PRACH Root Sequence Planning
1. Zadoff-Chu Sequence length=839 in LTE.
2. Every Cell needs 64 preambles.
3. To generate the needed 64 preamble for each cell, we use cyclic shift(CS):
x_{u,v}(n)=x_{u}((n+C_v) mod N_ZC), 0<=n<N_ZC
, where u: physical root sequence index; C_v: CS; N_ZC: Zadoff-Chu Sequence length
4. We need a larger CS for a larger cell radius, since the larger the cell radius, the longer the t
5. From 4, we need more root sequences to generate the needed 64 preambles for a larger cel
6. But too many root sequences used in a cell is not good because sequences obtained from c
not orthogonal.
Therefore, orthogonal sequences obtained by cyclically shifting a single root sequence shoul
sequences;
additional ZC root sequences should be used only when the required number of sequences (6
of a single root sequence.
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