Patent Publication Number: US-2022217714-A1

Title: Method and Device for Detecting Discontinuous Transmission (DTX) Assisted by Noise Estimation

Description:
FIELD OF THE INVENTION 
     The invention relates to a method and device for detecting Discontinuous Transmission (DTX) assisted by noise estimation. The invention relates particularly, but not exclusively, to an improved method and device for determining that a signal received on an uplink (UL) at an Uplink Control information (UCI) receiver in a wireless communications system comprises a linear block encoded signal. The invention also relates to a method and device for improved detection of DTX on a UL at a UCI receiver particularly for small block encoded signals. 
     BACKGROUND OF THE INVENTION 
     In long-term evolution (LTE) communications systems, in a downlink (DL), a data payload is carried by transport blocks which are encoded into codewords which are sent over a DL physical data channel called the Physical Downlink Shared Channel (PDSCH). The scheduling information of the PDSCH codeword(s), including its resource allocation in the subframe and its modulation and coding scheme, is included in the physical control channel, called the Physical Downlink Control Channel (PDCCH). Generally, the receiving user equipment (UE) decodes the messages in PDCCH and, where it finds that a PDSCH has been assigned to it, it decodes the PDSCH codeword(s) according to the scheduling information decoded from the PDCCH. In other words, correctly decoding PDCCH is a prerequisite for properly decoding PDSCH. 
     In order to prevent the loss of transport blocks, LTE has adopted the Hybrid Automatic Repeat Request (HARQ) scheme. In the physical layer of Evolved UMTS Terrestrial Radio Access Network (E-UTRA), HARQ is implemented both in the UL and the DL. The acknowledgement message in E-UTRA is denoted as HARQ-ACK. 
     HARQ-ACK may be transmitted by the UE in response to certain PDSCH transmissions and includes one or several acknowledgements, either positive (ACK) or negative (NACK) in response to transport blocks transmitted in the DL. HARQ-ACK may be transmitted on one of the physical channels Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH). 
     But if the UE is not able to correctly decode the PDCCH, it cannot correctly decode the PDSCH, and may even not know that it needs to send the HARQ feedback. This is called Discontinuous Transmission (DTX). 
     If the eNodeB (base station (BS)) detects ACK instead of DTX, a so called ACK false detection, the eNodeB will erroneously consider the corresponding DL transport block as correctly received. Since the transport block has not been correctly received by the UE, corresponding data will not be passed to the Medium Access Control (MAC) layer and from the MAC layer to the Radio Link Control (RLC) layer. Data will hence be missing in the RLC layer. This will cause ARQ retransmissions in the RLC layer which introduce delay and possibly large retransmissions which is very undesirable. Also, if a NACK is detected erroneously that in reality is DTX, the eNodeB will retransmit the packet in such a way that the UE will not be capable of decoding it. 
     As already indicated, a problem arises when the UE is not aware of the presence of the PDSCH assigned to it if it fails to decode the PDCCH successfully. In this case the UE will not generate ACK/NACK information. This situation has been well recognized and the UE response in such case is DTX, that is, neither an ACK nor a NACK signal is transmitted to the eNodeB. Since the eNodeB has no prior knowledge of whether the UE has failed to detect the PDCCH, it expects or deems, that the symbols of the predetermined positions are ACK/NACK symbols and extracts them for the ACK/NACK decoder to decode. If the eNodeB disregards the possibility of DTX, either an ACK or NACK message will be returned by the ACK/NACK decoder to a higher layer upon the decoding of the extracted symbols, which are, in fact. conveying no information. In general, both ACK and NACK messages are equally likely to be returned. 
     The consequence of wrongly detecting a DTX as an ACK is more adverse to the system performance than wrongly detecting a DTX into a NACK. 
     Similarly, in 5G (or new radio (NR)) wireless communication systems, a message feedback scheme is also used for re-transmission control. ACK or NACK (AN) signals are used to indicate whether the signal is received successfully or not by the UE and whether the BS needs to retransmit the data. If the UE misses a DL control signal, the UE may encounter DTX in DL and the UE will not send any message back to the BS. However, the BS needs to detect one of three possible feedback states, i.e. ACK, NACK or DTX, for rearranging a next transmission to the UE. 
       FIG. 1  illustrates a method by which UL signals from the UE to the BS control transmission of payload control data and payload data on the DL from the BS to the UE. In the example of  FIG. 1 , it can be seen that, in response to a first “DL control for payload allocation #1” message from the BS to the UE, the UE, in this instance, responds with a UCI “NACK” message. The NACK message is received by the UCI receiver at the BS and, as a consequence, the BS is configured to retransmit to the UE the first “DL control for payload allocation #1” message and its associated first “DL payload data #1” message. In this example, the UE then returns a UCI “ACK” message to the UCI receiver in response to the retransmitted control signal message and, as a consequence, the BS is configured to then transmit to the UE the second “DL control for payload allocation #2” message and its associated second “DL payload data #2” message (not shown in  FIG. 1 ).  FIG. 1  therefore illustrates how data is retransmitted by the BS to the UE when the UE indicates that is has not successfully received a DL data control message. 
     In contrast,  FIG. 2  illustrates what may happen when the UE misses a DL data control message. In this example, the UE has missed the first “DL control for payload allocation #1” message and consequently sends no ACK/NACK message back to the BS in response. This scenario represents a DTX state. The UCI receiver at the BS only receives noise but processes this as though it comprises a UL UCI signal with the result that, in this example, the UCI falsely detects or determines receipt of an ACK message from the UE and thus outputs a false ACK message. This causes the BS to commence a new control and payload data transmission in response to the false ACK message, e.g. “DL control for payload allocation #2”, etc. 
