Many antennas,[1] is a smart antenna technique, which overcomes the performance limitation of single user multiple-input multiple-output (MIMO) techniques. In cellular communication, the maximum number of considered antennas for downlink is 2 and 4 to support 3GPP Long Term Evolution (LTE} and IMT Advanced requirements, respectively. Since the available spectrum band will probably limited while the requirement of data rate will continuously increase in beyond IMT-A to support the mobile multimedia services, it is highly probable that the number of transmit antennas at the base station must be increased up to 8–64 or more. The installation of many antennas at single base stations can have many challenges so it requires to develop several high technologies: new SDMA engine, new beamforming algorithm and new antenna array.
The table summarizes the recent history of multiple antenna techniques in cellular communications. The table includes the future prediction as well for IMT-A and beyond.
| Standards | WCDMA | HSDPA | LTE | IMT Advanced |
|---|---|---|---|---|
| Deployment | 2003 | 2006 | 2012 | 2015 |
| Peak rate (bit/s) | 384 k | 14 M | 100–320 M | 1 G |
| Bandwidth (MHz) | 5 | 5 | 20 | 40–100 |
| Tx antennas in a macro-cell | 2 | 2 | 2–4 | 4–8 |
| Paradigm | Reliability | Data rate | Peak rate | Average rate |
| Spatial processing | Spatial diversity: circuit | Spatial diversity: packet | Spatial multiplexing (2–4) | Spatial division (2–4) |