doc.: 15-07-0615-00-003c submission march 2007 juinn-horng deng (csist corporation)slide 1 project:...

March 2007

Juinn-Horng Deng (CSIST Corporation)Slide 1

doc.: 15-07-0615-00-003c

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [A new MC-CDMA structure for WPAN physical layer proposal]Date Submitted: [March 2007]Source: [Juinn-Horng Deng1, Jeng-Kuang Hwang2, Yu-Lun Chiu2, and Rih-Lung Chung2, and Yu-Min Chuang1] Company: [CSIST Corporation1, Yuan-Ze University2 ] Address1: [P. O. Box No. 22-14 Luan-Tan, Tao-Yuan, 325, Taiwan, R.O.C.] Address2: [135, Far-East Rd., Chung-Li, Tao-Yuan, 32026, Taiwan, R.O.C.] E-mail: [[email protected], [email protected], [email protected]]Abstract: [This contribution describes a new MC-CDMA structure proposal for WPAN physical layer]

Purpose: [Contribution to 802.15 TG3c at March 2007 meeting in USA]

Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

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Outline

• Introduction• Transmitter Block Diagram of Multi-Code

CS-MBOK MC-CDMA Systems• Receiver Block Diagram of Multi-Code CS-

MBOK MC-CDMA Systems • Simulation results• Summary• References

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Introduction

• We propose the physical layer transceiver structure of a new class of MC-CDMA systems, which is used for 60 GHz WPAN system

• The proposed MC-CDMA system uses the cyclic-shift M-ary biorthogonal keying (CS-MBOK) symbol mapping in terms of the Chu sequence multi-codes with perfect orthogonality

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Introduction

• The proposed MC-CDMA system involves the following key features:– To have low-complexity transceiver structure– To have much lower PAPR– To have better bandwidth efficiency– Can be used in both the LOS and non-LOS

multipath channel environments

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Transmitter Block Diagram of Multi-Code CS-MBOK MC-CDMA Systems

De-

Mux

CS-MBOKMapping & Spreading

Repeater

12j f ne

IFFTAdd

CyclicPrefix

RF


Repeater

2 pj f ne


Repeater

2 Pj f ne

is

(1)is

( )pis

( )Pis

(1)ic

( )pic

( )Pic

Fig. 1

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Transmitter Block Diagram of Multi-Code CS-MBOK MC-CDMA Systems

• Proposed multi-code multi-carrier CDMA transmitter system involves the following schemes– CS-MBOK mapping and spreading– Repeater and frequency shift modulation– IFFT and Add cyclic prefix

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M-ary Bi-Orthogonal Keying (MBOK)

• Denote the ith MBOK symbol as an R-bit codeword si=[si,0 … si,R-1]T

– MBOK uses a set of N orthogonal codes, i.e., M=N

– The R-bit codeword with R=log2N

– The Tx bit rate can be “R times” of that of the conventional single-code BPSK MC-CDMA system

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M-ary Bi-Orthogonal Keying (MBOK)

• Example: – Consider 8-BOK with N=8 spreading codes {c(0) c(1) c(2) … c(7)}

– The mapping between si and ci is done as follows:

0 0

1 1

2 2

3 3

='000' ; ='111'

='001' ; ='110'

='010' ; ='101'

='011' ; ='100'

i i

i i

ii i

i i

if if

if if

if if

if if

c s c s

c s c sc

c s c s

c s c s

4

5

6

7

c

c

c

c

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N-points Poly-phase Chu sequence

• To construct the set of N spreading codes, we choose a N-point polyphase Chu sequence

• For even N, a Chu sequence can be easily found as:

for some integer q with gcd(q,N)=1

(0) 0 1 1

T

Nc c c c

2 / 0 1j n q Nnc e n N

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Cyclic Code Shift Keying (CCSK)

• CCSK uses the discrete shifts of Chu sequence c(0), as the N MBOK codes

• The mth cyclic shifts of the code c(0) is designed as c(m)

• These cyclic shifted Chu sequences have the desired orthogonality property, i.e.,

1 0 1

T

m N mm c c c c c

, 0, for k j k j c c

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• Cyclic shifted Chu sequence has the following properties:– Perfect auto correlation – Cross correlation with perfect orthogonality– N-point IFFT of Chu sequence has constant

modulus in time domain, i.e., low PAPR

( ) ( )

0 2 ( / ) 2 ( / )( 1)(0)

IFFT

IFFT

m m

Tj j m N j m N Ne e e

t c

c

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-50 0 50 1000

5

10

15

20

25

30

35

Time lag

The auto-correlation of Chu sequence

(a) (b)

0 5 10 15 20 25 30 355.6569

5.6569

5.6569

5.6569

5.6569

5.6569

5.6569

5.6569

5.6569

Frequency index

The complex evenlop of Chu sequence in freq. domain

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QPSK-CS-MBOK Symbol Mapping and Spreading

