Transcript 12-Specific_system_Cellular-Part-1

Specific Systems
Cellular
Part 1
#12
Victor S. Frost
Dan F. Servey Distinguished Professor
Electrical Engineering and Computer Science
University of Kansas
2335 Irving Hill Dr.
Lawrence, Kansas 66045
Phone: (785) 864-4833 FAX:(785) 864-7789
e-mail: [email protected]
http://www.ittc.ku.edu/
All material copyright 2006
Victor S. Frost, All Rights Reserved
#12 1
Outline
• Part 1
–
–
–
–
Basic components
3G
Overview of W-CDMA/UMTS
HSPDA
• Part 2
– EV-DO overview
– Case study: Mitigating scheduler-induced
starvation in 3G wireless networks
#12 2
Cellular Network: Physical Topology
Mobile Stations
Base station
• Transmits to users on
forward channels
• Receives from users on
reverse channels
Mobile Switching
Center
•
BSS
BSS
Internet
MSC
HLR
VLR
Controls connection
setup within cells & to EIRAC
telephone network
AC = authentication center
BSS = base station subsystem
EIR = equipment identity register
HLR = home location register
STP
PSTN
SS7
Wireline
terminal
MSC = mobile switching center
PSTN = public switched telephone network
STP = signal transfer point
VLR = visitor location register
Modified from: Leon-Garcia & Widjaja: Communication Networks
#12 3
Components
• Mobile stations (MS)
– Transmit/Receive over the air interface
• Signaling
• User information
– Voice
– Internet
– Video
– Will set up multiple “channels” for
communication
• Signaling/Control
– Set up and maintain calls
– Establish relationship between mobile unit and nearest
BS
• User voice/data channels traffic channels
#12 4
Components
• Base station (BS)
– Transmit/Receive over the air interface
to multiple mobile stations
– Terminates radio signals
– Packages information for transport to a
controller (MSC) for routing
– Sends information to Mobile Switching
Center
#12 5
Components
•
Mobile Switching Center (MSC)
•
Home location register (HLR)
–
–
–
–
–
Connects to many BSs
Performs call set up
Provides routing functions
Typically associated with voice calls
Sometines called Mobile Telecommunications Switching Office (MST0)
– Wireless service provider (WSP) maintains a database
• Subscriber personal information, e.g., phone number,, mobile identification
number, electronic serial number (ESN) of phone
• Service Profile
• Current location of subscriber
•
– One HLR may serve several MSCs
Visitor location register (VLR)
– Data base containing temporary information of subscribers
– For subscribers away from home service area
– VRL information retrieved from the HLR
#12 6
Process
•
•
•
Registration
– Turn on cell phone
– BS continually transmit
signals on control channels
– Cell phone scans for strongest
signal
– Cell phone decodes control
signal to determine
• System Id
• Initial Tx power setting
• Radio channels to use for
further communications
Cell phone registers with
network
Note as the MS moves it may
need to cancel registration in
old area and re-register in
new area
#12 7
Process
• Mobile Call Initiation
– To make a call the
mobile keys the phone
# and hits send
– Phone # transmitted
over preselected
control channel
– The BS relays
information to the MSC
– MSC looking into the
control message to get
the # and processes
the call, i.e., does the
routing
#12 8
Process
• Call initiation to mobile
– Call routed to home MSC
– MSC checks HLR to
determine location of
subscriber
– MSC has current visiting
MSC stored in the HLR
– Home MSC communicates
with the visiting MSC to
rout the call
– The MSC sends a paging
message to the paging
message to BS
– The BS then send the
paging message on to the
subscriber on an assigned
control (paging) channel
#12 9
Process
• Call accepted
– MS sees the paging signal
and responds to the BS
– The BS send response to
the MSC
– The MSC sets up the call
to the BS
– The MSC also assigns a air
interface channel for the
BS to use for the call
– The MS communicates of
the assigned channel
• Here the call is between
two mobiles
• The communications is
monitored for the ongoing
call
#12 10
Process
• Handoff (or handover)
– MS continually scans for
control signals of BS
– Knowledge of the results
of scans is used by MSC,
e.g., power of control
signal drops below some
threshold
– Upon that event the MSC
will initiate a handoff
procedure
– Handoff procedures can
be implemented
transparent to the users,
no interruption
– The handoff procedure
tells the MS to use a
specific channel to
communicate with the new
BS
#12 11
Process
• Handoffs
– Hard: communications with old BS is terminated and a
new communications to a new BS is established
– Soft:
• Soft: mobile station temporarily connected to more than
one base station simultaneously
• Softer: mobile station temporarily connected to more than
one sector of the same base station simultaneously
• Soft-softer: mobile station temporarily connected to more
than one sector of the same base station and more than one
base station simultaneously
• Provides diversity
• Occurs at boundaries of sectors/cells
#12 12
Other Functions
• Call blocking
– if all traffic channels busy
• Call termination
– when user hangs up
• Call drop
– when BS cannot maintain required signal strength
#12 13
Other Functions
Power control CDMA
• Purpose
–
–
–
–
Removes near far effect.
