PATENT DOCUMENT

Publication Number: US-10728903-B2
Application Number: US-201615128264-A
Country: US
Kind Code: B2

Title: Apparatus, systems and methods for adaptive downlink scheduling and link adaptation

Abstract:
Described herein are apparatuses, systems and methods for adaptive downlink scheduling and link adaptation. The methods including, at a base station connected to a user equipment (“UE”), determining an initial modulation and coding scheme (“MCS”) for a plurality of subframes to be transmitted to the UE, wherein each MCS relates to a coding rate value for the subframes, determining an MCS pattern for the plurality of subframes based on the initial MCS, wherein an MCS for one of the subframes has a higher coding rate value than the initial MCS, and transmitting the plurality of subframes to the UE according to the MCS pattern.

Claims:
What is claimed is: 
     
       1. A method, comprising:
 at a base station connected to a user equipment (“UE”):
 determining an initial modulation and coding scheme (“MCS”) for a plurality of subframes to be transmitted to the UE, wherein the initial MCS relates to a coding rate for the plurality of subframes; 
 determining an MCS pattern for the plurality of subframes based on the initial MCS for the plurality of subframes, wherein the MCS pattern includes an MCS for each subframe of the plurality of subframes and wherein an MCS for at least one subframe of the plurality of subframes has a lower coding rate than the initial MCS; 
 transmitting the plurality of subframes to the UE according to the MCS pattern for the plurality of subframes; 
 receiving feedback from the UE in response to the plurality of subframes; 
 determining that a type of the feedback is ambiguous feedback; and 
 retransmitting only the at least one subframe of the plurality of subframes with the lower coding rate than the initial MCS based on the ambiguous feedback. 
 
 
     
     
       2. The method of  claim 1 , wherein the initial MCS is based on a signal-to-noise ratio (“SNR”) value in a communication channel between the base station and the UE. 
     
     
       3. The method of  claim 1 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is higher than the coding rate of the initial MCS. 
     
     
       4. The method of  claim 1 , wherein the one subframe of the plurality of subframes is a first subframe of the plurality of subframes transmitted to the UE. 
     
     
       5. The method of  claim 1 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is lower than the coding rate for the initial MCS. 
     
     
       6. The method of  claim 1 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is equal to the coding rate for the initial MCS. 
     
     
       7. The method of  claim 1 , wherein the transmitting of the plurality of subframes to the UE includes multiplexing an acknowledgment and negative acknowledgment (“ACK/NACK”) reporting set. 
     
     
       8. The method of  claim 1 , wherein determining that the type of feedback is ambiguous feedback is based on mapping payload data included in the feedback to different interpretations of an ACK/NACK status. 
     
     
       9. An evolved Node B (“eNB”), comprising:
 a transceiver configured to enable the eNB to establish a connected to a user equipment (“UE”) within a Long Term Evolution (LTE) network; and 
 a processor configured to:
 determine an initial modulation and coding scheme (“MCS”) for a plurality of subframes to be transmitted to the UE, wherein the initial MCS relates to a coding rate for the plurality of subframes, 
 determine an MCS pattern for the plurality of subframes based on the initial MCS for the plurality of subframes, wherein the MCS pattern includes an MCS for each subframe of the plurality of subframes and wherein an MCS for at least one subframe of the plurality of subframes has a lower coding rate than the initial MCS, 
 transmit the plurality of subframes to the UE according to the MCS pattern for the plurality of subframes 
 receiving feedback from the UE in response to the plurality of subframes, 
 determining that a type of the feedback is ambiguous feedback, and 
 retransmitting only the at least one subframe of the plurality of subframes with the lower coding rate than the initial MCS based on the ambiguous feedback. 
 
 
     
     
       10. The eNB of  claim 9 , wherein the initial MCS is based on a signal-to-noise ratio (“SNR”) value in a communication channel between the base station and the UE. 
     
     
       11. The eNB of  claim 9 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is higher than a coding rate of the initial MCS. 
     
     
       12. The eNB of  claim 9 , wherein the one subframe of the plurality of subframes is a first subframe of the plurality of sub frames transmitted to the UE. 
     
     
       13. The eNB of  claim 9 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is lower than the coding rate for the initial MCS. 
     
     
       14. The eNB of  claim 9 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is equal to the coding rate of the initial MCS. 
     
     
       15. The eNB of  claim 9 , wherein the transmitting of the plurality of subframes to the UE includes multiplexing an acknowledgment and negative acknowledgment (“ACK/NACK”) reporting set. 
     
     
       16. An integrated circuit configured to execute instructions, wherein execution of the instructions causes the integrate circuit to perform operations, comprising:
 determining an initial modulation and coding scheme (“MCS”) for a plurality of subframes to be transmitted to a UE, wherein the initial MCS relates to a coding rate for the plurality of subframes; 
 determining an MCS pattern for the plurality of subframes based on the initial MCS, wherein the MCS pattern includes an MCS for each subframe of the plurality of subframes and wherein an MCS for at least one subframe of the plurality of subframes has a lower coding rate than the initial MCS; 
 preparing the plurality of subframes to be transmitted to the UE according to the MCS pattern; 
 receiving feedback from the UE in response to the plurality of subframes; 
 determining that a type of the feedback is ambiguous feedback; and 
 retransmitting only the at least one subframe of the plurality of subframes with lower coding rate than the initial MCS based on the ambiguous feedback. 
 
