7 votes
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Capacity of cascade binary symmetric channels

A binary symmetric channel (BSC) can be characterized by its complemented probability $p$. Its well-known capacity is $$C = 1 - H(p) = 1 - (-p\log(p) - (1-p)\log(1-p))$$ where $H(p)$ is binary ...
AlexTP's user avatar
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7 votes
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System Frame Number in LTE Specifications

System Frame Number (SFN) is really just a counter. As its name, it tells us the index of system frame modulo 1024, the index is from 0 to 1023 (10 bits). SFN does not help the physical ...
AlexTP's user avatar
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6 votes

How to determine the FFT size of LTE downlink receiver?

You don't need to sample at cell FFT rate. Just shifted the received signal to the desired subcarrier and take a lowpass filtering, then sample at user-specific bandwidth (see attached image). The ...
AlexTP's user avatar
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4 votes

Why do we ever use low-order modulation schemes?

As we go for higher modulation order, detection complexity increases by exponentially , Hypothesis grows and detection becomes computationally intensive task. Also in use cases where channel condition ...
Nimisha Naruka's user avatar
4 votes
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What is the forward error correction in 802.11a?

From the official standard, IEEE Std 802.11a-1999, Part 11, section 17.3.5.5 Convolutional encoder, see the rate 1/2 code: The resulting two streams A and B are interleaved bit-alternatingly. The ...
Marcus Müller's user avatar
4 votes
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What is the difference between Antenna port and Physical Antenna in LTE?

This answer is for LTE standard, not 5G NR. However I do believe that the basic concept does not change since. (Logical) Antenna port is defined formally as in 3GPP 36.211 An antenna port is ...
AlexTP's user avatar
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3 votes

Combiner vs mixer vs coupler?

These are typical references to RF analog components where the three of these terms are used in the same context. They are often passive devices but can be implemented as active devices (requiring ...
Dan Boschen's user avatar
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2 votes

Capacity of cascade binary symmetric channels

A cascade of $L$ binary symmetric channels (BSCs) with cross-over probability $p$ is the same as a single BSC with cross-over probability $$p_L = \left.\left.\frac 12 \right(1 - (1-2p)^L\right).\tag{...
Dilip Sarwate's user avatar
2 votes
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P2 symbol constellation in DVB-T2

Ok, question solved. I found out that indeed L1 pre/post constellations are not rotated. The constellation above comprises: L1 pre (BPSK) L1 post (64-QAM) Data PLP from P2 symbol (rotated 16-QAM) ...
z3dd's user avatar
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2 votes
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Serial to Parallel Converter

So, I myself have taught based on material that uses that scheme, "P/S" and "S/P" after and before the transforms. Personally, it's nonsense. What the author tries to say is: The IFFT is a ...
Marcus Müller's user avatar
2 votes

Quality of experience engineer

In my experience in the defense industry, the quality assurance engineers are mostly just “box checkers” that have limited understanding of how all of the individual facets of the algorithms and ...
vintagevogue's user avatar
2 votes

5G uplink switching from CP OFDM to DFT-s-OFDM

The term is transform precoding. Whether it is enabled is configured semi-statically by RRC messages, which are usually broadcasted (periodically) in System information (SI) messages. If the system ...
AlexTP's user avatar
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2 votes
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In wireless communications, is it true to say: The more the range, the more the delay spread?

more delay spread is more probable? exactly, if the shortest path is 2m, then you won't get a "detour" for a signal that's 200m long and still contributes significant power (measured to the ...
Marcus Müller's user avatar
2 votes
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Did Dialup Modem use closed or open loop power/volume control? How did they determine Tx level?

Did Dialup Modem use closed or open loop power/volume control? Yes. How did they determine Tx level? "Dialup Modem" is a very big term that spans > 50 years of technological ...
Marcus Müller's user avatar
1 vote

OQPSK and MSK receiver sensitivity comparison

MSK is a band efficient modulation type with 1 bit/sec/Hz. On the other hand, OQPSK is of 2 bit/sec/Hz. MSK is equivalent to BPSK as well as OQPSK is equivalent to QPSK in terms of bit error rate. ...
Okan Erturk's user avatar
1 vote

What are the features/aspects/characteristics of any signal?

