Electronic density - Revision history

en>Colonies Chris: /* Definition */sp, date & link fixes; unlinking common words, replaced: Hartree-Fock → Hartree–Fock using AWB

2014-03-13T22:36:13Z

Definition: sp, date & link fixes; unlinking common words, replaced: Hartree-Fock → Hartree–Fock using AWB

← Older revision		Revision as of 00:36, 14 March 2014
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	~~Emilia Shryock~~ is ~~my title but you can call me anything you like~~. ~~Minnesota has usually~~ been ~~his home but his wife wants them to transfer~~. ~~One of~~ the ~~things~~ he enjoys ~~most is ice skating but he is struggling to find time for~~ it~~. Hiring is his profession~~.<br><br>~~My web blog:~~ [http://~~www~~.~~alemcheap.fi~~/~~people~~/~~anhipkiss std testing at home~~]		Oscar is how he's called and he completely enjoys this name. To perform baseball is the pastime he will never stop performing. For years he's been operating as a receptionist. Years in the past he moved to North Dakota and his family members enjoys it.<br><br>Also visit my site; std testing at home ([http://muzikoman.com/profile-682/info/ please click the following webpage])

en>NickPenguin: no consensus to merge

2014-03-03T19:12:01Z

no consensus to merge

← Older revision		Revision as of 21:12, 3 March 2014
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	~~'''Complementary Code Keying''' (CCK)~~ is a [[modulation]] scheme used with [[wireless network]]s (WLANs) that employ the [[IEEE 802.11b]] specification. In 1999, CCK was adopted to supplement the [[Barker code]] in wireless digital networks to achieve data rate higher than 2 Mbit/s at the expense of shorter distance. This is due to the shorter chipping sequence in CCK (8 bits versus 11 bits in Barker code) that means less spreading to obtain higher data rate but ~~more susceptible to narrowband interference resulting in shorter radio transmission range~~. ~~Beside shorter chipping sequence, CCK also~~ has ~~more chipping sequences~~ to ~~encode more bits (4 chipping sequences at 5~~.~~5 Mbit/s and 64 chipping sequences at 11 Mbit/s) increasing~~ the ~~data rate even further. The Barker code, however, only has a single chipping sequence.~~		Emilia Shryock is my title but you can call me anything you like. Minnesota has usually been his home but his wife wants them to transfer. One of the things he enjoys most is ice skating but he is struggling to find time for it. Hiring is his profession.<br><br>My web blog: [http://www.alemcheap.fi/people/anhipkiss std testing at home]

	~~The complementary codes first discussed by Golay were pairs of binary complementary codes and~~ he noted that when the elements of a code of length N were either [-1 or 1] it followed immediately from their definition that the sum of their respective autocorrelation sequences was zero at all points except for the zero shift where it is ~~equal~~ to ~~K*N. (K being the number of code words in the set).~~

	CCK is a variation and improvement on M-ary Orthogonal Keying and utilises ‘polyphase complementary codes’. They were developed by Lucent Technologies and Harris Semiconductor and were adopted by the 802.11 working group in 1998. CCK is the form of modulation utilised when 802.11b operates at either 5.5 or 11 Mbit/s. CCK was selected over competing modulation techniques as it ~~utilised approximately the same bandwidth and could utilise the same preamble and header as pre-existing 1 and 2 Mbit/s wireless networks and thus facilitated interoperability.~~

	~~Polyphase complementary codes, first proposed by Sivaswamy, 1978, are codes where each element is a complex number of unit magnitude and arbitrary phase, or more specifically for 802~~.~~11b~~ is ~~one of [1,-1, j,-j].~~

	~~Networks using the 802.11g specification employ CCK when operating at 802.11b speeds.~~

	~~==Mathematical description==~~
	~~The CCK modulation used by 802~~.11b transmits data in symbols of eight [[Direct-sequence spread spectrum\|chips]], where each chip is a complex [[QPSK]] bit-pair at a chip rate of 11Mchip/s. In 5.5 Mbit/s and 11 Mbit/s modes respectively 4 and 8 bits are modulated onto the eight chips of the symbol c<~~sub~~>0<~~/sub~~>~~,...,c<sub>7<~~/~~sub>, where~~

	~~<math>\mathbf{c}=(c_0,\ldots,c_7)=(~~
	~~e^{j(\phi_1+\phi_2+\phi_3+\phi_4)},~~
	~~e^{j(\phi_1 +\phi_3+\phi_4)},~~
	~~e^{j(\phi_1+\phi_2 +\phi_4)},~~
	~~-e^{j(\phi_1 +\phi_4)},~~
	~~e^{j(\phi_1+\phi_2+\phi_3 )},~~
	~~e^{j(\phi_1 +\phi_3 )},~~
	~~-e^{j(\phi_1+\phi_2 )},~~
	~~e^{j \phi_1 })<~~/~~math>~~

	~~and <math>\phi_1,\ldots,\phi_4</math> are determined by the bits being modulated~~.

