chapter2 channel assignment strategies in cellular network.pdf
DESCRIPTION
channel assignment strategies deals multiple mobile devices can be connected in single cell by allocating the frequency spectrum. hand off techniques is introducedTRANSCRIPT
NCCU Wireless Comm. Lab.
Channel Assignment Strategies
• Introduction
• Channel assignment strategies for coordination-based systems
• Channel assignment strategies for measurement-based systems
2-1
NCCU Wireless Comm. Lab.
Introduction
• Frequency allocation should be carefully planned to avoid
degradation caused by co-channel interference
• Fixed channel assignment, dynamic channel assignment,
and hybrid channel assignment
• Coordination-based (Planning-based) vs. measurement-based
2-2
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Coordination-based Systems
• Under the control of a central processor
• Classification
Fixed Channel Assignment
Dynamic Channel Assignment
Hybrid Channel Assignment
FCA with Borrowing
Directed Retry
Load Sharing
2-3
NCCU Wireless Comm. Lab.
Fixed Channel Assignment
Channels can only be used in designated cells
Different groups of radio channels may be assigned to adjacent
cells, but the same groups must be assigned to cells separated by a
certain distance (reuse distance) to reduce co-channel interference
The easiest one, but provides the worst channel utilization
Advanced Mobile Phone System (AMPS) [1]
2-4
NCCU Wireless Comm. Lab.
Dynamic Channel Assignment
Channels are temporarily assigned for use in cells for the duration
of the call
After the call is over, the channel is returned and kept in a central
pool
To avoid co-channel interference, any channel that in use in one
cell can only be reassigned simultaneously to another cell in the
system if the distance between two cells is larger than minimum
reuse distance
Needs more tranceivers for each base station
Behaves worse performance than FCA under heavy loads2-5
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Coordination-based Systems
• Channel selection Algorithms for DCA (see Fig. 1)
First available (FA)
Mean square (MSA) :
Nearest neighbor (NN)
Nearest neighbor plus one (NN+1)
DDDDn j
n
jj 21
1
2 ≤≤∑=
2-6
NCCU Wireless Comm. Lab.
Channel Assignment Strategies
Fig.7 Examples illustrating switching strategies
2-7
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Coordination-based Systems
• Hybrid channel AssignmentDivide the total number of channels into two groups , one
of which is used for fixed allocation to the cells , while theother is kept as a central poor to be shared by all users.Mixes the advantages of FCA and DCA.Needs fewer transceivers than DCA.Saves the CPU time.Still performs worse than FCA for heavy traffic load.[3]The optinum ratio of dynamical channels to fixed channelsdepends on the traffic load.Can be performed with ReAssignment strategy
2-8
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Coordination-based Systems
• FCA with BorrowingFirst proposed by L.G. Anderson.[4]Three algorithms ( see Figs. 2-5 ).Ordered channel borrowing with switching strategies ( see Figs. 6-7 ) proposed by Elnoubi et al.[5-6]
2-9
NCCU Wireless Comm. Lab.2-11
Channel Assignment Strategies for Coordination-based System
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Coordination-based System
2-12
Fig. 4 Channel assignment Algorithm II
NCCU Wireless Comm. Lab.
Fig5. Channel assignment Algorithm III.
Search sequence
Channel Assignment Strategies for Coordination-based Systems
2-13
NCCU Wireless Comm. Lab.
Channel Assignment Strategies
2-14
NCCU Wireless Comm. Lab.
Channel Assignment Strategies
Fig.7 Examples illustrating switching strategies
2-15
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Measurement-based Systems
• A distributed measurement-based method can alleviate the
processing time of the central processor
• QFCA was proposed by J. C-I Chang (1991) [7] for PACS.
• In QFCA, frequency assignment and portable access are separately
performed
• Flow chart of frequency assignment (see Fig. 8)
2-16
NCCU Wireless Comm. Lab.
Frequency assignment for QFCA
Fig.8
2-17
NCCU Wireless Comm. Lab.
• Portable access procedureRadio-port selection and channel (time-slot) selectionThe former is based on maximun received powerThe latter is based on Erlang B-type random idle time-slotselectionNew algorithms, including LIBTA, FABTA, and HIBTA, have been studied for the latter[8]Adaptive threshold concept has been proposed for time-slot selection (see Fig.9) [8]Flow chart of portable radio access (see Fig.10)
Channel Assignment Strategies for Measurement-based Systems
2-18
NCCU Wireless Comm. Lab.
Algorithm with adaptive threshold
9
2-19
NCCU Wireless Comm. Lab.2-20
Portable Access Procedure
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Measurement-based Systems
•Directed RetryProposed by Eklundh(1986)[9]
(overlapped probability is achieved by change of transmitted power)Portable keeps a decreased-order list for port IDs in received signal strengthAccess procedure (see Fig.10)
2-21
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Coordination-based Systems
Fig. 11
2-22
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Measurement-based Systems
•Load Sharing Also proposed by Eklundh and Karlsson (1989) [10] An extension of directed retryDuring conversation, portable must periodically measure the signal strength for all carrier frequencies, and ranks them according to the received carrier powerThe received carrier power from the optimum radio port besides the current communicating port should be sent to the RPCU periodicallyAccess procedure (see Fig.12)
2-23
NCCU Wireless Comm. Lab.
