What does gsm cdma mean? The order in which voice data passes through the mobile station until it is sent on the air
Hello dear readers. Most owners mobile phones there is only one technology to worry about called global system for mobile communications or GSM. As the name suggests, this standard has been widely adopted and is used for communication via cellular communications.
But not everyone has jumped on the GSM train. An alternative standard known as Code Division Multiple Access, or CDMA, is also used by many operators around the world. This standard is most popular in the USA and Russia, but is also used in some African and Asian countries, where it competes with GSM.
Here's what cell phone owners should know before purchasing a device that supports one of these technologies.
This is the first question potential owners will ask, and it's a valid one. But in this case there is no simple answer.
GSM and CDMA- This different ways achieving the same goal. And the fact that popular networks have been built on the basis of each of them proves that it is not the standard that is important, but the quality of the network. For example, in the US, two of the four largest carriers (Verizon and Sprint) use CDMA, while the other two (AT&T and T-Mobile) have chosen GSM.
From a technical point of view, no standard has an advantage in terms of quality. But there are some things you should take into account. GSM phones can be unlocked and transferred to other operators, and CDMA phones are most often locked to one operator and nothing can be done about it.
Additionally, most phones support either GSM or CDMA, so your choice of phone may determine which standard you end up using. Apart from that, it all depends on what operators are available in your territory. Some areas are better covered by GSM providers, while in others CDMA providers may have an advantage.
Many phones are compatible with GSM or CDMA, but not both. In the case of CDMA phones, you will have to purchase a device made specifically for your operator. The easiest way is to buy it directly from this operator. For example, if you want to use an iPhone on Verizon's network, you need to purchase a branded iPhone from Verizon, not Sprint or AT&T. However, if you decide to switch to another operator, you will not be able to take the phone with you, as it is locked.
If you don't want to limit yourself to one carrier, you can look for unlocked GSM phones from third-party retailers. Such phones will work with any GSM operator; you just need to change the SIM card. For example, Amazon sells many unlocked GSM phones. The Nexus 5 model from Google and some devices in versions are also unlocked. Any retail or online store that sells cell phones must provide information about what networks each specific device can work with.
Be careful with phone compatibility. Devices sold in markets where both standards operate most often support either GSM or CDMA. Only some phones are compatible with both standards. If you purchased a CDMA phone from a third party retailer, you will have to call your carrier to activate it. If you purchase a GSM phone, you will need to purchase a SIM card and insert it into the device to activate its network capabilities.
CDMA phone owners don't have to worry about SIM cards, but that's a curse rather than a blessing. CDMA devices are mired in compatibility restrictions that are difficult to get around, and GSM phone owners can simply remove the SIM card and replace it with another one. Most CDMA networks will not allow you to use a phone purchased from another operator, even if it is technically compatible. It is very important to remember this limitation when choosing a CDMA network. If you later decide to switch providers, you'll likely have to buy a new phone, even if the network you're switching to also uses CDMA.
Even though GSM is more open, access may still be limited to the frequency range supported by the phone. Frequencies vary from 380 to 1900 MHz and depend on local operators. You should check what frequencies your operator operates on and make sure that the phone you are about to buy supports them. However, GSM is concentrated around four main bands: 850, 900, 1800 and 1900 MHz. A phone that supports all four will work in most countries. This is why GSM phones that are compatible with all major frequency bands are called “world phones”.
If you understand the importance GSM and CDMA, Great! Now let's completely destroy your arrogance by talking about the newcomer, LTE (Long Term Evolution).
LTE is the new standard, which has come into fashion over the past few years. Although it is based on the principles of GSM, it is still a separate standard that operates outside the GSM and CDMA networks. This is truly the fourth generation of cellular data transmission.
LTE is most widespread in South Korea, where the standard is used by most of the market, but it is also popular in Japan, Australia, Sweden and the United States. For now, it is mainly used for data transmission, but LTE can also serve as a replacement for traditional cellular networks. The American company Verizon Wireless, for example, announced its plans to release LTE phones at the end of 2014.
This standard uses SIM cards, so users will be able to switch to other networks, if the device supports them, of course, simply by changing the SIM card. However, now LTE is used mainly for data transmission, not voice. This means that owners of CDMA/LTE phones will still not be able to use other networks. This will change when carriers like Verizon fully switch to LTE networks. But this may take several years.
Although this standard has great potential, there are obstacles to its adoption. Outside of South Korea, LTE does not account for more than a quarter in any market. South Korea, in general, and Verizon Wireless in the US are actually exceptions to the rule. In most markets, even carriers that offer LTE only offer it in limited areas.
There is also a problem with the spectrum. Remember that GSM/CDMA operate on many different frequencies? The same is true for LTE. You will have to check that your phone is compatible with the frequency bands supported by the operator, and you will not be able to use an LTE phone on another network with the same standard but different frequencies. It is not yet clear whether this standard will become “worldwide” in the same sense as GSM, which settled on four main frequencies supported by most GSM phones.
Summarizing
Take a deep breath. It's time to sum up everything that has been said.
First of all, neither GSM, neither CDMA have no advantage over each other from a technical point of view. They are designed for one purpose, and the quality of the network depends on the operator, not the standard it uses.
Secondly, GSM phones can be unlocked and used with another operator, while CDMA is locked to one operator. It is usually cheaper to purchase unlocked GSM phones than contracted CDMA devices.
Thirdly, you need to carefully check the frequencies supported by the phone. Most are compatible with either GSM or CDMA, and both standards can operate on different frequency bands depending on the region.
Finally, LTE has the potential to become a global standard, but falls prey to even greater frequency division than GSM and CDMA. This technology is relatively new and has not yet been widely implemented.
I hope that cleared everything up. Cellular networks are constantly evolving, and the standards supported by phones may change from year to year. Feel free to ask any questions you have in the comments.
Dessert Iphone 6
Enjoy watching!
https://www.youtube.com/watch?v=jKjXbwPIiHM
Despite the overwhelming majority of subscribers to GSM networks, the future lies in technologies using CDMA (Code Division Multiple Access - multiple access based on code division) in the radio channel. On GSM networks It is possible to provide certain services of third generation cellular networks (GSN) 3G. However, their entire set, as well as services of subsequent generations, can be implemented in full only if there is a radio interface with a code division multiple access method. The market share occupied by CDMA systems is steadily growing, including due to the transition of subscribers to GSM systems.
Are common specifications CDMA standard
The standard for code division systems for cellular networks appeared in 1990 - this is TIA IS-95, developed by Qalcomm.
CDMA principle
CCC uses three basic multiple access principles: FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA. In CDMA, the carrier is modulated with a binary sequence, which expands the spectrum of the signal and changes its shape. All signals are emitted in one frequency radio channel.
