Enric Vilar | University of Portsmouth (original) (raw)

Papers by Enric Vilar

Ieee Global Telecommunications Conference and Exhibition Communications For the Information Age, 1988

Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-V... more Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-Variant Structure of Microwave Line-of-Sight Multipath Phenomena Wing Hong Lau, John Austin, Alan Hewitt, Enric Vilar, Member, ZEEE, and Louis Martin ...

Electronics Letters, 1989

International Conference on Antennas and Propagation, Apr 4, 1989

The cumulative distribution, variance, and spectral density of nonskewed amplitude scintillations... more The cumulative distribution, variance, and spectral density of nonskewed amplitude scintillations measured at three sites during the summers of 1982-1985 are analyzed and compared together with the combining elevations. Theoretical expressions are presented for the low elevation condition that the radius of the first Fresnel zone is larger than the outer turbulence scale, and good agreement is found. Empirical expressions for the variance as a function of GHz and elevation are also presented.

A Collaborative Research Programme with the Radio Communications Research Unit, at CCLRC-Rutherfo... more A Collaborative Research Programme with the Radio Communications Research Unit, at CCLRC-Rutherford Appleton Laboratory.

For radio frequencies above 10 GHz, rain is a major source of attenuation on an atmospheric propa... more For radio frequencies above 10 GHz, rain is a major source of attenuation on an atmospheric propagation path. In a practical system, this is unlikely to be compensated for by available fade margin alone. A number of fade mitigation techniques have been proposed to increase the potential availability of a system; one of which, site diversity, is due to be

MTT/ED/AP/LEO Societies Joint Chapter United Kingdom and Republic of Ireland Section. 1997 High Frequency Postgraduate Student Colloquium, 1997

A wideband experimental system designed to analyse an 11.647 GHz transhorizon channel subject to ... more A wideband experimental system designed to analyse an 11.647 GHz transhorizon channel subject to troposcatter and anomalous propagation conditions is described. The evolution of the channel during multipath fading condition is presented with the aid of the estimated channel impulse response. The fading statistics of wideband and narrow band signals for a period of 8 months is presented

Annales Des Télécommunications, 1988

An investigation into the effect of the integration time T on the rain rate distribution P(R) is ... more An investigation into the effect of the integration time T on the rain rate distribution P(R) is presented using a rainfall rate data bank of 49 years recorded at Barcelona (CCIR - Zone L), using a rapid response Jardi rain rate gauge. T extends from 1 to 60 min and P(R) extends to less than 10-3 %. The relation between

Tenth International Conference on Antennas and Propagation (ICAP), 1997

ABSTRACT A statistical approach using a parametric spectral conversion of singular value decompos... more ABSTRACT A statistical approach using a parametric spectral conversion of singular value decomposition-Prony (SVD-P) is introduced to provide a better resolution in channel characterization. The approach has been applied to analysing the transfer function of a transhorizon channel captured using a wideband channel sounder. The procedure is presented for the estimation of delay power spectrum, delay spread and coherence bandwidth of the experimental channel

Transplantation, 2010

Delayed graft function (DGF) has a major impact on long-term renal transplant survival. However, ... more Delayed graft function (DGF) has a major impact on long-term renal transplant survival. However, it is a diagnosis made retrospectively with little opportunity to modify treatment protocols. A classification based on creatinine reduction ratio between days 1 and 2 (CRR2) suggests that patients with CRR2 less than or equal to 30% (nondialysis requiring DGF [ND-DGF]) have similar outcomes to those with dialysis-requiring delayed graft function (D-DGF). We retrospectively applied this definition in our cohort of patients to examine outcomes. We studied the association between CRR2 and graft outcomes in all 367 patients transplanted between 1996 and 2004 at our center. Patients were divided into the following three groups: IGF (immediate graft function; CRR2 >30%), D-DGF, and ND-DGF. Mean follow-up was 4.2 years. IGF accounted for 36% of patients, D-DGF for 22%, and ND-DGF for 42%. CRR2 was inversely correlated with serum creatinine on days 7, 30, 90, and 365 (r ranging from -0.65 to -0.22, P<0.001). Graft survival at 5 years was 98% (IGF), 74% (D-DGF), and 89% (ND-DGF). There was a significant difference in graft survival between IGF and D-DGF (P<0.001) and IGF and ND-DGF (P=0.005). In a multivariate analysis adjusting for recipient age and sex, donor age and sex, and human leukocyte antigen mismatch, graft failure was 2.4 times more likely to occur in patients with D-DGF than those with ND-DGF(P=0.02). Our study shows CRR2 influences long-term graft outcomes. Unlike the original description, patients with ND-DGF carry an intermediate risk and perhaps should be considered on day 2 for alternative treatment protocols.

