Introduction to Radio Communication Part 1

JRC Tech Seminar Vol.2

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We will introduce some basics about radio communication, the seminar will be divided into two parts and in this blog, we will focus on the following five parts.

1. What is a Radio Wave
2. Radio Wave Propagation
3. Power (W, dBm, dB)
4. Radio Propagation Design
5. Impedance

What is a Radio Wave

An electric field and a magnetic field propagating through space while vibrating.

• 　Sound is propagated through the air, similar to radio waves.
• 　Radio waves are similar to light because they do not require a medium (they can propagate without air).
  

Frequency: Number of vibrations per second (Hz)

Wavelength: Periodic length of a wave (wave motion) (m)

Wavelength (λ) [m] = propagation velocity [m]/frequency [Hz]

Propagation velocity = speed of light = 299,792,458 m/s (300,000 km/s)

e.g. A wavelength with a frequency of 50 MHz is 300[Mm/s]/50[MHz]=6m

Radio Wave Propagation

By creating an electric potential difference in space, a radio wave (electric field) proportional to the voltage is radiated.

The strength of the radio wave emitted from the antenna is called Transmitting power (W).

Radio wave propagation: Radio waves travel through the air and reach a distant place.

The direction in which the electric field vibrates is called polarization.

Power (W, dBm, dB)

dBm means that 1mW is expressed as 0dBm.

Relationship between 1mW and 0dBm:

D=10log₁₀P

P=10^(D/10)

P is Mw, D is dBm

The dB is not a unit of absolute value or quantity, but a relative unit of ratio or magnification.

Radio Propagation Design

Perform desk calculations to determine if wireless communication is feasible. (Can the required service area be secured?)

Free space loss: Virtual space with nothing in it. Since no reflection occurs, the received power attenuates with the square of the theoretical distance.

When there is no obstacle, antenna height is high, and there is no influence of buildings, etc.

Two-wave model: A space where there is plane earth that is totally reflected. At the receiving point, two waves (direct wave and earth-reflected wave) arrive and interfere with each other.

At the point where the direct wave and the reflected wave are in opposite phases, they cancel each other out and the received power becomes small (dead point).

The point where the received power drops often occur in the vicinity of a few meters.

Okumura - Hata Model: This is an approximate curve (model) created based on aggregate data from actual measurements of radio propagation characteristics of wireless devices in different environments (open areas, suburbs, small and medium-sized cities, and large cities) during the development stage of mobile radio (car phone) and cellular. It was used in the construction of cell phone networks and is still widely used today.

Source: https://link.springer.com/article/10.1007/s00502-018-0639-y

The possible approximation conditions:

• Frequency f (MHz): 150 MHz to 1.5 GHz
• Communication distance d(m): 1 km to 20 km
• Antenna height of base station hb(m): 30 m to 200 m
• Antenna height of mobile station hm(m): 1m - 10m
  

It is intended for use over medium to long distances, so the difference becomes large when the distance between wireless devices is as short as several tens of meters.

Impedance