The difference between CDPD and GPRS

The ultimate goal of GPRS and CDPD Mobile communication technology is to help people realize the dream of mobile interconnection, what are their technical features?

The concept of two kinds of technology

GPRS represents the integrated packet wireless service, which is a set of wireless transmission modes developed using the "packet Switching" (packet-switched) concept. GPRS uses 4 different encoding methods, each time slot can provide a transmission rate of CS-1 (9.05kbps), CS-2 (13.4kbps), CS-3 (15.6kbps) and CS-4 (21.4kbps), each user can use up to 8 time slots, so GPRS Maximum transmission rate is 171.2kbps. CDPD (cellular Digital Packet data, cellular digital packet), is a wireless data communication technical specification, which is introduced by 8 major companies, such as Mobile Communications Corporation (AMCI), USA. The development of this standard marks the reality of wireless data transmission. It is the mobile wireless data communication technology based on the digital packet data technology and the cellular mobile communication as the networking mode.

CDPD Network is a new type of wireless WAN system, which is different from the wireless LAN in the market now, it works in the 800 MHz frequency band, which has a certain penetration and diffraction ability and less interference. The network can achieve a channel rate of 19.2kbps, remove packet packet data packaging and channel multiplexing Some of the costs, for users, data transmission rate is generally 5k~10kbps, the maximum can reach 15kbps or so. The communication system composed of CDPD technology uses Full-duplex communication mode, so it can send and receive data simultaneously, and the communication network through forward error correction (FEC) and automatic feedback retransmission technology to ensure that the data transmitted on its network will not be wrong. (Computer science)

The composition of two kinds of systems

GPRS network is based on the existing GSM network to achieve. Some nodes need to be added to the existing GSM network, such as GGSN (Gateway GPRS supporting node) and SGSN (serving GSN). CDPD network system consists of base station, switch and network management system. Each base station can install up to 6 channel board, each channel board provides a 19.2kbps air interface for the mobile terminal, enables the mobile terminal to carry on the Full-duplex packet data transmission, simultaneously also is responsible for the spectrum monitoring, the frequency management. It connects to the switch through a 64kbps frame relay. All the components on the base station can be hot-swappable and the service will not be affected when the components are replaced. The CDPD switch consists mainly of two parts, which are grouped servers and management servers. The packet server is responsible for packet data exchange, the Management Server is responsible for user account management and billing information management. Each module in the switch is dual, hot-backed, and automatically switched to another if a module fails. The network management system is responsible for the entire CDPD network management, any part of the network failure, management system can be observed immediately, and can be set up and modified remotely.

The application of two kinds of technology

GPRS is a new type of packet data transmission service in the existing GSM network, and GPRS can provide a series of interactive services on the basis of the standardized network protocol with GPRS carrying business support:

Point-to-Point connection-oriented data service;

Point to multi point business;

Point to Point Connectionless Network service.

CDPD applicable to a wide range of business, the use of flexible methods. At present, mainly used in the following areas:

Financial transactions;

remote monitoring;

Traffic and transportation;

Wireless stock.

The difference between two kinds of technology

GPRS and CDPD can provide data service, from the technology and application aspects have its characteristics, for operators, the choice of what kind of data network is the prerequisite and key to provide data services. The following GPRS and CDPD performance for a simple comparison.

1. Select analysis

CDPD from 1992 to the present, the technology has been very mature, and has a complete set of CDPD specifications, each operator can be based on this unified standard for development and application. In many countries and regions, CDPD has been widely used in many fields. Wireless data network operators can only select a private network before CDPD is present. At present in the United States and even around the world, CDPD has become a competitive wireless data network, and GPRS standards so far still not standardized, and GPRS is not in the GSM network transmission data in the final technology. In the process of data technology evolution of GSM network, from the Circuit data service, HSCSD, GPRS, Edge to the final IMT-2000, these technologies are not all realized, some will only become the transition technology.

