Hello Mi Fans,
Hope you guys are having loads of fun here on Mi Community.
In this "Tech Class," we will take you through the topic - MIMO Technology and much more. So let's get started.
MIMO (Multiple Inputs, Multiple Outputs) is an antenna technology for wireless communications in which multiple antennas are used at both the source (transmitter) and the destination (receiver). The antennas at each end of the communications circuit are combined to minimize errors and optimize data speed. MIMO is one o the several forms of smart antenna technology, the others being MISO (Multiple Inputs Single Outputs) and SIMO (Single Input, Multiple Outputs).
In conventional wireless communications, a single antenna is used at the source, and another single antenna is used at the destination. In some cases, this gives rise to problems with multipath effects. When an electromagnetic field (EM field) is met with obstructions such as hills, canyons, buildings, and utility wires, the wavefronts are scattered, and thus they take many paths to reach the destination. The late arrival of scattered portions of the signal causes problems such as fading, cut-out (cliff effect), and intermittent reception (picket fencing). In digital communications systems such as wireless Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas, along with the transmission of multiple signals (one for each antenna) at the source and the destination, eliminates the trouble caused by multipath wave propagation, and can even take advantage of this effect.MIMO technology has aroused interest because of its possible applications in the digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications.
MIMO has become an essential element of wireless communication standards including IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi), HSPA+ (3G), WiMAX (4G), and Long Term Evolution (4G). More recently, MIMO has been applied to power-line communication for 3-wire installations as part of ITU G.hn standard and HomePlug AV2 specification.
At one time, in wireless, the term "MIMO" referred to the use of multiple antennas at the transmitter and the receiver. In modern usage, "MIMO" specifically refers to a practical technique for sending and receiving more than one data signal simultaneously over the same radio channel by exploiting multipath propagation. MIMO is fundamentally different from smart antenna techniques developed to enhance the performance of a single data signal, such as beamforming and diversity.
Invention of MIMO
Arogyaswami Paulraj and Thomas Kailath proposed an SDMA-based inverse multiplexing technique in 1993. Their US patent (No. 5,345,599 issued in 1994, described a method of broadcasting at high data rates by splitting a high-rate signal "into several low-rate signals" to be transmitted from "spatially separated transmitters" and recovered by the receive antenna array based on differences in "directions-of-arrival." Paulraj was awarded the prestigious Marconi Prize in 2014 for "his pioneering contributions to developing the theory and applications of MIMO antennas. ... His idea for using multiple antennas at both the transmitting and receiving stations – which is at the heart of the current high-speed WiFi and 4G mobile systems – has revolutionized high-speed wireless."
In an April 1996 paper and subsequent patent, Greg Raleigh proposed that natural multipath propagation can be exploited to transmit multiple, independent information streams using co-located antennas and multi-dimensional signal processing.The paper also identified practical solutions for modulation (MIMO-OFDM), coding, synchronization, and channel estimation. Later that year (September 1996) Gerard J. Foschini submitted a paper that also suggested it is possible to multiply the capacity of a wireless link using what the author described as "layered space-time architecture.
Greg Raleigh, V. K. Jones, and Michael Pollack founded Clarity Wireless in 1996, and built and field-tested a prototype MIMO system. Cisco Systems acquired Clarity Wireless in 1998.Bell Labs built a laboratory prototype demonstrating its V-BLAST (Vertical-Bell Laboratories Layered Space-Time) technology in 1998.Arogyaswami Paulraj founded Iospan Wireless in late 1998 to develop MIMO-OFDM products. Iospan was acquired by Intel in 2003. V-BLAST was never commercialized, and neither Clarity Wireless nor Iospan Wireless shipped MIMO-OFDM products before being acquired.
Applications of MIMO
Spatial multiplexing techniques make the receivers very complex, and therefore they are typically combined with Orthogonal frequency-division multiplexing (OFDM) or with Orthogonal Frequency Division Multiple Access (OFDMA) modulation, where the problems created by a multi-path channel are handled efficiently. The IEEE 802.16e standard incorporates MIMO-OFDMA. The IEEE 802.11n standard, released in October 2009, recommends MIMO-OFDM.
MIMO is also planned to be used in Mobile radio telephone standards such as recent 3GPP and 3GPP2. In 3GPP, High-Speed Packet Access Plus (HSPA+) and Long Term Evolution (LTE) standards take MIMO into account. Moreover, to fully support cellular environments, MIMO research consortia including IST-MASCOT propose to develop advanced MIMO techniques, e.g., multi-user MIMO (MU-MIMO).
MIMO technology can be used in non-wireless communications systems. One example is the home networking standard ITU-T G.9963, which defines a powerline communications system that uses MIMO techniques to transmit multiple signals over multiple AC wires (phase, neutral and ground).
MIMO Technology and Speed Internet
In the theoretical world, the biggest factor limiting speed is bandwidth. Each phone tower has a given total width of frequencies it can transmit on, with each person that connects being allocated a small channel of a certain width. This means that each tower has a limited number of customers it can serve before becoming congested. So the most obvious way to increase speed would be to give each customer a wider range of frequencies to transmit on, but this means fewer people per phone tower, which means building more phone towers, which is expensive!
Instead, the first step in increasing speed is to exploit the other factors aside from bandwidth. 3G technologies like HSPA take advantage of digital modulation techniques like Quadrature Phase Shift Keying (and many other tricks) to increase the symbol rate, which is the second major factor that limits speed. Speed is also limited by Signal-to-Noise ratio, to which we can increase the power (or loudness) of the transmission so the phone tower can 'hear' us better, but this results in quickly diminishing returns.
Once we've squeezed out all the performance we can from antenna-to-antenna transmission we have to approach the problem differently. This is where MIMO comes in to play - if we're unable to improve air transmission, why not increase the number of antennas?
By using multiple antennas we can forget about the difficulties in transmitting over the air and instead place the burden on the signal processing hardware in your modem. Because all the antennas transmit at the same frequencies, no extra per-user bandwidth is required from the phone tower. Spatial Multiplexing is a set of clever modulation techniques that allow us to transmit independent streams from multiple antennas on the same frequencies without garbling the information we send.
Normal 3G and 4G signals are broadcast vertically polarised, where the wave travels "up and down". LTE MIMO waves are slant polarised where each wave is rotated 45 degrees from the horizontal, mirrored so the first is at 45 degrees and the other at 135 degrees. This smart little trick is called polarisation diversity and allows your modem to distinguish two independent streams of data over the same frequency allocated by the cell tower because our modem has two internal antennas each responsible for receiving one stream of data, it is absolutely crucial we have two separate external antennas. We cannot use a 'Y' patch lead or some other trick to connect both ports of the modem into one antenna, nor can we connect both external antennas into one port.
It is important to know MIMO is switched on and off by the modem. The decision whether to use MIMO is negotiated with the cell tower, whereby the quality of the received and transmitted signals are assessed (a metric is known as CQI). When signal strength or quality is low it's difficult for the modem to distinguish between the two data streams, so when signal levels drop below a certain threshold level, MIMO is switched off and the modem operates with only one antenna (Port 1 on Sierra Wireless modems).
Technology is advancing. 3G & 4G all are now getting old as Snapdragon already started testing of 5G which is an advanced model developed from MIMO Technology and one of the great Device which is recently launched by Xioami in India named Mi Mix 2 supports lot of advanced technology based on MIMO Technology and I will Explain that in my next thread stay tuned......
Credits: Google Images, Wikipedia, Google
Special Thanks to Device Team Members and our Lead @paramgagan Sir
A Tech Class Recap
Class 6: Internet of Things & Mi Home
Class 7: (IR) Infrared Blaster
Class 8: CPU Architecture, CPU, GPU
Class 9: Megapixels and Photo Quality
Class 10: PDAF and its different with CDAF
Class 11: All About Network Bands
Class 12: All About Rooting
Class 13: All About kernel
Class 14: All you need to know about Wi-fi
Class 15: All CPU Cores
Class 16: All About TWRP
Class 17: All About RAM
Class 18: All About Memory Cards
Class 19: All About Data Cables
Class 20: All About Batteries
Class 21: All About Speakers
Class 22: All About Sensor
Class 23: All About Display
Class 24: All About Barcodes
Class 25: All About QR Codes.
Class 27: All You Need To Know About APN
Class 28: All About IP(Ingress Protection)Ratings
Class 30: All about USB Debugging
In order to fulfill the basic functions of our service, the user hereby agrees to allow Xiaomi to collect, process and use personal information which shall include but not be limited to written threads, pictures, comments, replies in the Mi Community, and relevant data types listed in Xiaomi's Private Policy. By selecting "Agree", you agree to Xiaomi's Private Policy and Content Policy .