Chapter: 6 p 6 Introduction Multi-antenna configurations g - - PowerPoint PPT Presentation

3G Evolution

Chapter: 6 p 6

M lti t t h i Multi-antenna techniques

Vanja Plicanic vanja plicanic@eit lth se Department of Electrical and Information Technology vanja.plicanic@eit.lth.se

3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband 1

Outline

• Introduction
• Multi-antenna configurations

g

• Multi-antenna techniques
• Multiple receiver antennas, SIMO
• Multiple transmitter antennas MISO
• Multiple transmitter antennas, MISO
• Multiple antennas at both RX and TX, MIMO

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Introduction

Multi-antenna systems Multi-antenna techniques Smart antennas

Multiple antennas at the receiver and/or transmitter

+

Smart signal processing

+

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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

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Antenna configurations cont.

• Configuration of the antennas is decided by the requirement on the antenna

g y q mutual coupling and correlation (low/high)

• Thus, configuration decided by choice of
• spatial distance between the antennas

Low mutual coupling and correlation when: p g BS: >10 wavelengths (due to small AoA in macro cell, shorter distance in micro cells) MS: >0 5 wavelengths (due to wide AoA) MS: >0.5 wavelengths (due to wide AoA)

• polarization directions of the antennas

A t ith diff t l i ti f b th BS d MS i l t l Antennas with different polarizations for both BS and MS gives lower mutual coupling and correlation.

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Antenna configurations cont.

• However, the case of MS at low frequencies < 900 MHz

q => 0.5 wavelengths is large distance for low frequencies Common phone size allows for 0 25 wavelengths distance at 850 MHz! Common phone size allows for ~0.25 wavelengths distance at 850 MHz! => Polarization diversity hard to implement due to antenna + chassis radiation, difficult to rotate chassis wave-mode

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Multi-antenna techniques cont.

Why? How ?

• To improve system capacity (more users per cell),

better link reliability DIVERSITY

• To improve coverage (possibility for larger cells)

BEAM-FORMING

• To achieve higher data rates per user,

higher spectral efficiency SPATIAL MULTIPLEXING

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Figures above Courtesy of Ericsson

Multi-antenna techniques cont.

DIVERSITY

• Antennas at receiver and/or transmitter
• Mitigates fading in the radio channel
• Low mutual coupling required

Low mutual coupling required BEAM-FORMING

• Antennas at receiver and/or transmitter

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

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p g q

Figures above Courtesy of Ericsson

Multiple receiver antennas, SIMO

Smart signal processing techniques: RX di i

• RX diversity
• Receive beam-forming
• Adaptive space time processing

Adaptive space time processing

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Multiple receiver antennas, SIMO

RX diversity

• aims to:

aims to:

• mitigate fading
• suppress specific interferer

Linear receiver antenna combining

• All information is exploited by combining copies of the signal from all the antennas (in

All information is exploited by combining copies of the signal 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)

Interference limited system:

• Interference limited system:
• Maximum Ratio Combining (MRC)
• Interference Rejection Combining (IRC)
• Minimum Mean Square Error (MMSE)

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Multiple receiver antennas, SIMO

RX diversity

Linear receiver antenna combining in: N i li it d

• Noise limited case:
• Maximum Ratio Combining (MRC)

I t f li it d t

• Interference limited system:
• Maximum Ratio Combining (MRC)

Interference Rejection Combining (IRC) 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband

• Interference Rejection Combining (IRC)
• Minimum Mean Square Error (MMSE)

Multiple receiver antennas, SIMO

RX diversity

Maximum Ratio Combining (MRC) A lit d d h i hti

• Amplitude and phase weighting
• 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. g g g

• Diversity gain and array gain
• For noise limited environments

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Multiple receiver antennas, SIMO

RX diversity RX diversity

Interference Rejection Combining (IRC)

For interference limited environment

Interference Rejection Combining (IRC)

For interference limited environment

• For interference limited environment
• Uplink intra-cell interference suppression, Spatial Division Multiple Access (SDMA)
• Able to suppress Nr-1 interferers, however large noise increment after combining
• For interference limited environment
• 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.

