Aproximación de la calidad de voz y cobertura en una red GSM de emergencia

This paper contains the results obtained by measuring the voice quality parameters in a mobile telecommunications network for disaster attention in an emergency situation. The infrastructure used free software, an IP telephony system based on Asterisk, to interconnect calls, also used communications protocols of GSM (Global System Mobile) in the DCS-1800 (Digital Cellular Service band - 1800MHz) that facilitates the use of any commercial mobile terminal. The system also used USRP (Universal Software Radio Peripheral), that  is responsible for emulating the operation of a BTS (Base Transceiver Station) performing the functions of a PBX (Private Branch Exchange), further allows the coordination of different entities in charge of responding to these type of emergencies. The measurements of network performance were made from three probabilistic parameters: GoS (Grade of Service), DCR (Dropped Call Rate) and MOS (Mean Opinion Score). Using eight mobile stations and choosing a GoS of 2%, traffic up to 3.6 Erlang was generated. This measurement was performed using probabilistic models of Erlang B. Comparison the coverage of the BTS is carried out by applying the model Okumura-Hata without amplifiers.En este documento se muestran los resultados obtenidos al medir los parámetros de calidad de voz en una solución propuesta de telecomunicaciones para la atención de desastres en situaciones de emergencia, haciendo uso de software libre para interconectar llamadas, protocolos de comunicaciones empleados en las redes GSM (Global System Mobile) en la banda DCS-1800 (Digital Cellular Service - 1800MHz), que facilita el uso de cualquier terminal móvil comercial, utilizando un USRP (Universal Software Radio Peripheral) en conjunto con sistema de telefonía IP basado en Asterisk. El USRP se encarga de emular la operación de una BTS (Base Transceiver Station) al ejecutar las funciones de un PBX (Private Branch Exchange), permitiendo la coordinación de las entidades responsables de responder y atender este tipo de emergencias. Las mediciones del desempeño de la red se realizaron a partir de tres parámetros probabilísticos: GoS (Grade of service), DCR (Dropped Call Rate) y MOS (Mean Opinion Score). Con el uso de 8 terminales y escogiendo un GoS del 2% se generó un tráfico de hasta 3,6 Erlang. Esta medición se realizó empleando modelos probabilísticos de Erlang B. Se realiza el comparativo de la cobertura de la red aplicando el modelo Okumura-Hata sin el uso de amplificadores

Estudio y diseño de un prototipo de bajo costo para emergencias utilizando software defined radio sdr y servidor asterisk para aplicaciones en sitios de bajo cobertura.

en este proyecto se realiza el diseño, desarrollo e implementación de un sistema de telecomunicaciones de bajo costo mediante software defined radio, el cual brinda acceso al servicio móvil avanzado y simula un canal de comunicación con una entidad de emergencia. el sistema diseñado está compuesto por dos servidores interconectados mediante una local area network privada la cual se establece mediante un access point. en el primer servidor, se emplea como hardware un universal software radio peripheral u2920 de national instruments y como software el proyecto openbts para la implementación de una estación base. mientras en el segundo servidor, se emplea como software el proyecto asterisk para el establecimiento de una central telefónica con call center e interactive voice responseIn this project the design, development and implementation of a low-cost telecommunications system through software defined radio is detailed, which provides advanced mobile service access and simulates a communication channel with an emergency entity. the designed system is composed of two interconnected servers through a private local area network which is established using an access point. at the first server, an universal software radio peripheral u2920 from national instruments as hardware and openbts project as software for a base transceiver station implementation are used. although, in the second server, asterisk project to establishment a telephone exchange with call center and interactive voice response is used

Experimental evaluation of a software defined radio-based prototype for a disaster response cellular network

