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WPAN IEEE 802.15.4 (ZigBee) WWAN < 15 km 802.20, GSM, GPRS, CDMA, 2.5G, 3G, 4G WMAN < 5 km 802.16 – 70 Mbps LMDS – 38 Mbps WLAN < 150 m 11 – 54 Mbps 802.11 HiperLAN/2 WPAN < 10 m Bluetooth、UWB、 Zigbee 无线通信网络分类图 Common Aliases for Wireless Standards 802.11 Wi-Fi 802.15.1 Bluetooth 802.15.3 Ultra Wideband 802.15.4 ZigBee 802.16 WiMAX IEEE 802.15 Working Group for Wireless Personal Area Networks • The 802.15 WPAN effort focuses on the development of consensus standards for Personal Area Networks (PAN) or short distance wireless networks • WPANs address wireless networking of portable and mobile computing devices such as: PCs, Personal Digital Assistants (PDAs), peripherals, cell phones, pagers, and consumer electronics; allowing these devices to communicate and interoperate with one another. Example of home equipment demanding network operations IEEE Project 802 Standards WLAN WPAN WMAN LR-WPAN IEEE 802.15 Working Group IEEE 802.15 Protocol Architecture Wireless Local Networks Bluetooth • In 1998 – Ericsson, IBM, Toshiba, Nokia and Intel form Bluetooth Special Interest Group (SIG). • Harald Bluetooth – Danish king who lived more than 1000 years ago • • • • • Universal short-range wireless capability Uses 2.4-GHz band Available globally for unlicensed users Devices within 10 m can share up to 720 kbps of capacity Supports open-ended list of applications – Data, audio, graphics, video • Data rate – 1 Mbps Bluetooth Applications Landline Cable Replacement Data/Voice Access Points - Synchronization - Cordless Headset …and combinations! Personal Ad-hoc Networks It is reported that more than two billion Bluetooth-ready devices were shipped during 2012 – over 50 millions every day. Radio Specification • Classes of transmitters (on which Bluetooth products are available): – Class 1: Outputs 100 mW for maximum range • Power control mandatory • Provides greatest distance – up to 100 m • Products: still available – Class 2: Outputs 2.4 – 2.5 mW at maximum • Power control optional • Transmission distance – 10 m • Products: most common – Class 3: Nominal output is 1 mW • Lowest power • Transmission distance – 10 cm – 1 m • Products - rare Bluetooth Standards Documents • Core specifications – Details of various layers of Bluetooth protocol architecture • Profile specifications – Use of Bluetooth technology to support various applications Bluetooth Protocol Stack Bluetooth Protocol Stack Composed of protocols to allow Bluetooth devices to locate each other and to create, configure and manage both physical and logical links that allow higher layer protocols and applications to pass data through these transport protocols Applications IP SDP Data Audio Transport Protocol Group RFCOMM L2CAP Link Manager Baseband RF Bluetooth Protocol Stack Applications IP SDP Middleware Protocol Group RFCOMM Data L2CAP Additional transport protocols to allow Audio Link Manager existing and new applications to Baseband operate over Bluetooth. Packet based RF telephony control signaling protocol also present. Also includes Service Discovery Protocol. Bluetooth Protocol Stack Applications IP Application Group SDP RFCOMM Data Consists of Bluetooth aware as well as un-aware applications. Audio L2CAP Link Manager Baseband RF Link Manager Protocol Applications IP SDP RFCOMM Data Audio L2CAP Link Manager Baseband RF LMP Setup and management of Baseband connections • Piconet Management • Link Configuration • Security L2CAP Applications IP SDP RFCOMM L2CAP - Logical Link Control and Adaptation Protocol Data Audio L2CAP Link Manager Baseband RF L2CAP provides • Protocol multiplexing • Segmentation and Re-assembly • Quality of service negotiation RFCOMM (Radio Frequency Communication) -- Serial Port Emulation using RFCOMM Applications IP SDP RFCOMM Data Audio L2CAP Link Manager Baseband RF Serial Port Serial Port emulation on top of a packet oriented link • Similar to HDLC (High level Data Link Control protocol) • RS232 • For supporting legacy apps Usage Models • • • • • • File transfer Internet bridge LAN access Synchronization Three-in-one phone Headset Piconets and Scatternets • Piconet – Basic unit of Bluetooth networking – Master and one to seven slave devices – Master determines channel and phase • Scatternet – Device in one piconet may exist as master or slave in another piconet – Allows many devices to share same area – Makes efficient use of bandwidth Physical Links between Master and Slave • Synchronous connection oriented (SCO) – Allocates fixed bandwidth between point-to-point connection of master and slave – Master maintains link using reserved slots – Master can support three simultaneous links • Asynchronous connectionless (ACL) – Point-to-multipoint link between master and all slaves – Only single ACL link can exist Connection Setup • Inquiry(查询消息) – Master 查找附近的蓝牙 设备,以便通过收集来自 从节点响应查询消息中得 到该节点的设备地址( 48b)和时钟 • Inquiry – scan(查询扫描) – Slave设备周期地监听来自其他设备的查询消 息,以便自己能被发现,并在监听到后发送它 的地址和时钟信息。 