The IEEE 802.15.4 standard enables device level wireless connectivity in personal area networks. Its medium access control (MAC) protocol supports the exclusive use of a wireless channel through guaranteed time slots (GTS). However, the bandwidth underutilization problem occurs in GTSs when the used bandwidth is less than the available. In addition to the standard GTS allocation scheme, two other alternatives, namely i-GAME and granulated allocation scheme, have been proposed. This paper presents a performance comparison study of the three GTS allocation schemes using network calculus.