Mutual Interference of Frequency Hopping with Collision Avoidance Systems

The aim of this article is to quantify and analyze mutual interference of Frequency Hopping with Collision Avoidance (FH/CA) systems. The FH/CA system is a frequency hopping system where stations select the least jammed channel from several possible before the next jump. The article describes a mathematical model that allows determining the upper limit of the probability of collision of multiple FH/CA systems operated in a common band. The dependence obtained for mutual interference of FH/CA systems is compared with the dependence for mutual interference of conventional FH systems. The result of the comparison is a conclusion that, in terms of mutual interference, it is more advantageous to operate the FH/CA systems than the conventional FH systems

Possibilities of Error Controls in Frequency hopping Stations

Doktorská práce se zabývá problematikou návrhu kódového zabezpečení pro stanice s kmitočtovým skákáním v pásmu s intenzivním rušením. U digitálních modulací dochází vlivem rušení k chybnému určení modulačního stavu na straně přijímače. Důsledkem jsou chybně přenesené symboly zprávy. Vzniklé chyby během přenosu je možné eliminovat za použití zabezpečovacích kódů. Zároveň je také možné těmto chybám předcházet pomocí algoritmů (technik) frekvenčního skákání, které provádí výběr vhodného komunikačního kanálu. Vhodným komunikačním kanálem se rozumí kanál s nižší pravděpodobností vzniku chybných symbolů ve zprávě. Hlavní přínos této práce spočívá v návrhu nové techniky frekvenčního skákání s předcházením kolizí (FH/CA). Stanice s technikou FH/CA provádí před každým skokem měření úrovně signálu v několika uvažovaných kanálech. Na základě provedených měření je pak vybrán nejvhodnější kanál, tj. kanál s nejnižší naměřenou hodnotou úrovně signálu. S vyšší pravděpodobností tak dochází ke skoku na kanál neobsazený nějakým přenosem. Pomocí matematického modelu byla porovnána výkonnost nově navržené techniky FH/CA se současně užívanými technikami FH a AFH. Porovnávacím kritériem byla pravděpodobnost kolize mezi komunikačním systémem FH/CA a statickými rušiči (zařízení vysílající nepřetržitě na stálém kmitočtu) nebo dynamickými rušiči (tj. jinými FH nebo AFH systémy). Porovnáním hodnot pravděpodobnosti rušeného přenosu byly zjištěny nesporné teoretické výhody nové techniky FH/CA oproti současně užívaným technikám FH a AFH. Technika FH/CA vždy dosahuje lepších nebo stejných výsledků v porovnání s technikou FH v případě rušení jak statickými tak i dynamickými rušiči. Technika FH/CA je většinově výhodnější než technika AFH v pásmu se statickými a dynamickými rušiči. Významný přínos techniky FH/CA je vidět zejména v oblasti dynamických rušičů. Naopak v oblasti statických rušičů je technika FH/CA oproti technice AFH v určitých situacích horší. Správnost matematických modelů byla ověřena simulačním modelem, který byl vytvořen v rámci řešení této doktorské práce v prostředí MATLAB. Na základě získaných dat z modelu byl následně proveden návrh kódového zabezpečení pro stanice s kmitočtovým skákáním s novou technikou frekvenčního skákání FH/CA, které jsou určeny pro přenos dat o malém objemu v pásmu s intenzivním rušením.The doctoral thesis deals with design of coding for frequency hopping stations in band with intensive jamming. In digital modulations erroneous determination of the modulation state occurs due to jam at the receiver side. The result is erroneously transferred symbols of the message. Errors created during the transmission can be eliminated by using error control systems. It is also possible to prevent these errors by using algorithms (techniques) of frequency hopping which select the appropriate channel. Appropriate communication channel is a channel with a lower probability of erroneous symbol in the message. The main contribution of this thesis is to design a new frequency hopping technique with collision avoidance (FH/CA). The station with FH/CA technique measures signal levels in the considered several channels before every jump. Based on the measurements the most appropriate channel with the lowest value of measured signal level is selected. Therefore, it is more probable that a jump to an unoccupied channel with a transmission will occur. Using a mathematical model, the performance of the newly proposed FH/CA technique is compared with the currently used techniques FH and AFH. Comparison criteria are the probability of a collision between an FH/CA communication system and a static (device transmitting continuously at a fixed frequency) or dynamic jammer (i.e. other FH or AFH systems). By comparing the values of the probability of jammed transmission, indisputable theoretical advantages of the new FH/CA technique were found, compared to the currently used FH and AFH techniques. The FH/CA technique always has better or equal results compared with the FH technique in the case of interference by static and dynamic jammers. The FH/CA technique in a band with static and dynamic jammers usually has better results than the AFH technique. A significant contribution of the FH/CA technique can be seen in the case of dynamic jammers. On the other hand, in the case of static jammers the FH/CA technique is in certain situations worse than the AFH technique. The accuracy of the mathematical models were successfully verified on a simulation model that was created as a part of this thesis in the MATLAB environment. Based on the obtained data from the model there was designed coding for frequency hopping stations with the new technique of frequency hopping FH/CA which is designed for small-volume data transfer in a band with intensive jamming.

Faster mt decoding through pervasive laziness

Syntax-based MT systems have proven effective—the models are compelling and show good room for improvement. However, decoding involves a slow search. We present a new lazy-search method that obtains significant speedups over a strong baseline, with no loss in Bleu.

John Jeffries Martin: Myths of renaissance individualism. Basingstoke, New York, Palgrave Macmillan, 2004, 187 str

John Jeffries Martin: Myths of renaissance individualism. Basingstoke, New York, Palgrave Macmillan, 2004, 187 str

Domain-wall coercivity in ferromagnetic systems with nonuniform local magnetic field

Domain-wall (DW) coercive field, H-CW, which characterizes pinning of DW's in soft magnetic materials, decreases strongly with increasing value of gradient, G, of the effective local DW-position-restoring magnetic field. Particular shapes of the dependence, H-CW(G), can be calculated from the mean energy dissipation of the DW moving over the particular profile of the DW pinning field, H-p. In this paper, H-CW(G) is calculated from a wall-pinning field, H-p, which is expressed as a stochastic function of the DW coordinate, x(DW). The wall-pinning field, H-p, is described as a Wiener-Levy stochastic process modified by two correlation lengths in such a way that H-p is stationary for large DW displacements and dH(p) /dx(DW) is well defined for small DW displacements. The computed H-CW(G) is close to a hyperbolic decrease, but it approaches finite values if G-->O and it decreases in a much steeper way than alpha 1/G for high values of G, which agrees with the experimental observations. Experimentally, the dependence H-CW(G) was measured on close-packed arrays of cylindrical bubble domains in two thin films of magnetic garnets, where the local field gradient, G, was controlled within the range 10(9)-10(10) A/m(2) by changing distances between neighboring DW's. The DW coercive field, H-CW, extrapolated from the measured values for G-->O was close to 80 A/m for both samples, while H-CW(G approximate to 10(10) A/m(2)) was several times smaller. Fitting the calculated H-CW(G) dependence to the experimental data, we obtained values of the Wiener-Levy correlation lengths well comparable to the DW width parameters

Barreras de acceso de la población inmigrante a los servicios de salud en Catalunya

