I did some research. I’m not sure if this helps you or not.
n the previous part (1 out of 3) we discussed the relationship between the preamble format and the cell radius. In this delivery, we will discuss how the ZeroCorrelationZoneConfig parameter affects the cell radius.
The parameters ZeroCorrelationZoneConfig and RootSequenceIndex are used to generate 64 random access signatures in each cell (all these access signatures should be different in each cell). Both, the ZeroCorrelationZoneConfig and the RootsequenceIndex paramaters are broadcast in SIB2. The random access sequences are built via the selection of a Zadoff-Chu sequence (one out of 839) given by RootSequenceSequence and a cyclic shift (used 64 times to generate the 64 random access signatures from the Zadoff-Chu sequence selected). The cyclic shift is indirectly given to the UE by the parameter ZeroCorrelationZoneConfig, as shown in the table below (see columns two and three and note that the cyclic shift has limited values). The available cyclic shifts are listed in 3GPP TS 36.211 table 5.7.2.-2.
The cyclic shift is also related to the cell size. The relationship between the cyclic shift and the cell size is given by equation (1):
(NCS - 1) * (800 μs/839) ≥ RTD + Delay Spread (1)
In the equation, RTD stands for Round Trip Delay (twice the cell radius). Hence:
RTD = 2 R/c (2)
Then, the cell radius is given by:
R ≤ [c/2][(NCS - 1)(800 μs/839)-Delay spread] (3)
For instance, if we assume that ZeroCorrelationZoneConfig is 12, then from the table above, Ncs = 119. Furthermore, if the delay spread = 6 μsec, then the cell size will be approximately 15.97km. Note that the smaller the cyclic shift, the smaller cell size.
The delay spread in the equation above should be calculated by the RF engineer after a drive test is carried out in the areas of interest. The value of the delay spread is typically different for rural, suburban, urban and dense urban environments.