Escalation in the use of Internet of Things (IoT) devices gives rise to the number of networks operating in the license-free 2.4-GHz frequency band. This prepares the ground for networks to experience interference from coexisting networks and thus performance degradation. Time-slotted channel hopping (TSCH), as an operational medium access mode of the IEEE 802.15.4 technology, was introduced to ensure the reliability of IoT networks when they undergo coexistence. It uses frequency hopping as a protective strategy against long-term packet losses due to interference. However, when several independent TSCH networks coexist, they are prone to interfere with one another. In extreme scenarios, coexisting TSCH networks may block links of one another for an extended duration of time, leading to application failure. In this article, we propose a novel technique called time hopping to secure the reliability of coexisting TSCH networks. The developed technique synchronously and periodically alters the timing of nodes within a TSCH network to avoid coexisting TSCH networks from getting stuck in extreme coexistence scenarios and long-term continuous collisions. We evaluate the effectiveness of the proposed technique through extensive simulations. The results clearly show that the proposed time hopping technique substantially improves the worst case internetwork collision ratio, with as much as 50% improvement in some tested scenarios. The implementation of the technique is very simple, with almost no communication or computation overhead for the constrained wireless nodes; it is done and tested on real nodes for proof of concept.

Wireless Body Area Networks (WBANs) have made their way into many smart and ubiquitous healthcare and wellness applications. A low-power, efficient, and reliable communication protocol is of paramount importance for the success of WBANs in satisfying the requirements of the health applications. The IEEE 802.15.4 standard is always one of the main options due to its efficiency and low-complexity. However, it suffers from the impact of other wireless technologies using the same frequency band such as WiFi and Bluetooth. Time Slotted Channel Hoping (TSCH) is an operational mode of the IEEE 802.15.4e standard, which is originally developed for reliable industrial wireless networks. TSCH has Time Division Multiple Access (TDMA) and frequency hopping features, which increase the network robustness against effects such as noise, interference, and multi-path fading. This paper proposes to exploit TSCH for communications in WBANs, and studies its performance. The features of TSCH like power efficiency, TDMA-based operation, and heterogeneity support fit very well with the requirements of many health monitoring applications. The performance of the TSCH standard for WBAN communications is investigated through real-world experiments in various conditions. The results show that TSCH outperforms the basic IEEE 802.15.4 standard in terms of communication reliability against interferences from coexisting wireless devices.

In this paper, a novel framework for optimizing the caching of popular user content at the level of wireless user equipments (UEs) is proposed. The goal is to improve content offloading over wireless device-to-device (D2D) communication links. In the considered network, users belong to different social communities while their UEs form a single multi-hop D2D network. The proposed framework allows us to exploit the multi-community social context of users for improving the local offloading of cached content in a multi-hop D2D network. To model the collaborative effect of a set of UEs on content offloading, a cooperative game between the UEs is formulated. For this game, it is shown that the Shapley value (SV) of each UE effectively captures the impact of this UE on the overall content offloading process. To capture the presence of multiple social communities that connect the UEs, a hypergraph model is proposed. Two line graphs, an influence-weighted graph, and a connectivity-weighted graph, are developed for analyzing the proposed hypergaph model. Using the developed line graphs along with the SV of the cooperative game, a precise offloading power metric is derived for each UE within a multi-community, multi-hop D2D network. Then, UEs with high offloading power are chosen as the optimal locations for caching the popular content. Simulation results show that, on the average, the proposed cache placement framework achieves 12, 19, and 21 percent improvements in terms of the number of UEs that received offloaded popular content compared to the schemes based on betweenness, degree, and closeness centrality, respectively.

In this paper, a novel protocol is proposed in which mobile terminals (MT) form a virtual Multiple-input Multiple-output (MIMO) uplink by means of device relaying on Device to Device (D2D) tier in 5G Cellular Network. The competitive scenario is considered in which each of the selfish MTs tries to transmit its own data and not relay others' data in the formed virtual MIMO. The main focus is to design an incentive for MTs to form the virtual MIMO and cooperate in relaying others data. A direct revelation on-line mechanism for the BS is designed, in order to assist forming a stable virtual MIMO. A self-punishment mechanism is also proposed in which MTs autonomously punish malicious MTs that do not cooperate in relaying. We prove that our designed direct revelation on-line mechanism and proposed self-punishment mechanism enforce all-cooperation (all-C) profile as a Nash equilibrium (NE), under uncertainty in the presence of MTs in the formed virtual MIMO. Our simulation results confirm that the proposed protocol, even in the competitive scenario, increases the bit rate and decreases power consumption at the same time. The proposed protocol can improve the energy efficiency up to 35 percent compared to a non-cooperative case, i.e., Single-Input Multiple-Output (SIMO) uplink. Moreover, if the multi-user MIMO transmission is used for the uplink medium access layer, the proposed protocol can improve the energy efficiency up to 42 percent compared to SIMO uplink with multi-user MIMO transmission. Under the proposed OCVM protocol with Shapley value fairness, the price of anarchy reaches to 0.78 in the competitive scenario. In addition, the energy efficiency improvement of our proposed protocol is almost robust to the preferences of MTs. Simulation results show that if BS employs our on-line mechanism and MTs autonomously punish malicious MTs, the malicious MTs cannot gain by defecting from relaying other MTs' data.

