Efficient MAC protocol design for wireless sensor networks 無線センサーネットワークのための有効なMACプロトコルに関する研究
Efficient MAC protocol design for wireless sensor networks
The past two decades have seen increasing interests in the field of wireless sensor networks(WSNs), which have potential applications covering all aspects of the human life. The majorissue in WSNs is power conservation since wireless sensors are usually battery-powered.In a typical sensor node, the wireless interface consumes the largest share of the powerbudget. Hence, an energy efficient medium access control (MAC) protocol is vital. The MACprotocol always adopts the duty cycling mechanism to reduce idle listening, which is the mostsignificant energy wastage. The mechanism, however, has negative effects on latency andthroughput performance. Meanwhile, an increasing number of prospective applications notonly imposes requirements on energy efficiency but also on other Quality of Services (QoS)parameters. Therefore, it is great of importance to design new efficient MAC protocols,which meet the energy efficiency and QoS requirements.We first focus on designing energy efficient, low latency MAC protocols for low data rateWSNs. The traditional approach is letting a duty cycling MAC protocol forward packetsvia multiple hops in a cycle, i.e., the multi-hop MAC. However, the original multi-hop MACprotocol incurs a large control overhead, and a so-called long listening period problem. Wepropose a low latency, low control overhead MAC protocol (the LO-MAC), which overcomesthe mentioned disadvantages by exploiting the physical properties of wireless channel. LO-MAC introduces a new traffic adaptive scheme based on carrier sensing characteristics. Thescheme effectively controls the length of listening period following the traffic load. Moreover,LO-MAC takes full advantages of the broadcast nature and lets a packet containing diffierentmeanings during its transmission. Therefore, the number of transmitting packets and thecontrol overhead is significantly reduced.Secondly, we introduce an approach in designing efficient MAC protocols for dynamic loadenvironments. We propose MAC2 protocol, a novel Multi-hop Adaptive MAC protocol withpacket Concatenation. MAC2 achieves a better performance than a state-of-the-art protocolin terms of energy efficiency, low latency and high throughput. The proposed protocolcontrols the adaptation to the traffic load by combining a signalling traffic adaptive schemeand a demand wakeup manner. The scheme and the manner are based on a synchronizationprocess and a proportional mapping function, respectively. Besides that, the protocol has aconcatenation scheme, which concatenates several queued packets into a bigger one beforesending out of a node. The concatenation scheme reduces not only the control overhead butalso the average latency. Additionally, MAC2 is numerically optimized to achieve minimumlatency and guarantee no data transmission collision.Finally, we also target the dynamic load environments, but take an asynchronous approachof the efficient MAC design. We propose an Asynchronous MAC protocol with QoS awareness(the AQ-MAC), which is energy efficient and provides different QoS levels to relevant typesof traffic. AQ-MAC achieves energy efficiency and collision avoidance by utilizing a receiver-initiated transmission and the concatenation scheme derived from MAC2. Moreover, AQ-MAC adopts the diffierentiate service (DiffServ) model to provide QoS. Data packets areprovided diffierent transmission strategies depending on their levels of importance.