Analysis of hierarchical cellular networks with mobile base stations

In this paper. we develop and evaluate a hierarchical cellular architecture for totally mobile wireless networks (TMWNs). Extensive performance tests were conducted to evaluate the performance of a two-tier system and compare its throughput, handoff blocking rate and new call success rate with those obtained by a one-tier model. Our tests have shown that when the total number of channels is kept the same, the two-tier system outperformed the one-tier counterpart under all load conditions. Under the constraint of equal power consumption, the two-tier system still achieved improvement over the one-tier system. especially at light and medium load levels. The improvement of the two-tier system over the one-tier system was observed to diminish as the degree of randomness in the mobility model is reduced scenarios where the one-tier system outperforms the two-tier system are given. Load balancing schemes based on the concept of reversible handoffs are introduced and their performance improvements are analyzed. Comparison results on the percentage of terminal coverage are presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. The model extends the Markov chain approach previously used in hierarchical architectures with stationary base stations and uses a corrected derivation for the handoff blocking probability

Supporting differentiated quality of service in optical burst switched networks

We propose and evaluate two new schemes for providing differentiated services in optical burst switched (OBS) networks. The two new schemes are suitable for implementation in OBS networks using just-in-time (JIT) or just-enough-time (JET) scheduling protocols. The first scheme adjusts the size of the search space for a free wavelength based on the priority level of the burst. A simple equation is used to divide the search spectrum into two parts: a base part and an adjustable part. The size of the adjustable part increases as the priority of the burst becomes higher. The scheme is very easy to implement and does not demand any major software or hardware resources in optical cross-connects. The second scheme reduces the dropping probability of bursts with higher priorities through the use of different proactive discarding rates in the network access station (NAS) of the source node. Our extensive simulation tests using JIT show that both schemes are capable of providing tangible quality of service (QoS) differentiation without negatively impacting the throughput of OBS networks

Effective preemptive scheduling scheme for optical burst-switched networks with cascaded wavelength conversion consideration

We introduce a new preemptive scheduling technique for next-generation optical burst switching (OBS) networks considering the impact of cascaded wavelength conversions. It has been shown that when optical bursts are transmitted all optically from source to destination, each wavelength conversion performed along the lightpath may cause certain signal-to-noise deterioration. If the distortion of the signal quality becomes significant enough, the receiver would not be able to recover the original data. Accordingly, subject to this practical impediment, we improve a recently proposed fair channel scheduling algorithm to deal with the fairness problem and aim at burst loss reduction simultaneously in OBS environments. In our scheme, the dynamic priority associated with each burst is based on a constraint threshold and the number of already conducted wavelength conversions among other factors for this burst. When contention occurs, a new arriving superior burst may preempt another scheduled one according to their priorities. Extensive simulation results have shown that the proposed scheme further improves fairness and achieves burst loss reduction as well

Architecture and sparse placement of limited-wavelength converters for optical networks

Equipping all nodes of a large optical network with full conversion capability is prohibitively costly. To improve performance at reduced cost, sparse converter placement algorithms are used to select a subset of nodes for full-conversion deployment. Further cost reduction can be obtained by deploying only limited conversion capability in the selected nodes. We present a limited wavelength converter placement algorithm based on the k-minimum dominating set (k-MDS) concept. We propose three different cost-effective optical switch designs using the technologically feasible nontunable optical multiplexers. These three switch designs are flexible node sharing, strict node sharing, and static mapping. Compared to the full search heuristic of O(N-3) complexity based on ranking nodes by blocking percentages, our algorithm not only has a better time complexity O(RN2), where R is the number of disjoint sets provided by k-MIDS, but also avoids the local minimum problem. The performance benefit of our algorithm is demonstrated by network simulation with the U.S Long Haul topology having 28 nodes (91 is 5) and the National Science Foundation (NSF) network having 16 nodes (91 is 4). Our simulation considers the case when the traffic is not uniformly distributed between node pairs in the network using a weighted placement approach, referred to as k-WMDS. From the optical network management point of view, our results also show that the limited conversion capability can achieve performance very close to that of the full conversion capability, while not only decreasing the optical switch cost but also enhancing its fault tolerance

International Consensus Statement on Rhinology and Allergy: Rhinosinusitis

Background: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR‐RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR‐RS‐2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence‐based findings of the document. Methods: ICAR‐RS presents over 180 topics in the forms of evidence‐based reviews with recommendations (EBRRs), evidence‐based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary. Results: ICAR‐RS‐2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence‐based management algorithm is provided. Conclusion: This ICAR‐RS‐2021 executive summary provides a compilation of the evidence‐based recommendations for medical and surgical treatment of the most common forms of RS

