Abstract:
A method of exchanging data in a communications network is provided. A control channel channelization code is assigned for transmitting user specific data channel allocation information to a particular mobile station (MS). The data channel allocation information indicates which part of the transmission time interval (TTI) available for data can be used by that particular MS. The control channel channelization code is shared in a TDMA fashion between the MSs during the TTI in a proportion equal to that in which the data channel channelization code is shared between the MSs such that each MS is allocated a share of the control channel channelization code in that part of the TTI. The control channel channelization code is then transmitted in a part of the TTI corresponding to that in which the data channel channelization code is transmitted for a particular MS.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention generally relates to a method of exchanging data in a communications network. More particularly, the invention relates to reducing the latency/delay in 3GPP HSPA networks. 
       BACKGROUND OF THE INVENTION 
       [0002]    The demand for higher data rates and the growth of mobile broadband services continues to push the need to advance HSPA (high speed packet access) technology. 
         [0003]    For example, 3GPP HSDPA (high speed downlink packet access) with Multiple Input Multiple Output (MIMO) transmission has been defined in 3GPP Release 7 to enable a 28 Mbps data rate. The combination of MIMO and 64QAM provides a 42 Mbps in Release 8 and in Release 9, dual cell HSDPA and MIMO and 64 QAM are defined to enable 84 Mbps. Release 10 will be approaching even higher data rates with 168 Mbps being achievable by having four carriers and MIMO. With the increased data rates, the buffer sizes in the devices (user equipment or UEs) also increase when the delay is unchanged. 
         [0004]    As the data rates keep increasing in the future, the resulting buffers will grow even more and earlier solutions employed in HSPA will not be able to reduce the resulting latency/delay. 
         [0005]    Therefore a solution is required for HSPA networks, which increases efficiency and reduces delay when the data rates, and therefore the size of the buffers, increase. 
       SUMMARY OF THE INVENTION 
       [0006]    Accordingly, a method of exchanging data in a communications network is provided. The method includes sharing a data channel channelization code in a downlink transmission part of a data channel in a TDMA fashion between mobile stations during a transmission time interval such that each mobile station is allocated a share of the data channel channelization code in a part of the transmission time interval. A control channel channelization code is assigned for transmitting user specific data channel allocation information to a particular mobile station. The data channel allocation information indicates which part of the transmission time interval available for data can be used by that particular mobile station. The control channel channelization code is shared in a TDMA fashion between the mobile stations during the transmission time interval in a proportion equal to that in which the data channel channelization code is shared between the mobile stations such that each mobile station is allocated a share of the control channel channelization code in that part of the transmission time interval. The control channel channelization code is transmitted in a part of the transmission time interval corresponding to that in which the data channel channelization code is transmitted for a particular mobile station. 
         [0007]    The data channel channelization code is shared between the mobile stations on the data channel over a time slot so that each mobile station has a share of the code allocated to it in its share of the time slot on the data channel. The share of the data channel channelization code is then transmitted to a particular mobile station in its share of the time slot. Control channel channelization code is then also divided between the mobile stations on the control channel over the time slot so that each mobile station receives a share of the control channel channelization code in the same part of the time slot as it received the data channel channelization code. 
         [0008]    In this way, radio performance is improved and HSPA latency is reduced since the downlink transmission delay is decreased. Furthermore the MIMO performance is improved and made more efficient since code multiplexing is reduced. Due to the shorter latency on the radio transmission, the application data rate (/TCP/IP performance) is increased. 
         [0009]    During uplink transmission, each mobile station may use its own uplink code for uplink feedback in an uplink feedback timeslot. The uplink code can then occupy the transmission time interval corresponding to that in which the data channel and control channel channelization code is transmitted for that particular mobile station. 
         [0010]    This provides the advantage that fewer HARQ processes are required (the number of HARQ processes is reduced from 6 to 4) and therefore a reduced amount of memory and buffer size is required in the UE devices. 
         [0011]    Each uplink feedback time slot may carry an acknowledgment of a downlink transmission of a corresponding downlink time slot. Alternatively, if a channel quality indicator is scheduled for the mobile station, a first uplink time slot can carry a sum of acknowledgments from each TDMA multiplexed data allocation. Second and third uplink time slots can then carry the channel quality indicator for each time slot. 