     For 5G UCI, 3GPP Technical Specification 38.212 requires the support of two types of channel codes, namely polar code and small block code as illustrated respectively by  FIGS. 3 and 4 . Polar code relates to the situation where the number of payload bits is greater than 11. Small block code relates to the situation where the number of payload bits is equal to or less than 11. 
     As shown in  FIG. 3 , in a conventional polar code-based receiver, a cyclic redundancy check (CRC) may assist in detecting whether or not DTX occurs. The output from the polar code decoder comprises UCI bits but the CRC check function (module) enables the polar code-based receiver to distinguish between DTX on the one hand and UCI bits indicative of ACK or NACK on the other hand. 
     In  FIG. 4  which shows a conventional small block code-based receiver where a CRC function is not available, incorrect detection of the ACK, NACK, or DTX signals leads to a waste of resources for retransmission and/or a loss of data packets. In the conventional small block code-based receiver where CRC is not available, ACK and NACK each issue with about 50% probability where the UE misses a DL control message and transmits nothing to the UE such that the BS receives only noise. In the small block code-based receiver, the output from the small block code decoder are assumed to be UCI bits leading to possible false ACK or false NACK outcomes. In other word, there is no means for distinguishing between DTX on the one hand and UCI bits indicative of ACK or NACK on the other hand. 
     In the conventional small block code-based UCI receiver of  FIG. 4 , the resource element (RE) demapper output will be treated by an equalizer module to generate an equalized signal. The equalized signal will then be treated by a demodulation module to generate a demodulated soft bit sequence (SEQ). The demodulated soft bit SEQ will be handled by a descrambling module to create a descrambled soft bit SEQ. The descrambled soft bit SEQ will then be handled by a rate de-matching module to create a de-matched soft bit SEQ. The de-matched soft bit SEQ will be decoded through a decoder for small block code module to generate UCI bits (ACK/NACK). The soft bits comprise real signal values which differ from hard bits which are resolved to binary values. 
     As already explained with respect to  FIGS. 1 and 2 , if a UE loses a DL control signal, the UE will not send UCI ACK/NACK feedback, i.e. a DTX state will occur. The BS treats DTX as an unsuccessful DL transmission. Re-transmission is required if and when DTX occurs. But if the DTX is falsely detected as ACK, re-transmission will not be performed. 
     CN105262568 relates to ACK/NACK and DTX detection in a wireless communication system where the DTX status threshold is calculated based on the statistics of signal-to-noise ratio (SNR). However, it can be challenging to obtain accurate noise estimations. 
     CN102740316 relates to a method for detecting an uplink DTX state. The method comprises receiving data information from uplink user equipment of the current cell; calculating a confidence value corresponding to the data information, wherein the confidence value is used for reflecting the accuracy of data information decoding carried out by a receiving terminal; comparing the confidence value with a preset DTX judgment threshold; and determining whether the uplink user equipment is in the DTX state or not according to a comparative result. Here, the preset DTX judgment threshold must change for different channel conditions and thus determination of the DTX judgment threshold requires considerable computational effort. 
     U.S. Pat. No. 8,315,185 relates to ACK/NACK detection in an LTE wireless communication system. The ACK/NACK detector has a soft decoder and decision-maker. A threshold value is used to determine whether the transmitted signal from the UE contains an ACK/NACK transmission when the threshold value is met. If the threshold value is not met, the transmission is determined to be DTX. The threshold value is based on a power estimate of soft data bits. 
     U.S. Pat. No. 8,891,591 discloses a receiver circuit which includes an estimation unit configured to estimate a noise power of a transmission channel, a calculation unit configured to calculate a decision variable based on the noise power, and a decision unit configured to make a ternary decision based on the decision variable. 
     What is desired is a method of improving detection of DTX on a UL at a UCI receiver and/or a method of determining that a signal received on a UL at a UCI receiver comprises a linear block encoded signal. What is also desired is a method for detecting acknowledgment (ACK), negative acknowledgment (NACK) and discontinuous transmission (DTX) signals more accurately in wireless communication systems. 
     Objects of the Invention 
     An object of the invention is to mitigate or obviate to some degree one or more problems associated with known methods of determining that signals received on a UL at a UCI receiver comprise linear block encoded signals. 
     The above object is met by the combination of features of the main claims; the sub-claims disclose further advantageous embodiments of the invention. 
     Another object of the invention is to provide an improved method of detecting DTX on a UL at a UCI receiver especially for small block encoded signals. 
     Another object of the invention is to provide an improved UCI receiver and/or UCI decoder. 
     One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention. 
     SUMMARY OF THE INVENTION 
     The invention concerns a method for processing a signal received at an uplink control information (UCI) receiver in a wireless communication system. The method comprises processing a signal received on an uplink (UL) at said UCI receiver to transform said received signal into a likelihood calculation of possible transmitted codewords (θ 1  . . . θi . . . θ N ) and determining a maximum magnitude θ max  value from said likelihood calculation. The method includes comparing said maximum magnitude θ max  value to a selected, calculated or predetermined scaled threshold S·τ where τ is a threshold and S is a scaling factor for the threshold r. The comparison step is such that, where |θ max | 2 &gt;S·τ, the method comprises determining that the signal received on the UL at said UCI receiver comprises a linear block encoded signal. In the method, prior to said comparison step, the scaling factor S is selected from a plurality of scaling factor options. One scaling factor option is a scaling factor S RE  derived from a combination of estimated noise and/or signal power at an output of a resource element (RE) demapper module and an estimated channel response from an equalizer module of said UCI receiver. 
