Comparison of the Link Budget with Experimental Performance of A
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Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2009, Article ID 247436, 8 pages doi:10.1155/2009/247436 Research Article Comparison of the Link Budget with Experimental Performance ofaWiMAXSystem Jeffrey De Bruyne, Wout Joseph, David Plets, Leen Verloock, Emmeric Tanghe, and Luc Martens Department of Information Technology, Ghent University/IBBT, Gaston Crommenlaan 8 box 201, 9050 Ghent, Belgium Correspondence should be addressed to Wout Joseph, [email protected] Received 6 March 2009; Revised 20 August 2009; Accepted 12 November 2009 Recommended by David Laurenson The performance of different modulation schemes of a broadband fixed wireless 802.16 (WiMAX) system in a sector is experimentally determined and compared to link budget calculations using different path loss models. A link budget based on path loss measurements of the actual WiMAX signal at 3.5 GHz for a typical residential scenario in a suburban environment is determined. The link budget calculations show a reasonable agreement with actual performance measurements with certified WiMAX modems. Carefulness is advised when these models are used for the actual deployment of a WiMAX network in a specific area. Copyright © 2009 Jeffrey De Bruyne et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction system operating in Non-Line-of-Sight (NLOS) conditions at 3.5 GHz with a channel bandwidth of 3.5 MHz in a suburban Fixed Wireless Access (FWA) systems such as Worldwide environment of Ghent, Belgium. For this analysis a path loss Interoperability for Microwave Access (WiMAX), based model at 3.5 GHz is developed for suburban environments on the standards IEEE 802.16 [1] and HiperMAN [2], in Belgium for a transmitter and receiver height of 15 m are being installed for field trials nowadays and become and 2.5 m, respectively. Moreover, link budget calculations increasingly important. The advantages of fixed broadband have been made using the path loss model and exisiting ones wireless access over wired systems are mainly the lower cost and compared to actual performance measurements of the and the flexibility for the deployment of the system. The WiMAX system. competitiveness of WiMAX will largely depend upon the Sections 2 and 3 describe the configuration and method- actual data rates and ranges that can be achieved. ology of this analysis. The path loss model and link In [3–5], link budget calculations (which are in fact budgets are discussed in Section 4. The validation with actual ff coverage estimations) have been performed using di erent performance measurements is described in Section 5. Finally, path loss models. However, these coverage estimations have conclusions are presented in Section 6. not been validated by performance tests. Theoretical analyses and simulations of the performance of 802.16-based systems have been investigated in [3, 4, 6–12]. In [11], measurements 2. Configuration of the carrier-to-interference-noise ratio (CINR) are shown and the actual measured performance of an 802.16-based 2.1. Frequency Band Selection. When planning a FWA net- system is investigated in [13]. work, the operator has to make a choice between the available The objective of this paper is to validate link budget frequency bands. The selection of the frequency band to be calculations with actual performance results. Therefore the used has a major effect on the dimensioning and planning of coverage is investigated in a sector for an IEEE 802.16-2004 the FWA network. 2 EURASIP Journal on Wireless Communications and Networking Here, the 3.5 GHz FWA band was chosen. The decision Base station antenna was based on the fact that the band is licensed and interfer- ence is under control. Higher transmission powers are also allowed and the frequencies of the band are sufficiently low to obtain a better range and coverage than, for example, at 5.8 GHz. The 3.5 GHz FWA band is a licensed band and powers of 35 dBm into the BS antenna are allowed [14], while, for example, in the 2.4 GHz industrial, scientific and medical (ISM) band only an equivalent isotropically radiated power (EIRP) of 20 dBm is allowed. 