491 research outputs found
On the Reverse Link Capacity of CDMA Macrodiversity Systems
No full textThis paper will discuss the intermediate results towards that direction. In a system which has more than 2 users, the correlation coefficient becomes too complicated to work with. Therefore, a new expression called percent correlation, OE, which describes the intensity of the correlation between the interference components at the combiner branches, is defined. Subsequently, simulation analysis are performed in order to obtain OE for the more general case of Paper submission to CWIT'99: On the Reverse Link Capacity of CDMA Macrodiversity Systems H. Yanikomeroglu -- Carleton U. 3 AE's with many users. Next, the most general case of many AE's with many users is be considered. For L? 2, the correlation analysis becomes further complicated by the necessity for the piecewise consideration of the AE's. In [4], although the correlation coefficient is obtained, its effects on the system capacity are not studied; indeed, we are ultimately interested in the quantification of such a degradation. Therefore, a mapping from OE to the corresponding performance degradation has to be found. In other words, a function (or a plot) showing the relation between OE and the yielding performance loss should be obtained. In this paper, we will present results which achieves this mapping for the simplest nontrivial case of L=2 and K= 2. The extension of the work in [4] to the most general case of many AE's with many users is expected to enable us to answer many important questions. For instance, in a given service area, can we put as many AE's as we wish without an upper limit? In other words, are the reverse link performance benefits of a macrodiversity system linear, even for large numbers of AE's? It is interesting to note that if the answer were yes, then we would be able to support any num..
Base Station Placement in Integrated Aerial and Terrestrial Wireless Cellular Networks
No full textBase station (BS) location is an important problem in designing cellular networks since its solution has a profound impact on the overall network performance. An optimal BS location depends on the traffic distribution, propagation pathloss and many system parameters, which renders its analytical study difficult so that numerical algorithms are widely used instead. In this thesis, the problem is studied analytically from a fundamental perspective. By formulating the problem as a convex optimization problem, we can characterize the globally-optimum location and obtain a number of closed-form solutions and insights.
Afterwards, we consider drones as aerial BSs that can enhance network coverage or capacity by moving supply towards demand when required. Utilizing drone-BSs (DBSs) is a promising approach to boost the agility and flexibility of future wireless networks. The specific attributes of drones such as mobility could be especially useful for future applications with extreme demands. DBSs can play a remarkable role as a communication network facilitator when the temporal and spatial variations in user densities and rates are expected to result in difficult-to-predict traffic patterns.
However, deploying DBSs in a network presents several challenges. One important issue is finding the efficient 3D placement of DBSs to satisfy the dynamic requirements of the system. Another challenge is the limited wireless backhaul capacity of DBSs and consequently, higher latency incurred. This issue can be alleviated by providing content caching in DBSs to decrease backhaul congestion and latency.
In this thesis, we find locations of DBSs for various network objectives such as minimizing the number of DBSs or the transmit power, maximizing the number of covered users or total rate of the users in a wireless network, while considering the restrictions of the network such as finite backhaul capacity, disparate quality of service requirement of users, and limited access bandwidth into account. To this end, we propose various mathematical frameworks and efficient algorithms to design, optimize, and deploy drone-based communication systems.
We also obtain user-BS associations and bandwidth allocations in different scenarios which is an involved problem due to mobility of DBSs.
Extensive simulation results demonstrate the effectiveness of the proposed algorithms and provide useful insights that can be used to develop design
guidelines
Backhaul-Aware Optimization of Uav Base Station Location and Bandwidth Allocation for Profit Maximization
No full texttavli, bulent/0000-0002-9615-1983; Tavli, Bulent/0000-0002-9615-1983; Yanikomeroglu, Halim/0000-0003-4776-9354; Cicek, Cihan Tugrul/0000-0002-3532-2638; Gultekin, Hakan/0000-0002-5416-3249Unmanned Aerial Vehicle Base Stations (UAV-BSs) are envisioned to be an integral component of the next generation Wireless Communications Networks (WCNs) with a potential to create opportunities for enhancing the capacity of the network by dynamically moving the supply towards the demand while facilitating the services that cannot be provided via other means efficiently. A significant drawback of the state-of-the-art have been designing a WCN in which the service-oriented performance measures (e.g., throughput) are optimized without considering different relevant decisions such as determining the location and allocating the resources, jointly. In this study, we address the UAV-BS location and bandwidth allocation problems together to optimize the total network profit. In particular, a Mixed-Integer Non-Linear Programming (MINLP) formulation is developed, in which the location of a single UAV-BS and bandwidth allocations to users are jointly determined. The objective is to maximize the total profit without exceeding the backhaul and access capacities. The profit gained from a specific user is assumed to be a piecewise-linear function of the provided data rate level, where higher data rate levels would yield higher profit. Due to high complexity of the MINLP, we propose an efficient heuristic algorithm with lower computational complexity. We show that, when the UAV-BS location is determined, the resource allocation problem can be reduced to a Multidimensional Binary Knapsack Problem (MBKP), which can be solved in pseudo-polynomial time. To exploit this structure, the optimal bandwidth allocations are determined by solving several MBKPs in a search algorithm. We test the performance of our algorithm with two heuristics and with the MINLP model solved by a commercial solver. Our numerical results show that the proposed algorithm outperforms the alternative solution approaches and would be a promising tool to improve the total network profit.Scientific and Technological Research Council of Turkey (TUBITAK) under 2211 Ph.D. ScholarshipThis work was supported in part by the Scientific and Technological Research Council of Turkey (TUBITAK) under 2211 Ph.D. Scholarship
