Syllabus Unit 1 Review of wireless and cellular radio communication: The cellular concept, system design fundamentals, frequency reuse, reused distance, cluster size, channel assignment strategies, handoff strategies, co-channel interference and system capacity, trunking and grade of service. Unit 2 Speech coding for wireless system applications and broadcast systems, coding techniques for audio and voice and popular speech codes. Brief introduction to radio channel characterization, multi-path propagation, co-channel interference, exponential power delay profile, propagation effects, scattering, ground reflection, fading, long normal shadowing, coherence bandwidth.
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SyllabusUnit 1
Review of wireless and cellular radio communication: The cellular concept, system design fundamentals, frequency reuse, reused distance, cluster size, channel assignment strategies, handoff strategies, co-channel interference and system capacity, trunking and grade of service.
Unit 2 Speech coding for wireless system applications and broadcast systems, coding techniques for audio and voice and popular speech codes. Brief introduction to radio channel characterization, multi-path propagation, co-channel interference, exponential power delay profile, propagation effects, scattering, ground reflection, fading, long normal shadowing, coherence bandwidth.
Unit 3 Modulation techniques for mobile and satellite communication, their generation and detection, performance of spectral and power efficiency. Physical layer technique, diversity, spread, spectrum, frequency hopping, direct sequence, adaptive equalization, Orthogonal Frequency Division Multiplexing (OFDM).
Unit 4 MAC Protocols: IEEE 802.11 and its variants, ETSI-HIPERLAN type 1 MAC protocol, multiple access with collision avoidance.
Unit 5 Introduction to GEO, MEO and LEO satellite systems, Antenna positioning in GEO and Link calculations, wideband CDMA concepts principles.
Reference Book1. Wilkies and Garg, Principles of GSM
technology, PHI
2. Schiller J., Mobile Communications, Addison Wesley
3. Viterbi A, CDMA, Addison Wesley
4. Gokhle, Introduction to Telecommunications, Delmer Thomson
1. “Wireless Communication”, T.S. Rappaport
Review of Wireless and Cellular Radio Communications
Introduction
• Since the mid 1990s, the cellular communications industry has witnessed explosive growth.
First Generation Cellular Networks
• First generation cellular systems that relied exclusively on
– FDMA(Frequency Division Multiple Access)/FDD (frequency-division duplexing)Frequency Division Multiple Access or FDMA is a Channel Access Method used in multiple-access protocols as a channelization protocol. It is important to distinguish between users.
First Generation Cellular Networks
FDMA and frequency-division duplexing (FDD). While FDMA allows multiple users simultaneous access to a certain system, FDD refers to how the radio channel is shared between the uplink and downlink (for instance, the traffic going back and forth between a mobile-phone and a base-station).
SheikhooOo
Basics: Multiple Access Methods
Time
Frequency
Codes
TDMA: Time Division Multiple Access FDMA:
Frequency Division Multiple Access
CMDA: Code Division Multiple Access
First Generation Cellular Networks
– Analog FM
Frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency.
Second Generation Cellular Networks
• Second generation standards use multiple access techniques– digital modulation formats – TDMA/FDD – CDMA/FDD
Second Generation Cellular Networks
The most popular second generation standards include three TDMA and one
CDMA standard• Global System Mobile(GSM)
Supports eight time slotted users for each 200 KHz radio channel and has been deployed widely by service providers in Europe, Asia, Australia, South America, and some parts of the US.
Second Generation Cellular Networks
– Interim Standard 136 (IS-136)
Also known as North American Digital Cellular (NADC), which supports three time slotted users for each 30 KHz radio channel and is popular choice for carriers in North America, South America and Australia.
– Pacific Digital Cellular (PDC)
A Japanese TDMA standard that is similar to IS-136. More than 50 million users use this standard.
Second Generation Cellular Networks
– The popular 2G CDMA standard Interim Standard 95 Code Division Multiple Access (IS-95)
Also known as CDMAOne . CDMA is widely deployed by carriers in North America, as well as in Korea, Japan, China, South America and Australia.
Second Generation Cellular Networks
• Second generation were first introduced in the early 1990s
• Evolved (Growth) from the first generation of analog mobile phone systems (e.g, AMPS, ETACS, and JTACS).
• Today, many wireless service providers use both first generation and second generation equipment in major markets
Second Generation Cellular Networks
and often provide customers with subscriber units that can support multiple frequency bands and multiple air interface standards.
• For example, in many countries it is possible to purchase a single tri-mode cellular handset phone that supports CDMA in the cellular band and PCS (personal communications services) bands in addition to analog first
Second Generation Cellular Networks
First generation technology in the cellular band.
• Such tri-mode phones are able to automatically sense and adapt to whichever standard is being used in a particular market.
Key Specification of Leading 2G Technology
Modulation
• Modulation is the process of conveying a message signal, that can be physically transmitted.
• BPSK stands for Binary Phase shift keying modulation
• GMSK stands for Gaussian Minimum Shift Keying
• DQPSK stands for differential quadrature phase shift keying
Difference between carriers and channels
• When we talk about carrier, it is more related to a signal that usually carries your data.Signals of different frequencies are called channels. A carrier can contain different channels.
• For example radio signals: The radio signals (FM or AM) are carriers because they carry the voice data along with them. But within the same range of frequency, you can tune different stations (different frequencies) i.e. your channels.
2.5G Mobile Radio Networks
Weaknesses of 2G• 2G technologies use circuit-switched data
modems that limit data users to a single circuit-switched voice channel. Data transmission in 2G are thus generally limited to the data throughput rate of an individual user, and this rate is of the same order of magnitude of the data rate of the designated speech coders given in Key Specification of Leading 2G Technologies.
