- Email: [email protected]
Performance Analysis of Anti-Interference UWB-OFDM System
THE JOURNAL OF CHINA UNIVERSITIES OF POSTS AND TELECOMMUNICATIONS Vol.13, No.2, Jun.2006
Performance Analysis of Anti-Interference UWB-OFDM System ZHANG Shi-binglY2, CAO Shi-ke',
ZHANG Li-jun'
1.Communication and information Engineering Institute, Nanjing University of Posts and Telecommunications. Nanjing 210003, P. R . China: 2.School of Electronics and Information, Nantong University, Nantong 226007, P. R. China)
This paper examines the robustness of anti-interference Ultra- Wide-Band UWB-OFDM ( AI-UWH) systems in presence of narrow-band interference. It analyzes the bit error rate perjormance of the systems in both the single-user und multi-user mode.%,and compares its robustness in different code matrixes. By encoding transmitted symbols and spreading their power over all sub-bands, AI-UWB systems can make full use of the frequency diversity ucross the sub-bands and have more robustness to the narrowband interference. Simulating results show that different codes have almost the same robustness to the narrowband interference. The encoding and spreading could suppress the narrowband interference effectively. Cvrnpured with the ISUWB systems, our approach has more than 5 dB interference murgin . Key words: UWB; anti-interference ; bit error rate ; coding ; spreading
Abstract:
CLC number:
1
TN914.51
Document code:
A
Article ID: l005-8885(2006)02-0O06-O4
all sub-bands rather than one sub-band in IS-UWB system. In this paper, we analyze the performance of the AIUWB system in both single-user as well as multi-user and examine the robustness to .interference under different orthogonal code matrix. We provide the mathematical analytical relation and simulating results. It is shown that the different codes have almost the same robustness to the narrowband interference. Encoding and spreading could enhance the robustness of the system to interference or frequency-selective fading, especially to wideband interference.
Introduction
Due to the robustness to multipath fading, high rate, low in cost and small power consumption, UWB communication is a promising technique for short rang, high-speed wireless applications" -'I . But UWB system design has many challenges. One of the main challenges is dealing with a lot of interference or jamming that come from the other narrowband wireless systems working simultaneously in the UWB. Significant attention has been paid to the potential impacts between UWB system and the wireless systems which are operating in the same frequency range as 2 The Brief of AI-UWB System UWB[9-'41, but a little has been paid to the cure for enhancing the robustness of IJWB system to the interAll sub-channels in the AI-UWB system"43 are dividferences. In Ref. [ 12 ], an interference suppressing ed into M sub-bands, each sub-band comprises J subUWB-OFDM ( I S U W B ) system is described. It pro- channels, J X M = N . In n th period of the frame, the vides redundancy when one or more sub-channels are af- N parallel symbol streams x,, for i = 0, 1, N - 1, fected by narrowband interference. But, when the are separated into J groups and form a J x M-order bandwidth of the interference is wider than a few of symbol matrix as X and encoded by an M-order orthogsub-bands, the symbol transmitted would be lost out. onal code matrix A into This system has little robustness to wideband interferto t] ... LJ( M - 1 ) ence or frequency-selective fading. In Ref. [ 131, an ... t J ( M - 1) + 1 tl tJ+l UWB pulse design for multiple narrowband interference suppression is proposed. In Ref. [ 141, we proposed an t]-1 t2J - 1 " * tN-1 anti-interference UWB-OFDM ( AI-UWB) system, in , ~ ~denotes / ] J , the rewhich all sub-channels are separated into M sub-bands where t i = ~ x k + ~ r ~ / ~ l a krx1 mainder of x Lx ], denotes the integer of x. and the power of each transmitted symbol is spread over * . a ,
Received date: 2005-10-17 Foundation item: This work
was
supported by Universities Natural Science Research Project of Jiangsu Province (05KJuSlOl01)
No. 2
ZHANG Shi-bing,
et
el. : Performance Analysis of Anti-Interference UWBOFDM System
The encoded symbol streams is modulated corresponding sub-carrier fiinto
7
by M-l
N-l
I
s; = ~ t k e x p [ j 2 x E ) i =
0,1,**., N - 1 (2)
~ x k + M ~ I / J l a k , ~ l /+J ~zlC 1+ j
I
(8)
k=O
k-O
At the receiver, the received signal can be expressed as
r ( t ) =s ( t ) * c ( t )+ z ( t ) (3) where c ( t ) is the impulse response of UWB channel, z ( t is AWGN and interference or jamming, * denotes the convolution. After A/D converting and FFT, we obtain
>
- . - d
U=TC+N+J
(4)
where C is the equivalent discrete coefficient vector of
where I = 0, 1, * * * , N - 1, C L represents the complex coefficients of 1 th sub-channel and is given by
(9) and Zl is the corresponding demodulated Additive White Gaussian Noise ( AWGN) of l t h sub-channel with zero mean and variance &, Jl is the corresponding demodulated interference of 1th sub-channel with zero mean and variance 0:1. They are given respectively by
