9 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 9 / 9
Yayın A priority based packet scheduler with deadline considerations(IEEE Computer Soc, 2006) Dağ, Tamer; Gökgöl, OralQoS issues have become a focal point of research on Next Generation Networks (NGNs). In order to supply the various QoS requirement for different kinds of applications, new scheduling policies need to be developed and evaluated. This paper introduces a new kind of packet scheduler which tries to integrate an important QoS parameter (the delay) with the classical schedulers. The two sets of algorithms introduced; Static Priority with Deadline Considerations (SPD) and Dynamic Priority with Deadline Considerations (DPD); not only simplify the complexity and overhead of a classical Earliest Deadline First (EDF) or Static Priority (SP) algorithm, but also provide a better QoS based on the results of the simulations conducted.Yayın An Analog beamformer for integrated high-frequency medical ultrasound imaging(IEEE, 2011) Gürün, Gökçe; Zahorian, Jaime; Tekeş, Coşkun; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventWe designed and fabricated a dynamic receive beamforming integrated circuit (IC) in 0.35-mu m CMOS technology. This beamformer is suitable for integration with an ultrasound annular array for high-frequency (30-50 MHz) intravascular ultrasound (IVUS) imaging. The beamformer IC is capable of buffering, delaying and preamplification for 8 receive channels. We explored an analog delay cell based on a currentmode first-order all-pass filter, which is used as the basic building block to form an analog dynamic delay line. We also explored a bandwidth enhancement method on the delay cell that improved the overall bandwidth of the delay line by a factor of 6. Each delay cell consumes 2.1 mW of power and is capable of generating a tunable delay between 1.75 ns to 2.5 ns, enabling dynamic receive beamforming over a focal range from 1.4 mm to 2 mm. We successfully integrated the fabricated beamformer IC with an 8-element annular array. Our experimental test results demonstrated the desired buffering, preamplification and delaying capabilities of the beamformer.Yayın The investigation of the effect of saturation flow on the average vehicle delay at signalized intersections(Izmir Democracy University, 2021-12-18) Çakıcı, Ziya; Aksoy, GökerSaturation flow (s) is one of the most important parameters used for determining of signal timings at signalized intersections. Therefore, this parameter directly affects the various intersection performance criteria such as queue length, average delay, the level of service and capacity. In this study, determination of the effect of saturation flow rate on the average vehicle delay is aimed. In the scope of the study, firstly, an optimization model which minimizes the average vehicle delay at the intersection is set. Then, a software which optimizes the signal timings at the intersection by using Differential Evolution Algorithm (DEA) is prepared in MATLAB environment. In the second stage, 15 traffic volume scenarios which have different total traffic volume from each other for a four-leg signalized intersection are created in order to test different traffic cases. Created scenarios are classified in 3 groups as Low Volume (LV), Moderate Volume (MV) and High Volume (HV). In the next stage, each scenario is analyzed considering 9 different saturation flow rates (s=1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000 vehicle/hour/lane), separately. In case of implementing of these saturation flow rates, obtained signal optimum timings and average vehicle delay for each scenario are evaluated in details. In the last stage of the study, the average vehicle delays obtained by using s=1800 vehicle/hour/lane which is frequently encountered in many studies in the literature are compared with the average vehicle delays obtained by using other saturation flow rates, relatively. As a result of the comparisons, it is determined that the differences between average vehicle delays are quite low (between -0.9% and +1.2%) in case of Low Volume. In case of Moderate Volume, differences between -20.8% and +37.2% are seen. In case of High Volume, it can be said that the differences change between -41.4% and +116.3%. This situation clearly demonstrate that accurate and faultless measurement of saturation flow rate is quite important in terms of the performance of the intersection, especially in case of moderate and high volume.Yayın Examination of delay and travel time at highway toll booths using a micro simulation program: example of Northern Marmara Highway Kurnaköy(2022-04) Özdemir, Ümitcan; Gürsoy, Mustafa; Aksoy, GökerThe aim of this study is to reveal that barrier toll booths are inefficient in terms of delay and travel time when compared to non-barrier toll booths. In our study, Kurnaköy toll booth, on the Northern Marmara Highway, was examined. The toll booth was modeled using the PTV Vissim micro simulation program. Currently, 8 toll booths are in active service and are operated with barriers. As an alternative to the current operation, 4 different operations were modeled: 8 toll booths without barriers, 10 toll booths without barriers, 12 toll booths without barriers and finally 4 toll booths with free passage system. The designed models were run under 3 different demand levels as low, medium and high, and compared using the PTV Vissim program. When the current barrier toll booth and the non-barrier operations were compared with medium demand, it was seen that there is a significant difference in delay. A bottleneck problem was also encountered due to the geometry of the barrier-free toll booth operation. The optimum operation was found by comparing the alternative operations.Yayın SPD (Static Priority with Deadline