83180 Wireless LANs - 9.3. 2005 LR-WPAN Low-Rate Wireless Personal Area Networks

1. 83180 Wireless LANs - 9.3. 2005LR-WPANLow-Rate Wireless Personal Area Networks Toni Huovinen: Coexistence Among Wireless Standards Lauri Anttila: IEEE 802.15.4 Low-Rate WPAN - Overview Jarno Niemelä: IEEE 802.15.4 MAC for LR-WPAN applications Tero Isotalo: Low-Rate WPAN Examples, Trends and Products

2. Coexistence Among Wireless Standards Toni Huovinen Lauri Anttila Jarno Niemelä Tero Isotalo 9.3.2005

3. 3 Introduction Both WLAN and WPAN operate in the same ISM band mutual interference between the systems severe performance degradations are possible Many factors effect the level of interference the distance between the WLAN and WPAN devices the amount of data traffic flowing over each of the two networks the power levels of the various devices the data rate of the WLAN types of information being sent over the wireless networks Performance degradations might discourage consumers to use more wireless devices

4. 4 Introduction (cont’d) If nothing is done devices that transmit with relatively higher power or more interference resistant protocols get their data through where as the other devices suffers Coexistence is defined as ability of one system to operate in shared environment. Good coexistence policy is such that it do not increase an interference to other systems using the same wireless channel.

5. 5 IEEE 802.15.2 IEEE 802.15 working group released a recommended practice ‘IEEE 802.15.2 – Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Band’ in 2003. IEEE 802.15.2 defines coexistence methods for an IEEE 802.15 WPAN to operate in the presence of frequency static or slow-hopping WLAN devices Basically the scope of IEEE 802.15.2 is limited to coexistence of Bluetooth/IEEE 802.15.1 devices and IEEE 802.11b devices. It was expected that devices using these standards will have the largest market share among devices using 2.4 GHz ISM band Some of the proposed coexistence methods can be used also with other WPAN and WLAN standards.

6. 6 IEEE 802.15.2 (cont’d) There are two categories of coexistence methods: Collaborative methods Exchange information between WPAN and WLAN network. A wired communication link between system is needed. Applicable only if WPAN master and WLAN station are located in the same physical equipment (like laptop). Three different methods are defined. Non-collaborative methods Do not exchange information between two wireless networks. WPAN and WLAN devices do not have to be in the same equipment. Five different methods defined. It is possible to use several coexistence methods at the same time These coexistence mechanisms are only applicable after a WLAN or WPAN are established and user data is to be sent. They do not help in the process for establishing a WLAN or WPANThese coexistence mechanisms are only applicable after a WLAN or WPAN are established and user data is to be sent. They do not help in the process for establishing a WLAN or WPAN

7. 7 Collaborative methods

8. 8 Alternating wireless medium access (AWMA) AWMA is collaborative time division method. Recall that IEEE 802.11b station sends a beacon roughly periodically. In AWMA, part of each beacon period is allocated for WLAN traffic and rest for WPAN traffic. Lengths of these periods are included in the beacon. Synchronization between WPAN and WLAN devices is needed. One WLAN station and WPAN master need wired connection. WLAN station sends a synchronization signal to WPAN master via this connection.

9. 9 Alternating wireless medium access (Cont’d) Recall that Bluetooth/IEEE 802.15.1 use either ACL or SCO connection. AWMA is suitable only for ACL connections. AWMA can prevent interference between WPAN devices in one piconet and all WLAN (IEEE 802.11b) devices connected to same access point (AP) than the one which have physically co-located with WPAN master. Interference between WLAN devices that are connected to some other AP is prevented only if the APs are synchronized. AWMA is quite ineffective in the sense that transmissions of one system are not allowed during the “empty” time windows reserved for the other system. In ACL connections a packet flow is fully controlled by master device, and especially a slave is allowed to start sending an ACL packet in some time slot only if it have first received an ACL packet from the master in the previous time slot. Consequently, the master in piconet can ensure that slaves are transmitting only during time periods reserved for WPAN devices. In practice, this means that the master sends ACL packets only, if there is enough time left in the current WPAN time window for slave to reply with a maximum length ACL packet. SCO connections are mainly meant for live audio traffic. In these connections, a WPAN device sends typically a long flow of SCO packets, such that each packet is sent on a regular basis with a fixed period. (A length of one SCO packet and time gap between consecutive packets depends on used SCO packet type.) In practice, the time windows reserved for WLAN traffic are a way longer than duration of SCO packets and time gap between them, and therefore significant part of SCO data flow would fall into WLAN time windows. On the other hand, the transmitting WPAN device can not hold transmission during the (relatively long) WLAN time windows, because of the nature of data being transmitted via SCO connections. For this reason AWMA is not suitable for SCO connections. The reason why AWMA can prevent interference between WPAN devices in one piconet and all WLAN (IEEE 802.11b) devices connected to same access point (AP) than the one which have physically co-located with WPAN master is that all of these WLAN devices are synchronized i.e. they share a beacon, and thus have a same beacon periods. Similarly, if there are WLAN devices connected to different APs present and APs are synchronized, all the devices have same beacon periods. IEEE 802.15.2 co-existence standard do not give any methods for this AP synchronization. The standard do not deal, either, with case of several WPAN piconets being in the same area with one WLAN network. However, AWMA can be naturally used also then if each WPAN masters is co-located with some WLAN station and share a wired communication link with it.In ACL connections a packet flow is fully controlled by master device, and especially a slave is allowed to start sending an ACL packet in some time slot only if it have first received an ACL packet from the master in the previous time slot. Consequently, the master in piconet can ensure that slaves are transmitting only during time periods reserved for WPAN devices. In practice, this means that the master sends ACL packets only, if there is enough time left in the current WPAN time window for slave to reply with a maximum length ACL packet. SCO connections are mainly meant for live audio traffic. In these connections, a WPAN device sends typically a long flow of SCO packets, such that each packet is sent on a regular basis with a fixed period. (A length of one SCO packet and time gap between consecutive packets depends on used SCO packet type.) In practice, the time windows reserved for WLAN traffic are a way longer than duration of SCO packets and time gap between them, and therefore significant part of SCO data flow would fall into WLAN time windows. On the other hand, the transmitting WPAN device can not hold transmission during the (relatively long) WLAN time windows, because of the nature of data being transmitted via SCO connections. For this reason AWMA is not suitable for SCO connections. The reason why AWMA can prevent interference between WPAN devices in one piconet and all WLAN (IEEE 802.11b) devices connected to same access point (AP) than the one which have physically co-located with WPAN master is that all of these WLAN devices are synchronized i.e. they share a beacon, and thus have a same beacon periods. Similarly, if there are WLAN devices connected to different APs present and APs are synchronized, all the devices have same beacon periods. IEEE 802.15.2 co-existence standard do not give any methods for this AP synchronization. The standard do not deal, either, with case of several WPAN piconets being in the same area with one WLAN network. However, AWMA can be naturally used also then if each WPAN masters is co-located with some WLAN station and share a wired communication link with it.

