Abstract image of a woman sitting on books and studying on a laptop

2-frequencyreusenb-130206113258-phpapp02.pdf

K
KumarSaurabh314476

The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity. Cellular networks divide geographic areas into smaller cell sites served by lower-power base stations. Neighboring cells are assigned different groups of channels to minimize interference. This frequency reuse allows the same frequencies to be used in multiple cells across an area.

Engineering
1 of 85
Download to read offline
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
3.2 FREQUENCY RE USE AJAL.A.J Assistant Professor –Dept of ECE, Federal Institute of Science And Technology (FISAT) TM MAIL: ec2reach@gmail.com The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity.
Cellular Concept Cellular Concept  The limited capacity of the first mobile radio-telephone services was related to the spectrum used…not much sharing and a lot of bandwidth dedicated to a single call. – good coverage – interference: impossible to reuse the same frequency  The cellular concept addressed many of the shortcomings of the first mobile telephones – Frequency reuse – Wasted spectrum allocated to a single user  In 1968, Bell Labs proposed the cellular telephony concept to the FCC  It was approved and then the work began! – FCC allocated spectrum (took away TV UHF channels 70-83) in the 825-845 MHz and 870-890 MHz bands
Cellular Concept Cellular Concept  developed by Bell Labs 1960’s-70’s  areas divided into cells  a system approach, no major technological changes  a few hundred meters in some cities, 10s km at country side  each served by base station with lower power transmitter  each gets portion of total number of channels  neighboring cells assigned different groups of channels, interference minimized  hexagon geometry cell shape
What is a Cell? • Cell is the Basic Union in The System – defined as the area where radio coverage is given by one base station. • A cell has one or several frequencies, depending on traffic load. – Fundamental idea: Frequencies are reused, but not in neighboring cells due to interference.
Cellular Concept  Limited number of frequencies => limited channels  Single high power antenna => limited number of users  Smaller cells => frequency reuse possible => more number of users  Base stations (BS): implement space division multiplex – Each BS covers a certain transmission area (cell) – Each BS is allocated a portion of the total number of channels available – Cluster: group of nearby BSs that together use all available channels  Mobile stations communicate only via the base station – FDMA, TDMA, CDMA may be used within a cell  As demand increases (more channels are needed) – Number of base stations is increased – Transmitter power is decreased correspondingly to avoid interference
Cellular Concept  Cell size: – 100 m in cities to 35 km on the country side (GSM) – even less for higher frequencies – Umbrella cell: large cell that includes several smaller cells • Avoid frequent handoffs for fast moving traffic  Cell shape: – Hexagonal is useful for theoretical analysis – Practical footprint (radio coverage area) is amorphous  BS placement: – Center-excited cell: BS near center of cell • omni-directional antenna – Edge-excited cell: BSs on three of the six cell vertices • sectored directional antennas
Cellular Concept  Advantages: – higher capacity, higher number of users – less transmission power needed – more robust, decentralized – base station deals with interference, transmission area etc. locally  Problems: – fixed network needed for the base stations – handover (changing from one cell to another) necessary – interference with other cells: co-channel, adjacent-channel  Important Issues: – Cell sizing – Frequency reuse planning – Channel allocation strategies Bottom line: Attempt to maximize availability of channels in an area
• Cells labeled with the same letter use the same group of channels. • Cell Cluster: group of N cells using complete set of available channels • Many base stations, lower power, and shorter towers • Small coverage areas called “cells” • Each cell allocated a % of the total number of available channels • Nearby (adjacent) cells assigned different channel groups – to prevent interference between neighboring base stations and mobile users
Cell characteristics • Implements space division multiplex: base station covers a certain transmission area (cell) • Mobile stations 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, transmission area etc. locally • Problems: – fixed network needed for the base stations – handover (changing from one cell to another) necessary – interference with other cells • Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM) - even less for higher frequencies
Shape of Cells  Square  Width d cell has four neighbors at distance d and four at distance d  Better if all adjacent antennas equidistant  Simplifies choosing and switching to new antenna  Hexagon  Provides equidistant antennas  Radius defined as radius of circum-circle  Distance from center to vertex equals length of side  Distance between centers of cells radius R is R  Not always precise hexagons  Topographical limitations  Local signal propagation conditions  Location of antennas 2 3
Cellular Geometries
Cell Footprint
Cellular Network Architecture Cellular Network Architecture Mobile Switching Center Public Telephone network and Internet Mobile Switching Center Wired network
Frequency Reuse Frequency Reuse  Adjacent cells assigned different frequencies to avoid interference or crosstalk  Objective is to reuse frequency in nearby cells – 10 to 50 frequencies assigned to each cell – transmission power controlled to limit power at that frequency escaping to adjacent cells – the issue is to determine how many cells must intervene between two cells using the same frequency
Frequency Reuse Frequency Reuse  each cell allocated a group k channels – a cluster has N cells with unique and disjoint channel  groups, N typically 4, 7, 12  total number of duplex channels S = kN  Cluster repeated M times in a system  Total number of channels that can be used (capacity) – C = MkN = MS  Smaller cells  higher M  higher C + Channel reuse  higher capacity + Lower power requirements for mobiles – Additional base stations required – More frequent handoffs – Greater chance of ‘hot spots’
Frequency planning f1 f2 f3 f2 f1 f1 f2 f3 f2 f3 f1 f2 f1 f3 f3 f3 f3 f3 f4 f5 f1 f3 f2 f6 f7 f3 f2 f4 f5 f1 f3 f5 f6 f7 f2 f2 f1 f1 f1 f2 f3 f2 f3 f2 f3 h1 h2 h3 g1 g2 g3 h1 h2 h3 g1 g2 g3 g1 g2 g3 3 cell cluster 7 cell cluster 3 cell cluster with 3 sector antennas
Figure Frequency reuse patterns
Frequency planning • Frequency reuse only with a certain distance between the base stations • Standard model using 7 frequencies: f4 f5 f1 f3 f2 f6 f7 f3 f2 f4 f5 f1
