5 PSSS Schwetlick

7/28/2019 5 PSSS Schwetlick

1/46

Fachhochschulefr

Technik und

Wirtschaft

Berlin

University of

Applied

Sciences

FHTW

PSSS -

Parallel Sequence Spread SpectrumA Potential Physical Layer for OBAN?

Horst Schwetlick


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Schwetlick PSSS Physical Layer for OBAN OBAN Workshop at the 14th IST Dresden FHTW-Berlin3

Problems in Wave Propagation

OBAN faces the well known problems of wave propagation andinterference, which can be seen in every wireless application

Technically this refers to the following aspects:

1. Link Budget Starting with a certain transmission power itdescribes all contributions of attenuation during the path of traveluntil arriving at the receiver and hence the resulting signal to noise

ratio at the receiver side

2. Multipath Propagation Due to reflection, diffraction and refractionthe paths from transmitter to receiver do not travel on only one

straight line, rather than of a multiple of propagation paths

3. Co- and adjacent channel interference - Since the ISM bands areto be used freely, the received signal might be disturbed fromtransmitters on same channel or on an arbitrary near neighboringfrequencies

OBAN

Requirements


4/46Schwetlick PSSS Physical Layer for OBAN OBAN Workshop at the 14th IST Dresden FHTW-Berlin4

Loss in Freespace

-130.0

-120.0

-110.0

-100.0

-90.0

-80.0

-70.0

-60.0

-50.0

-40.0

10 100 1000 10000

m

dB

380

900

1900

2500

3500

5200

(Picture Huber & Suner)

Frequency Dependence for Freespace

Propagation Essential for the Link BudgetOBAN

Requirements



Material: at 2,4 GHz at 5 GHz

Brick 11,5 cm - 7 dB - 10 dB

Brick 36 cm - 26 dB - 50 dB

Light Concrete 11,5 cm - 12 dB - 19 dB

Light Concrete 30 cm - 26 dB - 35 dBLimestone 11,5 cm - 22 dB - 36 dB

Reinforced Concrete 16 cm - 20 dB - 32 dB

Frequency Dependence of Material

Attenuation

Increased attenuation by walls at higher frequencies,

Hence, in some cases lower frequencies might have

advantages like the 900 MHZ range

OBAN

Requirements



Multipath Propagation and Delay Spread

The combination of

indoor- and outdoor environment

LOS and NLOS Propagation

places difficult conditions on the physical layer

Special design of the Physical Layer might reduce theseeffects

Spreading

OFDM

(NLOS - Non Line of Sight, LOS - Line of Sight)

OBAN

Requirements



Simulation at 2.4 GHz

Building Walls

Room

Transmitter

Position

Simulation by REMCOMAt FHTW-Berlin



Co- and Adjacent Channel Interference

The ISM-Bands are not restricted within certain limits

So interference can be induced by networks,working at neighboring frequencies

and

working at the same frequency

Mitigation the effects by

Directing antennas

Processing of baseband signals

Using other, less heavy used frequencies

OBAN

Requirements



Discussion

Can OBAN work with other systems than 802.11x in the 2.4

GHz Band?

The future might bring other systems to WLANs for

serving of facilities in households and offices,

eg. systems at the 802.15 xx might leave free capacities

Different interfaces at the host PC, working simultaneously

with different systems and at different frequency ranges

could serve the availability of network access depending on

the presence of wireless networks in the certain environment

Spacial-, System- and Frequency-Roaming

One of these additional systems might be PSSS?

OBAN

Requirements



Parallel Sequence Spread Spectrum

PSSS uses the CDMA-principle and sends in parallel a

superposition of orthogonal sequences with M-arymodulation

It combines code multiplex of cyclically shifted M-sequences with block transfer of short data segments

This approach combines scalable the advantages ofspreading with the transmission of higher data rates

PSSS-

Principle


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Basic Principle

Special correlation properties of M-sequences are

utilised: Cyclic Correlation of a bipolar version with an unipolar

version of the same M-sequence yields a discrete delta

impulse

PSSS-

Principle

Unipolar

Sequence

Resulting Delta

Impulse

Bipolar

Sequence


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Basic Principle

Hence

one data bit is spreaded by the M-sequence

Send through the transmission channel

Received

Despreaded to a single pulse using cyclic correlation

Cyclic shifted impulses are orthogonal and can be

superpositioned to a multivalent sequence No sidelobes due to the cyclic correllation appear

- Therefore no increase of intersymbol interference

PSSS-

Principle


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Cyclic Correlation

M-sequence of lengthL

Unipolar representation

Cyclical correlation

Results in a delta impuls

{ }1 2 ... ...i LA a a a a=1

-1

ka+

=

{ }1 2 ... ...i LB b b b b=

( )mod1

L

i ki k L

i

a b c+

=

=C A B=

1for =02

0 elsek

Lkc

+=

PSSS-

Principle

11

02

kk

ab

+= =


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Cyclic Correlation

If the sequence

is cyclically shifted

by a displacement i

then, after the correlation

the resulting delta impulse

is also shifted by the same

displacement

i iC A B=

{ } ( )

