Patent Publication Number: US-2012033750-A1

Title: Transport block size

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of GB Application No. 1013039.1 filed on Aug. 3, 2010, entitled “TRANSPORT BLOCK SIZE, commonly assigned with this application and incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to the transport block size used for transmission of data on an uplink channel. In particular, the present invention relates to adapting the transport block size. 
     BACKGROUND 
       FIG. 1  illustrates a cell  104  which is a part of a communication network  100 . A Node-B  102  can communicate with user equipment (UE) present in the cell  104 .  FIG. 1  shows, as an example, two UEs  106  and  112  present in the cell  104 , but there may be many more UEs present in the cell at any one time, as would be apparent to a person skilled in the art. The Node-B  102  can send data to UE  106  on a downlink channel  110  and can receive data from UE  106  on an uplink channel  108 . Similarly, the Node-B  102  can send data to UE  112  on a downlink channel  116  and can receive data from UE  112  on an uplink channel  114 . The communication channels between the Node-B  102  and the UEs in the cell  104  may be enhanced dedicated channels (E-DCHs) in uplink. 
     Data is grouped together into transport blocks for transmission over the channels in the network  100 . The amount of data that can be transmitted over a channel depends upon the size of the transport blocks used to transmit the data. The transport block sizes used on the various channels in cell  104  can be controlled by the Node-B  102 . 
     A reference channel exists on the downlink (e.g. from the Node-B  102  to UE  106  ), and the quality of data received on the reference channel can be used to determine conditions on the downlink channel  110 . The information regarding the conditions on the downlink channel can be used at the Node-B  102  to adapt the transport block size used for transmission of data on the downlink channel  110  to suit the current downlink channel conditions. 
     However, on the uplink (e.g. from UE  106  to the Node-B  102 ) there is no reference channel. A scheduler in the Node-B  102  uses information received from each UE in the cell  104  to allocate a grant which sets a maximum power that can be used by each UE for transmitting data on the uplink channels. For example, the grant may be expressed as a maximum allowed power ratio of the E-DCH Dedicated Physical Data Channel (EDPDCH) and the Dedicated Physical Control Channel (DPCCH). 
     When UE  106  receives a grant from the Node-B  102  it then has knowledge of the maximum power limit it has at its disposal for transmitting data on the uplink channel  108 . Based on this knowledge, the UE  106  can then autonomously select the maximum transport block size for which the required transmission power is not higher than the allocated grant. In this way the Node-B  102  can control the size of the transport blocks used in the uplink as well as in the downlink. 
     The information sent from the UEs to the Node-B  102  in order for the Node-B  102  to allocate the grants comprises (i) the Total E-DCH Buffer Status (TEBS) which provides information on the amount of data at the UE waiting to be transmitted on the uplink channel, and (ii) the UE power headroom (UPH). The scheduler in the Node-B  102  allocates the grants to the UEs in such a way as to reduce the amount of interference in the cell  104  whilst also taking into account the information received from the UEs. 
     SUMMARY 
     According to a first aspect of the invention there is provided a method of transmitting data in transport blocks from a device on an uplink channel of a network, the method comprising: determining information indicative of a current condition on the uplink channel; based on the determined information, adapting a transport block size for use in transmitting data on the uplink channel; and transmitting data from the device on the uplink channel in transport blocks having the adapted transport block size. 
     According to a second aspect of the invention there is provided a device for transmitting data in transport blocks on an uplink channel of a network, the device comprising: determining means for determining information indicative of a current condition on the uplink channel; adapting means for adapting, based on the determined information, a transport block size for use in transmitting data on the uplink channel; and transmitting means for transmitting data on the uplink channel in transport blocks having the adapted transport block size. 
     According to a third aspect of the invention there is provided a network comprising: a device for transmitting data in transport blocks on an uplink channel of the network; and a node for receiving the transmitted data on the uplink channel. The device includes: determining means for determining information indicative of a current condition on the uplink channel; adapting means for adapting, based on the determined information, a transport block size for use in transmitting data on the uplink channel; and transmitting means for transmitting data on the uplink channel in transport blocks having the adapted transport block size. 
     According to a fourth aspect of the invention there is provided a computer program product comprising computer readable instructions for execution by computer processing means at a device for transmitting data in transport blocks from the device on an uplink channel of a network, the instructions comprising instructions for: determining information indicative of a current condition on the uplink channel; based on the determined information, adapting a transport block size for use in transmitting data on the uplink channel; and transmitting data on the uplink channel in transport blocks having the adapted transport block size. 
    
