Deploying WiMAX Networks

Most recently, BVS has launched the first mobile WiMAX analyzer in the world, yellowfin ™ WiMAX, which uses the Tablet PC Samsung Q1 UMPC as an interface. The Yellowfin provides a comprehensive analysis of spectrum and WiMAX packet demodulation. The full spectrum analysis allows field engineers to measure both signals as interference through power shot, search / peak hold, markers, and various traces and waveforms.

The receiver sweeps from 2.0 to 5.9 GHz with an accuracy of ± 1.5 dB. Since the instrument has the unique ability to demodulate packets can be displayed many crucial parameters needed to evaluate system performance, eg indicator of received signal strength (RSSI), Carrier-interference-noise ratio (CINR), magnitude vector error (EVM) as the symbol frequency offset profile, multi-path delay, cell identifiers and segments. The optional antenna "Direction Finding (DF) allows engineers to determine the sources of interference from WiMAX base stations and even underground hackers. Yellowfin ™ has an optional software that allows users to conduct studies to determine the RSSI and CINR coverage, a reliable analysis, and identify overlaps and dead of a WiMAX network.


Introduction to Wimax
WiMax is described by the WiMAX Forum as "a technology that enables the delivery of last mile wireless broadband access as an alternative to cable and DSL. WiMAX is designed to deliver faster wireless data transmission, longer range and more efficient use of bandwidth. The available spectrum for WiMAX services is in principle the 2.5 GHz band in the U.S. and the 3.5 GHz band in other countries. Yellowfin ™ WiMAX analyzer works between 2.0 and 5.9 GHz, which can be used to measure and control of a WiMAX network efficiently.
The mobile WiMAX or WiBro (IEEE 802.16e) is based on OFDMA technology. It also supports Scalable OFDMA modulation. The cyclic prefix for mobile WiMAX is 1 / 32, 1 / 16, 1 / 8 and 1 / 4 of the symbol. The cyclic prefix is a repetition of the symbol at the top end, which lets you choose the multipath before reaching the main data receiver. WiMAX supports channel bandwidths of 5 MHz, 7 MHz, 8, 5 MHz and 10 MHz and can optionally support channel bandwidths from 1.25 MHz to 20 MHz also supports adaptive modulation and coding in upstream channel and downlink packet sizes. The scalability of bandwidth, variable length of the cyclic prefix, and adaptive modulation and coding that WiMAX will provide a better performance than most existing wireless technologies. Applying these advanced technologies and the deployment of WiMAX networks require an accurate measurement of channel response, interference, frequency reuse and other key parameters.

Deployment of WiMAX networks
A study of the area measured fading due to the terrain, also known as scale fading [2]. This fading can be suppressed by increasing transmitter power or other diversity techniques. After conducting a study with the respective software Yellowfin ™, RF coverage can be validated and the transmission power of base station can be verified. However, wireless access systems are also dependent on small-scale fading Rayleigh type and cia. Usually this fading is caused by the delay in the spread, which not only distorts the received signal, but also cause inter-symbol interference [3]. As the fading has a significant impact on system performance and should use techniques specific signal processing to mitigate these effects [3]. Therefore, the effects of small-scale fading successfully be addressed in the deployment of WiMAX networks. Different demodulation techniques can be used to measure the impact of small-scale fading extracting the parameters necessary for demodulation algorithms of signal processing. Yellowfin VHL WiMAX analyzer demodulates the preambles of the measures RSSI, CINR, delay multi-path power, carrier offset frequency, cell ID, and segments.
The demodulation process shows the impact of small-scale fading through the verification of the transmission power of base station. This loss is represented by measuring the RSSI and the interference level is measured by the CINR. While OFDM technology can be used to successfully suppress the frequency selective fading [3], is subject to inter-symbol interference if the delay exceeds the cyclic prefix length. The delay power by multi-path (multi-path) will serve as a guide to the required cyclic prefix length. To properly demodulate the preamble, the analyzer Yellowfin compensation applies frequency and time offset, a delicate complex calibration and other techniques to minimize the impact due to the instrument, such as errors introduced by non-ideal filters for RF. Due to the use of a high-precision clock txco, Yellowfin can perform the necessary frequency measurement with an accuracy less than 2 ppm. Therefore, the measurement data are the upper limit of performance as a mobile WiMAX system can reach.
To deploy a base station, the engineer has to do a site survey to verify the signal quality and quantity of the assigned frequency interference. The RSSI measures the total signal quality and CINR shows the level of interference. Interference may degrade system performance considerably. The CINR is the relationship between the desired signal and noise interference. The carrier is the desired signal, and interference can be noise or co-channel interference or both. To which the recipient may be able to decode the received signal, the signal must be at an acceptable value of CINR. The CINR for different frequency factors (1 or 3) is also evaluated. For frequencies reused in factor 3, the CINR is the estimated CINR on modulated subcarriers of the preamble; Frequency factor 1, the CINR estimating CINR is over all subcarriers of the preamble [4]. The CINR is calculated using a method similar to the EVM. The EVM represents the relationship between the error vector magnitude and magnitude of the reference waveform. The signal spectrum and EVM measurement can be used to measure the quality of the signal in the subchannels. If another base station that uses the same frequency in the area, the analyzer can find its location Yellowfin with a DF antenna based on signal strength. By using the spectrum analysis, engineers are able to identify and eliminate potential interference before installation of WiMAX base stations. The application software is shown in Figures 2, 3 and 4.

Conclusions
Yellowfin analyzer from Berkeley Varitronics WiMAX provides a full spectrum analyzer and packet demodulator WiMAX. The complete spectrum analyzer enables engineers to measure and study the signals and interference. The demodulator package allows them to measure important parameters relating to system performance, such as RSSI, CINR, frequency offsets, power losses by multipath cell identifiers and segments, and many more. Therefore, the analyzer WiMAX Yellowfin VHL in an efficient tool for the deployment of WiMAX networks and monitoring system performance.

References
[1] J. Yu, RF Propagation Measurement and Validation For WiMAX Networks., RF GlobalNet, Feb.2007.
[2] T. Rappaport, Wireless Communi-cations: 2nd Edition, Prentice Hall; 2001
[3] B. Sklar, Digital Communications: Fundamentals and Applications, 2nd Edition, Prentice Hall, 2001.
[4] IEEE Std IEEE Std 802.16e2005 and 802.162004/Cor 12005 (Amendment and Corrigendum to IEEE Std 802.162004); "IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operations in Licensed Bands and Corrigendum 1 ", Feb.2006.

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