Mobile Wireless access Technology scanning

Introduction
At present, with the development of computer and communication technology, wireless network has become a part of people's life. In the area of commercial communications, with the rapid development of internet-based data communications services and the increasing number of mobile users, a new trend is emerging in the field of information transmission, namely the combination of wireless networks and the Internet. It allows users to access the Internet from anywhere, at any time, to read e-mail messages, to query important data for work, or to upload a Web page to a portable PC or personal digital assistant (PDA). How to connect to the Internet for data communication becomes the technical problem that people pay attention to.
Mobile Access wireless data communication is more time-sensitive and requires the access to data information in the process of moving. Access to the Internet through mobile and wireless communication systems are divided into two categories: one is based on the cellular access technology, such as cellular digital packet Data (CDPD), General Packet Radio transmission Technology (GPRS), edge, etc.; the second is based on LAN technology, such as IEEE802.11 WLAN, Bluetooth,homerf and so on.
Mobile Cellular access Technology
Mobile cellular Internet access technology has: based on the first generation of analog cellular amps system CDPD technology, based on the second generation of digital cellular systems GSM and IS-136 GPRS and on this basis edge technology.
1. Cellular Digital Packet Data CDPD
CDPD Technology is developed on the amps system, full use of the original Amps spectrum and facilities, can not only use a dedicated frequency, in the prescribed channel transmission data, can also use the FH mode, the mobile phone calls in the idle channel to transmit data. In the existing analog cellular telephone network by adding mobile data base station (MDBs), mobile data intermediary system (MDIs) and mobile Data Terminal (MES), wireless packet data communication, suitable for small data, real-time requirements are not high. It uses packet switching instead of circuit-switched technology. In a typical mobile phone system, the mobile phone always sends an audio signal, while a packet-switched mobile phone sends a single packet of data to the base station and disconnects. This greatly reduces the idle time.
When using CDPD, the data sent by user mobile data terminal is modulated, first transmitted to mobile data base station by Radio Wave, the management of wireless channel is completed by mobile data base station, receiving and demodulation of wireless signal, then the data obtained after demodulation is transmitted to mobile data intermediary system, The data intermediary system completes the CDPD network Packet Exchange, the route as well as to the user movement location tracking, the roaming, sends to the CDPD NET data will complete with other such as DDN, PSTN, CHINANET, Chinapac and so on public network connection. At the same time, in order to ensure the correct transmission of data, CDPD uses IP High Level network protocol, high reliability of forward error correction technology to improve the transmission rate, so that the rate of up to 19.2kbit/s, while the system to the TCP/IP header compression, The data is V.42bis compressed to improve the channel utilization.
CDPD uses the public random access, the data transmits in the form of the packet in the wireless channel, the channel is not completely fixed assigns to a user in the transmission process, therefore many user's data may share one channel, the channel utilization rate is high. But because the data transmits in the form of grouping, the transmission delay is large. CDPD uses TCP/IP protocol Internet address numbering, the user by the National unified Planning address, each user's IP address fixed, so call establishment time is very short. In view of the above characteristics, CDPD for many points, a wide range, short information, large volume and the frequency of a more dense burst of business has advantages, can be used in finance, securities, traffic intelligent scheduling, remote monitoring, information query and so on, so suitable for Internet access.
2. General Packet Radio Service GPRS
GPRS is a packet-switching protocol defined by GSM standard, it realizes the ' forever online ' connection between the mobile terminal and the network, and the network capacity is occupied only when the transmission is actually carried out. It is an efficient way to transmit data based on packet switching, which is to increase the packet switching function in GSM network, and to X.25 and TCP/IP protocol packet Exchange data communication in GSM platform. It can provide up to 115KBIT/S air interface transfer rate. GPRS enables several mobile users to share a wireless channel simultaneously, and a mobile user can also use multiple wireless channels. Users that do not actually send or receive packets account for only a small portion of network resources. Its data rate is more than 10 times times the existing GSM, the huge throughput has changed the single text-oriented wireless application, making the multimedia business including picture, voice and video realized.
In order to realize GPRS, 3 kinds of new logical network entities need to be introduced in the existing GSM network, the service GPRS support node, the Gateway GPRS support node and the packet Control Unit (PCU).
