Easter eggs are behind!
In a wireless communication system, multiple users communicate with other users through the same base station at the same time, and different characteristics must be given to the signals sent by different users and base stations. These characteristics enable the base station to distinguish which user's mobile phone sent the signal from the signals transmitted by many mobile phones; each user's mobile phone can identify which one is sent to itself among the signals sent by the base station. In wireless communication systems, multiple access techniques are used for addressing.
Multiple access technology is divided into frequency division multiple access FDMA, time division multiple access TDMA, code division multiple access CDMA, space division multiple access SDMA.
1. Frequency Division Multiple Access (FDMA) Technology
It is to let different earth communication stations occupy different frequency channels for communication. Because each user uses channels of different frequencies, there is no mutual interference. Early mobile communication is to use this technology.
2. Time Division Multiple Access (TDMA) Technology
This multiple access technology allows several earth stations to share a channel, but we slice a carrier at different times and divide it into 8 time slots for 8 users. Since the occupied time is different, the mutual will not interfere. Obviously, in the case of the same number of channels, using time-division multiple access can accommodate more users than frequency-division multiple access.
3. Code Division Multiple Access (CDMA) technology
This multiple access technology also uses a channel jointly by multiple earth stations. But each earth station is assigned a unique "code sequence", which is different and orthogonal to all other "code sequences", so there is no interference between users. Because different "code sequences" are used to distinguish different earth stations, it is called "code division multiple access". Using CDMA technology can accommodate more users than the time division multiple access method.
In addition to the above three multiple access technologies, there is also a technology called "space division multiple access".
4. Space Division Multiple Access (SDMA) technology
It is a technology that uses space division to form different channels.
Space-division multiple access is a way to increase channel capacity, which can realize frequency reuse and is conducive to making full use of frequency resources. Space division multiple access can also be compatible with other multiple access methods, so as to realize combined multiple access technology, such as "space division - code division multiple access (SD-CDMA)".
Cocktail party example:
This is a classic example given by Qualcomm to let everyone understand CDMA. Qualcomm likens various wireless technologies to gathering in a building.
Frequency-division multiple access is like dividing a party hall into small rooms. Both parties in the room can clearly hear each other’s speech, but the disadvantage of this method is also obvious, that is, the number of guests that can be accommodated is too small, only 20 The room fills up the hall, and no one else can enter.
Time-division multiple access is based on frequency-division multiple access. It is stipulated that people in each room can only speak continuously for 10 minutes. Leave it to the next couple, and when it's your turn next time, you can occupy this room to speak. In this way, more people can participate in the reception, as long as the interval (10 minutes in the example) is within your tolerable range, then there will be no problem; CDMA is Code Division Multiple
Access Means, everyone is in the hall, there are no small rooms, the hall can accommodate many, many people, but you and Zhang San speak Chinese, Alice and Bob speak English, Cici and Coco speak Italian, although everyone is chattering But you can still understand what Zhang San said very clearly, because you can only understand Chinese, but not English and Italian, so you filter out other languages as noise.
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Copyright statement: This article is an original article of CSDN blogger "Li Shui Dumpling", following the CC 4.0 BY-SA copyright agreement, please attach the original source link and this statement.
Original link:
https://blog.csdn.net/weixin_40228289/article/details/83024292
https://blog.csdn.net/weixin_44535200/article/details/107974650