Improving GSM Services in Nigeria Through Interference Mitigation
Since the early days of wireless communication till today, there has been the simple dipole (oneelement) antenna which functions by radiating and receiving radio frequency (RF) energy equally well in all directions. This rather unfocussed/indiscriminate approach of radiating RF signals is just adequate for simple RF environments where no specific knowledge of the whereabouts of the gsm user is available. It is very clear that as huge amounts of RF power is radiated into the environment, only a small portion of it is received. Given this limitation therefore, this present and obsolete technique attempts at overcoming its challenges by simply boosting the power levels of the signal which it pushes blindly into the atmosphere. Unfortunately, all the gsm operators in Nigeria and indeed in many countries, have continued to deploy obsolete antenna systems (Omnidirectional and Sector antennas) which are characterized by colossal waste in RF energy and interference. This paper presents the result of an investigation and combination of two techniques of Direction of Arrival (DOA) Estimation and Beam Pattern Synthesis (BPS) for suitable implementation in antenna system, the combination of which will ensure that (a) RF energy is not available in areas where gsm users are non-existent (b) RF energy is available in only the areas where there is at least one gsm user with wireless device turned on. The DOA estimation technique proposed in this paper is the Multiple Signal Classification (MUSIC). For the BPS, the Least Mean Square (LMS) technique is used. Validation of the workings of these two applications, which form the Digital Signal Processing (DSP) algorithm for the antenna system, was carried out using the Matlab as the simulation tool. In the case of the MUSIC technique, the simulation was run for four different signals originating from different directions (or angles) using a fixed number of antenna elements. The results show clearly the ability of the system to identify each gsm signal and its direction of arrival. In the case of LMS technique, simulation was run for two signals, one desired and the other undesired (interferer). The results for the pair of signals are displayed graphically, where the unwanted signal is seen mitigated by the system. The combination of DOA and BPS for implementation in gsm networks ensures that the huge waste in RF energy and interference will be a thing of the past as the energy will be available only in the area needed. 
 DOI: 10.5901/jesr.2013.v3n4p121