Frank M. Caimi Chief Scientist, SkyCross frank.caimi@skycross.com

Antenna Advancements Enable High Order MIMO for LTE

Presented at the Antenna Systems Conference November 6-7, 2014 Las Vegas, NV

MIMO Basics

2

•Motivation: – Current wireless systems are

Capacity constrained – Quality of Service and

Coverage issues exist •MIMO exploits spatial path independence to provide capacity, range, and reliability

•Multipath is now an ally rather than a liability!

Why MIMO?

•Signal fading SNR variability

• Time Spread (delay spread) Frequency selectivity

Multipath Communications Channel

The propagation channel is characterized by multipath propagation due to the transmitted signal being scattered from different objects

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Multipath Signal Independence

• Two signals r1 and r1 arriving at receiver from different paths

• The signals can be considered independent if the correlation between the two envelopes calculated using:

is much less than 1 (E is the expected value

operator and the bar signifies time-average)

r1 (envelope)

r2 (envelope)

( )( )[ ]

( )[ ] ( )[ ]2

22

2

11

2211

rrErrE

rrrrEe

−−

−−=ρ

•Two independent channels but some knowledge of the transmission channel required for decoding

MIMO Principle: Simple Example

Plan

Leave

Signal processing

channel info

Plan

Leave

Channel Usage Possibilities

Different numbers of Transmit and Receive Antennas

Channel Matrix

H

Nt Nr

MIMO System Characteristics

• MIMO systems have multiple transmit and receive antennas • Channel is characterized by transmission matrix H of rank R • With perfect channel estimates at Tx and Rx, decomposes

into independent channels

- RH -fold capacity increase over SISO system - Antennas can also be used for diversity and

beamforming - Allows capacity versus diversity tradeoff

x Hx

H-1 ~x

MIMO Performance Improvements •MIMO results in four major Performance improvements:

- Array Gain - Diversity Gain - Spatial Multiplexing Gain - Interference Reduction

Spatial Multiplexing Gain

• Transmitters use same frequency and modulation • Sub-streams are independent (no coding across the transmit antennas -

each sub-stream can be individually coded) • Individual transmit powers scaled by 1/Nt , so the total power is kept

constant • Channel estimation burst by burst using a training sequence • Requires near–independent channel coefficients

MIMO: Space-Time Coding: How does it work?

• Typically used in SU-MIMO • Data intelligently reordered in time • Assume interference or fade at time “x” • Bits lost are duplicated elsewhere in the different streams • Allows handling of interference, range extension, capacity

improvement

SISO

Added diversity stream

Transmit Diversity Tradeoff Same data is coded and transmitted through different antennas, which effectively doubles the power in the channel, increasing cell edge performance

Combined Advantages of MIMO

Capacity (bps)

BER/Spectral Efficiency (bps/Hz)

Coverage (bps/km2)

• Multi-user MIMO (MU-MIMO) – No modification of UE RF-module

• MU-MIMO applies an extended version of space-division multiple access (SDMA) to allow multiple transmitters to send separate signals and multiple receivers to receive separate signals simultaneously in the same band

• For advanced transmit processing, the channel state information has to be known at the transmitter (CSIT).

MU-MIMO vs. SU-MIMO

MU-MIMO-BC

•Single user MIMO (SU-MIMO) • In contrast, single-user MIMO considers a single multi-antenna transmitter communicating with a single multi-antenna UE

MU-MIMO vs. SU-MIMO

LTE- A and the Mobile Device Antenna

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Enables more users, more applications, and a better experience

Source: Rysavy Research/4G Americas, 2012

LTE 2010 to 2013 •5 or 10 MHz Radio Channels •2X2 Multiple Input Multiple Output (MIMO)

LTE- A 2013 to 2016 Higher Capacity/Throughput and/or Efficiency

•Wider Radio Channels: 20 MHz •Carrier Aggregation: up to 100 MHz •Advanced Antenna Configurations: 4x2,4x4 •More Advanced MIMO (Higher Order, Multi-User, Higher Mobility) •Coordinated Multipoint Transmission •Het-nets (Microcells/Picocells/Femtocells)

•T-Mobile deploying 4x2 MIMO to enhance cell edge coverage

•Sprint deploying 4x2 MIMO in key cities at 2.6 GHz with intent to improve cell edge coverage

•Verizon: UL 10 MHz 1x2 28 Mbps; DL 10MHz 2x2 86Mbps (peak DR)

•802.11ac pushing over 1 Gbps limit with 4x4 MIMO

Announced 2014 MIMO plans

•Release 10 of 3GPP (Document 460009) : – 8x8 DL-MIMO (4x4 anticipated deployment) – 4x4 UL-MIMO (desired)

MIMO support in LTE-Advanced

• SU-MIMO UL 4 stream supports requirement for peak spectrum efficiency (15 bps/Hz)

MIMO in uplink channel needed for ITU requirement

LTE-A: Impact on the Antenna System

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• Can 4x4 MIMO be deployed successfully in a handset or 8x8 in anticipated mobile devices?

