1774 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 68, NO. 2, FEBRUARY 2019
nario where task requesters and data collectors are all moving
in the same area. The paper deduced the inter-meeting time dis-
tributions among users and proposed efficient task assignment
algorithms to minimize the t ask completion time. [32] stud-
ied both deterministic and probabilistic models in vehicle-based
mobile crowdsensing and proposed efficient vehicle recruitment
algorithms to minimize the overall recruitment cost.
B. Task Assignment in Participatory Sensing
Participatory sensing can be classified into discontinuous-
moving-based and continuous-moving-based. In discontinuous-
moving-based participatory sensing, a mobile user can perform
multiple tasks in his/her moving range, each at a distinct loca-
tion. In this case, only the distance from the resident location
of the user to each task location is counted. Continuous mov-
ing between different task locations is not considered. Such
discontinuous-moving assumption can greatly simplify the task
assignment problem and also largely reduce the complexity for
solving the task assignment problem. In continuous-moving-
based participatory sensing, the platform determines each user’s
moving path and also tasks to perform. The problem has close
similarity with the well-known Traveling Salesman Problem
(TSP) problem. In this case, design of sophisticated task assign-
ment schemes is usually needed to maximize the task quality or
minimize the total incentive cost.
Typical discontinuous-moving-based participatory sensing
mechanisms are as follows. [14] aims to maximize task com-
pletion rate and also platform profit under constraints of task
deadlines, task performing capacity, and Euclidean travel dis-
tance constraints. The authors modeled the problem as a maxi-
mum weight bipartite matching problem, and proposed an online
approximate matching algorithm. [33] studied the assignment
problem of minimizing incentive payout under constraints of
travel distance and expected task quality.
Some typical continuous-moving-based participatory sensing
mechanisms are as follows. [34] proposed a task management
framework which aims to maximize the task completion rate
and the coverage area of sensor trajectories simultaneously. [27]
aims to maximize the platform profit (defined as incomes from
task requesters minus rewards paid to users) subject to user
travel distance budget and proposed an approximate algorithm
by applying local-ratio technique such that the task assignments
and itineraries for all users are determined in an offline manner.
The objective in [19] is to maximize the number of completed
tasks and also minimize the sum of travel distance of all mo-
bile users. The problem was first modeled using minimum cost
maximum flow theory. A heuristic solution was then proposed,
which restricts each mobile user to select tasks from his/her
closest k tasks. [35] studied the moving path scheduling prob-
lem to minimize total task tardiness penalty. Tardiness penalty
is an increasing function of task expiration time. The authors de-
signed a genetic algorithm to address this problem. A common
assumption on user movement in [19], [27], [35] is that mobile
users only have starting points but without destination points.
[36] focused on the online task assignment where mobile users
and tasks arrive dynamically. The objective is to maximize total
task quality under constraints of users’ travel distance budgets
and task performing capacity (more exactly, maximum amount
of tasks that each user is allowed to perform during an itinerary).
In [36], each user is assumed to have a start point, a destination
point, and a travel distance budget. In [36], a Quality-Aware On-
line Task Assignment algorithm (QAOTA) was proposed and it
uses depth-first search with branch and bound for optimal task
assignment for each arriving user. The computational complex-
ity of QAOTA is O(N
M
), where M and N are the task perform-
ing capacity of a user and the total number of tasks, respectively.
Our work in this paper belongs to the continuous-moving-based
participatory sensing category and the user- and task- related
assumptions used in this paper are the same to those in [36].
However, we do not put restriction on task capacity to achieve
improved task assignment performance.
C. Task Assignment for the Orienteering Problem in
Operational Research
Task assignment and path planning in participatory sensing is
very similar to the orienteering problem in operational research.
Orienteering problem is to find a path (with limited length) that
visits some vertices (each with a score) to maximize the sum of
scores.
Many researchers had proposed heuristics [29], [37]–[41]
to tackle the orienteering problem. [37] proposed a Monte-
Carlo-based stochastic algorithm, a sector-separating-based
deterministic algorithm, and a route-improvement algorithm.
[38] designed a heuristic including four phases: vertex inserting,
cost improvement, vertex deletion, and maximal insertions.
[39] first uses a greedy method to construct an initial solution
and improves the solution by four steps: one-point movement,
two-point exchange, clean up, and reinitialization. [29] pro-
posed a heuristic based on Pareto Ant Colony Optimization
(PACO) and a post-processing procedure. The post-processing
procedure includes three improvement methods: path shorten-
ing, vertex inserting, and vertex exchanging. Path shortening
is to reduce the path length by rearranging the vertex sequence.
Path shortening is the most important one among these three
methods since it can make room for vertex inserting and vertex
exchanging. The method used for path shortening in [29] is
2-opt local improvement algorithm which selects two vertices
in the path and reverses the vertex sequence between these two
vertices. [42] proved t hat upper bounds on the average number
of iterations by 2-opt with n vertices in a Euclidean square is
O(n
10
logn) for any n ≥ 8, which is computationally intensive.
Vertex inserting is to insert a vertex out of the path into the
path. Vertex exchanging is to replace a vertex in the path with
another vertex out of the path. Vertex inserting and vertex
exchanging can increase the total score of a path. [40] showed
that the PACO algorithm in [29] is a competitive solution for
the orienteering problem and also it outperforms the algo-
rithms proposed in [37]–[39]. For more information regarding
solutions for the OP problem, please refer to [40], [41].
Team orienteering problem is one variant of orienteering
problem and its objective is to determine several paths, one
for each member in a team. Several algorithms for this problem