# Questions tagged [spectral-efficiency]

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### Does "keying on" a sine wave at a zero-crossing reduce its bandwidth?

I understand that a pure sine wave of infinite duration occupies no bandwidth, i.e. it is only the modulation of a carrier that gives it sidebands. Does the exact timing of a sudden modulation make ...
2answers
115 views

### How is it that a dial-up modem can achieve 33.6Kbit/s with only 3100Hz of bandwidth?

My understanding is that plain old telephone service passes frequencies between 300Hz and 3400Hz. How is it that a V.34 modem in the late 90s would be able to achieve data rates of 33,600bits/s with ...
4answers
429 views

### Are capacity and spectral efficiency identical for a dicrete-time digital signal?

I saw this answer and saw on the wikipedia page that both spectral efficiency and capacity can be measured in bpcu i.e. 'bits/symbol'. I just want to confirm then that they are identical for a ...
1answer
308 views

### FFT subset output yields computational efficiency

The traditional FFT gives $N=2^k$ outputs for $N=2^k$ inputs (generally complex.) The time effort is $O(N \cdot \log(N))$. If all I want is a compact subset of $M \ll N$ output frequency points, is ...
1answer
190 views

### Find Bandwith from Spectral Efficiency and Eb/N0

to give you a short intro of why I am asking here. My Uni is offering a TeleCom Lecture, I love the topic but all they teach is electronics, the exercise sheets are still TeleCom, we get no supporting ...
1answer
162 views

### About combination between QAM and PAM

I have confused question regarding the possibility of combination between QAM modulation and PAM in order to improve the spectral efficiency. Is that possible? As you see in the below Figure, it's ...
1answer
78 views

### Capacity and channel estimation algorithms: explanation of results

I study a spectral efficiency of a system with a precoding scheme with different channel schemes. Algorithm A for channel estimation gives a smaller estimation error instead of Algorithm B. I have ...
0answers
76 views

### Space-Time coding uses large amount of block codes to acheive maximum spectral efficiency

Assume I have a MIMO system with $M=8$ transmit antennas, and an arbitrary number of receive antennas. This MIMO systems uses space-time coding. the block codes (matrices) transmitted are part of a ...
1answer
31 views

### Spectral efficiency of with OFDM vs without OFDM?

OFDM has advantage over frequency selective channel with addition of cyclic prefix after IFFT of MPSK or MQAM symbol. but I wonder that the spectral efficiency of with OFDM vs without OFDM.
1answer
81 views

0answers
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### Is FFT sub matrix degeneracy a problem in OFDMA for some type of noise?

Say that the discrete Fourier transform (DFT) is used in OFDMA. There are a number of degenerate (singular, non invertible) sub matrices of some DFT matrices. Does this result in any problems? One ...
1answer
71 views

### Relationship between spectral efficiency and PAR

Low PAR means less fluctiations in the magnitude of a signal and hence analog signal processing (e.g., power amplifier) is tremendously reduced. For example, constant envelope modulation schemes like ...
1answer
84 views

### A priori spectral efficiency of OFDM scheme

Of course I can compute the spectral efficiency as the ratio of the measured bit-rate (of data bits, no header, no preable, nor redundancy bits included) and the measured spectral bandwidth. This ...
0answers
45 views

### ًWhy we use fourier transform in most of spectrum estimation approaches?

I wonder why in all spectrum estimation techniques, the analysis depend on the Fourier transform? Why not deal with the signals in time domain?