Adaptive Mobility Prediction For Location Management Using Mobile Positioning

In this paper, an adaptive location management scheme for mobile wireless networks is presented based on the Gauss-Makov mobility model proposed in [LIA99]. The scheme exploits the mobility information gathered from mobile positioning devices (e.g., GPS) to help predict the future position of the mobile. A conventional dead-reckoning approach is used to determine the appropriate time to perform location updates; the mobile periodically compares its current location (obtained by the location positioning device) with the predicted location and sends an autonomous location update whenever the prediction error exceeds a certain threshold. The scheme adapts well to the changes of the user\u27s mobility model since it uses the latest measured mobility information. A simulation model has been used to evaluate the prediction scheme. The performance results show that the simple average velocity based prediction algorithm gives improvement over the non-predictive distanced-based scheme and achieves a good performance on less random mobility models. It has a good balance of low paging cost and acceptable location update overhead. Moreover, we give an approximation method to estimate the user\u27s mobility parameters and evaluate the performance of the algorithm with these parameters. With the availability of GPS mobility measurements, the system can disable the predictive scheme and revert to the traditional distance based scheme when the degree of movement randomness exceeds certain level. On the long run, this feature reduces the computational overhead and power consumption of the location management scheme

Eco-Friendly Thermal Aware Routing Protocol For Habitat Monitoring

One of the major applications of wireless sensor networks is in the field of environmental monitoring of the diverse and unique ecosystems and animal habitats. The networks of wireless sensor nodes are used to monitor the microclimates in the animal habitats and the animal behavior patterns. One of the main requirements of a habitat monitoring infrastructure is inconspicuous operation, which means the system should not alter the behavior of the species under study. These sensor networks produce heat as they have to communicate wirelessly, resulting in rise of the node\u27s temperature. If the amount of heat produced by the nodes is too much or the temperature rise in the nodes due to communication is too high, the behavior of the species being monitored might be affected and the ecological balance might be disturbed. In this paper, we propose a routing protocol that reduces the amount of heat produced by the sensor nodes and also the maximum temperature rise in a node. The proposed protocol performs better in terms of reducing the amount of heat produced and maximum temperature rise compared to the shortest hop routing algorithm. Our protocol also maintains low packet delivery delay and low power consumption

Improving Fairness With Novel Adaptive Routing In Optical Burst-Switched Networks

In most existing studies of optical burst-switched networks, adaptive routing is based on deflection routing and/or feedback from the past intervals which often introduces excessive transmission delay and architectural complexity. Our proposed novel adaptive routing schemes, however, consider the transient link congestion at the moment when the bursts arrive and have potential to reduce the overall burst loss probability. Moreover, they can utilize the same offset times for the same node pairs implying zero additional transmission delay and simplicity. The proposed hop-by-hop routing schemes also aim to address the intrinsic unfairness defect of existing popular signaling protocols by increasing the effective link utilization. The results show that the proposed schemes generally outperform shortest path routing and depending on the routing strategy involved, the network topology and the traffic load, this improvement can be substantial. We develop analytical loss models to demonstrate the need for such an adaptive routing scheme at each hop and show its effectiveness. We also verify the analytical results by simulation. © 2009 IEEE

A Tunable Cross-Layer Congestion Reducing Medium Access Control (Crmac) Protocol For Wireless Networks

In recent years, development of a large variety of mobile computing devices have led to wide scale deployment and use of wireless ad hoc and sensor networks. Ad hoc Wireless LANs (WLANs) and sensor networks are prone to network congestion due to the bursty nature of data traffic. This results in an increase in the number of packets dropped due to buffer overflow, decrease in the overall network throughput and increase in packet delivery latency. In this paper, we propose a contention based, tunable cross-layer congestion reducing medium access control (CRMAC) protocol that uses buffer-status information from the network layer to reduce congestion and buffer overflows by giving prioritized medium access to congested nodes in the MAC layer. The performance of CRMAC has been compared with that of 802.11 and a generalized contention based fair medium access control protocol. Simulation results show that CRMAC can be easily tuned to meet the application-specific performance requirements and performs much better than the other two algorithms in terms of reducing the packet drops, increasing the network throughput and reducing the packet delivery delay or latency as needed by the application. © 2007 IEEE

Modeling And Performance Evaluation Of Optical Burst Switched Ring Networks With Efficient Adaptive Routing

We proposed earlier three novel adaptive routing schemes which aimed to improve both loss fairness among bursts with various hop counts and overall burst loss performance in optical burst switched networks. This paper presents a reduced load fixed point approximation analysis to evaluate burst loss probabilities for symmetrical ring networks operating under the previously proposed routing. The analysis is based on a two-dimensional Markov chain model and its accuracy is validated by simulation. © 2008 IEEE