Diversity technology

According to signal theory principle, if there are other attenuation extent of the original copy provide sends a signal receiver, conduce to the correct decision received signal. This by providing signals multiple transcripts to increase rate of received signal correct judgment method called diversity. Diversity technology is designed to compensate for the loss of fading channel, it usually use wireless transmitting environment the same signal independent sample between unrelated features, the use of certain signal merger technology improve receiving signals, to resist decay caused adverse effects. Spatial diversity means it can overcome space selective decline, but the diversity of the distance between the receiver should satisfy more than 3 times the wavelength of fundamental conditions.

Diversity technology is introduced

Decline effect is the effect of wireless communication quality one of the main factors. One of the fast fading depth can amount to 30 ~ 40dB, if want to use increase transmission power, increasing antenna dimension and height to overcome this method such as deep decay is unrealistic, and will cause damage to other radio interference. And use diversity method, in several branch receives minimal correlation between the carrying the same message signal, and then through mergers technology will each branch again merge output signal, then can in the receiving terminal greatly reduce the probability of deep decline. The corresponding still need to adopt the diversity in the influence of receiving technique alleviate decline to obtain diversity gain, improve rx sensitivity, this technology has been widely used in mobile communication, including the shortwave communication channel with and etc. In the second and third generation mobile communication system, these diversity receiving technique has been widely used.

Diversity technology research significance

In actual mobile communication system, mobile station buildings in cities usually work or other complicated geographical environment, and move speed and direction is arbitrary. A signal sent by a passes reflection, scattering of propagation paths, arrive after receiving the signal amplitude and phase is often more different signal of superposition, make received signal amplitude appears random fluctuation, forming multipath fading. Different paths of signal components with different propagation delay, phase and amplitude, and additional have channel noise, they will make the superposition of composite signal mutual offset or strengthening, cause serious decline. The decline will reduce the availability of the useful signal power and increase interference effects, resulting in the received signal receiver, waveform distortion caused the detuning, waveforms overlap and distortion, even cause communication system modem output errors, or even completely to be a massive cannot communications. In addition, if receiver transmitter or a mobile state, or channel changing environment, can cause channel properties with random time change, received signals due to the doppler effect will produce more serious distortion. In actual mobile communications, in addition to the multipath fading outside and shadow decline. When a signal is tall buildings (such as mobile platform moves to the deviation of the base building before) or terrain ups and downs etc preventing, received signal amplitude will decline. In addition, weather conditions change also influence the signal transmission, make received signal amplitude and phase change. These are mobile channel unique characteristic, it gives a mobile communication brings adverse effects.

In order to improve the performance of mobile communication system, can use diversity, balanced and channel coding the three technology to improve received signal quality, both can be used alone, also can be combined.

The basic principle of diversity technology

The basic principle of diversity is through multiple channels (time, frequency or space) receives bearing the same information multiple copies, because the transmission properties of multiple channels are different, the decline of the signal multiple copies will never be the same. Receiver using multiple copies of information contained can compare the correct recovers original signalling. If does not use the diversity technology, the noise limited conditions, the transmitter must send the higher power, ability assures channel circumstance in weak link normal connection. In the mobile wireless hand-held terminals environment, because the battery capacity is very limited, so backward link will get the power was also limited, and use diversity method can reduce transmission power, in the field of mobile communication is very important.

Diversity technology includes two aspects: one is scattered transmission, make the receiver can get many statistics independent, carrying the decline of the same information signal, 2 it is processed centrally, namely the receiver receive many statistics independent declined signal merger in order to reduce the influence of decline. Therefore, to obtain the most important condition for diversity effect between various signal should be "irrelevant".