FREQUENCY REUSE • The allotted frequency spectrum for mobile communication • during the 1 G is in the range of  (800- 900 ) Mhz • but ,Using this small bandwidth, thousands of subscribers need to be served over a large area. • To manage this situation, a technique called ‘’frequency reuse ‘’ is adopted.
FREQUENCY REUSE
2-frequencyreusenb-130206113258-phpapp02.pdf
Cellular Networks • Propagation models represent cell as a circular area • Approximate cell coverage with a hexagon - allows easier • analysis • Frequency assignment of F MHz for the system • The multiple access techniques translates F to T traffic channels • Cluster of cells K = group of adjacent cells which use all of the systems frequency assignment
2-frequencyreusenb-130206113258-phpapp02.pdf
Frequency reuse concept Frequency reuse concept ALPHABETICAL REPRESENTATION
Wrong implementation
END Result of Wrong implementation
Correct implementation
2-frequencyreusenb-130206113258-phpapp02.pdf
2-frequencyreusenb-130206113258-phpapp02.pdf
2-frequencyreusenb-130206113258-phpapp02.pdf
31 Freq reuse Advantage Freq reuse: Several cells in coverage area that use same set of frequencies Cochannel cells: Those cells using same freqs Cochannel interference: The mobile in cell A also gets signals from other Co channel cells Cluster1 Cluster2 Cluster3
Cellular Concepts In this case N=19 (i=3, j=2)
Frequency Reuse  Power of base transceiver controlled  Allow communications within cell on given frequency  Limit escaping power to adjacent cells  Allow re-use of frequencies in nearby cells  Use same frequency for multiple conversations  10 – 50 frequencies per cell  E.g.  The pattern consists of N cells  K total number of frequencies used in systems  Each cell has K/N frequencies  Advanced Mobile Phone Service (AMPS) K=395, N=7 giving 57 frequencies per cell on average
Characterizing Frequency Reuse  D = minimum distance between centers of cells that use the same band of frequencies (called cochannels)  R = radius of a cell  d = distance between centers of adjacent cells (d = R)  N = number of cells in repetitious pattern  Reuse factor  Each cell in pattern uses unique band of frequencies  Hexagonal cell pattern, following values of N possible  N = I2 + J2 + (I x J), I, J = 0, 1, 2, 3, …  Possible values of N are 1, 3, 4, 7, 9, 12, 13, 16, 19, 21, …  D/R=  D/d = N 3 N
35 Distance D R R
36 4 1 3 6 5 2 7 4 1 3 6 5 2 7 4 1 3 6 5 2 7 4 1 3 6 5 2 7 4 1 3 6 5 2 7 D R
Example of frequency reuse factor or pattern 1/4 The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to some books) where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).
38 Reuse Ratio : q N q R D 3 = = where: D: Distance between the centres of cells R: Radius of the cell q: Reuse ratio N: Cluster size Assuming hexagonal shape cells of equal size
39 Example R N D 3 = For N = 7 and R 5 km 5 7 3 × × = D The minimum distance at which the same frequency can be reused is approximately 4.6 times R, which is in this case 22.91 km 91 . 22 5 583 . 4 = × = D
Frequency Reuse Patterns
N=7, 32 cells, R=1.6km, in total 336 channels
So what is FREQUENCY REUSE ? • After allotting the available total bandwidth among a set of cells , the same frequency band will be used in another set of cells . • This kind of reuse can be adopted until the entire area to be covered is exhausted . • Note • Seven cells in a set is the most frequently used configuration.this configuration usually operates with a cell diameter of 1- 3 km range
Cellular architecture One low power transmitter per cell Frequency reuse–limited spectrum Cell splitting to increase capacity A B Reuse distance: minimum distance between two cells using same channel for satisfactory signal to noise ratio Measured in # of cells in between
Reuse distance 2 – reuse pattern One frequency can be (re)used in all cells of the same color
Reuse distance 3 – reuse pattern
Signal-to-interference ratio S/I or SIR
50 Capacity calculation—FDMA n: capacity (number of total users) m: number of cells to cover the area N: frequency reuse factor (# cells/cluster) B: bandwidth per user W: total available bandwidth (spectrum) B W N m n =
Problem In an FDMA system calculate frequency re use factor ? • m= 70 • W= 100 • n=10 • B=100 • N = ? cells/cluster
52 Capacity calculation—FDMA In the previous example, • m=20, • W=25 MHz, • N=4, and • B=30 KHz. 166 , 4 30 25000 4 20 = = = B W N m n
53 Capacity calculation—TDMA • n: capacity (number of total users) • m: number of cells to cover the area • N: frequency reuse factor (# cells/cluster) • B: bandwidth per user • W: total available bandwidth (spectrum) • Nu: number of time slots per carrier u N B W N m n =
54 Capacity calculation—TDMA (contd.) Assuming again, • m=20, • W=25 MHz, • N=4, • B=200 KHz, • Nu=4. 500 , 2 4 200 25000 4 20 = = = u N B W N m n
55 Capacity of CDMA n: number of users W: total bandwidth R: data rate Sr: signal to noise ratio r S R W n × =
56 Capacity per cell (CDMA) Assume: W=1.25MHz=1,250,000 Hz R=9600 bps Sr should be larger than 3dB => 2 times users S R W n r 65 2 9600 1250000 = × = × =
System architecture • A set of seven cells will be controlled by a BSC  base station controller • The terminal station located in every cell will have access to the BSC. • 7 base terminal stations will have one BSC • For every frequency reuse , 1 BSC is required. The elements that determine frequency reuse are the reuse distance and the reuse factor
Scenario • For 100 BTS we require more than 14 BSC’s • All BSC are connected to a Mobile Switching centre. • Here mobile stations are connected to BTS by wireless means • All Base stations are connected to their respective BSC’sby cables. • In modern communication , fibre optic cables are used to connect BTS
Fig: Advanced cellular mobile communication system Architecture @ 3G
Cell Planning (1/3) • The K factor and Frequency Re-Use Distance K = i2 + ij + j2 K = 22 + 2*1 + 12 K = 4 + 2 + 1 K = 7 i j 1 2 3 4 5 6 7 Frequency re-use distance is based on the cluster size K The cluster size is specified in terms of the offset of the center of a cluster from the center of the adjacent cluster D = √3K * R D = 4.58R 1 2 3 5 6 7 D R
Cell Planning (2/3) A3 A1 A2 G3 G1 G2 C3 C2 B3 B1 B2 F3 F1 F2 D3 D1 D2 E3 E1 E2 G3 G1 G2 F3 F1 F2 C3 C1 C2 A3 A1 A2 B3 B1 B2 E3 E1 E2 D3 D1 D2 7-cell reuse pattern Frequency reuse C1
Cell Planning (3/3) • Cell sectoring – Directional antennas subdivide cell into 3 or 6 sectors – Might also increase cell capacity by factor of 3 or 6 • Cell splitting – Decrease transmission power in base and mobile – Results in more and smaller cells – Reuse frequencies in non-contiguous cell groups – Example: ½ cell radius leads 4 fold capacity increase
