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Multiple antennas raise the speed
Today's mobile networks will soon reach their upper limit, but by using multiple antennas, further development becomes possible. This antenna technology is also part of the 3G Long Term Evolution.
October 17, 2006
The Multiple Input Multiple Output (MIMO) technology uses two or more antennas at both the base station and the terminal. The idea is to significantly raise the transmission speed by sending information over multiple channels.
A number of research projects is ongoing, some of which are financed by money from the European Union. The WINNER project, which started in 2004 with members from the entire mobile industry, has just finished its first basic phase, and MIMO is also part of the WCDMA Evolved and the 3G Long-Term Evolution (LTE) standardization projects in 3GPP for the future of mobile networks.
At CTIA Wireless 2006 in April, Ericsson demonstrated MIMO with two antennas giving more than 20Mbps in the downlink, which is roughly twice as much as today's 3G HSPA (High Speed Packet Access).
Sören Andersson, manager for antenna systems and propagation at Ericsson Research, says that 3G LTE should preferably be able to handle four antennas in the base station and two - or sometimes four - in a terminal (or laptop).
Ericsson works actively in the 3GPP research but also studies MIMO internally, both for HSPA using 5MHz channels and for the coming 3G LTE networks with 20MHz bandwidth and modulation technology OFDM (Orthogonal Frequency Division Multiplex) - which is used today in WiFi (WLAN), digital TV, and WiMAX.
"We are building a test system with real antennas, a real base station, and mobile prototypes," Andersson says. "The important area to address from a research perspective is to understand the performance impact of different ways to take advantage of polarization features and the number and the sizes of the antennas. Further on we will also need to tackle issues like site installations of more antennas than today and finding enough space in the terminals for more antennas."
This is not easy to solve, because already a mobile has two or three built-in antennas: one for each mobile frequency, one for Bluetooth, and sometimes one for WLAN. With MIMO, this would be at least doubled.
| Fact box The question is how to use multiple antennas at both the base station and the terminal in the most efficient way. Each mobile is treated as an individual and must constantly report its signal status to the base station so that it uses both the right transmission technique and speed. Multiple parallel data stream transmissions works best over shorter distances where the signals are strong, so the system has to know when it can use multiple streams transmission for each terminal. At further distances, the transmission from the base station should use other techniques to optimize performance, e.g. some diversity transmission technique where only one data stream is sent from the several antennas at the base station to be received by the multiple antenna terminal. |
