cnas2071_rahul_agrawal

8/4/2019 CNAS2071_rahul_agrawal

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RAHUL AGRAWAL

09CO71

[email protected]

COMPUTER NETWORKS (CO303)

Course Instructor: Mr B R Chandavarkar

ASSIGNMENT 2 (CNAS2071_rahul_agrawal)

Problem Statement:

Study and write short notes on the features and services provided by Physical Layer in 1G, 2G, 3G

and 4G networks.

1. Brief Description of the PHYSICAL LAYER of the TCP/IP architecture

The Physical Layer consists of the basic hardware transmission technologies of a network.It is a

fundamental layer underlying the logical data structures of the higher level functions in a network.

Due to the plethora of available hardware technologies with widely varying characteristics, this is

perhaps the most complex layer in the OSI architecture.

The Physical Layer defines the means of transmitting data bits rather than packets over a physical

link connecting network nodes. The bit stream may be grouped into code words or symbols and

converted to a physical signal that is transmitted over a hardware transmission medium. The Physical

Layer provides an electrical, mechanical, and procedural interface to the transmission medium.

In a nutshell, the Physical Layer translates logical communications requests from the Data Link Layer

into hardware-specific operations to affect transmission or reception of electronic signals.

2. Physical Layer Technologies/ Features in Wireless Networks

The Physical layer takes care of the following issues in wireless data transmission

Spectrum The part of the electromagnetic spectrum is used, what is the overall bandwidthavailable, how is thi s segmented into channels? Ensures that mechanisms are available to controlutilised bandwidth to ensure coexistence with other users of the same spectrum.


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Propagation - Power levels that are permitted by regulatory authorities in the spectrum inquestion. The mechanisms are available to control the transmitted power or propagation pattern

to minimise co-channel interference for other users, maximise effective range or util ise spatial

diversity to increase throughput.

Modulation - How is encoded data carried on the physical medium, for example by modulating oneor more carriers in phase and/or amplitude, or by modulating pulses in amplitude and/or position?Data encoding Describes how are the raw bits of a data frame coded into symbols for

transmission and the functions these coding mechanisms serve.

Media access Deals in how is access to the transmission medium controlled to ensure that thebandwidth available for data transmission is maximised and that contention between users is

efficiently resolved.

The wireless communication has developed over the years from basic 1G (1st

generation wireless

networks) to 2G, 3G and finally 4G (available in some countries only).

3. Physical layer features in 1G wireless network

In the 1G network data transmission, the physical layer is basically involved in transmission of analog

data. Normal modulation techniques NMTs such as AM, FM, PM are used to modulate the carrier

wave.

The main issue with this generation of mobile communication is the crosstalk. Also a high amount of

noise would appear while conversing over long distances. In NMT the voice traffic is not encrypted

and so anyone with a receiver tuned to the frequency could intercept the communication link.

3.1. Amplitude Modulation AM

It is a technique used in electronic communication, most commonly for transmitting information via

a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the

information being sent. For example, changes in the signal strength can be used to specify the

sounds to be reproduced by a loudspeaker, or the light intensity of television pixels.


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3.2. Frequency Modulation FM

FM conveys information over a carrier wave by varying its instantaneous frequency. This is in

contrast with amplitude modulation, in which the amplitude of the carrier is varied while its

frequency remains constant.

In analog applications, the difference between the instantaneous and the base frequency of the

carrier is directly proportional to the instantaneous value of the input signal amplitude

FM is widely used for broadcasting of music and speech, and in two-way radio systems, in magnetic

tape recording systems, and certain video transmission systems.

In radio systems, frequency modulation with sufficient bandwidth provides an advantage in

cancelling naturally-occurring noise.

3.3. Phase Modulation PM

PM is a form of modulation that represents

information as variations in the instantaneous

phase of a carrier wave.

Unlike FM, PM is not very widely used for radio

transmissions. This is because it tends to require

more complex receiving hardware and there can

be ambiguity problems in determining whether,

for example, the signal has changed phase by

+180 or -180. PM is used, however, in digitalmusic synthesizers.


The second generation of wireless networking introduced digital to analog conversion of data for

data transfer carried out by the physical layer. The various techniques used in this area are FDMA,

TDMA and CDMA etc. Apart from this the physical layer also performs circuit switching techniques to

transfer data bits.

4.1. Frequency Division Multiple Access FDMA

FDMA is a channel access method used in multiple-access protocols as a channelization protocol.

FDMA gives users an individual allocation of one or several frequency bands, or channels. It is

particularly commonplace in satellite communication. FDMA, like other Multiple Access systems,

coordinates access between multiple users.

Issues: Crosstalk may cause interference among frequencies and disrupt the transmission.


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In FDMA all users share the satellite simultaneously but each user transmits at single frequency.FDMA can be used with both analog and digital signal.FDMA is not vulnerable to the timing problems that TDMA has. Since a predetermined frequency

band is available for the entire period of communication, stream data (a continuous flow of data

that may not be packetized) can easily be used with FDMA.

