2,264,987 research outputs found
Dataset: Throughput and Delay Analysis of Cognitive Go-Back-N Hybrid Automatic Repeat reQuest Using Discrete-Time Markov Modelling
No full textDataset supporting:
Ateeq Ur Rehman et al "Throughput and Delay Analysis of Cognitive Go-Back-N Hybrid Automatic Repeat reQuest Using Discrete-Time Markov Modelling".</span
Dataset for Delay and Throughput Analysis of Cognitive Go-Back-N HARQ in the Face of Imperfect Sensing
No full textDataset supporting:
Rehman, Ateeq Ur, Yang, Lie-Liang and Hanzo, Lajos (2017) Delay and Throughput Analysis of Cognitive Go-Back-N HARQ in the Face of Imperfect Sensing.
In order to mitigate spectrum scarcity, the cognitive radio (CR) paradigm has been invoked for improving the overall exploitation of the licensed spectrum by identifying and filling the free spectrum holes without degrading the transmission of primary users (PUs). Hence, we conceive a CR communication scheme, which enables a cognitive user (CU) to sense the activity of the PUs over a primary radio (PR) channel, which is exploited to transmit data using the modified Go-Back-N hybrid automatic repeat request (GBN-HARQ) protocol, when PR channel is free from the PUs. This arrangement is termed as the cognitive GBN-HARQ (CGBN-HARQ), where the activity of PUs on the PR channel is modelled as a two-state Markov chain having `ON' and `OFF' states. However, the CU may wrongly detect the `ON'/`OFF' activity of the PUs in the channel, hence resulting in false-alarm or mis-detection. Therefore, the two-state Markov chain is extended to four states by explicitly considering all the wrong sensing decisions. In this paper, we analytically modelled the CGBN-HARQ scheme with the aid of a Discrete Time Markov Chain (DTMC). Explicitly, an algorithm is developed for deriving all the legitimate states and for eliminating the illegitimate states, which assists us in reducing both the dimensionality of the state transition matrix and the associated computational complexity. Furthermore, based on DTMC modelling, we derive closed-form expressions for evaluating the throughput, the average packet delay and the end-to-end packet delay of CGBN-HARQ in realistic imperfect sensing environment. The results are also validated by our simulations. Our performance results demonstrate that both the achievable throughput and the delay are significantly affected by the activity of the PUs, as well as by the reliability of the PR channel and by the number of packets transmitted per TS. To attain the maximum throughput and/or the minimum transmission delay, the number of packets transmitted within a TS should be carefully adapted based on the activity level of the PUs and on the quality of the PR channel.</span
Dataset: Performance of Cognitive Selective-Repeat Hybrid Automatic Repeat Request
No full textDataset supporting:
Ateeq Ur Rehman et al, "Performance of Cognitive Selective-Repeat Hybrid Automatic Repeat Request".
In this paper, a novel transmission protocol is proposed based on the classical Selective-Repeat Hybrid Automatic Repeat to access a primary user (PU) channel, which is referred to as the CSR-HARQ.
We assume that the PU transmits information based on time-slots (TSs). During a TS, the cognitive radio (CR) transmitter first senses the PU channel. Once a free TS is found, it transmits a number of packets to the CU receiver based on the principles of the SR-HARQ.
In this paper, we analyze the throughput, average packet delay and end-to-end packets delay of the CSR-HARQ. We proposed a pair of analytical approaches. The first one is probability based, while the second one relies on the classic discrete time markov chain (DTMC) principles. Finally, we study the throughput, average packet delay as well as the end-to-end packet delay of the CSR-HARQ both by simulations and by evaluating our formulas. The simulation-based studies agree well with the analytical results. The performance of the CSR-HARQ systems is significantly impacted by the activity of the PU channel and by the reliability of the spectrum sensing.</span
Hybrid automatic repeat request assisted cognitive radios
No full textIt is widely known that the Cognitive Radio (CR) paradigm has the potential of improving the exploitation of the earmarked but momentarily unoccupied spectrum, which is exclusively allocated to the primary users (PUs) based on the conventional fixed spectrum allocation policy. The CR systems first have to sense, whether the PU’s band is unoccupied and then dynamically access it. Naturally, CR systems suffer from the same propagation impairments as the traditional wireless communication systems, such as interference, fading and noise, which affect both the reliability and the attainable data rate. In order for the CR system to achieve both reliable data transmission as well as a high throughput and low delay, we propose novel CR-aided Hybrid Automatic Repeat Request (HARQ) protocols, which intrinsically amalgamate the CR functions with HARQ protocols and study their performance. Both perfect and imperfect spectrum sensing are considered.Specifically, we propose the cognitive stop-and-wait-HARQ (CSW-HARQ), cognitive Go-Back-N-HARQ (CGBN-HARQ) as well as the cognitive selective-repeat (CSR-HARQ) schemes and