how to INCREASING CELLULAR CAPACITY

Cell Seplitting : subdividing a congested cell into smaller cells. Sectoring ; Directional AAntennas to control the interference and frequncy reuse. Coverage zone; Distributing the coverage of a cell and extends the cell boundary to hard-to-reach place

why to INCREASING CELLULAR CAPACITY

Cell Seplitting : subdividing a congested cell into smaller cells. Sectoring ; Directional AAntennas to control the interference and frequncy reuse. Coverage zone; Distributing the coverage of a cell and extends the cell boundary to hard-to-reach place

explane Umbrella Cells

Use different antenna hights and transmit power level to provide large and small coverage multiple antenna and transmit can be co-located at signal location if necessary (saves on obtaining new tower licences) laser cell ;high speed traffic fewer handoffs small cell speed traffic Example areas interstate Highway passing through urban Center office park or near by shopping mall center.

Imporing Capacity in Cellular System

Cell Seplitting : subdividing a congested cell into smaller cells.
Sectoring ; Directional Antennas to control the interference and frequncy reuse.
Coverage zone; Distributing the coverage of a cell and extends the cell boundary to hard-to-reach place

Why cell splitting and cell sectoring

As users increase channel capacity decreases.
Technique are needed to provide extra channels.
Cell Splitting and cell Sectoring increase the capacity.

Cell Splitting

The process of sub diving a congested cell into smaller cell.
Each with its own base station and a corresponding reduction in antenna height.
Leads to increase in capacity.

Limitations

Handoff are more frequent.
Channel assignment become difficult.
All cells are split simultaneously so special care have to be taken for proper allocation of problem

Cell sectoring

The co-Channel interference in a cellular system may be reduced by replacing a single Omni-directional antennas radiating with in specified sectors.
A Cell is normally partitioned in three 120 degree sectors or six 60 degree sectors.
A given cell will receive interference and transmit with only a fraction of the available co-Channel cells.
In the sectoring scheme the Co-Channel interference is reduced and thus system capacity is improved.
Co-Channel interference is reduce because the number of interferer gets reduced.

Advantage

It improve S/I ratio.
It reduces interference which increase system capacity.
It enables to reduce the cluster size and provides additional freedom in assigning Channels.

Limitations

Increased number of antennas at each base stations.
Sectoring reduces the coverage area of a particular group of Channel the number of handoffs increases as well.

Umbrella Cells

Use different antenna hights and transmit power level to provide large and small coverage
multiple antenna and transmit can be co-located at signal location if necessary (saves on obtaining new tower licences)
laser cell ;high speed traffic fewer handoffs
small cell speed traffic
Example areas interstate Highway passing through urban Center office park or near by shopping mall center.

Multiple Access

To transmit a signal from one user to another, the information must be sent over a channel that is possibly shared with many other users simultaneously transmitting their own channels

TDMA – Time Division Multiple Access
FDMA – Frequency Division Multiple Access
CDMA – Code Division Multiple Access

WHAT IS TDMA ?

Time-division multiple access (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.
In other words each user uses the whole channel BW for a fraction of time.
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 a type of time-division multiplexing (TDM), with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters.

Advantages of TDMA

Permits a flexible bit rate
No frequency guard band required
Shares single carrier freq. with multiple users
Occupy the entire system BW
Slots can be assigned on demand
Extended battery life
BW supplied on demand
Less power control needed

Disadvantages to using TDMA

Propagation time for a signal from a MS to a BS varies with its distance to the BS
Demands high peak power in transmit mode (uplink) that shortens the battery life
Multipath distortion
Equalization necessary for high data rates

WHAT IS FDMA ?

In this BW of the available spectrum is divided into separate channels, each individual channel frequency being allocated to a different user
FDMA allows multiple users to send data through a single communication channel by dividing the bandwidth of the channel into separate non overlapping frequency channels and allocating each sub-channel to a separate user.
It is used in satellite communication systems and telephone trunk lines

Advantages of FDMA

Individual Channel to individual user
If channel is not in use, it sits idle
Channel bandwidth is relatively narrow (30kHz)
Best suited for analog links
Fairly efficient when the number of stations is small and the traffic is uniformly constant
No need for network timing
No equalization required
No framing or synchronization bits needed
Simplest system

Disadvantages to using FDMA

Requires high performance RF filters to minimize adjacent channel interference
Maximum bit rate per channel is fixed
Handles only voice transmission. It can’t manage other form of data.
FDMA is a wasteful of BW

CDMA

Decades ago, the military organization of the world adopted the CDMA scheme to meet the need for highly secure communication.
CDMA uses a spreading code to mix up the data & spread the BW.
CDMA allows every one to transmit at the same time.
Each user’s signal is spread over the entire BW by a unique spreading code.
At the receiver the unique spreading code is used to recover the signal.
In CDMA each couple talk at the same time(in a room full of people), but they all use a different language that does not cause a real problem

