# MAC Layer Protocols for Internet of Things: A Survey
## 2 Short Range MAC Layer Protocols
### Near Field Communication (NFC)  
For short-range communications, NFC technology is important since its massive adoption by mobile device vendors has popularized its use, making it accessible to the public for applications such as label reading or even peer-to-peer data exchange. The devices involved exchange information between themselves as a machine-to-machine connection mode [18]. Standardization of NFC is assisted by the International Organization for Standardization (ISO) conjoined with the International Electrotechnical Commission (IEC) and NFC Forum.  
Near Field Communication is a short range transmission technology that uses low-power transmission links that, differently from Bluetooth, do not require pairing for transmission. Just bringing one device close enough to the other allows communication. This feature forces the user of the device to be handling it during use. As the facility of the device works only with is owner, it is a manner to ensure the safe security of the technology usage. Its operation is comparable to RFID technology because NFC devices can act as both a reader and a tag. The communication is performed in active or passive mode, operating in the 13.56 MHz band. A typical range from another device is about 0.2 m and it is sensitive to near fields or even the touch, its transmission rate can reach 424 Kbps. In the passive mode communication, the active device initiates the connection by transmitting a carrier wave that activates the passive device. Thus, the passive device makes use of this carrier to modulate and transmit its data. In the active mode of communication, both the communication initiating device and the target device communicate by generating their own carrier waves. These devices need to be powered by external power sources.  
NFC tags and readers can operate in three different modes: card emulation, reader/writer and peer to peer (or point to point). In NFC Card Emulation mode, usually the active device reads the passive device tag types. Both of them can be active or passive devices. In the NFC Peer to Peer (Point to Point) mode standardized according to the ISO/IEC 18092 [19], two nodes are connected to each other by a peer to peer or ad hoc mode in order to exchange data [20]. The massive deployment of NFC came to join the use of RFID as complementary technology and, as a consequence, are becoming important technological solutions for pay-machines, smart objects, smart wearables, and many other devices. These technologies are commonly used in applications, such as tracking objects and people, to offer personalized information and services such as in e-health applications. This scenario brings a new concept of \"thing\" or object socialization. In this concept, the link between the ported object and the person who carries it establishes a unique co-ownership and relationship. This relationship is capable of influencing decisions in human environment interactions and raising the level of the consciousness of the object [21; 22].  
On the physical layer of NFC, RF communication data rates are 106, 212, 424 as well as 848 Kbps depending on the combination of modulation and code techniques used. The available modulation schemes are ASK (Amplitude Shift Keying) using 10% or 100% modulation depth, Non-Return-to-Zero Level (NRZ-L), Binary Phase Shift Keying (BPSK) and Manchester or Modified Miller coding are used for the data transfer. The International Organization for Standardization (ISO), International Electrotechnical Commission (IEC), and Federal Communications Commission (FCC) regulate the transmission power to be 20 or 23 dBm according to region [23; 24; 25; 26]. The NFC MAC layer is also responsible for connection handling, message exchange, emulation modes, anti-collision bit transmission, activation procedures, data transport, and others. Figures 2 and 3 illustrate these functionalities [18].  
Figure 2: NFC passive to active device communication protocol stack.