The technical details of Resource Elements (REs) in wireless communication systems, particularly in cellular networks like LTE (Long-Term Evolution) and 5G.
- Resource Element (RE):
- An RE is the fundamental unit of time-frequency resources.
- It represents the smallest granularity at which resources are allocated for transmitting data or control information.
- Each RE corresponds to a physical resource and is uniquely identified by its position in the frequency domain (index k) and time domain (symbol position l).
- The complex value associated with an RE is denoted as (a_{k,l})_{p,\mu}, where:
- p represents the antenna port.
- μ indicates the subcarrier spacing configuration.
- Resource Grid:
- The resource grid consists of subcarriers along the frequency axis and OFDM symbols along the time axis.
- There is one set of resource grids assigned per transmission direction (uplink or downlink).
- Each antenna port (p) has its own resource grid based on the subcarrier spacing configuration (μ).
- The size of the resource grid is determined by higher-layer parameters such as carrier bandwidth and starting position.
- In 5G NR, the resource grid supports (N_{\text{grid}}, x) size, μ \times N_{\text{SC}} RB subcarriers, and μ \times N_{\text{symb}} OFDM symbols.
- Resource Block (RB):
- An RB consists of 12 consecutive subcarriers in the frequency domain.
- Each RB is a group of resource elements.
- There are multiple RBs within a resource grid.
- RBs are further grouped into Physical Resource Blocks (PRBs), each containing 12 subcarriers.
- Numerology and Carrier:
- For each numerology and carrier, a resource grid of (N_{\text{RB}})_{\text{max},\mu} subcarriers and (N_{\text{symb}})_{\text{max},\mu} OFDM symbols is defined.
- Resource grids for different subcarrier spacings overlap.
REs play a crucial role in allocating resources efficiently across time and frequency in 5G and LTE networks. They enable reliable communication by providing fine-grained control over data transmission and channel estimation.
