Quad band Wi-Fi™ is a wireless technology which supports communications in four different frequency bands on the same device. Many regions of the world utilize several unique frequency ranges for their mobile phone systems. The four most common bands cover most of the world's networks. Quad band technology is specific to Global System for Mobile Communications (GSM) networks. It is frequently used by business travelers to enable communications and roaming in different countries with the same mobile device.
A GSM quad band phone can utilize any of the frequency bands for which it is designed on a GSM network. Two of the common Quad band Wi-Fi™ frequency ranges which cover the largest area are 850 and 1900 Megahertz (MHz). These bands are widely used in North, Central and South America. The other two GSM ranges most often used are 900 and 1800 MHz. They cover much of the rest of the world, with 900 MHz being the most widely used of the two.
Each Quad band Wi-Fi™ frequency band actually contains two ranges. The 850 MHz band uses 824 to 849 MHz to uplink while utilizing 869 to 894 MHz to downlink. The uplink for the 1900 MHz band is 1850 to 1910 MHz and the downlink is 1930 to 1990 MHz. The downlink for the 900 MHz GSM band is 935 to 960 MHz, while the uplink is 890 to 915 MHz. For the 1800 MHz frequency band, 1710 to 1785 MHz is the uplink and 1805 to 1880 MHz is the downlink.
Universal Mobile Telecommunications System (UMTS) networks use some of the same 14 frequency bands that GSM does. Many multi-band UMTS phones work with GSM networks, but not vice versa. Some multi-mode phones do support both UMTS and Quad band Wi-Fi™ GSM on the same frequency bands. Japan and some other countries don't support GSM networks at all.
Tri band technology only supports three different frequency bands on the same device. The country where the phone is purchased usually determines which three frequencies are included. For example, a tri band GSM phone from North America generally supports the common Americas frequencies of 850 and 1900 MHz. It often includes 1800 MHz as the third frequency band, providing limited coverage in the rest of the world. In contrast, a European phone may support the local 900 and 1800 MHz bands as well as 1900 MHz to partially cover other regions.