The Flowchart of Load Sharing
START
Is timeslot available in thefirst selected port?
Doesdirected retry tothe second port
succeed?
One portable oncommunication is
selected by the originalport according to some
criterion
The original portbroadcasts a message
with the selectedportable ID & initiate a
timer
Theselected portablecorrectly receive
Request?
Switch to the newcarrier
Succeed?
Send an ACK to theoriginal port to indicate the
switching success
The original port sendsACK to the new call toindicate that the call has
been set up
Access succeed
Call is blocked
The original portsends NACK to thenew call to indicatethat this attempt fails
Anotherportable onconversationavailable
Send an NACK to theoriginal port
Call is blocked
timeoutfor switchingprocedure
The original port timesout for current request
The new port sendsACK to theportable
Port sends ACK tothe portable
Access succeed
Y
Y
N
N
N
N
Y
N
Y
N
Y
Fig. 12 The flowchart of load sharing
Y
2-24
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Measurement-based Systems
•Portable Selection Algorithms in Load Sharing Systems
HCPATA (Highest Carrier Power Above Threshold Algorithm)HCPA (Highest Carrier Power Algorithm)FAATA (First Available Above Threshold Algorithm)FAA (First Available Algorithm)
2-25
NCCU Wireless Comm. Lab.
Channel Assignment Strategies for Measurement-based Systems
•Two Time-solt Selection Algorithms[11-12]
LIBTA (Least Interference Below Threshold Algorithm)Hybrid Time-solt Selection HIBTA with adaptive threshold for the first accessLIBTA with adaptive threshold for the remaining access
2-26
NCCU Wireless Comm. Lab.
Simulation Results
2-27
NCCU Wireless Comm. Lab.
Simulation Results
2-28
NCCU Wireless Comm. Lab.
Simulation Results
2-29
NCCU Wireless Comm. Lab.
Simulation Results
2-30
NCCU Wireless Comm. Lab.
Simulation Results
2-31
NCCU Wireless Comm. Lab.
Simulation Results
2-32
NCCU Wireless Comm. Lab.
Comments for Measurement-band Systems
•Load sharing system outperforms the other two systemssignificantly, especially in terms of blocking rate
•Hybrid time-slot selection algorithm yields better gradeof service
•With hybrid time-slot selection algorithm, load sharing system is better than directed system by around 0.7 Erlangs and better than QFCA system by around 2 Erlangs
2-33
NCCU Wireless Comm. Lab.
References
[1]EIA/TIA ANSI 533, Mobile station-land station compatibility specification.
[2]D. C. Cox and D. O. Reudink, “Dynamic channel assignment in high capacity mobile communication systems,” Bell Syst. Tech. J., pp. 1833-1875, July/Aug. 1971.
[3]D. C. Cox and D. O. Reudink, “Increasing channel occupancy in large-scale mobile radio systems: dynamic channel reassignment,” IEEE Trans. Veh. Tech., vol. VT-22, pp. 218-222, Nov, 1973.
[4]L. G. Anderson, “A simulation study of some dynamic channel assignment algorithms in a high capacity mobile telecommunication system,” IEEE Trans. Veh. Tech., vol. VT-22, pp. 210-217, Nov. 1973.
2-34
NCCU Wireless Comm. Lab.
References
[5]S. M. Elnoubi, R. Singh, and S. C. Gupta, “A new frequency channel assignment algorithm in high capacity mobile communication system,” IEEE Trans. Veh. Tech., vol. VT-31, pp. 125-131, Aug. 1982.
[6]S. S. Kuek and W. C. Wong , “Ordered dynamic channel assignment scheme with reassignment in highway microcells,”IEEE Trans. Veh. Tech. vol. VT-41, no. 3, Aug. 1992.
[7]J. C.-I. Chuang, “Autonomous adaptive frequency assignment for TDMA portable ratio systems,” IEEE Trans. Veh. Tech. vol. VT-40, pp. 627-635, Aug. 1991.
2-35
NCCU Wireless Comm. Lab.
References
[8]J. H. Wen, W. J. Chen and S. Y. Lin, “Time-slot selection algorithms for quasi-fixed frequency assignment TDMA cellular systems”, J. of the Chinese Institute of Electrical Engineering, vol. 5, no. 3, pp. 223-233, Aug. 1998.
[9]B. Eklundh, “Channel utilization and blocking probability in a cellular mobile telephone system with directed retry, “ IEEE Trans. Comm., vol. COM-34, pp. 530-535, May 1989.
[10]J. Karlsson and B. Eklundh, “A cellular mobile telephone system with load sharing-an enhancement of directed retry,”IEEE Trans. Comm., vol. COM-37, pp. 530-535, May 1989.
2-36
NCCU Wireless Comm. Lab.
References
[11]J. H. Wen, W. J Chen and J. K. Ho, “Time-slot selection algorithm with directed retry/load sharing for personal communication systems,” Proceedings of the NSC, part A: Physical Science and Engineering, vol. 21, no. 6, pp. 631-636, Nov. 1997.
[12]J. H. Wen, W. J. Chen, S. Y. Lin and K. T. Huang, “Performance evaluation of LIBTA/hybrid time-slot selection algorithm for cellular systems,” IASTED International Conference Modeling, Simulation and Optimization, Singapore, pp. 178-181, Aug. 1997.
2-37