A new directsequence UWB transceiver based on Bridge function sequence
ABSTRACT This paper reports how a novel directsequence UWB transceiver, utilizing Bridge function sequence as direct sequence, works in the wireless multipath environment. It is acknowledged that the Bridge function sequences have zero correlation zones (ZCZs) in their autocorrelation functions (ACFs). Due to the ZCZ properties of Bridge function sequences, the proposed directsequence UWB, using Bridge function sequence with properly chosen shift parameter, features a better performance on avoiding multipath interference than the one utilizing other spreading sequences without ZCZ. The theoretical justification of the proposed approach, together with its achievable performance in computer simulation, is presented in detail.
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ABSTRACT: This paper proposes a directsequence UWB Gaussian pulse of cognitive radio systems based on bridge function smart sequence matrix and the Gaussian pulse. As the system uses the spreading sequence code, that is the bridge function smart code sequence, the zero correlation zones (ZCZs) which the bridge function sequences’ autocorrelation functions had, could reduce multipath fading of the pulse interference. The Modulated channel signal was sent into the IEEE 802.15.3a UWB channel. We analysis the ZCZs’s inhibition to the interference multipath interference (MPI), as one of the main system sources interferences. The simulation in SIMULINK/MATLAB is described in detail. The result shows the system has better performance by comparison with that employing Walsh sequence square matrix, and it was verified by the formula in principle. KeywordsUWBBridge functionSmart codeBERCognitive radioMPI01/1970: pages 4146;
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201O Second International Conference on Computational Intelligence and Natural Computing (CINC)
A New Directsequence UWB Transceiver Based on Bridge Function
Sequence
Sheng Hong, Member, IEEE, Kefei Liu, Ying Li**, Hang Zou, Yunping Qi*,
Beihang University,Beijing, China
* yunpqi@126.com
**liying.1983@yahoo.com.cn
Kan Hong
Department of Informatics & Sensors
Defence Academy of The United Kingdom
Cranfield University, SN68SA, UK
Abstract
This paper reports how a novel directsequence
UWB transceiver, utilizing Bridge jUnction sequence as
direct sequence, works in the wireless multi path
environment. It is acknowledged that the Bridge
function sequences have zero correlation zones (ZCZs)
in their autocorrelation functions (ACFs). Due to the
ZCZ properties of Bridge function sequences, the
proposed directsequence UWB, using Bridge function
sequence with properly chosen shift parameter, features
a better performance
interference than the one utilizing other spreading
sequences without ZCZ The theoretical justification of
the proposed approach, together with its achievable
performance in computer simulation, is presented in
detail.
on avoiding multi path
1. Introduction
Ultra wideband(UWB) has been one of the most
appealing wireless communication technology. It can
be used in high speed and short rang communication to
aid the developing of wireless personal area network [1,
2] and an evolutional technology towards cognitive
radio [3].
Since the binary random sequence could not
satisfy the antiinterference requirement of UWB, more
and more attention focuses on the UWB application of
ternary sequence [46]. Bridge function sequence with
builtin ZCZs is a kind of well established ternary
mutually orthogonal sequences,
employed in the fields such as multicarrier CDMA,
Haar wavelet, passive beamformer etc [710]. In this
paper, a new UWB transceiver is provided with Bridge
function sequence as direct sequence. The proposed
UWB transceiver, using Bridge function sequence with
which is being
9781424477036/1 0/$26.00 ©201O IEEE
209
properly chosen shift parameter, has the advantage that
it can mitigate multi path interference effectively in
typical indoor communication
comparison to other conventional spreading sequences
without zero correlation zones.
The remainder is provided as following parts. II
shows the principle of the DSUWB transceiver. III
demonstrates the properties of Bridge function. IV
shows the simulation result of DSUWB transceiver
based on Bridge function sequence. V is the conclusion.
environment in
2.System
transceiver
structure of the DSUWB
The diagram of DSUWB system model for one
user is shown in Fig. I.
