Just as consumers expect mobile phone and wireless data coverage everywhere indoors and underground, they will have the same expectation of Wimax services. In fact, it is expected that the vast majority of wireless data interaction will take place indoors - in venues such as homes and office buildings, plus busy public metros, shopping centres and airport terminals.
Consequently, carriers are already exploring the level of coverage that will be required in these so-called confined spaces, and how to achieve it.
The practical approach will be to obtain as much coverage as possible from the outdoor network, which will be the starting point for deployment. But, although people's homes and some office buildings may be serviced in this way, a great many other key venues cannot be adequately penetrated by the outdoor network signal. This calls for the deployment of dedicated RF infrastructure to distribute the signal indoors.
Fundamentally, the principle of achieving wireless indoor solutions for Wimax is no different from 2G, 3G and Wi-Fi networks. Indeed, many key buildings around the region already have confined coverage infrastructure in place to support mobile phone, wireless data, and various radio services. These generally take the form of passive or active broadband distributed antenna systems (DAS) that support multiple services and carriers, and which now can be leveraged to provide coverage for Wimax as well.
Adapt and adopt
Wimax operates at frequencies up to 6 GHz, including the licensed and unlicensed 2.3-2.7 GHz, 3.3-3.7 GHz and 5.1-5.8 GHz bands. At these higher frequencies, both signal propagation and cable loss characteristics are likely to be quite different, providing new challenges for coverage planners.
One challenge is how strong the signal needs to be for terminal reception. This will vary significantly depending on whether the subscriber is stationary (such as sitting in an airport terminal), or moving (such as sitting on a subway train). In addition to signal level, Wimax reception at high speeds is highly dependent on the number of signal carriers and the type of signal modulation used.
The interaction of the indoor microcell with the outdoor network must also be considered in order to minimize interference. In cases where wireless services are allocated a single RF channel operating in single-frequency network (SFN) mode, licensees are likely to incorporate any indoor microcells as well as the outdoor network.
Conventional outdoor SFNs operate using complex signal timing and strict power levels to avoid co-channel interference. Although network planning is a challenge, the finely tuned network is essentially static once on-air. The introduction of indoor SFN microcells creates a dynamic environment that must therefore be carefully controlled, lest the balance of the total SFN is disrupted. Conventional indoor planning targets the indoor signal being stronger than what penetrates from outdoors, but when operating in SFN mode it is also important to exert strict control over the signal timing and power levels to ensure optimal coverage is achieved without interference.
Infrastructure evolution
Despite the broadband nature of much of the existing RF infrastructure, there is still much development work being done to allow systems to be upgraded in support of the new services.