Performance of Slotted-Aloha over TH-UWB

In the IEEE 802.15.4a UWB-PHY standard for Low Rate WPANs (LR-WPANs), the UWB-PHY provides Time-Hopping (TH) to enable multiple users to transmit simultaneously, thereby potentially increasing the overall system throughput. However, the intrinsic properties of the impulse-based UWB renders existing narrowband MAC protocols which make use of carrier sensing unsuitable for use in UWB systems. In the standard, Aloha has been proposed as the MAC protocol. In this paper, we study the throughput performance of slotted-Aloha, an enhanced version of the Aloha MAC protocol, over the TH-UWB physical layer, using both theoretical analysis and simulations. Our results show that random time-hopping can be detrimental to the throughput performance of the network. An optimal method of assigning TH codes to the different symbols in each packet is necessary in order to exploit the benefits of time-hopping, which can potentially allow concurrent transmissions in multiuser systems.