# Um interface

Use TDM frame - 8 bits

Mobile and BTS interface by Air

### ARFCN - Downlink & Uplink

#### FDMA

#### TDMA

TDMA Frame has 8 time slots or physical channels - 4.62 ms

1. Hyperframe
2. Superframe
3. 51 multiframe
4. 26 multiframe

### Modulation

GMSK

TDMA (Time Division Multiple Access) is a channel access method for shared-medium networks. It allows multiple users to share the same frequency channel by dividing the signal into different time slots. Each user transmits in rapid succession, one after the other, each using their own time slot. This prevents interference from multiple transmissions over a single frequency.

In TDMA, a frame consists of 8 time slots, or physical channels, each occupying 4.62 ms. This structure is organized as follows:

1. **Hyperframe**: The highest level in the GSM hierarchy, consisting of 2,048 Superframes.
2. **Superframe**: Comprises 51 Multiframes.
3. **51 Multiframe**: Contains 51 TDMA frames.
4. **26 Multiframe**: Contains 26 TDMA frames, typically used for control channels.

Modulation in TDMA uses GMSK (Gaussian Minimum Shift Keying), a type of continuous-phase frequency shift keying that minimizes bandwidth and power requirements.


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