Patent Publication Number: US-2021184789-A1

Title: Methods and apparatuses for repetition transmission

Description:
FIELD 
     Embodiments of the present disclosure generally relate to the field of communications, and in particular, to methods and apparatuses for repetition transmission. 
     BACKGROUND 
     In the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) Release 13, a LTE Machine Type Communication (LTE-M) standard has been proposed to support the Machine Type Communication (MTC) or Internet of Things (IoT) applications. LTE-M provides low-cost LTE-M terminal devices suitable for massive MTC and IoT applications with an enhanced coverage compared to the normal LTE terminal devices. In the LTE-M communication networks, a MTC User Equipment (UE) should be controlled with different radio resource allocation algorithms and search spaces. Therefore, the physical control or data channels and downlink scheduler may be re-designed to meet the new requirements in 3GPP LTE-M communication networks. 
     In order to improve the coverage in LTE-M communication networks, a repetition transmission has been widely used. Generally speaking, there is a relationship between the number of repetition transmission and the repetition gain. For example, if the number of repetition transmission for a signal is doubled in the transmitting side, a 3 dB repetition gain can be achieved in the receiving side by combining the received multiple copies of the signal from the transmitting side. However, the increment of the number of repetition transmission will reduce the spectrum efficiency and the capacity of the LTE-M communication networks, which may be undesirable for some capacity-limited application scenarios. 
     SUMMARY 
     In general, example embodiments of the present disclosure provide methods and apparatuses for updating a repetition level for a downlink channel from a network device to a terminal device in a communication network. 
     In a first aspect, there is provided a method implemented at a network device. According to the method, a first channel quality of a downlink channel between the network device and a terminal device is determined, based at least in part on uplink transmission from the terminal device to the network device. A second channel quality of the downlink channel is determined based on a set of parameters associated with a target performance of the downlink channel. A repetition level for the downlink channel is updated based on the first channel quality and the second channel quality. The repetition level indicates the number of repetition transmissions in the downlink channel. 
     In a second aspect, there is provided a network device. The network device comprises a processor and a memory coupled to the processor. The memory stores instructions that when executed by the processor, cause the network device to performs actions. The actions comprise: determining a first channel quality of a downlink channel between the network device and a terminal device, based at least in part on uplink transmission from the terminal device to the network device; determining a second channel quality of the downlink channel based on a set of parameters associated with a target performance of the downlink channel; and updating a repetition level for the downlink channel based on the first channel quality and the second channel quality. The repetition level indicates the number of repetition transmissions in the downlink channel. 
     In a third aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor, cause the at least one processor to carry out the method according to the first aspect. 
     In a fourth aspect, there is provided a computer program product that is tangibly stored on a computer readable storage medium. The computer program product includes instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to the first aspect. 
     Other features of the present disclosure will become easily comprehensible through the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein: 
         FIG. 1  shows a schematic diagram of a communication environment in which embodiments of the present disclosure can be implemented; 
         FIG. 2  shows a diagram illustrating a process of repetition transmission in a downlink channel in accordance with some embodiments of the present disclosure; 
         FIG. 3  shows a flowchart of a method for updating a repetition level of a downlink channel in accordance with some embodiments of the present disclosure; 
         FIG. 4  shows a block diagram of an apparatus in accordance with some embodiments of the present disclosure; and 
         FIG. 5  shows a simplified block diagram of a network device that is suitable for implementing some embodiments of the present disclosure. 
     
    
    
