Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:[Extending the MAC Superframe of 802.15.4 Spec] Date Submitted: [7 July 2008] Source: [Ghulam Bhatti] Company [MERL] [Zafir Sahinoglu] Company [MERL] Address [] Voice:[], E-Mail: [gbhatti@merl.com, zafer@merl.com] Re: [] Abstract: We present a comprehensive mechanism for channel access in a multi-hop wireless networks. As opposed to IEEE802.15.4e-2006 spec, the proposed system is scalable and efficient. Contrary to TDMA-based schemes, which are ideal for single hop-networks (such as a star topology), our scheme facilitates a simple and easy channel hopping mechanism without a need for micro-management of time-slots. Minimal support from higher layers is required in the proposed system. Purpose: We presenting it as a candidate frame structure in task group 15.4e 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. Bhatti, Sahinoglu

2. Distributed Beacon Enabled Wireless Networks Dr. Ghulam Bhatti and Dr. Zafer Sahinoglu MERL 7 July 2008 Bhatti, Sahinoglu

3. Contents • Motivation and Goals • Overview of Proposed System • Proposed System – scheme 1 • Proposed System – scheme 2 • Proposed MAC Frame Structure • How to Get a Beacon Slot Bhatti, Sahinoglu

4. Motivation and Goals • Wireless sensor networks are getting increasing attention for deployment under industrial and commercial environments. • Scalability, reliability, and latency are challenging issues. • IEEE802.15.4-2006 standard fails to satisfy stringent requirements in industrial deployments. • Beacon-enabled mode is not scalable. • Non-beacon mode fails to satisfy latency and reliability requirements. • Pure TDMA schemes are good only for single-hop systems. • We propose a MAC that: • Operates in a distributed fashion. • Offers automatic resource management and is scalable. • No help from higher layers is needed for channel access management. • Uses channel hopping for higher reliability and better channel efficiency. • Dynamically allocates channel for retransmission of failed transmissions. • Dynamically allocate additional time-slots on demand in the same superframe. Bhatti, Sahinoglu

5. Proposed System - Overview • All nodes periodically transmit their beacons on a fixed channel • Nodes grab a beacon slot by using a distributed algorithm • A few time slots on the same fixed channel is used for transmitting control messages and data broadcasts • A node jumps to another channel for transmission of the data part of its superframe • A node selects a suitable communication channel for its superframe while grabbing its beacon slot on joining (can be changed later) • In any part of the network, as many (or more) nodes may be simultaneously communicating as the number of channels • Each node can operate its own cluster of sleeping child nodes • Our superframe structure allows ReTx attempts for failed transmissions • The superframe structure allows allocations of additional time slots dynamically Bhatti, Sahinoglu

6. GACK1 GACK1 GACK1 GACK1 GACK2 GACK2 GACK2 GACK2 ECFP ECFP ECFP ECFP CAP1 CAP1 CAP1 CAP1 CAP2 CAP2 CAP2 CAP2 CFP CFP CFP CFP Proposed System – Scheme 1 A n n o u n c e m e n t C y c l e M1 … M4 B1 B2 B3 --- Bk I D L E M1 … M4 B1 B2 B3 --- Bk --- --- Bhatti, Sahinoglu

7. Notes on Scheme 1 • All nodes must finish their communications before the start of control slots (M1-M4) of next Announcement Cycle. • Right after transmitting its beacon, a nodes switches over to its channel and starts transmitting its superframe. • Channel hopping (based on slots) can optionally be used for communications during the superframes. • This scheme allows the nodes to have superframes of different sizes. • A node using beacon slot B1, for example, can have longer superframe than the superframe of a node that uses B2 for its beacon transmission. • Variable sized superframes allow more busy nodes (e.g. nodes closer to sink) a longer time for channel access. Bhatti, Sahinoglu

8. GACK1 GACK2 ECFP CAP1 CAP2 CFP Channel C1 for OwnerNode(B1) CAP1 CAP2 CFP ECFP Channel C2 for OwnerNode(B2) ECFP CAP1 CAP2 CFP Channel Ck for OwnerNode(Bk) Proposed System – Scheme 2 A n n o u n c e m e n t C y c l e M1 … M4 B1 B2 B3 --- Bk M1 … M4 B1 B2 B3 --- Bk --- I D L E --- Bhatti, Sahinoglu