Iee Proceedings H Microwaves, Optics and Antennas, 1983

A procedure is presented for the improved design of low phase-noise microwave-feedback oscillator... more A procedure is presented for the improved design of low phase-noise microwave-feedback oscillators. The measured circuit parameters of the individual circuit elements are used in a nonlinear model which, in conjunction with a parametric computer-aided-design technique, allows one to predict the operating point of the circuit, namely the oscillation frequency and output power level. From this, together with the amplifier noise figure and Q-factor of the feedback element, the phase-noise spectral density of the oscillator output signal is derived. Theoretical and experimental results are compared and found to be in good agreement. The computer-aided design technique is also used to study the effects of various S-parameter variations upon the output power and phase spectral density. From perturbation studies it is shown how optimum sets of S-parameters can be derived to obtain either maximum output power or minimum phase noise, as desired. A correcting network for a first amplification...

Radio Science, 2001

The paper describes a 31.25 MHz bandwidth wideband channel sounder used to characterize a transho... more The paper describes a 31.25 MHz bandwidth wideband channel sounder used to characterize a transhorizon path over the English Channel (La Manche) at 11.64 GHz. The measurements were done continuously for a period of 8 months (June 5, 1996, to January 5, 1997), capturing 515 Mb of data each day. A nonlinear regression technique, singular value decomposition prony (SVD-P), was

Radio Science, 2003

1] The paper describes an extensive wideband channel sounding measurement campaign to investigate... more 1] The paper describes an extensive wideband channel sounding measurement campaign to investigate signal propagation through vegetation. The measurements have been conducted at three frequencies (1.3, 2 and 11.6 GHz) at sites with different measurement geometries and tree species. The data have been used to evaluate current narrowband empirical vegetation attenuation models and study the prevailing propagation mechanisms. Evaluation of the modified exponential decay (MED), maximum attenuation (MA) and nonzero gradient (NZG) models show that on a site by site basis, the NZG model gives the best prediction of excess attenuation due to vegetation. The MA model has been found to be the worst of the three models. The studies have shown that the measurement site used to obtain the NZG model parameter values given in International Telecommunication Union (ITU) [2001] is influenced by metal lampposts and passing traffic, and thus was based on corrupted data. The results show that the leaf state, measurement geometry and vegetation density are more important factors influencing signal attenuation than tree species or leaf shape. Generally, the 11.6 GHz signal was attenuated much more than the 1.3 and 2 GHz signals by vegetation in-leaf, but the differences in attenuation were not significant in the out-of-leaf state. A successful excess attenuation model due to vegetation must consider the measurement geometry and vegetation descriptive parameters as well as any contributions from ground reflection and/ or diffraction over the top or round edges of the trees.

Nephrology Dialysis Transplantation, 2009

The importance of residual renal function is well recognized in peritoneal dialysis but its role ... more The importance of residual renal function is well recognized in peritoneal dialysis but its role in haemodialysis (HD) has received much less attention. We studied 650 incident patients in our incremental high-flux HD programme over a 15-year period. Target total Kt/V urea (dialysis plus residual renal) was 1.2 per session and monitored monthly. Renal urea clearance (KRU) was estimated 1-3 monthly. KRU declined during the first 5 years of HD from 3.1 +/- 1.9 at 3 months to 0.9 +/- 1.2 ml/min/1.73 m(2) at 5 years. The percentage of patients with KRU >or= 1 ml/min at these time points was 85% and 31%, respectively. Patients with KRU >or= 1 ml/min had a significantly lower mean creatinine (all time points), ultrafiltration requirement (all time points) and serum potassium (6, 12, 36 and 48 months). Nutritional parameters were also significantly better in respect to nPCR and serum albumin (6, 12, 24 and 36 months). Patients with KRU >or= 1 ml/min had significantly lower erythropoietin requirements and erythropoietin resistance indices (12, 24, 36 and 48 months). Mortality was significantly lower in patients with a KRU >or= 1 at 6, 12 and 24 months after HD initiation, this benefit being maintained after correcting for albumin, age, comorbidities, HDF use and renal diagnosis. Our unique finding was that these benefits occurred despite those with KRU >or= 1 ml/min having a significantly lower dialysis Kt/V at all time points. The associations demonstrated suggest that residual renal function contributes significantly to outcome in HD patients and that efforts to preserve it are warranted. Comparative outcome studies should be controlled for residual renal function.