At the receiver, the useful signal is accumulated using a “correlator”, which allows you to select a signal that is shaped according to a specific binary sequence. All other signals are perceived by the receiver as noise. The frequency spectrum of such a signal is much wider than that of a narrowband signal. This type of signal is called spread spectrum or noise-like signals.
The signal-to-noise ratio can be increased by expanding the frequency bandwidth at the same information rate. This is called increasing the base of the noise-like signal. The first widespread CCC with CDMA was standardized in the USA - this is the TIA IS - 95 standard.
CDMA MSNs have more efficient frequency reuse than FDMA MSNs. In CDMA, there is essentially no inter-channel interference.
Frequency reuse in narrowband CCCs with frequency-frequency or time-frequency multiple access is limited to a channel signal-to-noise ratio of 18 dB. This limitation does not allow the same frequency channels to be used in neighboring cells/sectors. In CDMA wideband SSNs, frequency reuse occurs in each cell/sector since they all use the same frequency band.
Efficiency reuse CDMA frequencies depend on the signal-to-noise ratio and, accordingly, on the number of subscribers in neighboring cells. In SSN with FDMA and TDMA, each of the cells (sectors) is served by its own transmitter with low output power and a limited number of radio channels. This allows the radio frequencies of this transmitter to be reused without interference in another cell located at a considerable distance. Neighboring cells (sectors) use different frequencies. In a CDMA SSN, such transmitters can also be used in neighboring cells. The frequency reuse ratio for CDMA relative to narrowband FDMA is between 2/3 and 1/7.
To reduce interference from neighboring cells and increase the battery life of a mobile phone, the power of emitted radio signals is controlled. This allows you to adjust the level of the MS transmitter and base station (BS) to improve performance.
CDMA Network Capacity Determination
The main parameters that determine the capacity of the SPS network with CDMA are:
- · base of used noise-like signals;
- · signal-to-noise ratio per information bit of a pseudo-random sequence (PSR);
- · speed of digital transmission of speech signals;
- · efficiency of frequency reuse;
- · number of sectors in a cell.
Reduce signal/noise by 1 bit (Ev/No)
Ev/No - the ratio of the signal power per bit of a binary sequence to the spectral power of the noise. The efficiency of modulation technology allows for signal separation with a ratio of Ev/No = 7.5 dB.
This parameter is completely similar to the signal-to-noise ratio for a frequency-modulated signal, which should be 18 dB under similar reception conditions.
Power control allows you to maintain the Ev/No indicator at the input of the mobile terminal receiver at a level no more than the minimum acceptable to ensure the required quality of work (7.5 dB).
Detection of pauses in speech
Typically, in a full-duplex system with two-way speech transmission, the speaker activity coefficient does not exceed 35% (the ratio of the duration of speech to the duration of the conversation as a percentage). The CDMA system uses pause detectors, which allow only active speech to be transmitted, without transmitting pauses.
Without taking into account mutual interference from signal interference different subscribers The system capacity increases by 2-2.5 times.
Frequency reuse efficiency
The total interference in the system consists of the interference of subscriber signals within one cell, subscriber signals from neighboring cells, and the level of background noise.
In a fully loaded system, the power of the interference signals of subscribers of a neighboring cell is half the power of the interference signals of the cell in question. The frequency reuse factor in a system with an omnidirectional antenna is defined as the ratio of the power of interference signals from other subscribers in the cell in question to the total power of interference signals from all other cells. The capacity of a cell that has neighboring cells is about 2/3 that of an isolated cell.
Using multiple sectors in a cell
When using directional antennas, interference is reduced by almost three times, since more than a third of the subscribers in a given cell are in the antenna sector. The capacity of the SSS accordingly increases almost three times.
Soft transmission
In CDMA SSS there are three types of call control transfer to the BS:
- · hard - transfer of call control from the BS with one frequency radio channel to the BS with another frequency radio channel;
- · soft - transfer of call control from a BS to another, provided that they work with the same frequency radio channels;
- · ultra-soft - transfer of call control between sectors within a cell of one BS.
If the BS operates in the same frequency radio channel, then it is possible to carry out the so-called “soft transfer” of MS from one base station to another. At the border of the BS service area, the radio channels of two neighboring stations are used for transition simultaneously while the MS is moving from one cell to another (Figure 4.1).
Figure 4.1 - Soft transmission in CDMA
The MS simultaneously receives and processes signals from two BSs. This allows not only to significantly increase the coverage area, but also to provide higher quality communications in “problem” places where the radio signal attenuation is greater than in the rest of the coverage area, for example, in basements.
Power management
In CDMA, the network capacity depends on the Ev/No level for each simultaneously operating MS. Therefore, the Ev/No level must be minimized while maintaining the required level of radio channel quality.
For efficient processing of NPS, it is necessary to have the same average power density of the signals at the receiver input. The signal of each subscriber is a component of interference for other subscribers.
Achieving the same average signal power density is ensured by dynamic control of the transmitter power of the MS and BS via a feedback system.
Unlike the direct channel, the signals arriving at the base station do not fade smoothly, but can vary in relation to each other in a dynamic range of about 80 dB. Thus, the power control process in the reverse link is significantly different from the algorithm used for the forward link. It consists of two stages: measuring the power of the MS and correcting the power of the MS and BS.
The CDMA standard provides a high degree of protection against active and passive interference, which allows operation at low signal-to-noise ratios (3 - 5 dB) with significantly lower transmitted signal power. Thus, information signals are simultaneously transmitted in the same radio frequency channel large group users.
The use of spread spectrum has solved two major technical problems facing terrestrial cellular networks - mutual interference from multiple users and multipath propagation of radio signals. The solution to the first problem is to convert extraneous signals into noise, which is easily eliminated using digital demodulation and error correction decoding. The second solution is that reflected signals, received as copies of the original signal, but with different time delays, are summed up, improving the quality of reception.
It has also been said that in a CDMA system no frequency scheduling is required since neighboring cells can use the same radio frequencies. The same factor allows for smooth transfer (“soft switching”) of a call from cell to cell, invisible to the subscriber, providing simultaneous communication with two or even three base stations.
The CDMA cellular system uses a very complex transmission power control algorithm, which allows not only to maintain the quality of reception at the same level, regardless of the distance of the subscriber terminal to the base station, but also to further increase the operating time of the terminal without recharging the batteries. That is, CDMA technology uses exactly the minimum signal level that is necessary to ensure high-quality reception.
CDMA radio equipment operates at radiated power levels 100-1000 times less than those at which radio equipment of other technologies operates.
The service area of a CDMA base station can be significant, and they are determined by the range of the subscriber terminals. For TDMA technology, distances of up to 20 km are preferred, while conventional CDMA equipment does not have such limitations.
