Timo Unger

04/20/23 | Timo Unger

Multiple-antenna two-hop relaying for bi-directional transmission in wireless communication systemsTimo Unger


Future wireless communication systems

2

high data rate services

increasing bandwidth

higher center frequencies

higher order modulation

NodeS2

NodeS1

non-sufficient SNR

typical problem solutions

higher transmit powers EMC, health

additional base stations infrastructure costs


Relaying: providing high data rate services to shadowed areas

Relay Station RS

2

non-regenerative relaying

linear signal processing

no error propagation

no delay due to decoding

transparency to modulation and coding of S1 and S2

relaying

lower transmit powers

no additional base stationsNode

S2

NodeS1


Relay Station RS

NodeS2

multiple antennas adaptive beamforming spatial multiplexing

NodeS1

Relaying: providing high data rate services to shadowed areas

2

relaying schemes one-way relaying two-way relaying

assumptions

non-regenerative relaying

bi-directional transmission

multiple antennas


Time slot allocation

S1 S2RS

time

time slot

3

one-way relaying

S1 S2RS

two-way relaying

time

cancellation of duplex interference (CDI)


Overview

System with

full capabilities

Systems with

limited capabilities availability of channel

state information (CSI) node capabilities

one-way relaying

two-way relaying

single-antenna

maximumsum rate

maximumsum rate

multiple-antenna

obtaining CS

I

maximum sum rate

linear beamforming algorithms: MMSE, ZF, MF

[Munoz ´05, Hammerström ´06]

[Shannon ´61, Rankov ´05]

[v. d. Meulen ´71]

novel contributionsstate of the art

4


Overview

System with

full capabilities

one-way relaying

two-way relaying

single-antenna

maximumsum rate

maximumsum rate

multiple-antenna



[v. d. Meulen ´71]


4


Problem formulation: maximization of sum rate

subject to: Tx power constraints at S1 & S2

Tx power constraint at RS

=1/4 for one-way

1/2 for two-way

S1 S2RS

: covariance matrix of useful signal

: covariance matrix of noise plus interference

5



S1 S2RS

time

time slot

6

one-way relaying


Sum rate maximization in one-way relaying

S1 S2RS

7

time

S1 S2


singular value decomposition (SVD)

adaptation to the eigenmodes

orthogonal spatial sub-channels

(2)1

(2)2

(1)1

(1)2

eigenvalues



8

S1 S2RS

two-way relaying

time



Sum rate maximization in two-way relaying

S1 S2RS

time

S1 S2

9

(2)1

(2)2

(1)1

(1)2

(1)1

(1)2

(2)1

(2)2

BF cannot be adapted to the eigenmodes of both channels simultaneously

numerical optimization of G, Q(1), Q(2): sequential quadratic programming



10

S1 S2RS

two-way relaying

time




S1 S2RS

two-way relaying

time10



Average sum rate vs. SNR

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(2) in dB

SNR(1) =20 dB

SNR(2)

i.i.d. Rayleigh fading channel

two-way

one-way

upper bound:“2*one-way“

rate loss due to retransmission of already

known data

11


Average sum rate vs. number of antennas

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(1) =10 dB


two-way

one-way

12

… SNR(2) =10 dB

number L of antennas at RS


Multiple-antenna gains

ave

rage

sum

ra

te in

bit/

s/H

z

L

SNR(1) =10 dB


two-way

one-way

13

… SNR(2) =10 dB

spatial multiplexing gain

one bit/s/Hz per antenna

diversity and array gain


Overview

System with

full capabilities

Systems with



one-way relaying

two-way relaying

single-antenna

maximumsum rate

maximumsum rate

multiple-antenna



[v. d. Meulen ´71]


14


Availability of channel state information (CSI)

RSS1 S2

System with …

Availability of CSI

full capabilities

limited capabilities at RS no CSI

local CSI at S1 & S2

limited capabilities at S1 & S2 no CSI no CSI

15


Node capabilities

16

System with …

Node capabilities

full capabilitiesadaptive BF

+ CDIadaptive BF

adaptive BF+ CDI

limited capabilities at RSadaptive BF

+ CDIequal

weightingadaptive BF

+ CDI

local CSI at S1 & S2equal weighting

+ CDIadaptive BF

equal weighting+ CDI

limited capabilities at S1 & S2 equal weighting adaptive BF equal weighting

adaptivebeamforming (BF)

equalweighting

RSS1 S2


Overview

System with

full capabilities

Systems with



one-way relaying

two-way relaying

single-antenna

maximumsum rate

maximumsum rate

multiple-antenna

maximum sum rate



[v. d. Meulen ´71]


