9.
•
•
•
•
WIRELESS ATM
Anywhere, Anytime Access to ATM Networks.
Voice, Data, Video, and Images in Any Combination, Anywhere,
Anytime with Convenience and Economy.
Fixed Wireless & Mobile Users
Wireless Equipment.
Problems
– Noisy Wireless Channels
High BER.
– Wireless Channel
Very bandwidth limited.
ATM designed for bandwidth-rich environment.
– Overhead
Every ATM cell has overhead of 10%.
For wireless channel, we need more control information which can
far exceed the overhead limit.
Wireless ATM Network Architecture
HLR
ATM Network
VLR
MSC
Base Station
VLR: Visitor Location Register
HLR: Home Location Register
MSC: Mobile Switching Center (also ATM switch)
Wireless ATM in Digital Battlefield
Fixed ATM Network
Satellite
Wireless LAN
FSC: Fixed Switch Center
(ATM Switch)
MBS: Mobile Base Station
Military and Commercial
Wireless ATM Networks
Commercial
Static network topology
Typically single hop
Static allocation n-band user
and data channels
Maximum number of
users/hertz/area
Privacy
Fixed infrastructure for open
access
Military
Highly dynamic topology
Multi hop
Dynamic bandwidth
allocations; Priorities
Maximum transfer rate in
hostile environment
High security
Constrained access
Quality of Service (QoS) Parameters
1.
2.
3.
4.
5.
6.
7.
8.
9.
Throughput
Delay
Also in wired ATM network
Jitter
Loss Probabilities
Probability of Dropping the Call
Expected BER; Packet Error Rate
Expected Disruption Time During Handoffs
Minimum or Maximum Level of Mobility
QoS Renegotiation
Personal Mobility vs. Terminal Mobility
User
Terminal
Wired
Wireless
Terminal Mobility
Personal Mobility
Networ
k
Protocol Stack For Wireless ATM
Quality Critical
Applications
Time Critical
Applications
TCP
UDP
IP
AAL Layer
ATM Layer
IP
Layer
ATM
Layer
Error Control
Link
Medium Access Control
Layer
Physical Layer (Wireless Channel)
Specific Requirements for PHY Layer
Low Speed Wireless PHY
Frequency Band
Cell Radius
Transmit Power
5.15-5.35 GHz, 5.725-5.875 GHz
HIGH Speed Wireless PHY
59 GHz - 64 GHz
80 m
10 - 15 m
100 mW
10 – 20 mW
Frequency Reuse Factor
up to 12
7
Channel Bandwidth
30 MHz
150 / 700 MHz
Data Rate
Modulation
MAC Interface
Fixed Packet Length
25 Mbit/s
155 / 622 Mbit/s
16 tone DQPSK
32 tone DQPSK
par., transf. speed 3.127 Mbyte/s
par., transf. speed 87.5 Mbyte/s
PHY header + MAC header + 4*ATM cells
System Architecture and Protocol Model
Wireless Workstation
Host
User Applications
(Quality-Critical Traffic)
TCP/IP
ATM
Backbone Network
AAL Subsystem
ATM
Sonet
Host
DL Subsystem
Wireless Workstation Wired Line Wireless Link
Error Control
Time Critical
Applications
Quality
Critical
Applications
FEC
Hybrid ARQ
Why FEC?
• ATM HEC performance is too low for
wireless ATM.
• High CLR and payload errors
• Cell delineation problem
FEC (for Time-Critical Applications)
• To correct channel errors at the expense of
bandwidth by adding redundancy
Concatenated FEC Scheme
Cells
RS Outer
Encoder
Symbol
Interleaver
Conv. Inner
Encoder
Transmitter FEC
Cells
RS Outer
Decoder
Symbol
Deinterleaver
Viterbi
Decoder
Receiver FEC
Bit Level
Interleaver
Wireless
Channel
Bit Level
Deinterleaver

Why Hybrid ARQ? (for Quality Critical Traffic)
– ARQ provides high reliability at good and moderate
channel qualities.
– The throughput drops rapidly, if the channel error
rate is high as in wireless channels.

Hybrid ARQ
– FEC first tries to correct the frequent error patterns.
If it fails, then ARQ takes over.

