With the rapid growth of wireless data traffic, now greatly exceeding voice traffic in many developed markets, operators are anxious to quickly expand the capacity and coverage of their wireless networks. To address these demands for increased capacity in a cost effective way, 3GPP standards have incorporated powerful techniques for using “smart antennas.”
“The gains in spectral efficiency being advanced by new wireless air interface technologies, such as LTE and LTE-Advanced, will be enabled by the application of MIMO and other smart antenna technologies,” stated Kevin Linehan, Vice President and Chief Technology Officer – Base Station Antenna Systems, Andrew Solutions. Linehan, one of the project leaders for the creation of the 3G Americas report continued, “It is critical that operators and others in the industry appreciate these advanced technologies and their practical application.”
The term smart antennas refers to adaptive array antennas – those with electrical tilt, beam width and azimuth control that can follow relatively slow-varying traffic patterns; intelligent antennas, which can form beams aimed at particular users or steer nulls to reduce interference; and MIMO antenna schemes, predominately featured in LTE and LTE-Advanced.
The white paper was created by a 3G Americas technical work group and concentrates on the practical aspects of antennas and their deployment for 3G and 4G wireless systems, specifically downlink antenna techniques available in 3GPP LTE Release 8. The comprehensive report highlights a substantial and growing body of theoretical and field experience that provides reliable guidance on the tradeoffs of various antenna configurations. Some of the areas addressed in the paper include:
- Smart antennas provide the next substantial increase in throughput for wireless networks. The peak data rates tend to be proportional to the number of send and receive antennas, so 4X4 MIMO is theoretically capable of twice the peak data rates as 2X2 MIMO systems. For another example, in upgrading from HSPA (1X2) to LTE (2X2) a gain of 1.6x is seen (Rysavy Research, 2009).
- The practical tradeoffs of performance with the realistic constraints on the types of antennas that can be realistically installed, cognizant of zoning, wind loading, size, weight and cabling challenges and constraints from legacy terminals and other equipment. Constraints are, of course, present in both the base station and the terminal side of the air interface, where MIMO technology promises useful gains if multiple antennas, amplifiers, receivers and baseband processing resources can be made available in terminals.
- Beyond the single antenna or beamforming array cases, 3GPP Release 8 of the LTE standard supports MIMO antenna configurations. This includes Single-User (SU-MIMO) protocols using either Open Loop or Closed-Loop modes as well as Transmit Diversity and MU-MIMO. Closed-Loop MIMO mode, which supports the highest peak data rates, is likely to be the most commonly used scheme in early deployments. However, this Closed-Loop MIMO scheme provides the best performance only when the channel information is accurate, when there is a rich multipath environment and is appropriate in low mobility environments such as with fixed terminals or those used at pedestrian speeds.
The white paper, MIMO and Smart Antennas for 3G and 4G Wireless Systems: Practical Aspects and Deployment Considerations, was written collaboratively by members of 3G Americas and is available for free download HERE.
While MIMO and Smart Antennas for 3G and 4G Wireless Systems concentrates on the practical aspects of deploying antennas in emerging wireless markets, 3G Americas’ June 2009 white paper, MIMO Transmission Schemes for LTE and HSPA Networks, provides additional background information on the processing gains feasible with smart antennas.