full duplexing

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Full duplex communication-system implications

Kavitha.R, Alaka.S.P

Department of Electrical Communication EngineeringIndian Institute of Science, Bangalore

November 22, 2014

Kavitha.R, Alaka.S.P (Department o f Electrical Communication EngineeringIndian I nstitute of Science, Bangalo


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Table of Contents

IntroductionTime division duplexingFrequency division duplexingSelf interference problem

Designs currently presentFull duplex radiosComparison between MIMO and Full duplexMIMO full duplex

Secure MIMO communicationFull duplex-Advantages



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Introduction



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Time division duplexing

Time delaysRequire a guard time or guard interval between transmission andreception.The channel efficiency falls.Also transmit receive switching must be fast

Figure: Time division duplexing(TDD)

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Frequency division Multiplexing

Transmission and reception of signals are achieved simultaneouslyusing two different frequenciesPossible to transmit and receive signals simultaneouslyCapacity in either direction can only be made by re-allocatingchannels.Filters are normally required to prevent the transmitter block and

de-sensitising the receiver.

Figure: Frequency division duplex ing (FDD0Kavitha.R, Alaka.S.P (Department o f Electrical Communication EngineeringIndian I nstitute of Science, BangaloFull duplex communication-system implications Nove mber 22, 2014 5 / 50
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In-band full duplex communication

main idea-a radio transmit and receive on the same frequency atthe same time,an attractive solution for increasing the throughput of wirelesscommunication systems and networks.Beyond spectral efficiency, full-duplex concepts can also beadvantageously used beyond the physical layer, such as at theaccess layer.

Figure: A simplied block diagram of a RF receiver



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Self-interference problem

Figure: An in-band full duplex system

self-interference high as h 1 h

50 110 db greater than signal of interest

femto base stations and mobile handsets transmit at 21 dBm witha receiver noise oor of 100 dBm.Assume 15db isolation between the base stations transmit andreceive signal pathsIt must suppress self-interference by more than 106 dB

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The ADC-problem

Why self-interference cannot be cancelled by substracting transmittedsignal from recieved signal??

The effective dynamic range of an ADC is closer to 6.02(ENOB-2)dB.If the IBFD terminal uses a 14-bit ADC with ENOB = 11 bits,4thus yielding an effective dynamic range of 6.02(11 - 2)= 54 dB.Residual interference oor will remain at 6-54 = -48 dBm, which is-48 - (-100) = 52 dB above the desired femto-cellreceiver-noise-oor of -100 dBm.

hence ADC can quantize away someinformation from the receivedsignal since the self-interfernce is extremely strongReduce self-interference before ADC!!!

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Figure: Illustrative example of residual self-interference motivated bycontemporary femto-cell cellular systems

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Self-interference reduction techniques

wireless propogation -domain techniques ,eg: uses antennadirectionality, beam forming, cross-polarisation

Analog-circuit domain techniques:uses knowledge of thetransmission before it is digitaliseddigital-circuit domain techniques:operates on digital samples

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Jain, Choi,Kim,Bharadis,Seth ,Sreenivasan, Philip Levis, Katti Sinha, Practical,real-time Fullduplex, Mobicom,11 ,301-312,New York ,NY,ACM

Sabharwal, Schniter, Guo, Bliss, Rangarajan, Wichman, In-Band Full Duplex Wireless:Challenges

and Oppurtunities, arXiv:1311-0456v3,[CS:IT] ,20 may,2014

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Antenna cancellation

In conjunction with existing RF interference cancellation anddigital baseband intereference cancellation, achieves the amount of self-interference cancellation required for full duplex operation.The basic idea behind antenna cancellation is to use two transmitand one receive antenna.For a wavelength , the two transmit antennas are placed at

distances d and d + 2 away from the receive antenna.

