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DIRECTORY
Cellular standards
CDMA Code Division Multiple Access (IS-95) Code Division Multiple Access. CDMA is not a new technology. It has been used in military satellite communications systems for many years. QUALCOMM Corporation, recognizing the enormous potential of CDMA for wireless applications, has developed the key innovations necessary to make this standard a highly efficient and affordable technology for mobile systems. This technology can greatly increase the capacity and quality of cellular communication systems around the world. Unlike existing analog and other digital systems, which divide the available range into narrow channels and allocate one channel for each conversation (or several), CDMA does not divide the operating range into channels, but uses a wide spectrum of frequencies for each conversation. Each phone or call is assigned a unique code by which it stands out from the many simultaneous data transmissions in the same frequency range. Therefore, as long as the receiving device has the correct code, it can select the desired conversation from a variety of others. Features and Benefits Outstanding voice quality. CDMA provides excellent voice quality, comparable even to wired systems. Also filter out background noise, interference and other interference, which greatly increases the quality of communication and confidentiality. Large coverage area at a lower cost. The CDMA spread spectrum signaling system provides greater coverage than other wireless technologies, both home and mobile. CDMA networks require fewer base stations to cover a given area than other radio technologies. With a smaller number of base stations, a mobile operator can significantly reduce costs, both during the development of a cellular network and during its operation. Less power consumption - smaller phones. CDMA devices typically transmit data at significantly lower energy levels than devices using other technologies due to the use of varying voice coding levels. This allows the battery to last longer. Less broken conversations. Using a proprietary method of transferring calls between cells, known as "soft handover", CDMA significantly reduces the chance of a call being dropped or lost in transit. Increased security and privacy. In addition to filtering out background noise and other interference, noise-like, digitized and encrypted CDMA transmissions are securely protected from eavesdropping. Voice coding in the CDMA standard, along with 4.4 trillion codes, also fully guarantees the impossibility of cloning and other types of information leakage. Increased capacity. CDMA provides greater spectrum efficiency than any other analog or digital technology, allowing cellular operators to support more network users and more network traffic for the same radio bandwidth. Considering the ever-increasing number of users and talk times, a large network capacity is a very important advantage and a factor for increasing profits. Network Services CDMA technology gives users access to a wide range of services, including caller ID, short message system (SMS) and Internet access. Simultaneous transmission of data and voice is also possible. Perspectives of the standard CDMA, and to be more precise WCDMA (Wide-CDMA) are currently the most promising technologies. Networks and telephones have already been developed in Japan that allow video transmission, the data transfer rate in these networks will be from 384kbs to 2Mbps. WCDMA is likely to become the global standard for cellular communications in the new millennium, being the new third generation of cellular communications. DAMPS Digital Advanced Mobile Phone Service - digital enhanced mobile telephone service. Digital modification of the AMPS standard. Designed for North America, but having gained popularity in other countries, in 1993 appeared in Russia. Frequency range 825 - 890 MHz. Features Network capacity is much higher than NMT-450 and AMPS. Ability to operate mobile devices in both digital and analog modes. A wide range of services. The capacity of cellular networks operating in this standard is lower than in fully digital systems, but still significantly higher than in analog ones. If, during roaming, a subscriber from an AMPS analog network gets into a digital one - D-AMPS, analog channels are allocated to him for work . However, in this case, the benefits of digital communications, paid in advance, are not available to him. Prospects AMPS networks will gradually be replaced by networks operating in the digital version of this standard. The latest IS-136 modification of the D-AMPS standard brings it closer to GSM in terms of technical capabilities. Automatic roaming is also developing. Cellular networks have their own "peak hours" when mobile subscribers cannot get through or are forced to interrupt the conversation. This is especially true for large cities, where the bulk of users are concentrated. To solve this problem and meet the growing needs of subscribers in the service, operators are moving from analog to modern digital standards. GSM 900 Global System for Mobile Communications - global mobile communication system. Pan-European digital standard, frequency range 890-960 MHz. Features Smaller compared to analog standards, the size and weight of telephones with more time without recharging the battery. This is mainly achieved by the base station equipment, which