30Oct01.ppt 1001KB Jun 23 2011 12:33:32 PM
Coverage Enhancement through
Two-hop Relaying in Cellular
Radio Systems
Van Sreng
vsreng@sce.carleton.ca
Supervised by
Prof. David D. Falconer
Prof. Halim Yanikomeroglu
ddf@sce.carleton.ca
halim@sce.carleton.ca
Department of Systems and Computer Engineering
Page 1
Outline
MOTIVATION
BACKGROUND
SIMULATION SCENARIOS:
Relay Node/Path Selection Schemes
Channel Selection Schemes
SIMULATION MODEL
SIMULATION RESULTS
CONCLUDING REMARKS
FUTURE STUDY
Department of Systems and Computer Engineering
Page 2
Motivation
Current problems exist in Cellular systems:
Poor coverage due to a lack of LOS (Line of Sight) or
severe fading.
95% - 99% area coverage goal set by service providers
is impossible to meet.
Some solutions exist today:
Use of repeaters (installation planning & costs)
Sectorized cells (more costs)
Smart antennas (costs & long deployment period)
Our proposed solution:
Relaying using mobile nodes with a good link to the
base station to relay traffic for those with a poor link.
Department of Systems and Computer Engineering
Page 3
Background
Relaying began in Packet Radio Systems
(infrastructureless), starting with the DARPA (Defense
Advanced Research Projects Agency) project.
Characteristics of a PR network include:
Store-and-forward form of packet forwarding
Low bandwidth
Shared radio channel
Communications are mainly in a broadcast mode
Is highly dynamic because links come and go
Requires high connectivity establishment
Radios have low transmission range
Inherent Problems:
Hidden Terminal
Routing Loop
Department of Systems and Computer Engineering
Page 4
Background (cont.)
Figure 1. Illustration of a Packet
Radio Network
Hidden Terminal Problem:
Figure 2. Example of a hidden
terminal problem.
Routing loop problem:
Figure 3. Example of a routing
loop problem.
Department of Systems and Computer Engineering
Page 5
Background (cont.)
Routing objectives:
Minimize number of hops
Minimize interference
Avoid routing loop and hidden terminal problems
Coping with the topology change in order to have a reliable
communication.
Today’s relaying networks have become known as Ad-hoc
Networks (still infrastructureless); purpose is now geared
towards commercial applications such as:
Conferences/Meetings/Lectures (slides/files sharing)
Workshops
Emergency services
Law Enforcement
Department of Systems and Computer Engineering
Page 6
Background (cont.)
Relaying in Cellular Networks:
Advantages:
There is a central controller and communications must go
through it.
Packets forwarding requires less number of hops.
Routing is simplified since links are only established as
needed.
Provides a receiver capture effect, through power control &
separate channels, that will result in a desired signal
improvement.
Disadvantages:
Requires a strategic relay node/path selection scheme.
Requires additional channels for relaying purposes.
Requires cooperation among nodes (where in ad-hoc
networks, this is a given).
Department of Systems and Computer Engineering
Page 7
Background (cont.)
Figure 4. A scenario depicting poor
coverage regions where the signal from the
base station cannot cover or reach the
mobile nodes at these locations.
Figure 5. A conventional solution to the
coverage problem presented in Fig. 4 by
using repeaters to extend the coverage to
these locations.
Figure 6. A new proposed solution to
the coverage problem presented in Fig.
4 by using mobile terminals with a good
link to the base station to relay traffic
for those with a poor link to the base
station.
Department of Systems and Computer Engineering
Page 8
Simulation Scenarios
Relay Node/Path Selection Schemes (Two-hop relaying):
Let PLn1 & PLn2 be the path-losses (based on distance attenuation and
lognormal shadowing) associated with the first and the second hop,
respectively, along the nth route, and R the set of potential relay nodes,
then for:
Smart Selection Scheme, the selected path, ps, is:
ps arg min (max{PLn1, PLn 2 })
(1)
all n
Semi-Smart Selection Scheme, the selected path, ps, is:
ps arg min{PLn 2 }, (C / I ) n1 t
(2)
all n
Simple Selection Scheme, the selected path, ps, is:
ps rand( R )
Department of Systems and Computer Engineering
(3)
Page 9
Simulation Scenarios
Figure 7. An illustration of relayer selection, using path-loss as the
decision criterion, based on Smart Selection scheme.
Department of Systems and Computer Engineering
Page 10
Simulation Scenarios (cont.)
