Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [digital-communications]

Digital Communication is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel.

Under Digital Communication, the data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying wave forms (passband transmission), using a digital modulation method. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment, most commonly.

Source: Wikipedia.

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How to estimate and compensate for doppler shift in wireless signals?

I was wondering what good method(s) exist for the estimation (and subsequent compensation) of doppler shift for transmitted signals, be they acoustic or RF, in the context of comms. The question: Specifically, if the degree of doppler shift is…
Spacey
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Information Theory - units of channel capacity

In a first course in Information Theory, when the operational interpretation of channel capacity is introduced, it is said to be the highest data rate (in bits/channel-use) of reliable communication. While reading a few papers, I came across channel…
rk2
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Why are QAM Constellations regular and rectangular?

In most IQ graphs of QAM noise, it seems like the constellation ends up with more distortion the farther you get from the center: What causes this non-linear distortion, and why are QAM constellations not shaped like the following?
Mitch
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BPSK vs $\pi/2$ BPSK, what the benefits?

I have come across modulation techniques that have $\pi/2$ phase shifts from the regular constellations. For example $\pi/2 $ BPSK vs constellation the regular BPSK. Other examples include $\pi/2 $ QPSK vs. QPSK I am wondering what are the benefits…
Tyrone
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orthogonal family and pulse shaping filter

I am a beginner in digital communications and I have a question on the pulse shaping filter. For example, I have an orthogonal family $ \{s_1,...,s_N \}$. Can we preserve the orthogonality with a pulse shaping filter $g$ as a raised cosine filter,…
user40695
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ADC quantization +thermal noise

ADC noise can affect the overall noise performance of a receiver. The noise is partially quantization noise and partially thermal noise and as a general rule it extends up to the Nyquist frequency = Fs/2 . A simplification or assumption in receiver…
Hatem Tawfik
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Timing error detector used for symbol timing synchronization

The Gardner timing error detector is independent of carrier phase and frequency error, and is also quite immune to self noise (to my understanding, I may wrong about that). Can one assume that it is a recommended timing error detector for these…
Hatem Tawfik
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Golay complementary sequences for channel estimation - MATLAB

There are set of complementary sequences known as Golay sequences that are used for channel estimation because of the nice property they have which is that the sum of the autocorrelation function of each gives dirac function. For example, these are…
Tyrone
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Understanding what channel gain is and why it is important side information

I have a two part related question. Channel gain is often being considered the side-information that the Rx and Tx usually know. Why is channel gain such an important side-information? And second, what exactly is channel gain? I am reading many…
user23040
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What is the coherence bandwidth of the channel?

I read the following sentence. "In wideband systems, the transmission bandwidth of a single channel is much larger than the coherence bandwidth of the channel." What is 'coherence bandwidth of the channel'?
Seetha Rama Raju Sanapala
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DSSS/CDMA: Number of distinguishable users with gold codes

From wikipedia, I know that Gold codes have length $2^n-1$, where $n$ is number of LFSR elements and that there are $2^n-1$ different Gold sequences for this case. E.g. assuming that $n=6$, I have a Gold sequence with a length of $63$ bits. But how…
bonanza
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cyclic prefix in ofdm

In ofdm systems after applying IDFT we take the last N/x samples and place them before these N samples. This is called cyclic prefix(CP).So why to use a cyclic prefix? Why is the CP known to combat the inter symbol interference.Why can't we use…
phanitej
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Manchester decoding

Is there any method of decoding a Manchester encoded signal (IEEE 802.3) that is independent of the bit period? Suppose the data I want to send is $\rm 10110$. The Manchester code of this data will be $\rm 0110010110$ (according to IEEE standard).…
Shreyan Chowdhury
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dsss and correlation

Generally, a DSSS (Direct Sequence Spread Spectrum) communication is used to secure a communication. However, because of the repetition of the spreading sequence, a cyclostationary analysis makes it possible to locate the communication. Moreover,…
user63090
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systematic way to determine best bit mapping policy

So in class, we've been asked to find the best bit mapping policy for QAM modulation schemes (4-QAM, 8-QAM, 128-QAM, etc). Best meaning the one that will provide the lowest bit error Probability ($P_{be}$). I think I understand the concept, which is…
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