How Does a Wider LoRa Bandwidth Increase Data Rate

How Does Bandwidth Determine Speed?

We often think of bandwidth as a “pipe”: the wider the pipe, the more water can flow through it.

In the world of LoRa, however, increasing bandwidth works in a slightly different physical way. Instead of simply widening a channel, it actually speeds up how fast the signal scans across frequencies.

Put simply, bandwidth determines how “steep” a LoRa signal is.

The wider the bandwidth, the faster the signal changes, and the less time it takes to transmit the same data symbol. It is like switching from “walking” to “sprinting.” Therefore, with the spreading factor (SF) fixed, increasing bandwidth is the most direct way to increase LoRa throughput and data rate.

But this acceleration comes at a cost.

Bandwidth is not only the track the signal runs on—it is also the window through which environmental noise enters the receiver. When you widen the bandwidth (open the window wider) to gain higher data rates, more noise flows in as well. As a result, receiver sensitivity drops and communication range shortens.

There is no single “correct” LoRa bandwidth setting.

In the following sections, we will explain the key concepts step by step to answer the core question: How does a wider LoRa bandwidth increase data rate?

Understanding Bandwidth Through Sound

To better understand LoRa modulation and its spread-spectrum behavior, it helps to think in terms of sound.

LoRa uses Chirp Spread Spectrum (CSS) modulation. A chirp signal is like a bird call: its frequency slides over time, either from low to high or from high to low.

Bandwidth (BW): The frequency range that the “bird call” sweeps through.

For example, if the frequency slides from 100 Hz to 200 Hz, the bandwidth is 100 Hz.

Typical LoRa examples:

● 125 kHz bandwidth: The signal sweeps across a 125,000 Hz frequency range.

● 500 kHz bandwidth: The signal sweeps across a much wider 500,000 Hz range.

A wider bandwidth means the signal sweeps across a larger frequency range in less time. This directly compresses transmission time, allowing information to be delivered more quickly.

The Fundamental Mechanism Behind Higher Data Rates

Why does occupying more spectrum allow LoRa to transmit faster?

The answer lies in how LoRa demodulation works. Three key concepts explain this relationship:

1. Chip rate

2. Chirp slope

3. Bit rate

1. Bandwidth Is Essentially the Chip Rate

LoRa follows a simple rule: Numerically, bandwidth equals chip rate.

● Chip: The smallest time unit in a LoRa signal

● Chip rate (Rc): The number of chips transmitted per second

With a 125 kHz bandwidth, the system processes 125,000 chips per second.

With 500 kHz, it processes 500,000 chips per second.

When the system’s fundamental “clock” runs faster, data transmission naturally becomes faster as well.

2. Signal Slope Determines How Fast Symbols Are Sent

Bandwidth not only increases the number of chips per second—it also changes the shape of the signal.

On a frequency–time graph, a LoRa chirp appears as a diagonal line. Increasing bandwidth means the signal must sweep across a wider frequency range in a shorter amount of time.

Chirp slope formula:

Physical meaning:

When bandwidth doubles, the chirp slope increases by four times.

An analogy helps here:

● A narrow bandwidth signal is like a gentle slide, where the signal moves slowly.

● A wide bandwidth signal is like a steep cliff, where the signal rushes down almost instantly.

This increased steepness compresses time, which directly increases data rate.

3. From Symbols to Bits: The Complete Data Rate Formula

This explains why doubling bandwidth halves the symbol duration Tsym.

But the more practical question is: how many bits per second can LoRa transmit?

Each symbol carries a fixed amount of information determined by the spreading factor (for example, SF7 carries 7 bits per symbol). When coding rate (CR) is included, the full bit rate formula becomes:

Where:

● SF: Spreading Factor (bits per symbol)

● BW: Bandwidth (processing capacity per second)

● CR: Coding Rate (error correction overhead, e.g., 1–4 corresponds to 4/5, 4/6, etc.)

Conclusion:

Bandwidth appears in the numerator of the equation, which proves that LoRa data rate is directly proportional to bandwidth. Doubling bandwidth directly doubles throughput.

4. A Concrete Calculation Example

Let’s verify this with numbers. Assume:

● SF = 7 (27 = 128 chips per symbol)

● CR = 1 (4/5)

Scenario A: Narrow Bandwidth (125 kHz)

Symbol duration: approximately 1.024 ms

Scenario B: Wider Bandwidth (250 kHz)

Symbol duration: approximately 0.512 ms

When bandwidth increases from 125 kHz to 250 kHz, the symbol duration is halved and the data rate doubles.

