This document discusses handoff management in wireless networks. It covers handoff basics, detection, assignment and examples of handoff in GSM networks. It also discusses handoff requirements and goals such as latency, scalability and quality of service. Advanced issues covered include handoff failure, different types of radio link transfers during handoff, and differences between hard and soft handoff.
Introduction to basics of wireless networks such as
• Radio waves & wireless signal encoding techniques
• Wireless networking issues & constraints
• Wireless internetworking devices
Universal mobile telecommunication System (UMTS) is actually the third generation mobile, which uses WCDMA. The Dream was that 2G and 2.5G systems are incompatible around the world.
-Worldwide devices need to have multiple technologies inside of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted around the world.
-One device should be able to work anywhere.
Increased data rate.
- Maximum 2048Kbps
UMTS is developed by 3GPP (3 Generation Partnership Project) a joint venture of several organization
3G UMTS is a third-generation (3G): broadband, packet-based transmission of text, digitized voice, video, multimedia at data rates up to 2 Mbps
Also referred to as wideband code division multiple access(WCDMA)
Allows many more applications to be introduce to a worldwide
Also provide new services like alternative billing methods or calling plans.
The higher bandwidth also enables video conferencing or IPTV.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities.
Introduction to Cellular Mobile System,
Performance criteria,
uniqueness of mobile radio environment,
operation of cellular systems,
Hexagonal shaped cells,
Analog Cellular systems.
Digital Cellular systems
Introduction to basics of wireless networks such as
• Radio waves & wireless signal encoding techniques
• Wireless networking issues & constraints
• Wireless internetworking devices
Universal mobile telecommunication System (UMTS) is actually the third generation mobile, which uses WCDMA. The Dream was that 2G and 2.5G systems are incompatible around the world.
-Worldwide devices need to have multiple technologies inside of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted around the world.
-One device should be able to work anywhere.
Increased data rate.
- Maximum 2048Kbps
UMTS is developed by 3GPP (3 Generation Partnership Project) a joint venture of several organization
3G UMTS is a third-generation (3G): broadband, packet-based transmission of text, digitized voice, video, multimedia at data rates up to 2 Mbps
Also referred to as wideband code division multiple access(WCDMA)
Allows many more applications to be introduce to a worldwide
Also provide new services like alternative billing methods or calling plans.
The higher bandwidth also enables video conferencing or IPTV.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities.
Introduction to Cellular Mobile System,
Performance criteria,
uniqueness of mobile radio environment,
operation of cellular systems,
Hexagonal shaped cells,
Analog Cellular systems.
Digital Cellular systems
GENERAL DESCRIPTION OF THE PROBLEM , CONCEPT OF FREQUENCY CHANNELS, CO-CHANNEL iNTERFERENCE REDUCTION FACTOR , DESIRED C/I FROM A NORMAL CASE IN A OMNI DIRECTIONAL ANTENNA SYSTEM , CELL SPLITTING , CONSIDERATION OF THE COMPONENTS OF CELLULAR SYSTEM.
Product Guide to Converged Networks and Data Center Switching. A comprehensive offer by Alcatel-Lucent Enterprise.
Para más información visite: https://www.ez-tech.com.mx/Alcatel-Lucent/
GENERAL DESCRIPTION OF THE PROBLEM , CONCEPT OF FREQUENCY CHANNELS, CO-CHANNEL iNTERFERENCE REDUCTION FACTOR , DESIRED C/I FROM A NORMAL CASE IN A OMNI DIRECTIONAL ANTENNA SYSTEM , CELL SPLITTING , CONSIDERATION OF THE COMPONENTS OF CELLULAR SYSTEM.
Product Guide to Converged Networks and Data Center Switching. A comprehensive offer by Alcatel-Lucent Enterprise.
Para más información visite: https://www.ez-tech.com.mx/Alcatel-Lucent/
Wap based seamless roaming in urban environment with wise handoff techniqueijujournal
This paper highlights the studies performed to arrive at a novel handoff scheme in achieving uninterrupted connectivity. Every wireless communication user prefers seamless mobility and uninterrupted communication. Achieving this scenario is quite challenging both technologically and economically. Few of the reasons are geographical and man made constraints. Dynamic changes in environment and ever changing geographical landscape also pose serious difficulties to engineers involved in design of wireless systems. The following schemes have been suggested in an effort to improve Q.o.S of wireless mobile communication scenarios.