         [0012]    Data may be transmitted using at least partially HS-PDSCH and the control channel can be a HS-SCCH. 
         [0013]    In one embodiment, the control channel indicates if TDMA is in use during the downlink transmission time interval, which can be 2 ms. The transmission time interval can be divided into three parts. 
         [0014]    Advantageously, the method further comprises allocating a CDMA share of the data channel channelization code to a further mobile station over the whole transmission time interval. This means that legacy mobile stations may operate as they have done previously and will not be aware of any difference in operation in the network. 
         [0015]    The invention also provides a method of transmitting data in a communications network, in which during downlink transmission part of a data channel channelization code is shared in a TDMA fashion between a group of mobile stations in the network during a transmission time interval. This means that each mobile station is allocated a share of the data channel channelization code in a part of the transmission time interval. A control channel channelization code is assigned to a particular mobile station in the group over the transmission time interval. The control channel channelization code is assigned for transmitting user specific data channel allocation information and is shared in a CDMA fashion between the group of mobile stations during the transmission time interval. The data channel allocation information indicates which part of the transmission time interval available for data can be used by that particular mobile station. During uplink transmission, each mobile station uses its own uplink code for uplink feedback in an uplink feedback timeslot. The uplink code occupies the transmission time interval corresponding to that in which the data channel channelization code is transmitted for that particular mobile station. 
         [0016]    The data channel channelization code is shared between the mobile stations on the data channel over a time slot so that each mobile station has a share of the code allocated to it in its share of the time slot on the data channel. The share of the data channel channelization code is then transmitted to a particular mobile station in its share of the time slot. Control channel channelization code is then assigned to each mobile station over the whole time slot on the control channel. During uplink transmission, each mobile station may use its own uplink code for uplink feedback in an uplink feedback timeslot. The uplink code can then occupy the transmission time interval corresponding to that in which the data channel channelization code is transmitted for that particular mobile station. 
         [0017]    In this way, latency is reduced in downlink transmissions and fewer HARQ processes are required. This provides the advantage that a reduced amount of memory and buffer size is required in the UE devices. 
         [0018]    Each uplink feedback time slot may carry an acknowledgment of a downlink transmission of a corresponding downlink time slot. Alternatively, if a channel quality indicator is scheduled for the mobile station, a first UL time slot carries a sum of acknowledgments from each TDMA multiplexed data allocation and second and third UL time slots carry the channel quality indicator for each time slot. 
         [0019]    Data can be transmitted using at least partially HS-PDSCH and the control channel can be a HS-SCCH. The control channel may further indicate if TDMA is in use during the downlink transmission time interval, which can be 2 ms and may also be divided into three parts. 
         [0020]    The invention further provides a mobile station. The mobile station includes a receiver configured to receive a TDMA share of channelization code in a data channel in a part of a transmission time interval. 
         [0021]    The receiver is also configured to receive assigned control channel channelization code containing user specific data channel allocation information. The user specific data channel allocation information indicates which part of the transmission time interval available for data can be used by the mobile station. The receiver is further configured to receive a TDMA share of control channel channelization code during the transmission time interval in a proportion equal to that of the received TDMA share of data channel channelization code, and to receive the control channel channelization code in a part of the transmission time interval corresponding to that in which the data channel channelization code is received. The mobile station further includes a transmitter configured to transmit an uplink code for uplink feedback in an uplink feedback timeslot. The uplink code occupies the transmission time interval corresponding to that in which the data channel channelization code was received by the receiver. 
         [0022]    In this way, fewer HARQ processes are required, which provides the advantage that the memory and buffer size (and the amount of memory required) in the mobile station can be reduced. 
         [0023]    The transmitter may be further configured to transmit in each uplink feedback time slot an acknowledgment of a corresponding downlink time slot received at the receiver. 
         [0024]    Alternatively, if a channel quality indicator is scheduled for the mobile station, the transmitter is further configured to transmit in a first UL time slot a sum of acknowledgments from the mobile station and to transmit in second and third UL time slots the channel quality indicator for each time slot. 