BTS • BTS acts as an interface between the Mobile unit & BSC • BTS connects mobile units by wireless means to the BSC BTS Antenna • BTS has got an antenna usually at an elevation location. • Invariantly , Roof tops, • Small steel towerare used for erecting the BTS antenna.
Omni directional coverage= coverage in all directions • Compact power supply systems (some even chargeable batteries) are used at the base terminal stations. • BTS is usually located at the centre of the cell area for omni directional coverage. INDIAN ANALOGY
Bandwidth vs mobility • The wireless interface at BTS and wired topologytopology between BTS- BSC & BSC – MSC necessitates certain translation in protocols. • Upto the stage of BTS , air interface protocols are used. After BTS , the transmission media happen to be wired one , mostly fibre optic communication. • Hence at the BTS or BSC stage , there is a need for the translation of these protocols
Illustration – of translation requirement • In mobile communication at the mobile user’s unit the speech signal is connected into 13 kbps digitized voice. This conversion is is required to have an air interface with bandwidth efficiency. • But the backbone network through which the voice has to travel in certain applications can provide 64 kbps. Contd…
Contd… • PCM digitization is adopted in fixed telephone network which make use of these backbone network. • When mobile unit converts the analog information into 13kbps digital information , the BSC converts the same into 64 kbps information.
[ [68 68] ] Frequency reuse revisited: cluster size and reuse distance Frequency reuse revisited: cluster size and reuse distance D D frequency group A frequency group B Cluster with cluster size N Co-channel cells
[ [69 69] ] The geometry of a hexagonal cell The geometry of a hexagonal cell Unit scale is distance between neighboring cell centers. For cell radius To find the distance from the origin, , of point , convert convert axis:
[ [70 70] ] The geometry of a hexagonal cell [continue] The geometry of a hexagonal cell [continue] – So, – Using this equation to locate co-channel cells, we start from a reference cell and move i hexagons along the u-axis and then j hexagons along the v-axis. – The distance between co-channel cells in adjacent clusters is – The number of cells in a cluster, N, is hence since i and j can only take integer values. – The frequency reuse factor frequency reuse factor, Q, is defined by
Frequency Reuse Factor  Effective reuse of resources can highly enhance the system capacity  Frequency reuse factor (FRF) K defines frequency reuse pattern  With a smaller frequency reuse factor (FRF), more available bandwidth can be obtained by each cell
Previous Frequency Reuse Schemes  With the usage of FRF-1, the most user terminals (UTs) are afflicted with heavy Inter-cell interference (ICI)  Especially near the cell edge  The conventional method to figure out this problem is by increasing the FRF  mitigate the ICI efficiently  but decrease on available bandwidth  The most representative approaches improving cell-edge performance while retaining spectrum efficiency  Soft Frequency Reuse (SFR) scheme  Incremental Frequency Reuse (IFR) scheme
Soft Frequency Reuse (SFR) Scheme Incremental Frequency Reuse (IFR) Scheme Enhanced Fractional Frequency Reuse (EFFR) FREQUENCY REUSE SCHEME
Soft frequency Reuse CCU: cell-centre users CEU: cell-edge users
Soft Frequency Reuse (SFR) Scheme CCU: cell-centre users CEU: cell-edge users
Limitations of SFR  How to define the borderline to divide cell area for CCUs and CEUs is a key issue  Generally, there are more CEUs than CCUs in a cell  since the outer surface area is much larger than the inner part  CEUs have maximum one third of the entire bandwidth to utilize, which results in lower spectrum efficiency  More ICI could happen even in a low traffic-load situation, while there are still subchannels in idle and underutilized in the system  The resource allocation via the SFR scheme starts always from the first subchannel up
Incremental Frequency Reuse (IFR) Scheme (1)  The only difference between the IFR design and the classical reuse-1  Classical reuse-1: allocate resources always from the first subchannel  IFR: start dispensing resources from different points
Incremental Frequency Reuse (IFR) Scheme (2)  IFR scheme can overcome the low spectrum reuse efficiency problem and the more ICI at low loading traffic problem  IFR scheme only performs better when just fewer traffic exists in a system  When the loading factor is greater than 0.3, it is inferior to the SFR scheme
Enhanced Fractional Frequency Reuse (EFFR) (1)  Enhanced Fractional Frequency Reuse (EFFR) scheme intends to retain the advantages of the both approaches  Concept  Define 3 cell types for directly contiguous cells in a cellular system  Reserves for each cell-type a part of the whole frequency band named Primary Segment  The Primary Segments among different type cells should be orthogonal  The Primary Segment of each cell will be further divided into  reuse-3 part: cannot be reused by directly neighboring cells  reuse-1 part: is at the same time a part of the Secondary Segments belonging to the other two cell-types HYBRIDS
Enhanced Fractional Frequency Reuse (EFFR) (2)
Power Allocation and SINR Estimation  Transmission Power Allocation  Any cell-type is not allowed to use the reuse-3 subchannels dedicated to the other two cell types  The power allotted to the reuse-3 subchannels can be tripled  Signal-to-Interference-Ratio (SINR) Estimation  A cell acts on the Secondary Segment as a guest, and occupying secondary subchannels is actually reuse the primary subchannels belonging to the directly adjacent cells  Reuse on the Secondary Segment should conform to two rules:  monitor before use  resource reuse based on SINR estimation  Each cell listens on every secondary subchannel all the time  Before occupation, a cell makes SINR evaluation and chooses resources with best estimation values for reuse  If all available secondary resources are either occupied or not good enough to a link, this cell will give up scheduling resources
Worst Case Interference Worst Case Interference  S/I ~ R-4 /[2(D-R)-4 + 2(D+R)-4 + 2D-4 ]
2-frequencyreusenb-130206113258-phpapp02.pdf
2-frequencyreusenb-130206113258-phpapp02.pdf
In CDMA reuse patterns are not required. Subscriber in every cell can use the same frequency at the same time. Subscriber is discriminated from another by the assignment of a unique code to every conversation. In GSM freq. Reuse pattern of 7 is used. Frequency Reuse @ CDMA
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
Solution: Topology of Different Areas 100 100 100 20 60 100 100 60 60 20 20 20 20 20 20 60 40 20 20 Town Rural Suburb Highway
Q Q UERRIES ? ?