Connection Setup • Page (寻呼) – Master 通过在不同的跳频序列发送消息,来激活一个从 节点, 并建立连接。调频序列由slaver的地址码计算出 • Page – scan(寻呼扫描) – Slaver 周期性地在扫描窗间隔时间内唤醒自己,并监听 自己的访问码, Slaver节点每隔1.28s在这个扫描窗上根 据寻呼跳频序列选择一个扫描频率 Master Active Slave Parked Slave -Connected -Not in Pico Standby Bluetooth Packet Fields • Access code – used for timing synchronization, offset compensation, paging, and inquiry • Header – used to identify packet type and carry protocol control information • Payload – contains user voice or data and payload header, if present Frame Format of Bluetooth Packets • • The 48 bit address unique to every Bluetooth device is used as the seed to derive the sequence for hopping frequencies of the devices. Four types of access codes: – – – – • Type 1: identifies a “M” terminal and its piconet address Type 2: identifies a “S” identity used to page a specific “S”. Type 3: Fixed access code reserved for the inquiry process Type 4: dedicated access code reserved to identify specific set of devices such as fax machines, printers, or cell phones. Header: 18 bits repeated 3 times with a 1/3 FEC code 72 54 access code packet header 4 preamble 64 sync. (4) (trailer) 3 S address 4 type 0-2745 payload 1 flow bits 1 ARQN 1 SEQN 8 HEC bits WPAN: IEEE 802.15 • • 802.15-2: Coexistence – Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local Area Networks (802.11), quantify the mutual interference 802.15-3: High-Rate – Standard for high-rate (20Mbit/s or greater) WPANs, while still low-power/low-cost – Quality of Service isochronous protocol – Ad hoc peer-to-peer networking – Security – Low power consumption – Low cost – Designed to meet the demanding requirements of portable consumer imaging and multimedia applications ZigBee • ZigBee - a specification set of high level communication protocols designed to use small, low power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs) • This technology is designed to be simpler and cheaper than other WPANs (such as Bluetooth) • ZigBee uses the IEEE 802.15.4 Low-Rate Wireless Personal Area Network (WPAN) standard to describe its lower protocol layers—the physical layer (PHY), and the medium access control (MAC) portion of the data link layer (DLL). ZigBee Applications monitors sensors automation control monitors diagnostics sensors INDUSTRIAL & COMMERCIAL CONSUMER ELECTRONICS TV VCR DVD/CD remote ZigBee PERSONAL HEALTH CARE consoles portables educational Reference from ZigBee Alliance Inc. LOW DATA-RATE RADIO DEVICES TOYS & GAMES HOME AUTOMATION PC & PERIPHERALS security HVAC lighting closures mouse keyboard joystick Development of the Standard APPLICATION Customer ZIGBEE STACK SILICON ZigBee Alliance IEEE 802.15.4 • ZigBee Alliance – 50+ companies – Defining upper layers of protocol stack: from network to application, including application profiles • IEEE 802.15.4 Working Group – Defining lower layers : MAC and PHY IEEE 802.15.4 Overview • Wireless Personal Area Networks (WPANs) – short distance – small (ultra low complexity) – low duty-cycle (<0.1%) – power efficient (the most important factor) – inexpensive (ultra low cost) solutions. • Typically operating in the Personal Operating Space (POS) of 10 meters. • Supporting star and peer-to-peer topologies – controlled by the PAN coordinator IEEE 802.15.4 standard • Includes layers up to and including Link Layer Control – LLC is standardized in 802.1 • Supports multiple network topologies including Star, Cluster Tree and Mesh • Channel scan for beacon is included, but it is left to the network layer to implement dynamic channel selection ZigBee Application Framework • Low complexity: 26 service primitives versus 131 service primitives for 802.15.1 (Bluetooth) Networking App Layer (NWK) Data Link Controller (DLC) IEEE 802.15.4 