SGSN is the interface between GPRS backbone network and wireless access network, which provides the interactive operation between GPRS network and external packet data network. It switches the packet to the correct in-station subsystem (BSS). Its tasks include providing encryption, authentication, session management, mobility management, and logical link management for mobile stations. It also provides connections to databases such as HLR. GGSN is the network joint point between the external packet data Network (IP) or packet switched Data network (X.25/X.75) and the GPRS core network. If the external network is an IP network, GGSN can be viewed as an ordinary IP router that serves all the IP addresses of the mobile station. Nodes can include firewalls and packet filtering mechanisms. In addition, GGSN assigns a SGSN to the location of the mobile station. In the BSC of BSS, a Packet control unit (PCU) is included, which supports communication protocols for all GPRS air interfaces. PCU is responsible for the management of packet segmentation and planning, wireless channel, transmission maturity detection and automatic retransmission, channel coding schemes. Quality control, power control and so on, and support the handover, radio resource allocation and the letter Dow matching functions. MSC/VLR, HLR, and SMS (Short message Service) Centers are functional entities in the GSM system for common telephone exchange. These nodes realize interoperability with GPRS by adding additional interfaces.
GPRS features include: Make full use of spectrum resources, wide transmission bandwidth, applicable to sudden business.
GPRS technology calls to establish a short time, support point-to-point, point to multiple points, up and down link asymmetric transmission. From the effective use of network resources and reduce the cost of users, GPRS is very suitable for such as the Internet business, such as sudden, public-oriented business.
3.EDGE (Enhanced Data rate for GSM Evolution)
Edge is Ericsson Company as a GSM evolution program submitted to ETSI, thus paving the way for the ongoing standardization process. Technically, the edge has mainly improved the wireless interface, but in a more general sense, edge is to improve the transmission rate, and thus promote the cellular mobile system to the third generation of functional evolution of the effective universal wireless interface technology.
The idea of edge specification is to make use of the existing GSM data service type as much as possible and to improve its data communication rate. The bit rate and quality control of Edge Wireless Link is based on three basic principles: multi-gap connection, link adaptation and incremental redundancy. The edge can achieve higher bit rate through multi-slot operation. Edge mainly affects the wireless access part of the network, but it does not affect the applications based on circuit switching and packet switching, through the mobile Switching Center (MSC) and the Service GPRS support node (SGSN), the edge can be retained using the existing network interface; in fact, the edge is the evolution version of GSM, Allows the highest transfer speed of 38k. Unlike GPRS, the edge needs to be different from the current GSM modulation technology, a large investment. Some operators see the edge for GPRS development to 3G/UMTS transition technology. Whether it will be widely used depends on the timing of equipment, terminals and related applications. Because of the large number of users in GSM and TDMA-136 system, the market potential of introducing edge in existing system is very great.
The access technology based on wireless LAN
1. Wireless local Area network (WLAN)
In recent years, with the wide range of applications of LAN and the changing of modern communication mode, especially the development of mobile and portable communication, wireless local area network (WLAN) has come into being.
Wireless LAN is a local network which can support higher data rate (2-11MBIT/S), adopt micro-honeycomb, pico-honeycomb structure, and manage computer locally. It can use radio or infrared as the transmission medium, using the extended spectrum technology, mobile terminals can access the Internet through the wireless access point. There are two major standards in this area of WLAN: IEEE802.11 and HiperLAN (high perfomace Radio the local areas network).
IEEE has extended the 802.11 standard at a high speed. High-speed expansion has two versions: one is ieee802.11a, working in the 5GHz band, using OFDM modulation, transmission rate of 6-54mbit/s or 11mbit/s.
WLAN uses conventional LANs (such as 10/100/1000mbit/s Ethernet) and its Interconnect devices (routers) to form backbone support networks, using wireless access points (APs) and wireless Access server (was) to enable mobile Terminal (MT) movement and roaming. The function of wireless access server is to provide access management and mobility management of wireless terminals. Multiple communities can be supported within the jurisdiction of the wireless access server (called the service area). The function of wireless access point is to complete the bridge between WLAN and LAN, realize the transformation of Wireless Air interface protocol to LAN protocol, and realize the mobile user management of the cell. Mobile IP Server software is running on the wireless access server, and moving IP client can be supported on mobile terminal.
2. Blue tooth Technology (Bluetooth)
Bluetooth technology is an open global specification for wireless data and voice communication, which is based on low-cost near-distance wireless connection and establishes a special connection for fixed and mobile device communication environment. Bluetooth works in the global 2.4GHz ISM (ie, industrial, scientific, medical) band. The data rate of Bluetooth is 1mbit/s-time duplex transmission scheme is used to achieve full-duplex transmission. Compared with other systems working in the same band, Bluetooth is faster and has shorter packets, which makes Bluetooth more stable than other systems. The use of Forward error correction (FEC) inhibits the random noise of long-distance links. Frequency hopping transceivers using binary FM (FM) technology are used to suppress interference and prevent fading.