More Related Content

PPT
Thr cellular concept
Sajid Marwat
 
PPT
Cellular concept
vish0110
 
PPT
wireless-communication-architecture
jhcid
 
PPTX
Presentation1
tapubhai
 
PPTX
Bab 3 konsep sistem komunikasi bergerak
ampas03
 
PPT
WC PPT UNIT-II.ppt
santhyamuthu1
 
PPT
Cellular network
Mr SMAK
 
PPT
cellular-communications
jhcid
 
Thr cellular concept
Sajid Marwat
 
Cellular concept
vish0110
 
wireless-communication-architecture
jhcid
 
Presentation1
tapubhai
 
Bab 3 konsep sistem komunikasi bergerak
ampas03
 
WC PPT UNIT-II.ppt
santhyamuthu1
 
Cellular network
Mr SMAK
 
cellular-communications
jhcid
 

Similar to 2-frequencyreusenb-130206113258-phpapp02.pdf (20)

PPTX
section5.pptx
NourhanTarek23
 
PPTX
Cellular concepts
Priya Hada
 
PPT
frequency re use nb
AJAL A J
 
PPSX
Concepts of & cell sectoring and micro cell
Kundan Kumar
 
PDF
03. Chapter- Three Elements of Cellular Radio System Design1.pdf
samiulsuman
 
PDF
Wireless communication, UNIT 3, EC students, 8th sem
SURESHA V
 
PPT
fdocuments.net_1-cellular-system-design-fundamentals-chapter-3-wireless-commu...
GeoffreyAlleyne
 
PDF
20121213092949132(1)
vishalnimavat
 
PDF
Lec 2 Cell Planning Principles lecture notes
DrAdeelAkram2
 
PPTX
wireless communication chapterr 2 part 1
kingdahireditor
 
PPT
UNIT 1 wireless wide area network for wireless network
karthikprabubeec
 
PDF
Unit 1 Lect 2 Cellular Fundamentals and Frequency Reuse.pdf
SulochanaDevi2
 
PDF
Wireless network planning and operation
RAVIKIRAN ANANDE
 
PPT
lecture3PLMN stands for Public Land Mobile Network.ppt
vimalgaur7
 
PPT
lecture3.ppt cellular system topics are covered
bandiprathyu
 
PPT
power point presentation of wireless communications
ugenderacsegnitc
 
PPT
lecture3_wireless communication_intro.ppt
sadoopatola
 
PPTX
lec.2 Multiple Access.pptx
Muhammed A
 
PPTX
lec.2 Multiple Access.pptx
Muhammed A
 
PPT
Freq reuse detail.ppt
javeriazafeer
 
section5.pptx
NourhanTarek23
 
Cellular concepts
Priya Hada
 
frequency re use nb
AJAL A J
 
Concepts of & cell sectoring and micro cell
Kundan Kumar
 
03. Chapter- Three Elements of Cellular Radio System Design1.pdf
samiulsuman
 
Wireless communication, UNIT 3, EC students, 8th sem
SURESHA V
 
fdocuments.net_1-cellular-system-design-fundamentals-chapter-3-wireless-commu...
GeoffreyAlleyne
 
