OWA324030 WCDMA HSPA+ RAN13 Principles ISSUE1.00

WCDMA HSPA+ Principles

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Downlink Enhanced L2: Downlink enhanced L2 allows flexible PDU sizes at the RLC layer

and segmentation at the MAC layer on the Uu interface. The feature prevents L2 from

becoming the bottleneck of Uu rate increasing by multiple-input multiple-output (MIMO)

and 64QAM.

Downlink MIMO: Downlink MIMO increases transmission rates through spatial

multiplexing and improves channel qualities through space diversity. The network side can

dynamically select single- or dual-stream transmission based on channel conditions. The

peak rate at the MAC layer can reach 28Mbps.

Downlink 64QAM: Downlink 64QAM allows the use of 64QAM in HSDPA to increase the

number of bits per symbol and thus to obtain higher transmission rates. The peak rate at

the MAC layer can reach 21Mbps.

Downlink Enhanced CELL_FACH Operation: Downlink Enhanced CELL_FACH Operation

allows the use of HSDPA technologies for the UEs in CELL_FACH, CELL_PCH, and

URA_PCH states (RAN11 only supports HSDPA reception in CELL_FACH state.). The

purpose is to increase the peak rates in these states, reduce the signaling transmission

delay during service setup or state transition, and improve user experience.

CPC: Continuous packet connectivity (CPC) allows uplink and downlink transmissions at

regular intervals. CPC reduces the transmit power and thus prolongs the UE battery life

because the UE does not have to monitor and transmit overhead channels in each TTl. The

reduction in the transmit power also helps to increase the uplink capacity by decreasing

the total interference. This improvement is significant when users such as VoIP users

transmit data discontinuously.

The CPC feature consists of DTX-DTX, and HS-SCCH Less Operation.



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New HSPA+ features in RAN13:

Uplink 16QAM: 16QAM modulation can be used for HSUPA to improve uplink

peak date rate to around 11Mbps.

Uplink Enhanced L2: Some modifications are introduced in Uu interface layer 2 in

uplink direction to support higher data rate and improve uplink transmission

efficiency.

Downlink MIMO + 64QAM: Before RAN12 MIMO and 64QAM can not be used

by one UE simultaneously. In RAN12 downlink MIMO and 64QAM can be used

simultaneously by one UE to receive HSDPA data. With this technology, the

theoretical downlink peak rate can reach 42Mbps.

DC-HSDPA (Dual-cell HSDPA): DC-HSDPA allows a UE to set up HSDPA

connections with two inter-frequency time-synchronous cells that have the same

coverage. Theoretically, DC-HSDPA with 64QAM can provide a peak rate of

42Mbps in the downlink.



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The MIMO and 64QAM features are introduced by 3GPP in R7. These two features can be

used respectively. In R7 restricted by the capabilities of UEs, however, a single user cannot

be configured with 64QAM and MIMO at the same time.

In R8, 64QAM+MIMO can be used by one UE simultaneously to achieve a higher

throughput and better QoS, greatly improving user experience.



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There are three types of HS-SCCH for HSPA+ operation:

HS-SCCH type 1: HS-SCCH type 1 is used when the UE is not configured in MIMO

mode, and the conditions for usage of HS-SCCH type 2 are not met.

HS-SCCH type 2: HS-SCCH type 2 is used for HS-SCCH-less operation.

HS-SCCH type 3: HS-SCCH type 3 is used when the UE is configured in MIMO

mode.

HS-SCCH type 3 is used for downlink MIMO with 64QAM.

When the three bits are 101, the modulation scheme for the secondary transport block (TB)

and the transmission mode are indicated by the last bit of Channelization-Code-Set (CCS):

If the last bit of CCS is 0, the number of TBs is 2 (that is, the transmission mode is

dual-stream mode) and the modulation scheme for the secondary TB is QPSK.

If the last bit of CCS is 1, the number of TBs is 1 (that is, the transmission mode is

single-stream mode).



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Due to the rapid development of data services, the UMTS needs to improve the spectrum

resource utilization continuously to improve the downlink air interface capabilities and

enrich the service experience of users. The new DC-HSDPA technology introduced in R8

aims to improve the user throughput through larger spectrum bandwidth.

Dual-cell HSDPA (DC-HSDPA) enables users to receive the HSDPA data sent from two inter-

frequency downlink cells under the same coverage at the same time. The network side can

dynamically select between two carriers for HSDPA transmission.



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DC-HSDPA users belong to both anchor and supplementary carrier cells. The DC-HSDPA

users can be scheduled in each cell. Compared with a single cell, the number of users who

can be scheduled is doubled, users with high-quality channels can be selected through DL

scheduling, and the system throughput is increased. In addition, the channel attenuation

of DC-HSDPA users is different in the two cells, and the probability of high-quality

channels is higher than that of SC-HSDPA users (frequency-selective gain). Therefore, the

throughput of users is increased, and the service delay is reduced.



