Forums

Echo cancellation to share radio channel

Started by Fender123 February 19, 2012
Reading up a 1988 edition of Lee & Messerschmitt's "Digital Communication",
I came across this gem (Ch18 pg 643):

"In principle, echo cancellation could be used to share any medium, such as
a radio channel, for the two directions... would be of great practical
interest... but unfortunately is impractical in today's technology..."

And the punch-line: "However, we cannot rule it out for the future".


Just how far are we in 2012? Any takes on when and how this might become
reality? Can MIMO be considered a more practically realisable form of
this?

Brian.
it's an analog problem, mainly. 
As an order-of-magnitude example, the signal quality of a typical cellular
signal is between 30 and 40 dB (cellular mobile and basestation).
Simply put, that means 0.01 to 0.1 % of my transmitted signal power appear
as noise at the receiver. 
When your received signal power is is 0.0000000001 % of your own
transmitted signal power (typical numbers from cellular radio, -100 dBm @
Rx vs +20 dBm @ Tx), all the digital algorithm magic is clearly off for a
bad start.

Today's systems use time slots or different frequencies for
uplink/downlink, and this is unlikely to change soon.
On Feb 19, 8:18&#2013266080;am, "Fender123" <joeborg123@n_o_s_p_a_m.excite.com>
wrote:
> Reading up a 1988 edition of Lee & Messerschmitt's "Digital Communication", > I came across this gem (Ch18 pg 643): > > "In principle, echo cancellation could be used to share any medium, such as > a radio channel, for the two directions... would be of great practical > interest... but unfortunately is impractical in today's technology..." > > And the punch-line: "However, we cannot rule it out for the future". > > Just how far are we in 2012? Any takes on when and how this might become > reality? Can MIMO be considered a more practically realisable form of > this? > > Brian.
Clearly echo cancellation can be used to facilate full duplex communications. It's done every day over the land-based telephone network, and was being done in 1988. The problem with radio was the scaling of the frequency. I.e, how to run the technology of 1988 at radio frequency (HF and higher) speeds. That, too, seems to have been largely solved with A/Ds running in the GHz.
maury <maury001@core.com> wrote:

(snip)
> Clearly echo cancellation can be used to facilate full duplex > communications. It's done every day over the land-based telephone > network, and was being done in 1988. The problem with radio was the > scaling of the frequency. I.e, how to run the technology of 1988 at > radio frequency (HF and higher) speeds. That, too, seems to have been > largely solved with A/Ds running in the GHz.
It is also used by gigabit ethernet, which sends in both directions on all four pairs in a Cat 5 cable at the same time. -- glen
>On Feb 19, 8:18=A0am, "Fender123" <joeborg123@n_o_s_p_a_m.excite.com> >wrote: >> Reading up a 1988 edition of Lee & Messerschmitt's "Digital
Communication=
>", >> I came across this gem (Ch18 pg 643): >> >> "In principle, echo cancellation could be used to share any medium, such
=
>as >> a radio channel, for the two directions... would be of great practical >> interest... but unfortunately is impractical in today's technology..." >> >> And the punch-line: "However, we cannot rule it out for the future". >> >> Just how far are we in 2012? Any takes on when and how this might
become
>> reality? Can MIMO be considered a more practically realisable form of >> this? >> >> Brian. > >Clearly echo cancellation can be used to facilate full duplex >communications. It's done every day over the land-based telephone >network, and was being done in 1988. The problem with radio was the >scaling of the frequency. I.e, how to run the technology of 1988 at >radio frequency (HF and higher) speeds. That, too, seems to have been >largely solved with A/Ds running in the GHz. >
There is a huge difference between echo cancelling a relatively stable PSTN channel and an endlessly changing radio channel. Steve
On Feb 21, 7:06&#2013266080;am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote:
> >On Feb 19, 8:18=A0am, "Fender123" <joeborg123@n_o_s_p_a_m.excite.com> > >wrote: > >> Reading up a 1988 edition of Lee & Messerschmitt's "Digital > Communication= > >", > >> I came across this gem (Ch18 pg 643): > > >> "In principle, echo cancellation could be used to share any medium, such > = > >as > >> a radio channel, for the two directions... would be of great practical > >> interest... but unfortunately is impractical in today's technology..." > > >> And the punch-line: "However, we cannot rule it out for the future". > > >> Just how far are we in 2012? Any takes on when and how this might > become > >> reality? Can MIMO be considered a more practically realisable form of > >> this? > > >> Brian. > > >Clearly echo cancellation can be used to facilate full duplex > >communications. It's done every day over the land-based telephone > >network, and was being done in 1988. The problem with radio was the > >scaling of the frequency. I.e, how to run the technology of 1988 at > >radio frequency (HF and higher) speeds. That, too, seems to have been > >largely solved with A/Ds running in the GHz. > > There is a huge difference between echo cancelling a relatively stable PSTN > channel and an endlessly changing radio channel. > > Steve- Hide quoted text - > > - Show quoted text -
Changing channels is not new to echo cancellation. It's called reconvergence. Any "good" acoustic echo canceller made to operate in a closed area (room) must contend with changing characteristics (the room impulse response changes as people move around). Echo cancellers for DSL must also contend with changing channels. The question was can it be done.
On Tue, 21 Feb 2012 06:44:50 -0800 (PST), maury <maury001@core.com>
wrote:

