无线传感器网络的MAC协议精华

需积分: 3 200 浏览量更新于2024-07-31 收藏 1.18MB PDF 举报

"mac essentials - CDMA和TDMA融合算法在无线传感器网络中的应用" 在无线通信领域，MAC（Medium Access Control）协议是至关重要的，它管理着设备如何共享无线信道，避免冲突并高效传输数据。"mac essentials" 主题中提到的CDMA（Code Division Multiple Access，码分多址）和TDMA（Time Division Multiple Access，时分多址）是两种不同的无线通信技术，它们在早期的移动通信系统中广泛使用。 CDMA是一种通过使用不同的编码序列来区分不同用户的技术，每个用户的数据在相同的频率上发送，但通过独特的编码进行区分，从而实现多用户同时通信。这种技术的优点在于抗干扰性强，容量大，但实现起来相对复杂。 TDMA则是将时间划分为多个时隙，每个用户分配一个时隙进行通信，这样在同一频率上可以轮流为多个用户提供服务。这种方法简化了硬件设计，但对时间同步的要求较高。在无线传感器网络（WSNs）中，由于节点数量众多、电池供电且需要长时间无维护运行，因此对MAC协议有特殊的需求。现有的WSN MAC协议主要关注降低能量消耗，因为这直接影响到网络的生存时间。论文"MAC Essentials for Wireless Sensor Networks"深入探讨了WSN MAC协议的设计原则和挑战，以及现有方案的优缺点。作者Abdelmalik Bachir、Mischa Dohler、Thomas Watteyne和Kin K. Leung详细分析了如何在资源受限的环境中优化MAC协议，以实现更高效的能量利用。他们指出，WSN MAC协议设计时通常需要考虑以下因素： 1. 能量效率：由于WSN节点通常由电池供电，因此MAC协议必须尽可能减少不必要的能量消耗，例如通过休眠模式、低功耗通信和高效调度。 2. 网络寿命：通过优化数据传输策略和功率控制，延长网络的整体工作时间。 3. 可靠性：在高干扰环境下确保数据的准确传输，可能需要采用错误检测和纠正机制。 4. 容量和延迟：在满足低功耗要求的同时，提供足够的网络容量和合理的传输延迟。 5. 灵活性和可扩展性：随着网络规模的变化，MAC协议应能适应不同的部署场景和节点密度。 6. 安全性：考虑到WSN可能面临的攻击，MAC协议需要具备一定的安全特性，如防止窃听和篡改数据。 7. 自组织能力：WSN节点应能自我配置和自我修复，因此MAC协议需要支持动态调整和故障恢复。通过对CDMA和TDMA等传统技术的融合和改进，可以开发出更适合WSN的MAC协议。例如，结合两者的优点，创建一种新的多址接入方法，以提高频谱效率，同时降低功耗。 "mac essentials" 提供了对WSN MAC协议的深入理解，强调了在有限资源条件下优化协议设计的重要性，并指出了未来的研究方向，包括新兴技术如认知无线电、软件定义网络等如何影响和改进MAC协议。这些研究不仅对无线传感器网络，也对整个物联网（IoT）领域的通信效率和可持续性具有重要意义。

BACHIR et al.: MAC ESSENTIALS FOR WIRELESS SENSOR NETWORKS 227

TABLE I

UMMARY OF MAC IMPROVEMENTS FOR CANONICAL SOLUTIONS.

Function Protocols

Reducing Collisions CSMA/CA [17], MACA [22], Sift [24]

Reducing Overhead CSMA/ARC [19]

Reducing Overhearing PAMAS [25]

Reducing Idle Listening PSM [26]

the trafﬁc exchange. Note that the latency issue can be

alleviated because the node can switch to normal mode

when it expects high activity periods.

In multihop ad hoc networks with no infrastructure, there is

no central node being active in permanence to coordinate and

manage sleeping periods of the other nodes. This complicates

the task o f letting nodes sleep without causing deafness.

From the above discussed protocols, which have been sum-

marized in Table I, it becomes clear that WSNs require very

speciﬁc MAC protocols that ought to be designed taking their

peculiarities into account. In the reminder of the paper, we

explore the key ideas and the main energy efﬁcient protocols

available in the literature. Since WSNs are highly a pplica-

tion tailored [7], we ﬁrst dwell on Scheduled Protocols in

Section III wh ich are optimized for periodic high-load trafﬁc

(typical to e.g. multimedia applications); second, we deal with

Protocols with Common Active Periods in Section IV that are

well suited for medium-load trafﬁc scenarios (typical to e.g.

industrial applications); third, we discuss Preamble Sampling

Protocols that are the most convenient for rare reporting events

in Section V (typical to e.g. metering application s); and ﬁnally

we will also expose some hybrid protocols in Section VI which

combine the beneﬁts of several protocols. Since we divert from

the typical MAC taxonomy, we also expose switching points

between these protocols according to our trafﬁc-dependent

taxonomy in Section VI-B6.

