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Load Modulated MIMO Ralf R. Mller Friedrich-Alexander Universitt Erlangen-Nrnberg (FAU) Norwegian University of Science & Technology (NTNU) 17-May-2016 This work was supported in part by the EU-FP7 project Ralf Mller (FAU &

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Load Modulated MIMO

Ralf R. Müller

Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) Norwegian University of Science & Technology (NTNU)

17-May-2016

This work was supported in part by the EU-FP7 project

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 1 / 23

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SLIDE 2

History

History

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 2 / 23

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SLIDE 3

History

2001: Wennström & Svantesson

λ 8

λ 4 λ 200

Figure 11.1: A five element monopole SPA. The center element is active and connected to the transceiver. The four passive antenna elements can be switched in or out of resonance using appropriately biased pin diodes.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 3 / 23

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SLIDE 4

History

2001: Wennström & Svantesson

λ 8

λ 4 λ 200

Figure 11.1: A five element monopole SPA. The center element is active and connected to the transceiver. The four passive antenna elements can be switched in or out of resonance using appropriately biased pin diodes.

”With n switches, there are 2n different modes, or settings of the switchable diodes.“ ”The receiver switches through and samples the chosen modes during one symbol interval.“

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 3 / 23

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History

2001: Wennström & Svantesson

λ 8

λ 4 λ 200

1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 10

−2

10

−1

10

Capacity [b/s/Hz] CCDF

i.i.d. Array−Array Array−Parasitic Parasitic−Parasitic

Figure 11.5: The complementary cumulative distribution function of the MIMO channel capacity for the N=M=4 case. The SNR is 4 dB and the scattering disc radius is 50λ. The parasitic antenna is shown in Figure 11.1.

”With n switches, there are 2n different modes, or settings of the switchable diodes.“ ”The receiver switches through and samples the chosen modes during one symbol interval.“

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 3 / 23

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History

2005: Kalis & Carras

The mutual information of a communication link Y = f (X) + N is determined by the differential entropy H(Y) at the receiver input. For any invertible function f (·) modelling the propagation channel, the differential entropy at the receiver H(Y) is an increasing function of the entropy at the transmitter H(X). Thus, getting large H(X) is equally well as large H(Y) and equally well as large mutual information or large entropy at any point on the propagation channel (”aerial entropy“). The wavefield on air is given by the data D and the array factor of the antenna denoted by A. For X = (D, A), we have H(X) = H(D|A) + H(A).

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 4 / 23

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History

2007: Kalis, Papadias & Kanatas

A technical structure to utilize aerial entropy. An active antenna is fed by an RF-signal cor- responding to a binary data stream. Another binary data stream is used to switch two parasitic antennas between short and

  • pen creating alternating mirrors.

The configuration is shown to achieve a mul- tiplexing gain of 2. In the sequel, the authors published several papers to generalize from binary to non-binary data streams.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 5 / 23

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History

2011: Alrabadi et al.

The first working prototyp.

SPA GND @ f c LM6171 SBC62 DSP 2nd Bit Streams 1st Bit Streams V

cc1

V

cc2

DAC40 Up−Convert XOR Waveform RF Filter DC Cable

−4000 −3000 −2000 −1000 1000 2000 3000 4000 −4000 −2000 2000 4000

First Substream

−4000 −3000 −2000 −1000 1000 2000 3000 4000 −4000 −2000 2000 4000

Second Substream

  • x1

x1

  • x2

x2

−

− − −

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 6 / 23

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Theory

Theory

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 7 / 23

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Theory

Classical vs. Load Modulated MIMO

(a)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN Coupling matrix Z

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 8 / 23

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Theory

Classical vs. Load Modulated MIMO

(a)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN Coupling matrix Z (b)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN No coupling Z = ZselfIN

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 8 / 23

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Theory

Classical vs. Load Modulated MIMO

(a)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN Coupling matrix Z (b)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN No coupling Z = ZselfIN (c)

  • • •
  • • •

Coupling matrix Z Zs x2 xN-1 vs

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 8 / 23

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SLIDE 13

Theory

Classical vs. Load Modulated MIMO

(a)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN Coupling matrix Z (b)

  • • •
  • • •

Z1 Z2 ZN v1 v2 vN No coupling Z = ZselfIN (d)

  • • •
  • • •

X1 x2 xN vs No coupling Z = ZselfIN (c)

  • • •
  • • •

Coupling matrix Z Zs x2 xN-1 vs

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 8 / 23

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Theory

Generic Advantages of Load Modulation

Load Modulator

t)

1

  • i

R

c

i

1

L

1

D

3

L

3

D

2

L

3

D

Only a single power amplifier is needed.

◮ Same phase noise on all antenna elements.

