FIELD OF THE INVENTION

The invention generally relates to a method of ex ^¬ changing data in a communications network. More par- ticularly, the invention relates to reducing the latency/delay in 3GPP HSPA networks.

BACKGROUND OF THE INVENTION

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) technol ^¬ ogy.

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 Re ^¬ lease 9, dual cell HSDPA and MIMO and 64 QAM are de ^¬ fined to enable 84 Mbps. Release 10 will be ap ^¬ proaching 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 de ^¬ vices (user equipment or UEs) also increase when the delay is unchanged. 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.

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

Accordingly, a method of exchanging data in a commu- nications 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 channeliza ^¬ tion code in a part of the transmission time interval. A control channel channelization code is as ^¬ signed for transmitting user specific data channel allocation information to a particular mobile sta- tion. The data channel allocation information indicates which part of the transmission time interval available for data can be used by that particular mo ^¬ bile station. The control channel channelization code is shared in a TDMA fashion between the mobile sta- tions during the transmission time interval in a pro ^¬ portion equal to that in which the data channel chan ^¬ nelization 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 chan ^¬ nel 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.

The data channel channelization code is shared be ^¬ tween 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 con ^¬ trol channel over the time slot so that each mobile station receives a share of the control channel chan ^¬ nelization code in the same part of the time slot as it received the data channel channelization code.

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 multi ^¬ plexing is reduced. Due to the shorter latency on the radio transmission, the application data rate (/TCP/IP performance) is increased.

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 particu ^¬ lar mobile station.

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.

Each uplink feedback time slot may carry an ac ^¬ knowledgment of a downlink transmission of a corre ^¬ sponding 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 allo ^¬ cation. Second and third uplink time slots can then carry the channel quality indicator for each time slot .

Data may be transmitted using at least partially HS- PDSCH and the control channel can be a HS-SCCH.

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.

Advantageously, the method further comprises allocat ^¬ ing 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 previ ^¬ ously and will not be aware of any difference in op ^¬ eration in the network. 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 mo ^¬ bile 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 con ^¬ trol 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 informa ^¬ tion indicates which part of the transmission time interval available for data can be used by that par ^¬ ticular 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.

The data channel channelization code is shared be ^¬ tween 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 transmis ^¬ sion, 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.

In this way, latency is reduced in downlink transmis ^¬ sions 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.

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 sta ^¬ tion, a first UL time slot carries a sum of acknowl ^¬ edgments from each TDMA multiplexed data allocation and second and third UL time slots carry the channel quality indicator for each time slot.

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 .

The invention further provides a mobile station. The mobile station includes a receiver configured to re ^¬ ceive a TDMA share of channelization code in a data channel in a part of a transmission time interval. 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 chan ^¬ nel 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 re ^¬ ceived by the receiver.

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 mo ^¬ bile station can be reduced.

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 .

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.

The invention further provides a network node for a wireless communications network. The network node includes a processor configured to share a data chan ^¬ nel channelization code in a downlink transmission part of a data channel in a TDMA fashion between mo ^¬ bile 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 al ^¬ location information to a particular mobile station. The data channel allocation information indicates which part of the transmission time interval avail ^¬ able 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 con ^¬ trol 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 cor ^¬ responding 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 up- link feedback in an uplink feedback timeslot, with the uplink code occupying the part of the transmis ^¬ sion time interval corresponding to that in which the data channel channelization code is transmitted for that particular mobile station.

The invention will now be described, by way of exam ^¬ ple only, with reference to specific embodiments, and to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified schematic diagram of a wire ^¬ less communications network in which a method accord ^¬ ing to an embodiment of the invention may be imple ^¬ mented;

Figure 2 is a simplified schematic diagram of a net ^¬ work node according to an embodiment of the inven ^¬ tion;

Figure 3 is a simplified schematic diagram of a mo ^¬ bile station according to an embodiment of the inven- tion;

Figure 4 is a schematic diagram of a channel struc- ture for a communications network according to an em- bodiment of the invention; Figure 5 is a schematic diagram of a channel struc ^¬ ture for a communications network according to an embodiment of the invention;

Figure 6 is a flow diagram illustrating a method according to an embodiment of the invention;

Figure 7 is a schematic diagram of a channel struc ^¬ ture for a communications network according to an embodiment of the invention;

Figure 8 is a schematic diagram of a channel struc ^¬ ture for a communications network according to an embodiment of the invention; and

Figure 9 is a flow diagram illustrating a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figure 1 shows a radio access network 1, which is part of a wireless communications network. The net ^¬ work illustrated here is a UMTS (WCDMA) network but the invention as described herein is not limited to this type of communications network.

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 Figure 2 and includes a transmitter Tx, a receiver Rx and a processor P. Mobile stations or user equipment (UE) UE1, UE2 and UE3 may access the network 1 via the Node B 2 over the Uu interface.

The UEs UEl, UE2 and UE3 may be mobile telephones, computers, personal digital assistants (PDAs) or any device capable of accessing and exchanging data with the network 1. Each UE UEl, UE2, UE3 includes a transmitter Tl and a receiver Rl, as shown in Figure 3.

Figures 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 il ^¬ lustrating the method according to the first embodi- ment is shown in Figure 6. The HS-PDSCH channel carries user data and the HS-SCCH is a fixed data rate control channel carrying channelization code informa ^¬ tion necessary for HS-PDSCH demodulation by the UE UEl, UE2, UE3. The HS-DPCCH is the channel on which acknowledgements are sent by the UEs UEl, UE2 and UE3 to the Node B 2 on the uplink. All the UEs UEl, UE2 and UE3 are configured in MIMO mode.