9. Notes on Scheme 2 • All nodes listen during control slots (M1-M4). • All nodes listen for beacons from neighbor nodes. • All nodes start data communication part of their superframe simultaneously. • Each node uses a different channel. • Channel hopping (based on slots) can optionally be used for communications during the superframes. • Announcement channel can also be included in hopping sequence. • Peer nodes communicate using contention based channel access or using a guaranteed time slots (GTS). • Minimal or no intervention from higher layers is needed for channel and GTS allocations. Bhatti, Sahinoglu

10. A n n o u n c e m e n t C y c l e M1 M2 M3 M4 B1 B2 B3 B4 BC M1 M2 M3 M4 B1 B2 B3 Beacons from the same device Proposed MAC Frame Structure (1) Beacons: A fixed Announcement Channel is used for beacons tx • The channel is selected at the time of starting a PAN • Time between two consecutive beacons transmitted by the same device is called Announcement Cycle • The size of Announcement Cycle may vary in different parts of a network • The minimum and maximum size for this cycle is configurable • Beacon slots are allocated by a distributed algorithm • The first several slots are used for control messages and data broadcasts • CSMA/CA is used for channel access in this part --- --- Bhatti, Sahinoglu

11. GACK1 GACK2 ECFP CAP1 CAP2 CFP Proposed MAC Frame Structure (2) Superframe:A separate channel is used by each node for its superframe • Superframe consists of fixed-size time slots and has several parts • CAP1: Allows contention-based CSMA/CA channel access (optional) • CFP: Consists of zero or more pre-allocated GTSs • GACK1: Group ACK frame to acknowledge for GTS frames received in CFP • ECFP: Extended CFP used for ReTx of failed GTS transmissions and additional slot allocations on demand • GACK2: Group ACK frame to acknowledge for data frames received in ECFP • CAP2: Just like CAP1 but subject to availability of time in superframe • Used for ReTx of failed GTS frames in ECFP • Can be used for transmitting any other data frames • Superframe has the same size for all nodes in a PAN Bhatti, Sahinoglu

12. Proposed MAC Frame Structure – Information in Beacon {F0} {F0} {F1} {F3} {F4} {F9} {F2} {F5} GTS GTS Extended CFP Listen/Sleep CFP CAP CFP CAP2 CAP GTS GTS GTS GTS Sequence Number Available Virtual Time Slots (AVTS) GTS Device List GTS Indices GTS Directions Frame Control Source ID PAN ID Beacon Interval Super frame Interval Channel Index for superframe Information in the GACK GACK {F3} {F6} GTS GTS Listen CFP CAP CFP CAP CFP GTS GTS GTS GTS Group ACK Flags CAP Channel Index Extended CFP Channel Index Source ID {F6} {F3} Bhatti, Sahinoglu

13. How to Get a Beacon Slot? • Before joining a PAN, a node performs a scan for sufficiently long • It finds the size of Announcement Cycle • Determines empty/available beacon slots • Decides which channel is good for its data communications • It gets Neighbor Group (NG) of each of its neighbor • It constructs its Extended Neighbor Group (ENG) from received NGs • It transmits it claim in a control slot of next Announcement Cycle • It claims the lowest empty slot available in its ENG • It declares the channel it will be using for its superframe Bhatti, Sahinoglu

14. 4 x 8 7 9 5 5 6 9 1 2 3 2 Beacon Scheduling BG[x] = {x, 5, 8, 9} BG[x] = {x} BG[x] = {x, 5} BG[x] = {x, 5, 8} BG[5] = {5, 8} BG[8] = {1, 5, 8} BG[9] = {1, 7, 9} EBG[x] = {x, 1, 5, 7, 8, 9}  x = 2 BG[x] = {2, 5, 8, 9} Bhatti, Sahinoglu

15. M1 M2 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 …. BC BG[5] = {5, 8} M1 M2 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 …. BC BG[8] = {1, 5, 8} M1 M2 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 …. BC BG[9] = {1, 7, 9} M1 M2 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 …. BC BG[2] = {2, 5, 8, 9} Synchronization among nodes • Any given node listens only a part of Announcement Period (i.e. no activity detected in some beacon slots) • Nodes must have good clocks for reliable synchronization Bhatti, Sahinoglu