doc.: IEEE g Submission Myung Lee at al May 2009 Slide 1 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Robust Multi-Channel Adaptation for Smart Utility Networks] Date Submitted: [8 May, 2009] Source: [Gahng-seop Ahn, Junsun Ryu, Myung Lee, ChangSub Shin, Seong-soon Joo] Companies [CUNY, ETRI] Address [140 th St. and Convent Ave, New York, NY, USA] Voice:[ ], FAX: [], Re: [IEEE P g] Abstract:[This document proposes an robust multi-channel adaptation for smart utility networks] Purpose:[Discussion in g Task Group] Notice:This document has been prepared to assist the IEEE P 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 P doc.: IEEE g Submission Myung Lee at al May 2009 Slide 2 Robust Multi-Channel Adaptation for Smart Utility Networks CUNY, ETRI doc.: IEEE g Submission Myung Lee at al May 2009 Slide 3 Objectives MAC Modifications needed to support outdoor Low Data Rate Wireless Smart Metering Utility Network requirements Robustness Scalability High reliability Energy efficiency doc.: IEEE g Submission Myung Lee at al May 2009 Slide 4 Motivation Densely deployed large scale network in geographically large area The variance of channel condition is large. Channel Asymmetry. Common channel approach is limited Therefore, multi-channel adaptation is required. Concentration Point Smart Meter doc.: IEEE g Submission Myung Lee at al May 2009 Slide 5 Multi-channel Adaptation 1.Asynchronous approach Non-beacon mode Multi-channel Meshed Tree (15.5 based) 2.Synchronous approach Beacon-enabled mode EGTS: Enhanced Guaranteed Time Slots doc.: IEEE g Submission Myung Lee at al May 2009 Slide 6 1. Asynchronous Approach doc.: IEEE g Submission Myung Lee at al May 2009 Slide 7 Receiver-based Channel Use (1) Each device is listening to its designated channel. The sender device switch to the channel of the receiver device and transmit a DATA frame. The sender device switch back to its own channel. The receiver device switch to the channel of the sender device and transmit a ACK frame (if requested). The receiver device switch back to its own channel. DAT A ACK Sender Receiver doc.: IEEE g Submission Myung Lee at al May 2009 Slide 8 Receiver-based Channel Use (2) If the sender knows that it can hear receivers channel as well. (The sender can find out whether it can hear the receivers channel during association or by performing multi-channel probing.) Each device is listening to its designated channel. The sender device switch to the channel of the receiver device and transmit a DATA frame with a flag indicating that the sender can hear receivers channel. The receiver device transmit a ACK frame (if requested) using receivers channel. The sender device switch back to its own channel after it receives the ACK. DAT A ACK Sender Receiver doc.: IEEE g Submission Myung Lee at al May 2009 Slide 9 Channel Selection A PAN can be configured to use a block of channels C max channels among all C total channels. Motivation: to reduce the active scanning time. Considering adjacent channel interference and coherent bandwidth. For example, if there are 16 channels (channel 11 to channel 26): PAN1 uses channel 11, 17, 23. PAN2 uses channel 13, 19, 25. PAN3 uses channel 15, 21. doc.: IEEE g Submission Myung Lee at al May 2009 Slide 10 Multi-channel Active Scan Coordinator New Device Channel Association Response C4C4 C1C1 C2C2 C3C3 C3C3 C2C2 C1C1 C3C3 C2C2 C1C1 C4C4 C3C3 Beacon Request Beacon Association Request For example, C max = 4, Coordinators designated channel is C 4, New devices good channel is C 3. T C4C4 C3C3 C4C4 C4C4 T A device perform active scan for all C max channels twice at worst case. doc.: IEEE g Submission Myung Lee at al May 2009 Slide 11 Channel selection based on link quality (optional) Coordinator New Device Channel Association Response C4C4 C1C1 C2C2 C3C3 C3C3 C2C2 C1C1 C3C3 C2C2 C1C1 C4C4 C1C1 Beacon Request Beacon Association Request For example, C max = 4, Coordinators designated channel is C 4, New devices good channel is C 1, C 3. T C4C4 C1C1 C4C4 C4C4 T A device perform active scan for all C max channels twice and choose the best RSSI among the received beacons. doc.: IEEE g Submission Myung Lee at al May 2009 Slide 12 Multi-channel