Adaptive Modulation and Power Control for throughput enhancement in cognitive radios

To regulate the transmit-power and enhance the total throughput, a novel Transmit Power Control Game （TPCG） algorithm and an adaptive Modulation TPCG （M-TPCG） algorithm which combine bandwidth allocation, adaptive modulation and transmit-power control based on Space Time Block Coding （STBC） OFDM-CDMA system are designed and a cross-layer framework of database sharing is proposed. Simulation results show that the TPCG algorithm can regulate their transmitter powers and enhance the total throughput effectively, M-TPCG algorithm can achieve maximal system throughput. The performance of the cognitive radio system is improved obviously.     

Maximum throughput of an input queueing packet switch with twopriority classes

The maximum throughput of an N×N nonblocking packet switch with input queues and two priority classes is analyzed. Packets are of fixed length and the switch operation is slotted. Packets of both priority classes are queued when waiting for service. High-priority packets preempt low-priority ones and move ahead of all low-priority packets waiting in the queue. A new method of analysis is employed. The calculated results of the maximum throughput obtained are close to the simulation results     

AID‐based backoff for throughput enhancement in 802.11ah networks

IEEE 802.11ah is a WiFi standard developed to address requirements associated with the heterogeneous nature of the Internet of Things. It uses the sub‐1 GHz bands to enable long‐range transmissions for low‐power devices. However, long‐range coverage exacerbates the hidden node problem. To mitigate this problem, sectorization and grouping have been proposed by the standard. In this paper, hierarchical clustering and a modified Welsh‐Powell algorithm are combined to create hidden node‐free groups in a sectorized wireless local area network. An analytical model is developed for a deterministic backoff technique that uses association identifiers to set the backoff in order to eliminate collisions. The performance of the deterministic backoff technique is compared with that of existing schemes. Our results show that this approach results in higher throughput and lower latency than other deterministic backoff techniques.     

Link scheduling with power control for throughput enhancement in multihop wireless networks

Joint scheduling and power control schemes have previously been proposed to reduce power dissipation in wireless ad hoc networks. However, instead of power consumption, throughput is a more important performance concern for some emerging multihop wireless networks, such as wireless mesh networks. This paper examines joint link scheduling and power control with the objective of throughput improvement. The MAximum THroughput link Scheduling with Power Control (MATH-SPC) problem is first formulated and then a mixed integer linear programming (MILP) formulation is presented to provide optimal solutions. However, simply maximizing the throughput may lead to a severe bias on bandwidth allocation among links. To achieve a good tradeoff between throughput and fairness, a new parameter called the demand satisfaction factor (DSF) to characterize the fairness of bandwidth allocation and formulate the MAximum Throughput fAir link Scheduling with Power Control (MATA-SPC) problem is defined. An MILP formulation and an effective polynomial-time heuristic algorithm, namely, the serial linear programming rounding (SLPR) heuristic, to solve the MATA-SPC problem are also presented. Numerical results show that bandwidth can be fairly allocated among all links/flows by solving the MILP formulation or by using the heuristic algorithm at the cost of a minor reduction of network throughput. In addition, extensions to end-to-end throughput and fairness and multiradio wireless multihop networks are discussed.     

A method for throughput enhancement in Wi-Fi backscatter communications using power-level modulation

An improved data rate technology from tag to reader in Wi-Fi backscatter systems is proposed. The proposed system applies a power-level modulation to the conventional backscatter communication system. This technology can improve the data rate dramatically. It also adopts the Euclidean distance evaluation during demodulation, which looks for the most similar signal to enhance the BER performance. We analyze the error performance of the proposed decoding method, and the numerical results are presented. The power level is formed ranging from 2-level to 8-level. The performance of the detecting algorithm is compared to the conventional system, which utilizes the received power of selected sub-carriers.     

Linear-complexity algorithms for QoS support in input-queuedswitches with no speedup

We present several fast, practical linear-complexity scheduling algorithms that enable provision of various quality-of-service (QoS) guarantees in an input-queued switch with no speedup. Specifically, our algorithms provide per-virtual-circuit transmission rate and cell delay guarantees using a credit-based bandwidth reservation scheme. Our algorithms also provide approximate max-min fair sharing of unreserved switch capacity. The novelties of our algorithms derive from judicious choices of edge weights in a bipartite matching problem. The edge weights are certain functions of the amount and waiting times of queued cells and credits received by a virtual circuit. By using a linear-complexity variation of the well-known stable-marriage matching algorithm, we present theoretical proofs and demonstrate by simulations that the edge weights are bounded. This implies various QoS guarantees or contracts about bandwidth allocations and cell delays. Network management can then provide these contracts to the clients. We present several different algorithms of varied complexity and performance (as measured by the usefulness of each algorithm's contract). While most of this paper is devoted to the study of “soft” guarantees, a few “hard” guarantees can also be proved rigorously for some of our algorithms. As can be expected, the provable guarantees are weaker than the observed performance bounds in simulations. Although our algorithms are designed for switches with no speedup, we also derive upper bounds on the minimal buffer requirement in the output queues necessary to prevent buffer overflow when our algorithms are used in switches with speedup larger than one     

Virtual time-slot allocation scheme for throughput enhancement in a millimeter-wave multi-Gbps WPAN system

