|Tuesday, 15 August 2006|
Wireless modems enable mobile computer devices to communicate with other computer devices without requiring physical access to a land line communication port. The wireless modem processes data and signals for transferring data between the wireless interface and the user interface. A typical portable communication device includes an integrated modem and processor for controlling the operation of the handset. Wireless radio frequency modems cooperatively operate with a host computing device. Wireless modems generally modulate an RF carrier with a stream of data packets, and then amplify the modulated carrier for transmission from an internal antenna. A wireless modem typically consists of a radio portion (an RF front end or an RF head), a modulator/demodulator portion (baseband processing unit or baseband chip), a processor, memory, and an interface. The radio portion contains the transmitter, receiver and associated circuitry to provide for RF communications. The transmitter is used to generate RF signals using a baseband signal to modulate a carrier signal. The receiver produces a baseband signal from RF signals by demodulating an RF signal received at the antenna to produce a demodulated baseband signal. The baseband portion provides a baseband signal to the transmitter and accepts baseband signals from the radio portion receiver. The baseband portion decodes the baseband signals to provide data and encodes data to provide a baseband signal for transmission by the transmitter. The baseband PCMCIA adapter is attached via a flat cable to its radio portion.
The transmitters, receivers, and other signal processing components typically found in RF wireless modems are constructed on an RF circuit. These modem components collectively operate during a wireless communications process to receive and transmit an electromagnetic radio frequency signal and operate to perform three principal modem functions: RF conversion, baseband processing and protocol stack control. These modem components translate the digital signals from the computer to analog signals for transmission on an analog telephone network, and also demodulate the received analog telephone network signals into a digital form usable by the computer. A commonly used communication technique in RF wireless communications is spread spectrum. In spread spectrum communication the transmitted signal is spread over a frequency band that is significantly wider than the minimum bandwidth required to transmit the information being sent.
A wireless modem may be installed as an adapter card or in an adapter slot such as a PCMCIA slot. Many wireless modems are usually in the form of a Personal Computer Memory Card International Association (PCMCIA) card. PCMCIA (Personal Computer Memory Card International Association) is an organization that develops and promotes standards for PC cards that could provide additional memory resources for the host computer and other types of electronic devices. Many modern portable computers, including laptops and personal digital assistants (PDAs), have a built-in PCMCIA slot for accepting another electronic device packaged in a PC card conforming to the PCMCIA standard. Other interfaces between the wireless RF modem and the host computer are RS-232, USB, Parallel Port, IrDa, or Compact Flash. Additionally, some wireless handsets having built-in modems also provide an interface that is reserved for the host computer system.
The portable handset provides a user interface for interacting with a user and a wireless interface providing an air interface for wireless telephony. Some of the various cards that are increasingly used in computer systems are wireless modem cards. Wireless modem cards that operate according to the Code Division Multiple Access (CDMA) technology are increasingly used in portable computer systems and devices for wireless communications in various system configurations and media such as digital cellular network, wireless personal communication services (PCS), wireless local loop, etc. A CDMA wireless modem card contains many components that are designed and implemented to perform various signal processing functions required in wireless communications. Existing GSM modems operate similarly to landline modems, such as Hayes compatible modems. They generally act primarily as a transport mechanism for moving data between two devices.