Its goal is to achieve the highest data transmission speed of 1Mbps (the effective transmission speed is 72 1kbps), and the maximum transmission distance is 10 meter. Users can use the 2.4GHz ISM (industrial, scientific and medical) band without permission, and set 79 channels with the bandwidth of 1MHz on it, switching 65,438 times per second. This is the origin and characteristics of Bluetooth technology. Devices that use Bluetooth technology to communicate can be divided into "calling party" and "receiving party", which determine the frequency hobbing mode. The calling party can communicate with seven recipients at the same time. Therefore, the calling party can connect to a subnet called piconet with 7 receivers and 8 devices. The receiver in a piconet can be the receiver of more than two piconets at the same time. 1July, 999, Bluetooth released the formal specification BluetoothVersion 1.0. Mobile phones and laptops that meet this specification will be available at the end of 1999 or the beginning of 2000. Companies that claim to commercialize Bluetooth technology are increasing day by day. At present, the number of member enterprises of Bluetooth standardization organization "BluetoothSIG" has increased to more than 800.
The original intention of Bluetooth technology is to use a small, low-cost wireless communication technology instead of cables to connect smart phones with notebook computers, palmtop computers and various digital information devices. Then form a personal network, so that all kinds of information-based mobile portable devices within its scope can share resources seamlessly. According to the prediction of foreign authoritative organizations, in a few years, hundreds of millions of digital mobile phones, PCs and various information devices around the world will use the wireless interface based on Bluetooth technology as the standard configuration. Bluetooth technology will develop rapidly in many fields, and its typical application environment includes wireless office, automobile industry, medical equipment and so on. Bluetooth will play an important role in people's daily life and work, with great market potential. This technology is becoming the investment hotspot in 2 1 century.
The so-called Bluetooth technology is actually a short-distance wireless communication technology. Bluetooth technology can effectively simplify the communication between mobile communication terminal devices such as palmtop computers, notebook computers and mobile phones, and can also successfully simplify the communication between these devices and the Internet, thus making the data transmission between these modern communication devices and the Internet faster and more efficient, and broadening the road for wireless communication. More generally speaking, Bluetooth technology enables modern portable mobile communication equipment and computer equipment to access the Internet without cables, and its practical application can be extended to various household appliances such as automobiles, consumer electronics and information appliances, forming a huge wireless communication network.
The background of the formation of "Bluetooth" is as follows:1In May, 1998, five famous manufacturers, such as Ericsson, Nokia, Toshiba, IBM and Intel, put forward Bluetooth technology when jointly carrying out the standardization activities of short-distance wireless communication technology, with the aim of providing a short-distance and low-cost wireless transmission application technology. The five vendors also set up a Bluetooth Special Interest Group to make Bluetooth technology the future wireless communication standard. Chip overlord Intel is responsible for the development of semiconductor chips and transmission software, Ericsson is responsible for the development of radio frequency and mobile phone software, and IBM and Toshiba are responsible for the development of notebook computer interface specifications. 1999 In the second half of the year, five famous industry giants, including Microsoft, Motorola, Sankang, Lucent and Bluetooth Task Force, initiated the establishment of a Bluetooth technology promotion organization, which set off a worldwide "Bluetooth" craze. The global industry is about to develop a large number of applications of Bluetooth technology, which makes Bluetooth technology present an extremely broad market prospect, indicating that a magnificent global wireless communication wave will be ushered in at the beginning of 2 1 century.
What is Bluetooth?
Bluetooth is a technical standard for short-range wireless data communication proposed by Toshiba, Ericsson, IBM, Intel and Nokia in May 1998. It can realize wireless data and sound transmission from single point to multipoint within the radius of 10 meter, and the data transmission bandwidth can reach 1Mbps. The communication medium is electromagnetic wave with frequency between 2.402GHz and 2.480GHz.
FM
frequency modulation
We are used to referring to general FM broadcasting (76- 108MHz, 87.5- 108MHz in China and 76-90MHz in Japan). In fact, FM is also a modulation method. Even in the short wave range of 27-30MHz, it is also used as the band of amateur radio, space and satellite communication. FM radio is FM radio.
FM FM is a radio function. As an additional function of MP3, from a practical point of view, the current MP3 is not very good in this respect. It should be said that it is not as good as ordinary radios, and there is still a gap in receiving range and accuracy. Can only be said to be a useful supplement. Of course, if you pay attention to this function, there are also products that do well. On the specific model, according to different FM products, whether the selected channels can be saved and how many channels can be saved, stereo and ordinary channels can be set by themselves or by machine.
Frequency modulation (FM) synthesis technology
Frequency modulation is one of the most effective synthesis technologies in electronic music. It was first proposed by Dr. JohnChowning of Stanford University in the United States. In 1960s, Ning Zhuo began to use different types of vibrato at Stanford University. He found that when the frequency of the modulated signal increases and exceeds a certain point, the vibrato effect disappears in the modulated sound and is replaced by a new and more complex sound.
Today, it seems that only the most commonly used FM technology in Ning Zhuo (namely FM broadcasting) is broadcasting. However, Ning Zhuo's unexpected discovery made this traditional FM technology have a new use in sound synthesis. When Ning Zhuo understood the basic principle of FM modulation, he immediately began to study the synthesis technology of FM theory, and became the first person to make music by using FM technology in 1966.
fundamental principle
The change of audio signal is usually periodic. One of the most understandable examples of audio modulation technology is violin and string kneading. Rubbing the strings quickly vibrates on the strings through fingers and wrists, which makes the length of the strings change rapidly and finally affects the softness of the violin sound. Like "FM radio waves", "fm synthesis Theory" also has two elements: pronunciation body (carrier) and modulation body. Voice body, or carrier body, is a frequency oscillator that actually emits sound; Modulator, or modulator, is responsible for adjusting the sound produced by changing carriers. Carrier frequency, modulation frequency and modulation value are important factors influencing fm synthesis theory.
The most basic FMinstrument includes two sinusoidal oscillators, one is a stable fc(carrierfrequency (FC) oscillator; One is the FM oscillator. The carrier frequency is added to the output of the modulation oscillator. The carrier oscillator is a simple sine wave frequency with fc frequency. When the modulator occurs, the signal from the modulation oscillator, that is, the sine wave with fm frequency, drives the frequency of the carrier oscillator to change up or down. For example, a modulated wave with a sine wave of 250Hz modulates a carrier wave with a sine wave of 1000Hz, which means that the frequency of 1000Hz generated by the carrier wave will be affected 250 times per second. Both oscillator and carrier are periodic or quasi-periodic oscillators with frequency, amplitude and waveform.
In frequency modulation technology, the amplitude of modulator also plays a key role in frequency modulation. The amplitude of the modulator affects the depth of carrier frequency modulation. If the amplitude of the modulated signal is 0, there is no modulation. Therefore, just as the frequency of the modulator in AM affects the amplitude of the carrier, the frequency change of the carrier in FM is also affected by the amplitude change of the modulator.
So in the process of frequency modulation, we can find: 1. The frequency of the modulator affects the speed change of the carrier frequency. 2. The amplitude of the modulator affects the depth change of the carrier frequency. 3. The waveform (or timbre) of the modulation body affects the waveform change of the carrier frequency. 4. The amplitude of the carrier remains constant during frequency modulation.