Global Systems for Mobile Communication (GSM) is the main technology used by the international digital wireless systems and cell phones; however, GMS is used only by a small percentage of cell phone carriers in the United States. GSM is interesting in that it uses a modified and far more efficient version of TDMA (Time Division Multiple Access). GSM keeps the idea of timeslots on frequency channels, but corrects several major shortcomings. Since the GSM timeslots are smaller than TDMA, they hold less data but allow for data rates starting at 300 bits per second. Thus, a call can use as many times slots as necessary up to a limit of 13 kilobits per second. When a call is inactive (silence) or can be compressed more, fewer timeslots are used. To facilitate filling in gaps left by unused timeslots, calls do frequency hopping in GSM. This means that calls will jump between channels and timeslots to maximize the system’s usage. A control channel is used to communicate the frequency hopping and other information between the antenna tower and the phone.
The architecture used by GSM consists of three main component, a mobile station, a base station subsystem, and a network subsystem. These components work in tandem to allow a cell phone user to travel seamlessly without interruption of service, while offering the flexibility of having any GSM cell phone device used permanently or temporarily by any user. Utilizing the three separate components of the GSM network, this type of communication is truly portable. A cell phone user can place an identification card called Subscriber Identity Module (SIM) in the wireless device, and the device will take on the personal configurations and information of that user. This includes telephone numbers, home system, and billing information. Although the United States has migrated towards CDMA and TDMA as the premier mode of wireless communications, a large part of the world uses GSM.
Benefits of GSM
GSM networks cover the most wireless users around the world and the technology is gaining favor in the United States because of the following benefits:
- Provides integrated voice, high-speed two-way data, face and short message services capabilities
- Offers advanced features such as caller ID, text messaging in the cell phones
- Offers superior voice clarity and overall call quality
- Provides personal identification tied to a Subscriber Information Module (SIM) card that can be used in multiple phones, not tying the user to one cell phone
- Offers voice privacy
- Uses less battery power (when compared to analog)
- Enables a single technology handset to work around the world where GSM is available (as long as the frequencies are accessible by the handset)
