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.