Mehmet Karaca

Bio: Mehmet Karaca is an academic researcher from Lund University. The author has contributed to research in topics: Scheduling (computing) & Throughput. The author has an hindex of 11, co-authored 48 publications receiving 331 citations. Previous affiliations of Mehmet Karaca include Sabancı University.

Optimal scheduling in cooperate-to-join Cognitive Radio Networks

Abstract: Optimal transmission scheduling in wireless cognitive networks is considered under the spectrum leasing model.We propose a cooperative scheme in which secondary nodes share the time slot with primary nodes in return for cooperation. Cooperation is feasible only if the system's performance is improved over the non-cooperative case. First, we investigate a scenario where secondary users are interested in immediate rewards. Then, we formulate another problem where the secondary users are guaranteed a portion of the primary utility, on a long term basis, in return for cooperation. In both scenarios, our proposed schemes are shown to outperform non-cooperative scheduling schemes, in terms of both individual and total expected utility, for a given set of feasible constraints. Based on Lyapunov Optimization techniques, we show that our schemes are arbitrarily close to the optimal performance at the price of reduced convergence rate.

Data collection with "UYANIK": too much pain; but gains are coming

Abstract: In this paper, we present data collection activities and preliminary research findings from the real-world database collected with “UYANIK,” a passenger car instrumented with various sensors, CAN-Bus data logger, cameras, microphones, data acquisitions systems, computers, and support systems. Within the shared frameworks of DriveSafe Consortium (Turkey) and the NEDO (Japan) International Collaborative Research on Driving Behavior Signal Processing, close to 9 Terabytes of driver behavior, vehicular, and road data has been collected from more than 50 drivers on a 25 km route consisting of both city roads and highway in Istanbul, Turkey. Challenge of collecting data in a metropolis with around 12 million people, famous with extremely limited infrastructure yet driving behavior defying all rules and regulations bordering madness could not be “PAINLESS.” Both the experience gained and the preliminary results from still on-going studies using the database are very encouraging and give comfort.

Resource Management for OFDMA based Next Generation 802.11ax WLANs

Abstract: Recently, IEEE 802.11ax Task Group has adapted OFDMA as a new technique for enabling multi-user transmission. It has been also decided that the scheduling duration should be same for all the users in a multi-user OFDMA so that the transmission of the users should end at the same time. In order to realize that condition, the users with insufficient data should transmit null data (i.e. padding) to fill the duration. While this scheme offers strong features such as resilience to Overlapping Basic Service Set (OBSS) interference and ease of synchronization, it also poses major side issues of degraded throughput performance and waste of devices' energy. In this work, for OFDMA based 802.11 WLANs we first propose practical algorithm in which the scheduling duration is fixed and does not change from time to time. In the second algorithm the scheduling duration is dynamically determined in a resource allocation framework by taking into account the padding overhead, airtime fairness and energy consumption of the users. We analytically investigate our resource allocation problems through Lyapunov optimization techniques and show that our algorithms are arbitrarily close to the optimal performance at the price of reduced convergence rate. We also calculate the overhead of our algorithms in a realistic set-up and propose solutions for the implementation issues.

Standard-Compliant LTE-A Uplink Scheduling Scheme With Quality of Service

Abstract: In this paper, we focus on uplink scheduling with the practical constraints imposed by the Long-Term Evolution/Long-Term Evolution-Advanced (LTE/LTE-A) standard. We consider multimedia traffic generated by mobile users with heterogeneous quality-of-service (QoS) requirements. To tackle the resulting time and frequency problem, we then propose an adaptive and potential aware scheduling scheme (APASS), which is standard compliant and covers a wide range of scheduling objectives. This scheduling scheme is composed of three algorithms, which work jointly to provide an efficient solution. Our performance evaluation shows that the APASS outperforms other state-of-the-art scheduling schemes in terms of user satisfaction and delay.