c ( t ), is the demodulated vector of AWGN, is the demodulated vector of interference or jamming. Decoded by orthogonal code, the output of the receiver can be expressed as M- I
Yi =
C Uu+tl/MJak,rliMi
(5)
k=O
Performance Analysis
3 3.1
In fact, the narrow-band interference exists only in a fraction of the UWB channel. If there is interference only in mo sub-bands of system, the interference in the m t h sub-band can be modeled as
Single-User
Without loss of generality, we consider the UWB-
OFDM symbol detection over the time interval O < t < where J 0 is the average interference power spectral denT , in the n th transmission frame, where T , = T p+ T, sity over sub-band due to the interferers, p is the duty is the frame duration, T p is the signal duration, T , is cycle of the interference and is defined as the guard interval duration. The transmitted signal can be represented in continuous-time form as
cc N-1 M - I
s(t) =
,=I
k=O
Assuming that the channel is an AWGN channel and xk+Mrl/Jlak,Lt/JJP(t)d2n(4+1fn)t all sub-channels have the same AWGN variance, it follows that the output of the system can be expressed as
(6)
where 1 z, 1 is the QPSK symbol that is transmitted in the n th transmission interval over the UWB channel, p ( t ) is a general lowpass signal, f, is the 0th sub-carrier frequency, fa is the fundamental frequency and equal to 1/ T P . The received signal can be rewritten in the continuous-time form as r(t)=jws(t
-
0
jo
r ) c ( r ) d r + n ( t >+ j ( t ) =
N-I M-l
~,zk+MrI/Jluk.Li/JIP(t- r ) c ( r )
&2n(f, + 1"Kt
-r)
dr+n(t)+j(t) (7) where n ( t ) is AWGN, j ( t ) is interference or jamming, Assuming perfect synchronization, after A/D and FFT operating, the output of the 1th sub-channel at time T p is
M-l
xi
M-1
+ ni+jj
where is the stationary stochastic process with the same distributing and variance as Z;, j i is the stationary stochastic process with the same distributing as J but the power spectral density is 1 0 . The Bit Error Rate (BER) performance of the AIUWB system can be obtained by averaging the BER of the all sub-channels. Using the result in Ref. [ 151, we get the BER as ,
Pb-AI=
Q(
-,
J*)No
+J
o
where Q ( z ) is Q function, Eo is the signal energy per bit, N o is the AWGN power spectral density.
8
T h e Journal of CHUPT
For the C-UWB system, the BER is given by
The function Q ( 3 )decreases exponentially instead of linearly as x . Generally we obtain (17) It is obvious that the coding and spreading could improve the anti-interference performance of the system. But it has no effect on AGWN. It is because that the interference exists in a fraction of the band but the AGWN exists over the band. We obtain more interference margin in the AI-UWB system than in the C-UWB system. This enhances the robustness of the AI-UWB system to interferences or frequency-selective fading. The margin depends on p or M . The larger M is, the larger margin is.
3.2
Multi-User
One simple method for multiple access is to assign some of the parallel data streams s,to every user upon request by the users. Another method is to transmit user information in packets over the UWB channel where we regard the N parallel data streams .r, as N packets. When users have one or more packets to transmit, they access the channel. Since x, } are independent data streams, i. e. , user data are independent each other, the performance that has been described above for single-user communications is directly applicable and no new problems are encountered in multiple access environment, except for the additional task of assigning users to available data streams or packets. In other words, the performance of multiuser communication is the same as one of single-user communication.
4
2006
here. One is modeled as partial-band Gaussian random process described in Eq. ( 1 2 ) . Another is modeled as multi-tone continuous wave which is randomly spaced within the IEEE 802.11 band ( most notably coexistence with IEEE 802. l l a system in the 5 GHz band) and given by K -1
J ( t ) = 2h/3,cos(2nf~t +
(18)
Sk>
k=O
where /3, is a statistically independent random variable with variance f, is the jamming frequency in the 802. l l a band, 19k is statistically independent random variable with uniform distribution over (0, 2 n ) . Fig. 1 and Fig. 2 illuminate the BER performance versus Signal-to-Interference Ratio ( S I R ) ( EO/Jo) using Hadamard code in the presence of partial-band interference and multi-tone jamming respectively when Signalto-Noise Ratio (SNR) = 10 dB.
03,
E
I
\
-AI-UWR -
10-4,0
I
1
-5
0 (EJJo)/dB
5
10
Fig. 1 BER performance using Hadamard c d e in the case of of partial-band interference
- - - - - - - _ _ _ _- -_- - - _ _
Simulation Results
We choose the multipath model proposed in Ref. [ 161 for the simulation. The main parameters of the system considered are tabulated in Table 1.
3 m
- - IS-UWB
..'.. ..
