Call-fail-safe and Distribution-effective
Methods for Multi-band Multi-carrier Traffic
Allocation in 3GB Wireless Networks
- Parthasarathy
Guturu
EE Department,
University of North Texas, Denton
Agenda
Overview of 3G CDMA/WCDMA
wireless communications
Single Band Multi-carrier Traffic
Allocation Problem
Multi-band Multi-carrier Traffic
Allocation- How to contain increased
call failure probability?
A class of Multiband Algorithms
Simulation Results
Summary and Conclusion
Power
– FDMA (Frequency
Division Multiple
Access). Each user has
a private frequency
– TDMA (Time Division
Multiple Access). Each
user has a private time
on a private frequency
– CDMA (Code Division
Multiple Access). Users
co-mingle in time and
frequency, but each
user has a private code.
FDMA
TDMA
Power
How multiple users
can share the same
medium (air interface)
simultaneously?
Power
Multiple Access Technologies
CDMA
CDMA- Spreading Principle
Receiver 1
Transmitter 1
Medium (Air)
User 1
Data
User 1
Data
1.288 MHZ Spreading Code 1
Transmitter 2
User 2
Data
1.288 MHZ Spreading Code 1
Receiver 2
User 2
Data
1.288 MHZ Spreading Code 2
1.288 MHZ Spreading Code 2
Orthogonal Codes
Two Codes are orthogonal if Exclusive OR
operation on them yields equal number of 0’s and
1’s.
Orthogonal (Walsh) Code generation recursively:
H2 =
H1
H1
H1
H1
0
00
01
0000
0101
0011
0110
Almost orthogonal
– Short PN (Pseudo-Noise)
– Long PN
Walsh codes used in forward (down, base-station
to mobile) link. PN sequences used in reverse
(up) link for transmission and scrambling at
down link.
Frequency Reuse: Cell Planning in
AMPS/TDMA/GSM
1
4
7
6
1
2
3
5
4
7
6
1
2
3
6
1
4
7
6
1
1
2
3
5
1
Since separation of users in CDMA is via orthogonal codes, frequency
can be reused virtually every cell.
Generations of Wireless Technologies
First Generation (1G)
– AMPS (Analog Mobile Phone Service)
using FDMA
– NAMPS (Narrow-band AMPS) using FDMA
– DAMPS (Digital AMPS) using TDMA
2G. Ex: GSM (European 2G TDMA)
3G
– Some distinctive features compared to
2G (Next slide)
– CDMA & WCDMA (Wideband CDMA) used
CDMA Network Architecture
VLR
MSC
MSC
HLR
AC
PSTN
BSC
VMS
BSC
MSC- Mobile Switching Center
BSC- Base Station Controller
BTS- Base-station Transceiver
System
VLR- Visiting Location Register
HLR- Home Location Register
MC- Messaging Center
VMS- Voice Mail System
ACAuthentication Center
MC
IWF
RNC
BSC
PPDN
BSC
Wireless
MS
BTS
BTS
174285C396
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PSTN- Public Switching Telephone Network R
PPDN- Public Packet Data Network
IWF- Inter Working Function
Distinctive Features of 3G
Addressing of 2G limitations:
– Bandwidth limitations (14.4 – 64 Kbps)
– Designed originally for voice; low capacity
– Low data rates (up to 14.4 Kbps)
– Limited Roaming Capabilities
– Limited support for packet data
– single-service networks
– No Multimedia
Asymmetric Data Rates
Bandwidth on Demand
Always Connected (concept of Dormant
states)
3G Wireless Systems & Standards
3G Wireless Standards & Systems
CDMA- Code Division Multiple
Access
CDMA 2000
(Successor of IS-95)
1xRTT
UMTS- Universal Mobile
Telecommunications System
RTT- Radio Transmission
Technology
FDD W-CDMA
3xRTT
UMTS
TDD W-CDMA
FDD- Frequency Division Duplex
TDD- Time Division Duplex
1x EVDO
1x EVDV
EV- Evolution DO- Data Only DV- Data
and Voice.
Spectrum Allocation
800 MHZ (cellular) Band
– 824-894 MHz, divided into sub-bands, carriers
from paired sub-bands used for up/down link
communications.
– Each RF Carrier is 1.25 MHZ wide
– Cellular spectrum of 1 operator is 12.5 MHZ
wide, but only 9 carriers can be accommodated
because of the need to support AMPS
1900 (PCS) MHZ
– 1850-1990 MHZ, divided into A, B, C sub-bands
with 30 MHz each (for 11 carriers) and D, E, F
