Talk:Spectral efficiency

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[edit] added D-AMPS to table

I added D-AMPS to comparison table. some notes:

  • D-AMPS (formal standards IS-54 and later IS-136) is actually 6 time slots, not 3 slots. but in real world installations 2 slots were always paired to achieve 13kbps, since 6.5kbps vocoders were not good enough at the time. so i wrote 13kbps * 3 slots in the table.
  • technically, 13kbps is the data rate used for voice. for data transmission, the theoretical maximum data rate is 16kbps. since it was rarely achieved in practice, i kept the widely-known 13kbps figure.
  • mentioned 1/7 reuse factor comes from the common hexagonal tile configuration. this is widely known fact - you'll find a hexagonal tile diagram & explanation in virtually any book about cellular communications.
  • common literature mentions reuse factor of 1/4 or 1/5 when using sector antennas, but this is true for most other communication systems and not just D-AMPS. i kept with the conservative 1/7 reuse factor here, so that we'll have a apples-to-apples comparison with other standards. keep in mind that if you change reuse factors in other standards, you might want to change the factor for D-AMPS. it all depends on the antenna configurations... —Preceding unsigned comment added by 85.250.43.101 (talk) 16:21, 10 May 2008 (UTC)
  • D-AMPS is a common name in the US only. in other parts of the world, it is referred to IS-54 and then later IS-136, not D-AMPS. —Preceding unsigned comment added by 85.250.43.101 (talk) 16:15, 10 May 2008 (UTC)

[edit] Review

The definition could be a bit more general as it applies to more than digital. It could apply to analogue. It could apply to how spectrum is allocated by regulatory agencies.

What units of measurement do you have in mind? I mentioned system spectral efficiency in Erlangs/MHz/cell in the article, which also can be applied to analogue. Mange01 (talk) 22:16, 21 February 2008 (UTC)

The Shannon theorem formula should be here so that you can calculate bits per Hertz.

Telephone modem example is not strictly correct. If the bandwidth is filtered to the 3100 Hertz you will not get the 56000 bit rate through. To get that rate there will have to be less filtering. The channel will be quantized to 8 bits and so can only carry 16 bits per Hertz at the most.

correction: channel is quantized (on both sides) at 13 to 14 bits, and then u-law or a-law companded to 8 bits. 89.138.246.240 (talk) 00:12, 16 February 2008 (UTC)
I somewhat doubt that the baseband waveform used for digital modulation undergoes A/mu-law companding. Oli Filth(talk) 02:02, 16 February 2008 (UTC)
The modem compensates for the A/mu-law companding, meaning that it expands the 8 bit signal to a 13 bit signal before it sends it. So the modem can only use 8 bits per sample. (In Europe. Is it 7 or 8 bit in the U.S.?)Mange01 (talk) 22:16, 21 February 2008 (UTC)

"In wireless networks, the system spectral efficiency in bit/s/Hz/area unit, bit/s/Hz/cell or bit/s/Hz/site is a measure of the quantity of users or services that can be simultaneously supported by a limited radio frequency bandwidth in a defined geographic area."

This sentence packs in too many units - probably better to break it into two sentences with one unit in the first, and then an extension to the variations. Otherwise it is too confusing to read.

It would be good to add some analogue systems eg single sideband instead of AM or FM. We could have a bit of regulatory requirements. We could also have the tradeoffs, eg more power to get more signal to noise ratio, but more spectrum can reduce the power required.

In the comparason table it would be good to add some more, for example those landline modems, and some amateur digital radio schemes, some satellite transmission systems.

We could have a section on how efficiency can be improved, some techniques are mentioned in passing already.

Wouldn't that be the same as the article radio resource management? Mange01 (talk) 22:16, 21 February 2008 (UTC)

If I can find the time I may get around to some improvements over the next few months.

GB 22:47, 24 January 2007 (UTC) --

I see that Mehwoot has had a go at recalculating the spectral efficiency of a V.92 modem. However the raw bandwidth at the exchange is 0-4000 Hertz sampled at 8 bits at 8000 samples per second. An antialias filter will reduce this bandwidth somewhat below the 4000 Hertz limit. I will confirm what the rates are for what bandwidths. The maximum data throughput that could happen would be 64000 bits per second or 16 bits per Hertz. GB 06:30, 28 January 2007 (UTC)

Mehwoot was being an idiot and just changing random numbers, I'm pretty sure. It was probably correct the way it was.58.106.7.5 12:35, 27 April 2007 (UTC)

Good section. I like the take on bits/hz per area. This is particulary important for wireless broadband and converged wired-wireless networks.

Robert Syputa

[edit] Bit/s/Hz

Huh? Hz = s-1, therefore Hz-1 = s. Hence, bits * s-1 * Hz-1 = bits * s-1 * s Hence, bits/s/Hz = bits.

So, why use units of bits/s/Hz for spectral efficiency, when "bits/s/Hz" is just a confusing way of saying "bits"? —The preceding unsigned comment was added by 124.189.8.183 (talk) 03:46, 3 March 2007 (UTC).

Because to say, for example, that GSM has a spectral efficiency of 0.52 bits would sound more confusing (although dimensionally correct). bits/s/Hz is the standard unit. Oli Filth 02:10, 10 March 2007 (UTC)
Actually, bit/s/Hz is even more common according to google. Just like bit/s is much more common than bits/s. Mange01 22:37, 30 April 2007 (UTC)
bits/s is incorrect, you can't add English "s" to a unit and make a unit plural, just like meters per second is not ms/s

By the way bits/s/Hz is not a unit, it violates at least two of metric system rules. If we want to keep Hz and s (which is allowed in metric system and makes sense here), it should be written as bit/Hz·s (or bit/s·Hz).

actually, the article correctly says "bit" not "bits", just the heading here doesn't —The preceding unsigned comment was added by 203.173.44.87 (talk) 01:15, 7 May 2007 (UTC).