2.2. Selected Parameters and Scenario. We will investigate (a) an outdoor scenario for residential applications in Ghent. The height of the base station (BS) h is 15 m. We analyze BS CPE antenna the outdoor receiver (Rx) height of hRx equal to 2.5 m (representing the first floor of a house). At this height, the Rx will be typically installed in residential neighborhoods. The Rx is positioned at 2.5 m using a telecopic mast. The input power Pi to the BS antenna is 35 dBm (3.2 W). The considered WiMAX system is based on the IEEE Telescopic mast 802.16-2004 standard. The base station (BS) antenna is a 120◦ sector antenna, with vertical polarization. The electrical beam tilt is −2◦ (i.e., 2◦ below the horizontal plane). No mechanical tilt is used. The dimensions of the antenna are 717 × 158 × 62 mm3. The Customer Premises Equipment (CPE) antenna is a 60◦ directional antenna with dimensions (b) × × 3 of 150 140 50 mm . We consider outdoor CPE here. The Figure 1: Pictures of (a) base station antenna on roof (hBS = 15 m) frequency under consideration is 3520 MHz (downlink (DL) and (b) CPE antennas mounted on telescopic mast. frequency). Figure 1(a) shows the BS on the roof and part of the environment, and Figure 1(b) shows the CPE antennas at aheightof2.5m. − Table 1 summarizes the selected parameters and the coding rate. These values are valid for BER = 10 6 (bit error scenario under investigation. The gains of BS and Rx rate) in a 3.5 MHz channel at 3.5 GHz. correspond to a typical residential modem scenario, that is, a = = BS antenna gain Gi 14 dBi and an Rx antenna gain Gr 3. Methodology 9.5 dBi. The BS feeder loss is 0.5 dB and the Rx feeder loss is 2.5 dB. The channel bandwidth (BW) of WiMAX systems Figure 2 shows a flow graph with the procedure to compare can be varied from 1.25 to 28 MHz [1, 2]. In this paper we the link budget calculations with the actual performance of assume a BW of 3.5 MHz, because this bandwidth is typical the considered system. First, the path loss and link budget for Europe and this BW was granted by the authority for the methodology, which is used for estimating the ranges for WiMAX field trial in Ghent. the different modulation schemes of the WiMAX system will be explained. Secondly, the validation methodology, where 2.3. Receiver Sensitivity. The minimum required Rx sen- the actual WiMAX performance measurements are executed, sitivity (Pmin [dBW]) can be calculated from the minimal will be discussed. required receiver noise input power (Pn [dBW]) and SNR (signal-to-noise ratio) by using the following formulas: 3.1. Path Loss and Link Budget Methodology (Figure 2) Pn = F +10· log(kT0B), 3.1.1. Path Loss. The Rx antenna for the path loss mea- (1) surements is an omnidirectional Jaybeam antenna type = Pmin Pn +SNR, MA431X21 [15]. For the adjustment of the height of the Rx we use a telescopic mast. The measurements are performed where F is the receiver noise figure (6 dB), k is Boltzmann’s with a Rohde & Schwarz FSEM30 spectrum analyzer (SA). constant (1.38.10–23 Ws/K), T0 the absolute temperature The output of the SA is sampled and stored on a laptop. (290 K), and B the receiver noise bandwidth [Hz]. Table 2 The center frequency is 3520 MHz (DL), the frequency span shows the receiver sensitivity and SNR for the subscriber ter- is 20 MHz, and the resolution bandwidth (RBW) is 5 MHz. minal of the residential modem system under consideration Figure 3 shows a trace measured with the SA (with described for a 3.5 MHz channel. Table 2 shows that the Rx sensitivity settings) of the actual WiMAX signal as a function of the and required SNR depend on the type of modulation and frequency. The measurement positions are acquired with a EURASIP Journal on Wireless Communications and Networking 3 Table 1: Characteristics of the considered WiMAX system. Parameter Value Carrier DL frequency 3.520 GHz Modulation adaptive BPSK 1/2, QPSK 1/2, QPSK 3/4, 16-QAM 1/2, 16-QAM 3/4, 64-QAM 2/3, 64-QAM 3/4 Channel bandwidth 3.5 MHz Cyclic prefix 1/16 BS power 35 dBm (3.2 W) Maximum theoretical throughput 12.7 Mbps hBS 15 m h 2.5 m Settings PHY CPE BS antenna gain Gi 14 dBi BS feeder loss 0.5 dB Polarization Vertical Electrical beam tilt −2o Dimensions 717 × 158 × 62 mm3 CPE antenna gain Gr 9.5 dBi Rx feeder loss 2.5 dB Distance between Rx antennas 15 cm Table 2: Rx sensitivity for the subscriber terminal of the WiMAX − WiMAX system system for 3.5 MHz channel width (BER = 10 6, AWGN channel). Path loss and link Modulation Coding rate SNR (dB) Rx sensitivity (dBm) budget methodology Validation methodology BPSK 1/2 11.5 −91 QPSK 1/2 14.5 −88 Spectrum analyzer − QPSK 3/4 16.5 86 measurements CPE measurements 16-QAM 1/2 21.5 −81 − 16-QAM 3/4 23.5 79 Received power (dBm) 64-QAM 2/3 28.5 −74 True performance 64-QAM 3/4 29.5 −73 (modulation scheme) Path loss model GPS device.