Figure 8. A block diagram of a relay path (in a real system) which is made up of two hops; the figure
illustrates the importance of the link at 2 which governs the link quality at 3. If the node at 3 has a
higher SNR threshold requirement than that at 2, then there may not be sufficient resources (in terms
of transmitting power) at 1 to satisfy the node at 3 via 2.
Department of Systems and Computer Engineering
Page 11
Simulation Scenarios (cont.)
Channel Selection Schemes (adjacent-cell channel reuse in a TDMA based
system) for downlink scenario only:
Let (C/I)i,c be the carrier-to-interference ratio received at the relayed node i, on
channel c, and B the set of all base stations that use channel c. Then,
(G Pj ,c ) path-loss
(,Cwhere
/ I ) i ,c Gji isji the
(Gki Pk ,c )
coefficient between the relayed node (4)
i and the relay node j, and Pj,c is the transmitted power of the relay node j. Then, for:
Smart Channel Selection, the channel selected, ls, is :
kB
(5)
ls arg max ((C / I )i ,c ), (C /( I new I old N )) j ,c t , K L,
all cK
where Inew is the interference due to the candidate relay link, Iold is the interference due to the
existing links, N is thermal noise,
is the
minimum threshold required, K is the set of reusable
t
channels and L the set of all channels available in the adjacent cells.
Semi-Smart Channel Selection, the channel selected, ls, is :
ls arg max ((C / I ) i ,c ) (6)
all cL
Simple Channel Selection, the channel selected, ls, is :
ls rand( L)
(7)
Department of Systems and Computer Engineering
Page 12
Simulation Scenarios (cont.)
Channel Reusability Check (Downlink scenario):
Let G, where G = {Gij}, be the link gain (path-loss coefficient) matrix of all the
co-channel links associated with the channel of interest, then with q mobile
nodes involved G will be a q x q matrix. Then:
Z = {Zij}, where Z Gij ,
ij
(8)
Gii
rewriting the condition in (5) using the relationship given in (4), and through
manipulation and using matrix notation we obtain:
1 t
(
)P ZP.
t
(9)
A maximum achievable (C/I), is then determined from the largest real
eigenvalue of this Z matrix according to the following:
= 1 / (where is the largest real eigenvalue of this matrix.
If t, then there exists a positive power vector such that all the links
belonging to the co-channel set of the channel under question can be active
simultaneously.
Department of Systems and Computer Engineering
Page 13
Simulation Model
Environment & Parameter assumptions:
Urban environment with pass-loss exponent: n = 4
Lognormal shadowing: = 10 dB
Flat Rayleigh fading
Omnidirectional antennas for both the base station &
subscriber terminal
RF Carrier = 2.5 GHz, BW = 2 MHz
Thermal Noise: Noise Figure = 8 dB
Max. number of hops = 2
Max. number of relayed nodes = 7
Simulation area: 6x6 square cells (wrap-around edges), 4-cell
clusters, cell size varies from 400x400 m to 2x2 km
Subscribers uniformly distributed
Max. base station transmit power per node: 1 W
SNR Threshold = 10 dB
Department of Systems and Computer Engineering
Page 14
Simulation Model (cont.)
Model Assumptions:
Same path-loss model for both: between base station to
subscriber and between one subscriber to another.
Number of channels available per cell increases linearly with
cell density (focusing on coverage aspects, rather than
channel capacity aspects, of performance).
Doppler effects ignored (reasonable with low mobility).
Adjacent-channel interference ignored.
When handing off from a relay node, a mobile node is forced
to link up with the base station first if this link is good.
Due to large bandwidth and high noise figure assumption,
digital form of relaying is assumed so that no noise is
propagated.
Coverage is defined as Pr[SINR Threshold] 95%.
Downlink scenario only.
Department of Systems and Computer Engineering
Page 15
Simulation Results
User Coverage for Noise-limited System:
Figure 9. User Coverage v.s Cell Density (for 2x2 km
cell size, No Power Control, Smart Relayer Selection,
Semi-Smart Channel Selection).
Department of Systems and Computer Engineering
Figure 10. User Coverage v.s Cell Density (for 2x2
km cell size, Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Page 16
Simulation Results (cont.)
Figure 11. User Coverage v.s Cell Density (for 1x1
km cell size, No Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Department of Systems and Computer Engineering
Figure 12. User Coverage v.s Cell Density (for 1x1
km cell size, Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Page 17
Simulation Results
(cont.)
