Complete wireless access technology analysis

Wireless access technology is worth learning a lot. Here we mainly introduce mobile cellular access technology, including wireless access technology based on wireless LAN and Internet Protocol of mobile wireless access technology, we hope to have a more comprehensive understanding of wireless access technology. At present, with the development of computer and communication technologies, wireless networks have become part of people's lives. In the commercial communication field, with the rapid development of Internet-based data communication services and the increasing number of mobile users, a new trend is emerging in the information transmission field, that is, the combination of wireless networks and the Internet. It allows users to access the Internet from anywhere at any time to read emails and query the important data they need, or upload the Web page to a portable PC or Personal Digital Assistant PDA ). How to use wireless access technology to communicate data over the Internet has become a technical concern.

Mobile access to wireless data communication focuses more on timeliness and requires that data information be accessed during the mobile process. Internet access through mobile and wireless communication systems can be divided into two categories: one is cellular-based wireless access technology, such as cellular digital grouping data CDPD), and the other is universal grouping wireless transmission technology (GPRS ), EDGE, etc. Second, lan-based technologies, such as IEEE802.11WLAN, Bluetooth, and HomeRF.

Mobile Access Technology
1. Cellular Digital grouping data CDPD
CDPD technology is developed on the AMPS system. It fully uses the original spectrum and facilities of AMPS, and can transmit data through a specified channel in a dedicated frequency mode, you can also use the Frequency Hopping Method to transmit data through idle channels in mobile phone calls. In the existing simulated cellular telephone network, the Mobile Data Base Station (MDBS), mobile data intermediary system (MDIS), and mobile data terminal (MES) are added for wireless grouped data communication, suitable for scenarios with small data volumes and low real-time requirements. It uses the group switching technology rather than the circuit switching technology. In a general mobile phone system, mobile phones always send audio signals, while group-switched mobile phones send a single data group to the base station, and then disconnect. This greatly reduces the idle time.

When using CDPD, after the data sent by the user's mobile data terminal is modulated, the data is first transmitted to the mobile data base station through radio waves, the mobile data base station manages wireless channels and receives and demodulation wireless signals, and then transmits the obtained data to the mobile data intermediary system, the data mediation system performs Packet Exchange and routing in the CDPD network, and tracks and roaming users' mobile locations, data sent outside the CDPD network will be connected to other public networks, such as DDN, PSTN, CHINANET, and CHINAPAC through routers. At the same time, to ensure correct data transmission, CDPD uses the IP high-level inter-network protocol and adopts a high-reliability forward Correction Technology to Improve the transmission rate, so that the rate can reach up to 19.2 kbit/s, meanwhile, the system compresses TCP/IP headers and compresses V.42bis to improve the channel utilization.

CDPD uses public random access, and data is transmitted over a wireless channel in the form of groups. The channel is not completely allocated to a user during the transmission process. Therefore, data of multiple users can be shared to one channel, high channel utilization. However, because data is transmitted in groups, the transmission latency is high. CDPD uses the TCP/IP protocol as the Internet address number. Users plan IP addresses in a unified manner nationwide, and each user's IP address is fixed. Therefore, the call establishment time is very short. In view of the above features, CDPD has advantages for burst businesses with multiple nodes, wide areas, short information, large volumes of data, and high frequency of data encryption, it can be used in finance, securities, intelligent traffic scheduling, remote monitoring, information query, and other fields. Therefore, it is suitable for Internet wireless access technology.

2. General grouping wireless service GPRS
GPRS is a Packet Exchange Protocol defined according to the GSM standard. It establishes a "always-Online" connection between the mobile terminal and the network, and the network capacity is occupied only when the network capacity is actually transmitted. It is an efficient way to transmit data based on group exchange. It adds the group exchange function in the GSM network. On the GSM platform, it refers to the Packet Exchange data communication between X.25 and TCP/IP. It provides an air interface transmission rate of up to 115 kbit/s. GPRS enables several mobile users to share a wireless channel at the same time, and a mobile user can also use multiple wireless channels. Users who do not actually send or receive data packets only occupy a small part of network resources. The data rate is more than 10 times that of the existing GSM, and the huge throughput has changed a single text-Oriented Wireless Application, enabling multimedia services including images, voice and video.

