User's Manual

Table Of Contents

2. System Description 27

Crosspoint

Switch

Framer

Modem East Modem West

Up to 32 E1

Up to 16E1

Optional IO

Crosspoint

Switch

Framer

Modem East Modem West

Up to 32 E1

Up to 16E1

Optional IO

Repeater Example

Add/Drop Example

Figure 2-13. (a) Crosspoint Switch used a passthrough in repeater

configuration. (b) Crosspoint Switch allows access for add/drop.

2.13Power Management

RF power management is a radio design feature that controls the power level (typically

expressed in dBm) of the RF signal received from a transmitter by a receiver. The

traditional goal of power management is to ensure that the RF signal at a receiver is

strong enough to maintain the radio link under changing weather and link conditions.

The Quadrature Amplitude Modulation (QAM) is not a constant envelope waveform.

Therefore, the average power and peak power are different. The difference in peak and

average power depends on the constellation type and shaping factor, where spectral

efficiency such as more constellation points or lower shaping factor leading to peak

powers higher than average powers. The peak power is typically 5-7 dB greater than the

average power and never exceeds 7 dB. Regulatory requirements are sometimes based

on peak EIRP which is based on peak power and antenna gain.

Traditional power management techniques such as Constant Transmit Power Control

(CTPC) and Automatic Transmit Power Control (ATPC) transmit at a high power level to

overcome the effects of fading and interference. However, these techniques continue to

operate at a higher power level than needed to maintain the link in clear weather.

Because transmit power remains high when the weather clears, the level of system

interference increases.

Radios operating at high transmit power will interfere with other radios, even if the

interfering source is miles away from the victim. High interference levels can degrade

signal quality to the point that wireless radio links become unreliable and network

availability suffers. The traditional solution to system interference is to increase the

distance between radios. However, the resulting sparse deployment model is

inappropriate for metropolitan areas.