         [0025]    The invention further provides a network node for a wireless communications network. The network node includes a processor configured to share a data channel channelization code in a downlink transmission part of a data channel in a TDMA fashion between mobile stations during a transmission time interval such that each mobile station is allocated a share of the data channel channelization code in a part of the transmission time interval. The processor is also configured to assign a control channel channelization code for transmitting user specific data channel allocation information to a particular mobile station. The data channel allocation information indicates which part of the transmission time interval available for data can be used by that particular mobile station. The processor is further configured to share the control channel channelization code in a TDMA fashion between the mobile stations during the transmission time interval in a proportion equal to that in which the data channel channelization code is shared between the mobile stations. This means that each mobile station is allocated a share of the control channel channelization code in that part of the transmission time interval. A transmitter is configured to transmit the control channel channelization code in a part of the transmission time interval corresponding to that in which the data channel channelization code is transmitted for that particular mobile station. Furthermore, a receiver is provided, which is configured to receive an uplink code as uplink feedback in an uplink feedback timeslot, with the uplink code occupying the part of the transmission time interval corresponding to that in which the data channel channelization code is transmitted for that particular mobile station. 
         [0026]    The invention will now be described, by way of example only, with reference to specific embodiments, and to the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a simplified schematic diagram of a wireless communications network in which a method according to an embodiment of the invention may be implemented; 
           [0028]      FIG. 2  is a simplified schematic diagram of a network node according to an embodiment of the invention; 
           [0029]      FIG. 3  is a simplified schematic diagram of a mobile station according to an embodiment of the invention; 
           [0030]      FIG. 4  is a schematic diagram of a channel structure for a communications network according to an embodiment of the invention; 
           [0031]      FIG. 5  is a schematic diagram of a channel structure for a communications network according to an embodiment of the invention; 
           [0032]      FIG. 6  is a flow diagram illustrating a method according to an embodiment of the invention; 
           [0033]      FIG. 7  is a schematic diagram of a channel structure for a communications network according to an embodiment of the invention; 
           [0034]      FIG. 8  is a schematic diagram of a channel structure for a communications network according to an embodiment of the invention; and 
           [0035]      FIG. 9  is a flow diagram illustrating a method according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0036]      FIG. 1  shows a radio access network  1 , which is part of a wireless communications network. The network illustrated here is a UMTS (WCDMA) network but the invention as described herein is not limited to this type of communications network. 
         [0037]    The network  1  includes a Node B  2  coupled to a radio network controller (RNC)  3  over an Iub interface. The Node B  2  is shown in more detail in  FIG. 2  and includes a transmitter Tx, a receiver Rx and a processor P. Mobile stations or user equipment (UE) UE 1 , UE 2  and UE 3  may access the network  1  via the Node B  2  over the Uu interface. 
         [0038]    The UEs UE 1 , UE 2  and UE 3  may be mobile telephones, computers, personal digital assistants (PDAs) or any device capable of accessing and exchanging data with the network  1 . Each UE UE 1 , UE 2 , UE 3  includes a transmitter T 1  and a receiver R 1 , as shown in  FIG. 3 . 
         [0039]      FIGS. 4 and 5  are schematic block diagrams of the channel structure used in the method according to a first embodiment of the invention. A flow chart illustrating the method according to the first embodiment is shown in  FIG. 6 . The HS-PDSCH channel carries user data and the HS-SCCH is a fixed data rate control channel carrying channelization code information necessary for HS-PDSCH demodulation by the UE UE 1 , UE 2 , UE 3 . The HS-DPCCH is the channel on which acknowledgements are sent by the UEs UE 1 , UE 2  and UE 3  to the Node B  2  on the uplink. All the UEs UE 1 , UE 2  and UE 3  are configured in MIMO mode. 