In post disaster situations it is vital to restore voice and data communication services quickly. Currently, portable wireless systems are used as a temporary solution. However, these solutions have a lengthy setup, limited coverage, and typically require the use of expensive satellite backhaul. Solutions based on cognitive radio mesh networks have been proposed, to exploit self-configuration and spectrum agility. To evaluate their potential, we build a software-radio-based prototype for a multi-cell network that uses an IEEE 802.11's unlicensed wireless communication band for backhaul, and an open-source GSM stack for access. The prototype provides voice communication services. We evaluate the prototype in an open environment. We demonstrate that under the right conditions, the system can support large numbers of simultaneous calls with acceptable quality. However, when the unlicensed band is heavily used, call quality quickly degrades because of interference on the backhaul link. We conclude that in order to provide acceptable quality of service it is desirable to exploit idle licensed spectrum for backhaul communication between base stations

Alternative and emergency cellular system based on OpenBTS and SDR

The Global System for Mobile Communications (GSM) has been widely accepted around the world. The implementation of this system for a comunity are expensive because to use high-cost equipment, but thanks to the development of software-defined radio systems, it is possible to develop this type of network at a reduced cost. Access to telecommunications services in rural communities in Cuba is today a great challenge, mainly caused by the geographical location and the small number of habitants that make the deployment of infrastructure not economically feasible. The main contributions of the present work focus in an alternative cellular system and GSM network management software. It was shown that it is possible to build a mobile telephone network using free software components and low-cost hardware, which can be used in sparsely populated rural communities, as well as in emergency situations

Modular wireless networks for infrastructure-challenged environments

While access to Internet and cellular connectivity is easily achieved in densely-populated areas, provisioning of communication services is much more challenging in remote rural areas. At the same time Internet access is of critical importance to residents of such rural communities. People's curiosity and realization of the opportunities provided by Internet and cellular access is the key ingredient to adoption. However, poor network performance can easily impede the process of adoption by discouraging people to access and use connectivity. With this in mind, we evaluate performance and adoption of various connectivity technologies in rural developing regions and identify avenues that need immediate attention to guarantee smoother technology adoption. In light of this analysis we propose novel system designs that meet these needs. In this thesis we focus on cellular and broadband Internet connectivity. Commercial cellular networks are highly centralized, which requires costly backhaul. This, coupled with high price for equipment, maintenance and licensing renders cellular network access commercially-infeasible in rural areas. At the same time rural cellular communications are highly local: 70% of the rural-residential calls have an originator-destination pair within the same antenna. In line with this observation we design a low-cost cellular network architecture dubbed Kwiizya, to provide local voice and text messaging services in a rural community. Where outbound connectivity is available, Kwiizya can provide global services. While commercial networks are becoming more available in rural areas they are often out of financial reach of rural residents. Furthermore, these networks typically provide only basic voice and SMS services and no mobile data. To address these challenges, our proposed work allows Kwiizya to operate in coexistence with commercial cellular networks in order to extend local coverage and provide more advanced services that are not delivered by the commercial networks. Internet connectivity in rural areas is typically provided through slow satellite links. The challenges in performance and adoption of such networks have been previously studied. We add a unique dataset and consequent analysis to this spectrum of work, which captures the upgrade of the gateway connectivity in the rural community of Macha, Zambia from a 256kbps satellite link to a more capable 2Mbps terrestrial link. We show that the improvement in performance and user experience is not necessarily proportional to the bandwidth increase. While this increase improved the network usability, it also opened opportunities for adoption of more demanding services that were previously out of reach. As a result the network performance was severely degraded over the long term. To address these challenges we employ white space communication both for connectivity to more capable remote gateways, as well as for end user connectivity. We develop VillageLink, a distributed method that optimizes channel allocation to maximize throughput and enables both remote gateway access as well as end user coverage. While VillageLink features lightweight channel probing, we also consider external sources of channel availability. We design a novel approach for estimation of channel occupancy called TxMiner, which is capable of extracting transmitter characteristics from raw spectrum measurements. We study the adoption and implications of network connectivity in rural communities. In line with the results of our analyses we design and build system architectures that are geared to meet critical needs in these communities. While the focus of analysis in this thesis is on rural sub-Saharan Africa, the proposed designs and system implementations are more general and can serve in infrastructure-challenged communities across the world

