Browse Prior Art Database

A Low-Power MAC Protocol for Wireless Sensor Networks

IP.com Disclosure Number: IPCOM000117296D
Original Publication Date: 2005-Mar-31
Included in the Prior Art Database: 2005-Mar-31
Document File: 6 page(s) / 115K

Publishing Venue

IBM

Abstract

The disclosure is directed towards a low-power MAC protocol for a wireless, low data-rate sensor network in which very simple and transmit only sensor nodes (SNs) communicate with multiple cluster heads (CHs). The data sent by the SNs should be received by as many CHs as possible. The CHs cooperate with each other to improve the performance of the wireless links between them and the SNs.

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A Low-Power MAC Protocol for Wireless Sensor Networks

1 Introduction

This disclosure is directed towards a low power MAC protocol for low data-rate wireless sensor networks (WSN), which consists of many very simple and low-cost sensors nodes (SNs) communicating wirelessly with a few distributed and cooperating cluster heads (CHs). To keep the cost of the SNs as low as possible, it is assumed that the SNs have only transmit capability. Thus the SNs just broadcast their data packets to the air without knowing whether they are received by any CH. The system is deployed in such a way that data packets sent by the SNs could be received by as many CHs as possible. Exploiting the space diversity of the system the CHs cooperate with each other to decode the data packets received and reduce the packet error rate. The cooperation algorithm between the CHs is however out of scope of this disclosure.

Because the SNs can only transmit, uncoordinated multi-access protocols can be efficiently applied here, i.e. the SNs just send their data and hope that their transmissions do not collide with other transmissions. To avoid catastrophic collisions between the SNs, a SN could for example wait for a random delay before it start its transmissions (ALOHA like).

In many sensor applications, the SNs are idle for long time if no sensing event happens. To save energy the SNs can therefore turn off their radio and sleep during those idle times. They need only to wake up when they have something to send. Although this simple method is well appropriate for those low traffic conditions, it has the disadvantage of requiring the CHs to have their radio receivers always turned on, because they do not know when a SN would start sending, thus wasting energy for idle listening.

In this disclosure we will describe a MAC protocol that also allows the CHs to switch their receiver off and save energy during the idle phases.

2 Prior art
2.1 IEEE 802.11/802.15.4 Power Save Mode

Both IEEE 802.11 and 802.15.4 specify the same scheme for power saving mode for the wireless stations. The access point is assumed to be always on.

All downlink traffic is buffered in the access point. The access point transmits periodically a beacon, which contains a so-called "Traffic Indication Map (TIM)". The TIM lists the addresses of the wireless stations for which data packets have been buffered. To save energy the wireless stations turn off their radio transceivers during the idle periods (power save or "sleep" mode). They however know the beacon transmit schedule of the access point, and wake up regularly to receive the TIM. If they discover their address in the TIM, they poll the access point to receive the buffered packet(s). The wake-up period can be freely chosen by the wireless stations as a multiple of the beacon period.

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2.2 W. Ye et al, "Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks", IEEE/ACM Trans. Networking, vol 12, no 3, Jun...