The communication distance that a wireless communication system can achieve is determined by various factors such as the various devices that make up the system and the communication environment. The relationship between them can be expressed by the following communication distance equation.
If the transmission power of the transmitting device of the communication system is PT, the transmission antenna gain is GT, and the operating wavelength is λ. The sensitivity of the receiving device receiver is PR, the receiving antenna gain is GR, and the distance between the receiving and transmitting antennas is R, within the visual distance and in the environment without electromagnetic interference, the following relationship exists:
PT(dBm)-PR(dBm)+GT(dBi)+GR(dBi)=20log4pr(m)/l(m)+Lc(dB)+ L0(dB) In the formula, Lc is the feeder insertion loss of the base station transmitting antenna; L0 is the radio wave loss during the propagation.
When designing the system, sufficient margin should be left for the last item, the radio wave propagation loss L0.
Generally, a margin of 10 to 15 dB is required when passing through woods and civil buildings; a margin of 30 to 35 dB is required when passing through reinforced concrete buildings.
For 800MH, 900ZMHz CDMA and GSM frequency bands, it is generally believed that the receiving threshold level of mobile phones is about -104dBm, and the actual received signal should be at least 10dB higher to ensure the required signal-to-noise ratio. In fact, in order to maintain good communication, the received power is often calculated as -70 dBm. Assume that the base station has the following parameters:
The transmitting power is PT = 20W = 43dBm; the receiving power is PR = -70dBm;
The feeder loss is 2.4dB (approximately 60m feeder)
Mobile phone receiving antenna gain GR = 1.5dBi;
Working wavelength λ = 33.333cm (equivalent to frequency f0 = 900MHz);
The above communication equation will become:
43dBm-(-70dBm)+ GT(dBi)+1.5dBi=32dB+ 20logr(m) dB +2.4dB + propagation loss L0
114.5dB+ GT(dBi) -34.4dB = 20logr(m)+ propagation loss L0
80.1dB+ GT(dBi) = 20logr(m)+ propagation loss L0
When the value on the left side of the above formula is greater than the value on the right side, that is:
GT(dBi) > 20logr(m)-80.1dB+propagation loss L0. When the inequality holds, it can be considered that the system can maintain good communication.
If the base station uses an omnidirectional transmitting antenna with a gain of GT=11dBi and the distance between the transmitting and receiving antennas is R=1000m, the communication equation further becomes 11dB>60-80.1dB+propagation loss L0, that is, when the propagation loss L0<31.1dB, good communication can be maintained within a distance of 1 km.
Under the same propagation loss conditions as above, if the transmitting antenna gain GT = 17dBi, that is, an increase of 6dBi, the communication distance can be doubled, that is, r = 2 kilometers. Others can be deduced in the same way. However, it should be noted that the base station antenna with a gain GT of 17dBi can only have a fan-shaped beam coverage with a beam width of 30°, 65° or 90°, etc., and cannot maintain omnidirectional coverage.
In addition, if the transmitting antenna gain GT=11dBi remains unchanged in the above calculation, but the propagation environment changes, the propagation loss L0=31.1dB-20dB=11.1dB, then the reduced 20dB propagation loss will increase the communication distance tenfold, that is, r=10 kilometers. The propagation loss term is related to the surrounding electromagnetic environment. In urban areas, there are many high-rise buildings and the propagation loss is large. In suburban rural areas, the farmhouses are low and sparse, and the propagation loss is small. Therefore, even if the communication system settings are exactly the same, the effective coverage range will be different due to the difference in the use environment.
Therefore, when choosing omnidirectional, directional antennas and high-gain or low-gain antenna forms, it is necessary to consider using base station antennas of different types and specifications according to the specific conditions of the mobile communication network and application environment.
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Post time: Jul-25-2025
