MIMO
Technology Overview
Modern radiocommunications standards employ multiple antenna systems, also known as multiple-input multiple-output (MIMO) systems. The techniques increase either the signal-to-noise ratio or the data throughput for a defined resource, or both. In a MIMO system, different signals are transmitted from the antennas at the same time and frequency. There are three different concepts of multiple antenna systems:
- In the diversity mode, the same content is transmitted from the antennas with different coding (space-time coding). Diversity leads to an increase in the signal-to-noise ratio.
- Spatial division multiplexing refers to a system where different data streams are transmitted from the antennas. The different fading channels make it possible to distinguish between the data streams and thus increase the data rate.
- Beamforming is a technique where the signals are not transmitted omnidirectionally but where antenna arrays form a beam aimed toward each mobile phone. This reduces interference between subscribers. Beamforming is further in the future than diversity and multiplexing.
Rohde & Schwarz Supports MIMO Testing
Performance tests on MIMO receivers require not only a multiple vector signal generator but a multichannel fading simulator as well. The R&S® SMU200A vector signal generator can do all this in one box. For tests on a 2 x 2 MIMO receiver, two standard-conforming signals may be generated and four fading channels simulated. The same functionality is available for the R&S® AMU200A baseband generator and fading simulator.
For a complete test scenario, the analysis of MIMO signals is also necessary. The R&S® FSQ from Rohde & Schwarz offers MIMO functionality for LTE, WiMAX 16e, and WLAN 11n. The MIMO functionalities in the R&S® TS89xx conformance test systems are flexible and standard-conforming.
Standardization
MIMO is implemented in the following standards:
| MIMO Parameters in | WiMAX IEEE 802.16e-2005 | HSPA+ 3GPP Release 7 | LTE 3GPP Release 8 | WLAN IEEE 802.11n | UMB 1xEV-DO Rev C |
|---|---|---|---|---|---|
| Tx Diversity | Yes | Yes | Yes | Yes | Yes |
| DL Spatial Multiplexing | Yes | Yes | Yes | Yes | Yes |
| DL Beamforming | Yes | Yes | Yes | Yes | Yes |
| DL Precoding | Yes | Yes | Yes | Yes | Yes |
| DL Space Time Coding (STC) / DL Space Frequency Coding (SFC) | STC | - | SFC | STC | STC |
| UL Multi User MIMO / Collaborative MIMO | Yes | - | Yes | Yes | |
| Max Number of BS Antennas | 2 (8 partly for Beamforming) | 2 (4) | 4 | 4 | 4 |
| Max Number of MS Antennas | 2 (8 partly for Beamforming) | 2 | 2 (4) | 4 | 4 |
