Protocol Architecture

The physical layer

The physical layer gives data transmission service and interface to the physical layer management entity. It also gives access to all layer management function and database of information to the related personal area networks. By means of Physical layer, channel selection and signal management functions can be performed. Also, physical RF transceiver could be managed.

The physical layer uses one of the 3 unlicensed frequency bands written below:

1)      868.0 – 868.8 MHz: Europe (one communication channel 2003 – 2006)

2)      902 – 928 MHz: North America (2003 – 10 channels, 2006 – 30 channels)

3)      2400 – 2483.5: worldwide usage, allows up to 16 channels 2003 – 2006.

The original of the standard is 2003 version which specifies two physical layers based on direct sequence and spread spectrum techniques. Whereas direct sequence works in the 868 / 915 MHz bands with transfer rates 20 and 40 kbit/s, spread spectrum techniques work in 2450 MHz band with transfer rate of 250 kbit/s.

After 2003, it is revised in 2006, 2007 and 2009. Specification are explained in the following:

Firstly, 2006 revision improved both maximum data and transfer rates. 868 – 915 MHz mostly uses phase shift keying or sometimes offset quadrature phase shift keying. It is also defined by means of binary and amplitude shift keying combination. Also, it supports dynamic switching between layers.

Secondly, it is improved in 2007. Improvements are made by means of Direct Dequence Ultra-wideband (frequency ranges are between 3 GHz and 5 GHz and between 6 GHz and 10 Ghz) and Chirp Spread Spectrum usage (2450 MHz ISM band spectrum)

Finally, in 2009 extra physical layers have been released such as 780 MHz band using O-QPSK or MPSK and 950 MHz band using GFSK or BPSK. Also. It varies in China and Japan. In China, 314 – 316 MHz, 430 – 434 MHz and 779 – 787 MHz bands are newly opened. In Japan, 950 – 956 MHz is newly opened.

 

The MAC layer

The Medium Access Control layer enables the transmission of MAC frames through the use of physical channel. The good point is that it offers data service, management interface and access to physical channel. In addition, frame validation is controlled by MAC. Finally, time slots and node associations are guaranteed.

Higher Layers

There are different type of higher layers. Firstly, ZigBee was built on this standard and it offers integral solutions. In addition, it is used by TinyOS, Unison RTOS and DSPnano RTOS.