Wireless channel

The path between sender and receiver in wireless communication

The wireless channel is right wireless communication A figurative metaphor of the path between the sending end and the receiving end in radio waves For example, it is transmitted from the sending end to the receiving end without a physical connection, and its propagation path may be more than one. In order to visually describe the work between the sending end and the receiving end, we can imagine that there is an invisible road connection between the two. This connection path is called a channel, and the wireless channel is also known as the wireless "channel" ”。

Chinese name: Wireless channel
Foreign name: Wireless channel

Unit: Bit/sec (b/s)
Bandwidth: 13.5kHz

catalog

channel capacity

Announce

edit

channel capacity Reflects the maximum transmission capacity of the channel information content 。

The channel capacity can be expressed as the binary digit The number of bits of Data transmission rate ， Bit rate ）, expressed in bit/second (b/s), abbreviated as bps 。

Channel bandwidth

Announce

edit

Channel bandwidth It defines the lower limit frequency and upper limit frequency of signals allowed to pass through the channel, which can be understood as a frequency Passband 。 For example, if the allowable passband of a channel is 1.5kHz to 15kHz, the bandwidth is 13.5kHz.

Delay spread

Announce

edit

The propagation of radio waves in wireless channels is not a single path, but many paths from many reflected wave Synthesis of.

Because the distance of radio waves passing through each path is different, the arrival time of reflected waves from each path is different, that is time delay Different. When the transmitter sends an extremely narrow pulse signal, Mobile station The received signal consists of many pulses with different time delays, which we call Delay spread 。

Signal fading

Announce

edit

Because the arrival time of the reflected wave from each path is different, the phase is also different. Multiple signals of different phases are stacked at the receiving end, sometimes they are stacked to strengthen (in the same direction), sometimes they are stacked to weaken (in the opposite direction), resulting in a sharp change in the amplitude of the received signal, that is Fast fading 。 This kind of fading is caused by multiple paths, so it is called multipath fading 。

Receive signal division Instantaneous value In addition to rapid decline, Median field strength （ average value ）There will also be slow changes, mainly due to changes in regional location and weather conditions Caused by changes so that the refraction propagation of radio waves changes with time, Multipath propagation The delay of the signal arriving at the fixed receiving point changes accordingly. This is caused by Shadow effect And meteorological reasons, called Slow fading 。

Doppler effect

Announce

edit

because mobile communication Of middle mobile station mobility , exists in the wireless channel Doppler effect 。 In mobile communication, when the mobile station moves to the base station, the frequency becomes higher and the wavelength becomes shorter. We should fully consider the "Doppler effect" in mobile communication. Although, due to our daily life Movement speed It is impossible to bring about a very large frequency offset due to the limitation of. However, it will undeniably affect mobile communication. In order to avoid this impact causing problems in our communication, we have to take various technical considerations. It also increases the complexity of mobile communication.

Novice on the road

Growth task Getting Started with Editing Edit Rule Edit by myself

I have questions

Content query Online Service Official post bar Feedback

Complaints and suggestions

Report bad information Failed to appeal through entries Complaint of infringement information Blocking query and unblocking

Jinggong Network Anbei No. 1100000200001