Smart Antenna

JasonYoo

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　Key technologies of TD-SCDMA - Smart antennas
Smart antennas are bidirectional antennas installed at the base station site, which
obtain directivity through a group of fixed antenna units with programmable electronic phase relationships. And the directional characteristics of each link between the base station and the mobile station can be obtained simultaneously. The high efficiency of TD-SCDMA smart antennas operating in TDD
mode is based on the symmetry of the wireless paths of the uplink and downlink (
the wireless environment and transmission conditions are the same). In addition, smart antennas can reduce both inter-cell interference and
intra-cell interference. These characteristics of smart antennas can significantly improve the spectrum efficiency of mobile communication systems.
In order to achieve the highest spectrum efficiency, the system design of TD-SCDMA, which combines smart antennas and joint detection, is moving towards
system optimization controlled by DSP. These two technologies have laid the foundation for the software optimization design of mobile communication systems.
And the application of TD-SCDMA smart antennas is effective for all 3G services.
Specifically, in the basic structure of the TD-SCDMA system, the smart antenna is composed of a concentric array of 8 antenna units
. The diameter of this array is 25cm. Compared with omnidirectional antennas, it can obtain 8dB gain. The principle is to arrange and excite a group of
antennas and corresponding transceivers in a certain way, and use the interference principle of waves to generate a strong
directional radiation pattern. Using the DSP method, the main lobe is adaptively pointed in the direction of the mobile station, so as to achieve
the purpose of improving the signal's carrier-to-interference ratio and reducing the transmission power. The above performance of smart antennas allows more intensive frequency reuse, which
significantly improves the spectrum efficiency.
A major feature of CDMA technology is that most user signals can be transmitted in parallel at the same time and on the same carrier.
However , considering that among the mobile wireless multi-point-to-point users, each user has a different location in the cell.
On the one hand, this requires the antenna to be multi-directional, and on the other hand, it requires that each independent directional system must
be able to .
The above requirements can be achieved by controlling the user's directional measurement through DSP, and it allows a large number of independent users to be
calculated . The tracking of each user is measured by the arrival angle. In the TD-SCDMA system, since the length of the wireless subframe is
5ms, it can be measured at least 200 times per second. The uplink and downlink transmissions of each user occur in the same direction. Through the directivity and tracking of smart antennas
, its best performance can be obtained.
A further advantage of TD-SCDMA in TDD mode is that both the transmission and reception of user signals occur at exactly the same frequency
. Therefore, the directional smart antenna presents exactly the same bidirectional antenna pattern, so the transmission conditions in both directions
are identical or symmetrical. The symmetry (TDD) enables the smart antenna to minimize inter-cell interference, thereby
achieving optimal system performance.
The higher spectrum utilization achieved by smart antennas allows the number of base stations required in high-traffic density cities and urban areas to be
correspondingly lower. In addition, in rural areas with sparse traffic, the directionality of smart antennas can
double the wireless coverage. The increase in wireless coverage reduces the number of base stations required to
one-fourth of the usual number in wide areas covered by major services.
Therefore, the use of smart antennas in TD-SCDMA is an important part of the design of highly economical systems, which can reduce operators' investments and
increase their economic benefits. The advanced design of TD-SCDMA technology with smart antennas, joint detection and adaptive wireless resource allocation capabilities with symmetric and asymmetric services
is an important step towards software radio.

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N array antennas. The signal received by each array element is S(t)*exp(jnu). When the corresponding weighted value is exp(-jnu), the output Y is N*S(t). If noise filtering is considered and an adaptive algorithm is used, should the reference signal be N*S(t) or S(t)?