Another important advantage of the CDMA system is the greatest efficiency in using the radio spectrum. This means that the largest number of information channels can be placed in the same frequency range. In IS-95, in the 1.23 MHz band, under the conditions of a single base station, up to 61 information channels (plus 3 service channels) can be transmitted. In reality, for mobile communications, 20 - 25 conversational channels are implemented in one radio channel. If we compare these indicators with any real network of some other standard, where it is impossible to use the same frequencies in neighboring network cells and it is necessary to engage in frequency planning, then, all other things being equal, the subscriber capacity of the CDMA network is higher. And it is the largest when servicing fixed subscribers (when there is no need to reserve channels in neighboring cells).
All of the above properties determine the main economic benefits of using CDMA - the increase in coverage provided by cells at the start of service and the increase in network and cell capacity at the planned level of market penetration. For example, “soft switching” at least halves the number of base stations that need to be deployed at the start of service, and network capacity with CDMA (IS-95) technology increases by 3-5 times compared to TDMA (D- AMPS, GSM, DCS) and 10-20 times compared to analog FDMA (AMPS, NMT).
CDMA networks guarantee high quality speech transmission - clear sound and the absence of extraneous noise, unusual for radiotelephones. The CDMA network provides various additional services that are provided to subscribers of digital cellular networks (call forwarding, voice mail, number identification, IN services, etc., including roaming).
Another feature of the CDMA standard is low power electromagnetic radiation from base stations and telephones. This indicator is for standard telephone sets
CDMA(Code Division Multiple Access) - a communication technology, usually radio, in which transmission channels have a common frequency band, but different code modulation. It became most famous at the everyday level after the advent of cellular mobile communication networks that use it, which is why it is often mistakenly identified exclusively with it (cellular mobile communications). Wireless subscriber access WLL (Wireless Local Loop), implemented on the basis of the latest digital technology CDMA code division.
For this standard characterized by excellent sound quality and low level background noise. Increased Capacity system, which is 10 times higher than that of AMPS and 3-5 times higher than that of GSM, is determined by the maximum possible number of active users of the system in the territory of its service area. CDMA improves communication quality in congested areas and hilly areas where interference from reflected signals occurs. CDMA increases system capacity by “virtually” screening busy, cross-talk, and hung calls. This is made possible by reusing the same frequency channel across all cells. Increasing system capacity is facilitated by the use of a power and speech activity control mechanism, which reduces mutual interference that affects system capacity and other factors. As a result, subscribers do not suffer from call blocking during peak network hours.
Principle of operation
There are two main resources for radio systems - frequency and time. Dividing pairs of receivers and transmitters by frequency in such a way that each pair is allocated a part of the spectrum for the entire duration of the connection is called FDMA (Frequency Division Multiple Access). Time division in such a way that each receiver-transmitter pair is allocated the entire spectrum or most of it for a designated period of time is called TDMA (Time Division Multiple Access). In CDMA (Code Division Multiple Access), each node is allocated the entire frequency spectrum at all times. CDMA uses special codes to identify connections. Traffic channels with this method of dividing the medium are created through the use of a broadband code-modulated radio signal - a noise-like signal transmitted into a channel common to other similar transmitters, in a single wide frequency range. As a result of the operation of several transmitters, the air in a given frequency range becomes even more noise-like. Each transmitter modulates the signal using its assigned this moment each user of a separate numeric code, a receiver tuned to a similar code can isolate from the general cacophony of radio signals that part of the signal that is intended for this receiver. There is no explicit time or frequency separation of channels; each subscriber constantly uses the entire channel width, transmitting a signal to the common frequency range, and receiving a signal from the common frequency range. At the same time, broadband reception and transmission channels are on different frequency ranges and do not interfere with each other. The frequency band of one channel is very wide, subscribers' broadcasts overlap each other, but since their signal modulation codes are different, they can be differentiated by the receiver's hardware and software.
Code modulation uses a multiple access spread spectrum technique. It allows you to increase throughput while maintaining the same signal strength. The transmitted data is combined with a faster, noise-like pseudorandom signal using a bitwise XOR operation. The image below shows an example demonstrating the application of the method to generate a signal. A data signal with pulse duration Tb is XORed with a signal code whose pulse duration is equal to (reference: the bandwidth is proportional to where = the transmission time of one bit), hence the bandwidth of the data signal is equal and the bandwidth of the received signal is equal to . Since much less, the bandwidth of the received signal is much greater than that of the original transmitted data signal. The value is called the propagation factor or signal base and determines to a certain extent the upper limit on the number of users supported by the base station at the same time.
Advantages
- · Flexible resource distribution. With code separation no strict restrictions by the number of channels. As the number of subscribers increases, the probability of decoding errors gradually increases, which leads to a decrease in channel quality, but not to service failure.
- · Higher channel security. Select desired channel Without knowledge of its code it is very difficult. The entire frequency band is uniformly filled with a noise-like signal.
- · CDMA phones have lower peak emitting power and may therefore be less harmful.
CDMA - Code Division Multiple Access - code division multiple access is a subset of cellular communication standards, the main difference of which from other standards is the principle of organizing multiple access of subscribers to one base station.
Cellular operators have always faced two main problems:
Constant increase in the subscriber base;
Ensuring communication security.
It was the solution to these two problems that was the reason for the improvement of cellular communication standards, as well as the emergence of new ones.
Today, there are three main methods of organizing cellular communications:
1. FDMA - Frequency Division Multiple Access - frequency division multiple access - cellular communication standards in which a certain frequency range is allocated to each subscriber. The most well-known FDMA technology standards:
AMPS - Advanced Mobile Phone Service - improved mobile telephony service - analog standard with a frequency range of 30 kHz.
DAMPS - (Digital) digital implementation of the AMPS standard;
NAMPS - (Narrow-band) AMPS with a reduced frequency range of 10 kHz - allows you to increase cell capacity.
TACS - Total Access Communication System - general access communications system - channel width 25 kHz.
2. TDMA - Time Division Multiple Access - multiple access with time division of channels. In contrast to the frequency division method, the time division method allows several subscribers to use the same frequency range, while the transmission of signals between them and the base station is time quantized. The most well-known TDMA technology standards:
IS-54 is an extension of the AMPS standard - 30 kHz frequency channels are divided into three time slots.
PDC - 25 kHz channels with three time slots each.
GSM - Global System for Mobile communications - global mobile communications system - 200 kHz band with 8 time slots.
3. CDMA. Unlike the first two methods, the code division method allows all subscribers to operate in the same frequency range. Moreover, this range in CDMA is much wider than in the first two methods. Thus, in the most common implementation of CDMA - IS-95, the bandwidth is 1.25 MHz. The latest third generation CDMA (3G) standard, CDMA2000, uses the same bandwidth.
