## 3 Measurement Results of System Evaluation
### System Performance Evaluation
We expect this feature to help the iTDS users with better spatial separation between their tongue commands, allowing for achieving a higher level of accuracy and increased number of tongue commands. Figure 14: Performance comparison among the eTDS, the iTDS-v1, and the iTDS-2 with (**a**) the deviation at maze-navigation task; (**b**) the completion time at the maze-navigation task; (**c**) the throughput at the center-out task; and (**d**) FOM\({}_{1}\) for six-command classification. Table 2 summarizes the performance evaluation results of the iTDS-2 in the center-out tapping task and compares them with the iTDS-1, the eTDS, the ITCS, the iTCS, the sup-n-puff and a computer mouse using results from previous publications [12, 25, 57]. The iTDS-2 shows 73% improved performance over the sup-n-puff, which is one of the most popular ATs among those for tetraplegia. The computer mouse still outperforms the iTDS-2 by a factor of 3 to 1. However, this gap is expected to narrow as the iTDS users gain more experience and future versions of the iTDS become smaller, while using more power-efficient circuitry. Development of more advanced sensor signal processing algorithms to extract more information from the raw magnetic sensor data, while attenuating external interference and correcting user errors will also help with this trend. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Specifications** & **iTDS-2** & **iTDS-1 [12]** & **iTCS [17]** & **Optical Tongue** \\ \hline \multirow{2}{*}{**Process**} & 0.35-\(\mu\)m std. & 0.5-\(\mu\)m std. & \multirow{2}{*}{Off-the-shelf} & \multirow{2}{*}{Off-the-shelf} \\  & CMOS & CMOS & & \\ \hline
**Die Area** & 2.4 \(\times\)5.0 (mm\({}^{2}\)) & 3.8 \(\times\)3.7 (mm\({}^{2}\)) & - & - \\ \hline \multirow{4}{*}{**Sensor**} & **VDD** & 1.8 (V) & 1.8 (V) & - & - \\ \cline{2-6}  & **Type** & Magnetoresistive & & Inductive & Infrared proximity \\ \cline{2-6}  & **Channel** & 12 & 12 & 18 & 4 \\ \cline{2-6}  & **Sensitivity** & 1.8 (mV/gauss) & 1.8 (mV/gauss) & - & 0.2–0.5 (V/mm) \\ \cline{2-6}  & **Sampling** & 64 (Hz) & 64 (Hz) & 30 (Hz) & 90 (Hz) \\ \hline \multirow{4}{*}{**RF**} & **Frequency Band** & 27/432 (MHz) & 27/432 (MHz) & 2.4 (GHz) & \\ \cline{2-6}  & **Switching between Bands** & Automatic & Manual & Single band & \\ \cline{2-6}  & **Data rate** & 250 (kbps) & 64 (kbps) & - & \\ \hline \multirow{4}{*}{**Power**} & **P\({}_{\text{avr}}\) (27 MHz)** & 2.8 (mW) & 3.7 (mW) & - & \\ \cline{2-6}  & **P\({}_{\text{avr}}\) (432 MHz)** & 3.3 (mW) & 4.7 (mW) & & \\ \cline{2-6}  & **Battery Type** & Li-Ion 50 mAh & Li-Ion 45 mAh & Li-Ion 20 mAh & Hardwired \\ \cline{2-6}  & **Battery** & 27.3 (h), & 17.2 (h), & 15 (h) & \\ \cline{2-6}  & **Lifetime** & worst case & worst case & & \\ \hline \multirow{4}{*}{**Prototype**} & **Shape** & Arch shape & Palatal shape & Palatal shape & Palatal shape \\ \cline{2-6}  & **Size** & 54 \(\times\)28 \(\times\)15 & 49 \(\times\)42 \(\times\)15 & 35 \(\times\)25 \(\times\)15 & 41 \(\times\)38 \(\times\)15 \\ \cline{2-6}  & **Size** & (mm\({}^{3}\)) & (mm\({}^{3}\)) & (mm\({}^{3}\)) * & (mm\({}^{3}\)) * \\ \cline{2-6}  & **Volume** & 12 (mL) & 20 (mL) & - & - \\ \cline{2-6}  & **Weight** & 30 (g) & 75 (g) & - & - \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of specifications of the iTDS-2 and benchmarking with other intraoral tongue-operated ATs [12, 14, 17]. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Specifications** & **iTDS-2** & **iTDS-1 [12]** & **eTDS [25]** & **ITCS [57]** & **Sip’n’Puff [25]** & **Mouse [25]** \\ \hline Throughput (bits/s) & 1.25 & 0.83 & 1.48 & 0.85 & 0.72 & 3.66 \\ Number of commands & 6 & 6 & 6 & 8 & 4 & - \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of performance of the iTDS-2 for a computer access task and comparison with iTDS-1, eTDS, ITCS, sup-n-puff, and mouse [12, 25, 57].