1. Introduction to Wireless Networking
ECE/CSC 575 – Section 1
Introduction to Wireless Networking
Lecture 9 Dr. Xinbing Wang

2. Current Wireless Systems: Cellular Systems--UMTS
Fundamentals of cellular communications
System capacity
frequency reuse
Cell splitting
Admission control
handoff
Universal mobile telecommunication system (UMTS)
Network architecture
Functional units
Quality of service
Mobility management
In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties.
Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere.
However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low.
Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G).
With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications.
The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years.
So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems.
Dr. Xinbing Wang

3. Handoff Management
Initial Phase: make decision based on the measures of received signal strength
Without hysteresis: a handoff is initiated as soon as the average signal level from the new base station exceeds that from the current BS.
With hysteresis: a handoff is initiated when the average signal level from the new BS exceeds that from the current BS by a threshold amount specified by the hystersis level.
Execution phase
Channel assignment
Exchange of control messages
Dr. Xinbing Wang

4. Handoff Strategies
Mobile controlled handoff (MCHO): the MT initiates and controls the procedure of handoff.
Network controlled handoff (NCHO): the network (e.g., MSC) makes decision and initiates handoff based on the measurements informed by BSs/APs.
MT assisted handoff (MAHO): the MT measures the network (e.g., MSC) makes decision and initiates handoff based on the measurements collected by the MT.
Dr. Xinbing Wang

5. Types of Handoff
Hard handoff is characterized by an MT having a radio link with only one BS/AP at any time.
This mode of operation is referred to as break (old connection) before make (new connection).
Soft handoff in which an MT can simultaneously communicate with more than one BS/AP during the handoff.
This mode of operation is referred to as make (new connection) before break (old connection).
Backward handoff: The handoff is predicted ahead of time and initiated via the existing radio link.
May be affected by a sudden loss or rapid deterioration of radio links
Forward handoff: The handoff is initiated via the new radio link.It may result in large delay when combined with hard handoff.
Dr. Xinbing Wang

6. Handoff Performance
Call dropping probability – probability that a call is terminated due to a handoff
Handoff blocking probability – probability that a handoff cannot be successfully completed
Handoff probability – probability that a handoff occurs before call termination
Rate of handoff – number of handoffs per unit time
Interruption duration – duration of time during a handoff in which a mobile is not connected to either base station
Handoff delay – distance the mobile moves from the point at which the handoff should occur to the point at which it does occur
Dr. Xinbing Wang

7. Current Wireless Systems: Cellular Systems--UMTS
Fundamentals of cellular communications
System capacity
frequency reuse
Cell splitting
Admission control
handoff
Universal mobile telecommunication system (UMTS)
Network architecture
Functional units
Quality of service
Mobility management
In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties.
Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere.
However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low.
Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G).
With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications.
The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years.
So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems.
Dr. Xinbing Wang

8. Introduction to UMTS
UMTS (Universal Mobile Telecommunications System) is the European version of a 3rd Generation (3G) mobile communication system.
It is proposed by 3GPP (3rd generation partnership project).
It includes two parts: UTRAN (Universal Terrestrial Radio Access Network) and the Core network inherited from GSM (Global System for Mobile Communications).
UMTS is a wideband, circuit- and packet-based transmission systems of text, digitized voice, video, and multimedia with data rates up to 2 Mbps (possibly higher).
Dr. Xinbing Wang

9. UMTS Services and Their Relationship to the Internets
Service Category
Session Type
Protocols
Internet Elements
Location-based info- and entertainment
WWW
HTTP, WML,
cHTML, xHTML
ISP, portal, servers
Intranet access (mobile VPN), mobile office, mobile commerce
All types-transparent tunnel
IP, higher layers transparent
ISP, firewall server, corporate portal
Internet access
ISP, portal
Multimedia messaging
SMS, , downloading
SMTP, SMS, IP
ISP, , SMS-server
Audio, video, download
File transfer, streaming
MP3, MPEG-4, FTP, IP-based SIP
ISP, portal, database server
Voice, real-time audio, video
Interactive/dialog streaming/one-way
SIP
Media gateway
Dr. Xinbing Wang

