2 research outputs found
Pengelolaan Arsip Secara Digital Menggunakan Algoritma LZSS Modifikasi untuk Kompresi File
Dokumen yang menumpuk dalam bentuk hardcopy dapat menimbulkan suatu masalah, baik dalam penataan, keamanan dokumen maupun ruang penyimpanan dokumen. Selain itu perawatan ekstra diperlukan untuk mencegah kerusakan pada dokumen penting yang disebabkan oleh serangga dan lain-lain. Dengan teknologi sekarang ini dokumen dapat disimpan dalam bentuk file dan sekaligus ukuran file dapat diperkecil untuk meminimalkan media penyimpanan dan penyusunan dokumen dapat ditata dengan baik sehingga pada saat pencarian dokumen menjadi lebih mudah. File merupakan data digital yang berisi informasi. Untuk memperkecil ukuran file yaitu dengan cara dipadatkan atau biasa disebut dengan kompresi sehingga ukuran file menjadi lebih kecil dari ukuran semula. Pada penelitian ini, metode yang digunakan untuk kompres file adalah LZSS (Lempel Ziv Strorer-Szymanski) yang telah dimodifikasi untuk menghasilkan kompres yang lebih optimal. Algoritma kompresi LZSS modifikasi dikembangkan berdasarkan konsep algoritma kompresi LZSS (pengkodean (offset,len)) serta penambahan pengkodean (offset,-len). Dari 9 sampel file yang dipilih sebagai data simulasi, diperoleh rata-rata rasio kompresi algoritma LZSS adalah 75,40% dan rata-rata kompresi algoritma LZSS modifikasi adalah 67,86%. Hal ini menunjukkan bahwa algoritman LZSS modifikasi menghasilkan tingkat kompresi yang lebih baik
Cooperative Transmission Techniques in Wireless Communication Networks
Cooperative communication networks have received significant interests from both
academia and industry in the past decade due to its ability to provide spatial diversity
without the need of implementing multiple transmit and/or receive antennas at the
end-user terminals. These new communication networks have inspired novel ideas
and approaches to find out what and how performance improvement can be provided
with cooperative communications. The objective of this thesis is to design and analyze
various cooperative transmission techniques under the two common relaying signal
processing methods, namely decode-and-forward (DF) and amplify-and-forward
(AF).
For the DF method, the thesis focuses on providing performance improvement
by mitigating detection errors at the relay(s). In particular, the relaying action is
implemented adaptively to reduce the phenomenon of error propagation: whether or
not a relay’s decision to retransmit depends on its decision variable and a predefined
threshold. First, under the scenario that unequal error protection is employed to
transmit different information classes at the source, a relaying protocol in a singlerelay
network is proposed and its error performance is evaluated. It is shown that
by setting the optimal signal-to-noise ratio (SNR) thresholds at the relay for different
information classes, the overall error performance can be significantly improved.
Second, for multiple-relay networks, a relay selection protocol, also based on SNR
thresholds, is proposed and the optimal thresholds are also provided. Third, an
adaptive relaying protocol and a low-complexity receiver are proposed when binary
frequency-shift-keying (FSK) modulation is employed and neither the receiver nor the
transmitter knows the fading coefficients. It is demonstrated that large performance
improvements are possible when the optimal thresholds are implemented at the relays
and destination. Finally, under the scenario that there is information feedback
from the destination to the relays, a novel protocol is developed to achieve the maximum
transmission throughput over a multiple-relay network while the bit-error rate
satisfies a given constraint.
With the AF method, the thesis examines a fixed-gain multiple-relay network
in which the channels are temporally-correlated Rayleigh flat fading. Developed is
a general framework for maximum-ratio-combining detection when M-FSK modulation
is used and no channel state information is available at the destination. In
particular, an upper-bound expression on the system’s error performance is derived
and used to verify that the system achieves the maximal diversity order. Simulation
results demonstrate that the proposed scheme outperforms the existing schemes for
the multiple-relay network under consideration