802.11n And Its Role In 4G


IEEE 802.11n is a proposed amendment to the IEEE 802.11-2007 wireless networking standard to significantly improve network throughput over previous standards, such as 802.11b and 802.11g, with a significant increase in raw (PHY) data rate from 54 Mbit/s to a maximum of 600 Mbit/s. Most devices today support a PHY rate of 300 Mbit/s, with the use of 2 Spatial Streams at 40 MHz. Depending on the environment, this may translate into a user throughput (TCP/IP) of 100 Mbit/s.

According to the book "WI-Fi, Bluetooth, Zigbee and Wimax" :

802.11n is the 4th generation of wireless LAN technology.
• First generation (IEEE 802.11) since 1997 (WLAN/1G)
• Second generation (IEEE 802.11b) since 1998 (WLAN/2G)
• Third generation (802.11a/g) since 2000 (WLAN/3G)
• Fourth generation (IEEE 802.11n) (WLAN/4G)

The distinguishing features of 802.11n are:

• Very high throughput (some hundreds of Mbps)
• Long distances at high data rates (equivalent to IEEE 802.11b at 500 Mbps)
• Use of robust technologies (e.g. multiple-input multiple-output [MIMO] and space time coding).

In the N option, the real data throughput is estimated to reach a theoretical 540 Mbps (which may require an even higher raw data rate at the physical layer), and should be up to 100 times faster than IEEE 802.11b, and well over ten times faster than IEEE 802.11a or IEEE 802.11g. IEEE 802.11n will probably offer a better operating distance than current networks. IEEE 802.11n builds upon previous IEEE 802.11 standards by adding MIMO. MIMO uses multiple transmitter and receiver antennae to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity and powerful coding schemes. The N system is strongly based on the IEEE 802.11e QoS specification to improve bandwidth performance. The system supports basebands width of 20 or 40MHz..

Note that there is 802.11n PHY and 802.11n MAC that will be required to achieve 540Mbps.

To achieve maximum throughput a pure 802.11n 5 GHz network is recommended. The 5 GHz band has substantial capacity due to many non-overlapping radio channels and less radio interference as compared to the 2.4 GHz band. An all-802.11n network may be impractical, however, as existing laptops generally have 802.11b/g radios which must be replaced if they are to operate on the network. Consequently, it may be more practical to operate a mixed 802.11b/g/n network until 802.11n hardware becomes more prevalent. In a mixed-mode system, it’s generally best to utilize a dual-radio access point and place the 802.11b/g traffic on the 2.4 GHz radio and the 802.11n traffic on the 5 GHz radio.

 

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Cognitive Radio:A Solution to Wireless Jamming


Cognitive Radio:To avoid future wireless traffic jams, Heather “Haitao” Zheng is finding ways to exploit unused radio spectrum.It’s a local effect — within 30 to 60 meters of a transceiver — but there’s just no more space in the part of the radio spectrum designated for Wi-Fi.
Imagine, then, what happens as more devices go wireless — not just laptops, or cell phones and BlackBerrys, but sensor networks that monitor everything from temperature in office buildings to moisture in cornfields, radio frequency ID tags that track merchandise at the local Wal-Mart, devices that monitor nursing-home patients. All these gadgets have to share a finite — and increasingly crowded — amount of radio spectrum.
Heather Zheng, an assistant professor of computer science at the University of California, Santa Barbara, is working on ways to allow wireless devices to more efficiently share the airwaves. The problem, she says, is not a dearth of radio spectrum; it’s the way that spectrum is used.
The Federal Communications Commission in the United States, and its counterparts around the world, allocate the radio spectrum in swaths of frequency of varying widths. One band covers AM radio, another VHF television, still others cell phones, citizen’s-band radio, pagers, and so on; now, just as wireless devices have begun proliferating, there’s little left over to dole out.
But as anyone who has twirled a radio dial knows, not every channel in every band is always in use. In fact, the FCC has determined that, in some locations or at some times of day, 70 percent of the allocated spectrum may be sitting idle, even though it’s officially spoken for.
Zheng thinks the solution lies with cognitive radios, devices that figure out which frequencies are quiet and pick one or more over which to transmit and receive data. Without careful planning, however, certain bands could still end up jammed. Zheng’s answer is to teach cognitive radios to negotiate with other devices in their vicinity. In Zheng’s scheme, the FCC-designated owner of the spectrum gets priority, but other devices can divvy up unused spectrum among themselves.
But negotiation between devices uses bandwidth in itself, so Zheng simplified the process. She selected a set of rules based on “game theory” — a type of mathematical modeling often used to find the optimal solutions to economics problems — and designed software that made the devices follow those rules. Instead of each radio’s having to tell its neighbor what it’s doing, it simply observes its neighbors to see if they are transmitting and makes its own decisions.