In this paper, we consider revenues of the NSP (network service provider) when there exists a "congestion externality." In particular, we compare revenues obtained using a flat price and two-part tariff and analyze the effect of congestion on the revenue loss when using a simple entry fee in lieu of the two-part tariff. Previous study has shown that when there is no delay disutility the revenue loss is small, which leads to a low "Price of Simplicity." However, in this study, we show that in an extreme case where all users are identical, the price of simplicity is substantial. Then we consider a more practical scenario where users have different preferences, and show that even in this case, under congestion externality, the price can be extremely high.

Femtocells are a promising technology for handling exponentially increasing wireless data traffic. Although extensive attention has been paid to resource control mechanisms, for example, power control and load balancing in femtocell networks, their success largely depends on whether operators and users accept this technology or not. In this paper, we study the economic aspects of femtocell services for the case of monopoly market, and aim to answer questions on operator's revenue, user surplus, and social welfare by considering practical service types and pricing strategies. We consider three user subscription services, that is, users can access only macro BSs (mobile-only), or deploy femto BSs in their house and open / exclusively use their femto BSs (open- / closed-femto). For pricing strategies, flat pricing and partial volume pricing are exploited. The main messages include the following: 1) open-femto service is beneficial to both users and providers; 2) in flat pricing, the impact on operator revenue of allowing or blocking the access of mobile-only users to open femto BSs is minor; and 3) compared with partial volume pricing, flat pricing is advantageous to the operator when users are sensitive to price.

The femtocell is an enabling technology to handle exponentially increasing wireless data traffic. Despite extensive attentions paid to resource control, e.g., power control and load balancing in femtocell networks, the success largely depends on whether operators and users accept this technology or not. In this paper, we study the economic aspects of femtocell services with game theoretic models between providers and/or users. We consider three services: users can access only macro BSs (mobile-only), or open/exclusively use their femto BS (open or closed-femto). The main messages include: 1) it is better off for the operator to provide just the open-femto service than a mix of closed and open-femto services; 2) two polices of allowing or blocking the access of mobile-only users to open femto BS are not significantly differentiated in the revenue.

The Network Utility Maximization (NUM) has been extensively used in both wired and wireless networks and has been very helpful to provide insight on optimal controls of various parameters such as power, scheduling and rate control. However, the popular opportunistic scheduling mechanism, that improves the system performance by exploiting time varying channel conditions at different receivers, has not been incorporated in the framework yet. In this paper, we extend the framework and derive optimal flow control and link scheduling for wireless multihop networks with opportunistic scheduling. More precisely, we formulate the NUM problem with new resource constraints to include the benefits of opportunistic scheduling and then proceed to solve the problem. The formulation turns out to be a non-convex problem, however we propose an algorithm that approximates the optimum solution. Numerical results show that the proposed algorithm achieves significant throughput gain.

We present a unified analytical framework that maximizes generalized utilities of a wireless network by network-wide opportunistic scheduling and power control. That is, base stations in the network jointly decide mobile stations to be served at the same time as the transmission powers of base stations are coordinated to mitigate the mutually interfering effect. Although the maximization at the first glance appears to be a mixed, twofold and nonlinear optimization requiring excessive computational complexity, we show that the maximization can be transformed into a pure binary optimization with much lower complexity. To be exact, it is proven that binary power control of base stations is necessary and sufficient for maximizing the network-wide utilities under a physical layer regime where the channel capacity is linear in the signal-to-interference-noise ratio. To further reduce the complexity of the problem, a distributed heuristic algorithm is proposed that performs much better than existing opportunistic algorithms. Through extensive simulations, it becomes clear that network-wide opportunistic scheduling and power control is most suitable for fairness-oriented networks and under loaded networks. We believe that our work will serve as a cornerstone for network-wide scheduling approaches from theoretical and practical standpoints.

