iQueue-MAC：一种流量自适应的多信道MAC协议

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"本文介绍了一种适用于无线传感器网络(WSNs)的动态时隙分配的流量自适应多信道介质访问控制(MAC)协议——iQueue-MAC。该协议旨在解决低功耗周期性工作模式下系统寿命延长与吞吐量、延迟之间的矛盾，特别是在变量流量模式下。" 在无线传感器网络中，为了延长系统的工作寿命，通常采用低功耗周期性工作策略。然而，这种方法会导致通信吞吐量受限和延迟增加，当网络流量变得不规则或突发时，问题更为突出。iQueue-MAC协议是为了解决这一问题而设计的，它是一种结合了载波监听多址(CSMA)和时分多址(TDMA)的混合型MAC协议。在轻负载情况下，iQueue-MAC利用竞争型CSMA机制，提供低延迟并允许分散传输，这有利于提高网络效率。当网络流量增加时，发送端会检测到形成回路的信号，此时iQueue-MAC会切换到无竞争的TDMA机制，动态分配传输时隙。通过这种方式，iQueue-MAC减少了数据包缓冲，降低了数据包延迟，同时结合了TDMA的高效性和CSMA的灵活性。本文还展示了iQueue-MAC如何在单信道和多信道模式下运行，并将其与其他参考WSN协议一起在SIM32W108芯片上实现，进行比较。实验结果显示，在轻负载情况下，iQueue-MAC表现出与对照协议类似的性能指标。 iQueue-MAC协议的创新之处在于其动态适应性，可以根据网络条件灵活调整操作模式，有效地平衡了能量效率、吞吐量和延迟之间的关系。这对于动态变化的无线传感器网络环境至关重要，因为它能够确保在网络流量波动时仍然保持良好的通信性能。此外，多信道支持使得iQueue-MAC能够利用多个频段进行通信，进一步提高了网络容量和可靠性。 iQueue-MAC协议是无线传感器网络中一种实用的流量自适应MAC解决方案，它克服了传统低功耗策略的局限性，为WSNs提供了更高效、延迟更低的通信方式，特别适用于变量流量环境。这种技术对于未来WSN的设计和优化具有重要的参考价值。

protocol, receivers are assigned with slots in which the

senders need to compete for transmissions. In EM-MAC

[26], each node uses a pseudo-random function to dynami-

cally decide its wake up time and channel sequence, aiming

to spread the trafﬁc load to different channels. TMCP

[27] divides the network into several sub-trees and allo-

cates unique channels to every sub-tree. In [28], a new

frequency allocation methodcalledFAVORthatjointly

takes into account frequency and distance in a continu-

ous manner is proposed to further enhance the through-

put of multi-channel WSNs. WirelessHart [29], ISA100

[30] and the new IEEE802.15.4e standard [31] are cur-

rently the most popular wireless solutions for industrial

applications. These standards utilize Time Slotted Chan-

nel Hopping (TSCH) technique to provide deterministic

transmissions and robustness. However, currently, they

lack link scheduling algorithms which are crucial for

assigning s lots/frequency resources in WSNs.

Compared to existing solutions, iQueue-MAC mitigates

contention and retransmission by shifting intensive senders

into the TDMA slots period. The senders’ queue-length

information is piggybacked on data packet, so that the time

slots are assigned right upon queueing detection. The crux of

iQueue-MAC is an efﬁcient closed loop control mechanism

that uses nodes’ queue-length as the measured output and

uses adaptive time slots assignment as the control input to

mitigate packets queueing. In fact, prior to iQueue-MAC, the

similar idea emerged in the FTT (Flexible Time-Triggered)

paradigm [32] which is originally proposed for CAN and

Ethernet, iQueue-MAC makes it more suitable for WSNs.

3DESIGN OF IQUEUE-MAC

In this section, we elaborate the basic scheme of iQueue-

MAC and discuss the main features of the protocol.

