MIMO Techniques in 3G LTE
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Transcript of MIMO Techniques in 3G LTE
8/3/2019 MIMO Techniques in 3G LTE
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3G Evolution
Chapter:
66u -an enna ec n ques
Vanja Plicanic
Department of Electrical and Information Technology
. . .
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 1
Outline
•Introduction
•Multi-antenna confi urations
•Multi-antenna techniques
•Multiple receiver antennas, SIMO
,
•Multiple antennas at both RX and TX, MIMO
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 2
Introduction
Multi-antenna systems
Multi-antenna techniques
Smart antennas
Multiple antennas at the receiver and/or transmitter
+
Smart signal processing
+
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3
Multi-antenna configurations
Base station (BS) User Equipment (UE),
ex. Mobile station (MS)
Single-input single-output
Single-input multiple-output
Multiple-input single-output
Multiple-input single-output
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 4
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Antenna configurations cont.
- Configuration of the antennas is decided by the requirement on the antenna
mutual coupling and correlation (low/high)
- Thus, configuration decided by choice of
- spatial distance between the antennas
Low mutual coupling and correlation when:
BS: >10 wavelengths (due to small AoA in macro cell, shorter distance in micro cells)
.
- polarization directions of the antennas
Antennas with different polarizations for both BS and MS gives lower mutual
coupling and correlation.
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Antenna configurations cont.
- However, the case of MS at low frequencies < 900 MHz
=> 0.5 wavelengths is large distance for low frequencies
~ .
=> Polarization diversity hard to implement due to antenna + chassis radiation,
difficult to rotate chassis wave-mode
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multi-antenna techniques cont.
Why? How ?
- To improve system capacity (more users per cell),
better link reliabilityDIVERSITY
- To improve coverage (possibility for larger cells)BEAM-FORMING
- To achieve higher data rates per user,
higher spectral efficiencySPATIAL MULTIPLEXING
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 7
Figures above Courtesy of Ericsson
Multi-antenna techniques cont.
DIVERSITY
- Antennas at receiver and/or transmitter
- Mitigates fading in the radio channel
- Low mutual cou lin re uired
BEAM-FORMING
- Antennas at receiver and/or transmitter
- Shaping of antenna beams to maximize gain
in certain direction or suppress specific interferer
- Low or high mutual coupling required
SPATIAL MULTIPLEXING
- Antennas at both receiver and transmitter
- Sending several data streams on multiple parallel
channels
- Low mutual coupling required
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 8
Figures above Courtesy of Ericsson
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Multiple receiver antennas, SIMO
Smart signal processing techniques:
- RX diversity
- Receive beam-forming
-
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple receiver antennas, SIMO
RX diversity-
• mitigate fading
• suppress specific interferer
Linear receiver antenna combining
- All information is ex loited b combinin co ies of the si nal from all the antennas in
comparison to switched/selection diversity)
- Assumes non-time variant channel
- Weights the signal copies with corresponding amplitude
and phase correction
- Noise limited system:- Maximum Ratio Combining (MRC)
-
- Maximum Ratio Combining (MRC)
- Interference Rejection Combining (IRC)
- Minimum Mean Square Error (MMSE)
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple receiver antennas, SIMO
RX diversity
Linear receiver antenna combining in:
- o se m e case:
- Maximum Ratio Combining (MRC)
- n er erence m e sys em:
- Maximum Ratio Combining (MRC)
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
-
- Minimum Mean Square Error (MMSE)
Multiple receiver antennas, SIMO
RX diversity
Maximum Ratio Combining (MRC)
- mp u e an p ase we g ng- Phase weights- adjustment to assure that signals from two antennas are aligned
- Amplitude weights- adjustment of the received signals to correspond to the channels gain, higher
weight for stronger signals.
- Diversity gain and array gain
- For noise limited environments
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
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Multiple receiver antennas, SIMO
RX diversityRX diversity
Interference Rejection Combining (IRC)Interference Rejection Combining (IRC)
-
- Uplink intra-cell interference suppression, Spatial Division Multiple Access (SDMA)
- Able to suppress Nr-1 interferers, however large noise increment after combining
-
- Uplink intra-cell interference suppression, Spatial Division Multiple Access (SDMA)
- Able to suppress NR-1 interferers, however large noise increment after combining
Minimum Mean Square Error (MMSE)Minimum Mean Square Error (MMSE)
- Weights to minimize the difference between the estimated and transmitted signal.- Weights to minimize the difference between the estimated and transmitted signal.
