In third-generation (3G) wireless data networks, mobile users experiencing poor channel quality usually have low data-rate connections with the base-station. Providing service to low data-rate users is required for maintaining fairness, but at the cost of reducing the cell's aggregate throughput. In this paper, we propose the Unified Cellular and Ad-Hoc Network (UCAN) architecture for enhancing cell throughput, while maintaining fairness. In UCAN, a mobile client has both 3G cellular link and IEEE 802.11-based peer-to-peer links. The 3G base station forwards packets for destination clients with poor channel quality to proxy clients with better channel quality. The proxy clients then use an ad-hoc network composed of other mobile clients and IEEE 802.11 wireless links to forward the packets to the appropriate destinations, thereby improving cell throughput. We refine the 3G base station scheduling algorithm so that the throughput gains of active clients are distributed proportional to their average channel rate, thereby maintaining fairness. With the UCAN architecture in place, we propose novel greedy and on-demand protocols for proxy discovery and ad-hoc routing that explicitly leverage the existence of the 3G infrastructure to reduce complexity and improve reliability. We further propose a secure crediting mechanism to motivate users to participate in relaying packets for others. Through extensive simulations with HDR and IEEE 802.11b, we show that the UCAN architecture can improve individual user's throughput by up to 310% and the aggregate throughput of the HDR downlink by up to 60%.

In multi-hop cellular networks, data packets have to be relayed hop by hop from a given mobile station to a base station and vice-versa. This means that the mobile stations must accept to forward information for the benefit of other stations. In this paper, we propose an incentive mechanism that is based on a charging/rewarding scheme and that makes collaboration rational for selfish nodes. We base our solution on symmetric cryptography to cope with the limited resources of the mobile stations. We provide a set of protocols and study their robustness with respect to various attacks. By leveraging on the relative stability of the routes, our solution leads to a very moderate overhead.

We propose a micro-payment scheme for multi-hop cellular networks that encourages collaboration in packet forwarding by letting users benefit from relaying others' packets. At the same time as proposing mechanisms for detecting and rewarding collaboration, we introduce appropriate mechanisms for detecting and punishing various forms of abuse. We show that the resulting scheme -- which is exceptionally lightweight -- makes collaboration rational and cheating undesirable.

Integrated cellular and ad hoc relaying systems (iCAR) is a new wireless system architecture based on the integration of cellular and modern ad hoc relaying technologies. It addresses the congestion problem due to unbalanced traffic in a cellular system and provides interoperability for heterogeneous networks. The iCAR system can efficiently balance traffic loads between cells by using ad hoc relaying stations (ARS) to relay traffic from one cell to another dynamically. This not only increases the system's capacity cost effectively, but also reduces transmission power for mobile hosts and extends system coverage. In this paper, we compare the performance of the iCAR system with conventional cellular systems in terms of the call blocking/dropping probability, throughput, and signaling overhead via analysis and simulation. Our results show that with a limited number of ARSs and some increase in the signaling overhead (as well as hardware complexity), the call blocking/dropping probability in a congested cell and the overall system can be reduced.

Abstract — We propose a multi-hop wireless LAN architecture and demonstrate its benefits to wireless clients. For this architecture, we define implementation paths that allow interoperation with existing wireless LANs which can lead to an incremental deployment of this system. We quantify the performance benefits of the proposed schemes through measurements in realistic wireless LAN environments. We also examine the performance of such multi-hop wireless LANs through detailed simulation studies. Our results show that these multi-hop extensions can significantly improve the wireless access experience (in terms of data throughput, latency, etc.) for clients who enable such mechanisms. More interestingly, when multi-hop extensions are enabled by some of the clients, it also positively impacts the performance at other clients that are completely unaware of these extensions. I.

Few real-world applications of mobile ad hoc networks have been developed or deployed outside the military environment, and no traces of actual node movement in a real ad hoc network have been available. In this paper, we propose a novel commercial application of ad hoc networking, we describe and evaluate a multitier ad hoc network architecture and routing protocol for this system, and we document a new source of real mobility traces to support detailed simulation of ad hoc network applications on a large scale. The proposed system, which we call Ad Hoc City,isa multitier wireless ad hoc network routing architecture for generalpurpose wide-area communication. The backbone network in this architecture is itself also a mobile multihop network, composed of wireless devices mounted on mobile fleets such as city buses or delivery vehicles. We evaluate our proposed design through simulation based on traces of the actual movement of the fleet of city buses in the Seattle, Washington metropolitan area, on their normal routes providing passenger bus service throughout the city. 1.

