RFID mifare card reader, Tags & Reader

The concept

As you may know a few things are needed to have an operational RFID system in place:

• A reader, that is connected to (or integrated with)
• An antenna, that sends out a radio signal
• A tag (or transponder) that returns the signal with information added

The reader usually is connected to a third party system that is accepting (and storing) RFID related events and uses these events to trigger actions. In the security industry that system might be a building access control system, in the parking industry it is most likely a parking 

management or vehicular access control system. In libraries it might be a library management system.

Let’s have a closer look at access control systems. These systems usually consist of:

• RFID access control cards that, are read by
• Access control RFID mifare card readers next to the door, that are connected to
• Access control panels (a physical controller), hardware that is able to open door locks and that is connected to
• An access control management system (software) that manages building access credentials and authorizations.

Many different access control systems exist worldwide. Most of these systems store access control rights for people (or vehicles) and also link those people to something that identifies them. Usually a number that is stored on an access control card. When an access control card (the RFID tag) is shown to the access control reader next to the door (the RFID reader with RFID antenna), that specific number is sent to the access control panel (a physical controller). The control panel connects with the access control management software (at a server or in the cloud) to check who is connected to that number and if he/she has access to the door that is approached. When the person is authorized an event is stored at the server (for the event log book) and the access control panel is asked to open the door (by telling the physical lock to unlock).

The basic principle is easy. But a lot of software components and hardware devices are put to work to physically open the door when someone with the right access rights is showing their RFID card to the RFID reader.

You will probably know that RFID is a generic word for a wide variety of different systems that use radio frequencies to identify something. All that variation is the reason that RFID tags and readers are not always interoperable. And that again is the reason that RFID manufacturers and vendors ask so many questions when you try to purchase their systems: they would like to make sure that whatever RFID systems you procure, it is really working well.
 

The model

The following model is an abstract representation of the access control system that was mentioned in the previous paragraph:


 

The model shows three columns with a few layers. The first column represents the tag. The tag is presented to the reader (center column) and the reader is connected to the access control system in the third column.

Each column is connected to another column at several virtual layers:

1. Tags are programmed with a number. That number needs to be in a format that is understood by the reader and that format should also be known in the access control system so that it can be processed. Tags usually have a facility code number (also called client code or facility code) and a card number. The facility code number links the tag to a specific installation, country or application. The card number should be unique for the installation with that facility code and is used to identify an individual carrier (like a person or car).
2. The number is encoded in a specific way so that it can be sent through the air. This 
3. communication protocol makes sure that tag and reader understand each other.
4. The encoded number is sent using radio waves at a specific frequency. The frequency of the reader and tag should be the same so they are able to communicate.
5. The reader is physically connected through wires in a cable with a controller that is part of the access control system. A reader communication protocol is applied to encode information sent over the physical line.

6. The difference between layer 2 and 3 is that in layer 3 the reader can actually ‘hear’ the tag, but it does not understand it until they speak the same ‘language’ in layer 2. The specification of layer 2 enables basic compatibility between tag and reader. The ‘EPC Gen 2’ standard used in UHF (or RAIN RFID) is an example of a standardized air interface: a combination of a selected frequency with a specified communication protocol.
   
   Level 4 is about the physical connection between the reader (with antenna) and the access control system. What type of cable should be used and what ‘language’ is spoken? An example of that is Wiegand, a standard that is used a lot all over the world and that specifies how to use two data wires and one ground wire.