In an intermittently connected environment, access points are sparsely distributed throughout an area. As mobile users travel along the roadway, they can opportunistically connect, albeit temporarily, to roadside 802.11 (Wi-Fi) APs for Internet access. Networking characteristics of vehicular opportunistic Internet access in an intermittently connected environment face numerous challenges, such as short periods of connectivity and unpredictable connection times. To meet these challenges, we propose an access point report (APR) protocol where mobile stations opportunistically collaborate by broadcasting an APR to other mobile stations to fully utilize the short-lived connection periods. APR can optimize the use of short connection periods by minimizing the scanning delay and also act as a hint that enables mobile users to predict when connection can be established.

In ISM bands, many wireless protocols proliferate such as 802.11, Bluetooth, and ZigBee. However, these incompatible protocols create complex coexistence and connectivity problems. If the same trend continues, similar interference and performance problems will continue to exist in future unlicensed bands. As new unlicensed bands open up, one can take a different approach to spectrum sharing. Instead of proposing a new MAC protocol for each type of application, we propose a family of parameterized MAC protocols called WiFlex that can tailor to different application needs ranging from wireless sensors to media center. Yet, these protocols within this family are compatible with each other to allow communication and spectrum-sharing coordination among different types of devices. We envision this family to be based on an OFDM-like multichannel physical layer. The contribution of this paper includes the discovery of an asynchronous split phase (ASP) protocol with dynamic priority support. This protocol enables powerful devices to achieve a high throughput and protects low power devices with urgent but only occasional transmissions. It is distributed and data collision-free. Moreover, it can support low delays for real time applications. The performance of the protocols are evaluated using an extension of NS-2. The results demonstrate the coexistence of devices with disparate radio characteristics and the support of applications with different requirements with good performance.

This paper compares, analytically and through simulations, a number of multichannel MAC protocols. We first classify these protocols into four categories based on their principles of operation: Dedicated Control Channel, Common Hopping, split phase, and parallel rendezvous protocols. We then examine the effects of the number of channels and devices, channel switching times, and traffic patterns on the throughput and delay of the protocols. Here are some of the conclusions of our study: 1) Parallel Rendezvous protocols perform generally better than Single Rendezvous protocols; 2) Dedicated Control Channel protocols can be a good approach with its simplicity when the number of channels is high and the packets are long; 3) Split Phase protocol is very sensitive to the durations of the control and data phases. Our study focuses on a single collision domain.

We consider a multicast resource allocation problem for the downlink in OFDM-based wireless cellular network systems. In a conventional multicast system, to accommodate users with bad channel conditions, the transmission is based on the worst case user. We show that such a multicast system saturates the capacity when the number of users increases in fading environments. We exploit the multicarrier nature of OFDM and advances in coding techniques such as MDC (multiple description coding), in which arbitrary combinations of layers can be decoded at the receiver. Different MDC layers are carried over different subcarriers and users with good channels receive data from more subcarriers than users with poor channel conditions. We present an optimal subcarrier/bit allocation method requiring full search of possible candidates. To reduce the complexity, we propose a two-step suboptimum algorithm by separating subcarrier allocation and bit loading. Numerical results show that the proposed heuristics significantly outperform the conventional multicast transmission scheme. The difference between optimum and heuristic solutions is less than 5%.

We propose a new polling method for non-real-time traffics for the uplink of the 802.16 wireless MAN systems. Though the standard supports various polling services for uplink data transmission, it leaves the details to the vendors. Our proposal is an extension of the proportional fair (PF) scheduling and we apply the idea of the PF to non-real-time polling services. It uses channel quality information and tries to achieve QoS guarantee. The simulation results confirm the effectiveness of our algorithm.

Many multiple channel MAC protocols for wireless networks have been proposed to make efficient use of multiple channels where each node has a single radio which allows it to send or receive on one channel at a time. However, most of the proposed protocols are single rendezvous protocols that are subject to the congestion of the control channel. The paper proposed a new parallel rendezvous protocol, McMAC, to avoid control channel congestion so that it can scale to use a large number of channels efficiently. The authors validate the protocol design using simulation and implementation.

