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ترميز القناة
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Created by
reham mhamad
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عند تصميمنا لأي نظام اتصال فإننا نتعرض لعدة عوائق تتعلق أحياناً بالبيئة المحيطة بمكونات هذا النظام (مرسل – قناة – مستقبل) , إن قناة الاتصال هي أكثر هذه المكونات عرضة للتأثر بما قد يغير أو يعطب البيانات المرسلة (من : ضجيج أو تشويش إن كان متعمد أو غير متعمد ... ) لأننا بتصميمنا للنظام لا نضمن مكان وجود هذه القناة وخصوصاً إذا كانت لاسلكية . فلذلك و عندما يتطلب هذا النظام لموثوقية عالية فإننا نضطر لوضع آلية لضمان عدم حدوث أي خطأ في جهة الاستقبال , تمككنا النظم الرقمية من تحقيق ذلك بمرونة
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- مقرر "تراسل معطيات 2"... جامعة تشرين... الدكتور إحسان شريتح.
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Abstract Direct decoding for task-oriented dialogue is known to suffer from the explaining-away effect, manifested in models that prefer short and generic responses. Here we argue for the use of Bayes' theorem to factorize the dialogue task into two
models, the distribution of the context given the response, and the prior for the response itself. This approach, an instantiation of the noisy channel model, both mitigates the explaining-away effect and allows the principled incorporation of large pretrained models for the response prior. We present extensive experiments showing that a noisy channel model decodes better responses compared to direct decoding and that a two-stage pretraining strategy, employing both open-domain and task-oriented dialogue data, improves over randomly initialized models.
Current language models are usually trained using a self-supervised scheme, where the main focus is learning representations at the word or sentence level. However, there has been limited progress in generating useful discourse-level representations.
In this work, we propose to use ideas from predictive coding theory to augment BERT-style language models with a mechanism that allows them to learn suitable discourse-level representations. As a result, our proposed approach is able to predict future sentences using explicit top-down connections that operate at the intermediate layers of the network. By experimenting with benchmarks designed to evaluate discourse-related knowledge using pre-trained sentence representations, we demonstrate that our approach improves performance in 6 out of 11 tasks by excelling in discourse relationship detection.
A common challenge in designing a wireless system is to overcome
the effects of the wireless channel, such as multi-path propagation,
and Inter-symbol Interference. and the ability of OFDM to combat
the effects of multi-path propagation made it th
e modulation of
choice for third and fourth generation networks.
In OFDM system we transmit data symbols on a large number of
subcarriers, and these data symbols exposed to changes in
amplitude and phase, caused of noise and frequency selective
fading and Doppler shift .
To get the transmitted data at the receiver we must cope with these
changes, so we need to know the channel response at every
subcarrier and every symbol, and for that reason we use PILOTS
and we use many methods to estimate the channel response depend
on pilots, and the most important channel is LMMSE Method.
We will discuss in these issue the wiener filtering method
(LMMSE) which give best performance but it is very complicated,
so we will use Discrete Fourier Transform (DFT) to reduce the
complexity of these method and we will study the BER and MSE in
both case when we use QPSK or 16QAM Modulation .
This research contains an analysis of performance of multiple
access protocols when using for satellite channel to connect between
earth station(HUB) and VSAT through satellite .The performance
of those protocols has been compared through the foll
owing points:
1)the transmission power which is required by the earth station.
2) the transmission power which is required by the satellite's
transponder .
3)the require frequency bandwidth.
4)the maximum number of the earth stations in the network.
5)the delay which is caused by using those protocols.
This study has introduced head lines to choose the proper multiple
access protocol for the required service from the satellite channel
preserving the lowest cost to have the ideal performance for satellite
channel.
Network coding isone of the important researches in multi-hop wireless networks domain
and it widely participates in improving the performance of these networks, since it benefits from
the broadcasting nature of transmission processes to transmit m
ore than single packet in one
broadcasting transmission. So it achieves double use of the available bandwidth, which can
increase the throughput of the network and reduce the congestion.Our aim in this research is to
verify the improvement that network coding presents to theperformance of multi-hops wireless
Ad-hoc networks, and to study the accelerating of research process for coding chances through
constructing a virtual queues according to the packets flows that pass the node, and applying
affective manner to manage this queues.
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