doc.: IEEE g Submission [CUNY] [ETRI] 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: [2 May, 2009] Source: [Gahng-seop Ahn, Junsun Ryu, Myung Lee, 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 enhancement to IEEE MAC Layer with distributed multi-channel mesh extension] 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 [CUNY] [ETRI] May 2009 Slide 2 Robust Multi-Channel Adaptation for Smart Utility Networks CUNY, ETRI

doc.: IEEE g Submission [CUNY] [ETRI] 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 [CUNY] [ETRI] 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 [CUNY] [ETRI] May 2009 Slide 5 Multi-channel Adaptation 1.Synchronous approach –Beacon-enabled mode –EGTS: Enhanced Guaranteed Time Slots 2.Asynchronous approach –Non-beacon mode –Multi-channel Meshed Tree (15.5 based)

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 6 2. Synchronous Approach

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 7 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 [CUNY] [ETRI] May 2009 Slide 8 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 [CUNY] [ETRI] May 2009 Slide 9 Flexible Multi-superframe (1) Depending on the application requirement, use N multiple superframes as one Multi-superframe (MSF) -We define MO (multi-superframe order) such that N = 2 (MO – SO). -MO should be greater than or equal to SO. Multi-superframe Duration MD = aBaseSuperframeDuration*2 MO symbols Number of slots in a multi-superframe S = 16 channels * (7 *2 (MO – SO) ) time slots The allocation pattern of these S slots is repeated every multi-superframe. BO = 6, SO = 3, MO = 5

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 10 Various combination of BO, SO, and MO can be set depending on the application requirement. For high data rate : MO = SO -Each node can have only 7 slots because a node cannot Tx or Rx multiple channels at the same time slot -Hence, each node can have no more than 2 child For scalability : MO > SO -Maximum data rate is bounded by MD. -Nodes can use multiple time slots for some of the paths that require high data rate. BO = 6, SO = 3, MO = 5 Flexible Multi-superframe (2)

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 11 For low duty cycle : MO > SO 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 (3)

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 12 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 [CUNY] [ETRI] May 2009 Slide 13 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 [CUNY] [ETRI] May 2009 Slide 14 ABT sub-block Entire bitmap may be too big to be transmitted by Beacon or EGTS command frames Example (MO = 7, SO = 3) ABT size = 224 bytes 0: Vacant,1: Allocated. Row: time slot, Column: channel Solution: Send a ABT sub-block (with an index indicating beginning & ending of a block) Example: 28 bytes sub-block. … …

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 15 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 [CUNY] [ETRI] May 2009 Slide 16 Three-way-handshake EGTS Allocation (2) Source Requesting destination Three command frames are transmitted during CAP period –EGTS request –EGTS reply –EGTS notify Schedule Update –Those nodes who are reachable by EGTS Rep and EGTS Notify. Beacons do not carry EGTS allocation information –Entire EGTS bitmap may be too big. –Periodically sending EGTS bitmap is energy consuming.

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 17 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 [CUNY] [ETRI] May 2009 Slide 18 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 neighbor’s 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 [CUNY] [ETRI] May 2009 Slide 19 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 [CUNY] [ETRI] May 2009 Slide 20 Tree-based Slot Allocation (1) Tree establishment (Beacon scheduling) and slot allocation are arranged simultaneously. Tree establishment (Beacon scheduling) –Option 1: Piggybacked in EGTS three-way-handshake –Option 2: Beacons provide two-hop information EGTS Slot allocation –Assign Slot for every uplink from each node to the PAN Coordinator. –For downlink Option 1: use the established link –some latency issue Option 2: simultaneously establishing both uplink and downlink considering the direction of traffic. Option 3: on-demand basis

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 21 TREE-Based Slot Allocation (2) Optional: 1 slot for each link Default: 1 slot for each source Slot = tuple (time slot, channel) If one slot can handle multiple packets. If data aggregation is performed.

