8
votes
Accepted
System Frame Number in LTE Specifications
System Frame Number (SFN) is essentially a counter. As its name suggests, it indicates the index of a system frame modulo 1024, with the index ranging from 0 to 1023 (10 bits).
SFN does not aid in ...
- 6,725
7
votes
Accepted
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 ...
- 6,725
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 ...
- 6,725
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 ...
4
votes
Accepted
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 ...
- 6,725
4
votes
Accepted
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 ...
- 32.5k
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 ...
- 55k
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{...
- 20.9k
2
votes
Accepted
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 ...
- 32.5k
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 ...
- 6,725
2
votes
Accepted
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 ...
- 32.5k
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 ...
- 863
2
votes
Accepted
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 ...
- 32.5k
1
vote
How jamming resistant is UWB communication?
What is the effective range of UWB jamming (i.e. up to what distance around a jammer is a UWB communication impossible?)
The questions you ask can't be answered without knowing at the very least ...
- 32.5k
1
vote
Why do we ever use low-order modulation schemes?
As indicated by the figure quoted by the OP, indeed, Ungerboeck discovered that in AWGN channel, with high-order modulation scheme to transmit lower number of bits per symbol is more power efficient ...
- 292
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 ...
- 11
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. ...
- 423
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, ...
- 32.3k
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 ...
- 35.7k
1
vote
Accepted
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, ...
- 13.3k
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 ...
- 20.9k
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 ...
- 55k
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 ...
- 3,042
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 ...
- 32.5k
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 ...
- 15.4k
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 ...
- 21
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 ...
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 ...
- 28.4k
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 ...
- 415
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