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Multiple receiver antennas, SIMO

Adaptive space-time processing

• Frequency selective channel
• Linear time domain filtering/equalization, linear processing to signals received at different

times (MRC Zero forcing MMSE) times (MRC, Zero-forcing, MMSE)

• Linear receive antenna combining, linear processing to signals received at different

antennas

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Multiple receiver antennas, SIMO

Receive beam-forming

• Switched beam antennas
• Antenna array that can form pattern beams pointing in certain discrete direction

i hi l h “b ” b f d i d i l

• switching selects the “best” beam for down conversion and post processing, goal to

maximize the SNR

• simple implementation, since only one signal to post process
• limited flexibility, since only fixed directions

y, y

• Amplitude and phase weights

MRC => a receiver beam with maximum gain NR in the direction of the target signal IRC => a receiver beam with high attenuation in the direction of the IRC > a receiver beam with high attenuation in the direction of the target signal 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband

Multiple receiver antennas, SIMO

Receive beam-forming

Switched antenna array Adaptive antenna array Switched antenna array Adaptive antenna array

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Figures above Courtesy of jackwinters.com

Multiple transmit antennas

Smart signal processing techniques:

• TX diversity
• Transmit beam-forming

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Multiple transmit antennas

TX diversity

• Does not require channel knowledge at the receiver
• Techniques:

Techniques:

• Delay/Temporal diversity
• Cyclic-delay diversity
• Space time/frequency coding (STBC/STFC)

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Multiple transmit antennas

TX diversity

Delay/Temporal diversity

• Time variant channel
• Time variant channel

=> signals received at different times are uncorrelated => delay diversity already there and can be extracted in advanced receivers (ex GRAKE) (ex. GRAKE)

• 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 - HSPA and LTE for Mobile Broadband

Multiple transmit antennas

TX diversity

Cyclic-delay diversity

A li li hift i t d f li d l

• Applies cyclic shift instead of linear delays

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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 array gain, only diversity

No array gain, only diversity

• Space-time trellis to provide full diversity, array gain and coding gain

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Multiple transmit antennas

TX Diversity

Space-frequency block coding (SFBC)

• Space-frequency Transmit Diversity (SFTD)

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Multiple transmit antennas

Transmit beam-forming

• Requires channel knowledge
• Antenna configurations with high mutual coupling

S

• Small antenna distances
• Different phase shifts applied to steer

the direction of the beam

• “CLASSICAL BEAM-FORMING”

Hi h i di i i

• High array gain, no diversity gain
• Antenna configurations with low mutual coupling
• Large antenna distances or different polarization

Large antenna distances or different polarization

• 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

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

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Multiple antennas at both RX and TX

Smart signal processing techniques:

• Spatial multiplexing
• Pre-coder based spatial multiplexing

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Multiple antennas at both RX and TX

Spatial multiplexing

Background:

• SIMO and MISO

SIMO and MISO

Low SNR => capacity increase ~ SNR increase (NTxNR) High SNR => capacity increase ~ log2(SNR)

• Spatial multiplexing

Th it i i {N N } Thus, capacity increase ~ min {NT, NR} 3/26/2009 3G Evolution - HSPA and LTE for Mobile Broadband

Multiple antennas at both RX and TX

Spatial multiplexing

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Multiple antennas at both RX and TX

Pre-coder based spatial multiplexing Pre coder based spatial multiplexing

• If SNR low => beam-forming better than spatial multiplexing
• If N =number of multiplexed streams = N
• If NL=number of multiplexed streams = NT

Pre-coding=> “orthogonalizes” parallel streams, better signal isolation

• If NL< NT

=> combination of beam-forming and spatial multiplexing used => combination of beam-forming and spatial multiplexing used

• Depending on the channel information pre-coder code-books chosen

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Multiple antennas at both RX and TX

Some SM detection techniques

• Maximum-Likelihood ML

La ered space time architect res (BLAST)

• Layered space time architectures (BLAST)
• Successive Interference Cancellation (SIC)
• Single and Multi-codeword Transmission

P A t R t C t l (PARC)

• Per Antenna Rate Control (PARC)

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Chapter summary

Multi-antenna techniques

SIMO Diversity gain and array gain MISO Diversity gain and/or array gain MIMO Diversity gain and/or array gain and/or multiplexing gain SIMO Diversity gain and array gain MISO Diversity gain and/or array gain MIMO Diversity gain and/or array gain and/or multiplexing gain MIMO Diversity gain and/or array gain and/or multiplexing gain MIMO Diversity gain and/or array gain and/or multiplexing gain

Multiplexing gain Link reliability Spectral efficiency Diversity gain Diversity gain and array gain Coverage Link reliability

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References

[1] Dahlman E. et al., 3G evolution-HSPA and LTE for Mobile Broadband, 2nd edition, El i UK 2008 Elsevier, UK 2008 [2] Paulraj A. et al., Introduction to Space-Time Wireless Communications, Cambridge, UK 2003 [3] Molisch A.F., Wireless Communications, IEEE Press, Wiley & Sons, US 2006 [3] Molisch A.F., Wireless Communications, IEEE Press, Wiley & Sons, US 2006

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