     
     
       17. The integrated circuit of  claim 16 , wherein the initial MCS is based on a signal-to-noise ratio (“SNR”) value in a communication channel between a base station and the UE. 
     
     
       18. The integrated circuit of  claim 16 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate that is higher than the coding rate of the initial MCS. 
     
     
       19. The integrated circuit of  claim 16 , wherein the one subframe of the plurality of subframes is a first subframe of the plurality of subframes to be transmitted to the UE. 
     
     
       20. The integrated circuit of  claim 16 , wherein the MCS pattern includes an MCS for at least one further subframe of the plurality of subframes having a coding rate clue that is one of lower than the coding rate of the initial MCS or equal to the coding rate of the initial MCS.

Description:
BACKGROUND 
     In wireless telecommunication networks, Long-Term Evolution, or “LTE,” is defined as a standard for wireless communication of high-speed data for mobile phones and data terminals. The LTE standard is developed by the Third Generation Partnership Project (“3GPP”) and the Institute of Electrical and Electronics Engineers (“IEEE”). An exemplary LTE access network is a wireless network of base stations, or evolved NodeBs (“eNBs”), that are interconnected without a centralized intelligent controller. 
     Long-term evolution (“LTE”) is a wireless communication standard used for high-speed data for mobile devices and data terminals. LTE-Advanced is a major enhancement to the LTE standard. Within the LTE-Advanced standard, carrier aggregation is used to increase the bandwidth, and thereby increase the bitrates. Carrier aggregation has been introduced in the 3rd Generation Partnership Project (“3GPP”) Release 10 (LTE-Advanced standard) to provide wider than 20 MHz transmission bandwidth to a single device (e.g., user equipment or “UE”) while maintaining the backward compatibility with legacy UEs. Specifically, carrier aggregation may be defined as the aggregation of two or more component carriers in order to support wider transmission bandwidths. Carrier aggregation configuration may be defined as a combination of carrier aggregation operating bands, each supporting a carrier aggregation bandwidth class by a UE. The bandwidth class may be defined by the aggregated transmission bandwidth configuration and maximum number of component carriers supported by a UE. 
     For intra-band contiguous carrier aggregation, a carrier configuration may be a single operating band supporting a carrier aggregation bandwidth class. For each carrier aggregation configuration, requirements may be specified for all bandwidth combinations contained within a bandwidth combination set, as indicated by the radio access capabilities of the UE. Accordingly, a UE may indicate support of several bandwidth combination sets for each band combination. 
     Under the current standards, each aggregated carrier is referred to as a component carrier, and each component carrier can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz and a maximum of five component carriers can be aggregated. As illustrated in  FIG. 1 , two exemplary component carriers may each have a bandwidth of 10 MHz to combine for a total bandwidth of 20 MHz. With carrier aggregation (“CA”) features enabled, the LTE-Advanced standard device supporting 20 MHz carrier aggregation may achieve downlink throughput of 100 Mbps. 
     In the frequency division duplex (“FDD”) CA case, the number of aggregated carriers can be different in the downlink (“DL”) and the uplink (“UL”). However, the number of UL component carriers is always equal to or lower than the number of DL component carriers. The individual component carriers can also be of different bandwidths. For time division duplex (“TDD”) CA case, the number of component carriers, as well as the bandwidths of each component carrier, will normally be the same for DL and UL. 
     SUMMARY 
     Described herein are apparatuses, systems and methods for adaptive downlink scheduling and link adaptation. The methods including, at a base station connected to a UE, determining an initial modulation and coding scheme (“MCS”) for a plurality of subframes to be transmitted to the UE, wherein each MCS relates to a coding rate value for the subframes, determining an MCS pattern for the plurality of subframes based on the initial MCS, wherein an MCS for one of the subframes has a higher coding rate value than the initial MCS, and transmitting the plurality of subframes to the UE according to the MCS pattern. 
     Further described herein is an eNB comprising a transceiver configured to enable the eNB to establish a connected to a UE within an LTE network, and a processor configured to determine an initial MCS for a plurality of subframes to be transmitted to the UE, wherein each MCS relates to a coding rate value for the subframes, determine an MCS pattern for the plurality of subframes based on the initial MCS, wherein an MCS for one of the subframes has a higher coding rate value than the initial MCS, and transmit the plurality of subframes to the UE according to the MCS pattern. 
     Further described herein is an eNB comprising a transceiver configured to establish a connection to a UE using an outer loop link adaptation (“OLLA”) and an inner link adaptation loop, and a processor configured to receive and decode a physical uplink control channel (“PUCCH”) message from UE, identify a status indication from the PUCCH message, when the status indication identifies a designation of a first feedback type, set an update rate of the OLLA to a first value, wherein the first value is less than a maximum update rate of the OLLA, and when the status indication identifies a designation of second feedback type, set an update rate of the OLLA to a second value, wherein the second value is less than a maximum update rate of the OLLA. 