Looking Ahead: The Antenna Farm Challenge

• What will be the impact on Antenna Performance?

• What limitations can be expected?

Antenna Challenges for Higher Level MIMO 1. Greater band coverage +MIMO in accepted form factor allocated

space PLUS Support for Carrier Aggregation

2. Greater Number of Antennas with Restricted Space Allocation: 1000 cubic millimeters or less (handsets)

3. Need for high isolation between elements: 15-20 dB

4. Higher ASP stemming from number of antennas and possible feedline extension

5. Correlation between antenna signals due to sharing of common modes on PCB

6. Feedline losses: FEM to antenna Page 23

• Easiest way to arrange aggregation: use contiguous component carriers within the same operating frequency band (as defined for LTE), so called intra-band contiguous.

• May not always be possible, due to frequency allocation scenarios.

• For non-contiguous allocation it could either be intra-band, i.e. the component carriers belong to the same operating frequency band, but are separated by a frequency gap, or it could be inter-band, in which case the component carriers belong to different operating frequency bands.

Carrier Aggregation Considerations

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Interband Required!

Antenna Co-Location

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MIMO Channel Dependence

• MIMO performance is sensitive to channel matrix invertibility • Degradation of the channel matrix condition due to:

– Antenna correlation caused by: • small antenna spacing, or • small angle spread

H: rank 1: Non-invertible

Large angular spread reduces antenna

spacing requirement Knowing the channel

is key!

Spatial Correlation: Antenna Spacing depends on Multipath Angular Spread

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•Correlation factors below 0.5 desirable

•Degradation most at low SNR

Capacity vs. Correlation

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Antenna Correlation: …from S-Parameters

• Envelope correlation can be determined from S parameters under certain conditions: – Antennas are lossless – Uniform Isotropic Channel Model

• For real antennas, the uncertainty of the result increases with decreasing radiation efficiency*

*Hallbjorner, Antennas and Wireless Propagation Letters, V4 2005

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Correlation Calculation from Antenna Pattern

• Calculation of the envelope correlation for a 2-antenna system in a Rayleigh fading environment: – Channel Parameters

• X is the cross-polarization ratio Sθ /Sφ (where S is power)

• pθ and pφ represent the probability distribution of the angle of arrival

– Antenna Parameters • Enθ and Enφ are the complex far-

field potentials for the theta and phi polarizations for antenna n ( ) φθθ

ρ

φφφ

φφφ

φφφ

dddΩ

dΩAdΩA

dΩA

pEEpEEXA

pEEpEEXA

pEEpEEXA

e

*θ

*θθ

*θ

*θθ

*θ

*θθ

sin

2211

2

12

222222

111111

212112

=

≈

+=

+=

+=

∫∫

∫

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Lossless Dipoles Result

• Pattern and S parameter calculations agree

• Isolation S21/S21 much below -10 dB desirable

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Lossless Dipoles Gain Patterns

• Azimuthal gain patterns for 4 different dipole separation distances (in wavelengths)

• Close spacing undesirable due to Gain Loss and Pattern Similarity

λ

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Antenna Proximity Problem • Far apart

– Negligible coupling between antennas

– spatial separation makes antenna patterns unique

– How far: generally more than about half wavelength (17 cm at 900 MHz) – size not feasible for many consumer products

• Close together - coupling between antennas may

be a problem (RX saturation or desense, TX distortion)

- coupling hurts radiation efficiency as power goes into neighboring antenna and not to far field

- patterns lose uniqueness and are highly correlated (loss of MIMO capacity or loss of diversity gain)

- Reality of many consumer products

Antenna starts to couple more to its neighbor than to the far-field

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LTE-700 Corner to Corner Conventional Antenna Design

VSWR: <2:1 Efficiency:

30-40%

CC: >0.8 Coupling:

-4dB

Patterns almost identical

Enabling Technologies

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The MIMO Antenna Solution for 4G

: Isolated Mode Antenna Technology

• iMAT is a patented technology that allows a single antenna structure to behave like multiple antennas through the use of multiple feed points.

• Each feed point accesses the single antenna as if it consisted of 2, 3, or more independent antennas that are highly isolated with superior link performance gain.

• This compact solution is applicable to any mobile device! iMAT supports legacy networks and is essential for next generation protocols that require diversity or MIMO.