10. 10 Packet traffic arbitration (PTA) This method can be used in case that coexisting WLAN device and WPAN device are in the same equipment. Both devices are connected to packet traffic arbitrator (PTA-block). Before a device can send a packet it must request a approval for transmission from PTA-block. If the transmission do not results in a collision, PTA-block grants the approval. If both devices send their requests (almost) simultaneously, the one with higher priority is approved to transmit and the other have to wait. Notice, that this method prevents interference only between physically co-located devices, not between all WPAN devices in one piconet and WLAN devices connected to same AP. PTA does not replace CSMA/CA-procedure of IEEE 802.11b WLAN, but takes place after the CSMA/CA. Thus when WLAN device sends a PTA request, it has already made sure that other WLAN devices are not transmitting at same time.Notice, that this method prevents interference only between physically co-located devices, not between all WPAN devices in one piconet and WLAN devices connected to same AP. PTA does not replace CSMA/CA-procedure of IEEE 802.11b WLAN, but takes place after the CSMA/CA. Thus when WLAN device sends a PTA request, it has already made sure that other WLAN devices are not transmitting at same time.

11. 11 PTA (Cont’d) Priorities can be selected deterministically IEEE 802.11b ACK packet (highest) IEEE 802.15.1 SCO packet IEEE 802.11b data packet IEEE 802.15.1 ACL packet (lowest) or in random manner or using some other fairness criteria. This method can be used also with SCO links. And it is also more efficient than previous method. (No need to wait own time window unless collisions are occurring.) Random priority assignment given in IEEE 802.15.2 is as follows: priority ‘2’ is assigned to IEEE 802.11b packet with probability p and priority ‘0’ with probability 1-p. All IEEE 802.15.1 packets have priority ‘1’.Random priority assignment given in IEEE 802.15.2 is as follows: priority ‘2’ is assigned to IEEE 802.11b packet with probability p and priority ‘0’ with probability 1-p. All IEEE 802.15.1 packets have priority ‘1’.

12. 12 Deterministic interference suppression Recall, that Frequency hopping bandwidth of Bluetooth/IEEE 802.15.1 is roughly 1 MHz. Thus, it can be considered as a narrowband interference to IEEE 802.11b (or other frequency static or slow-hopping) WLAN devices. WLAN receiver can mitigate this narrowband interferer by programmable notch filter whose stop band of ~1 MHz is hopping according to hopping process of WPAN device. WLAN device must have an integrated WPAN unit which provides frequency hopping information of interfering WPAN transmission. This method works purely on physical layer and mitigates only interference caused by WPAN devices to WLAN devices.

13. 13 Non-collaborative methods

14. 14 Adaptive Interference Suppression This co-existence method is similar to Deterministic Interference Suppression However, now WLAN device do not need explicit knowledge of FH pattern nor timing of frequency hopping WPAN interferer WLAN transmitter uses adaptive signal processing methods to estimate the location of narrowband interference caused by WPAN and then filter out those frequencies. Also this method works purely on physical layer and mitigates only interference caused by WPAN devices to WLAN devices.

15. 15 Adaptive Interference Suppression (Cont’d) Block diagram of adaptive interference suppression structure. The adaptive filter uses the uncorrelated nature of the wideband IEEE 802.11 signal to predict the unwanted narrowband IEEE 802.15.1 signal. Block diagram of adaptive interference suppression structure. The adaptive filter uses the uncorrelated nature of the wideband IEEE 802.11 signal to predict the unwanted narrowband IEEE 802.15.1 signal.

16. 16 Adaptive packet selection Recall that Bluetooth/IEEE 802.15.1 defines various packet types for both ACL and SCL connections Packet types differ especially in the FEC code used and the amount of channel occupied The basic idea in ‘Adaptive Packet Selection’ is to dynamically select packet types, given either an ACL or SCO link, such that maximal total network capacity is achieved. E.g. if WPAN connection is range limited (rather than interference limited), packet types with stronger FEC coding provide better throughput. SCO packet types are preferred in order HV1, HV2 and HV3 ACL packet types DM1, DM2, DM5 are preferred over DH1, DH2 and DH5 In range limited connection, the background noise is the main limiting factor. Thus in that case FEC coding helps to achieve better throughput, since bit errors have random nature.In range limited connection, the background noise is the main limiting factor. Thus in that case FEC coding helps to achieve better throughput, since bit errors have random nature.

17. 17 Adaptive packet selection (Cont’d) In turn, if WPAN connection is interference limited, FEC coding does not help that much WPAN throughput, but cause more interference to WLAN. SCO packet types are preferred in order HV3, HV2 and HV1. ACL packet types DH1, DH2, DH5 are preferred over DM1, DM2 and DM5. WPAN device can determine the limiting factor by monitoring RSSI (received signal strength indication) and BER (bit error rate) Low RSSI value (and BER) indicates range (noise) limited channel High RSSI value together with high BER indicates interference limited channel In interference limited cases, bit errors tend to have some non-random structure and, for that reason FEC coding does not help much. However, FEC coding always increase the amount of data needed to be sent and, in that way, also the interference to other system is increased.In interference limited cases, bit errors tend to have some non-random structure and, for that reason FEC coding does not help much. However, FEC coding always increase the amount of data needed to be sent and, in that way, also the interference to other system is increased.