The principles of a wideband test system for measuring the complex transmittance of a line-of-sig... more The principles of a wideband test system for measuring the complex transmittance of a line-of-sight (LOS) microwave radio link subject to fading and multipath are discussed. The technique which uses cross-correlation between pseudo-binary random sequences falls into the realm of spread spectrum techniques. The system described is designed cover 1 GHz bandwidth at 19 GHz and has the objective of measuring both co-polar and cross-polar transmittance thus generating the complex transmittance matrix. Computer simulations and preliminary experimental results are presented together with a brief initial comparison with other systems.

International Journal of Satellite Communications and Networking, 2005

ABSTRACT This article is concerned with using time-varying uniformly spaced rainfall data to inve... more ABSTRACT This article is concerned with using time-varying uniformly spaced rainfall data to investigate the concept and values of instantaneous diversity gain. This has been obtained on a minute-by-minute basis in order to illustrate the behaviour of a VSAT communication system which switches to the most reliable link every minute. The simulations have been carried out using a whole year of rain data obtained from the recordings of a dense rain gauge network located in Barcelona.After illustrating the concept of instantaneous diversity gain, this paper shows the results obtained for various site separations and 20 GHz. These results have been plotted together with the values given by some long-term-based models. The comparison shows that such models are not appropriate for dynamic site diversity. This was found to increase the reliability of a VSAT system, especially under severe rain conditions in which the rainfall rates are spatially arranged in rain cells and the attenuation experienced by the two sites is strongly decorrelated. The correlation coefficient between the attenuation series calculated for several separation distances has also been obtained to illustrate this concept. Finally, the paper gives the attenuation distributions calculated for a VSAT system with and without site diversity and for several site separations. Copyright © 2005 John Wiley & Sons, Ltd.

International Journal of Satellite Communications, 1991

A theoretical and experimental study of Doppler correction strategies for elliptical orbit satell... more A theoretical and experimental study of Doppler correction strategies for elliptical orbit satellite communications is presented. Exact analytical expressions for Doppler shift and elevation angle as a function of perigee time of the ground-station are also presented. It is shown that for a 63" inclined Molnya orbit and a U.K. observer, the Doppler shift remains below about -+ 10 ppm and the Doppler rate below about 6 x ppm/s. Various strategies for continuous Doppler correction of the onboard oscillators are reviewed or proposed. These include a closed loop ground-satellite system and an on-board programmable correction approach. Two detailed theoretical and experimental studies of on-board encoded Doppler correction distribution systems are presented in the context of the UK CERS / TSAT mobile communications experiment. A frequency lock system which requires the distribution of only one signal and a phase-lock system requiring a master reference and the timevariant code word are described. Numerical values for a 1.5 GHz carrier are presented throughout but can be scaled to other frequencies.

IET Microwaves, Antennas & Propagation, 2007

The spatio-temporal variation of rain fields is a key input into the development of radio systems... more The spatio-temporal variation of rain fields is a key input into the development of radio systems which operate at frequencies above 10 GHz in a spectrally efficient fashion. Fractal methods have been proven helpful in the analysis and synthesis of rain fields. A fractal model is presented for the simulation of meteorologically representative rain fields, using an additive iterative process in the logarithmic domain. The resulting simulated rain fields are monofractal fields that have appropriate spectral density exponent, fractal dimension and behaviour that is consistent with radar analyses of convective or stratiform types of events. Justification to use a monofractal method of simulation is presented through the analysis of the moment scaling function for fields of rain rate and log rain rate values recorded by the Chilbolton Advanced Meteorological Radar, based in the south of England. The results of the analysis indicate that log rain fields can be analysed and simulated by using monofractal techniques with sufficient accuracy for the purposes of synthesising rain fields for communication systems design and operation. Cumulative distributions of rain rate exceedance derived from the simulated fields are compared with the measured rain gauge data and curves calculated from the ITU-R rain models, with promising results.

IEEE Transactions on Communications, 1991

Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-V... more Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-Variant Structure of Microwave Line-of-Sight Multipath Phenomena Wing Hong Lau, John Austin, Alan Hewitt, Enric Vilar, Member, ZEEE, and Louis Martin ...

