In this paper, we focus on the energy efficiency aware architecture of caching the necessary production messages and the transaction process to support a readable and tamper proof internet of things (IoT). To achieve this, blockchain can provide a reliable distributed storage of the messages, because any changes of the cached messages will break the structure of the blockchain. Specifically, we assume that the access points belonging to different telecom operators collect the messages in the IoT network, wherein multiple servers used for either caching or computing are placed at each access point. We define that the caching servers can be divided into the data loading caches for caching the received wireless IoT data and the data transmission caches for transmitting the IoT data into the blockchain based cloud caching servers. The blocks generated in the data loading caches at each access point will be written into the blockchain based on both the proof-of-work and the capacity of the data loading caches at each access point. Then, we formulate the optimization problem maximizing the system energy efficiency by optimizing the allocation of cache, computation and communication resources by a geometric programming model. By the CVX tool in matlab software, the geometric programming model can be solved effectively. We study the impact of different parameters involved in the blockchain on the system performance, and verify the effectiveness of our proposed energy efficiency aware optimization mechanism in the blockchain based IoT.

The pervasive adoption of IEEE 802.11 radios in the past decade has made possible for the easy Internet access from a vehicle, notably drive-thru Internet. Originally designed for the static indoor applications, the throughput performance of IEEE 802.11 in the outdoor vehicular environment is, however, still unclear especially when a large number of fast-moving users transmitting simultaneously. In this paper, we investigate the performance of IEEE 802.11 DCF in the highly mobile vehicular networks. We first propose a simple yet accurate analytical model to evaluate the throughput of DCF in the large scale drive-thru Internet scenario. Our model incorporates the high-node mobility with the modeling of DCF and unveils the impacts of mobility (characterized by node velocity and moving directions) on the resultant throughput. Based on the model, we show that the throughput of DCF will be reduced with increasing node velocity due to the mismatch between the MAC and the transient high-throughput connectivity of vehicles. We then propose several enhancement schemes to adaptively adjust the MAC in tune with the node mobility. Extensive simulations are carried out to validate the accuracy of the developed analytical model and the effectiveness of the proposed enhancement schemes.

The newly emerged vehicular ad hoc network adopts the contention based IEEE 802.11 DCF as its MAC. While it has been extensively studied in the stationary indoor environment (e.g., WLAN), the performance of DCF in the highly mobile vehicular environment is still unclear. On addressing this issue, we propose a simple but accurate analytical model to evaluate the throughput performance of DCF in the high speed vehicle-to-infrastructure (V2I) communications. We unveil the impacts of nodes mobility (velocity and moving directions) on the system throughput. Particularly, we show that with node velocity increasing, the throughput of DCF decreases monotonically, which demonstrates the inefficiency of DCF in the highly mobile environment. Via extensive simulations, we validate the accuracy of the developed analytical model and finally discuss the method to optimize DCF towards the maximal throughput.

This paper presents a protocol-independent approach to reveal a new insight into the performance of carrier sense multiple access with collision avoidance (CSMA/CA) protocols: the family of CSMA/CA protocols, independent of implementation details, share the same optimal operation point where the maximum protocol capacity is achieved. The protocol- independent analysis is inspired by the concept of virtual time slot. At the timescale of virtual-slot, all the CSMA/CA protocols show the same behavior pattern and, therefore, a generic virtual- slot based S-G (VS S-G) analysis is developed to compute the optimal operation point. The accuracy of the VS S-G analysis is benchmarked against the precise protocol-specific analysis, in particular, for the 802.11 distributed coordination function (DCF) and the 802.15.4 contention access period (CAP). Furthermore, this paper discusses how to integrate the network-layer queueing analysis with the VS S-G analysis at the medium access control (MAC) layer to form a generic cross-layer framework for call- level network capacity analysis.

In this paper, we propose a simple yet accurate analytical model for the slotted non-persistent carrier sense multiple access protocol with binary exponential backoff, as specified in the medium access control (MAC) protocol of the IEEE 802.15.4 standard for the contention access period. The model is based on a three-level renewal process, which leads to a general analytical framework applicable to the protocol variants of either single or double sensing, in a saturated or unsaturated case, under a general traffic arrival distribution and with various backoff policies. The analytical model can be used to obtain some important performance metrics, such as MAC throughput and average frame service time. The accuracy of the analytical model is demonstrated by extensive simulation results. The applicability of this model to the performance analysis of other slotted MAC protocols is also briefly discussed.

