![]() ![]() The outermost elements have (should have) an almost zero amplitude,įor mode B only the central 206 out of the 256 carriers contain (Note that while the FFT was done over 256 elements (using mode B), Looking at the strength of the carriers in the FFT output,Īnd noticing a strength difference is the way to go. The width of the spectrum can be deduced from the words in the So, a continuous monitoring that the time synchonization is still OK is a This might imply that after the transmitter has sent a number samples, the In the decoder compared to the clock in the transmitter. Of course, by detecting the mode, the first sample of a word isĪ minor issue, though not unimportant is that there might be a clock offset In order to get a more reliable result, the process is done over a range Mode detection is then simply byĬorrelating the prefix with the supposed end of word and finding the best Mentioned before, is different for each mode. The Mode can be determined by correlation, the length of the prefix, Of course, the first question that needs to be solved is what modeĪnd spectrum occupancy the transmission has and where do the "words" start. A superframe contains data, good for 1.2 secondsĪ decoder gets as input a sample stream, in our case the sample stream The FAC contains information on whether the frame is the first or the The bitsĪre often encoded in QAM64, sometimes in QAM16.Īctually, a group of three subsequent frames forms a so-called super frame, MSC, Master Service Channel, containing the audio and data services. The bits for the SDC content are usuallyĮncoded in QAM16 (in DRM+ they are encoded QAM4) SDC, Service Description Channel, containing detailed information on theĪctual payload, the audio and data services that areĬarried in the transmission. Information, such as the mode and the spectrum, the number of services, Such a frame contains three types of valuesįAC, Fast Access Channel, values, containing QAM4 encoded bits with general the value should be as precise as possible the The QAM4, QAM16 and QAM64 values requireĬoherent decoding, i.e. With the values that are actually found are used to reconstruct the signalĪs it was at the transmitter side. In the frequency domain frame, a number of predefined locations Note that in the time domain such a frame takes 4800 samples, and withĪ samplerate of 12000 samples a second, slightly less than 3 frames a second Values, with 3090 cells with useful values. ![]() Such as frame then has 3840 cells with complex Given the bandwidth of 10 KHz, the frequency distance between successive carriersĪ group of these "words" forms a frame. On each end of the spectrum, are (supposed to be) zeros. As always, not all carriers carry useful information,įor Mode B, 206 of the 256 carriers are the useful ones, the remaining ones, 25 These "words" with frequency domain values (carriers) are then the basis forįurther processing. To values (carriers) in the frequency domain. the samples following the prefix,Īre fed into an FFT processor, mapping the samples as they were in the time domain, The 256 "useful" samples of the word, i.e. Such a prefix, a copy of the last samples of the word, is very helpful inĭetermining both the first sample of a word as wellĬomputing the frequency offset of the signal. ![]() With other modes, the prefix length may differ. For this mode, the first 64 samples of each word, a prefix, are a copy of the Modes are defined in terms of symbols or words, Each complex sample then tellsĪbout the amplitude and the phase of the signal at the sampling time. Processing DRM requires sampling an analog input signal, usually withġ2000 (complex) samples per second. Other spectra are 4.5, 5, 9, 18 and 20 KHz.ĭifferent Modes are defined such that they perform optimal with given fading patterns. TransmissionsĪre relatively scarce here in Western Europe, but is seems that elsewhereįor DRM signals there are different Modes and Spectra, here is WesternĮurope transmissions can be received in Mode B, with a spectrum of 10 KHz. ![]() Here, it shows a test with two occurrences running on the sameįrequency, just to test some loop antennas (ine running an RSP I,ĭRM, Digital Radio Mondiale, is a form of digital radio. The drm receiver is an experimental tool, a heavily reduced swradio, Rumenia still has a regular DRM transmission. In the first decade of the century already stopped. In Europe drm is not very popular, most transmissions that started Redesign and re-implementation of the drm decoderĭRM (Digital Radio Mondiale) is - as the name suggests - a form of digital ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |