The main developers of the Altai system were VNIIS (Voronezh Science Research Institute of Communications) and GSPI (State Specialized Project Institute). It was placed in the trunk of the vehicles of high-ranking officials and used a standard handset in the passenger compartment. To serve more customers, Kupriyanovich proposed the device, which he called "correlator." In 1958, the USSR also started the development of the " Altai" national civil mobile phone service for cars, based on the Soviet MRT-1327 standard. In 1958, Kupriyanovich made the new experimental "pocket" model of mobile phone. The base station, as described by the author, could serve several customers. LK-1 has a weight of 3 kg, 20–30 km operating distance, and 20–30 hours of battery life. The technology of CDMA was used in 1957, when the young military radio engineer Leonid Kupriyanovich in Moscow made an experimental model of a wearable automatic mobile phone, called LK-1 by him, with a base station. It was shown that through the use of linear methods, there are three types of signal separation: frequency, time and compensatory. In the Soviet Union (USSR), the first work devoted to this subject was published in 1935 by Dmitry Ageev. Further research in the context of jamming and anti-jamming was carried out in 1952 at Lincoln Lab. In the US, one of the earliest descriptions of CDMA can be found in the summary report of Project Hartwell on "The Security of Overseas Transport", which was a summer research project carried out at the Massachusetts Institute of Technology from June to August 1950.
The technology of code-division multiple access channels has long been known. Many carriers (such as AT&T and Verizon) shut down CDMA networks in 2022, rendering CDMA handsets unusable for calls, even to 911. Other schemes use subcarriers based on binary offset carrier modulation (BOC modulation), which is inspired by Manchester codes and enable a larger gap between the virtual center frequency and the subcarriers, which is not the case for OFDM subcarriers.
CDMA is often used with binary phase-shift keying (BPSK) in its simplest form, but can be combined with any modulation scheme like (in advanced cases) quadrature amplitude modulation (QAM) or orthogonal frequency-division multiplexing (OFDM), which typically makes it very robust and efficient (and equipping them with accurate ranging capabilities, which is difficult without CDMA). Due to their very advantageous auto- and crosscorrelation characteristics, these spreading sequences have also been used for radar applications for many decades, where they are called Barker codes (with a very short sequence length of typically 8 to 32).įor space-based communication applications, CDMA has been used for many decades due to the large path loss and Doppler shift caused by satellite motion. In these schemes, the message is modulated on a longer spreading sequence, consisting of several chips (0es and 1es).
It can be also used as a channel or medium access technology, like ALOHA for example or as a permanent pilot/signalling channel to allow users to synchronize their local oscillators to a common system frequency, thereby also estimating the channel parameters permanently. IS-95, also called "cdmaOne", and its 3G evolution CDMA2000, are often simply referred to as "CDMA", but UMTS, the 3G standard used by GSM carriers, also uses "wideband CDMA", or W-CDMA, as well as TD-CDMA and TD-SCDMA, as its radio technologies. It is used as the access method in many mobile phone standards. ĬDMA optimizes the use of available bandwidth as it transmits over the entire frequency range and does not limit the user's frequency range. To permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme (where each transmitter is assigned a code). This allows several users to share a band of frequencies (see bandwidth). CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. Code-division multiple access ( CDMA) is a channel access method used by various radio communication technologies.
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