III. S

CHEDULED PROTOCOLS

A. Basic Idea

Periodic and high-load trafﬁc is most suitably accommo-

dated by means of reservation-based protocols, i.e. those

which build a speciﬁc schedule. Generally, in the context of

WSNs, such protocols are variants of TDMA (Time Division

Multiple Access) combined with FDMA (Frequency Division

Multiple Access) where different time slots and frequency

channels can be used by different nodes. TDMA is attractive

because - onc e the schedule is set up - there are no collisions,

no overhearing, and minimized idle listening. In addition,

TDMA offers bounded latency, fairness and good throughput

in loaded (but not saturated) trafﬁc conditions.

The central concern of TDMA type protocols is how to set

up and maintain a speciﬁc schedule. To this end, three methods

are u sed in the context of WSNs:

• Scheduling of communication links: This fairly tra-

ditional approach sets up a unique slot dedicated to a

speciﬁc sender and speciﬁc receiver, thereby minimizing

idle listening and eliminating collisions and overhearing.

Since transmitter and receiver know exactly when to wake

up, this is the most energy efﬁcient solution given the

schedule is set up and that packets need to be transmitted;

however, varying trafﬁc conditions, imprecise clocks and

network dynamics require new schedules to be set up

which incurs large overheads.

• Scheduling of senders: In this approach the slot is

speciﬁed which is used by the sender which requires

all receiving nodes to listen. It hence minimizes idle

listening, eliminates collisions and r educes overheads to

a certain extend (since any changes at the receiving side

remain transparent to the established schedule); however,

overhearing remains a problem of such an approach.

A node, however, m ay minimize overhearing further

through header ﬁltering, i.e. when the packet is destined

to another node, the receiver goes back sleeping during

that slot.

• Scheduling of receivers: Here, the receiving slots are

speciﬁed. Overhearing is elim inated, idle listening mini-

mized and overheads are reduced (since network dynam-

ics at th e transmitting side are transparent to the sched-

ule). However, collisions between various transmissions

can potentially occur if more than one transmitter wishes

to reach a speciﬁc receiver; suitable contention resolution

methods are hence needed.

The ﬁrst two variants of TDMA are suited to periodic, delay

sensitive and fairly high-load trafﬁc, the third to periodic and

medium-load trafﬁc. Whilst many variants of above protocols

exist, such as the beacon-enabled guaranteed time slot trans-

mission during the collision free period of the IEEE 802.15.4

MAC to be exposed in Section VI, we shall discuss the

recently emerged Time Synchronized Mesh Protocol (TSMP)

[27] to exemplify its functioning.

TSMP is TDMA-based and hence requires network-wide

synchronization. Access is controlled b y means of a tunable

amount of timeslots which form a frame. The protocol is

designed such that a node can participate in multiple frames

at once allowing it to have multiple refresh rates for different

tasks. TSMP employs in addition FDMA and frequency hop-

ping, i.e. different links use differing frequency slots and the

same link hops during its life time across different frequency

slots. This yields high robustness against interference and

other channel impairments.

A traditional approach to facilitate synchron ization is bea-

coning, where longer frame lengths decrease the refresh rate

at which synchronization is performed and hence power

consumption and shorter frame lengths conversely invoke the

opposite. TSMP does refrain from doing so because it requires

long listening windows which consume power. Instead, TSMP

nodes maintain a precise sense of time and exchange only

offset information with neighbors to ensure alignment. These

offset values are exchanged during active periods together with

the usual data and acknowledgement packets hence invoking

negligible overhead. TSMP nodes are active in three states:

1) sending a packet to a neighbor; 2 ) listening for a neighbor

to talk; and 3) interfacing with an embedded hardware com-

ponent. The duration of active periods, i.e. the duty cycling,

is very ﬂexible in TDMA; typical applications require duty

cycles of less than 1%.

When applied, the sink typically retrieves the list of nodes,

their neighbors and their requirements in terms of trafﬁc gener-

ation. From this information, it constructs a scheduling table

Authorized licensed use limited to: Nanchang University. Downloaded on June 23,2010 at 05:15:26 UTC from IEEE Xplore. Restrictions apply.

剩余26页未读，继续阅读

genius666666

粉丝: 0
资源: 1

无线传感器网络的MAC协议精华

Apple Training Series - Mac OS X Support Essentials v10,6.pdf

Navicat Data Modeler Essentials 2.1-mac-x64

MacOS-PHP-Essentials：为Mac设置PHP环境

Apple Training Series Mac OS X Support Essentials v10.6（中文）

drupal-essentials

Wireshark revealed essentials

Springer DSP Architecture Essentials

Unity Game Development Essentials

Computing Essentials 2003 课件

Unity iOS Essentials pdf

最新资源