2. Transmission speed

Compared with CDPD, GPRS transmission rate is higher, but its high speed is obtained by sacrificing channel resources. If GSM 8 channels of a carrier frequency are all GPRS occupied, the transmission rate can reach 115kbps (theoretically), if only 1 channels, remove protocol and error correction and other information, really used to transmit data only 14kbps. And most of the existing data applications are some low-speed data, CDPD has a 19.2kbps is enough to more than 90% of the application needs.

3. Information Resources

GPRS is the use of GSM voice channel to transmit data, which is bound to the already congested GSM brought greater burden, the development of data users will be limited by voice users. Moreover, GPRS has certain limits on the number of users sharing the channel, and only a few users can share the channel. and CDPD as a dedicated data network, its number of users can be achieved a lot, for each PS, can have 15,000 users registered, for a group, the number of users is up to a hundred thousand of, and at the same time can have more than 20 users to share the channel for data transmission.

4. Mobile Terminal

CDPD Development to today, the development of terminal products manufacturers have a lot. With the advent of terminal products suitable for a variety of applications, terminal prices have shown a rapid downward trend. Compared with the GPRS terminal, CDPD Terminal has a great price advantage.

5. Construction costs

After calculating, in the GSM network each development one user's cost is about 2000 yuan, the GRPs user's cost is according to the network scale decision. Generally speaking, in the initial stage of CDPD, the base station number will not be many, plus the necessary switch and network management investment, the cost of each user is about 2500~3000 yuan. With the scale of network coverage and the expansion of network capacity, the cost of users will be significantly reduced.

6. Safety Assurance

Although GPRS can also encrypt the transmission data, but the encryption authentication mechanism does not have the CDPD network strong, CDPD uses RC4 encryption technology, 40 bit key, the positive and negative channel uses the different key, simultaneously the system uses the dynamic key management, namely the network automatic allocation random address. Users can log on to the Internet after the key at one end of the server matches the key of the user's wireless modem. The keys are not the same each time you boot up.

7. System type

GPRS is based on GSM network, common GSM frequency (900/1800mhz), share the majority of GSM network infrastructure, and CDPD is a amps based wireless WAN, it is a special data network.

8. Communication capacity

GPRS data user capacity is limited by traffic volume, and CDPD network can register 15000 user/ps at the same time.

9. Working frequency

GPRS and GSM common frequency band, GSM uses TDMA/FDMA multiple access mode, each channel has 8 time slots (8 channels). According to the number of community users (density), GSM can be used in different community frequency multiplexing mode. CDPD is working in the Amps band, only 1MHz bands. Because GPRS available frequency band is wide, so the number of channels that can be used for data in each cell of GPRS is much larger than that of CDPD, it is easy to meet the need of the channel number of the public network.

10. Coding method

GPRS uses convolutional coding, recommend 4 kinds of coding methods: Cs-1~cs-4 (CS-1, 1/2 of the code rate; CS-2, Code rate 2/3), by reducing error-correcting bits to adapt to different transmission channel quality requirements. For example, CS-1 and CS-2 coding error-correcting ability, suitable for transmission channel quality is poor circuit. CS-3 and CS-4 (no error correction) coding error correction ability, suitable for transmission channel good quality circuit use, flexible and convenient use. CDPD Channel FEC encoding only one reed-solomon, not as flexible as GPRS.

11. Quality of Service

GPRS settings service priority level 3 can be negotiated, set transmission delay level 3 can be negotiated to determine, set transmission reliability level of 3, but also set the user throughput level of 19 can be negotiated to determine, so that operators can provide users with a variety of effective services. But CDPD does not have the above function.

12. Receiving sensitivity

The receiver sensitivity of GPRS base station is lower than that of CDPD, one of the reasons is that the BER limit value of different channel types of GSM is different, and the sensitivity of receiver is improved because the CDPD adopts spatial diversity technology.