5.8 GHz, THE BEST CHOICE FOR RTLS
The 5.8 GHz band is the best choice in terms of price and accuracy for real-time location system The use of higher frequencies for location applications such as tracking of people and equipment has many advantages over other frequencies. Systems built on higher frequencies provide a reduction in production costs and high-speed transport data between the badges, tags and r eceivers. In addition, they offer the best compromise to transmit a wireless signal, by leaky wave, by reflections in crowded spaces such as a refinery. The use of higher radio frequencies offers the ability to manufacture small devices with unparalleled efficiency for real-time location systems (RTLS) and active RFID tags. The physics of wireless technology shows four main factors affecting the quality of communication and system perfor mance:
1. 1. Traffic in the band
2. 2. Problems of propagation and behavior when faced with obstacles and depending on the distance
3. 3. Spectral efficiency
4. 4. Device effectiveness
1. Traffic in the band
High Traffic in 433 MHz, 900 MHz and 2.4 GHz bands
433 MHz, 900 MHz and 2.4 GHz bands are w idely used in consumer devices such as monitors, ovens, microwaves, Bluetooth, local communication devices. 433 MHz band has been used for decades for short-range communications. However, these RFID networks operating in these bands suffer from disturbances in the low frequency signals from other wireless devices. The higher traffic in the band, the higher the receptor complexity must be to reject noise and interfer ence and maintain sign al quality. The result is an increase in complexity and price of the unit. It is therefore better to use an uncluttered and larger band as the 5.8 GHz band, to better manage lar ge capacity real-time location systems, such as Purelink RTLS.
2. Problems of propagation and behavior when faced with obstacles and depending on the distance
Better signal propagation characteristics at 5.8GHz
Most short-range communications occur around human structures, such as vehicles and buildings. For middle ranges in distances of 0-1 km and for the same level of transmitting power, the 5.8 GHz band has almost the same communication range as the 433 MHz band.
The 5.8 GHz band offers a Fresnel diffraction zone the smallest compared to the bands 433 MHz, 900 MHz and 2.4 GHz. Because of its shorter wavelength, the signal at 5.8 GHz can pass through the narrowest of spaces. At the same time, it maintains its ability to penetrate through almost similar mater ials such as waves in the 433 MHz band. Ther efore, when the waves at 433 MHz are blocked or diffracted by obstacles, due to the signal wavelength of more than 70 cm, the signal at 5.8 GHz can easily pass through these obstacles because of its very short wavelength of only 5.17cm.
The wavelength of the signal determines the device size and performance. Ther efore, in general, pr oducts exploiting the high frequencies are more compact and have better efficiency.
Frequency Wavelength
5.8 GHz 5.17 cm
2.4 GHz 12.5 cm
900 MHz 32.7 cm
433 MHz 69.3 cm
Frequency Distance
5.8 GHz with direct spread spectr um 100 - 670 m (300 - 2000 pi)
2.4 GHz with direct spread spectr um 100 - 670 m (300 - 2000 pi)
900 MHz w ith direct spread spectrum 100 - 500 m (300 - 1500 pi)
433 MHz 25 - 133 m (75 - 400 pi)
At 5.8GHz, the wavelength being shorter, the antennas are smaller, the penetration through holes in obstacles and the transmission by leaky waves ar e better. In addition, the components used in 5.8 GHz badges or tags are smaller and more energy efficient.
The propagation char acter istics of signals at 433 MHz, 900 MHz, 2.4 GHz and 5.8 GHz in free space are similar in situation of rain. This is important to consider in tropical climates and continental for outdoor applications.
The figure below shows how the propagation at long r ange, for almost all frequencies below 10 GHz, is affected the same way for different types of rain conditions. Under heavy rain, all frequencies below 10 GHz suffer nearly 0.1 dB of attenuation pe r kilometer of propagation. r eal-time location systems in ar e generally built with tag / receiver lines of communication of less than 500 m. Therefore, one should consider the frequency effectiveness, noise in the communication band and interference to select the best frequency for your location-based applications or active RFID tags.