     Throughout the drawings, the same or similar reference numerals represent the same or similar element. 
     DETAILED DESCRIPTION 
     Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below. 
     In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs. 
     As used herein, the term “network device” or “Base Station” (BS) refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB), an Evolved NodeB (eNodeB or eNB), a next generation NodeB (gNB), a Transmission Reception Point (TRP), a Remote Radio Unit (RRU), a radio head (RH), a Remote Radio Head (RRH), a low power node such as a femto node, a pico node, and the like. For the purpose of discussion, in the following, some embodiments will be described with reference to TRP as examples of the network device. 
     As used herein, the term “terminal device” refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, UE, personal computers, desktops, mobile phones, cellular phones, smart phones, Personal Digital Assistants (PDAs), portable computers, image capture devices such as digital cameras, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. For the purpose of discussion, in the following, some embodiments will be described with reference to UE as examples of the terminal device. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to.” The term “based on” is to be read as “at least in part based on.” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment.” The term “another embodiment” is to be read as “at least one other embodiment.” The terms “first,” “second,” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below. 
     Communication discussed in the present disclosure may conform to any suitable standards including, but not limited to, New Radio Access (NR), LTE, LTE-Evolution, LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the First Generation (1G), the Second Generation (2G), 2.5G, 2.75G, the Third Generation (3G), the Fourth Generation (4G), 4.5G, the Fifth Generation (5G) communication protocols. 
       FIG. 1  shows a schematic diagram of a communication environment in which embodiments of the present disclosure can be implemented. The network  100  includes a network device  110  and a terminal devices  120  served by the network device  110 . The serving area of the network device  110  is referred to as a cell. It is to be understood that the number of network devices and terminal devices is only for the purpose of illustration without introducing any limitations. The network  100  may include any suitable number of network devices and terminal devices adapted for implementing the present disclosure. Although not shown, it would be appreciated that more terminal devices may be located in the cell and served by network device  110 . 
     In order to improve the coverage of the network  100 , the network device  110  may perform a repetition transmission in the downlink channel from the network device  110  to the terminal device  120 . The repetition transmission refers to a plurality of retransmissions for the same signal in the downlink channel. The terminal device  120  may perform a combining operation for the plurality of copies of the same signal from the repetition transmission, in order to improve the receiving signal quality. The combining operation may be a Maximum Ration Combining (MRC), a Selective Combining (SC) or an Equal Gain Combing (EGC). 
     Although the coverage of the network can be improved through a repetition transmission in the downlink channel, the spectrum efficiency and the network capacity may be linearly decreased due to a repetition transmission. For example, if the number of repetition transmission is doubled, the spectrum efficiency of the downlink channel will be reduced by half, which will be undesirable especially for the throughout-sensitive applications. Moreover, if the predetermined number of the repetition transmission is large; the processing delay for the repetition transmission in the terminal device will be undesirable, which is unacceptable for the delay sensitive application scenarios, such as real-time control and monitoring applications or some emergency calling applications. 
     Example embodiments of the present disclosure provide a solution for updating the repetition level of the repetition transmission in the downlink channel. According to the embodiments described herein, the repetition level indicates the number of repetition transmissions in the downlink channel from the network device  110  and the terminal device  120 . The repetition level of the downlink channel may be dynamically updated according to the channel quality of the downlink channel and the target channel quality associated with a target performance of the downlink channel. For example, if the downlink channel is in good channel condition, the repetition level of the downlink transmission may be reduced in order to decrease the number of retransmission and thereby improve the spectrum efficiency of the communication network. Therefore, the network device may determine the repetition level according to different conditions of the channel quality, thereby achieving a better overall performance for the communication network. 
       FIG. 2  shows a diagram illustrating a process of repetition transmission in a downlink channel in accordance with some embodiments of the present disclosure. The method  200  may be carried out by the network device  110 , for example. 
     The terminal device  120  performs  210  an uplink transmission from the terminal device  120  to the network device  110 . For example, in some embodiments, the terminal device  120  may transmit the Channel Quality indicator (CQI), which indicates the channel quality of the downlink channel. As another example, the terminal device  120  may also transmit Acknowledgement/Negative Acknowledgement (ACK/NACK) feedbacks for the received downlink data, indicating the performance of the downlink channel. In still another example, the terminal device  120  may perform a Discontinuous Transmission (DTX) in the uplink channel, which means the terminal device  120  may not successfully decode the downlink control information in for example, such as the Downlink Control Information (DCI) in the downlink channel from the network device  110  to the terminal device  120 . 