18. 18 Packet scheduling for ACL links This method consists of two parts: channel classification and master delay policy First, each Bluetooth/IEEE 802.15.1 device (adaptively) classify each of its FH channels to be ‘good’ or ‘bad’ (more on channel classification later on). Master device collects a table of channel conditions of all devices in piconet. Recall, that in ACL links all slave transmissions are always followed right after master transmission. Consequently, the master can check both the slave's receiving channel and its own receiving channel before choosing to transmit a packet in a given frequency hop. If one (or both) of the channels are marked as ‘bad’, master delays its own transmission until both channels are ‘good’. Notice, that in this coexistence method master must know channel condition table of all slaves. Consequently, an explicit message exchange between the master and the slave device may be required. Nevertheless, IEEE 802.15.2 standard do not propose how this message exchange should be organized. It is also possible to use implicit classification methods such as negative ACKs, in which cases the slave does not have to send any information about its channel classification to the master. Again, this method cannot be used with SCO links for the same reason as collaborative method ‘Alternating wireless medium access’ described earlier. Notice, that in this coexistence method master must know channel condition table of all slaves. Consequently, an explicit message exchange between the master and the slave device may be required. Nevertheless, IEEE 802.15.2 standard do not propose how this message exchange should be organized. It is also possible to use implicit classification methods such as negative ACKs, in which cases the slave does not have to send any information about its channel classification to the master. Again, this method cannot be used with SCO links for the same reason as collaborative method ‘Alternating wireless medium access’ described earlier.

19. 19 Packet scheduling for SCO links A new SCO packet type, EV3, is proposed This packet is based on HV3 packet no FEC coding 240 bits payload one packet for every 6 slots. New features of EV3: Slave transmissions are allowed only right after master transmission. Master can selected which two consecutive time slots of six (three options) are used.

20. 20 Packet scheduling for SCO links (Cont’d) Selection of time slots are again made according to channel classification tables such that both receiving channels (slaves and masters) are ‘good’ if possible.

21. 21 Adaptive frequency hopping (AFH) This method is defined in IEEE 802.15.1 This method dynamically changes the FH sequence of the Bluetooth/802.15.1 system in order to avoid the interference. Global channel classification is needed. Original FH pattern is mapped to subset of channels classified to be ‘good’. The mapping is such that also a new FH pattern becomes pseudorandom.

22. 22 AFH (Cont’d) To work properly, the method requires that there is enough ‘good’ channels. In some countries (like USA), regulatory bodies have set a minimum number of FH channels. Small number of FH channels also affect on system’s robustness. If number of ‘good’ channels is too small, some ‘bad’ channels can be included in hopping pattern. In this case QoS can be guaranteed, if SCO packets are preferred over ACL packets in allocation of ‘good’ channels.

23. 23 Channel classification Most of non-collaborative coexistence methods needs a channel classification information. In channel classification each Bluetooth/IEEE 802.15.1 device classifies each FH channels to be either ‘good’ or ‘bad’. The major concern of the quality should be interference caused by some other system. IEEE 802.15.2 do not define exactly how this classification should be implemented, but it suggests that classification can be based e.g. on RSSI, PER or carrier sensing. RSSI = Received Signal Strength Indicator PER = Packet Error Rate RSSI = Received Signal Strength Indicator PER = Packet Error Rate

24. 24 Channel classification (Cont’d) Since master device needs channel condition tables of its slaves, the tables can be exchanged using LMP messages. It is also possible to use implicit classification methods such as negative ACKs, in which cases the slave does not have to send any additional information to the master. Overall classification time can be reduced by grouping channels to blocks, which naturally reduce the accuracy. LMP = Link Manager Protocol ACK = AcknowledgementLMP = Link Manager Protocol ACK = Acknowledgement

25. 25 Channel classification (Cont’d) In ‘Adaptive Frequency Hopping’ method, global state of each FH channel is needed. The master obtains it by taking a weighted average of its own channel state and all the active slaves’ channel states. Finally, a global channel state for one sub-channel is obtained by threshold comparison of the average, which have value in [0,1]. Before taking an average, channel states, values ‘bad’ or ‘good’, are naturally converted to binary values 0 and 1. If e.g. master device use some more reliable classification method than slaves, it can give more weight to its own channel state value. Before taking an average, channel states, values ‘bad’ or ‘good’, are naturally converted to binary values 0 and 1. If e.g. master device use some more reliable classification method than slaves, it can give more weight to its own channel state value.

26. 26 Current Status of Coexistence Method Development Citation from IEEE 802.15.2 task group’s web page: “The task group is now in hibernation until further notice. ” Several vendors are developing hardware and software coexistence solutions, which are based on IEEE 802.15.2 standard. New WPAN standards (like 802.15.3 and .4) deal also with coexistence issues particular to those systems

27. 27 References IEEE 802.15.2-2003, “IEEE Recommended Practice for Telecommunications and Information exchange between systems – Local and metropolitan area networks Specific Requirements - Part 15.2: Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Band”, IEEE, 2003. T. Cooklev, “Wireless Communication Standards, A Study of 802.11, 802.15, and 802.16”,  IEEE Press, 2004. IEEE 802.15 Working Group for WPAN, http://ieee802.org/15/index.html

28. IEEE 802.15.4 Low-Rate WPAN- Overview Toni Huovinen Lauri Anttila Jarno Niemelä Tero Isotalo

29. 29 Outline Introduction Standardization Device Types and Functions Network Topologies Protocol Architecture Physical Layer Power Consumption Issues References

30. 30 802.15.4 Introduction WPAN – Wireless Personal Area Network Motivation for 802.15.4 : A standard for WPANs with Short-range RF connectivity (typ. < 10 m) Reliable transfer w/ low data rate (20-250 kb/s) Low power consumption (battery life >> 1 month) Very low cost Low complexity Applications: sensors, meter reading, smart tags /badges, light switches, home automation, interactive toys etc. - Many applications require short-range connectivity that is different from Bluetooth. - Two important parameters that Bluetooth cannot address: very low power consumption and very low cost. - Trades off data rate for longer battery life. For the simplest devices, and with careful design, battery life can exceed 10 years. - Basically, the main objective is a simple, but flexible and efficient protocol. - Many LR-WPANs already before this standard, e.g. RF Identification systems.- Many applications require short-range connectivity that is different from Bluetooth. - Two important parameters that Bluetooth cannot address: very low power consumption and very low cost. - Trades off data rate for longer battery life. For the simplest devices, and with careful design, battery life can exceed 10 years. - Basically, the main objective is a simple, but flexible and efficient protocol. - Many LR-WPANs already before this standard, e.g. RF Identification systems.

