CDMA standard is not as popular as well-known and loved by GSM operators. However, it has its pros and cons. Therefore, when buying a new cell phone, you should pay special attention to CDMA-GSM phones. This will be the best option.
What is this?
Code Division Multiple Access - this is how the abbreviation of this communication standard stands for. By this is meant the use of multiple code division channels. At the same time, during a telephone conversation, personal data and the voice itself are transmitted through separate channels and at different frequencies. In addition, there is more space for the data transmission itself than with the GSM standard.
CDMA phone - what is it? This is a gadget that provides services such as direct landline and mobile number, packet data exchange and messaging at speeds up to 2.3 Mbps. The CDMA principle consists in some expansion of a certain spectrum of the information signal. Two methods are used for this: direct sequence and frequency hopping. In the first case, the main carrier frequency changes its value in a certain range. In this case, the receiver works according to the same algorithm. This ensures the selection and processinga specific channel. The direct sequence method uses noise-like signals. In addition, each individual signal is modulated with a unique code that expands the spectrum of the information signal itself.
What is GSM?
A lot more is known about CDMA's main competitor. It is he who is actively used in the work of domestic cellular networks. The GSM standard uses TDMA technology and is based on a frequency division algorithm. There are as many as four ranges:
- Single band. Rarely used.
- Dual band. Here, phones are tied to a specific region.
- Tri-band. Standards used are 900/1800/1900 and 850/1800/1900.
- Quadband. Almost all new smartphones are provided with such functionality.
There is one feature of GSM devices that CDMA phone cannot boast. What it is? Availability of an additional SIM card. With it, you can easily and quickly change the operator.
History of Technology
Despite the promise and safety, this standard is not used so often. And many ask the following question: "CDMA phone - what is it?". Its history began in the 30s of the last century.
In the USSR, the famous academician Ageev D. V. was engaged in relevant research. In 1935, he published his own work, Code Channel Division. The brochure did not become a bestseller because more related to future developments. But soon other famous scientists picked up this topic. That's how it was createdstarting base for further development of CDMA technology.
Already in the late 50s, the US used this standard for military purposes. And only in the 80s the technology was declassified and presented to the world. Dr. Irwin Marc Jacobs was able to adapt it. Later, he even created his own company, Qualcomm, dealing with satellite communications, telephony and cellular systems.
Thanks to this American, since 1992, the new standard has been actively implemented around the world. And since 1996, CDMA-GSM phones have been used equally. At the same time, at that time, about 24 countries of the world participated in the project.
CDMA standards
Despite the fact that this technology is united by the principle of action, it has several directions. Actually, the CDMA system uses certain sets of channels with a width of 1.23 MHz. The voice itself is encoded at a rate of 8.55 kbps. Sometimes this data stream is truncated to 1.2 kbps. This standard is used by the simplest Nokia CDMA phones. Their plus is reliability and quality.
The CDMAOne standard exists in provisional models IS-95a, IS-95b and J-STD-008. The declared signal speed here ranges from 9.6 kbps to 115.2 kbps. Network data appeared back in 1995 in America. Now the standard is quite common in Asia. In Russia, it is allowed to provide only certain fixed-line services using such a system.
The CDMA2000 standard is the successor to CDMAOne. It almost completely corresponds to the 3G generation. Another feature and value of it lies in the fact that it is on the basis of thisstandard, new systems of mobile operators are being developed.
WCDMA standard
It is widely distributed in Japan. This technology is used in high-speed transmission of various multimedia, videoconferencing and Internet access. China is also a leader in the use of such networks, but along with WCDMA, TD-SCDMA and CDMA-2000 networks are being promoted here.
If we talk about the principle of operation, then we can say that this is also a system of multiple access with code division of existing channels and direct expansion of the spectrum of action. At the same time, the stream speed reaches 384 kbps, and the bandwidth is up to 5 MHz. This is achieved through multi-code combinations and the use of a variable spreading factor.
The main advantage of this communication standard is that it does not have a global reference to time and GPS. Therefore, it can work regardless of the city or country in which it is located. CDMA GSM phones are the same (Odessa is also covered by this network).
