Throughput performance of slotted nonpersistent CSMA with an adaptive array

In conventional slotted nonpersistent CSMA, a packet is generated during a slot, and the terminal senses the channel at the beginning of the next slot. It is known that slotted CSMA has better throughput performance than unslotted CSMA. However, because of the propagation delay, if more than two packets are generated during the same slot, later packets might sense the channel as idle, and they will cause a conflict. Furthermore, when the CSMA modes are used in practical radio communication systems, the hidden-terminal problem should be considered. We propose a slotted nonpersistent CSMA with an adaptive array at the receiver to improve throughput performance. In our proposed model, in order for an adaptive array to distinguish packets during the same time slot and acquire the first arriving packet, the starting times of packet transmission from all terminals are randomized over the interval which is the difference between the slot width and the packet width. First, we analyze the performance of the throughput and the average number of transmissions and schedulings. We also evaluate the performance by means of computer simulation in order to consider the hidden-terminal problem in the CSMA mode. It is found that the theoretical results of the proposed model agree well with the computer simulated results, and the proposed model attains higher throughput and smaller average numbers of transmissions and schedulings than the conventional slotted nonpersistent CSMA. It is also shown that the performance of the proposed model with an adaptive array due to hidden-terminal degradation is smaller compared to the conventional CSMA.