What Kind of Technology?
A conventional wireless communications system cannot easily transmit multiple signals on the same frequency at once due to wave interference. Not only does this make it difficult to use frequency resources effectively, for enhanced efficiency, but it also limits wireless transmission speed itself.
A MIMO (Multiple-Input, Multiple-Output) communications system employs multiple antennas at both the transmitter and receiver ends, and uses spatial multiplexing to enable different signals to be sent on the same frequency concurrently. As Figure 1 shows, MIMO communication takes advantage of the way radio waves bounce off building walls and floors on their way to their destination.
Broadly speaking, there are three types of MIMO technology as shown in Figure 2.
Type (a) : This Technique is regarded as the most basic method, but requires some means of removing interference at the receiving end, as well as needing complex signal processing in terminals to realize high performance.
Type (b) : Here Antenna Directivity is controlled in advance in the transmitter (beam-forming), reducing the load on terminals. With this method, the important factor is how this beam-forming is implemented in the transmitter.
Type (c) :A further extension of type (b) is type (c), Multiuser MIMO (MU-MIMO), technology enabling communication with multiple terminals.
Compared to types (a) and (b), which can be referred to as single-user MIMO or SU-MIMO in distinction from the multiuser type, MU-MIMO achieves higher transmission capacity in the system as a whole with simple terminals.
Going from (a) to (b) to (c), however, the technological hurdles become progressively higher. There are many issues to be resolved in realizing MU-MIMO systems, but at the NTT Network Innovation Laboratories, not only for enhancing the speed of wireless communications but also from the standpoint of larger capacity (increasing the number of multiple concurrent accesses).
The number of antennas that can be implemented on user terminals is limited by size and cost issues. In conventional MIMO technology, no matter how much functionality is built into base stations, this limitation on user terminal antennas prevents further increases in transfer rate. Multiuser MIMO, by exchanging signals with multiple user terminals at the same time, makes simultaneous use of the antennas of multiple users. The result is the formation of virtual large-scale MIMO channels, thanks to the large number of antenna elements in base and terminal stations. Compared to conventional single-user MIMO, a significant increase in transmission speed should be realized for the system as a whole.
What Does the Future Hold?
Multiuser MIMO technology makes it possible to raise wireless transmission speed by increasing the number of antennas at the base station, without consuming more frequency bandwidth or increasing modulation multiple-values. It is therefore a promising technology for incorporating broadband wireless transmission that will be seamlessly connected with wired transmission in the micro waveband (currently used for mobile phones and wireless LAN, and well suited to mobile communications use), where frequency resources are in danger of depletion. Since it also allows multiple users to be connected simultaneously, it is seen as a solution to the problem specific to wireless communications, namely, slow or unavailable connections when the number of terminals in the same area increases (see Figure 9).
For More details, please see the Link
A conventional wireless communications system cannot easily transmit multiple signals on the same frequency at once due to wave interference. Not only does this make it difficult to use frequency resources effectively, for enhanced efficiency, but it also limits wireless transmission speed itself.
A MIMO (Multiple-Input, Multiple-Output) communications system employs multiple antennas at both the transmitter and receiver ends, and uses spatial multiplexing to enable different signals to be sent on the same frequency concurrently. As Figure 1 shows, MIMO communication takes advantage of the way radio waves bounce off building walls and floors on their way to their destination.
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| 4g-longtermevolution.blogspot.com |
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| 4g-longtermevolution.blogspot.com |
Type (b) : Here Antenna Directivity is controlled in advance in the transmitter (beam-forming), reducing the load on terminals. With this method, the important factor is how this beam-forming is implemented in the transmitter.
Type (c) :A further extension of type (b) is type (c), Multiuser MIMO (MU-MIMO), technology enabling communication with multiple terminals.
Compared to types (a) and (b), which can be referred to as single-user MIMO or SU-MIMO in distinction from the multiuser type, MU-MIMO achieves higher transmission capacity in the system as a whole with simple terminals.
Going from (a) to (b) to (c), however, the technological hurdles become progressively higher. There are many issues to be resolved in realizing MU-MIMO systems, but at the NTT Network Innovation Laboratories, not only for enhancing the speed of wireless communications but also from the standpoint of larger capacity (increasing the number of multiple concurrent accesses).
The number of antennas that can be implemented on user terminals is limited by size and cost issues. In conventional MIMO technology, no matter how much functionality is built into base stations, this limitation on user terminal antennas prevents further increases in transfer rate. Multiuser MIMO, by exchanging signals with multiple user terminals at the same time, makes simultaneous use of the antennas of multiple users. The result is the formation of virtual large-scale MIMO channels, thanks to the large number of antenna elements in base and terminal stations. Compared to conventional single-user MIMO, a significant increase in transmission speed should be realized for the system as a whole.
What Does the Future Hold?
Multiuser MIMO technology makes it possible to raise wireless transmission speed by increasing the number of antennas at the base station, without consuming more frequency bandwidth or increasing modulation multiple-values. It is therefore a promising technology for incorporating broadband wireless transmission that will be seamlessly connected with wired transmission in the micro waveband (currently used for mobile phones and wireless LAN, and well suited to mobile communications use), where frequency resources are in danger of depletion. Since it also allows multiple users to be connected simultaneously, it is seen as a solution to the problem specific to wireless communications, namely, slow or unavailable connections when the number of terminals in the same area increases (see Figure 9).
 |
| 4g-longtermevolution.blogspot.com |
For More details, please see the Link
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