where are the relay capacity gains in cellular systems?ctw2010.ieee-ctw.org/mon/heath.pdf ·...
TRANSCRIPT
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The Wireless Networking and Communications Group
Where are the Relay Capacity Gains inCellular Systems?
Robert W. Heath Jr.Steven Peters, Kien Truong, and Ali Yazdan-Panah
The University of Texas at AustinWireless Networking and Communications Group
http://www.ece.utexas.edu/~rheath
* Funded by a gift from Huawei
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Introduction to Relays
Relays assist communication
May be fixed (infrastructure), mobile (bus) or cooperative (other users)
Single antenna, multiple antennas, multiple relays, multiple users
Main purpose of relays
Coverage (large-scale effects), diversity (small-scale) [?], and capacity [??]
2
relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cell
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Types of Relays
3
One-wayfull duplex
relay
base station
user ii
user i
strong linkstrong link
transmission cell
One-wayhalf duplex
relay
base station
user ii
user i
strong linkstrong link
transmission cell
1st time-slot2nd time-slot
One-waymulti-hop
relay
base station
user ii
user i
strong linkstrong link
transmission cell
Two-wayhalf duplex
relay
base station
user ii
user i
strong linkstrong link
transmission cell
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Relay Operation
4
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
DeMOD Detect MOD
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
1
Multi-User Bidirectional Communications:
Schemes for the Shared Relay Concept
Ali Y. Panah§†
and Robert W. Heath, Jr.†
[email protected] and [email protected]
The University of Texas at Austin
The Department of Electrical and Computer Engineering
Wireless Networking Communications Group
1 University Station C0803, Austin, TX, USA 78712− 0240
r
r = γr
r = Q (r)
r = Γr
E{|r|2} ≤ Pr
Abstract
abstract here.
• Four-phase one-way DF relaying
• Three-phase two-way DSF relaying
• Two-phase two-way ASF relaying
§Corresponding author.
†This work was supported by a gift from Huawei Technologies Ltd.
May 6, 2010 DRAFT
Compress
Amplify-and-forward
Relay scales RX signal
Seems practical; less interest in standards
Decode-and-forward
Relay decodes RX signal
Very practical
Compress-and-forward
Relay compresses RX sig
Receiver decodes with partial information
Less industry interest
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Expected Gains of Relays
The maximum capacity gain over the direct transmission
As , bps/Hz (DF is the best)
As , bps/Hz (CF is the best)
If , bps/Hz
5
relay
base station
user ii
user i
strong linkstrong link
transmission cell
1
d 1-d
Linear system: full-duplex relay, no fading & same transmit powers [KraEtAl05]
d→ 0d→ 1
d = 0.5 α ∈ [2, 5)
Rrelay −Rdirect = log(1 + k P )− log(1 + P )→ log(k) � ∆R∞ as P →∞
∆R∞ = 2
∆R∞ = 1
∆R∞ = log(1 + 2α) ≈ α path-loss exponent
Capacity gains of relays are modest (there is diversity as well)
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relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cellCellular Systems Interference Limited
Relay deployments 7% indoor coverage improv. [DoppEtAl08]
30% improvement in outage SINR w/ fast PC [SreEtAl02]
Better uplnk coverage, 10% rate improvement 3GPP [IrmDie08]
6% rate improvement downlink LTE-A [LinEtAl09]
6
relay
base station
user ii
user i
strong linkstrong link
transmission cell
Lots of interference
With interference, capacity gains seem to reduce further
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Purpose of this Talk
(1) Discuss performance of different relaying strategies
(2) Suggest some solutions to make relays better
Compare with no relay & coordinated transmission (via DPC)
7
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Simulation Framework
Channel
IEEE 802.16j Type E channel model
46 dBm base station transmit power
37 dBm relay transmit power
24 dBm mobile transmit power
Configuration
3 cells, 6 sectors per cell, 1 antenna UE
Compute throughput on ring
Switch from direct to relay link as move from BTS [ring based]
8
Interfering Sectors
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0 100 200 300 400 500 600 700 800 9000
0.5
1
1.5
2
2.5
3
3.5
4
MS distance from BS (m)
1 us
er a
chie
vabl
e ra
te (b
ps/H
z)
Direct transmissionBS CoordinationSingle−antenna relay
0 100 200 300 400 500 600 700 800 9000
1
2
3
4
5
6
7
MS distance to BS (m)
1 us
er a
chie
vabl
e ra
te (b
ps/H
z)
Direct transmissionBS Coordination
Relay Performance
9
No gain from a single relay (ouch!!!)