• The CS-MBOK symbol is constructed by combining the cyclic shifted Chu sequence and MBOK

• As shown in CS-MBOK block diagram, the ith QPSK symbol of the pth substream can be spreaded by CS-MBOK code sequence

( ) ( ) ( )p p pi i ide c

( ) ( ) ( ), , 1

p p pi i R i Rd s js

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• The is the CS-MBOK mapping and spreading signal of the pth substream, which the pth substream transmits the source signal being

– i.e., Bits per symbol R+2 log2N + 2

– ex. FFT Points N=32 R+2=7 bits/symbol

( )pie

( ) ( ) ( ) ( ) ( ),0 , 1 , , 1

Tp p p p pi i i R i R i Rs s s s s

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2 bit

R-2 bits

0 1,s s

mc

icis

2 1Rs s XOR

Cyclic Code Mapping

QPSK

Bin to Dec m

id

N-chip Base Chu Seq.

0 1 1[ ] Rs s s

1[ ] R Rs s

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Repeater and Frequency Shift Modulation

• Under the same bandwidth and number of FFT points, we propose multi-code QPSK-CS-MBOK MC-CDMA system which can result in P-fold increase in bit rate

• As shown in Fig.1, the multi-code QPSK-CS-MBOK MC-CDMA system consists of P-substreams QPSK-CS-MBOK symbols

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Repeater and Frequency Shift Modulation• Each substream uses the different frequency

shift modulation and repeater to construct the multi-code parallel transmission system

• For the pth substream, the operation of repeater is designed to duplicate CS-MBOK data with P times, i.e.,

– Where the vector size of is PNx1 and is the repeated cyclic shifted Chu sequence

( )pie

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( )

[ ]

Tp p p p T p p p pi i i i i i i i

p pi i

d

d

f e e e c c c

c

P

( )pif

( )pic

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• Using the frequency shift operation to modulate the pth repeated CS-MBOK symbol

– Where denotes pairwise multiplication and is the pth substream frequency shift operation

– is the frequency shift repeated CS-Chu sequence

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )p p p p p p p pi i i i i id d g f w c w c

( )pw

2 2 ( )( ) 0 , p pTj f j f NPp j

pe e e f p NP w ( )pic

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• These frequency-shift repeated CS-Chu sequence have the desired orthogonality property, i.e.,

• The N-point IFFT of the pth frequency-shift repeated CS-Chu sequence has the zero-inserting property

( ) ( ) 0, , p qi j p q i j c c

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– i.e.,

where QH is IFFT operation and the N-point IFFT of { } is

– Since has the operation of the different zero-insertion, it has the orthogonality property:

( ) ( ) ( )

( ) ( ),0 ,1 0 0 0 0 0

p p H pi i i

p pi i

IFFT

t t

c c Q c

pth element (p+P)th element

( )pic ( ) ( ) ( ) ( )

,0 ,1 , 1[ ]p p p pi i i i Nt t t t

( )pic

( ) ( ) 0, , p qi j p q i j c c

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IFFT and Add Cyclic Prefix

• Combining the P-substreams and taking its IFFT, we can acquire the transmitted signal:

( ) ( ) ( ) ( )

1 1

( ) ( )

1

(0) (0) (1) (1) ( ) ( ) (0) (0) (1) (1) ( ) ( ),0 ,0 ,0 ,1 ,1 , 1

P Pp p H p pi i i i

p p

Pp pi i

p

P P P Pi i i i i i i i i i i i N

IFFT d d

d

d d d d d d

x c Q c

c

c c c c c c

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IFFT and Add Cyclic Prefix

• Since each element of the x involves the constant envelope in time domain, the multi-code MC-CDMA system has the same property as the SC-CDMA system which has much lower PAPR

• Add cyclic prefix used to combat multipath channel effect

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Receiver Block Diagram of Multi-Code CS-MBOK MC-CDMA Systems

MUXFFTChannelEqualizer

RF

MBOKDemapping &

Decision

RepeatedChu-Seq.

Despreading

12j f ne

(1)ˆ ( )is

MBOKDemapping &

Decision

RepeatedChu-Seq.

Despreading

2 pj f ne

( )ˆ ( )p is

MBOKDemapping &

Decision

RepeatedChu-Seq.

