In recent years, communication operators are competing to improve the status of wireless local area networks (WLANs), not only as an aid to wired broadband access, but also to raise them to strategic heights, and to improve the network quality and user experience of wireless local area networks. focus. This article introduces you to one of the key technologies of wireless LAN - Beamforming, including basic concepts and trends.
Background origin
Beamforming is a combination of antenna technology and digital signal processing technology for directional signal transmission or reception. Beamforming is not a new term, but it is a classic traditional antenna technology. As early as the 1960s, array signal processing technology using antenna diversity reception was highly valued in electronic countermeasures, phased array radar, sonar and other communication equipment. The adaptive array interference zeroing technology based on digital beamforming (DBF) can improve the anti-interference ability of the radar system, and is a key technology that must be used in the new generation of military radar. The positioning communication system acquires the sound field information through the microphone array, and uses the beamforming and power spectrum estimation principles to process the signal to determine the direction of the signal, so that the source can be accurately oriented. However, because semiconductor technology was still in the micron class in the early years, it did not play an ideal state in civilian communications.
In the WLAN phase, especially in personal communications, signal transmission distance and channel quality, as well as anti-interference problems in wireless communications, have become bottlenecks. Supporting high throughput is the key to the development of WLAN technology. 802.11n mainly combines the optimization of the physical layer and the MAC layer to fully improve the throughput of WLAN technology. At this point, beamforming has come into play.
Fundamental
Beamforming is derived from a concept of adaptive antennas. The signal processing at the receiving end can be weighted and synthesized by each signal received by the multi-antenna array element to form a desired ideal signal. From the perspective of the antenna pattern, this is equivalent to forming a beam on a prescribed direction. For example, the original omnidirectional reception pattern is converted into a lobe pattern with zero points and maximum pointing. The same principle applies to the transmitter. Amplitude and phase adjustment of the antenna element feed can form a pattern of the desired shape.
If beamforming is to be used, the premise is that a multi-antenna system must be used. For example, multiple input and multiple output (MIMO), not only multiple receive antennas, but also multiple transmit antennas. Since multiple sets of antennas are used, the wireless signals from the transmitting end to the receiving end correspond to the same spatial stream (spaTIal streams), which are transmitted through multiple paths. At the receiving end, a certain algorithm is used to process the received signals of multiple antennas, so that the signal-to-noise ratio of the receiving end can be significantly improved. Better signal quality is achieved even at the receiving end.
MIMO can greatly increase network transmission rate, coverage and performance. When multiple independent spatial streams are simultaneously transmitted based on MIMO, the throughput of the system can be multiplied. The number of spatial streams supported by a MIMO system depends on the minimum of the transmit and receive antennas. If the number of transmit antennas is 3 and the number of receive antennas is 2, the supported spatial stream is 2. In the market, after three years of 3 & TImes; 3 mode of mass production run-in period, this year's 4X4 model emerged, immediately attracted the attention of the industry.
Application examples
This article lists a 4x4 three-space stream 802.11n solution.
Marvell this year released the Avastar series that supports 4x4-3SS Wi-Fi 802.11n performance. This will significantly improve the performance of notebooks, desktops, tablets, smartphones, e-readers, printers, routers, set-top boxes, HDTVs, gaming devices, DVD players and more. Its beamforming technology greatly improves the link durability between 1x1- 4x4 MIMO products and legacy devices. Take the dual-frequency access hotspot (AP) as an example. It has the following features:
Performance up to 450 Mbps data rate
Support for 802.11n technical specifications
Support for 802.11ac technical specifications
Implemented by digital signal processing DSP, no additional special hardware required
Beamforming is not necessarily supported, but with it, especially when both ends are supported, the gain is maximized.
Efficient power management module for low power consumption
Bluetooth technology and multiple wireless coexistence states, reducing mutual interference between Wi-Fi and Bluetooth simultaneously
work process
What is the working process of beamforming? Taking a hotspot as an example, the base station periodically sends an acoustic signal to the client, and the client feeds back the channel information to the base station, so that the base station can send the steering data packet to the client according to the channel state. The high-speed data calculation process gives an indication of the complex shape, the gain in the direction of the client is strengthened, the pattern is shaped, and the transmission distance in the corresponding direction is also increased. If the AP uses 4 sets of transmit antennas 4x4 three sets of spatial streams, it can obtain larger spatial diversity gain based on the gain obtained by multiple antennas.
From the structure and settings, beamforming supporting the 802.11n standard can be divided into two categories: explicit beamforming and stealth beamforming. Explicit beamforming is set up on both the AP and the client, greatly increasing the distance and link durability. The advantage of recessive beamforming is that the client does not need to do the corresponding processing, and the device implementation is relatively simple, which also helps to increase the distance and durability.
Taking the hot spot of the dominant beamforming as an example, the wireless LAN signal transmission process starts like this:
Continuous handshake between the base station and the client (sending acoustic signals, channel matrix feedback)
The client feeds back channel information to the hotspot
The hotspot sends a complex data packet to the client according to the channel state information, and strengthens the strength of a client direction.
This gives the spatial diversity gain + transmit array gain (this is related to the number of transmit antennas)
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