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Complementary Code Keying
Complementary code keying (CCK) is a modulation scheme used with wireless networks (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 8 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 ˆ’1 or 1it follow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals, each modulated with a different television channel, are transported through a sing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
