DIMENSIONING CERTAINTY AND MARGINS

As stated above, dimensioning accuracy is crucial. For vendors/integrators, it is essential that an RFP response should be financially prudent to increase chances for a contract award. However after the award, the network should be deployable, and considering that the majority of RFPs concern turn-key projects, a rough or underestimated offer can lead to miscalculation of the required network size and hence increase the implementation costs at the vendor’s/integrator’s expense. A balanced condition can be achieved by incorporating operating/performance and certainty margins. An operating margin is applied to coverage estimations, where the system range is selected smaller than the maximum. The same applies to capacity estimations where, for the average sector throughput, usually a small margin is considered. Considering the overlapping effect of various margins, a careless consideration can lead to overestimation. Specifically for coverage and capacity margins, the network will be either coverage-limited or capacity-limited. Therefore, in practice only one of the previously mentioned margins has impact on the financial offer. An important factor for defining margins is the quality of the provided business plan. The provision of extensive information would facilitate more accurate dimensioning.

It should be noted that in addition to the operating margins, another issue to consider is the network implementation margins. Although the RF designers take great caution to predict any possible causes of degradation, in many occasions problems may occur during the implementation. An engineering team, which is not well trained, or pays little attention to details, can make the difference between a successful and poor deployment. In cases where existing infrastructure is utilized, such as sharing of GSM sites, the condition of these sites or the restrictions posed by an operator usually cause problems. For example to save cost of antenna poles, operators may install WiMAX antennas below GSM antennas. This is contradictory to best practice since WiMAX operates in higher band and hence experiences higher propagation losses, and furthermore there is the issue of equipment RF isolation where a minimum separation distance should be maintained. Another example is with the installation of fixed-outdoor CPEs. Careless installation will result in suboptimum performance of such units, compromising their competitive advantage which is high capacity and robustness. In general, past deployment experience can make the difference in dimensioning, and it is preferred that the RF network designers which are involved in presales activities are the same that will have the responsibility of carrying out the final design and deployment supervision.