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I am from an Instrumentation background and recently have been working on an OFDM project. With my research, I was unable to find the solution to the below question.

  1. How to choose the Pilot Carriers/pilot symbols? Suppose from one example which I am referring they have chosen pilot carriers as 8 counts for the Subcarrier count of 64 and with Cyclic prefix is 16. and in the second example pilot carriers = 346 for the subcarrier count = 224 with CP = 16. I am really confused about how to choose the pilot count?
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It is a tradeoff. The more pilot subcarriers, the better then channel estimation, but the fewer subcarriers usable for data. Simulations and testing of performance can help in making the choice.

You probably have some numbers wrong. If you have 224 subcarriers, you cannot have 346 of them as pilot carriers.

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  • $\begingroup$ My Parameters looks like this! P = struct; % OFDM core symbol size P.Nfft = 256; % no. of active subcarriers P.Ncarriers = 224; % cyclic prefic length in samples P.Ncp = 16; % no. of OFDM symbols in frame P.Muplink = 50; P.Mdownlink = 40; % modulation order (QPSK) P.M = 4; % payload bits in downlink (Controller -> Client) P.NbDownlink = 8320; P.NbUplink = 256; %% Pilot Symbols P.pilots = struct; % no. of pilot symbols P.NpDownlink = 346; P.NpUplink = 544; $\endgroup$ – Yulia May 26 at 12:49
  • $\begingroup$ Looks like you're talking about a frame, and you have, like 346 pilot symbols per frame in the downlink? Makes sense, the pilot symbols would be spread out over the OFDM symbols in each frame, typically in different subcarriers to allow better channel estimation. Anyway, yes, it is a tradeoff, and you'd need to look at the system requirements to select the number and locations of the pilot symbols $\endgroup$ – auspicious99 May 26 at 13:23
  • $\begingroup$ ok thank you for the clarification. Just a last question why the frame is considered? what is the advantage of it? $\endgroup$ – Yulia May 26 at 13:59
  • $\begingroup$ In many comms systems, e.g., LTE, the data that is sent is organized into frames for different scales of synchronization. In LTE, with OFDMA (like OFDM), there are multiple OFDM symbols per frame. Frames are used also for things that repeat over longer periods of time, e.g., patterns of pilot symbols may be spread out over many OFDM symbols, and repeat about a period like a frame. $\endgroup$ – auspicious99 May 26 at 15:26

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