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Testing HSUPA Devices

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Testing HSUPA devices

Release 6 of the 3GPP standard adds high-speed uplink packet access (HSUPA). A complement to HSDPA, HSUPA allows uplink rates of up to 5.74Mbps. However, with this increase in data rate comes a much more complex and dynamic uplink signal that requires more robust transmitter design and verification. These high data rates also stress the device’s process-ing power and internal transfer speeds, especially when used in conjunction with HSDPA, requir-ing careful analysis of the device’s application performance and actual throughput while sending and receiving high-speed data.

There are several changes in the uplink signal for HSUPA:

• The addition of two new physical channels in the up-link results in a higher crest factor in the uplink signal than in HSDPA.

• Uplink code channel relative power differences can be up to 45Db.

• Large power changes in the uplink (up to 27dB) can oc-cur at the Transmission Time Interval (TTI) boundaries, e.g. when HSUPA transmission turns off or on.

• The uplink configuration is very dynamic. The number of E-DCH Dedicated Physical  Data Channels (E-DPDCHs), their spreading factors and power levels can change each TTI.

These changes can result in a worsening of transmitter distor-tion and modulation quality. It is not sufficient to simply test the HSDPA capability of a high-speed packet access (HSPA) device. It must also operate properly while transmitting HSUPA channels.

HSUPA overview

Although HSDPA and HSUPA are independent services, they will typically be used together for ap-plications such as VoIP and mobile gaming. HSPA is an industry term for HSDPA + HSUPA.

HSUPA uses Hybrid Auto-matic Repeat-reQuest (ARQ) as in HSDPA—but in HSUPA, the Node B acknowledges the user equipment's (UE) data trans-mission. Node B dynamically allocates power among the UEs on a TTI basis. The UE’s serving grant (power allocation) effec-tively determines the data rate at which it may transmit. To achieve 5.74Mbps in the uplink, UEs must support the (optional) 2ms TTI defined for HSUPA. Early (category 5) devices support only the 10ms TTI, limiting the uplink data rate to 2Mbps.

HSUPA introduces several new uplink and downlink channels. The Enhanced Dedicated Channel (E-DCH) uplink transport channel carries one block of data per TTI. The E-DPDCH carries the uplink user data. The UE can transmit up to four E-DPDCHs, at a spreading factor of SF256 to SF2. 2*SF2 E-DPDCHs are required to achieve 2Mbps, the maximum data rate supported by early devices. The E-DCH Dedicated Physical Con-trol Channel (E-DPCCH) uplink channel carries the control in-formation needed by Node B to decode the uplink E-DPDCH, such as the E-DCH Transport Format Combination Indicator (E-TFCI), which indicates block size, Retransmission Sequence Number and the Happy Bit, which indicates whether the UE is happy with its current serving grant. The three new downlink physi-cal channels are as follows: the E-DCH HARQ Acknowledgement Indicator Channel is used to acknowledge the UE’s data; the E-DCH Absolute Grant Channel provides the absolute limit of the power resources (serving grant) the UE may use; and the E-DCH Relative Grant Channel moves the UE’s serving grant up or down (or signals a hold).

A new HSUPA loopback using Radio Bearer Test Mode is defined in 3GPP TS 34.109. It requires an HSDPA downlink with a carefully chosen data rate such that the UE is provided a steady stream of data to loop back up on its HSUPA channels, but without excessively overflowing its buffers.

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