LTE organizes all radio resources on a two-dimensional grid where frequency runs vertically and time runs horizontally. The smallest addressable point on this grid is the Resource Element, defined as one subcarrier in one OFDM symbol period. The scheduler, however, does not allocate individual resource elements. Instead it works with Resource Blocks, each spanning 12 contiguous subcarriers over one half-millisecond slot. A single resource block therefore occupies 180 kHz of bandwidth and contains 84 resource elements when using the normal cyclic prefix configuration with seven symbols per slot.