M(i) is calculated. That is, the matching of the RC filter coefficient to the measured power profile is performed N times.
 
     The metric may be corrected for the finite noise floor power, bias, by subtracting the value of the noise floor power from the normalized measured power profile. The value of the noise floor power depends on a signal to noise ratio. For example, with a high signal-to-noise ratio, bias may be set to 0. With a low signal-to-noise ratio, the radio receiver  120  needs to set bias to a small value to remove noise in the power estimation. 
     Action  403   d    
     Among the N values of M(i), the radio receiver  120  obtains the value of the minimum metric, M min , and the sampling timing shift index, i min , corresponding to the minimum metric. Thus, when the sampling timing shift is τ i     min   , the matching of the RC filter coefficient to the measured power profile achieves the minimum difference M min =M(i min ). The best matching filter coefficients of the template are represented by R(i min ,f). 
     Action  403   e    
     The minimum value of the metric is unstable over time and may need to be filtered in order to stabilize such that the radio receiver  120  is able to make a determination as to whether the received channel is an AWGN channel. Thus, the radio receiver  120  may filter the minimum value of the metric, M min , according to M filtered =λ 1 (M min −M filt )+M filt , wherein M filtered  represents the filtered version of the minimum value of the metric, M filt  represents a value used for filtering the minimum value of the metric, and λ 1  represents the filter coefficient to stabilize the metric. 
     Action  404   
     The radio receiver  120  determines that the propagation channel is an AWGN channel when the filtered version of the minimum value of the metric M filtered  is lower than a threshold value, e.g. 0.05. In other words, the propagation channel is considered to be a model AWGN channel when the difference between the power profile of the sampled propagation channel and the matched power profile of the AWGN model is sufficiently small. By determining that a propagation channel is an AWGN channel the radio receiver  120  is able to set itself in a mode dedicated to receiving signals transmitted on AWGN channels. Such a mode may lead to a reduction of the power consumption due to, for example, a lower complexity of the detection. 
     Action  405   
     When the propagation channel has been determined to be an AWGN channel, the radio receiver  120  may set itself in a mode dedicated to receiving signals transmitted on AWGN channels. 
     As mentioned above, the radio receiver  120  may further comprise the turbo decoder  350 . In such a case the radio receiver  120  may reduce the number of decoding iterations, such as the maximum number of decoding iterations, in the turbo decoder  350  as a consequence of setting itself in a mode dedicated to receiving signals transmitted on AWGN channels. 
     In some embodiments, the radio receiver  120  further comprises the first receiving antenna  311  and the second receiving antenna  312 . This action of setting the radio receiver  120  in a mode dedicated to receiving signals transmitted on AWGN channels may then comprise turning off one of the first receiving antenna  311  and the second receiving antenna  312 . 
     It will further be appreciated that other elements of the receiver, e.g., one or more rake fingers  341 ,  342 , may be switched off to reduce power consumption when the radio receiver  120  is set in the mode dedicated to receiving signals transmitted on AWGN channels. 
     Action  406   
     In order to be able to correct for a sampling timing error in the A/D converter  330 , the radio receiver  120  may determine a value of the sampling timing error in the rake receiver  340  when the propagation channel has been determined to be an AWGN channel. The value of the sampling timing error corresponds to a filtered-sampling timing shift index, i filtered , of the minimum value of the metric:
 
 i   min =arg min  M  ( i )
 
 i   filtered =λ 2 ( i   min   −i   filt ) +i   filt  
 
where λ 2 , represents a filter coefficient to stabilize the minimum sampling timing shift index, i min , and i filt  represents a value used for filtering the minimum sampling timing shift index. The filtered sampling timing shift, which may be represented by τ i     filtered   , is determined to be the sampling timing error in the A/D converter  330 .
 