BS-RS interference limited BS-RS interference limited
Downlink (DL) Uplink (UL)
Half duplex relay, ignore direct link, DF, optimum time sharing
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Add Multiple Antennas
First phase: Receive MMSE RX receive filter
Second phase: TX beamforming (BF) at relays
MRT (max. ratio trans.): maximizing desired signal power to its own user
ZF (zero-forcing): minimizing sum of leakage powers to other users
SLNR (signal-to-leakage-plus-noise ratio): balancing MRT & ZF (like MMSE)10
leakage signals
desired signal
relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cell
relay
base station
user ii
user i
strong linkstrong link
transmission cell
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One-Way Relay with Antennas
Using multiple antennas at relays provide significant gains
Better than direct trans./single-ant. relays from half of cell radius to cell-edge
Interference cancellation is good only for DL cell-edge users
11
Downlink (DL) Uplink (UL)
Enhanced relay functionality reduces gap to full coordination
0 100 200 300 400 500 600 700 800 9000
0.5
1
1.5
2
2.5
3
3.5
4
MS distance from BS (m)
1 u
se
r a
ch
ieva
ble
ra
te (
bp
s/H
z)
Single antenna + Direct
BS coordination
MRT 2 antennas + Direct
ZF 2 antennas + Direct
SLNR 2 antennas + Direct
MRT 3 antennas + Direct
ZF 3 antennas + Direct
SLNR 3 antennas + Direct
MRT 4 antennas + Direct
ZF 4 antennas + Direct
SLNR 4 antennas + Direct
0 100 200 300 400 500 600 700 800 9000
1
2
3
4
5
6
7
MS distance from BS (m)
1 u
se
r a
ch
ieva
ble
ra
te (
bp
s/H
z)
Single antenna + Direct
BS coordination
MRT 2 antennas + Direct
ZF 2 antennas + Direct
SLNR 2 antennas + Direct
MRT 3 antennas + Direct
ZF 3 antennas + Direct
SLNR 3 antennas + Direct
MRT 4 antennas + Direct
ZF 4 antennas + Direct
SLNR 4 antennas + Direct
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Shared Relaying
Multi-antenna relay placed at cell intersection [PetEtAl09]
Relay shared among multiple base stations
Inter-cell interference removed through MU-MIMO techniques
Performs a decode and forward operation
12
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0 100 200 300 400 500 600 700 800 9000
0.5
1
1.5
2
2.5
3
3.5
4
MS distance to BS (m)
1 us
er a
chie
vabl
e ra
te (b
ps/H
z)
3−Antenna Shared Relay + Direct4−Antenna Shared Relay + Direct5−Antenna Shared Relay + Direct6−Antenna Shared Relay + DirectBS CoordinationDirect transmission
Shared Relay Performance
13
UplinkDownlink
Enhanced relay functionality reduces gap to full coordination
0 100 200 300 400 500 600 700 800 9000
1
2
3
4
5
6
7
MS distance from BS
1 us
er a
chie
vabl
e ra
te (b
ps/H
z)
3−Antenna Shared Relay + Direct4−Antenna Shared Relay + Direct5−Antenna Shared Relay + Direct6−Antenna Shared Relay + DirectBS CoordinationDirect transmission
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Two-Way Shared Relay
14
inter-sector interf. other MS interf.
4
at the signal level to construct
ti = si1
�1 + γ
2+ xi1
�1− γ
2, −1 ≤ γ ≤ 1, i = 1, 2, 3. (7)
Next, to spatially separate the BS-MS pairs, the relay assigns unique beamforming vectors wi to each
ti. The transmitted vector from the relay is tR =√
Pr�3
i=1 witi =√
PrWt, where W �= [w1,w2,w3]
with tr(WW∗) = 1, t �= [t1, t2, t3]T , and Pr is the total average power from the relay terminal. Assuming
reciprocity in the channels, the received signal in first sector of the ith BS is
yi = h∗i1tR + ni, (8)
where ni ∼ CN (0, N0) is AWGN. Similarly, at the ith MS
zi = g∗i1tR + vi, (9)
where vi ∼ CN (0, N0) is AWGN. Viewing these signals in corresponding pairs we define the 2 × 1
vector di�= [yi, zi]T so that
di = [hi1 gi1]∗tR + [ni, vi]T
=�
PrFiWt + ni
=�
PrFiwiti +�
Pr
�
j �=i
Fiwjtj + ni, (10)
where Fi�= [hi1 gi1]∗ is a composite BS-MS channel for the ith cell and ni ∼ CN (0, N0I2). To enforce
spatial separation in (10), i.e. cancel the interference from other BS-MS pairs, we set the following
constraint on the beamforming vectors Fiwj = 02, ∀j �= i. By defining the 4 × M matrix Fi�=
[F∗1 · · · F∗i−1 F∗i+1 · · · F∗3]∗, the beamforming vectors may be obtained from a “block diagonalization”
constraint Fiwi = 04, i = 1, 2, 3. Denote the SVD of Fi as Ui[Σi 04×M ]V∗i , where Vi = [V(1)
i V(0)i ]
and Ui are unitary matrices, Σi is a 4 × 4 diagonal matrix with nonzero elements and the columns of
V(1)i are the corresponding right singular vectors. The M×(M−4) matrix V(0)
i represents the null-space
of Fi which for M = 5 consist of a single column vector that may be chosen for the beamforming vector
wi (with normalization by√
3 to preserve the power constraint since ||V(0)i ||22 = 1).