Mitigates fading.
Compensates changes in propagation conditions.
In the system level
• decrease interference from other users
• increase capacity of the system
• Uplink
– Power control in uplink must make signal powers from
different users nearly equal in order to maximize the
total capacity in the cell.
• Downlink
– In downlink the power control must keep the signal at
minimal required level in order to decrease the
interference to users in other cells.
#12 14
Other Functions
Power control CDMA
• Types
– Open loop
• set initial power for MS
• Each MS sets power based on individual
measurements
• Coarse scale
– Closed loop
• BS knows receive power from each MS
• BS can tell each MS to set its power to achieve
system goals.
• Fast power control can mitigate fast fading
• Three steps:
– Transmission
– Measurement
– Feedback
#12 15
3G
• 1G: Analog Cellular Phones. Needs a modem.
9.6 kbps max.
• 2G: Digital Cellular Phones. No modem
required. 19.3 kbps max.
• 2.5G: General Packet Radio Service (GPRS)
144kbps. Data only.
• 3G: Future high-speed data with Voice. 64
kbps to 2 Mbps.
– W-CDMA/UMTS (Universal Mobile
Telecommunications System
– CDMA2000
#12 16
Organizations
– 3GPP 3rd Generation Partnership Project.
– 3GPP is responsible for writing and
maintaining the UMTS specifications
– … CDMA2000 ….
– Internet Engineering Task Force (IETF)
Modified from: www.ccs.neu.edu/home/rraj/G250Projects/NachiketMehta.ppt
#12 17
3G- Advantages
3G phones promise :• Improved digital voice communications
• Larger Bandwidth – Higher Data rate
• Greater subscriber capacity
• Fast packet-based data services like e-mail, short
message service (SMS), and Internet access at
broadband speeds.
• Most carriers also expect consumers to want :–
–
–
–
–
location services
interactive gaming
streaming video
home monitoring and control
and who knows what else, while being fully mobile
anywhere in the world.
Modified from: www.ccs.neu.edu/home/rraj/G250Projects/NachiketMehta.ppt
#12 18
3G Capabilities
• Voice quality comparable to the public switched
telephone network
• 144 Kbps- user in high-speed motor vehicles
• 384 Kbps- pedestrians standing or moving slowly
over small areas
• Up to 2 Mbps- fixed applications like office use
• Symmetrical/asymmetrical data transmission
rates
• Support for both packet switched and circuit
switched data services like Internet Protocol (IP)
traffic and real time video
Modified from: www.ccs.neu.edu/home/rraj/G250Projects/NachiketMehta.ppt
#12 19
Technologies
• 3G is superior to the other digital standards like:-
– GSM (Global System for Mobile) communications standard used
worldwide
– And IS-136 TDMA standard used primarily in North America.