31. 31 Introduction (cont’d) More 802.15.4 in a nutshell 802.15.4 defines Physical and MAC layers Uses the ISM bands 2.4 GHz, 915 MHz, and 868 MHz with data rates 250, 40, and 20 kb/s, respectively. Direct Sequence Spread Spectrum (DSSS) Access method is Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) Automatic network establishment by the network coordinator Supports star and peer-to-peer network topologies Network can accommodate up to 2^16 devices (cmpr to Bluetooth) 2 addressing modes: 64-bit IEEE address or 16-bit short address Support for critical latency devices, such as joysticks Aims at a certain level of coexistence w/ other standards

32. 32 802.15.4 Standardization 802.15.4 is a recent standard, approved 12 May 2003 Original task group TG4 put to “hibernation” Currently two new task groups TG4a is developing an alternative PHY (Q2 2006 ?) High precision ranging/location capability (< 1 meter) Adding scalability to data rates Longer range (indoors 20-40 m, outdoors up to 1 km) Even lower power consumption and cost TG4b is considering specific enhancements and clarifications to the original 802.15.4-2003 standard Protocol layers above MAC are left to the manufacturers (the ZigBee Alliance) TG4a to be published in the second quarter of 2006 Will add scalability to data rates, which are now fixed at 250 / 40 / 20 kb/s Longer range: indoors 20-40 m, outdoors 300-1000 m T4Gb is “chartered to create a project for specific enhancements and clarifications to the IEEE 802.15.4-2003 standard such as resolving ambiguities, reducing unnecessary complexity, increasing flexibility in security key usage, considerations for newly available frequency allocations, and others.” TG4a to be published in the second quarter of 2006 Will add scalability to data rates, which are now fixed at 250 / 40 / 20 kb/s Longer range: indoors 20-40 m, outdoors 300-1000 m T4Gb is “chartered to create a project for specific enhancements and clarifications to the IEEE 802.15.4-2003 standard such as resolving ambiguities, reducing unnecessary complexity, increasing flexibility in security key usage, considerations for newly available frequency allocations, and others.”

33. 33 Device can act in 3 modes: a network coordinator, a coordinator or a network device A network device can initiate or terminate communications, a coordinator can also route messages Standard defines two device types: Full-function device (FFD) Can be all of the above Reduced-function device (RFD) Can only be a network device No routing ability, and no communication between RFDs Extremely simple applications (light switch, passive sensor) Do not have to send large amounts of data Can be implemented with minimal resources & memory Devices are battery (usually) or mains powered Devices can be fixed, portable and/or moving 802.15.4 Device Types and Functions

34. 34 802.15.4 Network Topologies - In star topology, network devices only communicate with the PAN coordinator. Communications is one-hop, so no routing actually needed. - In P2P, any device can communicate with any other device as long as they are in range of one another. Multi-hop communications possible. - Connectivity to other networks is possible only through the PAN coordinator - In star topology, network devices only communicate with the PAN coordinator. Communications is one-hop, so no routing actually needed. - In P2P, any device can communicate with any other device as long as they are in range of one another. Multi-hop communications possible. - Connectivity to other networks is possible only through the PAN coordinator

35. 35 Two basic network topologies: 1) Star topology One-hop communications, only between PAN coordinator and the network devices Typical applications are home automation, toys, games, PC peripherals 2) Peer-to-peer topology Any device can communicate with any other device as long as they are in range of one another Can be ad-hoc, self-organizing, and self-healing Enables more complex network topologies to be implemented, e.g. cluster-tree networks Multi-hop network formation is defined in the network layer, not part of 802.15.4 Industrial control and monitoring, sensor networks, security Network Topologies (cont’d)

36. 36 802.15.4 Protocol Architecture Standard defines PHY and MAC PHY includes the RF transceiver and its low-level control functions MAC provides access to the physical channel IEEE 802.2 Type 1 logical link control (LLC) can access the MAC sublayer through the service specific convergence sublayer (SSCS) The ZigBee Alliance is working on the upper layers (www.zigbee.org) ZigBee is an alliance of roughly 130 companies (at the moment) that are aiming at developing 802.15.4 compliant products. ZigBee is an alliance of roughly 130 companies (at the moment) that are aiming at developing 802.15.4 compliant products.

37. 37 PHY responsible for the following tasks: Activation/Deactivation of the radio transceiver Energy Detection (ED) within the current channel Link Quality Indication (LQI) for received packets Clear Channel Assessment (CCA) for CSMA-CA Channel frequency adjustment Data transmission and reception PHY provides 2 services PHY data service PHY management service 802.15.4 Physical Layer (PHY) Operates in the ISM bands 2.4 GHz (worldwide), 16 channels 915 MHz (U.S.), 10 channels 868 MHz (Europe), 1 channel Operates in the ISM bands 2.4 GHz (worldwide), 16 channels 915 MHz (U.S.), 10 channels 868 MHz (Europe), 1 channel

38. 38 PHY – Frequency Bands and Data Rates

39. 39 PHY – Frequency Bands and Data Rates

40. 40 PHY –2.4 GHz Mode Each symbol (i.e. 4 bits) is represented by one of 16 32-chip sequences First 8 sequences are cyclic shifts of one 32-chip sequence, last 8 are cyclic shifts of another sequence (see next slide)

41. 41 PHY –2.4 GHz Mode

42. 42 PHY –2.4 GHz Mode Chip modulation is offset-QPSK, in which the Q-branch signal is delayed by one chip period (Tc) with respect to the I-branch signal Pulse shape is half-sine with period 2Tc The result is a constant-envelope signal! (actually, it is equivalent to MSK) Good in terms of Power Amplifier (PA) efficiency, and thus important for low power consumption