PSSS-

Principle

mod

,1, ,2, , , ,

1 1... ... ,

02

k i L

i i i i k i L i k

aB b b b b b

++

= = =

{ }1, 2,1

... ... ,1

k L kA a a a a a+

= =

1for

2

0 else

i

Lk i

C

+=

=


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Cyclic Correlation

Orthogonality of the shifted sequencesBi is maintained

when sequencesBi are multiplied by a data word, i.e.+1 or -1

and by superposition of sequences

The presence or polarity of a certain sequences in

number of superpositioned sequences is detected by the

cyclic correlation and threshholding a delta function

Hence, the presence or polarity of a certain sequence can

represent one bit of information

PSSS-

Principle


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Superposition of the Shifted Sequences

The payload information is represented by the data sequence

D of length K

i i iC B d=

}1 2 ... ...i KD d d d d=1 for a 1-Bit

, 0 -11 for a 0-Bit

id i K

+=

1

L

i

i

C X=

=

PSSS-

Principle

The sequence to be transmittedXis multivalent and of length L

{ } ( )mod

,1, ,2, , , ,

1 1... ... ,

02

k i L

i i i i k i L i k

aB b b b b b

++

= = =


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PSSS-Sequence

The code sequenceX(referred to as PSSS-sequence) is

the base band signal of the PSSS-procedure

After modulation, RF-transmission, reception and

demodulation the sequenceX is received

The cyclical correlation of the multivalent sequenceX

leads to a sequence of soft bits D

The data sequence is reconstructed by threshholding

these soft bits

PSSS-

Principle


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Transmission of a PSSS-Sequence

B1

Bj

dk

Bk

dj

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

Summarization of the process of spreading, superposition and correlation

d1

d2

dj

dk

Multivalued

Code Sequence C

Receiver


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The PSSS Data Stream

Guard Interval

PSSS-Signal

Cyclic Correlation

Channel

Impulse

Response

PSSS-

Principle


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Transmission of a PSSS-Sequence

B1

Bj

dk

Bk

dj

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

Summarization of the process of spreading, superposition and correlation

d1

d2

dj

dk

Multivalued

Code Sequence C

Receiver

Guard Interval

Appended

PSSS-

Principle


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Generatiom of the Sequences at the

Transmitter Side

PSSS-

Principle

Assume that one block of PSSS-data includes K data bits

Each of these K data bits is multiplied with one cyclically

shifted spreading sequence

B1

dk

Bk

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

d1

d2

dj

dk

Multivalued

Code Sequence C

Receiver

S iti f S di S


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Superposition of Spreading Sequences

at the Transmitter SidePSSS-

Principle

All K sequences are added and form one PSSS-sequence

The resulting multivalent sequence is modulated andtransmitted

B1

dk

Bk

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

d1

d2

dj

dk

Multivalued

Code Sequence C

Receiver


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Appending a Guard IntervalPSSS-Principle

A guard interval is appended to avoid interference

between subsequent PSSS-Blocks

B1

dk

Bk

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

d1

d2

dj

dk

Guard Interval

Appended

Receiver


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Reconstruction at the Receiver SidePSSS-Principle

The PSSS-sequence is reproduced by the demodulation

The cyclic correlation of the received sequence with the

original spreading sequence yields the original data bits

B1

dk

Bk

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

d1

d2

dj

dkReceiver

Transmitted Sequence

Reassembling Data Bits at the


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Reassembling Data Bits at the

Receiver SidePSSS-

Principle

These data bits are reassembled to the original data

stream

B1

dk

Bk

B2

d2

d1

Transmitter

CyclicCorrelation

Cwith A

Selection

of

Data Bits

d1

d2

dj

dkReceiver

Transmitted Sequence

PSSS Overlap of 31 Sequences and


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PSSS Overlap of 31 Sequences and

Reconstruction

The Example with ofK = L bits shows the spreading sequence oflength 31, the original data sequence, the multivalent PSSS-sequence and the reconstructed sequence

PSSS-

Principle


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Comparison: OFDM versus PSSS

Frequency

Time

Code

Guard Interval

Frequency

PSSSOFDM

Data

Data

Guard

PSSS-

Principle

Increasing Multipath Fading


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Increasing Multipath Fading

Resistance by Scaling PSSS

With the multivalent sequenceXof lengthL a maximum

number of Kbits can be transmitted L = K

For a scaled usage, not allL shifted sequences must be

used

Since the gaps between the reconstructed delta

functions get larger, this increases the resistance to

multipath fading

Hence, a tradeoff between interference resistance and

data rate is achieved

PSSS-

Principle

Amplitude Distribution of PSSS-


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Amplitude Distribution of PSSS-