– IS-95 CDMA systems
• 3G Technologies:-
– WCDMA or UMTS-FDD (Universal Mobile Telecommunications
System - Frequency Division Duplex)---Direct Spread
– CDMA2000 - 1x-EvDO/EvDV---Multi carrier
– UMTS – TDD (Time Division Duplex) or TD-SCDMA (Time Division Synchronous Code Division Multiple Access) ---Time Code
– CDMA2000 and WCDMA or UMTS-FDD have similar architectures
Modified from: www.ccs.neu.edu/home/rraj/G250Projects/NachiketMehta.ppt
#12 20
Evolution Paths
cdmaOne
IS-95A
cdmaOne
IS-95B
Cdma2000 1X
Cdma2000
1xEV-DV
TDMA
IS-41 Core Network
EDGE
GSM
Cdma2000
1xEV-DO
WCDMA
GPRS
GSM Map Core Network
2G
2.5G
3G
Modified from: www.ccs.neu.edu/home/rraj/G250Projects/NachiketMehta.ppt
#12 21
WCDMA
• Spectrum
– 1920 MHz – 1980 MHz (uplink)
– 2110 MHz – 2170 MHz (downlink)
or
– 1850 MHz – 1910 MHz (uplink)
– 1930 MHz – 1990 MHz (downlink)
– Channel Spacing 5 Mhz
• WCDMA is connected to the FDD Phy and the
associated protocols  Focus here
• UTRAN-Universal Terrestrial Radio Access
Network- is associated with the WCDMA radio
Access Network
• UMTS refers to the whole network
#12 22
UMTS-FDD / WCDMA
• Wideband Direct Sequence Code Division
Multiple Access
• Does not assign a specific frequency to
each user. Instead every channel uses the
full available spectrum.
• Individual conversations are encoded with a
pseudo-random digital sequence
• See http://www.umtsworld.com/technology/overview.htm
#12 23
WCDMA Parameters
Channel B.W
5 MHz
Forward RF Channel Structure
Direct Spread
Chip Rate
3.84 Mcps
Frame Length
10 ms (38400 chips)
No. of slots/frame
15
No. of chips/slot
2560chips (Max. 2560 bits)
Power Control
Open and fast close loop (1.6 KHz)
Uplink Spreading Factor
4 to 256
Downlink Spreading Factor
4 to 512
#12 24
Spreading Operation
•
•
Spreading means increasing the signal bandwidth
Strictly speaking, spreading includes two
operations:
– Channelisation (increases signal bandwidth) using
orthogonal codes
– Scrambling (does not affect the signal bandwidth) using
pseudo noise codes
#12 25
Codes
Channellization Code
Scrambling Code
Usage
UL: Separation of physical data
and control channels from same UE
DL: Separation of different users
within one cell
UL: Separation of terminals
DL: Separation of
cells/sectors
Length
UL:4-256 chips
DL:4-512 chips
38400 chips
No. of codes
No. of codes under one scrambling
code= SF
UL: Several million
DL: 512
Code Family
Orthogonal Variable Spreading Factor
Long 10ms code: Gold code
Short code: Extended S(2)
code Family
Increase B.W?
YES
NO
#12 26
UMTS Architecture
Core Network
Access Network
Cell site
User Equipment
Modified from: M. D. Yacoub, Wireless Technology, Protocols, Standards, and
Techniques, CRC Press, 2002
#12 27
UMTS Architecture
From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/Lecture-5%206%20slides%20per%20page.pdf
#12 28
UMTS Architecture
• User equipment-UE
– UMTS Subscriber Identity Module –USIM
– Mobile Equipment- cell phone
• UMTS Terrestrial Radio Access Network
– Radio Network Subsystem
• Node B- BS
–
–
–
–
Transceiver
Rate adaptation
Radio resource management
Power control
#12 29
UMTS Architecture
• Radio Network Controller – RNC
–
–
–
–
Radio access control
Connection control
Load, congestion and admission control
Code allocation
– Core Network
•
•
•
•
MSC
VLR
HLR
Gateway MSC – GMSC
– Supports circuit switched connections
• Serving GRPS Support Node – SGPRS
– Logical interface to UTRAN for packet transport
» Session management
» Logical link management
• Gateway GPRS Support Node – GGSN
– Supports packet switched transport
– This is an IP router
#12 30
UMTS Protocol Architecture
- User Plane
FP= Framing Protocol
GTP-U= GPRS Tunneling Protocol-User
PDCP =Packet Data convergence Protocol
From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/Lecture-5%206%20slides%20per%20page.pdf
#12 31
UMTS Protocol Stack
• Radio Resource
Control-RRC
• Broadcast/mulitcast
control- BMC
• Packet Data
convergence
Protocol- PDCP
– Header compression
Modified from: M. D. Yacoub, Wireless Technology, Protocols, Standards, and
Techniques, CRC Press, 2002
#12 32
Packet SAR
Modified from: M. D. Yacoub, Wireless Technology, Protocols, Standards, and
Techniques, CRC Press, 2002
#12 33
Physical Layer
• The physical layer offers information transfer services to the
MAC layer. These services are denoted as Transport channels
(TrCh’s). There are also Physical channels.