     In a first main aspect, the invention provides a method of processing a signal received at a UCI receiver in a wireless communication system, the method comprising: processing a signal received on a UL at said UCI receiver to transform said received signal into a likelihood calculation of possible transmitted codewords (θ 1  . . . θi . . . θ N ); determining a maximum magnitude θ max  value from said likelihood calculation of possible transmitted codewords (θ 1  . . . θi . . . θ N ); and comparing said maximum magnitude θ max  value to a selected, calculated or predetermined scaled threshold S·τ where τ is a threshold and S is a scaling factor for the threshold r and said scaled threshold S·τ is a product of the threshold τ and the scaling factor S, the comparison being such that, where |θ max | 2 &gt;S·τ, the method comprises determining that the signal received on the UL at said UCI receiver comprises a linear block encoded signal; wherein, prior to said comparison step, the scaling factor S is selected from a plurality of scaling factor options. 
     Preferably, where |θ max | 2 ≤S·τ, the method comprises outputting a discontinuous transmission (DTX) signal. 
     In a second main aspect, the invention provides a UCI receiver in a wireless communication system, the UCI receiver comprising: a memory storing machine-readable instructions; and a processor for executing the machine-readable instructions such that, when the processor executes the machine-readable instructions, it configures the receiver to implement the first main aspect of the invention. 
     In a third main aspect, the invention provides a method of processing a signal received at a UCI receiver in a wireless communication system, the method comprising: processing a signal received on a UL at said UCI receiver to transform said received signal into a likelihood calculation of possible transmitted codewords (θ 1  . . . θi . . . θ N ); determining a maximum magnitude θ max  value from said likelihood calculation of possible transmitted codewords (θ 1  . . . θi . . . θ N ); and comparing said θ max  value to a selected, calculated or predetermined scaled threshold &amp;r where τ is a threshold and S is a scaling factor for the threshold τ and said scaled threshold S·τ is a product of the threshold τ and the scaling factor S, and where the scaling factor is S derived from a combination of estimated noise and/or signal power at an output of a resource element (RE) demapper module of the UCI receiver and an estimated channel response from an equalizer module of said UCI receiver, the comparison being such that, where |θ max | 2 &gt;S·τ, the method comprises determining that the signal received on the UL at said UCI receiver comprises a linear block encoded signal. 
     In a fourth main aspect, the invention provides a UCI receiver in a wireless communication system, the UCI receiver comprising: a memory storing machine-readable instructions; and a processor for executing the machine-readable instructions such that, when the processor executes the machine-readable instructions, it configures the receiver to implement the third main aspect of the invention. 
     The summary of the invention does not necessarily disclose all the features essential for defining the invention; the invention may reside in a sub-combination of the disclosed features. 
     The forgoing has outlined fairly broadly the features of the present invention in order that the detailed description of the invention which follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It will be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and further features of the present invention will be apparent from the following description of preferred embodiments which are provided by way of example only in connection with the accompanying figures, of which: 
         FIG. 1  is a signal diagram illustrating message exchanges between a BS and a UE for retransmission of control data and payload data; 
         FIG. 2  is a signal diagram illustrating errant transmission of control data and payload data from a BS to a UE when a UCI receiver at the BS determines a false ACK message; 
         FIG. 3  is a block schematic diagram of a conventional polar code-based receiver for a 5G communications system; 
         FIG. 4  is a block schematic diagram of a conventional small block code-based receiver for a 5G communications system; 
         FIG. 5  is a block schematic diagram of a UCI receiver in accordance with the invention; 
         FIG. 6  is a block diagram illustrating an improved scaling factor determination method in accordance with one aspect of the present invention; 
         FIG. 7  is a diagram schematically illustrating method steps in accordance with the invention performed by the UCI receiver of  FIG. 5  utilizing the improved scaling factor determined by the method of  FIG. 6 ; 
         FIG. 8  is a block diagram illustrating a combined scaling factor determination method in accordance with another aspect of the present invention; 
         FIG. 9  is a block diagram illustrating a scaling factor selection method in accordance with another aspect of the present invention; 
         FIG. 10  is a diagram schematically illustrating method steps in accordance with the invention performed by the UCI receiver of  FIG. 5  utilizing a scaling factor derived from a multi-dimensional DFT of the signal received on the UL at said UCI receiver; 
         FIG. 11  is a block diagram illustrating a combined scaling factor determination method based on the improved scaling factor determined by the method of  FIG. 6  and the scaling factor derived from the multi-dimensional DFT of the signal received on the UL at said UCI receiver, and 
         FIG. 12  is a block diagram illustrating a scaling factor selection method in accordance with another aspect of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect. 
     Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments, but not other embodiments. 
     It should be understood that the elements shown in the FIGS, may be implemented in various forms of hardware, software or combinations thereof. These elements may be implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices, which may include a processor, memory and input/output interfaces. 
     The present description illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. 
     Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
     Thus, for example, it will be appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of systems and devices embodying the principles of the invention. 
     The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (“DSP”) hardware, read-only memory (“ROM”) for storing software, random access memory (“RAM”), and non-volatile storage. 
     In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements that performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. It is thus regarded that any means that can provide those functionalities are equivalent to those shown herein. 
     The invention relates to a method for detecting acknowledgment (ACK), negative acknowledgment (NACK) and discontinuous transmission (DTX) signals accurately in uplink control information (UCI) in wireless communication systems. It is particularly useful for DTX detection in small block code-based receivers where cyclic redundancy check CRC is not available for DTX detection. 
       FIG. 5  shows an exemplary embodiment of an improved UCI receiver device  100  in accordance with concepts of the present invention. In the illustrated embodiment, the UCI receiver device  100  may comprise communication equipment such as a network node, a network card, or a network circuit communicatively connected to or forming part of a BS  103  (denoted by dashed line in  FIG. 5 ), etc. operating in a 5G communications system environment  115 , although the improved UCI receiver device  100  of the invention is not limited to operating in a 5G communications system but could comprise a UCI receiver device for a 4G cellular network or any cellular network. The BS  103  communicates with one or more UEs  125 . 
     The UCI receiver device  100  may comprise a plurality of functional blocks for performing various functions thereof. For example, the UCI receiver device  100  includes receiver module  110  providing received signal processing and configured to provide received signals and/or information extracted therefrom to functional block module(s)  120  such as may comprise various data sink, control element(s), user interface(s), etc. Although receiver module  110  is described as providing received signal processing, it will be appreciated that this functional block may be implemented as a transceiver providing both transmitted and received signal processing. Irrespective of the particular configuration of receiver  110 , embodiments include signal detection module  130  disposed in association with the receiver module  110  for facilitating accurate processing and/or decoding of a received channel signal in accordance with the invention. Channel signals may be received via an antenna module  105 . 
     Although the signal detection module  130  is shown as being deployed as part of the receiver module  110  (e.g. comprising a portion of the receiver module control and logic circuits), there is no limitation to such a deployment configuration according to the concepts of the invention. For example, the signal detection module  130  may be deployed as a functional block of UCI receiver device  100  that is distinct from, but connected to, receiver module  110 . The signal detection module  130  may, for example, be implemented using logic circuits and/or executable code/machine readable instructions stored in a memory  140  of the UCI receiver device  100  for execution by a processor  150  to thereby perform functions as described herein. For example, the executable code/machine readable instructions may be stored in one or more memories  140  (e.g. random access memory (RAM), read only memory (ROM), flash memory, magnetic memory, optical memory or the like) suitable for storing one or more instruction sets (e.g. application software, firmware, operating system, applets, and/or the like), data (e.g. configuration parameters, operating parameters and/or thresholds, collected data, processed data, and/or the like), etc. The one or more memories  140  may comprise processor-readable memories for use with respect to one or more processors  150  operable to execute code segments of signal detection module  130  and/or utilize data provided thereby to perform functions of the signal detection module  130  as described herein. Additionally, or alternatively, the signal detection module  130  may comprise one or more special purpose processors (e.g. application specific integrated circuit (ASIC), field programmable gate array (FPGA), graphics processing unit (GPU), and/or the like configured to perform functions of the signal detection module  130  as described herein. 
       FIG. 6  provides a block diagram illustrating an improved scaling factor Su determination method and utilization of the improved scaling factor determined thereby in determining a DTX state in accordance with one aspect of the present invention. The scaling factor S RE  is determined, calculated or derived from a combination of estimated noise and/or signal power at an output of the RE demapper module of the UCI receiver device  100  and an estimated channel response from the equalizer module of said UCI receiver device  100 . By improving the scaling factor S, the determination of a DTX state becomes more accurate. The improved scaling factor S RE  makes use of the estimated noise and/or signal power at the output of the RE demapper module which has not previously been effectively used. Consequently, where |θ max | 2 &gt;S RE ·τ, where τ is a predetermined threshold, the method comprises determining that the signal received on the UL at said UCI receiver device  100  comprises a linear block encoded signal and conversely, where |θ max | 2 ≤S RE ·τ, the method comprises determining that the signal received on the UL at said UCI receiver device  100  comprises a DTX state. 
     The scaling factor S RE  is preferably derived from the equation: 
     