Sequences

Every element of the PSSS-sequence forms a

multivalent chip, which is transmitted with one

modulation symbol

It is noticed that the amplitude distribution of the PSSS-

sequence is data-dependent and not uniformly

distributed approximately a Gauss distribution

The maximum of the amplitude distribution is at

zero

small values appear more often as higher values

Modulation

Non-Uniform Amplitude Distribution


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Non-Uniform Amplitude Distribution

of the PSSS - Baseband SignalPSSS-

Principle


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MODULATION

Different Modulation Methods can transmit the PSSS

sequenceX, e.g.:

M-PAM

M-QAM

M-QPSK

Performance


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PSSS with M-PAM

The simplest modulation method is given with M-PAM.

The PSSS-signal is transmitted by a double side bandmodulation

Transfer rates up to 1 bit/symbol are obtained by this

procedure

If not all possible sequences are overlapped, lower data

rates are possible with a corresponding spreading gain

Performance


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PSSS with M-PAMPerformance

PSSS i h M PAM


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PSSS with M-PAMPerformance

PSSS i h M QAM


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PSSS with M-QAM

An increased data rate can be achieved with M-QAM

In this case two PSSS-Sequences as I- and Q-Signal are

fed to the modulator

The corresponding curves for M-QAM are plotted for

comparison in the diagram

M was chosen 17*17=289, were the higher amplitude

values are rare or do not appear

Performance

Constellation diagram and BER(EbN0)


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g ( )

with M-QAMPerformance

PSSS ith M PSK


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PSSS with M-PSK

M-PSK as a modulation method has the advantage,

sending with a largely constant power since the PSSS-sequence controls the phase angle

Due to the amplitude distribution a 16-PSK was used

Bit error performance is slightly less than with QAM

Performance

Constellation diagram and BER(EbN0)


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g ( )

with M-PSKPerformance

PSSS T i H d


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PSSS-Transceiver Hardware

MAXIM Eval-Board

Here as transmitter

32 - QAM

DAC - Board CESYS - Spartan2FPGA (Virtex)

Performance

PSSS Performance and ResultsP f


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PSSS Performance and Results

In the current version of investigation data rates from 2

bit/s/Hz scalable down to lower rates with the

advantages of signal spreading

Bit Error Rate is comparable to unipolar BPSK

Advantageous bit error structure favorably compatible

with an outer channel coding

Implementation advantages simpler hardware

Rake Receiver is not necessary

Hence low electricity consumption

Performance

Application Areas of PSSSC l i


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Application Areas of PSSS

General Radio Link

Cable Substitute for General Applications

Areas with Multipath Fading

WLAN / WPAN

Wireless industrial control

Home automatisation and controlAudio-/ video-/ general data transmission in home

applications

Conclusion

Integration of PSSS into IEEE 802 15 4 bC l i


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Integration of PSSS into IEEE 802.15.4.b

PSSS is in the ongoing discussion for IEEE 802.15.4.b

Potential Physical Layer for ZigBee

Data Rate of 250 kbit/s

Frequency Range: Low Band 868 MHz and 915 MHz M-Sequence of Length 31 ( 25-1 )

At 20 Superpositioned Sequences

Conclusion

Future PotentialConclusion


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Future Potential

Subjects of application and further investigations are

Integration of channel equalization Integration of MIMO

Point to multi-point connections with different channels

Pre-Coding using the amplitude statistics Dynamic assignment of transfer capacities to adapt to

different channel requirements including

data rate multipath fading and

delay spread

Conclusion

ConclusionConclusion


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Conclusion

When an increasing number of networks, also other than

WLAN in the 2.4 GHz Range become present, additional

capacities might become available These networks might not be heavily used all time

With a proper priorisation between internal and guest

usage these capacities could be made available

PSSS might become one of this technlogies, particular if

extended to higher data rates

These capacities might serve OBAN as well

Conclusion

FHTW


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Fachhochschule

fr

Technik und

Wirtschaft

Berlin

University ofApplied

Sciences

Thank You

This work was partly sponsored by the BMBF AIF FH3 Program

References


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References

A. Kuzminskiy, H.R. Karimi, E. Edvardsen, J. C. Francis,

Interference Scenarios in Future Wireless Open Access

Networks, WWRF 11th Meeting, Oslo-Norway (2004)

A. Wolf, German Patentschrift zu PSSS (2003)

H. Schwetlick, A. Wolf: PSSS (Parallel Sequence Spread

Spectrum) Application in RF-Communication, 8th IEEE

International Symposium on Consumer Electronics,Reading, UK (2004)

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5 PSSS Schwetlick