Wireless communications wouldn’t be as advanced as they are today without FHSS or DSSS. Both FHSS and DSSS are early technologies used to make wireless communications more resilient. In fact, DSSS was first theorized in 1942, and DSSS is built on top of FHSS which came before it.

Given FHSS vs DSSS, which one should you use and why, and why are both so important? 

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There are a lot of reasons why you may want to use DSSS instead of FHSS. For instance, if you’re a spy and want to obfuscate your communications, DSSS is a far better option. 

If you want to know why, and wireless communications is something you’ve been meaning to brush up on, consider studying for the Certified Wireless Network Administrator certification. The CWNA cert requires that you understand things like how radio waves work, the physics of light, and how we harness electromagnetism to send and receive data. Are you ready to start a CWNA online training course? Then get started right now!

What is FHSS?

FHSS stands for frequency hopping spread spectrum. It’s a method of bending the laws of physics to make wireless transmissions less susceptible to interference. Here’s how it works. 

High-frequency radio waves carry more data, but they bounce off things easier than low-frequency radio waves. For example, a 2.4 GHz WiFi signal can penetrate walls much easier than a millimeter wave 5G connection. So, if we send a wireless communication on a single high-frequency radio wave, there is a good chance we won’t receive it thanks to pesky meat space objects. 

However, if we divide data into chunks and send those chunks in different frequencies, there is a better chance we will receive most of it. This is the idea behind FHSS. 

FHSS divides data into chunks. After data is divided into chunks, the first chunk is sent on one frequency. After the first chunk is sent, the transmitter hops to a different frequency and sends the second chunk of data. And so forth. 

The group of frequencies a transmitter can hop between is predefined. Those predefined frequencies are called spectrums. We spread data through spectrum, so it is a spread spectrum, and because the transmitter hops between those frequencies, it is a frequency hopping spread spectrum.

What is DSSS?

DSSS is built on top of FHSS. Instead of hopping between frequencies, though, DSSS-capable transmitters send data on an entire spectrum of frequencies at once. 

But, DSSS has a few tricks up its sleeves. Because DSSS uses the entire spectrum to send out a single bit of data, each bit of data is broken down into chunks. An algorithm is used to determine the value of each of those chunks. Those chunks are transmitted as new bits wirelessly. A receiver nabs those bits from the air and uses an algorithm to convert them back into the original data.  

FHSS vs DSSS

We’ve already covered one of the core differences between FHSS vs DSSS. FHSS hops between frequencies when data is transmitted. Instead of hopping between frequencies when data is sent, DSSS sends data on every frequency in the designated spectrum at once. 

Differences in Transmission Resiliency 

One of the core reasons that both FHSS and DSSS exist is to make wireless communications more resilient. Both FHSS and DSSS do this by splitting and sending data on multiple frequencies instead of using just one. 

DSSS has parity built into it, though. DSSS turns a single bit into multiple new bits. An algorithm is used to add pseudo noise to those new bits. The receiver uses the same algorithm to remove that pseudo noise from those bits of data. 

Because all those bits of data were created from a single origin value, most of them are redundant. The radio receiver only needs to receive enough data to determine what the original bit value is and to confirm it. For the Barker 11 spec for 802.11 WiFi, a wireless device only needs to receive 2 of the 11 bits. There’s a lot of redundancy built in. 

Can FHSS handle noise better than DSSS?

So, if DSSS has built-in parity, why shouldn’t that be the standard? As it turns out, FHSS is more resilient than DSSS. FHSS can handle very noisy and congested environments much better than DSSS-encoded radio signals can. 

Compare FHSS wireless communications to UDP. UDP sends data in a spray-and-pray fashion. Because we don’t verify data is received, UDP connections can be faster than TCP connections. This is why UDP is typically used for video streams, and when we get garbage mid-video streams, that means some of those UDP packets didn’t make it to us. 

FHSS is similar. We may not receive all the data sent over the air, but sometimes it’s acceptable to lose some data in a noisy area if the alternative is receiving no data at all. 

Is FHSS slower than DSSS?

In the example above, we compared FHSS to the UDP protocol and stated that UDP can be faster at transmitting data than TCP. However, FHSS is a slower connection than DSSS. That part of the analogy does not fit. FHSS has a max speed of 3Mbps while DSSS has a max bandwidth of 11 Mbps. 

Broadcast Preferences

Why else would we want to use FHSS vs DSSS? There are a lot of reasons, but let’s only discuss one more. FHSS is a much better choice for a one-to-many type of communication while DSSS is better situated for one-to-one communication methods. Otherwise, FHSS is better for FM radio signals while DSSS is better for 802.11 WiFi transmissions. Learn more about networking with CBT Nuggets today!