Research on an uplink carrier sense multiple access algorithm of large indoor visible light communication networks based on an optical hard core point process

Abstract

The IEEE 802.15.7 protocol suggests that it could coordinate the channel access process based on the competitive method of carrier sensing. However, the directionality of light and randomness of diffuse reflection would give rise to a serious imperfect carrier sense (ICS) problem [e.g., hidden node (HN) problem and exposed node (EN) problem], which brings great challenges in realizing the optical carrier sense multiple access (CSMA) mechanism. In this paper, the carrier sense process implemented by diffuse reflection light is modeled as the choice of independent sets. We establish an ICS model with the presence of ENs and HNs for the multi-point to multi-point visible light communication (VLC) uplink communications system. Considering the severe optical ICS problem, an optical hard core point process (OHCPP) is developed, which characterizes the optical CSMA for the indoor VLC uplink communications system. Due to the limited coverage of the transmitted optical signal, in our OHCPP, the ENs within the transmitters' carrier sense region could be retained provided that they could not corrupt the ongoing communications. Moreover, because of the directionality of both light emitting diode (LED) transmitters and receivers, theoretical analysis of the HN problem becomes difficult. In this paper, we derive the closed-form expression for approximating the outage probability and transmission capacity of VLC networks with the presence of HNs and ENs. Simulation results validate the analysis and also show the existence of an optimal physical carrier-sensing threshold that maximizes the transmission capacity for a given emission angle of LED.

Hybrid CSMA/CA and HCCA uplink medium access control protocol for VLC based heterogeneous users

“…Multiple studies have proposed handling of interference, maximizing throughput, hidden node, and exposed node problems by modifying the CSMA/CA mechanism [5,18,19]. For example, [5] integrates WiFi and LiFi by reducing interference without considering the MAC layer.…”

MSAM: Modular Statistical Analytical Model for MAC and Queuing Latency of VLC Networks under ICS Conditions

“…The authors of [17] develop a mathematical model to assess the outage probability and transmission capacity of the uplink communications of multi-point to multipoint VLC networks operating the CSMA-CA mechanism of 802.15.7. This model assumes that all VLNs within a VLC network are scattered according to the homogenous Poisson point process.…”

“…However, one of the main flaws of the CSMA-CA is the so-called Imperfect Carrier Sensing (ICS) [14][15][16][17], which characterises the situations under which the carrier sensing mechanism is insufficient to limit packet collisions, i.e., the exposed node problem and hidden node problem. ICS has detrimental effects on the performance of a wireless network operating CSMA/CA, as it can lessen the throughput, enlargement packet's queuing and medium access delay, as well as degrading channel utilisation.…”

“…ICS has detrimental effects on the performance of a wireless network operating CSMA/CA, as it can lessen the throughput, enlargement packet's queuing and medium access delay, as well as degrading channel utilisation. Interestingly, these effects become more detrimental in VLC due to the narrow sensing range of optoelectronic devices and the directionality of the light beams [16,17]. Evaluating the effects of the ICS on the performance of IEEE 802.15.7 CSMA-CA is a challenge as ICS results from the interaction amongst several stochastic processes; specifically, the stochastic processes that generate packets, manage durations between two consecutive CSMA-CA channel assessments and outline the directivity of light beams.…”

“…Evaluating the effects of the ICS on the performance of IEEE 802.15.7 CSMA-CA is a challenge as ICS results from the interaction amongst several stochastic processes; specifically, the stochastic processes that generate packets, manage durations between two consecutive CSMA-CA channel assessments and outline the directivity of light beams. Several works have been devoted to overcoming this challenge by employing one or more simplification assumptions, such as a transmitter that can see all ongoing transmissions from other nodes [18][19][20][21][22], or when the traffic generated by a node is set in accordance with the channel status, as proposed in [16,17].…”