The radio part of Bluetooth uses the ISM segment of 2400 GHz, 2483.5-1600 MHz, the channel interval is 1 MHz, gfs modulation, and frequency hopping technology, at least times per second. After the connection is completed, the frequency of hops is 1600 times/s, and the time of inquiry and page is 3200 times/s.
1. Clock
There are three types of CLK, for example, CLK is the master clock, representing a piconet is the clock. Slave adjusts its clock to be consistent with the master clock:
Clke is used in the page process. The clock adjustment process is as follows:
2. AddressThe Bluetooth device has a unique 48-bit address (bd_addr). The structure is 0x9e8b00-0x9e8b3f, which is a reserved segment of the lap for inquiry operations. All active devices in piconet have an active Member Address (am_addr) and a 3bit. Therefore, a piconet device can have up to eight active devices. If am_addr is set to all-zero, it indicates the broadcast address. For parked devices in piconet, there are parked Member Address (pm_addr) and 8-bit, so a maximum of 256 devices in the parked status can be found.
3. physical channel
Four phasical channnel types are defined: Basic piconet channel and adapted piconet channel are used for communication between two connected devices, inquiry scan channel is used to discover remote devices, and the page scan channel is used to connect devices.
4. Physical linksA physical link represents the connection between two devices on the baseband layer. Generally, a physical link is associated with a physical channel.
5. Logical transportA total of five forms of logical transport are defined:
Synchronous logical transports periodically uses reserved slots. If SCO creates a slots, the ACL can only use slots other than these slots. Each logical transport has an address (lt_addr ). In a piconet, each active device has a 3-bit lt_addr. All 0 represents broadcast, and the master has no lt_addr. [This is similar to am_addr. What does it mean ??] (1) SCO and escomaster support a maximum of three SCO links. They can be between a master and an slave, or between a master and several slave. SCO is often used for synchronous data such as voice, and there is no retransmission mechanism. Compared with SCO, ssco adds a retransmission window after a fixed slot and supports retransmission. (2) aclmaster and slave can only have one link. In the case of SCO link, the ACL can only transmit data on slots other than slots reserved for SCO. The ACL supports retransmission.
6. Logical linksDefine the logical links in 5:
LC is in the header part of packet, and other logical links are in the payload part of packet. Note: ACL-C can be used in SCO or ACL logical transport; SCO-S and ESCO-s are used in synchronous logical transports; ACL-U is typically used in ACL logical transport. The ACL-C and ACL-U logical links are specified by the Logical Link ID (llid) in the header of the payload section in packet. (1) LC carries the underlying control information. Except the id packet, all packages contain LC information. (2) The ALC-C carries the control information exchanged by the link manger layer, using DM1 or DV packets. (3) The ALC-U carries the user information at The L2CAP layer, which may be transmitted by one or more baseband packets. (4) SCO-S and ESCO-s carry synchronized user data. ALC-C has the highest priority compared to several logical links except LC.
7. PacketsThe packet format of basic rate is as follows:
The format of general enhanced data rate packet is as follows:
Note: When baseband layer data is little-Endian, LSB first transmits. When the access code is 68bit, it is called the shortened access code. When it is used in paging, inquiry, and park, the shortened access code does not have a trailer.
8. Access CodeAccess code is required for transmission on physical channel. Three access codes are defined:
IAC is divided into Giac and DIAC. Giac is used for general inquiry operations, and DIAC is used for dedicated inquiry operations. Each packet of baseband starts with access code. The format of Acess code is as follows:
There are several types of access code:
The preamble section is as follows:
Sync is calculated based on 24 bit address (LAP. The trailer part is as follows:
The header consists of six parts:
After 1/3 FEC encoding, it becomes 54bit, and LSB is transmitted first. (1) The main functions of type are as follows: 1. decide on which logical transport to transfer (SCO, Esco, or ACL) 2. enhanced Data rate3. which packet (SCO, Esco, or ACL) is enabled)
Packet type: There are five common packet types: ID packet, null packet, Poll packet, FHS packet and DM1 packet. These types are called Link control packets:
(1) SCO packetshv1 packet, HV2 packet, hv3 packet, and DV packet. (2) ESCO packetev4, ev5 for basic Rate2-EV3, 3-ev3, 2-ev5, 3-ev5 for enhanced data rate (3) ACL packrtdm1, dh1, dm3, DH3, dm5, DH5 and aux1 for basic Rate2-DH1, 3-dh1, 2-dh3, 3-dh3, 2-dh5 and 3-dh5 for Enhanced Data Rate payload part: synchronous data + asynchronous data. ACL packets only have the asynchronous datafield and the SCO and ESCO packets only have the synchronous data field with the exception of the DV packets which have both. ACL payload structure:
Llid is defined as follows:
Bluetooth Baseband description
