Continuing our posts about data transmission technologies, we’ll talk about UMTS (Universal Mobile Telecommunication System), posterior technology of other studied here. If you missed something over previous technologies, read more through the links below:
Although initially concurred with EVDO, UMTS just emerging as the technology adopted by all Brazilian operators that already offer 3G access, including “Claro” (now offer plans based on 3G UMTS from the end of 2007) “TIM”, the “OI” and even “Vivo”, which started to operate a mixed network with UMTS and EVDO.
Versão em português.
As in the case of GSM, which supports the use of GPRS and EDGE, UMTS provides two access modes, which are used according to availability, reception quality and the mode supported by the device.
The most basic is the WCDMA (not to be confused with CDMA, which is the GSM competing technology), which offers data rates up to 384 kbits, both for download and for upload. Although on paper the value be close to 236.8 kbits offered by EDGE, in practice the WCDMA offers much better latency times and a much more usable connection. A good example of the difference is the use of VoIP applications, which are almost unusable in EDGE, due to the lag in transmission, but flow satisfactorily in WCDMA.
Then we have the HSDPA, a newer protocol that reduces latency and increases the download rate significantly. Using HSDPA as the transport protocol, UMTS supports rates 1.8, 3.6, 7.2 and 14.4 megabits, according to the implementation used by the operator (in Brazil version 7.2 megabits is the most common). Of course, the actual speed varies depending on the signal quality and the number of users connected to the same broadcast station, but it is always much higher than in WCDMA.
The major problem is that HSDPA works well only relatively short distances, so the apparatus will automatically switch to the WCDMA smaller coverage areas, so that the transmission rate is reduced. Another limitation is that the HSDPA only increases the download rate, doing nothing regarding the upload, it remains only 384 kbits, as in WCDMA.
In conclusion …
HSDPA is considered a 3.5G protocol and (in most units) you can check which system is being used simply looking at the connection icon. A “3.5G” indicates that you are using the HSDPA a “3G” that is in use WCDMA, an “E” being used EDGE and a “G” you are in an area where only the old GPRS is available.
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MORIMOTO, Carlos Eduardo. Smartphones, guia prático / Carlos Eduardo Morimoto. – Porto Alegre: Sul Editores, 2009. Pages 313-314.