Wireless access network based on Bluetooth technology

Summary: At present, how to realize the seamless Internet access of mobile users has become a hot topic in the field of communication, this paper firstly introduces the principle of two wireless access technologies based on Bluetooth technology, and discusses its routing technology briefly, and puts forward a simple solution for the handoff problem. Finally, several realization schemes of Pico Network in Bluetooth access network are given.

1 overview

With the gradual popularization of notebook computer and personal digital assistant (PDA), people's expectation of communication technology is more and more high, we hope to be able to access the Internet at any time and realize mobile interconnection.

The concept of wireless access network refers to the existence of the network in the presence of multiple wireless points, mobile terminals through its vicinity of the wireless access point access to the local area network. At this point, the mobile terminal can access other devices within the LAN, or through routers, gateways to access resources on the Internet. Wireless LAN Support user roaming, that is, when users move from one location to another location, automatic switching to maintain the continuity of communication. At present, according to the realization of wireless access network can be divided into a fixed wireless networks and mobile wireless connect network.

Bluetooth technology based wireless access is referred to as BLUEPAC (Bluetooth public Access), this article mainly introduces the Bluetooth technology based on wireless access.

2 Bluetooth Introduction

Bluetooth is an open global specification for wireless data and voice communication, which enables the exchange of information between many devices, including mobile phones, PDAs, laptops, related peripherals and home appliances. Bluetooth works in the global 2.4GHz ISM (ie, industrial, scientific, medical) band. Bluetooth data rate of 1MB/S, communication range of 10 meters to 100 meters, can support both data and voice transmission.

The basic unit of the Bluetooth network is the Pico Network (piconet), which consists of a primary device (master) unit (the device that initiates the link) and a device (Slave) unit. Bluetooth uses a self-organizing network (AD-HOC), a pico-net, with a main device unit and up to 7 units from the unit. The main unit is responsible for providing the clock synchronization signal and frequency hopping sequence, from the device unit is generally controlled synchronization of the device unit, accept the main equipment unit control. For example, an office PC can be a master unit. The main unit is responsible for providing the clock synchronization signal and frequency hopping sequence, from the device unit is generally controlled synchronization of the device unit, accept the main equipment unit control. For example, an office PC can be a master unit, while a wireless link, wireless mouse, and wireless printer can act as a role from a device unit. A group of tiny nets that are interconnected together in a particular way form a distributed network (scatternet), and a primary device unit in a Pico network can also be used as a device unit in another Pico network, which is also known as a composite unit of equipment. Bluetooth's unique networking approach gives it the power of wireless access, while 7 mobile Bluetooth users can connect to the Internet through a network node.

3 Cellular IP and mobile IP

There are two main technologies for using TCP/IP protocol for mobile users: Cellular IP Mobile and mobile IP. In this paper, we will discuss the working principle of Bluetooth technology separately.

3.1 The concept of cellular IP (cellular IP) Working principle

TCP/IP is designed under the assumption that the terminal device is fixed, and the high level protocol based on TCP/IP can not meet the requirements of terminal mobility. When wireless LAN access is applied to mobile users, the fast handoff between different base stations is bound to cause serious routing problems, thus introducing the technology of mobile users using a subnet-dependent IP address, which is cellular IP. Bluetooth technology to apply the principle of cellular IP is as follows:

Mobile Bluetooth users (hereinafter referred to as BT users) need wireless access, it will issue a query command, when the base station can accept new users, the connection is established. At this time, the BT user will send the registration request to the Bluetooth agent through the base station, the Bluetooth proxy is validated to return a packet containing the temporary IP address, proxy server port address, and DNS address assigned to the BT user. BT users receive this group, you can use the IP address to the Internet to send and receive data, but also with the local area network other BT users to communicate.

When the BT user moves the location, if the BT user's receive signal strength (RSSI) is less than a threshold value, it will issue a query command to find out if there is a closer base station, and if so, a connection will be established with the new base station, when the BT user will send a registration request to the Bluetooth agent via the new base station. The Bluetooth agent returns a new packet containing the temporary IP address, proxy server port address, and DNS address that the BT user sends data to the Internet via the IP address.

3.2 Concept and working principle of mobile IP

and the working mechanism of cellular IP is different, in mobile IP, mobile users can use a fixed IP address in any way to connect to the Internet, when mobile users to move to another network or subnet, mobile users can not change the IP address in the case of still maintain communication, Mobile IP is the current research hotspot of mobile communication. The application of mobile IP in Bluetooth technology is as follows:

• Local agents (routers on the local network where BT users reside) and foreign agents (routers on the current web of BT users) constantly send agent messages to the Internet to prove their presence.

· BT users receive these messages, determine whether they are in the local network or in the field network.

• If a BT user discovers that he or she is on a local network and receives a message from a local agent, it does not start the mobile function: If you still receive a message from a foreign agent, send a command to the local agent to unregister the original location (field network) and declare that you have returned to the local network

• When a BT user detects that it has been moved to a foreign network, it will get a referral address that contains two information: one is the IP address of the foreign agent, and the other is the network address of the foreign agent through some mechanism with the BT user.

• Then the BT user registers with the local agent, indicating that he or she has left the local network and notifies the local agent of the received address.

• After registration, all packets leading to BT users will be intercepted by local agents and sent by the local agent through the IP tunnel (tunnel) to the foreign agent. After the foreign agent receives, the packet is forwarded to the BT user. In this way, even if BT users have moved from one subnet to another, the data communication of BT users can continue.

· BT users sent to the field packet is generally based on the IP path to send out, do not have to pass the local agent. It is worth mentioning that the mobile I-object routing problem, traditional mobile IP using the triangular road by technology.

BT users send information to the end of the communication, directly through the field agent, but from the communication to the end of the data sent to the BT users by the local agent intercept, and then according to the address in the address information, using tunneling technology sent to the field agent, the field agent to the BT users. The disadvantage of this scheme is that it increases the burden on the local agent, and the routing is not the best choice, which increases the delay of the route. One of the improvements proposed by the IETF is as follows: the communication to the end before sending data to the BT user first registered to the local agent, so that the transfer address of BT users, and then according to the address information, directly to the BT users. If the local agent is too late to refresh the forwarding address information, it will easily result in the loss of the packet when the BT user moves frequently in the area. Here we give a simple way to solve the problem of handoff.