Long Code
Application:
The PN chips from the long code are used to provide several randomizing functions in the IS-95 system. These include providing chips for message- scrambling privacy on the forward and reverse links, for identifying individual mobiles and Access Channels on the reverse links by using unique offsets for each entity, for randomizing the location of the power control bits on the forward traffic channels, and for randomizing the output of the data burst randomizer on the reverse traffic channels.
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© 1999 DR. ERNEST SIMO - SPACE2000
Long Code
Example:
The period of 242-1 equals about 4.398x1012 chips. At the chipping rate of 1.2288 Mchips/sec, the long code repeats itself about every 41.425 days. The long PN code is generated in a 42 stage linear shift register generator with the output of the 42nd stage input into the first stage and modulo-2 added with the outputs of stages 1, 2, 3, 5, 6, 7, 10, 16, 17, 18, 19, 21, 22, 25, 26, 27, 31, 33, and 35 as depicted in the figure below. The output of the long code generator is taken after the output of each flip-flop in the generator has been added with a corresponding bit in a 42-bit mask which is unique to each user, access, and paging channel.
See Long Code Masking and Equivalent Offset
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© 1999 DR. ERNEST SIMO - SPACE2000
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