Earth-Sky Link Quality Performance for Fixed and Mobile Scenarios in Tropical Regions
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Progress In Electromagnetics Research C, Vol. 39, 61{75, 2013 EARTH-SKY LINK QUALITY PERFORMANCE FOR FIXED AND MOBILE SCENARIOS IN TROPICAL REGIONS Ali M. Al-Saegh1, *, A. Sali1, J. S. Mandeep2, Alyani Ismail1, and Abdulmajeed H. J. Aljumaily1 1Department of Computer and Communication Systems Engineering, Universiti Putra Malaysia (UPM), Serdang, Selangor 43400, Malaysia 2Department of Electrical, Electronic and Systems Engineering, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor 43600, Malaysia Abstract|Recent advances in satellite communication technologies in the tropical regions have led to signi¯cant increase in the demand for services and applications that require high channel quality for ¯xed and mobile satellite terminals. Due to lack of reliable investigations regarding accurate performance evaluation, experiments, and analysis on the satellite communication link in tropical regions under atmospheric impairments for both scenarios, accurate signal quality performance analysis is necessary. This paper presents the link characteristics observations and performance analysis with propagation measurements done in tropical region to provide an accurate database regarding rain attenuation in the tropics for ¯xed and mobile scenarios. The paper also presents a newly developed extension attached to the measurements setup for improved packet error rate (PER) performance evaluation related to the degradations occur in channel quality for di®erent types of impairments (rain, mobility, and physical obstacles) for 4 modulation schemes, namely QPSK, 8-PSK, 16-QAM and 32-QAM. The results show that the rain impairments at Ku band cause up to 12.5 dB and 23 dB at 77.5± and 40.1± elevation angles respectively in two tropical regions inside Malaysia for ¯xed scenario with a signi¯cant increase in PER at higher M-ary modulation schemes. For mobile scenario the PER appeared at higher M-ary scheme due to the lower signal power degradation in which, in turn, exceeded 1 dB when the vehicle speed exceed 100 km/hr Received 27 February 2013, Accepted 8 April 2013, Scheduled 12 April 2013 * Corresponding author: Ali Mohammed Al-Saegh ([email protected]). 62 Al-Saegh et al. at clear sky. The obstacles at the satellite communication link are shown to have signi¯cant e®ect on the power and PER received by satellite terminal especially at higher M-ary modulation schemes. 1. INTRODUCTION As signal propagates through the medium between the satellite and Earth stations, it su®ers from impairments that may occur according to di®erent obstacles that absorb, scatter, or even block the signal energy, such as shadowing due to physical objects (primarily by buildings or trees), rain, and clouds. The amount of losses depends on several parameters, particularly the transmission parameters (such as frequency, elevation angle, and modulation scheme), the Earth station mobility and position parameters, and the atmospheric parameters (such as rain rate and rain height). Due to lack of reliable performance analysis in tropical regions [1{ 3] and to identify the e®ects of these impairments on the signal quality level in terms of packet error rate (PER), this paper presents a newly developed error rate software (ERS) extension to improve the satellite/Earth station quality performance assessment and analyzes regarding the e®ects of the above mentioned parameters. This analysis is associated with the new measurement database provided worldwide for ¯xed and mobile scenarios in the tropics. The transmission parameters' e®ect on the signal quality performance for ¯xed and mobile scenarios will be presented in Section 2 with the link topology scenarios. The atmospheric e®ects will be presented in Section 2.1, along with the ERS block design process for ¯xed scenario. And then the mobility e®ects will be presented in Section 2.2 with ERS block for mobile scenario. 2. METHODOLOGY Transmission parameters signi¯cantly a®ect the performance evalua- tion of the quality of service (QoS) of the signal. In particular, the frequency and elevation angle present e®ects that should be identi¯ed by satellite system designers prior to the design process. According to Friis transmission equation, the frequency is directly proportional to the signal power attenuation and, hence, to the carrier- to-noise ratio, which could also lead to the increase in the error rates. For lower frequencies, below 3 GHz, the ionospheric scintillation signi¯cantly a®ects the signal quality. This e®ect starts to disappear as the frequency increases above that value [4]. Moreover, raindrops in the link between the satellite and Earth station