Research On Wireless Access And Transmission Scheme In Mobile Internet

In mobile Internet, users connects the Internet through mobile devices they carry. It is the convergence of mobile communication and Internet. In recent years, it has be-come the hot topic in both the industrial and academic areas. As the applications on mobile Internet grow, the traditional wireless access and transmission mode through cellular networks has to be improved. Femtocell networks have been introduced and the users can enjoy higher data transmission rate. In addition, this type of networks benefits the operators because the power efficiency of the femtocell base stations will be higher than the marco base stations. Since it is beneficial for users and operators, special attention for developing femtocell solutions has been received recently from a lot of researchers. Besides the development of wireless access method, a new transmis-sion mode based on the contact between two mobile users has been proposed. Due to the lack of continuously connected paths between every pair of nodes, communication usually adopts the "store-carry-and-forward" manner. Because opportunistic transmis-sion is usually through Wi-Fi or Bluetooth devices, it’s free of charge and generates no traffic on the cellular infrastructure network. Thus, it can decrease the overhead and improve the service quality.In Femtocell networks, communication between different base stations and users may interfere with each other. To optimize the performance, the macrocell and all in-volved different femtocells need to allocate the communication resources to a group of users cooperatively, such as power and channels. We investigate the resource allocation problem in femtocell networks. For opportunistic transmission, some nodes are chosen as gateways to connect with the Internet via cellular networks. We address the problem of choosing suitable gateways from all the nodes to reduce traffic overhead and delay of information access in mobile wireless networks. After the gateways get data from the Internet, they can deliver it to others. Because a large proportion of the data which the users are interested in is bulk data, we study how to design transmission protocols with high throughput for it. For all pairs of source and destination, there are two dif-ferent transmission modes. One is without the help of gateways, which is similar with opportunistic transmission. The other is through gateways, which is like the traditional infrastructure based transmission. We investigate the trade-offs between delay and ca-pacity in mobile wireless networks with infrastructure support. In this paper, the main contributions are as follows.(1) For the resource allocation in femtocell networks, we target at maximizing the minimal throughput among the cells. We discuss two different cases. When the power can be adjusted continuously, a joint optimization over power control, channel allocation and user association is considered and the problem is then formulated as a non-convex mixed integer non-linear problem (MINLP). For the sub-problem of channel allocation and user association, we prove they are both NP-complete. Furthermore, we prove that when the number of channels is equal or larger than3, there is no polynomial-time algorithm with approximation ra-tio ρ≥1for the channel allocation problem unless NP=P. Similarly, we also prove that there is no polynomial-time algorithm with approximation ra-tio1≤ρ<2for the user association problem unless NP=P. To solve this problem, we proposed an alternating optimization based algorithm, which applies branch-and-bound and simulated annealing in solving sub-problems at each optimization step. When there are different discrete levels for the power to set, a joint optimization problem over power control and channel allocation is formulated. We propose a particle swarm optimization based algorithm PCASO, in which we define three operations for generating a new particle, such as mu-tation, local crossover and global crossover. We demonstrate the efficiency of PCASO by numerical experiments.(2) For gateway selection in mobile wireless networks, we formulate it as K-GW Selection problem, where K nodes are selected as gateways to distribute data in order to minimize the expected broadcast delay. We prove that the problem is#P-hard. To solve it, we propose four heuristic algorithms, namely Random, MCS (Monte Carlo-based gateway Selection), CBS (Centrality Based gateway Selection), and FT (Frequent Trajectory based gateway selection). Based on generating function, we propose a theoretical method for the calculation of the expected broadcast delay in Random. Intuitively, the delay can be regarded as an upper bound for that in MCS, CBS and FT. Through simulations, we compare the performance of the four algorithms. It is found that FT outperforms Random by about15%when the network size n=30. The algorithm CBS outperforms Random by10%when n=40,...,100.(3) For bulk data transmission in mobile wireless networks, we introduce feedback-less segmented network coding. Based on the knowledge of the contact rate among nodes, we model the data reception process at the destination using dif-ferential equation, and calculate the probability that it can receive K coded pack-ets successfully during a period of time in closed-form. To our best knowledge, we are the first to derive the upper bound of the maximum sustained throughput in a closed-form when feedbackless segmented network coding is involved. We provide two necessary conditions, i.e., the intra-segment coding condition and the inter-segment scheduling condition, for achieving this optimal performance. Based on the understanding of these conditions, we then propose a practical SNC protocol that approaches the theoretical bound asymptotically. The segment de-lay of the proposed protocol is also analyzed. Correctness of our theoretical analysis is verified through simulations. Also, the experiment results prove the effectiveness our proposed protocol.(4) For the trade-offs between capacity and average packet delay in mobile wireless networks with infrastructure support, we consider two synthetic models I.I.D mo-bility model, random walk mobility model with constant speed and Levy flight mobility model which is based on human mobility. For I.I.D mobility model and random walk mobility model with constant speed (?)(-/(?)n), we give theoretical results of the average packet delay when capacity is (?)(1),(?)(1/(?)) individually. n is the number of nodes in the network. It is proved that capacity is bounded above by; when the average packet delay is optimized. K is the number of gateways in the network. The bounds of the average packet delay divided by capacity under the three models are established, as well as the criti-cal average delay for the capacity comparing with that in static hybrid wireless networks. Our work provides useful theoretical insights on the performance of mobile wireless networks with infrastructure support, and will help the schedul- ing and routing protocol design.