LLC IEEE 802.2 LLC, Type I IEEE 802.15.4 MAC IEEE 802.15.4 868/915 MHz PHY IEEE 802.15.4 2400 MHz PHY IEEE 802.15.4 Features • Media access is contention based. – Using carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol – Similar to IEEE 802.11 CSMA/CA protocol, but not the same • Provide the optional Superframe structure – The PAN coordinator periodically allocates guaranteed time slots (GTS) to low latency devices • Dynamic device addressing – Two kinds of address of a device – 16-bit Short Address – 64-bit Extended Address • Fully acknowledged protocol for transfer reliability. Device Classes • There are two different device types : – A full function device (FFD) – A reduced function device (RFD) • The FFD can operate in three modes serving – Device – Coordinator – PAN coordinator • The RFD can only operate in a mode serving: – Device • Coordinator provides synchronization information to other devices FFD vs RFD • Full function device (FFD) – Any topology – Network coordinator capable – Talks to any other device • Reduced function device (RFD) – – – – Limited to star topology Cannot become a network coordinator Talks only to a network coordinator Very simple implementation Network Topologies • Star and Peer2Peer Topologies Network Topologies • Star network formation: – An FFD may establish its own network and become the PAN coordinator. – All star networks operate independently. – Choosing a PAN identifier, which is not currently used by any other network within the radio sphere of influence. – Both FFDs and RFDs may join the network. • Peer-to-peer network formation: – Each device is capable of communicating with any other device. – One FFD device will be nominated as the PAN coordinator. Star Topology • Home Application FFD RFD FFD PAN coordinator RFD RFD RFD FFD Cluster Tree Topology • Only one PAN coordinator • No detail yet Cluster Head PAN coordinator Cluster Tree Establishment • The PAN coordinator forms the first cluster by establishing itself as the cluster head (CLH) with a cluster identifier (CID) of zero. • Choosing an unused PAN identifier (PANID) and broadcasting beacon frames to neighboring devices. • A candidate device receiving a beacon frame may request to join the network at the CLH. • If the PAN coordinator permits the device, it will add the new device as a child device in its Access Control List (ACL). • The newly joined device will add the CLH as its parent in its ACL, and begin transmitting periodic beacons. • Other candidate devices may then join the network at that device. A larger network (PAN) is possible by forming a mesh of multiple neighboring clusters. • The PAN coordinator may instruct a device to become the CLH of a new cluster adjacent to the first one. • Other devices gradually connect and form a multi-cluster network structure. Addressing Methods • Two or more devices with a POS communicating on the same physical channel constitute a WPAN which includes at least one FFD (PAN coordinator) • Each independent PAN will select a unique PAN identifier • All devices operating on a network shall have unique 64-bit extended address. This address can be used for direct communication in the PAN • The address can use a 16-bit short address, which is allocated by the PAN coordinator when the device associates • Addressing modes: – Network + device identifier (star) – Source/destination identifier (peer-peer) – Source/destination cluster tree + device identifier (cluster tree) MAC/PHY Functions • Functions in PHY sublayer – – – – – activation and deactivation of the radio transceiver energy detection link quality indication clear channel assessment (CCA) - carrier sense transmitting/receiving bit stream • Functions in MAC sublayer – – – – – – – – beacon management channel access (slotted or unslotted CSMA/CA) guarantee time slot management (QoS) frame validation acknowledged frame delivery association disassociation security mechanisms (AES) PHY Specifications • The standard specifies two PHYs : – 868 MHz/915 MHz direct sequence spread spectrum (DSSS) PHY (11 channels) • 1 channel (20Kb/s) in European 868MHz band • 10 channels (40Kb/s) in 915 (902-928)MHz ISM band – 2450 MHz direct sequence spread spectrum (DSSS) PHY (16 channels) • 16 channels (250Kb/s) in 2.4GHz band PHY Specification • PHY functionalities: – – – – – – Activation and deactivation of the radio