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The expected operating scenarios of fifth-generation (5G) pose a great challenge to orthogonal frequency division multiplexing which has poor out of band spectral properties, stringent synchronisation requirements and large symbol duration. Generalised frequency division multiplexing (GFDM) which is the focus of this work has been suggested in the literature as one of the possible solutions to meet 5G requirements. In this study, the analytical performance evaluation of minimum mean square error (MMSE) receiver for GFDM is presented. The authors also proposed precoding techniques to enhance the performance of GFDM. A simplified expression of signal-to-interference and noise ratio (SINR) for MMSE receiver of GFDM is derived using special properties related to the modulation matrix of GFDM, which are described in this study. This SINR is used to evaluate the bit error rate performance. Precoding schemes are proposed to reduce complexity of GFDM–MMSE receiver without compromising on the performance. Block inverse discrete Fourier transform (BIDFT) and discrete Fourier transform (DFT)-based precoding schemes are found to outperform GFDM–MMSE receiver due to frequency diversity gain while having complexity similar to zero-forcing receiver of GFDM. It is shown that both BIDFT- and DFT-based precoding schemes reduce peak-to-average power ratio significantly. Computational complexities of different transmitters and receivers of precoded and uncoded GFDM are also presented.

Satellite Based Augmentation Systems (SBAS) for navigational services rely heavily on the accu- rate estimation of the Total Electron Content (TEC) along the slant ray path. The Wide Area Augmentation Sys- tem (WAAS) estimates and transmits the delay corrections by assuming a 5x5 degree ionospheric grid (in lati- tude and longitude) at 350 km altitude using a single shell model. The user interpolates these delay values at hislher position using bilinear interpolation. In this paper, the effect of the variation of grid size on the interpo- lation of the TEC is analyzed using TEC data from the year 2005. It is observed that the reduction of grid size from 5x5 to I xl degree and the choice of Kriging technique to interpolate the TEC both at the IGP as well as at the user side result in more accurate estimation of the delay for the GPS Aided Geo Augmented Navigation (GAGAN) system over the Indian region.

Future Satellite Based Navigation Systems based on GPS, like US Wide Area Augmentation Sysytem (WAAS), are of global interest to the scientific community. Precise estimation of ionospheric delay is most crucial for successful implementation of the systems. Due to the complex ionospheric structure and large variation of Total Electron Content (TEC) in low latitudes, it is necessary to compare and validate the efficiency of the existing algorithms in this region. In this study, performances of the various interpolation algorithms for TEC calculation at ionospheric grid point (IGP) and user position for gridbased Single Shell Model have been tested for 72 test days of 2005. Based on the results obtained from this analysis, it has been found that, for the Indian region, it would be more suitable to use Ordinary Kriging in place of Planar Fit to estimate delay at an IGP (as used by US WAAS). It has also been found that Ordinary Kriging performs better than the Bilinear Interpolation technique at the user end.

Satellite based automatic identification system (AIS) is currently being investigated as a remote traffic monitoring system for global maritime surveillance. Because of it being a TDMA based communication system, large number of ships using same communication channel comes under the big field of view (FOV) of the satellite leading towards collisions of the transmissions. This causes the reception performance to drop down drastically. Performance improvement of satellite based AIS receiver is therefore an urgent need to providing more efficient surveillance to a large number of ships. A novel dual channel dual antenna based beam scanning mechanism, the first of its kind is developed to improve the reception capacity of satellite based AIS. 37% more number of ships is received using beam scanning compared with large single beam antenna. The improvement in the number of correct burst reception is also obtained as a part of the major claim of this scheme.

Tropospheric effect of Ka-band signals are significant and to study that a beacon receiver is designed and its digital signal processing section is implemented in Simulink. The design is based on Maximum Likelihood Estimator to determine both the amplitude and phase of the signal. The implemented receiver is different from commonly used fast Fourier transform based ones and appears simpler. The implemented receiver is tested with the simulated signal, taken from a RF generator and shown to give desired performance.

Satellite based 'Automatic Identification System' (AIS) for global maritime applications is being highly investigated in recent years. A receiver of such a system receives simultaneous transmissions from different self organized areas, which may lead to collision of information received at satellite; thereby reduce the scope of detection. In this paper we investigate the reception performance for class-A and class-B ships moving together with different reporting rates in the observation area. Comparisons of performances for various orbital configurations have been shown for a space based observational scheme and it is observed that reception capacity can be enhanced using constellation of satellites rather than using single satellite.

Satellite based ‘Automatic Identification System’ (AIS) for global maritime applications is of current interest. The challenge of the system mainly lies in the detection capability of the receiver due to multiple transmissions from different ships received at the satellite simultaneously. To estimate the performance of the receiver proper modeling of the channel access scheme is important. In this paper we propose a generalized methodology of the Self Organized Time Division Multiple Access (SOTDMA) in an extended observation area for satellite based AIS. The performance of the proposed scheme is compared with an existing model and more realistic reception performance by a satellite based receiver is shown.

The large bandwidth available in Ka-band of the satellite channel is one of the prime motivations for broadband communication via satellite. In tropical regions where there are heavy rains, the link availability due to rain fade is a major concern in the Ka-band. Rain fade mitigation techniques are required to address the problem. Methods for Adaptive Modulation and Coding (AMC) controlled from the application layer, which can be applied to any typical modem which supports multiple data rates, in order to maintain link availability is presented in this work. Algorithms for estimating the link quality, from the application layer, which is essential for successful implementation of AMC is also detailed in this work.

The bulk of beacon signal attenuation or fading is due to clear-air gaseous absorption (oxygen, water vapour) and stronger attenuation in hydrometeor events (rain, snow, clouds). In this paper, the results of the measurements of rain-induced attenuation in the Radio Wave signal propagating at 11.6995 GHz is presented. This paper also gives the comparison of the measurement result with several models, like ITU-R Model, Crane Global Model, SAM Model, Korea Model and others.

[1] Intersite separation (ISS) between two terminals is one of the important parameters required for implementation of site diversity (SD), as a fade mitigation technique (FMT), in moderate to heavy rain conditions usually encountered in tropical climates. This paper presents the findings of an experiment during the monsoon periods of years 2007 and 2008. It establishes the existence of micro rain cell (MRC) at a tropical site, Ahmedabad (23.06°, 72.62°), India, using measurements from tipping bucket rain gauge network. Spatial extent of MRCs and derived attenuation cells is examined on the basis of their maximum occurrence for initial to mid and last spells of years 2007 and 2008. The analysis also presents ISS statistics of monsoon periods for both the years. Microscale SD as FMT has been discussed on the basis of the calculated diversity gain at Ka band frequency in view of the proposed GSAT-4 satellite. These are the very first findings of their kind over the region of study.