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 22 Tree-Based Slot Allocation (3) MO = SO = 3, BO = 6 Multi-channel aspect is omitted in this figure for simplicity

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 23 Mesh-Based Slot Allocation (1) Slot = tuple (time slot, channel) Reactive (On-demand): Assign slots for multihop mesh link only when necessary (1)Setup a backup route in the face of route failure (2)Peer-to-peer communication

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 24 Mesh-Based Slot Allocation MO = SO = 3, BO = 6 Multi-channel aspect is simplified in this figure

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 25 Slot Allocation Rule Slot = tuple (time slot, channel) First, randomly choose a time slot, which has at least one vacant channel. Then, choose a channel that is available in that time slot –Considering adjacent channel interference avoidance (to be discussed in the following).

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 26 Adaptive Channel Diversity Link Condition Estimation –Packet Loss Rate = 1- (The number of Acks received / The number of transmitted frames). –RSSI, LQI If detected a bad channel –Send EGTS request with a (bad) flag set. –EGTS reply with a flag : select a channel that is the most far from the current, and then select a available slot –EGTS notify with a flag.

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 27 Adjacent Channel Interference (ACI) Avoidance Passive Scanning –RSSI of neighborhood nodes ACI detection and avoidance –Detection method: RSSI and rejection comparison –Avoidance method: Each node performs ACI detection before allocating an adjacent slot. If the possibility of ACI is detected, the node avoids allocating the adjacent slot.

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 28 Rejection Performance from CC 2420 datasheet Channel Frequency [MHz] Rejection Rejection = Interferer level – Transmitter signal level [dB], when PER is 1% (in view of a receiver) ACI happens when Interferer level – Transmitter signal level > Rejection [dB].

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 29 Passive Scanning Get RSSI when listening to Beacon, EGTS signals (Req, Rep, Notify), Data packets Neighbor RSSI Table –Example: at node 3 : Blacklist of neighbors –Those nodes that have RSSI greater than (Receiver Sensitivity Threshold + Adjacent Channel Rejection) –Example: at node 3 : Node IDRSSI 1-60 dBm 2-40 dBm 4-70 dBm Node IDRSSIAllocated Slot 2-40 dBm (9,21), (12,15)

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 30 ACI Detection (Example) Transmitter signal Transmitter channel Interferer signal Interferer channel Interferer signal – transmitter signal RejectionResult -80 [dB]16-70 [dB]17 (+5 MHz) 10 [dB]35 [dB] (+5MHz) OK -80 [dB]16-40 [dB]17 (+5 MHz) 40 [dB]35 [dB] (+5MHz) ACI -80 [dB]16-40 [dB]18 (+10 MHz) 40 [dB]55 [dB] (+10MHz) OK -80 [dB]16-20 [dB]18 (+10 MHz) 60 [dB]55 [dB] (+10MHz) ACI

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 31 Bitmap assisted beacon scheduling (1/3) Beacon scheduling method 1.New joining node(D) listen neighbor’s beacons during maximum BI 2.Select blank SD(2) in two hop boundary from beacon’ bitmap info. 3.Node D notify allocation SD information to its neighbor nodes during CAP 4.Node D transmit own beacon in blank SD(2) 5.Neighbor nodes(A, C, E) update bitmap info from node D’s beacon

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 32 Bitmap assisted beacon scheduling (2/3) Beacon slot collision prevention method 1.Node D, E select same blank SD(2) at the same time 2.Node D, E try to transmit allocation-notify command frame in blank CAP 3.First, node D broadcast allocation-notify command frame 4.Second, node E broadcast allocation-notify command frame 5.If a node(A) receive both allocation-notify commands, it transmits deallocation-notify command frame to the latter requesting node(E). 6.Node D allocate blank SD(2) as own beacon slot.

doc.: IEEE g Submission [CUNY] [ETRI] May 2009 Slide 33 Bitmap assisted beacon scheduling (3/3) Beacon collision detection method 1.If there are beacon collisions several times, Node A notifies the collision to neighbor nodes with CAP or Beacon. 2.If nodes(D, E) listen collision information, try to select other blank SD. 3.Nodes (D, E) retry for a new allocation.