No, bits/s/Hz = bits is incorrect. Hz is cycles per second, so Hz-1 is seconds per cycle, so bit/s/Hz is bits per cycle. But s and Hz are SI units, and cycle is not, so we say bit/s/Hz or some appropriate variant. Dicklyon (talk) 02:57, 16 February 2008 (UTC)


(ec) I'm not convinced this logic is correct, or if it is, we tend to ignore the issue in everyday usage. Take another example, Eb/No. We know that
\frac{E_b}{N_0} = \frac{P_s T_b}{P_n / B}
where Ps and Pn are signal and noise power, Tb is bit period, and B is bandwidth. Therefore, the units according to the above logic are
\frac{\mathrm{W}.\mathrm{s}.\mathrm{bit}^{-1}}{\mathrm{W}.\mathrm{Hz}^{-1}} = \frac{\mathrm{W}.\mathrm{s}.\mathrm{bit}^{-1}}{\mathrm{W}.\mathrm{s}.\mathrm{cycle}^{-1}}
or "cycles per bit". But we always refer to Eb/No as "dimensionless". Oli Filth(talk) 11:50, 16 February 2008 (UTC)

Well, at least it is established in literature and publications. A Google search and Google Book Search gives:

  • bit/s/Hz — 42.900 web hits, 453 books [1]
  • bits/s/Hz — 30.400 web hits, 360 books [2]
  • b/s/Hz — 9.610 web hits, 291 books
  • bits/sec/Hz — 4.760 web hits, 234 books
  • system spectral efficiency — 2.440 web hits, 98 books [3]
  • bit/sec/Hz — 1.830 web hits, 141 books
  • bits per second per Hertz — 959 web hits, 198 books
  • system spectrum efficiency — 904 web hits, 37 books [4]
  • area spectral efficiency — 703 web hits, 41 books [5]
  • bit/s/Hz/site — 411 web hits, 1 book
  • bit per second per Hertz — 357 web hits, 24 books
  • bits/s/Hz/cell — 250 web hits, 8 books [6]
  • b/s/Hz/sector — 181 web hits, 5 books [7]
  • bit/s/Hz/sector — 155 web hits
  • b/s/Hz/m^2 — 89 web hits
  • bits/s/Hz/m^2 — 58 web hits
  • bit/s/Hz/m^2 — 36 web hits
  • bit/s/Hz/km^2 — 31 web hits
  • bits/s/Hz/km^2 — 9 web hits

Mange01 (talk) 11:47, 16 February 2008 (UTC)

Revised by Mange01 (talk) 22:47, 13 April 2008 (UTC)

[edit] Survey: bit/s/Hz, (bit/s)/Hz or bit·s−1·Hz−1 as Spectral efficiency unit?

Please vote at Talk:Eb/N0#Survey on which unit that should be used at Wikipedia for measuring Spectral efficiency. For a background discussion, see Talk:Spectral_efficiency#Bit/s/Hz and Talk:Eb/N0#Bit/s/Hz. Mange01 (talk) 07:21, 16 April 2008 (UTC)

[edit] Vandalized

There was a very nasty picture that made my stomach sick when I opened this page, but it vanished before I could do anything. Did any good soul remove it, or we have a hole in Wikipedia?

There was no image link in page source. Probably reverted between the time I downloaded vandalized version and the time it was fixed. There are some very ill people out there. You have my continuing support in fighting them.

P.S.

Anyone thought of AI software that would try to establish whether the image submitted is something vulgar and notify administrators? I have a few clues to start with. Thx. -- Mtodorov 69 13:47, 7 May 2007 (UTC)

[edit] Spectral effiency of analog transmission modes

What is the spectral effiency of analog transmission modes as AM ( A3), SSB, FM, analogue TV, etc.? —Preceding unsigned comment added by 91.46.209.184 (talk) 20:00, 15 April 2008 (UTC)

I have found one article that seems to be measuring number of simultaneous calls per bandwidth unit in Erlang/Hz. [doi.wiley.com/10.1002/0470020121.ch7] However, I don't have access to the full text version, only the Google search result, so I might have misunderstood it. There are several articles measuring the area capacity in Erlang/MHz/area unit or Erlang/MHz/cell, as I mentioned in the System spectral efficiency section. Mange01 (talk) 18:45, 16 April 2008 (UTC)

[edit] WiMAX spectral efficiency?

Not sure if this is the right place to put this but there is a misleading inconsistency in this page and the main wimax page [8] with regards to the spectral efficiency of wimax (802.16d), this page states an efficiency of (4.8 bit/s)/Hz but the main wimax page states for 802.16d a spectral efficiency of 3.7 (bit/s)/Hz

Spectral efficiency for any adaptive scheme (like WiMAX or LTE) is a bit tricky to nail down, since Marketing wants to quote the maximum value while Engineering cringes and generally talks in terms of averages. Also, many efficiency calculations depend on the exact overhead structure used, etc., so it's not at all unusual to have different authoritative sources quote figures that vary by even that much. NX7U (talk) 04:49, 10 June 2008 (UTC)

195.59.43.240 (talk) 13:01, 7 May 2008 (UTC)Rob

[edit] Additional 3G table entries

I split the table entry for CDMA2000 1x into separate entries for voice and PD (packet data), and made some corrections to the frequency reuse and resultant calculations. Also added a new entry for CDMA2000 1x EV-DO. NX7U (talk) 04:44, 10 June 2008 (UTC)