     Action  407   
     When the value of the filtered sampling timing shift τ i     filtered    is non-zero, the radio receiver  120  may correct the sampling timing of the A/D converter  330  according to the determined sampling timing error. In this way, the radio receiver  120  may align the single propagation channel path with the A/D sampling. The more aligned the propagation channel path is to the sampling of the A/D converter  330 , the fewer rake fingers  341 ,  342  are needed for equalization, which translates into a lower current consumption of the radio receiver  120 . 
     To perform the method actions for detecting an AWGN channel in the radio receiver  120  described above in relation to  FIG. 4 , the radio receiver  120  comprises the arrangement depicted in  FIG. 3 . As mentioned above the radio receiver  120 , which comprises a rake receiver  340 , may be comprised in the radio node  121 . 
     The radio receiver  120  further comprises a determining circuit  360  configured to determine that the propagation channel carrying signals transmitted by a transmitter and received at the radio receiver  120  is an AWGN channel when a filtered version of a minimum value of the metrics is lower than a threshold value. Each of the N metrics relates to a difference between a normalized measured power profile of the propagation channel and the corresponding normalized power template. Each of the N normalized power templates is dependent on a different one of N predetermined sampling timing shifts and on rake finger  341 ,  342  positions within the rake receiver  340 , where each metric is calculated for a different one of the predetermined sampling timing shifts. 
     In some embodiments, each normalized power template comprises a raised cosine filter. The filter coefficients for the i th  sampling timing shift are dependent on the i th  predetermined sampling timing shift when matching the raised cosine filter coefficient to the measured power profile, and on the rake finger  341 ,  342  positions within the rake receiver  340 . 
     In some embodiments, the determining circuit  360  further is configured to determine a value of the sampling timing error in the rake receiver  340  corresponding to a sampling timing shift index of the filtered version of the minimum value of the metric when the propagation channel has been determined to be an AWGN channel. 
     The radio receiver  120  may further comprise a calculation circuit  365  configured to calculate the normalized measured power profile for the same rake finger  341 ,  342  positions as used to calculate the normalized power templates by taking the square of the absolute value of the measured channel estimation, which channel estimation is calculated from the despread propagation channel symbols. 
     In some embodiments, the calculation circuit  365  is further configured to calculate the metric, for each of the normalized power templates, by taking the square root of the sum of the absolute square of the differences of the normalized measured power profile and the corresponding calculated normalized power template, where the summation is performed for the different rake finger  341 ,  342  positions for the corresponding sampling timing shift index. 
     The calculation circuit  365  may further be configured to correct the metric for a finite noise floor power by subtracting the value of the noise floor power from the normalized measured power profile. 
     In some embodiments, the calculation circuit  365  is further configured to filter the minimum value of the metric, M min , according to M filtered =λ 1 (M min −M filt )+M filt , where M filtered  represents the filtered version of the minimum value of the metric, M filt  represents a value used for filtering the minimum value of the metric, and λ 1  represents the filter coefficient to stabilize the metric. 
     The radio receiver  120  may further comprise a setting circuit  370  configured to set the radio receiver  120  in a mode dedicated to receive signals transmitted on AWGN channels when the propagation channel has been determined to be an AWGN channel. 
     In some embodiments the radio receiver  120  further comprises the turbo decoder  350  that decodes the output signal from the rake receiver  340 . The setting circuit  370  may be configured to reduce the number of decoding iterations in the turbo decoder  350  when the propagation channel has been determined to be an AWGN channel. 
     In some other embodiments, the radio receiver  120  further comprises a first receiving antenna  311  and a second receiving antenna  312 . The first and second receiving antennas  311 ,  312  may be used for receiver diversity or spatial multiplexing in order to increase the bitrate and/or coverage. The setting circuit  370  may be configured to turn off one of the first receiving antenna  311  and second receiving antenna  312  when the propagation channel has been determined to be an AWGN channel. 
     In order to correct for the sampling timing error in the A/D converter  330 , the radio receiver  120  may further comprise a correcting circuit  380  configured to correct the sampling timing error of the A/D converter  330  comprised in the radio receiver  120  according to the predetermined sampling timing shift when the value of the predetermined sampling timing shift is non-zero. 
     The embodiments herein for detecting an AWGN channel may be implemented through one or more processors, such as a processor  390  in the radio receiver  120  depicted in  FIG. 3 , together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the in the radio receiver  120 . One such carrier may be in the form of a solid-state memory, such as a flash memory or a Read-Only Memory (ROM). The computer program code may furthermore be provided as pure program code on a server and downloaded to the radio receiver  120 . 
     The radio receiver  120  may further comprise a memory  395  comprising one or more memory units. The memory  395  is arranged to store information about, for example, the parameters and measurements used in the calculation of the metric and the predetermined sampling timing shifts used to correct the sampling timing error. The memory  395  may also store configurations and applications to perform the methods herein when being executed in the radio receiver  120 . 
     Those skilled in the art will also appreciate that the determining circuit  360 , setting circuit  370 , and correcting circuit  380  described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in a memory, that when executed by the one or more processors, such as the processor  390 , perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single application-specific integrated circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC). 
     When using the word “comprise” or “comprising” it shall be interpreted as non-limiting, i.e. meaning “consist at least of”. 
     The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.