User Coverage for
Interference-limited System:
Figure 13. User Coverage v.s Cell Density (for
400x400 m cell size, No Power Control, Smart
Relayer Selection, Semi-Smart Channel Selection).
Department of Systems and Computer Engineering
Figure 14. User Coverage v.s Cell Density (for
400x400 m cell size, Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Page 18
Simulation Results
(cont.)
Impact of Relay
Node/Path Selection on Coverage:
Figure 15. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Random Relayer
Selection, Semi-Smart Channel
Selection).
Figure 16. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Semi-Smart
Relayer Selection, Semi-Smart
Channel Selection).
Department of Systems and Computer Engineering
Figure 17. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Semi-Smart Channel
Selection).
Page 19
Simulation Results (cont.)
Impact of Channel Selection on Coverage:
Figure 18. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Random Channel
Selection).
Figure 19. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Semi-Smart Channel
Selection).
Department of Systems and Computer Engineering
Figure 20. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Smart Channel
Selection).
Page 20
Simulation Results (cont.)
Worst Case Performance v.s Best Case Performance :
Figure 21. User Coverage v.s Cell Density (for
400x400 m cell size, Power Control, Random
Relayer Selection, Random Channel Selection).
Department of Systems and Computer Engineering
Figure 22. User Coverage v.s Cell Density (for
400x400 m cell size, Power Control, Smart Relayer
Selection, Smart Channel Selection).
Page 21
Concluding Remarks
Relaying can have a significant improvement on coverage
provided a good relay node selection is implemented.
Even without extra channels reserved for relaying, with power
control and a good relay node selection this improvement is quite
insensitive to the channel selection schemes. Hence, perhaps it
is more advantageous to opt for the simple scheme while
sacrificing a slight performance return.
Relaying helps lower power consumption.
Need to have accurate channel measurements when performing
relay node selection or channel selection (except for the Simple
Selection scheme); it has been assumed here.
Department of Systems and Computer Engineering
Page 22
Concluding Remarks (Cont.)
Relaying in cellular systems is opportunity driven, thus:
The unlicensed band spectrum (902 MHz - 928 MHz, 2.4
GHz - 2.483 GHz, 5.725 - 5.85 GHz) seems very attractive
for using it for relaying purposes.
Since a good LOS must be obtained via relaying, higher
throughput can be delivered to individual relayed nodes,
through adaptive modulation, without requiring the transmitter
to use greater power.
Pending question: how much relaying is allowed?
i.e., since long relay sessions will drain the battery of the relay
node’s terminal, should relaying be enforced only when
coverage becomes very poor or should it be carried out as
much as possible in a strive to always achieve a higher
performance?
Department of Systems and Computer Engineering
Page 23
Future Study
Performance analysis of multihop relaying in cellular
systems.
Propagation & channel characterization study between low
height transmitting terminals.
Effectiveness of using directional antennas at the
subscriber terminals.
Effectiveness of Adaptive Modulation to increase individual
node’s throughput.
Market survey on users’ willingness to cooperate in this
type of network (provided there is an incentive for them).
Department of Systems and Computer Engineering
Page 24
References
[1] E. H. Drucker, “Development and Application of a Cellular Repeater,” IEEE Vehicular
Technology Conf., pp. 321-325, June 1988.
[2] E. M. Royer and C. Toh, “A Review of Current Routing Protocols for Ad Hoc Mobile
Wireless Networks,” IEEE Personal Communications, pp. 46-55, April 1999.
[3] G. N. Aggelou and R. Tafazolli, “On the Relaying Capability of Next Generation GSM
Cellular Networks,” IEEE Personal Communications, pp. 40-47, February 2001.
[4] T. J. Harold and A. R. Nix, “Intelligent Relaying for future Personal Communications
Systems,” Centre for Communications Research, University of Bristol, 2000.
[5] H. Wu, C. Qiao, and O. Tonguz, “Performance Analysis of iCAR (Integrated Cellular and
Ad-hoc Relay System),” to appear in International Conf. for Communications, 2001.
[6] S. Papavassiliou and L. Tassiulas, “Improving the Capacity in Wireless Networks Through
Integrated Channel Base Station and Power Assignment,” IEEE Transactions on Vehicular
Technology, vol. 47, no. 2, pp. 417-427, May 1998.
