1 Introduction
2 Related studies
3 System model for moving networks
3.1 Interference identification for MNs
3.2 Fairness between regular UEs and VUEs
4 Time domain interference coordination for the backhaul links of MNs
4.1 Configuration of ABSs
4.2 Scheduling restriction schemes
5 Multi-antenna solutions for backhaul links of MNs
5.1 Maximum ratio combining
5.2 SINR maximization by interference suppression
6 Interference coordination for access links of MNs
7 Performance evaluation
Component
|
Configuration parameters
|
---|---|
Buildings and streets | Nine buildings 120 by 120 m with six floors (3.5 m height of each floor), see Figure 1. |
Road width 21 m (including sidewalks and parking lanes) | |
Macro BS | Height: 5 m above the top of the middle building (see Figure 1) |
Maximum transmit power (per 10 MHz): 43 dBm | |
Carrier: 800 MHz | |
Bandwidth: 20 MHz | |
Antenna configuration: 17 dBi gain, three sectors (one antenna per sector), 0°, 120°, and 240° with respect to the north | |
Micro BS | Height: 10 m above the ground close to middle point of south and east walls |
Positions: see Figure 1
| |
Maximum transmit power (per 10 MHz): 30 dBm | |
Carrier: 2.6 GHz | |
Bandwidth: 80 MHz | |
Cell range expansion bias: 5 dB | |
Antenna configuration: 17 dBi gain, two sectors (one antenna per sector), pointing to the main street with an angle of 20° with respect to the closest wall | |
Moving network | Full-duplex |
Speed: 50 km/h | |
Height: 3.5 m above the ground | |
Mobility model: public transportation vehicles enter each street through a Poisson process with an inter-arrival time of 2 min | |
Maximum transmit power indoor (per 10 MHz): 10 dBm | |
Carrier: 800 MHz for backhaul links, and 2.6 GHz for access links | |
Bandwidth: 20 MHz for backhaul links and 80 MHz for access links | |
Antenna configuration both indoor and outdoor: single antenna, | |
0 dBi gain omnidirectional antenna | |
Receiver noise figure: 5 dB | |
Outdoor UEs (macro UE, micro UE) | Speed: 0 to 3 km/h |
Height: 1.5 m above the ground | |
Positions: uniformly randomly dropped, 50 UEs per road | |
Cell selection: based on received power with 5 dB CRE bias for micro cells | |
Receiver noise figure: 9 dB | |
VUEs | Height: 1.5 m above the ground |
Position: uniformly randomly dropped inside a vehicle | |
Number of VUEs in each vehicle: 1) uniformly from the interval | |
[1, 50]; 2) 25 VUEs per vehicle | |
Cell selection: 1) same as macro UEs (baseline case); 2) always connect to the MN of their own vehicles (other cases) | |
Receiver noise figure: 9 dB |
7.1 Performance analysis for macro UEs and VUEs
7.2 Performance analysis for micro UEs
Backhaul schemes
| ||||
---|---|---|---|---|
Number of VUEs and VPL
|
IRC
|
MRC
|
30% ABS
|
37% ABS
|
Random VUEs, 15 dB VPL | 0.0920 | 0.0813 | 0.0740 | 0.0663 |
25 VUEs, 15 dB VPL | 0.0884 | 0.0848 | 0.0671 | 0.0697 |
Random VUEs, 30 dB VPL | 0.0250 | 0.0250 | 0.0250 | 0.0250 |
25 VUEs, 30 dB VPL | 0.0250 | 0.0250 | 0.0250 | 0.0250 |
8 Discussion
8.1 Complexity of the considered schemes and potential impact on the current LTE-A systems
8.2 Limitations in the current LTE-A systems
8.3 Further works
9 Conclusions
9.1 Table of notations
Symbol
|
Meaning
|
---|---|
b(l, m, u) | The scheduling decision for the uth user in mth PRB in the lth subframe |
b
p(n) | Total number of PRBs scheduled for device n over \(\mathcal {R}_{\mathrm {p}}\)
|
b
np(n) | Total number of PRBs scheduled for device n over \(\mathcal {R}_{\text {np}}\)
|
d(n) | A function that measures channel quality difference for the nth device over the protected and non-protected PRBs |
i
v
| The number of active VUEs on the vth MN |
j
| The index of an interferer |
k
| The time index of received signal |
l
| The index of a subframe |
m
| The index of a PRB in a given subframe |
n
| The index of an arbitrary device, i.e., either a UE or an MN, connecting to a macro cell |
n
∗(l, m) | The device is selected to be scheduled at the mth PRB in the lth subframe in the macro cell |
p
| The number of antennas equipped at the backhaul link of an MN |
\(q_{n_{1}}\)
| An arbitrary device served by macro BS sector 1 |