Hybrid ARQ Types
– Type I Hybrid ARQ scheme
– Type II Hybrid ARQ scheme: only additional parity
bits are retransmitted to combine with the previous
packet (incremental redundancy).
Medium Access Control for Wireless ATM Networks
MT
MT
MT
Categorization of MAC Protocols

Based on Channel Organization
–
–
–
–

TDMA-Based MAC Protocols
CDMA-Based MAC Protocols
Random MAC Protocols
Hybrid MAC Protocols
Based on Duplex Mode of Uplink and
Downlink
– Time Division Duplex (TDD) (One Carrier Frequency)
– Frequency Division Duplex (FDD) (Two Carrier
Frequencies)
* Frequency
Division Duplex (FDD)
(Two Carrier Frequencies)
– Uplink frequency carries traffic from terminal to BS while
downlink frequency carries traffic from BS to terminal.
– FDD allows almost immediate feedback from the BS enabling
terminal to find out quickly if its contending reservation
request was unsuccessful and a retransmission is necessary.
– Thus, FDD impacts the delay encountered by user traffic as
well as the resource availability of the wireless channel.
TDMA Based MAC Methods
– Dynamic Packet Reservation Multiple Access (DPRMA), by Dyson
and Haas in 1999. FDD
– Mobile Access Scheme Based on Contention and Reservation for
ATM (MASCARA), by Bauchot et al. in 1996, and Passas et al. in
1997. TDD
– PRMA with Dynamic Allocation (PRMA/DA), by Kim and Widjaja in
1996. FDD
– PRMA with Adaptive TDD (PRMA/ATDD), by Priscoli in 1996. TDD
– Dynamic TDMA with Piggyback Reservation (DTDMA/PR), by Qiu
et al. in 1996. FDD
– Distributed Queuing Request Update Multiple Access (DQRUMA),
by Karol et al. in 1995. FDD
– Dynamic TDMA with TDD (DTDMA/TDD), by Xie et al. in 1995.
TDD
Packet Reservation Multiple Access (PRMA) Protocol (Goodman’91)







Time is divided into slots of equal duration, and slots are
grouped into frames.
Each slot in a frame is either “reserved” or “available”.
BS controls the upstream traffic and broadcasts a continuous
stream of packetized information through the downstream
channel
The status of a slot is provided in feedback information supplied
by BS.
Terminals can send two types of information: “Periodic”
information such as speech or “Random” information such as
data.
Frame rate is identical to the arrival rate of the speech packets.
Uses S-ALOHA for time slot reservation and TDMA for data
transmission.
Packet Reservation Multiple Access (PRMA) Protocol (Goodman’91)






A station contends for an available slot using S-ALOHA.
If transmission is successful, BS responds with an ACK message and the
slot is reserved in subsequent frames until the terminal relinquishes it by
leaving the slot empty.
A terminal with “random packets” contends for slots in the same way, but
cannot reserve the same slot in a subsequent frame even after a
successful transmission.
Thus, terminal must contend again for another available time slot.
For unsuccessful transmission, a terminal with “periodic” packets
retransmits the packet with certain probability in subsequent unreserved
slots until it receives an ACK signal from BS.
Similarly, a terminal with “random” packets retransmits a packet in
unreserved slots with certain probability.
Packet Reservation Multiple Access (PRMA) Protocol
(Goodman’91)
Advantages:
 Simple
Disadvantages:
* Upon congestion, the speech packet dropping rate and
data packet delay both increase.
* Feedback information may cause waste of bandwidth.
PRMA/DA — Services and the Frame Structure


Supports Multimedia Traffic
– Constant Bit Rate (CBR), Variable Bit Rate (VBR), Available Bit
Rate (ABR).
Frame Structure
– It is organized according to traffic types.
– Downlink transmission is not considered. FDD
Request packet
PRMA/DA
header
PRMA/DA
trailer
ATM cell
1
2
…
Na
Available slots
1
2
Variable
Variable
Variable
…
Nc 1
CBR reservation slots
PRMA/DA
header
2
…
Nv 1
VBR reservation slots
ATM cell
Wireless Packet
2
…
Nd
ABR reservation slots
PRMA/DA
trailer
Operation Procedures of PRMA/DA



Send Requests in Available Slots
– Contention-based transmission.
– Slotted ALOHA is used.
Reserve Time Slots for each Successful Request
– Dynamic allocation algorithm is used to allocate time slots
for CBR, VBR, and ABR connections.
– The allocated time slots are reserved for the lifetime of a
connection.
– Dynamic allocation algorithm is also used for updating
available time slots for the transmission of requests.
Transmit Packets in Reserved Time Slots
– Since time slots are reserved, contention is free in this
phase.
Contributions and Shortcomings of PRMA/DA


Contributions
– Dynamic allocation of slots for each sub-frame.
• Variable boundary can be easily implemented.
• Bandwidth can be utilized efficiently.
• Collisions can be resolved quickly
– No mini-slots; Easy for synchronization.
– Multiple traffic classes supported.
Shortcomings
– A request packet has the same length as a data packet.
• If traffic rate high, this would cause inefficiency.
– No mechanism is used to dynamically update VBR resources.
• VBR bandwidth is allocated according to the average rate. The
bursty requirement has to rely on the leftover bandwidth. QoS
of VBR cannot be guaranteed.
MASCARA
(Mobile Access Scheme based on Contention and Reservation for ATM)