With this solution (10) reduces to di = Fiwiti +ni. The self-interference is manifested in the received
January 28, 2010 DRAFT
4
at the signal level to construct
ti = si1
�1 + γ
2+ xi1
�1− γ
2, −1 ≤ γ ≤ 1, i = 1, 2, 3. (7)
Next, to spatially separate the BS-MS pairs, the relay assigns unique beamforming vectors wi to each
ti. The transmitted vector from the relay is tR =√
Pr�3
i=1 witi =√
PrWt, where W �= [w1,w2,w3]
with tr(WW∗) = 1, t �= [t1, t2, t3]T , and Pr is the total average power from the relay terminal. Assuming
reciprocity in the channels, the received signal in first sector of the ith BS is
yi = h∗i1tR + ni, (8)
where ni ∼ CN (0, N0) is AWGN. Similarly, at the ith MS
zi = g∗i1tR + vi, (9)
where vi ∼ CN (0, N0) is AWGN. Viewing these signals in corresponding pairs we define the 2 × 1
vector di�= [yi, zi]T so that
di = [hi1 gi1]∗tR + [ni, vi]T
=�
PrFiWt + ni
=�
PrFiwiti +�
Pr
�
j �=i
Fiwjtj + ni, (10)
where Fi�= [hi1 gi1]∗ is a composite BS-MS channel for the ith cell and ni ∼ CN (0, N0I2). To enforce
spatial separation in (10), i.e. cancel the interference from other BS-MS pairs, we set the following
constraint on the beamforming vectors Fiwj = 02, ∀j �= i. By defining the 4 × M matrix Fi�=
[F∗1 · · · F∗i−1 F∗i+1 · · · F∗3]∗, the beamforming vectors may be obtained from a “block diagonalization”
constraint Fiwi = 04, i = 1, 2, 3. Denote the SVD of Fi as Ui[Σi 04×M ]V∗i , where Vi = [V(1)
i V(0)i ]
and Ui are unitary matrices, Σi is a 4 × 4 diagonal matrix with nonzero elements and the columns of
V(1)i are the corresponding right singular vectors. The M×(M−4) matrix V(0)
i represents the null-space
of Fi which for M = 5 consist of a single column vector that may be chosen for the beamforming vector
wi (with normalization by√
3 to preserve the power constraint since ||V(0)i ||22 = 1).
With this solution (10) reduces to di = Fiwiti +ni. The self-interference is manifested in the received
January 28, 2010 DRAFT
4
at the signal level to construct
ti = si1
�1 + γ
2+ xi1
�1− γ
2, −1 ≤ γ ≤ 1, i = 1, 2, 3. (7)
Next, to spatially separate the BS-MS pairs, the relay assigns unique beamforming vectors wi to each
ti. The transmitted vector from the relay is tR =√
Pr�3
i=1 witi =√
PrWt, where W �= [w1,w2,w3]
with tr(WW∗) = 1, t �= [t1, t2, t3]T , and Pr is the total average power from the relay terminal. Assuming
reciprocity in the channels, the received signal in first sector of the ith BS is
yi = h∗i1tR + ni, (8)
where ni ∼ CN (0, N0) is AWGN. Similarly, at the ith MS
zi = g∗i1tR + vi, (9)
where vi ∼ CN (0, N0) is AWGN. Viewing these signals in corresponding pairs we define the 2 × 1
vector di�= [yi, zi]T so that
di = [hi1 gi1]∗tR + [ni, vi]T
=�
PrFiWt + ni
=�
PrFiwiti +�
Pr
�
j �=i
Fiwjtj + ni, (10)
where Fi�= [hi1 gi1]∗ is a composite BS-MS channel for the ith cell and ni ∼ CN (0, N0I2). To enforce
spatial separation in (10), i.e. cancel the interference from other BS-MS pairs, we set the following
constraint on the beamforming vectors Fiwj = 02, ∀j �= i. By defining the 4 × M matrix Fi�=
[F∗1 · · · F∗i−1 F∗i+1 · · · F∗3]∗, the beamforming vectors may be obtained from a “block diagonalization”
constraint Fiwi = 04, i = 1, 2, 3. Denote the SVD of Fi as Ui[Σi 04×M ]V∗i , where Vi = [V(1)
i V(0)i ]
and Ui are unitary matrices, Σi is a 4 × 4 diagonal matrix with nonzero elements and the columns of
V(1)i are the corresponding right singular vectors. The M×(M−4) matrix V(0)
i represents the null-space
of Fi which for M = 5 consist of a single column vector that may be chosen for the beamforming vector
wi (with normalization by√
3 to preserve the power constraint since ||V(0)i ||22 = 1).