Table 1 System parameters Parameters Bandwidth
Values 5.125 GHz
Sub-bandwidth
5 MHz
Number of data streanis( N )
1 024
Number of groups( M ) Information length( T o )
32 200 ns
Guard interval( T,)
40 ns
Symbol length( T , )
240 ns
Constellation
QPSK
Two different interference models are considered
L -5 0 5 10
10: 10
(Ew'Jo)/dB Fig.2 BER performance using Hadamard code in the case of multi-tone jamming
As SIR increases, the BER degrades rapidly. But when the SIR is about 5 dB, the BER degrades slowly. When the SIR is more than 10 dB, the UER curve becomes flat. Then the effect of SNR on the BER is unfolded and the BER begins to be depended on SNR mainly. When the SIR is very small ( - 9 dB in the
No. 2
ZHANG Shi-bing, et a l . : Performance Analysis of Anti-Interference UWB-OFDM System
9
presence of partial-band interference or - 4 dB in the presence of multi-tone jamming), the BER is so high 5 Conclusions that the systems could not work up to snuff. In this case, we should give up the sub-channels that are badly In this paper, we derived some expressions that quanaffected by interference or jamming. tify the AI-UWB system performance including the roCompared with IS-UWB system, the AI-UWB sys- bustness to narrow-band interference in different code tem improves the performance about 5 dB in SIR. In matrixes. It indicates that the encoding and spreading other words, the AI-UWB system has about 5 dB mar- would exploit the frequency diversity across the subgin in SIR than the IS-UWB system in the presence of bands as well as sub-channels and enhance the robustinterference. It is because that the power of the trans- ness of AI-UWB system to narrow-band interference. mitted symbol in AI-UWB system is distributed over ev- When some sub-channels or sub-bands are affected by ery sub-band rather than one sub-band in IS-UWB sys- interference or jamming or frequency-selective fading, tem. the coded bits can be received from the others. ComFig. 3 and Fig. 4 illuminate the different effect on the pared with IS-UWB system, the AI-UWB system imBER performance of AI-UWB system by different codes proves the performance about 5 dB in SIR. But the different code matrixes have almost the same effect on narrow-band interference. Encoding and spreading is an effective cure for UWB-OFDM system to enhance the ro----_ bustness to narrow-band interference. ---C-UWB 10’
-Hadamard - - DCT - - P4
3 m
References: [ l ] WIN M 2, SCHOLTZ R A. Ultra-wide bandwidth time-
Fig. 3 BER performance using different code in the presrnre of partial-band interference
- - - - - _ _ -_- - - - _
10 *
- - - C-UWB
-Hadamard
E 10
’:
t 1u
-5
5
0
10
hopping spread-spectrum impulse radio for wireless multipleacces9 communications [ J ] . IEEE Trans on Communications, 2000, 48(4) : 679 - 691. [2] WIN M Z, SCHOLTZ R A. Impulse radio: how i t works [ J ] . IEEE Communications Letters, 1998, 2 ( 2 ) : 36 - 38. [3] WIN M Z, SCHOLTZ R A. Characterization of ultra-wide bandwidth wireless indoor channels: A communication-theoretic view [J 1. IEEE Journal on Selected Areas in Communications, 2002, 2 0 ( 9 ) : 1613 - 1627. 141 ZHANG S B, ZHANG 1- J . Ultra wideband radio communication and its key technology [ J ] . Telecommunication Engineering, 2004, 44( 1 ) : 1 - 6 . [S] AIE1,I.O G R. Challenges for Ultra-WideBand ( U W B ) CMOS integration [ C ] // Proceedings of IEEE MTT-S International Microwave Symposium Digest: Vol 1 , Jun 8 13, 2003, Philadephia, PA, USA. Piscataway, NJ, USA: IEEE, 2003: 361 -364. [ 6 ] CUOMO F, MARTEILO C, BAIOCCHI A. Radio resource sharing for Ad Hoc networking with UWB [ J ] . IEEE Journal on Selected Areas in Communications, 2002,
( EJJo )/dB
Fig. 4 BER performance using different codein the presence of multi- tone jamming
in the presence of interference when SNR is 10 dB. It is apparent that there is a little difference among Hadamard code matrix, DCT code matrix and P4 code matrix. This is because that there is a little different frequency diversity across the sub-bands and sub-channels when the transmitted symbols are encoded and spread by different code matrix. Comparatively speaking, P4 code matrix is most effective and DCT code is worst.
[7]
[8]
20(9) : 1722- 1732. HU J , YANG Y I-, XIE X 2 . A multi-access UWB-OFDM based on FFH [ J ] . Journal of Chongqing University of Posts and Telecommunications, 2005, 17(2) : 177 - 179. HE Jian-hui, QUAN Zi-yi, MEN Ai-dong. PARR reduction in OFDM systems with large number of sub-carriers by carrier interferometry approaches [ J ] . The Journal of China University of Posts and communications, 2004, 1 1 ( 4 ) :
91 - 94. [9]
NAKAGAWA M, ZHANG H, SAT0 H. Ubiquitous homelinks based on IEEE 1394 and ultra wideband solutions [ J 1. IEEE Gmmunications Magazine, 2003, 41 ( 4 ) :
74 - 82.
