MIMO wireless technology Overview

I believe many of my friends have heard of MIMO wireless technology, which marks the 802.11n technology. Its Reference improves the existing network performance, increases the throughput, and increases the capacity. The principles of this document are described in detail.

A mimo (Multiple-InputMultiple-Out-put) system is a technology used for 802.11n. 802.11n is the next generation 802.11 standard and can increase throughput to 100 Mbps. At the same time, the proprietary MIMO wireless technology can improve the performance of the existing 802.11a/B/G network. This technology was first proposed by Marconi in 1908. It uses multiple antennas to suppress channel fading. MIMO can also include SIMO (Single-InputMulti-ple-Output) system and MISO (Multiple-InputSingle-Output) system.

MIMO wireless technology Overview

MIMO indicates multiple inputs and multiple outputs. Read/maimo/or/mimo/. Generally, the former is American, the former is British, and more experts in this field read/maimo /. It is usually used for IEEE802.11n, but can also be used for other 802.11 technologies. MIMO is sometimes called space diversity because it uses multi-space channels to transmit and receive data. MIMO can be deployed only when the site mobile devices) or access point AP (AP) Support MIMO.

MIMO can increase the wireless range and improve the performance. The 802.11n site connected to the old 802.11g access point can connect to farther distances at a higher speed. For example, if you use an old site, the connection speed from 25 feet to the access point is 1 Mbps, and the site speed is 2 Mbps when you use 802.11nMIMO. Increased to 2 Mbps, allowing users to maintain connections at a further distance.
When a radio signal is reflected, multiple signals are generated. Each signal is a spatial stream. The current or old system that uses single-input, single-output, and single-output SISO can only send or receive one space stream at a time. MIMO allows multiple antennas to send and receive multiple spatial streams at the same time. It allows the antenna to transmit and receive data simultaneously.

The old Access Point sends and receives only one space stream to the old client.

MIMO access point to MIMO client-send and receive multiple spatial streams at the same time.

We can see that the channel capacity increases linearly as the number of antennas increases. That is to say, the MIMO channel can be used to increase the capacity of the wireless channel exponentially. without increasing the bandwidth and antenna transmission power, the spectrum utilization can be doubled.

MIMO wireless technology can improve the channel capacity, improve the channel reliability, and reduce the error rate. The former uses the space multiplexing gain provided by the MIMO channel, and the latter uses the space diversity gain provided by the MIMO channel. The algorithms that implement the Space multiplexing gain mainly include Bell's BLAST algorithm, ZF algorithm, KNN algorithm, and ML algorithm. The ML algorithm has good decoding performance, but the complexity is relatively large. Wireless Communication with high real-time requirements cannot meet the requirements. The ZF algorithm is simple and easy to implement, but it requires a high signal-to-noise ratio of the channel. The optimal performance and complexity are the BLAST algorithm. This algorithm is actually obtained by using the ZF algorithm and interference deletion technology. At present, another hot topic in MIMO wireless technology is empty-time encoding. Common empty time codes are block codes and empty time periods. The main idea of empty time code is to use space and time Encoding to implement certain spatial and time diversity, thus reducing the channel bit error rate.

Generally, multi-path fading is considered a harmful factor. However, the results show that multi-path routing can be used as a favorable factor for MIMO systems. The MIMO system uses multi-antenna (OR array antenna) and multi-channel at the transmitting end and receiving end. The multi-input and multi-channel MIMO wireless technology is designed for multi-path wireless channels. Transmitting information stream s (k) is encoded to Form N information substreams ci (k), I = 1 ,......, N. The N sub-streams are transmitted by N antennas, and received by M receiving antennas after passing through spatial channels. Multi-antenna receivers can separate and decode these data substreams using advanced space-time Encoding to achieve optimal processing.

In particular, the N substreams are sent to the channel at the same time, and each transmit signal occupies the same band, so the bandwidth is not increased. If the channel response between the transmitting and receiving antennas is independent, the multi-incoming and multi-output systems can create multiple parallel spatial channels. Through these parallel spatial channels, information is transmitted independently, and the data rate will inevitably increase.

MIMO wireless technology regards multi-path wireless channels and transmitting and receiving as a whole for optimization, so as to achieve high communication capacity and spectrum utilization. This is a kind of diversity and Interference Cancellation processing that is close to the optimal joint in the airspace time domain.

System capacity is one of the most important indicators of the communication system, indicating the maximum transmission rate of the communication system. For a multi-input multi-output MIMO system with N antennas and M antennas, assume that the channel is an independent channel with a large number of N and M, the channel capacity C is similar to: C = [min (M, N)] Blog2 (p/2 ).

Where B is the signal bandwidth, p is the average signal-to-noise ratio of the receiver, min (M, N) is M, and N is smaller. The above formula indicates that, when the power and bandwidth are fixed, the maximum capacity or capacity ceiling of the multi-entry multi-output system increases linearly with the increase of the minimum number of antennas. Under the same conditions, the capacity of an ordinary smart antenna system that uses multiple antennas or antenna arrays at the receiving end or transmitting end increases only with the increase of the number of daily lines. Relatively speaking, the multi-Inbound and multi-outbound traffic has great potential to increase the capacity of the wireless communication system.