Hello A device can send a multi-channel hello message to its one-hop neighbors to inform its designated channel. The device should send the same hello message on each channel sequentially starting from its designated channel. Optional: The device can request hello reply by setting a flag in the hello message. Neighbor 1 New Device Channel C4C4 C1C1 C4C4 C3C3 C2C2 Two Neighbor Example: C max = 4, Coordinators designated channel is C 4, New devices good channel is C 3. T C3C3 C2C2 Neighbor 2 Channel C3C3 C3C3 Hello Hello Reply C2C2 C4C4 doc.: IEEE g Submission Myung Lee at al May 2009 Slide 13 Three-way Handshake Channel Probing The requesting device sends a channel probe request frame to one of its neighbors on the designated channel of the neighbor (e.g., brown) indicating the channel to probe (e.g., red). The neighbor sends a channel probe reply frame back on the requesters channel (e.g., green). The neighbor sends a channel probe frame using the channel indicated in the probe request (e.g., red). Channel Probe Request RequesterNeighbor Channel Probe Reply Channel Probe doc.: IEEE g Submission Myung Lee at al May 2009 Slide 14 Recovery from Bad Channel Condition Recovery from the case when the designated channel of a device has gone bad The neighboring devices can immediately find a backup route bypassing the device (for example, using the feature of 15.5 meshed tree). The device can check the condition of its designated channel and switch to a better channel. (Using the channel probing). ? Concentration Point Smart Meter X X doc.: IEEE g Submission Myung Lee at al May 2009 Slide 15 Channel Adaptation The device can check the condition of its designated channel using three-way handshake channel probing with one of its neighbors. If the channel condition is bad, the device can probe other channels and switch to a better channel. After switching the channel, the device shall broadcast a multi-channel hello to its one-hop neighbors. ? Concentration Point Smart Meter X X Concentration Point Smart Meter ! doc.: IEEE g Submission Myung Lee at al May 2009 Slide 16 Optimizing the Channel Diversity Channel diversity has its cost. The device have to switch its channels frequently if each neighbors are using a different channel. To minimize the number of diverse channels, Among the good channels, choose the channel that is being used by the majority of its neighbors. Smart Meter doc.: IEEE g Submission Myung Lee at al May 2009 Slide Synchronous Approach For details, refer to e-distributed-multi-channel- mesh-extension doc.: IEEE g Submission Myung Lee at al May 2009 Slide 18 EGTS: Enhanced Guaranteed Time Slots Beacon-enabled mode Robust and reliable communication Multi-channel support for GTS (Guaranteed Time Slot). Co-channel interference avoidance (EGTS three-way handshake). Adjacent channel interference avoidance (Passive RSSI monitoring). Dynamic channel diversity Detection of bad channel condition and reallocation of the slot to a better channel. Beacon collision avoidance Bit-map assisted beacon scheduling. doc.: IEEE g Submission Myung Lee at al May 2009 Slide 19 EGTS Multi-channel Extension Common channel : Beacon and CAP use a fixed common channel for all nodes. Multi-channel: EGTS uses multi-channel for a different set of source and destination. EGTS slot = tuple (time slot, channel) Allocates each link (Tx & Rx pair) with one or more slots. When MO = SO (to be explained in the following), 112 slots (7 time slots * 16 channels) are available in a superframe. EGTS doc.: IEEE g Submission Myung Lee at al May 2009 Slide 20 EGTS Mesh Extension EGTS allocation do not rely on PAN coordinator. Allows EGTS for peer-to-peer connection. Allows EGTS for nodes beyond one hop distance from PAN coordinator. Multi-channel aspect is omitted in this figure for simplicity doc.: IEEE g Submission Myung Lee at al May 2009 Slide 21 For low duty cycle Active Beacon, CAP During EGTS time slots that are allocated to the node Inactive During EGTS time slots that are not allocated to the node BLE in CAP periods Beacon slot where none of the neighbors are transmitting a beacon. BO = 6, SO = 3, MO = 5 Inactive / sleep Active / awake Node Flexible