On Wed, 19 Oct 2005 10:44:36 -0500, "lanbaba" <lanbaba@gmx.ch> wrote:>> To your second question; if the channels aren't known and are to be >> estimated using the preamble (which is often the case), then it isn't >> possible to apply STBC to the preambles. Since decoding of the STBC >> requires not only synchronization but knowledge of the channels, it's >> tough to apply an STBC to the preamble. > > >I don't catch you point. > >In Alamouti's scheme (2x2 STBC) your transmitted signal is orthogonal. If >such an orthogonal design is applied to the preamble for each subcarrier, >then the channel estimation is straight forward given synchronization. Or >do you mean the synchronization is too difficult?From a different perspective, what would be the benefit of applying STBC to the preamble? I think synchronization may be a bit more difficult if the correlation properties of the preamble are degraded by application of the STBC. In other words, if you're relying on nice correlator peaks to achieve synchronization if the code splatters the peaks it'll make synchronization harder. I'm not sure what benefit would be gained by applying the STBC to the preamble, but I can see some definite complications by doing so. Perhaps my "not possible" comment was too strong, but "more difficult" is certainly arguable. Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
MIMO OFDM FFT Symbol timing estimation
Started by ●October 15, 2005
Reply by ●October 19, 20052005-10-19
Reply by ●October 20, 20052005-10-20
>From a different perspective, what would be the benefit of applying >STBC to the preamble?Not more than the round-robbin approach, but it is a feasable way. In case of 4 Tx antennas, round-robbin is even better in the sense that only 4 symbol periods are needed while STBC needs 8. But concerning the nonlinearity of Tx power amplifier STBC allows a lower transmit power per antenna compared to round-robbin. This reduces the nonlinear distortion.>I think synchronization may be a bit more difficult if the correlation >properties of the preamble are degraded by application of the STBC. >In other words, if you're relying on nice correlator peaks to achieve >synchronization if the code splatters the peaks it'll make >synchronization harder. I'm not sure what benefit would be gained by >applying the STBC to the preamble, but I can see some definite >complications by doing so. Perhaps my "not possible" comment was too >strong, but "more difficult" is certainly arguable.I agree. This message was sent using the Comp.DSP web interface on www.DSPRelated.com
Reply by ●October 20, 20052005-10-20
I checked few of the papers and I would like to make some correction what i said earlier...>Hi vikram > i think there is serious misunderstanding on the OFDM itself on >your side... for diversity scheme you have to take one FFT only...Not always true.....Not for all Dieversity schemes..... depends upon which channel model is used... e.g Jakes,raliegh etc... and how things are implemented in specific....>use linear combiner at the reciver... to recover individual signals...if >you understand equalisation concept in OFDM it would be much easier for >you to make out how things really fits wellThat may be one way of implemeining things .... Aplying adavnced STBC codes is another option... they provide better orthogonality but increase computation complexity by a lot.. dont know much about MMSE or RLS equalisation schems for STBC codes...> about preambles i can say that there are multiple >ways of implementing detection schemes... i would rather prefer sending >some pattern from one antenna while sending nothing from other and a >distinct pattern from other antenna while switching off the otherone...> and dont confuse things with what some of the papers might be saying.. > >you can refer almouti paper for details...certainly this is one of the options... Again not very sure about all the the things..thats how i understand things.... May be somebody else can answer in a better way ...anybody ??? sandeep> > > > >>Thanks for the replies. >> >>I cannot assume that the signals are arriving at equal time/phase. >>I have to perform frequency and FFT symbol window synchronization for >>each of the transmitted signals within a single receive signal. >>Won't each signal act as an interferer for the other signal to make the >>timing estimation more difficult... >> >>My guess is that the preambles should be made orthogonal/shift >>orthogonal (as is mentioned in a paper by Stuber), but the spectrum of >>the resultant signal is no longer band-limited, as we are sending >>pseudorandom quasiorthogonal modulated sequences.. >> >>Thanks >>Vikram >> >> > > > >This message was sent using the Comp.DSP web interface on >www.DSPRelated.com >This message was sent using the Comp.DSP web interface on www.DSPRelated.com
