3G, WiFi Vs. Wimax

The throughput capabilities of WiMAX depend on the channel bandwidth used. But 3G systems has a fixed channel bandwidth, WiMAX defines a selectable channel bandwidth from 1.25MHz to 20MHz, which allows for a very flexible deployment. When deployed using the more likely 10MHz TDD (time division duplexing) channel, assuming a 3:1 downlink-to-uplink split and 2 x 2 MIMO, WiMAX offers 46Mbps peak downlink throughput and 7Mbps uplink. The reliance of Wi-Fi and WiMAX on OFDM modulation, as opposed to CDMA as in 3G, allows them to support very high peak rates. The need for spreading makes very high data rates more difficult in CDMA systems.

More important than peak data rate offered over an individual link is the average throughput and overall system capacity when deployed in a multicellular environment. From a capacity standpoint, the more pertinent measure of system performance is spectral efficiency. The fact that WiMAX specifications accommodated multiple antennas right from the start gives it a boost in spectral efficiency. In 3G systems, on the other hand, multiple-antenna support is being added in the form of revisions. Further, the OFDM physical layer used by WiMAX is more amenable to MIMO implementations than are CDMA systems from the standpoint of the required complexity for comparable gain. OFDM also makes it easier to exploit frequency diversity and multiuser diversity to improve capacity. Therefore, when compared to 3G, WiMAX offers higher peak data rates, greater flexibility, and higher average throughput and system capacity.

Another advantage of WiMAX is its ability to efficiently support more symmetric links—useful for fixed applications, such as T1 replacement—and support for flexible and dynamic adjustment of the downlink-to-uplink data rate ratios. Typically, 3G systems have a fixed asymmetric data rate ratio between downlink and uplink.In terms of supporting roaming and high-speed vehicular mobility, WiMAX capabilities are somewhat unproven when compared to those of 3G. In 3G, mobility was an integral part of the design; WiMAX was designed as a fixed system, with mobility capabilities developed as an add-on feature.