HSUPA (Enhanced Uplink)

ByPraveen Kumar

Overview

• High Speed Uplink Packet Access (HSUPA) is also known as Enhanced Uplink.

• What it Does ?– Provides the Improvement in WCDMA uplink

capabilities and performance in terms of • Higher data rates• Reduced Latency• Improved System Capacity

• It is a complement to HSDPA

Difference Between the HSDPA and HSUPA

HSDPA (DL) HSUPA (UL)

The Shared resource is transmission power and code space, located at NodeB

Shared resource is the amount of allowed uplink interference which depends on the transmission power of multiple distributed UE.

The scheduler and the transmission buffer are located at the same place in NodeB

The scheduler is located at NodeB and transmission buffers are distributed in the UEs. Therefore UE needs to signal buffer status information to the scheduler.

Different transmit channel are orthogonal. In HSDPA, where a (more or less) constant transmission power with rate adaptation is used.

WCDMA uplink is inherently non-orthogonal and subject to interference between uplink transmission within the same cell. Therefore Fast Power Control is essential for uplink to handle near-far problem.

Difference Between the HSDPA and HSUPA

HSDPA (DL) HSUPA (UL)

No Soft handover. Transmission from multiple cells in case of HSDPA is cumbersome and with questionable benefit.

Soft handover is supported. Receiving data from a terminal in multiple cell is fundamentally beneficial as it provides diversity

HSUPA Scheduling - 1

• Scheduler at NodeB controls when and at what data rate the UE is allowed to transmit.– High date rate ≈ High Power transmitted by Ues– High Power ≈ Higher Interference (due to UL non orthogonality)

• Scheduler needs to manage the UL interference– If Interference is too high, UL transmission may not

received properly.– If interference is too low, the full system capacity

not exploited.

HSUPA Scheduling - 2

• Since the scheduler and transmission buffer are not co-located, there is Request/Grant mechanism is defined. UE sends the Scheduling Request, indicating its buffer occupancy. Scheduling Grant sent by the UEs to control the UE transmission activity. The Scheduling Grants control the maximum allowed E-DCH-to-pilot power ratio the terminal may use; a large grant means higher data rate but also contributes more to interference level in cell.

HSUPA Scheduling - 3

• As the interference increases in the cell, it affects the neighbor cell also, so inter-cell interference needs to be controlled. The scheduler has allowed a UE to transmit at a high data rate based on an acceptable intra-cell interference level, this may cause non-acceptable interference to the neighboring cell. Therefore in soft handover, the serving cell has the main responsibility for the scheduling operation, but UE monitors scheduling information from all cells with which the UE is in soft handover.

HSUPA Scheduling - 4

HSUPA HARQ (soft combining)

• It provide robustness againt occasional transmission errors. A similar scheme as for HSDPA

• One main difference compared to HSDPA from the use of soft handover in uplink.– When UE is in soft handover, HARQ is terminated in

multiple cells. It is possible that few NodeB has not received data correctly and some NodeB has received correctly. So If the UE receives an ACK from at least one of the NodeBs, the UE consider the data to be successfully received .

HSUPA Architecture

Enhanced Uplink - TTI• A new transport channel type is introduced Enhanced

Dedicated Channel (E-DCH). It can be configured with one or several DCHs.

• Introduction of 2ms TTI for efficient packet-data support. It allows for rapid adaptation of transmission parameters and reduction of the end-user delays associated with packet-data transmission. But for large cells a longer TTI may be beneficial as the payload in a 2ms TTI can become unnecessarily small and the associated relative overhead too large. Hence the E-DCH supports two TTI lengths, 2 and 10ms and the network can configure the appropriate value.

Channel Structure with HSDPA and HSUPA

Channel Structure with HSDPA and HSUPA

• E-HICH -> HARQ ACK/NAK information is sent on a new downlink dedicated physical channel, the E-DCH Hybrid ARQ Indicator channel.

• E-AGCH -> Scheduling grants sent from the scheduler to the UE, using the shared E-DCH Absolute Grant Channel. The E-AGCH is sent from the serving cell only as this is the cell having main responsibility for the scheduling operation and is received by all UEs with an E-DCH configured. It is typically used for large changes in the data rates

Channel Structure with HSDPA and HSUPA• E-RGCH -> Scheduling grant information can also be

conveyed to the UE through and E-DCH Relative Grant Channel. It is typically used for small adjustment during on going data transmission.

• E-DPCCH -> In the uplink, control signaling is required to provide the NodeB with the necessary information to be able to demodulate and decode the data transmission. Even though serving cell has this information but non serving cells in soft handover clearly don't have this information. Also E-DCH also supports non-scheduled transmission. Hence there is a need of out-band signaling in UL.

Channel Structure with HSDPA and HSUPA

• UL by design is non-orthogonal, fast closed-loop power control is necessary to address the near-far problem. E-DCH is power controlled in the same way as other uplink channels. Power control commands can be transmitted using DPCH or to save channelization codes, the fractional DPCH (F-DPCH)

Physical Layer Processing

MAC-es/e UE Side

MAC-es/e

MAC – Control

Associated Uplink Signalling E-TFC

(E-DPCCH)

To MAC-d

HARQ

Multiplexing and TSN setting E-TFC Selection

Associated Scheduling Downlink Signalling

(E-AGCH / E-RGCH(s))

Associated ACK/NACK signaling (E-HICH)

E-TFC (E-DCH Transport Format Combination)

• Only the UE has accurate knowledge about the buffer situation and power situation in the UE at the time of transmission of the transport block in the UL. Hence the UE is allowed to autonomously select the data rate or E-TFC.

• E-TFC is responsible for selecting the TF of the E-DCH and to control MAC-e multiplexing.

• NodeB scheduler handles resource allocation between UEs, the E-TFC Selection controls resource allocation between flows within the UE.

E-TFC (E-DCH Transport Format Combination)

• E-DCH needs to be coexist with DCHs. Therefore a basic requirement is to serve DCH traffic first and only spend otherwise unused power resources on the E-DCH.

• TFC Selection is two step process. First the normal DCH TFC selection is performed then UE estimates the remaining power and TFC Selection step is performed where E-DCH can use the remaining power.

E-TFC (E-DCH Transport Format Combination)

MAC-es UTRAN Side

MAC-es

MAC – Control

From MAC-e in NodeB #1

To MAC-d

Disassembly

Reordering Queue Distribution

Reordering Queue Distribution

Disassembly

Reordering/ Combining

Disassembly

Reordering/ Combining

Reordering/ Combining

From MAC-e in NodeB #k

MAC-d flow #1 MAC-d flow #n

MAC-e UTRAN Side

MAC-e

MAC – Control

E-DCH Associated ACK/NACK

Downlink Signalling (E-HICH)

Associated E-TFC Uplink

Signalling (E-DPCCH)

MAC-d Flows

De-multiplexing

HARQ entity

E-DCH

Control

E-DCH

Scheduling

Associated Scheduling Downlink Signalling

(E-AGCH / E-RGCH(s))