>On Feb 21, 7:06=A0am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote: >> >On Feb 19, 8:18=3DA0am, "Fender123" <joeborg123@n_o_s_p_a_m.excite.com> >> >wrote: >> >> Reading up a 1988 edition of Lee & Messerschmitt's "Digital >> Communication=3D >> >", >> >> I came across this gem (Ch18 pg 643): >> >> >> "In principle, echo cancellation could be used to share any medium, su= >ch >> =3D >> >as >> >> a radio channel, for the two directions... would be of great practical >> >> interest... but unfortunately is impractical in today's technology..." >> >> >> And the punch-line: "However, we cannot rule it out for the future". >> >> >> Just how far are we in 2012? Any takes on when and how this might >> become >> >> reality? Can MIMO be considered a more practically realisable form of >> >> this? >> >> >> Brian. >> >> >Clearly echo cancellation can be used to facilate full duplex >> >communications. It's done every day over the land-based telephone >> >network, and was being done in 1988. The problem with radio was the >> >scaling of the frequency. I.e, how to run the technology of 1988 at >> >radio frequency (HF and higher) speeds. That, too, seems to have been >> >largely solved with A/Ds running in the GHz. >> >> There is a huge difference between echo cancelling a relatively stable PS= >TN >> channel and an endlessly changing radio channel. >> >> Steve- Hide quoted text - >> >> - Show quoted text - > >Changing channels is not new to echo cancellation. It's called >reconvergence. Any "good" acoustic echo canceller made to operate in a >closed area (room) must contend with changing characteristics (the >room impulse response changes as people move around). Echo cancellers >for DSL must also contend with changing channels. > >The question was can it be done.
I've been struggling with what is meant by "echo canceller" in this context. I'm getting a sense of deja vu as I think this has been discussed before in comp.dsp and I had the same confusion. Just cancelling the channel echos/reflections is routinely done with an equalizer, and I know you know that. So I don't think that's it. If you mean cancelling the transmit signal so that the same channel can be used in both directions, that can be done, too, and is done in some modern applications. I recall the previous time this came up it involved a discussion of telephone modem hybrids, which did that job for that application, so that the digital "echo canceller" only had to deal with equalizing the reflections in the channel. Is there another meaning that I'm missing? Eric Jacobsen Anchor Hill Communications www.anchorhill.com
>On Feb 21, 7:06=A0am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote: >> >On Feb 19, 8:18=3DA0am, "Fender123"
<joeborg123@n_o_s_p_a_m.excite.com>
>> >wrote: >> >> Reading up a 1988 edition of Lee & Messerschmitt's "Digital >> Communication=3D >> >", >> >> I came across this gem (Ch18 pg 643): >> >> >> "In principle, echo cancellation could be used to share any medium,
su=
>ch >> =3D >> >as >> >> a radio channel, for the two directions... would be of great
practical
>> >> interest... but unfortunately is impractical in today's
technology..."
>> >> >> And the punch-line: "However, we cannot rule it out for the future". >> >> >> Just how far are we in 2012? Any takes on when and how this might >> become >> >> reality? Can MIMO be considered a more practically realisable form
of
>> >> this? >> >> >> Brian. >> >> >Clearly echo cancellation can be used to facilate full duplex >> >communications. It's done every day over the land-based telephone >> >network, and was being done in 1988. The problem with radio was the >> >scaling of the frequency. I.e, how to run the technology of 1988 at >> >radio frequency (HF and higher) speeds. That, too, seems to have been >> >largely solved with A/Ds running in the GHz. >> >> There is a huge difference between echo cancelling a relatively stable
PS=
>TN >> channel and an endlessly changing radio channel. >> >> Steve- Hide quoted text - >> >> - Show quoted text - > >Changing channels is not new to echo cancellation. It's called >reconvergence. Any "good" acoustic echo canceller made to operate in a >closed area (room) must contend with changing characteristics (the >room impulse response changes as people move around). Echo cancellers >for DSL must also contend with changing channels. > >The question was can it be done.