20121213092949132(1)
vishalnimavat
 
Lec 2 Cell Planning Principles lecture notes
DrAdeelAkram2
 
wireless communication chapterr 2 part 1
kingdahireditor
 
UNIT 1 wireless wide area network for wireless network
karthikprabubeec
 
Unit 1 Lect 2 Cellular Fundamentals and Frequency Reuse.pdf
SulochanaDevi2
 
Wireless network planning and operation
RAVIKIRAN ANANDE
 
lecture3PLMN stands for Public Land Mobile Network.ppt
vimalgaur7
 
lecture3.ppt cellular system topics are covered
bandiprathyu
 
power point presentation of wireless communications
ugenderacsegnitc
 
lecture3_wireless communication_intro.ppt
sadoopatola
 
lec.2 Multiple Access.pptx
Muhammed A
 
lec.2 Multiple Access.pptx
Muhammed A
 
Freq reuse detail.ppt
javeriazafeer
 
Ad

Recently uploaded (20)

PDF
UEFA_Carbon_Footprint_Calculator_Methology_2.0.pdf
tuchinad02
 
PDF
Abrasive, erosive and cavitation wear.pdf
nfandraden
 
PPTX
tack Data Structure with Array and Linked List Implementation, Push and Pop O...
usham61
 
PDF
Artificial Superintelligence (ASI) Alliance Vision Paper.pdf
SonaliPatil325517
 
PDF
distributed database system" (DDBS) is often used to refer to both the distri...
Hemlathadhevi Annadhurai
 
PPTX
Principal presentation for NAAC (1).pptx
GMKosgiker
 
PDF
Soil Improvement Techniques Note - Rabbi
rahmatideal000
 
PDF
Implantable Drug Delivery System_NDDS_BPHARMACY__SEM VII_PCI .pdf
SabsKhan1
 
PPTX
Module 8- Technological and Communication Skills.pptx
Ramya Nellutla
 
PPTX
Measurement Uncertainty and Measurement System analysis
jayabal subbaian
 
PDF
First part_B-Image Processing - 1 of 2).pdf
barabre
 
PDF
Accra-Kumasi Expressway - Prefeasibility Report Volume 1 of 7.11.2018.pdf
JeorgeWilsonKingson1
 
PPTX
A Brief Introduction to IoT- Smart Objects: The "Things" in IoT
KeerthanaSahadevan1
 
PDF
LOW POWER CLASS AB SI POWER AMPLIFIER FOR WIRELESS MEDICAL SENSOR NETWORK
RandyClara
 
PDF
Applications of Equal_Area_Criterion.pdf
Puja Gurav
 
PPTX
CyberSecurity Mobile and Wireless Devices
RobinRohit2
 
PPT
Chapter 1 - Introduction to Manufacturing Technology_2.ppt
garciajeremiah070
 
PPTX
Amdahl’s law is explained in the above power point presentations
sangeetha952248
 
PDF
Unit I -OPERATING SYSTEMS_SRM_KATTANKULATHUR.pptx.pdf
HarshDudhatra4
 
PPTX
Petroleum Refining & Petrochemicals.pptx
choksihimanshu
 
UEFA_Carbon_Footprint_Calculator_Methology_2.0.pdf
tuchinad02
 
Abrasive, erosive and cavitation wear.pdf
nfandraden
 
tack Data Structure with Array and Linked List Implementation, Push and Pop O...
usham61
 
Artificial Superintelligence (ASI) Alliance Vision Paper.pdf
SonaliPatil325517
 
distributed database system" (DDBS) is often used to refer to both the distri...
Hemlathadhevi Annadhurai
 
Principal presentation for NAAC (1).pptx
GMKosgiker
 
Soil Improvement Techniques Note - Rabbi
rahmatideal000
 
Implantable Drug Delivery System_NDDS_BPHARMACY__SEM VII_PCI .pdf
SabsKhan1
 
Module 8- Technological and Communication Skills.pptx
Ramya Nellutla
 
Measurement Uncertainty and Measurement System analysis
jayabal subbaian
 
First part_B-Image Processing - 1 of 2).pdf
barabre
 
Accra-Kumasi Expressway - Prefeasibility Report Volume 1 of 7.11.2018.pdf
JeorgeWilsonKingson1
 
A Brief Introduction to IoT- Smart Objects: The "Things" in IoT
KeerthanaSahadevan1
 
