Duty-cycling technique has been widely adopted in MAC protocols for wireless sensor networks to conserve energy. However, low duty-cycle also leads to limited throughput in most of existing solutions. In this paper, we propose iQueue-MAC to provide immediate yet energy-efficient throughput enhancement for dealing with burst or heavy traffic. Combined with CSMA/CA, iQueue-MAC makes use of queue length of each sensor node and allocates suitable TDMA slots to them for packets transmission. During light traffic period, no extra slots will be allocated; iQueue-MAC acts like other low duty-cycle MACs to conserve power. While in burst or heavy traffic period, iQueue-MAC senses the build up of packet queues and dynamically schedules adequate number of slots for packet transmission. We have implemented iQueue-MAC on STM32W108 chips that offer IEEE 802.15.4 standard communication. We set up several realworld experimental scenarios, including a 46 nodes multi-hop test-bed for simulating a general application, and conducted numerous experiments to evaluate iQueue-MAC, in comparison with other traffic adaptive duty-cycle protocols, such as multichannel version RI-MAC and CoSenS. Results clearly show that iQueue-MAC outperforms multi-channel version of RI-MAC and CoSenS in terms of packet delay and throughput.
Existing low-power MAC protocols only provide low throughput because of the fixed low duty-cycle. This often leads to poor performance when dealing with timeconstrained burst traffic. In this paper, we propose a new hybrid CSMA/TDMA MAC protocol, called Queue-MAC, that dynamically adapts the duty-cycle according to the current network traffic. The queue length of nodes is used as the network traffic indicator. When the traffic increases, the active CSMA period is accordingly extended by adding dynamic TDMA slots, allowing thus to efficiently handle burst traffic under real-time constraints. This protocol is implemented on the STM32W108 SOC chips and compared with both a fixed duty-cycle reference protocol and an optimized IEEE802.15.4 MAC protocol. Through extensive experimental measurements, we showed that our queuelength aware hybrid CSMA/TDMA MAC protocol largely outperforms the compared protocols. The proposed protocol can be easily implemented through slight adaptation of the IEEE802.15.4 standard. It presents an optimal bandwidth and energy allocation scheme according to the traffic to be carried. In fact, low-duty cycle, so low power consumption is preserved during light traffic load period, while high throughput is obtained during heavy burst load period.. 1
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