S.Srimathi, P.Kannan
International Journal of Scientific & Engineering Research Volume 4, Issue 2, February-2013 1
ISSN 2229-5518
S.Srimathi, P.Kannan
Abstract— Performance evaluation of time-hopping UW B using various modulation techniques has been proposed. Then the performance im- provement is analysed based on the BERs of various existing methods. Recently a new method called TH-BPSK UW B system is proposed which provides a better performance than all other existing systems. The literature survey discusses all the existing techniques of UW B communication.
Index Terms— time hopping, ultra wideband communication, code division multiple access system, spread spectrum, multiuser interference, pulse position modulation, binary phase shift keying.
—————————— ——————————
In a spread spectrum system, the transmitted signal will oc- cupy extremely larger bandwidth even in the absence of data modulation. In this case ,a signal is transmitted with a band- width much larger than the data modulation bandwidth
&with reduced power spectral density. The key motivations for using TH-SS impulse radio are the ability to highly resolve multipath and to generate UWB signals with relatively low complexity.
An UWB-TH CDMA system employing a binary pulse
band in which the signal propagate well but instead com- municates with a time hopping (TH) baseband signal com- posed of sub nanosecond pulses. The TH-SS impulse radio is used because of its ability to resolve multipath and to generate UWB signals with relatively low complexity.
A time hopping kth impulse radio transmitter output sig-
nal is given by (1)
position modulation signaling has been introduced. Here a
s(k) (u, t (k) ) = ∑∞
wtr (t (k) − jTf − c
(k)
Tc − d
(k)
(u))
(1)
data is transmitted using short pulses with duration less than
:::-∞
(t)
1ns. This technique is called impulse radio (IR). The BER per-
formance of TH-PPM in the presence of MUI and AWGN channel based on Gaussian Quadrature Rules is proposed. It is done to improve the performance of multilevel digital signals with ISI.
Where t (k)is the transmitter clock time &wtr represents the
transmitted monocycle waveform.
When Nu transmitters are active in the multiple access sys-
tem,the received signal at the output of this receiver antenna is
modeled as (1)
Several modulation techniques have been proposed for
UWB signals such as PPM, PAM, BPSK. But currently TH-
r(u, t) = ∑Nu A u, t − ζ (u) + η(u, t)
(2)
PPM & TH-BPSK UWB system are often used . The perfor- mance of both the systems are analysed and compared using different pulse parameters.
2.1 Ultra wide bandwidth time hopping spread spectrum
Moe Z. Win & Robert A. Scholtz (1) proposed a spread spectrum system for high data rate transmission using ultra wide bandwidth communication. The SS radio system does not use a sinusoidal carrier to raise the signal to a frequency
————————————————
Kannan.P is currently a Professor in PET engineering in Vallioor.
Where Nu is the number of active users,Ak & ζk are the chan-
nel attenuation and delay.
2.2 Multiple access system with coded and uncoded schemes
Amir R. Forouzon, Masoumeh Nasiri Kenari and Jawad A. Salehi (3) proposed an ultra wide bandwidth time hopping spread spectrum code division multiple access system which employs a binary pulse position modulation (PPM) signaling. Here in this system ,a data is transmitted using short pulses with duration less than 1ns. This technique is called impulse
radio (IR).In a uncoded scheme, every transmitter sends Ns
pulses for each data bit. These pulses are located apart in se-
quential frames, each with a duration Tf . Here a BPPM is used
in which the pulses corresponding to 1 bit are sent δ seconds
later than pulses corresponding to bit 0. The transmitter signal
of user k is (3)
(k)
(k)
(k)
str (t)=∑ wtr (t − jTs − -
− δ d )
(3)
Where the index j indicates the frame number, wtr (t) repre-
IJSER © 2013
International Journal of Scientific & Engineering Research Volume 4, Issue 2, February-2013 2
ISSN 2229-5518
sents the transmitted pulse & - (k) is the dedicated pseudoran- dom sequence for user k with integer components.
yBPSK
= 5BPSK
+ IBPSK
+ ry
BPSK
(9)
The transmitted signal is transmitted through a free
Where ryBPSK is a Gaussian noise with zero mean and vari-
2 2
space propagation channel with AWGN to the receiver. The
received signal of the kth user at the receiver antenna output is
(3)
ance ur)BPSK = NO Ns /(2Eb )
(l)
BPSK O
Al Ns (10)
(k) (t) = ∑ w
(t − jT − - (k) T − d(k) ) (4) I
is the total MAI in the TH-BPSK UWB system which
5rrc
rrc f c
BPSK
is given by. (4)
Where wrrc (t) is the received pulse with duration Tw . The
Nu γk -l
(k)
(k)
Ns -l
(k)
(k)
total received signal is (3)
IBPSK = ∑k:::2 Ak [∑j:::O
dO R(θj
) + ∑j:::γ dl
R(θj
)] (11)
NU (t)
(k)
(k)
r(t)=∑k:::l Ak 5rrc (t − (k ) + ry(t)
(5)
Where θj
=∝k + e
Tc.
where Nu is the no of active users Ak & (k are the channel at-
tenuation delay.
In a coded sheme , a simplified repetition block code with
rate 1/Ns is used. This repetition code is not a good code. So a
near optimal code is used instead of the above code. It pro-
vides better system performance.
2.3 TH-PPM UWB system in the presence of multiuser in- terference
G.Durisi and S.Benedetto (2) proposed a time hopping combined pulse position modulation for UWB systems. A Gaussian Quadratue Rules (GQR) are used to the BER perfor- mance of TH-PPM in the presence of MUI and AWGN chan- nel.
