HSUPA introduction introduction, HSUPA

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High-Speed Uplink Packet Access
From Wikipedia, the free encyclopedia
 
High-Speed Uplink Packet Access (HSUPA) is a data access protocol for mobile phone networks with extremely high upload speeds up to 5.76 Mbit/s. Unlike HSDPA (High-Speed Downlink Packet Access) which is 3.5G, HSUPA is considered 3.75G.
 
The specifications for HSUPA are included in Universal Mobile Telecommunications System Release 6 standard published by 3GPP.
 
 
Technology
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 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 scheduler 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 foresee 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 scheduler will not be able to provide the very short delay time and constant bandwidth required.
 
The standard foresees 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 different terminals like this is done in HSDPA on a shared downlink channel.
 
Since 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. When a larger part of the UE's power is assigned to DPDCH, the payload bit rate achievable on that channel increases. Conversely, less power is left for DPCCH and transmission of signaling on that channel becomes less reliable. 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.
 
Another difference with HSDPA is that HSUPA will not use higher-order modulations. In principle, using a higher-order modulation is a standard way to increase the throughput of a communications system without increasing the bandwidth. Higher-order modulations were introduced in the downlink in EDGE, HSDPA, 1xEV-DV and 1xEV-DO, etc. So why not use them in HSUPA? The answer is because HSUPA is an uplink technology where the limited battery capacity of a handheld terminal (the mobile) has to be considered. Here is the reasoning: higher-order modulations are more vulnerable to noise and interference, particularly those types which keep constant amplitude envelope (for them the amplitude changes little, or not at all, between different transmitted symbols). Over noisy and interference-prone radio channels modulations with not constant envelope must be used to allow reliable demodulation. They result in higher peak-to-average ratio of the modulated signal, which requires transmitter amplifiers with greater linear range in their amplitude response (also called dynamic range). Such amplifiers are less energy efficient – to produce the same output power they on average draw larger current, which in the case of a mobile would come from its battery and reduce its talk time. This would not be acceptable for HSUPA since the subscribers expect from any new technology to offer longer talk times. Hence it was decided for HSUPA to keep the presently standard UMTS modulation (QPSK), which has lower peak-to-average ratio. In HSDPA and other downlink technologies the transmitter is at the base station and its power supply is not limited in time, but more importantly the dynamic range of its amplifier is inherently greater, which made the choice of higher-order modulations more attractive.
 
 
Deployment
In Austria, T-Mobile is planning to introduce HSUPA in 2007 or 2008.
 
In Italy, Telecom Italia is planning to introduce HSUPA in 2007.
 
In South Korea, KTF is planning to introduce HSUPA in 2007.
 
In United States, Cingular Wireless plans to do field tests on HSUPA late 2006 and then conduct live tests with devices in early 2007.