BUKU ABSTRAK - Universiti Putra Malaysia

Science, Technology & Engineering
Spectrum Efficiency Enhancement in Dynamic Space Coded Multiple Access
(DSCMA) System
Assoc. Prof. Dr. Nor Kamariah Noordin
Borhanuddin Mohd. Ali and Ng Chee Kyun
Faculty of Engineering, University Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.
+603-8946 6181; nknordin@eng.upm.edu.my
In cellular mobile communication systems using coded modulations, the spectrum efficiency of the system
is related to the number of available codes. Recently, large area synchronous (LAS) CDMA codes, which exhibit
a region called interference free window (IFW) within some delay-spread, have been accepted as one of fourthgeneration
(4G) wireless communication systems. However, the number of synthesized LAS codes is very low
due to the low duty ratio of the sequence. In this invention, a dynamic space coded multiple access (DSCMA)
scheme which utilises the spatial diversity from smart antenna system is proposed to overcome the low spectrum
efficiency in LAS CDMA system. In the DSCMA, a modified version of LAS codes called LAS where even
ternary (LAS-ET) codes is proposed. These codes are used together with a novel algorithm called dynamic space
code (DSC), which will decrease the code length so that the spectrum efficiency can be increased. By taking
advantage of dynamic code reuse assignment in spatial diversity, the spectrum efficiency of the DSCMA can be
further increased significantly.
Keywords: Spectrum efficiency, LAS CDMA, IFW, smart antenna, code reuse, duty ratio, beamwidth
Unsteady Flow Across a Stretching Surface
Assoc. Prof. Dr. Norihan Md. Arifin
Fadzilah Md. Ali, Roslinda Nazar, Norihan Md. Arifin, Anuar Ishak and Ioan Pop
Institute of Mathematical Research, University Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.
+603-8946 6850; norihan@math.upm.edu.my
The problem of unsteady uniform flow across a stretching surface in an arbitrary direction is studied
theoretically, where the unsteadiness is caused by the impulsive motion of the stretching surface. Numerical
results of the governing partial differential equations are obtained using an implicit finite difference scheme for
the whole transient from the early or initial unsteady-state flow to the final steady-state flow. The early unsteadystate
flow is solved analytically. The numerical solution obtained for the reduced skin friction coefficient is
compared with previously reported results and the results for velocity profiles, h and g profiles are also presented
in this paper. It is found that there is a smooth transition from the small-time solution (initial unsteady flow) to the
large-time solution (final steady-state flow).
Keywords: Unsteady flow, boundary layer, stretching surface
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