43. 43 PHY –2.4 GHz Mode

44. 44 PHY –868/915 MHz Mode

45. 45 PHY –Power levels, PSD masks, sensitivity Tramsmit power is greater than -3 dBm Maximum defined by local authorities (Europe 100 mW, U.S. 1 W !) Maximum received power -20 dBm Sensitivity: -85 dBm (2.4 GHz) or -92 dBm (868/915 MHz)

46. 46 PHY –Packet Structure

47. 47 802.15.4 standard developed for low power consumption Low complexity protocols and physical implementation Additional power management techniques can be used in the physical implementation Area of manufacturer differentiation Battery-powered devices will use duty-cycling Most of the time in sleep-mode (up to 99 %) However, they must listen to network beacons, and stay synchronized to the network ? balance between power consumption and message latency Power Consumption Issues

48. 48 References T. Cooklev, Wireless Communications Standards, A Study of 802.11, 802.15, and 802.16, IEEE Press, 2004. http://standards.ieee.org/getieee802 J. Zheng, M.J. Lee, Will IEEE 802.15.4 Make Ubiguitos Networking a Reality?: A Discussion on a Potential Low Power, Low Bit Rate Standard, IEEE Comm. Magazine, June 2004.

49. IEEE 802.15.4 MAC for LR-WPAN applications Toni Huovinen Lauri Anttila Jarno Niemelä Tero Isotalo

50. 50 Outline Overview of MAC for IEEE 802.15.4 Functionalities Frame types and structures Data transfer Security

51. 51 IEEE 802.15.4 MAC objectives Extremely low cost Easy implementation Reliable data transfer Short range operation Very low power consumption Certain level of security

52. 52 Device classes Full Function Device (FFD) Functions in any topology Able to talk to RFDs or other FFDs Operate in three modes (PAN coordinator, coordinator, and device) Reduced Function Device (RFD) Limited to star topology Can only talk to an FFD (coordinator) Cannot become a coordinator Unnecessary to send large amounts of data Extremely simple Can be implemented using minimal resources and memory capacity In an IEEE 802.15.4 network, at least one FFD is required (working as network coordinator). However, the rest of the devices may be RFDs in order to reduce the system costs and the complexity.In an IEEE 802.15.4 network, at least one FFD is required (working as network coordinator). However, the rest of the devices may be RFDs in order to reduce the system costs and the complexity.

53. 53 An example network

54. 54 MAC functionalities MAC provides two services, namely, the MAC data service and the MAC management service. MAC provides two services, namely, the MAC data service and the MAC management service.

55. 55 Beacon management Beacon enabled mode Slotted CSMA/CA Beacon disabled mode CSMA/CA (similar to one in IEEE 802.11) Generation of beacons if a device is a coordinator Either broadcasting or unicasting of beacons Synchronization performed using beacons An FDD can work either in a beaconless (also beacon disabled) or beacon enabled mode. Moreover, an FDD not operating as PAN coordinator can transmit beacon frames only during an association with a PAN. In a beacon enabled network, a coordinator broadcasts beacons periodically to synchronize the attached devices. On the other hand, in beacon disabled network, the synchronization is performed by polling of coordinator for data.An FDD can work either in a beaconless (also beacon disabled) or beacon enabled mode. Moreover, an FDD not operating as PAN coordinator can transmit beacon frames only during an association with a PAN. In a beacon enabled network, a coordinator broadcasts beacons periodically to synchronize the attached devices. On the other hand, in beacon disabled network, the synchronization is performed by polling of coordinator for data.

56. 56 Association and disassociation Support for WPAN self-configuration (ubiquotous networks) Enables a star to be setup automatically Allows also the creation of self-configuring, peer-to-peer (p2p) network Orphaning offers a way to detect link and/or node failures A realignment procedure can take place An FFD may indicate its presence on a PAN to other devices by transmitting beacon frames. This allows other devices to perform device discovery. An FFD that is not a PAN coordinator begins transmitting beacon frames only when it has successfully associated with a PAN. Association of a device starts after having completed either an active channel scan or a passive channel scan. The passive scan, like an active scan, allows a device to locate any coordinator transmitting beacon frames within its personal operating space (POS) whereas the beacon request command is not required for passive scan. When a coordinator wants one of its associated devices to leave the PAN, it shall send the disassociation notification command to the device using indirect transmission. If an associated device wants to leave the PAN, it shall send a disassociation notification command to the coordinator. Upon reception, the coordinator sends ack. Even if the ack is not received, the device shall consider itself disassociated. A device is considered orphaned if it missed aMaxLostBeacons (default value 4) beacons from its coordinator in a row. Orphaning mechanism is not used by devices that are in beacon disabled mode or in beacons enabled mode but not using beacons tracking. When orphaning happens, the device will try to relocate its coordinator through realignment procedure.An FFD may indicate its presence on a PAN to other devices by transmitting beacon frames. This allows other devices to perform device discovery. An FFD that is not a PAN coordinator begins transmitting beacon frames only when it has successfully associated with a PAN. Association of a device starts after having completed either an active channel scan or a passive channel scan. The passive scan, like an active scan, allows a device to locate any coordinator transmitting beacon frames within its personal operating space (POS) whereas the beacon request command is not required for passive scan. When a coordinator wants one of its associated devices to leave the PAN, it shall send the disassociation notification command to the device using indirect transmission. If an associated device wants to leave the PAN, it shall send a disassociation notification command to the coordinator. Upon reception, the coordinator sends ack. Even if the ack is not received, the device shall consider itself disassociated. A device is considered orphaned if it missed aMaxLostBeacons (default value 4) beacons from its coordinator in a row. Orphaning mechanism is not used by devices that are in beacon disabled mode or in beacons enabled mode but not using beacons tracking. When orphaning happens, the device will try to relocate its coordinator through realignment procedure.