The steerable loads operate at baseband frequency. Implicit digital to analog conversion. Digital control of antenna impedances.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 9 / 23

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Theory

A Generic Problem of Load Modulation

Hard switching of loads = ⇒ abrupt changes of wavefield = ⇒ out-of-band radiation

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 10 / 23

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Theory

A Generic Problem of Load Modulation

Hard switching of loads = ⇒ abrupt changes of wavefield = ⇒ out-of-band radiation

Yousefbeiki & Perruisseau-Carrier 2014: Prototype with p-i-n diode switches.

em en eir

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 10 / 23

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Theory

A Generic Problem of Load Modulation

Hard switching of loads = ⇒ abrupt changes of wavefield = ⇒ out-of-band radiation

Yousefbeiki & Perruisseau-Carrier 2014: Prototype with p-i-n diode switches.

em en eir

Possible countermeasure in the low GHz range: Analog pulse shaping by surface acoustic wave (SAW) filters right at the antennas.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 10 / 23

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Implementations

Implementations

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 11 / 23

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Implementations

ESPAR Arrays

Electronically steerable passive array radiators (ESPARs) were originally proposed for beam steering, not for spatial multiplexing. If beam steering is performed on a symbol by symbol basis, though, the entropy rate of the beam steering is large enough to create a significant multiplexing gain.

DC Cable

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 12 / 23

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Implementations

ESPAR Arrays

Electronically steerable passive array radiators (ESPARs) were originally proposed for beam steering, not for spatial multiplexing. If beam steering is performed on a symbol by symbol basis, though, the entropy rate of the beam steering is large enough to create a significant multiplexing gain.

DC Cable

The passive elements are inductively fed by the active antenna. Very small geometry possible. Several working prototypes at AIT. Limits the number of elements. Mutual coupling drives complexity.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 12 / 23

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Implementations

Galvanic Load Modulation

In 2014, Sedaghat et al. proposed to galvanically feed the load modulators. All elements are fed by a high power unmodulated sine carrier.

  • io1

Tunable load network #1 io2 iin ic Tunable load network #2 B A R Vs ioN Tunable load network #N Matching network PA

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 13 / 23

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Implementations

Galvanic Load Modulation

In 2014, Sedaghat et al. proposed to galvanically feed the load modulators. All elements are fed by a high power unmodulated sine carrier.

  • io1

Tunable load network #1 io2 iin ic Tunable load network #2 B A R Vs ioN Tunable load network #N Matching network PA

The data is solely modulated by steering the loads. No mutual coupling. Matching by law of large numbers. Class F amplifiers will work. Load can be two-port network. No prototype yet. Implementation of star point.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 13 / 23

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Implementations

Reflect Arrays

In 2013/14, Khandani proposed the use of reflect arrays to implement load modulation.

  • from http://www.cst.uwaterloo.ca/content/Media-based-ISIT2014.pdf

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 14 / 23

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Implementations

Reflect Arrays

In 2013/14, Khandani proposed the use of reflect arrays to implement load modulation.

  • from http://www.cst.uwaterloo.ca/content/Media-based-ISIT2014.pdf

Reflect array illuminated by a horn antenna c Ticra Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 14 / 23

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Implementations

Reflect Arrays

In 2013/14, Khandani proposed the use of reflect arrays to implement load modulation.

  • from http://www.cst.uwaterloo.ca/content/Media-based-ISIT2014.pdf

Similar to ESPAR without modu- lated active antenna. Allows for large number of passive elements. Class F amplifiers will work. Tradeoff between power efficiency & mutual coupling.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 14 / 23

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Receivers

Receivers

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 15 / 23

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Receivers

Classical Antenna Arrays

Load modulation is just an alternative way to create an electromagnetic wave field

  • n air in order to save space, cost, power, or complexity.

The best receivers to demodulate signals from load modulated transmitters are classical antenna arrays. Depending on the implementation of the load modulated array, some modulation formats, e.g. OFDM, can be difficult or impossible to implement (OFDM requires two-port networks).

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 16 / 23

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Receivers

Virtually Rotating Arrays

Load modulators can be used to built vir- tually rotating arrays as proposed by RM, Bains & Aas in 2005. These can be used as receive arrays with a single active element. Virtually rotating arrays are just an alter- native way to sample an electromagnetic wave field on air into discrete time in order to save space, cost, power, or complexity.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 17 / 23

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Receivers

Virtually Rotating Arrays

Load modulators can be used to built vir- tually rotating arrays as proposed by RM, Bains & Aas in 2005. These can be used as receive arrays with a single active element. Virtually rotating arrays are just an alter- native way to sample an electromagnetic wave field on air into discrete time in order to save space, cost, power, or complexity.

