Network-modernizationWireless data demands continue to grow as consumers drive usage levels ever higher. Given constraints on operating and capital budgets, every effort is being made to utilize existing assets more efficiently. Mohamed Hamdy recently wrote about one of the options that network operators have – using multibeam antennas to add more sectors at macro sites. His white paper “Multibeam antennas planning—limitations and solutions” explores some of the technical challenges and solutions to multibeam antenna deployments.

Multibeam antennas make it possible to reconfigure a 3-sector site to have 4 to 6 sectors, thus increasing the capacity of the site. These “higher orders of sectorization” are often used in specific, high traffic areas, and in some cases, even more than 6-sectors can be deployed, if needed. 

Another technique that wireless operators utilize for adding capacity is MIMO (multiple input/multiple output). MIMO systems are already commonplace for LTE networks with 2x2 MIMO being table stakes now. (2x2 MIMO is essentially two streams of data for transmit and receive pathways; 4x4 MIMO is four streams).

Many operators are in the midst of evolving to the next level of sophistication in antenna configuration, planning the move from 2-way receive to 4-way receive. With 4-way receive, the connection from the mobile unit to the base station is improved, which gives a primary benefit that the user can experience better call quality when they are far from the site.  This is especially important for technologies like Voice over LTE (VoLTE). 

4X2 MIMO will further improve the traffic carrying capability of the RF path and increase the capacity of the link from the base station to the mobile. The 4-way receive configurations will also ease the transition to 4X2 downlink MIMO because the same number of antenna ports are needed for 4-way receive as are needed for 4X2 MIMO.  Going to 4X2 MIMO often also requires additional equipment to share paths and keep the number of antennas on the tower to a minimum number. 

These methods of improving the capacity of a wireless network improve spectral efficiency without adding more sites. They are one tool in the toolkit of the radio engineer working to efficiently add more data handling capability.

What challenges are you dealing with as you transition your network to 4X2 MIMO? Leave me a comment if you want to discuss.

About the Author

Ray Butler

Ray Butler is vice president of Mobility Network Engineering at CommScope, responsible for wireless technical sales leadership in outdoor RF products. Before, Ray led the R&D team responsible for base station antennas, filters, combiners, remote radio heads and RF power amplifiers. He previously worked for Andrew Corporation as vice president of Base Station Antennas Engineering as well as Systems Engineering and Solutions Marketing. He has served as director of National RF Engineering with AT&T Wireless and vice president of Engineering, Research and Development, and International Operations at Metawave Communications, a smart antenna company. Ray was technical manager of Systems Engineering for Lucent Technologies Bell Laboratories, having also held other management positions responsible for the design of RF circuits, filters and amplifiers. Ray holds a Bachelor of Science degree in electrical engineering from Brigham Young University and a Master of Science in electrical engineering from Polytechnic University, and is a member of national engineering honor societies Eta Kappa Nu and Tau Beta Pi.

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5 comments for "The Move to 4x2 MIMO in Wireless Networks"
Pankaj Friday, April 22, 2016 8:42 AM

Excellent post !

Richard Friday, February 03, 2017 4:17 AM

I'm working in a project deploying this feature 4x2 closed loop mimo, but i found an issue when it's activated degradation of intra ho via X2 interface in the enodeb have you some idea why this happen, i have to tell you i saw a rach completion success rate degrade too, could this be leading to the ho degradation?

thanks a lot

Ray Butler Monday, February 06, 2017 7:01 PM

Here are a couple of steps for you to try as a start -
1) Check the vendor documentation to see if any parameter changes are recommended when upgrading from 2 to 4Tx (CRS scaling, etc).
2) Check all RACH counters in the cell as there are usually different counters for different failure causes (e.g. if RACH resources are congested at busy hour)

khaled.fayez Wednesday, November 14, 2018 3:11 PM

Does 4X2 give a gain to handest that support 2x2 only?

Ray Butler Wednesday, November 14, 2018 4:49 PM

4X2 MIMO will benefit the downlink when the handset is capable of operating in rank 4, receiving 4 simultaneous data streams. the base station will benefit from having 4 Receive antennas even if the UE/Mobile does not have 4 transmit antennas. The 4 RX antennas will typically use either maximal ratio combining or interference reduction combining to improve the uplink performance as compared to a system with just 2 receive antennas.
Is this how you see it as well?

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