    
     
       BRIEF DESCRIPTION 
       For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made, by way of example, to the following drawings in which: 
         FIG. 1  is a schematic representation of an embodiment of a cell of a communication network constructed according to principles of the disclosure; 
         FIG. 2  is a block diagram representing an embodiment of user equipment constructed according to the principles of the disclosure; and 
         FIG. 3  is a flow chart for an embodiment of a process of transmitting data from user equipment carried out according to the principles of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure realizes that the prior art does not take account of channel dependent information in determining the transport block size to be used on an uplink channel. Furthermore, the disclosure realizes that it can be beneficial to determine the transport block sizes for use on an uplink channel at the UE itself. The Node B should still fix the maximum grant or the maximum transport block size as it is the only entity in the cell having the knowledge of the interference level of all UEs in the cell. However, the UE  106  can decide to use a smaller transport block than that set by the grant in order to improve throughput on the uplink channel  108  in bad radio conditions. 
     The disclosure realizes that by adapting the transport block size according to a current condition on the uplink channel, the throughput of data on the uplink channel can be improved. In particular, when channel conditions on the uplink are good, it may be preferable to use a relatively large transport block size on the uplink channel which will increase the rate of data transfer (and thereby the throughput of data) over the uplink channel. However, when channel conditions on the uplink are bad, it may be preferable to use a relatively small transport block size, such that the loss of a transport block during transmission over the uplink channel has a smaller effect on the throughput of the data on the uplink channel. 
     Provided herein is a device for transmitting data in transport blocks on an uplink channel of a network according to the principles of the disclosure. In some embodiments, the device is a UE in a communication network. The data transmitted from the UE may, for example, be modulated using a quadrature amplitude modulation (QAM) scheme, such as a 16-QAM modulation scheme. 
     The UE may transmit data to a Node-B over the uplink channel. The UE may determine the number of Hybrid Automatic Repeat Request (HARQ) retransmissions transmitted on the uplink channel as a measure of the current condition on the uplink channel. Hybrid Automatic Repeat Request (HARQ) is a variation of the Automatic Repeat Request (ARQ) error-control method. In standard ARQ, error detection bits (such as cyclic redundancy check (CRC) bits) are added to data to be transmitted. In Hybrid ARQ, forward error correction (FEC) bits (such as Reed-Solomon code or Turbo code) are also added to the existing error detection bits and the combination of FEC bits and error correction bits can be referred to as “error correction code”. In the HARQ method both error detection bits and FEC bits are transmitted. When a coded data block is received, the receiver decodes the error correction code. If the channel quality is good enough, all transmission errors are correctable, and the receiver can obtain the correct data block. If the channel quality is bad, and not all transmission errors can be corrected, the receiver will detect this situation using the error detection code, then the received coded data block is discarded and a retransmission of the data block is requested by the receiver, similar to ARQ. In this sense, the receiver sends either a positive acknowledgement message (ACK) to the transmitter indicating that the data has been received correctly or a negative acknowledgment message (NACK) to the transmitter indicating that the data cannot be recovered at the receiver and that the transmitter should retransmit the data. 
     The disclosure realizes that a determination of the number of HARQ retransmissions that have been sent on the uplink channel provides an indication of the current condition (or quality) of the uplink channel. In some embodiments, the number of HARQ retransmissions that have been sent on the uplink channel in a time interval T can be determined at the UE for use in adapting the transport block size. Despite the absence of a reference channel on the uplink, information indicative of a current condition on the uplink channel can be provided in the form of the number of HARQ retransmissions sent over the uplink channel. In other embodiments, the UE can determine information indicative of the current condition on the uplink channel using information other than the number of HARQ retransmissions. For example, in general, the UE may receive feedback from the Node-B on the quality of data received over the uplink channel from the device. This feedback may comprise the HARQ ACK/NACK messages, or messages containing any other type of information from which the UE can determine information indicative of the current condition on the uplink channel. 