• Physical layer comprises following functions:
–
–
–
–
–
–
–
􀂉 Various handover functions
􀂉 Error detection and report to higher layers
􀂉 Multiplexing of transport channels
􀂉 Mapping of transport channels to physical channels
􀂉 Fast Close loop Power control
􀂉 Frequency and Time Synchronization
􀂉 Other responsibilities associated with transmitting and
receiving signals over the wireless media.
– Measurements
• SIR
• Tx power, Frame error rate, etc
• Physical channel is assigned a specific code
#12 34
Transport & Physical Channels
Transport Channel
Physical Channel
(UL/DL) Dedicated Channel DCH
Dedicated Physical Data Channel DPDCH
Dedicated Physical Control Channel DPCCH
(UL) Random Access Channel RACH
Physical random access channel PRACH
(UL) Common packet channel CPCH
Physical common packet channel PCPCH
(DL) Broadcast channel BCH
Primary common control physical channel PCCPCH
(DL) Forward access channel FACH
(DL) Paging channel PCH
Secondary common control physical channel SCCPCH
(DL) Downlink shared channel DSCH
Physical downlink shared channel PDSCH
Signaling physical channels
Synchronization channel SCH
Common pilot channel CPICH
Acquisition indication channel AICH
Paging indication channel PICH
CPCH Status indication channel CSICH
Collision detection/Channel assignment indicator
channel CD/CA-ICH
#12 35
UMTS FDD frame structure
From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/Lecture-5%206%20slides%20per%20page.pdf
#12 36
MAC Layer
• The MAC layer offers Data transfer to RLC and
higher layers.
• The MAC layer comprises the following functions:
– Selection of appropriate Transport Format (TF), basically bit
rate, within a predefined set, per information unit delivered
to the physical layer
– Service multiplexing on RACH, FACH, and dedicated channels
– Priority handling between ‘data flows’ of one user as well as
between data flows from several users—the latter being
achieved by means of dynamic scheduling
– Access control on RACH
– Address control on RACH and FACH
– Contention resolution on RACH
– Traffic volume measurements
#12 37
Physical Layer
From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/Lecture-5%206%20slides%20per%20page.pdf
#12 38
RRC Layer
• The RRC layer offers the core network the following
services:
– General control service, which is used as an information
broadcast service
– Notification service, which is used for paging and notification
of a selected UEs
– Dedicated control service, which is used for
establishment/release of a connection and transfer of
messages using the connection.
• The RRC layer comprises the following functions:
– Broadcasting information from network to all UEs
– Radio resource handling (e.g., code allocation, handover,
admission control, and measurement reporting/control)
– QoS Control
– UE measurement reporting and control of the reporting
– Power Control, Encryption and Integrity protection
#12 39
RLC Layer
• The RLC layer offers the following services to the higher layers:
– Layer 2 connection establishment/release
– Transparent data transfer, i.e., no protocol overhead is appended to
the information unit received from the higher layer
– Assured and un assured data transfer
• The RLC layer comprises the following functions:
– Segmentation and assembly
– Transfer of user data
– Error correction by means of retransmission optimized for the
WCDMA physical layer
– Sequence integrity-In sequence delivery (used by at least the
control plane)
– Duplicate detection
– Flow control
– Ciphering
#12 40
RLC Layer-Modes
• Transparent-TM
– No header attached
– SAR
– SDU discard
• Delete SDU if not sent before timer expires
– Used for
• Voice
• Some signaling
• Unacknowledged (UM)
–
–
–
–
–
Header with Seq number
SAR
Pad
SDU discard
Provides some reliability
• Acknowledged Mode (AM)
– Siding window-ARQ
– Selective repeat
#12 41
RLC Layer
From, Juan J. Alcaraz, Fernando Cerdan, and Joan García-Haro,
“Optimizing TCP and RLC Interaction in the
UMTS Radio Access Network”, IEEE Network • March/April 2006
#12 42
UE-Call states
• Designed to
– Take advantage of bursty nature of data
– Save batter power
– Maintains logical session and tracks
mobility but when appropriate
– releases dedicated resources to increase
overall capacity
– asleeps the UE
#12 43
UE-Call states
From: http://www.umtsworld.com/technology/RCC_states.htm
#12 44
UE-Call states
• Idle mode
– No active session
– UE monitors Paging
CH
– Sleeps between
paging cycles
From: http://www.umtsworld.com/technology/RCC_states.htm
#12 45
UE-Call states
•
CELL_DCH state (Dedicated)
– A dedicated physical channel
is allocated to the UE in uplink
and downlink.
