Wireless sensor networks (WSNs) are one of the most important ingredients in the Internet of Things. Thus it is vital to design a good power saving protocol, which operates at the medium access control (MAC) layer, for a WSN since sensors are generally battery-powered. On the other hand, organizing a WSN into coronas centered at the sink is a simple effective technique to achieve low-overhead routing where every sensor needs neither to broadcast beacons nor to maintain routing/neighbor tables. Hence in this paper, we propose an optimal and maximized configurable power saving protocol, named Green-MAC, for a corona-based WSN, which has the following attractive features. (i) By using the generalized Chinese remainder theorem, Green-MAC guarantees that any two sensors in the neighboring coronas can simultaneously wake up in bounded time regardless of their schedule offset as well as their respective cycle lengths. (ii) Given the cycle length, the ATF-ratio (i.e. the fraction of awake time frames in a cycle) of each sensor reaches the theoretical minimum. (iii) Under the minimum ATF-ratio constraints, the number of configurable ATF-ratios of each sensor reaches the theoretical maximum. (iv) An ATF-ratio configuration scheme is proposed for Green-MAC such that the power consumption of a WSN can be minimized while the worst event-to-sink delay requirement can be fulfilled with high probability. Both theoretical analysis and simulation results demonstrate that Green-MAC greatly outperforms existing power saving protocols for corona-based WSNs, including Q-MAC and Queen-MAC, in terms of ATF-ratio, configurability, network lifetime, delay violation ratio, and event-to-sink throughput.

Abstract This paper presents a capacity degradation model under interferences for sectorized cellular networks with fractional frequency reuse. In a sectorized fractional frequency reuse network, allocated bandwidth consists of a number of frequency partitions. To avoid intra‐cell interferences, each frequency partition is then assigned to two different groups, the super group (Sup‐G) and the regular group. However, because a Sup‐G in a cell employs the same frequency partition as the other Sup‐Gs in the neighboring cells, inter‐cell interferences may become serious when the radius of the Sup‐G is largely increased. In the worse case, the largely increasing inter‐cell interferences will eventually degrade the overall system capacity. Additionally, different density distributions of mobile stations may have different levels of impact on the capacity degradation. In this paper, both folded normal distribution and uniform distribution are considered in building the capacity degradation model. Numerical simulations show that by carefully adjusting the ratio between the radius of the Sup‐G and the radius of a cell, (i) an mobile station could receive the same capacity no matter where it is residing, and (ii) the maximum system capacity can be therefore achieved. Copyright © 2013 John Wiley & Sons, Ltd.

Abstract In this paper, we construct mathematical models to analyze the probabilities of new call blocking and handoff call (HC) dropping for a sectorized cellular network with fractional frequency reuse (FFR). Because a sectorized FFR network (SFN) consists of two areas, the super group (SG) and the regular group (or sectors), three different types of HCs may happen when a mobile station (MS) moves from the SG to a sector, from a sector to the SG, or from one sector to another sector. To characterize three types of HCs, we first derive the area transition probability, which is defined as the reciprocal of MS's average residence time in an area (i.e., sector or SG). Moreover, we construct the model of Markov chains and derive the state transition rates. Then on the basis of the stationary probabilities of Markovian states, we derive the three types of blocking probabilities of new calls and two types of dropping probabilities of HCs. Finally, we conduct extensive numerical simulations. From the results of numerical simulations, we reveal two important rules for choosing the optimal radius of the SG, with which the system blocking and dropping probability can be effectively minimized. Copyright © 2014 John Wiley & Sons, Ltd.

Recently, the integration of smart antenna technology into existing wireless local area networks (WLANs) has been one of the hot spots of research work. In this paper, we design an IEEE 802.11-compliant medium access control (MAC) protocol, named M-HCCA, that fully takes advantage of multi-beam smart antennas equipped at the access point (AP) to not only boost the overall capacity of a WLAN, but also support quality-of-service (QoS) and power conservation for individual mobile users. Specifically, M-HCCA has the following attractive features: (i) since being a polling-based MAC scheme, M-HCCA can innately conquer the problems induced by carrier sensing or directional signals, including beam-synchronization constraint, receiver blocking problem, and unnecessary defer problem; (ii) M-HCCA achieves high real-time throughput by adaptively adjusting the sector configuration to quickly resolve contention/collision and to increase data transmission parallelism; (iii) M-HCCA employs beam-location-aware polling scheduling to not only solve the beam-overlapping problem and back/side-lobe problem, but also let real-time stations save as much energy as possible; (iv) M-HCCA adopts the mobile-assisted admission control technique such that the AP can admit as many newly streams as possible while not violating QoS guarantees made to already-admitted streams; (v) M-HCCA offers a location updating mechanism to promptly renew the beam-location information of a non-responsive station such that the miss-hit problem can be effectively alleviated. Extensive simulation results show that, in terms of throughput, real-time throughput, and energy throughput, M-HCCA significantly outperforms existing protocols even in uneven station distribution, imperfect beam-forming, and high mobility environments.

