Telecommunication basics

A very brief idea of Telecom system for beginners & interested ones

1. Telecommunication Basics Kuntal Banerjee

2. Contents • What is Telecommunication? • Basic terms and concepts of Telecommunication • Technical overview of the telephone service • Cellular Telephony •2G,3G, LTE & Vo-LTE •ADSL System

3. What is Telecommunication ? Telecommunication Telecommunication occurs when the exchange of information between two entities (communication) includes the use of technology. Communication technology uses channels to transmit information (as electrical signals), either over a physical medium (such as signal cables), or in the form of electromagnetic waves.

4. What is Telecommunication ? Basic elements- A transmitter that takes information (e.g. voice or text) and converts it to a signal. A transmission medium, also called the "physical channel" that carries the signal. An example of this is the "free space channel, copper wire, coaxial cable or Fiber Optic cable, etc.". A receiver that takes the signal from the channel and converts it back into usable information. Transceiver: a single box of electronics working as both a transmitter and a receiver, or a transceiver. For example, a cellular phone is a transceiver. Communication Channel- The term "channel" has two different meanings. In one meaning, a channel is the physical medium that carries a signal between the transmitter and the receiver. The other meaning of the term "channel" in telecommunications is seen in the phrase communications channel, which is a subdivision of a transmission medium so that it can be used to send multiple streams of information simultaneously.

5. Basic Terms and Concepts Half duplex vs Full duplex A duplex communication system is a point-to-point system, usually in fixed-line telephone network, composed of two connected parties or devices that can communicate with one another in both directions. In a full duplex system, both parties can communicate to the other simultaneously. An example of a full-duplex device is a telephone. In a half-duplex system, there are still two clearly defined paths/channels, and each party can communicate to the other but not simultaneously; the communication is one direction at a time. An example of a half-duplex device is a walkie-talkie.

6. Basic Terms and Concepts Modulation The shaping of a signal to convey information is known as modulation. Modulation can be used to represent a digital message as an analog waveform. This is commonly called “Keying”. Modem: “ Modulator – Demodulator”, A to D and D to A because the voice network is analog. Analog Signaling vs Digital Signaling Analog signaling: Human friendly | AM, FM | Noise cancellation (Signal tuning is the core technology) Digital signaling: Computer friendly | Error correction, Encryption enabled

7. Basic Terms and Concepts Switching (“The Cloud”) Switching makes better use of the “Cloud” Circuit switching, Packet switching (Internet), Broadcasting, Cellular Voice network vs. Data network Voice network: PSTN (Public Switched Telephone Network)- Basically transmitting the voice Data network: LAN, WAN (often (usually) use voice network transmission facilities)- Anything goes (e.g. text, image, voice, video, etc.) Where do networks come from? Voice network: Telcos, Long distance carriers Data network: ISP (Internet Service Provider

8. Basic Terms and Concepts Circuit Switching- End-to-end circuit Sequenced communication PSTN Traditional telephony Not cost efficient Less Delay Highly reliable, but failures typically mean the circuit must be rebuilt Packet Switching- Packets represent piece of data Unordered transmission Internet VoIP Shared cost model Highly Delay Less reliable, but can reroute around failures

9. Basic Terms and Concepts Multiplexing Multiplexing is the set of technique that allow the simultaneous transmission of multiple signals across a single data link (transmission medium) Multiplexor is a mechanism that implements the concept

10. PSTN: Mostly Digital with Analog Local Loops Today, everything is digital except for the Local Loop access line and residential telephones. The actual Local Loop line can carry either analog or digital signals, but the equipment at both ends is analog.

11. Cellular Telephony In Cellular technology, the region is divided into smaller cells. In each cell, a Cell-site ( Base Station) serves cell-phones in the cell. When a subscriber moves from one cell to another in a cellular system, this is called a handoff. When a subscriber moves from one city to another, this is roaming. The Mobile Telephone Switching Office (AKA Mobile Switching Center) coordinates the Cell-sites and implements signaling and handoffs.

12. Cellular Telephony Microwave uses radio transmission for PSTN trunk lines Each circuit is sent in a separate channel and if each channel bandwidth is large, there will be fewer channels. Frequency Division Multiplexing (FDM) used in AMPS (Advanced Mobile Phone System.) Voice uses 4 KHz-wide channels.

13. GSM (Global Service for Mobile communication) GSM is the worldwide standard for cellular voice – especially Europe. Uses Time Division Multiplexing (TDM) Uses 200 kHz channels Divides each second into many frame periods Divides each frame into 8 slots Gives same slot in each frame to a conversation

14. CDMA (Code Division Multiple Access) Code Division Multiple Access (CDMA) Used in the United States and Korea | A form of spread spectrum transmission Unlike traditional spread spectrum technology, multiple users can transmit simultaneously 1.25 MHz channels | Can support many users per channel Can use the same channel in adjacent cells So can only reuse a channel in every cell

15. 3G Services 3G – Third generation of mobile telecommunication technology This is based on a set of standards used for mobile devices and mobile telecommunications use services and networks that comply with the International Mobile Telecommunications-2000 (IMT-2000) specifications. 3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls (e.g. show) and mobile TV. The original and most widespread radio interface is called WCDMA (Wideband CDMA).

16. 3G Services HSPA (High Speed Packet Access) HSPA is that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA protocols. HSDPA: The first step required to upgrade WCDMA to HSPA is to improve the downlink by introducing HSDPA. The improved downlink provides up to 14Mbit/s with significantly reduced latency. HSPA+ (evolved High Speed Packet Access): Evolved HSPA provides data rates up to 84 Mbit/s in the downlink and 10.8 Mbit/s in the uplink (per 5 MHz carrier) with multiple input, multiple output (2x2 MIMO) technologies and higher order modulation (64 QAM). With Dual Cell technology, these can be doubled.

17. LTE – Long Term Evolution LTE – Long Term Evolution LTE, commonly marketed as 4G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements. Peak download rates up to 299.6 Mbit/s and upload rates up to 75.4 Mbit/s depending on the user equipment category (with 4×4 antennas using 20 MHz of spectrum). Five different terminal classes have been defined from a voice centric class up to a high end terminal that supports the peak data rates. All terminals will be able to process 20 MHz bandwidth.

18. LTE – Long Term Evolution Voice Calls- Circuit-switched fallback (CSFB): TE just provides data services, and when a voice call is to be initiated or received, it will fall back to the circuit-switched domain. Simultaneous voice and LTE (SVLTE): the handset works simultaneously in the LTE and circuit switched modes, with the LTE mode providing data services and the circuit switched mode providing the voice service.

19. ADSL: Asymmetrical Digital Subscriber Line Asymmetric digital subscriber line- Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voice band modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time.