Page 51 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 3: Radio Frequency and Light Signal Fundamentals

3.2.2 RF Signal Pros and Cons Notes

Advantages of RF include:

z z Efficiency: RFID tags do not require line-of-sight to be deciphered They can be read through
cardboard, plastic, wood and even the human body. RFID tags can easily track moving
objects and send the required information back to the reader. This eliminates human errors,
reduces labor and provides quick access to a wealth of information.

z z Return on Investment (ROI): RFID costs more to implement than a barcode system, but
provides a good return on investment in the long run, since RFID is significantly more
efficient.

z z Less Vulnerable to Damage: RFID tags are less susceptible to damage. An RFID tag is
securely placed within an object or embedded in plastic, enabling the system to be used
in a variety of harsh environments, such as areas of high temperature or moisture, or with
exposure to chemicals or the outdoors.
Disadvantages of RF include:
z z Expense: RFID systems are typically more expensive than alternatives such as barcode
systems. While passive tag reading is similar to (and generally less expensive than) barcode
reading, active tags are costly due to their complexity. Active tags consist of an antenna,
radio transceiver and microchip, increasing the overall cost of an RFID system.

z z Collision: Tag collision and reader collision are common problems with RFID. Tag
collision occurs when numerous tags are present in a confined area. The RFID tag reader
energizes multiple tags simultaneously, all of which reflect their signals back to the reader.
This results in tag collision, and the RFID reader fails to differentiate between incoming
data. RFID reader collision results when the coverage area managed by one RFID reader
overlaps with the coverage area of another reader. This causes signal interference and
multiple reads of the same tag.

z z Security: RFID technology gives rise to numerous security concerns. Since the system is not
limited to line-of-sight, external (and malicious) high-intensity directional antennas could
be used to scan sensitive tags. Fraud is always a possibility when the technology is used for
high-security operations, such as payment verification.

3.2.3 RF Signal Impairments

Interference and multipath propagation causes lower performance in the communication
between the sender and receiver.

3.2.4 Interference

Electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals,
as a by-product of their normal operation, and which causes unwanted signals (interference or
noise) to be induced in other circuits. The most important means of reducing RFI are: use of
bypass or “decoupling” capacitors on each active device (connected across the power supply, as
close to the device as possible), rise time control of high speed signals using series resistors and
VCC filtering. Shielding is usually a last resort after other techniques have failed because of the
added expense of RF gaskets and the like.
The efficiency of the radiation is dependant on the height above the ground or power plane (at RF
one is as good as the other) and the length of the conductor in relationship to the wavelength of
the signal component (fundamental, harmonic or transient (overshoot, undershoot or ringing)).
At lower frequencies, such as 133 MHz, radiation is almost exclusively via I/O cables; RF noise

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