An analytical model is proposed for the perfor- mance study of IEEE 802.11 distributed coordination function (DCF) with finite traffic load. Based on the model, average medium access control (MAC) sublayer service time of a frame and channel throughput are obtained. The model is further extended for the performance analysis of DCF with mixed voice and data traffic. The maximum number of voice connections supported in IEEE 802.11 WLAN under various background data traffic is derived. The results are useful for effective call admission control in IEEE 802.11 WLAN. Extensive simulations are performed to validate our analysis. I. INTRODUCTION The IEEE 802.11 standard (1) has been widely deployed around the world. Its medium access control (MAC) sublayer specifies two modes, the mandatory distributed coordination function (DCF) and the optional point coordination function (PCF). DCF is a distributed random access mechanism that is suitable for ad hoc networks, while PCF is a centralized polling based mechanism that can only work in infrastructure- based wireless LANs (WLANs). Due to its inefficient polling schemes and limited Quality-of-Service (QoS) provisioning, PCF is not widely implemented in practice. Therefore, in this paper, we study the performance of the dominant DCF in various scenarios. To date most research work in the literature (e.g., (2)-(4)) focuses on the study of DCF performance in the saturation case, in which every station in the network always has frames waiting for transmission. However, when there are more than In this paper, we first propose an analytical model to study the DCF throughput and average MAC service time under various load conditions for a single traffic type. It is based on the fundamental relationship between the mean MAC service time and the mean traffic arrival rate, and thus applicable to general traffic arrival processes. The proposed model improves the one in (10) in several aspects such as more accurate calculation of the average backoff time and the average number of transmission trials of a frame. Moreover, by comparing the obtained average MAC service time for a frame with the given average frame inter-arrival time, whether or not a station is in the saturated state can be accurately determined with the proposed model. The maximum number of stations that can be supported in such a network is also obtained. This information is critical to the design of admission control schemes that are usually adopted for QoS support in a network. It is worthy to note that this information cannot be readily obtained from the analysis of a saturation case. As VoIP over WLAN becomes more and more popular, it is instructive to study analytically the performance of DCF in a WLAN with mixed voice and data traffic. However, little work on this thread has been reported. In this paper, we carefully extend the proposed model to study the performance of DCF in such a situation. Using the extended model, the maximum number of voice stations that can be supported in the presence of a certain amount of data traffic can be obtained. On the other hand, the data throughput can also be obtained, given the number of voice stations in the WLAN. The rest of the paper is organized as follows. The IEEE 802.11 DCF is briefly reviewed in Section II. Section III presents the proposed analytical model for a single traffic type. Section IV extends the model to mixed voice and data traffic. Numerical results of both analysis and simulations for the two scenarios are given in Section V. Finally, we conclude the paper in Section VI.

Distributed prioritized channel access mechanisms have been adopted by the IEEE 802.11e enhanced distributed channel access (EDCA) and the Multiband OFDM Alliance prioritized channel access (PCA) to support service differentiation. In this paper, we propose a novel analytical model for performance study of such mechanisms. The proposed model gives the average frame service time first and then the per station and network normalized throughput, which makes it applicable to both saturated and unsaturated stations. Furthermore, the model is especially helpful in understanding the different effects of the same prioritizing mechanisms in saturated and unsaturated conditions. To the best of our knowledge, there is no similar work reported in the open literature. The accuracy of the analytical model is demonstrated by extensive simulation.

In this paper, we demonstrate that traffic modeling with the fractional Brownian motion (FBM) process is an efficient tool for end-to-end performance analysis over a network provisioning differentiated services (DiffServ). The FBM process is a parsimonious model involving only three parameters to describe the Internet traffic showing the property of self-similarity or long-range dependence (LRD). As a foundation for network-wide performance analysis, the FBM modeling can significantly facilitate the single-hop performance analysis. While accurate FBM based queueing analysis for an infinite/finite first-in-first-out (FIFO) buffer is available in the existing literature, we develop a generic FBM based analysis for multiclass single-hop analysis where both inter-buffer priority and intra-buffer priority are used for service differentiation. Moreover, we present both theoretical and simulation studies to reveal the preservation of the self-similarity, when the traffic process is multiplexed or randomly split, or goes through a queueing system. It is such self-similar preservation that enables the concatenation of FBM based single-hop analysis into a network-wide performance analysis.

This paper presents a novel, simple yet accurate analytical model for the IEEE 802.15.4 contention access period MAC protocol. The model is based on a three-level renewal process, which leads to a general analytical framework applicable for the protocol variants of either single or double sensing, in a saturated or unsaturated case, under a general traffic arrival distribution. The analytical model is used to obtain some important performance metrics, such as MAC throughput and average frame service time. The accuracy of the analytical model is demonstrated by extensive simulation results.

