TDD WCDMA uses spreading factors 4 - 512 to spread the base band data over ~5MHz band. Spreading factor in dBs indicates the process gain. Spreading factor 128 = 21 dB process gain). Interference margin is calculated from that:
Interference Margin = Process Gain - (Required SNR + System Losses)
Required Signal to Noise Ration is typically about 5 dB
System losses are defined as losses in receiver path. System losses are typically 4 - 6 dBs
