Design Article
Making MIMO Work: Test architectures for MIMO RFICs (part 2 of 2)
Christopher D. Ziomek and Matthew T. Hunter, ZTEC Instruments, Inc.
6/1/2012 12:39 PM EDT
Measurement Challenges
For MIMO testing, it is challenging to synchronize multiple instruments. Modular instruments such as PXI or PXIe are ideally suited to MIMO due to their easily integrated instrument-on-a-card architectures. A PXI/PXIe RF test set can be configured with multiple VSAs, multiple VSGs, or both. Figure 10 shows a modular PXIe test set with four synchronized ZT8651 VSAs for x4 MIMO transmitter testing.
Triggers and timebase clocks routed over the PXI/PXIe backplane enable time and phase synchronization between instruments for MIMO configurations. Figure 11 shows the trigger and clock routing requirements of a PXIe backplane. The backplane triggers allow all instruments to synchronize to and operate upon the same WLAN packet(s). A common timebase of either 10 MHz or 100 MHz is distributed over the PXI/PXIe backplane which enables phase synchronization between instruments. With the PXI/PXIe instruments locked to the same timebase, the relative phase between instruments can be adjusted in software.
MIMO adds complexity to wireless RFIC testing. In a cabled RF environment, the multipath effects that enable MIMO functionality are not present, and consequently other techniques must be used to characterize and verify design performance of RFIC devices. Fortunately, modern test equipment offers a number of techniques that can be used to test RFIC devices that will accurately quantify device performance and operation in a true MIMO environment.
References
[1] W. C. Jakes, Microwave Mobile Communications, John Wiley & Sons, Chapter 1, 1974
[2] S. M. Alamouti, “A Simple Transmit Diversity Technique for Wireless Communications” IEEE Journal on Selected Areas in Communications, October 1998
[3] IEEE 802.11 Standards. [online] available: http://standards.ieee.org/findstds/standard/802.11...
[4] C. D. Ziomek and M. T. Hunter, “Extending the Useable Range of Error Vector Magnitude (EVM) Testing” [online] available: http://www.ztecinstruments.com/zconnect/wp-content/uploads/2012/03/EVM_Optimization.pdf
[5] ZTEC Instruments, “ZT8650 Series Vector Signal Analyzer Specifications” [online] available: http://www.ztecinstruments.com/products/rf-test-equipment/series/ZT8650/
[6] A. Georgiadis. “Gain, Phase Imbalance, and Phase Noise Effects on Error Vector Magnitude” IEEE Transactions on Vehicular Technology, March 2004.
[7] P. Almers, F. Tufvesson, and A. F.Molisch, “Keyhole Effect in MIMO Wireless Channels: Measurements and Theory,” IEEE Transactions on Wireless Communications, December 2006.
[8] A. Adjoudani, et. al., “Prototype Experience for MIMO BLAST Over Third Generation Wireless System,” IEEE Journal on Selected Areas in Communications, April 2003.
For MIMO testing, it is challenging to synchronize multiple instruments. Modular instruments such as PXI or PXIe are ideally suited to MIMO due to their easily integrated instrument-on-a-card architectures. A PXI/PXIe RF test set can be configured with multiple VSAs, multiple VSGs, or both. Figure 10 shows a modular PXIe test set with four synchronized ZT8651 VSAs for x4 MIMO transmitter testing.
Figure 10) A PXIe MIMO transmitter test set eliminates challenges of instrument synchronization.
Triggers and timebase clocks routed over the PXI/PXIe backplane enable time and phase synchronization between instruments for MIMO configurations. Figure 11 shows the trigger and clock routing requirements of a PXIe backplane. The backplane triggers allow all instruments to synchronize to and operate upon the same WLAN packet(s). A common timebase of either 10 MHz or 100 MHz is distributed over the PXI/PXIe backplane which enables phase synchronization between instruments. With the PXI/PXIe instruments locked to the same timebase, the relative phase between instruments can be adjusted in software.
Figure 11: Triggers and timebase clocks can be routed over a PXIe backplane.
MIMO adds complexity to wireless RFIC testing. In a cabled RF environment, the multipath effects that enable MIMO functionality are not present, and consequently other techniques must be used to characterize and verify design performance of RFIC devices. Fortunately, modern test equipment offers a number of techniques that can be used to test RFIC devices that will accurately quantify device performance and operation in a true MIMO environment.
References
[1] W. C. Jakes, Microwave Mobile Communications, John Wiley & Sons, Chapter 1, 1974
[2] S. M. Alamouti, “A Simple Transmit Diversity Technique for Wireless Communications” IEEE Journal on Selected Areas in Communications, October 1998
[3] IEEE 802.11 Standards. [online] available: http://standards.ieee.org/findstds/standard/802.11...
[4] C. D. Ziomek and M. T. Hunter, “Extending the Useable Range of Error Vector Magnitude (EVM) Testing” [online] available: http://www.ztecinstruments.com/zconnect/wp-content/uploads/2012/03/EVM_Optimization.pdf
[5] ZTEC Instruments, “ZT8650 Series Vector Signal Analyzer Specifications” [online] available: http://www.ztecinstruments.com/products/rf-test-equipment/series/ZT8650/
[6] A. Georgiadis. “Gain, Phase Imbalance, and Phase Noise Effects on Error Vector Magnitude” IEEE Transactions on Vehicular Technology, March 2004.
[7] P. Almers, F. Tufvesson, and A. F.Molisch, “Keyhole Effect in MIMO Wireless Channels: Measurements and Theory,” IEEE Transactions on Wireless Communications, December 2006.
[8] A. Adjoudani, et. al., “Prototype Experience for MIMO BLAST Over Third Generation Wireless System,” IEEE Journal on Selected Areas in Communications, April 2003.
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