Patented Technology

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Enables Multiple Antennas in Small Spaces

Antenna Requirements • Diversity/MIMO • High isolation • High radiation efficiency • Low correlation coefficient • Small size

d

Conventional Smart Antenna

Approach

Isol

atio

n dB

0

-10

-20

-30 Frequency

60

50

40

30

Effi

cien

cy %

ISO

EFF

SkyCross iMAT Solution

Isol

atio

n dB

0

-10

-20

-30 Frequency

60

50

40

30

Effi

cien

cy %

ISO

EFF

1 2

The iMAT solution offers high efficiency, superior isolation, and low correlation coefficient while maintaining equivalent return loss, with a single antenna!

Technology Applications • WiFi and/or WiMAX • 4G/LTE • HSDPA / HSUPA • 1XEVDO • 802.11n, 802.11ac • Mobile video (CMMB, T-DMB,

DVB-H) 1 3 . . . 3 . . .

d

2

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iMAT: Far-Field Patterns

• Each resonance mode has a unique far field pattern • With iMAT approach each antenna port couples to a different

combination of the two fundamental modes • The resulting far-field patterns are also unique to each other

resulting in low ECC

Combination

- =

+ =

Pattern phase reversal

Farfield pattern from Port 1

Farfield pattern from Port 2

Common Mode

Differential Mode

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iMAT: Concurrency of Isolation and ECC

• With iMAT Port-to-port isolation and low far-field correlation are obtained from the same design optimization at the same frequency

• Both result from the condition where the

near fields associated with Port 1 are orthogonal from those associated with Port 2

• The proper conditions are achieved

through resonance and so are inherently optimized to a particular frequency band or bands

Port-to-Port Coupling

Pattern Correlation

frequency

frequency

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iMAT LTE-700 Antenna Design

VSWR <2.2:1

Isolation:

<-13 dB

Efficiency 50-58%

CC: <0.35

Significantly different patterns

50x100mm GP

iMAT Advantage vs. Dual Antenna: Correlation Coefficient

iMAT Antenna Patterns

Dual Antenna Patterns

Greater pattern diversity results in lower Correlation Coefficient for iMAT vs. Dual Co-polarized Antenna

Independent analysis of iMAT vs. Conventional antenna for handsets shows iMAT delivers significant improvement in Correlation Coefficient

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LTE-A: 4x4 MIMO

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Operator’s Key Motivators for 4x4 MIMO

Confidential Page 43

Network Cell Capacity

Increased Coverage

End User Experience

Marketing: Peak Rate

Performance

Talk Time Increase

• A leading issue in 2014 World Mobile Congress was faster LTE-A technologies.

• 4x4 MIMO requires 4 antennas in one handset. – No space for 4

antennas in normal smartphones.

– Needed: New antenna solution to reduce antenna size required for 4x4 MIMO.

4x4 MIMO+2 Band CA Dual iMAT Antenna (Field Trial Unit)

Confidential Page 44

Return Loss Isolation

Efficiency ECC

Target Spec.

Field LTE-A Test Unit for CA Band 3+7 with 4x4 MIMO

Mobile Operator Field Trial Test Results (2014) : SkyCross Dual iMAT Antenna

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4x4MIMO benefit in

typical user experience

4x4 MIMO Cell edge

benefit

4x4 MIMO multiple dB coverage benefit in

noise limited area

4x4 MIMO peak

thruput >580 Mbps

• 580 Megabit per second peak speed and ultimate cell edge performance on a live LTE network environment

• Demonstrated combined LTE-A 4x4 MIMO plus Carrier Aggregation to deliver the best-in-class user experience

• Drives LTE Advanced innovation in the industry by enhancing peak data rates more than three times compared to existing LTE networks

CPE Example: 4x4 MIMO, Low + High Bands

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LTE 3

LTE 1

LTE 2

LTE 4

• Size : 190 x 174 mm

• LTE MIMO Support: 4x4 with CA B3/B7/B20

• WiFi: Two dual-band WiFi antennas

• Product Size: 177 x 193 x 34 mm

LTE Return Loss and Efficiency

CPE Example: 4x4 MIMO Low+High Bands Average Performance

better worse don't care

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• The most limiting parameter is low-low (Band 20) coupling between LTE antennas using a target of -15 dB

• For a 190 x 174 mm PCB size the coupling between antennas was about -10 dB in Band 20

Summary

1. LTE-A requirements are driving the need for new, more complex antenna technologies to support higher order MIMO (4 antennas) PLUS CA

2. Close attention to the antenna early in the design stage is even more critical due to higher levels of complexity

3. Antenna designs that may utilize a combination of technologies can be used as a competitive advantage that allows for product differentiation

4. System performance will ultimately depend on correlation characteristics of the channel in association with the antenna.

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Many challenges BUT an exciting time for Antenna Systems Development!

THANK YOU!