     Upon receipt of the information of the uplink transmissions from the terminal device  120 , the network device  110  determines  220  the channel quality of the downlink channel based on the uplink transmissions. The channel quality may be determined from, for example, CQI, information of the ACK/NACK feedbacks, detection of DTX in the uplink channels from the terminal device  120 , and the like. 
     The network device  110  also determines  230  a target channel quality of the downlink channel based on one or more parameters associated with a target performance of the downlink channel. In one example, the target channel quality may be related to the link level parameter in the physical layer, such a target error rate of the downlink channel, a transmission power of the network device  110  and a transmission power of the terminal device  120 . In another example, the target channel quality may be related to the network level parameters in the higher layers, such as a coverage range of the communication network  100 , and a traffic model of the communication network  100 . Moreover, the target channel quality may be dynamically updated by the telecommunication operators or vendors according to some predefined higher level operation rules, by taking different priority levels of the communication network  100  into account for example. It is to be understood that the target channel quality of the downlink channel may be obtained based on aforementioned link level and/or network level parameters, through the link level, system level computer simulations and/or field tests. More details on the determination of the target channel quality will be illustrated below. 
     The network device  110  updates  240  the repetition level according to the determined channel quality and the target channel quality. For example, the network device  110  may employ the updated repetition level to perform the downlink transmission to the terminal device  120 . 
     In addition, in  250 , if the repetition level is changed, the network device  110  may also send the updated repetition level to the terminal device  120  by downlink signaling in the downlink channel. Alternatively, the network device  110  may not send the terminal device  120  explicit information of the updated repetition level by downlink signaling; and instead, the terminal device  120  may perform a blind detection for the repetition level in order to obtain the updated repetition level by the terminal device  120  itself. 
     With the operations by the network device  110 , compared with the traditional fixed repetition level solutions, the repetition level for the downlink transmission in the present disclosure may be dynamically changed or updated according to the channel condition of the downlink channel. Since the repetition level for the downlink channel is dynamically updated to adapt to the change of the channel conditions, by using the methods in the present disclosure, a better spectrum efficiency and network capacity may be achieved in the communication network  100 , such as the MTC and IoT communication networks. 
       FIG. 3  shows a flowchart of a method  300  for updating a repetition level of a downlink channel in accordance with some embodiments of the present disclosure. The method  300  may be implemented at the network device  110  in the network  100  for example. 
     In block  310 , the network device  110  determines a channel quality (referred to as “a first channel quality”) of a downlink channel between the network device  110  and the terminal device  120 , based at least in part on uplink transmission from the terminal device  120  to the network device  110 . 
     In some embodiments of the disclosure, the downlink channel may be a downlink control channel, such as the Physical Downlink Control Channel (PDCCH) in LTE communication networks and the MTC Physical Downlink Control Channel (MPDCCH) in LTE-M communication networks. The first channel quality for the downlink control channel may be determined according to information obtained from the uplink transmission. In one example, the network device  110  may determine the first channel quality from the CQI received in the uplink channel according to a CQI and channel quality mapping relationship. For instance, the CQI and channel quality mapping relationship may be predetermined and then organized in a lookup table. If the network device  110  obtains the CQI from the uplink channel, it may simply determine the first channel quality according to the lookup table. In another example, the network device  110  may also detect a DRX in the uplink transmission channel, which means the terminal device  120  may not successfully decode the control information in the downlink channel. Therefore, if the network device  110  detects a DRX from the uplink channels, it may have an estimation of the downlink channel, based on which the network device  20  may adjust the first channel quality by a predefined DRX offset. 
     In the following description, an example for the determination of the first channel quality for downlink control channel is presented only for illustration purpose. It is to be understood that the first channel quality for the downlink control channel may be represented by a Signal to Interference plus Noise Ratio (SINR) or a Signal to Noise Ratio (SNR). Without loss of any generality, in the following description, the SINR will be used to illustrate how to obtain the first channel quality based on the uplink transmissions. For example, the first channel quality of the downlink control channel may be represented by the SINR of the downlink channel, indicated by SINR_first for example. The SINR_first can be determined as below: 
       SINR_first=10 log 10 SINR CQI +DTX_offset  (1)
 
