Questions about cell phones

Bluetooth is a radio technology that supports devices to communicate over short distances (generally within 10m). It can exchange information wirelessly between many devices including cell phones, PDAs, wireless headsets, laptops, related peripherals, and so on. The standard of Bluetooth is IEEE802.15, working in 2.4GHz frequency band, bandwidth of 1Mb/s.

"Bluetooth" (Bluetooth) was originally a king in the 10th century to unify Denmark, who united Sweden, Finland and Denmark at that time. Naming this new technology standard after him means unifying a fragmented situation. Bluetooth technology uses advanced technologies such as high-speed frequency hopping (FH, Frequency Hopping) and time division multiple access (TDMA, Time DivesionMuli-access) to most cheaply connect several digitalized devices in close proximity (various mobile devices, fixed communication devices, computers and their terminal equipment, various digital Data systems, such as digital cameras, digital video cameras, and even a variety of household appliances, automation equipment) in a network link. Bluetooth technology will be the network of a variety of peripheral devices interface to the unified bridge, which eliminates the connection between the device, replaced by a wireless connection.

Bluetooth is a short-range wireless communication technology that allows electronic devices to be connected to each other via Bluetooth, eliminating the need for traditional wires. Through the wireless receiver on the chip, electronic products equipped with Bluetooth technology can communicate with each other within a distance of ten meters, and the transmission speed can reach 1 megabyte per second. In the past, infrared interfaces required electronic devices to be within line-of-sight distance, and now with Bluetooth technology, this trouble can be eliminated.

Bluetooth (Bluetooth) is a technology standard for short-range wireless digital communications proposed by Toshiba, Ericsson, IBM, Intel, and Nokia in May 1998***. Its goal is to achieve the highest data transmission speed of 1Mb / s (effective transmission speed of 721kb / s), the maximum transmission distance of 10 meters, the user does not have to apply for the use of 2.4GHz ISM (industrial, scientific, medical) band, in which the establishment of 79 bandwidth for the 1MHz channel, with the switching of the frequency 1600 times per second, the hobble way of spectrum diffusion technology to realize the The technology is used to send and receive radio waves.

Advantages of Bluetooth technology: support for voice and data transmission; the use of radio technology, transmission range is large, can penetrate different substances as well as diffusion between substances; the use of frequency hopping spread spectrum technology, anti-interference, not easy to eavesdrop; the use of unrestricted spectrum in all countries, theoretically, there is no interference problems; low power consumption; low cost. Disadvantages of Bluetooth: slow transmission speed. Bluetooth's technical performance parameters: effective transmission distance of 10cm ~ 10m, increase the transmit power can reach 100 meters, or even farther. The transceiver operates at 2.45GHz and covers 79 channels separated by 1MHz (from 2.402GHz to 2.480GHz). The data transmission technology uses short packets, frequency hopping spread spectrum technology, 1600 times/second, to prevent eavesdropping and avoid interference; one packet is transmitted at a time, the size of the packet ranges from 126 to 287 bits; the contents of the packet can contain information about different services such as data or voice. The data transmission bandwidth is 32.6Kbps in each direction for synchronous connections, which is close to 10 times the analog connection rate of a typical 56kb/s Modem, and asynchronous connections allow for data transmission rates of up to 721kb/s in one direction for uploads or downloads, when the rate in the opposite direction is 57.6kb/s; the data transmission channels are reserved for three concurrent, synchronous voice channels, each with 64kb/s bandwidth. Each has a bandwidth of 64kb/s; voice and data can also be mixed in one channel, providing a 64kb/s synchronous voice connection and an asynchronous data connection. Network connection using encryption technology, while the use of password authentication connected devices, can be simultaneously with other devices within 7 constitute a Bluetooth micro-network (Piconet), a Bluetooth device can be added to 8 different micro-networks at the same time, each micro-network are 1Mb / s transmission bandwidth, when more than 2 devices **** enjoy a Channel, can constitute a Bluetooth micro-network, and one device dominates the transmission volume, and when one device dominates the transmission volume, when two or more devices *** enjoy a Channel, can constitute a Bluetooth micro-network, and one device dominates the transmission volume. one of the devices dominates the transmission volume, when the device has not yet joined the Bluetooth micro-network, it first enters standby mode.