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We investigate the network utility maximization (NUM) problem when layered modulation is used at the physical layer of a downlink wireless system. The key idea is to transmit to more than one users with favorable and unfavorable channel qualities at the same time by employing hierarchical constellations. We demonstrate that average throughput of users with unfavorable channel conditions are significantly...
Wireless communications over water may suffer from serious multipath fading due to strong specular reflections from conducting water surfaces. Cognitive radios enable dynamic spectrum access over a large frequency range, which can be used to mitigate this problem. In this paper, we study how to leverage cognitive radios for effective communications in wireless networks over water. We formally define...
Power-controlled multiple access (PCMA) is a distributed algorithm for transmitter power control of autonomous communication links in wireless networks. By allowing links to trade off transmission power for packet delay, PCMA has been demonstrated to outperform standard approaches (e.g., the Foschini-Miljanic constant signal-to-interference ratio algorithm) in terms of maximum throughput, especially...
The growing problem of spectrum scarcity and the inefficient spectrum utilization in the licensed bands, are addressed by the emerging Cognitive Radio (CR) paradigm. It is seen that the choice of the spectrum bands, called as spectrum decision, must be organized carefully by considering the challenges in the spectrum availability over time, the short term fluctuations in the availability, and the...
In order to improve transmission throughput of a multi-hop wireless network, many efforts have been made in recent years to reduce traffic and hence transmission collisions by constructing backbone networks with minimum size. However, many other important issues need to be considered. Instead of simply minimizing the number of backbone nodes or supporting some isolated network features, in this work,...
Optimal capacity analysis in multi-radio multi-channel wireless networks by nature incurs the formulation of a mixed integer programming, which is NP-hard in general. The current state of the art mainly resorts to heuristic algorithms to obtain an approximate solution. In this paper, we propose a novel concept of multi-dimensional conflict graph (MDCG). Based on MDCG, the capacity optimization issue...
In this paper, we consider the problem of exploiting spectrum resources for a secondary user (SU) of a wireless communication network. We suggest that Upper Confidence Bound (UCB) algorithms could be useful to design decision making strategies for SUs to exploit intelligently the spectrum resources based on their past observations. The algorithms use an index that provides an optimistic estimation...
Efficient utilization of Multi Channel - Multi Radio (MC-MR) Wireless Mesh Networks (WMNs) can be achieved only by intelligent Channel Assignment (CA) and Link Scheduling (LS). Due to the dynamic nature of traffic demand in WMNs, the CA has to be reconfigured whenever traffic demand changes, in order to achieve maximum throughput in the network. The reconfiguration of CA requires channel switching...
We consider multiuser scheduling in wireless networks with channel variations and flow-level dynamics. Recently, it has been shown that the MaxWeight algorithm, which is throughput-optimal in networks with a fixed number users, fails to achieve the maximum throughput in the presence of flow-level dynamics. In this paper, we propose a new algorithm, called workload-based scheduling with learning, which...
MaxWeight algorithm, a.k.a., back-pressure algorithm, has received much attention as a viable solution for dynamic link scheduling in multi-hop wireless networks. The basic principle of the MaxWeight algorithm is to select a set of interference-free links with the maximum overall link weights in the network, where the link weight is determined by the queue difference between the transmitter and the...
In this paper we validate through simulations the convergence properties of our earlier proposed balls and bins channel allocation algorithm. The algorithm supports dynamic channel allocation based on local link quality information and does not require exchange of network information. Each radio evaluates periodically a cost function related to the desired QoS. Based on the calculated cost the radio...
Cognitive radio has been proposed as a novel approach for improving the utilization of the limited radio resources by dynamically changing its operating parameters. This paper deals with the problem of channel and power allocation for cognitive radio networks. In particular, we consider the scenario where the transmission of secondary users is controlled by cognitive base station. We propose an autonomic...
Reinforcement - Learning methods are widely used in routing problems. These methods interact with the network changes, so are called Adaptive routing methods. Q - Learning algorithms has some quantities which are labeled Q, and are known as headers in routing methods which apply this algorithm. As a result, if we add forward exploration to backward One, their header will be increased. We tried in...
The spectrum-agile cognitive radio has been developed to significantly increase spectrum utilization and relieve the spectrum exhaustion problem, by enabling secondary users to dynamically access the licensed spectrum bands. As such cognitive radio will be a key feature of future wireless technologies. In this paper, we propose an architecture for cognitive radio network (CRN). Our architecture uses...
Traditional medium access control (MAC) protocols utilize temporal mechanism to do contention resolution. This paper explores an alternative approach by adapting the space occupied by a transmission to resolve contention. Each successful transmission in a wireless network needs to occupy a certain part of space in which there are no other simultaneous transmissions. The size of the space occupied...
In this paper, a new packet approximation algorithm based on WF2Q+ of TGPS (T-WF2Q+) has been proposed in multicast orthogonal frequency division multiplexing (OFDM) systems. By using Lambda(t) instead of Lambda, the TGPS scheme could preserve the service guarantees provided by WF2Q+ algorithm for enabling to support the OFDM wireless dynamic communication systems. The proposed resource management...
Spectrum access scheme is a fundamental component in building efficient wireless networks. Conventional methods such as proactive channel assignment is costly due to large amount of protocol overhead. Also, those algorithms suffer from its inability in dealing with channel dynamics. The opportunistic methods however, spend more time on probing, and suffer from the myopic decisions as well. We present...
As a new type of wireless network architecture, because of its self-organization, and support multi-hop and heterogeneous networks, Wireless Mesh networks has played an important role in building ldquowireless citiesrdquo and become an research spot in academia and industry. In practical applications, network capacity is the most important need and high network throughput is the most important network...
This paper considers the channel-assignment and scheduling in wireless mesh networks that employ multiple radios and multiple channels. In contrast to the various algorithms available in the literature, we explicitly model the delay overhead that is incurred during channel switching, and use that delay in the design of algorithms. We prove that the well known Greedy Maximal Scheduling (GMS) algorithm...
Most of recent mobile equipment now supports different network technologies (WiFi, WiMax, LTE, Bluetooth and such like). Meanwhile, network operators offer services through these different technologies. The superposition of the different technologies (using different frequency band) increases the potential throughput of the system and hence global performance.
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