Mark Kai Ho Yeung

Wireless cache invalidation schemes with link adaptation and downlink traffic

Providing on-demand data access in client-server wireless networks is an important support to many interesting mobile computing applications. Caching frequently accessed data by mobile clients can conserve wireless bandwidth and battery power, at the expense of some system resources to maintain cache consistency. The basic cache consistency strategy is the use of periodic invalidation reports (IRS) broadcast by the server. Recently, IR-based approaches have been further improved by using additional updated invalidation reports (UIRs) (i.e., the IR+UIR algorithm) to reduce the long query latency. However, the performance of the IR+UIR approach in a practical system is still largely unknown. Specifically, previous results are based on two impractical simplifying assumptions: 1) broadcast traffic is error-free and 2) no other downlink traffic (e.g., voice) exists in the system. The first assumption is clearly unrealistic as signal propagation impairments (e.g., multipath fading) and, hence, packet reception failures are inevitable in a practical situation. The second assumption is also inapplicable in real life because mobile devices are usually multipurposed (e.g., a mobile phone equipped with a browser may be used for Web surfing while having a phone conversation). In this paper, we first study the performance of the IR+UIR approach under a realistic system model: The quality of the wireless channel is time-varying, and there are other downlink traffics in the system. Our simulation results show that query delay significantly increases as a result of broadcast error and the additional downlink traffics experience longer delay due to extended broadcast period. Exploiting link adaptation (i.e., transmission rate is adjusted dynamically according to channel quality), we then propose three schemes to tackle these two problems. Our results indicate that the proposed schemes outperform IR+UIR under a wide range of system parameters.

Game Theoretic Peer Selection for Resilient Peer-to-Peer Media Streaming Systems

Peer-to-peer (P2P) media streaming quickly emerges as an important application over the Internet. A plethora of approaches have been suggested and implemented to support P2P media streaming. In our study, we first classified existing approaches and studied their characteristics by looking at three important quantities: number of upstream peers (parents), number of downstream peers (children) and average number of links per peer. We find that in existing approaches, peers are assigned with a fixed number of parents without regard to their contributions, measured by the amount of outgoing bandwidths. Obviously, this is an undesirable arrangement as it leads to highly inefficient use of the P2P links. This observation motivates us to model the peer selection process as a cooperative game among peers. This results in a novel peer selection protocol such that the number of upstream peers of a peer is related to its outgoing bandwidth. Specifically, peers with larger outgoing bandwidth are given more parents, which makes them less vulnerable to peer dynamics. Simulation results show that the proposed protocol improves delivery ratio with similar number of links per peer, comparing with existing approaches in a wide range of settings.

A game theoretic approach to power aware wireless data access

We consider a basic scenario in wireless data access: a number of mobile clients are interested in a set of data items kept at a common server. Each client independently sends requests to inform the server of its desired data items and the server replies with a broadcast channel. We are interested in studying the energy consumption characteristics in such a scenario. First, we define a utility function for quantifying performance. Based on the utility function, we formulate the wireless data access scenario as a noncooperative game - wireless data access (WDA) game. Although our proposed probabilistic data access scheme does not rely on client caching, game theoretical analysis shows that clients do not always need to send requests to the server. Simulation results also indicate that our proposed scheme, compared with a simple always-request one, increases the utility and lifetime of every client while reducing the number of requests sent, with a cost of slightly larger average query delay. We also compare the performance of our proposed scheme with two popular schemes that employ client caching. Our results show that caching-only benefits clients with high query rates at the expense of both shorter lifetime and smaller utility in other clients

On Game Theoretic Peer Selection for Resilient Peer-to-Peer Media Streaming

Peer-to-peer (P2P) media streaming quickly emerges as an important application over the Internet. A plethora of approaches have been suggested and implemented to support P2P media streaming. In our study, we first classified existing approaches and studied their characteristics by looking at three important quantities: number of upstream peers (parents), number of downstream peers (children), and average number of links per peer. In existing approaches, peers are assigned with a fixed number of parents without regard to their contributions, measured by the amount of outgoing bandwidths. Obviously, this is an undesirable arrangement as it leads to highly inefficient use of the P2P links. This observation motivates us to model the peer selection process as a cooperative game among peers. This results in a novel peer selection protocol such that the number of upstream peers of a peer is related to its outgoing bandwidth. Specifically, peers with larger outgoing bandwidth are given more parents, which make them less vulnerable to peer dynamics. Simulation results show that the proposed protocol improves delivery ratio using similar number of links per peer, comparing with existing approaches under a wide range of system parameters.

Game-theoretic scalable peer-to-peer media streaming

Peer-to-peer media streaming framework has been widely considered as a promising platform for delivering high quality multimedia content on the global scale. A fundamental requirement is that each peer needs to contribute outgoing bandwidth to deliver media packets to its neighbors. Although most existing protocols mandate such contribution, misbehaving peers may still deliberately limit their outgoing bandwidth to conserve their own resources. This would inevitably lead to performance degradation of other well-behaving peers. It is crucial to have an effective incentive mechanism such that peers are encouraged to contribute. In this paper, we formulate two strategic games to model the interactions between server and its immediate peers and between neighboring peers, respectively. We have devised the equilibrium strategies which relate a peers streaming performance to its contribution. Simulation results show that the proposed game-theoretical incentive mechanism protects well-behaving peers from being exploited by misbehaving counterparts.

Energy efficient media streaming inwireless hybrid peer-to-peer systems

With the proliferation of sophisticated wireless devices with more than one network interfaces, it is now possible for the devices to form hybrid wireless networks. Specifically, we consider a hybrid wireless networking scenario in which each device has two heterogeneous wireless network interfaces: a server interface (e.g., a CDMA2000 cellular interface) and a peer interface (e.g., a IEEE 802.1 Ig WLAN interface). Our insight is that we could exploit the heterogeneity in energy consumption in such a dual-interface networking capability. In view of the higher energy consumption in using the server interface compared with using the client interface, we propose two novel protocols where neighboring clients form either a master-slave or peer-to-peer relationship to reduce their energy consumption. For the master-slave relationship, each master retrieves media packets from the server and sends them to its slaves via the peer interface. On the other hand, each peer-to-peer relationship consists of one coordinator and at least one helpers. Both coordinator and helpers are responsible for retrieving media packets from the server. Our analysis shows that the two proposed relationships reduce the energy consumption of participating clients. Furthermore, the relationships are stable where rational clients would not voluntarily leave and unilaterally deviate from the coalition. We evaluate their performance in homogeneous and heterogeneous client distributions. Simulation results indicate that both relationships improve streaming performance without violating the energy consumption constraints of clients.

A game theoretic approach to energy efficient cooperative cache maintenance in MANETs

There have been an increasingly large number of mobile handsets equipped with dual or multiple network interfaces. The server interface (e.g., GPRS, EDGE, UMTS) is responsible for communicating with the network operator, while the peer interfaces (e.g., Bluetooth, IEEE 802.11) are used to connect with other computing devices. However, they are usually used separately. In this paper, we investigate the use of both network interfaces to support energy efficient data applications among mobile clients. Specifically, we proposed a fully distributed protocol for mobile handsets to form cooperative groups to maintain cache consistency with minimal communication with the network operator. Our proposed protocol takes advantage of the low power consumption and high data rate of the peer interface. The aim is to reduce the use of the server interface, which is typically slower and involves higher power consumption. Furthermore, we also consider the presence of selfish clients. It is shown that groups formed by the proposed protocol constitutes a pure Nash equilibrium. This suggests that our protocol is robust even in the presence of selfish clients. Simulation results confirm that, given the same energy resource, mobile clients running the proposed protocol complete more queries, experience longer lifetime and achieve smaller query latency

New invalidation algorithms for wireless data caching with downlink traffic and link adaptation

Summary form only given. Caching frequently accessed data by mobile clients can conserve wireless bandwidth and battery power, at the expense of some system resources to maintain cache consistency. The basic cache consistency strategy is the use of periodic invalidation reports (IRs) broadcast by the server. Recently, IR-based approaches have been further improved by using additional updated invalidation reports (UIRs) (i.e., the IR+UIR algorithm) to reduce the long query latency. However, the performance of the IR+UIR approach in a practical system is still largely unknown. Specifically, previous results are based on two impractical simplifying assumptions: (1) broadcast traffic is error-free; and (2) no other downlink traffic (e.g., voice) exists in the system. The first assumption is clearly unrealistic as signal propagation impairments (e.g., multipath fading), and hence, packet reception failures, are inevitable in a practical situation. The second assumption is also inapplicable in real life because mobile devices are usually multipurposed (e.g., a mobile phone equipped with a browser may be used for Web-surfing while having a phone conversation). We first study the performance of the IR+UIR approach under a realistic system model: the quality of the wireless channel is time-varying; and there are other downlink traffics in the system. Our simulation results show that query delay significantly increases as a result of broadcast error and the additional downlink traffics experience longer delay due to extended broadcast period. Exploiting link adaptation (i.e., transmission rate is adjusted dynamically according to channel quality), we then propose three schemes to tackle these two problems.

On energy efficient wireless data access: caching or not?

We consider a typical wireless data access scenario: a number of mobile clients are interested in a set of data items kept at a common server. A client sends a request to inform the server of its desired data item while the server replies in the common broadcast channel. To study the energy consumption characteristics in such a scenario, we first define a power aware utility function. Based on the utility function, we propose a novel wireless data access scheme, which is a non-cooperative game—wireless data access (WDA) game. Although it does not rely on client caching (without-cache), our theoretical analysis shows that it is not always necessary for clients to send requests to the server. Simulation results confirm that our proposed scheme, compared with a simple always-request one, increases both the utility and lifetime of every client while reducing the number of requests sent, at the cost of slightly larger average query delay.

Design and analysis of channel adaptive wireless cache invalidation strategies with downlink traffic

In this paper, we study the performance of the IR+UIR wireless data cache invalidation approach under a realistic system model: the quality of the wireless channel is time-varying; and there are other downlink traffics in the system. Our analysis and simulation results show that query delay significantly increases as a result of broadcast error and the additional downlink traffics experience longer delay due to extended broadcast period. Exploiting link adaptation (i.e., transmission rate is adjusted dynamically according to channel quality), we then propose three schemes to tackle these two problems. Our results indicate that the proposed scheme outperform IR+UIR under a wide range of system parameters.