Usage of link-level performance indicators for HSDPA network-level simulations in E-UMTS

The paper describes integration of HSDPA (high-speed downlink packet access) link-level simulation results into network-level simulations for enhanced UMTS. The link-level simulations model all physical layer features depicted in the 3GPP standards. These include: generation of transport blocks; turbo coding; rate matching; spreading; scrambling; modulation. At the receiver side, all complementary blocks are designed, with soft-decision demodulation, and a turbo decoder using the MAP (maximum a posteriori) algorithm with 8 iterations. An analytical formula is defined that fits the CQI (channel quality indicator) dependent BLER (block error rate) versus E/sub b//N/sub 0/ results in an AWGN channel. This formula models the physical layer in the network-level simulator. A further extension for frequency selective fading channels has been defined. The network-level simulator includes propagation models that provide SNR values. Based on these SNR values and the simplified physical layer model, an algorithm selects the CQI, and determines the actual BLER at time of reception. The rounding down and delaying of the CQI reporting, which corresponds to the W-CDMA standard, has a significant impact on throughput and transfer delay of the HS-DSCH. Some compensation can be found in a modified transmission. The integration of the link-level and network-level simulators gives accurate and realistic results that can be used in more studies that focus on network layer aspects of packet based services over HSDP

CLIFT: a Cross-Layer InFormation Tool for Latency Analysis Based on Real Satellite Physical Traces

New mobile technology generations succeed in achieving high goodput, which results in diverse applications profiles exploiting various resource providers (Wifi, 4G, 5G, . . . ). Badly set parameters on one of the network component may severely impact on the transmission delay and reduce the quality of experience. The cross layer impact should be investigated on to assess the origin of latency. To run cross-layer (from physical layer to application layers) simulations, two approaches are possible: (1) use physical layer models that may not be exhaustive enough to drive consistent analysis or (2) use real physical traces. Driving realistic measurements by using real physical (MAC/PHY) traces inside network simulations is a complex task. We propose to cope with this problem by introducing Cross Layer InFormation Tool (CLIFT), that translates real physical events from a given trace in order to be used inside a network simulator such as ns-2. Our proposal enables to accurately perform analysis of the impact of link layer reliability schemes (obtained by the use of real physical traces) on transport layer performance and on the latency. Such approach enables a better understanding of the interactions between the layers. The main objective of CLIFT is to let us study the protocols introduced at each layer of the OSI model and study their interaction. We detail the internal mechanisms and the benefits of this software with a running example on 4G satellite communications scenarios

Throughput and Collision Analysis of Multi-Channel Multi-Stage Spectrum Sensing Algorithms

Multi-stage sensing is a novel concept that refers to a general class of spectrum sensing algorithms that divide the sensing process into a number of sequential stages. The number of sensing stages and the sensing technique per stage can be used to optimize performance with respect to secondary user throughput and the collision probability between primary and secondary users. So far, the impact of multi-stage sensing on network throughput and collision probability for a realistic network model is relatively unexplored. Therefore, we present the first analytical framework which enables performance evaluation of different multi-channel multi-stage spectrum sensing algorithms for Opportunistic Spectrum Access networks. The contribution of our work lies in studying the effect of the following parameters on performance: number of sensing stages, physical layer sensing techniques and durations per each stage, single and parallel channel sensing and access, number of available channels, primary and secondary user traffic, buffering of incoming secondary user traffic, as well as MAC layer sensing algorithms. Analyzed performance metrics include the average secondary user throughput and the average collision probability between primary and secondary users. Our results show that when the probability of primary user mis-detection is constrained, the performance of multi-stage sensing is, in most cases, superior to the single stage sensing counterpart. Besides, prolonged channel observation at the first stage of sensing decreases the collision probability considerably, while keeping the throughput at an acceptable level. Finally, in realistic primary user traffic scenarios, using two stages of sensing provides a good balance between secondary users throughput and collision probability while meeting successful detection constraints subjected by Opportunistic Spectrum Access communication

Modeling of multipath fading channels for network simulation

Development of accurate physical layer models is very important for generating realistic network simulation results. Significant effort has been put into setting up physical layer models for wireless channels that emulate the impact of the channel on the higher layers of the network. Setting up the models is especially difficult for a frequency selective channel. In this thesis the use of non-linear functions to convert the frequency selective channel to an equivalent flat fading channel is examined. The analytical expressions for the statistics of the equivalent flat fading process that are needed to set up the physical layer models are derived. These results are used to set up the physical layer model for the frequency selective channel. Extensive simulations are performed to verify the accuracy of the model against a detailed physical layer implementation. The statistics of the model and the actual channel are seen to match, validating the method of setting up the models

Wireless Mesh Networks: Energy - Capacity Tradeoff and Physical Layer Parameters

International audienceThis paper is focused on broadband wireless mesh networks based on OFDMA resource management, considering a realistic SINR model of the physical layer with a fine tuned power control at each node. A linear programing model using column generation leads to compute power efficient schedules with high network capacity. Correlation between capacity and energy consumption is analyzed as well as the impact of physical layer parameters - SINR threshold and path-loss exponent. We highlight that there is no significant tradeoff between capacity and energy when the power consumption of idle nodes is impor- tant. We also show that both energy consumption and network capacity are very sensitive to the SINR threshold variation

A Multi-objective Optimization of Broadband WMN: Energy-Capacity Tradeoff and Optimal System Configuration