3.1 The Basic Scheme

iQueue-MAC mainly targets data collection applications

(e.g., enviroment/process monitoring and target tracking)

that have tree or DODAG topologies. After the network

deployment, upper layer protocol like RPL or LEACH is

responsible for organizing the topology of the network,

forming clusters and selecting cluster heads (or, branch

nodes in the tree topology). By applying iQueue-MAC, clus-

ter heads play the ”router” role of the protocol, while son

devices play the ”simple node” role. Simple nodes are associ-

ated and locally synchronized with neighbor routers through

their beacons. Routers collect data packets from simple

nodes and forward them to the sink in the multi-hop manner.

All the devices are equipped with half duplex radios.

iQueue-MAC uses asynchronous duty-cycle among neigh-

bor routers without the need of global synchronization.

The basic idea of iQueue-MAC is to use adaptive slots

assignment to deal with heavy/burst trafﬁc loads, thus to

gain high throughput and efﬁciency. To this end, iQueue-

MAC piggybacks the sender’s queue-length information

onto the data packet to accuratel y inst ruct the c ommu ni-

cation requirement. Fig. 1 shows the data packet structure

of iQueue-MAC. The ﬁrst byte ﬁeld of the data packet is

set to be the queue-length indicator without violating the

existing IEEE 802.15.4 standard. In this way, e ach time

when a simple node sends a data packet to a router, the

simple node implicitly informs the router for the potential

slots assignment and instructs exactly how many slots the

simple no de needs.

In the protocol, each router periodically broadcasts bea-

cons to maintain its local superframe structure. The main

principles of iQueue-MAC are implemented on the router

side. For saving energy, simple nodes only wake up and get

synchronized to the router when they have packets to trans-

mit (we will see later that they can periodically wake up if the

optional downstream communication must be supported).

Note that a simple node can be dynamically associated to a

router after hearing its beacon. We can choose either the ﬁrst

received beacon from the routers in its reception range, or the

best one which provides the best link quality. If the ﬁrst asso-

ciated router fails, a simple node can join another neighbor

router’s community by locating the latter’s beacon.

Fig. 2 shows the superframe structure of iQueue-MAC.

The superframe is started by a beacon and contains a sub-

frame period, a short contention access period CP, and a

burst transmission period TP. The subframe period is fur-

ther composed of a sleeping period (SP) and a variable

TDMA period (vTDMA). The vTDMA is made up of slots

that are assigned to speciﬁc simple nodes. Its duration is a

variable value which is associated with the number of allo-

cated slots. In the sleeping period, all of the devices turn off

to sleep, while the router still wakes up periodically based

on a predeﬁned wake-up interval to check for potential pre-

amble packets from other routers (dotted lines in the SP

period). According to the application requirements, the

wake-up interval can be adjusted to obtain either extreme

low duty-cycle or quick event reaction capability. When

the network is with light trafﬁc, there are no allocated slots,

the subframe consists of only SP. When trafﬁc grows, more

slots will be accordingly allocated (we will see later how

slots allocation is done), which results in longer vTDMA

and shorter SP. To avoid beacons from continuously collid-

ing among nearby routers, before a new superframe cycle

begins, a router sets the subframe duration to a random

value with a predeﬁned average S and varying between

0:5  S and 1:5  S, similar to RI-MAC.

The contention access period CP follows the subframe

and works as the initial entrance window for simple nodes.

Simple nodes that have pending packets ﬁrst use CSMA/

CA mechanism to compete for transmissions in CP. With

the piggybacked queue-length indicator, the packets trans-

mitted during CP implicitly inform the router to allocate

slots for potential pending packets. To reduce the

Fig. 1. The data packet structure.

Fig. 2. The superframe structure of iQueue-MAC.

1602 IEEE TRANSACTIONS ON MOBILE COMPUTING, VOL. 15, NO. 7, JULY 2016

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