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Abstract: The quality of reception from the GSM (global system for mobile communication) services in Nigeria has been on a rapid decline lately and thereby denying the users access to good quality services. This study used Ibadan North Local Government area as a case study and verified the effect of topography on GSM signal reception. The study shows that high-rise buildings and undulating topography were some of the factors that affect the reception quality requiring further system augmentation to enable sustainable quality of reception in such area.
Key words: Base transceiver station, topography, repeaters, GSM, signal strength, reception, base station controller.
(mobile station) connected to a BTS (base transceiver station) via air interface. This BTS contains equipment called TRX (transceiver), which is responsible for the transmission and reception of several RF (radio frequency) signals to and from the end user [2]. BTS is then connected to the BSC (base station controller) via Abis interface. The BSC is connected to the MSC (mobile switching centre). The BSC manages calls and handover between cells while the MSC controls the switching in order to route a call through [3].
GSM came to Nigeria in year 2001. This brought relief to the people, as there was hope of beating the barrier created by the sole Communication Company(called NITEL) and as a solution to bridging the communication divide between the rural and urban areas. Since GSM was inception in Nigeria, many operators have come to stay in the country. This brought about competition, which has made the GSM services affordable to the common man. Ever since then, Nigeria has witnessed an explosion especially by the users of this service. Regrettably, the system has a poor quality reception services delivered by the operators in the country. The poor quality services are
attributable to attenuation suffered by the signals as they navigate a variety of man-made structures, or those imposed by nature such as terrain and topography [4]. One of these effects is path loss which occurs when the received signal becomes weaker and weaker due to increasing distance between MS and BTS, even with or without obstacles along the transmitting (Tx) path. The path loss problem rarely causes dropped call because before the problem becomes extreme, a new transmission path is established via another BTS. Also if there are obstacles such as buildings and mountains between the, a factor known as shadowing results. This causes the signals to be redirected from its path of transmission causing reflection of the signals. Each of the problems described above occurs independently of each other. However, in most calls, some of these problems may occur at the same time. An illustration of what the signal strength may look like at the MS Rx antenna when moving away from the BTS Tx antenna is shown in Fig. 1. The problems of path loss, shadowing and Rayleigh fading are present for this transmission path. The signal strength as a global mean value decreases with the distance (path loss) and finally results in a lost connection. Around this global mean, slow variations are present due to shadowing effects and fast variations are present due to Rayleigh fading.
The lowest signal strength value required for a specified output is called receiver sensitivity level. To detect the information sent from Tx antenna, X watts must be received. If the signal falls below X, the information will be lost and the call may be dropped. To ensure that no information is lost, the global mean value must be as many dB above the receiver sensitivity level as the strongest (deepest) fading dip gives rise to. This fading margin is the difference between the global mean value and the receiver sensitivity [4].
All these factors contribute to variation in the signal level, which result in variation of the signal coverage and quality in the network. The network performance and QoS (quality of service) evaluation are the important steps for the mobile operators as the revenue and customer satisfaction are directly related to network performance and quality [5].
mobile phone with the SIM (subscriber identity module) of the operator to compare the reception quality of the three BTSs up to 2 km. The sensitivity of the receiver(user terminal) was taken to be -60 dBm. The measurements were plotted as shown in Fig. 2 where the effect of topography on the received signal strength is observed.
improve reception quality in the severely affected areas.
Key words: Base transceiver station, topography, repeaters, GSM, signal strength, reception, base station controller.
(mobile station) connected to a BTS (base transceiver station) via air interface. This BTS contains equipment called TRX (transceiver), which is responsible for the transmission and reception of several RF (radio frequency) signals to and from the end user [2]. BTS is then connected to the BSC (base station controller) via Abis interface. The BSC is connected to the MSC (mobile switching centre). The BSC manages calls and handover between cells while the MSC controls the switching in order to route a call through [3].
GSM came to Nigeria in year 2001. This brought relief to the people, as there was hope of beating the barrier created by the sole Communication Company(called NITEL) and as a solution to bridging the communication divide between the rural and urban areas. Since GSM was inception in Nigeria, many operators have come to stay in the country. This brought about competition, which has made the GSM services affordable to the common man. Ever since then, Nigeria has witnessed an explosion especially by the users of this service. Regrettably, the system has a poor quality reception services delivered by the operators in the country. The poor quality services are
attributable to attenuation suffered by the signals as they navigate a variety of man-made structures, or those imposed by nature such as terrain and topography [4]. One of these effects is path loss which occurs when the received signal becomes weaker and weaker due to increasing distance between MS and BTS, even with or without obstacles along the transmitting (Tx) path. The path loss problem rarely causes dropped call because before the problem becomes extreme, a new transmission path is established via another BTS. Also if there are obstacles such as buildings and mountains between the, a factor known as shadowing results. This causes the signals to be redirected from its path of transmission causing reflection of the signals. Each of the problems described above occurs independently of each other. However, in most calls, some of these problems may occur at the same time. An illustration of what the signal strength may look like at the MS Rx antenna when moving away from the BTS Tx antenna is shown in Fig. 1. The problems of path loss, shadowing and Rayleigh fading are present for this transmission path. The signal strength as a global mean value decreases with the distance (path loss) and finally results in a lost connection. Around this global mean, slow variations are present due to shadowing effects and fast variations are present due to Rayleigh fading.
The lowest signal strength value required for a specified output is called receiver sensitivity level. To detect the information sent from Tx antenna, X watts must be received. If the signal falls below X, the information will be lost and the call may be dropped. To ensure that no information is lost, the global mean value must be as many dB above the receiver sensitivity level as the strongest (deepest) fading dip gives rise to. This fading margin is the difference between the global mean value and the receiver sensitivity [4].
All these factors contribute to variation in the signal level, which result in variation of the signal coverage and quality in the network. The network performance and QoS (quality of service) evaluation are the important steps for the mobile operators as the revenue and customer satisfaction are directly related to network performance and quality [5].
mobile phone with the SIM (subscriber identity module) of the operator to compare the reception quality of the three BTSs up to 2 km. The sensitivity of the receiver(user terminal) was taken to be -60 dBm. The measurements were plotted as shown in Fig. 2 where the effect of topography on the received signal strength is observed.
improve reception quality in the severely affected areas.