Modifying Backoff Freezing Mechanism to Optimize Dense IEEE 802.11 Networks

Abstract: From experience, it has been well known that the performance of IEEE 802.11 wireless local area networks significantly drops in dense settings, largely driven by poor capacity of the medium access control (MAC) layer. The current 802.11 MAC mechanism utilizes a contention window (CW) for random access, and the CW size is dictated to take discrete values from a bounded finite set. In this paper, with focus on a saturated network scenario, we closely investigate the impacts of the aforementioned constraint and show that the limitations on the CW size are the main MAC bottleneck in dense conditions. Then, in order to tackle this bottleneck, we propose a new backoff scheme that does not attempt to tune the CW but makes a small modification in the backoff freezing process to determine the optimal configuration. We prove that our backoff scheme can achieve the maximum network throughput even under densely populated networks (i.e., many contenders), while a maximal compliance with the mentioned constraints is maintained. Then, we turn our attention to minimizing the channel access delay, and propose a variant of our backoff algorithm to accomplish this aim. We further present a new result on the theoretical relation between the optimal configurations for which the throughput is maximized and the delay is minimized. Finally, we note that our modified backoff mechanism does not penalize legacy users and is, therefore, practical for implementation in existing networks, which removes co-existence concerns.

Wireless Access in Ultra-Reliable Low-Latency Communication (URLLC)

Abstract: The future connectivity landscape, and notably, the 5G wireless systems will feature Ultra-Reliable Low Latency Communication (URLLC). The coupling of high reliability and low latency requirements in URLLC use cases makes the wireless access design very challenging, in terms of both the protocol design and of the associated transmission techniques. This paper aims to provide a broad perspective on the fundamental tradeoffs in URLLC, as well as the principles used in building access protocols. Two specific technologies are considered in the context of URLLC: massive MIMO and multi-connectivity, also termed interface diversity . This paper also touches on the importance of the proper statistical methodology for designing and assessing extremely high-reliability levels.

Toward Haptic Communications Over the 5G Tactile Internet

Abstract: Touch is currently seen as the modality that will complement audition and vision as a third media stream over the Internet in a variety of future haptic applications which will allow full immersion and that will, in many ways, impact society. Nevertheless, the high requirements of these applications demand networks which allow ultra-reliable and low-latency communication for the challenging task of applying the required quality of service for maintaining the user’s quality of experience at optimum levels. In this survey, we enlist, discuss, and evaluate methodologies and technologies of the necessary infrastructure for haptic communication. Furthermore, we focus on how the fifth generation of mobile networks will allow haptic applications to take life, in combination with the haptic data communication protocols, bilateral teleoperation control schemes and haptic data processing needed. Finally, we state the lessons learned throughout the surveyed research material along with the future challenges and infer our conclusions.

A Survey on Opportunistic Scheduling in Wireless Communications

Abstract: Wireless technology advancements made opportunistic scheduling a popular topic in recent times. However, opportunistic schedulers for wireless systems have been studied since nearly twenty years, but not implemented in real systems due to their high complexity and hardly achievable requirements. In contrast, today's popularity of opportunistic schedulers extends to implementation proposals for next generation cellular technologies. Motivated by such a novel interest towards opportunistic scheduling, we provide a taxonomy for opportunistic schedulers, which is based on scheduling design's objectives; accordingly, we provide an extensive review of opportunistic scheduling proposals which have appeared in the literature during nearly two decades. The huge number of papers available in the literature propose different techniques to perform opportunistic scheduling, ranging from simple heuristic algorithms to complex mathematical models. Some proposals are only designed to increase the total network capacity, while others enhance QoS objectives such as throughput and fairness. Interestingly, our survey helps to unveil two major issues: (i) the research in opportunistic is mature enough to jump from pure theory to implementation, and (ii) there are still under-explored and interesting research areas in opportunistic scheduling, e.g., opportunistic offloading of cellular traffic to 802.11-like networks, or cooperative/distributed opportunistic scheduling.

5G Ultra-Reliable Low-Latency Communication Implementation Challenges and Operational Issues with IoT Devices

Abstract: To meet the diverse industrial and market demands, the International Telecommunication Union (ITU) has classified the fifth-generation (5G) into ultra-reliable low latency communications (URLLC), enhanced mobile broadband (eMBB), and massive machine-type communications (mMTC). Researchers conducted studies to achieve the implementation of the mentioned distributions efficiently, within the available spectrum. This paper aims to highlight the importance of URLLC in accordance with the approaching era of technology and industry requirements. While highlighting a few implementation issues of URLLC, concerns for the Internet of things (IoT) devices that depend on the low latency and reliable communications of URLLC are also addressed. In this paper, the recent progress of 3rd Generation Partnership Project (3GPP) standardization and the implementation of URLLC are included. Finally, the research areas that are open for further investigation in URLLC implementation are highlighted, and efficient implementation of URLLC is discussed.