Due to the frequency filtering, FDMA is not sensitive to near-far problem which is pronounced forCDMA.

Each user transmits and receives at different frequencies as each user gets a unique frequency slot

4.2. Time Division Multiple Access TDMA

TDMA is a channel access method for shared medium networks. It allows several users to share the

same frequency channel by dividing the signal into different time slots. The users transmit in rapid

succession, one after the other, each using its own time slot. This allows multiple stations to share

the same transmission medium (e.g. radio frequency channel) while using only a part of its channel

capacity. TDMA is used in the digital 2G cellular systems such asGlobal System for Mobile

Communications (GSM).

Shares single carrier frequency with multiple users Non-continuous transmission makes handoff simpler Slots can be assigned on demand in dynamic TDMA Less stringent power control than CDMA due to reduced intra cell interference Higher synchronization overhead than CDMA

Advanced equalization may be necessary for high data rates if the channel is "frequencyselective" and creates Inter-symbol interference

Cell breathing (borrowing resources from adjacent cells) is more complicated than in CDMA Frequency/slot allocation complexity Pulsating power envelope: Interference with other devices

4.3. Code Division Multiple Access CDMA

CDMA is a channel access method used by various radio communication technologies.

One of the basic concepts in data communication is the idea of allowing several transmitters to sendinformation simultaneously over a single communication channel. This allows several users to share


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a band of frequencies. This concept is called multiple access. CDMA employs spread-spectrum

technology and a special coding scheme to allow multiple users to be multiplexed over the same

physical channel. By contrast, time division multiple access (TDMA) divides access by time, while

frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of spread-

spectrum signalling, since the modulated coded signal has a much higher data bandwidth than the

data being communicated.ANALOGY: An analogy to the problem of multiple access is a room (channel) in which people wish to

talk to each other simultaneously. To avoid confusion, people could take turns speaking (time

division), speak at different pitches (frequency division), or speak in different languages (code

division).

4.4. Circuit Switching

This technique is used in telecommunications technology by which two network nodes establish a

dedicated communications channel (circuit) before the nodes may communicate. The circuit remains

connected for the duration of the communication session. The circuit functions as if the nodes were

physically connected as with an electrical circuit.

The bit delay is constant during a connection, as opposed to packet switching, where packet queues

may cause varying packet transfer delay. Each circuit cannot be used by other callers until the circuit

is released and a new connection is set up. Even if no actual communication is taking place, the

channel remains unavailable to other users.


5.1. Wideband Code Division Multiple Access WCDMA

Wideband Code Division Multiple Access or UMTS is an air interface standard found in 3G mobile

telecommunications networks.

Key features of WCDMA are listed below:

Radio channels are 5 MHz wide. Supported mode of duplex: frequency division (FDD), Time Division (TDD) Employs coherent detection on both the uplink and downlink based on the use of pilot symbols

and channels.

Supports inter-cell asynchronous operation. Variable rate transmission on a 10 ms frame basis. Multicode transmission. Adaptive power control based on SIR (Signal-to-Interference Ratio). Multiuser detection and smart antennas can be used to increase capacity and coverage. Multiple types of handoff (or handover) between different cells including soft handoff, softer

handoff and hard handoff.

1:1 frequency reuse scheme


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5.2. Packet oriented multiple access schemes

Packet switching is a digital networking communications method that groups all transmitted data

regardless of content, type, or structure into suitably sized blocks, calledpackets. Packet switching

features delivery of variable-bit-rate data streams (sequences of packets) over a shared network.

When traversing network adapters, switches, routers and other network nodes, packets are

buffered and queued, resulting in variable delay and throughput depending on the traffic load in the

network.

Packet switching contrasts with another principal networking paradigm, circuit switching, a methodwhich sets up a limited number of dedicated connections of constant bit rate and constant delay

between nodes for exclusive use during the communication session. In case of traffic fees, for

example in cel lular communication services, circuit switching is characterized by a fee per time unit

of connection time, even when no data is transferred, while packet switching is characterized by a

fee per unit of information.

Two major packet switching modes exist; (1) connectionless packet switching, also known as

datagram switching, and (2) connection-oriented packet switching, also known as virtual circuit

switching. In the first case each packet includes complete addressing or routing information. The

packets are routed individually, sometimes resulting in different paths and out-of-order delivery. In

the second case a connection is defined and pre-allocated in each involved node during a connection

phase before any packet is transferred. The packets include a connection identifier rather than

address information, and are del ivered in order.

5.3. GPRS (2.5G) and EDGE (2.75G)

A. GPRS (2.5 G) General Packet Radio Service. The 2G network although much more advanced than

the earlier 1G technology was low for internet services. Hence, in order to enhance data rates, a

packet switched network was brought up. The packet switched network has an IP gateway (X.25).

The connection provided packetized data and coupled with higher modulation techniques the data

rates were enhanced.