This paper presents an analytical approach to determining the maximum number of on/off voice flows that can be supported over a wireless local area network (WLAN), under a quality of service (QoS) constraint the authors consider multiclass distributed coordination function (DCF) based medium access control (MAC) that can provision service differentiation via contention window (CW) differentiation. Each on/off voice flow specifies a stochastic delay bound at the network layer as the QoS requirement. The downlink voice flows are multiplexed at the access point (AP) to alleviate the MAC congestion, where the AP is assigned a smaller CW compared to that of the mobile nodes to guarantee the aggregate downlink throughput. There are six-fold contributions in this paper: 1) a nonsaturated multiclass DCF model is developed; 2) a cross-layer framework is proposed, which integrates the network-layer queueing analysis with the multiclass DCF MAC modeling; 3) the channel busyness ratio control is included in the framework to guarantee the analysis accuracy; 4) the framework is exploited for statistical multiplexing gain analysis, network capacity planning, contention window optimization, and voice traffic rate design; 5) a head-of-line outage dropping (HOD) scheme is integrated with the AP traffic multiplexing to further improve the MAC channel utilization; 6) performance of the proposed cross-layer analysis and the associated applications are validated by extensive computer simulations.

This paper presents an analytical model for evaluating the capability of wireless LANs (WLANs) to provision quantitative quality of service (QoS) guarantees. We consider a distributed medium access control (MAC) with class differentiation, where mobile nodes belonging to different classes may have heterogeneous traffic arrival processes or different contention windows. With on/off inputs, our analysis shows that the WLAN admission region under the QoS constraint can be significantly improved, when the statistical multiplexing effect is taken into account. Moreover, the statistical multiplexing gain can be further improved by aggregating the downlink flows at the access point (AP). We also demonstrate that the proper selection of contention windows plays an important role in improving the WLAN QoS capability, while the optimal contention window for each class and the maximum admission region can be jointly solved in our analytical model.

Vertical handoff is a switching process between heterogeneous wireless networks in a hybrid 3G/WLAN network. Vertical handoffs from WLAN to 3G network often fail due to the abrupt degrade of the WLAN signal strength in the transition areas. In this paper, a Handoff Trigger Table is introduced to improve the performance of vertical handoff. Based on this table, a proactive handoff scheme is proposed. Simulation results show that with the proposed scheme, the vertical handoff decisions will be more efficient so that dropping probability can be decreased dramatically.

This paper presents an analytical model for evaluating the statistical multiplexing effect, admission region, and contention window design in multiclass wireless LANs (WLANs). We consider a distributed medium access control (MAC) which provisions service differentiation via contention window differentiation, where mobile nodes belonging to different service classes have different quality of service (QoS) requirements. With bursty input traffic, we show that the WLAN admission region under the QoS constraint can be significantly improved by exploiting the statistical multiplexing gain. Moreover, the statistical multiplexing gain can be further improved by aggregating the downlink flows at the access point (AP). We also demonstrate that the selection of contention windows plays an important role in improving the WLAN's QoS capability, while the optimal contention window for each class and the maximum admission region can be jointly solved from our analytical model. The analysis accuracy and the resource utilization improvement are demonstrated by extensive numerical results.

The two-state Markov chain has been widely used to model fading channels in the performance study of upper-layer communication protocols in wireless networks. It can be used to model transmission success/failure based on the physical characteristics of the transmission channel. However, for shared wireless links, packet transmission depends on both the status of the link and the scheduling strategy used. In this poster, we propose a novel four-state Markov model, which takes into consideration the impacts of channel fading and scheduling on packet transmission over shared wireless links. It is further abstracted to an effective two-state Markov chain to facilitate analytical performance evaluation. To demonstrate the efficacy of the proposed model, we apply it to study the throughput, delay and delay jitter of a saturated traffic source, and the packet dropping probability at the network layer for data traffic under a buffer overflow dropping policy. Simulation results to demonstrate the reasonableness of the proposed model are also presented. © 2006 ACM.

In wireless channels, the bursty nature of block errors render immediate packet retransmissions at the link level ineffective. Cooperative communication is a promising technique to combat the negative impacts of channel fading by providing diverse channels between peers in wireless ad-hoc networks. In this paper, an analytical model is proposed for the throughput of the node cooperative automatic repeat request scheme for wireless ad-hoc networks. The model is based on a two-state Markov model for block errors in the wireless fading channels. Simulation results are given to demonstrate effectiveness of the analytical model

Dynamic channel assignment (DCA) schemes can provide a more efficient solution than fixed channel assignment (FCA) schemes for future mobile cellular networks to meet the requirements of the ever-growing number of mobile users. This is due to due to its better adaptability to unevenly-distributed and changing traffic load. However, it is observed that in DCA with the soft handoff policy, a handoff call will suffer a higher dropping probability than the blocking probability of a new call in the case of no handoff prioritization. This is definitely undesirable from the user's point of view. The channel carrying approach, which allows a mobile station to continue to use its currently occupied channel when it handoffs to a new cell, can easily change the stated situation above. We investigate two channel carrying strategies through simulations, and find that the one called "channel carrying last" performs better.