Despreading

2 Pj f ne

( )ˆ ( )P is

Detected

Data

ˆ( )is

Fig. 2

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RX Design of CS-MBOK MC-CDMA System• The multi-code MC-CDMA receiver is shown in

Fig. 2

• After discarding the cyclic prefix, the received sample block y is first taken its DFT, yielding:

where is the frequency-domain channel response

( ) ( )

1

( ) ( )

1

PH p p

i ip

Pp pi i

p

d

d

Y Qy Λ Qx Λ QQ c

Λ c

Λ

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RX Design of CS-MBOK MC-CDMA System

• Assume the frequency-domain channel response can be estimated, we can acquire the equalized signal with equalizer processing for the ith symbol is denoted by

where is the AWGN noise

Λ

1

( ) ( )

1

i

Pp pi i i

p

d

z Λ y

c n

in

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• Due to the frequency-shift repeated CS-Chu sequence with orthogonality property, we can use the pth frequency-shift repeated CS-Chu sequence to despread the equalized signal to acquire the ith symbol data of the pth substream:

( )pic

( ) ( ) ( ) ( ) ( )

1

( ) ( ) ( ) ( ) ( )

( )

, (where 0, )

H H

H H

Pp p p p pm m i m i i i

p

p p p p qi m i i m i

z i d

d p q

c z c c n

c c n c c

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• Since CS-MBOK symbol mapping with N cyclic shift, we can find the maximum despreaded value to estimate the CS-MBOK mapped data with the (R-2) bits per symbol

( ) 2

0 1 1

ˆ ˆarg max ( ) , 0 2 1

ˆ ˆ ˆ ˆ ˆ( ) [ ( ) ( ) ( )] 2

p Rm

m

MBOK R

m z i m

i s i s i s i dec bin m

s

0 1 1ˆ ˆ ˆ ˆ( ) [ ( ) ( ) ( )]MBOK Ri s i s i s is

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• Finally, adopting the maximum despreading value and applying the slicer, we can estimate the QPSK symbol, i.e.,

• So the ith symbol of the pth substream can be detected:

ˆ ( )m iz

1ˆ ˆ ˆ( ) [ ( ) ( )]QPSK R Ri s i s is

ˆ0 1ˆ ˆ ˆ( ) [ ( ) ( )] ( )QPSK mi s i s i decision z i s

( )ˆ ˆ ˆ( ) [ ( ) ( )]pMBOK QPSKi i is s s

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Simulation Results

• 2 path channel : delay spread =[0.8 0.6];

0 2 4 6 8 10 12 14 16 18 2010

-5

10-4

10-3

10-2

10-1

100

Eb/N

0, dB

BE

Rh=[0.8 0.6 zeros(1,30)]

LS with sync.

LS

Constrain LS with sync.Constrain LS

ideal channl est.

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Simulation Results

• h=[0.8 0.2+0.4j zeros(1,3) 0.1+0.1j]

0 2 4 6 8 10 12 14 16 18 2010

-6

10-5

10-4

10-3

10-2

10-1

100

Eb/N

0, dB

BE

R

LS with sync.

LS

Constrain LS with sync.Constrain LS

ideal channl est.

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Summary of System Merits

• Spread spectrum Processing gain against interference

• CP insertion multipath channel mitigation

• CS-MBOK = CCSK + MBOK– Higher bandwidth efficiency than conventional

single-code CDMA system– Improved BER Performance as N gets larger– Simple code correlator through using FFT

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Summary of System Merits

• Chu sequence as spreading Code– Perfect autocorrelation property for MBOK– Lower PAPR TX signal for asymmetrical

application

• Repeater and Frequency Shift Modulation– Improve the spectral efficiency

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References

[1] L. Hanzo et al., OFDM and MC-CDMA for Broadband Multi-User Communications, WLANs and Broadcasting, John Wiley & Sons, 2003.

[2] H. Hara, and P. Prasad, “Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels,” IEEE Trans. Vehicular Technology, vol. 48, pp. 1584-1595, Sep. 1999.

[3] J. Linnartz, “Performance analysis of synchronous MC-CDMA in mobile Rayleigh channel with both delay and Doppler spreads,” IEEE Trans. Vehicular Technology, vol. 50, pp. 1375-1387, Nov. 2001.

[4] M. K. Simon, S. M. Hinedi, and W. C. Lindsey: Digital Communication Techniques, Prentice-Hall, 1995.

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References

[5] D. C. Chu, “Polyphase codes with good periodic correlation properties,” IEEE Trans. Inform. Theory, vol. 18, no. 4, pp. 531–532, 1972.

[6] G.M. Dillard, M. Reuter, J. Zeidler, and B. Zeidler, “Cyclic code shift keying: a low probability of intercept communication technique,” IEEE Transl. on Aerospace and Electronic Systems, vol. 39, issue 3 Page(s):786 – 798, July 2003. D. R. Wehner: High-Resolution Radar, 2nd-Ed., Artech House, 1995. (Chap. 4,5)

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Thank you for your attention !!

doc.: 15-07-0615-00-003c submission march 2007 juinn-horng deng (csist corporation)slide 1 project:...

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