Advantages of CDMA

Many users of CDMA use the same frequency, TDD or FDD may be used
Multipath fading may be substantially reduced because of large signal bandwidth
No absolute limit on the number of users
Easy addition of more users
Impossible for hackers to decipher the code sent
Better signal quality

Disadvantages to using CDMA

As the number of users increases, the overall quality of service decreases
Self-jamming
Near- Far- problem arises
Complex Hardware required
High BW is required
Synchronization Problem

Comparison b/w FDMA, TDMA & CDMA

Spread Spectrum

It is a technique that increases signal BW beyond the minimum required for data communication.
Principle of SS:
The signal occupies a BW much larger than the required.
SS modulation is done using a spreading code.
De-spreading at the receiver is done by correlating the received signal with a synchronized copy of the spreading code.

W-CDMA/UMTS

Wideband CDMA is a 3G wireless standard which allows use of both voice & data and offers data speeds of up to 384 Kbps.
WCDMA is also called UMTS (Universal Mobile Telecommunications System) and the two terms have become interchangeable.
UMTS is a third generation mobile cellular system for networks based on the GSM standard, developed and maintained by the 3GPP (3rd Generation Partnership Project)
W-CDMA uses the DS-CDMA channel access method with a pair of 5 MHz wide channels.

WCDMA

The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the base-to-mobile (uplink) and 2110–2200 MHz for the mobile-to-base (downlink).

In the US, 1710–1755 MHz and 2110–2155 MHz are used instead, as the 1900 MHz band was already used.

Architecture of UMTS Network

As shown in the figure there are three main components in UMTS network architecture.
User Equipments is composed of Mobile Equipment (ME) and USIM.
Radio Access Network is composed of NodeB and RNC.
Core Network is composed of circuit switched and packet switched functional modules.
For Circuit switched (CS) operations MSC and GMSC along with database modules such as VLR, HLR will be available.
For packet switched (PS) operations SGSN and GGSN will serve the purpose.
GMSC will be connected with PSTN/ISDN in CS case.
GGSN is connected with Packet data Network (PDN) for PS case.

HSPA

High Speed Packet Access (HSPA) is an combination of two mobile protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing 3G mobile telecommunication networks using the WCDMA protocols.
The system provides an enhancement on the basic 3G WCDMA / UMTS cellular system, providing much greater data transfer rates.
The system provides many advantages for users over the original UMTS system

The two technologies are summarised below

HSDPA - High Speed Downlink Packet Access: HSDPA provides packet data support, reduced delays, and a peak raw data rate (i.e. over the air) of 14 Mbps. It also provides around three times the capacity of the 3G UMTS technology defined in Release 99 of the 3GPP UMTS standard.

HSUPA - High Speed Uplink Packet Access: HSUPA provides improved uplink packet support, reduced delays and a peak raw data rate of 5.74 Mbps. This results in a capacity increase of around twice that provided by the Release 99 services.

LTE (Long Term Evolution)

In telecommunications, Long-Term Evolution (LTE) is a standard for wireless broadband communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA technologies.

LTE Architecture

The high-level network architecture of LTE is comprised of following three main components:
The User Equipment (UE).
The Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).
The Evolved Packet Core (EPC).
The E-UTRAN handles the radio communications between the mobile and the evolved packet core and just has one component, the evolved base stations, called eNodeB or eNB.
Each eNB is a base station that controls the mobiles in one or more cells. The base station that is communicating with a mobile is known as its serving eNB.
LTE Mobile communicates with just one base station and one cell at a time and there are following two main functions supported by eNB:
The eBN sends and receives radio transmissions to all the mobiles using the analogue and digital signal processing functions of the LTE air interface.
The eNB controls the low-level operation of all its mobiles, by sending them signalling messages such as handover commands.
EPC (Evolved Packet Core) contains information about all the network operator's subscribers, communicates with the outside world, forward the data b/w base station & gateways

GPRS

General Packet Radio Service (GPRS) is a new bearer service for GSM that greatly improves and simplifies wireless access to packet data networks
GPRS is a step towards 3G & is often referred to as 2.5G

👉Benefits of GPRS

New Data Services
High Speed (Data Rate 14.4 – 115 kbps)
Efficient use of radio bandwidth
Circuit switching & Packet Switching can be used in parallel
Constant connectivity

👉Salient Features of GPRS

Important step on the path to 3G
GPRS is an overlay network over the GSM
Provides Data Packet delivery service
Billing based on volume of data transferred

👉GPRS Terminals or Classes

Class A

MS supports simultaneous operation of GPRS and GSM services

Class B

MS able to register with the n/w for both GPRS & GSM services simultaneously. It can only use one of the two services at a given time.