We present a unified analytical framework that maximizes generalized utilities of a wireless network by network-wide opportunistic scheduling and power control. That is, base stations in the network jointly decide mobile stations to be served at the same time as the transmission powers of base stations are coordinated to mitigate the mutually interfering effect. Although the maximization at the first glance appears to be a mixed, twofold and nonlinear optimization requiring excessive computational complexity, we show that the maximization can be transformed into a pure binary optimization with much lower complexity. To be exact, it is proven that binary power control of base stations is necessary and sufficient for maximizing the network-wide utilities under a physical layer regime where the channel capacity is linear in the signal-to-interference-noise ratio. To further reduce the complexity of the problem, a distributed heuristic algorithm is proposed that performs much better than existing opportunistic algorithms. Through extensive simulations, it becomes clear that network-wide opportunistic scheduling and power control is most suitable for fairness-oriented networks and underloaded networks.

Several TCPs have been proposed to cope with the change of networks. They have mainly focused on modifying congestion control. However, even ideal congestion control for wireless networks cannot achieve remarkable throughput increase. In this paper, we verify that the reason for this exists in a vulnerable point where existing loss recovery algorithms do not consistently work as packet loss rate increases due to ack starvation during loss recovery. In this paper, we propose a novel loss recovery algorithm using packet transmission order, which shows a steady loss recovery ability even though packet loss rate increases. This leads to significant throughput increase of wireless TCP.

We consider a multicast resource allocation problem for the downlink in OFDM-based wireless cellular network systems. In a conventional multicast system, to accommodate users with bad channel conditions, the transmission is based on the worst case user. We show that such a multicast system saturates the capacity when the number of users increases in fading environments. We exploit the multicarrier nature of OFDM and advances in,coding techniques such as MDC (multiple description coding), in which arbitrary combinations of layers can be decoded at the receiver. Different MDC layers are carried over different subcarriers and users with good channels receive data from more subcarriers than users with poor channel conditions. We present an optimal subcarrier/bit allocation method requiring full search of possible candidates. To reduce the complexity, we propose a two-step suboptimum algorithm by separating subcarrier allocation and bit loading. Numerical results show that the proposed heuristics significantly outperform the conventional multicast transmission scheme. The difference between optimum and heuristic solutions is less than 5%.

Wireless ad hoc network design with cross layer approach has been recently studied considering different layer information. Especially, the design of the optimal transport control protocol has been one of intensive research topics, but the issue is not fully addressed yet. Although researches on end-to-end semantics are prevailed in transport layer issue, relatively smaller scalability than wired networks and unreliable channel state give strong advantages on hop-by-hop approach. We consider the hop-by-hop congestion control algorithm with network utility optimization. We formulate and solve a new transport layer problem based on the hop-by-hop algorithm, which reaches the optimal rate point stably by jointly considering MAC layer and transport layer information. Simulation results show that the hop-by-hop congestion control has better performance on the aspect of the schedulability, stability, convergence speed and optimality.

In this paper, we revisit the optimization based control problem of wireless ad-hoc networks. Even though much work has been done so far, they are limited either in their practicality or in their efficiency. We develop another framework based on independent set and propose an implementable heuristic algorithm. Our heuristic is based on the longest queue first (LQF) policy and the neighborhood price.

This paper compares, through analysis and simulation, a number of multichannel MAC protocols for wireless networks. We first classify these protocols into 4 categories based on their principles of operation. We then examine the effects of the number of channels and devices, channel switching times, and traffic patterns on throughput and delay. Our study focuses on a single collision domain.

In this paper, we demonstrate the existence of fair end-to-end window-based congestion control protocols for packet-switched networks with first come-first served routers. Our definition of fairness generalizes proportional fairness and includes arbitrarily close approximations of max-min fairness. The protocols use only information that is available to end hosts and are designed to converge reasonably fast. Our study is based on a multiclass fluid model of the network. The convergence of the protocols is proved using a Lyapunov function. The technical challenge is in the practical implementation of the protocols.

We propose some improvements of TCP Vegas and compare its performance characteristics with TCP Reno. We argue through analysis that TCP Vegas, with its better bandwidth estimation scheme, uses the network resources more efficiently and fairly than TCP Reno. Simulation results are given that support the results of the analysis.