# Opportunities and Challenges for Error Control Schemes for Wireless Sensor Networks: A Review
## 3 Standard, Network and Channel Models
### Standard  
The basic communication standard for WSN is IEEE 802.15.4 [46] and its definition includes the Physical layer (PHY) and medium access control (MAC) sublayer for short-range wireless transmission with low power consumption, low complexity, low cost and low-data-rate for fixed, portable and moving devices with very limited battery consumption. PHY contains the transceiver and its control mechanism, whereas the MAC sublayer allows access to radio channels for all kinds of transfer. The standard also provides precision ranging permission modes. The standard IEE 802.15.4 has gone through a number of releases and there are a number of variations that serve different forms of physical layers. The different versions to date are: IEEE 802.15.4-2003, IEEE802.15.4.2006, IEEE802.15.4a, IEEE802.15.4c, IEEE802.15.4d, IEEE802.15.4e, IEEE802.15.4f, and IEEE802.15.4g. The IEEE 802.15.14 standard is used by other higher layer standards. As the basic PHY and MAC layers are already specified, higher layers can be designed differently for specific purposes. Some of the derived standards and their main features are summarised as follows [47; 48]:  
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2. Zigbee: Supported by Zigbee Alliance, provides higher requirement for low power radio control system like heating, lighting, etc., not suitable for industrial application
3. Wireless HART: Open standard, developed by HART Communication foundation, uses 2.4 GHz ISM band, provides time synchronized, self organized, and self healing mesh architecture. 4. RF4 CE: Radio control for low power audio video applications. 5. MiWi: Designed by Microchip Technology, caters for low data transmission rate, short distance, low cost network, application areas are building automation, remote control, etc. Figure 6: Channel adaptive model. * ISA100.11a: Developed by ISA for industrial automation. * 6 LoWPAN: It uses IPV6 packets formats
* WIA-PIA: designed for measuring, monitoring and controlling industrial process  
The IEEE 802.15.4 standard operates in two types of network typologies based on the application requirements: start topology and peer-to-peer topology. IEEE 802.15.4 standard uses licence free global radio bands of 2.4 GHz that is included in ISM bands. Multiple PHYs are defined in the standard so that it supports a variety of frequency bands, and different countries have considered other frequency bands like 314-316 MHz, 430-434 MHz, 779-787 MHz, 868-868.6 MHz, and 902-928 MHz. Because the ISM band is commonly used for the low cost radios such as IEEE 802.11 (WLAN) and IEEE 802.15.1 (Bluetooth), an unrestricted access to the industrial scientific and medical unlicensed band exposes the IEEE 802.15.4 devices to a high level of interference. For different available PHY, a separate set of the bit rate, symbol rate and modulation are specified; 250 Kbits/sec, 62.5 Ksymbols/sec and offset-quadrature phase shift keying (O-QPSK) is one of the set. The 802.15.4 PHY layer manages the radio channel and controls packet data flow. The PHY layer is responsible to activate and deactivate the radio transceiver, detect energy within the current channel, indicate link quality for received packets, and assess a clear channel for Carrier Sense Multiple Access-Collision Avoidance (CSMA-CA), channel frequency selection, data transmission and reception. The core channel access method is CSMA-CA, but there are different variations in the standard. The MAC layer of IEEE802.15.4 provides the interface between physical layer and application layer, and it has two components named MAC Management Service and MAC data Service. The first component looks after the management function like database control and the second component provides the data transport service between the peers. The MAC data service allows the transmission and reception of MAC Protocol Data Units (MPDUs) through the PHY data service. Common features of MAC layer include managing beacon, accessing channel, managing Guaranteed Time Slot (GTS), validating frame, acknowledging frame delivery, associating and disassociating.