In cellular communications, the CDMA method was used relatively recently - the first CDMA operator appeared in 1995. Prior to this, the code separation method was quite widely used in military communications.
Main advantages
High noise immunity.
Thanks to special coding and “smearing” of the signal (see Organization of multiple access) over the frequency range, high protection of useful information from accidental (or intentional) interference is achieved. Even if information is partially lost from narrowband interference, the information transmitted in the rest of the signal will be quite sufficient to restore the original high-quality analog signal.
Large cell capacity.
The capacity of a cell depends on the “independence” of the codes used by subscriber units when encoding information for communication within one cell. The more codes, the lower their “independence” and, thus, the more mutual interference.
Large cell capacity is also ensured by the fact that all cells operate on the same frequency, so that frequencies do not have to be specifically allocated to cells (as required in FDMA and TDMA - neighboring cells must operate on different frequencies).
Safety.
Communication security in the CDMA standard is ensured, firstly, by a very complex radio interface, which uses six channels to transmit data and control information. Secondly, the use of a noise-like signal (NLS) to transmit information through the air interface makes it quite difficult to intercept, and the use of a unique coding sequence together with data encryption ensures the safety of the data from decryption.
With the specific implementation of the CDMA method in cellular communication standards, protection of subscribers from “replanting” is ensured. Thus, in the IS-95 standard, such protection against unauthorized use of their account is provided using the AKEY mechanism - an eight-byte key stored in the cell phone and which is a unique identifier for each subscriber. It is entered into the device upon sale and is also stored in the operator’s database.
In addition to security in terms of information protection, CDMA is also safe for the health of subscribers. Due to the low intensity signal, the total level of electromagnetic radiation is much lower than in other standards, such as GSM, AMPS.
Flaws
Today we can say that CDMA has no disadvantages. As a technology, CDMA is already well established. There are several standards based on it, for which there are several manufacturers providing the entire required spectrum hardware- base stations, cell phones.
Organization of multiple access
Picture 1
Signal spread spectrum
In Fig. Figure 1 shows the principle of expanding the spectrum of a useful signal (top graph) - voice information into a CDMA signal - a broadband noise-like signal.
Multiple access in CDMA is implemented through special signal coding. The analog voice signal is converted into digital packets, which are then passed through a Walsh sequence (number of codes - 64 or more). The conversion function also uses a pseudo-random number (one of 2199023255551 numbers) unique to each subscriber within a cell. The result is a broadband signal with a frequency range of 1.23 MHz, which is transmitted through the air interface.
CDMA2000
CDMA2000 is the latest third generation (3G) cellular communication standard based on the CDMA method. IN currently A fully functional CDMA2000 network, which is in commercial operation, is only available in Japan (cellular operator DOCOMO).
In terms of its capabilities, CDMA2000 is superior in many respects to the CDMA standard IS-95, called CDMAOne in the new context.
Thus, CDMA2000 allows you to transfer data at speeds of up to 2 Mbit/s, which is quite enough for real-time video transmission.
CDMA2000 is fully compatible with CDMAOne, making it easy and inexpensive for mobile operators to migrate to the new standard.
CDMA in Russia
The situation with CDMA in Russia from the very beginning of its appearance was unsuccessful. Having affected the interests of several influential structures at once, CDMA encountered resistance from the Ministry of Communications and law enforcement agencies. The fact is that for synchronization on mobile CDMA communications GPS is used - Global Positioning System - A global positioning system based on the use of satellites is by no means Russian production- It was impossible to just leave it like that. And CDMAOne in Russia lost GPS, and with it mobility.
Under the license of the Ministry of Communications and the State Committee for Communications, cellular operators were allowed to use only CDMA networks with fixed subscribers operating at a frequency of 800 MHz.
Over the course of 3 years since the appearance of the first CDMA networks in Russia - 1998-2001 - operators have not managed to win back CDMA mobile communications.
Since 2001, the MCC company (Moscow Cellular Systems), and at the beginning of this year in St. Petersburg (Delta Telecom), began deploying a CDMA2000 network, so far only in a test version. The frequency range that has been provided for CDMA2000 is 450 MHz. What is most important is that the permit issued by the State Commission on Radio Frequencies (SCRF) allows the deployment of mobile (read mobile) radio communication networks.
Phones
Today, the choice of cell phones that support CDMA2000 is not so large. On Russian market Mostly devices from the Korean company Samsung are presented: SCH X120, X130, X230, X250, X350, X420 (see Table 1).
Additional Information
http://www.minsvyaz.ru - Website of the Ministry of Communications of the Russian Federation.
http://www.sotovik.ru - Cellular communications news.
http://www.cdma.ru - CDMA in Russia.
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Ministry of Education of the Russian Federation
VORONEZH STATE TECHNICAL
UNIVERSITY
Essay
by subject digital devices on the topic of:
CDMA cellular standard.
Implementation and operation problems
in Russia.
Completed:
Student of the SSK group - 972
Litvinov A.
Supervisor:
Shifrin V.M.
Voronezh
Plan:
1 CDMA as a tool for solving economic problems;
2 Digital cellular code division mobile radio systems:
2.1. principles of code division of channels;
2.2. cellular mobile radio communication system with code division of channels of the IS-95 standard;
2.3. security aspects in IS-95 standard;
2.4. IS-95 standard mobile station;
2.5. IS-95 standard base station;
2.6. application of CDMA in systems wireless communication type WILL;
3. Mobility in CDMA systems.
4. Problems of CDMA functioning in Russia.
5. Conclusion.
CDMA as a tool for solving economic problems
There are three tasks for regional operators that lead to economic success:
1. development telephone network.
2. Reconstruction and renewal of the existing network, improvement of communication quality.
3. Expansion of types and number of services.
The development of the telephone network, in turn, is based on three basic requirements of a solvent consumer:
Speed of execution of the application;
Installing a telephone in any geographical location;
Fast connection and high call quality;
System location CDMA in the development of telecommunications in the region.
Modern communication technologies from the first days of work make it possible to avoid unproductive labor at all stages, from design to construction and operation. The ease of design and installation of a CDMA system is assessed.
This system immediately became popular. It has secured a stable demand, characteristic, however, of all radio systems, which create the possibility of immediate installation of telephones in those areas where they have not been reached for years wired networks. These are one-story urban areas, suburban dacha plots, suburban farms.
Customer reviews have confirmed the benefits of CDMA. The system is different best quality voice transmission and connection reliability. Guaranteeing the quality of security against unauthorized access plays a significant role. Reasonable tariff policy and quality of communication, convenient local numbering create the necessary popularity for the system.
The need to change technologies.
