Characterization of the equatorial F2-region plasma drift using doppler interferometry at Parit Raja

The ionosphere has long been used as a medium for long-distance transmission before the advent of satellites. There has now been a resurgence in its research after events that have occured in Iraq and Aceh where, ground-based infrastructures are destroyed from the effects of war or natural disasters. The bulk of research work in this area of study which uses the ionosphere as a channel medium comes from advanced countries representing the midlatitude regions of the world. It is therefore the objective of this thesis to characterize the behaviour of the ionosphere which is more representative of the equatorial regions. This work presents the measurements of plasma drifts from the ionospheric F2-layer at the equatorial station of Parit Raja (1° 52' N and 103° 48' E) using the technique of Doppler interferometry. Analysis is carried out from data gathered during periods of low solar and geomagnetic activities of 2005 with a view to statistically model or characterize its properties. As a result of plasma drift, Doppler effects are observed on the reflected echoes due to scattering from the irregular and non-uniform reflection layer. An approximation for the ionospheric F2-layer as a non-selective flat Rayleigh channel is first developed using an FIR filter that follows a Jakes’ Doppler channel response with the assumptions that multipaths are not resolvable and appear as one at the receiver with uniform Doppler rate. Since the actual ionosphere is non-flat with frequency-selectivity and also exhibits time-variability, a more realistic modelling of the ionospheric structure is needed. This is achieved by subdividing the operating bandwidth of the ionospheric medium into an aggregate of narrowband and orthogonal subchannels, where each is narrowband enough to possess flat Rayleigh fading. By adopting this technique of multicarrier transmission, each subchannel can be considered as flat and uniformly time-varying, which can be practically implemented using an IIR filter. The effect of variable Doppler rates is addressed by employing the techniques of upsampling and interpolation. The channel modelling is based on the Jakes Doppler response for 35 KHz in bandwidth which is more appropriate for equatorial region as opposed to ITU-R F.1487 that adopts the Gaussian spectral response with 10 KHz of bandwidth for midlatitude regions. Empirical simulation of results for the developed models using measured data and the performance measures have been reasonably accurate in characterizing the channel as having a Jakes Doppler response with Rayleigh fading within limits of +/-2 Hz Doppler shifts or +/-100 m/s plasma drifts

Ionospheric Drift Motions and Velocities at UTHM's Parit Raja Station During Periods of Low Solar and Geomagnetic Activities

Measurements relating to ionospheric plasma drift have been made by the Wireless and Radio Science Centre (WARAS) at Universiti Tun Hussein Onn Malaysia (UTHM) Parit Raja station in Batu Pahat, Johor, since 2004. This is done using a digital doppler interferometer which allows investigations into the dynamics of the ionosphere at this equatorial station to be carried out. These measurements include Doppler shifts and angles of arrival of the reflected HF signals that also allows simultaneous determination of plasma drift directions, drift distance covered and velocities as well as virtual heights of reflection, from ionospheric scattering point sources embedded within the moving plasma. By employing Doppler inteferometry reception technique at four receivers connected to four square array antennas nearby, it is possible to identify the locations, movements and velocities of the bulk scattering points reflected from the ionospheric F-region from the vertically incident HF waves. These waves are transmitted at frequencies of 6MHz, 7MHz, and 8MHz which cover the local F-layers since the critical frequencies lie between 5.9MHz and 8MHz. This work is based on data collected from the F2-layer of this local station at about 300km of virtual height during the measurement period of 2005

Ionospheric Drift Motions and Velocities at UTHM’s Parit Raja Station During Periods of Low Solar and Geomagnetic Activities

Measurements relating to ionospheric plasma drift have been made by the Wireless and Radio Science Centre (WARAS) at Universiti Tun Hussein Onn Malaysia (UTHM) Parit Raja station in Batu Pahat, Johor, since 2004. This is done using a digital doppler interferometer which allows investigations into the dynamics of the ionosphere at this equatorial station to be carried out. These measurements include Doppler shifts and angles of arrival of the reflected HF signals that also allows simultaneous determination of plasma drift directions, drift distance covered and velocities as well as virtual heights of reflection, from ionospheric scattering point sources embedded within the moving plasma. By employing Doppler inteferometry reception technique at four receivers connected to four square array antennas nearby, it is possible to identify the locations, movements and velocities of the bulk scattering points reflected from the ionospheric F-region from the vertically incident HF waves. These waves are transmitted at frequencies of 6MHz, 7MHz, and 8MHz which cover the local F-layers since the critical frequencies lie between 5.9MHz and 8MHz. This work is based on data collected from the F2-layer of this local station at about 300km of virtual height during the measurement period of 2005

Performance evaluation of wireless multicarrier modem with DQPSK modulation for HF communications

This thesis presents the bit error rate performances and throughput analysis over an HF radio channel using wireless multicarrier modem for voice and data services based on differential quaternary phase shift keying or DQPSK modulation in the presence of additive white Gaussian noise (AWGN) affected by slow Rayleigh fading. It combines two technologies – the highfrequency or HF band in the range of 3 – 30MHz to provide wireless long-distance and repeaterless communication links (eg. as used in the military) as well as multicarrier or parallel modem technology that provides simultaneous operations with the suppression of multipath components and other phenomena introduced by the ionosphere and also other narrowband interferences. In addition to conventional military applications for the fading radio channel, this implementation is also suitable for point-to-point links in the HF rural telecommunications area. The communications infrastructure for rural populations poses several problems which includes the generally long distances involved over which communication takes place as well as the low population densities which are also sparsely distributed. Thus, very expensive infrastructures like satellite links or long-haul repeater systems need to be employed which is aggravated by the fact that rural communities are in no position to pay for such facilities. A solution would thus require low cost wireless equipments incorporating HF and multicarrier technologies connecting the widely separated communities together as well as to the outside world. It is to be noted that multicarrier communication which employs HF radio technology will do away with third party equipments as well as the per-minute costs associated with satellite service