– The UE is known on cell level
according to its current
active set.
– Dedicated transport channels,
downlink and uplink (TDD)
shared transport channels,
and a combination of these
transport channels can be
used by the UE.
– Call types
• Circuit Switched always in
this state
• Packet Switched in this state
if transferring large volume
of data
Modified rom: http://www.umtsworld.com/technology/RCC_states.htm
#12 46
UE-Call states
•
CELL_FACH state
(Forward Access Ch)
– No dedicated physical channel is
allocated to the UE.
– The UE continuously monitors a
FACH in the downlink.
– The UE is assigned a default
common or shared transport
channel in the uplink (e.g. RACH)
that it can use anytime according
to the access procedure for that
transport channel.
– The position of the UE is known by
UTRAN on cell level according to
the cell where the UE last made a
cell update.
– Radio not put to sleep
– For packet switched sessions
Modified rom: http://www.umtsworld.com/technology/RCC_states.htm
#12 47
UE-Call states
•
CELL_PCH state (Paging Ch)
– No dedicated physical channel
is allocated to the UE.
– The UE selects a PCH with
the algorithm, and uses DRX
for monitoring the selected
PCH via an associated PICH.
– No uplink activity is possible.
– Sleep between pages
– A logical session is still up
– The position of the UE is
known by UTRAN on cell level
according to the cell where
the UE last made a cell
update in CELL_FACH state.
Modified rom: http://www.umtsworld.com/technology/RCC_states.htm
#12 48
UE-Call states
•
URA_PCH State
– No dedicated channel is
allocated to the UE.
– The UE selects a PCH with
the algorithm, and uses DRX
for monitoring the selected
PCH via an associated PICH.
– No uplink activity is possible.
– The location of the UE is
known on UTRAN Registration
area level according to the
URA assigned to the UE
during the last URA update in
CELL_FACH state.
– Similar to CELL_PCH state
only the at the URA level
Modified rom: http://www.umtsworld.com/technology/RCC_states.htm
#12 49
Power Control-PC
• Fast Closed Loop PC – Inner Loop PC
– Feedback information.
– Uplink PC is used for near-far problem. Downlink PC is to
ensure that there is enough power for mobiles at the cell
edge.
• Two special cases for fast closed loop PC:
– Soft handover:- how to react to multiple power control
commands from several sources. At the mobile, a “power
down” command has higher priority over “power up” command.
– Compressed mode:- Large step size is used after a
compressed frame to allow the power level to converge more
quickly to the correct value after the break.
#12 50
Power Control
• Open loop PC
– No feedback information.
– Make a rough estimate of the path loss by
means of a downlink beacon signal.
– Provide a coarse initial power setting of the
mobile at the beginning of a connection.
– Apply only prior to initiating the
transmission on RACH or CPCH.
