| Applicable Versions | NetSim Standard | NetSim Pro |
| Applicable Releases | v12 | v13 |
NetSim's 802.15.4 implementation runs on a 2 MHz channel, utilizing spread spectrum communication over a chip-stream of 2 million chips per second. In this chip-stream, 32 successive chips constitute one symbol, thereby yielding 62,500 symbols per second (62.5 Ksps; (2×106)32=62,500). Here, we observe that a symbol duration is 32×12×106=16 ?sec. Binary signaling (OQPSK) is used over the chips, yielding 232 possible sequences over a 32 chip symbol. Of these sequences, 16 are selected to encode 4 bits (24=16). The sequences are selected so as to increase the probability of decoding in spite of symbol error. Thus, with 62.5 Ksps and 4 bits per symbol, the IEEE 802.15.4 PHY provides a raw bit rate of 62.5×4=250 Kbps.
The frequency, modulation and chip rates are therefore fixed in NetSim per the 802.15.4 definitions.
Since NetSim is a packet simulation, the details of the modulation and chiprates are abstracted as a PHY data-rate. Data rate is fixed to 250 Kbps as per the standard. It is available in the 802_15_4.c file as shown below:
The modulation type also impacts the BER calculations as highlighted in the BERcalculation.c file shown below:
