Considerations of digital phase modulation for narrowband satellite mobile communication

The Inmarsat-M system for mobile satellite communication is specified as a frequency division multiple access (FDMA) system, applying Offset Quadrature Phase Shift Keying (QPSK) for transmitting 8 kbit/sec in 10 kHz user channel bandwidth. We consider Digital Phase Modulation (DPM) as an alternative modulation format for INMARSAT-M. DPM is similar to Continuous Phase Modulation (CPM) except that DPM has a finite memory in the premodular filter with a continuous varying modulation index. It is shown that DPM with 64 states in the VA obtains a lower bit error rate (BER). Results for a 5 kHz system, with the same 8 kbit/sec transmitted bitstream, is also presented

Non-perfect channel estimation in OFDM-MIMO-based underwater communication

The main focus in this publication is on the mean square error of underwater acoustic channel estimators as function of the delay and Doppler spreads of the channel, and the effect this estimation error has on the bit error rate performance of the system both using conventional single antennas (SISO) and when using multiple antennas (MIMO). It is investigated at which delay and Doppler spreads the decoding of the signal in the receiver becomes erroneous. It is assumed that there is no non-uniform Doppler shift. The radio communication standard IEEE 802.16e is modified to match underwater communication conditions. The system parameters are taken from measurements conducted in the Trondheim harbour in Norway in 2007. The channel estimator used is not optimal in the Wiener interpolator sense. Hence, the estimator is sub-optimal, but shows good performance and has relatively low complexity. For the described communication system to perform well the results indicate that movements in the water should be less than 0.01-0.1 m/s, and delay spreads should be less than 0.05-0.5 ms. In systems where the main problem is large Doppler spread, the number of sub-carriers should be small. In systems where the main problem is large delay spread, the number of sub-carriers should be large. The use of MIMO makes the system more robust against estimation errors. The density of pilot symbols may be increased to reduce the channel estimation error somewhat, at the expense of reduced efficiency. Considering the Trondheim harbour channel measurement results and their variability throughout the year, we find that the tested system copes well with the summer conditions while the winter conditions seems to be more challenging.Non-perfect channel estimation in OFDM-MIMO-based underwater communicatio

Effects of Channel Estimation Errors in OFDM-MIMO-based Underwater Communications

State-of-the-art radio communication systems are in a large extent based on multi-carrier communication (OFDM) and multiple antennas (MIMO). In this paper the performance of such systems adapted to an underwater acoustic communication channel is assessed. The effect of the channel characteristics on an OFDM-MIMO scheme similar to that used in WiMAX (IEEE802.16e) is analyzed, in particular related to channel estimation error. Simulation results illustrate the relation between estimation error and BERperformance for single antenna systems (SISO) and when a MIMO technique is applied.Effects of Channel Estimation Errors in OFDM-MIMO-based Underwater Communication

Automated tuning of MapReduce performance in Vespa Document Store

MapReduce is a programming model for distributed processing, originally designed by Google Inc. It is designed to simplify the implementation and deployment of distributed programs. Vespa Document Store (VDS) is a distributed document storage solution developed by Yahoo! Technologies Norway. VDS does not currently have any feature allowing distributed aggregation of data. Therefore, a prototype of the MapReduce distributed programming model was previously developed. However, the implementation requires manual tuning of several parameters before each deployment. The goal of this thesis is to allow as many as possible of these parameters to be either automatically configured or set to universally suitable defaults. We have created a working MapReduce implementation based on previous work, and a framework for monitoring of VDS nodes. Various VDS features have been documented in detail, this documentation has been used to analyse how the performance of these features may be improved. We have also performed various experiments to validate the analysis and gain additional insight. Numerous configuration options for either VDS in general or the MapReduce implementation have been considered, and recommended settings have been proposed. The propositions are either in the form of default values or algorithms for computing the most suitable setting. Finally, we provide a list of suggested further work, with suggestions for both general VDS improvements and MapReduce-specific research

Predicting Near-Time Satellite Signal Attenuation at Ka-band Using Tropospheric Weather

There are satellite communication applications where it is desirable to predict near time (e.g. 2 to 12 h) propagation losses at Ka-band due to hydrometeor precipitation. We present results from a project investigating the possibility and quality of short term prediction of satellite link attenuation at Ka-band. The starting point is a 67 h near time numerical weather prediction data from the Norwegian Meteorological Institute. A period of 3 months and for 3 sites in Norway have been studied. Based upon these accumulated 9 months of data, the precipitation along the satellite link to the ground terminal is calculated for every hour. The attenuation results from the model is compared to high accuracy contemporary measurements of the same path. If the forecast is predicting the presence of precipitation correctly, the predicted attenuation error has a low bias and the standard deviation value is typically in the order of 1.5 dBacceptedVersio