     where CQI represents a CQI received from the uplink channels in the User Control Information (UCI) in the Physical Uplink Control Channel (PUCCH) and MTC Physical Uplink Control Channel (MPUCCH), SINR CQI  represents the determined SINR for the downlink control channel from the received CQI according to the CQI and channel quality mapping relationship, and DTX_offset represents an offset of the channel quality due to the detection of the uplink DRX. 
     As discussed above, the first channel quality, (e.g., the SINR in Equation (1)) may represent an estimated channel condition for the physical downlink channel as a function of different information associated with the uplink transmission, such as the CQI in the uplink channel and a detection of DRX in the uplink channel and etc. It is to be understood that the detection of the DRT may imply that the terminal device  120  cannot successfully decode the control information in the downlink channel such as the DCI. Therefore, for example, DTX_offset may be a negative offset parameter, if the network device  110  detects a DRX in the uplink channels, such as the PUCCH and Physical Uplink Shared Channel (PUSCH) in LTE systems. 
     In some embodiments of the disclosure, the downlink channel may be a downlink data channel, such as the Physical Downlink Shared Channel (PDSCH) in LTE communication networks and MTC Physical Downlink Shared Channel (MPDSCH) in LTE-M communication networks. In these embodiments, the first channel quality for the downlink data channel may be also determined according to information obtained from the uplink transmission. 
     In one example, the network device  110  may determine the first channel quality from the CQI received from the uplink channel according to the CQI and channel quality mapping relationship. For instance, the CQI and channel quality mapping relationship may be predetermined and organized in a lookup table. In this case, if the network device  110  obtains the CQI from the uplink channel, it may simply determine the first channel quality according to the lookup table. 
     In another example, the network device  110  may receive the ACK/NACK feedback in the PUCCH and MPUCCH from the terminal device  120 , from which a statistics of the ACK and NACK may be calculated by the network device  110 . For instance, the statistics of the ACK and NACK may be a percentage of the number of the NACKs in the total number of the ACK and NACK feedbacks, which may represent an estimation of the Block Error Rate (BLER) of the downlink data transmission. 
     As another instance, the statistics of the ACK and NACK may be a predetermined number of NACKs. If more NACKs are received in the uplink transmission from the terminal device  120 , it means that the channel quality of the downlink data channel is in relatively worse channel conditions. In this case, the first channel quality of the downlink channel should be updated by adjusting with a negative offset, in order to take the statistics of the ACK and NACK feedback into account. It is to be understood that the offset for the first channel quality with respect to a statistics of ACK and NACK may be predetermined through the link level, system level simulations and/or field tests. 
     In another example, the first channel quality may be determined according to the value of Control Format Indicator (CFI) for the downlink control channel. The value of a CFI indicates the number of the Orthogonal Frequency Division Multiplexing (OFDM) symbols in the control region in one downlink subframe. The impact of CFI on the estimated first channel quality for the downlink data channel may be represented by another offset value. 
     For instance, if there are less OFDM symbols in the control region (e.g., CFI=1), it means there are more OFDM symbols used to transmit data in PDSCH in the subframe, which will lead to a better decoding performance for the downlink data channel. In this case, the first channel quality should be correspondingly adjusted by a positive offset in order to make a more reasonable estimation of the first channel quality for the downlink data channel. It is to be appreciated that the offset for the first channel quality with respect to a value of the CFI may be also predetermined by the link level, system level simulations and/or field tests. 
     An example embodiment for the determination of the first channel quality for downlink data channel will now be described, only for illustration purpose. It is to be understood that the first channel quality for the downlink data channel may be represented by a SINR or a SNR. Without loss of any generality, a SINR will be employed to illustrate how to obtain the first channel quality based on the uplink transmissions. The first channel quality of the downlink data channel may be represented by the SINR of the downlink channel, indicated by SINR_first for example. The SINR_first can be determined as below: 
       SINR_first=10 log 10 SINR CQI +NACK offset +CFI_offset  (2)
 