Modern equipment leaves us no chance to build and operate networks according to the old rules. If we change the coordinate station to a digital one, we are forced to carry out a certain reconstruction of the subscriber network, change almost the entire network of subscriber lines. There is no return to multi-kilometer pole lines, bare communication cables with low insulation. At the same time, we will not be able to build lines for four or five subscribers in a farm or village with an armored cable buried at least a meter into the ground to protect against gusts for economic reasons. Modern radiotelephone systems are one of the most acceptable, in our opinion, ways to provide telephones to areas with low population density.
Coordinate and ten-step stations make up 80% of switching equipment in the region. Cable facilities and overhead communication lines are older than switching systems. The problem that all operators are forced to solve is the problems of the village. Complete reconstruction and renewal of rural telephone communication can become a reality only when the solvency of the population is restored, but a solution must be prepared today. One should not discount the possibility of a certain economic development, when the wear and tear of rural networks will present the operator with the task of forced reconstruction.
Reconstruction of rural telephone communications and CDMA .
One of the main tasks that CDMA allows to solve is the replacement of worn-out rural stations and subscriber lines. The system allows you to serve subscribers within a radius of 30 kilometers or more. With the help of CDMA, it is possible to release and transfer telephone exchanges that are still capable of operating from areas where base stations are installed, although similar solutions can only be temporary and forced.
It is advisable to use the recently certified remote concentrators of the QCT - 8000 series, which allow telephone installation of individual buildings and compact villages. A standard wired telephone set is installed in users' apartments, which is 5-6 times cheaper than radiotelephones.
In addition to the tasks of development and reconstruction, it was very important to solve the problem of providing modern additional services, including for the most distant rural settlements. These are data transmission and fax services, Internet services. Tests of the latest modification of the Qualcomm QCT-1000 device have shown that data transfer is possible on high level, which significantly expands the circle of consumers.
Currently, various research organizations are paying considerable attention to the development of mobile radio communication systems of a new generation of cellular and microcellular structures with code division of channels (CDMA). One such development is the CJDIT project, funded under the RACE program by the European Community. Until recently, the implementation of the CDMA system was hampered by the lack of a number of technical solutions, including the problems of implementing subscriber stations with acceptable consumer qualities.
One of the first cellular mobile radio communication systems with code division of channels was developed by Qualcomm (USA), the principles of its construction are the basis of the CDMA standard of the US IS-95.
An assessment of the state and directions of development of cellular communication systems with code division of channels is of interest to operators and future subscribers of these networks.
Principles of code division of channels
On September 28, 1995, Hutchison Telephone (Hong Kong) launched commercial operation of the world's first Code Division Digital SMPS (CDMA). The network is built on Motorola equipment: SC9600 base stations and EMX2500 switching station
The principles of code division of communication channels (CDMA - Code Division Multiple Access) have been studied in detail and discussed in many works. They are based on the use of wideband signals (WFS), the bandwidth of which is significantly higher than the frequency bandwidth required for conventional message transmission, for example, in narrowband frequency division systems (FDMA). The main characteristic of the NPS is the signal base, defined as the product of the width of its spectrum F and its duration T:
In digital communication systems that transmit information in the form binary characters, the duration of the broadband T and the message transmission speed C are related by the relation T = 1/C. Therefore, the signal base B = F/C characterizes the expansion of the broadband spectrum relative to the message spectrum. Expanding the frequency spectrum of transmitted digital messages can be carried out using two methods or a combination of them:
1. direct expansion of the frequency spectrum;
2. abrupt change in carrier frequency;
Existing and developing cellular communication systems predominantly use broadband networks, the formation of which is carried out using the direct spectrum expansion method (DS-CDMA-Direct Sequence-CDMA).
The creation of cellular mobile radio communication systems with code division of subscribers was hampered by the lack of technical and technological capabilities for the implementation of small-sized, low-power and multifunctional broadband compression devices. Currently, these problems have been successfully solved by American companies Qualcomm, InterDigital, Motorola. Based on proposals from Qualcomm, the US adopted the IS-95 standard for a cellular mobile radio communication system with code division of channels.
Coded cellular mobile radio system
standard channel separation IS-95.
The public cellular code spread mobile radio system (CDMA) was first developed by Qualcomm (USA). The main goal of the development was to increase the capacity of the cellular communication system compared to the analog one by at least an order of magnitude and, accordingly, increase the efficiency of using the allocated frequency spectrum.
Technical requirements to the CDMA system are formed in a number of standards.
Qualcomm's CDMA system is designed to operate in the 800 MHz frequency range.
Security or privacy is a feature of CDMA technology, so in many cases cellular network operators will not require special message encryption equipment.
The Qualcomm CDMA system is built using the direct frequency spread method based on the use of 64 types of sequences formed according to the law of Walsh functions. To transmit voice messages, a speech converting device with the CELP algorithm with a conversion rate of 8000 bps (9600 bps per channel) was selected. Operating modes at speeds of 4800, 2400 and 1200 bps are possible.
Communication protocols in CDMA, as well as in the AMPS and N-AMPS standards, are based on the use of logical channels.
In CDMA, the channels for transmission from the base station are called forward, and for reception by the base station - reverse. The channel structure in CDMA in the IS-95 standard is shown in the figure:
Direct Reverse
Forward Channel Reverse Channel
 |
 |
Pilot channel Access channel
Pilot Channel Access Channel
Call channel
|
Direct traffic channel
Forward Traffic Channel
Structure of communication channels in the CDMA standard IS-95
Direct channels in CDMA:
· master channel - used by the mobile station for initial synchronization with the network and control of base station signals in time, purity and phase;
· synchronization channel - provides identification of the base station, the level of radiation of the pilot signal, as well as the phase of the pseudo-random sequence of the base station. Once the specified synchronization steps are completed, connection establishment processes begin;
· calling channel - used to call the mobile station. After receiving the call signal, the mobile station transmits an acknowledgment signal to the base station, after which information about the connection establishment and the assignment of the communication channel is transmitted via the call channel to the mobile station. The paging channel starts to operate after the mobile station has received all the system information (carrier frequency, clock frequency, signal delay along the synchronization channel);
· direct access channel - designed for transmitting voice messages and data, as well as control information from the base station to the mobile station.
Return channels in CDMA:
· access channel - provides communication between the mobile station and the base station when the mobile station is not using the traffic channel. The access channel is used to establish calls and respond to messages sent over the call channel, commands and requests to register with the network. Access channels are combined (combined) with call channels;
· reverse traffic channel - ensures the transmission of voice messages and control information from the mobile station to the base station.
The following figure will show the procedure for establishing a normal call (incoming call to a mobile station).