     Further described herein is a method comprising, at a base station connected to a UE using an OLLA and an inner link adaptation loop, receiving and decoding a PUCCH message from UE, identifying a status indication from the PUCCH message, when the status indication identifies a designation of a first feedback type, setting an update rate of the OLLA to a first value, wherein the first value is less than a maximum update rate of the OLLA, and when the status indication identifies a designation of second feedback type, setting an update rate of the OLLA to a second value, wherein the second value is less than a maximum update rate of the OLLA. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary network arrangement  100  according to various embodiments described herein. 
         FIG. 2  shows the UE configured to establish a connection with the eNB of the LTE-RAN according to various embodiments described herein. 
         FIG. 3  shows the eNB of the LTE-RAN configured to establish a connection with the UEs according to various embodiments described herein. 
         FIG. 4  shows a table for transmission of HARQ-ACK multiplexing, wherein there are four bits (M). 
         FIG. 5  shows an exemplary method for adaptive per subframe DL scheduling at a mobile device, such as the UE, in a wireless network, such as the LTE-RAN, according to various embodiments described herein. 
         FIG. 6  shows an exemplary system including the UE in communication with the eNB using link adaptation loops according to various embodiments described herein. 
         FIG. 7  shows an exemplary method for adaptive link adaptation at the outer loop according to various embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The exemplary embodiments describe an apparatus, system and method for adaptive downlink scheduling and link adaptation. Furthermore, exemplary embodiments also describe adaptive link adaptation for outer loop in carrier aggregation scenarios. Within these exemplary embodiments, a mobile device will be described as user equipment (“UE”) and the base station will be described as an evolved Node B (“eNB”) base station, which is generally known as being a base station associated with a Long-Term Evolution (“LTE”) radio access network (“LTE-RAN”). However, it will be understood by those skilled in the art that UEs and base stations operating in accordance with other network standards may also implement the exemplary embodiments in accordance with the functionalities and principles described herein. 
     The LTE-RAN may be a portion of the cellular networks deployed by cellular providers or operators (e.g., Verizon, AT&amp;T, Sprint, T-Mobile, etc.). These networks may include, for example, base client stations (Node Bs, eNodeBs, HeNBs, etc.) that are configured to send and receive traffic from UEs that are equipped with an appropriate cellular chip set. In addition to LTE-RAN, the operators may also include legacy RANs that are generally labeled as 2G and/or 3G networks and may utilize circuit switched voice calls and packet switched data operations. Those skilled in the art will understand that the cellular providers may also deploy other types of networks, including further evolutions of the cellular standards, within their cellular networks. 
       FIG. 1  shows an exemplary network arrangement  100  according to various embodiments described herein. The exemplary network arrangement  100  is illustrated as including UEs  115 ,  120 . In this example, it is assumed that a respective, different user is using each of the UEs  115 ,  120 . For example, a first user may be utilizing the UE  115  while a second user may be utilizing the UE  120 . Those skilled in the art will understand that the UEs  115 ,  120  may be any type of electronic component that is configured to communicate via a network, e.g., mobile phones, tablet computers, desktop computers, smartphones, phablets, embedded devices, wearables, etc. It should also be understood that an actual network arrangement may include any number of UEs being used by any number of users and being associated with any number of these users where the user may be associated with one or more of the UEs. That is, the example of two UEs  115 ,  120  is only provided for illustrative purposes. 
     Each of the UEs  115 ,  120  may be configured to communicate with one or more networks. According to the exemplary embodiments, the UEs  115 ,  120  may communicate with a LTE radio access network (LTE-RAN)  105 . Specifically, the UEs  115 ,  120  may connect to the LTE-RAN  105  via an base station (which may be an access point) such as an evolved Node B (eNB)  110 . The LTE-RAN  105  may be a cellular network that may be deployed by a cellular provider (e.g., Verizon, AT&amp;T, Sprint, T-Mobile, etc.). The LTE-RAN  105  may include, for example, base stations such as the eNB  110  (or other types such as Node Bs, HeNBs, etc.) that are configured to send and receive traffic from UEs that are equipped with the appropriate LTE cellular chip set. Those skilled in the art will understand that the cellular providers may also deploy other types of networks, including further evolutions of the cellular standards, within their cellular networks. 
     More specifically, the eNB  110  may include one or more antenna groups which are configured to exchange data with the UEs  115 ,  120 . The data may be exchanged in communications where data transmitted from the eNB  110  to the UEs  115 ,  120  comprise a downlink or forward link and data transmitted from the UEs  115 ,  120  to the eNB  110  comprise an uplink or reverse link. Based upon the type of LTE-RAN  105 , the communication links under a frequency division duplex (FDD) system may use different frequencies for communications, particularly between the UE  115  and the UE  120  while communication links under a time division duplex (TDD) system may use a common frequency but at differing times. It should be noted that the communication between the UEs  115 ,  120  and the LTE-RAN  105  via the eNB  110  may include further parameters such as an operating area of the eNB  110  and diversity techniques (e.g., spatial multiplexing, spatial diversity, pattern diversity, etc.). The exemplary embodiments may utilize any of these properties of the LTE-RAN  105 . 