Class C

MS can be active in either GPRS or GSM mode, but not at the same time

👉GPRS Network Elements

GPRS Architecture is same as GSM except few hardware modifications :

GPRS includes GSNs

SGSN : Serving GPRS Support Node
GGSN : Gateway GPRS Support Node

GPRS Register

👉GPRS Architecture

👉SGSN – Serving GPRS Support Node

Delivers data packets to mobile stations & vice-versa
Detect and Register new GPRS MS in its serving area
Packet Routing, Transfer & Mobility Management
Authentication, Maintaining user profiles
Its location register stores location info. & user profiles

👉GGSN – Gateway GPRS Support Node

Interfaces GPRS backbone network & external packet data networks
Converts the GPRS packets from SGSN to the PDP format
Converts PDP addresses to GSM addresses of the destination user
Stores the current SGSN address and profile of the user in its location register
Performs authentication
Many-to- many relations among SGSNs & GGSNs

👉Applications of GPRS

Web browsing
Corporate & Internet Email
Vehicle Positioning
Remote LAN Access
Home Automation
Document Sharing/Collaborative working

👉Comparison of GSM & GPRS

👉Enhanced Data Rate for GSM Evolution (EDGE)

EDGE is a technology that gives GSM Networks the capacity to handle services for 3G.
EDGE was developed to enable the transmission of large amounts of data at peak rates of up to 472kbps.
Users can experience average speeds of 80 kbps to 130 kbps.
EDGE devices are backwards compatible with GPRS and will be able to operate on GPRS networks where EDGE has not yet been deployed.

👉EDGE

In 1st G AMPS(Advanced Mobile system ) developed in U.S in 1983
In 2ndG there was introduction of CDMA,TDMA and GSM
Between 2nd and 2.5thG of GPRS
Between 2.5th and 3thG there was an introduction EDGE technology
EDGE- Enhanced Data rate for GSM Evolution
Developed to increase the BW of GPRS technology
EDGE increases the BW from 144 Kbps to 384 Kbps

GSM

Global System for Mobile (GSM)
GSM is a 2G cellular standard developed to provide voice & data services using digital modulation.
Commonly used frequency bands are 900MHz & 1800 MHz
Uplink 890-915 MHz
Downlink 935-960 MHz

👉GSM Services

Tele-services: provide mobile telephony & emergency calling
Bearer services or data services: includes SMS, voice mailbox
Supplementary services: Call waiting, call hold, call barring, call forwarding, multi party call conferencing

👉GSM Network Architecture

GSM architecture is mainly divided into three

Subsystems

Base Station Subsystem (BSS)
Network & Switching Subsystem (NSS)
Operations & Support Subsystem (OSS)

Mobile Station (MS)

Mobile Equipment (ME)
Subscriber Identity Module (SIM)

Base Station Subsystem

Base Transceiver Station (BTS)
Base Station Controller (BSC)
Network Switching Subsystem (NSS)

MSC

HLR

VLR

AUC

EIR

👉Mobile Station

ME is a portable handheld device uniquely identified by IMEI
SIM contains the IMSI, It allows the users to send & receive calls

👉Base Station Subsystem

BSS handles traffic and signalling between a mobile phone and the network switching subsystem.
BTS, contains the equipment for transmitting and receiving radio signals (TRX unit). It encodes, encrypts, multiplexes, modulates & feeds the RF signal to antenna. It communicates with MS and BSC

👉Base Station Controller

Typically a BSC has tens or even hundreds of BTSs under its control.
The BSC handles allocation of radio channels, receives measurements from the mobile phones, and controls handovers from BTS to BTS

👉Network Switching Subsystem (NSS

NSS carries out telephone exchange and mobility management functions (where the subscribers are, allowing calls)
MSC is responsible for routing voice calls and SMS as well as other services (such as conference calls, FAX, and circuit-switched data). The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging
HLR: Stores information about each subscriber that belongs to its MSC. As soon as the mobile subscriber leaves its current local area, the information in HLR is updated.
VLR: Temporary database which updates whenever new MS enters its area, by HLR database. It assigns a TMSI to each MS entering the VLR area which keep on changing. It also controls those mobiles roaming in its area
Authentication center (AuC): Contains the algorithims for authentication as well as the keys for encryption. It also protects network operator from fraud
Equipment identity register (EIR): Stores all devices identification registered for this network. It handles real-time requests to check the IMEI of mobile devices that come from the switching equipment (MSC)

👉Operation & Maintenance Centre

They support management functions such as network inventory, network configuration and fault management, Storage of system software & data

Comparison b/w GSM & CDMA system