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Antenna Cancellation

In the most basic implementation the transmitted signal from anode is split among two transmit antennas.This causes their signals to add destructively and cancel one

another.creates a null position where the receive antenna hears a muchweaker signal.Then apply noise cancellation and digital interference cancellationon the weaker signal to remove any residue

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limitations of Antenna Cancellation

The self-intereference signal at a receiver after AC is given by :

A ant : Amplitude of the base band signal x t at the receiverA

ant : difference between the two received signals at the receiverd ant : error in receiver antenna placement,-PROBLEM!!!

captutre effect of bandwidth on cancellation

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Jain, Choi,Kim, Sreenivasan, Philip Levis, Katti Sinha, Achieving single channel Full duplexwireless communication, Proceedings of sixteenth annual international conference on Mobilecomputing and networking,Mobicom,10 ,1-12,New York ,NY,ACM

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Rice design

considers a combination of antenna separation, analog cancellationand digital cancellationconsiders transmission powers and distances between nodes andinterfering antennas that are typical to Bluetooth and WiFisystems.The self interfering signal suppressed by more than 70 dB.Considers 3 mechanisms

Antenna Separation and Digital Cancellation.

Antenna Separation and Analog Cancellation.Antenna Separation, Analog and Digital Cancellation.

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rice design

Figure: Rice implementation

Antenna separation and digital cancellation (ASDC) :

self interfering signal at N1 = h ab x 1 and N2= h AB x 2 .noisy estimates :

h ab and

h AB .After ASDC, the residual interference are (h ab

h ab )x 1 and

(h AB

h AB )

x 2.Kavitha.R, Alaka.S.P (Department o f Electrical Communication EngineeringIndian I nstitute of Science, BangaloFull duplex communication-system implications Nove mber 22, 2014 19 / 50

i d i
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rice design

Antenna separation and analog cancellation(ASAC)

sends the canceller signal c 1 through an additional transmitterradio taht converts the signal to RF and adding to the output.c 1 = h ab h z x 1 ideally.Noisy estimate of h z =

h z .The interfering signal at N1 = ( h ab h z (

h ab

h z )) x 1 .The interfering signal at N2 = ( h AB h z (

h AB

h z )) x 2 .


Antenna separation,analog and digital cancellation(ASADC)


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Antenna separation,analog and digital cancellation(ASADC)

use digital cancellation after ASAC.Dene h N 1ASAC = ( h ab h z (

h ab

h z )) .

Dene h N 2

ASAC = (h

AB h

z (

hAB

hz )) .

noisy estimates - h N 1ASAC , h N 2ASAC .self interfering power at N1 and N2-(h N 1ASAC h N 1ASAC )x 1 , (h N 2ASAC h N 2ASAC )x 2 .

ASADC and ASDC perform better than half-duplex with the sameresources

Figure: Comparison of the three methodsKavitha.R, Alaka.S.P (Department o f Electrical Communication EngineeringIndian I nstitute of Science, BangaloFull duplex communication-system implications Nove mber 22, 2014 21 / 50
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Mellisa Duarte, Ashutosh Sabharwal, Full duplex Wireless Communications using Off-the shelf radios-Feasibility and First results, Fourty fourth Asilomar conference on signals, systems and components,2010


B ll ll ti
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Ballun cancellation

Figure: Ballun Cancellation

a radio needs to obtain the perfect inverse of a signal.

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Figure: Wired setup to measure the performance of ballun cancellation vsantenna cancellation

Luckily, there is a component that does exactly that: abalanced/unbalanced (balun) transformer.our goal is to reduce :


Advantages of Ballun Cancellation
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Advantages of Ballun Cancellation

Figure: comparison between ballun and antenna cancellation for increasingsignal bandwidth

requires only two antennas and RF fronts, no limitation on powerand bandwidth.cancels about 73 db at 10 MHz when combined with digitalcancellation


Practical Limitations
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Practical Limitations

To obtain perfect cancellation the radio must apply identicalattenuation and delay to the inverted signal

Ballun active components introduce non-linearity and limit theperformance

Digital cancellation depends on channel estimation

Ballun circuit not frequency at; different components of the bandinverted with different bands

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FD radios


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FD radios

Figure: FD radios block diagram


FD radios
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FD radios

Analog cancellationxed delays and programmable variable attenuators attenuates thecopy of transmitted signal.reconstruct approximate replica of SI.provides analog cancellation of 60dB,linear as well as non linearcancellation.