To implement GPRS, three new logical network entities need to be introduced in the existing GSM network; Service GPRS Support nodes, Gateway GPRS Support nodes and group control unit PCU ). SGSN is an interface between the GPRS backbone network and the wireless access technology network. It provides interaction between the GPRS network and the external grouped data network. It switches groups to the correct Station Subsystem BSS ). Its tasks include providing encryption, authentication, session management, mobility management, and Logical Link Management for the mobile device. It also provides connections to databases such as HLR. GGSN is the gateway node between the external group data network IP address or the Packet Exchange data network X.25/X.75) and the GPRS core network. If the external network is an IP network, GGSN can be considered as a common IP router, which serves all the IP addresses of the Mobile Station. Nodes can include firewalls and group filtering mechanisms. In addition, GGSN specifies an SGSN for the mobile station based on its location. The bss bsc includes a group control unit PCU. It supports communication protocols for all GPRS air interfaces. PCU manages grouping segmentation and planning, wireless channels, transmission maturity detection, automatic resend, and channel coding solutions. Quality control, power control, and other functions, including cross-zone switching, radio resource configuration, and channel configuration. MSC/VLR, HLR, and SMS Short Message Service) centers are functional entities in the general telephone exchange GSM system. These nodes can communicate with GPRS by adding additional interfaces.

GPRS has the following features: fully utilizing spectrum resources, wide transmission bandwidth, and applicable to burst services. GPRS technology provides short call establishment time, supports point-to-point, point-to-point, and asymmetric transmission of upstream and downstream links. In terms of effectively utilizing network resources and reducing user fees, GPRS is very suitable for sudden and public-oriented services such as Internet services.

3. EDGEEnhancedDatarateforGSMEvolution)
EDGE was submitted to ETSI as a GSM Evolution solution, paving the way for ongoing standardization processes. Technically, EDGE mainly improves wireless interfaces, but in a more general sense, EDGE improves the transmission rate, therefore, it is an effective universal wireless interface technology that promotes the evolution of cellular mobile systems to third-generation features.

The idea of EDGE specification is to make full use of existing GSM data business types and increase the data communication rate. EDGE wireless link bit rate and quality control are based on three basic principles: multi-time slot connection, link self-adaptation, and gradual increase of redundancy. EDGE achieves a higher bit rate through multi-time slot operations. EDGE mainly affects the wireless access technology of networks, but it does not affect applications based on circuit switching and group switching. It supports node SGSN through mobile switching center MSC) and service GPRS ), EDGE can retain the use of existing network interfaces; in fact, EDGE is an evolutionary version of GSM, allowing the highest transmission speed of 38 K. Different from GPRS, EDGE needs to be different from the current GSM modulation technology, with a large investment. Some carriers use the EDGE technology as a transitional technology for GPRS to develop to 3G/UMTS. Whether it will be widely used depends on the time when devices, terminals, and related applications work together. Due to the large number of users in GSM and TDMA-136 systems, EDGE has great market potential in existing systems.

Wireless Access Technology Based on Wireless LAN
1. WLAN)
In recent years, with the ever-expanding application of LAN and the ever-changing modern communication methods, especially the development of mobile and portable communications, wireless lan wlan has emerged. A wireless LAN is a local computer network that supports a high data rate of 2-11 Mbit/s. It adopts a micro-cell and micro-cell structure and is managed by itself. It can use radio or infrared rays as transmission media and Extended Spectrum Technology. Mobile Terminals can access the Internet through wireless access points. There are two main standards in the field of Wireless LAN: 802.11 and HIPERLANHighPerfomaceRadioLocalAreaNetwork ). IEEE implements high-speed expansion of the 802.11 standard. Two high-speed extensions are available: IEEE802.11a, which operates in the 5 GHz band and uses OFDM modulation. The transmission rate is 6-54Mbit/s or 11 Mbit/s.

WLAN uses a conventional LAN, such as 10/100/1000 Mbit/s Ethernet) and its interconnected equipment routers, to form a backbone support network, using wireless access point AP) and Wireless Access Server WAS) to support mobile terminal MT). Wireless Access Server is used to provide wireless terminal access management and mobility management. It is called a service area within the jurisdiction of the wireless access server. It supports multiple residential areas. A wireless access point is used to bridge between a WLAN and a LAN, convert the wireless air interface protocol to the LAN protocol, and manage the mobile users of a residential area. Run the Mobile IP server software on the Wireless Access Server, and run the Mobile IP client on the mobile terminal to support the Mobile IP function.

2. Bluetooth Technology)
Bluetooth is an open global specification for wireless data and voice communication. It establishes a special connection for a fixed and mobile device communication environment based on low-cost, short-range wireless connections. Bluetooth works in the global 2.4GHzISM (industrial, scientific, and medical) band. The Bluetooth data rate of 1 Mbit/s is used for full duplex transmission. Compared with other systems that work in the same frequency band, Bluetooth provides faster frequency hopping and shorter data packets, making Bluetooth more stable than other systems. Forward correction FEC) can reduce the random noise of long-distance links. The frequency-hopping transceiver using the binary FM) technology is used to suppress interference and prevent fading.

