Jorma Kilpi

Improved Mapping of Tropical Forests With Optical and SAR Imagery, Part II: Above Ground Biomass Estimation

Performance of the above ground (dry) biomass estimation with the medium resolution optical (ALOS AVNIR) data and radar (ALOS PALSAR) data was evaluated on a tropical forest site in Lao PDR (Laos). The average biomass of ground reference plots was relatively low, 78 t/ha, due to strong anthropogenic influence in most of the study area. The biomass estimates were computed using linear regression analysis and the Probability method that combines unsupervised clustering and fuzzy estimation. The predictions were validated with independent field plot data. With all the methods and data types, the root mean square error (RMSE) ranged from 33.6 t/ha to 40.1 t/ha (44.2% and 52.8% of mean biomass, respectively). The Probability method produced a larger dynamic range to the predictions than the regression models, which saturated at approximately 100 t/ha. Large errors for higher biomass plots increased the RMSE of Probability over the RMSE of the regression models. The bias ranged from -0.8 to 3.9% except with the Probability model for PALSAR data where the bias was 12.5%. Our study showed that PALSAR data were nearly as good for the biomass estimation as the AVNIR data. A combination of mono-temporal ALOS PALSAR and ALOS AVNIR data did not improve biomass estimation over the performance obtained with AVNIR data alone. For the Probability method, ground reference data should be more representative than that available in this study.

Micro- and macroscopic analysis of RTT variability in GPRS and UMTS networks

We study the data from a passive TCP/IP traffic measurement from a Finnish operator’s GPRS/UMTS network. Of specific interest is the variability of Round Trip Times (RTTs) of TCP flows. The RTTs are analysed at micro- and macroscopic level. The microscopic level involves detailed analysis of the RTTs of individual flows, and we are able to detect, e.g., periodic behavior (via Lomb periodogram) and rate changes in the radio channel. At the macroscopic level we focus on the impact of so called self-congestion caused by bandwidth sharing at the mobile device itself, and it is shown how this seriously affects the RTTs observed by a given flow, both in GPRS and in UMTS.

Improved Mapping of Tropical Forests With Optical and SAR Imagery, Part I: Forest Cover and Accuracy Assessment Using Multi-Resolution Data

This paper describes an improved concept for the mapping of tropical forest classes with ALOS AVNIR and ALOS PALSAR data. The improvement comes from a combination of a sample of very high resolution (VHR) satellite images with medium resolution wall-to-wall mapping in a statistical sampling framework. The approach developed makes it possible to obtain reliable information on mapping accuracy over the whole area of interest. A simulation study indicated that the sample of VHR images should be collected in a stratified manner using small (25 km) images. The VHR images should cover approximately one percent of the total area of interest, depending on the accuracy requirement. The recommended size of the reference plots (population units) that are selected within the VHR imagery is in the order of 50 m by 50 m. In a systematic selection the plots should be located at a distance of several hundred meters from each other. The forest variables were predicted with an unsupervised fuzzy classification method. The ALOS AVNIR-based forest/non-forest mapping accuracies varied between 68% and 97% of the areas of the VHR images. The corresponding ALOS PALSAR mapping accuracies were poorer. At AVNIR resolution, the area of natural forest was over-estimated, and the degree of disturbance underestimated in humid, heavily disturbed parts of the study area in Laos. The three predictions for the total forest fraction from VHR, AVNIR and PALSAR data over the area that was covered by the VHR images were 55.1%, 53.6%, and 52.8%, respectively.

Bivariate statistical analysis of TCP-flow sizes and durations

We approximate the distribution of the TCP-flow rate by deriving it from the joint bivariate distribution of the flow sizes and flow durations of a given access network. The latter distribution is represented by a bivariate extreme value distribution using the Pickand’s dependence A-function. We estimate the A-function to measure the dependencies of random pairs: TCP-flow size and duration, the rate of TCP-flow and size, as well as the rate and duration. We provide a method to test that the achieved estimate of A-function is good and perform the analysis with one concrete data example.

A portrait of a GPRS/GSM session

Some results from a GPRS/GSM traffic measurement are presented. First we define session arrivals, durations and volumes in such a way that they can be compared, for example, with measured values of dial-up sessions. Then we study the map of cumulative volume of a single session against elapsed time from the first observed packet of the session. With these maps we study the question of how the major data transfer is typically situated inside a single sessions active duration. For this purpose we introduce three simple statistics which can be used for a rough shape classification.

