From the 1988 ARRL Handbook. Page 18-3

	"All of the intelligence is contained in the sidebands, but two-thirds
	of the RF power is in the carrier. The carrier serves to only to
	demodulate the signal in the receiver. If this carrier is suppressed
	in the transmitter and reinserted in the proper phase in receiver,
	several significant advantages accrue. If the reinserted carrier is
	strong compared to the incomming double sideband signal, exalted
	carrier reception is achieved in which distortion caused by frequency
	selective fading is reduced greatly. A refinement of this technique,
	called synchronous detection, uses a phase-locked loop to enhance
	the rejection of the interference. Also, the lack of a transmitted
	carrier eliminates the heterodyne interference common to adjacent AM
	stations. Perhaps the most important of eliminating the carrier is that
	the overall effeciency is increased. The power consumed by the the
	carrier can be put to better use in the sidebands. The power in the
	carrier is continuous and an AM transmitter requires a heavy duty power
	supply. An SSB transmitter having the same power output as an AM
	transmitter can use a much lighter power supply because the duty cycle
	of voice operation is low."


	From the 1988 ARRL Handbook. Page 18-4

	"A further improvement in communtications effectiveness can be obtained 
	by transmitting only one of the sidebands. When the proper receiver
	bandwidth is used, a single-sideband signal will show an effective gain
	of up to 9dB over an AM signal of the same peak power. Because the
	redundant information is eliminated, the required information of an SSB
	signal is half that of a comparable AM or DSB emission. Unlike DSB the 
	phase of the local carrier generated in the receiver is unimportant."


While this pretains to suppressed carrier single-sideband it represents the
great benefits ISB with a reduced carrier level using synchronous detection
can offer. This would still leave the vast majority of power in the sidebands
where the signal is located. Eliminating most of the carrier has big economic
benefits for the broadcaster in transmitter equipment and electricity costs.
Only a small amount of carrier is needed, only enough to allow the PLL to lock,
otherwise the BFO frequency would tend to wander in relation to the
transmitter's carrier frequency and never fully sync up. On most SSB radios
that don't use a PLL BFO a clarifier control is used so the user can manually
sync up the detector with the carrier, an imperfect solution.


	From the 1988 ARRL Handbook. Page 18-13

	"Independent-Sideband Transmittion

	If two SSB exciters, one USB an the other LSB, share a common carrier
	oscillator, two channels of information can be transmitted from one
	antenna."


In a transition phase from envelope detection to synchronous detection enough
carrier could be provided to allow existing narrow bantwidth radios to
properly detect the signal without exceeding -100% modulation at the detector
even though the heavily pre-emphasized signal may exceed -100% modulation by
as much as 9dB before filtering. The broadcast pre-emphasis curve could
actually resemble the average de-emphasis curve of the current typical
narrow band radios thus also providing greater S/N ratios for the higher
frequencies. As these older radios are replacd by newer models that will
properly detect greater than -100% modulation carrier levels can be reduced
further until the minimum carrier level necessary for a good PLL lock will
still be maintained.

Besides the need for narrow bandwidths regarding AM band overcrowding a narrow 
bandwidth also greatly reduces the need for 10kHz notch filters to suppress
the carrier of an adjacent channel. Greatly reducing carrier levels
in relation to sideband energy allows the widening of receiver bandwidths
without the need of a notch filter in most cases. As to the overcrowding issue
moving some stations to the 120m (2.3-2.495mHz) MW commercial boradcast band
along with the 90m (3.2-3.4mHz) commercial SW band is an option. Using these
two bands would add 41 more channels spaced at 10kHz and along with the existing
118 channels from 530kHz to 1700kHz would provide a total of 159 channels, a
35% increase in channel space. In many cases these bands go mostly unused
compared to the regular MW band. 


	From the 1988 ARRL Handbook. Page 18-17

	"Amplitude Compandored Single SideBand

	Amplitude Compandoring

	Compression of voice signals is common in Amateur Radio SSB. What is
	 not common in Amateur SSB is to employ an expander at the receiving
	end. The term 'compandot is a fusion of the terms 'compressor' and
	'expandor'. The compandor circuitry provides an operator with a
	sensation similar to the 'capture effect' in FM. Thus when the signal
	strenghts are high, FM and ACSSB give comparable results with
	noticeably less flutter on ACSSB than on FM.
	.....
	Peliminary results indicate that with equal power (PEP and carrier),
	range and capture effect are about the same. ACSSB is quieter until
	lock is lost; in the fringe area, noise begins appear on voice peaks
	(because of compandoring)."

As with Amateur SSB compression is also common with AM broadcast although it is
usually non-reversible. If a definition for a reversable compression scheme
could be agreed upon a matching expandor could be used in the receiver. A 1.5:1
compression would offer a 30dB S/N ratio from a signal with only a 20dB S/N.
A 1.5:1 compression level is probably comparable to what is already being used
in AM broadcasting and the 'limiting and normalizing' done on modern CDs. With
the benefit of synchronous detection using a heavily suppressed carrier and
pre-emphasis this could offer another 10-15dB for a total of 40-45dB S/N from
a poor signal with a 20db S/N. If a good signal offered 36dB S/N after
expansion and pre-emphasis boost this could bring it up to 64-69dB S/N. This
puts AM on par with FM for quietness.

Compandoring schemes have been used in audio for years. Noise reduction has
been used for tape both Dolby & dbx and Analog NTSC TV also used dbx for the
L-R stereo and SAP channels with good success.