57. 57 MAC frame formats

58. 58 A superframe structure A super frame can have varying length (15 ms – 245 s). However, equal-spaced time slots aer applied. Moreover, a super frame is surrounded by frame beacons. During Contention Access Period (CAP), devices wishing to communicate use slotted CSMA/CA for channel access. On the other hand, an optional Contention Free Period (CFP) contains guaranteed time slots (GTS), which always appear in the end of the active superframe. GTS allow a dedicated bandwidth for low latency applications (or devices). There can be up to seven GTSs in more than one slot period. PAN coordinator is responsible of assigning and maintaining GTSs. A super frame can have varying length (15 ms – 245 s). However, equal-spaced time slots aer applied. Moreover, a super frame is surrounded by frame beacons. During Contention Access Period (CAP), devices wishing to communicate use slotted CSMA/CA for channel access. On the other hand, an optional Contention Free Period (CFP) contains guaranteed time slots (GTS), which always appear in the end of the active superframe. GTS allow a dedicated bandwidth for low latency applications (or devices). There can be up to seven GTSs in more than one slot period. PAN coordinator is responsible of assigning and maintaining GTSs.

59. 59 A superframe with an inactive part A superframe consists of active and inactive parts (bounded by beacons) The length of the superframe (i.e., beacon interval, BI) and the length of its active part (i.e., superframe duration, SD) are define as shown in figure. aBaseSuperframeDuration = 960 symbols BO = Beacon order SO = Superframe order BO and SO are defined by the coordinator. macBeaconOrder (BO) Interval between beacons Beacon Interval (BI) BI = aBaseSuperframeDuration * 2^BO macSuperframeOrder (SO) Length of active portion of the superframe Superframe duration (SD) SD = aBaseSuperframeDuration * 2^SO aBaseSuperframeDuration = 16 * aBaseSlotDuration 0<=SO<=BO<=14 If BO = SO = 15, no beacon -> unslotted CSMA-CAA superframe consists of active and inactive parts (bounded by beacons) The length of the superframe (i.e., beacon interval, BI) and the length of its active part (i.e., superframe duration, SD) are define as shown in figure. aBaseSuperframeDuration = 960 symbols BO = Beacon order SO = Superframe order BO and SO are defined by the coordinator. macBeaconOrder (BO) Interval between beacons Beacon Interval (BI) BI = aBaseSuperframeDuration * 2^BO macSuperframeOrder (SO) Length of active portion of the superframe Superframe duration (SD) SD = aBaseSuperframeDuration * 2^SO aBaseSuperframeDuration = 16 * aBaseSlotDuration 0<=SO<=BO<=14 If BO = SO = 15, no beacon -> unslotted CSMA-CA

60. 60 Network forming WPAN has to be initiated by a FFD Active or passive scan Selection of suitable PAN identifier An FDD becomes a coordinator The active channel scan consists of transmitting the beacon request command in every channel. If a PAN coordinator exists, in addition to response to a beacon request command, will start transmitting beacons. A passive scan is performed by merely listening for beacons in every channel.The active channel scan consists of transmitting the beacon request command in every channel. If a PAN coordinator exists, in addition to response to a beacon request command, will start transmitting beacons. A passive scan is performed by merely listening for beacons in every channel.

61. 61 Data transfer/transactions (1) From a device to a coordinator (2) From a coordinator to a device (3) From one peer to another in a peer-to-peer multihop network OR (1) Direct data transmission (2) Indirect data transmission (3) GTS (guarantee time slot) data transmission Direct data transmission applies to all data transfers, either from a device to a coordinator, from a coordinator to a device, or between two peers. Indirect data transmission applies to transfer from a coordinator to its devices. In this mode, a data frame is kept in a transaction list by the coordinator, waiting for extraction by the corresponding device. A device can find out if it has a packet pending in the transaction list by checking the beacon frames received from its coordinator. GTS data transmission is can be applied between a device and its coordinator, either from the device to the coordinator or from the coordinator to the device. No CSMA/CA is needed in GTS data transmission.Direct data transmission applies to all data transfers, either from a device to a coordinator, from a coordinator to a device, or between two peers. Indirect data transmission applies to transfer from a coordinator to its devices. In this mode, a data frame is kept in a transaction list by the coordinator, waiting for extraction by the corresponding device. A device can find out if it has a packet pending in the transaction list by checking the beacon frames received from its coordinator. GTS data transmission is can be applied between a device and its coordinator, either from the device to the coordinator or from the coordinator to the device. No CSMA/CA is needed in GTS data transmission.

62. 62 Communication from device to coordinator When a device wishes to transfer data to a coordinator in a beacon-enabled network, it first listens for the network beacon. When the beacon is found, it synchronizes to the superframe structure. At the right time, it transmits its data frame, using slotted CSMA-CA, to the coordinator. There is an optional acknowledgement at the end. When a device wishes to transfer data in a nonbeacon-enabled network, it simply transmits its data frame, using the unslotted CSMA-CA, to the coordinator. There is also an optional acknowledgement at the end. Hence, the applications transfers are completely controlled by the devices on a PAN rather than by the coordinator (energy-conservation feature).When a device wishes to transfer data to a coordinator in a beacon-enabled network, it first listens for the network beacon. When the beacon is found, it synchronizes to the superframe structure. At the right time, it transmits its data frame, using slotted CSMA-CA, to the coordinator. There is an optional acknowledgement at the end. When a device wishes to transfer data in a nonbeacon-enabled network, it simply transmits its data frame, using the unslotted CSMA-CA, to the coordinator. There is also an optional acknowledgement at the end. Hence, the applications transfers are completely controlled by the devices on a PAN rather than by the coordinator (energy-conservation feature).