REDUCING HANDOVER DELAY BY PRESELECTIVE SCANNING USING GPS ijdpsjournal
IEEE 802.11 based mobile communication towers is used very much in many personal and industrial purposes as it provides a continuous connectivity to Mobile Nodes (MNs) and allows them to change their attachment point from old Access Point (A)P to new AP while needed. But one main problem of continuous connectivity is handover latency which consists of scanning, authentication and re-association phases. Scanning is the most time consuming part of handover process. In this paper, we introduce a prescanning mechanism using Global Positioning System (GPS) to reduce handover delay. In our method, scanning is completed almost before actual handover starts. From the simulation results, it can be seen that our proposed mechanism reduces handover delay by a great deal.
Performance of symmetric and asymmetric links in wireless networks IJECEIAES
Wireless networks are designed to provide the enabling infrastructure for emerging technological advancements. The main characteristics of wireless networks are: Mobility, power constraints, high packet loss, and lower bandwidth. Nodes’ mobility is a crucial consideration for wireless networks, as nodes are moving all the time, and this may result in loss of connectivity in the network. The goal of this work is to explore the effect of replacing the generally held assumption of symmetric radii for wireless networks with asymmetric radii. This replacement may have a direct impact on the connectivity, throughput, and collision avoidance mechanism of mobile networks. The proposed replacement may also impact other mobile protocol’s functionality. In this work, we are mainly concerned with building and maintaining fully connected wireless network with the asymmetric assumption. For this extent, we propose to study the effect of the asymmetric links assumption on the network performance using extensive simulation experiments. Extensive simulation experiments were performed to measure the impact of these parameters. Finally, a resource allocation scheme for wireless networks is proposed for the dual rate scenario. The performance of the proposed framework is evaluated using simulation.
Enhanced Seamless Handoff Using Multiple Access Points in Wireless Local Area...IJERA Editor
The Mobility in wireless cellular communication systems is its backbone so as to enhance the quality of service and maintain the continuous service. Handoff is an important task in maintaining the continuity of call in cellular systems and its failure can result in ongoing call termination. In cellular mobile networks, the coverage region is divided into smaller cells in order to achieve high system capacity. Each cell has a Base-Station (BS), which provides the service to the Mobile Terminals (MTs), i.e. users equipped with phones, within its region. Before a mobile user can communicate with other user(s) in the network, a group of the frequency bands or channels should usually be assigned. The MTs is free to move across cells. When the mobile user crossing a cell boundary or by deterioration in quality of the signal in the current channel, handoff process is initiated. The scope of this project is to design 802.11 handoff schemes to solve the handoff problems in closely-spaced WLANs.The major problem in multiple WLANs are so many users trying to use same access point(AP), and interferences from nearby WLAN. The better hand off scheme based on signal strength and velocity of the nodes is proposed. The simulation results show that the proposed handoff scheme significantly reduces packet losses compared with existing handoff schemes.
Enhanced Seamless Handoff Using Multiple Access Points in Wireless Local Area...IJERA Editor
The Mobility in wireless cellular communication systems is its backbone so as to enhance the quality of service and maintain the continuous service. Handoff is an important task in maintaining the continuity of call in cellular systems and its failure can result in ongoing call termination. In cellular mobile networks, the coverage region is divided into smaller cells in order to achieve high system capacity. Each cell has a Base-Station (BS), which provides the service to the Mobile Terminals (MTs), i.e. users equipped with phones, within its region. Before a mobile user can communicate with other user(s) in the network, a group of the frequency bands or channels should usually be assigned. The MTs is free to move across cells. When the mobile user crossing a cell boundary or by deterioration in quality of the signal in the current channel, handoff process is initiated. The scope of this project is to design 802.11 handoff schemes to solve the handoff problems in closely-spaced WLANs.The major problem in multiple WLANs are so many users trying to use same access point(AP), and interferences from nearby WLAN. The better hand off scheme based on signal strength and velocity of the nodes is proposed. The simulation results show that the proposed handoff scheme significantly reduces packet losses compared with existing handoff schemes.
