What is a Resource Block in LTE?
In one of the previous articles, we explored how LTE uses OFDM to transmit data efficiently. Now, let me explain how that data is organized and sent — and that’s where Resource Blocks come in. If you understand Resource Blocks, you’ll have a clearer view of how the LTE network slices the available bandwidth and allocates it to users like you and me.
In LTE, the entire frequency spectrum isn’t used as one big pipe. Instead, it’s divided into smaller sections called Resource Blocks (RBs). Each Resource Block is the smallest unit of resource allocation that the LTE scheduler can assign to a user. These are defined in both the time and frequency domain, so let me break that down for you.
Each Resource Block spans 180 kHz in frequency, which includes 12 subcarriers spaced 15 kHz apart. In the time domain, it lasts for 1 millisecond (1 ms), which equals one Transmission Time Interval (TTI). This 1 ms is further split into two slots of 0.5 ms each. So, when your device sends or receives data, it’s not using a random chunk of spectrum — it’s using specific Resource Blocks scheduled by the eNodeB (base station).
Now, here’s where it gets practical. Based on several conditions — like your device’s channel quality, the amount of data to be transferred, and how congested the network is — the LTE scheduler dynamically assigns a number of RBs to you. The better your signal and network conditions, the more RBs you may get, which directly impacts your throughput.
This allocation happens separately for uplink and downlink, and the total number of available RBs depends on the system bandwidth. For example:
| Bandwidth | Available Resource Blocks |
|---|---|
| 1.4 MHz | 6 RBs |
| 3 MHz | 15 RBs |
| 5 MHz | 25 RBs |
| 10 MHz | 50 RBs |
| 15 MHz | 75 RBs |
| 20 MHz | 100 RBs |
So let’s say you’re connected to a 10 MHz LTE network. The base station has 50 RBs to manage across all active users. The scheduler will decide, millisecond by millisecond, how many of those to assign to your device depending on the traffic and radio conditions.
One more thing to note — these RBs don’t just carry user data. They can also be used to carry control signals, reference signals, and broadcast information, depending on the configuration. This makes RBs not just a transport mechanism but also a flexible resource the network uses for various needs.
Understanding how Resource Blocks work ties directly into other concepts like modulation schemes, throughput calculation, and QoS. If you’re following along with earlier topics such as how modulation and coding schemes are selected or how SINR affects throughput, you’ll start seeing how all these pieces come together.
So next time you see your phone switching between LTE bands or dealing with poor speeds, you’ll know that behind the scenes, it’s all about how many Resource Blocks are being assigned and how efficiently they’re being used.