#12 51
Packet Access in WCDMA
•
Packet allocations performed in the RNC by the packet scheduler (PS)
•
PS allocates traffic to specific channels
•
RNC can decide when and how to send packets based on type of packet
traffic,
–
–
–
–
Time, code or power
Bit rates
Holding times
Channel selection
–
–
–
Common
Delectated
Shared
–
Conversational class -> real-time connection, performed between human users,
really low delay, nearly symmetric, e.g., speech
Streaming class -> real-time connection, transferring data as a steady and
continuous, low delay, asymmetric, e.g., video
Interactive class -> non-real-time packet data, response requested from other
end-user, reasonable round-trip delay, e.g., Web browsing
Background class -> non-real-time packet data, no immediate action expected, less
sensitive to delivery time, e.g., e-mail
–
–
–
•
RNC can assign a packet to a specific channel
Modified from: P. Chong, www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
#12 52
Packet Access in WCDMA
•
Common channels - RACH in the uplink and FACH in the downlink
•
Common channels - CPCH in the uplink
•
Dedicated Channel - DCH in the uplink and downlink
– One or few RACH or FACH per sector
– Low setup time
– No feedback channel -> no fast closed loop power control, no soft
handover, use fixed power
– Poor link-level radio performance and generated more interference
– Suitable for small data amounts
– Bit rate can be high
– Support fast power control
– Suitable for small or medium data amounts
–
–
–
–
–
–
–
Use fast power control and soft handover
Better link-level radio performance and less interference
Longer setup time
Up to 2 Mbps
Suitable for large data amounts
Not suitable for bursty data
In case of changing bit rate in the downlink, the downlink orthogonal
code is reserved according to maximum bit rate.
From: P. Chong, www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
#12 53
Packet Access in WCDMA
•
•
In WCDMA packet scheduling algorithms can be done in two ways,
in a time or code division manner.
Time division scheduling
•
Advantages of time division scheduling
•
Disadvantages
–
–
–
–
one user is allocated a channel at a time (10 ms frame)
all available capacity can be allocated to that user
high data rate for a short period of time
increase more users, each user has to wait longer
– high bit rate required less energy per bit
– less interference
– shorter delay due to high bit rate
– high unused physical resources due to short transmission time and
– relatively long set up and release time
– high variations in the interference levels due to high bit rate and
bursty traffic
– limited uplink range of high bit rate due to mobile’s limited
– transmission power
From: P. Chong, www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
#12 54
Packet Access in WCDMA
• Code division scheduling
–
–
–
–
many users are allocated the channels simultaneously
the capacity is shared with all users
low data rate for a long period of time
increase more users, each user’s bit rate is decreased
• Advantages
– resources are in full usage due to longer transmission
time
– small variation in interference level
– longer uplink range due to lower bit rate
• Disadvantages
– longer transmission delay due to low bit rate
– high interference due to high energy per bit
– low total throughput
From: P. Chong, www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
#12 55
Packet Access in WCDMA
• Time division is normally used with
shared channels and code division is
normally used with dedicated channels.
From: P. Chong, www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
#12 56
Packet Access in WCDMA
• Transmission Power-based Scheduling
– The bit rate allocated to each packet data users could be
based on required transmission power
• Users close to the BS requires less transmission
power and can get a higher bit rate, whereas users
at the cell edge could get lower bit rate
• Advantages
– minimize the average power sent per bit
– less interference
– increase the throughput
• • Disadvantages
– accurate power estimation
– unfair resource allocation
From: P. Chong, www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
#12 57
HSDPA & Enhance Uplink
• HSDPA = High Speed Downlink Packet
Access
From: Stefan Parkvall, Eva Englund, Magnus Lundevall, and Johan Torsner,
“Evolving 3G Mobile Systems: Broadband and Broadcast Services in WCDMA”,
IEEE Communications Magazine, February 2006
#12 58
HSDPA & Enhance Uplink
• Remember it is better (more efficient) to have a large
number of users sharing a single server
• This lead to a desire to have fast allocation of shared
resources
• Downlink resources
– Transmit power (interference to other cells)
– Channelization code
• Uplink resources
– Interference at the BS
• Other fast mechanisms
– Fast scheduling