The information bit is transmitted using Ns consecutive pulses leading to a (Ns , 1) repetition code. These informations
are transmitted through an ideal free space propagation,
AWGN channel and then the received signal is given by (2)
2.5 Soft limiting receiver
Norman C. Beaulieu and Bo Hu [5] proposed a soft limiting receiver structure for detecting a time-hopping ultra wide-bandwidth signal in the presence of multiple-access in- terference (MAI). The receiver has a nonlinear limiter for sup- pressing the MAI. This soft limiting receiver provides better performance than the correlation receiver. The gain of this re- ceiver varies from around 10db at small values of signal to interference ratio (SIR) to 0db as the SIR becomes infinitely large.
A second receiver structure has an adaptive soft lim-
iter. The performance of this adaptive threshold soft-limiting receiver with optimized threshold always meets or exceeds both that of conventional matched filter receiver and that of the soft limiting receiver with fixed threshold.
2.6 SNR and SIR Estimation
y(t)=sl (t − (1) + ∑NU sk (t − ( ) + ry(t)
(6)
Yunfei Chen, Norman C. Beaulieu and Hau Shao (6)
proposed the estimation of signal to noise ratio (SNR) and
where (k for k=1,…..Nu is the delay associated to each user & ry(t) is a white Gaussian noise process with two sided power spectral density NO /2.
2.4 Performance evaluation of TH-PPM & TH-BPSK UWB
systems
Bo Hu and Norman C.Beaulieu compare the perfor-
mance analysis of the TH-BPSK UWB systems. Here first the performance analysis of the TH-PPM UWB system with mul- tiple access interference (MAI) is considered. An information
(k)
signal to interference ratio (SIR) for multiuser time hopping binary phase shift keying using the moment based method. The soft limiting receiver requires the knowledge of SNR & SIR in order to choose the optimum thresholds for detection. Therefore the SNR & SIR for TH-UWB IR systems are estimat- ed with multiple users. These estimators can estimate the SNR
, when there is no MAI or the SIR , when the noise is negligi- ble. The estimators are examined in terms of the normalized root mean squared error (NRMSE),(7) defined as the square root of the sample mean squared error divided by the true
bit di
ℰ{0,1} is used in this modulation scheme, no additional
value. The SNR & SIR estimators have NRMSEs of less than
time shift modulates the pulse p(t) when the data is 1. The
template waveform v(t) is of the form (4)
V(t)=p(t)-p(t-δ) (7) The correlation of the template v(t) with a time shifted pulse
is (4)
0.2 in most cases.
3 CONCLUSION
In this paper, a brief literature survey for performance
R(x)=∫∞ p(t − x) v(t) dt
The interfering signal is given by (4)
(8)
evaluation of various TH-UWB systems is discussed elaborate-
ly .TH spread spectrum , TH-spread spectrum coded & un- coded schemes, TH-PPM & TH-BPSK UWB systems are com-
The waveform used in TH-BPSK sytem is the pulse p(t). The
decision stastistic yBPSK is then given by (4)
pared. Among this TH-BPSK UWB system provides better performance than other modulation schemes. The simulation results of performance between TH-BPSK and TH-PPM UWB
IJSER © 2013 http://www.ijser.org
International Journal of Scientific & Engineering Research Volume 4, Issue 2, February-2013 3
ISSN 2229-5518
systems are shown in fig.1.
Fig.1. Comparison performance between TH-BPSK and TH- PPM UWB system models with our analytical approach.
Apart from the efforts of me, the success of my depends largely on the encouragement and guidelines of many others. I take this opportunity to express my gratitude to the people who have been instrumental in the successful completion of this work. I would like to extend my sincere thanks to all of them. I owe a sincere prayer to the GOD for his kind bless- ings and giving me full support to do this work. I wish to take this opportunity to express our gratitude to all, who helped me directly or indirectly to complete this paper.
[1] M.Z. Win and R.A.Scholtz, “ultrawide bandwidth spread spec- trum impulse radio for wireless multiple- access communica- tions” IEEE Trans. Commun..,vol.48,pp.679-691,Apr .2000
[2] G.Durisiand S.Benedetto,”Performance evaluation of TH-PPM UWB systems in the presence of multiuser interference,” IEEE Commun., Lett., vol.7,pp.224-226,May 2003.
[3] A.R. Forouzan, M.Nasiri-Kenari, and J.A. Salehi, “ Performance analysis of time hopping spread-spectrum multiple-access sys- tems; uncoded and coded schemes,” IEEE Trans. Wireless Commun., vol.1, pp.671-681 Oct .2002.
[4] B.Hu and N.C. Beaulieu, “ Accurate evaluation of multiple access performance in TH-PPM and TH-BPSK UWB systems,” IEEE Trans. Commun., vol.52, no. 10, pp.1758-1766,Oct.2004.
[5] N.C.Beaulieu and B.Hu,”soft- limiting receiver structure for time-hopping UWB in multiple access interference ,” IEEE Ninth International Symp. Spread Spectrum Techniques Appl.,2006.
[6] Y.Chen, N.Beaulieu and H.S.hao,”SNR and SIR estimation for multiuser UWB IR systems with TH-BPSK,” IEEE Signal Pro- cess. Lett., vol.17 no.5, May 2010.
[7] Y.Chen and N.C.Beaulieu , “SNR estimation methods for
UWB systems,” IEEE Trans. Wireless commun.,vol.6, pp.3836-
3845,Oct.2007.
IJSER © 2013 http://www.ijser.org