RF signal propagation and at mosphe ric attenuation for differe nt frequency bands
The 5.8 GHz band offers a range of communication similar (0-1 km) than other low frequency bands. However, at 5.8 GHz, the error rate per bit transmitted (BER) is much lower due to a less crowded bandwidth. The 5.8 GHz ISM band offers 75 MHz bandwidth communication. This is almost tw ice the bandw idth of 2.4 GHz band. This results in more energy-efficient products with higher data rates.
3. Frequency efficiency
High data rate modulation at 5.8 GHz
The data transfer rate is greater at 5.8 GHz because the frequency is higher. This is very important when it comes to track, locate and communicate w ith hundr eds of badges and tags in motion, such as people, equipment, vehicles or containers. Purelink location system allows to track a vehicle traveling at a speed exceeding 200 km / h w ithout problems of communication betw een the tag associated with the vehicle and the receptors located more than 200 meters from the road. The Doppler Effect may be important in systems with low frequency because of the slower modulation techniques in the bands 433 MHz, 900 MHz. How ever 5.8 GHz tags can be read at speeds of 250 km / h w ithout any misreading, even if the tag is hidden in the trunk!
The 5.8 GHz band pr ovides data rates from over 2 Mb / s to 100 Mb / s. The advanced modulation techniques can provide important data rates for real-time location systems such as the one manufactured by Purelink. When it comes to implementing security applications, applications for protection of people or commercial applications requir ing high reliability, high accuracy and reasonable cost, Purelink location systems are the most effective.
A higher modulation at 5.8 GHz can transmit large amounts of data. In many industrial applications where a real-time location system is required to process each second the position and status of hundreds of workers with an average error of ± 2 meters, only Purelink location system can meet the task.
Location systems at low frequency of 433 MHz, 900 MHz and 2.4 GHz cannot handle the large data rate modulation and they cannot provide consistency, robustness, accuracy and throughput.
4. Device efficiency
Better electronics design at 5.8 GHz
At 5.8 GHz, the ability to use transmission lines for antenna design leads to cheaper solutions with smaller circuit boards. The result is a device very compact, lower cost and greater energy efficiency.
Using the 5.8 GHz band provides the opportunity to make tags in a single chipset. The r esults are devices smaller and lighter, and a considerable increase the device energy efficiency.
At 5.8 GHz, the antennas are smaller and can be produced in a var iety of for ms.
The 5.8 Ghz band is compatible w ith CMOS technology
CMOS technology has many advantages:
Mature technology
Low bias voltage (<3V, even below 1V for SOI MOS)
Low power consumption (portable applications)
Possibility to build a single chip w ith both analog and digital circuits
High level integration possible
Compatible with micr omachining techniques (MEMS)
The result is a great technological superiority of devices at 5.8GHz such as Purelink technology.
Comparison of usual bands
Frequency Advantages Draw backs High Traffic 303.8MHz
418 MHz 433 MHz 868 MHz 915 MHz Good communication range
Good water/body penetration
Band authorized in many countr ies
Big devices and antennas
High energy consumption
Low integration of componenets
Limited transmission rate
Yes
2.45GHz Compact devices and antennas
Good communication range
High transmission rate
Sensitive to noise
Require sensitive r eceivers
High energy consumption
Require fr equent battery
changes
Expensive
Poor water/body penetration
Yes
5.8GHz Very compact devices and
antennas
High energy and spectral
efficiency
Very good communication range
Very high transmission rate
Can be build in one chip
Require sensitive r eceivers
Poor water/body penetration
No
Performance table
DILS WiFi Short range active RFID Characteristics 5.8 GHz 2.4 GHz 1.2 GHz 900 MHz UHF Available channels 8-16-32 4 4 3 Multiple Interference risk Very low High Medium Medium Medium Band type FM FM FM AM AM Resolution Excellent Excellent Excellent Good Medium Range Long Medium Medium Short Short Outdoor perfor mance Excellent Excellent Excellent Good Medium Position accur acy (X,Y)Excellent Low Low Low by Zone Secur ity Excellent Good Good Medium Low Licence requir ed No No Yes Yes No
Penetration capability :
Water/Body Low Low Good Good Good
Wood Medium Medium Good Very Good Excellent
Concrete Medium Medium Good Very Good
Excellent
Tinted w indow Low Low Low Low Low
Metal No No No No No
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