       FIG. 2  shows the UE  115  configured to establish a connection with the eNB  110  of the LTE-RAN  105  according to various embodiments described herein. Initially, it is noted that the description below relates to the UE  115 . However, the description for the UE  115  may also apply to the UE  120 . The UE  115  may include a processor  205 , a memory arrangement  210 , a display device  215 , an input/output (I/O) device  220 , a transceiver  225 , and other components  230 . The other components  230  may include, for example, an audio input device, an audio output device, a battery, a data acquisition device, ports to electrically connect the UE  115  to other electronic devices, etc. 
     The processor  205  may be configured to execute a plurality of applications of the UE  115 . It should be noted that the processor  205  may include an application processor and a baseband processor. For example, the application processor may be utilized for a plurality of applications executed on the UE  115  such as the web browser. In another example, the baseband processor may be utilized for operations associated with the LTE-RAN  105  and the connection thereto. The above noted applications each being an application (e.g., a program) executed by the processor  205  are only exemplary. The functionality associated with the applications may also be represented as a separate incorporated component of the UE  115  or may be a modular component coupled to the UE  115 , e.g., an integrated circuit with or without firmware. 
     The memory  210  may be a hardware component configured to store data related to operations performed by the UE  115 . The display device  215  may be a hardware component configured to show data to a user while the I/O device  220  may be a hardware component that enables the user to enter inputs. It should be noted that the display device  215  and the I/O device  220  may be separate components or integrated together such as a touchscreen. The transceiver  225  may be a hardware component configured to transmit and/or receive data. That is, the transceiver  225  may enable communication with the LTE-RAN  105 . The transceiver  225  may operate on a variety of different frequencies or channels (e.g., set of consecutive frequencies) that are related to the LTE-RAN  105 . Thus, an antenna (not shown) coupled with the transceiver  225  may enable the transceiver  225  to operate on the LTE frequency band. For example, the UE  115  may perform uplink and/or downlink communication functionalities via the transceiver  225  with the LTE-RAN  105 . 
       FIG. 3  shows the eNB  110  of the LTE-RAN  105  configured to establish a connection with the UEs  115 ,  120  according to various embodiments described herein. As discussed above, the eNB  110  may be any access point or base station of the LTE-RAN  105  that enables the UEs  115 ,  120  to establish a connection to the LTE-RAN  105 . The eNB  110  may be one of a plurality of base stations deployed for the LTE-RAN  105 . The eNB  110  may provide a portion of the operating area of the LTE-RAN  105 . The eNB  110  may include a baseband processor  305 , a transceiver  325 , a timing and control unit  330 , and a network interface unit  335 . 
     The baseband processor  305  may provide a radio communication with the UEs  115 ,  120  via the transceiver  325 , which may be coupled to an antenna (not shown). The transceiver  325  may be substantially similar to the transceiver  225  of the UE  115  such as operating on a predetermined frequency or channel of the LTE-RAN  105 . It should be noted that the transceiver  225  may include a separate transmitter and receiver or a combined unit that performs the functionalities of the transmitter and receiver. The baseband processor  305  may be configured to operate according to a wireless communications standard based upon the LTE-RAN  105  (e.g., a 3GPP LTE). The baseband processor  305  may include a processing unit  310  to process relevant information for the eNB  110 . The baseband processor  305  may also provide additional baseband signal processing operations as may be utilized such as a UE registration, a channel signal information transmission, a radio resource management, a connected discontinuous reception (“C-DRX”) functionality, etc. The baseband processor  305  may also include a memory arrangement  310  that is in communication with the processing unit  310  to store the relevant information including the various signal processing operations for the eNB  110 . The baseband processor  305  may further include a scheduler  320  which may provide scheduling decisions for the UEs  115 ,  120  serviced by the eNB  110 . 
     The timing and control unit  330  may monitor operations of the baseband processor  305 . The timing and control unit  330  may also monitor the operations of the network interface unit  335 . The timing and control unit  330  may accordingly provide appropriate timing and control signals to these units. The network interface unit  335  may provide a bi-directional interface for the eNB  110  to communicate with other network components of the LTE-RAN  105  such as a core network or a back-end network. This may enable a facilitation of administrative and call-management functionalities for the UEs  115 ,  120  operating in the LTE-RAN  105  through the eNB  110 . 
     The exemplary embodiments provide a mechanism for performing a channel state feedback (“CSF”) operation. The CSF operation may be used in generating a report for the eNB  110  to manage the connection between the UE  115  and the eNB  110 . The CSF operation may be associated with a link adaptation operation, particularly of an inner loop. Specifically, the mechanism of the exemplary embodiments set a block error rate (“BLER”) target value to be used in the CSF operation. 