       
         
           
             
               S 
               RE 
             
             = 
             
               
                 ∑ 
                 r 
               
               ⁢ 
               
                 
                   ∑ 
                   i 
                 
                 ⁢ 
                 
                   
                     ∑ 
                     k 
                   
                   ⁢ 
                   
                     
                       
                         g 
                         
                           r 
                           , 
                           l 
                           , 
                           k 
                         
                       
                       · 
                       
                         g 
                         
                           r 
                           , 
                           l 
                           , 
                           k 
                         
                         ″ 
                       
                     
                     
                       σ 
                       r 
                       2 
                     
                   
                 
               
             
           
         
       
     
     where σ R   2  is the estimated noise variance or signal power corresponding to the r-th receiver antenna obtained at the output of the RE demapper module; and 
     g r,l,k  is the estimated channel response obtained before the equalizer module as an input to the equalizer module with r comprising a receiver antenna index value, l comprising a time domain index value, e.g. an OFDM symbol index, and k comprising a frequency domain index value, e.g. a subcarrier index. 
       FIG. 7  schematically illustrates an improved linear block code-based (UCI) receiver device  100 / 200 , an improved decoder  210  for the improved linear block code-based (UCI) receiver device  100 / 200 , and improved and enhanced methods implemented by the signal detection module  130  comprising the improved decoder  210  for the improved linear block code-based (UCI) receiver device  100 / 200  or for the UCI receiver device  100  of  FIG. 5 . 
     As described in greater detail below, the signal detection module  130  comprising the improved decoder  210  is configured to implement improved detection or determination of acknowledgment (ACK), negative acknowledgment (NACK) and discontinuous transmission (DTX) signals accurately in uplink control information (UCI) in wireless communication systems. 
     In one embodiment, the UCI receiver device  100 / 200  is configured to receive a UL UCI signal as a demapper output signal. The demapper output signal is firstly equalized in a known manner in an equalizer module  202  to provide an equalized signal. The equalized signal is then demodulated and descrambled again in a known manner by a demodulation/descrambling module  204  which outputs soft bits to the improved decoder  210 . In  FIG. 6 , the improved decoder  210  is shown as a small block code decoder  210  but it will be understood that this is shown by way of example only. The small block code decoder  210  is configured to process said received signal in a transform module  210 A to transform, in step  300 , said received signal into a likelihood calculation of possible transmitted codewords in said received signal. Preferably, the likelihood calculation of possible transmitted codewords comprises a multi-dimensional discrete Fourier transform (DFT) (θ 1  . . . θi . . . θ N ) of said received signal. The UL UCI signal is received at the UCI receiver device  100 / 200  from a UE  125  operating in the 5G communications system environment  115  and which is wirelessly connected to the BS  103  via a UL channel. However, it will be understood that the signal received at the UCI receiver device  100 / 200  may only comprise noise in an instance where the UE  125  has missed a DL control message from the BS  103  and the UE  125  has therefore not issued any message or signal in response to the missed DL control message. In this case, the UCI receiver device  100 / 200  anticipates receiving a reply message from the UE  125  and therefore treats received noise as a UL UCI signal to be processed. In either case, the small block code decoder  210  processes the ‘received signal’ whether it is a real UL UCI signal from the UE  125  or whether it is a noise signal mistakenly taken as being a real UL UCI signal from the UE  125  to transform said signal into the multi-dimensional discrete Fourier transform (DFT) (θ 1  . . . θi . . . θ N ). 
     As indicated above, the signal detection module  130  of  FIG. 5  may comprise the improved decoder  210  for an improved linear block code-based (UCI) receiver device  100 / 200  of  FIG. 7  with, in one embodiment, the improved decoder  210  replacing the polar code decoder forming part of the conventional polar code-based receiver of  FIG. 3  or, more preferably, in another embodiment, the improved decoder  210  replacing, as shown in  FIG. 7 , the small block code decoder forming part of the conventional small block code-based receiver of  FIG. 4 . 
     It will be understood from the description that the signal detection module  130  comprising the improved decoder  210  may be implemented through any of software, firmware and/or hardware changes to conventional linear block code decoders, although it is possible to implement the improved decoder  210  of the invention by implementing only software changes. 
     The likelihood calculation of possible transmitted codewords in the UL UCI signal received at said UCI receiver device  100 / 200  may be expressed as likelihood values. The multi-dimensional DFT (θ 1  . . . θi . . . θ N ) may comprise a Hadamard transform of said received signal. The Hadamard transform is also known as the Walsh-Hadamard transform, the Hadamard-Rademacher-Walsh transform, the Walsh transform or the Walsh-Fourier transform. Herein, it will be referred to as the ‘Hadamard transform’ but encompasses all forms of said transform. 
     A module  210 B of the small block code decoder  210  is configured to determine, in step  305 , a maximum magnitude θ max  value from said likelihood calculation of possible transmitted codewords. The maximum magnitude θ max  value may be determined or calculated from a plurality of real numbers comprising said multi-dimensional DFT (θ 1  . . . θi . . . θ N ). 
     In conventional UCI receivers as exemplified by  FIGS. 3 and 4 , the UCI bits denoting ACK or NACK messages are derived from the maximum magnitude θ max  value&#39;s index and sign. Similarly, a UCI-bits module  210 C of the small block code decoder  210  is configured to generate, in a known manner in step  310 , UCI bits according to the index and sign of the maximum magnitude θ max  value. 
     As already described with respect to  FIG. 4 , the absence of a CRC function in the conventional small block code-based receiver prevents a determination of whether or not a received UL UCI signal is, in fact, indicative of a DTX state rather than an ACK or NACK message. In other words, the absence of a CRC function prevents a determination being made between DTX on the one hand and ACK/NACK on the other hand. 
     Comparing said θ max  value or, more preferably |θ max | 2 , to a selected, calculated or predetermined scaled threshold S·τ where S is the scaling factor for the threshold τ and said scaled threshold S·τ is obtained by multiplying the threshold τ by the scaling factor S, the comparison being such that, where |θ max | 2 &gt;S·τ, the method comprises determining that the signal received on the UL at said UCI receiver comprises a linear block encoded signal. 
     A first embodiment of the method of the invention includes, in step  315 , the step of comparing said |θ max | 2  value to the scaled threshold S RE ·τ. The scaling factor S RE  may be obtained by a DTX detector for UCI module  210 D by estimating the scaling factor S RE  from the combination of estimated noise and/or signal power at the output of the RE demapper module of the UCI receiver device  100 / 200  and the estimated channel response from the equalizer module  202  of said UCI receiver device  100 / 200 . 
     The DTX detector for UCI module  210 D for the small block code decoder  210  has loaded into a memory thereof the predetermined threshold τ. The threshold τ is preferably derived from a target detection performance and a number of detection occurrences in the signal received on the UL at said UCI receiver device  100 / 200 . The target detection performance may comprise any of: a target probability of detecting DTX as an acknowledgement message (ACK) (Pr(DTX→ACK)); a target probability of detecting DTX as a transmitted message (TX) (Pr(DTX→TX)); or a target probability of detecting a false alarm (Pr(FA)) in the signal received on the UL at said UCI receiver device  100 / 200 . 
     The number of detection occurrences is preferably determined from a number of payload bits and/or a number of encoded bits in the signal received on the UL at said UCI receiver device  100 / 200 . 
     The threshold τ may also be determined according to a tail probability of the distribution of the multi-dimensional DFT (θ 1  . . . θi . . . θ N ). 
     More particularly, the threshold τ is derived from: 
     
