802.11n for Mobiles: Here It Is!

By: By Raj Gawera, Mobile Handset Connectivity Business Unit, CSR
( 1 Jan 2009 )

Much has been made of the need for the upcoming IEEE802.11n wireless technology standard in desktop computing. It looks like the bandwidth demands of modern computing could outstrip the capacity of 802.11b/g technology in the not-too-distant future. The size and volume of music and video files being transferred is growing. Moreover we're seeing a growing tendency for systems to run multiple high-bandwidth applications, such as video streaming and wireless voice-over-IP (VoIP), simultaneously. Overall Wi-Fi still lacks the speed to replace wired networks.

802.11n PROFILE FOR MOBILES
Far less has been said about 802.11n for mobiles, even though roughly analogous trends also hold true in mobile usage. The mobile device is gradually taking on more bandwidth-intensive roles, functioning as a personal media player, mobile storage device and office organizer. The fact is, 802.11n using multiple antenna MIMO (Multiple-In, Multiple-Out) technology is too power-hungry and not a realistic design choice for use in mobile phones. This is the form of 802.11n that most people are familiar with, the one designed for desktop PCs, access points and home routers.

The 802.11n "handheld" profile promises to bring the advantages of 802.11n to handheld devices while still using a single antenna, and to do so without bleeding a handset's batteries dry. The technology behind the 802.11n standard is, by now, fairly well known. It works quite differently to 802.11g found in most Wi-Fi consumer products on the market today such as laptop computers and access points. The most obvious development on the Wi-Fi standard in 802.11n is the option for MIMO technology. MIMO allows for multiple data streams to be transmitted via different antennas on the same frequency; a technique known as spatial multiplexing.

802.11n actually benefits from the presence of objects and environmental interference. Slight differences in the path of each radio data stream mean that the two signals arrive at slightly different times, helping them to be distinguished and then amalgamated. Together with its more intelligent coding and wider bandwidth usage 802.11n allows for up to 600Mbps (possible with four antennas). The more common two-antenna version will manage up to 300Mbps; a significant improvement on 54Mbps possible with 802.11g. Many of the MIMO versions of 802.11n have done little more than re-use inefficient semiconductor IP designed for desktop PCs. Also, multiple transmission streams are, by their very nature, power-hungry. CSR has sought to reapply the principles of 802.11n from the ground up in order to make it more appropriate for mobile devices. So what is it that makes 802.11n for mobiles different? As mentioned, the "handheld" 802.11n profile uses a single antenna, primarily to overcome the limitations in power and space available in mobile devices. This does mean that the full capability of 802.11n MIMO is never going to be achieved in a handset.

However, 802.11n handheld is still capable of much greater speeds than existing single-antenna Wi-Fi standards. 802.11n handheld does not rely on MIMO. Through better coding and intelligent use of bandwidth, the single-antenna 802.11n handheld may reach speeds of up to 150Mbps. Even when using the same bandwidth as older standards (just one 20MHz channel in the 5.4GHz range instead of its usual 40MHz), 802.11n's better 5/6 coding rates for 64-QAM mean that it can achieve rates of up to 72Mbps, still a 25 percent improvement on 802.11g.

With use of the optional 802.11n features such as block acknowledgement and frame aggregation, you can improve the efficiency of the throughput of the network and achieve data throughput of up to 65Mbps—approximately 90 percent. With 802.11g for example you could only achieve up to about 50 percent.

Handheld 802.11n can communicate with both multiple-antenna and single-antenna systems. Included in the 11n handheld profile is Space Time Block Coding (STBC), which allows multiple transmit chains to be combined into a single receive antenna. Using STBC, the robustness of the signal is improved—giving enhanced range over existing single antenna solutions.

When 802.11n chips for mobiles arrive, consumers will start to benefit not only from faster mobile-to-mobile transfer; but also to allow mobile devices to take full advantage of the 802.11n ecosphere and transfer files from mobile to computer effectively. Spread the word: there's more to 802.11n than you've probably heard.

About the Author
Raj Gawera is Head of Marketing for CSR's Mobile Handset Connectivity Business Unit.