transceiver Energy detection within the current channel Link quality indication for received packets Clear channel assessment for CSMA-CA Channel frequency selection Data transmission and reception PHY Specification Operating Frequency Range BAND 2.4 GHz ISM 868 MHz 915 MHz ISM COVERAGE DATA RATE CHANNEL(S) Worldwide 250 kbps 16 Europe 20 kbps 1 Americas 40 kbps 10 • A total of 27 channels, numbered 0 to 26, are available across the three frequency bands. • 16 channels are for 2450 MHz, 10 are for 915 MHz an 1 is for 868 MHz. PHY Parameters • Transmit Power – Capable of at least 1 mW – Power reduction capability required if > 16 dBm (reduce to < 4 dBm in single step) • Transmit Center Frequency Tolerance – 40 ppm • Receiver Sensitivity – -85dBm (2450 MHz) – -92dBm (868/915 MHz) – 1% Packet Error Rate in PSDU = 20 Bytes) • RSSI Measurements – – – Packet strength indication Clear channel assessment Dynamic channel selection PHY PDU Format (PPDU) • PHY Packet Fields – A synchronization header • Preamble (32 bits) – 32 binary zeros used for synchronization • Start of Packet Delimiter (8 bits) – 10100111 – A PHY header • PHY Header (8 bits) – 7-bit frame length (0-127) and 1-bit reserved – A payload • PSDU (0 to 127 bytes) – Data field 4 Bytes 1 Byte 1 Byte Preamble Start of Packet Delimiter PHY Header 6 Bytes PHY Service Data Unit (PSDU) 0-127 Bytes MAC Options • Two channel access mechanisms – Non-beacon network • Standard CSMA-CA communications + ACK • Non-beacon mode is useful in situations where only light traffic is expected – Beacon-enabled network • Superframe structure – Set up by network coordinator to transmit beacons at predetermined intervals – 15ms to 252sec, slotted CSMA-CA – In general, the ZigBee protocols minimize the time the radio is on, so as to reduce power use. • In beaconing networks, nodes only need to be active while a beacon is being transmitted. • In non-beacon-enabled networks, power consumption is decidedly asymmetrical: some devices are always active, while others spend most of their time sleeping. Example of Non-Beacon Net • Commercial or home security – Client units (intrusion sensors, motion detectors, glass break detectors, standing water sensors, loud sound detectors, etc) • Sleep 99.999% of the time • Wake up on a regular yet random basis to announce their continued presence in the network (“12 o’clock and all’s well”) • When an event occurs, the sensor wakes up instantly and transmits the alert (“Somebody’s on the front porch”) – The ZigBee Coordinator, mains powered, has its receiver on all the time and so can wait to hear from each of these stations • Since ZigBee Coordinator has “infinite” source of power it can allow clients to sleep for unlimited periods of time to allow them to save power Example of Beacon Network • Now make the ZigBee Coordinator battery-operated also – Client registration to the network • Client unit when first powered up listens for the ZigBee Coordinator’s network beacon (interval between 0.015 and 252 seconds) • Register with the coordinator and look for any messages directed to it • Return to sleep, awaking on a schedule specified by the ZigBee Coordinator – Once client communications are completed, ZigBee coordinator also returns to sleep • Application examples: environmental sensors in the forest 数据到主协调器的通信顺序 Beacon-enabled network • 从设备监听网络的信标 • 从设备与超帧结构进行同步 • 从设备使用有时隙的CSMA-CA向主协调器发送数 据帧 • 当主协调器接收到该数据帧后,将返回确认帧 数据到主协调器的通信顺序 Non-Beacon-enabled network Beacon-enabled network 主协调器发送数据 •• 从设备从网络信标中发现存在有主协调器要发送 主协调器收到数据请求命令后,返回一个确认 从设备收到该数据帧后,将返回一个确认 主协调器收到确认帧后,将数据信息从主 主协调器发送网络信标中表明存在有要传 给它的数据信息时,采用有时隙的CSMA-CA机制 帧,并采用有时隙的CSMA-CA机制,发送要 帧,表示该数据传输事务已处理完成 协调器的信标未处理信息列表中删除 输的数据信息。 ,发送一个数据请求命令 。 传输的数据信息帧 Non-Beacon-enabled network 主协调器发送数据 • 非信标网络中传输数据给从设备时,主协调器存 储着要传输的数据,由从设备先发送请求数据传 输命令后,才能进行数据传输 MAC Specifications • Superframe Structure – Optional (named as beacon-enabled network) – The format of the superframe is define by the PAN coordinator – Bounded by network beacons and sent by the PAN coordinator – Divided into 16 equally sized slots and beacon is transmitted in the first slot – It consists of two periods • Contention Access Period (CAP) • Contention Free Period (CFP) – Objectives of the beacons • synchronize • identify the PAN • describe the structure of the superframes MAC Specifications • • • • • • The superframe can have an active