In this paper, a novel self-punishment based scheduling algorithm for a cooperative real- time content download application is designed. In the proposed protocol, selfish mobile devices autonomously form cooperative groups. For each formed group, the base station transmits the content to a selected mobile device designated as seed. Then, the seed shares the content with other mobile devices called sinks over device-to-device links. After analyzing the proposed protocol using a repeated game, new self-punishment mechanisms by revocation or by decreasing the bit rate, are proposed. Such self-punishment mechanisms enable the mobile devices in each cooperative group to autonomously punish selfish seeds without requiring any help from other mobile devices outside cooperative group. ‌Based on the proposed self-punishment mechanisms, a fair algorithm is designed to schedule the seeds in each cooperative group. Then, the designed scheduling algorithm is implemented using an Android application that is developed using Java in the Android Development Tool Bundle. The developed Android application does not depend on the operation system of mobile devices. Simulation results demonstrate that, on the average, the proposed protocol improves the energy efficiency of mobile devices to download real-time content of around 42 % compared to a traditional multicast scenario. Moreover, the proposed protocol does not let the energy efficiency of mobile devices degrade more than 11 %, on average, from the optimal solution even when all the mobile devises are selfish. The practical results show that the maximum difference in the run time of a real- time video over real-world smartphone screens is less than 500 milliseconds when the smartphones form a cooperative group using the developed Android application.

In this paper, the problem of random access contention between machine type devices (MTDs) in the uplink of a wireless cellular network is studied. In particular, the possibility of forming cooperative groups to coordinate the MTDs' requests for the random access channel (RACH) is analyzed. The problem is formulated as a stochastic coalition formation game in which the MTDs are the players that seek to form cooperative coalitions to optimize a utility function that captures each MTD's energy consumption and time-varying queue length. Within each coalition, an MTD acts as a coalition head that sends the access requests of the coalition members over the RACH. One key feature of this game is its ability to cope with stochastic environments in which the arrival requests of MTDs and the packet success rate over RACH are dynamically time-varying. The proposed stochastic coalitional game is composed of multiple stages, each of which corresponds to a coalitional game in stochastic characteristic form that is played by the MTDs at each time step. To solve this game, a novel distributed coalition formation algorithm is proposed and shown to converge to a stable MTD partition. Simulation results show that, on the average, the proposed stochastic coalition formation algorithm can reduce the average fail ratio and energy consumption of up to 36% and 31% for a cluster-based distribution of MTDs, respectively, compared with a noncooperative case. Moreover, when the MTDs are more sensitive to the energy consumption (queue length), the coalitions' size will increase (decrease).

One of the most significant issues in wireless sensor networks is the limited source of energy that sensors are supplied with. Since network lifetime has a direct relationship with the energy of the nodes, it would be important to efficiently manage the energy consumption of the nodes. To this end, a number of energy aware routing algorithms have been proposed in the literature to increase network lifetime. These routing algorithms usually try to find the path with minimum energy usage. However, using these paths for a long time may result in rapid energy depletion of some nodes. To overcome this problem, we propose a new routing algorithm with three different versions which uses load balancing technique by selecting the paths with maximum normalized energy in each transmission round.

Sensor networks have been proposed for military and scientific applications such as border security and environment monitoring. They are usually deployed in unattended and hostile environments, so security is a major concern. A fundamental requirement in wireless network security is the ability to establish keys between pairs of sensors. In this paper, we propose a new location-based key management protocol in which polynomial-based and random key pre-distribution are both used for key establishment between sensor pairs. Key establishment between near sensors is provided by the polynomials, while key establishment between far sensors is accomplished by random key pre- distribution. Using these two approaches simultaneously reduces the overhead required for key establishment. Analysis is presented which shows that the proposed scheme has good performance compared with other approaches.