The Bluetooth baseband protocol is a combination of circuit switching and group switching. Synchronous data packets can be transmitted in the reserved time slot, and each data packet is sent at different frequencies. A data packet occupies one time slot in name, but can be extended to five time slots. Bluetooth supports asynchronous data channels and up to three synchronous voice channels at the same time. It also supports simultaneous transmission of asynchronous data and synchronous voice over one channel. Each voice channel supports 64 kbit/s synchronous voice link. Asynchronous channels support 721 kbit/s at one end, 57.6 kbit/s at the other end, and 4.2 kbit/s symmetric connections.

The protocol in the Bluetooth protocol system is divided into four levels based on the specific interest group SIG:
1) Core protocols: BaseBand, LMP, L2CAP, and SDP;
2) cable replacement protocol: RFCOMM;
3) Telephone transfer control protocol: TCSBinary and AT command set;
4) Protocols: PPP, UDP/TCP/IP, OBEX, WAP, vCard, vCal, IrMC, and WAE.
In addition to the preceding protocol layer, the specification also defines the Host Controller Interface HCI. It provides command interfaces for baseband controllers, connection managers, hardware statuses, and control registers.

3. HomeRF
Sponsored by ITU, with the participation of companies like Compaq, Intel, Philips, HP, IBM, and Microsoft, the HomeRF team was positioned on the home network from the very beginning, it is committed to digital communication between PCs and other household appliances from different countries and manufacturers. The shared wireless access protocol SWAPShareWirlessAccessProtocol is developed by SWAPShareWirlessAccessProtocol. Combined with the features of DECT and 802.11, it provides support for voice and data services and is very suitable for communications in the home environment.

HomeRFSWAP) data rate is 1.6 Mbit/s. The layer of the SWAP protocol model has a certain ing relationship with the OSI network model, but not exactly one-to-one. In SWAP, the MAC medium access layer) corresponds to the data link layer. The protocol layer on the homeRF SWAP protocol model varies according to the service carried out, it uses TCP/IP to carry data services, UDP/IP to carry stream services, such as video data streams, and integrates the DECT protocol to provide high-quality voice services. All in all, is suitable for wireless networks in commercial environments. Bluetooth technology is suitable for interconnection between mobile devices, while HomeRF is suitable for communications in home environments.

Internet protocol for mobile wireless access technology
To promote the application and service technologies used for development in the wireless communication network environment, the WAP Forum has launched a widely recognized standard WAP. The WAP specification is a programming model and language for wireless applications. For the first time, it defines an open and globally unified standard structure and a standard application to implement wireless Internet access, the function is to introduce Internet content and data services to wireless mobile terminals, that is, WAP becomes a bridge between mobile communication and internet. WAP defines a layered and scalable architecture that provides a comprehensive solution for the wireless Internet. One of the principles of WAP protocol development is to be independent of air interfaces, that is, WAP applications can run on various wireless bearer networks, such as TDMA, CDMA, GSM, GPRS, and SMS. The WAP protocol includes the following layers:

◆ Wireless application environment WAE): a universal application environment based on the combination of WWW and mobile phone technology. The objective is to establish an environment that can be operated together and allow operators and service providers to create applications and services that can meet a large number of different wireless platforms in an effective way.
◆ Wireless conversation protocol (WSP): provides the WAP application layer with consistent interfaces to the two conversation services. The first is the connection-oriented service that operates on the WTP processing layer. The second is the non-Connection Service WDP operated on the secure or non-secure data packet service ).
◆ Wireless processing protocol (WTP): it runs at the top of the data packet service and provides common traffic-oriented protocols suitable for running on thin customer mobile network sites. WTP operates effectively on secure and non-secure Packet Networks and provides three types of transaction services: unreliable one-way requests, reliable one-way requests, and reliable two-way Request Response transactions) and optional user-to-user reliability, PDU cascade and asynchronous transaction processing.
◆ Wireless Transport Layer Security (WTLS): based on the industrial standard Transport Layer Security Protocol, it is designed for the use of WAP transfer protocols and is optimized for the use of low-bandwidth communication channels. 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 the wireless addressing information protocol (WDP. WDP runs on data that supports different network types of carrier services. As a common transmission service, WDP provides consistent services to the WAP upper-layer protocol and transparently communicates with the available carrier services.

With the increasing demand for Internet networks, wireless networks will inevitably develop rapidly, and with the development of multimedia technology, wireless networks also transmit data, real-time voice, images, and other information.

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