63. 63 Communication from coordinator to device When a coordinator wishes to transfer data to a device in a beacon-enabled network, it indicates in the network beacon that the data message is pending. The device periodically listens to the network beacon, and if a message is pending, transmits a MAC command requesting this data, using slotted CSMA/CA. The coordinator optionally acknowledges the successful transmission of this packet. The pending data frame is then sent using slotted CSMA/CA. The device acknowledged the successful reception of the data by transmitting an acknowledgement frame. Upon receiving the acknowledgement, the message is removed from the list of pending messages in the beacon. When a coordinator wishes to transfer data to a device in a nonbeacon-enabled network, it stores the data for the appropriate device to make contact and request data. A device may make contact by transmitting a MAC command requesting the data, using unslotted CSMA-CA, to its coordinator at an application-defined rate. The coordinator acknowledges this packet. If data are pending, the coordinator transmits the data frame using unslotted CSMA-CA. If data are not pending, the coordinator transmits a data frame with a zero-length payload to indicate that no data were pending. In a peer-to-peer network, every device can communicate with any other device in its transmission radius. There are two options for this. In the first case, the node will listen constantly and transmit its data using unslotted CSMA-CA. In the second case, the nodes synchronize with each other so that they can save power.When a coordinator wishes to transfer data to a device in a beacon-enabled network, it indicates in the network beacon that the data message is pending. The device periodically listens to the network beacon, and if a message is pending, transmits a MAC command requesting this data, using slotted CSMA/CA. The coordinator optionally acknowledges the successful transmission of this packet. The pending data frame is then sent using slotted CSMA/CA. The device acknowledged the successful reception of the data by transmitting an acknowledgement frame. Upon receiving the acknowledgement, the message is removed from the list of pending messages in the beacon. When a coordinator wishes to transfer data to a device in a nonbeacon-enabled network, it stores the data for the appropriate device to make contact and request data. A device may make contact by transmitting a MAC command requesting the data, using unslotted CSMA-CA, to its coordinator at an application-defined rate. The coordinator acknowledges this packet. If data are pending, the coordinator transmits the data frame using unslotted CSMA-CA. If data are not pending, the coordinator transmits a data frame with a zero-length payload to indicate that no data were pending. In a peer-to-peer network, every device can communicate with any other device in its transmission radius. There are two options for this. In the first case, the node will listen constantly and transmit its data using unslotted CSMA-CA. In the second case, the nodes synchronize with each other so that they can save power.

64. 64 Traffic types/examples Periodic data Application defined data rate (e.g., sensors) Intermittent data (generated ) Application / external stimulus defined data rate (e.g., ligth switch) Repetitive low latency data GTS Allocation of time slots (e.g., mouse) Periodic data can be handled using the beaconing system whereby the sensor will wake up for the beacon, check for any messages and then go back to sleep. Intermittent data can be handled either in a beaconless system or in a disconnected fashion. In a disconnected operation, the device will only attach to the network when it needs to communicate saving significant energy. Low latency applications may choose to the guaranteed time slot (GTS) option. GTS is a method of QoS in that it allows each device a specific duration of time each superframe to do whatever it wishes to do without contention or latency.Periodic data can be handled using the beaconing system whereby the sensor will wake up for the beacon, check for any messages and then go back to sleep. Intermittent data can be handled either in a beaconless system or in a disconnected fashion. In a disconnected operation, the device will only attach to the network when it needs to communicate saving significant energy. Low latency applications may choose to the guaranteed time slot (GTS) option. GTS is a method of QoS in that it allows each device a specific duration of time each superframe to do whatever it wishes to do without contention or latency.

65. 65 MAC QoS QoS can be provided by upper layers Different traffic types Priority in queuing during CAP (high or normal priority) In beacon enabled networks, contention free period provides QoS

66. 66 802.15.4 security overview Access control Prevents unauthorized access Message integrity Authentication and integrity provided using message integrity code (MIC) Message confidentiality Encryption applied Replay protection Packet numbering IEEE 802.15.4 security is provided by MAC

67. 67 MAC security modes Unsecured mode Mandatory for all devices However, does not provide any security ACL (access control list) mode Optional No cryptographical methods applied Secured mode Optional Advanced Encryption Standard (AES) If security is not an important factor for the application op the upper layer already provides sufficient security protection, a device can select unsecured mode for data transfer. ACL is composed of devices with which a key is shared. A device can use ACL to prevent unauthorized devices from accessing its data. However, any cryptographical methods are not applied. Secured mode has all four security services: - access control list - data encryption - frame integrity - sequential freshnessIf security is not an important factor for the application op the upper layer already provides sufficient security protection, a device can select unsecured mode for data transfer. ACL is composed of devices with which a key is shared. A device can use ACL to prevent unauthorized devices from accessing its data. However, any cryptographical methods are not applied. Secured mode has all four security services: - access control list - data encryption - frame integrity - sequential freshness

68. 68 Security suites Set of operations for ensuring security Indicates the symmetric cryptographic algorithm mode integrity code bit length Integrity done using AES The 802.15.4 specification defines eight different security suites (Table). Null – no security AES-CTR – encryption only (in counter mode) AES-CBC-MAC – authentication only (Cipher Block Chaining, CBC) AES-CCM encryption and authentication Message authentication code (MAC) = Message integrity code (MIC)The 802.15.4 specification defines eight different security suites (Table). Null – no security AES-CTR – encryption only (in counter mode) AES-CBC-MAC – authentication only (Cipher Block Chaining, CBC) AES-CCM encryption and authentication Message authentication code (MAC) = Message integrity code (MIC)

69. 69 Security suites (cont’d) AES-CTR Access control Encryption Sequential freshness AES-CBC-MAC (cipher block chaining, CBC) Access control Authentication AES-CCM Mixture of CTR and CBC-MAC modes (CCM) Provides all four security services

70. 70 References IEEE 802.15.4 Specifications: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs), available online: http://standards.ieee.org/getieee802/download/802.15.4-2003.pdf T. Cooklev, Wireless Communications Standards, A Study of 802.11, 802.15, and 802.16,  IEEE Press, 2004. N. Satyr, D. Wagner, “Security considerations for IEEE 802.15.4 networks,” Wise 2004, USA. S. Ergen, “Zigbee/IEEE 802.15.4 Summary,” available online: http://www.eecs.berkeley.edu/~csinem/academic/publications/zigbee.pdf J. Zheng, M. Lee, “Will IEEE 802.15.4 make ubiquitous networking a reality? –A discussion on a potential low power, low bit rate standard,” IEEE Communications Magazine, vol. 42, no. 6, Jun 2004 pp. 140-146

71. Low-Rate WPANExamples, Trends and Products Toni Huovinen Lauri Anttila Jarno Niemelä Tero Isotalo

72. 72 Contents Overview Zigbee Comparison to other 802.15 standards Other techniques RFID BodyLan FAN (Fabric area networks)

73. 73 Overview Need for lower power consuming and cheaper equipment standard compared to 802.11 and 802.15 WLAN/BT widely in use, but they are too expensive, consume too much battery and have too complicated protocol stack to be used in sensor-networks and in different wireless controlling Ready products using 802.15.4 not yet in the market However, 802.15.4/Zigbee compatible chipsets and plug-in units are already available Planned areas: wireless automated monitoring and control of facilities, home-appliance networks, home healthcare, etc. Zigbee using 802.11.4, similar systems: Bodylan, Wireless USB, ...

