Zadoff–Chu quence in LTE

hacperhacper

最近看LTE相關文獻時
看到下面關於 Zadoff–Chu quence 的敘述
請問大家
對於一個  length-31  的  Zadoff–Chu quence, 為何 available sequences  是 31-1 = 30  呢？
我覺得應該是 31 個才對啊 (從 0 ~ M_{ZC}-1)



Instead, for sequence lengths larger than or equal to 36, corresponding to transmission bandwidths
larger than or equal to three resource blocks, the reference-signal sequences are defined as cyclic exten-
sions of Zadoff–Chu sequences of length M_{ZC} , where M_{ZC} is the largest prime number smaller than
or equal to the desired reference-signal sequence length. For example, the largest prime number less
than or equal to 36 is 31, implying that reference-signal sequences of length 36 are defined as cyclic
extensions of Zadoff–Chu sequences of length 31. The number of available sequences is then equal to
30 – that is, one less than the length of the Zadoff–Chu sequence. For larger sequence lengths, more
sequences  are  available.  For  example,  for  a  reference-signal  sequence  length  equal  to  72,  there  are  
70 sequences available.