A strategy to make ICT accessible in rural Zambia: a case study of Macha

The problem discussed in this dissertation is to gather evidence of good practice and derive strategy for the development of ICT access in rural Zambia. Access to ICT services is important, also in rural areas of Africa. The challenges are many. There is a distinct void in tangible descriptions of the realities of ICT Access in rural areas or actionable guidelines for practitioners. This study involves a case study in the rural areas of Zambia. It does so through ethnography involving 10 years of observation of aspects of ICT access in rural Macha, Zambia. In this community, emerging from an articulated vision, ICT access in the form of the Internet arrived in 2004. Macha Works with its ICT unit LinkNet provides the basis for this interpretive approach from within the rural cultural setting. The purpose of the study is to benefit the local rural community, addressing the fundamentals of reality to add to the body of knowledge. The study involves cross cultural interaction and takes a trans-disciplinary view on science. It involves Participative Action Learning and Research aimed at recognising the complex adaptive systems while being aligned with the ethics of the rural African environment. Emphasis is on the needs of the community, rather than of the individual utilising empirical evidence. The good practices in Macha that inform strategy to make ICT accessible in rural areas are: engaging the community, building relationships; workforce development, unlocking productivity; thought leadership, establishing authority

Cognitive radio adaptive rendezvous protocols to establish network services for a disaster response

Disasters are catastrophic events that cause great damage or loss of life. In disasters, communication services might be disrupted due to damage to the existing network infrastructure. Temporary systems are required for victims and first responders, but installing them requires information about the radio environment and available spectrum. A cognitive radio (CR) can be used to provide a flexible and rapidly deployable temporary system due to its sensing, learning and decision-making capabilities. This thesis initially examines the potential of CR technology for disaster response networks (DRN) and shows that they are ideally suited to fulfill the requirements of a DRN. A software defined radio based prototype for multiple base transceiver stations based cellular network is proposed and developed. It is demonstrated that system can support a large number of simultaneous calls with sufficient call quality, but only when the background interference is low. It is concluded that to provide call quality with acceptable latency and packet losses, the spectrum should be used dynamically for backhaul connectivity. The deployment challenges for such a system in a disaster include the discovery of the available spectrum, existing networks, and neighbours. Furthermore, to set up a network and to establish network services, initially CR nodes are required to establish a rendezvous. However, this can be challenging due to unknown spectrum information, primary radio (PR) activity, nodes, and topology. The existing rendezvous strategies do not fulfill the DRN requirements and their time to rendezvous (TTR) is long. Therefore, we propose an extended modular clock algorithm (EMCA) which is a multiuser blind rendezvous protocol, considers the DRN requirements and has short TTR. For unknown nodes and topologies, a general framework for self-organizing multihop cooperative fully blind rendezvous protocol is also proposed, which works in different phases, can terminate when sufficient nodes are discovered, and is capable of disseminating the information of nodes which enter or leave a network. A synchronization mechanism is presented for periodic update of rendezvous information. An information exchange mechanism is also proposed which expedites the rendezvous process. In both single and multihop networks, EMCA provides up to 80% improvement in terms of TTR over the existing blind rendezvous strategies while considering the PR activity. A simple Random strategy, while being poorer than EMCA, is also shown to outperform existing strategies on average. To achieve adaptability in the presence of unknown PR activity, different CR operating policies are proposed which avoid the channels detected with PR activity to reduce the harmful interference, provide free channels to reduce the TTR, and can work with any rendezvous strategy. These policies are evaluated over different PR activities and shown to reduce the TTR and harmful interference significantly over the basic Listen before Talk approach. A proactive policy, which prefers to return to channels with recent lower PR activity, is shown to be best, and to improve the performance of all studied rendezvous strategies