With this solution (10) reduces to di = Fiwiti +ni. The self-interference is manifested in the received
January 28, 2010 DRAFT
phase I phase II phase III
BSMSRN (shared)
Cellular TopologyConcept
Phase I: Relay decodes BS signals under inter-sector interference
Phase II: Relay decodes MS signals under other MS interference
Phase III: UL/DL power control + spatial orthogonalization via block diag.
A single superposition of UL + DL signals is transmitted by relay
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Two-Way Shared Relay Uplink
15
Performance
Performance is reduced due to inter-sector and inter cell MS interference
Direct transmission is preferred unless MS closer to shared relay
Optimal time-share with phase III is also assumed (not shown in equation)
5
With this solution (10) reduces to di = Fiwiti +ni. The self-interference is manifested in the received
signals by substituting for the superposition from (7) into (8) and (9). For example, at the BSs we have
yi =�
Prh∗i1witi + ni
=�
Pr
2h∗i1wi
��1 + γsi1 +
�1− γxi1
�+ ni
=
�Pr(1 + γ)
2h∗i1wisi1
� �� �self−interference
+
�Pr(1− γ)
2h∗i1wixi1
� �� �desired
+ni, (11)
such that the desired signal from the MS may be detected from yi = yi−�
Pr(1+γ)2 h
∗i1wisi1. The uplink
sum-rate is then
R(III)UL (γ) =
3�
i=1
log2
�1 +
Pr(1− γ)2N0
h∗i1wiw
∗i hi1
�. (12)
Similarly at the MS, detection of the signal from the BS (via the relay) may be obtained from zi =
zi −�
Pr(1−γ)2 g
∗i1wixi1, and the downlink sum-rate is
R(III)DL (γ) =
3�
i=1
log2
�1 +
Pr(1 + γ)2N0
g∗i1wiw
∗i gi1
�(13)
Combining (2), (26), (5), and (25), the uplink and downlink sum-rates as a function of γ are given by
RDL(γ) =13
min{R(I)DL, R(III)
DL }
=13
min{log2 det(IM +Pb
N0 + σ2ζb
HH∗),
3�
i=1
log2
�1 +
Pr(1 + γ)2N0
g∗i1wiw
∗i gi1
�} (14)
RUL(γ) =13
min{R(II)UL , R(III)
UL }
=13
min{log2 det(IM +Pm
N0 + σ2ζm
GG∗),
3�
i=1
log2
�1 +
Pr(1− γ)2N0
h∗i1wiw
∗i hi1
�} (15)
B. Three-phase ASF relaying
A less sophisticated relay may choose not to decode the symbols in phase I and II but instead form
a scaled superposition tR = µdy(I)R + µuy
(II)R to broadcast in the third phase, where µu, µd > 0 are a
scalers chosen such that the average power constraint E{tr(tRt∗R)} = Pr is not violated at the relay. To
allow for a fair comparison with previous relay strategies while satisfying the power constraint for this
scheme we set
µ2d||y
(I)R ||22
µ2d||y
(II)R ||22
=1 + γ
1− γ
Pr = µ2d||y
(I)R ||22 + µ2
u||y(II)R ||22,
(16)
January 28, 2010 DRAFT
in presence of MS interference w/ block diagonalization
0 100 200 300 400 500 600 700 800 9000
1
2
3
4
5
6
7
MS distance from BS (m)
1 us
er a
chie
vabl
e ra
te [u
plin
k] (b
ps/H
z)
Two way + DirectDirectBS Coordination
Break Point (450m)
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Downlink Comparison
One-way shared relay is good for cell-edge users
One-way relay with multiple antennas help more-inner users
Two-way shared relay does not help DL transmission
16
Area Spectral Efficiency (ASE)
ConfigurationsASE
(bps/Hz/km2)
Single-antenna relay + direct 6.99
BS coordination 20.20
One-way SLNR (3x) 2 ants + Direct 8.53
One-way SLNR (3x) 4 ants + Direct 12.68
One-way shared relay 3 ants + Direct 10.31
One-way shared relay 6 ants + Direct 11.44
Two-way shared relay 6 ants + Direct 6.99
0 100 200 300 400 500 600 700 800 9000.5
1
1.5
2
2.5
3
3.5
4
MS distance from BS (m)