sub-bands 10 MHz each (supporting 3 carriers)
– 260 KHz Guard band
MCTA Algorithm
Available carrier capacity may be
assessed using either
– Forward link power still available for call
setup without service degradation
– Unused Walsh codes
Limiting the calls on a carrier based on
either of the above criteria guarantees
QOS.
MCTA is a class of load distribution
algorithms based on carrier capacities.
Multi-Band Situation- Cell
Coverage Problem
F
147258C369
*0L#
R
D
I
B
C
G
A
E
H
Naive Extension of MCTA to Multi-Band Situation
Cell
Site
No
Cell Site Data
Current Cell Site Data
Band
Band
Pref.
Other Band Cell
Sites covering the
original site range
BTS Data
BTS-1
…
450
800
1900
BTS-M
1
450
0
-
3,5
2
1900
2
1
3
-
3
800
1
1
-
2,4
4
1900
2
1
5
-
5
800
1
1
-
2,6
6
1900
2
1
3
-
…
…
..
…
…
…
…
…
…
Table-1: A typical Cell Site Data Table.
2,4,6
Problem with Naive Extension of
MCTA to Multi-Band Situation
Latest version of 3GGPP standard provides for up to
13 bands. Currently 800 and 1900 MHz bands are
operational. In Russia, they are trying to introduce
450 MHz band. Using all bands- not cost-effective.
1-1 overlay systems (cell sites) in different bands
may not always be co-located.
Even if they are, position of a mobile accessing a BTS
of one band may not covered by the co-located
system of the other band. (Radio coverage of the
carriers of 800 band is roughly 3 times that of the
1900 band carriers).
If call is redirected to the other band because of its
best capacity carrier, call may fail if the best capacity
carrier accessible to mobile has no capacity.
Our Min-Max Solution to the Dual
Band Traffic Allocation Problem
The rationale behind the algorithm:
If a mobile can access a cell site, it can be
allocated the best capacity carrier of the cell site.
It is not sure which of the other band cell sites
(covering the range of the original cell site of
access band) is accessible to the mobile because
of its position.
Hence find the best carrier of each one of the
other band cell sites and choose the worst among
them (min-max carrier) to compare with the
inband best carrier of non-zero capacity.
Call is redirected to the other band if the minmax carrier is better. Redirection is done even if
inband best carrier has no capacity and at least
one carrier in the other band has capacity.
Implementation of the Algorithm
Cell site information (addresses of colocated BTSes and the Cell site IDs of the
other band cell sites covering this one) is
provisioned and stored in an in-memory
database at the BSC.
When MSC sends Call setup request with
the original cell site information, BSC
requests Capacity information from all the
BTSes.
Considering all the responses arrived
within a pre-configured time, BSC finds
the best carrier of each cell site and
applies the min-max algorithm
Implementation of the Algorithm
anMS::MS
aBTS::BTS
anMSC::MSC
aBSC::BSC
cellSiteInfoTable:: Table
<< Mobile-Originated Call >>
Originate-Call()
Originate-Call()
Setup-Call (…)
<< Mobile-Terminated Call >>
Page-Mobile()
Page()
Process-PageResponse()
Process-PageResponse()
Setup-Call (…)
Get-Access-Carrier-Info (…)
Get-Carrier-And-BTS-Info-Lists (…)
Execute-MBTA-Algorithm (…)
Extensions to the MCTA Algorithm
Development of an Enhanced
Capacity Measure (ECM) by
augmenting mobile-user specific
preferences.
ND-Bit SC-Bit RC-Bit RB-bit BPR-Bits CPR-Bits
Capacity Magnitude Bits
CAC-Bit
IBC-Bit
ND- Non-downgraded
SC-: Spare Capacity
RC: Retain Carrier
BPR- Band Priority
CPR- Carrier Priority
CAC- Call Access Carrier
IBC- Inband Carrier
Extension of the dual-band algorithm
to the case of more than two bands.
Multi-band algorithms
Optimistic algorithm
 ECM Bi   ECM Bj 
Newcall 
 Band Bi  Bi, Bj T
 ECM Bi   0
AssignTo
1
ECM Bi  
ECM Sj 

