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Anonymous users2024-02-07Diversity technology is a receiving technology in communication that can greatly improve the performance of wireless links with a low investment, and the transmitter does not need to send a training code, so it saves money.
Diversity is achieved by finding and exploiting independent multipath signals in an infinitely propagating environment in nature. The concept of diversity can be summarized simply as follows: if a signal in one wireless propagation path experiences deep fading, then a relatively independent path may contain a stronger signal.
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Anonymous users2024-02-06The basic principle of diversity is that multiple copies carrying the same information are received over multiple channels (time, frequency, or space), and the fading of multiple copies of the signal will not be the same due to the different transmission characteristics of multiple channels. The receiver uses multiple copies of the information contained in it to recover the original transmitted signal more correctly. If diversity technology is not used, the transmitter must send higher power under noise-constrained conditions to ensure that the link is connected normally when the channel condition is poor.
In the mobile wireless environment, the power that can be obtained in the reverse link is also very limited due to the very limited battery capacity of the handheld terminal, and the diversity method can reduce the transmit power, which is very important in mobile communications. Figure 2 Diversity technique.
Diversity technology includes two aspects: one is decentralized transmission, which enables the receiver to obtain multiple statistically independent fading signals carrying the same information; The second is centralized processing, that is, the multiple statistically independent fading signals received by the receiver are combined to reduce the impact of fading. Therefore, the most important condition for the diversity effect is that the individual signals should be "uncorrelated".
Diversity refers to a technical measure to transmit the same information in two or more ways in order to mitigate the effects of decline. Diversity technology includes diversity sending technology and diversity receiving technology, from the type of diversity, the most used are spatial diversity and frequency diversity, in addition, there are the following:
The combination of spatial diversity and frequency diversity, that is, the sending station sends the same information at two frequencies, and the receiving station receives signals of different frequencies with two vertically separated antennas, and then synthesizes or selects, which is called hybrid diversity. In addition, there are site diversity, time diversity, angle diversity, etc.
Due to the harsh propagation environment, the microwave signal will produce deep fading and Doppler shift, etc., which will cause the reception level to drop to near the thermal noise level, and the phase will also change randomly with time, resulting in the degradation of communication quality. In this regard, the diversity receiving technology is used to reduce the impact of fading, obtain the diversity gain, and improve the receiving sensitivity.
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Anonymous users2024-02-05Diversity is used to compensate for fading channel loss, and it is usually achieved by two or more receiving antennas. Like equalizers, it improves the transmission quality of wireless communication channels without increasing transmission power and bandwidth. In mobile communications, diversity technology can be used in both base station and mobile station receivers.
Diversity is a method in which the fading characteristics received by the receiver are specifically processed independently of each other in order to reduce the fluctuation of the signal level. Diversity refers to decentralized transmission and centralized reception. The so-called decentralized transmission enables the receiving end to obtain multiple statistically independent fading signals carrying the same information.
Centralized reception is the receiver to merge (select and combine) multiple statistically independent fading signals received to reduce the impact of fading. According to the principle of signal theory, if a copy of the original transmitted signal with other degrees of attenuation is provided to the receiver, it will help to make the correct judgment of the received signal. This method of increasing the correct verdict rate of a received signal by providing multiple copies of the transmitted signal is known as diversity.
Diversity technology is used to compensate for fading channel loss, which usually takes advantage of the uncorrelated characteristics between independent samples of the same signal in the wireless propagation environment, and uses a certain signal merging technique to improve the received signal to resist the adverse effects caused by fading. Spatial diversity can overcome spatially selective fading, but the distance between diversity receivers must meet the basic condition of greater than 3 times the wavelength.
In the actual mobile communication system, the mobile station often works in urban buildings or other complex geographical environments, and the speed and direction of movement are arbitrary. After the transmitted signal passes through the propagation path of reflection and scattering, the signal arriving at the receiving end is often the superposition of multiple signals with different amplitudes and phases, so that the amplitude of the received signal fluctuates randomly, forming a multipath fading. The signal components of different paths have different propagation delays, phases, and amplitudes, and are accompanied by channel noise, and their superposition will cancel out or enhance the composite signals, resulting in severe fading.
This fading reduces the available useful signal power and increases the impact of interference, resulting in distortion, waveform broadening, waveform overlap and distortion of the receiver's received signal, and even a large number of errors in the output of the communication system's demodulator, to the point that communication is not possible at all. In addition, if the transmitter or receiver is in a moving state, or if the channel environment changes, the channel characteristics will change randomly over time, and the received signal will be more severely distorted due to the Doppler effect. In actual mobile communications, there is shadow fading in addition to multipath fading.
When the signal is blocked by tall buildings (e.g., a mobile station moving in front of a building that is moving away from the base station) or undulating terrain, the amplitude of the received signal decreases. In addition, changes in meteorological conditions also affect the propagation of signals, resulting in changes in the amplitude and phase of the received signals. These are unique features of mobile channels, which have a negative impact on mobile communications.
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Anonymous users2024-02-04At present, there are two main types of diversity methods commonly used: macro diversity and differential diversity.
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