     It will be appreciated by those skilled in the art that by adapting the transport block size based on information indicative of a current condition on the uplink channel, the transport block size can be adapted to suit the particular conditions on the uplink channel at the time at which the data is to be transmitted. By carrying out the steps of determining the information indicative of the current condition on the uplink channel and of adapting the transport block size at the UE, the transport block size can be quickly adapted to thereby quickly respond to changes in the condition on the uplink channel. Furthermore, no extra functionality is required at the Node-B, which means that the method can be employed in a large number of UEs within one cell of the network without placing a large extra burden on the network resources. In this way, the method is well suited to scaling up with regards to the number of users in the network. 
     The data transmitted from the UE may, for example, be modulated using a quadrature amplitude modulation (QAM) scheme, such as a 16-QAM modulation scheme. 
     Embodiments of the invention will now be described by way of example only. As described above,  FIG. 1  shows a cell  104  of a communications network  100  in which a Node-B  102  can transmit data on a downlink channel  110  to a user equipment (UE)  106  and can receive data on an uplink channel  108  from the UE  106 .  FIG. 2  is a block diagram representing functional blocks within the UE  106 . Corresponding functional blocks may be present in UE  112  also. As shown in  FIG. 2 , UE  106  comprises a CPU  202  which is coupled to a display  204  for outputting visual data to a user of the UE  106 , a memory  206  for storing data at the UE  106 , a microphone  208  for receiving audio data at the UE  106  (e.g. from the user), an input device such as a keyboard  210 , a speaker  212  for outputting audio data from the UE  106  (e.g. to the user) and an antenna block  214  for transmitting and receiving data to and from the Node-B  102  over the network  100 . The antenna block  214  may comprise an antenna which is used for both transmission and reception of data over the network  100 . Alternatively, the antenna block  214  may comprise separate antennas for transmission and reception of data over the network  100 . Therefore, the UE  106  comprises the necessary components for transmitting and receiving data to and from the Node-B  102  in the network  100 . The UE  106  may, for example, be a mobile phone. 
     As described above, data to be transmitted on the uplink channel  108  from the UE  106  to the Node-B  102  is grouped together into transport blocks for transmission, as is known in the art. Also as described above, the size of the transport blocks will affect the throughput of data on the uplink channel  108 .  FIG. 3  shows a flow chart for a process of transmitting data from user equipment  106  on the uplink channel  108 . 
     In step S 302  information indicative of a current condition on the uplink channel  108  is determined at the UE  106 . In some embodiments, the number of HARQ retransmissions transmitted on the uplink channel  108  to the Node-B  102  in a particular time interval, T, is determined. In this way, a HARQ retransmission rate can be determined. The rate of HARQ retransmissions on the uplink channel  108  provides an indication of the current condition (or “quality”) of the uplink channel  108 . It is useful to use the number (or rate) of HARQ retransmission on the uplink channel as an indication of the condition of the uplink channel  108  because for the uplink there is no reference channel which would provide a direct indication of the quality of the channel. Information indicative of a current condition on the uplink channel may be determined in step S 302  in different ways to those described herein without departing from the scope of the invention. 
     Based on the information determined in step S 302 , in step S 304  the transport block size is adapted in accordance with the condition on the uplink channel  108 . Steps S 302  and S 304  may be carried out in hardware or in software in the UE  106 . For example, steps S 302  and S 304  may be carried out by the CPU  202  of the UE  106 . A value for the transport block size to be used for transmission over the uplink channel  108  may be stored in the memory  206  of the UE  106 . 