study their throughput and delay both by analysis and simulation. To protect the PUs legal rights, we model their activity of occupying a primary radio (PR) channel as a two-state Markov chain consisting of ‘ON’ and ‘OFF’ states. In order to use the PR channel, the CR system first senses the presence of the PUs and once the PR channel is found to be free (i.e., in the OFF state), the CR system transmits its data packets relying on the principles of SW-HARQ, GBN-HARQ and SR-HARQ. Otherwise, the CR system continues sensing the channel until finding a free one. Naturally, the PR channel may be sensed erroneously, which results either in false alarm or in misdetection. Therefore, the channel may be modelled by a two-state Markov chain, provided that sensing is ideal, or by a four-state Markov chain, if sensing is non-ideal. Here, the four states are determined by the actual state of the PR channel and the state sensed by the CR system. We analyse both the throughput and delay of CR systems relying on different HARQ schemes. We invoke a pair of analytical approaches, namely the probability based approach and the Discrete Time Markov Chain (DTMC) based approach. Closed-form expressions are derived for the throughput, average packet delay and the end-to-end packet delay. Furthermore, for the end-to-end packet delay, we derive both the probability distribution and the average end-to-end packet delay. In the DTMCbased approach, we propose a state generation algorithm for eliminating the illegitimate states, which helps reduce both the dimensionality of the related state transition matrices and the associated computational complexity. All the equations obtained by analysis are validated by numerical simulations.Our performance results reveal that both the achievable throughput and delay of the CSWHARQ, CGBN-HARQ and the CSR-HARQ schemes are substantially affected by the activity of the PUs, by the reliability of the PR channels, by the unreliable sensing decisions and by the number of packets transmitted per time-slot (TS). Specifically, when the probability of the PR channel being busy is high and/or its reliability is relatively low, the throughput attained by these HARQ schemes becomes relatively low and their packet delay increases. Furthermore, for the CGBN-HARQ and CSR-HARQ, our results show that when the propagation environment is time-variant, the number of packets transmitted within a TS should be adapted accordingly, in order to attain the highest throughput and the shortest average transmission delay
Rauf Orbay'ın hatıraları
No full textTaha Toros Arşivi, Dosya No: 39-Rauf Orbay. Not: Makale ekli dokümanın 16. sayfasında yer almaktadır
THE EFFECTS OF THE HAMIDIYE CRUISER LED BY CAPTAIN RAUF ORBAY ON THE FIRST BALKAN WAR IN THE ERA OF THE OTTOMAN EMPIRE
No full textIn this extended essay, the effects of the Hamidiye Cruiser, led by captain Rauf Orbay , to the course of the First Balkan War were examined. The primary focus for this examination was the Raid Operation of the Balkan Wars, which has been the only succes for the Ottoman Empire. This operation was made by the Hamidiye Cruiser. The aim in doing this extended essay was to focus on the succes of the cruiser. The main question on the investigation process was to ask; How was the Raid Operation was succesful while the Ottoman Empire was on the verge of a defeat in the First Balkan War? Therefore, the actions of the Hamidiye Cruiser at the Raid Operation, The First Balkan War and the situation of the Ottoman Empire in the Balkans were examined.
Most of the information regarding of the events during the Raid Operation were taken from the books focused on the Hamidiye Cruiser. These books were taken from the Library of the Sea Museum at Istanbul, property of the Turkish Navy. These sources point out every movement of the cruiser in detail, so the course of the operation in this essay was written according to these sources. Another source for the operation was the documentary, “Akdeniz’de Bir Destan: Gazi Hamidiye ve Akın Harekatı”. As written in the outline document of the project, this documentary was made using the Naval Archives, so it contains some quotes from the journals of Rauf Orbay and an anonymous soldier from the cruiser. However, there weren’t enough quotes to center the essay around them, so they could only be used while writing about the Raid Operation.
The sources used when giving information about the First Balkan War were recommended by my supervisor. These sources gave a point of view of all the countries involved in the war, as well as the forces behind. So, the reasons and resolutions of the war were told in a big, Europe-wide perspective
Rauf Bey'le mülakat:Mert bir vazife hayatının tarihçesi
No full textTaha Toros Arşivi, Dosya No: 39-Rauf Orbay. Not: Belgenin tarihi 19 Kanun-ı Sani 1922'dir
[Hüseyin Rauf Orbay tarafından Hüseyin Nakip Turhan'a gönderilen mektup]
No full textTaha Toros Arşivi, Dosya No: 39-Rauf Orba
[Hüseyin Rauf Orbay tarafından Mustafa Kemal Atatürk'e gönderilen mektup]
No full textTaha Toros Arşivi, Dosya No: 39-Rauf Orba
[Hüseyin Rauf Orbay tarafından Reşad Bey'e gönderilen mektup]
No full textTaha Toros Arşivi, Dosya No: 39-Rauf Orba
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