Ieee Global Telecommunications Conference and Exhibition Communications For the Information Age, 1988

Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-V... more Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-Variant Structure of Microwave Line-of-Sight Multipath Phenomena Wing Hong Lau, John Austin, Alan Hewitt, Enric Vilar, Member, ZEEE, and Louis Martin ...

Electronics Letters, 1989

International Conference on Antennas and Propagation, Apr 4, 1989

The cumulative distribution, variance, and spectral density of nonskewed amplitude scintillations... more The cumulative distribution, variance, and spectral density of nonskewed amplitude scintillations measured at three sites during the summers of 1982-1985 are analyzed and compared together with the combining elevations. Theoretical expressions are presented for the low elevation condition that the radius of the first Fresnel zone is larger than the outer turbulence scale, and good agreement is found. Empirical expressions for the variance as a function of GHz and elevation are also presented.

A Collaborative Research Programme with the Radio Communications Research Unit, at CCLRC-Rutherfo... more A Collaborative Research Programme with the Radio Communications Research Unit, at CCLRC-Rutherford Appleton Laboratory.

For radio frequencies above 10 GHz, rain is a major source of attenuation on an atmospheric propa... more For radio frequencies above 10 GHz, rain is a major source of attenuation on an atmospheric propagation path. In a practical system, this is unlikely to be compensated for by available fade margin alone. A number of fade mitigation techniques have been proposed to increase the potential availability of a system; one of which, site diversity, is due to be

MTT/ED/AP/LEO Societies Joint Chapter United Kingdom and Republic of Ireland Section. 1997 High Frequency Postgraduate Student Colloquium, 1997

A wideband experimental system designed to analyse an 11.647 GHz transhorizon channel subject to ... more A wideband experimental system designed to analyse an 11.647 GHz transhorizon channel subject to troposcatter and anomalous propagation conditions is described. The evolution of the channel during multipath fading condition is presented with the aid of the estimated channel impulse response. The fading statistics of wideband and narrow band signals for a period of 8 months is presented

Annales Des Télécommunications, 1988

An investigation into the effect of the integration time T on the rain rate distribution P(R) is ... more An investigation into the effect of the integration time T on the rain rate distribution P(R) is presented using a rainfall rate data bank of 49 years recorded at Barcelona (CCIR - Zone L), using a rapid response Jardi rain rate gauge. T extends from 1 to 60 min and P(R) extends to less than 10-3 %. The relation between

Tenth International Conference on Antennas and Propagation (ICAP), 1997

ABSTRACT A statistical approach using a parametric spectral conversion of singular value decompos... more ABSTRACT A statistical approach using a parametric spectral conversion of singular value decomposition-Prony (SVD-P) is introduced to provide a better resolution in channel characterization. The approach has been applied to analysing the transfer function of a transhorizon channel captured using a wideband channel sounder. The procedure is presented for the estimation of delay power spectrum, delay spread and coherence bandwidth of the experimental channel

Transplantation, 2010

Delayed graft function (DGF) has a major impact on long-term renal transplant survival. However, ... more Delayed graft function (DGF) has a major impact on long-term renal transplant survival. However, it is a diagnosis made retrospectively with little opportunity to modify treatment protocols. A classification based on creatinine reduction ratio between days 1 and 2 (CRR2) suggests that patients with CRR2 less than or equal to 30% (nondialysis requiring DGF [ND-DGF]) have similar outcomes to those with dialysis-requiring delayed graft function (D-DGF). We retrospectively applied this definition in our cohort of patients to examine outcomes. We studied the association between CRR2 and graft outcomes in all 367 patients transplanted between 1996 and 2004 at our center. Patients were divided into the following three groups: IGF (immediate graft function; CRR2 >30%), D-DGF, and ND-DGF. Mean follow-up was 4.2 years. IGF accounted for 36% of patients, D-DGF for 22%, and ND-DGF for 42%. CRR2 was inversely correlated with serum creatinine on days 7, 30, 90, and 365 (r ranging from -0.65 to -0.22, P<0.001). Graft survival at 5 years was 98% (IGF), 74% (D-DGF), and 89% (ND-DGF). There was a significant difference in graft survival between IGF and D-DGF (P<0.001) and IGF and ND-DGF (P=0.005). In a multivariate analysis adjusting for recipient age and sex, donor age and sex, and human leukocyte antigen mismatch, graft failure was 2.4 times more likely to occur in patients with D-DGF than those with ND-DGF(P=0.02). Our study shows CRR2 influences long-term graft outcomes. Unlike the original description, patients with ND-DGF carry an intermediate risk and perhaps should be considered on day 2 for alternative treatment protocols.

