From my first blog, you may know that I have joined another firm recently. Here, I will be working in the same domain as my earlier one - IEEE 802.11 a.k.a Wi-Fi or Wireless LAN [WLAN], my personal favorite. Now that I am having some free time at my new firm since my joining formalities are not finished, I thought I will spend some time researching the new trends in wireless domain. It is then that I came across a commercial claiming a data rate of around 300Mbps for a wireless product. But the products which I worked in, 802.11g compliant, will provide a maximum of 54Mbps (raw data speed) only. I had some idea about 802.11n, but I never thought they will provide this much speed. And thus, I thought I’ll spend some of my time researching about 802.11n.
A word of caution before I go in to the details: I am assuming the reader of this blog is familiar with IEEE 802.11 basics, not in the user perspective, but in a developer one since this contains technical stuff unlike my other blogs. Non-technical people, skip to the summary section.
Setting the new standard
As I said, the wireless product I previously worked had a maximum data rate of 54Mbps. It was an 802.11g certified product. In the 802.11 base spec (1999), three PHY layers were defined, an FHSS (Frequency-Hopping spread spectrum), a DSSS (Direct Sequence Spread Spectrum), both in the 2.4GHz band and an Infrared PHY which is obsolete now. Then released were the 802.11b (DSSS) (July 1999) which supports 11Mbps, 802.11a (OFDM – Orthogonal Frequency Division Multiplexing) (July 1999), which supports the 54Mbps raw data rate. But 11a didn’t get in to that wide acceptance because of the very fact that it operated in the 5GHz spectrum. Then the 11g came with 54Mbps data rate which operated in 2.4GHz spectrum and is used by almost all the Wi-Fi certified products now. In the case of 802.11n, the draft specifies many ‘options’, like many configurations and we can make it work in any possible configurations. With every possible options turned on, you will get a raw data rate up to 600Mbps. (Data taken from http://www.broadcom.com/docs/WLAN/802_11n-WP100-R.pdf) I will give a comparative table to show the details rather than explaining.
A word of caution before I go in to the details: I am assuming the reader of this blog is familiar with IEEE 802.11 basics, not in the user perspective, but in a developer one since this contains technical stuff unlike my other blogs. Non-technical people, skip to the summary section.
Setting the new standard
As I said, the wireless product I previously worked had a maximum data rate of 54Mbps. It was an 802.11g certified product. In the 802.11 base spec (1999), three PHY layers were defined, an FHSS (Frequency-Hopping spread spectrum), a DSSS (Direct Sequence Spread Spectrum), both in the 2.4GHz band and an Infrared PHY which is obsolete now. Then released were the 802.11b (DSSS) (July 1999) which supports 11Mbps, 802.11a (OFDM – Orthogonal Frequency Division Multiplexing) (July 1999), which supports the 54Mbps raw data rate. But 11a didn’t get in to that wide acceptance because of the very fact that it operated in the 5GHz spectrum. Then the 11g came with 54Mbps data rate which operated in 2.4GHz spectrum and is used by almost all the Wi-Fi certified products now. In the case of 802.11n, the draft specifies many ‘options’, like many configurations and we can make it work in any possible configurations. With every possible options turned on, you will get a raw data rate up to 600Mbps. (Data taken from http://www.broadcom.com/docs/WLAN/802_11n-WP100-R.pdf) I will give a comparative table to show the details rather than explaining.
As you can see from the table, 11n has a very high data rate compared to others. But that is the raw data speed with the entire data rate options turned on. From the user level perspective, you will get around 100-200Mbps. Even that is a great boost from the conventional 802.11ga mode.
802.11n specific features
One of the great features of 11n is the use of multiple antennas which is known as MIMO - Multiple Input Multiple Output. Basically it uses more than one antenna to send the data packets in multiple streams. It exploits the phenomenon called multipath, which usually is treated as interference in radio communications. Two important benefits of MIMO are antenna diversity and time-space multiplexing. The draft specifies antenna configuration option of up to 4x4. This feature can be a power consuming one and so the draft n specifies a power save mode also. So the multiple antenna configurations are used only when maximum throughput and data rate is required.
Other options in the 11n specification are,
802.11n specific features
One of the great features of 11n is the use of multiple antennas which is known as MIMO - Multiple Input Multiple Output. Basically it uses more than one antenna to send the data packets in multiple streams. It exploits the phenomenon called multipath, which usually is treated as interference in radio communications. Two important benefits of MIMO are antenna diversity and time-space multiplexing. The draft specifies antenna configuration option of up to 4x4. This feature can be a power consuming one and so the draft n specifies a power save mode also. So the multiple antenna configurations are used only when maximum throughput and data rate is required.
Other options in the 11n specification are,
- Better OFDM - The OFDM in 11n is improved so that the maximum data rate which can be achieved is 65Mbps rather than 54Mbps in 11g.
- Wider channels – 11n provides options for 40MHz channels instead of the conventional 20MHz ones. But the downside is that the number of channels will be less and so it doesn’t give much space for other devices to transmit in the same airspace.
- Reduced Inter-frame Spacing [RIFS] - A smaller inter-frame spacing than that of 11a or g which uses the SIFS [Short IFS], PIFS [PCF IFS], DIFS [DCF IFS]& EIFS [Extended IFS]
- Aggregation - This feature is used in the case of inter-operability between the legacy modes 11b/g and 11n. It uses transmission burst in between the overhead communication there by improving the efficiency.
- Greenfield Mode - This is an optional mode which allows an all 11n network which doesn’t have to give any backward compatibility with the 11b/g devices.
These are some of the options which can be turned on and off. So by fine tuning them, you can attain really high data rates as compared to the present 11g devices.
Summary
Just going through the table above itself, we can see that the 802.11n will surely bring a revolution in the wireless domain in the case of both data rates and range. But only at the cost of MAC/PHY layer becoming more complex. The applications of 802.11n will become prominent in VoIP (Voice over IP), streaming video and music, gaming, NAS (Network Attached Storage) etc. Already there are around 70 products in the market which are 802.11n Draft 2.0 certified. The 11n standard is supposed to be ratified by fall 2007 or early 2008.
References
- IEEE 802.11 Specifications, 1999 Edition.
- IEEE 802.11a-1999 - Amendment 1: High-speed Physical Layer in the 5 GHz band
- IEEE 802.11b-1999 - Amendment 2: Higher-speed Physical Layer (PHY) extension in the 2.4 GHz band
- IEEE 802.11g-2003 - Amendment 4: Further Higher-Speed Physical Layer Extension in the 2.4 GHz Band
- http://www.broadcom.com/docs/WLAN/802_11n-WP100-R.pdf
- http://www.deviceforge.com/articles/AT5096801417.html
- http://en.wikipedia.org/wiki/802.11#802.11n
ps: If you come across any discrepancies, please do comment on it.
4 comments:
I belong to the 'only Summary' group. :[
its ok.. :)
hehe.. this looks like a design spec :-p good that u mentioned what audience u r expecting :-)
This is great info to know.
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