# Some factors needing attention in the prediction o

2022-10-02
• Detail

Some factors needing attention in wireless distance prediction

people who design short-range wireless systems must know that Friis formula and path prediction are very helpful:

PR is the signal power received by the antenna; PT is the transmission power; GT and GR are the transmit antenna gain and receive antenna gain respectively - the unit is the power ratio rather than dB, which comes from isotropic radiation; λ Is the wavelength of signal construction, in meters; D is the distance between the production line of transmitter and receiver developed and constructed by HONGNA (Dongguan) new material technology Co., Ltd., and the unit is also meter

you can convert the formula to predict the distance d:

friis formula is very easy to use in performance prediction, especially for UHF and microwave frequencies beyond the line of sight (LOS). The formula requires that the antennas at both ends adopt the same polarization mode. Although it is not suitable for all applications, it is still very practical

The Friis formula also provides practical insights into some key elements of wireless transmission. For example, wavelength is very important. The longer the wavelength or the lower the frequency, the longer the distance（ λ = 300/fMHz）。 This means that at the same power level, the transmission distance using 900MHz wireless connection is longer than that using 2.4GHz or 5GHz connection. Friis formula also indicates the importance of directional antenna. Gain antenna is a relatively simple method, which can increase distance and connection reliability without increasing transmission power and power consumption

other factors will also affect the prediction of transmission distance and performance, one of which is the sensitivity of the receiver. Receiver sensitivity is usually calculated according to the minimum trigger power of the receiver circuit, and the unit is how much DBM is lost. The sensitivity range of a typical chip wireless receiver is -80 to -110 DBM. The larger the number, the higher the sensitivity. However, it should be noted that the sensitivity range must be measured under specific data rate conditions. A lower data rate means a lower bit error ratio (BER) and higher reception sensitivity. Therefore, in order to improve the reliability of path and transmission distance, the lowest effective data rate should be used as far as possible in applications

another practical formula is path loss

the unit of F in the formula is MHz, and the unit of D is miles. Meters divided by 0.000621 can be converted into miles

when making path loss prediction, you can calculate the link budget in db/dbm

the power received by the receiving antenna is:

pt+gt+gr - path loss - margin

the figure obtained should be greater than the receiving sensitivity. Otherwise, the antenna gain should be considered first, because the method of increasing the antenna to enhance the transmission power is usually more difficult and expensive

conservatively, you can also include the margin, which takes into account the influence of electrical and environmental factors on signal strength. If the range is in dB, it is not bad, and it can also ensure that there is a reliable margin in the link

there are other factors to consider: the transmission line loss at this frequency may be amazing. Coaxial cable can transmit UHF or microwave signals normally, but the signal attenuation is very fatal. A few feet away may bring a considerable degree of signal attenuation. Therefore, the length of cable used is also a factor

remember that the above formula is based on the sight distance path. If the application requires passing through walls, trees or other obstacles, the above formula is not accurate. You can add path loss data to the above formula as a supplement, but the number range may be large (DB)

finally, all these predictors exclude noise. If the transmission power can be kept at a high level, the path loss can be kept low, and the acceptance sensitivity is high, the noise in any wireless system that only detects one cycle of torque can be overcome

these formulas are very useful. I have used them countless times in different wireless applications before. Maybe they can help you, too

Related Topics