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology.
Improved handoff mechanism for infiltrating user equipments in composite netw...IJECEIAES
The wireless technology and communication plays a vital role in our daily life. The end users are expecting more Quality of Experience (QOE) rather than the Quality of Service (QOS). In order to provide full signal coverage the entire cellular network coverage is divided in to small cells called as femtocells, those femtocells are covered with femtocell antennas which are very small in size compared with regular antennas. With these femtocell coverage problem is solved but when a user moves from one location to another location the user has to switch from one base station to so many base station which cannot be maintained with present handoff methods. The present hand off methods working on distance calculation approach, the proposed method is based on the velocity and device direction calculated based on GPS location toward the Base Station (BS) of the device which may ping pong handoff effect.
HANDOVER NECESSITY ESTIMATION FOR 4G HETEROGENEOUS NETWORKSijistjournal
One of the most challenges of 4G network is to have a unified network of heterogeneous wireless networks. To achieve seamless mobility in such a diverse environment, vertical hand off is still a challenging problem. In many situations handover failures and unnecessary handoffs are triggered causing degradation of services, reduction in throughput and increase the blocking probability and packet loss. In this paper a new vertical handoff decision algorithm handover necessity estimation (HNE), is proposed to minimize the number of handover failure and unnecessary handover in heterogeneous wireless networks. we have proposed a multi criteria vertical handoff decision algorithm based on two parts: traveling time estimation and time threshold calculation. Our proposed methods are compared against two other methods: (a) the fixed RSS threshold based method, in which handovers between the cellular network and the WLAN are initiated when the RSS from the WLAN reaches a fixed threshold, and (b) the hysteresis based method, in which a hysteresis is introduced to prevent the ping-pong effect. Simulation results show that, this method reduced the number of handover failures and unnecessary handovers up to 80% and 70%, respectively.
HANDOVER NECESSITY ESTIMATION FOR 4G HETEROGENEOUS NETWORKSijistjournal
One of the most challenges of 4G network is to have a unified network of heterogeneous wireless networks. To achieve seamless mobility in such a diverse environment, vertical hand off is still a challenging problem. In many situations handover failures and unnecessary handoffs are triggered causing degradation of services, reduction in throughput and increase the blocking probability and packet loss. In this paper a new vertical handoff decision algorithm handover necessity estimation (HNE), is proposed to minimize the number of handover failure and unnecessary handover in heterogeneous wireless networks. we have proposed a multi criteria vertical handoff decision algorithm based on two parts: traveling time estimation and time threshold calculation. Our proposed methods are compared against two other methods: (a) the fixed RSS threshold based method, in which handovers between the cellular network and the WLAN are initiated when the RSS from the WLAN reaches a fixed threshold, and (b) the hysteresis based method, in which a hysteresis is introduced to prevent the ping-pong effect. Simulation results show that, this method reduced the number of handover failures and unnecessary handovers up to 80% and 70%, respectively.
The study evaluated interference in a dense heterogeneous network using third-generation universal mobile telecommunication systems (UMTS) and fourth-generation long term evolution (LTE) networks LTE. The UMTs/LTE heterogeneous network determines the level of interference when the two communication systems coexist and how to improve the network by migrating from UMTs to LTE, which has a faster download speed and larger capacity. Techno lite 8 on third generation (3G) and Infinix Pro 6 on fourth generation (4G) were used to measure network the received signal strength (RSS) during site investigation. UE interference was detected and traced using a spectrum analyzer. UMTS and LTE path loss exponents are 2.6 and 3.2. Shannon's capacity theorem calculated LTE and UMTS capacity. When signal to interference and noise ratio (SINR) was used as a quality of service (QoS) indicator, MATLAB channel capacity plots did not match Shannon's due to neighboring interference. UMTS had an R2 of 0.54 and LTE 0.57 for the Shannon channel capacity equation. Adjacent channel interference (ACI) user devices reduce network capacity, lowering QoS for other customers.