Digital cancellationeliminate remaining linear and non linear distortionsIt includes 50dB linear and 20dB non linear distortions.

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Dinesh Bharadia,Emily McMilin,Sachin KattiFull duplex Radios, ACM 978-1-4503-2056-6/13/08 ,Aug 12-16, 2013, Hong Kong China


Comparison between Balun canc. and MIMO


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Figure: capacity comparison

FD can use maximum power of both communication nodes at thesame time.availability of channel state information maximize the sumcapacity in both direction.



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Jain, Choi,Kim,Bharadis,Seth ,Sreenivasan, Philip Levis, Katti Sinha, Practical,real-time Full

duplex, Mobicom,11 ,301-312,New York ,NY,ACM

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MIDU: Design


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Figure: g: a)Two level cancellation b)MIMO

Two level cancellation.combination of two antenna cancellation can contribute upto 45dB SI suppression25-30 dB of SI suppression by digital cancellation.

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Ehsan Aryafar,Mohammad (Amir) Khojastepour,Karthikeyan Sundaresan,Sampath Rangarajan,

and Mung Chiang, MIDU: Enabling MIMO Full Duplex, Mobicom,12 , August 22-26, Istanbul,

Turkey,ACM


Secure MIMO communication
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Figure: g:Articial noise generated by both Alice and Bob

FD can use maximum power of both communication nodes at thesame time.availability of channel state information maximize the sumcapacity in both direction.

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hidden node problem


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Figure: Hidden Node problem

Node N2 is unable to hear node N1s transmission to the accesspoint.It starts sending to the access point at the same time hencecolliding.

How full duplex solves this?As soon as it gets data from N1 access point starts sending back toN1 either whatever it hears (or some othe r data)


Reducing congestion at MAC level
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Figure: Multihop network

nodes N 1 , N 2 N 3 has got to send to N 4 , N 5 andN 6 respectively.if half duplex N 0 gets only 1/4 th of the total time i.e, aggregatenetwork throughput=1/4.If full duplex, aggregate network throughput=1.


Warmhole Routing in Multi-hop Networks
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Figure: Warm Hole routing

Multihop networks suffer from long end-to-end delays.N2 starts receiving a packet from N1.As soon as N2 has processed the packet header, it knows where to

forward the packet and starts transmittin g the packet to N3.Kavitha.R, Alaka.S.P (Department o f Electrical Communication EngineeringIndian I nstitute of Science, BangaloFull duplex communication-system implications Nove mber 22, 2014 44 / 50
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Similarly, N3 starts forwarding the packet to N4 and so on.Since N2 can use digital cancellation techniques to cancel N3 astransmissioned from N1.

This can act as an implicit ACK .

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Jain, Choi,Kim, Sreenivasan, Philip Levis, Katti Sinha, Achieving single channel Full duplex

wireless communication, Proceedings of sixteenth annual international conference on Mobile

computing and networking,Mobicom,10 ,1-12,New York ,NY,ACM .

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References


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Dinesh Bharadia,Emily McMilin,Sachin KattiFull duplex Radios,ACM 978-1-4503-2056-6/13/08 ,Aug 12-16, 2013, Hong Kong China

Ehsan Aryafar,Mohammad (Amir) Khojastepour,KarthikeyanSundaresan,Sampath Rangarajan, and Mung Chiang, MIDU:Enabling MIMO Full Duplex, Mobicom,12 , August 22-26,Istanbul, Turkey,ACM .

Yongkai Zhou, Zheng Zheng Xiang, Yan Zhu, Zhi Xue.,Application of Full-Duplex Wireless Technique into Secure MIMOCommunication: Achievable Secrecy Rate based Optimization,Signal Processing Letters, IEEE , Volume:21, Issue:7, 2014

kumunetworks.com

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