Active element Parasitic Varactor d L Parasitic elements

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 17 / 23

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Receivers

Virtually Rotating Arrays

Load modulators can be used to built vir- tually rotating arrays as proposed by RM, Bains & Aas in 2005. These can be used as receive arrays with a single active element. Virtually rotating arrays are just an alter- native way to sample an electromagnetic wave field on air into discrete time in order to save space, cost, power, or complexity.

Active element Parasitic Varactor d L Parasitic elements

Virtually rotating arrays may suffer from adjacent channel interference (ACI). ACI can be shielded by means of SAW notch filters or digitally mitigated in some cases (Zaidel & RM, 2015)

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 17 / 23

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Signal Design

Signal Design

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 18 / 23

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Signal Design

Particular Signal Design for Load Modulated MIMO

ESPARs are based on mutual coupling. They required pre-coding against the mutual coupling. This is a non-trivial task, but possible, e.g. Alrabadi et al. 2009.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 19 / 23

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Signal Design

Particular Signal Design for Load Modulated MIMO

ESPARs are based on mutual coupling. They required pre-coding against the mutual coupling. This is a non-trivial task, but possible, e.g. Alrabadi et al. 2009. Galvanic load modulation and reflect arrays are matched by the law of large numbers for massive arrays. For moderate number of elements, matching can be improved by multi-dimensional modulation placing the signal points on an hypersphere, e.g. Sedaghat et al. 2016.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 19 / 23

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Signal Design

Phase Modulation on the Hypersphere

Spherical k-means algorithm better distance EQ sphere partition algorithm lower complexity For only 8 antennas, PAPR below 0.5 dB after pulse shaping.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 20 / 23

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Literature

Literature

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Literature

References I

  • M. Wennström, T. Svantesson. An antenna solution for MIMO channels: the switched

parasitic antenna. IEEE Proc. PIMRC, San Diego, 2001.

  • A. Kalis, M. Carras. Aerial entropy and capacity of a MEA EM source. Proc. 26th Symp.
  • Inform. Theory in the Benelux, Brussels, 2005.

RM, R. Bains, J. Aas. Compact MIMO receive antennas. Proc. 43rd An. Allerton Conf.

  • Commun. Control & Comput., Monticello, IL, 2005.
  • A. Kalis, C. Papadias, A. Kanatas. An ESPAR antenna for beamspace-MIMO systems using

PSK modulation schemes. Proc. ICC, Glasgow, 2007.

  • A. Kalis, A. Kanatas, C. Papadias. A novel approach to MIMO transmission using a single

RF front end. IEEE J. Sel. Ar. Commun. (JSAC), vol. 26(6), 2008.

  • R. Bains, RM. Using parasitic elements for implementing the rotating antenna for MIMO
  • receivers. IEEE Trans. Wirel. Commun., vol. 7(11), 2008.
  • O. Alrabadi, C. Papadias, A. Kalis, R. Prasad. A universal encoding scheme for MIMO

transmission using a single active element for PSK modulation schemes. IEEE Trans. Wirel. Commun., vol. 8(10), Oct 2009.

  • O. Alrabadi, C. Divarathne, P. Tragas, A. Kalis, N. Marchetti, C. Papadias, R. Prasad.

Spatial multiplexing with a single radio: Proof-of-concept experiments in an indoor environment with a 2.6-GHz prototyp. IEEE Comm. Lett., vol. 15(2), 2011.

Ralf Müller (FAU & NTNU) Load Modulated MIMO 17-May-2016 22 / 23

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Literature

References II

  • A. Khandani. Media-based modulation: A new approach to wireless transmission. IEEE
  • Proc. ISIT, Istanbul, 2013.
  • A. Kalis, A. Kanatas, C. Papadias. Parasitic Antenna Arrays for Wireless MIMO Systems,

Springer, 2014.

  • M. Yousefbeiki, J. Perruisseau-Carrier. Towards compact and frequency-tunable antenna

solutions for MIMO transmission with a single RF chain. IEEE Trans. Antennas & Propagation, vol. 62(3), 2014.

  • M. Sedaghat, RM, G. Fischer. A novel single-RF transmitter for massive MIMO. Proc. 17th

Int’l ITG Workshop on Smart Antennas, Stuttgart, Germany, Mar 2014. RM, M. Sedaghat, G. Fischer. Load modulated massive MIMO. Proc. IEEE GlobalSIP, Atlanta, Dec 2014.

  • B. Zaidel, RM. On adjacent channel interference mitigation for rotating MIMO receivers.

IEEE Trans. Wirel. Commun., vol. 14(10), 2015.

  • M. Sedaghat, V. Barousis, RM, C. Papadias. Load modulated arrays: A low complexity
  • antenna. IEEE Communications Magazine, vol. 54(3), 2016.
  • M. Sedaghat, RM, C. Rachinger. (Continuous) phase modulation on the hypersphere. IEEE
  • Trans. Wirel. Commun., to appear 2016.

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