         [0040]    In the first embodiment of the invention, during downlink data transmission in the network, the processor P in the NodeB  2  selects whether to allocate more than one user during 2 ms TTI. In case more than one user is to be allocated, the processor P in the Node B  2  selects the channelization code of the HS-SCCH control channel C 1 , C 2  or C 3  to be used for each UE UE 1 , UE 2  and UE 3 , respectively, using time division multiplexing (TDMA) and code division multiplexing (CDMA) such that the channelization code used for the HS-SCCH control channel C 1 , C 2  or C 3  is shared between the UEs UE 1 , UE 2  and UE 3  in a TDMA fashion and also in a CDMA fashion over the TTI and corresponds to the part of the 2 ms frame to be allocated to a particular UE UE 1 , UE 2  or UE 3  (and to be received by the UE at its receiver R 1 ). 
         [0041]    In other words, the channelization codes C 1 , C 2  or C 3  of the control channel are “mapped” to a respective UE UE 1 , UE 2  or UE 3 , and the channelization codes on the HS-SCCH control channel are time multiplexed (Step S 1 ). Each code C 1 , C 2  and C 3  then takes up each ⅔ ms slot of the TTI. 
         [0042]    For example, in the case where the 2 ms TTI is allocated in the slot level, 3 HS-SCCHs are chosen and each of the channelization codes chosen by the network node NodeB for the HS-SCCH will also indicate the part of the 2 ms TTI to be chosen (so that, in this example, the TTI is divided into three parts or slots each of duration 0.667 ms). In the case that the UEs are legacy devices, the 2 ms TTI would be filled with time multiplexed and code multiplexed control channel channelization code and in that case the HS-SSCH code could be selected freely from the list of HS-SCCH codes signaled for each device. The channelization code C 1 , C 2  or C 3  on the HS-SCCH is assigned to each UE UE 1 , UE 2  and UE 3 , respectively, then indicates to each UE UE 1 , UE 2  and UE 3  which part of the 2 ms TTI to demodulate on the HS-PDSCH (Step S 2 ). Data is then coded with the three different codes C 1 , C 2 , C 3  and sent in the corresponding slot of the TTI which corresponds to the respective UE UE 1 , UE 2 , UE 3  and/or the HS-PDSCH (Step S 3 ). 
         [0043]    This results in an enhanced method, which multiplexes the HS-SCCH by codes and additionally by time, where timing of HS-SCCH is aligned to and adopted from the HS-PDSCH data channel(in which 1 UE per slot of TTI=2 ms). 
         [0044]    In other words, control information is sent during a 2 ms TTI by dividing it into 3 slots or segments each of 0.667 ms duration. The information of the first segment is coded with the first code C 1 , the second segment is coded with the second code C 2 , the third segment is coded with the third code C 3  and the 3 resulting segments related to one UE UE 1 , UE 2 , UE 3  are transmitted in one of the 3 slots of TTI, where the slot position corresponds to the slot position of the HS-PDSCH. 
         [0045]    During uplink transmission, each UE UE 1 , UE 2 , UE 3  uses its own respective uplink code for uplink feedback in its own uplink feedback timeslot on the HS-DPCCH (Step S 4 ). The uplink code occupies the corresponding part of the uplink transmission time interval to the part of the downlink transmission time interval in which the data channel and control channel channelization code was transmitted in the downlink on the HS-PDSCH and HS-SCCH channels, respectively, for that particular UE UE 1 , UE 2 , UE 3 . 
         [0046]    If it is determined that no channel quality indicator (CQI) is scheduled for any of the UEs UE 1 , UE 2 , UE 3  (Step S 5 ), each uplink feedback time slot carries an ACK or NACK acknowledgment of the downlink transmission from the corresponding downlink time slot (Step S 6 ), as shown in  FIG. 4  (where if an ACK is sent, this means all time slots of the TTI were decoded successfully, whereas if a NACK is sent at least one time slot was not decoded successfully). 
         [0047]    However, if it is determined that a channel quality indicator (CQI) is scheduled for the UE UE 1 , UE 2 , UE 3  (Step S 5 ), as shown in  FIG. 5 , the first uplink time slot carries a sum of the (N)ACK acknowledgments from all UEs UE 1 , UE 2  and UE 3  in each TDMA multiplexed data allocation. The second and third uplink time slots then carry the channel CQI for each time slot allocated to the UEs UE 1 , UE 2  and UE 3  (Step S 7 ). 
