**LR-WPAN device architecture:

**

• The IEEE 802.15.4 has been designed to be useful in a wide variety of applications such as automotive sensing, such as tire pressure monitoring; precision agriculture, such as the sensing of soil moisture.
• The largest application opportunities are in home automation and networking including heating, air conditioning; the control of objects such as curtains, windows; health monitoring, including diagnostics; and toys and games.

IEEE 802.15 LR-WPAN Device Architecture

• The device comprises a physical layer (PHY), which contains the RF transceiver along with its low-level control mechanism.
• A MAC sublayer provides access to the physical channel for all types of transfer.
• The upper layers consist of a network layer, which provides network configuration, manipulation, and message routing.
• The application layer provides the intended function of a device.
• An IEEE 802.2 logical link control (LLC) can access the MAC through the service specific convergence sublayer (SSCS).

Physical Layer

  * The PHY provides two services: the PHY data service and PHY management service interfacing to the physical layer management entity (PLME). * The PHY data service enables the transmission and reception of PHY protocol data units (PPDUs) across the physical radio channel. * The PHY management services are activation and deactivation of the radio transceiver, energy detection (ED), link quality indication (LQI), channel selection, clear channel assessment (CCA). * There are three frequency bands: 2.4GHz global, 915MHz America and 868MHz Europe. There is a single channel between 868 and 868.6 MHz, 10 channels between 902 and 928 MHz, and 16 channels between 2.4 and 2.4835 GHz. * The data rate is 250 kbps at 2.4 GHz, 40 kbps at 915 MHz, and 20 kbps at 868 MHz Receiver sensitivities are -85 dBm for 2.4 GHz and -92 dBm for 868/915 MHz. * The range of 10-20 meters is covered. To maintain a common simple interface with MAC, both PHY data service and management service share a single packet structure. * A typical packet size for home applications is of the order of 30-60 bytes. More demanding applications such as interactive games require larger size packets. (127 bytes maximum). * The maximum packet durations are 4.25 ms for the 2.4 GHz band, 26.6 ms for the 915 MHz band, and 53.2 ms for the 868 MHz band. * The standard provides two options based on the frequency band. Both are based on direct sequence spread spectrum (DSSS). * The 868/915 MHz PHY uses a simple DSSS approach in which each transmitted bit is represented by a 15-chip maximum length sequence with BPSK modulation. * The 2.4 GHz PHY uses a 16-ary quasi-orthogonal modulation technique based on DSSS methods with OQPSK modulation.

Data link Layer

• The data link layer is divided into two sublayers, the MAC and LLC sublayers.
• The logical link control is standardized in IEEE 802.2 and is common among all IEEE 802 standards.
• The MAC provides services to an IEEE 802.2 type logical link control through the service-specific convergence sublayer (SCCS), or a proprietary LLC can access the MAC services directly without going through the SCCS.
• The SCCS ensures compatibility between different LLC sublayers and allows the MAC to be accessed through a single set of access points.
• The features of the MAC are association and disassociation, acknowledged frame delivery, channel access mechanism, frame validation, guaranteed time slot management, and beacon management.
• The MAC provides two services to higher layers that can be accessed through two service access points (SAPs).
• The MAC data service is accessed through the MAC common part sublayer (MCPS-SAP), and the MAC management services are accessed through the MAC layer management entity (MLME-SAP).
• These two services provide an interface between the SCCS or another LLC and the physical layer.
• An important function of the MAC is to confirm successful reception of a received frame. Successful reception and validation of a data or MAC command frame is confirmed with an acknowledgment.
• Three levels of security are provided: no security of any type; access control lists (non-cryptographic security); and symmetric key security, using AES-128.

Network Layer

• The network layer of Zigbee (IEEE 802.15.4) is responsible for topology construction and maintenance as well as naming and binding services, which include the tasks of addressing, routing, and security.
• IEEE 802.15.4 supports multiple network topologies, including star, peer-to-peer, and cluster tree. The topology is an application design choice.