HSUPA: High-Speed Uplink Packet Access

High Speed Uplink Packet Access (HSUPA) is introduced in 3GPP Release 6 standards to improve the uplink UE data rate which was significantly low up to Release 5. To improve the uplink data rate some new functionality are added:

1. New MAC entities: MAC-e/es in UE and MAC-e in NodeB and MAC-es in RNC.
2. Transport channel: E-DCH
3. Physical channels: E-DPDCH/DPCCH, E-HICH, E-RGCH, E-AGCH
4. Transmission Time Interval: 2 ms or 10 ms
5. SF = 2 can be used
6. Fast Layer 1 transmission and retransmission
7. Hybrid- ARQ using soft combining and incremental redundancies
8. NodeB control grants or data rate
9. New Frame Protocol in Iub/Iur interface (E-DCH FP)

MAC Protocol

HSUPA introduced some changes in MAC protocol both in the UE and network side.

• MAC-e in the NodeB
• MAC-es in the SRNC
• MAC-e/es in the UE

MAC –e in the NodeB

The MAC-e entity is located in the NodeB. There is one MAC-e entity in the NodeB for each UE.

The MAC-e entity is responsible for

• Managing the cell resources related to HSUPA between UEs.
• Receiving the scheduling requests from the UEs and transmission of scheduling grants.
• De-multiplexing of MAC-e PDUs into MAC-es PDUs.
• Management of HARQ entity, which is responsible for transmitting ACK/NACK.

MAC-es in SRNC

For each UE there is one MAC-es entity in the SRNC. The MAC-es covers the following functionalities:

1. Combining and reordering the MAC-es PDUs according to TSN and NodeB tagging i.e. (CFN and subframe number)
2. Disassembling the MAC-es PDUs. When MAC-es PDUs are disassembled the MAC-es header is removed and MAC-d PDUs are extracted. Then the MAC-d PDUs are delivered to MAC-d entity.

MAC-e/es in UE

MAC-e/es handles the E-DCH specific functions in the UE. There are three different entities in MAC-e/es.

HARQ

HARQ entity is responsible for ACK/NACK handling. It receives ACK/NACK from the nodeB and act accordingly.

Multiplexing and TSN setting

Multiplexing and TSN setting entity is responsible for concatenating multiple MAC-d PDUs into one MAC-es PDU, and to multiplex several MAC-es PDUs into one MAC-e PDU.’

E-TFC selection

This entity is responsible for E-TFC selection taking the following into consideration:

1. Relative Grant
2. Absolute Grant
3. Serving Grant

E-DCH Transport Channel

On the uplink when E-DCH is supported, two CCTrCH are used simultaneously. The E-DCH transport channel can be configured with 10 ms TTI or with 2 ms TTI. 10 ms TTI is mandatory and must be supported by all UEs which support E-DCH, but 2 ms TTI is optional.

UE can have only one E-DCH transport channel at a given point of time. The E-DCH can be mapped onto one CCTrCH of E-DCH type at a given point of time and there will be only one Transport Block (TB) per TTI.

Physical Channels for HSUPA

Enhanced Dedicated Physical Data Channel (E-DPDCH)

The E-DCH transport blocks are carried on the E-DPDCH channel in the physical layer. E-DPDCH operates in 2 ms or 10 ms TTI. Release 6 E-DPDCH uses QPSK modulation and in Release 7 there is possibility to use 4 PAM modulations.

The E-DPDCH does not carry any other information other than data symbols. It depends on the DPCCH to carry pilot symbols and channel estimation and on E-DPCCH to carry E-TFC, Retransmission Sequence Number (RSN) and happy bit.

E-DPDCH uses multi-codes combinations to increase the data rate. Spreading Factor 2 (SF 2) can also be used.

So the different possibilities of data rates with code combinations:

Release-6 E-DPDCH

Release-7 E-DPDCH

Enhanced Dedicated Physical Control Channel (E-DPCCH)

E-DPCCH carries HSUPA-related physical layer control information. E-DPCCH always follows the TTI length of E-DPDCH.

The E-DPCCH carries the following information:

1. E-TFC information which is 7 bits long. E-TFC determines the data rate.
2. 2 bits of retransmission information. RSN tells whether the packet is a new or retransmission of a previously transmitted packet.
3. The last 1 bit is the happy bit which tells whether the UE can use a higher uplink data rate or not.

For 2 ms TTI Case

• The 10 information bits are coded into 30 bits over three consecutive time slots.

For 10 ms TTI Case

• The content of 2 ms subframes are simply repeated five times.

E-DCH Hybrid ARQ Indicator Channel (E-HICH)

E-HICH channel is used to send the ACK/NACK information in the downlink i.e. NodeB indicates whether a packet is correctly received from a UE or not.

E-HICH is shared by multiple users at the same time. Each user is allocated one orthogonal signature for E-HICH and one for E-RGCH. Since there are 40 orthogonal signatures are available so only 20 users can use the same code channel at a specific point of time.

E-DCH Relative Grant Channel (E-RGCH)

E-RGCH is used to step up or step down the output power used by the UE. So E-RGCH does not carry any exact value but an indication to go up or down relative to the current serving grant.

E-HICH uses the same code channel as E-HICH to save code space.

E-DCH Absolute Grant Channel (E-AGCH)

An E-DCH Absolute Grant Channel is transmitted by the serving E-DCH cell. It carries two kind of information:

1. AG value
2. AG scope

AG value is the exact E-DPDCH/DPCCH power ratio that the UE need to use in the next transmission.

AG scope tells whether the AG value will be used by a single HARQ process or will be used by all processes.

UE Capabilities

When establishing RRC connection UE sends it E-DCH capabilities to the NW. In the RRC CONNECTION SETUP COMPLETE, UE sends information about E-DCH Physical layer category.

Release 6

Release 7

References

Enhanced uplink; Overall description: 3GPP TS 25.319

UE Radio Access capabilities: 3GPP TS 25.306

FDD Enhanced Uplink;Overall description;Stage 2: 3GPP TS 25.309 

Medium Access Control (MAC) protocol specification: 3GPP TS 25.321

Related posts:

1. MAC (Medium Access Control) Architecture (25.321)
2. UMTS Logical Channels and Transport Channels
3. WCDMA Physical Layer: Principles and Features