To p.38
38
The Journal of CHUPT of public-key cryptography for wireless sensor networks[ C] //Proceedings of the 3rd International Conference on Pervasive Computing and Communications, Mar 8 - 12, 2005, Kauai Island, HI, USA. Im Alamitos, CA, USA: IEEE Computer Society, 2005: 324 - 328. SHAMIR A. Identity-based cryptography and signature schemes [ C 1 // Proceedings of Advances in Cryptology (CKYPT0’84), Aug 19 - 22, 1984, Santa Barbara, CA, USA. Berlin, Germany: Springer, 1984:47 - 53. FEIGE U, FIAT A, SHAMIR A. Zero-knowledge proofs of identity[J]. Cryptology, 1988,1(2) :77 - 94. FIAT A, SHAMIR A. How to prove yourself: practical solutions to identification and signature problems[ C] // Proceedings of Advances in Cryptology ( CRYPTO’86 ), Aug 11 - 15, 1986, Santa Barbara, CA, USA. Berlio, Germany: Springer, 1987: 186 - 194. BONEH D, FRANKLIN M. Identity-based encryption from the Weil pairing [ C ] // Proceedings of Advances in Cryptology(CRYPTO’2001), Aug 19 - 23, 2001, Santa Barbara, CA, USA. Berlin, Germany: Springer, 2001 : 213-229. BOYEN X . Multipurpose identity-based signcryption, a swiss army knife for identity-based cryptography[ C] //Proceedings of Advances in Cryptology(CRYPTO’2003), Aug 17 - 21, 2003, Santa Barbara, CA, USA. Berlin, Germany: Springer, 2003,2729 :383 - 399. CHEN I,, KUDLA C. Identity-based authenticated key agreement protocols from pairings [ R ] . Cryptology ePrint
From p . 9 ZHAO I,, HAIMOVICH A M. Performance of ultra-wideband communications in the presence of interference [ J 1 . IEEE Journal on Selected Areas in Communications, 2002, 20(9) : 1684 - 1691. DURlSI G , HENEDETTO S. Performance evaluation of TH-PPM UWB system in the presence of multiuser interferences [ J ] . IEEE Communications Letters, 2003, 7( 5 ) : 224 - 226. GERAKOUI-IS D, SAI-MI P . An interference suppressing OFDM system for ultra wide bandwidth radio channels [ C] //Proceedings of 2002 IEEE Conference on Ultra Wideband Symposium Systems and Technologies, May 21 23, 2002, Baltimore, MD, USA. Piscataway, NJ, USA: IEEE, 2002 : 259 - 264. LUO 2 D, GAO H, LIU Y A, et al. Ultra-wideband pulse design approach for multiple narrowband interference suppression [J] . Journal of Beijing University of Posts and Telecommunications, 2005, 28( 1) : 55 - 58. ZHANG S B, CAO S K, ZHANG L J . An anti-interference coding in UWBOFDM communications [ J 1. The Journal of China University of Posts and communications, 2005, 12(4) :32 37.
[25]
2006
Archive, Report 2002/184. http: //eprint. iacr. org/2002/ 184, 2002. WATERS B R . Efficient - identity-based encryption without random oracles[R] . Cryptology ePrint Archive, Report 2004/180, http: //eprint. iacr. org/2004/180, 2004. Biographies:CHENG Hong-hing, male, he is a Ph. D. Candidate of Nanjing University of Posts and Telecommunications. He is a lecturer in College of Information Engineering at Jiangsu Radio and T V University. His current research interest includes information security, grid computing, and computer networks.
YANG Geng, male, he received Ph. D. degree in Computer Science from Lava1 University in 1994 and was a post-doctoral research fellow in Center for Research on Computation and its Applications at University of Montreal from 1994 to 1996 in Canada respectively. He is a professor in College of Computer at Nanjing University of Posts and Telecommunications. He is dean of the College of Mathematics and Physics of NUPT. His current research interest includes network security, parallel and distributed computing, mobile computing. Dr. Yang is a member of the IEEE Computer Society and a Standing Member of Chinese Cnmputer Education Society.
[ 151 Proakis J G. Digital Communications (Fourth Edition), New York, McGraw-Hill, 2001. [ 161 ZHANG S B, ZHANG I, J. The modeling and simulation of UWB channel [ J ] . Journal of Nanjing University of Posts and Telecommunications, 2005, 25(3) : 50 - 53. Biographies: ZHANG Shi-bing, male, Ph. D. Candidate, associate professor. School of Electronics and Information of Nantong University, interested in the research on signal processing for communications, Ultra-Wideband communication.
