Contiki:RDC &CoAP

Paper:

<The ContikiMAC Radio Duty Cycling Protocol>

<A Low-power CoAP for Contiki>

主要讲了RDC中的三个优化措施：

1、Contiki Timing；

2、Packet Detection and fast  sleep；

3、Transmission phase-lock。

讲述了RDC层在contiki中的作用。及实现的原理。如下：

RDC：Radio duty cycling

ContikiMAC:uses a power efficient wake-up mechanism with a set of timing constraints to allow device to keep their transceivers off. reduce the consumption.

ContikiMAC is designed to be simple to understand and implement. ContikiMAC uses only asynchronous mechanisms, no signaling messages, and no additional packet headers. ContikiMAC packets are ordinary link layer messages. ContikiMAC has a significantly more power-efficient wake-up mechanism that previous duty cycling mechanisms. This is achieved by precise timing through a set of timing constraints. In addition, ContikiMAC uses a fast sleep optimization, to allow receivers to quickly detect false-positive wake-ups, and a transmission phase-lock optimization, to allow run-time optimization of the energy-efficiency of transmissions.

The wake-up mechanism:

Figure 1: ContikiMAC: nodes sleep most of the time and periodically wake up to check for radio activity. If a
packet transmission is detected, the receiver stays awake to receive the next packet and sends a link layer acknowledgment. To send a packet, the sender repeatedly sends the same packet until a link layer acknowledgment is received.

Broadcast Transmissions wake-up mechanism

Figure 2: Broadcast transmissions are sent with repeated data packets for the full wake-up interval.

Figure 3: The ContikiMAC transmission and CCA timing.

ti: the interval between each packet transmission.
tr: the time required for a stable RSSI, needed for a stable
CCA indication.
tc: the interval between each CCA.
ta: the time between receiving a packet and sending the
acknowledgment packet.
td: the time required for successfully detecting an ac-

knowledgment from the receiver.

Figure 4: A packet transmission must be long enough so that it does not fall between to subsequent CCAs.

Packet Detection and Fast Sleep

Figure 5: The ContikiMAC fast sleep optimization: if a silence period is not detected before tl, the receiver goes back to sleep. If the silence period is longer than ti, the receiver goes back to sleep. If no packet is received after the silence period, even if radio activity is detected, the receiver goes back to sleep.

这些是ContikiMAC的基本原理，

其中包括了，我们常说的休眠唤醒机制。

A Low-power CoAP for Contiki:

Figure 7. Low-power operation is done only in the Radio Duty Cycling (RDC) layer, thereby separating low-power operation from the application layer. This reduces complexity and follows the layered architecture that allowed the Internet to evolve.