     where CQI indicates a CQI received from the uplink transmission in the UCI in the PUCCH and MPUCCH, SINR CQI  represents the derived SINR of the downlink data channel from the received CQI according to mapping relationship between the CQIs and channel qualities, NACK offset  represents the offset of first channel quality with respect to the statistics of ACK and NACK and CFI_offset represents the offset of the first channel quality with respect to a value of CFI for a downlink control channel. It is to be appreciated the mapping relationship between the CQIs and channel qualities, the offset of first channel quality with respect to the statistics of ACK and NACK and the offset of the first channel quality with respect to a value of CFI for a downlink control channel may be predetermined by the computer simulations and/or field tests. 
     Still in reference with  FIG. 3 , in block  320 , the network device  110  determines a channel quality (referred to as “a second channel quality”) of the downlink channel based on a set of parameters associated with a target performance of the downlink channel. The second channel quality may be also represented by SINR or SNR. The second channel quality indicates a target channel quality for a target performance of the downlink channel under different link or system conditions in the communication network  100 . The target channel quality may depend on different link level parameters. Therefore, in one example, the set of parameters may include some link level parameters of the communication network  100 , such as a target decoding performance of the downlink channel, a transmission power of the network device  110 , and a transmission power of the terminal device  120 . The target decoding performance may be indicated by a target error rate, such as a target BLER for the downlink channel for example. The second channel condition may also depend on the network level parameters. In another example, the set of parameters may also include some network level parameters of the communication network  100 , such as a coverage range of the communication network  100 , a channel model of the communication network  100  and a traffic model of the communication network  100 . It is appreciated that the parameters are provided only for illustration. All the modification, variations and combinations of the parameters discussed above fall within the scope of the disclosure. 
     The relationship profile between a target performance of the downlink channel and the second channel quality under the set of link or network level parameters may be obtained by computer simulations and/or field tests. For instance, the relationship profile may be stored for further usage in a profile database at the network device  110 . The relationship profile may be also updated by the network device  110  in a periodic or event-trigger manner, as these link and network level parameters of the communication network  100  may vary at time. 
     Moreover, the second channel quality may be predefined and/or updated by the telecommunication operators or vendors based on various operational rules. The higher level operational rules may take different types of the time window in the communication network  100  and different priority levels of the cells or sectors in the communication network  100  into consideration. In one example, the target channel quality, i.e., the second channel quality may be determined lower for the time periods with a lower traffic load in the communication network  100 . In another example, the target channel quality may be determined larger for the cells or sectors with higher priority levels, thereby achieving a dynamic and flexible control of the network performance. 
     In some embodiments, modulation and Coding Scheme (MCS) may be fixed for the downlink control channel. In LTE communication systems, for example, the modulation scheme for the PDCCH is Quadrature Phase Shift Keying (QPSK) and the channel coding is Turbo coding with a coding rate of ⅓. All the specific numeral values are described only for illustration purpose, without suggesting any limitations as to the scope of the present disclosure. Therefore, the second channel quality for the downlink control channel may be determined according to a predetermined decoding performance for the downlink control channel. For example, with a target error rate of 1% for the downlink control channel, the second channel quality for the downlink control channel may be predetermined by link level or system level simulations and field tests. 
     In the LTE or LTE-M communication network, a MCS represent a specific modulation and coding scheme used for the transmission of data channel. For example, if the first channel quality is considered better, the modulation order will be larger and the coding rate will be also higher. For example, if the first channel quality (represented by the SINR) is higher than 15 dB, a high modulation order, for example a 64 Quadrature Amplitude Modulation (QAM) may be employed for downlink transmission. It is appreciated that the numerical values are described only for illustration, without suggesting any limitations as to the scope of the present disclosure. In order to determine the second signal quality for the downlink data channel, the network device  110  may determine a MCS based on the first channel quality, according to a mapping relationship between MCSs and downlink channel qualities for example. The mapping relationship between the MCSs and the downlink channel qualities may be predetermined according to different subframe structures by computer simulations and/or field tests. 