Currently, the increasing rate of routing lookups in Internet routers, the large number of prefixes and also the transition from IPV4 to IPV6, have caused Internet designers to propose new lookup algorithms and try to reduce the memory cost and the prefix search and update procedures times. Recently, some new algorithms are proposed trying to store the prefixes in a balanced tree to reduce the worst case prefix search and update times. These algorithms improve the search and update times compared to previous range based trees. In this paper it is shown that there is no need to treat the prefixes as ranges. It is only required to compare them like scalar values using a predefined rule. The method "scalar prefix search" which is presented here, is built on this concept and combining it with the proposed store and search methods, interprets each prefix as a number without any encoding, the need to convert it to the prefix end points or to use the trie based algorithms whose performance completely depends on IP address length. This method can be applied to many different tree structures. It is implemented using the binary search tree and some other balanced trees such as RB-tree, AVL-tree and B-tree for both IPV4 and IPV6 prefixes. Comparison results show better lookup and update performance or superior storage requirements for scalar prefix search in both average and worst cases, against current solutions like PIBT (Lu and Sahni, 2005) and LPFST (Wnn et al., 2005).

The problem of selecting a code for finite monotone sources with N symbols is considered. The selection criterion is based on minimizing the average redundancy (called Minave criterion) instead of its maximum (i.e., Minimax criterion). The average probability distribution PNmacr, whose associated Huffman code has the minimum average redundancy, is derived. The entropy of the average distribution (i.e., H(PNmacr)) and the average entropy of the monotone distributions (i.e., H(PNmacr)) are studied. It is shown that both logN-H(PNmacr) and logN-H(PNmacr) are asymptotically equal to a constant (sime0.61). Therefore, there is only a negligible penalty (at most 1.61 bits/symbol) in using a simple fixed-length code with respect to the optimal code. An efficient near-optimal encoding technique is also proposed. The consequences of the two approaches, i.e., Minave and Minimax, are compared in terms of their associated distributions and associated codes. In order to evaluate the average performance of the Minimax code, we prove that the informational divergence of the average distribution and Minimax distribution asymptotically grows as -2.275+loglogN

Multi-constraint quality-of-service routing has become increasingly important as the Internet evolves to support real-time services. Restricted shortest path (RSP) is one of the important problems studied in the field of QoS routing. Various solutions have been proposed for RSP and other problems related to the QoS routing, in practical situations. Restricted shortest path problem with concave route costs are studied in this paper. This is a special version of the traditional RSP problem and is widely applicable in wireless and mobile ad hoc networks. In this paper, we propose new algorithms for this kind of routing. The effectiveness of our proposed solutions is shown through analytical reasoning and simulations.

Future mobile handsets will often be multi-mode and may include both wireless LAN (WLAN) and cellular air interfaces. When this type of handset roams in and out of WLAN coverage, connections must be transferred to the new network point of attachment. In order to support real-time wireless services, seamless vertical handoff is an essential requirement. In this paper we propose the use of ad hoc relaying during vertical handoff in hybrid WLAN/Cellular systems. The proposed method improves handoff algorithm behavior in terms of handoff dropping probability and other mobility performance measures. Both analytic models and simulation results support the effectiveness of the proposed method.

The minimax distribution PFNdefined by the probabilities pi,FN= 1/lambdaN(i-1)(i-1)/iiplays an important role in the context of encoding finite monotone sources with unknown probabilities. The Shannon code for this distribution is a suboptimal minimax code. The average performance of this suboptimal code is considered in this paper. In order to evaluate the average performance of the minimax code, we compare it with the minave code which minimizes the average redundancy over all monotone sources with N symbols. To achieve this, we study the informational divergence of the minave and minimax distributions and prove that it asymptotically grows as -2.275+log log N. The log log N degradation in average performance should not be regarded as a drawback of the minimax code because the minimum average codeword length over the class of monotone sources grows as log N, which asymptotically dominates log log N

Multi-constraint quality-of-service routing becomes increasingly important as the Internet evolves to support real-time services. It is well known however, that optimum multi-constraint QoS routing is computationally complex, and for this reason various heuristics have been proposed for routing in practical situations. Among these methods, those that use a single mixed metric are the most popular. Although mixed metric routing discards potentially useful information, this is compensated for by the significantly reduced complexity. Exploiting this tradeoff is becoming increasingly important where low complexity designs are desired, such as in battery operated wireless applications. In this paper, a novel single mixed metric multi-constraint routing algorithm is introduced. The proposed technique has similar complexity compared with existing low complexity methods. Simulation results are presented which show that it can obtain better performance than comparable techniques in terms of generating feasible multi-constraint QoS routes.

In this paper, the average probability distribution P~/sup N/~ of equiprobable finite monotone sources, where N is the number of symbols, is derived and some properties of this distribution are investigated. The associated Huffman code has the minimum redundancy in the average sense. An efficient suboptimal encoding technique is proposed. We show that log N -H(P~/sup N/~) is a constant asymptotically, and consequently there is a negligible penalty (asymptotically) in using a fixed length code. The length of the shortest codeword should be modified such that lim/sub N/spl rarr//spl infin// l/sub N//l/sub 1/=2. This limit cannot be a constant for minimax and universal codes such as the /spl omega/ and /spl delta/ codes. These properties are also shown to hold when the number of symbols is unknown but bounded.