GPRS uses a multiple of the 1 to 8 radio channel timeslots in the 200 kHz-frequency band allocated

for a carrier frequency to enable data speeds of up to 115kbps. The data is packetized and

transported over Public Land Mobile Networks (PLMN) using an IP backbone so that mobile users

can access services on the Internet, such as SMTP/POP-based e-mail, ftp and HTTP-based Web

services.

B. EDGE (2.75G) -The data rates offered by EDGE (Enhanced Data rates for GSM Evolution) is triple tothat offered by GPRS. The modulation techniques are much more sensitive than those used in GPRS

but they support higher number of data bits/ symbol.

Theoretically a peak throughput of 384Kbps is poss ible with EDGE as compared to the 115 Kbps on

GPRS. Third Generation Mobile systems include a huge amount of architectural change in the 2G

architecture. The architecture stil l has a circuit switched and a packet switched network.


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The 4G wireless technology is totally IP-based doing away with the circuit-switched technology of

the 2G and 3G technologies.

4G uses the OFDM multiple access technique. Also, it facil itates the VoIP concept of telephony. The4G technology also uses higher amount of spectrum and hence, a lot of bandwidths open up for high

speed data transmission. The latency has also been reduced to less than 10ms. The HSPA+

technology provides data rates of up to 42 Mbps in downl ink and 11 mbps in uplink. The LTE aims at

providing 150 Mbps in downlink and 75 Mbps in uplink. All the data rates mentioned are the peak

data rates.

Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the popularOrthogonal frequency-division multiplexing (OFDM) digital modulation scheme. Multiple access is

achieved in OFDMA by assigning subsets of subcarriers to individual users as shown in the

illustration below. This allows simultaneous low data rate transmission from several users.

Advantages of OFDMA

Flexibility of deployment across various frequency bands with l ittle needed modification to theair interface.

Averaging interferences from neighbouring cells, by using di fferent basic carrier permutationsbetween users in different cells.

Interferences within the cell are averaged by using allocation with cyclic permutations. Enables Single Frequency Network coverage, where coverage problem exists and gives excellent

coverage.

Offers Frequency diversity by spreading the carriers all over the used spectrum.
http://en.wikipedia.org/wiki/File:OFDMA_subcarriers.png


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7. References

1. Physical layer http://en.wikipedia.org/wiki/Physical_Layer

2.http://setup-wireless.blogspot.com/2009/02/physical-layer-technologies.html

3. A white paper (under screening) on evolution of wireless network communication.4. Frequency Modulationhttp://webtools.delmarlearning.com/sample_chapters/MU-04.PDF

5. FDMA: Olenewa, J. & Ciampa, M. (2007). Wireless# Guide to Wireless Communications (2nd ed.).

Boston, United States: THOMSON COURSE TECHNOLOGY

6. TDMA and 2G & 3G:http://en.wikipedia.org/wiki/Time_division_multiple_access

7. OFDM and OFDMAhttp://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiple_access

8. Packet Switchinghttp://compnetworking.about.com/od/networkprotocols/f/packet-switch.htm

9. GPRShttp://en.wikipedia.org/wiki/General_Packet_Radio_Service

10. EDGEhttp://www.gsmarena.com/glossary.php3?term=edge

Thank you
http://en.wikipedia.org/wiki/Physical_Layerhttp://en.wikipedia.org/wiki/Physical_Layerhttp://setup-wireless.blogspot.com/2009/02/physical-layer-technologies.htmlhttp://setup-wireless.blogspot.com/2009/02/physical-layer-technologies.htmlhttp://webtools.delmarlearning.com/sample_chapters/MU-04.PDFhttp://webtools.delmarlearning.com/sample_chapters/MU-04.PDFhttp://en.wikipedia.org/wiki/Time_division_multiple_accesshttp://en.wikipedia.org/wiki/Time_division_multiple_accesshttp://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiple_accesshttp://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiple_accesshttp://compnetworking.about.com/od/networkprotocols/f/packet-switch.htmhttp://compnetworking.about.com/od/networkprotocols/f/packet-switch.htmhttp://en.wikipedia.org/wiki/General_Packet_Radio_Servicehttp://en.wikipedia.org/wiki/General_Packet_Radio_Servicehttp://www.gsmarena.com/glossary.php3?term=edgehttp://www.gsmarena.com/glossary.php3?term=edgehttp://www.gsmarena.com/glossary.php3?term=edgehttp://en.wikipedia.org/wiki/General_Packet_Radio_Servicehttp://compnetworking.about.com/od/networkprotocols/f/packet-switch.htmhttp://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiple_accesshttp://en.wikipedia.org/wiki/Time_division_multiple_accesshttp://webtools.delmarlearning.com/sample_chapters/MU-04.PDFhttp://setup-wireless.blogspot.com/2009/02/physical-layer-technologies.htmlhttp://en.wikipedia.org/wiki/Physical_Layer

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