     The link adaptation functionality may be a wireless communication that denotes a matching of modulation, coding, and other signal and protocol parameters to a radio link such as the connection between the UE  115  and the eNB  110 . For example, the denoting may be to a path loss, an interference such as from signals from other UEs, a sensitivity of a receiver, an available transmitter power margin, etc. The link adaptation functionality may also be referred to as an adaptive modulation and coding (“AMC”) functionality. Those skilled in the art will understand that the link adaptation functionality may be used with a rate adaptation functionality in adapting a modulation and coding scheme (“MCS”). This adaptation may be with respect to a quality of the radio channel in which the connection is established between the UE  115  and the eNB  110 . Therefore, the bit rate and robustness of a data transmission may be managed where the process of the link adaptation functionality is dynamic to change the signal and protocol parameters as the radio link conditions change. 
     An adaptive modulation system uses connection-related information, such as channel state information, at the transmitter of the UE  115 . Accordingly, connection parameters and metrics may be determined and utilized for this purpose. That is, connection-related information may include the connection parameters and metrics that are determined or calculated such as a channel estimation, a received signal strength, etc. Those skilled in the art will understand that the connection-related information may be determined based upon packets or signals received from the eNB  110  such as pilot signals. For example, in a TDD system, the channel from the transmitter to the receiver may be assumed to be approximately the same as the channel from the receiver to the transmitter. In another example, the information of the channel may be directly measured at the receiver and used with the transmitter. Through this mechanism of the adaptive modulation system, a rate of transmission and/or bit error rates may be improved through exploiting the channel state information that is determined at the transmitter of the UE  115 . 
     When carrier aggregation is used with the exemplary UE  115 , there may be a number of serving cells for each of the component carriers. The coverage of the serving cells may differ due to both component carrier frequencies and power planning, which is useful for heterogeneous network planning. A radio resource control (“RRC”) connection is handled by one cell, namely the primary serving cell (“PCell”), served by the primary component carrier (“PCC”) for uplink (“UL”) and downlink (“DL”). 
     The other component carriers may be referred to as secondary component carrier (“SCCs”) for UL and DL, serving the secondary serving cells (“SCells”). The SCCs are added and removed as required, while the PCC is changed at handover. Those skilled in the art will understand that the PCell and SCells are logical constructs allowing for the addition of SCells as needed. The PCell is the main cell that is used for all RRC signaling and control procedures, while the SCell is considered an augmentation to the PCell. 
     Within a TDD carrier aggregation, a typical scenario includes more than one configured serving cell with a physical uplink control channel (“PUCCH”) in format 1b with channel selection in order to carry to uplink control information. The PUCCH may be a stand-alone uplink physical channel, wherein the PUCCH control signaling channel may comprises hybrid automatic repeat request (“HARQ”) acknowledgments and negative acknowledgments (“ACK/NACK”), discontinuous transmissions (“DTX”), channel quality indicators (“CQIs”), rank indicators (“RIs”), precoding matrix indicators (“PMIs”), scheduling requests for uplink transmission, BPSK or QPSK used for PUCCH modulation, etc. 
     During a TDD CA scenario, more than 4 HARQ-ACK bits for multiple DL subframes may be associated with a single UL subframe (n). For the configuring serving cells, spatial HARQ-ACK bundling may be performed across multiple codewords within a DL subframe for all configured cells. Furthermore, the bundled HARQ-ACK bits for each configured serving cell may be transmitted using the abovementioned PUCCH format 1b with channel selection. Accordingly, payload b(0), b(1) sent on different PUCCH resources may be mapped to different ACK/NACK status for associated subframes. In addition, the same payload sent on the same PUCCH resource may be mapped to different interpretations of ACK/NACK status. This mapping to different interpretations may be referred to as ambiguity. 
     In a multiplexed set, if there is a NACK, the error may be propagated to other subframes due to this ambiguity. For instance, an exemplary eNB may not have the exact ACK/NACK/DTX information decoded. Therefore, the eNB may consider the feedback to be classified as DTX. If the actual decoded result of DL receptions at the UE  115  is ACK, the eNB would still retransmit these subframes due to the ambiguity. If the actual feedback is NACK, the eNB does not adjust the current MCS to a lower MCS, also due to the ambiguity. 
       FIG. 4  shows a table  400  for transmission of HARQ-ACK multiplexing, wherein there are four (4) bits (M). As depicted in the table  400 , there are entries for the Pcell (e.g., HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3)) the SCell (e.g., HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3)), the resource (e.g., PUCCH indicator), the constellation (e.g., b(0), b(1)), and RM code input bits (e.g., o(0), o(1), o(2), o(3)). It should be noted that the first subframe having the ACK/NACK result is significant due to the fact that if the first result is NACK/DTX, then all subsequent feedback is “any” and the eNB considers such feedback as DTX. Furthermore, it should be noted that while  FIG. 4  discusses the use of four bits (e.g., M=4), this is only an example of one embodiment, as any number of bits may be utilized (e.g., M=3, M=2, etc.). For instance, the further embodiments may be applied to alternative scenarios, such as transmission of HARQ-ACK multiplexing for M=3, where there may be ambiguity in UL report of ACK/NAK information of DL reception. Accordingly, the systems and methods described herein are not limited to the four bit, M=4, scenario depicted in table  400  of  FIG. 4 . 