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 CI, C2 or C3 to be used for each

UE UEl, UE2 and UE3, respectively, using time division multiplexing (TDMA) and code division multiplexing (CDMA) such that the channelization code used for the HS-SCCH control channel CI, C2 or C3 is shared between the UEs UE1, UE2 and UE3 in a TDMA fashion and also in a CDMA fashion over the TTI and corre ^¬ sponds to the part of the 2 ms frame to be allocated to a particular UE UE1, UE2 or UE3 (and to be re- ceived by the UE at its receiver Rl) .

In other words, the channelization codes CI, C2 or C3 of the control channel are "mapped" to a respective UE UE1, UE2 or UE3, and the channelization codes on the HS-SCCH control channel are time multiplexed

(Step SI) . Each code CI, C2 and C3 then takes up each 2/3 ms slot of the TTI.

For example, in the case where the 2 ms TTI is allo- cated 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 CI, C2 or C3 on the HS-SCCH is assigned to each UE UE1, UE2 and UE3, respectively, then indicates to each UE UE1, UE2 and UE3 which part of the 2ms TTI to demodulate on the HS-PDSCH (Step S2) . Data is then coded with the three different codes CI, C2, C3 and sent in the corresponding slot of the TTI which corresponds to the respective UE UE1, UE2, UE3 and/or the HS-PDSCH (Step S3) . 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 =2ms) .

In other words, control information is sent during a 2ms TTI by dividing it into 3 slots or segments each of 0,667ms duration. The information of the first segment is coded with the first code CI, the second segment is coded with the second code C2, the third segment is coded with the third code C3 and the 3 re ^¬ sulting segments related to one UE UE1, UE2, UE3 are transmitted in one of the 3 slots of TTI, where the slot position corresponds to the slot position of the HS-PDSCH.

During uplink transmission, each UE UE1, UE2, UE3 uses its own respective uplink code for uplink feed ^¬ back in its own uplink feedback timeslot on the HS- DPCCH (Step S4) . The uplink code occupies the corre ^¬ sponding part of the uplink transmission time interval to the part of the downlink transmission time in- terval 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 UE1, UE2, UE3. If it is determined that no channel quality indicator

(CQI) is scheduled for any of the UEs UE1, UE2, UE3 (Step S5) , each uplink feedback time slot carries an ACK or NACK acknowledgment of the downlink transmis ^¬ sion from the corresponding downlink time slot (Step S6) , as shown in Figure 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) .

However, if it is determined that a channel quality indicator (CQI) is scheduled for the UE UE1, UE2, UE3 (Step S5) , as shown in Figure 5, the first uplink time slot carries a sum of the (N)ACK acknowledgments from all UEs UE1, UE2 and UE3 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 UE1, UE2 and UE3 (Step S7) .

Figures 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 il ^¬ lustrating the method shown in Figures 7 and 8 is shown in Figure 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 UE1, UE2, UE3. All the UEs UE1, UE2 and UE3 are configured in MIMO mode .

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 CI, C2 or C3 to be used for each UE UE1, UE2 and UE3, respectively, using time division multiplexing (TDMA) (Step Sll) such that the channelization code used for the HS-SCCH control channel CI, C2 or C3 corresponds to the part of the 2 ms frame to be allocated to a particular UE UE1, UE2 or UE3 (and to be received by the UE at its receiver Rl) . In other words, the channelization codes CI, C2 or C3 of the control channel are "mapped" to a re ^¬ spective UE UE1, UE2 or UE3, although the channelization codes on the HS-SCCH control channel are code multiplexed .

For example, in the case where the 2 ms TTI is allo ^¬ cated 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 UE1, UE2, UE3 using TDMA over the 2ms TTI (Step S12) . Data is then transmitted on the downlink from the Node B 2 to the UE UE1, UE2, UE3 on the HS-PDSCH (Step S13) and the channelization code CI, C2 or C3 on the HS-SCCH assigned to each UE UE1, UE2 and UE3, respectively, then indicates to each UE UE1, UE2 and UE3 which part of the 2ms TTI to demodu- late on the HS-PDSCH.

During uplink transmission, each UE UE1, UE2, UE3 uses its own respective uplink code UCl, UC2, UC3 for uplink feedback in its own uplink feedback timeslot on the HS-DPCCH (Step S14) . The uplink code occupies the corresponding part of the uplink transmission time interval to the part of the downlink transmis ^¬ sion time interval in which the data channel and con- trol channel channelization code was transmitted in the downlink on the HS-PDSCH and HS-SCCH channels, respectively, for that particular UE UE1, UE2, UE3.

If it is determined that no channel quality indicator (CQI) is scheduled for any of the UEs UE1, UE2, UE3

(Step S15) , each uplink feedback time slot carries an ACK or NACK acknowledgment of the downlink transmis ^¬ sion from the corresponding downlink time slot (Step

516) , as shown in Figure 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) .

However, if it is determined a channel quality indi- cator (CQI) is scheduled for the UE UE1, UE2, UE3

(Step S15) , as shown in Figure 8, the first uplink time slot carries a sum of the (N)ACK acknowledgments from all UEs UE1, UE2 and UE3 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 UE1, UE2 and UE3 (Step

517) .

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further al ^¬ ternatives will occur to the skilled person, which lie within the scope of the invention as claimed.