Another significant factor in favor of this standard is its air interface. It works in such a way that not only multi-user reception can be easily used, but also the intelligent adjustment of the necessary adaptive antennas. This contributes to a significant increase in coverage and throughput.
CDMA-450
The introduction of this system has become an impetus for the development of new generation cellular networks. The advantage of this standard is that here they can fullyuse all frequency bands of mobile cellular systems. It is already beginning to be actively used by CDMA phones (Ukraine is also in the coverage area).
Such networks provide long range communication. That is why operators do not need to build many stations. In the field of providing mobile Internet, there are also a number of advantages over the usual GSM operators. EV-DO technology delivers broadband speeds up to 2.4 Mbps.
Transmitting data with this system is much safer because it uses a special encryption algorithm and cryptographic authentication of all mobile terminals. The technology under consideration will also be useful for ordinary citizens. This is explained by the fact that when the stations are operating, the radiation power is 11 times less than from GSM networks.
From all of the above, a quite logical question follows: why are CDMA-450 phones unpopular in Russia and the CIS? There are several reasons, as it turned out:
- No special equipment.
- There is no variety in the offered models and brands of CDMA phones.
- No roaming.
Benefit of CDMA
This technology is relatively new. And it is in many ways inferior to the GSM used by cellular operators. She has undeniable advantages:
- Privacy and security of personal information. Thanks to the coding technology used, the user is almost completely protected from various fraudulent activities. In addition, hereextraneous noise and the possibility of parallel conversations are completely eliminated.
- Less energy consumption. Due to optimized data transfer, CDMA-450 phones consume battery power much more slowly. This could allow manufacturers to create models that are much more compact and ergonomic.
- Virtually no interrupted conversations. The CDMA phones significantly increase the throughput of calls, eliminate busy and parallel lines.
- Extended network coverage area. CDMA uses a completely different telecommunication technology that allows you to significantly increase the coverage area.
- Additional services. This may be the transfer of operational important data and messages, the identification of any subscriber, etc.
That's why more and more users choose CDMA phone. What it is? The ability to get all the benefits at once!
Disadvantages of CDMA
Despite the obvious advantages over the GSM standard, these networks are actively used only in America. Europe is just beginning to get acquainted with this technology. Among the shortcomings that prevent the rapid and confident advancement of CDMA to the masses, the following can be distinguished:
- Cost. Despite quite tolerable tariffs for direct city numbers, such phones are more expensive than their GSM counterparts.
- Repair. Due to the fact that such gadgets are not common in the world, spare parts are quite difficult to find. In addition, not everyone is familiar with the repair technology either.
- No base stations on CDMA phone. What it is? These are telecommunications points that provide network coverage.
Two standard phones
As you can see from the article, both CDMA and GSM have their strengths and weaknesses. And our man, well, it is simply vital to use everything at once. That is why the dual-standard CDMA-GSM phone was invented. It combines all the advantages of both systems.
What is it? This is quite an ordinary mobile phone with an improved battery that can withstand more calls and conversations. In terms of design and functionality, it practically does not differ from standard relatives.
Such cell phones have recently become more and more popular. Therefore, gradually, all global mobile brands began to produce separate lines of two-standard gadgets.
For example, CDMA-450 phones are actively promoted by Skylink. You can also find models from Nokia, Huawei, Pantech, HTC and many others in various stores.
Features of dual standard phones
In addition to the functional contact book, where one subscriber can be assigned 4 or more numbers at once, as well as several email addresses, CDMA-GSM-cellular phones have several other significant differences:
- These are mostly monoblocks. Although lately you can find sliders or clamshells.
- Almost all phones support microSD.
- Cell phones are equipped with a camera of at least 2MP. Of course, with growthIn popularity, the line of phones on the market is also developing. More and more manufacturers are joining the competition, design is being developed, technical capabilities and characteristics are being added, etc.
In general, these models are standardized for familiar smartphones and phones. Manufacturers try to create them in a familiar design and with the same set of functions. Some cities are increasingly using CDMA phones. Odessa, for example, as a port center provides an opportunity to use all models. Inside the country, of course, there is less choice.