The Bluetooth baseband protocol is a combination of circuit switching and packet switching. Synchronous packets can be transmitted in a reserved time slot, and each packet is sent at different frequencies. A packet occupies a nominal time slot, but can actually be extended to occupy 5 slots. Bluetooth can support asynchronous data channels, up to 3 simultaneous simultaneous voice channels, and can simultaneously transmit asynchronous data and synchronous voice with a single channel. Each voice channel supports 64kbit/s synchronous voice links. An asynchronous channel can support a symmetric connection between one end with a maximum rate of 721kbit/s, and a 57.6kbit/s asymmetric connection at the other end.
The protocols in the Bluetooth protocol system are divided into four levels according to the Special Interest Group (SIG) Attention level:
(1) Core agreement: Baseband, LMP, L2cap, SDP;
(2) Cable substitution agreement: RFCOMM;
(3) Telephone Transfer Control Protocol: TCS Binary, at command set;
(4) Optional Protocol: PPP, UDP/TCP/IP, OBEX, WAP, VCard, vCAL, IRMC, Wae.
In addition to the above protocol layer, the specification defines the host Controller interface (HCI), which provides a command interface for the baseband controller, Connection Manager, hardware state, and control registers.
3.HomeRF
Sponsored by the ITU, with the participation of several major companies such as Compaq, Intel, Philips, HP, IBM and Microsoft, the HomeRF Working Group was set up from the outset in the home network, dedicated to the realization of PCs and other different countries, The digital communication between different manufacturers of household appliances equipment. Its shared wireless Access Protocol swap (Share wirless access Protocol) combines DECT and IEEE802.11 features to provide support for voice and data services and is ideal for communication in a home environment.
The data rate for HomeRF (SWAP) is 1.6mbit/s. The SWAP protocol model has a certain mapping relationship with the OSI network model, but it is not exactly one by one correspondence. In swap, the MAC (media access layer) corresponds to the data link layer, and the protocol layer on the HomeRF swap protocol model differs according to the business carried out, it uses TCP/IP to host the data service, UDP/IP the load stream service (such as video data stream), At the same time, in order to provide high-quality voice service, also integrates the DECT protocol.
All in all, IEEE802.11 is more suitable for wireless networks in a business environment, Bluetooth technology is suitable for the interconnection between mobile devices, and HomeRF is suitable for communication in the home environment.
Protocol for mobile wireless access to the Internet
To advance the technology used in the development of applications and services in the wireless communications network environment, WAP Forum has launched a widely recognized standard WAP in industry. The WAP specification, a programming model and language for wireless applications, defines, for the first time, an open and globally unified standard structure and a set of specifications for wireless Internet access, the role of which is to introduce the content and data services of Internet networks into wireless mobile terminals, That is, WAP becomes the mobile communication to the Internet bridge. WAP defines a tiered, scalable architecture that provides a comprehensive solution for the wireless internet. One of the principles of WAP Protocol development is to be independent of the air interface, which means WAP application can run on various wireless bearer networks, such as TDMA, CDMA, GSM, GPRS, SMS, etc. The WAP protocol includes the following layers:
* Wireless Application Environment (WAE): A general application environment based on WWW and mobile phone technology. The goal is to create a common operating environment that allows operators and service providers to build applications and services that can reach a large number of different wireless platforms in an effective way.
* Wireless Dialog Protocol (WSP): Provides a WAP application layer with a consistent interface to two conversation services. The first is the connection-oriented service which is operated on the WTP processing layer. The second is a connectionless service (WDP) that operates on a secure or unsecured packet service.
* Wireless Processing Protocol (WTP): Run at the top of the packet service and provide a common transport-oriented protocol suitable for the "thin" customer (mobile network station). WTP operates efficiently on secure and unsecured packet networks and provides three types of transactional services (unreliable one-way requests, reliable one-way requests, reliable two-way request answering transactions), optional user to user reliability, cascading and asynchronous transactions for PDUs.
* Wireless Transport Layer Security (WTLS): Based on the industrial standard Transport Layer Security protocol, it is designed for the use of WAP Transfer Protocol, and is optimized for use on low bandwidth communication channel. WTLS provides the following features: data integrity, confidentiality, and vacuum.
* Wireless Addressing Information Protocol (WDP): The Transport Layer protocol in the WAP architecture is submitted as a wireless addressing information Protocol (WDP). WDP is run on data that supports carrier services of different network types. As a universal transport service, WDP provides a consistent service to the WAP upper protocol and transparently communicates on the available carrier services.
With the increasing demand of Internet network, wireless network will also develop rapidly, and with the development of multimedia technology, wireless network will also be the data, real-time voice and image and other types of information.