Mobile station Base station
Accepts Search message Transmits Search message or
channel Divided search message (MIN) call
· Transmits Reply to a search message Accepts Reply to a search message
(MIN,ESN) channel Tuned to the assigned
access information channel using a common
long code.
Begins to transmit insignificant data via
direct traffic channel
Accepts Appointment message Transmits
channel channel (ESN, CDMA channel, channel code)
·Tunable to assigned call channel
communication using a common long code.
Receives N consecutive frames from
base station
Begins transmitting the channel preamble Receives the communication channel preamble from
connection to the return traffic channel. mobile station
Accepts confirmation command Transmits confirmation command
base station direct channel base station
· Begins discarding received traffic packets
with service requests and transfer
data on the return traffic channel.
Accepts Ready signal s Transmits Ready signal with
information message . direct channel information message
traffic (ringing signal, CNI - number caller)
· Gives a ringing signal to the mobile reverse channel
radiotelephone. traffic
· Displays CNI information on the display
mobile radiotelephone.
(The subscriber answers the call)
· Removes the ringing tone to
mobile radiotelephone.
· Transmits Connection command Accepts Connection command
· begins to transmit the information channel of the reverse
packets with traffic confirmation
service.
Receives confirmation Sends confirmation
Direct channel
(subscribers' conversation) (subscribers' conversation)
Procedure for establishing a normal connection (case of an incoming call at a mobile station). A call to a subscriber unit may include a phase where the specific service option required is established.
The figure shows the procedure for a normal call (outgoing call from a mobile station)
Mobile station Base station
Detects a call being sent Receives initial message
user of the mobile station. Channel Configures to the designated traffic channel,
· Transmits initial message access using a common long code in reverse
(ESN, MIN, dialed number characters) start traffic.
Begins transmitting insignificant traffic channel data on the forward link.
Accepts Appointment message Transmits Channel Assignment Message
channel. Call channel (ESN, CDMA channel, code channel).
· Configures to the traffic channel, Certifies the MIN and ESN of the mobile station.
using generic long code. Receives a traffic channel preamble from
· Receives N consecutive digits of the mobile station.
body frames from the base station.
Begins transmitting the channel preamble
Accepts Confirmation command Transmits Command to confirm the base
base station. Direct channel stations.
· Start transmitting traffic packets to traffic
Service options 1 and from service option 1.
Accepts Continuation of the initial
· Transmits Continuation of the initial Return channel messages.
messages. traffic
· Accepts confirmation. Sends confirmation.
Direct channel
Possible procedure (optional)
Accepts command Request transition Direct channel Transmits command Request transition to
to private long code. traffic private long code
· Sends confirmation along with Receives message Command o received
message Command o received Return channel
switching to private long code traffic
· Begins to transmit and receive Begins to transmit and receive information
information using a private long code using a private long code.
Possible procedure (optional)
Accepts Ready signal together Transmits Ready signal together
with an information message Direct channel with an information message(signal
ringback traffic)
· Sends confirmation. Accepts confirmation
Return channel
· Gives a traffic control signal
call via voice path.
(the called party answers the call)
Possible procedure (optional)
Accepts Ready signal together Transmits Ready signal together
with an information message. Direct channel with an information message.(silence)
Sends confirmation Receives confirmation
· Disables the ringback tone of the Back Channel
in the traffic path. traffic
(subscribers' conversation) (subscribers' conversation)
In the IS-95 standard, the signal power level emitted by the mobile station is adjusted over a dynamic range of 84 dB in 1 dB steps. This ensures that signals from mobile stations can be received by the base station at essentially the same power level, regardless of the distance to the base station. The closer the power level of signals from mobile stations at the base station input is to the minimum corresponding to the required communication quality, the lower the level of mutual interference in the system and, consequently, the higher its capacity.
The high requirements for adjusting the power level of the mobile station can be attributed to the disadvantage of the Qualcomm system. The second disadvantage of Qualcomm CDMA is the need to use cells of the same size throughout the network, otherwise there will be mutual interference from signals from mobile stations that are located in neighboring cells of different sizes.
The CDMA standard provides greater network capacity compared to traditional analog cellular networks. Increasing capacity can be achieved in two ways:
1) increasing the number of channels per MHz of the allocated frequency band;
2) increasing the reuse of communication channels in a given territory.
A factor that helps reduce mutual interference in a CDMA system and, therefore, increase its capacity is the use, similar to GSM, of a discontinuous speech transmission system.
During the communication session interval, the active part of the conversation is about 35%, 65% is accounted for by listening to messages from the opposite side and pauses. Emitting a signal from the mobile station only during speech activity intervals results in an additional reduction in system interference and an overall increase in CDMA system capacity.
The following table will show the main characteristics of CDMA and their brief description, which determines the advantages and prospects of cellular communication systems with code division of channels.
Characteristics and their description
High throughput.
Field tests conducted under a variety of conditions have confirmed that CDMA systems average 15 times the throughput of analog systems under high load conditions. Finally, when using existing vocoders that operate at half the bit rate, throughput increases by an additional 1.7 times. Additional sectorization (above 3) also increases throughput.
High quality communication.
The variable bit rate vocoder provides digital conversion of speech signals and high-quality speech reproduction. Background signals are muted even under heavy load. The soft handoff method (switching a subscriber from one radio channel to another), used in CDMA systems, provides almost transparent transfer of calls between cells. This reliable transmission method virtually eliminates call loss and reduces the load on switching equipment.
Possibility of further evolution of the system.
IN existing system search services and digital data transmission are provided. The existing control structure provides fax protocols. Higher transmission rates may also be possible. Portable subscriber stations based only on the CDMA method and compatible with cellular systems and PBXs can meet future requirements.
Possibility of introducing new functions.
If desired, from the same device you can access a wireless PBX, home cordless phone, public wireless digital telephones, personal communications networks and cellular networks. Interfaces to PBX, ISDN and PSTN are provided. Digital control signals enable a range of data services that can be added as the operator introduces new services. Variable bit rate vocoder and provided opportunity data transfers allow the introduction of different levels of service. The signal level and delay measurements provided in the system make it possible to determine the position of the mobile station.
Secrecy of communication.
Digital form of signals, transmission over a wide frequency band, protection of information for each recipient - all this ensures significantly higher communication secrecy than in other systems.
Easy to migrate (and compatible with analog systems)
CDMA allows almost tripling the existing analog network bandwidth and provides higher quality of service. Capacity and radio coverage allow CDMA to be introduced with significantly fewer cells than existing networks. Antenna radio coverage and sectorization are independent of the cell and are not as closely coupled as in narrowband systems. Subsequent expansion may be phased and may be local (to quickly provide radio coverage in a single location) or global.
