GSM technology can provide high-quality and secure mobile voice and data services for mobile users. The success of this technology is based on its inherent good support for global roaming and interoperability. These functions are the main source of profit for mobile operators.
GSM technology uses multiple frequency bands around the world. It can provide users with the widest choice of mobile services and mobile terminals in the market. The economies of scale of the whole GSM technology are based on its numerous manufacturers and service providers. Because the technology adopts open standards, it can ensure the investment safety of mobile operators and provide a way to successfully transition to the future mobile network technology.
GSM technology is a widely verified standard. Because GSM technology can provide a safe way to transition to EDGE and WCDMA, it can provide future services and attract new users, and maintain the mainstream position of mobile communication standards.
GPRS (General Packet Service) technology realizes the application of IP-based services in mobile networks. According to the demand, this technology can instantly realize network connection and send and receive the required information without dialing through a modem. This is also the reason why users who use GPRS can go to always online.
Using GPRS technology, we can break through the limitation of network speed and circuit switching and realize new services that traditional GSM network can not provide. Using GPRS technology, mobile network can fully support Internet applications that computers can realize, such as web browsing and chatting. The network based on GPRS technology can provide higher network capacity, support Internet-based content access, realize packet data service, browse colorful web pages, send and receive emails on the move, and provide powerful virtual communication, MMS and entertainment information services.
At present, the access speed of GPRS technology is between 30-40kbit/s. Because the network using GPRS technology can transmit information faster, more instantly and more effectively through the mobile network, the cost for operators to realize mobile data services using GPRS technology is lower than that of circuit switching.
From the point of view of network operators, packet switching is the key function needed by the network. Packet switching can divide data information into data frames for transmission, and reassemble the data frames at the receiving end to recover the information. Using packet switching means that all the wireless resources of the whole GPRS network can be provided to users who need to send and receive data. In this way, valuable wireless resources can be used more effectively, which means that more GPRS users can enjoy the same bandwidth and use the resources of the same cell.
Because of its advanced data service function, GPRS technology is rapidly popularized all over the world. Nokia's GPRS solution supports interoperability and roaming with 3GPP standards. Meanwhile, Nokia's GPRS network can be implemented on any existing GSM network.
CDMA has many unique advantages, one of which is inherent in spread spectrum communication system, and the other is brought by soft handover and power control technology. CDMA mobile communication network is a combination of spread spectrum, multiple access, cellular networking and frequency reuse, which includes the coordination of three-dimensional signal processing in frequency domain, time domain and code domain, so it has the characteristics of good anti-interference, anti-multipath fading, high security, multiple cells can reuse the same frequency, and the capacity and quality can be weighed. These characteristics make CDMA have very important advantages over other systems.
1, with large system capacity. Theoretically, the capacity of CDMA mobile network is 20 times larger than that of analog network, 10 times larger than that of analog network and 4-5 times larger than that of GSM.
2. Flexible system capacity configuration. In CDMA system, the increase of users is equivalent to the increase of background noise, which leads to the decline of voice quality. But there is no limit to the number of users, and operators can compromise between capacity and voice quality. In addition, multiple cells can be automatically balanced according to traffic and interference.
This characteristic is related to the mechanism of CDMA. CDMA is a self-jamming system, and all mobile users occupy the same bandwidth and frequency. For example, think of bandwidth as a big house, and everyone will enter the only big house. If they use completely different languages, they can clearly hear the voices of their peers, with only some other people's conversations interfering. Here, you can think of the air in the room as a broadband carrier and treat different languages as codes. We can keep adding users until the whole background noise limits us. If we can control the signal strength of users, we can accommodate more users while maintaining high-quality calls.
3. The call quality is better. The vocoder of CDMA system can dynamically adjust the data transmission rate and select different levels for transmission according to the appropriate threshold. At the same time, the threshold changes according to the change of background noise, so that even in the case of large background noise, better call quality can be obtained. In addition, the phenomenon of "dropped call" in CDMA system is obviously reduced. CDMA system adopts soft handover technology, "connect first and then disconnect", which completely overcomes the shortcoming that hard handover is easy to drop calls.
4. Frequency planning is simple. Users are distinguished by different sequence codes, so adjacent cells can use different CDMA carriers, and the network planning is flexible and the expansion is simple.
5. Using power control and variable rate vocoder to prolong the service life of mobile phone battery.
6. The network construction cost is low. CDMA network has large coverage, high system capacity and few base stations, which reduces the network construction cost.
Because of the above advantages of CDMA network, using CDMA mobile phone has become a new fashion. Compared with other mobile phones, the unique charm of CDMA mobile phones lies in:
1, high connection rate. People who surf the Internet are experienced, so they surf the Internet when there are few people looking for it, so that the network is not so congested and easy to connect. The same is true for mobile phones. CDMA comes from military anti-jamming system, in which the "processing gain" parameter is much higher than other systems. In addition, CDMA signals occupy the whole frequency band, which is almost seven times as efficient as ordinary narrowband modulation. So generally speaking, for the same bandwidth, the capacity of CDMA system is four to five times that of GSM system, the network congestion is greatly reduced, and the connection rate is naturally high.
There is almost no noise when talking on the phone. CDMA adopts advanced digital speech coding technology and uses multiple receivers to receive signals from different directions at the same time. It seems that you listen to several people telling a story from different aspects, and when you synthesize it, you understand the whole story, and at the same time omit some irrelevant content.
3, it is not easy to drop words. The base station is the guarantee for mobile phone calls. When the user moves to the edge of the coverage area of the base station, the base station should automatically "switch" to protect you, otherwise the call will be dropped. When the CDMA system is switched, the base station coverage is "single coverage-double coverage-single coverage", which automatically switches to the adjacent idle base station, that is, the mobile phone is disconnected from the original base station only when it is confirmed that it has moved to the single coverage area of another base station, thus ensuring that the mobile phone will not drop the call.
4. "Green mobile phone". The power of ordinary mobile phones (GSM and analog mobile phones) can generally be controlled below 600 MW. The advent of CDMA mobile phones has brought people the dawn of "green" mobile phones, because compared with GSM mobile phones, the transmission power of CDMA mobile phones is less than a small part. The maximum transmission power of CDMA system is only 200 MW, and the ordinary call power can be controlled at several tenths of MW. Its radiation effect can be ignored, and it has no adverse effect on health. The decrease of the transmission power of base stations and mobile phones will greatly prolong the talk time of mobile phones, which means that the life of batteries and mobile phones will be prolonged and the environment will be protected, so it is called "green mobile phones".
5. The phone will not be bugged. To tap the phone, you must find the code address. However, CDMA addresses are pseudo-random codes, and there are 4.4 trillion possible permutations, so it is too difficult to crack passwords or eavesdrop on calls.
CDMA networks can only use dedicated CDMA machines, which means CDMA mobile phones cannot be used in GSM and GPRS networks.