Supports CBR, real-time VBR (rt-VBR), non-real-time VBR (nrtVBR), ABR, UBR traffic.
Demand assignment scheme with contention based reservations.
Uplink subframe is divided into a contention period to transmit
reservation requests or some control information, and uplink
period for uplink data traffic.
Each period within a frame has a variable length depending on the
instantanous traffic to be carried.
FH Period Uplink Period
MPDU 1 MPDU 2
Downlink Period ContentionPeriod
……
MPDU n
PHY MPDU
MPDU payload: Cell train (many ATM cells)
Hdr Hdr
1 time slot
n time slots
Operation Procedures of MASCARA





If a terminal has cells to transmit, it sends a reservation request either
piggybacked in the MPDUs uplink period or in special control MPDUs sent
in the contention period.
Base station schedules transmissions of the next frame according to
reservation requests, arriving cells for each downlink connection, traffic
characteristics and QoS requirements of all connections.
In the Frame Header of the downlink, BS broadcasts information which
contains a descriptor of the current time frame (including the lengths of
each period), the results of the contention procedures from the previous
frame and the position of the slot allocated to each downlink and uplink
connection.
To minimize PHY layer overhead, MASCARA uses the concept of a CELL
TRAIN (a sequence of (1-n) ATM cells belonging to a terminal and having
a common header).
Length of overhead plus that of the MPDU header is equal to one time
slot, which is defined as the length of an ATM cell.
Priority Regulated Allocation Delay-Oriented Scheduling
(PRADOS)
* Assigns priorities for each connection according to its service class.
*
•
•
•
Traffic
Priority
Token Pool
CBR
5
Yes
rt-VBR
4
Yes
nrt-VBR
3
Yes
ABR
2
Yes
UBR
1
No
PRADOS combines priorities with a leaky bucket traffic regulator.
Regulator uses a token pool introduced for each connection.
Tokens are generated at a fixed rate equal to the mean ATM cell rate of each VC.
Size of the pool is equal to the maximum number of ATM cells that can be
transmitted with a rate greater than the declared mean.
• Starting at priority 5 and ending with priority 2, scheduler satisfies requests for
connections as long as tokens and slots are available.
• For every slot allocated to a connection, a token is removed from the
corresponding pool.
Contributions and Shortcomings of MASCARA


Contributions
– Cell train concept is used.
– A novel scheduling scheme - PRADOS.
– Dynamic TDD is implicitly implemented.
– Multiple traffic classes are supported.
Shortcomings
– With each request corresponding to a time slot, too many
requests are transmitted in the protocol. This results in
wasting bandwidth.
– Large size of request packet results in reduction of good
throughput.
– Connection admission control (CAC) is separate from the MAC
protocol. The overall performance of the integrated system is
unpredictable.
Comparisons of TDMA MAC Protocols
Protocols
PRMA/DA
MASCARA
DPRMA
Duplex Mode
FDD
TDD
FDD
Frame Type
Fixed
Variable
Fixed
Random Access
Slotted
ALOHA
Slotted
ALOHA
Reservation
ALOHA
Mini-slot
No
No
No
CAC
In MAC
Separate
Separate
Traffic Classes
CBR, VBR,
ABR
CBR, ntVBR, nrtVBR, ABR,
UBR
Voice, video,
data
Network Layer
ATM
ATM
ATM
Control Overhead
Medium
High
Medium
Mobility Management in W-ATM
Networks

Location
Management

Handoff
Management
Base Station
A
MT A is receiving a call !
How will the network
deliver the call to A ?
Types of Mobility



TERMINAL MOBILITY
(network should route calls to the MT
regardless of its point of attachment)
PERSONAL MOBILITY
(users should access the network wherever
they are; UPT (Universal Pers. Tel #))
SERVICE PROVIDER MOBILITY
(allow user to roam beyond regional
networks).
Location Management
Location Update
(Registration)
Call Delivery
(Paging)
Cost Tradeoff
Too Many Location Updates
Low Paging Costs
High Update Costs
Too Few Location Updates
High Paging Costs
Low Update Costs
Solution

Location Areas (GSM) = Registration Areas (IS-41)
Registration Area Boundary
Center Cell
Handoff Types
Intra-Cell
Inter-Cell
Soft Handoff
Hard Handoff
W-ATM Architecture
ATM Backbone Network
ATM
Switch
ATM
Switch
Wireline connections
to ATM switch
Wireless connections to BS
Cell
MT
BS
LOCATION MANAGEMENT TECHNIQUES FOR
W-ATM
LOCATION MANAGEMENT
LOCATION
SERVICE
TERMINAL
PAGING
TWO-TIER
DATABASES
LOCATION
ADVERTISEMENT
VIRTUAL
CONNECTION
TREE
LOCATION
REGISTERS
INTEGRATED
LOCATION
RESOLUTION
MOBILE PNNI

LOCATION SERVICE
* Use of DATABASES to maintain records of
MTs.
* When location information is obtained from
DATABASE, TERMINAL PAGING is used to
deliver calls to MTs.
* Requires signaling, querying and paging.