     In some embodiments of the disclosure, the maximum MCS for LTE or LTE-M communication network may be limited to a predefined level. In this case, the maximum MCS may be taken into consideration in the process of determining the second channel quality from the first channel quality of the downlink data channel. For example, a preliminary MCS may be first determined based on the first channel quality according to the mapping relationship between the MCSs and channel qualities. If the preliminary MCS is larger than the predefined maximum MCS, the MCS for the first channel quality may be configured as the predefined maximum MCS. On the other hand, if the preliminary MCS is smaller than the predefined maximum MCS, the MCS for the first channel quality may be configured as the preliminary MCS. 
     In some embodiments of the disclosure, in order to adapt the traffic model and reduce the undesirable segment of the downlink transmission, a minimum MCS for LTE or LTE-M communication network may be specified in advance. For example, the downlink data packet is 160 bits in 3GPP traffic model. In this case, the minimum MCS can be set to 1 (for a transmission block size of 208 bits). 
     For example, in some embodiments, a preliminary MCS may be first determined based on the first channel quality according to the mapping relationship between the MCSs and channel qualities. If the preliminary MCS is larger than the predefined minimum MCS, the MCS for the first channel quality may be configured as the preliminary MCS. On the other hand, if the preliminary MCS is smaller than the predefined maximum MCS, the MCS for the first channel quality may be configured as the predefined minimum MCS. 
     Alternatively, or in addition, both the maximum MCS and the minimum MCS may be predefined for the downlink data channel. The determination of the MCS from the first channel quality may take both the maximum MCS and the minimum MCS into consideration. It is to be understood that given the teachings and suggestions herein, any other ways for determining the MCS from the first channel quality of the downlink data channel can be envisaged and thus fall within the scope of the present disclosure. 
     In view of the determined MCS, the network device  110  may determine a second channel quality based the set of parameters associated with a target performance of the downlink data channel. More specifically, as discussed above, the second channel quality is a target channel quality for the downlink data channel with respect to a predetermined decoding performance. For a given MCS, the second channel quality may be obtained by computer simulations and/or field tests based on the set of parameters associated with the target performance of the downlink channel, such as a target decoding performance with a BLER of 1% for example. For example, the target decoding performance may be determined according to the specific applications and the priority levels of the terminal users. 
     In block  330 , the network device  110  updates the repetition level for the downlink channel based on the first channel quality and the second channel quality. As discussed, the repetition level indicates the number of repetition transmissions in the downlink channel. The downlink channel may be a downlink control channel or a downlink data channel from the network device  110  to the terminal device  120 . The first channel quality of the downlink channel may represent the channel condition of the physical downlink channel from the network device  110  to the terminal device  120 . On the other hand, the second channel quality of the downlink channel may represent an overall channel condition of the downlink channel in the terminal device  120 . 
     If the second channel quality is smaller than the first channel quality, it means the physical downlink channel condition is good enough to achieve the target channel quality in the terminal device  120 . In this case, the repetition level may be reduced by a predetermined level or just kept unchanged. 
     If the second channel quality is larger than the first channel quality, it means the physical downlink channel condition cannot fulfill the overall channel quality requirements in the terminal device  120  indicated by the second channel quality. In this case, more repetition transmissions are required to achieve the desired second channel quality with a target performance. 
     That is, the repetition level should be increased to fill the gap between the first channel quality and the second channel quality through downlink repetition transmission. The repetition gain of an increased repetition level may also represent a repetition coding gain through the simple repetition transmissions. 
     In some embodiments of the disclosure, if the first channel quality exceeds the second channel quality, the network device  110  may maintain the repetition level unchanged. As discussed, in this case, the physical downlink channel quality is good enough compared with the target channel quality. Therefore, the repetition level may be simply kept unchanged. 
     In some embodiments of the disclosure, if the first channel quality exceeds the second channel quality, the network device  110  may decrease the repetition level by a predetermined level in order to improve the spectrum efficiency of the communication network  100 . 
     Table 1 shows examples of decreasing the repetition level. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 r max   
                 r 1   
                 r 2   
                 r 3   
                 r 4   
               