constantly analyzes the level of the signal received from the subscriber's device. In cases where it is higher than required, the radiated power is automatically reduced. Relatively high network capacity. Low level of industrial interference in this frequency range. Maximum protection against eavesdropping and illegal use of the number (only GSM-1800 has higher protection), which is achieved by using public key encryption algorithms. Communication at a distance of no more than 35 km from the nearest base station, even when using amplifiers and directional antennas. SIM card. In the GSM-900 standard, for maximum protection against unauthorized connection, a special subscriber authentication module is used - a SIM card. This card, whose built-in microcircuit stores special information about a specific subscriber, is issued to him when the phone is connected and can be used with any model of a GSM mobile device. To prevent the thief from using it, a special identification number (PIN code) is entered into it, which must be dialed each time the device is turned on. However, a lazy subscriber can disable this feature. If you enter your PIN incorrectly three times in a row, your SIM card will be temporarily blocked. Using a SIM card is also convenient because when changing a device, the subscriber does not need to change his mobile number, he simply rearranges the card, and all the data stored on it (including the address book) becomes available in the new device. GSM 1800 Global System for Mobile Communications - global mobile communication system. Digital standard, frequency range 1710-1880 MHz. Modification of the GSM-900 standard Features The maximum radiated power of GSM-1800 mobile phones is 1W (for comparison, GSM-900 has 2W). High protection against eavesdropping and illegal use of the number. High network capacity, which is important for large cities. The maximum distance of the subscriber from the base station is 5-6 kilometers. SIM card. In the GSM-1800 standard, for maximum protection against unauthorized connection, a special subscriber authentication module is used - a SIM card. This card, whose built-in microcircuit stores special information about a specific subscriber, is issued to him when the phone is connected and can be used with any model of a GSM mobile device. To prevent the thief from using it, a special identification number (PIN code) is entered into it, which must be dialed each time the device is turned on. However, a lazy subscriber can disable this feature. If you enter your PIN incorrectly three times in a row, your SIM card will be temporarily blocked. Using a SIM card is also convenient because when changing a device, the subscriber does not need to change his mobile number, he simply rearranges the card, and all the data stored on it (including the address book) becomes available in the new device. NMT 450 The analog standard NMT-450 (Nordic Mobile Telephone) was developed in Scandinavia. Frequency range 453 - 468 MHz. Features Significantly larger compared to other standards, the coverage area of one base station and, accordingly, lower costs, as well as low signal attenuation in open space, which is optimal for vast areas with low population density. Long range - the ability to use communication at a distance of several tens of kilometers from the base station (theoretically up to 100 km, especially in summer) and even outside the guaranteed coverage area, if the subscriber can connect high-performance directional antennas and amplifiers. This is equally valuable both in hard-to-reach, sparsely populated areas of the North or the Far East, and in distant Nice. More natural than with digital standards, the sound of the human voice. Weak noise immunity - in this frequency range, the level of industrial interference is higher than in the 800, 900 and 1800 MHz bands. Less than in digital standards, the ability to provide a wide range of services. Eavesdropping vulnerability. It is useful for the NMT-450 subscriber to know that his conversations are easily received by the VHF receiver of the appropriate range. The dimensions, weight, energy consumption of batteries in telephone sets is greater than in digital systems, and the operating time is correspondingly shorter. In new models, these shortcomings are less pronounced. The likelihood of a decrease in the quality of communication indoors. The low subscriber capacity of networks, due to the range of frequencies used and the peculiarities of technical solutions, can increase the dialing time at peak times. For this reason, in large cities, the number of simultaneously used numbers within one cell of the NMT-450 standard is limited. Prospects In the process of modernization, new versions of the standard are being developed. To increase the capacity of cellular networks of the NMT-450 standard, it is planned to use a frequency grid step of 12,5 kHz instead of the standard step of 25 kHz, which will increase the number of working channels from 180 to 359. But only owners of new phone models will be able to use this privilege. It is supposed to use time division of channels, as in digital systems (work of several subscribers on one frequency). Satellite communication systems will not be able to seriously compete with NMT-450 networks in the near future due to the high cost of the services provided. Publication: radioman.ru
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