and an inactive portion. • During the inactive portion the coordinator shall not interact with its PAN and may enter a low power mode. The PAN coordinator may allocate portions of the active superframe to some applications and these portions are called guaranteed time slots (GTSs). The GTSs comprise the contention free period (CFP). The PAN coordinator may allocate up to 7 GTSs at the same time A GTS may occupy more than one slot period A sufficient portion of the CAP shall remain for contention. MAC Specifications • Any device wishing to communicate during the CAP between two beacons shall compete with other devices using a slotted CSMA-CA mechanism. • All transactions shall be completed by the time of the next network beacon • If the coordinator does not wish to use a superframe structure, it can turn off the beacon transmissions – named as non beacon-enabled network – Using Unslotted CSMA/CA Superframe Structure • The structure of this superframe is described by the values of macBeaconOrder (BO) and macSuperframeOrder (SO). – The macBeaconOrder describes the interval at which the coordinator shall transmit its beacon frames. – The macSuperframeOrder describes the length of the active portion of the superframe, which includes the beacon frame. Superframe Structure • The values of BO and the beacon interval (BI) are related as follows: BI = aBaseSuperframeDuration 2BO symbols, if 0BO14 • The values of SO and the superframe duration (SD) are related as follows: SD = aBaseSuperframeDuration 2SO symbols, if 0SOBO14 • Note : If BO = 15, the coordinator will not transmit beacon and the value of SO shall be ignored. (non beacon-enable network) Moreover, macRxOnWhenIdle defines whether the receiver is enabled during periods of transceiver inactivity (default : FALSE) • If SO = 15, the superframe will not be active after the beacon. • PANs that wish to use the superframe structure shall set 0SOBO14. General Frame Format PHY Layer MAC Layer Payload Synch. Header (SHR) PHY Header (PHR) MAC Header (MHR) MAC Service Data Unit (MSDU) MAC Protocol Data Unit (MPDU) PHY Service Data Unit (PSDU) MAC Footer (MFR) General MAC Frame Structure • Four Types of Frames Structure: – Beacon Frame - used by coordinator – Data Frame - used for all transfers of data – Acknowledgment Frame - used for confirming successful frame reception – MAC Command Frame - used for handling all MAC peer entity control transfers Beacon Frame Format Data Frame Format Acknowledgement Frame Format MAC Command Frame Format CSMA/CA Mechanism • unslotted CSMA/CA: – A device waits for a random period without carrier sense. – If the channel is idle, following the random backoff, it transmits its data. Otherwise, it waits for another random period before retry. • slotted CSMA/CA: – It is similar to the unslotted CSMA/CA but follows the backoff slot boundary.The backoff slots are aligned with the start of the beacon transmission. CSMA/CA Mechanism • Frame Acknowledgment – If the originator does not receive an ACK after some period. It will retry the frame transmission. If an ACK is still not received after several retries, the originator can choose either to terminate or to try again. • Power Consumption Considerations – Battery powerd devices will require duty-cycling to reduce power consumption. These devices will spend most of their operational life in a sleep state. They shall periodically listen to the RF channel to determine whether a message is pending. CSMA-CA Algorithm • The LR-WPAN uses two types of channel access mechanism, depending on the network configuration. 1. Non beacon-enabled networks use an unslotted CSMA-CA channel access mechanism. 2. Beacon-enabled networks use a slotted CSMA-CA channel access mechanism. In both cases, the algorithm is implemented using units of time called backoff periods, where one backoff period shall be equal to aUnitBackoffPeriod (=20) symbols. CSMA-CA Algorithm • In slotted CSMA-CA, the backoff period boundaries shall be aligned with the superframe slot boundaries – the start of the first backoff period of each device is aligned with the start of the beacon transmission. • In unslotted CSMA-CA, the backoff periods of one device are not related in time to the backoff periods of any other device in the PAN. • The CSMA-CA algorithm shall not be used for the transmission of – beacon frames – acknowledgement