Cellular Modems Information
Cellular modems are special types of modems used to modulate analog signals, such as telephone signals, to be transmitted using cellular networks. The modulated signal is used for phone or data communication with smart phones and similar devices.
Typical analog modems convert (or "prepare") a given analog signal (such as the human voice) to be efficiently transmitted through cable systems such as home phone cables, TV cables, or fiber optic cables. The modem takes the analog signal and modulates it (by adding to it a high frequency signal called the carrier). When the modulated signal reaches the destination, it is de-modulated back to the original signal. Modem is a word formed with the first letter of the words MODulation and DEModulation.
Cellular modems apply the same principle, but the destination of the modulated signal is the cellular phone towers. From there, the signal reaches digital cellular devices such as smartphones, tablets, and others. Cellular modems use the internet as the medium for transmission. Computers and other digital devices produce the digital signals to be modulated and transmitted.
The main specifications to select a cellular modem are the following.
Network type is the technology used by the modem to connect to a particular type of network. Among these, we have:
- Global System for Mobile (GSM) Communications is a digital cellular system that uses narrowband time division multiple access (TDMA) technology. It allows eight simultaneous calls on the same radio frequency.
- General Packet Radio Service (GPRS) is a standard for wireless communications that runs at speeds up to 115 kilobits per second.
- 3G is the third generation of mobile communication technology.
- 4G is the fourth generation of mobile communication technology.
- Code division multiple access (CDMA) technology is a channel access method.
Connectivity is the physical interface between the modem and connected devices. There are several types available. Some of the most important:
- Universal Serial Bus (USB) is a 4-wire, 12-Mbps serial bus for low-to-medium speed peripheral device connections to personal computers (PC), including keyboards, mice, modems, printers, joysticks, audio functions, monitor controls, etc. The USB design is standardized by the USB Implementers Forum (USBIF), an organization that includes leading companies from the computer and electronics industries. The current USB specification is USB 2.0, which supports data transfer rates of up to 480 Mbps.
- Ethernet (RJ-45 and others)
- Serial (RS-232, RS-422, RS-485, among others) Serial Ports (Asynchronous Serial Interface): A system-to-system communication interface. Data is sent over a single wire (serial). Transmission is asynchronous because no synchronization or clocking signal is present.
Form factor refers to the shape, size, and function of the device. There are basically two general types:
- External: An external modem is a module that is connected to the system by means of a physical port.
- Internal and embedded