3G Mobile Phones

Although originally designed to have EVDO, UMTS eventually emerging as the technology adopted by all national carriers that already offer 3G access, including the course (now plans to offer 3G UMTS based on the end of 2007), the TIM, the Hi and even to live, now operate a network mixed with the UMTS and EVDO.

As in the case of GSM, which supports the use of GPRS and EDGE, UMTS offers two modes of access, which are used according to availability, quality of reception and the mode supported by the device.

The most basic is the WCDMA (not to be confused with CDMA, which is the pattern of rival GSM), which offers transmission rates up to 384 kbits for both download and to upload. Although, on paper, the value is close to 236.8 kbits offered by EDGE, WCDMA in practice offers the very best times of onset and a connection much more usable. A good example of the difference is the use of VoIP applications, which are almost unusable on EDGE due to the lag in transmission, but flow in a satisfactory manner in WCDMA.

Then we have HSDPA, a more recent protocol, which reduces latency and increases the rate of download of the network so expressive. Using the HSDPA as the transport protocol, UMTS supports rates of 1.8, 3.6, 7.2 and 14.4 megabits in accordance with the implementation used by the operator (in Brazil the version of 7.2 megabits is the most common). Naturally, the actual speed varies with the quality of the signal and the number of users connected to the same station for transmission, but it is always higher than in WCDMA.

The big problem is that HSDPA works well only for relatively short distances, so the devices automatically switch to WCDMA in the areas of lowest coverage, making the rate of transmission is reduced. Another limitation is that the only HSDPA increases the rate of download, doing nothing with the upload, which remains the only 384 kbits, as well as WCDMA.

The HSDPA is considered a 3.5G protocol and (in most devices) you can see which system is being used simply looking at the icon of the connection. A "3.5G" indicates that you are using the HSDPA, a "3G" you are using the WCDMA, a "E" you are using the EDGE and a "G" you are in an area where only the old GPRS is available:

In Nokia, you will notice that the 3.5G icon appears only while the unit is transmitting data. This is why he really only uses the HSDPA while the connection is active. In the rest of the time, it switches back to the WCDMA, to save energy, making the icon back to "3G".