Luke Pensworth
How much transmit power do WiMAX nets need? asks Wireless Net DesignLine. Designers must find the optimal balance between high transmit power and low power consumption to ensure robust links, high data rates and good range for WiMAX services, they explain.
A typical WiMAX basestation transmits at power levels of approximately +43 dBm (20 W), and the mobile station typically transmits at +23 dBm (200 mW). There is a large difference between downlink power and uplink power. While a mobile can easily receive transmissions from a basestation, the mobile’s low transmit power makes it difficult for the basestation to hear it.
One technique to address the link imbalance is adaptive modulation. In this case, the mobile transmits using a lower order modulation compared with the basestation. For example, the mobile could transmit QPSK or 16QAM signals, while the basestation transmits using 64QAM.
Another way to combat this mismatch is with a technique called subchannelization. In effect, each mobile concentrates its power over a subset of all available subchannels, and the other subcarriers are simultaneously made available to other users.
When subchannelization and adaptive modulation are combined, a network operator can effectively balance the uplink and downlink budgets, and the network will operate bidirectionally.
Networks are currently being deployed specifying that the minimum transmit power is +23 dBm. Each user who enters a network transmitting at powers greater than +23 dBm increases overall network efficiency. However, delivering higher transmit powers comes at a cost to power consumption.
The Mobile WiMAX network will cover 120-140 million people in the U.S. by year-end 2010. If those people are using Android devices, Google will indeed become a force in the market, although still behind Symbian, Windows Mobile and Apple’s iPhone.
Apple, Research In Motion and Google are duking it out for consumers’ smartphone dollars this fall. But Time Warner’s AOL has just landed a giant contract to push Google’s G1 phone for the next two days through AOL’s Platform-A ad network. It has agreed to buy a billion impressions today and tomorrow, reports AdAge.
Practical Mobile WiMAX devices in small form factors may be a year off, say industry insiders. Intel Moorestown should enable practical battery life with integrated Wi-Fi/WiMAX chips.
LTE operators like femtocells because the cost of the broadband infrastructure can be shifted to end users. Part of the new Clearwire deal calls for 5 MHz of spectrum to be set aside solely for WiMax femtocells. Perhaps ‘free’ whitespace femtocells, in the tv band, will create new business models for end users and municipalities.