74. 74 Zigbee Bases on 802.11.4 MAC/PHY, sometimes used also as a nickname for 802.11.4 Ultra-low complexity, ultra-low cost, ultra-low power consumption, and low data rate (20-250 kb/s) wireless connectivity among inexpensive devices 64k (2^16) network nodes

75. 75 Zigbee Alliance Non-profit industry consortium defining a global specification for reliable, cost-effective, low power wireless applications based on the IEEE 802.15.4 standard. Six promoters (Honeywell, Invensys, Mitsubishi, Motorola, Philips, and Samsung) and more than 100 participants Performs marketing and compliance certification for 15.4 Not officially associated with the IEEE “Wireless Control that Simply Works™” www.zigbee.org

76. 76 Uses of Zigbee

77. 77 Zigbee / IEEE 802.15.4Protocol Stack Divided Responsibility Lower (MAC/PHY) stacks IEEE 802.15.4 Upper stacks Zigbee Alliance IEEE 802 compatible LLC protocol can be used

78. 78 Zigbee Protocol Stack There are ready programmed protocol stacks available in the market Some chip manufactors have specific stacks for their own chips, and some companies, i.e., Ember, Figure8, Helicomm, provide common stacks

79. 79 Zigbee Network Model (1) Star, mesh, or combined Star/Mesh –type network

80. 80 Zigbee Network Model (2) Flexible topology of Zigbee network consists of reduced function nodes, and full function nodes Reduced function nodes can not communicate with each others Communication goes through full function nodes, and requires also network coordinator Full function nodes can work as a coordinator => Star topology

81. 81 Zigbee Network Model (3) Network can consist also only of full function nodes In such case, all equipment are equal and can communicate with each others => Mesh topology Wider networks form from combined star and mesh topology networks

82. 82 Zigbee Network Model (4) 16/64 –bit addressing Large amount of network nodes, even up to 64k (16-bit) nodes (cf. 7 nodes in bluetooth) Can be used in wide automation networks that do not require large bandwidth

83. 83 Zigbee Module

84. 84 Business Trends Multiple of manufactors are developing Zigbee chips Compelete chips (PHY+MAC): Motorola/Freescale, Chipcon, Atmel, Panasonic,... RF chips (PHY): ZMD, CompXS, ... Chips already available on the market Chip sizes beginning from 20x15x1.8 mm First applications expected soon

85. 85 Commercial Example:iBean Product Family (1)

86. 86 Commercial Example:iBean Product Family (2) 802.15.4 and Zigbee compatible Also non-compatible products using other frequency bands More information: www.millennial.net

87. 87 Competitors for ZigBee In addition to other 802. techniques, there is some technique very similar to Zigbee competing from same applications Typically working at 2.4G ISM frequency i.e. Cypress, and finnish Espotel ERF

88. 88 Comparison to other standards (1)

89. 89 Comparison to other standard (2)

90. 90 Comparison to other standards (2)

91. 91 Competitors for ZigBee: Cypress Called WirelessUSB (different from Wireless USB) low memory consumption protocol stack (4kB vs 32kB in Zigbee) Star-topology network 50m range, low power consumption automatic interference regognition Used for PC mice/keyboards, but looking for new areas

92. 92 Competitors for ZigBee:Espotel ERF Designed to replace Bluetooth in industry automation sensors and embedded systems Lighter protocol stack compared to bluetooth Can use Zigbee chips, but does not fit into the standard Energy consumption at the same level with Zigbee Lower total cost due to missing standardization reguirements Missing standard makes it easier to fit customers need, but lack of compatibility may cause problems

93. 93 On-Body-Networking Provide connectivity between different sensors and other equipments in wearable electronics Sports, Medicine, Police, Fireman, Astronauts ... BodyLan, FAN (Fabric Area Network)

94. 94 BodyLan Consept

95. 95 Comparison of Different BodyLan Techniques

96. 96 Future..? Although present and close future world looks like totally networked, more is coming Independent sensors of size of 1c coin are already reality, but consept called ’smart dust’ is under development. Target is to have sensors size of a dust particle, and they would be everywhere around, and they would work with e.g. solar power Ability to form networs automatically Such projects are going on in many universities, also in TUT/TKT

97. 97 References [1] Roy L. Ashok Dharma P.Agrawal, ”Next-Generation Wearable Networks”, Computing Practices, IEEE Computer Society, 2003 [2] Philip Kuryloski and Sameer Pai, ”Our Crossbow Sensor Equipment and Zigbee”, wisl.ece.cornell.edu/presentations/MICAz.pdf, [3] Zigbee Alliance, ”Wireless Control That Simply Works” www.zigbee.org [4] Krister Wikström, ”Zigbee tuotteistuu”, Prosessori 1/2005 [5] Shigeru Fukunaga, Tadamichi Tagawa, Kiyoshi Fukui, Koichi Tanimoto, Hideaki Kanno, ” Development of Ubiquitous Sensor Network”, Oki Technical Review, October 2004/Issue 200 Vol.71 No.4

98. 98 Q: What is the origin of theZigBee name? The domestic honeybee, a colonial insect, lives in a hive that contains a queen, a few male drones, and thousands of worker bees. The survival, success, and future of the colony is dependent upon continuous communication of vital information between every member of the colony. The technique that honey bees use to communicate new-found food sources to other members of the colony is referred to as the ZigBee Principle. Using this silent, but powerful communication system, whereby the bee dances in a zig-zag pattern, she is able to share information such as the location, distance, and direction of a newly discovered food source to her fellow colony members. Instinctively implementing the ZigBee Principle, bees around the world industriously sustain productive hives and foster future generations of colony members. [3]