Medium Access Control Protocol for WBANS

Transcription

1 Medium Access Control Protocol for WBANS Using the slides presented by the following group: An Efficient Multi-channel Management Protocol for Wireless Body Area Networks Wangjong Lee *, Seung Hyong Rhee *, Youjin Kim ** and Hyungsoo Lee ** * Kwangwoon University, Korea, ** Electronics and Telecommunications Research Institute, Korea

2 Concept 1. Collision : Two nodes emit at the same time 2. Idle Listening : Node listens to an idle channel 3. Overhearing: Node listens for a message sent to another node

3 Energy in WBAN Battery lifetime is very important Required Lifetime Swallowable Camera Pills : 12 hours Cardiac Defibrillators and pacemakers : 5 years Reducing the waste of energy can maximize battery lifetime How to improve energy efficiency Routing Mobile Base Station Energy efficient MAC protocol 3

4 Major MAC Protocols Contention Based (CSMA/CA) Nodes need to perform CCA before transmission of data If the channel is busy, the node defers its transmission till it becomes idle. Its infrastructure-free Ad hoc feature Good adaptability to traffic fluctuation Schedule Based(TDMA) Channels are divided into fixed/variable time slots which are assigned to nodes that transmit during its slot period Free of idle listening, overhearing and packet collisions because of the lack of medium competition, But require tight time synchronization.

5 Wireless Body Area Networks Can be considered a successor of WPAN (Wireless Personal Area Network) WBAN have a range of 3 meters (9.8 ft) Medical or non-medical according to use In 2.4 GHz ISM band and 400 MHz band of MICS ISM: Industrial Scientific Medical, used for Wi-Fi MICS: Medical Implanted Communication Service 5

6 Technical Topic We need a protocol to reduce the interference in the MICS band Interference between MICS systems or between MICS and primary systems There is a an LBT (Listen-Before-Talk) protocol defined LBT isn t good for non-collision and emergency traffic This paper proposes an efficient way of multi-channel management The channel is reserved Channel aggregation makes a single wide channel and satisfies various traffic types 6

7 Outline Preliminary material Proposed scheme Simulation results 7

8 Preliminaries IEEE working to make WBAN standards through Task Group ITU-R issued Recommendation SA.1346 for MICS devices ITU-R: International Telecom. Union - Radiocommunication MHz METAIDS MICS METAIDS: Meteorological Aids SA.1346: MICS devices should limit to -16 dbm in a bandwidth of 300 khz to prevent interference with METAIDS Channel spacing of 25 khz with channel aggregation up to 300 khz Also, there is LBT specs MICS use low power, concluded there s no interference with METAIDS 8

9 Distributed and Beacon-Enabled MAC Protocol This is the proposed scheme MICS band consists of 10 channels with 300 khz bandwidth 1 channel is the control channel. The other 9 are data The control and data channels are not fixed Outbody device allocates the channels to inbody devices through the control channel Outbody device continuously sends a beacon frame on the control channel 9

10 Channel Assignment Outbody device initiates communication with inbody devices It also senses the channels to set up a control channel MICS devices are secondary users; transmit/received when METAIDS devices are silent They should coexist with other MICS; using LBT protocol Outbody device selects one channel as the control channel after sensing It also assigns a channel number to each channel except the control channel 10

11 Channel Assignment On control channel, a beacon superframe consists of 9 beacon slots Each beacon slot maps to a data channel A beacon in the 1 st slot means the 1 st channel is reserved No beacon in the n th means the n th channel is not reserved Inbody devices listen to control channel to know what channel to use Inbody devices then send a data packet to the outbody device on the reserved channel 11

12 Supporting Sleep State Inbody devices have 2 modes: wake mode & sleep mode There is a duty cycle: wake/sleep At wake up, inbody device listens to control channel If there is a channel allocated for it, it talks to outbody device During this time, a beacon is sent on the control to indicate the data channel is busy At end of communication, inbody device sleeps. Outbody device stops the beacon for the sleeping device If there was no data channel for it at wake up, inbody device sleeps 12

13 Channel Aggregation MICS frequency band has narrow channels This limits traffic types that need high bandwidth Outbody device can allocate aggregated data channels by transmitting the same beacon in adjacent beacon slots the channels are combined in a single wideband channel This scheme prevents a waste of resource by using channel guards It also reduces transmission failure caused by narrow channel 13

14 Single MAC for 2 PHYs Two PHYs for WBAN: ISM (2.4 GHz) and MICS (400 MHz) Use ISM for outbody communication and MICS for inbody communication Like MICS, ISM band is divided into non-overlapping channels the same proposed scheme can be used WBAN device has two PHY layers and one MAC layer 14

15 Simulation Results Simulation with ns-2, CMU wireless extension and MAC modules developed by Intel (refs.) Topology: 2 inbody devices communicating with 1 outbody device 15

16 Throughput of Proposed Scheme and LBT In proposed scheme, control channel is overhead In LBT, sensing before transmission is overhead sensing time is varied in simulation Listening Time = 0.05 ms Listening Time = 0.1 ms 16

17 Throughput with Channel Aggregation First case is one aggregate channel of 900 khz Second case is 3 separate channels of 300 khz each Aggregation increases the throughput Channel: 1 x 900 khz Channel: 3 x 300 khz 17