HotSpot@Home takes advantage of three rapidly emerging telecommunications technologies: dual-mode cell phones, home wireless networks (WiFi) and wireless VoIP (Voice over Internet Protocol) telephony.
Wireless VoIP telephony uses an IP network, rather than a network of cellular towers and switches, to connect a cell phone to the rest of the cellular network. And, since dual-mode cell phones contain WiFi radios, they're able to access these IP networks through WiFi routers. For more detailed information on how WiFi VoIP works, check out How WiFi Phones Work.
Dual-mode cell phones communicate over home WiFi networks through a technology standard called UMA (Unlicensed Mobile Access). A UMA-enabled phone can join any unlicensed WiFi network. An "unlicensed" WiFi network simply means that the network operates over a free, unrestricted radio frequency. For example, 802.11b/g routers, communicate over the unlicensed 2.4GHz spectrum. Companies or government agencies buy licensed spectrums for exclusive use [source: WiMax.com].
Since dual-mode phones contain both cellular and WiFi radios, they're able to send and receive calls over two separate networks: the Cellular Radio Access Network (RAN) and the Unlicensed Mobile Access Network (UMAN) [source: UMA Technology]. The phone decides which network to use based on which one has the best signal strength: cellular or WiFi.
A Cellular Radio Access Network (RAN) is the traditional cellular network that relies on a series of cellular towers and switching stations. For a detailed explanation of how cell phones work over a Cellular Radio Access Network (RAN), see How Cell Phones Work.
Here's how a dual-mode cell phone connects to the same mobile network over an Unlicensed Mobile Access Network (UMAN):
- A UMA-enabled phone comes within range of a WiFi network and the network grants it access
- The phone sends a request through the WiFi router and over the broadband IP network to something called the UMA Network Controller (UNC).
- The UNC decides whether or not to give the phone authorization to access GSM voice services over the unlicensed network. GSM is the global cell phone standard.
- The UNC then tells the central Mobile Telephone Switching Office (MTSO) the cell phone's location. Now all calls to and from the core mobile network will be routed through the WiFi network [list adapted from source: UMA Technology].
When a dual-mode cell phone moves out of the WiFi network's range, it automatically hands off to the cellular-radio network without any service interruption [source: UMA Technology].
Routing calls over two separate mobile networks is actually a huge money-saver for cellular service providers. The only way to improve coverage and keep up with heavy traffic on a traditional cellular radio network is to build more cellular towers [source: New York Times]. But with HotSpot@Home, T-Mobile is able to re-route a significant amount of that traffic onto broadband Internet networks -- which, incidentally, T-Mobile doesn't own and therefore doesn't have to maintain.
Services like HotSpot@Home appear to be the next big thing in telecommunications. In the already booming cell phone market, dual-mode phones are the fastest growing segment worldwide [source: cellular-news]. Infonetics Research predicts a compound annual growth rate of 198 percent for dual-mode phone sales from 2006 to 2010.
For more information on HotSpot@Home and related topics, check out the links below.