This is a presentation I did at the pre-Master studies at Ain shams University. It\'s about algorithms and techniques of call admission when a mobile node moves among cell in a wireless network.
The main aim of the assignment is to simulate handoff performance using MATLAB code.
In this assignment we have done the performance of handoff using matlab code.
Soft Handoffs are generally used in MS that employ Code Division Multiple Access (CDMA) or Wideband CDMA (WCDMA), and its associated services, and also in applications that require a continuous connection throughout, possibly for security purposes.
Hard Handoffs are implemented in TDMA devices, used in applications that can afford slight delays, such as Internet, and WiMAX.
Encryption in Microsoft 365 - ExpertsLive Netherlands 2024Albert Hoitingh
In this session I delve into the encryption technology used in Microsoft 365 and Microsoft Purview. Including the concepts of Customer Key and Double Key Encryption.
Welocme to ViralQR, your best QR code generator.ViralQR
Welcome to ViralQR, your best QR code generator available on the market!
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GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Observability Concepts EVERY Developer Should Know -- DeveloperWeek Europe.pdfPaige Cruz
Monitoring and observability aren’t traditionally found in software curriculums and many of us cobble this knowledge together from whatever vendor or ecosystem we were first introduced to and whatever is a part of your current company’s observability stack.
While the dev and ops silo continues to crumble….many organizations still relegate monitoring & observability as the purview of ops, infra and SRE teams. This is a mistake - achieving a highly observable system requires collaboration up and down the stack.
I, a former op, would like to extend an invitation to all application developers to join the observability party will share these foundational concepts to build on:
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Dev Dives: Train smarter, not harder – active learning and UiPath LLMs for do...UiPathCommunity
💥 Speed, accuracy, and scaling – discover the superpowers of GenAI in action with UiPath Document Understanding and Communications Mining™:
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Learn about the latest enhancements to out-of-the-box document processing – with little to no training required
Get an exclusive demo of the new family of UiPath LLMs – GenAI models specialized for processing different types of documents and messages
This is a hands-on session specifically designed for automation developers and AI enthusiasts seeking to enhance their knowledge in leveraging the latest intelligent document processing capabilities offered by UiPath.
Speakers:
👨🏫 Andras Palfi, Senior Product Manager, UiPath
👩🏫 Lenka Dulovicova, Product Program Manager, UiPath
State of ICS and IoT Cyber Threat Landscape Report 2024 previewPrayukth K V
The IoT and OT threat landscape report has been prepared by the Threat Research Team at Sectrio using data from Sectrio, cyber threat intelligence farming facilities spread across over 85 cities around the world. In addition, Sectrio also runs AI-based advanced threat and payload engagement facilities that serve as sinks to attract and engage sophisticated threat actors, and newer malware including new variants and latent threats that are at an earlier stage of development.
The latest edition of the OT/ICS and IoT security Threat Landscape Report 2024 also covers:
State of global ICS asset and network exposure
Sectoral targets and attacks as well as the cost of ransom
Global APT activity, AI usage, actor and tactic profiles, and implications
Rise in volumes of AI-powered cyberattacks
Major cyber events in 2024
Malware and malicious payload trends
Cyberattack types and targets
Vulnerability exploit attempts on CVEs
Attacks on counties – USA
Expansion of bot farms – how, where, and why
In-depth analysis of the cyber threat landscape across North America, South America, Europe, APAC, and the Middle East
Why are attacks on smart factories rising?
Cyber risk predictions
Axis of attacks – Europe
Systemic attacks in the Middle East
Download the full report from here:
https://sectrio.com/resources/ot-threat-landscape-reports/sectrio-releases-ot-ics-and-iot-security-threat-landscape-report-2024/
Securing your Kubernetes cluster_ a step-by-step guide to success !KatiaHIMEUR1
Today, after several years of existence, an extremely active community and an ultra-dynamic ecosystem, Kubernetes has established itself as the de facto standard in container orchestration. Thanks to a wide range of managed services, it has never been so easy to set up a ready-to-use Kubernetes cluster.
However, this ease of use means that the subject of security in Kubernetes is often left for later, or even neglected. This exposes companies to significant risks.
In this talk, I'll show you step-by-step how to secure your Kubernetes cluster for greater peace of mind and reliability.
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
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During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
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The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
2. Outline
Handoff Basics
Handoff Management
Handoff Detection
Handoff Assignment
Example: Handoff in GSM
Handoff Requirements and Goals
Advanced Issues of Handoff Management
Handoff Failure
Radio Link Transfer
Soft Handoff
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 2
3. Review:
Signal Strength within Cells
The contours may not be concentric and could be distorted by
atmospheric conditions and topographical contours
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 3
4. Handoff
A most common reason that the handoff is conducted:
When the phone is moving away from the area covered by
one cell and entering the area covered by another cell, the
call is transferred to the second cell to avoid call termination
when the phone gets outside the range of the first cell
The handoff process is of major importance within
any cellular networks
Failure for it to perform reliably can result in dropped calls,
and this is one of the key factors that can lead to customer
dissatisfaction
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 4
5. Basics of Handoff Management
Handover (Europe) = handoff (North America)
Handoff is the process that occurs when a mobile
is “handed over” from one access point to another,
i.e., the access point which the mobile is using
changes
Either handover or handoff can be abbreviated as
HO hereafter
Handoff Management
(Handoff detection) How do you detect that you
should handoff?
(Handoff assignment) Who initiates handoff?
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 5
6. How HO Happens?
As the MS moves away from the BS of the cell, the signal
strength weakens and the radio connection of MS is changed to
another adjacent cell
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 6
7. How HO Happens? (cont’d)
By starting to look for a new BS before you need it, there is
time to make a decision
X3: Start looking for a new BS
X5: Time to switch
TL: Threshold for looking around
TH: Threshold for handoff
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 7
8. Outline
Handoff Basics
Handoff Management
Handoff Detection
Handoff Assignment
Example: Handoff in GSM
Handoff Requirements and Goals
Advanced Issues of Handoff Management
Handoff Failure
Radio Link Transfer
Soft Handoff
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 8
9. “Ping-Pong” Effect
The name of the phenomenon implies that the MS
moves back and forth between the overlapped area
of two adjacent cells
Celli
Cellj
The solution is to allow MS continue maintain a radio
link with the current BSi, until the signal strength
from BSj exceeds that of BSi by some pre-specified
threshold value E (shown as Xth)
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 9
10. How HO Happens? (cont’d)
To avoid “ping-pong” effect, the MS continues to
maintain a radio link with BSi until Xth
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 10
11. Reality is More Complex
Three common measurements of the channel:
Word Error Indicator (WEI)
Based on if the receiver is able to decode the received signal
correctly
Received Signal Strength Indication (RSSI)
A measure of the received signal strength
Quality Indicator (QI)
Related to the signal to interference & noise ratio (S/I)
Handoff may depend more reliably on WEI of the
current channel rather than RSSI
If WEI is good, then handoff is not performed
However, it is necessary to accumulate WEI measurements
over a period of time, whereas RSSI is known
instantaneously
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 11
12. Reality is More Complex (cont’d)
To make the handoff decision accurately and quickly,
it is desirable to use both WEI and RSSI
However, to use a simple policy for handoff detection can be
feasible in practice
For example, GSM Specification introduces 6 basic
types of causes of HO with priority order
Uplink quality
Downlink quality
Uplink level
Downlink level
MS-BS distance
Power budget: To improve transmission quality in the lower
power level
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 12
13. Who Makes the HO Decision?
NCHO (network controlled handoff)
The network makes the decision
Used in CT-2 Plus and AMPS
MCHO (mobile controlled handoff)
The mobile decides for itself
Forward: the mobile initiates HO and sends the request to the
new AP
Backward: the mobile initiates HO and sends the request to the
old AP
Used in DECT, PACS and Mobile IP
MAHO (mobile assisted handoff)
The mobile provides data for the network to make the
decision
Used in GSM and IS-95 CDMA
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 13
14. NCHO
Network Controlled Handoff
The BS monitors the signal strength and quality from the BS
The network uses multiple (current and surrounding) BSs to
supervise the quality of all current connections by making
measurements of RSSI
The MSC makes the decision when and where to effect the
handoff
Drawback: Heavy network signaling traffic and
limited radio resources at BSs prevent frequent
measurements of neighboring links
Long handoff time: up to 10 sec. or more
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 14
15. MCHO
Mobile Controlled Handoff
The mobile decides for itself by monitoring signal strength
and quality from the current and candidate BSs
When it finds a better candidate, it initiates a handoff
In MCHO, most of the work is done by the mobile (as
it knows who it can hear, how well it can hear them,
and can even consider its battery level, etc)
Handoff time
DECT: 100~500 ms.
