^{*}

^{*}

We address the problem of interference as related to Satellite Personal Communication Networks (S-PCNs). Basic low Earth orbit (LEO) constellation is considered. The paper uses combined adaptive antenna arrays and adaptive filtering technique. This hybrid linear adaptive technique provides improved performance eliminating interference, particularly uncorrelated signals residing in the antenna sidelobes.

A Satellite personal communication network (S-PCN) provides universal access to a wide range of services and across transnational boundaries. It faces multitude of challenges particularly those related to user terminals, the space segment, regulatory challenges, [

An adaptive array antenna unit is designed, as in

variation due to the difference in propagation path length for any two elements, and 3) there is no significant difference in q - the direction-of-arrival (DOA) - of a particular plane wave at any two elements.

For N elements array of identical characteristics, the first pulse is taken as the phase centre f(t). The second pulse is advanced by τ and denoted by f(t-τ), the third pulse is advanced by 2τ and denoted by f(t-2τ), and so on. For convenience, five elements are used, so

where…are the weights/gains of each element of the array. In adaptive antenna array, the weights/gains of each element are taken to be the same (i.e.,), conforming to practical situation, and the elements to be equally spaced. Had the weights variable, there is possibility they may modulate the desired signal. Now, if the first pulse is Fourier transformed and is represented by, then

By multiplying (2) by and then subtracting the resulting expression from (1), and rearranging ensuing expression and using known geometric series expansion we have

Typical S-PCN frequencies of 1.376 and 1.80 GHz [6,7] are used to examine the antenna array’s behaviour using (3). Resulting graphs are shown in

ference received from adjacent satellites (and ground based signals operating on same bands), as well as in determining antenna noise temperature. To successfully eliminate, or reduce significantly, the effect of external interference, the sidelobes have to be attenuated, if not removed. The sidelobes are cancelled or removed in this paper by the adaptive array process.

Our approach models the effect of interferers on the S-PCN systems using interferences as recursive random processes, with the array antenna. The input to the processor in

Following

where is the system parameter; is optimum adaptive but weighted filter and is additive, uncorrelated system interference, assumed white, zeromean Gaussian and stochastic; and Y(t) filter (or measurement) output. The optimum interference is defined as

where N_{th} is the acceptable interference threshold, and k is the filter order. The proceeding coefficient of the filter

can be estimated from the present coefficient and other thresholds:

where h is the convergence constant.

The adaptive filter adapts the filter coefficients to achieve desired signal ensuring convergence; that is, minimizing error at each time index:

Ensuring fast convergence a local minimum is sought leading to establishing threshold value; i.e.,

where local minimum threshold. The adaptation gain is introduced for coefficient updating recursion for the period of the signal measurement:

where m is the period which the mobile terminal engages the network.

As shown in

The implication of our method is that the variation of the filter’s weights, as a result of movement of the mobile users, may affect the effectiveness of the system as the satellites move from orbit to another; low earth orbit (LEO) through to geostationary orbit (GEO), for example [

We have presented an antenna-array plus adaptive filtering model as a way of eliminating the effect of interference in satellite personal communication systems. This technique has shown that it can eliminate an uncorrelated signals residing in the antenna sidelobes successfully. This technique is easily adaptable to S-PCN in LEO operational environment as a result of shorter time required by LEO satellites to move across the sky.