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Questions tagged [telecommunications]

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2
votes
1answer
284 views

(Textbook error?) Nyquist's relation: telegraph speed of transmission

An Introduction to Information Theory: Symbols, Signals and Noise, by John R. Pierce, says the following: In 1917, Harry Nyquist came to the American Telephone and Telegraph Company immediately ...
1
vote
2answers
98 views

(When) Can I use Cat5e wiring to carry a POTS signal to a DSL modem?

According to this answer by @asndre, It is very bad idea to use Cat5e-based wiring/cabling to establish a xDSL connection. However, my telephone/internet provider technician recommended -- and ...
0
votes
2answers
35 views

Finding required BW with Bessel table

The FM signal (see image 1) is applied to a 50 Ohms antenna, and I am seeking the required bandwith with the Bessel table (image 2). From the FM signal, I deduced that the information frequency is ...
0
votes
1answer
63 views

Is it possible to generate user-defined signal using an android phone?

Is it possible to generate an electronic wave signal using an android phone? (Theorically) For example by customizing the firmware can I produce some signals like \$ f(t)=2 \sin 3.2×10^9t+3\cos 5×10^...
1
vote
2answers
86 views

Maximum rate Shanon Hartley

i am reading computer networks and i am trying to solve an excercise. the excercise is What is the theoretically the maximum rate at which data can be transmitted to a 4000Hz bandwidth ...
1
vote
1answer
35 views

Difference between a flared and not flared rectangular waveguide antenna

Someone can explain to me the difference in terms of performance between a flared rectangular waveguide antenna (precisely a pyramidal horn) and a not flared rectangular waveguide antenna? In horn ...
0
votes
1answer
62 views

Bandwidth-Noise-SNR relationship

Let’s say we have the noise figure F of a system of devices. We also have the bandwidth improvement coefficient ( as defined by my teacher ) $$BI=10log(\frac{B_{in}}{B_{out}})$$ where B1 is the ...
0
votes
2answers
133 views

Why aren't tethered balloons used instead of Cellphone towers? [closed]

If we use tethered balloons with wireless gateways fitted on them (let's say for Cellular or LPWAN communication), they can provide much more coverage. Why aren't they used then? While there are many ...
0
votes
1answer
31 views

How can Erlang C values be greater than one?

Here is an Erlang C plot I did myself. The x-axis represents the total traffic while the y-axis represents the probability. Each line represents a different total number of channels. As you can see, ...
1
vote
1answer
47 views

Why are Erlang B and Erlang C formulas different?

Erlang B determines the probability that a call is blocked and is defined as: $$Pr[blocking]= {{A^C \over C!} \over {\sum_{k = 0}^{C} {A^k \over k!}}}$$ while Erlang C determines the probability ...
0
votes
4answers
121 views

TDMA in telephone circuit switching - isn't there delay in transmitting a particular user's speech? [closed]

Let's do a simple case on the left with X and A user telephones. So the way an analog signal (user's speech X) is handled, is that it is sampled at 8000 bits / sec. The high-speed C-channel has 128 ...
1
vote
1answer
72 views

Some sort of Sim card in Fax machine

I took apart our old Fax machine. And I found some weird Sim Card (See size compared to a regular sim card). I wonder what such a card is doing in a fax machine. Also I'm wondering what else I could ...
-2
votes
1answer
110 views

What is needed link budget? [closed]

Assuming I want to send a signal 1 km away from a 2.4 GHz antenna with 5 DBI gain and recieving antenna of 2.15 DBI gain. What is the minimum needed power at the receiver (not the minimum transmitter ...
0
votes
5answers
298 views

Why are cell towers so high? [closed]

Why do cell towers need so much height? Does the height increase antenna gain because it may provide directionality?
-1
votes
1answer
229 views

Why microwave links on cell towers have high frequency?

Why microwave links are in the higher microwave spectrum (I don't know exactly but I guess it's around 20-40GHz). If by Friis Equation higher frequencies have lower range then why use higher frequency ...
1
vote
1answer
149 views

How can a phone transmit the signal back to tower? [closed]

If cellphones have such a low power transmitter (around 200mW for LTE) and also doesn't have directionality then how can they talk back to the tower even though they are so powerful and built ...
-5
votes
1answer
139 views

Do the FCC's regulations make any sense?

I have read on the following page that the maximum permissible exposure MPE standard FCC have is 1 mW/cm2 for RF wave above 1500 MHz for general population. http://www.rfcafe.com/references/electrical/...
-2
votes
2answers
104 views

Why FM has larger range than cellular network [closed]

I can receive FM signal about 50km away from the transmitting station but I lose signal from cell towers in about few km (1-3km)
-3
votes
1answer
56 views

How cell sites work? [closed]

In Mobile communication, how do cell sites communicate to each other to the point when they reach the cell site which is connected to the other mobile phone when I make a call . What is the medium of ...
15
votes
3answers
4k views

Why does WiFi have a shorter range than LTE? [closed]

It seems confusing that my phone receives -87 dbm LTE signal and shows a full 4 bars with the speeds of UPLOAD: 20Mbps DOWNLOAD:13.6Mbps But my WiFi is showing 1 bar at -89 dbm and I get ...
-1
votes
1answer
112 views

How can a pringles can act as WiFi booster? [closed]

How does a wifi transciever placed inside a Pringles can act as a wifi signal booster. I saw this trick on Mr robot TV series. Do WiFi routers emit less power than GSM or LTE. I know for : GSM - 2W (...
0
votes
0answers
45 views

What is the difference between Antenna port and Physical Antenna in LTE?

I have just started working on the 5G NR physical layer and I have difficulty understanding the concept of Antenna Port at the downlink. In release 10 there supposedly 15-22 antenna ports for CSIRS (...
0
votes
1answer
50 views

Meaning of Evolution in LTE (Long-Term Evolution)

The term Evolution/Evolved (E) is everywhere in communications, and simply put i don't understand why. The answer I am looking for is one that will help me know what meaning i should associate with ...
1
vote
1answer
43 views

Decide coherent time and fade duration through empirical studies on the channel and relate them to channel modeling

I. Scenario: TX floating in the lossy heterogeneous medium with undetermined positions within a limited region; RX fixed in the air and closed to the boundary of air-lossy medium; Frequency: 500 MHz ...
-2
votes
1answer
115 views

How does cellphone idle time work?

Imagine a basic cell phone which operates in only 2G network and able to provide voice call & SMS service. Does this cell phone transmit any data to BTS in idle time (that is when the cell phone ...
0
votes
1answer
58 views

Xbee pro s2c 2.4 ghz 10dbi Antenna and its effect

Just wondreing how to increase the range/distance of communication between two xbee modules operating in API mode, we are considering to replace the 2.4 ghz antenna of 5dbi gain with 10dbi high gain ...
1
vote
1answer
86 views

What is the difference between SNR of a wideband system and the SNR for a narrowband system

I was reading Wireless Communications by Andrea Goldsmith in the book the author has stated that the Noise power for a wideband system with Bandwidth B is (B*N/2). Could someone help me understand why ...
1
vote
0answers
60 views

20 mA current loop speed/distance trade offs?

By 20 mA current loop, I'm referring to digital current loop communications, e.g. the standard used by old Model 33 teletypes. (Image credit: By Rama & Musée Bolo - Own work, CC BY-SA 2.0 fr, ...
0
votes
1answer
34 views

Delta Modulation Frequency in the Integrator

Ok guys, I can't understand a thing, I have made this circuit, that is a delta modulator: As you can see with an input of 5Vpp, in the output of the integrator I found a square wave signal, that has ...
0
votes
0answers
30 views

Who assign MNC LTE values in the USA

I'm working on an up and coming project for a company involving private LTE networks. We're working on our long term strategy and it came up that the IMSI values that uniquely identify SIM cards on ...
0
votes
2answers
35 views

what is the performance of an OFDM system in one-path channel (Flat response channel),with no multi path propagation?

i work on modelling a OFDM system in a indoor optical wireless channel (LOS channel), since my channel is LOS there is no multi -path propagation , so the delay spread of my channel is much smaller ...
1
vote
1answer
263 views

Transform a sinusoidal wave into a square wave with op-amp

Ok guys, I can't understand a thing, how can I turn a sinusoidal wave into a square wave with an op-amp, for example watch this image: If you pay attention, you can see in the bottom of the image a ...
0
votes
1answer
214 views

