Wireless access of Bluetooth system

First, System introduction

--Bluetooth (Bluetooth) System Specification 1.1B Edition has been developed by the international organization SIG at the end of 1999. The Wireless Access Protocol (Wireless access) is the main part of the control of base-frequency processing on top of the physical layer (physical Layer). Bluetooth mobile communication technology provides a solution for short distance wireless communication network. Because of its technology has the support of international manufacturers, and should be a wide range, there is a huge forecast market (the 2002 Bluetooth module is expected to break the demand for 100 million sets), so the current Bluetooth technology has become the world's most advanced technology in the wireless communications technology is one of the most important. Although the 1.1b version of the Bluetooth system was developed by the international organization SIG before the end of 1999, however, due to the 1MB/S data transmission rate is still not enough to support wireless multimedia transmission, and its scheduling (scheduling) Problem and access control (MAC) also need to improve to improve the efficiency of bandwidth utilization, so SIG International organization is still in the development of new Next generation Bluetooth standard version. In a Bluetooth micro-network (piconet), the Bluetooth component is divided into master and slave. The Bluetooth device that opens the connection is called Master, while other Bluetooth devices in plconet are called slave. After the piconet is established, the roles of master and slave can be exchanged. The Bluetooth standard uses frequency hopping (FH) technology as the modulation of signal to overcome multipath attenuation of wireless communication and common channel interference. The frequency hopping sequence and the channel access code are determined by master in Piconet, and the Piconet only allows a set of FH sequences to be used as the communication between master and more than one slave. In addition, in the Bluetooth air interface, two kinds of links between master and slave are defined to establish the connection between them. Point-to-Point synchronous connection-oriented link (SCO) and point-to-point asynchronous connectionless link (ACL).

For Bluetooth wireless access process controller is divided into standby and connection two major states. In these two states are divided into paging (page), Paging scan (page Scan), call (Inquiry), and Inquiry Scan, and the four states; In addition, paging under the host response (Master Response) child-like, The paging scan has a server response (Slave Response) Sub state, and a call-response (Inquiry Response) Sub state is consulted. As shown in Figure 1, the Bluetooth component can leave the standby state and enter the page, page Scan, inquiry, or Inquiry_scan state, and then enter the connection state. In a Bluetooth piconet, Master uses page or inquiry to establish a link with slave. If Master does not know the address of the slave component to be connected, it begins to inquiry the program to find the slave component address and its clock in piconet, but if Master is aware of the slave component address to connect to, open the page program to find the other slave.



--The procedures for wireless access, connection mode and access control are described in the following sections.

Second, access (access) program

-When you start to establish a connected wireless link, master needs to know the slave Bluetooth component address. So when the Master Bluetooth component is in the inquiry state, it uses inquiry information to indicate which Bluetooth components need to respond to inquiry and collect all the Bluetooth component addresses and clocks that respond to slave. The Master Bluetooth component in the inquiry state continues to transmit inquiry information at different FH frequencies to find other slave bluetooth components.

-and once the slave Bluetooth component is found, it is regularly entered in the inquiry scan State to respond to inquiry information. The receiver uses a matching correlator (Matching correlator) to search for inquiry access codes (access code). This search time will continue to range from 16 FH frequencies. If an active (wake-up) Slave Bluetooth component can identify inquiry information, it enters the inquiry response state. The Bluetooth component in the standby state can use all of its resources to search for other inquiry access Code, while the Bluetooth component in the connection state will be able to connect its existing data link to a time-saving mode to search for other inquiry access Code. The above inquiry scan programs may be interrupted by the SCO session reserved.

-When the device Access Code (DAC) is known to connect to slave, Master opens the page program to look for the slave. In the page program, master repeats a different FH frequency to transmit the slave DAC to try the connection (see Figure 2). The steps for the page program are as follows.



--First, the FH frequency sequence of the page signal is determined by the slave DAC.

--master predicts the wake-up time and FH frequency of slave with the predicted slave clock.

--in each transfer period, master sequentially launches two different frequencies.

In each successive receiving period, the slave receiver, based on the hop frequency used by page scan, detects the two corresponding receiving frequencies sequentially.

The--page program may be interrupted by the SCO session reserved. When the slave component succeeds in receiving master page information, master and slave start a routine response to exchange information. The successful connection between master and slave is to use the same frequency access code that is exported by the Bluetooth component address (BD_ADDR) and the same FH frequency, and master and slave clocks need to be synchronized.

--The following describes the steps in the response State program.

--1.slave Response Status:

--(1) Slave after receiving the DAC from master, the FH frequency used by page response responds to this DAC as confirmation.

-(2) After transmitting the response information, the slave receiver opens and waits for the FH Sync (FHS) packet from master.

--(3) If slave correctly received this FHS packet, slave the FH frequency used in page response back to its DAC for confirmation.

--(4) slave can be FHS from the contents of the packet to learn the difference between the slave clock and master clock.

--(5) Slave after correcting this clock difference, can enter the connection state.

--(6) If slave before entering the connection state, the above steps to establish the connection fail, then slave back to page scan state.

-After entering the connection state, a poll packet is sent by master first. If slave has not successfully received this poll packet, master and slave will respectively return to page and page scan status.

--2.master Response State

--(1) master, after receiving the response information returned by slave, fixed its existing clock and entered it into the page FH frequency selection scheme.

-(2) master uses this selected page FH frequency to transmit FHS packets. This FHS packet contains all the information required to construct the channel access code.

--(3) after the master transmission FHS Packet, that is, waiting for slave confirmation.

--(4) if not received slave confirmation, Master will be updated with the clock to send FHS packet.

-(5) If a slave is received, Master enters the connection state and uses BD_ADDR to exchange the FH sequences used with the slave.

--(6) After entering the connection state, Master begins to transmit a poll packet.