Price and availability of equipment
Current estimates of the cost of a CDMA system for network and subscriber equipment indicate that the cost of the system is equivalent to existing analogue systems. Higher throughput allows communications with significantly fewer cells than analog and TDMA systems, reducing capital and operating costs. Proven custom integrated circuit technology has brought technology together complex circuits CDMA to very simple solutions.
The IS-95 standard provides a high degree of security for transmitted messages and subscriber data.
Communication security is also ensured by the use of authentication and message encryption procedures.
Encryption of messages transmitted over the communication channel (TCN) is also carried out using IS-54B standard procedures.
The IS-95 standard also uses a "frequent communication" mode, provided using a secret mask in the form of a long code.
Mobile station standard IS-95
Qualcomm and Motorola have developed dual-mode CDMA mobile stations that communicate with existing networks analog standards with frequency modulation (AMPS and N-AMPS). This circumstance provides significant advantages to CDMA subscribers, as it allows them to use their radiotelephone where existing analog cellular networks provide radio coverage.
The main difference between CDMA subscriber stations and existing stations of analog standards is the addition of digital signal processing functions to CDMA mobile stations.
Standard base station IS-95
CDMA communication systems use cells with omnidirectional antenna patterns or sector cells (typically 120-degree)
The following figure will show the block diagram of a base station (BTS) for a cell with a 360-degree antenna pattern with digital equipment containing channel blocks.
Amplifier
 |
Transceiver
GPS receiver
Cell controller
Block diagram of a CDMA base station
Each channel block can be configured as an information channel or as a service channel. A GPS (global positioning system) receiver is used to synchronize the network.
The transceiver compartment converts the intermediate frequency signals generated in the digital unit compartment into an RF signal at the carrier frequency and provides reverse conversion of the received signal to the intermediate frequency. In the transmit direction, the signal travels from the transceiver through a power amplifier and filter to the transmitting antenna. In the opposite direction, the reception path begins with receiving antennas, a filter, and an amplifier with a low noise figure. Then in the transceiver the signal is converted to an intermediate frequency and enters the compartment digital equipment. It should be noted that the transmitting and receiving paths are connected directly to their antennas.
The operating modes of digital equipment and the transceiver are controlled by the cell controller (CC)
Application of CDMA in wireless communication systems WILL
In recent years, significant attention has been paid to the development and implementation of wireless radio communication systems (WILL) for servicing landline subscribers in rural and hard-to-reach areas. The developments of Motorola, Alcatel, Siemens, etc. are known in this area. Under certain conditions related to the number of subscribers served and their distance from public telephone networks (PSTN), laying cable communication lines becomes economically ineffective compared to the introduction of radio channels to connect landline subscribers with PSTN. Typically, the use of WILL is considered appropriate for servicing subscribers remote from the PSTN at distances from several kilometers to several tens of kilometers.
As noted earlier, CDMA systems have a number of advantages over existing cellular networks and can increase network capacity. However, the advantages of CDMA are provided by the complication of the processes of functioning of the network and subscriber equipment, which become invisible when using advanced methods of digital signal processing, high-speed computing tools and modern technologies microelectronics.
In the version of a wireless communication network for fixed subscribers, continuous control over the adjustment of the power level of subscriber stations is not required; the radiation level can be recorded once when installing a subscriber station. To reduce system interference, directional antennas are used for subscriber stations (in the direction of the base station). All this allows for even greater capacity of the WILL CDMA network compared to the mobile cellular network.
In general, CDMA technology when used in a WILL network provides, according to Motorola estimates, an 18-20-fold increase in capacity compared to an analog AMPS network.
Fixed placement of subscriber stations, the use of directional antennas in the direction from the subscriber station to the base station makes it possible to implement 60-degree cells, that is, to ensure the simultaneous operation of 180 active subscribers. With a load from one subscriber to 0.025 Erlang, the number of subscribers served by one 60-degree cell will be about 7000. These results confirm the high efficiency of using CDMA for building wireless communication systems with a fixed subscriber.
Mobility in CDMA systems.
Operators of CDMA systems and those simply interested in the implementation of this technology in Russia are aware of the decision of the State Communications Committee board recognizing “it is appropriate to create in Russia only wireless access networks to local telephone networks based on the IS-95 standard in the 800 MHz range.” Thus, the “village link” of the most advanced mobile communication standard has been finally approved.
Let's consider the current situation from the point of view of a law-abiding CDMA communications network operator, for which we first define two important concepts.
What is mobility? In full - this is the service of a subscriber with a portable telephone with the possibility of roaming - national or international. Mobility is characterized by high pay traffic and its low intensity, external directional antennas are not used, and work zone is probabilistic in nature. The normative document will be the “Rules for the provision of mobile communication services” that are currently being developed.
“Stationarity” is a fixed installation of a radiotelephone with dimensions very close to a conventional telephone set, or a subscriber radio module with a standard telephone interface. High traffic intensity per subscriber and low cost are required. Very often external antennas and 100-way radio access to the telephone network are needed. The conditions for the provision of radio access services are governed by the “Rules for the provision of telephone services”.
At the same time, radio access provides relative mobility - the ability to work in different places within the radio coverage area and even in a moving car.
So, let's look at some of the problems that arise when using landline radiotelephones. Landline telephones from Qualcomm, Samsung and LG are available for sale. The phone comes with a battery power supply, which provides 8 hours of talk time when connected to the mains. This source allows you to operate the phone autonomously. Many subscribers realized the capabilities of CDMA phones and began to use them as mobile phones, transporting them in a car. Of course, such use is prohibited by our rules for the provision of communication services via the CDMA system, and this is noted in the contract with the subscriber, but how to identify the violator, how to prove the fact of the violation and what to do next?
First of all, it was necessary to decide technical problem mobile phone detection. An analysis of the billing records of the Qualcomm controller revealed two existing parameters - the number of sectors in which the conversation began and ended, and the value of the range to the phone in this conversation. Knowledge of the working sector turned out to be ineffective, since with a sector width of 120 0 and a system range of 20...25 km, the sector area is 400 km 2, and when installing a telephone on the border of two sectors, the working sector can change several times during one conversation (hand-off).
The most informative value is the distance to the phone. Has been analyzed a large number of billing records for known landlines and mobile phones. Based on the results of the analysis, it turned out that the range distribution function for calls from landline phones is close to normal and its value is 3σ ‹ 200 conventional units of the billing record. The range distribution function for mobile phones can be arbitrary, with maximums at ranges corresponding to the most frequent stops.
The stationarity criterion was established experimentally: 3σ ‹ 300 conventional units.
We have currently developed a program that automatically processes monthly billing records and prints phone numbers whose range range exceeds 300 conventional units.