         [0048]      FIGS. 7 and 8  are schematic block diagrams of the channel structure used in the method according to a second embodiment of the invention. A flow chart illustrating the method shown in  FIGS. 7 and 8  is shown in  FIG. 9 . The HS-PDSCH carries user data and the HS-SCCH is a fixed data rate control channel carrying channelization code information necessary for HS-PDSCH demodulation by the UE UE 1 , UE 2 , UE 3 . All the UEs UE 1 , UE 2  and UE 3  are configured in MIMO mode. 
         [0049]    In the second embodiment of the invention, during downlink data transmission in the network, the processor P in the NodeB  2  selects whether to allocate more than one user during 2 ms TTI. In case more than one user is to be allocated, the processor P in the Node B  2  selects the channelization code of the HS-SCCH control channel C 1 , C 2  or C 3  to be used for each UE UE 1 , UE 2  and UE 3 , respectively, using time division multiplexing (TDMA) (Step S 11 ) such that the channelization code used for the HS-SCCH control channel C 1 , C 2  or C 3  corresponds to the part of the 2 ms frame to be allocated to a particular UE UE 1 , UE 2  or UE 3  (and to be received by the UE at its receiver R 1 ). In other words, the channelization codes C 1 , C 2  or C 3  of the control channel are “mapped” to a respective UE UE 1 , UE 2  or UE 3 , although the channelization codes on the HS-SCCH control channel are code multiplexed. 
         [0050]    For example, in the case where the 2 ms TTI is allocated in the slot level, 3 HS-SCCHs are chosen and each of the channelization codes chosen by the network node NodeB for the HS-SCCH will also indicate the part of the 2 ms TTI to be chosen (so that, in this example, the TTI is divided into three parts or slots each of duration 0.667 ms). In the case that the UEs are legacy devices, the 2 ms TTI would be filled with code multiplexing and in that case the HS-SSCH code could be selected freely from the list of HS-SCCH codes signaled for each device. Data channel channelization code on the HS-PDSCH is shared between the UEs UE 1 , UE 2 , UE 3  using TDMA over the 2 ms TTI (Step S 12 ). Data is then transmitted on the downlink from the Node B  2  to the UE UE 1 , UE 2 , UE 3  on the HS-PDSCH (Step S 13 ) and the channelization code C 1 , C 2  or C 3  on the HS-SCCH assigned to each UE UE 1 , UE 2  and UE 3 , respectively, then indicates to each UE UE 1 , UE 2  and UE 3  which part of the 2 ms TTI to demodulate on the HS-PDSCH. 
         [0051]    During uplink transmission, each UE UE 1 , UE 2 , UE 3  uses its own respective uplink code UC 1 , UC 2 , UC 3  for uplink feedback in its own uplink feedback timeslot on the HS-DPCCH (Step S 14 ). The uplink code occupies the corresponding part of the uplink transmission time interval to the part of the downlink transmission time interval in which the data channel and control channel channelization code was transmitted in the downlink on the HS-PDSCH and HS-SCCH channels, respectively, for that particular UE UE 1 , UE 2 , UE 3 . 
         [0052]    If it is determined that no channel quality indicator (CQI) is scheduled for any of the UEs UE 1 , UE 2 , UE 3  (Step S 15 ), each uplink feedback time slot carries an ACK or NACK acknowledgment of the downlink transmission from the corresponding downlink time slot (Step S 16 ), as shown in  FIG. 7  (where if an ACK is sent, this means all time slots of the TTI were decoded successfully, whereas if a NACK is sent at least one time slot was not decoded successfully). 
         [0053]    However, if it is determined a channel quality indicator (CQI) is scheduled for the UE UE 1 , UE 2 , UE 3  (Step S 15 ), as shown in  FIG. 8 , the first uplink time slot carries a sum of the (N)ACK acknowledgments from all UEs UE 1 , UE 2  and UE 3  in each TDMA multiplexed data allocation. The second and third uplink time slots then carry the channel CQI for each time slot allocated to the UEs UE 1 , UE 2  and UE 3  (Step S 17 ). 
         [0054]    Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person, which lie within the scope of the invention as claimed.