This is the fundamental rule behind “the wider the bandwidth, the higher the data rate.”

The Sensitivity Trade-Off Behind Higher Data Rates

If wider bandwidth is both faster and seemingly better, why doesn’t LoRaWAN default to the maximum bandwidth of 500 kHz?

The reason is simple: in radio physics, noise is an unavoidable enemy.

1. More Noise Enters the Receiver

Bandwidth is not only the path for the signal—it is also a “window” through which environmental noise enters the receiver.

The wider the window, the more background noise power flows in.

According to the thermal noise equation:

When bandwidth B doubles, the noise floor power increases by 3 dB.

2. Spreading Gain Does Not Increase

This is a critical detail that is often overlooked:

Increasing bandwidth alone does not increase spreading gain.

The spreading gain is defined as:

It depends only on the spreading factor (SF), not on bandwidth.

Therefore, when bandwidth doubles:

● Noise floor increases by 3 dB

● Spreading gain remains unchanged

3. Receiver Sensitivity Ultimately Degrades

With higher noise and no gain compensation, receiver sensitivity directly worsens by 3 dB.

What does a 3 dB loss mean?

In a free-space propagation model, a 3 dB link budget loss corresponds to roughly a 30% reduction in coverage distance.

In simple terms:

● 500 kHz: Like speaking quickly in a loud room—fast, but the listener must be very close.

● 125 kHz: Like whispering in a quiet library—slow, but audible over long distances.

This illustrates the classic LoRa bandwidth vs range trade-off.

How to Choose Bandwidth for Different Scenarios

Once the mechanism and cost are clear, how should bandwidth be selected in real deployments?

Frequently Asked Questions (FAQ)

Q1: Does increasing LoRa bandwidth increase power consumption?

A: This is a common misconception.

Although wideband processing slightly increases instantaneous circuit power, the much higher LoRa data rate significantly shortens transmission time. Overall, wide bandwidth often reduces total energy consumption and extends battery life.

Q2: Why does LoRaWAN commonly use 125 kHz in Europe instead of 500 kHz?

A: This mainly depends on regional spectrum regulations.

In regions such as EU868 and CN470, 125 kHz is the standard configuration. ETSI regulations in Europe impose strict duty-cycle limits per channel. Narrowband signals have higher spectral density and better interference resistance, making them more suitable for crowded unlicensed bands.

In contrast, regions like US915 also define 500 kHz as a standard uplink bandwidth.

Q3: Which affects data rate more, spreading factor (SF) or bandwidth (BW)?

A: Both are related, but their effects differ in scale.

Changes in SF are exponential ( 2SF ), while changes in BW are linear. Reducing SF from SF12 to SF7 can increase data rate by several tens of times, whereas increasing BW from 125 kHz to 500 kHz provides only a 4× gain. In practice, SF is usually optimized first, followed by bandwidth.

Q4: Can I change bandwidth arbitrarily?

A: No.

Wireless communication is a two-way handshake. The transmitter (node) and receiver (gateway) must use exactly the same bandwidth configuration. Otherwise, the receiver’s filter cannot correctly capture the signal, resulting in complete communication failure.

Q5: How does 500 kHz bandwidth perform in urban environments?

A: Usually worse than 125 kHz.

Although wider bandwidth theoretically improves multipath tolerance, link budget and penetration are the dominant factors in cities. Compared to 125 kHz, 500 kHz increases noise floor by about 6 dB, significantly degrading sensitivity and reducing power spectral density. This directly weakens building penetration. Unless line-of-sight conditions are excellent, narrow bandwidth is generally safer in urban deployments.

Conclusion

Returning to the original question—How does a wider LoRa bandwidth increase data rate?

The answer lies in two key mechanisms:

1. Wider bandwidth increases chip rate
Bandwidth numerically defines the chip rate. Increasing BW from 125 kHz to 500 kHz accelerates the system’s processing rhythm by 4×, allowing more data to be transmitted per unit time.

2. Wider bandwidth creates steeper chirp slopes
A wider frequency sweep over a shorter time compresses the symbol duration. Faster symbols naturally lead to higher data rates, which is why the relationship
Rb ∝ BW holds true.

However, this acceleration comes at a cost. A wider bandwidth also opens the door to more noise, reducing receiver sensitivity and shortening communication range.

Ultimately, choosing LoRa bandwidth is a balance between data rate and coverage.

Once these mechanisms are understood, bandwidth selection becomes far more intuitive—whether the goal is long-range metering deep underground or high-speed industrial control, the right configuration becomes clear.