     According to the exemplary embodiments of the systems and methods described herein, different MCSs may be used for different subframes. Specifically, each previous subframe may have a lower MCS than the next subframe. The purpose of this arrangement is to ensure that the previous subframe is decoded successfully and to prevent the subsequent frames from being deemed as ambiguous. 
     When the exemplary UE  115  uses PUCCH format 1b with channel selection for the ACK/NACK feedback, table  400  illustrates that there are many items with the feedback bit set to “any.” In such a case, the exemplary eNB  110  cannot identify the real value. Thus, the eNB  110  would then consider all of these “any” bits to be DTX and therefore would retransmit the subframes again. If the UE  115  decodes these subframes correctly, but the eNB  110  retransmits the subframes because the eNB  110  could not identify the real value, this scenario will lead to wasted radio resources. On the other hand, if the UE  115  did not decode these subframes correctly, then it would be appropriate for the eNB  110  to retransmit the subframes. However, the problem is that the eNB  110  will not adjust the MCS while performing the outer loop link adaptation since the eNB  110  does not consider the feedback as a NACK, but rather just as ambiguous feedback. As a result, the performance will diminish since the eNB  110  will experience a much higher BLER when compared with non-carrier aggregation. The adaptive link adaptation for the outer loop will be described in greater detail below. 
       FIG. 5  shows an exemplary method  500  for adaptive per subframe DL scheduling at a mobile device, such as the UE  110 , in a wireless network, such as the LTE-RAN  105 , according to various embodiments described herein. The method  500  will be described with reference to the network arrangement  100  of  FIG. 1 . The exemplary embodiments show systems and methods for carrier channel selection (e.g., PCC and SCC) in TDD carrier aggregation enabled networks. 
     The exemplary method  500  described herein may enhance the performance of the eNB  110  by allowing the eNB  110  to allocate different MCS for different subframes in a multiplexed ACK/NACK reporting set. Specifically, the first subframe may be allocated with the lowest MCS and the last subframe may be allocated with the highest MCS. This is due to the fact that the first subframe is more significant considering the possible propagation effect of the first subframe. 
     In  510 , the eNB  110  determines the signal-to-noise ratio (“SNR”) at the UE  115  and the initial MCS of the subframes. For instance, the eNB  110  may determine that the SNR is 10 dB and the initial MCS is 16 for 4 scheduled subframes. Thus, in this example, the eNB  110  determines that the SNR having a value of 10 dB means that the coding value for the MCS should be 16. 
     In  520 , the eNB  110  determines an MCS pattern for each of the subframes. For instance, in the four-subframe example, Subframe 1 may have a MCS of 14, Subframe 2 may have a MCS of 15, Subframe 3 may have a MCS of 16 and Subframe 4 may have a MCS of 17. Those skilled in the art would understand that the MCS may be used to determine the coding rate, wherein the higher the MCS equates to a higher coding rate (e.g., a lower numerical MCS value is a more robust coding rate). In  530 , the eNB  110  then transmits the subframes to the UE  115  based on the MCS pattern determined in  520 . 
     In  540 , the UE  115  may decode the physical downlink shared channel (“PDSCH”) based on the MCS pattern determined by the eNB  110 . According to the example above, with the MCS of 16 at an SNR of 10, it is likely the UE  115  will decode the PDSCH correctly. Furthermore, when the MCS of the subframes is lower than the initial MCS (e.g., with MCS 14 and 15), the UE  115  may be assured of decoding these subframes correctly. The only possible incorrect decoding may be within subframes having a higher MCS, such as Subframe 4 with MCS 17. 
     In  550 , the UE  115  transmits the feedback to the eNB  110 . The exemplary per subframe DL scheduling limits the number of retransmissions of subframes by the eNB  110  to those having a higher numeric MCS value than that of the initial MCS. In other words, using the MCS pattern of  520 , the eNB  110  may only have the possibility to retransmit Subframe 4 since the MCS 17 of Subframe 4 is higher than the initial MCS of 16. That it, the eNB  110  is assured that the first three subframes have been decoded correctly because the MCS is at least as robust as required for the SNR being experienced on the channel. Accordingly, the eNB  110  and the network  105  can save more resources without the need for unnecessary retransmission due to multiplexing in TDD carrier aggregation scenarios. Furthermore, the eNB  110  may have more accurate knowledge of which subframe was, in fact, the cause of the ACK transmission. This more accurate knowledge of the ACK/NACK information from the UE  115  may be used by the eNB  110  to update the link adaptation outer loop according to an outer loop link adaptation update rate. 
       FIG. 6  shows an exemplary system  600  including the UE  115  in communication with the eNB  110  using link adaptation loops according to various embodiments described herein. The system  600  will be described with reference to the network arrangement  100  of  FIG. 1 . As depicted in  FIG. 6 , the system  600  may include an inner loop  610  and an outer loop  620  that may be the representative components of the link adaptation functionality between the eNB  110  and the UE  115 . 
