Hi, in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR for OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is that?
802.16e-2005 has different Rx SNR for OFDM and OFDMA
Started by ●July 9, 2008
Reply by ●July 10, 20082008-07-10
On Jul 10, 6:54�am, "minnows" <minn...@tom.com> wrote:> Hi, > in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR for > OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is > that?That's because the coding assumption is different. Table 266 assumes a concatenated RS-CC coding is used, while Table 338 assumes that a tail- biting convolutional code is used. The RS-CC has better coding gain, and hence the SNR requirement is lower. This has nothing whatsoever to do with the difference between OFDM and OFDMA. - Ravi
Reply by ●July 13, 20082008-07-13
>On Jul 10, 6:54=A0am, "minnows" <minn...@tom.com> wrote: >> Hi, >> in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNRfor>> OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is >> that? > >That's because the coding assumption is different. Table 266 assumes a >concatenated RS-CC coding is used, while Table 338 assumes that a tail- >biting convolutional code is used. The RS-CC has better coding gain, >and hence the SNR requirement is lower. This has nothing whatsoever to >do with the difference between OFDM and OFDMA. > >- Ravi >Thank you! But why using different coding scheme for OFDM and OFDMA? Why not use the better one for both OFDM and OFDMA?
Reply by ●July 17, 20082008-07-17
On Jul 14, 6:31�am, "minnows" <minn...@tom.com> wrote:> >On Jul 10, 6:54=A0am, "minnows" <minn...@tom.com> wrote: > >> Hi, > >> in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR > for > >> OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is > >> that? > > >That's because the coding assumption is different. Table 266 assumes a > >concatenated RS-CC coding is used, while Table 338 assumes that a tail- > >biting convolutional code is used. The RS-CC has better coding gain, > >and hence the SNR requirement is lower. This has nothing whatsoever to > >do with the difference between OFDM and OFDMA. > > >- Ravi > > Thank you! But why using different coding scheme for OFDM and OFDMA? Why > not use the better one for both OFDM and OFDMA?Remember that the "OFDM" section of the standard is intended to be used for fixed wireless while the "OFDMA" section is intended for mobile wireless. So while a fixed wireless receiver can afford to burn power decoding a concatenated RS-CC code, a mobile device cannot - at least, the increase in area/power does not justify the SNR improvement.
Reply by ●July 20, 20082008-07-20
On Wed, 16 Jul 2008 23:45:33 -0700 (PDT), Ravi Srikantiah <ravi.srikantiah@gmail.com> wrote:>On Jul 14, 6:31 am, "minnows" <minn...@tom.com> wrote: >> >On Jul 10, 6:54=A0am, "minnows" <minn...@tom.com> wrote: >> >> Hi, >> >> in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR >> for >> >> OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is >> >> that? >> >> >That's because the coding assumption is different. Table 266 assumes a >> >concatenated RS-CC coding is used, while Table 338 assumes that a tail- >> >biting convolutional code is used. The RS-CC has better coding gain, >> >and hence the SNR requirement is lower. This has nothing whatsoever to >> >do with the difference between OFDM and OFDMA. >> >> >- Ravi >> >> Thank you! But why using different coding scheme for OFDM and OFDMA? Why >> not use the better one for both OFDM and OFDMA? > >Remember that the "OFDM" section of the standard is intended to be >used for fixed wireless while the "OFDMA" section is intended for >mobile wireless. So while a fixed wireless receiver can afford to burn >power decoding a concatenated RS-CC code, a mobile device cannot - at >least, the increase in area/power does not justify the SNR improvement.RS-CC := Reed Soloman convolutional code?
Reply by ●July 21, 20082008-07-21
On Jul 20, 9:24�pm, A. Lurker <ab...@localhost.com> wrote:> On Wed, 16 Jul 2008 23:45:33 -0700 (PDT), Ravi Srikantiah > > > > <ravi.srikant...@gmail.com> wrote: > >On Jul 14, 6:31�am, "minnows" <minn...@tom.com> wrote: > >> >On Jul 10, 6:54=A0am, "minnows" <minn...@tom.com> wrote: > >> >> Hi, > >> >> in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR > >> for > >> >> OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is > >> >> that? > > >> >That's because the coding assumption is different. Table 266 assumes a > >> >concatenated RS-CC coding is used, while Table 338 assumes that a tail- > >> >biting convolutional code is used. The RS-CC has better coding gain, > >> >and hence the SNR requirement is lower. This has nothing whatsoever to > >> >do with the difference between OFDM and OFDMA. > > >> >- Ravi > > >> Thank you! But why using different coding scheme for OFDM and OFDMA? Why > >> not use the better one for both OFDM and OFDMA? > > >Remember that the "OFDM" section of the standard is intended to be > >used for fixed wireless while the "OFDMA" section is intended for > >mobile wireless. So while a fixed wireless receiver can afford to burn > >power decoding a concatenated RS-CC code, a mobile device cannot - at > >least, the increase in area/power does not justify the SNR improvement. > > RS-CC := Reed Soloman convolutional code?That's right - except that it's spelt "Solomon". The RS encoder is followed by a convolutional encoder.