PACS: 20~50 ms.
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 15
16. MAHO
Mobile Assisted Handoff
The mobile provides data which the network uses to make
the decision
Essentially, it is a variant of NCHO but uses the mobile to
help reduce the handoff time
Example: In GSM, the MS transmits measurements
twice a second ⇒ GSM handoff time ~ 1 sec.
Note in both NCHO and MAHO, if the network cannot
tell the mobile about the new channel / time slot / ...
to use before the link quality has decayed too far,
then the call may be terminated
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 16
17. Handoff in GSM
A handoff is decided by the network, not the MS
BSS criteria
Received signal level
Channel quality
Distance between MS and BTS
Network operation criteria
Current traffic load of the cell
Ongoing maintenance work
Link control for handoff preparation
Periodically, the MS checks the downlink signal strength of its
current BS and the neighboring BSs
Uplink signal quality is monitored by the network side
MS sends measurement report to its current BS and this report is to
be evaluated for handoff decisions by the network side
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 17
18. Handoff in GSM (cont’d)
Handoffs include several procedures: measurements,
decision and destination selection
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 18
19. Handoff in GSM (cont’d)
Use measurement results from the MS and BS
To identify possible other BSs as targets for handovers
To determine the optimal moment to execute the HO
Objective: to keep (#HO per cell change) small
Ideally, (#HO per cell change)=1
In reality, radio conditions are often not very stable when an
MS leaves the BS => (#HO per cell change)=1.5~5
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 19
20. Outline
Handoff Basics
Handoff Management
Handoff Detection
Handoff Assignment
Example: Handoff in GSM
Handoff Requirements and Goals
Advanced Issues of Handoff Management
Handoff Failure
Radio Link Transfer
Soft Handoff
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 20
21. Handoff Requirements
Requirements from a handoff scheme are:
Latency: the time required to effect the handoff should be
appropriate for the rate of mobility of the mobile terminal,
as well as the nature of data transferred
Scalability: the handoff procedure should support handoffs
within the same cell, between different base stations in the
same or in different networks
Minimal drop-off and fast recovery
Quality of service should be maintained or re-negotiatied
after the handoff is completed
Minimal additional signaling
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 21
22. Handoff Goals
Minimal impact on traffic
Making a handoff at the “right” time
Tolerance / adaptation for congestion and capacity
The new and old cells may have different levels of utilization,
available bandwidth, ...
Efficiency
The handoff should result in improved efficiency (in terms of traffic,
energy consumption, reduced interference, …)
The handoff process should try to minimize the resources it
consumes
Improve availability
Handoff should result in using a BS which provides better
bandwidth, lower cost, lower delay, low delay variance, ...
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 22
23. Handoff Goals (cont’d)
The mobile should be able to use the maximum set
of BSs (which may involve changing spreading code,
modulation, coding, or changing to a different radio
module) to achieve a better system optima
Fast handoff
Optimal BTS selection
Reduced signaling overhead
Increased speech quality
Avoidance of far-away-cell effect
Consideration of adjacent-cell capacity
Avoidance of ping-pong effect
Reduced handover failure
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 23
24. Outline
Handoff Basics
Handoff Management
Handoff Detection
Handoff Assignment
Example: Handoff in GSM
Handoff Requirements and Goals
Advanced Issues of Handoff Management
Handoff Failure
Radio Link Transfer
Soft Handoff
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 24
25. Handoff Failure
What happens if there are insufficient resources in
the new BS?
Existing calls cannot be handed over ⇒ forced terminations
New calls are blocked
Goals of channel assignment
To achieve high spectrum utilization
To maintain a given service quality
To use a simple algorithm
To require a minimum number of database lookups
Unfortunately, it is hard to do all of these at once!