~
~
ZHANG Li-jun, male, Professor and Ph. D. Tutor, Nanjing University of Posts and Telecommunications interested in the research on the areas of wireless data, access technology and system of wireless IP, mobile computing and its applications.
Performance Analysis of Anti-Interference UWB-OFDM System ZHANG Shi-binglY2, CAO Shi-ke',
ZHANG Li-jun'
1.Communication and information Engineering Institute, Nanjing University of Posts and Telecommunications. Nanjing 210003, P. R . China: 2.School of Electronics and Information, Nantong University, Nantong 226007, P. R. China)
This paper examines the robustness of anti-interference Ultra- Wide-Band UWB-OFDM ( AI-UWH) systems in presence of narrow-band interference. It analyzes the bit error rate perjormance of the systems in both the single-user und multi-user mode.%,and compares its robustness in different code matrixes. By encoding transmitted symbols and spreading their power over all sub-bands, AI-UWB systems can make full use of the frequency diversity ucross the sub-bands and have more robustness to the narrowband interference. Simulating results show that different codes have almost the same robustness to the narrowband interference. The encoding and spreading could suppress the narrowband interference effectively. Cvrnpured with the ISUWB systems, our approach has more than 5 dB interference murgin . Key words: UWB; anti-interference ; bit error rate ; coding ; spreading
Abstract:
CLC number:
1
TN914.51
Document code:
A
Article ID: l005-8885(2006)02-0O06-O4
all sub-bands rather than one sub-band in IS-UWB system. In this paper, we analyze the performance of the AIUWB system in both single-user as well as multi-user and examine the robustness to .interference under different orthogonal code matrix. We provide the mathematical analytical relation and simulating results. It is shown that the different codes have almost the same robustness to the narrowband interference. Encoding and spreading could enhance the robustness of the system to interference or frequency-selective fading, especially to wideband interference.
Introduction
Due to the robustness to multipath fading, high rate, low in cost and small power consumption, UWB communication is a promising technique for short rang, high-speed wireless applications" -'I . But UWB system design has many challenges. One of the main challenges is dealing with a lot of interference or jamming that come from the other narrowband wireless systems working simultaneously in the UWB. Significant attention has been paid to the potential impacts between UWB system and the wireless systems which are operating in the same frequency range as 2 The Brief of AI-UWB System UWB[9-'41, but a little has been paid to the cure for enhancing the robustness of IJWB system to the interAll sub-channels in the AI-UWB system"43 are dividferences. In Ref. [ 12 ], an interference suppressing ed into M sub-bands, each sub-band comprises J subUWB-OFDM ( I S U W B ) system is described. It pro- channels, J X M = N . In n th period of the frame, the vides redundancy when one or more sub-channels are af- N parallel symbol streams x,, for i = 0, 1, N - 1, fected by narrowband interference. But, when the are separated into J groups and form a J x M-order bandwidth of the interference is wider than a few of symbol matrix as X and encoded by an M-order orthogsub-bands, the symbol transmitted would be lost out. onal code matrix A into This system has little robustness to wideband interferto t] ... LJ( M - 1 ) ence or frequency-selective fading. In Ref. [ 131, an ... t J ( M - 1) + 1 tl tJ+l UWB pulse design for multiple narrowband interference suppression is proposed. In Ref. [ 141, we proposed an t]-1 t2J - 1 " * tN-1 anti-interference UWB-OFDM ( AI-UWB) system, in , ~ ~denotes / ] J , the rewhich all sub-channels are separated into M sub-bands where t i = ~ x k + ~ r ~ / ~ l a krx1 mainder of x Lx ], denotes the integer of x. and the power of each transmitted symbol is spread over * . a ,
Received date: 2005-10-17 Foundation item: This work
was
supported by Universities Natural Science Research Project of Jiangsu Province (05KJuSlOl01)
No. 2
ZHANG Shi-bing,
et
el. : Performance Analysis of Anti-Interference UWBOFDM System
The encoded symbol streams is modulated corresponding sub-carrier fiinto
7
by M-l
N-l
I
s; = ~ t k e x p [ j 2 x E ) i =
0,1,**., N - 1 (2)
~ x k + M ~ I / J l a k , ~ l /+J ~zlC 1+ j
I
(8)
k=O
k-O
At the receiver, the received signal can be expressed as
r ( t ) =s ( t ) * c ( t )+ z ( t ) (3) where c ( t ) is the impulse response of UWB channel, z ( t is AWGN and interference or jamming, * denotes the convolution. After A/D converting and FFT, we obtain
>
- . - d
U=TC+N+J
(4)
where C is the equivalent discrete coefficient vector of
where I = 0, 1, * * * , N - 1, C L represents the complex coefficients of 1 th sub-channel and is given by