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Compared with the traditional HSPA technology, DC-HSDPA brings the following gains:

Improving the peak throughput of users. When the DC-HSDPA and 64QAM

features are used together, the peak throughput can reach 42Mbps.

Compared with SC-HSDPA, DC-HSDPA features frequency-selective scheduling and

dynamic multi-carrier gain equalization, thus increasing the system capacity. The

gain is more obvious particularly when the load on the two carriers is unequal.

Greatly reducing the burst service and HTTP service delay. As the user peak rate is

increased, the HTTP service response delay can be greatly reduced, and user service

experience can be improved.

Improving the user experience of cell edge users and enhancing the DL coverage.



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DC-HSDPA can balance the load in two frequencies with same coverage and increase

system capacity. But by simulation, the system capacity gain decreases along with the

growth of user number with DC-HSDPA.



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Tcell is a parameter for cell configuration. It is Difference between the System Frame

Number (SFN) and NodeB Frame Number (BFN) of the NodeB which the cell belongs to.



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The following table shows the composite HS-DPCCH HARQ-ACK for DC-HSDPA.

HARQ-ACK

message to be transmitted

w0 w1 w2 w3 w4 w5 w6 w7 w8 w9

HARQ-ACK when UE detects a single scheduled transport block on the serving HS-DSCH cell

ACK 1 1 1 1 1 1 1 1 1 1

NACK 0 0 0 0 0 0 0 0 0 0

HARQ-ACK when UE detects a single scheduled transport block on the secondary serving HS-

DSCH cell

ACK 1 1 1 1 1 0 0 0 0 0

NACK 0 0 0 0 0 1 1 1 1 1

HARQ-ACK when UE detects a single scheduled transport block on each of the serving and

secondary serving HS-DSCH cells

Response to

transport block

from serving HS-

DSCH cell

Response to

transport block

from secondary

serving HS-DSCH

cell

ACK ACK 1 0 1 0 1 0 1 0 1 0

ACK NACK 1 1 0 0 1 1 0 0 1 1

NACK ACK 0 0 1 1 0 0 1 1 0 0

NACK NACK 0 1 0 1 0 1 0 1 0 1



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After DC-HSDPA is introduced in R8, MAC-ehs entity in NodeB side and UE side has two

HARQ entities. One HARQ entity is used by one frequency. The function of HARQ is same

with the previous version.

No change is introduced for MAC entities in RNC side.



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In implementation of RAN11.0 and earlier versions, a UL RLC works only in fixed PDU

mode, that is, the PDU size is fixed. Fixed-size PDUs cannot support high-speed services

effectively. When the window size is fixed, small PDUs cannot support high-speed services.

Large PDUs can support high-speed services, but the power on the cell edge may be

restricted. In addition, fixed-size PDUs may introduce some extra headers and fill bits,

which affects the transmission efficiency. For example, when a UE moves from the cell

center to the cell edge, the transmit power of the UE is restricted when it reaches a certain

distance. In this case, the throughput drops rapidly, and data transmission may be easily

interrupted.

3GPP introduces uplink L2 enhancement in R8. The UL RLC (in UM or AM mode) can

support flexible PDUs and fixed PDUs. When working in flexible PDU mode, the RLC can

receive PDUs with different sizes flexibly to reduce the uplink PDU size, and improve the

throughput under the restricted uplink transmit power.



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The MAC-i/is entity is used at MAC layer. The key difference between MAC-i/is and MAC-

e/es is that MAC-i/is supports data segmentation at MAC layer, and can select proper PDU

sizes according to the air interface quality to improve the transmission efficiency.



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Before RAN13, the modulation mode for HSUPA is QPSK. In RAN12, 16QAM for HSUPA is

introduced to improve the peak data.



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UE category 7 can support 2ms and 10ms. But if 16QAM is activated, only 2ms TTI is used.



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RAN13 does not support TTI change from 10ms to 2ms.

The basic procedure for dynamic TTI change is:

UE will measure uplink Tx power and report the measurement result to RNC.

If RNC finds the UE Tx power is too high, it means the coverage is not good. RNC

can change TTI from 2ms to 10ms.



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The basic procedure for dynamic TTI change is:

UE will measure uplink Tx power and throughput, report the measurement result

to RNC.

Based on the measurement result for UE Tx power and throughput, RNC can adjust

TTI between 10ms and 2ms.



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OWA324030 WCDMA HSPA+ RAN13 Principles ISSUE1.00