LOW POWER CLASS AB SI POWER AMPLIFIER FOR WIRELESS MEDICAL SENSOR NETWORK
RandyClara
 
Applications of Equal_Area_Criterion.pdf
Puja Gurav
 
CyberSecurity Mobile and Wireless Devices
RobinRohit2
 
Chapter 1 - Introduction to Manufacturing Technology_2.ppt
garciajeremiah070
 
Amdahl’s law is explained in the above power point presentations
sangeetha952248
 
Unit I -OPERATING SYSTEMS_SRM_KATTANKULATHUR.pptx.pdf
HarshDudhatra4
 
Petroleum Refining & Petrochemicals.pptx
choksihimanshu
 
Ad

2-frequencyreusenb-130206113258-phpapp02.pdf

  • 1. 3.2 FREQUENCY RE USE AJAL.A.J Assistant Professor –Dept of ECE, Federal Institute of Science And Technology (FISAT) TM MAIL: ec2reach@gmail.com The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity.
  • 2. Cellular Concept Cellular Concept  The limited capacity of the first mobile radio-telephone services was related to the spectrum used…not much sharing and a lot of bandwidth dedicated to a single call. – good coverage – interference: impossible to reuse the same frequency  The cellular concept addressed many of the shortcomings of the first mobile telephones – Frequency reuse – Wasted spectrum allocated to a single user  In 1968, Bell Labs proposed the cellular telephony concept to the FCC  It was approved and then the work began! – FCC allocated spectrum (took away TV UHF channels 70-83) in the 825-845 MHz and 870-890 MHz bands
  • 3. Cellular Concept Cellular Concept  developed by Bell Labs 1960’s-70’s  areas divided into cells  a system approach, no major technological changes  a few hundred meters in some cities, 10s km at country side  each served by base station with lower power transmitter  each gets portion of total number of channels  neighboring cells assigned different groups of channels, interference minimized  hexagon geometry cell shape
  • 4. What is a Cell? • Cell is the Basic Union in The System – defined as the area where radio coverage is given by one base station. • A cell has one or several frequencies, depending on traffic load. – Fundamental idea: Frequencies are reused, but not in neighboring cells due to interference.
  • 5. Cellular Concept  Limited number of frequencies => limited channels  Single high power antenna => limited number of users  Smaller cells => frequency reuse possible => more number of users  Base stations (BS): implement space division multiplex – Each BS covers a certain transmission area (cell) – Each BS is allocated a portion of the total number of channels available – Cluster: group of nearby BSs that together use all available channels  Mobile stations communicate only via the base station – FDMA, TDMA, CDMA may be used within a cell  As demand increases (more channels are needed) – Number of base stations is increased – Transmitter power is decreased correspondingly to avoid interference
  • 6. Cellular Concept  Cell size: – 100 m in cities to 35 km on the country side (GSM) – even less for higher frequencies – Umbrella cell: large cell that includes several smaller cells • Avoid frequent handoffs for fast moving traffic  Cell shape: – Hexagonal is useful for theoretical analysis – Practical footprint (radio coverage area) is amorphous  BS placement: – Center-excited cell: BS near center of cell • omni-directional antenna – Edge-excited cell: BSs on three of the six cell vertices • sectored directional antennas
  • 7. Cellular Concept  Advantages: – higher capacity, higher number of users – less transmission power needed – more robust, decentralized – base station deals with interference, transmission area etc. locally  Problems: – fixed network needed for the base stations – handover (changing from one cell to another) necessary – interference with other cells: co-channel, adjacent-channel  Important Issues: – Cell sizing – Frequency reuse planning – Channel allocation strategies Bottom line: Attempt to maximize availability of channels in an area
  • 8. • Cells labeled with the same letter use the same group of channels. • Cell Cluster: group of N cells using complete set of available channels • Many base stations, lower power, and shorter towers • Small coverage areas called “cells” • Each cell allocated a % of the total number of available channels • Nearby (adjacent) cells assigned different channel groups – to prevent interference between neighboring base stations and mobile users
  • 9. Cell characteristics • Implements space division multiplex: base station covers a certain transmission area (cell) • Mobile stations 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, transmission area etc. locally • Problems: – fixed network needed for the base stations – handover (changing from one cell to another) necessary – interference with other cells • Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM) - even less for higher frequencies
  • 10. Shape of Cells  Square  Width d cell has four neighbors at distance d and four at distance d  Better if all adjacent antennas equidistant  Simplifies choosing and switching to new antenna  Hexagon  Provides equidistant antennas  Radius defined as radius of circum-circle  Distance from center to vertex equals length of side  Distance between centers of cells radius R is R  Not always precise hexagons  Topographical limitations  Local signal propagation conditions  Location of antennas 2 3
  • 13. Cellular Network Architecture Cellular Network Architecture Mobile Switching Center Public Telephone network and Internet Mobile Switching Center Wired network
  • 14. Frequency Reuse Frequency Reuse  Adjacent cells assigned different frequencies to avoid interference or crosstalk  Objective is to reuse frequency in nearby cells – 10 to 50 frequencies assigned to each cell – transmission power controlled to limit power at that frequency escaping to adjacent cells – the issue is to determine how many cells must intervene between two cells using the same frequency
  • 15. Frequency Reuse Frequency Reuse  each cell allocated a group k channels – a cluster has N cells with unique and disjoint channel  groups, N typically 4, 7, 12  total number of duplex channels S = kN  Cluster repeated M times in a system  Total number of channels that can be used (capacity) – C = MkN = MS  Smaller cells  higher M  higher C + Channel reuse  higher capacity + Lower power requirements for mobiles – Additional base stations required – More frequent handoffs – Greater chance of ‘hot spots’
  • 18. Frequency planning • Frequency reuse only with a certain distance between the base stations • Standard model using 7 frequencies: f4 f5 f1 f3 f2 f6 f7 f3 f2 f4 f5 f1