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 25
26. Channel Assignment
Several schemes are introduced to reduce the number of forced
terminations, at the cost of increased blocking or decreased
efficiency, including:
Nonprioritized scheme (NPS)
A handoff call is treated the same as a new call
Reserved channel scheme (RCS)
To reserve some resources for handoffs
Queuing priority scheme (QPS)
To exploit the handoff area (i.e., cell overlap) to queue up mobiles
waiting for handoff
Subrating scheme (SRS)
To downgrade an existing call in the new cell and to share
resources with the call being handed over (e.g., by changing a full-
rate to a half-rate CODEC)
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 26
27. Radio Link Transfer
When performing handoff, it is sometimes necessary
to transfer radio link among system components
In the GSM network, several handoff types can be
enumerated:
Intra-cell HO
Inter-cell or inter-BS HO
Inter-BSC HO
Inter-MSC HO
Intersystem HO between two PCS networks (?!)
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 27
28. Preview:
Part of the GSM Architecture
BTS: base transceiver station
BSC: base station controller
MSC: mobile switching center
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 28
29. Different HO Types in the GSM
Network
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 29
30. Intra-cell & Inter-cell HOs
Intra-cell HO
For administrative reasons or because of channel quality (channel-
selective interferences)
Inter-cell HO
Because of weak signal field strength and bad channel quality
Also for administrative reasons (e.g., for traffic load balancing)
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 30
31. Flows of HO within One MSC
When both cells are connected to the same MSC, the
mobile can signal that it is going to change cells (by
providing measurements), then the MSC can set up
the correct resources deliver traffic in the new cell
This often involves setting up a bridge to copy traffic to both
the old and new channels
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 31
32. Inter-MSC HO
When the two cells are connected to different MSCs,
the situation is more complex
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 32
33. Inter-MSC HO (cont’d)
Anchor-based approach
Anchor
MSC
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 33
34. What Happens If the Mobile
Moves Again?
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 34
35. What Happens If the Mobile
Moves Again? (cont’d)
Note that the call always goes via the so-called
anchor MSC (in this case MSC1) to relay MSCs
This is because the phone attached to the PSTN knows
nothing about mobility and the originating exchange thinks
the call is still in existence
Without path minimization, the chain of chunks
between MSCs could continue to grow as long as the
call lasts and the mobile keeps moving to new MSCs
With voice calls, the call duration is generally rather limited,
but with data communication it could continue for a very
long time
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 35
36. Hard Handoff vs. Soft Handoff
Hard handoff
Break-before-make
The mobile connects only to a
single BS at a time
Soft handoff
Make-before-break
The mobile receives from &
transmits to multiple BSs
simultaneously
The signal of the best of all
connected channels is utilized
Generally used in CDMA systems
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 36
37. Hard Handoff
X
X
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 37
38. Soft Handoff
X
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 38
39. Softer Handoff
Softer handoff: In soft handoff, the network and the mobile
combine all the signals to produce a clearer copy of the signal in
both the up and down links
Received Power
Total at the MS
Cell A
Cell B
Distance
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 39
40. WCDMA Handoffs
Softer handoff is more advantageous to soft handoff
while soft handoff is more advantageous to hard
handoff. However, not all handoffs in CDMA systems
can be performed as softer handoffs
Example: In WCDMA systems, we have the following
scenarios:
Softer handoff
The handoff is within one cell between different sectors
Soft handoff
The handoff is between different BSs
Hard handoff
The handoff is between different frequencies or between
WCDMA and GSM
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 40
41. Soft Handoff in Multiple Forms
Some CDMA systems use very precise link level
timing to enable the signals from multiple BSs to
arrive additively at the mobile, thus leading to a
physically stronger signal
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 41
42. Advantages of Soft Handoff
Advantages of utilizing soft handoff include:
Reduces number of call drops
Increases the overall capacity
Mobile transmit power is reduced
Voice quality near the cell boundaries are
improved
Prof. W.-G. Teng, "Wireless & Mobile Networks", NCKU ES 42