Delay-Bounded OFDMA Transmission in Wireless Sensor Networks with Mixed Delay-Bounded Flows

Recently, the demand for data transfer with low loss and within permissible delays in wireless sensor networks that must be operated at low costs, e.g., for system control in smart factories, has increased. For such low-cost operations, it is essential to use the IEEE 802.11 standard; however, its random channel access makes it difficult to reduce frame transfer delays to permissible values. Orthogonal frequency-division multiple access (OFDMA) transmission, introduced by IEEE 802.11ax, enhances the feasibility of satisfying the demand because OFDMA transmission is performed by a sink in a centralized manner, and multiple frames are transferred simultaneously without collision. However, no OFDMA transmission methods have been proposed to suppress the transfer delays of aperiodic ally generated delay-bounded frames from source nodes to their sinks within permissible values, following the 802.11ax specification that OFDMA transmission is triggered when the sink obtains a transmission opportunity based on CSMA/CA. In this paper, we propose a delay-bounded frame transmission method with OFDMA to suppress frame transfer delays within permissible values while reducing frame loss. In this method, the start time of OFDMA transmission of delay-bounded frames is deferred within their permissible delays. This expects that new delay-bounded frames are generated during the deferral period, and more delay-bounded frames including the newly generated ones are transmitted without collision via OFDMA. Extensive simulation evaluations demonstrate that the proposed method transfers delay-bounded frames within their permissible values, where no samples exceed the deadlines among 10⁷ transfer trials. In addition, data frame loss is reduced compared with a representative related delay-aware OFDMA transmission method, which aims to minimize the average data upload time, and another benchmark that transfers delay-bounded frames with maximum prioritization and efficiency.