	~~In other words, the phase change <math>\phi_1<~~/~~math> is applied to every chip, <math>\phi_2<~~/math> is applied to all even code chips (starting with <math>c_0</math>), <math>\phi_3</math> is applied to the first two of every four chips, and <math>\phi_4</math> is applied to the first four of the eight chips. Therefore, it can also be viewed as a form of generalized [[Hadamard transform]] encoding.

	~~==References==~~
	* IEEE Std 802.11b-1999, §18.4.6.5

	~~{{DEFAULTSORT:Complementary Code Keying}}~~
	~~[[Category:Quantized radio modulation modes]]~~
	~~[[Category:Wireless networking]]~~
	~~[[Category:IEEE 802.11]~~]

89.176.230.113: /* Definition */

2012-03-29T23:25:39Z

Definition

New page

'''Complementary Code Keying''' (CCK) is a [[modulation]] scheme used with [[wireless network]]s (WLANs) that employ the [[IEEE 802.11b]] specification. In 1999, CCK was adopted to supplement the [[Barker code]] in wireless digital networks to achieve data rate higher than 2 Mbit/s at the expense of shorter distance. This is due to the shorter chipping sequence in CCK (8 bits versus 11 bits in Barker code) that means less spreading to obtain higher data rate but more susceptible to narrowband interference resulting in shorter radio transmission range. Beside shorter chipping sequence, CCK also has more chipping sequences to encode more bits (4 chipping sequences at 5.5 Mbit/s and 64 chipping sequences at 11 Mbit/s) increasing the data rate even further. The Barker code, however, only has a single chipping sequence.

The complementary codes first discussed by Golay were pairs of binary complementary codes and he noted that when the elements of a code of length N were either [-1 or 1] it followed immediately from their definition that the sum of their respective autocorrelation sequences was zero at all points except for the zero shift where it is equal to K*N. (K being the number of code words in the set).

CCK is a variation and improvement on M-ary Orthogonal Keying and utilises ‘polyphase complementary codes’. They were developed by Lucent Technologies and Harris Semiconductor and were adopted by the 802.11 working group in 1998. CCK is the form of modulation utilised when 802.11b operates at either 5.5 or 11 Mbit/s. CCK was selected over competing modulation techniques as it utilised approximately the same bandwidth and could utilise the same preamble and header as pre-existing 1 and 2 Mbit/s wireless networks and thus facilitated interoperability.

Polyphase complementary codes, first proposed by Sivaswamy, 1978, are codes where each element is a complex number of unit magnitude and arbitrary phase, or more specifically for 802.11b is one of [1,-1, j,-j].

Networks using the 802.11g specification employ CCK when operating at 802.11b speeds.

==Mathematical description==
The CCK modulation used by 802.11b transmits data in symbols of eight [[Direct-sequence spread spectrum|chips]], where each chip is a complex [[QPSK]] bit-pair at a chip rate of 11Mchip/s. In 5.5 Mbit/s and 11 Mbit/s modes respectively 4 and 8 bits are modulated onto the eight chips of the symbol c<sub>0</sub>,...,c<sub>7</sub>, where

<math>\mathbf{c}=(c_0,\ldots,c_7)=(
e^{j(\phi_1+\phi_2+\phi_3+\phi_4)},
e^{j(\phi_1 +\phi_3+\phi_4)},
e^{j(\phi_1+\phi_2 +\phi_4)},
-e^{j(\phi_1 +\phi_4)},
e^{j(\phi_1+\phi_2+\phi_3 )},
e^{j(\phi_1 +\phi_3 )},
-e^{j(\phi_1+\phi_2 )},
e^{j \phi_1 })</math>

and <math>\phi_1,\ldots,\phi_4</math> are determined by the bits being modulated.

In other words, the phase change <math>\phi_1</math> is applied to every chip, <math>\phi_2</math> is applied to all even code chips (starting with <math>c_0</math>), <math>\phi_3</math> is applied to the first two of every four chips, and <math>\phi_4</math> is applied to the first four of the eight chips. Therefore, it can also be viewed as a form of generalized [[Hadamard transform]] encoding.

==References==
* IEEE Std 802.11b-1999, §18.4.6.5

{{DEFAULTSORT:Complementary Code Keying}}
[[Category:Quantized radio modulation modes]]
[[Category:Wireless networking]]
[[Category:IEEE 802.11]]