Multi-superframe doc.: IEEE g Submission Myung Lee at al May 2009 Slide 22 CAP Period Reduction in MSF Motivation: Lower duty cycle, more GTS slots. Each multi-superframe (MSF) has only one CAP period. Beacon indicates the next CAP period time. Every node synchronizes the CAP period. Number of slots in a multi-superframe S = 16 channels * (7 + (2 (MO SO) -1) * 15) time slots The allocation pattern of these S slots is repeated every multi-superframe. BO = 6, SO = 3, MO = 5 doc.: IEEE g Submission Myung Lee at al May 2009 Slide 23 EGTS Allocation Bitmap Table (ABT) Each node maintains a Neighborhood Allocation Bitmap Table (ABT) Example (MO = SO = 3) ABT size = 14 bytes 0: Vacant,1: Allocated (self or neighbors) Row: time slot, Column: channel doc.: IEEE g Submission Myung Lee at al May 2009 Slide 24 Three-way-handshake EGTS Allocation (1) Source Requesting destination Three command frames are transmitted during CAP period EGTS request Unicast from a source to a destination. Providing locally available slots (28 byte ABT sub-block). Required number of slots (depending on data rate). EGTS reply Broadcast from the destination. Select appropriate slots in the sub-block and announce the assigned EGTS slots to all neighbors (28 byte ABT sub-block). EGTS notify Broadcast from the source Announce the assigned EGTS slots to all neighbors (28 bytes ABT sub-block) doc.: IEEE g Submission Myung Lee at al May 2009 Slide 25 EGTS Allocation Example (from node 3) 2. EGTS reply, broadcast Payload : Dst addr (3) new allocated ABT sub-block { } 1.EGTS request, unicast Payload : Number of slots ABT sub-block { } Assuming slot (9,21) is already assigned from node 4 for transmitting frames to node 3 Slot = tuple (time slot, channel) MO = SO Node 1 assigns slot (10,15) for Node 3 Every node that hears the broadcasts updates its allocation bitmap table (ABT) 3. EGTS notify, broadcast Payload : Dst addr (1) new allocated ABT sub-block { } doc.: IEEE g Submission Myung Lee at al May 2009 Slide 26 EGTS Duplicated Allocation Notification Duplicated allocation can happen Some nodes may miss some of EGTS reply or notify. (Broadcast is not reliable) New joining node requests a slot not knowing the slot allocation state in the area. Send EGTS collision notification during CAP period The existing owner of the slot detects duplicated allocation by hearing neighbors EGTS reply or notify. EGTS duplicated allocation notification (Unicast) from the existing owner. Duplicated slot id (time slot, channel). ABT sub-block (28 bytes) around the colliding time slot. Forces the source and the destination nodes to retry three-way-handshake EGTS allocation. doc.: IEEE g Submission Myung Lee at al May 2009 Slide 27 Hybrid Slot Allocation Proactive: tree-based slot allocation Tree establishment (Beacon scheduling) and slot allocation are arranged simultaneously Reactive: mesh-based slot allocation Assign slots on-demand basis Path reliability: backup route in the face of route failure Peer-to-peer communication doc.: IEEE g Submission Myung Lee at al May 2009 Slide 28 Discussion: Issue of EGTS in 15.4g EGTS set up (as proposed in 15.4e) is still based on common channel approach! Common channel : Beacon and CAP use a fixed common channel for all nodes. Multi-channel: EGTS uses multi-channel for a different set of source and destination. EGTS doc.: IEEE g Submission Myung Lee at al May 2009 Slide Common Channel Frequency Hopping Common Channels: Beacon, CAP Objective: Reliable communication in the face of time-varying and frequency-dependant radio conditions. Pre-defined hopping sequence: Example: 15 20 25 15 Trade-off is longer scanning time for new joining nodes. doc.: IEEE g Submission Myung Lee at al May 2009 Slide Beacon Frequency Hopping No common channel: Each node is listening to its designated channel. Each node broadcast beacons on each available channel sequentially. Objective: Robust communication in the face of asymmetric channel conditions. Pre-defined hopping sequence: Example: 15 20 25 15 Trade-off is longer scanning time for new joining nodes. doc.: IEEE g Submission Myung Lee at al May 2009 Slide 31 Thank you! We are open to further collaborations with 4g members!