Even after introducing HSDPA, operators continue pursuing operating cost cuts. Growth of downlink traffic load induces shortage of uplink capacity. In case of a business user, one attaches many files to e-mails and send them on portable laptops. Individual users, who prefer person-to-person communication, send video clips and songs each other, and upload audio files at web logs (Blogs). Shorter latency is inevitable for gaming and other interactive services. To meet the market demand, network operators aim their network to make:

• Improvement of uplink system throughput
• Increase of uplink user throughput
• Reduction of latency

To reduce latency and raise uplink throughput, Enhanced Uplink DCH (E-DCH), which is also called HSUPA (High Speed Uplink Packet Access), is introduced in 3GPP Release 6.The benefit of HSUPA is aimed to obtain:

• Improvement of UL Coverage / Throughput / Delay reduction
• Improvement of affinity for IP based services (Video clip, Game, Video Streaming etc.)

HSUPA is also expected to achieve significant improvement in overall system performance when operated together with HSDPA. HSUPA can support high-speed movement (120km/h~), while HSUPA is mainly optimized to the middle or low speed: less than 60km/h. However, the overall system performance is still under evaluation. In TS25.896 3GPP, the following performance improvements can be expected when compared with simulation results with Rel'99:

• System capacity increase: 70%
• Reduction in end user packet call delay: 55%
• User throughput increase: 50%

HSUPA has four key features:Hybrid ARQ, Fast Node B Scheduling, Soft Handover and Shorter TTI.


Fast retransmission scheme, Hybrid ARQ, employs HSUPA like downlink HS-DSCH. Hybrid ARQ in HSUPA is a ‘Stop and Wait’ between Node B and UE. Using Hybrid ARQ, it is expected that retransmission delay will be shorter compared with that of RLC at RNC in Rel’99.The target of the initial transmission error rate in physical layer can be set relatively high: from 10 to 20 %.Reducing transmission delay improves throughput. Hybrid AQR supports Chase Combining and Incremental Redundancy.In Chase Combining, Node B sends the same packet again. Node B provides additional coding by sending parity bits in incremental redundancy. There is some difference between Hybrid ARQ of HSUPA and HSDPA. Hybrid ARQ in HSUPA is based on synchronous retransmissions in uplink.No restrictions exist in uplink code resource unlike with downlink. The following chart illustrates a flow of Hybrid ARQ. Figure 1 Hybrid ARQ process


Node B controls the transmission rate and assigning of UE (Scheduling). Scheduling is performed by Node B in order to make the Noise Rise (Signal to Noise Power) of a required level. L1 Signal of Node B limits the maximum rate (Power Offset for DPCCH).
　　　Since the control delay is shorter than that of RNC, Adaptive Control is performed in correspondence with Noise 　　　Rise Fluctuation. When a smaller Noise Raise Margin is set, UL capacity will be increased.
　　　

Figure 2 Node B Scheduling and Target Noise Rise
UE sends control signals for UL as Rate Request to Node B. Node B returns UE L1 signals as Rate Grant. Layer 1 signal from UE for Rate Request has a rate-increasing requirement based on the total buffer size. UE sends Layer 2 signal as Rate Request including buffer size of the highest priority data flow and the total buffer size. Downlink control signals are Absolute Grant (AG) and Relative Grant (RG). AG means the absolute value of the power offset permitted for the power usage. Node B that controls a serving cell can send AG. No AG is transmitted from Node B that controls non-serving cells. RG is used for controlling fluctuations for power offset and is sent from all cells in HSUPA neighboring cells.


SRNC performs Soft Handover between two Node B. UE receives ACK/NACK from the both Node B. When UE receives any ANK from Node B, the UE recognizes the meaning of the signal and quits the retransmission process.In case of a new data transmission, UE registers the Retransmission Sequence Number (RSN) as ‘0’ and acknowledges that a new data isreceived. After receiving it as a new data, the Node B clears the data stored in the buffer. SRNC provides Diversity Combining and Re-ordering. SRNC decides one serving cell among active cells and indicates it to the Node B and the UE. The Node B with the serving cell sends AG or RG to the UE, while the other Node B sends RG to the UE as an over-load indicator to avoid larger interference. Figure 3 SRNC Soft Handover process between two Node B


All Categories support 10ms TTI. Category 2, 4 and 6 has 2ms TTI as an option. Maximum peak rate is 2Mbps in 10ms HSUPA TTI and 5.76 Mbps with 2ms HSUPA TTI. UL DCH peak rate is limited up to 64 Kbps in HSUPA. When 4 codes are transmitted in parallel, two codes shall be transmitted with SF2 and two with SF4.

Table1 UE Categories in HSUPA

HSUPA category	Maximum number of HSUPA codes transmitted	Minimum spreading factor	Support for 10 and 2 ms HSUPA TTI	Maximum number of bits transmitted within a 10 ms HSUPA TTI	Maximum number of bits transmitted within a 2 ms HSUPA TTI	Maximum Bit rate
Category 1	1	SF4	10 ms TTI only	7296	-	0.73 Mbps
Category 2	2	SF4	10 ms and 2 ms TTI	14592	2919	1.46 Mbps
Category 3	2	SF4	10 ms TTI only	14592	-	1.46 Mbps
Category 4	2	SF2	10 ms and 2 ms TTI	20000	5837	2.92 Mbps
Category 5	2	SF2	10 ms TTI only	20000	-	2.00 Mbps
Category 6	4	SF2	10 ms and 2 ms TTI	20000	11520	5.76 Mbps

• Downlink
  • DPCH (DPCCH/DPDCH) : Dedicated channel
  • E-HICH : Ack/Nack signaling for HARQ
  • E-RGCH : Relative Grant
  • E-AGCH : Absolute Grant

• Uplink
  • DPCH (DPCCH/DPDCH) : Dedicated channel
  • E-DPCCH : E-TFCI, RSN etc (Signaling)
  • E-DPDCH : E-DCH (User Data)

• MAC-es/MAC-e should be added under the MAC-d. The function such as HARQ Retransmission, Scheduling and MAC-d PDU multiplexing etc. was realized in MAC-es/MAC-e.

• MAC-e is added. HARQ retransmission, scheduling and MAC-e PDU de-multiplexing is performed

• MAC-es is added. Re-Ordering and a function of combining data from a different Node B as SHO are added.

Figure 4 HSUPA protocol Architecture

4 NEC deployment scenario

Global Market demands commercial release by 2007. The availability of terminals equipped with HSUPA is a key factor for HSUPA penetration. Some UE Categories in HSUPA have mandatory 10ms TTI and optional 2ms TTI. Downlink load is more than uplink load in packet access except in conversational services. Therefore, utilizing existing HW is preferable for an initial release.

Considering the market demand and the terminal capability, NEC predicts two-step migration scenario. In the first step, terminals equipped with 10ms TTI will be available in the market in 2007. Then in the next step, 2ms TTI capable UE will be available in the market in the latter part of 2008. NEC plans to execute HSUPA trial before the first commercial release. The first priority of operators is the utilization of current network elements. Introducing HSUPA, NEC provides the functionalities such as backward compatibility and gives no impact on HW. All current nodes with SW upgrading shall support HSUPA as well as seamless mobility for current Rel'99 or HSDPA cells.