Adaptive BU association and resource allocation M. Gong et al.
Table I. Notations.
Symbol Notation
R
n
The dat a rate of user n
˛ The path-loss exponent
d
0
The reference distance to BS antenna
N
0
The noise power
d
mn
The dist ance between user n and BS m
P
R
n
The signal power received by user n
P
I
n
The interference signal power received by user n
P
r
mn
The transmission power received by user n from
BS m
P
t
m
The transmission power of BS m
N The number of tot al users
M The number of tot al BSs
B The tot al wireless bandwidth
R
Req
n
The dat a rate required by user n
A
mn
The associating indicator of user n and BS m
Tp
mn
The normalized time slots allocated to user n
from BS m
x
jn
The associating indicator of user n and AM
∗
j
Tp
jn
The normalized time slots allocated to user n by
AM j
Tp
n
The normalized time slots allocated to user n
∗
AM: associating mode.
SINR
n
=
P
R
n
N
0
+ P
I
n
(2)
For the conventional wireless communications with Non
Cooperative Transmission (NCT) technology, one user is
associated with only one BS; say BS m is associating user
n. The received signal power (P
R
n
) can be estimated by
the radio wave propagation function f(·)of the transmission
power from BS m.
P
R
n
= P
r
mn
= f
P
t
m
(3)
The interference power (P
I
n
) is the summation of the
transmission power from the BSs other than the associating
one, formulated as follows.
P
I
n
=
M
k=1,k=m
P
r
kn
(4)
In the CPWN, one or more BSs can cooperatively trans-
mit same packets to one user. So, in Equation (5), P
R
n
is the
summation of the transmission power of all the associating
BS(s) [6], and P
I
n
is calculated by Equation (6).
P
R
n
=
M
m=1
A
mn
P
r
mn
(5)
P
I
n
=
M
m=1
(
1−A
mn
)
P
r
mn
(6)
Where
A
mn
=
1BSm associates user n
0 otherwise
(7)
For simplicity, we use following the path loss model [25]
to estimate the signal power of user n from BS m in our
simulation.
P
r
mn
= f (P
t
m
) = P
t
m
×
d
0
d
mn
α
(8)
The propagation model can be improved by combin-
ing the shadowing fading model [26] or small-scale fading
model [27]. However, the improvement does not affect the
simulation results. Because receive power and SINR of each
user are the parameters applied by our BUA-RA schemes.
In the real applications, these parameters are measured by
the users and fed back to the OLT [28].
3.2. Key technologies
Recent technological breakthroughs of coding, modulation,
and multiple access allow us to exploit the inherent charac-
teristics of CPWNs in the following three aspects:
(1) Multiple access: Orthogonal frequency division
multiplexing (OFDM) is a frequency division mul-
tiplexing (FDM) scheme utilized as a digital
multi-carrier modulation technique. Under OFDM,
data is divided into several parallel data streams
or channels, one for each sub-carrier. The primary
advantages of OFDM are efficient wireless frequency
usage, eliminated inter-symbol interference, low
complexity of implementation and Multiple-Input
and Multiple-Output (MIMO)-applicableness. The
combination of OFDM with Time Division Multi-
ple Access (TDMA) or Frequency Division Multiple
Access (FDMA), two basic multiple access tech-
niques, OFDM-TDMA and OFDMA, are adopted
by the IEEE 802.16e standard [29] as two options.
OFDM-TDMA is selected as the multi-access tech-
nology in this paper.
(2) Cooperative transmission (CT): This is another key
technology in the CPWN. With inter-cell coopera-
tive transmission, the data segments are coded with
different space-time codes in the associated BSs.
These orthogonal space-time codes are then transmit-
ted to the receiver where the same copy or a portion
of the data can be aggregated and jointly decoded.
In this way, the end-users’ Signal to Interference
plus Noise Ratio (SINR) can be improved signifi-
cantly. We aim to exploit the significant performance
benefits of inter-cell cooperative transmission to
achieve the aforementioned targets of the NG-BWA
network.
(3) Centralized network management: By the PON
architecture, a message from OLT is broadcasted to
Wirel. Commun. Mob. Comput. (2010) © 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/wcm