(9) and Zl is the corresponding demodulated Additive White Gaussian Noise ( AWGN) of l t h sub-channel with zero mean and variance &, Jl is the corresponding demodulated interference of 1th sub-channel with zero mean and variance 0:1. They are given respectively by
c ( t ), is the demodulated vector of AWGN, is the demodulated vector of interference or jamming. Decoded by orthogonal code, the output of the receiver can be expressed as M- I
Yi =
C Uu+tl/MJak,rliMi
(5)
k=O
Performance Analysis
3 3.1
In fact, the narrow-band interference exists only in a fraction of the UWB channel. If there is interference only in mo sub-bands of system, the interference in the m t h sub-band can be modeled as
Single-User
Without loss of generality, we consider the UWB-
OFDM symbol detection over the time interval O < t < where J 0 is the average interference power spectral denT , in the n th transmission frame, where T , = T p+ T, sity over sub-band due to the interferers, p is the duty is the frame duration, T p is the signal duration, T , is cycle of the interference and is defined as the guard interval duration. The transmitted signal can be represented in continuous-time form as
cc N-1 M - I
s(t) =
,=I
k=O
Assuming that the channel is an AWGN channel and xk+Mrl/Jlak,Lt/JJP(t)d2n(4+1fn)t all sub-channels have the same AWGN variance, it follows that the output of the system can be expressed as
(6)
where 1 z, 1 is the QPSK symbol that is transmitted in the n th transmission interval over the UWB channel, p ( t ) is a general lowpass signal, f, is the 0th sub-carrier frequency, fa is the fundamental frequency and equal to 1/ T P . The received signal can be rewritten in the continuous-time form as r(t)=jws(t
-
0
jo
r ) c ( r ) d r + n ( t >+ j ( t ) =
N-I M-l
~,zk+MrI/Jluk.Li/JIP(t- r ) c ( r )
&2n(f, + 1"Kt
-r)
dr+n(t)+j(t) (7) where n ( t ) is AWGN, j ( t ) is interference or jamming, Assuming perfect synchronization, after A/D and FFT operating, the output of the 1th sub-channel at time T p is
M-l
xi
M-1
+ ni+jj
where is the stationary stochastic process with the same distributing and variance as Z;, j i is the stationary stochastic process with the same distributing as J but the power spectral density is 1 0 . The Bit Error Rate (BER) performance of the AIUWB system can be obtained by averaging the BER of the all sub-channels. Using the result in Ref. [ 151, we get the BER as ,
Pb-AI=
Q(
-,
J*)No
+J
o
where Q ( z ) is Q function, Eo is the signal energy per bit, N o is the AWGN power spectral density.
8
T h e Journal of CHUPT
For the C-UWB system, the BER is given by
The function Q ( 3 )decreases exponentially instead of linearly as x . Generally we obtain (17) It is obvious that the coding and spreading could improve the anti-interference performance of the system. But it has no effect on AGWN. It is because that the interference exists in a fraction of the band but the AGWN exists over the band. We obtain more interference margin in the AI-UWB system than in the C-UWB system. This enhances the robustness of the AI-UWB system to interferences or frequency-selective fading. The margin depends on p or M . The larger M is, the larger margin is.
3.2
Multi-User
One simple method for multiple access is to assign some of the parallel data streams s,to every user upon request by the users. Another method is to transmit user information in packets over the UWB channel where we regard the N parallel data streams .r, as N packets. When users have one or more packets to transmit, they access the channel. Since x, } are independent data streams, i. e. , user data are independent each other, the performance that has been described above for single-user communications is directly applicable and no new problems are encountered in multiple access environment, except for the additional task of assigning users to available data streams or packets. In other words, the performance of multiuser communication is the same as one of single-user communication.
4
2006
here. One is modeled as partial-band Gaussian random process described in Eq. ( 1 2 ) . Another is modeled as multi-tone continuous wave which is randomly spaced within the IEEE 802.11 band ( most notably coexistence with IEEE 802. l l a system in the 5 GHz band) and given by K -1
J ( t ) = 2h/3,cos(2nf~t +
(18)
Sk>
k=O
where /3, is a statistically independent random variable with variance f, is the jamming frequency in the 802. l l a band, 19k is statistically independent random variable with uniform distribution over (0, 2 n ) . Fig. 1 and Fig. 2 illuminate the BER performance versus Signal-to-Interference Ratio ( S I R ) ( EO/Jo) using Hadamard code in the presence of partial-band interference and multi-tone jamming respectively when Signalto-Noise Ratio (SNR) = 10 dB.
03,
E
I
\
-AI-UWR -
10-4,0
I
1
-5
0 (EJJo)/dB
5
10
Fig. 1 BER performance using Hadamard c d e in the case of of partial-band interference
- - - - - - - _ _ _ _- -_- - - _ _
Simulation Results
We choose the multipath model proposed in Ref. [ 161 for the simulation. The main parameters of the system considered are tabulated in Table 1.
3 m
- - IS-UWB
..'.. ..
