42 bits
CDMA Long Code · 42 bits
The long code of the cdma2000 mobile phone standard (which includes the older IS-95 standard), made by a 42-stage shift register and given each phone's identity by a 42-bit mask.
When a CDMA mobile phone talked to a tower, it mixed its signal with a very long pattern of ones and zeros called the long code. A small machine built that pattern from a row of 42 switches, called a shift register. The pattern runs 2^42 - 1 steps before it repeats, which takes about 41 days at the network's speed. Each phone used its own 42-bit mask on that pattern, so the tower could pick one phone out of the crowd.
What it supports
An exact design count printed in the international standard itself (3GPP2 C. S0002, cdma2000 physical layer): "Long Code Mask. A 42-bit binary number that creates the unique identity of the long code." The long code "shall be periodic with period 2^42 - 1 chips," set by a polynomial that starts at x^42, and each chip comes from "a 42-bit mask and the 42-bit state vector of the sequence generator." The standard says the long code gives limited privacy and, on the uplink, uniquely identifies a mobile station. The polynomial is p(x) = x^42 + x^35 + x^33 + x^31 + x^27 + x^26 + x^25 + x^22 + x^21 + x^19 + x^18 + x^17 + x^16 + x^10 + x^7 + x^6 + x^5 + x^3 + x^2 + x + 1.
What it does not
Not 42 days: the pattern repeats after about 41.4 days at 1.2288 million chips per second, and that must not be rounded to 42. Not a part number or a version number. Not the short PN codes, which repeat after 2^15 chips. Not strong encryption: the standard itself says limited privacy. Shift-register lengths in other standards take many values, so this is one design choice, not a rare constant. Not Adams.
Calculation
(2^42 - 1) chips / 1,228,800 chips per second is about 3,579,139 seconds, about 41.4 days.
Period and chip rate as printed in 3GPP2 C.S0002 (Spreading Rate 1). Shown only to keep the repeat time honest; the object is the 42-bit register and mask, not the days.
ExactnessCount
Form42
Unitbits (long code register stages and mask)
Strengthhard
When2002 · 2011
Hung7 October 2026