3G/UMTS

Physical Layer - HSUPA

Introduction of new Channels in HSUPA. The channels in red are the ones used for HSUPA operation.

As in HSDPA, several new channels were introduced to implement HSUPA and they are as follows :

i) E-DPDCH

ii) E-DPCCH

iii) E-HICH

iv) E-RGCH

v) E-AGCH

Briefly speaking, E-DPDCH is equivalent version of HS-DPSCH and E-DPCCH is equivalent to HS-SCCH and E-HICH is equivalent to HS-DPCCH. But there is a main difference between these HSUPA channels and HSDPA channel. E-DPDCH and E-DPCCH are dedicated channels whereas HS-DPSCH and HS-SCCH are shared channel, but this is understandable because in HSDPA case the source and target of the data transmission is one-to-many but in HSUPA case the source and target is one-to-one, so it is understandable to use dedicated channels in HSUPA.

There are another big difference between HSDPA and HSUPA. It is about scheduling issue. Regardless of whether it is HSDPA or HSUPA, the scheduler (the decision maker) is on Node B, not on a UE. For scheduling we need two very important information, the channel quality and buffer status information. In HSDPA, the information that the decision maker (the scheduler) needs to get from the target of the transmission is only channel quality information and this information was provided via HS-DPCCH and the buffer status information is already available to the scheduler because the transmission buffer is located in the same place (node B) as the scheduler. So in HSDPA the transmitter (node B) can send the data anytime the situation is allowed, but in HSUPA case the transmitter (UE) cannot send the data anytime it wants to send. Before the UE send the data, it has to check whether the target (the reciever, Node B) is ready and has enough resource to recieve the data. For UE to check the status of the reciever (node B) and get the approval from the node B, E-AGCH (Absolute Grant Channel) and E-RGCH (Relative Grant Channel) are used. Node B (the scheduler) send the scheduling grants to UE on when and at what data rate the UE can transmit the data.

The difference between E-AGCH and E-RGCH are

i) E-AGCH is a shared channel and E-RGCH is a dedicated channel

ii) E-AGCH is typically used for large changes in the data rate and the E-RGCH is used for smaller adjustments.