What is mean by channel inversion in wireless communication

Regarding the title of the question, to my understanding, Channel Inversion means that "The transmitter adapts its power to maintain constant SIR at the receiver." It is a technique used for ...
0
votes
0answers
20 views

Practical assumptions for accomodating cellular, D2D and M2M devices

Question: Given Assumption 1 in a network model which accommodates device-to-device (D2D) communication within a cellular network in the underlay and overlay, make an assumption to accommodate machine-...
0
votes
0answers
25 views

Addition of Successive-interference cancellation in wireless transmission

I am looking to integrate the Successive-Interference Cancellation (SIC) technique into my system and would like to know if the following would work. Let me first explain the system as \$I_c\$ is ...
0
votes
0answers
62 views

What are the stationary & non-stationary characteristics of a channel?

I am not sure if this is the proper stackexchange site to ask this question but I couldn't find a dedicated telecommunications ask & answer site. dsp.stackexchange.com would be an alternative too ...
1
vote
1answer
55 views

Number of point to point link

I dont know if this is unrelevant here but i wish if someone could help me . The number of point to point links required in a fully connected network for 50 entities is (a) 1250 (b) 1225 (...
0
votes
5answers
898 views

What is the difference between narrowband and wideband?

Im a bit confused between the difference of Narrowband signals and Wideband signals. Is there a specific value of bandwidth which classifies a signal into Narrowband or Wideband? What values of ...
0
votes
0answers
39 views

RAKE reciever intuition

So I was reading answer by Jerry Coffin on question "how RAKE receiver works" but couldn't ask further questions since I don't have 50+ reps: How does a CDMA Rake Receiver work? Further questions: ...
1
vote
1answer
59 views

Problem understanding CDMA and W-CDMA

I found it relatively easy to understand TDMA and FDMA but I just can't figure out CDMA and W-CDMA. For CDMA I think it is something like TDMA without time slots. At transmission side you can use ...
1
vote
2answers
252 views

A Funny-Looking Sign Off on Television (Test Pattern Generator Image) [closed]

I came across this display on television while I visited the island of Mindanao in the Philippines in November 3, 2017. I thought this might be a sign-off display from a TV network, but I noticed that ...
1
vote
3answers
97 views

Wireless channel interpretation [closed]

Is there a way to estimate how fast a channel changes with respect to time in practical applications? While evaluating doppler effect for a user we use the frequency at which the channel changes. How ...
3
votes
1answer
636 views

SIMCOM vs UBLOX [closed]

I would like to know what are your thoughts on the following below. I am designing a GSM tracking device with a SIMCOM808 module and I am speaking to an antenna supplier that advises me to rather go ...
0
votes
0answers
216 views

Telephone line isolation

I have a small problem. I have a fiber connection at home, and I want to power both the router and the cordless phone attached to it from the same power supply. Now, if I attach either the router or ...
0
votes
1answer
572 views

Why the difference between the RSSI and Rx Level measurements is so big?

I'm new in Telecom. Today, I downloaded the Android APK called "Network Cell Info Lite". In my house, I got this measures: RSSI: -51 RXLEV: 60 I know this measurements represents the received ...
0
votes
0answers
46 views

Does radiation level of an antenna depend on the antenna's parameters?

I am a newbie when it comes to the theory of telecommunication. I wonder whether radiation exposure may exceed recommended safety levels after changing the antenna only? I'm asking since I've seen ...
2
votes
1answer
56 views

What is a Direct Radiating Collector Amplifier?

Reading the Space Systems/Loral press release SSL Achieves Milestone, 100 Satellites Delivered based on the 1300, a Platform for evolution, innovation I ran across the sentence(s): It was the ...
0
votes
1answer
59 views

Is there a network mapping tool for path-loss?

I am not sure if this is the proper forum. I am looking for a tool to evaluate the wireless network performance.For example, given a map where should I put a transmitter/or transmitter plus repeater ...
2
votes
2answers
857 views

Using Cat5 for DSL from NID - good idea to double up wires for signal integrity / strength?

I am doing some rewiring of our internal phone lines (almost entirely removal of unused lines). The issues we have run into is the router will every now and then simply not connect from the house to ...
20
votes
2answers
490 views

“56k modem” found in VHF band

While scanning the VHF spectrum with a SDR USB dongle, I found something that sounded like an old 56k modem (at around 160MHz, FM modulation, Europe region). After some research, I found out that is ...