# Digital Modulation, Telephone, Cable Television

Digital Modulation, Telephone, Cable Television Digital Modulation and Multiplexing NRZ and NRZI and Balanced Signals NRZ has a positive voltage represented by 1 and a negative voltage

represent by 0. NRZI has a transition represented by 1 and a 0 represents no transition. A balanced signal has an average voltage of 0 or having as much positive voltage as negative voltage. If the average is not 0, energy is wasted in the form of heat. Baseband and Passband

Baseband sends the signal without changing any frequency. Passband shifts the signal to a higher frequency then transmits it. When the signal gets to the receiver, it is shifted back to its original frequency. When a baseband of B Hz is sent and is shift up to occupy a passband of S, the frequency will become S + B Hz. Multiplexing

Multiplexing is the process of compressing multiple signals into the form of a single and complex signal and then sending that signal on a carrier. When it is recovered, the complex signal splits back to the original form of the signals. There are 5 types of multiplexing. 1) Frequency Division Multiplexing 2) Orthogonal Frequency Division Multiplexing 3) Time Division Multiplexing 4) Statistical Time Division Multiplexing

5) Code Division Multiplexing Frequency Division and Orthogonal Frequency Division Multiplexing Frequency Division Multiplexing divides the spectrum into frequency bands. Each user will have possession of a given band which they will use to send their signal. AM radio broadcasting uses Frequency Division Multiplexing

Orthogonal Frequency Division divides the channel bandwidth into subcarriers. These subcarriers then send the data. What type of radio signal uses frequency division multiplexing? Time Division Multiplexing (TDM)

Used widely as part of telephone and cellular networks Method of putting multiple data streams in a single signal by separating them into many segments Bits from each stream are taken in a fixed time slot Uses guard time in order for the stream to transmit simultaneously without interfering with one or another Code Division Multiplexing

A form of spread spectrum communication where a narrowband signal is spread out over a wider frequency band Allows multiple signals from different users to share the same frequency band and makes it more tolerant of interference Key to CDMA is the ability to extract a desired signal while ignoring everything else Chips Each bit time is subdivided into m short intervals Each station is assigned a unique m-bit code called a chip sequence

Code Division Multiplexing 0 Bit Chip Sequence (-1-1-1+1+1-1+1+1) 1 Bit Chip Sequence (+1+1+1-1-1+1-1-1) Uses 1MHz The chip rate is 100 chips per bit and has a bit rate of 10kbps across the channel. Statistical Time Division Multiplexing

A method to transmit several types of data simultaneously across a single transmission cable Used for managing data being transmitted through a LAN or WAN network Analyzes statistics related to the typical workload of each device Considered to be more efficient than the TDM method The telephone system

Structure of the telephone system The initial market was for the sale of telephones, which came in pairs. It was up to the customer to string a single wire between them Then came the single switching office Then came the need to connect the switching offices Second-level switching offices were invented and after a while,

multiple second-level offices were needed - the hierarchy grew to five levels The Telephone System Telephone system comprises multiple telephones used in an interconnected fashion that allows for advanced telephony features such as call handling and transferring, conference calling, call metering and accounting, private and shared voice message

boxes, and so on. In summary, the telephone system consists of three major components: 1. Local loops (analog twisted pairs going into houses and businesses). 2. Trunks (digital fiber optics connecting the switching offices). 3. Switching offices (where calls are moved from one trunk to another).

Structure of the Telephone System (a) Fully interconnected network. (b) Centralized switch. (c) Two-level hierarchy The Telephone System

Phone systems can function over the Public Switched Telephone Network , over the internet or over a combination of the two. Business telephone systems can also be delivered as a hosted. First Generation (1G) Mobile Phones

Established in the late 70s and 80s. Mobile phones in 1st G was used for public service with a speed of 2.4kps. Radio signals that 1G networks use are analog system. AMPS(Advanced Mobile Phone Service) was invented at Bell labs.

AMPS was first launched in the United States. The main idea of 1st G of cellular networks is that geographical area is divided into cells. Basically every 10-25Km. Each served by a base station. 1G can only be used for voice service. Second Generation (2G) Mobile Phones Established in the early 1990s. The second generation introduced GSM which stands as Global System for Mobile

Communications. Can be used in many countries supporting GSM. Radio signals that 2G networks use are digital. Data speed was up to 64Kps. 2G systems provide encryption to secure and have more data transmitted. Digital traffic in 2G allows to detect and correct giving clear voice transmitted. Availability of digital data services, such as SMS and email. Third Generation (3G) Mobile Phones

3G technology was Established in 2000s. Data speed 144Kps-2Mbps. Typically called Smart Phones.

The third generation of mobile phones made it possible for users to use video applications and audio. Public service usage Higher capacity and broadband data. Many benefits of 3G are High Speed web, advanced security and faster communications. Summary Question(1):What are the three telephone system major

components? Question(2): Radio signals that 1G networks uses is? Answer: Q(1): 1-Local Loops 2-Trunks 3-Switching Offices

Q(2): Analog system Coaxial/Cable service A- Outer plastic sheath B- Woven copper shield C- Inner dielectric insulator D- Copper core

Cable television is a system of delivering television programming and other services to paying subscribers via radio frequency (RF) signals transmitted through coaxial cables. This form of networking differs greatly from telephone lines and has advantages and disadvantages Internet over cable

Internet over cable widely available internet service available to many in the country Cable Internet connection is a form of broadband access. Through use of a cable modem, users can access the Internet over cable TV lines. Cable modems can provide some of the fastest speeds that are widely available to customers. Single cable system can grow and expand easily because of their design. One cable run can provide service to many locations via

taps in the cable line Coaxial for internet Original implementation of cable internet used only downstream data on the coaxial or cable network. A dial up connection was required for upstream data. Eventually, a spectrum of the cable frequency was dedicated for upstream data but this spectrum is smaller than the downstream spectrum, resulting in the difference we see in

upload/download speeds in regular cable internet. Cable modems Cable modems are devices that allows high speed access to networks such as internet via the same connection we use for cable television This physical device separates the computer data from the cable television video signal, but many people refer to the entire system a cable service

Modem is short for modulize/demodulize which is the process the cable modem uses to convert data from a frequency in the the coaxial cable into data that can be transferred over ethernet or other media Hybrid Fibre/Coxial Some modern cable systems use fibre to carry the bulk of data from the service provider to a node. From the node, coaxial cable is used to carry signal to the clients. Fibre is used to carry signal to the node

because of its higher bandwidth, eliminating the need to run multiple coaxial cables to the node. This is called FttN or fibre to the node. Cable is not the only system that can uses FttN Television and Internet in one cable Cable offers the ability to provide television, phone service and internet over on cable line. This is possible because of the broad spectrum of frequency that can be carried on Coaxial cable. Different frequencies, or spectrums are reserved for

specific services, allowing multiple signals to exists alongside each other without interfering. See the below image for reference Video on mobile networks and their technologies https://www.youtube.com/watch?v=ODB6d6MHAY8

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