We present an approach which addresses a fundamental scaling limitation for conventional switches. Instead of processing the data packets one by one, train queue processing groups multiple data packets together and processes them as one unit. There are two basic train queuing techniques, sequential train queuing and sequential-to-parallel train queuing. The sequential train queue processing can reduce the global switch processing frequency for the switch. The sequential-to-parallel train queue processing can reduce both the global switch processing frequency and data rate by using packet grouping and slicing mechanism. By employing train queuing techniques, a high bandwidth switch can be built and feasibly implemented.

In order to meet the ATM Forum recommendations, rates must be guaranteed to each individual ATM connections across a high-speed switch fabric in the face of thousands of individual connections, burstiness of traffic in individual connections, a wide diversity of rates, differing expectations of rates for different traffic classes, and the arrival and departure of hundreds of connections per second. In addition, the situation is compounded by the presence of multicast traffic which has rate guarantees. We describe an architecture and Implementation for an ATM switching system which address the above requirements. Our approach uses a novel two-level scheduling algorithm: a higher level scheduling algorithm for aggregated cell units called frames and a distribution scheme for cells within a frame. This approach has significant advantages in terms of implementation complexity. It is particularly effective in treating traffic with differing QoS requirements differently in the process of flow control across the switching fabric. It enables the fulfilment of arbitrary rate guarantees to individual connections in an easily controllable way. It makes the scheduling of multicast particularly efficient and easy. We describe all these advantages and present numerical results supporting our claims. Implementational features of the architecture are discussed to demonstrate the feasibility of such a design.

This paper develops a copy network architecture that can maintain the cell sequence integrity in multi-channel ATM switching. The architecture is internally nonblocking in the sense that the copying process of cells is constrained only by the availability of output channels. By using a relative ordering among the inputs, shared buffering, and a new switching paradigm called the nonblocking binary group network, we show how the cell sequence integrity can be maintained. Next, assuming the fanout request values of cells are distributed independently from cell to cell, we formulate a method of analyzing the performance of the copy network. This method uses the technique of tagged Markov chains to derive the stationary distributions for the number of cells in the copy network from which, delay, throughput, and cell loss probability can be accurately calculated as critical performance measures. We conduct a numerical study for the proposed architecture using this method wherein the effects of key network and traffic variables such as buffer and network sizes, and the mean and the variance of fanout request values are determined under arbitrary types of fanout distribution. Finally, we quantify the performance improvement due to fanout splitting which allows the fanout request from a single cell to be satisfied over multiple time slots.

The paper investigates multichannel switching as a promising alternative to traditional single-channel switching where virtual paths established in a switch are between a single input channel and a single output channel. A particular non-blocking condition is derived for flip networks, which is exploited to realize a multichannel switching architecture that supports an arbitrary number of channel groups. The architecture is internally nonblocking and bufferless. Using one flip network recursively a number of times based on the number of channel groups, the resulting architecture becomes efficient in the sense that the cross point complexity is O(N log/sub 2/ N) for N inputs. Other distinguishing features are the abilities to provide multicasting, superrate switching (i.e., rates that exceed the capacity of a single channel are accommodated), multirate switching (i.e., bit pipes of different rates are supported simultaneously), multiple performance requirements (i.e., services with different performance requirements are treated accordingly), and fair access to all inputs (i.e., no input is systematically discriminated against). In multichannel switching, cells belonging to a single session can traverse multiple channels. Providing the cell sequencing integrity becomes a challenging issue. The architecture proposed in the paper accomplishes the task without employing any cell resequencing mechanism.>

The paper presents a method of controlling the pattern of packet flow in the statistical data fork (SDF), such that the output channels are assigned to a channel group based only on their addresses and this assignment is maintained independently of the offered load to the SDF. The proposed method is realized by using a structural property of the SDF which is derived in the paper. It is shown that a sufficient condition for this property to hold is for the probabilities of packets destined for different channel groups to be certain permutations of each other. It is shown, using this property, that the flow of packets in the SDF can be governed by a two phase process wherein in the first phase, packets are routed in different subnetworks to result in the probability patterns that match the requirement of the structural property, and in the second phase, these packets are delivered to the channel groups which are partitioned only according to their addresses.>

The paper investigates multi-channel switching as a promising alternative to traditional single-channel switching where virtual paths established in a switch are between a single input channel and a single output channel. Building on a particular nonblocking condition for the flip networks, a multi-channel switching architecture that supports an arbitrary number of channel groups is formulated. In multi-channel switching, cells belonging to a single session can traverse multiple channels. The architecture proposed in the paper provides the time ordering integrity among those cells without employing any resequencing mechanism.>