The popularity of smart mobile devices has brought significant growth of data services for mobile service providers. Mobile users of data services are charged based on the amount of data used. Raising served data amount seemingly increases the profit; energy consumption rises correspondingly. Besides, spectral resources are licensed and limited for mobile operators to allocate. Increasing data services over the spectrum for the profit does not count the cost of energy. To assess the profitability, considered is the revenue-to-cost ratio. Optimizing the ratio is an economic incentive for mobile operators. Revenue is regarded as efficiency in spectrum use, the cost as energy consumption; therefore we interpret the revenue-to-cost ratio as spectrum-energy efficiency. In this paper, we study the spectrum-energy efficiency optimization problem where BSs are with the ability to perform cell zooming, sleep mode, and user migration. We formulate the problem into an integer linear program which is solvable by CPLEX to maximize spectrum-energy efficiency; meanwhile traffic demands by associated users in multicell/multiuser networks are met. To avoid high computation time, a heuristic algorithm is proposed to efficiently solve the formulated problem. Numerical analysis through case studies demonstrates energy consumption and efficiency improvements, and comparisons between near-optimal solutions against optimality.

IEEE 802.11 is currently the most popular medium access control (MAC) standard for mobile ad hoc networks (MANETs). On the other hand, clustering in MANETs is a promising technique to ensure the scalability of various communication protocols. Thus, we propose an optimal asymmetric and maximized adaptive power management protocol, called OAMA, for 802.11-based clustered MANETs, which has the following attractive features. 1) Given the length of schedule repetition interval (SRI), the duty cycles of both clusterheads and members reach the theoretical minimum. 2) Under the minimum duty cycle constraints, the numbers of tunable SRIs for clusterheads and members reach the theoretical maximum. 3) By means of factor-correlative coterie-plane product, OAMA guarantees bounded-time neighbor discovery between the clusterhead and its member, and between all clusterheads, regardless of stations' individual SRIs and the schedule offset between neighboring stations. 4) The time complexity of OAMA neighbor maintenance is O(1). 5) OAMA adopts a cross-layer SRI adjustment scheme such that stations can adaptively tune the values of SRI to maximize energy conservation according to flow timeliness requirements. Both theoretical analyses and simulation results show that OAMA substantially outperforms existing power management protocols for clustered MANETs, including AQEC [2] and ACQ [14], in terms of duty cycle, adaptiveness, data delay dropped ratio, network lifetime, and end-to-end energy throughput.

IEEE 802.16 was created to meet the need of highspeed wireless access in metropolitan-scale areas. Due to air interference and dynamic queue state changes in subscriber stations, the idling UL-subframe problem, uplink hole problem, and padding waste problem are inevitable in 802.16 point-to- multipoint networks. To the best of our knowledge, this is the first work that seriously studies these issues. In this paper, we proposed the UBAR protocol, which employs the proportionally fair sharing scheme to utilize bandwidth efficiently, and adopts the timeout-based UL-MAP retransmission scheme with uplink bandwidth reallocation algorithms to simultaneously solve three bandwidth waste problems. Simulation results reveal that the uplink good put of UBAR in error-prone environments can be very close to that in an error-free environment.