       
         
           
             
               τ 
               = 
               
                 
                   Q 
                   
                     - 
                     1 
                   
                 
                 ⁡ 
                 
                   ( 
                   
                     
                       1 
                       2 
                     
                     - 
                     
                       
                         1 
                         2 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             P 
                             detect 
                           
                           ) 
                         
                         
                           1 
                           
                             N 
                             detest 
                           
                         
                       
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     where 
     where Q −1 (⋅) is the inverse Q-function 
     N detect =2 N     bit     −1    
     P detect =1-2 Pr(DTX→ACK), or 1−Pr(DTX→TX), or 1−Pr(FA), and 
     N bit  is a number of payload bits and/or a number of encoded bits in the in the signal received on the UL at said UCI receiver device  100 / 200 . 
     In  FIG. 7 , only P detect =1-2 Pr(DTX→ACK) is shown for clarity of the drawing. 
     The threshold τ is dependent on two inputs, namely the target probability and the number of payload bits and/or a number of encoded bits as hereinbefore described. As such, the threshold τ can be predetermined and loaded into the memory  140  of the UCI receiver device  100 / 200 . As such, the threshold τ does not necessarily need to be determined in real-time. Furthermore, the scaled threshold S·τ is suitable for different channels or channel conditions which greatly simplifies the method of the invention and reduces the computational workload in the signal detection module  130 /small block code decoder  210 . 
     The small block code decoder  210  is configured, in step  315 , to determine whether or not the signal received on the UL at said UCI receiver device  100 / 200  comprises a linear block encoded signal when |θ max | 2 &gt;S·τ. However, where |θ max | 2 ≤S·τ, a discontinuous transmission (DTX) signal is outputted at step  315 . 
     In the case where |θ max | 2 &gt;S·τ, step  315  may be enhanced to output an acknowledgement (ACK) message or a negative-acknowledgement (NACK) message based on the generated UCI bits. 
     The method described with respect to  FIG. 7  make uses of only the improved scaling factor S RE  and therefore references to S in the above description can be taken to be references to S RE . However, in the following description S may comprise one of a number of scaling factor options as will be described and thus references to S may comprise references to any of said scaling factor options. 
     Referring to  FIG. 8 , provided is a block diagram illustrating a combined scaling factor S COMB  determination method and utilization of the combined scaling factor S COMB  determined thereby in determining a DTX state in accordance with another aspect of the present invention. The scaling factor S COMB  is determined, calculated or derived from a combination of the improved scaling factor S RE  and any other scaling factor S OTHER  suitable for determining a DTX state. S OTHER  may comprise known scaling factors for determining a DTX state. The scaling factor S COMB =f(S OTHER , S RE )=a(S OTHER ) λ ·(S RE ) 1-λ , where λ comprises a weighting value less than 1 and α comprises a combination coefficient. The scaling factor S COMB  is therefore derived from a function of the improved scaling factor S RE  and any other scaling factor S OTHER  suitable for determining a DTX state. The combination coefficient α may be derived from a payload bit length. In some embodiments, the combination coefficient α is equal to L The combination coefficient α can be a sigmoid function of the payload bit length l. The weighting value λ may be greater than 0.5, but is preferably equal to 0.667 (or ⅔), although it may take other values such as 0 or 1. 
     In some embodiments, the combination coefficient α can take the expression of the payload bit length l: 
     
       
         
           
             α 
             = 
             
               
                 c 
                 · 
                 
                   exp 
                   ⁡ 
                   
                     ( 
                     
                       - 
                       
                         
                           
                             ( 
                             
                               l 
                               - 
                               
                                 l 
                                 0 
                               
                             
                             ) 
                           
                           ω 
                         
                         d 
                       
                     
                     ) 
                   
                 
               
               + 
               
                 α 
                 0 
               
             
           
         
       