Table 1 System parameters Parameters Bandwidth
Values 5.125 GHz
Sub-bandwidth
5 MHz
Number of data streanis( N )
1 024
Number of groups( M ) Information length( T o )
32 200 ns
Guard interval( T,)
40 ns
Symbol length( T , )
240 ns
Constellation
QPSK
Two different interference models are considered
L -5 0 5 10
10: 10
(Ew'Jo)/dB Fig.2 BER performance using Hadamard code in the case of multi-tone jamming
As SIR increases, the BER degrades rapidly. But when the SIR is about 5 dB, the BER degrades slowly. When the SIR is more than 10 dB, the UER curve becomes flat. Then the effect of SNR on the BER is unfolded and the BER begins to be depended on SNR mainly. When the SIR is very small ( - 9 dB in the
No. 2
ZHANG Shi-bing, et a l . : Performance Analysis of Anti-Interference UWB-OFDM System
9
presence of partial-band interference or - 4 dB in the presence of multi-tone jamming), the BER is so high 5 Conclusions that the systems could not work up to snuff. In this case, we should give up the sub-channels that are badly In this paper, we derived some expressions that quanaffected by interference or jamming. tify the AI-UWB system performance including the roCompared with IS-UWB system, the AI-UWB sys- bustness to narrow-band interference in different code tem improves the performance about 5 dB in SIR. In matrixes. It indicates that the encoding and spreading other words, the AI-UWB system has about 5 dB mar- would exploit the frequency diversity across the subgin in SIR than the IS-UWB system in the presence of bands as well as sub-channels and enhance the robustinterference. It is because that the power of the trans- ness of AI-UWB system to narrow-band interference. mitted symbol in AI-UWB system is distributed over ev- When some sub-channels or sub-bands are affected by ery sub-band rather than one sub-band in IS-UWB sys- interference or jamming or frequency-selective fading, tem. the coded bits can be received from the others. ComFig. 3 and Fig. 4 illuminate the different effect on the pared with IS-UWB system, the AI-UWB system imBER performance of AI-UWB system by different codes proves the performance about 5 dB in SIR. But the different code matrixes have almost the same effect on narrow-band interference. Encoding and spreading is an effective cure for UWB-OFDM system to enhance the ro----_ bustness to narrow-band interference. ---C-UWB 10’
-Hadamard - - DCT - - P4
3 m
References: [ l ] WIN M 2, SCHOLTZ R A. Ultra-wide bandwidth time-
Fig. 3 BER performance using different code in the presrnre of partial-band interference
- - - - - _ _ -_- - - - _
10 *
- - - C-UWB
-Hadamard
E 10
’:
t 1u
-5
5
0
10
hopping spread-spectrum impulse radio for wireless multipleacces9 communications [ J ] . IEEE Trans on Communications, 2000, 48(4) : 679 - 691. [2] WIN M Z, SCHOLTZ R A. Impulse radio: how i t works [ J ] . IEEE Communications Letters, 1998, 2 ( 2 ) : 36 - 38. [3] WIN M Z, SCHOLTZ R A. Characterization of ultra-wide bandwidth wireless indoor channels: A communication-theoretic view [J 1. IEEE Journal on Selected Areas in Communications, 2002, 2 0 ( 9 ) : 1613 - 1627. 141 ZHANG S B, ZHANG 1- J . Ultra wideband radio communication and its key technology [ J ] . Telecommunication Engineering, 2004, 44( 1 ) : 1 - 6 . [S] AIE1,I.O G R. Challenges for Ultra-WideBand ( U W B ) CMOS integration [ C ] // Proceedings of IEEE MTT-S International Microwave Symposium Digest: Vol 1 , Jun 8 13, 2003, Philadephia, PA, USA. Piscataway, NJ, USA: IEEE, 2003: 361 -364. [ 6 ] CUOMO F, MARTEILO C, BAIOCCHI A. Radio resource sharing for Ad Hoc networking with UWB [ J ] . IEEE Journal on Selected Areas in Communications, 2002,
( EJJo )/dB
Fig. 4 BER performance using different codein the presence of multi- tone jamming
in the presence of interference when SNR is 10 dB. It is apparent that there is a little difference among Hadamard code matrix, DCT code matrix and P4 code matrix. This is because that there is a little different frequency diversity across the sub-bands and sub-channels when the transmitted symbols are encoded and spread by different code matrix. Comparatively speaking, P4 code matrix is most effective and DCT code is worst.
[7]
[8]
20(9) : 1722- 1732. HU J , YANG Y I-, XIE X 2 . A multi-access UWB-OFDM based on FFH [ J ] . Journal of Chongqing University of Posts and Telecommunications, 2005, 17(2) : 177 - 179. HE Jian-hui, QUAN Zi-yi, MEN Ai-dong. PARR reduction in OFDM systems with large number of sub-carriers by carrier interferometry approaches [ J ] . The Journal of China University of Posts and communications, 2004, 1 1 ( 4 ) :
91 - 94. [9]
NAKAGAWA M, ZHANG H, SAT0 H. Ubiquitous homelinks based on IEEE 1394 and ultra wideband solutions [ J 1. IEEE Gmmunications Magazine, 2003, 41 ( 4 ) :
74 - 82.