r(l, m, u) | The throughput of the uth macro UE at the mth PRB in the lth subframe |
r
0,i
(v) | The throughput of the access link of the vth MN when the ith subframe in the micro cells is configured as ABS |
r
1,i
(v) | Throughput of the access link of the vth MN when the ith subframe in the micro cells is not configured as ABS |
r
p(n) | The average rate of device n over \(\mathcal {R}_{\mathrm {p}}\)
|
r
np(n) | The average rate of device n over \(\mathcal {R}_{\text {np}}\)
|
s(n) | The average throughput of device n, which can be either a macro UE or the backhaul link of an MN |
s(u) | The average throughput of the uth macro UE |
s(v) | The average throughput of the backhaul link of the vth MN |
u
| The index of a macro UE |
u
∗(l, m) | The macro UE that is selected to be scheduled at the mth PRB in the lth subframe |
x
k
| The desired signal transmitted at time k
|
x
j, k
| The interfering signal from the jth interferer at time k
|
n
1
| The index of a device served by macro BS sector 1 |
v
| The index of an MN |
B
p
| The size of \(\mathcal {R}_{\mathrm {p}}\)
|
B
np
| The size of \(\mathcal {R}_{\text {np}}\)
|
G(ν) |
\(G(\nu)=N\,\frac {\nu }{\left (1+\nu \right)}\) for ν≥0, a function defined to facilitate the solution of problem (7) |
K
| A parameter used in the solution of (11), where K∈{0, 1, …, N−1} and G(d(K+1))≤K≤G(d(K)) |
L
| The number of total subframes in which the average throughput of a device in the macro cell is calculated |
M
| The total number of PRBs in each subframe |
N
| The total number of devices, i.e., N=N
u+N
m, connect to a macro cell |
N
1
| The number of devices served by macro BS sector 1 |
N
c
| The number of subcarriers in an OFDMA system |
N
L
| The number of interferers experienced at the backhaul link of an MN |
N
m
| The number of MNs in a macro cell |
N
u
| The number of macro UEs in a macro cell |
N
sf
| The number of total subframes that average throughput target of the backhaul link of the MNs are calculated in the micro cells |
\(\bar {R}(v)\)
| The average throughput target of the backhaul link of the vth MN during N
sf subframes |
α
| A parameter used in the solution of (11), where α=λ
p−K
|
γ
k
| The instantaneous output SINR at the MN backhaul receiver at time k
|
ε
| An averaging constant that is required in updating the average throughput of a given device |
λ
p
| A parameter used in the solution of (11), where λ
p= max(G(d(K+1)), K) |
λ
np
| A parameter used in the solution of (11), where λ
np=N−λ
p
|
\(\sigma _{\mathrm {n}}^{2}\)
| The noise power at each antenna |
μ(l, u) | The average throughput of user u
|
\(\mathcal {I}_{i}\)
|
\(\mathcal {I}_{i}\in \left \{ 0,\ 1\right \},\ i=1,\ 2,\ 3\ldots \,N_{\text {sf}}\) indicate the status of the ABSs at the micro cells |
The sets denotes all the macro UEs in a cell | |
\(\mathcal {R}_{\mathrm {p}}\)
| The set of protected PRBs in a macro cell |
\(\mathcal {R}_{\text {np}}\)
| The set of non-protected PRBs in a macro cell |
\(\mathcal {S}_{1}\)
| The set of users only scheduled in R
p
|
\(\mathcal {S}_{2}\)
| The set of users only scheduled in R
np
|
\(\mathcal {S}_{3}\)
| The set of users can be scheduled both in \(\mathcal {R}_{\mathrm {p}}\)and \(\mathcal {R}_{\text {np}}\)
|
To denote uniform distribution | |
The sets denotes all the MNs in a cell | |
h
k
| The channel vector of the desired signals at each reviver antenna of an MN at time k
|
h
j, k
| The channel vector of the jth interfering signal observed at each reviver antenna of an MN at time k
|
n
k
| The vector denotes the thermal noise at each receiver antenna of an MN at time k
|
w
k
| The vector that contains the weight applied at each receiver antenna of an MN at time k
|
y
k
| The vector that contains the received signal at each receiver antenna of an MN at time k
|
z
k
| The combined signal at the output of an MN backhaul receiver at time k
|
R
| The noise covariance matrix of the reviver antennas of an MN |
I
p×p
| The identity matrix of size p
|
(·)H
| To denote the complex conjugate transpose of a matrix |
EIGmax(·) | To denote the dominant eigenvector of a matrix |