     
     where c is a scaling coefficient, l 0  is a constant offset, d is a normalization factor, ω is the exponent and α 0  are parameters of the combination coefficient α. Typical values of the parameters may be c=02, ω=2, l 0 =2, d=25, α=09.45. 
     Consequently, in this aspect of the invention, the method comprises determining that the signal received on the UL at said UCI receiver device  100 / 200  comprises a linear block encoded signal when where |θ max | 2 &gt;S COMB ·τ and conversely, where |θ max | 2 ≤S COMB ·τ, the method comprises determining that the signal received on the UL at said UCI receiver device  100 / 200  comprises a DTX state. 
       FIG. 9  illustrates another aspect of the invention where the scaling factor S may be selected from a number of scaling factor options. The method includes selecting as the scaling factor S one of (i) S RE , (ii) S OTHER , or (iii) S COMB . The selection of which scaling factor option to choose may be based on one or more signal conditions. For example, option (i) may be selected if the estimated noise and/or signal power at the output of the RE demapper module is at an acceptable or better level; otherwise option (iii) may be selected if the number of UCI payload bits is large; otherwise option (ii) is selected. In some embodiments, option (ii) may be selected if a code mask is not applied at the encoder module of the UCI receiver; otherwise option (iii) may be selected if a code mask is applied. In yet other embodiments, option (ii) may be selected if a payload bit length is smaller than or equal to a maximum unmask bit payload length; otherwise option (iii) may be selected if the payload bit length is larger than the maximum unmask bit payload length. The maximum unmask payload bit length can take the value of 6 when the block code length is 32. 
     It will be noted that the step of selecting a scaling factor option is implemented prior to the step of comparing the resultant scaled threshold S·τ to the maximum magnitude θ max  value, i.e. to |θ max | 2 , or configured as a default option. 
     In some embodiments, S OTHER =S HAD .  FIG. 10  provides a diagram schematically illustrating method steps in accordance with the invention performed by the UCI receiver  100  of  FIG. 5  utilizing the scaling factor S HAD  derived from the multi-dimensional DFT of the signal received on the UL at said UCI receiver  100 . 
       FIG. 10  schematically illustrates the improved linear block code-based (UCI) receiver device  100 ′/ 200 ′, an improved decoder  210 ′A for the improved linear block code-based (UCI) receiver device  100 ′/ 200 ′, and improved and enhanced methods implemented by the signal detection module  130  comprising the improved decoder  210 ′ for the improved linear block code-based (UCI) receiver device  100 ′/ 200 ′ or for the UCI receiver device  100  of  FIG. 5 . 
     As described above, the signal detection module  130  comprising the improved decoder  210 ′ is configured to implement improved detection or determination of acknowledgment (ACK), negative acknowledgment (NACK) and discontinuous transmission (DTX) signals accurately in uplink control information (UCI) in wireless communication systems. 
     The UCI receiver device  100 ′/ 200 ′ receives the UL UCI signal as a RE demapper output signal which is firstly equalized in an equalizer module  202 ′ to provide an equalized signal. The equalized signal is then demodulated and descrambled again by a demodulation/descrambling module  204 ′ which outputs soft bits to the improved decoder  210 ′. 
     In  FIG. 10 , the improved decoder  210 ′ is shown as a small block code decoder  210 ′ but it will be understood that this is shown by way of example only. The small block code decoder  210 ′ is configured to process said received signal in a transform module  210 ′A to transform, in step  300 ′, said received signal into a likelihood calculation of possible transmitted codewords in said received signal. The likelihood calculation of possible transmitted codewords comprises a multi-dimensional discrete Fourier transform (DFT) (θ 1  . . . θi . . . θ N ) of said received signal. The UL UCI signal is received at the UCI receiver device  100 ′/ 200 ′ from a UE  125 ′ operating in the 5G communications system environment  115 ′ and which is wirelessly connected to the BS  103 ′ via a UL channel. The small block code decoder  210 ′ processes the ‘received signal’ whether it is a real UL UCI signal from the UE  125 ′ or whether it is a noise signal mistakenly taken as being a real UL UCI signal from the UE  125 ′ to transform said signal into the multi-dimensional discrete Fourier transform (DFT) (θ 1  . . . θi . . . θ N ). 
     The likelihood calculation of possible transmitted codewords in the UL UCI signal received at said UCI receiver device  100 ′/ 200 ′ may be expressed as likelihood values. The multi-dimensional DFT (θ 1  . . . θi . . . θ N ) may comprise a Hadamard transform of said received signal. 
     A module  210 ′B of the small block code decoder  210 ′ is configured to determine, in step  305 , a maximum magnitude θ max  value from said likelihood calculation of possible transmitted codewords. 
     A UCI-bits module  210 ′C of the small block code decoder  210 ′ is configured to generate, in a known manner in step  310 , UCI bits according to the index and sign of the maximum magnitude θ max  value. 
     A first embodiment of the method of the invention illustrated by  FIG. 10  includes, in step  315 , the step of comparing said θ max  value to a selected, calculated or predetermined scaled threshold S HAD ·τ. The scaling factor S HAD  may be obtained by a DTX detector for UCI module  210 ′D by estimating the scaling factor S HAD  from the multi-dimensional DFT (θ 1  . . . θi . . . θ N ) but is preferably obtained by obtaining an estimate of the noise variance after the DFT transform step. 
     The threshold τ is preferably determined in the manner described with respect to  FIG. 7 . 
     The small block code decoder  210 ′ is configured, in step  315 , to determine whether or not the signal received on the UL at said UCI receiver device  100 ′/ 200 ′ comprises a linear block encoded signal when |θ max | 2 &gt;S HAD ·τ. However, where |θ max | 2 ≤S HAD ·τ, a discontinuous transmission (DTX) signal is outputted at step  315 . 
     Referring to  FIG. 11 , provided is a block diagram illustrating a second combined scaling factor S COMB  determination method and utilization of the combined scaling factor Scows determined thereby in determining a DTX state in accordance with yet another aspect of the present invention. The scaling factor S COMB  is determined, calculated or derived from a combination of the improved scaling factor S RE  and the scaling factor S HAD  of  FIG. 10 . The scaling factor S COMB =f(S HAD , S RE )=α(S HAD ) λ·(S   RE ) 1-λ , where, as before, λ comprises a weighting value less than 1 and α comprises a combination coefficient. The scaling factor S COMB  is therefore derived from a function of the improved scaling factor S RE  and the scaling factor S HAD . The combination coefficient α may be derived from a payload bit length. In some embodiments, the combination coefficient α is equal to 1. The weighting value) may be greater than 0.5, but is preferably equal to 0.667, but may take other values as hereinbefore described. 
     Consequently, in this aspect of the invention, the method comprises determining that the signal received on the UL at said UCI receiver device  100 / 200 ,  100 ′/ 200 ′ comprises a linear block encoded signal when where |θ max | 2 &gt;S COMB ·τ and conversely, where |θ max | 2 ≤S COMB ·τ, the method comprises determining that the signal received on the UL at said UCI receiver device  100 / 200 ,  100 ′/ 200 ′ comprises a DTX state. 