     The inner loop  610  may be used by the UE  115  for providing the eNB  110  with a channel state feedback (“CSF”) report. The CSF report may include information such as CQI, RI, PMI, etc. Specifically, the UE  115  may perform CSF estimation based on the channel estimation on the DL pilot signals and report back to the eNB  110 . Accordingly, the inner loop  610  may also be used by the eNB  110  for scheduling MCS/RB based on filtered CSF. Specifically, the eNB  110  may schedule DL grants with corresponding MCSs, number of resource blocks (“RBs”), and multiple-input, multiple-output (“MIMO”) types. According to an exemplary embodiment, the CSF (e.g., CQI/PMI/RI) estimation may be targeted to achieve less than 10% BLER for additive white Gaussian noise (“AWGN”) channels. 
     The outer loop  620  may include a BLER target to be maintained by the eNB  110 . The BLER target may vary for different channel scenarios such as being Doppler dependent. The channel state feedback operation may have an estimation at the UE  115  that is not always reliable. Therefore, the eNB  110  may filter the BLER of the UE  115  based upon adjustments to the MCS type and/or MIMO type that is scheduled for the UE  115  by the eNB  110 . The BLER filtering of the outer loop  620  may be implemented in different manners. In a first example, the BLER filtering may be an infinite impulse response (“IIR”) filtering of errors in a cyclic redundancy check (“CRC”). In a second example, the BLER filtering may be a block-wise moving average. Furthermore, one or more hystereses may usually be applied to the BLER targets when an average BLER changes to a degree sufficiently large enough to trigger the MCS adjustment. 
     The outer loop  620  scheduling may particularly relate to a scheduling adjustment such as a MCS to RB. The scheduling adjustment may also be based upon a filtered BLER. For example, in the LTE-RAN  105 , the MCS that determines the coding rate where a higher MCS results in a higher coding rate may be adjusted based on the filtered BLER fluctuation. In addition, a step size of the MCS adjustment may also be of importance. To have a stable outer loop, the step size for the MCS to be adjusted upward is usually smaller compared to the step size for the MCS to be adjusted downward. This processing of the outer scheduling may result in the outer ACK, such as the ACK being included in a physical downlink shared channel (“PDSCH”). 
     Accordingly, the outer loop  620  may be used by the UE  115  for providing the eNB  110  with PDSCH ACK information. Furthermore, the use of the outer loop  620  by the eNB  110  to adjust scheduling (e.g., MCS/RB/MIMO types) may be referred to as an outer loop link adaptation (“OLLA”). For instance, there may be a BLER target to be maintained by the eNB  110 , wherein this BLER target may vary for different channel scenarios (e.g., such a Doppler dependency). Since the CSF estimation provided by the UE  115  may not be reliable, the eNB  110  may filter the UE BLER and adjust the MCS/MIMO type scheduled for the UE  115  based on this filtered BLER. 
     In regards to scheduling adjustments, such as within the LTE network  105 , the MCS may be adjusted by the eNB  110  based on the filtered BLER fluctuation. Furthermore, the step size of the MCS adjustment may also be of significance. For instance, in order to have a stable outer loop  620 , the step size for the MCS to be adjusted up may be smaller in comparison to the step size for the MCS to be adjusted down. 
     According to an exemplary carrier aggregation scenario, there may be two activated carriers and the UL-DL configuration may be presumed to be 2. Within such a TD-LTE DL CA scenarios, there are simply not enough bits available to fully represent the possibility of DL reception status (ACK/NACK/DTX) in the PUCCH. Accordingly, there are ambiguities of decoding PUCCH for obtaining the DL CRC status at the eNB  110 . For example, the table  400  discussed above demonstrates that there are ambiguities shown in the form of designations of “NACK/DTX” or “any.” 
     When handling such transmission of DL status information, the eNB  110  is unable to resolve the ambiguity of either “NACK/DTX” or “any.” Specifically, the eNB  110  may take conservative approaches of interpreting DL CRC status and apply different considerations to those in the link adaptation outer loop  620  for updating the outer loop BLER filtering. For instance, the eNB  120  may consider the “NACK/DTX” designation as NACK and update the outer loop BLER filtering accordingly. The eNB  120  may consider the “any” designation as DTX and skip the updating of the outer loop BLER filter. Otherwise, the eNB  120  may introduce a vast change to the BLER filtering and impact the stability of the OLLA. 
     It should be noted that since the interpretation by the eNB  120  of decoded PUCCH information for DL CA may be conservative due to ambiguity, there may be issues of not being able to adapt the BLER outer loop if the eNB  120  initial set point over-schedules with higher MCSs. Accordingly, this may lead to high BLER, and thus, lower total throughput. 
     Specifically, as noted above, the eNB  120  may skip the update to the outer loop  620  when the decoded PUCCH information is designated with “any,” and interpreted as a NACK at the eNB  120 . This may lead to the OLLA not being able to adjust to achieve a proper BLER target. Conversely, if all of the “any” designations are considered by the eNB  120  to be NACK due to ambiguity, the BLER OLLA loop may be over-adjusted. Such over-adjustments may lead to large fluctuations of the OLLA, and thus increase the time and/or complexity of loop convergence. 
       FIG. 7  shows an exemplary method  700  for adaptive link adaptation at the outer loop  620  according to various embodiments described herein. The method  700  will be described with reference to the network arrangement  100  of  FIG. 1  and system  600  of  FIG. 6 . According to the exemplary method  700 , the eNB  110  may adaptively adjust a OLLA update rate based on the decoded PUCCH message in DL CA scenarios within the TD-LTE network  105 . 