exert a paramount Progress In Electromagnetics Research C, Vol. 39, 2013 63 e®ect on the quality of the signal at higher frequencies, particularly above 10 GHz [5]. Figure 1 shows the attenuation variation for di®erent frequency values we calculated in Selangor, Malaysia for 0.01% of the time exceedance, using the International Telecommunication Union (ITU) prediction model [6, 7] which has been proven to be an acceptable prediction model for rain attenuation calculations in tropical regions [8{10]. Figure 1 clearly shows that the elevation angle also considerably a®ects the signal. Under the same environment parameters, if the Earth station in Selangor is connected to MEASAT 3/3A at 11.6 GHz transmission frequency at an elevation angle of 77.5±, the attenuation is approximately 16 dB, whereas it reaches to approximately 26 dB if it is connected to SUPERBIRD C2 with an elevation angle of 41.1± and to 61 dB if it is connected to INTLESAT 19 with an elevation angle of 17.4±. Figure 1. Rain attenuation as a Figure 2. Satellite/Earth station function of frequency and eleva- communication links. tion angle variations for 0.01% of time exceedance. To extract and analyze the atmospheric losses as well as the mobility e®ects out of the other impairments, several experiments were conducted, which considered ¯xed and mobile scenarios. Three scenarios considered in this study involved a broadcasting geostationary satellite linked to ¯xed or mobile Earth station(s) at Ku band as shown in Figure 2. 2.1. Error Rates for Fixed Scenario In satellite communications, several impairments can cause signi¯cant degradation in the signal quality in ¯xed Earth station scenario, such as transmission parameters' variations and atmospheric impairments. Rainfall exerts paramount e®ect on the received signal power at Ku 64 Al-Saegh et al. band. Raindrops absorb and scatter signal energy depending on the drop size, density, and shape [11]. Tropical regions usually have convective rainfall because of their more severe weather condition periods and larger raindrop size compared with those in the temperate regions [1, 3, 12, 13]. This special impairment increases the need to investigate the quality performance in tropical regions in terms of the error rates as appropriate indicators. The PER can be calculated theoretically using four modulation schemes, namely, QPSK, 8-PSK, 16-QAM, and 32-QAM. These modulation schemes are widely used in satellite communication systems. Error bits inside the packets are distributed in correlational manner; therefore, they cannot be calculated accurately. When the error bit distributions inside the packets are identical and independent, the following equation can calculate the approximate PER: PER = 1 ¡ (1 ¡ BER)Lp (1) where BER is the bit error rate and Lp the packet length. However, Equation (1) is not accurate in high-order QAM constellations, and the bits are usually distributed in a correlational manner [14]. Therefore, the improved PER calculation for M-QAM scheme for gray mapping, was expressed by Equation (2) [14]. logY2 I logY2 J Lp=[log2(I£J)] Lp=[log2(I£J)] PER=1¡ [1¡PI (a)] £ [1¡PJ (b)] (2) a=1 b=1 where ¡a ( " $ %# I(1¡2 )¡1 (a¡1) 1 X (a¡1) n £ 2 P (a) = £ (¡1)b(n£2 =I)c£ 2(a¡1) ¡ 0:5+ I I I n=0 Ãr !) 3 log (I £ J) £ EbNR £erfc 2 £ (2a + 1) (3) I2 + J 2 ¡ 2 and, ¡b ( " $ %# J(1¡2 )¡1 (b¡1) 1 X (b¡1) m£2 P (b) = £ (¡1)b(m£2 =J)c£ 2(b¡1) ¡ 0:5+ J J J m=0 Ãr !) 3 log (I £ J) £ EbNR £erfc 2 £ (2b + 1) (4) I2 + J 2 ¡ 2 EbNR is the bit energy-to-noise ratio, which can be calculated by the following equation: EbNR = CNR ¡ SR + BW (5) Progress In Electromagnetics Research C, Vol. 39, 2013 65 Using the Friis transmission equation, EbNR will be µ ¶ 4¼d EbNR = EIRP + G ¡ 20 log ¡ L ¡ L ¡ N ¡ SR (6) r ¸ A S o where EIRP is the e®ective isotropic radiated power, and Gr, LA, Ls, No and SR are the receiver gain, atmospheric losses, system losses, noise spectral density, and symbol rate, respectively. The term (4¼d=¸) is the free-space loss that depends on the link length (d) and the transmitted frequency. In the case of I = J, the PER can be calculated by 2 log I I(1¡2¡a)¡1 (" $ %# Y2 1 X n £ 2(a¡1) PER = 1 ¡ 2£ 41 ¡ £ 2(a¡1) ¡ 0:5+ I I a=1 n=0 Ãr !)#Lp=[log (M)] 3 log (M) £ EbNR 2 £erfc 2 £ (2a + 1) (7) 2M ¡ 2 Combining Equations (6) and (7) yields a new equation that obtains the PER according to the rain attenuation values, as expressed in Equation (8). This equation can be used to investigate the exact PER for the satellite-tropical region communication link. 2 log I I(1¡2¡a)¡1 (" $ %# Y2 1 X n£2(a¡1) PER=1¡2£ 41¡ £ 2(a¡1) ¡ 0:5+ I I a=1 n=0 Ãr !)#Lp=[log (M)] 3 log (M)£[CNR ¡L ¡SR] 2 £erfc 2 CS A £(2a + 1) (8) 2M ¡2 where the clear sky carrier to noise ratio CNRCS = EIRP + Gr ¡ 4¼d 20 log( ¸ ) ¡ LS ¡ No.