2.5G Mobile Radio Networks
Weaknesses of 2G• In 2G, original GSM, CDMA, and IS-136
standards which originally supported 9.6 kilobits per second transmission rates for data messages.
• Due to relatively small data rates, 2 G standards are able to support limited Internet browsing and sophisticated short messaging capabilities using a circuit switched approach.
2.5G Mobile Radio Networks
Weaknesses of 2G
• Short messaging Service (SMS) is a popular feature of GSM but the wireless markets are fragmented between many different types of technologies and network owners, and SMS presently only works between users of the same network.
2.5G Mobile Radio Networks
• The new standards represent 2.5G technology and allow existing 2G equipment to be modified and supplemented with new base station add-ons and subscriber unit software upgrades to support higher data rate transmissions for web browsing, e-mail traffic and location-based mobile services.
2.5G Mobile Radio Networks
• The 2.5 G technologies also support a popular new browsing format language, called Wireless Application Protocol (WAP), that allows standard web pages in a compressed format specifically designed for small, portable hand held wireless devices.
Various Upgrade paths for 2G Technologies
RTT: Radio Transmission Technology
Cellular Concept – System Design Fundamentals
Overview
• Fixed channel assignment
• Multicoloring – co-channel interference
• General problem statement
• Genetic algorithms
• Results and details
• Fixed/dynamic channel and power assignment
Cell structure• Implements space division multiplex: base station
covers a certain transmission area (cell)
• Mobile users communicate only via the base station
• Advantages of cell structures:– higher capacity, higher number of users– less transmission power needed– more robust, decentralized– base station deals with interference locally
• Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM) - even more for higher frequencies
Cellular architecture
One low power transmitter per cell
Frequency reuse–limited spectrum
Cell splitting to increase capacityA
B
Reuse distance: minimum distance between two cells using same channel for satisfactory signal to noise ratio
Measured in # of cells in between
Problems– Propagation path loss for signal power: quadratic or higher in
distance – fixed network needed for the base stations– handover (changing from one cell to another) necessary– interference with other cells:
• Co-channel interference: Transmission on same frequency
• Adjacent channel interference:Transmission on close frequencies
Reuse pattern for reuse distance 2?
One frequency can be (re)used in all cells of the same color
Minimize number of frequencies=colors
Reuse distance 2 – reuse pattern
One frequency can be (re)used in all cells of the same color
Reuse pattern for reuse distance 3?
Reuse distance 3 – reuse pattern
Frequency planning I• Frequency reuse only with a certain
distance between the base stations• Standard model using 7 frequencies:
• Note pattern for repeating the same color: one north, two east-north
f4
f5
f1f3
f2
f6
f7
f3f2
f4
f5
f1
Fixed and Dynamic assignment
• Fixed frequency assignment: permanent– certain frequencies are assigned to a certain cell– problem: different traffic load in different cells
• Dynamic frequency assignment: temporary– base station chooses frequencies depending on the
frequencies already used in neighbor cells– more capacity in cells with more traffic– assignment can also be based on interference
measurements
3 cell clusterwith 3 sector antennas
f1f1 f1f2f3
f2
f3
f2
f3h1
h2
h3g1
g2
g3
h1h2
h3g1
g2g3
g1g2g3
Cell breathing• CDM systems: cell size depends on current load
• Additional traffic appears as noise to other users
• If the noise level is too high users drop out of cells
Multicoloring• Weight w(v) of cell v = # of requested frequencies
• Reuse distance r
• Minimize # channels used: NP hard problem
• Multi-coloring = multi-frequencing
• Channel= Frequency= ColorChannel= Frequency= Color
• HybridHybrid CA = combination fixed/dyn. frequencies
• Graph representation: weighted nodes, two nodes connected by edge iff their distance is < r
• same colors cannot be assigned to edge endpoints
Hexagon graphs: reuse distance 2
What is the graph for reuse distance 3?
Lower bounds for hexagonal graphsD= Maximum total weight on any cliqueLower bound on number of channels: D
D/3
D/2 D/6
D/2
D/2 D/2
D/2
D/2
D/2D/2D/2
D/2
000
Odd cycle bound: induced 9-cycle, each weight D/2
Channels needed in this cycle: 9D/2
Each channels can be used at most 4 times.
Needs 9/8D channels
Fixed allocations – reuse distance 2D= maximum number of channels in a node or 3-cycle
• generate random combination of d[j] X’s and m-(c0+1)d[j] 0’s; replace each X by 100..0 (c0 0’s); shift circularly by random number in [0,c0]
Mutation• Each row=cell is mutated separately• Combinations in bit representation: x 1’s out of m bits• Mutation with equal probability for each bit: choose one out
of x 1’s and one out of m-x 0’s at random, swap: Ngo-Li ‘98
• Mutation with different probability for each bit: b[i]= # of conflicts of i-th selected channel with other channels in this and other cellsp[i]=b[i]/(b[1]+…+b[x])Repeat for 0’s: # of conflicts if that channel turned on
• Choosing bit with given probability: Generate at random r, 0 r 1, and choose i, p[1]+…p[i-1] r <p[1]+…+p[i]
Crossover• Regular GA crossover:
1011000110 1001111000 0101111000 0111000110
• Ngo-Li ’98: A and B two parents, each row separately, preserve # of 1’s in each row: push 10 and 01 columns in stack if top same;
pop for exchange if top different1011000110 1001101000 0101111000 0111010110
• Problem: # of swaps varies
New crossover• t= number of desired swaps in a row