               
                   
                   
               
             
            
               
                   
                 1 
                 1 
                 — 
                 — 
                 — 
               
               
                   
                 2 
                 1 
                 2 
                 — 
                 — 
               
               
                   
                 4 
                 1 
                 2 
                 4 
                 — 
               
               
                   
                   
               
               
                   
                 &gt;= 8 
                 
                   
                     
                       
                         
                           r 
                           max 
                         
                         8 
                       
                     
                   
                 
                 
                   
                     
                       
                         
                           r 
                           max 
                         
                         4 
                       
                     
                   
                 
                 
                   
                     
                       
                         
                           r 
                           max 
                         
                         2 
                       
                     
                   
                 
                 r max   
               
               
                   
                   
               
            
           
         
       
     
     In Table. 1, r max  represents a maximum repetition level, and r i  i=1, 2, 3, 4 represent a plurality of different repetition levels. Without any loss of generality, it is assumed that r max  is predefined as 4 and it is also assumed that current repetition level is r 3 , which is equal to 4. 
     As discussed above, if the first channel quality exceeds the second channel quality, the network device  110  may decrease the current repetition level by a predetermined level. In this specific example, the network device  110  may decrease the repetition level from r 3  to r 2  or r 1 . That is, in this case, the repetition level may be decreased from 4 to 2 or 1. 
     It is to be understood that the configuration of repetition level in Table. 1 is presented only for illustration, without introducing any limitation to the scope of the disclosure. It is also to be understood that all the numerical values in the present disclosure are described only for illustration, without suggesting any limitations as to the scope of the present disclosure. With the teachings and suggestions in the present disclosure, the skilled in the art may conceive other modifications or variations to the configurations for repetition level in the present disclosure, which shall fall within the scope of the present disclosure. 
     In some embodiments of the disclosure, if the first channel quality is less than the second channel quality, it means that there is a gap between the physical downlink channel quality (represented by the first channel quality) and the target downlink channel quality (represented by the second channel quality). In this situation, the network device  110  may increase the repetition level so that a repetition gain of the increased repetition level is larger than a difference between the first channel quality and the second channel quality. In this way, more repetition coding gain can be exploited through repetition downlink transmission in order to fill the gap between the second channel quality and the first channel quality. The repetition gain represents a channel quality gain of an increased repetition level with respect to the case of no repetition transmission in the downlink channel. The repetition gain for different repetition levels may be predetermined by link level, system level simulations and/or field tests. 
     In some embodiments of the disclosure, the network device  110  may also transmit the updated repetition level for the downlink channel in a downlink signaling to the terminal device  120 . For example, the updated repetition level may be explicitly informed from the network device  110  to the terminal device  120  in the DCI in PDCCH, Medium Access Control (MAC) Control Element (CE) or the Radio Resource Control (RRC) signaling. For another example, the updated repetition level may be obtained by the terminal device  120  in an implicit way. For instance, the terminal device  120  may derive the updated repetition level by performing a blind detection itself for example. 
       FIG. 4  shows a block diagram of an apparatus  400  in accordance with some embodiments of the present disclosure. The apparatus  400  may be implemented at the network device  110  in the network  100 . 
     The apparatus  400  includes a first determining unit  410 , a second determining unit  420  and an updating unit  430 . The first determining unit  410  may be configured to determine a first channel quality of a downlink channel between the network device  110  and a terminal device  120 , based at least in part on uplink transmission from the terminal device  120  to the network device  110 . The second determining unit  420  may be configured to determine a second channel quality of the downlink channel based on a set of parameters associated with a target performance of the downlink channel. The updating unit  430  may be configured to update a repetition level for the downlink channel based on the first channel quality and the second channel quality. The repetition level indicates a number of repetition transmissions in the downlink channel. 
     In some embodiments of the disclosure, the downlink channel is a downlink control channel, and the first determining unit  410  may be configured to determine the first channel quality based on at least one of a CQI from an uplink channel between the network device  110  and the terminal device  120 , and a detection of a DTX from the uplink channel. 
     In some embodiments of the disclosure, the downlink channel is a downlink data channel, and the first determining unit  410  may be configured to determine the first channel quality based on at least one of a CQI from an uplink channel between the network device  110  and the terminal device  120 , a statistics of ACK and NACK from the uplink channel, and a value of CFI for a downlink control channel. 
     In some embodiments of the disclosure, the second determining unit  420  may be further configured to determine the second channel quality of the downlink channel based on a predetermined error rate of the downlink channel. 
