"The sports world cannot be free from climate change." The J.League and the Ministry of the Environment have teamed up to take measures.
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On June 2021, 6, the Ministry of the Environment and the J League (Japan Professional Football League) took measures against climate change, etc ... → Continue reading
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The Huff Post Japan edition, an international media that creates conversations, delivers daily news with a value that values diversity.
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Wireless communicationInDiversity(English: diversity, British English:/ daɪˈvɜːsɪti /, American English: / dɪˈvɝsəti /) IswirelessMultiple signals with two or moreantennaでReceiveIt is a technology that improves the quality and reliability of communication by doing so.Specifically, the signal of an antenna having an excellent radio wave condition is preferentially used, or the signals received by a plurality of antennas are combined to remove noise.Not receiveSENDWhat was applied toSend diversityThat is.In old literature etc.Diversity"In some cases.
For example, on the side of a large buildingMobile phoneWhen you use, there are radio waves that arrive directly and radio waves that are reflected by the building, and there is a slight difference in arrival time between the two radio waves (Multipath), Two radio wavesinterferenceAnd the quality of communication deteriorates.Such coherenceFadingOf the diversity, spatial diversity is particularly effective.
- Spatial diversity.
- It is said that if the two antennas are separated by more than 2/1 wavelength, there is no correlation between the reception states of each antenna.
- Antenna selection method
- This is a method in which multiple antennas are prepared and the antenna with the stronger radio wave is simply switched with a switch.The purpose is to reduce fading, and the radio waves themselves do not become stronger.
- Maximum ratio synthesis method
- This is a method in which a plurality of antennas are prepared at appropriate intervals, and the antennas that pick up strong radio waves are aligned in phase and combined.While the above-mentioned antenna selection method does not strengthen the radio wave itself,gainCan be obtained.
- In addition, a variable attenuator / phase device is used to arbitrarily change the directivity (beam steering) to create a null point (dead point) (null steering), which is used to reduce interference.Adaptive arrayantenna(Beamforming).
- Further, by forming a plurality of spatially separated beams (multi-beam) by using a plurality of attenuators / phase systems, multiplex communication can be performed at the same time and at the same frequency.This isSpatial access method (SDMA)It is applied to.
- Polarization diversity
- PolarizationIn this method, antennas whose surfaces differ by 90 degrees are prepared, and the received signals are combined or switched to the polarized wave with the stronger radio wave.Since the polarization fluctuates due to reflection and diffraction, it may be better to receive with a polarization different from that of the transmitted wave.It is also effective when the angle of the antenna itself actually fluctuates as in a mobile phone.
- Furthermore, an adaptive array antenna is composed of a plurality of polarized antennas to suppress reflected waves and diffracted waves (including cross-polarized components) and reduce interference with direct waves (same as polarized waves at the time of transmission). ..
- Angle diversity
- A method in which antennas with multiple directivities are installed at different angles and the received signals are combined or switched to an antenna with a large reception output for reception.
- Multipath diversity
- Beam null point formation for adaptive array antennasMultipathWhen it is done for, it becomes multipath diversity.That is, if interference waves are removed by preparing elements for the number of multipaths, selective fading countermeasures can be taken.An LMS (Least Mean Square) adaptive array antenna is required to form beam null points for multipath.
- On the contrary, if the same beam / null point is formed for a plurality of multipaths on both the transmitting side and the receiving side, the multipaths can be used for multiplexing.thisMIMOApply to.
- Site diversity
- This is a method in which radio waves transmitted simultaneously from multiple transmitting stations are combined on the receiving side.
- Frequency diversity
- Since the fading pitch is different at different frequencies, the diversity effect can be obtained with one antenna, but it occupies twice the frequency.However, in the case of digital modulation, the occupied frequencies can be made equal by halving the original data rate.
- Time diversity
- When moving, the fading state changes from moment to moment, so by transmitting the same content at different times, the diversity effect can be obtained with a single antenna, but it takes twice as long to complete reception. It takes.Also,TDMAIn the case of, it occupies twice as many slots, but in digital modulation, the number of hours occupied can be equalized by halving the original data rate.
- Send diversity
- This method uses the antenna selected at the time of reception for transmission.The conditions for application are that the transmission and reception frequencies are the same and that the movement speed is slow. TDMA /T,TD-CDMAIt is adopted in the method.
- Resend diversity
Strongly susceptible to fadingMobile communicationWidely used in general.
Mobile phone / PHS base station
Mobile phone / PHS mobile station
Mobile phones and PHS mobile stations (terminals) have two or more antennas, and preferentially use the antenna with the better radio wave condition, which is widely adopted to improve the stability of calls.
It is said that if the two antennas are separated by more than 2/1 wavelength, there is no correlation between the reception status of each antenna...By the way, NTT DoCoMo's mobile phone "MOVAIs used by800MHz bandIn the case of, the 1/2 wavelength is about 18 cm, which does not satisfy the above conditions, but it has been reported that the correlation is actually low due to imperfections..
The antenna of a mobile phone or PHS is usually one that can be seen from the outside of the terminal housing (however, in recent years, there are many cases where all of them have multiple built-in antennas that cannot be seen from the outside), but there are multiple sub-antennas inside the main body. Some are.
For example,NTT DoCoMoMobile phone "MOVA"Has two antennas in the main body.CDMAWith technology-based mobile phonesLake receptionAs a result, the same effect as diversity can be obtained, so only one antenna is required.
- Radio control carDiversity antennas are also beginning to be used in the field of.
- Futaba Electronics IndustryHas released receivers using diversity (R603FS, R604FS, R604FS-E).
- Car AudioIs adopted to reduce multipath noise when receiving FM broadcasts and to switch to an antenna with good radio wave conditions for reception.AlsoIn-vehicle TVThen noiseGhost disorderMany models use diversity antennas to suppress the occurrence of noise and obtain stable audio and video.
- ^ References: Second-class land radio engineer exam questions 20092
- ^ References: Basics of Mobile Communication (Published by the Institute of Electronics, Information and Communication Engineers)
- ^ References: Tsunekawa, Kagoshima, Diversity characteristic analysis of horizontally arranged dipole antennas on a small housing, credential theory, J75-B-II, No. 9 (1992.9) pp.629-637