Department of Systems and Computer Engineering
Page 25
Two-hop Relaying in Cellular
Radio Systems
Van Sreng
vsreng@sce.carleton.ca
Supervised by
Prof. David D. Falconer
Prof. Halim Yanikomeroglu
ddf@sce.carleton.ca
halim@sce.carleton.ca
Department of Systems and Computer Engineering
Page 1
Outline
MOTIVATION
BACKGROUND
SIMULATION SCENARIOS:
Relay Node/Path Selection Schemes
Channel Selection Schemes
SIMULATION MODEL
SIMULATION RESULTS
CONCLUDING REMARKS
FUTURE STUDY
Department of Systems and Computer Engineering
Page 2
Motivation
Current problems exist in Cellular systems:
Poor coverage due to a lack of LOS (Line of Sight) or
severe fading.
95% - 99% area coverage goal set by service providers
is impossible to meet.
Some solutions exist today:
Use of repeaters (installation planning & costs)
Sectorized cells (more costs)
Smart antennas (costs & long deployment period)
Our proposed solution:
Relaying using mobile nodes with a good link to the
base station to relay traffic for those with a poor link.
Department of Systems and Computer Engineering
Page 3
Background
Relaying began in Packet Radio Systems
(infrastructureless), starting with the DARPA (Defense
Advanced Research Projects Agency) project.
Characteristics of a PR network include:
Store-and-forward form of packet forwarding
Low bandwidth
Shared radio channel
Communications are mainly in a broadcast mode
Is highly dynamic because links come and go
Requires high connectivity establishment
Radios have low transmission range
Inherent Problems:
Hidden Terminal
Routing Loop
Department of Systems and Computer Engineering
Page 4
Background (cont.)
Figure 1. Illustration of a Packet
Radio Network
Hidden Terminal Problem:
Figure 2. Example of a hidden
terminal problem.
Routing loop problem:
Figure 3. Example of a routing
loop problem.
Department of Systems and Computer Engineering
Page 5
Background (cont.)
Routing objectives:
Minimize number of hops
Minimize interference
Avoid routing loop and hidden terminal problems
Coping with the topology change in order to have a reliable
communication.
Today’s relaying networks have become known as Ad-hoc
Networks (still infrastructureless); purpose is now geared
towards commercial applications such as:
Conferences/Meetings/Lectures (slides/files sharing)
Workshops
Emergency services
Law Enforcement
Department of Systems and Computer Engineering
Page 6
Background (cont.)
Relaying in Cellular Networks:
Advantages:
There is a central controller and communications must go
through it.
Packets forwarding requires less number of hops.
Routing is simplified since links are only established as
needed.
Provides a receiver capture effect, through power control &
separate channels, that will result in a desired signal
improvement.
Disadvantages:
Requires a strategic relay node/path selection scheme.
Requires additional channels for relaying purposes.
Requires cooperation among nodes (where in ad-hoc
networks, this is a given).
Department of Systems and Computer Engineering
Page 7
Background (cont.)
Figure 4. A scenario depicting poor
coverage regions where the signal from the
base station cannot cover or reach the
mobile nodes at these locations.
Figure 5. A conventional solution to the
coverage problem presented in Fig. 4 by
using repeaters to extend the coverage to
these locations.
Figure 6. A new proposed solution to
the coverage problem presented in Fig.
4 by using mobile terminals with a good
link to the base station to relay traffic
for those with a poor link to the base
station.
Department of Systems and Computer Engineering
Page 8
Simulation Scenarios
Relay Node/Path Selection Schemes (Two-hop relaying):
Let PLn1 & PLn2 be the path-losses (based on distance attenuation and
lognormal shadowing) associated with the first and the second hop,
respectively, along the nth route, and R the set of potential relay nodes,
then for:
Smart Selection Scheme, the selected path, ps, is:
ps arg min (max{PLn1, PLn 2 })
(1)
all n
Semi-Smart Selection Scheme, the selected path, ps, is:
ps arg min{PLn 2 }, (C / I ) n1 t
(2)
all n
Simple Selection Scheme, the selected path, ps, is:
ps rand( R )
Department of Systems and Computer Engineering
(3)
Page 9
Simulation Scenarios
Figure 7. An illustration of relayer selection, using path-loss as the
decision criterion, based on Smart Selection scheme.
Department of Systems and Computer Engineering
Page 10
Simulation Scenarios (cont.)