       FIG. 12  illustrates a further aspect of the invention where the scaling factor S may be selected from a number of scaling factor options. The method includes selecting as the scaling factor S one of (i) S RE , (ii) S HAD , or (iii) S COMB . The selection of which scaling factor option to choose may be based on one or more signal conditions or other factors. For example, it is found that S HAD  can lead to over-estimation of noise variance at one end of the variance scale fundamentally due to the fact that the S HAD  and the |θ max | 2  both are obtained according to the same realizations of (θ 1  . . . θi . . . θ N ), and their monotonicity has a close and positive relationship. Consequently, under certain conditions it is better to use S RE  than S HAD  and vice-versa and, in yet other conditions, it is better to combine S RE  than S HAD  to provide S COMB . It is noted, however, that S RE  can lead to under-estimation of noise variance, especially for the case where the framework of used noise estimation method is based on subtracting the estimated signal portion (derived using the estimated channel) from the overall received signal. Moreover, the degree of under-estimation by S RE  may be more significant than the degree of over-estimation caused by S HAD . Consequently, it is preferred that the weighting value λ is greater than 0.5 and is preferably as high as 0.667. Simulated results show that a value of λ=⅔ (0.667) achieves near to 1% false alarm rate (FAR) which is desirable. 
     It has been found that using option (i) S RE  provides excellent results when there is a good noise estimator at the RE demapper output, where the noise estimation takes into consideration the channel/signal characteristics other than PUCCH such that the under-estimation effect will be weaker than other cases. This is the preferred option. However, if the noise estimation is poor and the number UCI payload bits is large. e.g., more than 6, then option (iii) S COMB  is preferred because, when the number UCI payload bits is above 6, the 3GPP standard 38.212 requires a code mask operation to be implemented where the influence of over-estimation by S HAD  is increased. In the event that neither of options (i) or (iii) are selected, i.e., deemed suitable, then option (ii) S HAD  is selected as the ‘baseline’ option. 
     It can be seen therefore that the methods of the foregoing aspects and embodiments of the invention can be most usefully, although not exclusively, utilized in a small block code-based receiver not having CRC functionality such as that exemplified by  FIG. 4  to determine if a signal received on the UL at the UCI receiver device  100 / 200 ,  100 ′/ 200 ′ comprises a linear block encoded signal and furthermore to detect or determine if the received signal, whether real or comprising noise, includes an ACK message from the UE  125 ,  125 ′ or a NACK message from the UE  125 ,  125 ′. In other words, not only can the method of the above embodiments determine if the received signal comprises a linear block encoded signal but it also enables the improved decoder  210 ,  210 ′ to distinguish between a DTX state on the one hand and ACK/NACK signals on the other hand. Consequently, the method of the above embodiments is particularly useful in wireless communication systems for DTX detection in small block code-based receivers where cyclic redundancy check CRC is not available for DTX detection. 
     The methods can therefore be utilized to determine that the signal received on the UL at the UCI receiver device  100 / 200 ,  100 ′/ 200 ′ comprises a small block encoded signal in a long-term evolution (LTE) communication system and, more particularly, to determine DTX in a small block encoded signal comprising a NR (5G) Physical Uplink Control Channel (PUCCH) format such as PUCCH format 2, PUCCH format 3, or PUCCH format 4. 
     It will be understood that the linear block code may be Reed-Muller (RM) code or RM-based super code. 
     Outputting a DTX state may comprise outputting a Boolean or binary value indicative of said DTX state. 
     In general, signal power varies over time. In a case of DTX, for example, where the received signal only comprises noise, the noise power is not constant over time. Therefore, it is necessary to estimate the noise power (e.g., based on all of (θ 1  . . . θi . . . θ N )), at one or more points in time. Otherwise, the maximum magnitude θ max  value derived from the received signal comprising only noise may still be such that the maximum magnitude θ max  value is greater than the threshold τ, due to the fact that (θ 1  . . . θi . . . θ N ) are all/mostly large on the whole, rather than due to the fact that θ max  is really outstanding among (θ 1  . . . θi . . . θ N ). Using a scaling factor S with the threshold τ helps to address this problem. 
     In other embodiments, it is possible that the scaling factor S can be omitted in, for example, the case where we have a priori knowledge of the noise power over a long period of time. In this case, it is possible to determine that noise on the UL channel does not vary rapidly over time or to determine that it follows a certain distribution. In this way, it is possible to treat the noise power as a constant or at least a known entity. Consequently, as long as a suitable level for the threshold τ is chosen, it may no longer become necessary to apply a scaling factor to the threshold τ. 
     The invention also provides a non-transitory computer-readable medium  140  storing machine-readable instructions, wherein, when the machine-readable instructions are executed by a processor  150 , they configure the processor  150  to implement the afore-described methods in accordance with the invention. 
     The apparatus described above may be implemented at least in part in software. Those skilled in the art will appreciate that the apparatus described above may be implemented at least in part using general purpose computer equipment or using bespoke equipment. 
     Here, aspects of the methods and apparatuses described herein can be executed on any apparatus comprising the communication system. Program aspects of the technology can be thought of as “products” or “articles of manufacture” typically in the form of executable code and/or associated data that is carried on or embodied in a type of machine-readable medium. “Storage” type media include any or all of the memory of the mobile stations, computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives, and the like, which may provide storage at any time for the software programming. All or portions of the software may at times be communicated through the Internet or various other telecommunications networks. Such communications, for example, may enable loading of the software from one computer or processor into another computer or processor. Thus, another type of media that may bear the software elements includes optical, electrical and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links or the like, also may be considered as media bearing the software. As used herein, unless restricted to tangible non-transitory “storage” media, terms such as computer or machine “readable medium” refer to any medium that participates in providing instructions to a processor for execution. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims. 
     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e., to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 
     It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art.