Zad-off Chu ( CAZAC sequences) in LTE

[ABC_XYZ]

Please somebody explain Zad-off Chu ( CAZAC sequences) in LTE .

thank you

[T_ADD]

Wiki ? to start off with...

http://en.wikipedia.org/wiki/Zadoff–Chu_sequence

Y (http://en.wikipedia.org/wiki/Zadoff–Chu_sequence)ou could also check the LTE A-Z book.

[dushyantsahni]

ZC sequences are non-binary unit-amplitude sequences , which satisfy a Constant Amplitude Zero Autocorrelation (CAZAC) property.
ZC sequences have the following important properties.
Property 1. A ZC sequence has constant amplitude, and its NZC-point DFT also has constant amplitude. The constant amplitude property limits the Peak-to-Average Power Ratio (PAPR) and generates bounded and time-flat interference to other users. It also simplifies the implementation as only phases need to be computed and stored, not amplitudes.

Property 2. ZC sequences of any length have ‘ideal’ cyclic autocorrelation (i.e. the correlation with the circularly shifted version of itself is a delta function).

Property 3.
The absolute value of the cyclic cross-correlation function between any two ZC sequences is constant and equal to 1/ sqrt(NZC) , if |q1 - q2| (where q1 and q2 are the sequence indices) is relatively prime with respect to NZC (a condition that can be easily guaranteed if NZC is a prime number). The cross-correlation of 1/ sqrt(NZC) at all lags achieves the theoretical minimum cross-correlation value for any two sequences that have ideal autocorrelation.

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[Gaara]

Hey, I am a beginner in LTE. I was reading about RACH procedure..There i came across this Zadoff-chu sequence. U may find this even in PSS.. The thing is that,

1) What is a zadoff sequence?
This is just a signal(sequence). Like all continuous time signals, even this can be expressed in an equation form. (which u can find in wiki).
2) Why do i need it?
As you already know, In LTE, the subcarriers are orthogonal to each other.(Leave the explanation of orthogonal), hence when you CYCLIC SHIFT the Zadoff-chu sequence(also called root sequence), you get another sequence which will have zero auto-correlation with the previous one i.e, they are orthogonal to each other.. look how easy it is to make two sequences orthogonal.

CAZAC = constant amplitude zero auto-correlation.

For more details, refer this http://jaekuryu.blogspot.in/2011/03/special-numbers-in-lte.html


Regards..
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