REG (resource element group)

In wireless communication systems, Resource Element Group (REG) is a term used to describe a specific allocation of resources within the physical layer of the system. REGs are fundamental building blocks of the resource grid used in cellular systems such as Long Term Evolution (LTE) and 5G.

To understand REGs, let's start with the basic concept of resource allocation in wireless communication. The available frequency spectrum is divided into smaller chunks called subcarriers, and the time is divided into slots or subframes. These subcarriers and slots are then organized into a two-dimensional grid known as the resource grid.

Each cell in the resource grid is called a resource element (RE), which represents the smallest unit of resource allocation in both frequency and time domains. In other words, an RE corresponds to a specific subcarrier at a specific time location.

Now, a Resource Element Group (REG) is formed by grouping together multiple adjacent REs in the frequency domain. The size of an REG can vary depending on the specific system design and configuration. In LTE, an REG consists of 4 adjacent REs in the frequency domain. In 5G, the size of an REG can be larger, such as 6 or 12 adjacent REs.

REGs are used to carry different types of signals and data in the system. The allocation of REGs is determined by higher-layer signaling and control mechanisms. Some common uses of REGs include:

1. Control Channels: Certain REGs are dedicated to carrying control information, such as reference signals, synchronization signals, and control signaling. These channels provide essential information for synchronization, channel estimation, and decoding at the receiver.
2. Data Channels: REGs are also used to carry user data in the form of physical downlink shared channels (PDSCH) or physical uplink shared channels (PUSCH). These channels are used to transmit actual user data and are dynamically allocated to different users based on their resource requirements.
3. Special Resource Blocks: In some cases, specific REGs or groups of REGs may be reserved for special purposes. For example, in LTE, the first and last REGs of each subframe are typically reserved for guard bands to mitigate interference between adjacent cells.

It's important to note that the concept of REGs is specific to the physical layer design of LTE and 5G systems. Other wireless communication technologies may have different terminologies and resource allocation schemes, but the general idea of dividing the available resources into smaller units for efficient utilization remains common across different systems.