Slotted ALOHA Systems Based on Multiple Access Schemes and Multiple Resources

Gain division multiple access (GDMA) is a multiple access scheme, where each user transmits its packet to a common base station through an independent fading channel. By applying GDMA to orthogonal frequency division multiplexing (OFDM) based slotted ALOHA system, we can have an efficient random access system, denoted OFDM-GDMA-ALOHA. High density signature code division multiple access (HDS-CDMA) can be regarded as combination of Q dependent GDMA systems where each GDMA is applied to one of the Q resources. By applying Q-resource HDS-CDMA to the OFDM based slotted ALOHA system, we have OFDM-HDS- Q-ALOHA. Under the condition of Q available resources, we compare the throughput performances of OFDM-GDMA- Q-ALOHA and OFDM-HDS- Q-CDMA, where OFDM-GDMA- Q-ALOHA is constructed by allowing each user to randomly choose one of the Q resources for transmitting the packet and then OFDM-GDMA-ALOHA is implemented for this resource.