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The role antennas play in a MIMO link
Dr Andre FourieCEO, Poynting Antennas
Overview
Where is MIMO used: Wi-Fi, WIMAX, LTE
SDMA – spacial division multiplexing (multiple access?)
Antennas – radiation pattern, polarisation
Channels – indoor vs outdoor
Radiation patterns
• Transmission interpretation
• Reception interpretation
Polarisation
• Defined in terms of electric field
• Often referenced to the earth
• Linear
• Circular
• Elliptical
• Cross pol gain
Channels
• Channel includes: Transmit antenna – path – receive antenna
• Free space example
Channel – single reflection
Channel – multiple reflections
Channel - Indoor vs outdoor
Channel – indoor vs outdoor
• Assume BER of 1E-4
• Then– Outdoor SNR = 8dB– Indoor SNR = 34 dB
• Thus indoor signal must be 400 times stronger (26 dB) for similar performance
MIMO
• Multiple input multiple output
• SDMA is a technique which attempts to send multiple streams of data over a link using the same frequency resource
• SDMA is more multiplexing than multiple access
MIMO – a contrived example
MIMO – using cross-pol antennas
MIMO – how it works
MIMO – how it works
MIMO – how it works
MIMO – estimating the channel
MIMO – estimating the channel
MIMO – estimating the channel
MIMO – estimating the channel
Poor signal de-correlation
Poor signal de-correlation
Assessing antenna quality
• Good de-correlation required? Let’s test…
Assessing antenna quality
• Download speedup vs de-correlation
Conclusion
• External antenna make a big difference even for non-MIMO technologies
• Well de-correlated external antennas are important for good MIMO performance