WIMAX TECHNOLOGY APPLICATION RESEARCH IN THE KLAIPEDA REGION

Transcription

1 WIMAX TECHNOLOGY APPLICATION RESEARCH IN THE KLAIPEDA REGION Arunas Andziulis, Valdemaras Pareigis, Violeta Bulbenkiene, Danielius Adomaitis, Mindaugas Kurmis, Sergej Jakovlev Klaipeda University, Department of informatics engineering, Bijunu str. 17, Klaipeda, Lithuania, Abstract. The main WiMAX wireless networks arising problems are related to the information signal loss on the emerging obstacles in his way. Signal strength and information transfer rate are directly related to the regional geographical and urban peculiarities. In this case to avoid partly leveling in this type of networks, technology based on OFDM is invoked which enables to adjust information packages transferred in WiMAX networks. Measured received signal strength indicator (RSSI) experimental results are associated with the established OFDM signal set limited thresholds, when WiMAX unfits for connect even with low-level modulation of a certain region points. Wireless network signal orthogonal frequencydivision multiplexing OFDM technology enables operators to effectively handle the direct and indirect "visibility" challenges only within a certain distance between stations. Keywords: WiMAX, RSSI, LOS, NLOS, OFDM, wireless. 1 Introduction WiMAX (Worldwide Interoperability for Microwawe Access) technology usage is becoming increasingly common in this rapidly expanding wireless technology. While applying this technology it is relevant to know in what distances will be given highest quality which is described by a set of performance indicators in a particular urban region: service unavailability, service activation time, service interruption rate, data flow quality, reconnection start failure ratio, service activation time, IP (internet protocol) -based service start failure ratio, IP service connection time, average data transfer rate, data interruption transmission ratio, activation failure ratio, service activation time [1, 2, 3, 5, 6, 7]. The paper analyses one of the most important WiMAX signal quality describing the RSSI (received signal strength indicator) parameter that influences the service performance indicators. The work carried measurements and calculations analysis with set limit values for thresholds of OFDM (Orthogonal frequencydivision multiplexing) signal, when WiMAX is obsolete to connect even with low-level modulation in a given region points. 2 WiMAX wireless networks information service environment WiMAX has two basic parts - the base station and subscriber station (Fig.1). All base stations are connected to the commutation center. Base stations antennas are mounted on special towers or high buildings rooftops. Frequency range from 3.4 to 3.6 GHz is used in Lithuania to connect base station with subscriber station. Base station can have one, two, three or four service areas. In the investigated case the base stations had three service areas, divided into 120 sectors. Figure 1. Interaction between a base station and subscriber equipment

2 Each sector and its serviced subscriber equipment have its own frequency, and the optimal modulation is automatically selected depending on the signal quality (Fig. 2). For example, if the subscriber station is far away from the nearest base station the connection is guaranteed to it, but with low-level modulation, that is the maximum speed is slowing down. It is investigated when signal is modulated with high-level modulation: QAM64 3/4 (Quadrature amplitude modulation), QAM64 2/3 and QAM16 3/4. Figure 2. Adaptive modulation [3] Measurements were made in Klaipeda region. WiMAX of ones base station s systems OFDM signals dispersion diagram in Klaipeda region is shown in Fig. 3. Figure 3. WiMAX model in Klaipeda region Technical equipment: WiMAX Base Station Alvarion BreezeMAX 3650; Subscriber station Alvarion BMAX-CPE-ODU-PRO-L-TDD-SA-3.5; comprised of an Outdoor radio unit (ODU) and indoor network interface unit (IDU). Integrated managed voice and data services. Various interface configurations: Up to 4 data ports, 2 voice ports and Wi-Fi. Suitable for corporate and rural installations. Dual FDD/TDD mode. Equipments parameters are shown in table 1. Table 1. Equipment used to obtain parameters of experimental results Standards Peak down link data rate one sector Peak uplink date rate one sector Bandwidth Modulation Multiplexing Duplexing Frequency Delay WiMAX IEEE Mbps 4-5 Mbps 5Mhz BPSK, QPSK,16QAM, 64QAM TDM TDD, FDD 3.5GHz 5ms

3 During experiments weather conditions were between -11o and -12o Celsius and cloudy days. Measurements were made in line of sight (LOS) and non line of sight (NLOS) conditions. Quality describing service performance indicators are presented in Table 2 based on [4] and the new following parameters IPTV, Peer 2 Peer, Skype were added to this table. Table 2. Individual services of performance indicators for the application Services No Performance indicators Peer 2 IPTV Peer Skype HTTP FTP 1. Service unavailability [%] Service activation time[s] + 3. Service interruption rate [%] + 4. Data flow quality + 5. Reconnection start failure ratio[%] + 6. Service activation time[s] IP-based service start failure ratio [%] IP service connection time[s] Average data transfer rate [kbit/s] Data interruption transmission ratio [%] Activation failure ratio [%] Service activation time[s] + Classic case of RSSI changes, moving further away from the base station is calculated: where r is the distance from the base station (km) [5]. RSSI = log( r) (1) The radio channel of a wireless communication system is often described as being either LOS (line of sight) or NLOS (non line of sight). In a LOS link, a signal travels over a direct and unobstructed path from the transmitter to the receiver. In a NLOS link, a signal reaches the receiver through reflections, scattering, and diffractions. The signals arriving at the receiver consists of components from the direct path, multiple reflected paths, scattered energy, and diffracted propagation paths. These signals have different delay spreads, attenuation, polarizations, and stability relative to the direct path. The multi path phenomena can also cause the polarization of the signal to be changed. Thus using polarization as a means of frequency re-use, as is normally done in LOS deployments can be problematic in NLOS applications [6]. LOS conditions are associated with well-known free space spreading model, whose loss is calculated by the COST 231 Walfisch-Ikegami model formula: LOS = ( log( d) + 20log( f )) (2) where d is the distance (km) between base station and subscriber station, and f is the stations operating frequency (GHz)[7]. Therefore, according (1) formula, that WiMAX works 3500MHz frequency in Lithuania the LOS signal flow change is calculated moving further away from the base station. WiMAX penetration of 30 km has been selected in LOS conditions. Classic case of urban area the mean path loss is calculated: NLOS = ( log( fc ) + 10η log(10d)) (3) fc where is carrier frequency (MHz), d - distance between base station and subscriber station (d>0.1km) [8], η is a factor that depends on the geographical terrain properties: c η = a b hbs + (4) h hbs Where describes the base station antenna height, mean power attenuation parameters: a =4.6, b =0.005 and c =20 [9]. BS