An echo canceller that cannot cope with some need for reconvergence would be useless. However, the rate at which radio channels change is a whole different class of problem from acoustic echoes. Remember that an unconverged audio canceller is just annoying (as long as it doesn't howl). A unconverged radio canceller pretty much means no communications. Steve
>On Tue, 21 Feb 2012 06:44:50 -0800 (PST), maury <maury001@core.com> >wrote: > >>On Feb 21, 7:06=A0am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote: >>> >On Feb 19, 8:18=3DA0am, "Fender123"
<joeborg123@n_o_s_p_a_m.excite.com>
>>> >wrote: >>> >> Reading up a 1988 edition of Lee & Messerschmitt's "Digital >>> Communication=3D >>> >", >>> >> I came across this gem (Ch18 pg 643): >>> >>> >> "In principle, echo cancellation could be used to share any medium,
su=
>>ch >>> =3D >>> >as >>> >> a radio channel, for the two directions... would be of great
practical
>>> >> interest... but unfortunately is impractical in today's
technology..."
>>> >>> >> And the punch-line: "However, we cannot rule it out for the
future".
>>> >>> >> Just how far are we in 2012? Any takes on when and how this might >>> become >>> >> reality? Can MIMO be considered a more practically realisable form
of
>>> >> this? >>> >>> >> Brian. >>> >>> >Clearly echo cancellation can be used to facilate full duplex >>> >communications. It's done every day over the land-based telephone >>> >network, and was being done in 1988. The problem with radio was the >>> >scaling of the frequency. I.e, how to run the technology of 1988 at >>> >radio frequency (HF and higher) speeds. That, too, seems to have been >>> >largely solved with A/Ds running in the GHz. >>> >>> There is a huge difference between echo cancelling a relatively stable
PS=
>>TN >>> channel and an endlessly changing radio channel. >>> >>> Steve- Hide quoted text - >>> >>> - Show quoted text - >> >>Changing channels is not new to echo cancellation. It's called >>reconvergence. Any "good" acoustic echo canceller made to operate in a >>closed area (room) must contend with changing characteristics (the >>room impulse response changes as people move around). Echo cancellers >>for DSL must also contend with changing channels. >> >>The question was can it be done. > >I've been struggling with what is meant by "echo canceller" in this >context. I'm getting a sense of deja vu as I think this has been >discussed before in comp.dsp and I had the same confusion. > >Just cancelling the channel echos/reflections is routinely done with >an equalizer, and I know you know that. So I don't think that's it. > >If you mean cancelling the transmit signal so that the same channel >can be used in both directions, that can be done, too, and is done in >some modern applications. I recall the previous time this came up it >involved a discussion of telephone modem hybrids, which did that job >for that application, so that the digital "echo canceller" only had to >deal with equalizing the reflections in the channel.
Telephone hybrids do little more than keep the returned signal below howling. The main job of a digital echo canceller on a telephone line is to cancel the 4 echoes from the 4 poor quality hybrids you typically have between 2 communicating parties. In fact, for really long international echoes, especially for modems, they insert 4 short time domain cancellers where the 4 echoes occur.
>Is there another meaning that I'm missing? > > >Eric Jacobsen
Steve
>Anchor Hill Communications >www.anchorhill.com >
On 2/21/2012 4:16 AM, glen herrmannsfeldt wrote:
> maury<maury001@core.com> wrote: > > (snip) >> Clearly echo cancellation can be used to facilate full duplex >> communications. It's done every day over the land-based telephone >> network, and was being done in 1988. The problem with radio was the >> scaling of the frequency. I.e, how to run the technology of 1988 at >> radio frequency (HF and higher) speeds. That, too, seems to have been >> largely solved with A/Ds running in the GHz. > > It is also used by gigabit ethernet, which sends in both directions > on all four pairs in a Cat 5 cable at the same time.
Thomas Edison was issued a patent for full-duplex telegraph signaling in 1892. http://www.google.com/patents/US480567 Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;