17


Average sum rate vs. number of antennas for different system capabilities

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(1) =10 dB


18

… SNR(2) =10 dB

full capabilities at all nodes

limited capabilities at RS


one-way

limited capabilitiesat S1 & S2



Overview

System with

full capabilities

Systems with



one-way relaying

two-way relaying

single-antenna

maximumsum rate

maximumsum rate

multiple-antenna

maximum sum rate




[v. d. Meulen ´71]


19


Adaptive beamforming only at the RS

minimize MSE ( MMSE)

minimize MSE under zero forcing constraint ( ZF)

maximize SNR ( MF)

problems are neither convex nor concave

local / global optima can be found by sequential quadratic programming

Other optimization problems(known from point-to-point)

20

local CSI at S1 & S2equal weighting

+ CDIadaptive BF

equal weighting+ CDI

limited capabilities at S1 & S2 equal weighting adaptive BF equal weighting

Sum rate maximization problem


Sum rate for different BF algorithms in a system with local CSI at S1 & S2

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(2) in dB

SNR(1) =20 dB

SNR(2)


MMSE

maximum sum rate

21

ZF

MF


Overview

System with

full capabilities

Systems with



one-way relaying

two-way relaying

single-antenna

maximumsum rate

maximumsum rate

multiple-antenna

obtaining CS

I

maximum sum rate




[v. d. Meulen ´71]


22


Obtaining CSI of at the S2

t

mone pilot symbol per transmit antenna

m: antenna indext: time

23

Pilot transmission schemes

S1 S2

Obtaining CSI of at the RS

t

m

S1 S2

retransmission of the same pilot symbols

RS

RS



one pilot symbol per transmit antenna

23


S1 S2RS


S1 S2RS

retransmission of the same pilot symbols

m

t

m

t




one pilot symbol per transmit antenna

23


S1 S2RS


S1 S2RS

m

t

m

t

CDI can also be applied for pilot symbols

t

m



Pilot transmission schemes - overview

System withfull capabilities

System with limitedcapabilities at RS

System with limitedcapabilities at S1 & S2

t

m

t

m

t

m

t

mSystem with local CSIat S1 & S2

24


Sum rate with degradation due to pilot overhead

SNR(1) =10 dB


… SNR(2) =10 dB

ave

rage

sum

ra

te in

bit/

s/H

z




local CSI at S1 & S2 limited capabilities

at S1 & S2

25

v = 20 km/h

f0 = 5 GHz

max = 2 s

uT = uB = 5


Sum rate with degradation due to pilot transmission

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(1) =10 dB


… SNR(2) =10 dB



local CSI at S1 & S2 limited capabilities

at S1 & S2

25


v = 20 km/h

f0 = 5 GHz

max = 2 s

uT = uB = 5


Conclusions

Two-way relaying significantly outperforms one-way relaying for bi-directional transmission

Categorizing systems of different capabilities with respect to CSI and signal processing capabilities

Performance bounds for the systems of different capabilities

Linear adaptive beamforming algorithms for systems with exclusive BF at the RS

Pilot transmission schemes for two-way relaying

Impact of imperfect CSI on the performance

Multiple access for two-way relaying

26


T. Unger and A. Klein, “Linear Adaptive Beamforming Algorithms for Multiple-Antenna Non-Regenerative Two-Way Relaying ," submitted for publication in: IEEE Transactions on Signal Processing, Dec. 2008

S. Berger, T. Unger, M. Kuhn, A. Klein, and A. Wittneben, “Recent advances in amplify-and-forward two-hop relaying,” accepted for publication in: IEEE Communications Magazine, 2009.

T. Unger and A. Klein, "Duplex Schemes in Multiple Antenna Two-Hop Relaying," EURASIP Journal on Advances in Signal Processing, vol. 2008, Article ID 128592, May 2008.

T. Unger and A. Klein, "Maximum Sum Rate for Non-regenerative Two-way Relaying in Systems of Different Complexities," in Proc. 19th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), Cannes, France, Sep. 2008 (invited paper).

T. Unger and A. Klein, "Applying Relay Stations with Multiple Antennas in the One- and Two-Way Relay Channel," in Proc. 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), Athens, Greece, Sep. 2007 (invited paper).

T. Unger and A. Klein, "On the Performance of Relay Stations with Multiple Antennas in the Two-way Relay Channel," in Proc.16th IST Mobile and Wireless Communications Summit, Budapest, Hungary, July 2007.

T. Unger and A. Klein, "Linear Transceive Filters for Relay Stations with Multiple Antennas in the Two-Way Relay Channel," in Proc. 16th IST Mobile and Wireless Communications Summit, Budapest, Hungary, July 2007.

References

27


Future wireless communication systems

Ubiquitous high data rate services

Increasingbandwidth

Higher ordermodulation schemes

Increased noise power Increased pathloss

Higher transmit power for sufficient SNR / smaller mobile radio cells

EMC, health and costs

Increased sensitivityto noise

Higher centerfrequencies

Approach Approach Approach

ProblemProblem Problem


Availability of channel state information (CSI)

Global CSI at the RS

required for adaptive beamforming (BF)

S1 S2RS

S1 S2RS

S2RSS1

Local CSI at S1 & S2

required for cancellation of duplex interference (CDI)

Global CSI at S1 & S2

required for adaptive BF


Node capabilities

Nodes of full capabilities

S1, S2 and RS perform adaptive BF

Limited capabilities at RS

RS cannot perform adaptive BF

Limited capabilities at S1 and S2

S1 and S2 cannot perform adaptive BF


System with

local CSI

at S1 & S2

Different cases of system capabilities

System with

full capabilities

System with

limited capabilities

at RS

System with


at S1 & S2

no CSIat RS

global CSIat all nodes

no CSIat S1 & S2

only local CSIat S1 & S2

adaptive BFat all nodes

CDI

equal weightingat S1 & S2

no CDI

equal weightingat S1 & S2

CDI


at RS

fullcapabilitiesat all nodes



equal weightingat RS

CDI



S1 S2RS

time

S1 S2



S1 S2RS

time

S1 S20

0

00

00

Waterfilling at RS





S1 S2RS

time

S1 S2


S1 S2RS

time

S1 S2

BF cannot be adapted to the eigenmodes of both channels simultaneously



RS: L ant.

time

S1: M ant. S2: M ant.

numerical optimization of G, Q(1), Q(2): sequential quadratic programming (SQP)

M2 optimization variables in Q(1) / Q(2), L2 optimization variables in G


S1 S2


time

projection to the range space of the joint receive channel

range spacenull space

for L > 2M

S1: M ant. RS: L ant. S2: M ant.



time

S1 S2

range spacenull space

projection to the range space of the joint transmit channel

number of optimization variables in G can be reduced for L > 2M:



Average sum rate vs. SNR for different system capabilities in two-way relaying

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(2) in dB

SNR(1) =20dB

SNR(2)

i.i.d. Rayleigh fading channelfull capabilities

at all nodes



one-way



Single antenna S1 & S2

single-antenna S1 & S2 (M = 1)

multiple-antenna RS (L ≥ 2)

transmission rate of the form:

sub-optimum approach:maximize individual SNRs


Sub-optimum BF algorithm

receive matched filtertransmit matched filter

weighting matrix



weighting matrix




weighting matrix

near-optimum and.

equal weighting



Average sum rate vs. SNRfor single-antenna S1 & S2

ave

rage

sum

ra

te in

bit/

s/H

z

SNR(1) =20dB

SNR(2)


SNR(2) in dB

optimum BF by SQP

MF with equal weighting

MF with non-equal weighting


Two-way relaying with multiple-antenna nodes

S1 S2RS

timetime slot

S2 RS RS S1

S1 RS RS S2

duplex interferenceduplex interference


Signal decomposition

S1 S2RS

usefulsignal

intersymbolinterference

duplexinterference

noise atRS and Sk

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