LOCATION ADVERTISEMENT
* No databases but location information is
broadcast throughout the network.
Location Service: Method 1:
Two Tier Database (Akyol/Cox’96)
Home
Tier
Visitor
Tier
HOME
ZONE
(3)
(4)
(5)
Home
Tier
Visitor
Tier
CURRENT
ZONE
(1)
(2)
Zone
Manager
Home
Tier
Visitor
Tier
PREVIOUS
ZONE
Explanation:
* Bi-level databases are distributed to ZONES throughout the
network.
* Each zone is maintained by a ZONE MANAGER controlling
the zone’s location update procedures.
* Each MT has a home zone where it is permanently
registered.
1.
2.
3.
4.
5.
MT transmits a location registration request message to the new
zone. Message contains User ID Number, authentication data and
ID of the previous zone.
Current zone manager determines the home zone of the MT from
the previous zone ID.
Current and home zone managers authenticate the user and
update home user profile with the new location information.
Home zone sends a copy of the profile to the current zone
manager which stores the profile in the visitor tier of its database.
Current zone manager sends a purge message to the previous
zone manager so that user’s profile is deleted from the visitor tier
before.
Location Advertisement: Method 1:
Virtual Connection Tree (Veeraraghavan et.al.’97)
Portable
Base Station (PBS)
MT’s Former
position
De-registration
message
Registration
message
Cell
Boundary








VCT advertises location information via provisioned virtual
paths.
A collection of PBSs connected via provisioned VPs forms a
connection tree.
PBSs are equipped with switching capabilities and limited
buffering capabilities.
Trees are based on the mobility indications of the MT.
Each PBS maintains a running list of resident MTs in its
coverage area.
Location registration occurs when MT is on/off or it moves to
a new service area.
On/Off case, MT sends a message to its local (current) PBS
which then adds/deletes the MT to/from the service list.
When MT moves to a new service area of a PBS, the PBS
sends a de-registration message to the old PBS on behalf of
the MT and enters the MT’s ID into its current list.
Comparison of Location
Management Techniques
Location Service
Advantages
Flexibility
Scalability
Disadvantages
Database Admin
Signaling Load
Location Advertisement
Advantages
Disadvantages
No Paging
No Scalability
No Database
Admin
Wasted
Bandwidth
Handoff Management
Full
Connection
Re-Routing
Route
Augmentation
InterWorking
Devices
Connection Extension
InterWorking
Devices
Connection Re-Routing
Multicast
Connection
Re-Routing
Partial
Connection
Re-Routing
Nearest
Connection
Node Re-Routing
Virtual
Connection
Tree Re-Routing
Hybrid
Connection
Re-Routing
Homing Base
Station
Re-Routing
Full Connection Re-Routing:
Maintains the connection by establishing a completely new
route for each handoff as if it were brand new call.
Route Augmentation:
Extends the original connection with a hop to the MTs next
location.
Partial Connection Re-Routing:
Re-establishes certain segments of the original connection,
while preserving the remainder.
Multicast Connection Re-Routing:
Combines the 3 techniques but includes the maintenance of
potential handoff connection routes to support the original
connection, reducing the time spent in finding a new route
for handoff.
Comparison of Handoff Management
Approaches
Full
Optimal
route;
existing
methodology
Extension
Partial
Advantages
Multicast
Fast;
maintains
cell
sequence
Fast;
maintains
cell
sequence
Maintains cell
sequence;
reduced
resource utilization
Disadvantages
Slow;
inefficient resource
re-assignment
Wastes bandwidth;
inefficient
connection route
Complex;
added switch
processing reqs
Added buffering
requirements;
bandwidth
pre-allocation
References:
J. McNair, “Mobility Management Protocols for Wireless ATM
Networks”, BWN Lab Technical Report, 1997. (Available on the
WEB).
I.F. Akyildiz, J. McNair, J. Ho, H. Uzunalioglu, W. Wang,
“Mobility Management in Next Generation Wireless Systems”,
Proceedings of the IEEE Journal, Vol, 87, No.8, pp.1347-1384,
August 1999.