Selecting a wireless module solution should be easy. In a perfect world you would simply pick the one with the longest range. That way, no matter how far apart your devices are deployed, they’d always be able to communicate. Alas, it’s not that simple. Fortunately, there are solutions that match any use case, from long range radio communication, to short range or in between.
 
Ask any Internet of Things expert which radio module is the best and the answer will be, “it depends.” That’s because each wireless device type has its own strengths and weaknesses. What’s great for one project may be terrible for another. For example, a module that uses very little battery power may also offer have low bandwidth. That’s a perfect solution for a wireless bathroom scale, but all wrong for streaming live video from a conference room, and vice versa.
 
With radio range, the same thing holds true. You need to evaluate the use case and have some understanding of how radio signals propagate depending upon both equipment and environment. In this article we look at all the considerations to determine the best choice in module range and type for your project.
 

Factors that Affect Wireless Signal Range

Range is defined as the maximum distance where communication can exist between two antennas in a wireless network. But range is not only about distance. Here are some important considerations:

• Obstacles, terrain, and radio physics all affect range.
• Another factor is antenna design, with considerations like frequency bands and impedence.
• Noise is another important factor. Just like it’s hard to hear someone at a crowded party, it’s tough to pick out a radio signal in environments with lots of radio noise.

The various considerations and factors that can impact how well the devices in your network communicate include 10 different factors.

1. Throughput

In IoT, you often need to communicate small amounts of data from remote locations. Data throughput has a significant impact on range. When data rate increases, the range for effective communication between devices can shrink. This is because fast data rates require a higher signal-to-noise ratio for successful demodulation.

If someone in a noisy room is speaking very rapidly they are hard to understand. If they slow down, they are easier to understand. Radios work similarly. Many IoT devices send as little as a single sensor value once per day. When that data is sent at a low bitrate, it can be detected much farther away.
 

2. Power

Radio signals require a lot of power because, unlike messages running through a wire, they decay in an accelerated fashion. As radio signals radiate away from their source, they rapidly spread out like ripples in a pool. Both sound and radio decay according to the inverse square law. Each time you double the distance, you require four times the amount of power, so traversing long distances uses vastly more energy compared to shorter ones.

3. Noise

In an RF network, the signal is the information transmitted between devices. Noise is anything else. Signal-to-noise (S/N) ratio is a metric that compares signal power levels to noise power levels. It's an important factor in determining the radio system's range, because range is about reliably distinguishing signal from noise, not the distance that a given radio signal can travel (which is infinite). Radio noise is part of the natural environment, which includes:

• Cosmic background radiation and solar interference
• Atmospheric sources like lightning
• Human sources like power lines, motors, fluorescent lighting, switches, computers and unrelated radio communications

4. Frequency

Lower frequency radio signals can easily diffract around objects and be bounced back by the atmosphere, increasing effective range. However, lower frequencies have limited bandwidth so throughput is constrained. Higher frequencies offer much higher throughput, but have difficulty diffracting around obstacles and will not be reflected back by the atmosphere, limiting their range.
 

5. Free space loss

As a radio signal travels through space, even in a vacuum, its signal will be diminished as it spreads out its energy over an ever wider area. This spreading follows the inverse square law, which describes the exponential loss of power over distance. We address free space loss at a given frequency by reducing the distance between transmitter and receiver.
 

6. Diffraction

When a radio signal meets an object in its path, it will scatter or diffract, with some of the energy bending around the object, but the remainder being directed away from the receiver and therefore lost. Sharp edges diffract better than rounded objects, which tend to absorb more of the signal. Diffraction is just one of many reasons for avoiding objects in the signal path.
 

7. Multipath

In ideal environments like outer space, signals sent by a transmitter always arrive directly, without reflecting off any surfaces or objects. Here on Earth, things are unavoidably more complicated. In cases where the line of sight is clear, some signals will arrive directly, but others will bounce off nearby objects and terrain, thereby distorting them. Radio protocols and systems are typically designed to address some multipath interference. Placing antennas high up and clear of obstructions also helps.
 

8. Absorption

Radio signals can travel an infinite distance across empty space; however, when they encounter objects, some of their energy is absorbed. Radio signals can travel through walls, but are attenuated in the process. Humidity in the air can absorb enough radio energy to disrupt high-frequency signals. Tree leaves and other vegetation in the signal path can dissipate enough of the signal to cause problems at lower frequencies.
 

9. Terrain

Hills or mountains can absorb, diffract, reflect or entirely block signals from reaching their destination. The makeup of the ground itself can have an effect at low frequencies, with signals traveling better over lakes, oceans or swamps than dry areas like deserts. The Fresnel Zone, a roughly football-shaped area between the antennas, should be as clear of terrain and obstacles as possible to optimize communications performance.
 

10. Antennas and Range

Antennas transform electrical signals into radio waves to transmit information "over the air." For receivers, radio waves are transformed back into electrical variations that computers can understand. Using the right antennas correctly is critical. Poor choices can limit range, waste battery power and turn an otherwise well-conceived system into a support nightmare. See our guide, Top 10 Antenna Design Considerations for more information.
 

Power and Battery Life Considerations for Communication Range

s we’ve seen, range and power are intertwined in wireless communications. Many applications today deploy thousands of wireless devices across a vast area, and it's important to account for the time and expense of managing batteries. Here’s a brief primer on the factors.

Power Management Budgets

Careful device power management can extend battery life from days to years. A great way to conserve power is by matching the range of the radio to the application requirements. Choosing shorter-range protocols or manually limiting transmission power to effectively reduce range will increase battery life.

Some protocols can limit transmission power automatically with an adaptive data rate function that dynamically limits the device to the lowest reliable transmission power. This is especially helpful when devices are mobile, or when the radio environment changes over time (seasonal foliage changes, daily changes in the radio noise environment, etc.)
 

Sleep Modes

To conserve energy and extend battery life, IoT devices often use sleep modes when they are not needed. A sleeping radio module generally won’t receive any transmissions. However, many IoT use cases require devices in the field to transmit and receive.

You can use a store-and-forward method, if the network or protocol design supports it. In certain protocols this is enabled by "parent" radio nodes that temporarily store transmissions intended for a sleeping "child" device until that child wakes up and requests them. In other protocols, a central network server acts as the parent, forwarding messages only when it detects a remote device wakeup. With proper power management, battery and solar-powered systems can run for multiple years without maintenance.

Summary

McCoy’ve covered wireless communication range and the many factors that affect it, demonstrating why the answer to the question of how far a radio signal will go is, “it depends.” Environment, building materials, terrain, reflections, weather, antennas, transmission power, protocols, frequencies and especially signal-to-noise ratio all come into play. So how do we figure out the best solution?
 
First, you must consider all the variables, including:

• Is the intended use case indoor or outdoor?
• Is the application mobile or fixed?
• What distance do you need to cover?
• What is the size and frequency of data will you be transmitting?
• Will there be a lot of radio noise?
• Will power come from coin cell batteries or can the devices be plugged into mains power?
• How many devices or nodes will be connected together?
• What type of building construction, or outdoor topography do you anticipate?
• In which regions of the world will devices be deployed?
• How much can the system cost and still provide the needed return on investment?

The McCoy team can help you assess each of these factors and select the perfect solution to fit your project requirements and cover the ranges needed. Contact us for help with your decision making.