  • 19. FREQUENCY REUSE • The allotted frequency spectrum for mobile communication • during the 1 G is in the range of  (800- 900 ) Mhz • but ,Using this small bandwidth, thousands of subscribers need to be served over a large area. • To manage this situation, a technique called ‘’frequency reuse ‘’ is adopted.
  • 22. Cellular Networks • Propagation models represent cell as a circular area • Approximate cell coverage with a hexagon - allows easier • analysis • Frequency assignment of F MHz for the system • The multiple access techniques translates F to T traffic channels • Cluster of cells K = group of adjacent cells which use all of the systems frequency assignment
  • 24. Frequency reuse concept Frequency reuse concept ALPHABETICAL REPRESENTATION
  • 26. END Result of Wrong implementation
  • 31. 31 Freq reuse Advantage Freq reuse: Several cells in coverage area that use same set of frequencies Cochannel cells: Those cells using same freqs Cochannel interference: The mobile in cell A also gets signals from other Co channel cells Cluster1 Cluster2 Cluster3
  • 32. Cellular Concepts In this case N=19 (i=3, j=2)
  • 33. Frequency Reuse  Power of base transceiver controlled  Allow communications within cell on given frequency  Limit escaping power to adjacent cells  Allow re-use of frequencies in nearby cells  Use same frequency for multiple conversations  10 – 50 frequencies per cell  E.g.  The pattern consists of N cells  K total number of frequencies used in systems  Each cell has K/N frequencies  Advanced Mobile Phone Service (AMPS) K=395, N=7 giving 57 frequencies per cell on average
  • 34. Characterizing Frequency Reuse  D = minimum distance between centers of cells that use the same band of frequencies (called cochannels)  R = radius of a cell  d = distance between centers of adjacent cells (d = R)  N = number of cells in repetitious pattern  Reuse factor  Each cell in pattern uses unique band of frequencies  Hexagonal cell pattern, following values of N possible  N = I2 + J2 + (I x J), I, J = 0, 1, 2, 3, …  Possible values of N are 1, 3, 4, 7, 9, 12, 13, 16, 19, 21, …  D/R=  D/d = N 3 N
  • 37. Example of frequency reuse factor or pattern 1/4 The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to some books) where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).
  • 38. 38 Reuse Ratio : q N q R D 3 = = where: D: Distance between the centres of cells R: Radius of the cell q: Reuse ratio N: Cluster size Assuming hexagonal shape cells of equal size
  • 39. 39 Example R N D 3 = For N = 7 and R 5 km 5 7 3 × × = D The minimum distance at which the same frequency can be reused is approximately 4.6 times R, which is in this case 22.91 km 91 . 22 5 583 . 4 = × = D
  • 41. N=7, 32 cells, R=1.6km, in total 336 channels
  • 42. So what is FREQUENCY REUSE ? • After allotting the available total bandwidth among a set of cells , the same frequency band will be used in another set of cells . • This kind of reuse can be adopted until the entire area to be covered is exhausted . • Note • Seven cells in a set is the most frequently used configuration.this configuration usually operates with a cell diameter of 1- 3 km range
  • 43. Cellular architecture One low power transmitter per cell Frequency reuse–limited spectrum Cell splitting to increase capacity A B Reuse distance: minimum distance between two cells using same channel for satisfactory signal to noise ratio Measured in # of cells in between
  • 44. Reuse distance 2 – reuse pattern One frequency can be (re)used in all cells of the same color
  • 45. Reuse distance 3 – reuse pattern
  • 47. 50 Capacity calculation—FDMA n: capacity (number of total users) m: number of cells to cover the area N: frequency reuse factor (# cells/cluster) B: bandwidth per user W: total available bandwidth (spectrum) B W N m n =
  • 48. Problem In an FDMA system calculate frequency re use factor ? • m= 70 • W= 100 • n=10 • B=100 • N = ? cells/cluster
  • 49. 52 Capacity calculation—FDMA In the previous example, • m=20, • W=25 MHz, • N=4, and • B=30 KHz. 166 , 4 30 25000 4 20 = = = B W N m n
  • 50. 53 Capacity calculation—TDMA • n: capacity (number of total users) • m: number of cells to cover the area • N: frequency reuse factor (# cells/cluster) • B: bandwidth per user • W: total available bandwidth (spectrum) • Nu: number of time slots per carrier u N B W N m n =
  • 51. 54 Capacity calculation—TDMA (contd.) Assuming again, • m=20, • W=25 MHz, • N=4, • B=200 KHz, • Nu=4. 500 , 2 4 200 25000 4 20 = = = u N B W N m n
  • 52. 55 Capacity of CDMA n: number of users W: total bandwidth R: data rate Sr: signal to noise ratio r S R W n × =
  • 53. 56 Capacity per cell (CDMA) Assume: W=1.25MHz=1,250,000 Hz R=9600 bps Sr should be larger than 3dB => 2 times users S R W n r 65 2 9600 1250000 = × = × =
  • 54. System architecture • A set of seven cells will be controlled by a BSC  base station controller • The terminal station located in every cell will have access to the BSC. • 7 base terminal stations will have one BSC • For every frequency reuse , 1 BSC is required. The elements that determine frequency reuse are the reuse distance and the reuse factor
  • 55. Scenario • For 100 BTS we require more than 14 BSC’s • All BSC are connected to a Mobile Switching centre. • Here mobile stations are connected to BTS by wireless means • All Base stations are connected to their respective BSC’sby cables. • In modern communication , fibre optic cables are used to connect BTS
  • 56. Fig: Advanced cellular mobile communication system Architecture @ 3G
  • 57. Cell Planning (1/3) • The K factor and Frequency Re-Use Distance K = i2 + ij + j2 K = 22 + 2*1 + 12 K = 4 + 2 + 1 K = 7 i j 1 2 3 4 5 6 7 Frequency re-use distance is based on the cluster size K The cluster size is specified in terms of the offset of the center of a cluster from the center of the adjacent cluster D = √3K * R D = 4.58R 1 2 3 5 6 7 D R
  • 59. Cell Planning (3/3) • Cell sectoring – Directional antennas subdivide cell into 3 or 6 sectors – Might also increase cell capacity by factor of 3 or 6 • Cell splitting – Decrease transmission power in base and mobile – Results in more and smaller cells – Reuse frequencies in non-contiguous cell groups – Example: ½ cell radius leads 4 fold capacity increase
  • 60. BTS • BTS acts as an interface between the Mobile unit & BSC • BTS connects mobile units by wireless means to the BSC BTS Antenna • BTS has got an antenna usually at an elevation location. • Invariantly , Roof tops, • Small steel towerare used for erecting the BTS antenna.