10. Data rate and Spectrum
Maximum data rate and maximum speed for different hierarchical layer
Macrolayer: 144 kbps with max. speed of 500km/h.
Microlayer: 384 kbps with max speed of 120km/h
Picolayer: 2Mbps with 10km/h
Bit Error Rate (BER)
Real-time applications: 10-3 to 10-7 with maximum constant delay: 20ms to 300 ms
No real-time applications: 10-5 to 10-8 with maximum delay >= 150ms.
Spectrum: 1900 MHz-2025 MHz, and MHz
FDD (macro- and micro- cells: uplink is from 1920 MHz to 1980 MHz, downlink is from 2110 MHz to 2170 MHz
TDD (pico- cells: not divided by use of different frequency carriers (not suitable for large prop delays).
Dr. Xinbing Wang

11. Network Architecture CN UTRAN VLR MSC GMSC HLR SGSN GGSN PSTN ISDN
Node B
Radio
Network
controller
MSC
UMTS
Subscriber
Identity
module
GMSC
ISDN
Node B
HLR
User
equipment
Radio
Network
controller
Node B
Mobile
equipment
SGSN
GGSN
Internet
Dr. Xinbing Wang

12. WCDMA Air Interface
In UMTS, the UTRAN (UMTS Terrestrial Radio Access Network) is used to keep the mobility management (MM) and connection management (CM) layers independent of the air interface radio technology
This idea is realized as the concepts of access stratum (AS) and non-access stratum (NAS)
AS: functional entity that includes radio access protocols between the user equipment (UE) and the UTRAN (terminate here).
NAS: includes core network (CN) protocols between the UE and the CN itself.
The NAS protocols can be kept the same, thus, the GSM’s MM and CM resources are used almost unchanged in 3G NAS.
Dr. Xinbing Wang

13. UMTS Architecture UE UTRAN CN Non-access Stratum Core network
protocols
Core network
protocols
Access Stratum
Radio
Protocols
Radio
Protocols lu
Protocols lu
Protocols
Uu-interface
Iu-interface
Dr. Xinbing Wang

14. Current Wireless Systems: Cellular Systems--UMTS
Fundamentals of cellular communications
System capacity
frequency reuse
Cell splitting
Admission control
handoff
Universal mobile telecommunication system (UMTS)
Network architecture
Functional units
Quality of service
Mobility management
In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties.
Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere.
However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low.
Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G).
With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications.
The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years.
So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems.
Dr. Xinbing Wang

15. Node B
Node B is the UMTS equivalent of a base station transceiver. It may support one or more cells, although in general only one cell one Node B.
It is a logical terminal and the base station is often used for physical entity.
Functions
Mapping of Node B logical resources onto hardware resources
Uplink power control
Reporting of uplink interference measurements and downlink power information
Contains the air interface physical layer, it has to perform many functions such as RF processing, modulations, coding, and so on.
Dr. Xinbing Wang

16. Radio Network Controller (RNC)
One RNC controls one or more Node Bs.
It may be connected via Iu interface to an MSC (IuCS), or to an SGSN via Iu (IuPS).
The interface between RNCs (Iur) is logical interface, and a direct physical connection does not necessarily exist.
An RNC is comparable to a base station controller (BSC) in GSM networks.
Dr. Xinbing Wang

17. RNC Functions Iub (Node B and RNC) transport resources management
Control of Node B logical O&M resources
System information management and scheduling
Traffic management of common channels
Soft handover
Power control for uplink and downlink
Admission control
Traffic management of shared channels
Macro diversity combining/splitting of data streams transferred over several Node Bs.
Dr. Xinbing Wang

18. Admission Control In 2G TDMA systems In 3G CDMA systems
The capacity in a TDMA cell is typically not interference limited, but it depends on the number of channel elements in the BS.
It is easy to determine the amount of unused resources such as the number of free time slots
Admission control is threshold-based
In 3G CDMA systems
A new call increases the overall interference level in the cells, and thus it has a direct effect on the QoS the other users in the cell
Uplink: most of the interference is intracell, but intercell interference has to be considered as well.
Downlink: orthogonal codes are used, and thus the capacity-limiting factor is mostly intercell interference
Dr. Xinbing Wang

