BigAir

One of the most often heard descriptions of WiMAX in the press is that it is "Wi-Fi on steroids". In truth, it is considerably more than that. Not only does WiMAX offer exponentially greater range and throughput than Wi-Fi (technically speaking 802.11b, although new variants of 802.11 offer substantial improvements over the "b" variant of 802.11), it also offers carrier grade quality of service (QoS) and security. Wi-Fi has been notorious for its lack of security. The "b" variant of 802.11 offered no prioritization of traffic making it less than ideal for voice or video.

The key message here is that the BigAir network is NOT using WLAN equipment. WLANs (eg. WiFi access points) use a contention based MAC (media access control) which means that every client has to "fight" for its bandwidth and share of the spectrum.

WiMax is not Wi-Fi

BigAir instead uses sophisticated equipment based on WiMAX which uses an OFDM (Orthogonal Frequency Division Multiple Access) based MAC. It uses a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations.

With OFDM BigAir is able to maximise distance and throughput and build resistance to interference in to the wireless broadband network. The spectrum is also divided into multiple sub-carriers and modulation (throughput) declines with distance.

BigAir uses ‘Licensed Spectrum'

The other important point in relation to spectrum is that ALL spectrum is licensed and regulated by the ACMA (Australian Communications Media Authority). There is no such thing as unlicensed spectrum. BigAir makes use of "Class License" spectrum. This spectrum is designed for co-existence of multiple users, so the maximum transmit power levels are restricted and wireless carriers like BigAir have designed the network for these power conditions. The amount of spectrum BigAir has available for BigAir's use is enormous - roughly 4 times as much spectrum as Unwired, and 30-50 times as much as the mobile carriers. This enables BigAir to offer much higher data rates than mobile phone networks.