Figure 8. A block diagram of a relay path (in a real system) which is made up of two hops; the figure
illustrates the importance of the link at 2 which governs the link quality at 3. If the node at 3 has a
higher SNR threshold requirement than that at 2, then there may not be sufficient resources (in terms
of transmitting power) at 1 to satisfy the node at 3 via 2.
Department of Systems and Computer Engineering
Page 11
Simulation Scenarios (cont.)
Channel Selection Schemes (adjacent-cell channel reuse in a TDMA based
system) for downlink scenario only:
Let (C/I)i,c be the carrier-to-interference ratio received at the relayed node i, on
channel c, and B the set of all base stations that use channel c. Then,
(G Pj ,c ) path-loss
(,Cwhere
/ I ) i ,c Gji isji the
(Gki Pk ,c )
coefficient between the relayed node (4)
i and the relay node j, and Pj,c is the transmitted power of the relay node j. Then, for:
Smart Channel Selection, the channel selected, ls, is :
kB
(5)
ls arg max ((C / I )i ,c ), (C /( I new I old N )) j ,c t , K L,
all cK
where Inew is the interference due to the candidate relay link, Iold is the interference due to the
existing links, N is thermal noise,
is the
minimum threshold required, K is the set of reusable
t
channels and L the set of all channels available in the adjacent cells.
Semi-Smart Channel Selection, the channel selected, ls, is :
ls arg max ((C / I ) i ,c ) (6)
all cL
Simple Channel Selection, the channel selected, ls, is :
ls rand( L)
(7)
Department of Systems and Computer Engineering
Page 12
Simulation Scenarios (cont.)
Channel Reusability Check (Downlink scenario):
Let G, where G = {Gij}, be the link gain (path-loss coefficient) matrix of all the
co-channel links associated with the channel of interest, then with q mobile
nodes involved G will be a q x q matrix. Then:
Z = {Zij}, where Z Gij ,
ij
(8)
Gii
rewriting the condition in (5) using the relationship given in (4), and through
manipulation and using matrix notation we obtain:
1 t
(
)P ZP.
t
(9)
A maximum achievable (C/I), is then determined from the largest real
eigenvalue of this Z matrix according to the following:
= 1 / (where is the largest real eigenvalue of this matrix.
If t, then there exists a positive power vector such that all the links
belonging to the co-channel set of the channel under question can be active
simultaneously.
Department of Systems and Computer Engineering
Page 13
Simulation Model
Environment & Parameter assumptions:
Urban environment with pass-loss exponent: n = 4
Lognormal shadowing: = 10 dB
Flat Rayleigh fading
Omnidirectional antennas for both the base station &
subscriber terminal
RF Carrier = 2.5 GHz, BW = 2 MHz
Thermal Noise: Noise Figure = 8 dB
Max. number of hops = 2
Max. number of relayed nodes = 7
Simulation area: 6x6 square cells (wrap-around edges), 4-cell
clusters, cell size varies from 400x400 m to 2x2 km
Subscribers uniformly distributed
Max. base station transmit power per node: 1 W
SNR Threshold = 10 dB
Department of Systems and Computer Engineering
Page 14
Simulation Model (cont.)
Model Assumptions:
Same path-loss model for both: between base station to
subscriber and between one subscriber to another.
Number of channels available per cell increases linearly with
cell density (focusing on coverage aspects, rather than
channel capacity aspects, of performance).
Doppler effects ignored (reasonable with low mobility).
Adjacent-channel interference ignored.
When handing off from a relay node, a mobile node is forced
to link up with the base station first if this link is good.
Due to large bandwidth and high noise figure assumption,
digital form of relaying is assumed so that no noise is
propagated.
Coverage is defined as Pr[SINR Threshold] 95%.
Downlink scenario only.
Department of Systems and Computer Engineering
Page 15
Simulation Results
User Coverage for Noise-limited System:
Figure 9. User Coverage v.s Cell Density (for 2x2 km
cell size, No Power Control, Smart Relayer Selection,
Semi-Smart Channel Selection).
Department of Systems and Computer Engineering
Figure 10. User Coverage v.s Cell Density (for 2x2
km cell size, Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Page 16
Simulation Results (cont.)
Figure 11. User Coverage v.s Cell Density (for 1x1
km cell size, No Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Department of Systems and Computer Engineering
Figure 12. User Coverage v.s Cell Density (for 1x1
km cell size, Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Page 17
Simulation Results
(cont.)