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple receiver antennas, SIMO
Adaptive space-time processing
- Frequency selective channel
- Linear time domain filtering/equalization, linear processing to signals received at different, - ,
- Linear receive antenna combining, linear processing to signals received at different
antennas
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple receiver antennas, SIMO
Receive beam-forming
- Switched beam antennas
- Antenna array that can form pattern beams pointing in certain discrete direction
- switching selects the “best” beam for down conversion and post processing, goal tomaximize the SNR
- simple implementation, since only one signal to post process
- limited flexibility, since only fixed directions
- Amplitude and phase weights
MRC => a receiver beam with maximum gain NR in the direction of the
target signal
=>
target signal
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple receiver antennas, SIMO
Receive beam-forming
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Figures above Courtesy of jackwinters.com
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Multiple transmit antennas
Smart signal processing techniques:
- TX diversity
- Transmit beam-forming
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple transmit antennas
TX diversity
- Does not require channel knowledge at the receiver -
- Delay/Temporal diversity
- Cyclic-delay diversity
- Space time/frequency coding (STBC/STFC)
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple transmit antennas
TX diversity
Delay/Temporal diversity
-
=> signals received at different times are uncorrelated
=> delay diversity already there and can be extracted in advanced receivers
ex.
- Time in-variant channel
=> create artificial time dispersion
(frequency selectivity)
=> transmit identical signals with
different delays from different antennas
- Delay diversity usually implemented by forward error correction, ARQ, repetition coding etc.- Delay diversity invisible to mobile terminal since it is just additional time dispersion handled by the
receiver
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple transmit antennas
TX diversity
Cyclic-delay diversity
- pp es cyc c s ns ea o near e ays
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Multiple transmit antennas
TX Diversity
Space-time block coding (STBC)
- Sending same but differently coded information on each of the antennas, ex. Alamouti
scheme
- used in 3G WCDMA standard as Space Time Transmit Diversity (STTD)
- Orthogonal STBC => full rate=1, full diversity gain only for two antennas
- No arra ain onl diversit ,
- Space-time trellis to provide full diversity, array gain and coding gain
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple transmit antennas
TX Diversity
Space-frequency block coding (SFBC)
- Space-frequency Transmit Diversity (SFTD)
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple transmit antennas
Transmit beam-forming
- Requires channel knowledge
- Antenna configurations with high mutual coupling
- Small antenna distances- Different phase shifts applied to steer
the direction of the beam
- “CLASSICAL BEAM-FORMING”
- High array gain, no diversity gain
- Antenna configurations with low mutual coupling-
- Different gain and phase shifts to steer the direction of the beam
- Pre-coding decided from:
- Channel feedback from mobile terminal average downlink estimate, ex. FDD
- Recommendation from mobile terminal
- Pre-coding for non-frequency-selective fading and white noise
- Maximum Ratio Transmission- instant channel estimate, “fast beam-forming”
- diversity gain and array gain
- Pre-coding for frequency-selective fading not possible, NB! OFDM time invariant sub-channels
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple antennas at both RX and TX
Smart signal processing techniques:
- Spatial multiplexing
- Pre-coder based spatial multiplexing
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
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Multiple antennas at both RX and TX
Spatial multiplexing
Background:- SIMO and MISO
Low SNR => capacity increase ~ SNR increase (NTxNR)
High SNR => capacity increase ~ log2(SNR)
- Spatial multiplexing
us, capac y ncrease ~ mn T, R
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple antennas at both RX and TX
Spatial multiplexing
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
Multiple antennas at both RX and TX
Pre-coder based s atial multi lexin
- If SNR low => beam-forming better than spatial multiplexing
- = =- L T
Pre-coding=> “orthogonalizes” parallel streams, better signal isolation
- If NL< NT
=> -
- Depending on the channel information pre-coder code-books chosen
3/26/2009 3G Evolution - H SPA and LTE for Mobile Broadband
Multiple antennas at both RX and TX
Some SM detection techniques
- Maximum-Likelihood ML
- ayere space me arc ec ures- Successive Interference Cancellation (SIC)
- Single and Multi-codeword Transmission
- er n e nna a e on r o
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband
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Chapter summary
Multi-antenna techniques
SIMO Diversity gain and array gain
MISO Diversity gain and/or array gain
SIMO Diversity gain and array gain
MISO Diversity gain and/or array gain
Multiplexing gain
Link reliability
Spectral efficiency
Diversity gain
Diversity gain and array gainCoverage
Link reliability
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 29
References
[1] Dahlman E. et al., 3G evolution-HSPA and LTE for Mobile Broadband, 2nd edition,
Elsevier, UK 2008
[2] Paulraj A. et al., Introduction to Space-Time Wireless Communications, Cambridge,
UK 20033 Molisch A.F. Wireless Communications IEEE Press Wile & Sons US 2006 . ., , , ,
3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 30