Judging & Output
Equalizer RAKE
Fig.1 The diagram of DSUWB system model
At the transmitter, the Bernoulli Binary Generator
block in the Data Source subsystem generates random
binary information data of 0 and 1, which are then fed
into the unipolar to bipolar converter block to transform
to sequence of 1 and 1. In the UWB Pulse Generator
subsystem, the 5th order derivative of Gaussian
function [11], as shown below,
CINC2010
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t t 3
) (
t 5
) ]exp(20'2)
t2
p(t)=[I5
0'
+10(
0'0'
(1)
is generated as the single pulse waveform of UWB
signal. The output single pulse signal is then modulated
into BPSK symbol by the bipolar binary information
data in the Data Modulation block. The modulated
signal is written as follows [11], whose corresponding
signal waveform is shown in Fig.2,
NsI
s(t) = I IdjgnP(tjT. n�)
co
(2)
j=«o n=O
where dj E {I, I} is the bipolar binary information
data of the user, gn E {I, I} the nth chip of the user's
PN sequence, T. is symbol period, and � is pulse
interval. The modulated signal is then sent to the
standard UWB(SV/IEEE 802.15.3a) channel [12].
0.2
0,3
0.4 '

'  '  ' ' ' '   ' ''
function sequence. All of the 2q sequences in this
matrix form a sequence set. Different shift parameter
generates different Bridge function sequence set, so q+ 1
sequence set are generated totally. Specially, Walsh
sequence set is generated at j=O, while blocks pulse
sequence set is generated at j=q. Different Bridge
function sequence is orthogonal to each other, and zero
correlation zone (ZCZ) exists. Besides, Bridge function
contains zero value, and nonzero values (±I) are
uniformlyspaced with 2i_I zeros between adjacent
elements.
Due to the fact that the Bridge function sequences
set at
� = � � � �
Time
Fig.2 The modulated signal waveform of DSUWB
system
Over an A WGN and multipath channel with
lognormal distributed fading, the received equivalent
baseband signal within noise is
ret) = set) * h(t) + net)
j=«o n=O
where "*"denotes convolution process, h(t) is channel
impulse response, net) is white Gaussian noise, and
vet) = pet) * h(t) is channel response of the pulse
signals existing in the multiple arriving paths with time
delays to the firstly arriving path. At the receiver, they
are firstly gathered in the Partial Rake (PRake) receiver
[11], which chooses the firstlyreached L multipath
signal and combines them with the minimal mean
square error(MMSE) criterion. Then they are processed
in the channel equalizer, which uses the recursive least
squares(RLS) equalization algorithm for mitigating
signal.
The above received signals are a series of energy
210
multipath channel effect. Through the judging unit and
Error Rate Calculation block, the bit error rate can be
calculated.
3. Properties of Bridge function
Bridge function is a kind of threevalue function
with +1,1 and 0 [7]. In terms of the generating method
and sequence structure, Bridge function sequence has
many same similarities with Walsh sequence. Based on
different copy and shift method there are four different
kind of Bridge function sequence with different
ordering, among which the Hadamardordering Bridge
function sequence can be obtained with the following
recursive procedure [7, 13],
{H!(J)=IP,
. =_ �.lp(J) U:Ip(J) <'< '=
...
_
.
a;AJ) v'2[ a;. ,U) �,(j) JoJ
where P = 2j, I P is P order unit matrix, j is shift
_g,l U ,g J
(4)
parameter, N=2q is the length of Bridge function
sequence generated.
H�q (j) is called as Bridge function matrix, each
of whose column vectors corresponds with a Bridge
different j(I::; j::; q 1) featuring similar
autocorrelation
generality, in this paper we use Bridge function
sequences set at j=2 when q=6 for illustration.
Comparison of aperiodic autocorrelation function of
Walsh function sequences
sequences is shown in Fig.3. As shown in Fig.3, there
ubiquitously exists zero aperiodic autocorrelation zones
(ZAAZ) for Bridge function sequences' autocorrelation
function. However, the
function of Walsh function sequence does not have any
ZAAZ.
characteristics, without loss of
and Bridge function
aperiodic autocorrelation
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60 L.': __ ' __ 'c _' _.. ''_
,:
'
.. _'
... .. .. . .. · �u
30 20 10 10 20 30
Time(chips)
Fig. 3 Aperiodic autocorrelation functions
of Walsh function sequence and
Bridge function sequence at j=2
4. Simulation Results
The system simulation structure is built within
SimulinklMatlab software environment. The number of
taps in the PRake receiver is L=1O, and the number of
taps in the equalizer is 5. Channel impulse response can
be one of 4 types (CMl, CM2, CM3 or CM4) [12].
