MIMO: using multi-dimensional Transmission solutions to increase transmission capacity (1)

MIMO technology can greatly improve the coverage range and transmission rate of WLAN.

When multimedia applications with low latency and high bandwidth requirements, such as home broadband network connections and real-time HDTV wireless communication, and applications with scattered and shared content for entertainment devices become more and more common, wireless communication technology is also required to improve its efficiency under the condition of limited spectrum.

We need technology that can transmit high-quality signals at a higher speed, and this technology does not use extra band bandwidths. Multi-input, multi-output, and multi-output (MIMO) technologies are the solutions to overcome the challenges of wireless communication, such as signal fading, increased interference, and limited spectrum. Without occupying more bandwidth, it not only doubles the transmission rate, but also increases the transmission range and stability.

A multi-dimensional transmission solution

MIMO is a technology that can send and receive two or more data streams in a single RF channel. It uses a multi-dimensional transmission scheme: one single RF channel is used to send and receive two or more signal streams. As a result, the wireless communication system can transmit data twice or more in a channel. In the system, use more than one high-integration RF upconverter) and antenna to transmit these multiple signals, and there is also more than one high-integration RF downconverter) and the antenna to receive these multiple signals. Using MIMO technology, the maximum data transmission rate of each channel will linearly increase with the number of different data streams transmitted in the channel.

Because of its ability to transmit multiple data streams at the same time, MIMO can multiply the transmission capability of wireless signals without the need for additional spectrum. The peak transmission rate (peakthroughput) of the MIMO system increases with the number of data streams transmitted in the microwave channel, because multiple signals are transmitted in different antennas and channels, MIMO signals are also called "multi-dimensional signals" multi-dimensionalsignal ).

In addition to doubling the signal rate in the same channel, the well-designed MIMO system can also increase coverage and stability by means of high-frequency spectral efficiency and higher remote transmission rate throughput-at-range. MIMO system improves the "effective transmission rate" effectivethroughput, and the transmission rate measured from a specific distance from the transmitter) compared to the "peak transmission rate" peakthroughput, which is measured from a very close location to the transmitter) independent tests show that a well-designed WLANMIMO system can increase the effective coverage by eight times and the effective transmission rate by six times.

MIMO is not an ordinary Smart Antenna System

Other multi-antenna transmission and receiving technologies are often confused with MIMO technologies, including transmitting beam forming transmitterbeam-forming) and receiving diversity receiverdiversity ). Although this type of technology can improve the coverage of the traditional radio element signal, it is also very suitable for outdoor point-to-point link wirelessbackhaul and other specific applications, but they still cannot achieve the real MIMO system to multiply the transmission capacity.

Although beam can provide a wider transfer range for some applications, some of its serious negative factors cannot be ignored, for example, the number of hidden nodes, the number of terminal devices that can be supported will be reduced, and the number of RF transmitter will be limited under the high power consumption limit.

Next, let's look at the antennadiversity solution. In order to receive the strongest signal and improve reliability, the Diversity antenna switches between several antennas, but since there is no additional signal processing, the signal quality has not changed. The receiving and merging technology is similar. Although it can process signals through multiple antennas, due to signal attenuation and multi-path reflection, this technology cannot increase the data transmission rate or transmission capacity.

Other technologies that will be confused with MIMO include data compression datacompression and RF channel consolidation radiochannelcombining ). In most network applications, the data compression technology does not actually increase the data transmission rate, while the information collection technology is in many countries, such as Japan) the band is not open and cannot be used legally. Another problem with the channel consolidation technology is that it may interfere with other network devices in the same network, which will negatively impact neighboring wireless networks, it is often regarded as a "bad neighbor" technology to consolidate information.

Unlike the channel consolidation technology, MIMO can achieve a higher data transmission rate without increasing the number of RF channels, MIMO has downward compatibility and interoperability with other devices, and does not interfere with other networks.

How MIMO works

Figure 3 illustrates how MIMO works: 1. the MIMO system divides a data stream into several data streams. 2. each data stream is modularized. 3. it is transmitted through different RF antenna chains in the same frequency channel at the same time; 4. after multi-path reflection, each receiving antenna RF chain has multiple linear convergence of transmission data streams; 5. the MIMO algorithm is used in the receiver to separate these data streams. The algorithm is used to estimate all channels between each transmitter and the receiver.

Each multi-path route can be considered an individual channel that creates multiple "virtual lines" and can be used to transmit signals. Multiple spacious separated antennas of MIMO can take full advantage of the virtual line created by multi-path and transmit more data. In addition to doubling the transmission rate, the transmission range can be increased because each receiving antenna computes individual transmitted data streams, which is also an advantage of antenna diversity.