How
Frequency Bands, and Choice of CDMA or GSM Technologies Impact Roaming
This article describes the key criteria for the road warrior to take into consideration when selecting a mobile device (cell phone, Smart phone, PDA Phone, mobility enabled laptop), be it for supporting field service or sales personnel covering an extensive regional territory, the coast-to-coast executive supporting multiple locations, or the frequent international traveler.
We wade through the murky waters of tri-mode, tri-band, quad-band, WCDMA tri-band, satellite tri-mode soup of terminology to shed light on what will be important to you.
Four criteria largely determine where you can use your mobile device when roaming:
This article focuses on air interface technologies and frequency bands. Your needs in these areas may narrow or dictate your choice of service providers.
The air interface technology options are largely in either the CDMA family or the GSM family. The CDMA family of air interface technologies include IS-95A (2G), IS-95B (2G + low-speed packet data), 1X-RTT (3G) and 1X-EVDO (3G+). CDMA coverage is pretty ubiquitous throughout North America and the so-called emerging markets of Brazil, China, India, and South Korea as well as several other locations
The GSM family of air interface technologies include GPRS (2G), EDGE (2.5G), UMTS (3G), HSDPA (3G+) and HSUPA (3G++) and pretty much blankets the globe with Japan and South Korea being notable exceptions).
The band(s) for a device refers to the frequency range(s) that it transmits and receives on.
Marketing blurbs referring to a device as being dual-mode, dual-band, tri-mode, or quad-band has some typical meanings but in reality is all quite ambiguous. It is important to focus on the actual frequencies and air interface technologies that a particular device supports. In North America, the 1900 MHz (PCS) and 850 (cellular) MHz frequency bands are available to service providers. On most other continents, 900 MHz is used for cellular and 1800 MHz is used for PCS.
A CDMA dual-band mobile device almost always refer to a phone that will operate on both the 1900 MHz (PCS) and 850 MHz (cellular) frequency bands. A dual-band GSM device sold in North America is today rather rare, but refers to a device that supports any two of the four GSM frequency bands. More commonly, GSM devices will have tri-band or quad-band capabilities.
Tri-band mobile devices usually supporting the 850/1800/1900 bands or the 900/1800/1900 bands. The former provides good coverage in North America whereas for the later, only the 1900 band is supported in North America. UMTS tri-band or equivalently HSDPA/UMTS tri-band refers to high-speed data over the 850/1900 and the relatively recently designated 2100 MHz frequency band for Africa, Europe and parts of Asia. North America does not support the 2100 MHz band but it may be important to you as high speed data continues to roll out if you frequently travel to those regions of the world.
Quad-band mobile devices typically refer to devices that support the GSM 850/900/1800/1900 band of frequencies but in recent times have also come to refer to the 900/1800/1900/2100 band of frequencies supporting high speed data. Only the 1900 MHz band from this later set is supported in North America.
Dual-mode for both CDMA and GSM usually imply support for analog but in recent times has also come to refer to devices that support Wi-Fi and either CDMA or GSM. A tri-mode phone is typically used to describe a CDMA phone that supports analog (also referred to as AMPS) 850, CDMA cellular (850) and CDMA PCS (1900). Tri-mode has also been used to refer to devices that support AMPS, CDMA and Globalstar satellite.
The key points to take away here are that a CDMA mobile device that supports CDMA 850 and CDMA 1900 supports roaming between the Sprint PCS and Verizon Wireless CDMA networks for example. A GSM mobile device that supports 850/900/1800/1900 will provide ubiquitous voice and data coverage in most places in the world and very high-speed data throughout North America. The GSM “world” phones offered through Cingular and T-Mobile, for example support pretty much global roaming.
If your needs are mostly regions of the United States, then there are many fine regional service providers supporting CDMA (AllTel, Cricket, MetroPCS and US Cellular) and GSM (CellularOne/Dobson and SunCom).
For completeness, we should mention the Integrated Digital Enhanced Network (iDEN) air interface technology created by Motorola. IDEN also supports walkie-talkie capabilities and is used by Sprint-Nextel and Southern LINC.
Given the ambiguity of common terms such as tri-mode and quad band, it is important to understand the specific air interface technologies and frequency bands that meet your needs. In this article we have focused on these capabilities in the context of choosing the device that best permits service in the places (regions, countries, continents) that you frequent.