Iee Proceedings H Microwaves, Optics and Antennas, 1983

A procedure is presented for the improved design of low phase-noise microwave-feedback oscillator... more A procedure is presented for the improved design of low phase-noise microwave-feedback oscillators. The measured circuit parameters of the individual circuit elements are used in a nonlinear model which, in conjunction with a parametric computer-aided-design technique, allows one to predict the operating point of the circuit, namely the oscillation frequency and output power level. From this, together with the amplifier noise figure and Q-factor of the feedback element, the phase-noise spectral density of the oscillator output signal is derived. Theoretical and experimental results are compared and found to be in good agreement. The computer-aided design technique is also used to study the effects of various S-parameter variations upon the output power and phase spectral density. From perturbation studies it is shown how optimum sets of S-parameters can be derived to obtain either maximum output power or minimum phase noise, as desired. A correcting network for a first amplification...

Radio Science, 2001

The paper describes a 31.25 MHz bandwidth wideband channel sounder used to characterize a transho... more The paper describes a 31.25 MHz bandwidth wideband channel sounder used to characterize a transhorizon path over the English Channel (La Manche) at 11.64 GHz. The measurements were done continuously for a period of 8 months (June 5, 1996, to January 5, 1997), capturing 515 Mb of data each day. A nonlinear regression technique, singular value decomposition prony (SVD-P), was

Radio Science, 2003

1] The paper describes an extensive wideband channel sounding measurement campaign to investigate... more 1] The paper describes an extensive wideband channel sounding measurement campaign to investigate signal propagation through vegetation. The measurements have been conducted at three frequencies (1.3, 2 and 11.6 GHz) at sites with different measurement geometries and tree species. The data have been used to evaluate current narrowband empirical vegetation attenuation models and study the prevailing propagation mechanisms. Evaluation of the modified exponential decay (MED), maximum attenuation (MA) and nonzero gradient (NZG) models show that on a site by site basis, the NZG model gives the best prediction of excess attenuation due to vegetation. The MA model has been found to be the worst of the three models. The studies have shown that the measurement site used to obtain the NZG model parameter values given in International Telecommunication Union (ITU) [2001] is influenced by metal lampposts and passing traffic, and thus was based on corrupted data. The results show that the leaf state, measurement geometry and vegetation density are more important factors influencing signal attenuation than tree species or leaf shape. Generally, the 11.6 GHz signal was attenuated much more than the 1.3 and 2 GHz signals by vegetation in-leaf, but the differences in attenuation were not significant in the out-of-leaf state. A successful excess attenuation model due to vegetation must consider the measurement geometry and vegetation descriptive parameters as well as any contributions from ground reflection and/ or diffraction over the top or round edges of the trees.

Nephrology Dialysis Transplantation, 2009

The importance of residual renal function is well recognized in peritoneal dialysis but its role ... more The importance of residual renal function is well recognized in peritoneal dialysis but its role in haemodialysis (HD) has received much less attention. We studied 650 incident patients in our incremental high-flux HD programme over a 15-year period. Target total Kt/V urea (dialysis plus residual renal) was 1.2 per session and monitored monthly. Renal urea clearance (KRU) was estimated 1-3 monthly. KRU declined during the first 5 years of HD from 3.1 +/- 1.9 at 3 months to 0.9 +/- 1.2 ml/min/1.73 m(2) at 5 years. The percentage of patients with KRU >or= 1 ml/min at these time points was 85% and 31%, respectively. Patients with KRU >or= 1 ml/min had a significantly lower mean creatinine (all time points), ultrafiltration requirement (all time points) and serum potassium (6, 12, 36 and 48 months). Nutritional parameters were also significantly better in respect to nPCR and serum albumin (6, 12, 24 and 36 months). Patients with KRU >or= 1 ml/min had significantly lower erythropoietin requirements and erythropoietin resistance indices (12, 24, 36 and 48 months). Mortality was significantly lower in patients with a KRU >or= 1 at 6, 12 and 24 months after HD initiation, this benefit being maintained after correcting for albumin, age, comorbidities, HDF use and renal diagnosis. Our unique finding was that these benefits occurred despite those with KRU >or= 1 ml/min having a significantly lower dialysis Kt/V at all time points. The associations demonstrated suggest that residual renal function contributes significantly to outcome in HD patients and that efforts to preserve it are warranted. Comparative outcome studies should be controlled for residual renal function.

