HI, I am new to this group. I have very basic doubt about digital modulation. We modulate the carrier frequency based on the digital input values... So is the output of modulator block a digital signal with samples representing the modulated carried signal or is it a modulated continous (analog) signal.. Thanks in advance, arun
Digital modulation - In digital domain or analog..?
Started by ●September 11, 2009
Reply by ●September 11, 20092009-09-11
"arun" <arunkumar.us@gmail.com> wrote in message news:d75babfd-2ac0-4e9d-9890-bd3dcaaca6f8@j9g2000prh.googlegroups.com...> I am new to this group. I have very basic doubt about > digital modulation. > We modulate the carrier frequency based on the digital input values... > So is the output of modulator block a digital signal with samples > representing the modulated carried signal or is it a modulated > continous (analog) signal..It can be both and depends upon the frequency of the carrier, the cycle time of the DSP and how much other processing has to be done in each cycle of the carrier wave. Eg, if the carrier is, say, 50kHz, for a modem, and the DSP runs at 100MIPs, then you'de be processing in digital. Almost certainly, independently of the DSP's cycle time, if the carrier frequency is in the 2.4GHz utility band, then you'd be modualting in analogue. As always, it's horses for courses.
Reply by ●September 11, 20092009-09-11
arun <arunkumar.us@gmail.com> writes:> HI, > > I am new to this group. I have very basic doubt about > digital modulation. > We modulate the carrier frequency based on the digital input values... > So is the output of modulator block a digital signal with samples > representing the modulated carried signal or is it a modulated > continous (analog) signal..arun, The output of any real-world modulator is always going to be analog. Even in the theoretical world, the purpose of the modulator is to transform from discrete-time to continuous-time. See, e.g., the modulator in Figure 1 here: http://www.digitalsignallabs.com/tutorial.pdf The modulator transforms its input into one of M symbols s and then produces a waveform x_s(t) from that symbol. When a stream of symbols is processed, the output of the modulator is x(t) = \sum_{m=-\infty}^{\infty} x_{s_m}(t-m*T), where T is the symbol period. Leon Couch has an excellent undergraduate textbook on digital and analog communication systems - I highly recommend it. --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} -- Randy Yates % "The dreamer, the unwoken fool - Digital Signal Labs % in dreams, no pain will kiss the brow..." mailto://yates@ieee.org % http://www.digitalsignallabs.com % 'Eldorado Overture', *Eldorado*, ELO
Reply by ●September 14, 20092009-09-14
On 11-09-2009 at 13:37:34 arun <arunkumar.us@gmail.com> wrote: (...)> We modulate the carrier frequency based on the digital input values...(...) Is your carrier digital? -- Mikolaj
Reply by ●September 14, 20092009-09-14
On 12 Sep, 00:13, Randy Yates <ya...@ieee.org> wrote:> arun <arunkumar...@gmail.com> writes: > > HI, > > > � �I am new to this group. I have very basic doubt about > > digital modulation. > > We modulate the carrier frequency based on the digital input values... > > So is the output of modulator block a digital signal with samples > > representing the modulated carried signal or is it a modulated > > continous (analog) signal.. > > arun, > > The output of any real-world modulator is always going to be > analog. Even in the theoretical world, the purpose of the modulator is > to transform from discrete-time to continuous-time. �Wouldn't this conversion be the task of the DAC? Once you have an anlog baseband (or intermediate format) signal, the modulator transforms it to some format that is suitable for transmission. Rune
Reply by ●September 14, 20092009-09-14
On 11 Sep, 13:37, arun <arunkumar...@gmail.com> wrote:> HI, > > � �I am new to this group. I have very basic doubt about > digital modulation. > We modulate the carrier frequency based on the digital input values... > So is the output of modulator block a digital signal with samples > representing the modulated carried signal or is it a modulated > continous (analog) signal..I'm not particular knowledgeable about comms, but here is how I understand the terms: - The modulator takes an analog signal and transforms it to a format that is suitable for transmission. - 'Digital Modulation' is a modulation format that somehow is suitable for digital encodings of the information. Keep in mind that 'analog' modulation formats, like AM and FM, produce signals from the 'raw' analog information-carrying signal. In 'digital' systems the raw analog signal is first sampled to a discrete sequence of numbers and then encoded into a discrete bit stream. So the task of the 'digital' modulator is to transform this discrete bit stream - as opposed to the raw analog signal - for transmission. Since the bit stream has quite different properties than the raw analog signal, it follows that there might be other modulation formats available for the bit stream than the raw analog signal. Such a modulation scheme would be a 'digital' modulation scheme. Rune