     As described above the Node-B  102  allocates a grant to each UE in the cell  104  expressed as a maximum power ratio of EDPDCH/DPCCH. From the grant received at the UE  106  from the Node-B  102 , the UE  106  has knowledge of the maximum power limit that it has at its disposal for transmission on the uplink channel  108 . 
     The transport block size is adapted in step S 304  to improve the throughput of data on the uplink channel  108  where possible. The transport block size is dynamically adapted. In this way the transport block size is adapted in real-time to suit the particular conditions currently on the uplink channel  108 . This allows the transport block size to be flexible. In other words the transport block size is responsive to current conditions on the uplink channel. For example, in bad radio conditions on the uplink channel  108 , the transport block size is reduced below that allowed by the grant from the Node-B  102 , such that the number of HARQ retransmissions is reduced which will in turn provide an improved throughput of data on the uplink channel  108 . In good radio conditions on the uplink channel  108 , the transport block size is set at the maximum allowed by the grant from the Node-B  102  to thereby maximise the data rate on the uplink channel  108 . 
     In step S 306  data is transmitted on the uplink channel  108  from the UE  106  in transport blocks having the transport block size as adapted in step S 304 . The precise mechanism for grouping the data into transport blocks and transmitting the transport blocks on the uplink channel  108  could be performed in a number of different ways, as is known in the art. 
     In one embodiment, there are two modes of operation and the UE  106  uses an algorithm to determine the channel conditions on the uplink channel  108  based on the number of HARQ retransmissions (ReTx%) measured over a certain period of time T. There is a threshold (ReTx_Threshold) for the number of HARQ retransmissions measured over the period T, such that if the number of HARQ retransmissions does not exceed the threshold (i.e. if ReTx%≦ReTx_Threshold) then it is determined that there is a good radio condition on the uplink channel  108  and if the number of HARQ retransmissions exceeds the threshold (i.e. if ReTx%&gt;ReTx_Threshold) then it is determined that there is a bad radio condition on the uplink channel  108 . 
     When it is determined that there is a good radio condition on the uplink channel  108  then the transport block size is adapted to be the maximum size allowed by the grant from the Node-B  102 . In particular, the transport block size may be in the configured Enhanced Transport Format Combination (ETFC) table, corresponding to ETFC index N. The ETFC table provides the format for use in transmitting data over the uplink channel  108 , and can be referenced using the ETFC index. By referencing the ETFC table with index N the maximum transport size allowed by the grant will be obtained. However, when it is determined that there is a bad radio condition on the uplink channel  108  then the transport block size is adapted to be reduced from the maximum size allowed by the grant from the Node-B  102 . In particular, the transport block size may be reduced by level L in the configured ETFC table, corresponding to ETFC index N-L. This means that by referencing the ETFC table with index N-L the reduced transport size will be obtained. 
     The number of HARQ retransmissions in a time interval T can be monitored on a continuous basis such that the device can switch between the two modes of operation in response to the current condition on the uplink channel  108  as appropriate. 
     The methods described herein have been tested for high transport block sizes (such as for Category  6  in the High Speed Uplink Packet Access (HSUPA) protocol) and have been shown to provide satisfactory results in terms of increasing throughput of data on the uplink channel  108 . The values used in the algorithm for ReTx Threshold, L and T need to be tuned to optimize the throughput of data on the uplink channel  108 . As well as for Category  6 , the methods described herein are particularly useful for any system using high data rates on the uplink channel  108 . For example, the methods described herein will be particularly useful for Category  7  with the introduction of a 16-QAM modulation scheme in the uplink. 
     Different categories (such as Category  6  and Category  7  mentioned above) have been defined for use by both terminals and network systems, depending on the supported features. A list of some of the already defined categories is shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 HSUPA Categories 
               
            
           
           
               
               
               
            
               
                   
                 Category 
                 Maximum Speed 
               
               
                   
                   
               
               
                   
                 Cat. 1 
                 0.71 Mbps 
               
               
                   
                 Cat. 2 
                 1.45 Mbps 
               
               
                   
                 Cat. 3 
                 1.45 Mbps 
               
               
                   
                 Cat. 4 
                 2.89 Mbps 
               
               
                   
                 Cat. 5 
                   2 Mbps 
               
               
                   
                 Cat. 6 
                 5.74 Mbps 
               
               
                   
                 Cat. 7 
                 11.5 Mbps 
               
               
                   
                   
               
            
           
         
       
     
     As described above, in order to adapt the transport block size an indication of the conditions on the uplink channel  108  can be determined by measuring the number of HARQ retransmissions. Therefore, the indication of the conditions on the uplink channel  108  is more accurate when the uplink channel  108  is a slow fading channel. For a slow fading channel, the conditions on the channel will not significantly change over the time period T over which the number of HARQ retransmissions is determined. The methods described herein could be used for channels other than slow fading channels, but the indication of the uplink channel conditions will be more accurate for a slow fading uplink channel than for a fast fading channel. 
     The method performed at the UE  106  and described above for transmitting data from the UE  106  on the uplink channel  108  may be implemented by way of executing computer program instructions from a computer program product using the CPU  202  of the UE  106 . The computer program product comprising the instructions can be stored in the memory  206  of the UE  106 . 
     In the embodiments described above, the steps S 302  and S 304  are performed at the UE  106 . In alternative embodiments, the steps S 302  and/or S 304  are performed at a node other than the UE  106  in the network  100 . For example, the Node-B  102  could determine an indication of the condition of the uplink channel  108  in step S 302 . This determination could be performed at the Node-B  102  based on the number of HARQ retransmissions that are required to be sent on the uplink channel  108 . Additionally or alternatively, the determination could be based on the quality of the data that is received over the uplink channel at the Node-B  102 . In embodiments in which the Node-B  102  determines the uplink channel condition in step S 302  then information indicative of the uplink channel condition may be transmitted to the UE  106  (e.g. on the downlink channel  110 ) such that the UE  106  can adapt the transport block size for use in transmitting data on the uplink channel  108 . Although it is possible for the Node-B  102  to perform the determination of an indication of the uplink channel condition, this step (step S 302 ) may be performed at the UE  106  rather than at the Node-B  102  because this eliminates the need to send extra information from the Node-B  102  to the UE  106  indicating the uplink channel condition, thereby improving the efficiency of data transfer between the Node-B  102  and the UE  106 . Furthermore, by performing step S 302  at the UE  106  rather than at the Node-B  102 , this reduces the processing resources required at the Node-B  102  which becomes particularly beneficial when the number of UEs in the cell  104  increases. 
     Furthermore, in some alternative embodiments, the step of adapting the transport block size (step S 304 ) can be performed at the Node-B  102  and the Node-B  102  can send an indication of the adapted transport block size to the UE  106  for use in transmitting data over the uplink channel  108 . Alternatively, the Node-B  102  could adjust the grant that it sends to the UE  106  according to its estimated channel conditions on the uplink channel  108 . However, step S 304  may be performed at the UE  106  rather than at the Node-B  102  because this reduces the processing resources required at the Node-B  102  which becomes particularly beneficial when the number of UEs in the cell  104  increases. 
     There has therefore been described above a method and device for dynamically adapting the transport block size used on the uplink channel  108 , responsive to current conditions on the uplink channel  108 . It will be appreciated that by doing so, the throughput of data on the uplink channel  108  can be improved. 
     At least a portion of the above-described devices and disclosed methods may be embodied in or performed by various digital data processors or computers, wherein the computers are programmed or store executable programs of sequences of software instructions to perform one or more of the steps of the methods. The software instructions of such programs may represent algorithms and be encoded in machine-executable form on conventional digital data storage media, e.g., magnetic or optical disks, random-access memory (RAM), magnetic hard disks, flash memories, and/or read-only memory (ROM), to enable various types of digital data processors or computers to perform one, multiple or all of the steps of one or more of the above-described methods. Accordingly, computer storage products with a computer-readable medium, such as a non-transitory computer-readable medium, that have program code thereon for performing various computer-implemented operations that embody the tools or carry out the steps of the methods set forth herein may be employed. A non-transitory media includes all computer-readable media except for a transitory, propagating signal. The media and program code may be specially designed and constructed for the purposes of the disclosure, or they may be of the kind well known and available to those having skill in the computer software arts. An apparatus may be designed to include the necessary circuitry or series of operating instructions to perform each step or function of the disclosed methods. 
     While this invention has been particularly shown and described with reference to embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the claims.