DSSS vs OFDM

Though wireless communication technologies are easy to understand on the surface, the more you dig into them, the more complex they become. For example, two wireless communication technologies we actively use today are DSSS and OFDM. 

Both are prevalent for wireless networking. So, let’s look at the differences between DSSS vs. OFDM and why we need to know what they are. 

What is DSSS?

DSSS is a spread spectrum specification. It’s used to ensure that all the data transmitted wirelessly is also received. Wireless communication has a nasty habit of bouncing off objects in meatspace. So, DSSS utilizes a spectrum of radio frequencies to transmit redundant copies of every single bit of data. 

It’s not that simple, though. DSSS purposefully introduces noise into those redundant bits of data when they are created. This noise is called psuedonoise. Each redundant bit of data created with that pseudonoise is called a chip. 

Both the transmitter and the radio receiver use the same algorithm to encode and decode those chips. Because each of those chips is redundant data, the radio receiver doesn’t need to physically catch every single chip. Only a few chips are needed to reconstruct the original data bit and verify that it is the correct value. 

Because data can be reconstructed by a radio receiver, DSSS-encoded data is more reliable than a wireless transmission sending information on a single frequency. 

What is OFDM?

OFDM stands for orthogonal frequency division multiplexing. It’s a method to achieve better wireless communication speeds by utilizing the amount of available spectrum more efficiently. How does it do that?

Spread spectrum technologies use a chunk of frequencies, or spectrum, to transmit data. Data is sent with multiple radio frequencies to improve reliability. However, radio frequencies have a nasty habit of colliding with each other and causing other types of issues. When we use radio waves for communication, there’s a lot more to worry about than the meatspace objects wireless communications bounce off.

Older types of spread spectrum technologies add buffer spaces between blocks of spectrum. Remember when doctors advised that we keep 6 feet of personal space between everyone during Covid lockdowns? It’s like that. 

Our radio waves are very finite and already congested. So, we need to utilize as much of it as possible. OFDM lets us transmit spread spectrum radio signals without buffer space. 

OFDM works by tightly timing the transmission of wireless communications. If we send radio signals at very specific moments, we ensure that those signals don’t collide with each other. Explaining how the complexities of OFDM work is beyond the scope of this article, but here’s a fast primer. 

Radio waves travel in a sine wave. That means they bobble up and down as they move forward. The delta between bobbles is extremely specific. The measurement unit of that bobble is called a hertz. The more hertz in a radio wave, the more data it carries. However, the more a radio wave bobbles as it travels, the more likely it is to bounce off something. This is the reason you never have a cell phone signal near the freezers in Walmart. 

OFDM times those bobbles so they don’t align with each other. When one radio wave is cresting at the top of its bobble, both neighboring radio waves are exactly in the middle of their bobbles. Because the bobbles don’t match, the radio waves don’t collide. 

DSSS vs. OFDM

DSSS and OFDM are similar. The biggest difference between the two is how they utilize the spectrum they are allotted. 

When DSSS splits a bit into multiple chips, it uses the entire available spectrum to transmit those chunks. However, OFDM takes its portion of spectrum and subdivides it. The OFDM-enabled transmitter transmits data on each of those subdivided segments of spectrum. Because those data transmissions are carefully timed, they don’t collide with each other. So, OFDM is able to send out more information in a given range of spectrum than traditional DSSS. 

This is simplifying things an awful lot. You don’t need to choose between using DSSS or OFDM. Many wireless communications use DSSS-encoded data through OFDM transmissions. The difference is that when DSSS is used in conjunction with OFDM, more chips can be created for each bit of data to increase reliability, and likewise, OFDM can transmit multiple sets of chips for different bits at the same time. 

Final Thoughts

The biggest takeaway from this article is that DSSS and OFDM are two different ways that we use to make wireless communications more efficient. OFDM transmits more data at faster speeds than plain jane DSSS, and DSSS can be used with OFDM.