The network-node equipment (NNE) provides the basic network gateway for connecting wireline network traffic to the LMDS bandwidth (see Figure 7). The NNE is equivalent to the base-station digital equipment. The network-node products provide processing, multiplexing, demultiplexing, compression, error detection, encoding, decoding, routing, modulation, and demodulation. The NNE may also provide ATM switching.

Figure 7. Network-Node Architecture

The following functions may be performed at the network node:

Digital Signal Compression

The conversion of analog television signals to highly compressed digital signals for distribution by the microwave system.

Wireline/Wireless Protocol Interfaces

Depending on an operator's service offerings, NNE may be configured to extend video, IP, and voice services over LMDS bandwidth. (ATM is emerging as a likely standard for the delivery of voice, data, Internet, and video services over LMDS.)

Modulation and Demodulation

Signals from the voice, video, and data multiplexing system are modulated before wireless transmission occurs. Similarly, traffic from the microwave receiver is demodulated before wireline transmission.

Modulation

A digital modulator accepts a digital stream and provides a 4–QAM, 16–QAM, or 64–QAM intermediate frequency (IF) signal for delivery over the LMDS bandwidth. The modulator performs all the functions required to modulate digital video, voice, and data to a standard IF for input to the wireless transmitters.

Demodulation

A QAM demodulator contains two separately addressable demodulator channels, each capable of accepting 4–QAM, 16–QAM, 64–QAM signals at symbol rates between 1 Mbps and 10 Mbps. TDMA systems may use differential QPSK modulation.