Module grid 

The OFDM resource grid: data and pilot resource elements.

A grid holds $K$ subcarriers × $L$ OFDM symbols; a PilotPattern marks the resource elements (REs) that carry known pilots, the others carry data. Pilots are unit-energy QPSK symbols drawn from a seed (known to the receiver), except those of a PilotTable, which carries its own values (the sequences and boosts of a standard).

Pattern	Pilots	Suited to
PilotPattern::Block	every subcarrier of one symbol in period	slow fading, frequency-selective channels
PilotPattern::Comb	one subcarrier in spacing, in every symbol	fast fading
PilotPattern::Lattice	one subcarrier in freq, one symbol in time	both, at a lower overhead
PilotPattern::Explicit	the positions and values of a PilotTable	the pilots of a standard (scattered, staggered, boosted)

The grid is stored symbol after symbol: RE $(k, l)$ is at index $l K + k$; ResourceGrid::data_indices lists the indices of the data REs in that order, the one walk of the grid that ResourceGrid::map, ResourceGrid::extract and the OFDM link share. ResourceGrid::check refuses a spacing of zero (which ResourceGrid::is_pilot would otherwise read as one) and a table of another size.

Examples

use comnum_waveform::ofdm::grid::{PilotPattern, ResourceGrid};
use comnum_math::C64;
let g = ResourceGrid { n_subcarriers: 12, n_symbols: 7, pattern: PilotPattern::Lattice { freq: 3, time: 3 }, seed: 1 };
assert_eq!(g.pilot_positions().len(), 4 * 3);
let d = vec![C64::new(1.0, 0.0); g.n_data()];
let grid = g.map(&d)?;
assert_eq!(g.extract(&grid)?, d);

References

1. S. Coleri, M. Ergen, A. Puri and A. Bahai, “Channel estimation techniques based on pilot arrangement in OFDM systems,” IEEE Trans. Broadcast., 48(3), 223–229, 2002.

Structs

PilotTable

The pilots of a grid given one by one: their positions and their values (the sequences, phases and power boosts that a standard prescribes).

ResourceGrid

A grid of n_subcarriers × n_symbols resource elements with pilots.

Enums

PilotPattern

The positions of the pilots in the grid.