CMl is a channel model with line of sight (LOS) path,
while other 3 channel models are channel models with
non line of sight (NLOS) path. Without the loss of
generality, we choose CMl and CM3 as simulation
scenarios respectively. Model
parameters of the two different types of UWB(SV/IEEE
802.l5.3a) channels are respectively setup according to
[12].
In our simulation, the number of transmitted
binary data is set to be 10000 bits with symbol period
of 5ns, and Walsh sequence and Bridge sequence of
length 64 are used as PN
respectively. Because simulation results significantly
depend on the particular realization of channel impulse
response, the channel influence should be correctly
assessed by averaging an amount of the channel
realizations. However, the simulation for averaging a
large amount of the channel realizations must arouse
great deal of time cost. Hence, in order to make a
suitable tradeoff between correct assessment of the
channel influence and the time cost, we adapt totally 25
actual realizations for each channel model and average
the error probability over them to obtain the average bit
error rate performance
Simulation results are shown in Fig. 4, where the curve
of bit error rate vs. Et1No represents the average BER
for CMl and CM3. Without the loss of generality,
characteristics and
spreading sequences
of the PRake receiver.
211
Fig.4(a) uses CMl as channel model with the 3rd
column of the sequence matrix in (4) as the spreading
sequence and Fig.4(b) uses CM3 as channel mode with
the 32th column of the sequence matrix in (4) as the
spreading sequence. It can be seen from these figures
that DSUWB system using Bridge function sequences
with proper shift parameter (e.g. j=3) has better
performance in terms of the bit error rate than that using
Walsh sequence. This is because Bridge function
sequences have an aperiodic autocorrelation function of
ZAAZ and thus suffer less multipath interference. In
Fig.4(a), compared with that using Walsh sequence,
DSUWB system using Bridge sequenceU=3) obtain
more than 3dB processing gain, when the bit error rate
is 104, while in Fig.4(b), DSUWB system using
Bridge sequenceU=3) obtain more ldB processing gain
than the one using Walsh sequence.
1� �������������������
........... ....................... ..............
:: : : : ::::::.:::::::: : : : .::::::::::::' .... :::.::�:: . Walsh
.
Bridge(j=1)
Bridge(j=2)
. ............ .
105 , ......
. . . . . . . . . . . . . . . . . .
106' '  '  '  '  '  '
2
Eb/No(dB)
. . . . . . . . . . . . . .
. .......... , ... . . . . .. . ; ...... .
,::::::::: :;:::::::::::: ..
 " Bridge(j=3)
_Bridge(j=4)
+ Bridge(j=5)
� � � �::::::::: � �::;; ..
. . . . . . . . . . � . .
o
4
. . . . . . . ..
. . . . . . . . . . . . . , . . . . . . . .
.... , ...... , ..
. . . ........ ...
6
(a)
. . . . . . .
. . ... .
.. . . .
. . . . . . . • . .
8
10
Walsh
.  Bridge(j=1)
Bridge(j=2)
 "  Bridge(j=3)
_Bridge(j=4)
+ Bridge(j=5)
12
106 " '  '  '  ' ' ' "   '  '
4
Eb/No(dB)
o
5 6 8 9
(b)
Fig. 4 (a) Comparison of bit error rate performance of
DSUWB systems spreaded by Walsh and Bridge
function sequence (Channel l, 3rd column)
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(b) Comparison of bit error rate performance of DS
UWB systems spreaded by Walsh and Bridge function
sequence (Channel 3, 32th column)
5. Conclusion
The paper proposes Bridge function sequence
based DSUWB system, whose performance in terms of
bit error rate is analyzed and compared with that of
Walsh sequence. Aperiodic autocorrelation function of
Walsh function sequences
sequences are simulated and compared. The result
demonstrates that there ubiquitously exists ZAAZs for
Bridge function sequences' autocorrelation function.
Hence, DSUWB system
sequence with properly chosen shift parameter tends to
have better antimuptipath fading performance, and
accordingly should have
performance than that
Simulation gives the satisfied results and verification.
and Bridge function
using Bridge function
better
using
bit error
sequence.
rate
Walsh
ACKNOWLEDGMENT
This paper is supported by Fundamental Research
Funds for the Central Universities in China under grant
No. YWF1O02023.
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