considerations) packet scheduling algorithm for achieving better QoS(IEEE, 2007) Dağ, TamerProviding quality of service (QoS) to applications with different traffic characteristics based on their needs is an important research area for today's and tomorrow's high speed networks. Various techniques have been proposed to achieve good QoS for diverse application types. Among these techniques, packet scheduling algorithms decide on how to process packets at network nodes; however they have limited support for better QoS. In order to supply the various QoS requirements for different kinds of applications, new scheduling policies need to be developed and evaluated. This paper proposes a new kind of packet scheduling algorithm, Static Priority with Deadline Considerations (SPD), which integrates an important QoS parameter (the delay) into the classical static priority packet scheduling algorithm and analyses the packet losses by considering the two different components of losses; buffer overflows and deadline violations. The proposed algorithm not only reduces the complexity of the static priority algorithm by introducing degree sorting but also solves the starving problem and provides fairness to applications with different priorities.Yayın Subarray delta-sigma beamforming for ultrasonic imaging(IEEE, 2002) Bilge, Hasan Şakir; Karaman, MustafaWe present a beamforming architecture based on subarray processing with non-uniform oversampling 1-bit delta-sigma (??) modulation. The subarray processing combines conventional phased array and synthetic aperture approaches to form a large aperture using small subarrays thus reduces active channel count. ??-based beamforming improves the efficiency of front-end processing further: oversampling permits precise delaying and single bit data processing simplifies beamforming operation. To reduce the number of firings we use a low beam density associated with the subarray size, and then increase the beam density by lateral interpolation prior to coherent beam summation. Our experimental test results show that the proposed scheme provides high-resolution beamforming while simplifying the front-end.Yayın Achievable rates for the three user cooperative multiple access channel(IEEE, 2008) Edemen, Çağatay; Kaya, OnurFor a three user Gaussian multiple access channel (MAC), we propose a new superposition block Markov encoding based cooperation scheme. Our scheme allows the three users to simultaneously cooperate both in pairs, and collectively, by dividing the transmitted messages into sub messages intended for each cooperating partner. The proposed encoding and decoding at the transmitters take into account the relative qualities of the cooperation links between the transmitters. We obtain and evaluate the achievable rate region based on our encoding strategy, and compare it with the achievable rates for the two user cooperative MAC. We demonstrate that the added diversity by the presence of the third user improves the region of achievable rates, and this improvement is especially significant as far as the sum rate of the system is concerned.Yayın An algorithm and its architecture for half-pixel variable block size motion estimation(IEEE, 2007) Fatemi, Mohammad Reza Hosseiny; Salleh, Rosli Bin; Ateş, Hasan FehmiThis paper presents an accurate half-pixel variable block size motion estimation algorithm and its hardware architecture. The proposed algorithm does not require interpolation of the reference frame pixels and has near performance to the conventional interpolation-search methods. These simplifications cause high level reduction in computational time and gate count without the need for internal or external half-pixel accuracy search memory. A simple, low latency, high throughput and fully utilized pipelined architecture of proposed algorithm is implemented in VHDL The proposed hardware architecture uses shift registers for multiplication and pipelining technique and can support half-pixel accuracy variable block size motion estimation for the real time HDTV format (1920 x1280 resolution and 30 Frames/sec).Yayın A tunable analog delay element for high-frequency dynamic beamforming(IEEE, 2009) Gürün, Gökçe; Şişman, Alper; Zahorian, Jaime S.; Satır, Sarp; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventImplementing beamforming for high frequency arrays is challenging because of the accurate delay requirements at high frequencies. High frequency digital beamforming is not suitable for catheter based applications as a large number of cables is required between the array and the external beamformer. A possible solution is to perform analog beamforming on an integrated circuit adjacent or monolithically integrated to the imaging array. In this study, we introduce an improved voltage in voltage out low pass filter as an analog delay cell for high frequency dynamic beamformers. This circuit can generate three times more delay with a given bandwidth when compared to conventional low pass filters. Delay of the circuit is tunable and the gain of the cell is inherently very close to unity. The proposed delay cell operates single ended and therefore is more suitable for CMUT operation which generates single ended output. We designed a test beamformer for a 30MHz, equal area, annular array with 100% bandwidth using the proposed delay cell and the unit-delay focusing architecture. Required delays are implemented using a delay line made up of improved delay elements with tunable delays. To demonstrate functionality we designed and fabricated a custom front-end IC in a 0.5µm standard CMOS process. The IC chip consists of 8 transimpedance amplifiers, voltage-to-current converters, the analog dynamic beamformer, and two buffers. We present results of preliminary imaging experiments that demonstrate the focusing capability.