nBi  Sj Bi T
ECM Sj   max ECM Ck 
Ck Sj
Best-fit algorihm
Newcall 
 Band Bi 
AssignTo
MinMaxECM Bi   min ECM Sj 
Sj Bi
MinMaxECM Bi   MaxMinMaxECM T
^ MinMaxECM Bi   0

MaxMinMaxECM T   max MinMaxECM Bi 
Bi T
Multi-band algorithms (continued)
Best-band algorithm
  ECM Bj 

ECM
B
i   max 
AssignTo
 Bi,Bj T -E

Newcall 
 Band Bi 
 ECM Bi   0
E
 B
i
iff MaxMinMaxECM T   0
MinMaxECM Bi 0
  , otherwise
Firs-fit algorithm
– Simply assign call the first band non-zero
MinMaxECM.
Call Distribution Effectiveness Measure
Between-and Dispersion
1
DB 
T .ECM T 
1
ECM T  
T
 ECM B   ECM T 
i
Bi T
 ECM B 
i
Bi T
Within-Band Dispersion
1
DW 
nT
ECM Sj   ECM Bi 
ECM Bi 
 BT Sj
Bi
Overall dispersion measure
i
D  W1.DB  W2.DW  W1  W2 
2
2
Simulation Experiment
Algorithms for comparison
– Optimistic, First-fit, Best-fit and Best-band
– Best Distribution (Post-call assignment dispersion)
AssignTo
Newcall 

 Band Bi   D Bi   D Bj 
Bi, Bj -E
1
D Bi  
 D Sk 
nBi  Sk  Bi
Criteria for comparative analysis
– Distribution efficiency & Robustness against call
failures
Setup
– 100000 8-site (Fig. 1) configurations with best
capacity of each site a random number between 0
and Max-Resources-Available-At-Any-Site.
– Experiment is repeated for values of the MaxResources-Available-At-Any-Site from 1 thru 35
Experimental Results
0.14
Best-Fit Min-Max
0.12
0.18
First-Fit Min-Max
Optimistic MBTA
Min-Max
Algorithms
Optimistic MBTA
Algorithm
0.14
0.12
0.1
0.1
Algorithm
Call Failure Probability -
0.16
Best-Band MinMax
Best-Distribution
Min-Max
0.08
0.06
0.08
0.06
0.04
0.04
0.02
0.02
0
0
0
10
20
30
Average Available Capacity of Sites
Figure 4: Variation of Call Failures with
Availability of Resources.
0
5
10
15
20
25
30
35
Average Avaialable Capacity of Sites
Figure 5: Variation in Distribution Efficiencies of
Algorithms with Call Resources
Conclusions and References
Conclusions
Rule out:
– Best-band- Computationally Intensive
– Optimistic- Failure-prone in overloaded network
– First-fit- Good for early call setup, but inefficient
from call distribution perspective
Best-fit and Best-band are competitive. Best-fit
may be preferable because of simplicity.
References
www.uspto.gov search Published patents on string
“guturu.’
Parthasarathy, Guturu and Abdennaceur, Lachtar, “An
Efficacious Method for Dual Band Multi-carrier Traffic
Allocation in CDMA Wireless Systems,” Proc. IEEE
GLOBECOM 2003, Vol. 1, pp.10-14. Also available in
IEEE Trans. On Wireless Comm., March 2006.