SCALABILITY | STRATEGY INTERACTION

As mentioned previously, the most significant advantage of WiMAX is the flexibility and scalability of the air-interface. Therefore the concept “pay as you grow” is definitely applicable in WiMAX commercial networks. Scalability allows the reduction of initial investment and risks, and thereafter the network is expanded based on the market penetration and revenues. The majority of business plans provide the subscriber numbers and services per deployment year and in this context the dimensioning should be presented according to the scalability plan (network size/performance per year). The complexity in this case is not the increase of subscriber numbers or service area size, but when in parallel the coverage type is upgraded or new products (based on recently released standards) have to coexist with deployed equipment. The main types of scalability plan that have to be considered during dimensioning are presented as follows:

• Network expansion: Expansion may be in terms of subscriber numbers, service rates, or service areas or a combination and involves the deployment of new PoP or addition of sectors in existing PoP. A great challenge, in such scenario, is to optimize the positioning of PoP to achieve the best coverage and capacity outcome. It is more appropriate to determine the network size and PoP positions for the last deployment year, and then deploy only a subset of PoP that would satisfy the objectives of the initial phase.
• Coverage upgrade: It is common to allow the use of more demanding terminal profiles (i.e., nomadic/mobile) in the network after the first year so as to allow time to test the performance of the wireless network. In this case, not only the network is expanded from first to second year, but also the coverage should be upgraded too. The same approach “design for the future, deploy for present” as above should be applied, and the only difference is that a more dense network is probably required.
• Technology upgrade: The major change in terms of equipment is between the IEEE 801.16-2004 and 802.16e standards. The new products are based on software defined radio technology and therefore future standard releases will probably be implemented with minor changes. It is quite challenging to upgrade an existing fixed WiMAX network to coexist with mobile WiMAX, unless there is provision for additional spectrum. The major challenge is to replace subscriber equipment and restore access and it is likely that this transition phase will take a long time.