02-10-2012, 02:26 PM
A Novel Orthogonal Minimum Cross-correlation Spreading Code in CDMA System
[attachment=35032]
Abstract
Code Division Multiple Access (CDMA) had been
used as an emergent technology in present generation Wireless
Communication System. In CDMA system, a large number of
users could be served over the same bandwidth by assigning a
unique code to each of the users. In order to support large
number of users in CDMA system, one of the primary objectives
of the mobile system designers had been to create a large number
of spreading codes by maintaining low Cross-correlation values
between them to mitigate the effect of Multiple Access
Interference (MAI). In this paper, we have proposed an algorithm
to generate an “Orthogonal Minimum Cross-correlation
Spreading Code” (OMCCSC), which can provide a large number
of distinct spreading codes as compared to the existing orthogonal
and near orthogonal spreading codes, namely Walsh code,
Orthogonal Gold code and Orthogonal Kasami code. The study of
cross-correlation property of the proposed code proves its
superiority over other existing codes. The proposed code has been
used as a spreading code in synchronous CDMA system and its
Bit Error Rate (BER) performance has been compared with other
existing spreading codes, in multi-user scenario.
INTRODUCTION
The Code Division Multiple Access (CDMA) technique has
been widely accepted in present generation wireless systems.
Spreading codes play an important role in CDMA system to
spread the user signals and distinguish among different users.
Among the different spreading codes, Walsh code has proved
its existence as a popular orthogonal code, whereas, Pseudo-
Noise (PN) sequence, Gold codes and Kasami codes have
established themselves as popular non-orthogonal binary
codes.
Walsh code is used in synchronous downlink CDMA
system. This code maintains orthogonality and thus produces
low Multiple Access Interference (MAI) in a CDMA system.
Walsh code set of length N can provide maximum N number
of distinct orthogonal spreading codes. So, Walsh code may
not be that effective to meet the increasing demand of users in
CDMA system. Again, capacity of CDMA system is limited
by MAI, where MAI is a function of the cross-correlation
value between different spreading-codes. Hence generation of
a large number of spreading codes with a minimum crosscorrelation
value can be treated as one of the challenging areas
in CDMA system.
Performance based on number of codes
Simulation of the proposed algorithm shows that it is
capable to generate a large number of distinct codes, each of
which can be used as a spreading code in CDMA system.
In general, the proposed orthogonal code is capable to
produce N × (N-1) number of distinct codes, each of length
N. A comparative study among the different orthogonal
codes, in terms of the number of distinct spreading codes
generated, has been illustrated in TABLE I.
CONCLUSIONS
Availability of more number of codes, minimum crosscorrelation
value, maximum auto-correlation value at zero
time shift and minimum Peak to Average Power Ratio
(PAPR) are some of the important features to be possessed by
a good spreading code in CDMA environment.
In this paper, an attempt has been made to generate a novel
orthogonal minimum cross-correlation CDMA spreading
code. The algorithm described for this purpose is efficient
enough to generate a large number of spreading codes as
compared to Walsh and Orthogonal Kasami code. In this
respect, the performance of the proposed code is similar to
Orthogonal Gold code. Regarding cross-correlation value, the
proposed code shows a significant improvement over all other
existing codes. As far as BER performance of synchronous
CDMA system is concerned, the proposed code either
outperforms or behaves similarly except the Orthogonal Gold
code, at a high value of SNR.
[attachment=35032]
Abstract
Code Division Multiple Access (CDMA) had been
used as an emergent technology in present generation Wireless
Communication System. In CDMA system, a large number of
users could be served over the same bandwidth by assigning a
unique code to each of the users. In order to support large
number of users in CDMA system, one of the primary objectives
of the mobile system designers had been to create a large number
of spreading codes by maintaining low Cross-correlation values
between them to mitigate the effect of Multiple Access
Interference (MAI). In this paper, we have proposed an algorithm
to generate an “Orthogonal Minimum Cross-correlation
Spreading Code” (OMCCSC), which can provide a large number
of distinct spreading codes as compared to the existing orthogonal
and near orthogonal spreading codes, namely Walsh code,
Orthogonal Gold code and Orthogonal Kasami code. The study of
cross-correlation property of the proposed code proves its
superiority over other existing codes. The proposed code has been
used as a spreading code in synchronous CDMA system and its
Bit Error Rate (BER) performance has been compared with other
existing spreading codes, in multi-user scenario.
INTRODUCTION
The Code Division Multiple Access (CDMA) technique has
been widely accepted in present generation wireless systems.
Spreading codes play an important role in CDMA system to
spread the user signals and distinguish among different users.
Among the different spreading codes, Walsh code has proved
its existence as a popular orthogonal code, whereas, Pseudo-
Noise (PN) sequence, Gold codes and Kasami codes have
established themselves as popular non-orthogonal binary
codes.
Walsh code is used in synchronous downlink CDMA
system. This code maintains orthogonality and thus produces
low Multiple Access Interference (MAI) in a CDMA system.
Walsh code set of length N can provide maximum N number
of distinct orthogonal spreading codes. So, Walsh code may
not be that effective to meet the increasing demand of users in
CDMA system. Again, capacity of CDMA system is limited
by MAI, where MAI is a function of the cross-correlation
value between different spreading-codes. Hence generation of
a large number of spreading codes with a minimum crosscorrelation
value can be treated as one of the challenging areas
in CDMA system.
Performance based on number of codes
Simulation of the proposed algorithm shows that it is
capable to generate a large number of distinct codes, each of
which can be used as a spreading code in CDMA system.
In general, the proposed orthogonal code is capable to
produce N × (N-1) number of distinct codes, each of length
N. A comparative study among the different orthogonal
codes, in terms of the number of distinct spreading codes
generated, has been illustrated in TABLE I.
CONCLUSIONS
Availability of more number of codes, minimum crosscorrelation
value, maximum auto-correlation value at zero
time shift and minimum Peak to Average Power Ratio
(PAPR) are some of the important features to be possessed by
a good spreading code in CDMA environment.
In this paper, an attempt has been made to generate a novel
orthogonal minimum cross-correlation CDMA spreading
code. The algorithm described for this purpose is efficient
enough to generate a large number of spreading codes as
compared to Walsh and Orthogonal Kasami code. In this
respect, the performance of the proposed code is similar to
Orthogonal Gold code. Regarding cross-correlation value, the
proposed code shows a significant improvement over all other
existing codes. As far as BER performance of synchronous
CDMA system is concerned, the proposed code either
outperforms or behaves similarly except the Orthogonal Gold
code, at a high value of SNR.