TDM

Modems designed to support single or multiple E1/T1, including E3 streams with capacity varying from few Mbps to 50 Mbps and higher. E1/T1 carry 2.048/1.554 Mbps respectively, and n x E1/T1 can be multiplexed in order to have required number of voice and data channels. The North American and Japanese hierarchies are based on multiplexing 24 voice-frequency channels and multiples thereof, whereas the European hierarchy is based on multiplexing 32 voice-frequency channels and multiples thereof. The number of E1/T1 may be typically anything between 1 to 32.

Alternatively, E3 data circuits are widely used in point to point microwave, which carries 34.368 Mbps. These are known as PDH radios.

TDM based radios are becoming less frequenct due to the migration to hybrid – TDM and Ethernet supported radios – or Carrier Ethernet radios. Typical features of TDM based modem:

• I/Q baseband, complex IF or real IF interface
• Input and output carrier frequencies are freely software configurable
• Transport stream is a multiplex of n x E1/T1 or E3
• Modulation: QPSK to 64QAM, optionally up to 256QAM
• Roll-Off factor: software configurable 16-25%
• Bandwidth: software configurable 5 to 28MHz
• Symbol rate: software configurable 4.5-25 MSym/s
• Includes PilotSync™ technology
• FEC Reed-Solomon encoder/decoder
• Interleaver/Deinterleaver depth: I = 1/2/3/4/6/12/17
• Configuration via 8bit parallel host interface or RS 232
• Single external analogue loop for AGC 18 bits
• Input from ADC: 11-12 bits (1 or 2 (I/Q) channels)
• Output to DAC: 10-16 bits (1 or 2 (I/Q) channels)
• Decision Feed-Forward Equalizer in the receiver channel
• Modem master clock / sampling rate: single, fixed 50 MHz clock source
• Shape Filter: Root-Raised-Cosine
• Internal PRBS generator and internal BER tester