Wednesday, December 7, 2011


WiMAX radio planning involves a number of steps ranging from tool setup to site survey. The process is similar to any wireless network. What differs between WiMAX and other technologies are the actual site configuration, KPIs, and the propagation environment as WiMAX may support mobile and fixed users where the latter may employ directional/rooftop antennas.
The final radio plan defines the site locations and their respective configuration. The configuration involves BTS height, number of sectors, assigned frequencies or major channel groups, types of antennas, azimuth and downtilt, equipment type, and RF power. The final plan will be tested against various KPI requirements mainly coverage criteria and capacity (or signal quality). Figure 1 can be used as a guide in developing a planning process. The planning process also largely depends on the planning tool used.

Figure 1: WiMAX radio planning process.
The planning process in Figure 1 includes measurements (i.e., drive test and verifications) after the site survey. This procedure is not mandatory for all sites if the site count is too large. Usually, site survey and the KPI analysis give an indication of which areas are expected to have poor RF quality and which sites are involved. This is usually done when the candidate site(s) are not located in ideal locations or if the site survey finds some discrepancies of the candidate(s).
The differences between WiMAX and 3G radio planning. WiMAX radio offers modest processing gain in a form of repetition coding and subchannelization. These features are only exploited when the signal quality demands more processing. To support high data rates, the radio plan must offer very good SINRs (signal to interference and noise ratio) even with very limited spectrum. For example, in the absence of subchannelization and repetition coding, the required SINR for the lower MCS (modulation and coding scheme) is around 5 dB and this needs to be achieved even with very tight frequency reuse factor of 1/3 or 1/4 in the presence of shadowing, where the reuse factor is the reciprocal of the number the cells using different frequencies and the sum of the frequencies presents the whole spectrum resource allocated to the planned system. Another consideration in the case of WiMAX planning is the high SINR requirements to support high data rates. Although a site is expected to support high data rates for CPEs closer to it, SINR values >30 dB are only possible in the absence of interference. This requires accurate modeling of the propagation and RF equipments. For example, in 3G, high data rates are possible even with C/(N) of < 10 dB as the processing gain enables the receiver to tolerate some amount of interference. In WiMAX, this is not the case as the processing gain is only provided through channel coding and limited coding repetition.
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