15-09-2017, 03:04 PM
Code Division Multiple Access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously through a single communication channel. This allows several users to share a frequency band (see bandwidth). To enable this without undue interference between users, CDMA employs extended spectrum technology and a special coding scheme (where each transmitter is assigned a code).
CDMA is used as the access method in many mobile phone standards. Often, the IS-95, also called "cdmaOne", and its 3G CDMA2000 evolution, are simply referred to as "CDMA", but UMTS, the 3G standard used by GSM companies, also uses CDMA or W- as well as TD-CDMA and TD-SCDMA, as their radio technologies.
The technology of code division multiple access channels has long been known. In Soviet Union (USSR), the first work dedicated to this subject was published in 1935 by Dmitry Ageev. It was demonstrated that through the use of linear methods, there are three types of signal separation: frequency, time and compensation. CDMA technology was used in 1957, when the young military radio engineer Leonid Kupriyanovich in Moscow made an experimental model of a portable mobile phone, called LK-1 by him, with a base station. LK-1 has a weight of 3 kg, 20-30 km operating distance, and 20-30 hours of battery life. The base station, as described by the author, could serve several customers. In 1958, Kupriyanovich made the new experimental model of "pocket" of the mobile phone. This phone weighed 0.5 kg. To serve more customers, Kupriyanovich proposed the device, named by him as a correllator. In 1958, the USSR also initiated the development of the national civilian "Altai" automobile telephone service, based on the Soviet standard MRT-1327. The telephone system weighed 11 kg (24 lb). It was placed in the trunk of senior officers' vehicles and a standard telephone was used in the passenger compartment. The main developers of the Altai system were VNIIS (Voronezh Institute of Scientific Research) and GSPI (State Specialized Project Institute). In 1963 this service began in Moscow, and in 1970 the Altai service was used in 30 cities of the USSR.
CDMA is used as the access method in many mobile phone standards. Often, the IS-95, also called "cdmaOne", and its 3G CDMA2000 evolution, are simply referred to as "CDMA", but UMTS, the 3G standard used by GSM companies, also uses CDMA or W- as well as TD-CDMA and TD-SCDMA, as their radio technologies.
The technology of code division multiple access channels has long been known. In Soviet Union (USSR), the first work dedicated to this subject was published in 1935 by Dmitry Ageev. It was demonstrated that through the use of linear methods, there are three types of signal separation: frequency, time and compensation. CDMA technology was used in 1957, when the young military radio engineer Leonid Kupriyanovich in Moscow made an experimental model of a portable mobile phone, called LK-1 by him, with a base station. LK-1 has a weight of 3 kg, 20-30 km operating distance, and 20-30 hours of battery life. The base station, as described by the author, could serve several customers. In 1958, Kupriyanovich made the new experimental model of "pocket" of the mobile phone. This phone weighed 0.5 kg. To serve more customers, Kupriyanovich proposed the device, named by him as a correllator. In 1958, the USSR also initiated the development of the national civilian "Altai" automobile telephone service, based on the Soviet standard MRT-1327. The telephone system weighed 11 kg (24 lb). It was placed in the trunk of senior officers' vehicles and a standard telephone was used in the passenger compartment. The main developers of the Altai system were VNIIS (Voronezh Institute of Scientific Research) and GSPI (State Specialized Project Institute). In 1963 this service began in Moscow, and in 1970 the Altai service was used in 30 cities of the USSR.