  • 61. Omni directional coverage= coverage in all directions • Compact power supply systems (some even chargeable batteries) are used at the base terminal stations. • BTS is usually located at the centre of the cell area for omni directional coverage. INDIAN ANALOGY
  • 62. Bandwidth vs mobility • The wireless interface at BTS and wired topologytopology between BTS- BSC & BSC – MSC necessitates certain translation in protocols. • Upto the stage of BTS , air interface protocols are used. After BTS , the transmission media happen to be wired one , mostly fibre optic communication. • Hence at the BTS or BSC stage , there is a need for the translation of these protocols
  • 63. Illustration – of translation requirement • In mobile communication at the mobile user’s unit the speech signal is connected into 13 kbps digitized voice. This conversion is is required to have an air interface with bandwidth efficiency. • But the backbone network through which the voice has to travel in certain applications can provide 64 kbps. Contd…
  • 64. Contd… • PCM digitization is adopted in fixed telephone network which make use of these backbone network. • When mobile unit converts the analog information into 13kbps digital information , the BSC converts the same into 64 kbps information.
  • 65. [ [68 68] ] Frequency reuse revisited: cluster size and reuse distance Frequency reuse revisited: cluster size and reuse distance D D frequency group A frequency group B Cluster with cluster size N Co-channel cells
  • 66. [ [69 69] ] The geometry of a hexagonal cell The geometry of a hexagonal cell Unit scale is distance between neighboring cell centers. For cell radius To find the distance from the origin, , of point , convert convert axis:
  • 67. [ [70 70] ] The geometry of a hexagonal cell [continue] The geometry of a hexagonal cell [continue] – So, – Using this equation to locate co-channel cells, we start from a reference cell and move i hexagons along the u-axis and then j hexagons along the v-axis. – The distance between co-channel cells in adjacent clusters is – The number of cells in a cluster, N, is hence since i and j can only take integer values. – The frequency reuse factor frequency reuse factor, Q, is defined by
  • 68. Frequency Reuse Factor  Effective reuse of resources can highly enhance the system capacity  Frequency reuse factor (FRF) K defines frequency reuse pattern  With a smaller frequency reuse factor (FRF), more available bandwidth can be obtained by each cell
  • 69. Previous Frequency Reuse Schemes  With the usage of FRF-1, the most user terminals (UTs) are afflicted with heavy Inter-cell interference (ICI)  Especially near the cell edge  The conventional method to figure out this problem is by increasing the FRF  mitigate the ICI efficiently  but decrease on available bandwidth  The most representative approaches improving cell-edge performance while retaining spectrum efficiency  Soft Frequency Reuse (SFR) scheme  Incremental Frequency Reuse (IFR) scheme
  • 70. Soft Frequency Reuse (SFR) Scheme Incremental Frequency Reuse (IFR) Scheme Enhanced Fractional Frequency Reuse (EFFR) FREQUENCY REUSE SCHEME
  • 71. Soft frequency Reuse CCU: cell-centre users CEU: cell-edge users
  • 72. Soft Frequency Reuse (SFR) Scheme CCU: cell-centre users CEU: cell-edge users
  • 73. Limitations of SFR  How to define the borderline to divide cell area for CCUs and CEUs is a key issue  Generally, there are more CEUs than CCUs in a cell  since the outer surface area is much larger than the inner part  CEUs have maximum one third of the entire bandwidth to utilize, which results in lower spectrum efficiency  More ICI could happen even in a low traffic-load situation, while there are still subchannels in idle and underutilized in the system  The resource allocation via the SFR scheme starts always from the first subchannel up
  • 74. Incremental Frequency Reuse (IFR) Scheme (1)  The only difference between the IFR design and the classical reuse-1  Classical reuse-1: allocate resources always from the first subchannel  IFR: start dispensing resources from different points
  • 75. Incremental Frequency Reuse (IFR) Scheme (2)  IFR scheme can overcome the low spectrum reuse efficiency problem and the more ICI at low loading traffic problem  IFR scheme only performs better when just fewer traffic exists in a system  When the loading factor is greater than 0.3, it is inferior to the SFR scheme
  • 76. Enhanced Fractional Frequency Reuse (EFFR) (1)  Enhanced Fractional Frequency Reuse (EFFR) scheme intends to retain the advantages of the both approaches  Concept  Define 3 cell types for directly contiguous cells in a cellular system  Reserves for each cell-type a part of the whole frequency band named Primary Segment  The Primary Segments among different type cells should be orthogonal  The Primary Segment of each cell will be further divided into  reuse-3 part: cannot be reused by directly neighboring cells  reuse-1 part: is at the same time a part of the Secondary Segments belonging to the other two cell-types HYBRIDS
  • 78. Power Allocation and SINR Estimation  Transmission Power Allocation  Any cell-type is not allowed to use the reuse-3 subchannels dedicated to the other two cell types  The power allotted to the reuse-3 subchannels can be tripled  Signal-to-Interference-Ratio (SINR) Estimation  A cell acts on the Secondary Segment as a guest, and occupying secondary subchannels is actually reuse the primary subchannels belonging to the directly adjacent cells  Reuse on the Secondary Segment should conform to two rules:  monitor before use  resource reuse based on SINR estimation  Each cell listens on every secondary subchannel all the time  Before occupation, a cell makes SINR evaluation and chooses resources with best estimation values for reuse  If all available secondary resources are either occupied or not good enough to a link, this cell will give up scheduling resources
  • 79. Worst Case Interference Worst Case Interference  S/I ~ R-4 /[2(D-R)-4 + 2(D+R)-4 + 2D-4 ]
  • 82. In CDMA reuse patterns are not required. Subscriber in every cell can use the same frequency at the same time. Subscriber is discriminated from another by the assignment of a unique code to every conversation. In GSM freq. Reuse pattern of 7 is used. Frequency Reuse @ CDMA
  • 83. 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
  • 84. Solution: Topology of Different Areas 100 100 100 20 60 100 100 60 60 20 20 20 20 20 20 60 40 20 20 Town Rural Suburb Highway