What is filtered OFDM?
Let me walk you through filtered OFDM, often referred to as f-OFDM. If you’ve already gone through earlier topics like OFDM and LTE waveform design, you’ll find this concept easier to grasp. Still, I’ll explain it here step by step so you and I can explore it clearly together.
Filtered OFDM is a waveform technique developed to improve spectrum efficiency and reduce interference in wireless communications. It’s especially useful in systems like 5G, where multiple services and diverse requirements need to coexist in a very flexible way. At its core, f-OFDM is based on standard OFDM (Orthogonal Frequency Division Multiplexing), but with a key difference — it applies filtering on a per-subband basis.
Now, let’s look at what that really means. In basic OFDM, all subcarriers are treated together in one big block, and there’s usually no specific filtering at the subband level. But in f-OFDM, you can split the entire bandwidth into several smaller chunks, or subbands, and apply a custom filter to each one. This added filter helps suppress out-of-band emissions, which simply means that unwanted signals spilling into adjacent frequency bands are reduced. That’s a big deal when you’re trying to avoid interfering with neighboring signals.
To make it even easier to understand, think of each subband as a lane on a highway. In traditional OFDM, all the lanes share the same speed and road rules. But in f-OFDM, each lane can be customized — like one lane for trucks, another for cars, and another for emergency vehicles. Each lane gets its own treatment to fit its specific traffic, which is how f-OFDM can support different service types such as low-latency communication, massive IoT, or high-data-rate video streaming — all at once, and without stepping on each other’s toes.
Here are the key advantages of f-OFDM that I want you to remember:
- Better spectral efficiency: By filtering individual subbands, you can pack them more tightly together, which means you can make better use of the available spectrum.
- Flexible bandwidth support: You and I both know that not all services need the same bandwidth. f-OFDM allows each subband to have its own width, tailored to the application it’s serving.
- Low out-of-band emission: This is crucial for systems like 5G, where coexistence with legacy technologies and other networks is necessary. The filters ensure that the signal doesn’t leak too much outside its designated band.
However, no technology is without trade-offs. In the case of f-OFDM, adding filters increases complexity in both transmitter and receiver design. Also, if the filters aren’t designed well, they can introduce delay or distort the signal. But the performance gains and flexibility usually outweigh these issues, especially in advanced wireless systems.
As we discussed in the earlier topic on spectral efficiency, f-OFDM plays a key role in achieving higher throughput within limited frequency resources. It’s a good example of how waveform design continues to evolve to meet the changing demands of modern communication systems.
So now when you come across filtered OFDM in any 5G or advanced wireless context, you’ll know that it’s not just another acronym — it’s a smart adaptation of OFDM that uses subband filtering to deliver better performance, flexibility, and spectrum management.