The principles of a wideband test system for measuring the complex transmittance of a line-of-sig... more The principles of a wideband test system for measuring the complex transmittance of a line-of-sight (LOS) microwave radio link subject to fading and multipath are discussed. The technique which uses cross-correlation between pseudo-binary random sequences falls into the realm of spread spectrum techniques. The system described is designed cover 1 GHz bandwidth at 19 GHz and has the objective of measuring both co-polar and cross-polar transmittance thus generating the complex transmittance matrix. Computer simulations and preliminary experimental results are presented together with a brief initial comparison with other systems.

International Journal of Satellite Communications and Networking, 2005

ABSTRACT This article is concerned with using time-varying uniformly spaced rainfall data to inve... more ABSTRACT This article is concerned with using time-varying uniformly spaced rainfall data to investigate the concept and values of instantaneous diversity gain. This has been obtained on a minute-by-minute basis in order to illustrate the behaviour of a VSAT communication system which switches to the most reliable link every minute. The simulations have been carried out using a whole year of rain data obtained from the recordings of a dense rain gauge network located in Barcelona.After illustrating the concept of instantaneous diversity gain, this paper shows the results obtained for various site separations and 20 GHz. These results have been plotted together with the values given by some long-term-based models. The comparison shows that such models are not appropriate for dynamic site diversity. This was found to increase the reliability of a VSAT system, especially under severe rain conditions in which the rainfall rates are spatially arranged in rain cells and the attenuation experienced by the two sites is strongly decorrelated. The correlation coefficient between the attenuation series calculated for several separation distances has also been obtained to illustrate this concept. Finally, the paper gives the attenuation distributions calculated for a VSAT system with and without site diversity and for several site separations. Copyright © 2005 John Wiley & Sons, Ltd.

International Journal of Satellite Communications, 1991

A theoretical and experimental study of Doppler correction strategies for elliptical orbit satell... more A theoretical and experimental study of Doppler correction strategies for elliptical orbit satellite communications is presented. Exact analytical expressions for Doppler shift and elevation angle as a function of perigee time of the ground-station are also presented. It is shown that for a 63" inclined Molnya orbit and a U.K. observer, the Doppler shift remains below about -+ 10 ppm and the Doppler rate below about 6 x ppm/s. Various strategies for continuous Doppler correction of the onboard oscillators are reviewed or proposed. These include a closed loop ground-satellite system and an on-board programmable correction approach. Two detailed theoretical and experimental studies of on-board encoded Doppler correction distribution systems are presented in the context of the UK CERS / TSAT mobile communications experiment. A frequency lock system which requires the distribution of only one signal and a phase-lock system requiring a master reference and the timevariant code word are described. Numerical values for a 1.5 GHz carrier are presented throughout but can be scaled to other frequencies.

IET Microwaves, Antennas & Propagation, 2007

The spatio-temporal variation of rain fields is a key input into the development of radio systems... more The spatio-temporal variation of rain fields is a key input into the development of radio systems which operate at frequencies above 10 GHz in a spectrally efficient fashion. Fractal methods have been proven helpful in the analysis and synthesis of rain fields. A fractal model is presented for the simulation of meteorologically representative rain fields, using an additive iterative process in the logarithmic domain. The resulting simulated rain fields are monofractal fields that have appropriate spectral density exponent, fractal dimension and behaviour that is consistent with radar analyses of convective or stratiform types of events. Justification to use a monofractal method of simulation is presented through the analysis of the moment scaling function for fields of rain rate and log rain rate values recorded by the Chilbolton Advanced Meteorological Radar, based in the south of England. The results of the analysis indicate that log rain fields can be analysed and simulated by using monofractal techniques with sufficient accuracy for the purposes of synthesising rain fields for communication systems design and operation. Cumulative distributions of rain rate exceedance derived from the simulated fields are compared with the measured rain gauge data and curves calculated from the ITU-R rain models, with promising results.

IEEE Transactions on Communications, 1991

Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-V... more Page 1. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 39, NO. 6, JUNE 1991 847 Analysis of the Time-Variant Structure of Microwave Line-of-Sight Multipath Phenomena Wing Hong Lau, John Austin, Alan Hewitt, Enric Vilar, Member, ZEEE, and Louis Martin ...