Openwifi : a free and open-source IEEE802.11 SDR implementation on SoC

Open source Software Defined Radio (SDR) project, such as srsLTE and Open Air Interface (OAI), has been widely used for 4G/5G research. However the SDR implementation of the IEEE802.11 (Wi-Fi) is still difficult. The Wi-Fi Short InterFrame Space (SIFS) requires acknowledgement (ACK) packet being sent out in 10μs/16μs(2.4 GHz/5GHz) after receiving a packet successfully, thus the Personal Computer (PC) based SDR architecture hardly can be used due to the latency (≥100μs) between PC and Radio Frequency (RF) front-end. Researchers have to do simulation, hack a commercial chip or buy an expensive reference design to test their ideas. To change this situation, we have developed an open-source full-stack IEEE802.11a/g/n SDR implementation — openwifi. It is based on Xilinx Zynq Systemon-Chip (SoC) that includes Field Programmable Gate Array (FPGA) and ARM processor. With the low latency connection between FPGA and RF front-end, the most critical SIFS timing is achieved by implementing Physical layer (PHY) and low level Media Access Control (low MAC) in FPGA. The corresponding driver is implemented in the embedded Linux running on the ARM processor. The driver instantiates Application Programming Interfaces (APIs) defined by Linux mac80211 subsystem, which is widely used for most SoftMAC Wi-Fi chips. Researchers could study and modify openwifi easily thanks to the modular design. Compared to PC based SDR, the SoC is also a better choice for portable and embedded scenario

Screening interacting factors in a wireless network testbed using locating arrays

Wireless systems exhibit a wide range of configurable parameters (factors), each with a number of values (levels), that may influence performance. Exhaustively analyzing all factor interactions is typically not feasible in experimental systems due to the large design space. We propose a method for determining which factors play a significant role in wireless network performance with multiple performance metrics (response variables). Such screening can be used to reduce the set of factors in subsequent experimental testing, whether for modelling or optimization. Our method accounts for pairwise interactions between the factors when deciding significance, because interactions play a significant role in real-world systems. We utilize locating arrays to design the experiment because they guarantee that each pairwise interaction impacts a distinct set of tests. We formulate the analysis as a problem in compressive sensing that we solve using a variation of orthogonal matching pursuit, together with statistical methods to determine which factors are significant. We evaluate the method using data collected from the w-iLab.t Zwijnaarde wireless network testbed and construct a new experiment based on the first analysis to validate the results. We find that the analysis exhibits robustness to noise and to missing data

Pareto Analysis and Multi-Objective Optimization in Wireless Networks

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Experimental Investigations and Numerical Modelling of Lateral Variations of Hydraulics and Sediment Transport in Braided Rivers

Measurement and prediction of cross section averaged bedload transport rates in braided rivers have been long standing problem. Moreover, because bedload transport is non-linear, width averaged calculations of sediment transport will underestimate the true bedload flux where there is marked spatial and temporal variability in hydraulic parameters. However, at present very little is known about this effect or the actual lateral distribution of bedload. This thesis presents results from a series of micro-scale laboratory experiments designed to quantify the role of lateral variation of sediment transport as controls on braided river evolution. The experimental approach follows the “similarity of processes” concept and is therefore not scaled to a real world prototype. In all the five runs, the water discharge was held constant and the sediment feed rate was varied to simulate consecutive aggradation and degradation scenarios. The qualitative observations of the experiments were supplemented with sediment transport data at the flume outlet and quantitative analysis of high resolution laser profiler attached to the experimental apparatus which measured bed elevations of the experimental channels as they evolved. This allowed the construction of a time series of data on the sediment storage and channel morphology and the changing lateral hydraulic variability on the channel. Aggradation was associated with channel multiplication and an increase in braiding intensity. During degradation, channel pattern was transformed to single thread. Simple averaging of sediment transport computations over the width of the channel is found to underestimate the sediment transport rate. A clear relationship appears to exist between braiding intensity and the width of shear stress distribution shape parameter. Maxima in braiding intensity and minima in shape parameter values occur around the flume outlet. In contrast, minima in braiding intensity and maxima in shape parameter values occur at the flume entrance. The experimental data generated provides a unique opportunity to observe in detail the spatial and temporal changes in the width of shear stress shape parameter that occurred on the channels as they evolved. The digital elevation models collected from the experiments were also used to run a two-dimensional hydraulic model that helped to understand the controls of shear stress on the experimental channels. A relationship was established that relates the width of shear stress distribution shape parameter and channel morphological parameters (channel width to depth ratio and braiding intensity) and the relationship was also compared with observations of the Megech gravel bed braided river in the Northern Ethiopia. Overall, the investigation has demonstrated the potential for micro scale physical models to investigate aggradation and degradation scenarios and provide rich data concerning the lateral variability of sediment transport in braided channels. These data demonstrate the idea that increasing braiding intensity is a morphological response to high sediment load from upstream. Channel aggradation increases sediment transport by promoting lateral flow variability. This in turn feeds back to further aggradation depending on the response of the channel. This process will continue up to a point where there is no substantial variation in channel width to depth ratio. Beyond this point, there will be a reduction in sediment transport rates as a result of reduction in mean shear stress. This will in turn feed back to promote further aggradation

Throughput optimization strategies for large-scale wireless LANs

Thanks to the active development of IEEE 802.11, the performance of wireless local area networks (WLANs) is improving by every new edition of the standard facilitating large enterprises to rely on Wi-Fi for more demanding applications. The limited number of channels in the unlicensed industrial scientific medical frequency band however is one of the key bottlenecks of Wi-Fi when scalability and robustness are points of concern. In this paper we propose two strategies for the optimization of throughput in wireless LANs: a heuristic derived from a theoretical model and a surrogate model based decision engine