In wireless ad hoc networks, IEEE 802.11 power management may completely fail if power-saving (PS for short) stations are out of synchronization. To fix this problem, Haas and Perlman (2001) proposed various cyclic quorum-based power management (CQPM) protocols, which, however, may also completely fail if some PS stations have different schedule repetition intervals (SRIs). To conquer all these problems, in this paper, we propose the AAPM (adaptive asynchronous power management) protocol, which has the following attractive features, (i) By using the novel AA-quorum space, AAPM ensures that any two asynchronous PS neighbors can discover each other in finite time regardless of their individual SRIs. (ii) The idle duty cycles of AAPM for all eligible SRI values are minimal, (iii) The time complexity of AAPM neighbor maintenance is constant, (iv) Two cross-layer SRI adjustment schemes are proposed such that a PS station in AAPM can dynamically vary its SRI according to the residual battery power or traffic QoS requirements. Primary numerical results show that AAPM achieves better energy efficiency than existing CQPM protocols.

In IEEE 802.15.4 beacon-enabled wireless personal area networks (WPANs), the PAN coordinator will periodically broadcast beacon frames to let its associated end devices keep synchronized. One of the benefits in a beacon-enabled WPAN is that end devices can thus turn off their transceiver during the inactive periods to preserve their energy. Another benefit is that the PAN coordinator can allocate contention-free GTSs (guaranteed time slots) for admitted devices. This paper, first pointed out slot size-induced bandwidth waste problem, which is due to the innate defect of the super frame structure. Then the authors propose the novel multi-beacon super frame (MBS) structure to overcome this problem. To demonstrate the power of MBS, we also propose a greedy GTS allocation algorithm. Simulation results reveal that a WPAN using MBS can attain relatively higher bandwidth utilization at the expense of only a small increase of the device's active period.

In IEEE 802.11 wireless ad hoc networks, the listen interval of a power-saving (PS) station should be fixed at one even there is no data traffic or its remaining battery power is low. However, if the listen interval is allowed more than two beacon intervals, 802.11 power management may completely fail. Hence we propose a new novel adaptive power management protocol, called APM, which not only equips the PS stations with dynamic listen interval adjustment ability, but also conquers the following problems: (i) the possibly forever loss of ATIM frames, (ii) the needless waste of ATIM frames, and (iii) neighbor maintenance problem. Above all, APM offers the PS station full flexibility in trading energy and latency by appropriately setting the listen interval and idle duty cycle. The primary numerical results demonstrate that APM attains better energy efficiency than existing protocols, including IEEE 802.11 and AQEC (Chao et al., 2006).

In IEEE 802.11 wireless ad hoc networks, the listen interval of a power-saving (PS) station should be fixed at one even there is no data traffic or its remaining battery power is low. However, if the listen interval is allowed more than two beacon intervals, 802.11 power management may completely fail. Hence we propose a new novel randomized power management (RPM), which not only equips the PS stations with dynamic listen interval adjustment ability, but also eliminates the following problems: (i) the possibly forever loss of ATIM frames, (ii) the needless waste of ATIM frames, and (iii) neighbor maintenance problem. Above all, RPM can offer the network designers full flexibility in trading energy, latency, and neighbor discovery probability versus each other by appropriately tuning system parameters. The primary numerical results show that, as compared with 802.11, RPM earns a significant reduction in power consumption at the expense of only a little additional delay.

We propose a new MAC protocol, named Q-PCF (quality-of-service PCF), which provides QoS guarantees to real-time multimedia applications for WLANs. Specifically, Q-PCF has the following attractive features. First, it supports multiple priority levels and guarantees that high-priority stations always join the polling list earlier than low-priority stations. Second, it provides fast reservation scheme such that real-time stations can get on the polling list in bounded time. Third, it employs dynamic bandwidth allocation scheme to support CBR/VBR transportation and provide per-flow probabilistic performance assurances. Forth, it adopts the novel mobile-assisted admission control technique such that the access point can admit as many newly flows as possible, while not violating admitted flows' guarantees. Simulation results do confirm that Q-PCF achieves high goodput and low frame delay dropped rate. Last but not least, we believe that the Q-PCF protocol can be easily applied to the current IEEE 802.11 products without major modifications.

In this paper, we propose and analyze a new interconnection network called bubblesort star graph, which is the merger of the bubblesort graph and the star graph. We present the deadlock-free wormhole routing algorithm for the proposed network. We also develop the method to embed a mesh into a bubblesort star graph with dilation two and expansion one. Besides, we use the recursive scheme to embed the multiple disjoint copies of the hypercube into a bubblesort star graph with all faults recovery capacity as well as constant expansion and dilation one or two. This reflects the fact that the embeddability of the bubblesort star graph is much better than that of the star graph.