Introduction - Energy Harvesting Autonomous Sensor Systems - page 8

TABLE 1.1
Basic Parameters of IEEE 802.15.4

Property Range

Raw data rate 868 MHz: 20 kb/s; 915 MHz: 40 kb/s; 2.4 GHz: 250 kb/s

Range 10-20 m

Channel access CSMA-CA and slotted CSMA-CA

Channels 868/915 MHz: 11 channels; 2.4 GHz: 16 channels

Frequency band Two PHYs: 868 MHz/915 MHz and 2.4 GHz

Addressing Short 8 bit or 64 bit IEEE

Latency Down to 15 ms

a standard with ultralow complexity, cost, and power for low-data-rate wire-
less connectivity among inexpensive fixed, portable, and moving devices. The
scope of Task Group 4 is to define the PHY and media access control (MAC)
layer specifications. IEEE 802.15.4 has some basic devices. These devices can
be a reduced-function device (RFD) or a full-function device (FFD). The RFD
can talk only to an FFD, but the FFD can operate in three modes, serving as
a personal-area network (PAN) coordinator, a coordinator, or a device. An
FFD can talk to an RFD or other FFDs. An RFD can be used in extremely
simple applications, such as a light switch or a passive infrared sensor. Most
of the time, RFDs will not have many data to send; hence, they communicate
with the FFD occasionally. They need fewer resources and minimum energy.
Tw oormore devices within a personal operating space (POS) communicat-
ing with all the same physical channels constitute a Wireless Personal Area
Network (WPAN) . However, a network will have at least one FFD operating
as the PAN coordinator. The basic parameters of IEEE 802.15.4 are presented
in Table 1.1 .
The layout of the IEEE 802.15.4 blocks is defined based on the Open Sys-
tem Interconnection (OSI) seven-layer model. Separation of the LR-WPAN
into blocks helps to understand the protocol. These blocks are called layers.
The higher layers receive their information from the following lower-level
layers. The interfaces between the layers serve to define the logical links. An
LR-WPAN device consists of PHY and MAC sublayers. A PHY sublayer has
the radio-frequency (RF) transceiver along with its low-level control mecha-
nism, an MAC sublayer provides access to the physical channel for all types
of transfer. The overview of the IEEE 802.15.4 architecture is depicted in
Figure 1.7 .
The upper layers consist of a network layer and the application layer. An ap-
plication layer provides the intended function of the device, and the network
layer provides network configuration and message routing. An IEEE 802.2TM
Type 1 logical link control (LLC) can access the MAC sublayer through the
service-specific convergence sublayer (SSCS).