High-Speed Uplink Packet Access

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(Redirected from 3.75G)

Mobile phone
standards

0.5G

2.5G

2.75G

3.5G

HSDPA

3.75G

HSUPA

HSUPA, High-Speed Uplink Packet Access, is a data access protocol for mobile phone networks with extremely high upload speeds up to 5.8 Mbit/s. Similar to HSDPA (High-Speed Downlink Packet Access), HSUPA is considered 3.75G or sometimes 4G.

The specifications for HSUPA are still under development (July 2005) and will be included in UMTS Release 6. It will be published on www.3GPP.org.

HSUPA is expected to use an uplink enhanced dedicated channel (E-DCH) on which it will employ link adaptation methods similar to those employed by HSDPA, namely:

shorter TTI (Transmission Time Interval) enabling faster link adaptation;

HARQ (hybrid ARQ) with incremental redundancy making retransmissions more effective.

Similarly to HSDPA there will be a packet scheduler, but it will operate on a request-grant principle where the UEs request a permission to send data and the schedular decides when and how many UEs will be allowed to do so. A request for transmission will contain data about the state of the transmission buffer and the queue at the UE and its available power margin. In addition to scheduled transmissions the standards also forsee a self-initiated transmission mode from the UEs - this mode can for example be used for VoIP services for which even the reduced TTI and the Node-B based schedular will not be able to provide the very short delay time and constant bandwidth required.

The standard forsees two basic scheduling methods: Long term grants are issued to several terminals which can then send their data simultaneously. The grants are increased or decreased according to the current load of the cell and the requirements of the terminals. Short term grants on the other hand are an alternative scheduling method to allow multiplexing terminals in the time domain instead of the code domain as is done for the long term scheduling. In order to allow multiplexing uplink transmissions of several terminals in both code and time domain the scrambling and channelisation codes are not shared between differents terminals like this is done in HSDPA on a shared downlink channel.

Because in the uplink the DPDCH and DPCCH are code-multiplexed and transmitted simultaneously in time the ratio of their transmit powers is important for the achievable pay-load bit rates. The greater part of the UE's power is assigned to DPDCH the higher the pay-load bit rate achievable on that channel but the less power is left for DPCCH and the less reliable the signalling in the link. In UMTS Release'99 the ratio between the power of DPDCH and DPCCH was set to a constant. In HSUPA this ratio will be controlled by the Node-B.

In HSUPA, unlike in HSDPA, soft and softer handovers will be allowed for packet transmissions. The control of UE's transmit power in soft/softer handover on E-DCH will be slightly different from that specified in Release'99 for DCH, namely: the main serving Node-B will be able to issue both power-up and power-down commands but all other Node-Bs participating in the handover will be able to issue only power-down commands. A power-down command will always have precedence over a power-up command.