To p.38
38
The Journal of CHUPT of public-key cryptography for wireless sensor networks[ C] //Proceedings of the 3rd International Conference on Pervasive Computing and Communications, Mar 8 - 12, 2005, Kauai Island, HI, USA. Im Alamitos, CA, USA: IEEE Computer Society, 2005: 324 - 328. SHAMIR A. Identity-based cryptography and signature schemes [ C 1 // Proceedings of Advances in Cryptology (CKYPT0’84), Aug 19 - 22, 1984, Santa Barbara, CA, USA. Berlin, Germany: Springer, 1984:47 - 53. FEIGE U, FIAT A, SHAMIR A. Zero-knowledge proofs of identity[J]. Cryptology, 1988,1(2) :77 - 94. FIAT A, SHAMIR A. How to prove yourself: practical solutions to identification and signature problems[ C] // Proceedings of Advances in Cryptology ( CRYPTO’86 ), Aug 11 - 15, 1986, Santa Barbara, CA, USA. Berlio, Germany: Springer, 1987: 186 - 194. BONEH D, FRANKLIN M. Identity-based encryption from the Weil pairing [ C ] // Proceedings of Advances in Cryptology(CRYPTO’2001), Aug 19 - 23, 2001, Santa Barbara, CA, USA. Berlin, Germany: Springer, 2001 : 213-229. BOYEN X . Multipurpose identity-based signcryption, a swiss army knife for identity-based cryptography[ C] //Proceedings of Advances in Cryptology(CRYPTO’2003), Aug 17 - 21, 2003, Santa Barbara, CA, USA. Berlin, Germany: Springer, 2003,2729 :383 - 399. CHEN I,, KUDLA C. Identity-based authenticated key agreement protocols from pairings [ R ] . Cryptology ePrint
From p . 9 ZHAO I,, HAIMOVICH A M. Performance of ultra-wideband communications in the presence of interference [ J 1 . IEEE Journal on Selected Areas in Communications, 2002, 20(9) : 1684 - 1691. DURlSI G , HENEDETTO S. Performance evaluation of TH-PPM UWB system in the presence of multiuser interferences [ J ] . IEEE Communications Letters, 2003, 7( 5 ) : 224 - 226. GERAKOUI-IS D, SAI-MI P . An interference suppressing OFDM system for ultra wide bandwidth radio channels [ C] //Proceedings of 2002 IEEE Conference on Ultra Wideband Symposium Systems and Technologies, May 21 23, 2002, Baltimore, MD, USA. Piscataway, NJ, USA: IEEE, 2002 : 259 - 264. LUO 2 D, GAO H, LIU Y A, et al. Ultra-wideband pulse design approach for multiple narrowband interference suppression [J] . Journal of Beijing University of Posts and Telecommunications, 2005, 28( 1) : 55 - 58. ZHANG S B, CAO S K, ZHANG L J . An anti-interference coding in UWBOFDM communications [ J 1. The Journal of China University of Posts and communications, 2005, 12(4) :32 37.
[25]
2006
Archive, Report 2002/184. http: //eprint. iacr. org/2002/ 184, 2002. WATERS B R . Efficient - identity-based encryption without random oracles[R] . Cryptology ePrint Archive, Report 2004/180, http: //eprint. iacr. org/2004/180, 2004. Biographies:CHENG Hong-hing, male, he is a Ph. D. Candidate of Nanjing University of Posts and Telecommunications. He is a lecturer in College of Information Engineering at Jiangsu Radio and T V University. His current research interest includes information security, grid computing, and computer networks.
YANG Geng, male, he received Ph. D. degree in Computer Science from Lava1 University in 1994 and was a post-doctoral research fellow in Center for Research on Computation and its Applications at University of Montreal from 1994 to 1996 in Canada respectively. He is a professor in College of Computer at Nanjing University of Posts and Telecommunications. He is dean of the College of Mathematics and Physics of NUPT. His current research interest includes network security, parallel and distributed computing, mobile computing. Dr. Yang is a member of the IEEE Computer Society and a Standing Member of Chinese Cnmputer Education Society.
[ 151 Proakis J G. Digital Communications (Fourth Edition), New York, McGraw-Hill, 2001. [ 161 ZHANG S B, ZHANG I, J. The modeling and simulation of UWB channel [ J ] . Journal of Nanjing University of Posts and Telecommunications, 2005, 25(3) : 50 - 53. Biographies: ZHANG Shi-bing, male, Ph. D. Candidate, associate professor. School of Electronics and Information of Nantong University, interested in the research on signal processing for communications, Ultra-Wideband communication.
~
~
ZHANG Li-jun, male, Professor and Ph. D. Tutor, Nanjing University of Posts and Telecommunications interested in the research on the areas of wireless data, access technology and system of wireless IP, mobile computing and its applications.