The couple time/amplitude denotes the domains of acquisition/representation of the measurement. Discrete or continuous are properties of the measurement or how the data is stored, with what symbols, ...
Laurent Duval's user avatar
1 vote

OFDM Query : Why In Phase and Quadrature Phase RF Conversion is needed?

Each IFFT complex result bin represents an amplitude and a phase for some frequency. You can use the sum of the a sine and a cosine in the appropriate ratios to produce a sinusoid of any phase (see ...
hotpaw2's user avatar
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1 vote
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OFDM Query : Why In Phase and Quadrature Phase RF Conversion is needed?

Because the output of the IFFT operation is a vector of complex numbers. An RF signal is a real thing, so you can't just multiply a sine wave by a complex number and get something sensible. However, ...
TimWescott's user avatar
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1 vote

NR PUSCH non-codebook based precoding

See the book entitled "5G NR The next generation of wireless access technology" by Erik Dahlman. On page 165, Chapter 9, says "There is also a possibility for the network to operate ...
Kzm_Izd's user avatar
  • 11
1 vote

Transition table / matrix for convolutional encoder K=3 understandings

The OP's question reveals many mis-understandings of the issues. The convolutional code in question is a nonsystematic $[2,1]$ convolutional code with constraint length $K = 3$. The specification is ...
Dilip Sarwate's user avatar
1 vote
Accepted

Hilbert transform Use as a Single Sideband Frequency Translator in Analog communication

There are many applications for the analog equivalent of the Hilbert Transform, often implemented with “90 degree power dividers” also referred to as “quadrature splitters” as well as broadband ...
Dan Boschen's user avatar
  • 50.2k
1 vote
Accepted

File size adjustment using FFT

The algorithm sets the high frequency DFT coefficients to zero hence effectively providing a lowpass filtering on the time domain signal. Your problem was on the line of creating Y1, which I replaced ...
Fat32's user avatar
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1 vote

Is the path loss exponent $\alpha$ is always 2 in friis equation model?

Path loss exponent is not always equal to 2, only in the free space scenario is this true. In general the received power $P_r$ is proportional to $d^{-\alpha}$, where $\alpha$ is somewhere around 2-6 ...
Engineer's user avatar
  • 3,022
1 vote

Radio Signal Stationarity

When working with such an RF signal, numerically transformed to a stochastic timeseries, to which extent can I consider the signal to be stationary? That depends on your signal model. We can't tell ...
Marcus Müller's user avatar
1 vote

What is Received power value when distance value is 0 in Friis equation

This formula is only valid for distances $d$ where the antennas are in the far field of each other, which implies that $d >> \lambda$. When the distance is $d=0$, then there is no attenuation ...
MBaz's user avatar
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1 vote

What is Received power value when distance value is 0 in Friis equation

This equation discribes the path loss in wireless communication link between two communicated devices. While eliminating one parameters will change the condition (wireless senario here) then we will ...
user3451927's user avatar
1 vote

Quality of experience engineer

My office is also struggling with this problem. We concluded that three skill sets required: signal processing, human centered computing (HCC), and computer science (CS). The algorithm development ...
Margaret Pinson's user avatar
1 vote

Difference between diversity gain and coding gain

One way to visualize coding gain vs diversity is by looking at the water fall curve (BER vs SNR) in a fading environment . While coding gain would shift the curve to the left without changing its ...
Hatem Tawfik's user avatar
1 vote
Accepted

Difference between diversity gain and coding gain

MIMO refers to any system with multiple antennas, where signals are transmitted over the same bandwidth and at the same time. Space-time coding (block or trellis, or a different one) is a specific ...
MBaz's user avatar
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