# Evaluation of IEEE802.15.4g for Environmental Observations
## 2 Materials and Methods
### IEEE802.15.4g PHYs
These PHYs accept further parametrization, either by modifying the data rate (more information per symbol transmitted or more symbols per unit of time) and/or channel bandwidth. In this study, each PHY with a specific set of parameters is defined as radio setting and identified by an \"alias\". In the 863-870 MHz frequency band, a total of 31 radio settings have been tested. Table 1 describes the radio settings for all the combinations of parameters using FSK and provides an \"alias\" to each of them. Tables 2 and 3 provide the same information for OFDM and O-QPSK, respectively. Only for the FSK radio settings implementing \(\frac{1}{2}\) rate FEC, the actual data rate is halved, since every two bits sent by the radio correspond to 1 bit of information. For the rest of the radio settings, the data rates stated in Tables 1-3 are the data rates of the actual information leaving the radio. \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**PHY**} & **FEC** & \multirow{2}{*}{**Data Rate**} & **Ch. Spacing** & **Alias** \\  & **1/2 Rate** & & & \\ \hline
2-FSK & No & 50 kbps & 200 kHz & 2 FSK-50 \\
2-FSK & No & 100 kbps & 400 kHz & 2 FSK-100 \\
4-FSK & No & 200 kbps & 400 kHz & 4 FSK-200 \\
2-FSK & Yes & 50 kbps & 200 kHz & 2 FSK-FEC-50 \\
2-FSK & Yes & 100 kbps & 400 kHz & 2 FSK-FEC-100 \\
4-FSK & Yes & 200 kbps & 400 kHz & 4 FSK-FEC-200 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Radio settings using FSK modulation. The values of these parameters are defined in the standard [22]. Data rate values consider the amount of bits per second leaving the radio. In the case where FEC is used, 1 bit of information is encoded in 2 bits leaving the radio, therefore the information rate reduces to half. Channel spacing is the separation between the center of two adjacent channels. The “Alias” column provides an identifier to each group of parameters. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Parameter**} & **OFDM Opt. 1** & **OFDM Opt. 2** & **OFDM Opt. 3** & **OFDM Opt. 4** \\ \hline Channel spacing (kHz) & 1200 kHz & 800 kHz & 400 kHz & 200 kHz \\ Number of sub-carriers & 104 & 52 & 26 & 14 \\ MCS0 (kbps) - 4x freq. rep. & 100 kbps & 50 kbps & - & - \\ MCS1 (kbps) - 2x freq. rep. & 200 kbps & 100 kbps & 50 kbps & - \\ MCS2 (kbps) - 2x freq. rep. & 400 kbps & 200 kbps & 100 kbps & 50 kbps \\ MCS3 (kbps) - 2x freq. rep. & 800 kbps & 400 kbps & 200 kbps & 100 kbps \\ MCS4 (kbps) - No freq. rep. & - & 600 kbps & 300 kbps & 150 kbps \\ MCS5 (kbps) - No freq. rep. & - & 800 kbps & 400 kbps & 200 kbps \\ MCS6 (kbps) - No freq. rep. & - & - & 600 kbps & 300 kbps \\ Alias & OFDM1\(\sim\)datarate\(>\) & OFDM2\(\sim\)datarate\(>\) & OFDM3\(\sim\)datarate\(>\) & OFDM4\(\sim\)datarate\(>\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Radio settings using OFDM modulation. The values of these parameters are defined in the standard [22]. Channel spacing is the separation between the centers of two adjacent channels. OFDM channels group a number of sub-carriers, option 1 being the widest one (the most number of sub-carriers), option 4 the narrowest (the least number of sub-carriers). The data rate depends on the combination of the MCS (Modulation and Coding Scheme) value and the OFDM option. Frequency repetition identifies the number of sub-carriers encoding the same information. The “Alias” of each radio setting is used to identify each set of parameter, e.g., OFDM1-400 identifies the PHY using OFDM option 1 and MCS2. Using sub-GHz bands has two main drawbacks. First, license-free sub-GHz bands are not at the same frequency in all countries--unlike the 2.4 GHz ISM band--and each country/region makes its own selection of frequency to be assigned to unlicensed users:  
* In Europe, 863-870 MHz, with upcoming availabilities in the 870-876 MHz (early stages). * In the United States, 902-928 MHz. * In Japan, 922.4-928 MHz. Second, each country/region imposes (different) regulations to these sub-GHz bands.