This paper is focused on broadband wireless mesh networks based on OFDMA resource management. We develop an extensible linear programing model using column generation to compute power efficient schedules with high network capacity. We adopt a more realistic model for the physical layer using SINR model with a fine tuned power control at each node. Correlation between capacity and energy consumption is analyzed as well as the impact of physical layer parameters - SINR threshold and path-loss exponent. We highlight that there is no significant tradeoff between capacity and energy when the power consumption of idle nodes is important. Furthermore, we include an adaptive modulation in each node combined with a variable transmission rate to find an optimal system configuration of the network. We also study the impact of power control, spacial reuse and adaptive modulation on capacity and energy consumption and we give some network engineering results

Monte Carlo modeling of multiply scattered laser ceilometer returns

February 1994.Also issued as Chan W. Keith's thesis (M.S.) -- Colorado State University, 1994.Includes bibliographical references.Initial analysis of the data from the laser ceilometer used during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) and Atlantic Stratocumulus Transition Experiment (ASTEX) programs indicated that clouds were sometimes not reported even though clouds were visible over the ceilometer. In order to understand this inconsistency, a model using Monte Carlo techniques has been refined to study the effect that multiple scattering and other physical processes have on near infrared laser ceilometer returns. The model traces photon paths through three orders of scattering within various scattering media and determines the photon's probability of returning to the receiver at each scattering point. The Monte Carlo model allows for a limited number of horizontal and vertical inhomogeneities in the extinction coefficient and scattering phase function within the scattering media. Clear air and background aerosol scattering, based on published standards are also introduced within the model. Results from the current model are compared with previously published results. Specific atmospheric media and laser ceilometer parameters are modeled, and a factor, a, is defined to measure the effects of each. Results from the model indicate that precipitation and extinction by the subcloud layer have the most significant impact upon the return signal. For clouds with the same optical depth, those with an increasing extinction with depth exhibited a flatter, smaller magnitude return signal than those with a constant or decreasing extinction. Rayleigh scattering and background aerosols in the subcloud layer decrease the return signal from the cloud and introduce a background level of return from below the cloud. Rain in the subcloud layer lowers the return signal from the cloud, but increases the signal from the subcloud layer due to its relatively large extinction, while realistic levels of absorption have no significant impact. Lastly, a quantitative assessment of detectability for clouds is made, based on amin as a threshold. Model results indicate that conditions can exist where a cloud may not be identified by the laser ceilometer.Sponsored by the National Oceanic and Atmospheric Administration grant NAG 1-1146, and the Office of Naval Research contract N00014-91-J-1422, P0004

Aggregation with fragment retransmission for very high-speed WLANs

In upcoming very high-speed WLANs the physical layer (PHY) rate may reach 600 Mbps. To achieve high efficiency at the medium access control (MAC) layer, we identify fundamental properties that must be satisfied by any CSMA/CA based MAC layer and develop a novel scheme called Aggregation with Fragment Retransmission (AFR). In the AFR scheme, multiple packets are aggregated into and transmitted in a single large frame. If errors happen during the transmission, only the corrupted fragments of the large frame are retransmitted. An analytic model is developed to evaluate the throughput and delay performance of AFR over a noisy channel, and to compare AFR with competing schemes in the literature. Optimal frame and fragment sizes are calculated using this model. Transmission delays are minimised by using a zero-waiting mechanism where frames are transmitted immediately once the MAC wins a transmission opportunity. We prove that zero waiting can achieve maximum throughput. As a complement to the theoretical analysis, we investigate by simulations the impact of AFR on the performance of realistic application traffic with diverse requirements. We have implemented the AFR scheme in the NS-2 simulator and present detailed results for TCP, VoIP and HDTV traffic. The AFR scheme described was developed as part of the 802.11n working group work. The analysis presented here is general enough to be extended to the proposed scheme in the upcoming 802.11n standard. Trends indicated by our simulation results should extend to any well-designed aggregation scheme

Maximizing the Probability of Delivery of Multipoint Relay Broadcast Protocol in Wireless Ad Hoc Networks with a Realistic Physical Layer

It is now commonly accepted that the unit disk graph used to model the physical layer in wireless networks does not reflect real radio transmissions, and that the lognormal shadowing model better suits to experimental simulations. Previous work on realistic scenarios focused on unicast, while broadcast requirements are fundamentally different and cannot be derived from unicast case. Therefore, broadcast protocols must be adapted in order to still be efficient under realistic assumptions. In this paper, we study the well-known multipoint relay protocol (MPR). In the latter, each node has to choose a set of neighbors to act as relays in order to cover the whole 2-hop neighborhood. We give experimental results showing that the original method provided to select the set of relays does not give good results with the realistic model. We also provide three new heuristics in replacement and their performances which demonstrate that they better suit to the considered model. The first one maximizes the probability of correct reception between the node and the considered relays multiplied by their coverage in the 2-hop neighborhood. The second one replaces the coverage by the average of the probabilities of correct reception between the considered neighbor and the 2-hop neighbors it covers. Finally, the third heuristic keeps the same concept as the second one, but tries to maximize the coverage level of the 2-hop neighborhood: 2-hop neighbors are still being considered as uncovered while their coverage level is not higher than a given coverage threshold, many neighbors may thus be selected to cover the same 2-hop neighbors