19. Admission Control (2)
The admission-control algorithm must reside in the RNC, which has sole access to all the required information to run an efficient admission control policy.
General idea
Estimate the increase in the usage of resources the new user would cause
If the estimation reveals that the new status would exceed the preset threshold, then the request for the resource has to be rejected
When the total level in a cell is low, an increase to the load level increases the interference level only by a small amount, otherwise, it will cause a large increase in the interference level.
Dr. Xinbing Wang

20. AC Procedure
Determine the amount of available channels, i.e., the number of channels for accepting new and handoff requests.
When the N-th request arrives, i.e., there are (N-1) ongoing services. If there are enough resources to admit the N-th request, then the new request is admitted. Otherwise, it will be denied.
In order to maintain the continuity of a handoff call, handoff calls are given higher priority than new call requests.
The prioritized call admission is implemented by reserving channels for handoff calls. This method is referred to as guard channels.
Fixed reservation and dynamic reservation.
Dr. Xinbing Wang

21. Fixed Channel Assignment (FCA)
Each cell is allocated a predetermined set of voice channels.
The BS is the entity that allocates channels to the requests. If all channels are used in one cell, it may borrow a channel from its neighbors through MSC.
Fast allocation, but may result high call blocking probabilities.
Dr. Xinbing Wang

22. Dynamic Channel Assignment (DCA)
Voice channels are not allocated to each cell permanently.
When a request is received at the BS, this BS request a channel from MSC.
DCA can reduce the call blocking probability, but it needs real-time data collection and signaling transmission between BS and MSC.
Dr. Xinbing Wang

23. Examples of AC
Admission control schemes are not specified in 3GPP technical specifications.
Signaling procedures and measurements are needed to support admission control.
Admission control algorithms are the internal functions of RNC, defined by the operator or by the equipment manufacturer.
It is very difficult to discuss because some services have never been used before.
The packet-level admission control is a new experience for mobile systems, which needs to consider the delay as a requirement whereas not equally evident for the wired networks.
Dr. Xinbing Wang

24. Ex1: Interference-based AC
Estimation of the increased interference level in uplink
Interference
Maximum allowed
Interference level
interference 2
load 2
load 1
load
interference 1
Dr. Xinbing Wang

25. Ex. 2: Received-power admission control (RPAC)
Assume the service-dependent threshold for a particular service i is Zit , and the total received power before the new user (at a BS) is Zk, then a new bearer service i will be admitted if
Zk < Zit
Service-dependent threshold is used to describe the preset parameters for a specific type of services, e.g., real-time voice service.
Dr. Xinbing Wang

26. Layered Architecture There are three protocol layers in the AS
Physical layer (L1)
Data link layer (L2)
Medium access control (MAC)
Radio link control (RLC)
Broadcast/multicast control (BMC)
Packet data convergence protocol (PDCP)
Network layer (L3)
Radio resource control (RRC)
There is one layer (L3) in the NAS
Mobility management
Call management
Dr. Xinbing Wang

27. RLC Services
These functions are provided to upper layers:
Segmentation and reassembly of higher-layer PDUs (Protocol Data Unit) into/from smaller RLC payload units
Padding
Transfer of user data
Error corrections
In-sequence delivery of higher-layer PDUs
Ciphering
Sequence number check
Dr. Xinbing Wang

28. RLC Functions
These functions (for itself) are supported by the RLC:
Segmentation and reassembly of higher-layer PDUs (Protocol Data Unit) into/from smaller RLC payload units
Padding
Transfer of user data
Error corrections
In-sequence delivery of higher-layer PDUs
Flow control
Ciphering
Sequence number check
Dr. Xinbing Wang

29. After Class Reading materials Exercises Chapter 10.5
Reading materials for UMTS
Exercises
What is handoff?
Describe the architecture of UMTS.
What is the main difference between UMTS and 2G systems?
List 3 functions of RNC and Node B, respectively
What is admission control? In which entity AC is implemented?
What is the difference between FCA and DCA?
Explain two schemes in the lecture notes.
Can you think of two other schemes?
Dr. Xinbing Wang