## 4 Implementation and Evaluation of the Mobile Social Music Karaoke System
### Experiment and Analysis  
In order to validate the proposed karaoke system, the performance of the user interface and mobile network stability with multiple devices were tested. The first experiment was to measure the accuracy of voice recognition while controlling the karaoke system. We utilized 4 smartphones and the voice commands consisted of mode selection, song and singer selection, and confirmation of starting and finalization. We collected voice recognition results while user groups were created and operated. During group singing mode, each user needed to select singing mode, specify the song, and confirm the selection. We obtained a total of 34 commands from 10 user sessions. As shown in Figure 9, the accuracy of the voice commands was 88% while the error of the voice commands was 12%. In other words, 30 of the 34 commands were recognized, while the remaining 4 commands failed. The 4 errors include system and timing errors in mode selection. In spite of such errors, the total recognition rate was high because the command was composed of very simple words to control the system. In addition, the network stability of smartphones was tested during music sharing. In order to support the social karaoke system, it is important to support real-time music streaming from a singing user to other listening users. For this purpose, two experiments were conducted to evaluate the singing voice packet transmission/reception performance between users' smartphones, which is the most important function in karaoke services. The first experiment was about transmission/reception performance in the minimum group environment consisting of two users and the second experiment was about the voice packet transmission/reception performance of larger groups. In the first experiment to evaluate the network streaming performance, the smallest group of two people was formed and each performance was tested in singing and listening, respectively. Then, packet transmission between the members, UDP relay, and reception characteristics were measured. As shown in the experiment result in Figure 10, the sending smartphone transmitted 1.6k voice recordings and data packets every 0.1 s, and the UDP server received the data packets from the singer and retransmitted them to the registered group members. It could be seen that the receiving user's smartphone received and played the voice packets at 0.1 s (\(+/-20\) ms). That is, the transmission/reception is carried out at the rate of 10 packets/s. Although there were slight delays in reception, since karaoke users are usually far away from each other, the slight delays had almost no effect on listening to the music. In the second experiment, the performance of singing data streaming was evaluated by increasing the number of group members. For this purpose, 3 small groups were tested by increasing the number of group users from 2 to 4. Four different types of smartphones,  
Figure 9: Evaluation of the accuracy of the voice interface. including recently released smartphones and low-performance smartphones, were utilized in order to test the possibility of smartphone performance. During each test, the 'Sing Together' mode was initiated, and small groups consisting of 2, 3, or 4 persons were formed. Thus, one user was singing and other users were listening. The smartphones were in the same location, where 5G Wi-Fi was covered, to validate the network performance between the social music cloud and smartphones. To evaluate the streaming transmission/reception performance, the same song was repeatedly sung and listened to by individual smartphones in turns, and the voice packet transmission/reception performance was measured. The sending smartphone of a singer transmitted 1.6k voice recordings and data packets every 0.1 s, and the UDP server received the data packets from the singer's smartphone and retransmitted them to the registered group members. As with the experiment result shown in Figure 11, while voice packets were transmitted at regular intervals, large deviations occurred in reception.