In this paper we study the performance trade-offs between conventional cellular and multi-hop ad-hoc wireless networks. We compare through simulations the performance of the two network models in terms of raw network capacity, end-to-end throughput, end-to-end delay, power consumption, per-node fairness (for throughput, delay, and power), and impact of mobility on the network performance. The simulation results show that while adhoe networks perform better in terms of throughput, delay, and power, they suffer from unfairness and poor network performance in the event of mobility. We discuss the trade-offs involved in the performance of the two network models, identify the specific reasons behind them, and argue that the trade-offs preclude the adoption of either network model as a clear solution for future wireless communication systems. Finally, we present a simple hybrid wireless network model that has the combined advantages of cellular and ad-hoc wireless networks but does not suffer from the disadvantages of either. 1.

While several approaches have been proposed in literature for improving the performance of wireless packet data networks, a recent class of approaches has focused on improving the underlying wireless network model itself. Several of such approaches have shown that using peer-to-peer communication, a mode of communication used typically in ad-hoc wireless networks, can result in performance improvement in terms of both throughput and energy consumption. However, the true impact of using the ad-hoc network model in wireless packet data networks has neither been comprehensively studied, nor characterized. In this paper, we investigate the benefits of using an ad-hoc network model in cellular wireless packet data networks. We find that while the ad-hoc network model has significantly better spatial reuse characteristics, the improved spatial reuse does not translate into better throughput performance. Furthermore, although considerable improvement is seen in energy consumption performance, we observe that using the ad-hoc network model as-is might actually degrade the throughput performance of the network. We identify and discuss the reasons behind these observations. Finally, using the insights gained through our performance evaluations, we discuss strawman versions of three techniques which when used in tandem with the ad-hoc network model result in better throughput, energy consumption, fairness, and mobility-resilience characteristics. Through our simulation results, we motivate that using the ad-hoc network model in conventional wireless packet data networks is a promising approach when the network model is complemented with appropriate mechanisms. 1.

In this paper we study the performance of TCP over mobile ad-hoc networks. We present a comprehensive set of simulation results and identify the key factors that impact TCP's performance over ad-hoc networks. We use a variety of parameters including link failure detection latency, route computation latency, packet level route unavailability index, and flow level route unavailability index to capture the impact of mobility. We relate the impact of mobility on the different parameters to TCP's performance by studying the throughput, loss-rate, and retransmission timeout values at the TCP layer. We conclude from our results that existing approaches to improve TCP performance over mobile ad-hoc networks have identified and hence focused only on a subset of the affecting factors. In the process we identify a comprehensive set of factors influencing TCP performance. Finally, using the insights gained through the performance evaluations, we propose a framework called Atra consisting of three simple and easily implementable mechanisms at the MAC and routing layers to improve TCP's performance over ad-hoc networks. We demonstrate that Atra improves on the throughput performance of a default protocol stack by 50-100%.

We study the capacity of a wireless ad hoc network with infrastructure, where well-connected base stations are placed in an ad hoc network to relay data traffic for wireless nodes. This network architecture presents a tradeoff between a cellular network and an ad hoc network in that data may be forwarded in a multi-hop fashion or through the infrastructure. It has been shown that the capacity of ad hoc network does not scale well with the number of nodes in the system [1]. In this work, we investigate the potential benefit of infrastructure network to improve ad hoc network capacity. Analytical expressions are obtained for the capacity of an ad hoc networks with infrastructure. For an ad hoc network of £ nodes with ¤ base stations, the results show that, if ¤ grows asymptotically slower than ¥ £ , the benefit of infrastructure network is insignificant. However, if ¤ grows faster than ¥ £ , the capacity increases linearly with the number of base stations, providing an effective improvement over ad hoc networks. Therefore, in order to achieve non-negligible capacity gain, the investment in the wired infrastructure should be sufficiently high.