Reply by ●September 14, 20092009-09-14
Rune Allnor wrote:> On 11 Sep, 13:37, arun <arunkumar...@gmail.com> wrote: >> HI, >> >> I am new to this group. I have very basic doubt about >> digital modulation. >> We modulate the carrier frequency based on the digital input values... >> So is the output of modulator block a digital signal with samples >> representing the modulated carried signal or is it a modulated >> continous (analog) signal.. > > I'm not particular knowledgeable about comms, but here > is how I understand the terms: > > - The modulator takes an analog signal and transforms it > to a format that is suitable for transmission. > - 'Digital Modulation' is a modulation format that somehow > is suitable for digital encodings of the information."Suitable for transmission" (and reception) implies that the signal can be radiated by an antenna, received by another, and tuned (i.e., run through a bandpass filter) to isolate it from other signals also received. Such a signal is analog. Do you see what too much immersion in Matlab can do? :-)> Keep in mind that 'analog' modulation formats, like AM and > FM, produce signals from the 'raw' analog information-carrying > signal. > > In 'digital' systems the raw analog signal is first sampled > to a discrete sequence of numbers and then encoded into a > discrete bit stream. So the task of the 'digital' modulator > is to transform this discrete bit stream - as opposed to > the raw analog signal - for transmission.Yes - transmission on an analog carrier.> Since the bit stream has quite different properties than > the raw analog signal, it follows that there might be > other modulation formats available for the bit stream > than the raw analog signal. Such a modulation scheme > would be a 'digital' modulation scheme.Absolutely. Nevertheless, as the OP surmised, the result is "a modulated continuous (analog) signal." Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●September 14, 20092009-09-14
On 14 Sep, 16:50, Jerry Avins <j...@ieee.org> wrote:> Rune Allnor wrote: > > On 11 Sep, 13:37, arun <arunkumar...@gmail.com> wrote: > >> HI, > > >> � �I am new to this group. I have very basic doubt about > >> digital modulation. > >> We modulate the carrier frequency based on the digital input values... > >> So is the output of modulator block a digital signal with samples > >> representing the modulated carried signal or is it a modulated > >> continous (analog) signal.. > > > I'm not particular knowledgeable about comms, but here > > is how I understand the terms: > > > - The modulator takes an analog signal and transforms it > > � to a format that is suitable for transmission. > > - 'Digital Modulation' is a modulation format that somehow > > � is suitable for digital encodings of the information. > > "Suitable for transmission" (and reception) implies that the signal can > be radiated by an antenna, received by another, and tuned (i.e., run > through a bandpass filter) to isolate it from other signals also > received. Such a signal is analog.Where did I say otherwise? Rune
Reply by ●September 14, 20092009-09-14
Rune Allnor wrote:> On 14 Sep, 16:50, Jerry Avins <j...@ieee.org> wrote: >> Rune Allnor wrote: >>> On 11 Sep, 13:37, arun <arunkumar...@gmail.com> wrote: >>>> HI, >>>> I am new to this group. I have very basic doubt about >>>> digital modulation. >>>> We modulate the carrier frequency based on the digital input values... >>>> So is the output of modulator block a digital signal with samples >>>> representing the modulated carried signal or is it a modulated >>>> continous (analog) signal.. >>> I'm not particular knowledgeable about comms, but here >>> is how I understand the terms: >>> - The modulator takes an analog signal and transforms it >>> to a format that is suitable for transmission. >>> - 'Digital Modulation' is a modulation format that somehow >>> is suitable for digital encodings of the information. >> "Suitable for transmission" (and reception) implies that the signal can >> be radiated by an antenna, received by another, and tuned (i.e., run >> through a bandpass filter) to isolate it from other signals also >> received. Such a signal is analog. > > Where did I say otherwise?You didn't. I misinterpreted "> arun, > > > > The output of any real-world modulator is always going to be > > analog. Even in the theoretical world, the purpose of the modulator is > > to transform from discrete-time to continuous-time. Wouldn't this conversion be the task of the DAC? Once you have an anlog baseband (or intermediate format) signal, the modulator transforms it to some format that is suitable for transmission." Maybe Matlab isn't a drug after all! :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●September 14, 20092009-09-14