Antecedentes El 15,9% de la población de Catalunya era inmigrante en el 2011. A pesar del reconocimiento legal del derecho a la atención sanitaria y del desarrollo de políticas específicas, las investigaciones sobre acceso a los servicios de salud (SS) de la población inmigrante (PI) en España apuntan hacia posibles barreras de acceso. Sin embargo, la evidencia existente es escasa, a menudo contradictoria y pocos factores quedan esclarecidos. Objetivo general Analizar, desde la perspectiva de la PI, los elementos que influyen en su acceso a los SS de Catalunya. Metodología Estudio cualitativo, fenomenológico descriptivo, basado en el marco conceptual de Aday y Andersen. El área de estudio comprende Barcelona, Lleida, Girona y Baix Empordà, y la población de estudio la PI residente en estos lugares. La muestra fue teórica, basada en diferentes perspectivas y relaciones con los SS (usuarios, mediadores de salud y representantes de asociaciones de inmigrantes); y diferentes procedencias (Pakistán, Rumanía, Senegal, Marruecos y Colombia). El tamaño final fue de 37 personas, determinado por saturación del discurso. Se realizaron entrevistas individuales semiestructuradas (2008-2009), grabadas y transcritas literalmente. Se realizó un análisis narrativo de contenido, los datos se segmentaron por informante, colectivo, y temas, y las categorías de análisis se generaron de manera mixta. Hubo triangulación de informantes y de analistas, y el proceso se documentó sistemática y detalladamente. Resultados La mayoría considera fácil el acceso, independientemente de la situación administrativa y laboral, y destacan la gratuidad de la atención. No obstante, la entrada al sistema es fácil solo si se dispone de tarjeta sanitaria (TS), cuya obtención se dificulta por la exigencia de empadronamiento y afiliación a la Seguridad Social, y el miedo a ser identificados por las autoridades. Además, emergen barreras que dependen de los SS y de la PI. En relación a SS: insuficiente provisión de información; horarios de atención primaria incompatibles; tiempos de espera excesivos; deficiente calidad técnica percibida; barrera lingüística; trato incorrecto y actitud negativa del profesional. En relación a la PI: desconocimiento de los SS y los idiomas locales; dificultad para ausentarse del trabajo y cumplir las bajas laborales; y rol social de la mujer. Aparece la percepción de discriminación en los SS. En consecuencia acuden a farmacias, urgencias hospitalarias, asociaciones y oenegés o centros privados; utilizan TS de otra persona; se automedican; y pagan por la atención pública y privada; retrasando la atención y empeorando la enfermedad. Conclusiones El acceso de los inmigrantes a los SS en Catalunya es fácil, pero se ve dificultado por elementos relativos a los SS y potenciados por características de la PI. La TS se configura como elemento clave, pero su obtención se basa en requisitos controvertidos y con frecuencia inalcanzables. El desconocimiento relacionado con la falta de provisión de información limita el acceso, y aunque es compensado parcialmente por el círculo social, éste no puede ni debe sustituir al sistema como fuente de información. La dificultad para ausentarse del trabajo se debe a la precariedad laboral y las prácticas abusivas e ilícitas de los empleadores, por lo que es necesario trasladar este conocimiento a las autoridades competentes y adecuar los horarios de los SS. La barrera lingüística, la falta de competencia cultural y la mala calidad técnica percibida deben ser tenidas en cuenta en la formación de profesionales y los recursos de mediación. Estos resultados denotan el incumplimiento de las leyes y la falta de implementación de las políticas, por lo que éstas deben ser revisadas, reforzadas, y mantenidas. El uso de las urgencias hospitalarias es consecuencia de muchas de estas barreras, por lo que su reducción conllevaría una mayor adecuación de la utilización de urgencias.Background 15.9% of the Catalan population was immigrant in 2011. Despite the legal recognition of the right to health care and the development of specific policies, research on access to health services (HS) of the immigrant population (IP) in Spain point to possible barriers to access. However, the evidence is scarce, often contradictory and few factors have been clarified. Main objective To analyze, from the IP perspective, the elements that influence their access to HS in Catalonia. Methodology Qualitative and phenomenological study, based on the conceptual framework of Aday and Andersen. The study area included Barcelona, Lleida, Girona and Baix Empordà, and the study population was defined as the IP living in these places. The theoretical sample was based on different perspectives and relationships with the HS (users, healthcare cultural mediators and immigrant associations' representatives), and different countries of origin (Pakistan, Romania, Senegal, Morocco and Colombia). The final size was 37 people, determined by saturation of the information. Semi-structured interviews were conducted (2008-2009), recorded and transcribed verbatim. A narrative content analysis was performed; data were segmented by informant, country of origin and themes; and categories of analysis were generated both based in the topics of the guide and the ones that emerged from the data. To enhance the quality of the analysis, triangulation of informants and analysts was carried out, and the process was systematically documented in detail. Results Most informants find it easy to access the HS regardless of their administrative and labour situation, and stress the access free of charge. However, entrance to the healthcare system is easy only if you have a health insurance card (HC), whose acquisition is hampered by the requirement of registration and Social Security affiliation, and the fear of being identified by authorities. In addition, barriers appear related to the HS and to characteristics of IP. Regarding the HS the following barriers appear: insufficient provision of information; primary care opening time; excessive waiting times; poor technical perceived quality of care; language barriers; unfair treatment and negative attitude of the professional. And in relation to the IP: ignorance of the HS and local languages, difficulty to leave work and comply with sick leave, and social role of women. There was also a perception of discrimination related to the HS. Due to these barriers, immigrants go to pharmacies, emergency departments, charitable associations or private institutions; use the HC of someone else; self-medicate; and pay for public and private care, thus delaying care and worsening the disease. Conclusions Access of immigrants to the HS in Catalonia is easy, but hampered by elements of the HS further intensified by features of the IP. The HC is configured as a key element, but its acquisition is based on requirements controversial and often unreachable. Lack of knowledge related to the lack of provision of information limits access, and although the social network partially assumes this provision, it cannot and should not replace the system as a source of information. The difficulty for missing work is due to job insecurity and abusive and illegal practices of employers; therefore it is necessary to transfer this knowledge to the competent authorities and adjust the opening times of HS. The language barrier, lack of cultural competence and perceived poor technical quality must be taken into account in the training of professionals and mediation resources. These results indicate non-compliance with laws and lack of policy implementation, so these must be reviewed, reinforced and maintained. As a result of many of these barriers immigrants use hospital emergency departments; their reduction would thus lead to greater adequacy of the utilization of the emergency departments