– Fast ARQ (hybrid ARQ) (this is in addition to the RLC AM)
• To be fast mechanisms must be close to the air interface
– Mechanisms in BS (Node B)
#12 59
HSDPA & Enhance Uplink
• UTRAN Architecture with HSDPA
and enhanced uplink
From: Stefan Parkvall, Eva Englund, Magnus Lundevall, and Johan Torsner,
“Evolving 3G Mobile Systems: Broadband and Broadcast Services in WCDMA”,
IEEE Communications Magazine, February 2006
#12 60
HSDPA & Enhance Uplink
• Changes
– shorter radio frame
– new high-speed downlink channels
– use of 16 QAM modulation in addition to QPSK
modulation
– code multiplexing combined with time multiplexing
– a new uplink control channel
– fast link adaptation using adaptive modulation and coding
(AMC)
– use of hybrid automatic-repeat-request (HARQ)
– medium access control (MAC) scheduling function moved
to Node-B (WCDMA packet scheduling was done in the
RNC)
From: Agilent, Applications note:
Concepts of High Speed Downlink Packet Access:
Bringing Increased Throughput and Efficiency to W-CDMA
#12 61
HSDPA & Enhance Uplink
• Gain in Performance
From: WCDMA Evolved:
High Speed Downlink Packet Access Mechanisms
and Capabilities, Alexander Wang
www.pcca.org/standards/architecture/hsdpa.pdf
#12 62
HSDPA
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Shared transmission mechanism
Definition of a new “channel”
High-speed downlink shared channel (HS-DSCH)
The HS-DSCH is dynamically use to transmit to
individual users
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Supports link adaptation, hybrid ARQ and scheduling
Always associated with a DPCH
Never in soft handover
Mapped to one or several channelization codes
• An associated control channel is also defined
• High Speed- shared control channel (HS-SCCH)
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HSDPA
• New frame structure
– Five subframes/W-CDMA
frame
– User data can be assigned
on a subframe basis
– System can adjust in 2ms
– Each subframe is a
transmission time interval
(TTI) = 2ms
*
*From: Agilent, Applications note:
Concepts of High Speed Downlink Packet Access:
Bringing Increased Throughput and Efficiency to W-CDMA
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HSDPA
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HS-DSCH structure both Code sharing and TDM
SF=16
15 different spreading codes
UE can send on multiple codes in a TTI
Main difference with W-CDMA is that the shared
resource is also in the time domain
From: Stefan Parkvall, Eva
Englund, Magnus Lundevall, and
Johan Torsner,
“Evolving 3G Mobile Systems:
Broadband and Broadcast
Services in WCDMA”,
IEEE Communications Magazine,
February 2006
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HSDPA
• Another view
*
Spreading Code
*From: Agilent, Applications note:
Concepts of High Speed Downlink Packet Access:
Bringing Increased Throughput and Efficiency to W-CDMA
#12 66
HSDPA
• Link Adaptation
– Remember the fast power control is commonly used
to:
• Maintain constant Energy/Noise ratio
• Reduce effect of fading
– This is suitable for constant bit rate transmissions
– Here bit rate can change  introducing delay
– Changing bit rate can also maintain constant
Energy/Noise while keeping the tx power constant
– The is called link rate adaptation
*
*From: WCDMA Evolved:
High Speed Downlink Packet Access Mechanisms
and Capabilities, Alexander Wang
www.pcca.org/standards/architecture/hsdpa.pdf
#12 67
HSDPA
– Bit rate changed by using
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• QPSK (2 bits per symbol time)
Or
• 16 QAM (4 bits per symbol time)
Modulation selected every 2 ms
Number of codes assigned selected every 2 ms
(Bit rate/code) * # codes = bit rate
Theoretical maximum
• Largest transport block = 27,952 bit in 2ms =
13.9Mb/s consumes most of cell’s resources for one
user
• 1 – 2 Mb/s closer to achievable under real conditions
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HSDPA
• To assign a modulation and bit rate/code the BS
(Node B) needs some link quality feed back from
the UE
• Each UE regularly transmits Channel Quality
Indicator (CQI) to the BS
– Configurable
– Can be every 2 ms
• CQI (0-30) each mapping into a modulation, SF,
etc.
• Note the “better” UE’s can ask for higher CQI’s,
e.g., a UE with interference suppression
•
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HSDPA
• Scheduling
– The scheduler decides which user should
get access to each TTI
– CQI provides input into a Scheduler
• Proportional Fair (PF) Scheduler can be uses
• Implementation Specific
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HSDPA
• Hybrid ARQ (HARQ)
– Uses incremental redundancy (IR)
– Note when UE close the BS the number
of spreading codes limits rate not power,
so likely receive first transmission
– At greater distances move from BS see
more errors, IR will require additional
transmission but not many.