     In  710 , the eNB  110  may receive and decode a PUCCH message. As detailed above and in table  400  of  FIG. 4 , the decoded message may provide the eNB  110  with transmission indicators for CRC status such as ACK, NACK, DTX, and any. 
     In  720 , the eNB  110  may determine if the designation is “NACK/DTX.” If the decoded CRC status is “NACK/DTX,” in  730  the eNB  110  may consider the designation as NACK and set the OLLA loop update rate to a first rate (e.g., rate α). According to an exemplary embodiment, the rate α may have a value of 0&lt;α&lt;1. That is, while the eNB  110  cannot resolve the ambiguity, the eNB  110  is not required to assume the most conservative approach, e.g., the CRC status is a NACK and adjust the OLLA at the full rate. Rather, the eNB  110  assumes the CRC status to be a NACK, but sets the OLLA update rate at a value α, that is less than the full rate. In this way, as the eNB  110  receives the ambiguous NACK/DTX feedback, the eNB  110  is not limited to only adjusting the OLLA at the full rate or not adjusting the OLLA at all. The α value for the OLLA update rate allows the eNB  110  to essentially assume a certain number of the NACK/DTX are NACKS and the remaining are DTXs because the OLLA update rate is a partial update rate. 
     The value of α may be set according to various manners. For example, it may be possible to collect data from UEs in a particular environment (e.g., location) and determine the number of actual NACKs and DTXs that have been recorded. This data may then be used by an administrator of the eNB  110  to set the α value. In another example, the eNB  110  (or a series of eNBs) may measure the overall performance of the OLLA updates using various α values and then converge to an appropriate α value. Those skilled in the art will understand that there may be other manners of determining the α value. It should also be noted that the α value may be variable for the eNB  110  based on various factors such as, but not limited to, loading, SNR, time of day, etc. 
     Continuing with the method  700 , if the decoded CRC status is not “NACK/DTX,” in  740  the eNB  110  may determine if the designation is “any.” If the decoded CRC status is “any,” in  750  the eNB  110  may set the OLLA loop update rate to a second rate (e.g., rate β). According to an exemplary embodiment, the rate β may have a value of β&lt;α. Since a feedback of “any” could be an ACK, NACK or DTX, the likelihood of a NACK is less than the likelihood of a NACK when the ambiguity is NACK/DTX. Thus, the value of β is set to a value that is less than α because there is a lower likelihood of the ambiguity actually being a NACK. That is, the values of α and β are set such that a higher value means a faster OLLA update. Since the NACK/DTX ambiguity (α value update rate) is more likely a NACK than the “any” ambiguity (β value update rate), the α value is normally set higher than the β value. However, this is not a requirement. Actual usage data may indicate circumstances where the β value is set higher than α value. The value of β may be set in a similar manner to the examples provided above for the value of α. 
     In  760 , the eNB  110  may update the OLLA loop  620  based on the update rate set in  730  and  750 . According an exemplary embodiment, the OLLA loop  620  may be updated based on a type of loop implementation, such as, but not limited to, an IIR BLER filtering loop, a sliding window loop, etc. Accordingly, if the loop  620  is implemented as an IIR BLER filtering loop, the filtering coefficients may be adjusted for adapting the rates. For example, a single-tap IIR may only have one coefficient to be adjusted. If the loop  620  is implemented as a sliding window, a lower rate may be achieved as a lower weight is placed on those CRC statuses while summing the weighted CRC feedback. It should be noted that if the eNB  110  definitively determines a NACK feedback, the eNB  110  may update the OLLA at the full rate. 
     The exemplary method  700  may provide improvements to the performance of the eNB  110  and the network  105 . Specifically, with an adaptive OLLA loop update rate, it is possible to take NACKs from an “any” designation into consideration while maintaining loop stability. Therefore, an improved convergence rate of OLLA may be achieved, and thus, lead to higher system throughputs. 
     It may be noted that the exemplary embodiments are described with reference to the LTE wireless communication system. However, those skilled in the art will understand that the exemplary embodiments may be applied to any wireless communication schemes including those having different characteristics from the LTE scheme. For instance, the exemplary embodiments may be applied within any 3GPP network including LTE, Universal Mobile Telecommunications System (“UMTS”), etc. 
     It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Metadata:
Filing Date: 20160108
Publication Date: 20200728
Grant Date: 20200728
Priority Date: 20160108
Inventors: JI, Zhu
WANG, YANXIA
ZHAO, BING
SEBENI, JOHNSON O.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W72/21", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/541", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W28/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W28/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/001", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0003", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0009", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/001", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0413", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W28/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/001", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0003", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/082", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0009", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 59273321