1 u
ser
achie
vable
rate
(bps/H
z)
Single antenna relay + Direct
BS coordination
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Uplink Comparison
Two-way shared relay is good for cell-edge users
One-way relay with multiple antennas help more-inner users
One-way shared relay does not help UL transmission
17
Area Spectral Efficiency (ASE)
ConfigurationsASE
(bps/Hz/km2)
Single-antenna relay + direct 4.78
BS coordination 10.61
One-way SLNR (3x) 2 ants + Direct 6.43
One-way SLNR (3x) 4 ants + Direct 9.08
One-way shared relay 3 ants + Direct 4.96
One-way shared relay 6 ants + Direct 5.16
Two-way shared relay 6 ants + Direct 7.580 100 200 300 400 500 600 700 800 9000
1
2
3
4
5
6
7
MS distance from BS (m)
1 u
se
r a
ch
ieva
ble
ra
te (
bp
s/H
z)
Single antenna relay + Direct
BS coordination
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Uplink / Downlink Sum Comparison
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Area Spectral Efficiency (ASE)
ConfigurationsASE
(bps/Hz/km2)
Single-antenna relay + direct 5.89
BS coordination 15.41
One-way SLNR (3x) 2 ants + Direct 7.48
One-way SLNR (3x) 4 ants + Direct 10.88
One-way shared relay 3 ants + Direct 7.63
One-way shared relay 6 ants + Direct 8.30
Two-way shared relay 6 ants + Direct 7.28
0 100 200 300 400 500 600 700 800 9000
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
MS distance from BS (m)
1 u
se
r a
ch
ieva
ble
ra
te (
bp
s/H
z)
Single antenna relay + Direct
BS coordination
Two-way shared relay is not as good as one-way shared relay
![Page 19: Where are the Relay Capacity Gains in Cellular Systems?ctw2010.ieee-ctw.org/mon/Heath.pdf · multi-hop relay base station user ii user i strong link transmission cell Two-way half](https://reader034.vdocuments.site/reader034/viewer/2022042406/5f205e5d245ae2263916bb5b/html5/thumbnails/19.jpg)
Where are the Capacity Gains?Not here: Relays that neglect interference
They arguably suck even without interference
Here: Relays that deal with interference
Multiple antennas improve mid-range cell performance
Multiple antenna shared relay improves edge of cell performance
Combination of relay strategies seems very attractive
Future work: Two-way, relay selection, power control
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References[DoppEtAl08] K. Doppler, C. Wijting, and K. Valkealahti, “On the Benefits of Relays in a Metropolitan Area Network”, VTC 2008.
[SreEtAl02] V. Sreng, H. Yanikomeroglu, and. D. Falconer, “Coverage enhancement through two-hop relaying in cellular radio systems,” WNCC 2002.
[IrmDie08] R. Irmer and F. Diehm,”On coverage and capacity of relaying in LTE-advanced in example deployments," PIMRC 2008.
[LinEtAl09] Huang Lin, Daqing Gu, Wenbo Wang, Hongwen Yang , "Capacity analysis of dedicated fixed and mobile relay in LTE-Advanced cellular networks," ICCTA 2009.
[PetEtAl09] S. W. Peters, A. Y. Panah, K. T. Truong, and R. W. Heath, Jr., ``Relaying Architectures for 3GPP LTE-Advanced,'' EURASIP Journal on Advances in Signal Processing, special issue on 3GPP LTE and LTE Advanced, vol. 2009, Article ID 618787, 14 pages, doi:10.1155/2009/618787, 2009.
[KraEtAl05] G. Kramer, M. Gastpar, and P. Gupta, “Cooperative strategies and capacity theorems for relay networks”, IEEE Trans. Info. Theory, no. 9, vol. 51, pp. 3037-3063, Sep. 2005
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