– HARQ only retransmit upon an ACK or
NACK
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HSDPA
From: Mohamad Assaad, Zeghlache Djamal TCP Performance Over UMTS-HSDPA
Systems, CRC Press, 2007
#12 72
HSDPA
• Key concepts
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Shared Channel Transmission
Higher order Modulation
Short Transmission Time Interval (2 ms)
Fast Hybrid ARQ with Soft Combining
Fast Link Adaptation
Fast Radio Channel Dependent
Scheduling
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Enhance Uplink (HSUPA)
• Enhanced dedicated channel (E-DCH)
• Needs power control for near-far problem
so no higher order modulation  can not
trade off data rate for E/N
• Shared resource is CDMA interference at
the BS (Node B) desire to maintain a
target interference level at Node B
• Interference a fuction of
– UE SF data rate (higer rate more interference)
– UE transmission time
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Enhance Uplink (HSUPA)
• A scheduler is used to control
– When each UE transmits
– What rate each UE transmits at
• Goal of the scheduler is to assign resource to
those UEs with data to send
• There are two types of grants:
– The Absolute Grants provide an absolute limitation of the
maximum amount of UL resources the UE may use;
– The Relative Grants increase or decrease the resource
limitation compared to the previously used value;
• UE sends scheduling requests with
– Available Tx power
– UE buffer state
– Priority of buffered data (to provide QoS)
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Enhance Uplink (HSUPA)
• BS (Node B) sends scheduling grants
– BS knows
• Instantaneous interference level
• All requests
– Then determines which grants to sent
• This resource allocation scheme more
efficient for bursty traffic allowing more
liberal connection admission control.
• HARQ is also used on the uplink
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References #12
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Attar, R., et al., Evolution of cdma2000 cellular networks:
multicarrier EV-DO. Communications Magazine, IEEE, 2006. 44(3):
p. 46-53.
Bhushan, N., et al., CDMA2000 1xEV-DO revision a: a physical layer
and MAC layer overview. Communications Magazine, IEEE, 2006.
44(2): p. 37-49.
Ekstrom, H., et al., Technical solutions for the 3G long-term
evolution. Communications Magazine, IEEE, 2006. 44(3): p. 38-45.
Guangyi, L., et al., Evolution map from TD-SCDMA to FuTURE B3G
TDD. Communications Magazine, IEEE, 2006. 44(3): p. 54-61.
Parkvall, S., et al., Evolving 3G mobile systems: broadband and
broadcast services in WCDMA. Communications Magazine, IEEE,
2006. 44(2): p. 30-36.
Sanjiv Nanda, K.B., Sarath Kumar,, Adaptation Techniques in
Wireless Packet Data Services. IEEE Communications Magazine,
2000(1): p. 54-64.
Sarikaya, B., Packet mode in wireless networks: overview of
transition to third generation. Communications Magazine, IEEE,
2000. 38(9): p. 164-172.
Yavuz, M., et al., VoIP over cdma2000 1xEV-DO revision A.
Communications Magazine, IEEE, 2006. 44(2): p. 50-57.
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References #12
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Leon-Garcia & Widjaja: Communication Networks, McGraw Hill,
2004
www.ccs.neu.edu/home/rraj/G250Projects/NachiketMehta.ppt
M. D. Yacoub, Wireless Technology, Protocols, Standards, and
Techniques, CRC Press, 2002
Geert Heijenk,
wwwhome.cs.utwente.nl/~heijenk/mwn/slides/Lecture5%206%20slides%20per%20page.pdf
Juan J. Alcaraz, Fernando Cerdan, and Joan García-Haro,
“Optimizing TCP and RLC Interaction in the UMTS Radio Access
Network”, IEEE Network • March/April 2006
http://www.umtsworld.com/technology/RCC_states.htm
P. Chong,
www.comlab.hut.fi/opetus/238/lecture9_PacketAccess.pdf
Agilent, Applications note: Concepts of High Speed Downlink Packet
Access: Bringing Increased Throughput and Efficiency to W-CDMA
Alexander Wang , WCDMA Evolved: High Speed Downlink Packet
Access Mechanisms and Capabilities,
www.pcca.org/standards/architecture/hsdpa.pdf
Mohamad Assaad, Zeghlache Djamal TCP Performance Over
UMTS-Hsdpa Systems, CRC Press, 2007
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