Microwave Journal

MIMO.... and All That Jazz

April 15, 2012

To deliver higher data rates, greater coverage areas, and lower operational costs, 4G wireless technologies such as LTE and LTE-Advanced employ enhanced spectral efficiency through the use of MIMO antennas. In MIMO systems, a transmitter sends multiple spatial streams using multiple transmit antennas. These streams are transmitted over-the-air through a channel consisting of multiple paths, arriving at multiple receive antennas at different times. The receiver then decodes the received signal vectors into the original information.

Multiple antenna techniques include:
1.) “pre-coding” or multi-stream beamforming, whereby the same signal is emitted from each transmitter antenna with appropriate phase weighting in order to maximize the signal power at the receiver input 2.) “spatial multiplexing” whereby a high rate signal is split into multiple lower rate streams and each stream is transmitted through the channel at the same frequency and 3.) “diversity coding” whereby the signal is emitted from each transmit antenna with full or near orthogonal coding, exploiting the independent fading in the antenna links to enhance signal diversity.

Coding and signal processing are key elements in a successful implementation of MIMO. Every communication channel represents a major factor in the performance of a wireless system and therefore is the focus of much research. Because MIMO operates at an unprecedented level of complexity in order to exploit the channel space-time resources, a new level of understanding of the channel space-time characteristics is required to assess the potential performance of practical multi-antenna links. MIMO terminal performance is a combination of antenna characteristics, radio propagation conditions, RF, baseband hardware, and software, and therefore they need to be well understood through some form of MIMO Over-the-Air (OTA) test system. The conventional way of testing the antenna characteristics and the signal processing performance separately does not assess the MIMO device performance realistically.

Last year, Microwave Journal teamed up with MIMO OTA test experts from ETS-Lindgren, Agilent Technologies, Spirent, and Elektrobit to present a two-hour panel session at CTIA Wireless 2011. The live forum and simultaneous webcast focused on the fundamentals of MIMO OTA testing as an accurate and cost-effective solution to validate complex MIMO device performance, providing an understanding of the core elements that facilitate systematic and repeatable measurements.

Last year’s forum highlighted the technical features of the test system, including the chamber, software and instrumentation. The speakers presented information on cost-effective ways to perform MIMO OTA characterization using antenna pattern measurements, concepts and underlying assumptions behind MIMO OTA models and the importance of radio channel modeling and validation in MIMO OTA testing. An interactive panel discussion with the speakers allowed audience members to explore a range of related topics with these experts firsthand.

The CTIA Wireless 2011 MIMO Expert Forum Q&A session explored a range of topics. Moray Rumney (Agilent), Dr. Michael Foegelle (ETS-Lindgren), Doug Reed (Spirent Communications) and Jukka-Pekka Nuutinen (Elektrobit) took turns answering questions on OTA system calibration, validation through field mapping, the current situation on OTA standards and more. To see a sample of the CTIA Wireless 2011 MIMO panel discussion, go to
mwjournal.com/CTIAW2011_MIMO_QandA.

Madhusudhan Gurumurthy

Speaking of Beamforming and 8 Antenna MIMO support for TD-LTE…..
Interview with Madhusudhan Gurumurthy, Senior Applications Specialist for channel emulation products at Spirent Communications
Microwave Journal talks with Mr. Gurumurthy about TD-LTE deployments in China and across the Globe. Gurumurthy discusses TD-LTE MIMO requirements and explains how 8xn systems and beamforming techniques are currently being developed for networks targeting single-band spectrum for use in densely populated areas and how beamforming will require accurate per-user channel estimation in order to properly direct energy to a specific user device.
www.mwjournal.com/Spirent_interview

CTIA Wireless 2012 Partner Event Series

Based on the success of last year’s MIMO Expert Forum, Microwave Journal will once again feature a panel of speakers from ETS-Lindgren, Agilent, Elektrobit and Spirent Communications. In addition, the Journal is pleased to announce an all new technical session addressing OTA signal challenges for LTE featuring a second panel of industry measurementexpertsfrom Anritsu, Rohde & Schwarz, Azimuth and EMITE Ing.

Over-the-Air Signal Challenges and Implications: Recommendation for LTE RAN
Wednesday, May 9th (10:45 AM - 1:00 PM)

Moderated by: David A. Sánchez-Hernández

CEO, EMITE Ing

Sponsored by: Anritsu, Azimuth, Rohde & Schwarz and Electro Rent

Speakers from Anritsu, Rohde & Schwarz and Azimuth will discuss signal challenges for MIMO based LTE networks, base station analysis and characterization of the channel through field drive tests and software emulation. This forum will provide an overview of multi-path signal challenges, OTA testing and considerations for evaluating how well a MIMO transmitter is functioning. Topics include: how drive test software based on the full channel bandwidth can be applied to 4×2 and 2×2 MIMO systems to estimate MIMO functionality in the field, during network performance measurements, drive tests or in buildings

MIMO OTA Measurements: The Next Generation Platform for Wireless Testing
Thursday, May 10th (11:45 AM - 2:00 PM)

Moderated by: Mr. Bryan Sayler, President and General Manager of ETS-Lindgren

Sponsored by: Agilent Technologies, ETS-Lindgren, Elektrobit & Spirent Communications

Extensive efforts are underway to standardize on a next generation platform for performance testing of wireless devices, taking into account LTE, A-GPS, uncertainty budgets and use of head/hand phantoms. This Forum, featuring experts from Agilent, ETS-Lindgren, Elektrobit and Spirent Communications will provide an understanding of system performance and discuss how the core elements such as the measurement chamber, software and instrumentation are used to facilitate systematic and repeatable measurements of MIMO devices. The emphasis of this panel will be to look at the standards that are defining OTA test for the end-user device.