User Coverage for
Interference-limited System:
Figure 13. User Coverage v.s Cell Density (for
400x400 m cell size, No Power Control, Smart
Relayer Selection, Semi-Smart Channel Selection).
Department of Systems and Computer Engineering
Figure 14. User Coverage v.s Cell Density (for
400x400 m cell size, Power Control, Smart Relayer
Selection, Semi-Smart Channel Selection).
Page 18
Simulation Results
(cont.)
Impact of Relay
Node/Path Selection on Coverage:
Figure 15. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Random Relayer
Selection, Semi-Smart Channel
Selection).
Figure 16. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Semi-Smart
Relayer Selection, Semi-Smart
Channel Selection).
Department of Systems and Computer Engineering
Figure 17. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Semi-Smart Channel
Selection).
Page 19
Simulation Results (cont.)
Impact of Channel Selection on Coverage:
Figure 18. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Random Channel
Selection).
Figure 19. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Semi-Smart Channel
Selection).
Department of Systems and Computer Engineering
Figure 20. User Coverage v.s Cell
Density (for 400x400 m cell size,
Power Control, Smart Relayer
Selection, Smart Channel
Selection).
Page 20
Simulation Results (cont.)
Worst Case Performance v.s Best Case Performance :
Figure 21. User Coverage v.s Cell Density (for
400x400 m cell size, Power Control, Random
Relayer Selection, Random Channel Selection).
Department of Systems and Computer Engineering
Figure 22. User Coverage v.s Cell Density (for
400x400 m cell size, Power Control, Smart Relayer
Selection, Smart Channel Selection).
Page 21
Concluding Remarks
Relaying can have a significant improvement on coverage
provided a good relay node selection is implemented.
Even without extra channels reserved for relaying, with power
control and a good relay node selection this improvement is quite
insensitive to the channel selection schemes. Hence, perhaps it
is more advantageous to opt for the simple scheme while
sacrificing a slight performance return.
Relaying helps lower power consumption.
Need to have accurate channel measurements when performing
relay node selection or channel selection (except for the Simple
Selection scheme); it has been assumed here.
Department of Systems and Computer Engineering
Page 22
Concluding Remarks (Cont.)
Relaying in cellular systems is opportunity driven, thus:
The unlicensed band spectrum (902 MHz - 928 MHz, 2.4
GHz - 2.483 GHz, 5.725 - 5.85 GHz) seems very attractive
for using it for relaying purposes.
Since a good LOS must be obtained via relaying, higher
throughput can be delivered to individual relayed nodes,
through adaptive modulation, without requiring the transmitter
to use greater power.
Pending question: how much relaying is allowed?
i.e., since long relay sessions will drain the battery of the relay
node’s terminal, should relaying be enforced only when
coverage becomes very poor or should it be carried out as
much as possible in a strive to always achieve a higher
performance?
Department of Systems and Computer Engineering
Page 23
Future Study
Performance analysis of multihop relaying in cellular
systems.
Propagation & channel characterization study between low
height transmitting terminals.
Effectiveness of using directional antennas at the
subscriber terminals.
Effectiveness of Adaptive Modulation to increase individual
node’s throughput.
Market survey on users’ willingness to cooperate in this
type of network (provided there is an incentive for them).
Department of Systems and Computer Engineering
Page 24
References
[1] E. H. Drucker, “Development and Application of a Cellular Repeater,” IEEE Vehicular
Technology Conf., pp. 321-325, June 1988.
[2] E. M. Royer and C. Toh, “A Review of Current Routing Protocols for Ad Hoc Mobile
Wireless Networks,” IEEE Personal Communications, pp. 46-55, April 1999.
[3] G. N. Aggelou and R. Tafazolli, “On the Relaying Capability of Next Generation GSM
Cellular Networks,” IEEE Personal Communications, pp. 40-47, February 2001.
[4] T. J. Harold and A. R. Nix, “Intelligent Relaying for future Personal Communications
Systems,” Centre for Communications Research, University of Bristol, 2000.
[5] H. Wu, C. Qiao, and O. Tonguz, “Performance Analysis of iCAR (Integrated Cellular and
Ad-hoc Relay System),” to appear in International Conf. for Communications, 2001.
[6] S. Papavassiliou and L. Tassiulas, “Improving the Capacity in Wireless Networks Through
Integrated Channel Base Station and Power Assignment,” IEEE Transactions on Vehicular
Technology, vol. 47, no. 2, pp. 417-427, May 1998.
Department of Systems and Computer Engineering
Page 25