China Communications • April 2015
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as follows: for the request for vertical handoff
from VT’s user, with the help of other VTs
and CC, users can determine whether there
is a candidate wireless network for vertical
handoff request around. If there were, the
system would select the best candidate wire-
less network for the switching request; but, if
there were not, the request of vertical handoff
would be blocked. This model can make VT
share vehicle heterogeneous wireless networks
according to the best utility function.
Fig. 1 shows the coordination mechanism
based on VTs and CC, WiMAX and TD-LTE
compose the vehicle heterogeneous wireless
network model. Due to their different require-
ments of personalization operations and QoS
for the VT, terminals acquire the candidate pa-
rameter information in a collaborative manner
from other VTs and the CC. The VT makes
the vertical handoff by constructing the utility
function.
System model uses dynamic resource allo-
cation model. Network state is evaluated by
number of two dimensional resource unit and
SNR indicator. In order to make the algorithm
more generic, different physical layers of ac-
cess network all use the multi-user orthogonal
frequency division multiplexing (OFDM)
technology. For each radio access network
system, firstly, in the frequency domain all
the subcarriers are divided into a variety of
sub-channels in the continuous manner, the
frame length is divided into a variety of equal
time slots (one slot comprises an integral num-
ber of OFDM period), so that a sub-channel is
execution incomes and communication service
incomes after handoff, the optical network
to handoff will be selected. Experimental re-
sults show that the algorithm can improve the
blocking rate and the average packet loss rate
of the VT , ensure the high load balancing,
reduce ping-pong effect, and ensure vehicle
user’s QoS while entering the candidate net-
work. The main contributions of the literature
can be summarized as follows:
(1) The algorithm using the markov process
to predict wireless network status changes
after handoff decision. At the service time that
VT switches and enters network, wireless net-
work’s status attribute is constantly changing
for the mobility of vehicles. Thus the network
status can be abstracted as a discrete markov
process, with the use of the state transition
probabilities to predict the network’s state af-
ter handoff decision. According to this paper’s
author, using the markov process to predict the
network status and then optimizing the perfor-
mance of vertical handoff algorithm research,
are still rarely reported.
(2) Among the handoff algorithms based on
multi-attribute utility function, the design of
optimal utility function is particularly import-
ant. In this paper, we use the markov process
and the fuzzy logic method, combining with
handoff decision, handoff execution and tran-
sition probability after switching execution, to
design an optimal vertical handoff utility func-
tion of the multiple state attributes.
II. SYSTEM MODEL
In the vehicle heterogeneous wireless net-
works, the VT ‘s use of the candidate network
is managed by the central controller (CC), the
CC first collects various parameter informa-
tion of heterogeneous wireless network, then
builds a set of candidate wireless networks,
through exchanging access information be-
tween multiple VTs, and ultimately achieve
the global optimum of vertical handoff pro-
cess.
Vertical handoff mechanism of vehicle het-
erogeneous wireless network can be described
Fig.1 Vehicle heterogeneous wireless networks model
WiMAX
TD-LTE
TD-LTE
VT
CC
VT
AP
BS
Track 1
Track 2