Radio frequency beamforming technology improves TD-LTE cell edge performance

Since long ago, multi-antenna technology has been used in mobile wireless systems. In the early period of base station transmission and vehicle mobile station reception, multi-path propagation in large cell network topology will produce selective fading, thus affecting signal quality, especially in urban areas. The problem is more serious. The previous approach was to use base station transmission and vehicle receiver antenna diversity to solve this problem. As mobile phones become smaller and smaller, in-vehicle communication devices begin to adopt Bluetooth audio connectivity technology after simplification, and receive diversity in mobile devices has gradually been eliminated. However, this trend will soon change: the latest wireless LAN implementation uses multiple antenna spatial streams, which can increase the transmission bandwidth and speed. With the advent of low-cost hardware implementing this advanced technology, the first released 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard, especially its TDD (Time Division Duplex) version, has proposed and implemented various multiple antennas technology.

Again, the basic wireless channel uses a single-transmit and single-receive antenna, called SISO (single input single output). This simple wireless channel sets the benchmark for signal transmission performance, on which all more complex transmission configurations can be measured. SIMO (Single Input Multiple Output) provides greater receive antenna redundancy than the SISO benchmark and supports the use of receive diversity techniques in the receiver, such as maximum ratio combining. This can improve the SINR observed on the device receiver and help improve performance under channel fading conditions. MISO (Multiple Input Single Output) provides transmit antenna redundancy. As in the case of LTE, it supports the use of transmit diversity techniques such as AlamouTI symbol coding or space frequency block coding (SFBC). Like SIMO, this can also improve the SINR observed on the device receiver and can help provide protection against channel fading. Neither SIMO nor MISO can improve the data throughput, but they can reduce the bit error rate, thereby reducing the amount of data that needs to be retransmitted.

MIMO (Multiple Input Multiple Output) provides additional transmit and receive antenna redundancy. If the same data is sent to the transmit antenna, this redundancy can be used to improve the SINR on the device receiver using the same transmit and receive diversity techniques described above, or some or all of the possible SINR performance improvement can be sacrificed in order to obtain higher Spectral efficiency. Spatial multiplexing transmission technology (using a transmission antenna to send independent data streams) can provide a single user with higher data throughput (SU-MIMO or single-user MIMO), or increase the system cell capacity (MU-MIMO or multi-user) MIMO).

In addition to these diversity and spatial multiplexing techniques, multiple antenna configurations can also be used to focus transmission or reception in a specific direction. This technique is called beamforming. Depending on the specific application, fixed beamforming or variable beamforming can be used and can improve system performance. Beamforming technology can be used in many different frequency applications, including sonar and seismology, acoustics, wireless communications, radio astronomy, and radar.

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