Cellular-connected UAV in Next-Generation Wireless Networks
No full textUnmanned aerial vehicle (UAV) technology has gained a great interest in communication
systems due to its ability to host a cellular base station (BS) and thus act as an aerial BS
(UAV-BS). The inheritance of mobility in the airspace makes the deployment of UAV-BSs
flexible and agile aiming to mainly complement the terrestrial network, extend its coverage,
and serve as a capacity injector in high-throughput demand scenarios. Besides, a
UAV can also act as an aerial user (UAV-UE) for various use cases, such as aerial data
collection and cargo delivery. Such UAV-UE missions need reliable cellular communication
links in order to safely operate in beyond visual line-of-sight (BVLoS). Since terrestrial
networks were not primarily designed to serve aerial users, due to their down-tilted BS
antennas, re-coursing solely to these networks for aerial users’ cellular connectivity might
not be a viable approach as a long-term solution. Alternatively, deploying UAV-BSs in
this context can substantially improve both aerial and terrestrial users coverage and capacity.
One of the challenging issues is how to characterize the UAV-UE performance in
integrated aerial/terrestrial networks, called vertical heterogeneous networks (VHetNets).
First, we thoroughly study the aerial user’s performance in terms of coverage probability
in a VHetNets setup. Under a more realistic system model, we revisit the coverage
and throughput performances of an aerial user in VHetNets, considering LoS and non-LoS
(NLoS) transmissions and under different spectrum sharing policies among separate aerial
and terrestrial networks. Some insights have been concluded on the integration of aerial
BSs and UAV-UEs with the existing terrestrial network. Specifically, optimal positioning
of UAV-BSs for maximized aerial users coverage was investigated for various aerial users
distribution and spectrum allocations. Moreover, visioning that UAV technology will revolutionize
the cargo delivery industry, we proposed a new concept of 3D aerial highways,
which designs coordinated routes for a massive number of UAVs used mainly for delivery
purposes. In this context, multiple network technologies were proposed and discussed to
guarantee the cellular connectivity of cargo-UAVs in 3D aerial highways. For the particular
case of connectivity supported by terrestrial cellular networks, an optimal energy-efficient
and low-handoff trajectory planning for a cargo-UAV mission was proposed, with respect to disconnectivity constraints. Consequently, associated design guidelines and recommendations
have been drawn. Leveraging reinforcement learning (RL) tools, we proposed a
novel algorithm for path planning and cell association for the cargo-UAV that maximizes
its cellular service reliability and minimizes the handoff events. Finally, we introduced a
new paradigm, intermittently tethered UAV (iTUAV), as a trade-off between mobility and
energy availability for providing cellular connectivity in temporary events
Multi-antenna systems & interconnection strategies for CDMA wireless access networks
No full textInterference management is utmost important in CDMA systems, since any reduction in inter-ference translates into a direct increase in capacity. The main objective of this thesis is to utilize antennas in novel ways so as to achieve performance bene ts at the system level through spatial interference management. To this end, we study CDMA multi-antenna wireless access networks (where the transmission and reception are through multiple antennas distributed in the service area), and compare the performance of such networks with that of the conventional types where there is only one central antenna (CA), which is the base station antenna. It is well known that CDMA distributed antenna (DA) provides coverage and diversity. We analyze the impact of these features on the power control process, and demonstrate that even with few antenna elements (AE's), power control dynamic range can be reduced signi cantly, by eliminating the occasional requirements for transmission at impractically high power levels in order to attain perfect power control; this yields a notable reduction in the outage. We also study the relation between the number of AE's and the yielding reverse link SIR (signal-to-interference ratio). Although the capacity of a DA system may be considerably higher than that which employ
Indoor communication over TV gray spaces based on spectrum measurements
No full textThe spectrum scarcity is a known problem for a multitude of services. Several bands have been licensed, and nowadays it is difficult to find unused spectrum. Cognitive radio networks have been proposed as a possible solution to contrast the experienced spectrum scarcity. One case of particular interest come from the scarce utilization of TV frequencies, which form the so-called TV White Spaces. In this paper we investigate the utilization of occupied frequencies by secondary devices for indoor communication. We conduct spectrum measurements to quantify the availability of spectrum, and study how indoor communications could impact the DTV receiver. We show that this portions of spectrum, called gray spaces, can be utilized under certain circumstances, for example in highly populated areas, which is the scenario in which it is harder to find TV White Spaces. Simulation studies show the impact gray spaces can have on the available spectrum for opportunistic use
On the role of the input power constraint in the beamforming optimality range in TIMO channels
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