Non-perfect channel estimation in OFDM-MIMO-based underwater communication

The main focus in this publication is on the mean square error of underwater acoustic channel estimators as function of the delay and Doppler spreads of the channel, and the effect this estimation error has on the bit error rate performance of the system both using conventional single antennas (SISO) and when using multiple antennas (MIMO). It is investigated at which delay and Doppler spreads the decoding of the signal in the receiver becomes erroneous. It is assumed that there is no non-uniform Doppler shift. The radio communication standard IEEE 802.16e is modified to match underwater communication conditions. The system parameters are taken from measurements conducted in the Trondheim harbour in Norway in 2007. The channel estimator used is not optimal in the Wiener interpolator sense. Hence, the estimator is sub-optimal, but shows good performance and has relatively low complexity. For the described communication system to perform well the results indicate that movements in the water should be less than 0.01-0.1 m/s, and delay spreads should be less than 0.05-0.5 ms. In systems where the main problem is large Doppler spread, the number of sub-carriers should be small. In systems where the main problem is large delay spread, the number of sub-carriers should be large. The use of MIMO makes the system more robust against estimation errors. The density of pilot symbols may be increased to reduce the channel estimation error somewhat, at the expense of reduced efficiency. Considering the Trondheim harbour channel measurement results and their variability throughout the year, we find that the tested system copes well with the summer conditions while the winter conditions seems to be more challenging.Non-perfect channel estimation in OFDM-MIMO-based underwater communicatio

Non-perfect channel estimation in OFDM-MIMO-based underwater communication

State-of-the-art radio communication systems are in a large extent based on multi-carrier communication (OFDM) and multiple antennas (MIMO). In this paper the performance of such systems adapted to an underwater acoustic communication channel is assessed. The effect of the channel characteristics on an OFDM-MIMO scheme similar to that used in WiMAX (IEEE802.16e) is analyzed, in particular related to channel estimation error. Simulation results illustrate the relation between estimation error and BERperformance for single antenna systems (SISO) and when a MIMO technique is applied.Effects of Channel Estimation Errors in OFDM-MIMO-based Underwater Communication

Satellittkommunikasjon til nordområdene - En behovsundersøkelse -

-Prosjektet hadde som mål gjennom en spørreundersøkelse for å identifisere aktører og kartlegge deres brukerbehov for kommunikasjonsløsninger i nordområdene de kommende år fram mot 2020. Prosjektet oppsummeres med en anbefaling for videre arbeid mot hvordan aktørenes fremtidige behov kan dekkes. Generelt ble det avdekket et stort behov for økte båndbredder og forbedret tilgjengelighet som en fellesnevner fra alle brukersektorer i denne undersøkelsen. En annen faktor av betydning for en forbedret kommunikasjonsdekning i nordområdene, som ikke kom klart fram i denne spørreundersøkelsen, er betydningen av å ha en effektiv kommunikasjonsløsning for beredskap - og for redningstjenesten som et resultat av økende aktivitet i de polare strøk. Det fastslås at et kommunikasjonsbehov i nordområdene allerede er tilstede. Behovet forventes å vokse de nærmeste årene. Imidlertid er det vanskelig å anslå hvor mye behovet vil vokse og hva det vil koste å innfri det. Det er nødvendig å bearbeide problemstillingene videre, som underlag for norsk holdning til hele problemstillingen - og som underlag for å delta i relaterte prosjekter både i ESA, i EU og bilateralt

Satellittkommunikasjon til nordområdene - En behovsundersøkelse -

-Prosjektet hadde som mål gjennom en spørreundersøkelse for å identifisere aktører og kartlegge deres brukerbehov for kommunikasjonsløsninger i nordområdene de kommende år fram mot 2020. Prosjektet oppsummeres med en anbefaling for videre arbeid mot hvordan aktørenes fremtidige behov kan dekkes. Generelt ble det avdekket et stort behov for økte båndbredder og forbedret tilgjengelighet som en fellesnevner fra alle brukersektorer i denne undersøkelsen. En annen faktor av betydning for en forbedret kommunikasjonsdekning i nordområdene, som ikke kom klart fram i denne spørreundersøkelsen, er betydningen av å ha en effektiv kommunikasjonsløsning for beredskap - og for redningstjenesten som et resultat av økende aktivitet i de polare strøk. Det fastslås at et kommunikasjonsbehov i nordområdene allerede er tilstede. Behovet forventes å vokse de nærmeste årene. Imidlertid er det vanskelig å anslå hvor mye behovet vil vokse og hva det vil koste å innfri det. Det er nødvendig å bearbeide problemstillingene videre, som underlag for norsk holdning til hele problemstillingen - og som underlag for å delta i relaterte prosjekter både i ESA, i EU og bilateralt