     In some embodiments of the disclosure, the downlink channel is a downlink data channel, and the second determining unit  420  may be configured to determine a MCS based on the first channel quality; and determine second channel quality based on the set of parameters associated with the performance of the downlink channel under the determined MCS. 
     In some embodiments of the disclosure, the second determining unit  420  may be configured to determine a MCS based on the first channel quality and a relationship between MCSs and channel qualities. 
     In some embodiments of the disclosure, the updating unit  430  may be configured to in response to the first channel quality exceeding the second channel quality, keep the repetition level unchanged or decrease the repetition level. 
     In some embodiments of the disclosure, the updating unit  430  may be configured to in response to the first channel quality being less than the second channel quality, increase the repetition level so that a repetition gain of the increased repetition level is larger than a difference between the first channel quality and the second channel quality. 
     In some embodiments of the disclosure, the apparatus  400  may include a transmitting unit, which may be configured to transmit the updated repetition level for the downlink channel to the terminal device  120 . 
     In some embodiments of the disclosure, the first channel quality and the second channel quality are at least one of a SINR and SNR. 
     In some embodiments of the disclosure, the communication network is a MTC network, and the downlink channel is at least one of MPDCCH and MPDSCH. 
     It is also to be understood that the apparatus  400  may be respectively implemented by any suitable technique either known at present or developed in the future. Further, a single device shown may be alternatively implemented in multiple devices separately, and multiple separated devices may be implemented in a single device. The scope of the present disclosure is not limited in these regards. 
     Additionally, the apparatus  400  may be configured to implement functionalities as described with reference to  FIG. 3 . Therefore, the features discussed with respect to the method  300  may apply to the corresponding components of the apparatus  400 , and the features discussed with respect to the method  300  may apply to the corresponding components of the apparatus  400 . It is to be appreciated that the components of the apparatus  400  may be embodied in hardware, software, firmware, and/or any combination thereof. For example, the components of the apparatus  400  may be respectively implemented by a circuit, a processor or any other appropriate device. Those skilled in the art will appreciate that the aforesaid examples are only for illustration not limitation. 
     In some embodiment of the present disclosure, the apparatus  400  may comprise at least one processor. The at least one processor suitable for use with embodiments of the present disclosure may include, by way of example, both general and special purpose processors already known or developed in the future. The apparatus  400  may further comprise at least one memory. The at least one memory may include, for example, semiconductor memory devices, e.g., RAM, ROM, EPROM, EEPROM, and flash memory devices. The at least one memory may be used to store program of computer executable instructions. The program can be written in any high-level and/or low-level compliable or interpretable programming languages. In accordance with embodiments, the computer executable instructions may be configured, with the at least one processor, to cause the apparatus  400  to at least perform according to the method  300  as discussed above. 
     Based on the above description, the skilled in the art would appreciate that the present disclosure may be embodied in an apparatus, a method, or a computer program product. In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the embodiments of this disclosure may be illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. 
     The various blocks shown in  FIG. 4  may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). At least some aspects of the embodiments of the disclosures may be practiced in various components such as integrated circuit chips and modules, and that the embodiments of this disclosure may be realized in an apparatus that is embodied as an integrated circuit, FPGA or ASIC that is configurable to operate in accordance with the embodiments of the present disclosure. 
       FIG. 5  is a simplified block diagram of a network device  500  that is suitable for implementing embodiments of the present disclosure. As shown, the network device  500  includes one or more processors  510 , one or more memories  520  coupled to the processor(s)  510 , one or more transmitters and/or receivers (TX/RX)  540  coupled to the processor  510 . 
     The processor  510  may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, Digital Signal Processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The network device  500  may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor. 
     The memory  520  may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. 
     The memory  520  stores at least a part of a program  530 . The TX/RX  540  is for bidirectional communications. The TX/RX  540  has at least one antenna to facilitate communication, though in practice the network device  500  mentioned in this disclosure may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements. 
     The program  530  is assumed to include program instructions that, when executed by the associated processor  510 , enable the network device  500  to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to  FIGS. 2 and 3 . That is, embodiments of the present disclosure can be implemented by computer software executable by the processor  510  of the network device  500 , or by hardware, or by a combination of software and hardware. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any disclosure or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular disclosures. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it is to be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Various modifications, adaptations to the foregoing embodiments of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and embodiments of this disclosure. Furthermore, other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these embodiments of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. 
     Therefore, it is to be understood that the embodiments of the disclosure are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a generic and descriptive sense only and not for purpose of limitation.