Wi-Fi Radio Modulation
WiFi systems use two primary radio transmission techniques.
- 802.11b (<=11 Mbps): The 802.11b radio link uses a direct sequence spread spectrum technique called complementary coded keying (CCK). The bit stream is processed with a special coding and then modulated using Quadrature Phase Shift Keying (QPSK).
- 802.11a and g (<=54 Mbps): The 802.11a and g systems use 64-channel orthogonal frequency division multiplexing (OFDM). In an OFDM modulation system, the available radio band is divided into a number of sub-channels and some of the bits are sent on each. The transmitter encodes the bit streams on the 64 subcarriers using Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or one of two levels of Quadrature Amplitude Modulation (16, or 64-QAM). Some of the transmitted information is redundant, so the receiver does not have to receive all of the sub-carriers to reconstruct the information.
The original 802.11 specifications also included an option for frequency hopping spread spectrum (FHSS), but that has largely been abandoned.
WiFi make use of adaptive modulation and varying levels of forward error correction to optimize transmission rate and error performance.
As a radio signal loses power or encounters interference, the error rate will increase. Adaptive modulation means that the transmitter will automatically shift to a more robust, though less efficient, modulation technique in those adverse conditions.
Wi-Fi Major Issues
There are following issues which are assumed to be the cause of the sluggish adoption of Wi-Fi technology:
- Security Problems: Security concerns have held back Wi-Fi adoption in the corporate world. Hackers and security consultants have demonstrated how easy it can be to crack the current security technology known as wired equivalent privacy (WEP) used in most Wi-Fi connections. A hacker can break into a Wi-Fi network using readily available materials and software.
- Compatibility and Interpretability: One of the bigger problems with Wi-Fi is compatibility and interpretability; for example, 802.11a products are not compatible with 802.11b products, due to the different operating frequencies and 802.11a hotspots would not help a 802.11b client. Due to lack of standardization, harmonization and certification, different vendors come out with products that do not work with each other.
- Billing Issues: Wi-Fi vendors are also looking for ways to solve the problem of back-end integration and billing that has dogged the roll-out of commercial Wi-Fi hotspots. Some of the ideas under consideration for Wi-Fi billing include per day, per hour and unlimited monthly connection fees.
Wi-Fi Useful Resources
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- Wi-Fi Aliance - Official website of Wi-Fi Alliance, the best resource for Wi-Fi information.
- Wi-Fi.com - WiFi.com is a wireless Internet portal offered by Salient Properties, LLC.
- WiMAX Forum - Official website of WiMAX Forum, the best resource for WiMAX information.
- IEEE 8092.16 Specification - The IEEE 802.16 Working Group on Broadband Wireless Access Standards.
- WiMAX Forum White Papers - Read more about WiMAX wireless technology and how it addresses market problems through these white papers.
- WiMAX Industry - Find latest news and market trends about WiMAX.
- WiMAX Global Forum - The WiMAX Global ComForum, co-located with Broadband World Forum Europe 2005 at the Palacio Municipal de Congresos in Madrid, Spain, tackled the technology and business challenges in implementing WiMAX wireless broadband networks.
- WiMAX.com - Latest WiMAX news, market trends, WiMAX Forums, etc.