4 Knowing the Klaipeda region building heights, potential buildings were a base station could be fitted average height is 50 meters. Klaipeda region can also be considered plain, because there are no mountains or high hills. NLOS propagation has been calculated on the basis of formulas 3 and 4. 3 Results The schedule shows the experimental points obtained using Alvarion WiMAX technical equipment. It also shows the RSSI curve (calculated by 1 formula), LOS (calculated by formula 2), NLOS (calculated in accordance with 3, 4 formulas). Figure 4. RSSI, LOS and NLOS change from base station The study of experimental points showed that the high productivity in services is consistent with the results is clustered in the first 7 km from the base station. The further distances from the base station lack of experimental points show that the distance from the base station more than 7 km is very difficult to achieve good standards of service performance indicators because of: high percentage of service unavailability, long service activation time, high service interruption rate, bad data flow quality, big reconnection start failure ratio, long service activation time, consistent IP-based service start failure ratio, long IP service connection time, low average data transfer rate, high data interruption transmission ratio, high activation failure ratio and long service activation time. Done calculations showed that LOS dependence (green long dash line) loss signal curve considerably goes down to around 13 km, then when moving further away from the base station signal is not so much gradually weakening. Yellow square dot shaded curve shows that the signal is uniformly weakening while operating in NLOS conditions, the weakening of the received signal is almost linear. From 8 km the signal in NLOS conditions reaches OFDM signal threshold limit, and therefore it is no longer suitable for WiMAX connection, even with low-level modulation, the service achieves a high percentage of unavailability. From the graph we notice that the flows of the transmission losses are always lower under circumstances of LOS. Therefore, it is possible the equipment should be built in a way that would achieve LOS conditions, what makes a good service performance indicator. The first three kilometers of the signal spreading the differences between the LOS and NLOS is not so great that s why the average data transfer speed difference are not significant, as moving further away from the base station. The signal for connection in NLOS conditions of the WiMAX is unsuitable 4 km away from base station, due to high service interruption rate, it remains appropriate in NLOS conditions until 11 km. RSSI curve shows that the signal from 20 km distance is no longer suitable for WiMAX subscriber station to connect, as the value reaches the threshold of 97 dbm marginal importance to WiMAX, which supports low-level WiMAX BPSK ½ modulation. Majority of experimental points are located around RSSI curve. Some of the points are away to the top of the line more, because in good LOS conditions RSSI value increases and service performance indicators improve. The points that are more remote from the RSSI curve to the bottom work in NLOS condition, which increases the probability of connection errors. These points are only in the first 8km, where WiMAX signal is able to function properly in NLOS conditions

5 4 Conclusions Done measurements show that good performance indicators corresponding to the service points are clustered in the first 7 km from the base station, so if the account reaches a high quality internet access the subscriber station cannot be separated further than 7 km from the base station. From the results of measurements, we see that the RSSI signal depends on the distance and the connection conditions (LOS or NLOS), and that the limit distance from the station is 20 km and in a greater distance the signal is too weak to connect the WiMAX. The measurements results let affirm that in LOS conditions propagated signal quality and performance indicators are always better than the NLOS conditions. Under the distance further than 4 km NLOS conditions, the signal is unsuitable for connection of low productivity rates. Calculations and measurements showed that high-quality Internet access with good performance indicators is available at the distance of 8 km, unless there is a perfect line of sight conditions. References [1] Shyy, D. J., Ma, J., Refaei, M. T., WiMAX RF Planner. Testbeds and Research Infrastructures for the Development of Networks & Communities and WorkshopsTridentCom th International Conference on p [2] Wu, R. H., Lee, Y. H., Tseng, H. W., etc. Study of Characteristics of RSSI Signal. Industrial Technology. ICIT IEEE International Conference p 1 3. [3] Nuaymi, L. WiMAX - Technology for Broadband Wireless Access. John Wiley and Sons Publication p 286. [4] European Telecommunications Standards Institute. Standards. 2.htm. [5] Grøndalen, O., Grønsund, P., Breivik, T., Engelstad, P. Fixed WiMAX Field Trial Measurements and Analyses. Proceedings of the 16th IST Mobile and Wireless Communication Summit (MobileSummit 2007). Budapest. Hungary [6] WiMAX Forum. WiMAX NLOS general p/10. [7] IT - Instituto de Telecomunicações. COST Action Chapter [8] Erceg V. Anempirically based path loss model for wireless channels in suburban environments. IEEE Journal on Selected Areas in Communications. 1999, volume 17. [9] Erceg V. Channel models for fixed wireless applications. IEEE BWA Working Group