frames – data frames transmitted in the CFP. CSMA-CA Algorithm • Each device shall maintain three variables for each transmission attempt: – NB (no. of backoff – also known as retry count) (4) – CW (contention window size, perform PHY CCA) – BE (backoff exponent) • NB is the number of times the CSMA-CA algorithm was required to backoff while attempting the current transmission; this value shall be initialized to 0 before each new transmission attempt. • CW is the contention window length, defining the number of backoff periods that need to be clear of channel activity before the transmission can commence; this value shall be initialized to 2 before each transmission attempt. The CW variable is only used for slotted CSMA-CA. • BE is the backoff exponent which is related to how many backoff periods a device shall wait before attempting to assess a channel. Flow Chart Frame Transmission • If the source address (SA) field is not present, the originator of the frame shall be assumed to be the PAN coordinator. • If the destination address (DA) field is not present, the recipient of the frame shall be assumed to be the PAN coordinator. • If both SA and DA addresses are present, the MAC shall compare the destination and source PAN identifiers – If the PAN identifiers are identical, the intra PAN subfield of the frame control field shall be set to 1 and the source PAN identifier shall be omitted from the transmitted frame. • Save bandwidth, only carry the destination PAN identifier – If the PAN identifiers are different, the intra PAN subfield of the frame control field shall be set to 0 and both destination and source PAN identifier fields shall be included in the transmitted frame. Frame reception and rejection 1. The frame type subfield shall not contain an illegal frame type. 2. If the frame type indicates that the frame is a beacon frame, the source PAN identifier shall match macPANId unless macPANId is equal to 0xffff, in which case the beacon frame shall be accepted regardless of the source PAN identifier. 3. If a destination PAN identifier is included in the frame, it shall match macPANId or shall be the broadcast PAN identifier (0xffff). 4. If a short DA is included in the frame, it shall match either macShortAddress or the broadcast address (0xffff). Otherwise, it shall match aExtendedAddress. 5. If only SA fields are included in a data or MAC command frame, the frame shall only be accepted if the device is a PAN coordinator and the source PAN identifier matches macPANId. GTS allocation and management • Guaranteed time slot (GTS) allows a device to operate on the channel without interferences. • A GTS only be allocated by the PAN coordinator and is used for communications between PAN coordinator and device. • A data frame transmitted in an allocated GTS shall use only short address • The PAN coordinator shall send all frames within a receive GTS with AR=1 • The PAN coordinator may allocate up to seven GTSs at the same time, provided there is sufficient capacity in the superframe. GTS allocation and management • A single GTS occupies one or more superframe slots • GTSs are allocated on a first-come-first-served basis and all GTSs shall be placed contiguously at the end of the superframe and after the CAP • For each GTS, the PAN coordinator records – – – – starting slot length (in superframe slots) direction associated device address • For each allocated GTS, the device records – starting slot – length – direction ZigBee and Bluetooth Optimized for different applications • ZigBee • Bluetooth – Smaller packets over large network – Mostly Static networks with many, infrequently used devices – Home automation, toys remote controls – Energy saver!!! – Larger packets over small network – Ad-hoc networks – File transfer; streaming – Cable replacement for items like screen graphics, pictures, hands-free audio, Mobile phones, headsets, PDAs, etc. ZigBee and Bluetooth • Bluetooth and 802.15.4 transceiver physical characteristics are very similar • Protocols are substantially different and designed for different purposes • 802.15.4 designed for low to very low duty cycle static and dynamic environments with many active nodes • Bluetooth designed for high QoS, variety of duty cycles, moderate data rates in fairly static simple networks with limited active nodes Summary • 802.15.1 • 802.15.4 (ZigBee)