Describe the LTE frame structure and its key parameters.

LTE uses OFDMA (downlink) and SC-FDMA (uplink) with a specific frame structure. Radio frame: 10ms duration containing 10 subframes. Subframe: 1ms duration containing 2 slots. Slot: 0.5ms containing 7 OFDM symbols (normal CP) or 6 symbols (extended CP). Resource Block (RB): 12 subcarriers × 1 slot = 84 resource elements (normal CP); smallest schedulable unit. Subcarrier spacing: 15 kHz. Bandwidth options: 1.4, 3, 5, 10, 15, 20 MHz (6 to 100 RBs). Cyclic prefix: Normal (4.7µs) or Extended (16.7µs) for high delay spread. Reference signals (pilots) enable channel estimation. This structure supports both FDD and TDD modes.