Multipath routing for mmWave WMN backhaul

Static Wireless Mesh Networks (WMN) based on high capacity pencil-beam millimeter wave (mmWave) links offer an attractive solution for small cell backhauling in 5G networks. However, the delay targets in 5G are such that it is quite challenging to develop adequate link scheduling and routing mechanisms. Furthermore, the susceptibility of mmWave radio links to adverse weather conditions and other obstructions in the line-of-sight line makes it necessary that routing is able to cope with frequent link degradations and failures. We propose an approach that divides the problem into two parts - finding first a suitable set of so called primary paths and then optimizing the link schedules for those paths. In this paper, we present a routing algorithm that produces the required primary paths and several backup paths for all source-destination pairs. Furthermore, we describe a hierarchical fault recovery system that includes various protection and restoration methods that are acting in different time scales to ensure fast reaction to failures and then optimal adaptation to the changed situation.

Radio resource management for heterogeneous millimeter-wave backhaul and access network

This paper explores network design requirements and radio resource management (RRM) functionalities required to enable a heterogeneous millimeter-wave (mmW) network in both backhaul and access links. First, the envisioned design of a heterogeneous mmW network is outlined highlighting the main functional blocks and the key differentiating factors from non-mmW architectures. Next, the RRM functionalities required in both backhaul and access networks are discussed in detail, focusing on routing, link scheduling, dynamic TDD in the backhaul and dynamic “beam cell” management on the access links. Finally, some recent findings are presented, highlighting the impact of identified functionalities on network-wide performance indicators including latency and packet loss ratio.

Integrating WMN Based Mobile Backhaul with SDN Control

Resilient high capacity and low delay millimeter wave wireless mesh networks (WMNs) can provide suitable backhaul connections for future broadband mobile networks. The WMN solution is best suited in cases where base stations are installed in locations without optical fiber connection to transport network, e.g., small-cell deployment to hot spots in dense urban areas. Recently software defined network (SDN) concept has become popular in many networking areas including mobile networks. One of the key promises is to provide an efficient way for network operators to extend and create new services. As the whole network is controlled by a single central entity that is based on software code, it would be easy to make large scale network upgrades without need to wait that updates are available for all network elements (NEs). There is, however, a clear conflict between SDN ideas and WMN operation. The performance and reliability of the latter one is heavily depended on fast local reactions to, e.g., link degradations. Centralized control would introduce longer delays in reactions. In this paper, we are proposing a concept which solves these problems and allows for combining the best features of both WMN and SDN.

Potential of Different Optical and SAR Data in Forest and Land Cover Classification to Support REDD+ MRV

The applicability of optical and synthetic aperture radar (SAR) data for land cover classification to support REDD+ (Reducing Emissions from Deforestation and Forest Degradation) MRV (measuring, reporting and verification) services was tested on a tropical to sub-tropical test site. The 100 km by 100 km test site was situated in the State of Chiapas in Mexico. Land cover classifications were computed using RapidEye and Landsat TM optical satellite images and ALOS PALSAR L-band and Envisat ASAR C-band images. Identical sample plot data from Kompsat-2 imagery of one-metre spatial resolution were used for the accuracy assessment. The overall accuracy for forest and non-forest classification varied between 95% for the RapidEye classification and 74% for the Envisat ASAR classification. For more detailed land cover classification, the accuracies varied between 89% and 70%, respectively. A combination of Landsat TM and ALOS PALSAR data sets provided only 1% improvement in the overall accuracy. The biases were small in most classifications, varying from practically zero for the Landsat TM based classification to a 7% overestimation of forest area in the Envisat ASAR classification. Considering the pros and cons of the data types, we recommend optical data of 10 m spatial resolution as the primary data source for REDD MRV purposes. The results with L-band SAR data were nearly as accurate as the optical data but considering the present maturity of the imaging systems and image analysis methods, the L-band SAR is recommended as a secondary data source. The C-band SAR clearly has poorer potential than the L-band but it is applicable in stratification for a statistical sampling when other image types are unavailable.

Link scheduling for mmWave WMN backhaul

A new link scheduling approach for millimeter wave wireless mesh network is presented. The proposed link scheduling solution is designed to work together with a multiple overlapping spanning trees-based routing schemes on a mesh network topology. The link schedule computation will minimize the end-to-end delay along a subset of shortest-hop paths from non-gateway nodes to a gateway node of the mesh, where each path is obtained from one of the spanning trees. The link schedule itself consists of cyclic repetition of a vector of transmission sets, where a transmission set is a maximal collection of links that can be active simultaneously. Simultaneous activity of the links is limited by radio interference and by shared resources. Algorithms for the computation of the link schedule are provided and computational issues of the algorithms are discussed.