This processing of the first 400 CDMA subscribers identified 20% of mobile and multi-site phones. Letters were sent to these subscribers with a proposal to stop using CDMA phones in violation of the Rules of Use and the provisions of the Agreement. Almost everyone using the phone at multiple locations has registered their second/third work locations. Some mobile operators have stopped carrying phones in the car, but work continues with the rest.
Along the way, several interesting circumstances emerged:
For some subscribers, the range distribution function showed the phone operating at two points. It turned out that the phone was used only at one point, but it works with the built-in antenna and for some external reasons switches to another base station, the quality of work is satisfactory. Installation of external antennas “tied” the phone to the selected base stations and improved the communication quality to excellent;
Several subscribers constantly complained about poor call quality; It turned out that they were using a mobile phone. Warning letters were sent to them. The complaints have stopped!
So what can be done to stop the mobile use of landlines? Technical and administrative measures were considered.
Technical measures. Linking the phone to the work sector is the most effective technical solution, although it is not 100% effective. Unfortunately, this cannot be done in a Qualcomm controller. Probably, such a task was not originally set. In addition, if any sector fails, all its subscribers will be lost, although in today's situation many of them remain operational, as they switch to reflected signals from other sectors.
The use of concentrators. This will completely solve the mobility problem, but there are several limiting reasons:
There are still no CDMA certified hubs. The Qualcomm QCT-8000 hub has only recently passed certification tests;
The concentrator is most applicable on newly constructed facilities, when it is included in advance in the design of a large residential building, office or industrial building. In the existing infrastructure of a city or village, the use of a concentrator does not solve the problem of the “last mile”, reducing it only to the level of the last hundreds of meters;
Wealthy buyers, as a rule, are great individualists and perfectly understand all the advantages of a personal radiotelephone. It is impossible to drive them into a radiotelephone "communal room".
Selling phones without battery power.
In many situations this is unacceptable, since communication is especially needed during a power outage. And there will always be craftsmen who will connect the phone to the car network.
Administrative measures.
Such measures could be:
Warning about violation of the Rules and provisions of the Agreement and an offer to arrange a second/third work point;
Disabling a malicious mobile operator for systematic violation of the Terms and Conditions of the Agreement, but in this case real income is lost and a complex legal situation may arise;
Purpose of the “mobile” tariff, i.e. actual recognition of mobility and deviation from the decisions of the State Communications Committee.
Conclusion:
Today we do not have a reliable technical means, prohibiting mobile use of landline telephones. You can only identify them and warn subscribers about a possible disconnection. However, disconnection not only creates a complex legal situation, but also leads to losses of part of the income, which is unacceptable in today's situation, when there is a struggle to attract and retain each subscriber. This uncertain situation regarding mobile use of landlines may continue for quite some time, at least as long as there is capacity to spare.
What's next? Only one thing can be said with confidence - the number of subscribers using a landline telephone in a mobile version, in the back seat of a car, is steadily increasing. We learn this by analyzing new mobility program reports every month. In addition, subscribers have already stopped hiding and directly ask: “Can I travel with him?” “No,” we say, and they, nodding their heads in understanding, leave!
There are two ways out of this situation: 1. Categorically prohibit mobile use and demand that operators disconnect all mobile subscribers and thereby “throw out the baby with the bathwater,” because practically close the CDMA standard in Russia. 2. Allow the mobility of CDMA subscribers, legalizing the introduction of “mobile” traffic and introducing competition into a civilized channel.
Selling portable phones with reasonable price mobile traffic, subject to limited mobility within one controller, can attract additional subscribers and significantly increase the income of CDMA operators, among which more than 30% are representatives of telecommunications.
Problems.
The problems that should be paid attention to are well known to the vast majority of operators, but we look for ways to solve these problems alone and often find not the best or cheapest ones. These problems do not allow the operator to fully use CDMA to solve technological and economic problems. Such problems can only be solved collectively, and all participants must realize that not only can and should benefit from the association, but they will also have to sacrifice some of their interests.
Work on paperwork in government organizations.
Work on the design, installation and commissioning of radiotelephone systems has shown that design work in government agencies of the Russian Federation takes 5-6 times longer than delivery, installation and commissioning combined.
Frequency resource.
Today this problem is especially pressing, and not only because the Russian frequency distribution is very different from world principles. Today CDMA operates in the 800 MHz spectrum and occupies the 1.23 MHz frequency band. Science says that a change in equipment generations and the transition to 3rd generation broadband and high-speed technologies will require a 10-15-fold expansion of the spectrum. The operator today must know what he needs to do within what time frame, what he needs to do so that his business is not taken over by others.
GPS - a necessary tool for the functioning of the system.
Setting up, synchronizing and maintaining the CDMA network in optimal condition is carried out using standard scheme using satellite systems such as GPS. The whole world uses only these systems. However, operators learn about the difficulties of using them in Russia after the fact, when the equipment has already been purchased. When moving to the 3rd generation, new problems are added when the location in space, speed and direction of movement of the terminal will be fixed up to a meter. Science, an association, a holding company must anticipate such phenomena and tell the operator what to work on legally and economically. The State Telecommunications Committee must formulate a legal framework in advance.
State and problems.
Solving a number of problems is impossible without the participation of the State Committee for Telecommunications and other government agencies. It is necessary to solve a number of direct prohibitions and problems that cause economic damage to operators and the state and prevent consumers from using all the capabilities of CDMA systems.
Allowing at least limited mobility and intra-domain inter-controller communication with two or more controllers will significantly increase the attractiveness of the system.
Coordinating the transition to 3rd generation systems when operators working in GSM standards, AMPS and CDMA, will be forced to unite on a single technological platform, which should be carried out under the patronage of the State Telecommunications Committee.
These are the problems that we face at the current stage of implementation of this technology.
List of used literature:
1 Avdeeva L.V. Introduction of radiotelephone systems in Russia
CDMA communications: history and problems // Mobile systems.
Special issue on the CDMA standard. - M., 1998. - 30-34 p.
2 Wireless access of subscriber lines. Volume 1. Handbook of mobile landline communications. - M., 1997. - p. 346.
3 Varakin L.E. Theory of signal systems. - M., 1978. - p. 304.
4 Varakin L.E. Communication systems with noise-like signals. - M., 1985. - p.384
6 Gromakov Yu.A. Digital cellular mobile radio communication systems with code division of channels. - M., 1996. - 49 p.
7 Dixon R.K. Broadband systems. - M., 1979. - p.304
8 Pyshkin I.M., Duty I.I. Mobile radio communication systems. - M., 1986. - p. 328.
9 Tuzov G.I. Statistical theory of reception of complex signals. - M., 1987. - p.400
10 Tuzov G.I., Sivov V.A. Noise immunity of radio systems with complex signals. - M., 1985. - p. 265.