Pattern (Custom IQ)
sets the synchronization pattern that the demodulator uses when Pattern Search Enable is selected.
The minimum pattern length is recommended as follows:
Minimum of 3 symbols or log2(constellation state count). Examples given below for expected minimum pattern length for reliable synchronization when using an arbitrary constellation definition assuming sufficiently randomized data symbols:
| Format | Minimum (symbols) | Minimum (bits) |
| QPSK Quadrature phase shift keying (4 states) | 3 | 6 |
| 16QAM (16 states) | 4 | 16 |
| 64QAM (64 states) | 6 | 36 |
| 256QAM (256 states) | 8 | 64 |
Symbols and Search Pattern
The search pattern is entered in binary only (‘1’ and ‘0’ ), regardless of the modulation format.
The demodulator can search only for patterns that are a multiple of the number of bits-per-symbol (see below).
The demodulator can only search for patterns that are a multiple of the number of bits-per-symbol. Internally, the demodulator assembles the pattern into an integer number of symbols. When the demodulator assembles the final bits in the search pattern, if there are not enough bits to form a symbol, the demodulator ignores the final bits.
For example, if the number of bits/symbol is 4 (as with 16 QAM Quadrature Amplitude Modulation), the number of bits in the pattern should be a multiple of four. If the search pattern contains 18 bits, the demodulator ignores the last two bits. In other words, the demodulator uses only the first 16 bits during the pattern search and constellation synchronization.
See Also
