June, 2010 IEEE P802.15-10-0433-00-0006
IEEE P802.15
Wireless Personal Area Networks
Project / IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Title / Power managementmechanism for wireless BAN devices
Date Submitted / [July6, 2010]
Source / [Wangjong Lee]
[MyongjiUniversity]
[San 38-2 Namdong, Choin, Yongin, Gyeonggi, 449-728, Korea]
[Seung Hyong Rhee]
[KwangwoonUniversity]
[447-1Wolgye, Nowon, Seoul, 139-701, Korea] / Voice:[+82-2-2202-6976]
Fax:[+82-2-2202-6976]
E-mail:[
Voice:[+82-2-943-7607]
Fax:[+82-2-943-7607]
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Abstract / [This document suggests to adopta way of transmission mechanism based on a reservation schemefor the WBAN devices. It also provides power management mechanisms in order to reduce power consumption of WBAN MAC.]
Purpose / [Providing technical contributions to IEEE 802.15 TG6]
Notice / This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release / The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
Power Management Mechanism for Wireless BAN Devices
1Introduction
This document describes a new way of power management mechanism that that providescommunication between the outbody device and inbody devices for WBAN. To reduce power consumption of WBAN devices, the outbody device manages multiple channels on the MICS frequency band based on the channel reservation. In addition, thereservation based multi channel protocol would be backward compatible with conventional mechanisms: LBT(listen before talk) and AFA (adaptive frequency agile). WBAN devices have two states: awake and sleep. These devices repeat awake and sleep state periodically in order to reduce unnecessary power consumption.
2 Beacon-based Transmission Mechanism
The contention mechanism with sensing and hopping, AFA and the LBT, prevents collisions between the devices, but cannot guarantee a reliable transmission because not just any device can maintain the channel occupancy. A device is allowed to transmit one data at a time with a sensing operation. This repeated sensing results in a long delay in a transmission. The proposed reservation based scheme can guarantee a reliable transmission by allocating a channel via the control channel. Also, it improves channel utilization and aggregates the throughput by reducing the sensing and hopping process.
2.1 Channel Plan
The current MICS frequency band consists of 10 channels with 300 kHz bandwidth. To support for the reservation based multiple access, the outbody device shall be able to detect whether channels are used and allocate these channels to inbody devices. Figure 1 illustrates one example of how 10 channels may be allocated.One is used as the control channel and other channels are used for data transmission.
To allocate data channels to inbody devices, the outbody device transmits beacons on the control channel. Beacon transmission is based on the superframe, which is illustrated in figure 1. The superframe is composed of 9 beacon slots. The duration of each beacon slot is less than 5ms and is enough time for transmission of one beacon and one ACK. By listening to the control channel, inbody devices know which channels are used and reserved for communications between the outbody device and themselves.The outbody device and the inbody device communicate on the data channel that is negotiated on the control channel.
Figure 1 Proposed Channel Plan
2.2Transmission Mechanism
In the reservation based scheme, the coordinate sends beacons in order to allocate data channels efficiently. All devices know the information of the channel allocation by listening to the control channel. So it is important to transmit beacons on the control channel. But LBT technique allows a device to occupy the channel when the channel is idle for more than 5ms. If there are no beacons during some adjacent beacon slots, the device that uses LBT can occupy the control channel. In this case the coordinator cannot send beacons any more on the control channel.
To prevent the LBT device from occupying the control channel, the coordinator uses the beacon repeat mechanism. After the coordinator sends a beacon, it checks whether the coordinator will transmit a beacon for the next slots or not. If there are no beacons for two consecutive slots the coordinator copies the previous beacon and sends it during the second slot. This prevents the idle duration from exceeding more than 5ms.
Figure 2 Data Transmission Mechanism
The coordinator sends beacons via control channels periodically. The devicewill be in the awake during the one superframe to receive beacons, which indicate all reservation of sub-channels. After the data channel negotiation, two devices move to the allocated data channel.
To prevent the data channel from using the allocated data channel by the LBT device, the coordinator sends a RTS within 5ms after it transacts to the data channel (Figure 2). The RTS is transmitted at a certain interval, which does not exceed 5ms, until the device sends data. The device starts to send data after receiving the RTS and the coordinator transmits ACK in response to this data.
3The Proposed Mechanism
In the applications of wireless BANs, there are many cases where the device transmits with a certain period. The device that is in a sleep state awakes and checks that it starts to communication or not. If the device has the need to communicate with the coordinator, it maintains the awake state and finds an unused channel by LBT and AFA. On the other hand, if the coordinator reserves the channel which communicates with the device, the device starts to communicate immediately without searching an unused channel. There are two power management mechanism defined in this section: Asynchronous wakeup mechanism and Wakeup call mechanism.
3.1Asynchronous Wakeup
The device alternates between a sleep state and an awake state depending on its duty cycle to consume lower power. When the coordinator requires the device to transmit data, the coordinator sends the beacon continuatively on the control channel. The awake device shall maintain the awake state during one superframe and check, if the coordinatorrequires it to transmit data. If the device does not receive the beacon, it falls into the sleep state again. As thedevice receives the beacon, it sends ACK via the control channel and moves to the allocated data channel. After receiving the RTS, the device sends its data to the coordinator and receivesACK from the coordinator. Then the device changes back to the sleep state. Figure 2 shows above asynchronous wakeup.
Figure 3 Asynchronous wakeup
3.2Wakeup Call
Asynchronous wakeup mechanism starts the transmission by receiving the beacon during the awake duration. The state conversion depends on duty cycle of the device. The emergency call, such as immediate transmission, may occur in the medical applications of the wireless BANs. The coordinator can not wait for the device to awake. The coordinator sends the wakeup call signal to the device. If the device receives the wakeup call signal, it awakes independent of its duty cycle. As shown in figure 4, the device awakes and listens to beacons on the control channel, and then the device sends its data to the coordinator via the data channel.
Figure 4 Wakeup call mechanism
References
[1]B. Zhen et al, “TG6 Technical Requirements Document (TRD),”IEEE P802.15-08-0644-0-006, September 2008
[2] H. Li et al, “IEEE 802.15.6 Regulation Subcommittee Report,” IEEE P802.15-08-0034-10-006, November 2008
[3]Y. Kim, H. Lee, S. Rhee, W. Lee, H. Lee and S. Park, “Distributed and beacon-enable multiple access control for WBAN,”IEEE 802.15-08-0439-01-0006, July 2008
[4] Y. Kim, H. Lee, S. Rhee and W. Lee, “Beacon-based Multi-Channel MAC for WBAN,” IEEE 802.15-08-0732-00-0006, October 2008
[5] S.-L. Wu, C.-Y. lin, Y.-C. Tseng and J.-P. Sheu, “A New Multi-Channel MAC protocol with on demand channel assignment for mobile ad-hoc networks,” Proc. ISPAN ’00, pp.232, December 2000.
[6] W. Lee, S. Rhee, Y. Kim and H. Lee, “An Efficient Multi-channel Management Protocol for Wireless Body Area Networks,” presented at the ICOIN 2009, January 2009
[7] W. Lee, S. Rhee, “Coexistence mechanism for wireless BAN devices,” IEEE P802.15-09-0470-00-0006, IEEE, July 2009.
[8] W. Lee, S. Rhee, “Channel Management Protocol for Wireless Body Area Networks,” Lecture Notes in Computer Science, vol. 5787, pp.494-497, September 2009.
SubmissionPage 1Lee and Rhee <MJU/KWU>