This paper proposes a virtual time-slot allocation (VTSA) scheme for throughput enhancement to realize a multi-Gbps time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment. TDMA system without time-slot-reuse mechanism conventionally allocates one TDMA time-slot to only one communication link at a time. In the proposed VTSA scheme, taking advantage on the large path loss in the millimeterwave band, a single TDMA time-slot can be reallocated and reused by multiple communication links simultaneously (hence the name virtual), thus significantly increasing system throughput. On the other hand, allowing multiple communication links to occupy the same time-slot causes the generation of co-channel interference (CCI). The cross layer VTSA scheme is therefore designed to be able to maximize the throughput improvement by adaptively scheduling the sharing of time-slots, and at the same time monitor the potential performance degradation due to CCI. As a result, it is found that the VTSA scheme is capable of improving system throughput as much as 30% in both AWGN and multipath channels (line-of-sight (LOS) and non-line-of-sight (NLOS) environment). Additionally, by coupling with higher-order modulation schemes, the system is able to achieve up to a maximum throughput of 3.8 Gbps. It is also observed that higher-order modulations although have higher maximum achievable throughput in low CCI environment, the tolerance against increasing CCI is considerably lower than that of the lower-order modulations.     

POWMAC: a single-channel power-control protocol for throughput enhancement in wireless ad hoc networks

Transmission power control (TPC) has great potential to increase the throughput of a mobile ad hoc network (MANET). Existing TPC schemes achieve this goal by using additional hardware (e.g., multiple transceivers), by compromising the collision avoidance property of the channel access scheme, by making impractical assumptions on the operation of the medium access control (MAC) protocol, or by overlooking the protection of link-layer acknowledgment packets. In this paper, we present a novel power controlled MAC protocol called POWMAC, which enjoys the same single-channel, single-transceiver design of the IEEE 802.11 ad hoc MAC protocol but which achieves a significant throughput improvement over the 802.11 protocol. Instead of alternating between the transmission of control (RTS/CTS) and data packets, as done in the 802.11 scheme, POWMAC uses an access window (AW) to allow for a series of request-to-send/clear-to-send (RTS/CTS) exchanges to take place before several concurrent data packet transmissions can commence. The length of the AW is dynamically adjusted based on localized information to allow for multiple interference-limited concurrent transmissions to take place in the same vicinity of a receiving terminal. Collision avoidance information is inserted into the CTS packet and is used to bound/ the transmission power of potentially interfering terminals in the vicinity of the receiver, rather than silencing such terminals. Simulation results are used to demonstrate the significant throughput and energy gains that can be obtained under the POWMAC protocol.     

Novel distributed algorithm for coalition formation in cognitive radio networks for throughput enhancement using matching theory

In this paper, a novel algorithm is proposed for increasing the throughput in cognitive radio networks by forming coalitions among cognitive radio users in AWGN and fading channel environment. Although there have been numerous studies exploring the benefits of coalition formation in cognitive radio networks from the game theory perspective, there are several limitations in their application. To overcome the limitations of game theory, concepts from matching theory are used. Specifically, the stable marriage problem is used to formulate the interactions among the cognitive radio users as a matching game for collaborative distributed spectrum sensing under target detection probability constraint. The utility function is defined as the average probability of false alarm per cognitive radio user. The advantage of stable marriage is that it always converges to a stable matching and is Pareto optimal when the preferences of cognitive radios are strict. In the proposed model, the stable matching problem is extended to propose a novel algorithm to form coalitions of varying sizes for improving the utility of CR (false alarm and throughput). The coalitions formed using the algorithm are stable and do not deviate from the final matching. Using simulations and mathematical analysis, it is shown that the proposed algorithm leads to stable coalitions and returns significant improvement in terms of reduced probability of false alarm and improved throughput per cognitive radio user as compared to the noncooperative scenario.     

Concurrent enhancement of network throughput and fairness in optical burst switching environments

In this article, we propose and evaluate a preemption-based scheme for the concurrent improvement of network throughput and burst fairness in optical burst switched networks. The scheme uses a preemption weight consisting of two terms: the first term is a function of the size of the burst and the second term is the product of the hop count times the length of the lightpath of the burst. The second term is adjusted by a minimum function to prevent the problem of reverse unfairness. Extensive simulation tests showed that the application of the scheme results in higher throughput and at the same time improves the fairness coefficient. The scheme is further enhanced by combining it with a fairness-improving scheme previously proposed in the literature. Detailed performance tests are presented and analyzed.     

Bifurcated convolutional network for specular highlight removal

Specular highlight usually causes serious information degradation, which leads to the failure of many computer vision algorithms. We have proposed a novel bifurcated convolution neural network to tackle the problem of high reflectivity image information degradation. A two-stage process is proposed for the extraction and elimination of the specular highlight features, with the procedure starting at a coarse level and progressing towards a finer level, to ensure the generated diffuse images are less affected by visual artifacts and information distortions. A bifurcated feature selection module is designed to remove the specular highlight features, thereby enhancing the detection capability of the network. The experiments on two types of challenging datasets demonstrate that our method outperforms state-of-the-art approaches for specular highlight detection and removal. The effectiveness of the proposed bifurcated feature selection module and the overall network is also verified.     

Solving the trade-off between fairness and throughput: Token bucket and leaky bucket-based weighted fair queueing schedulers

In this article, we present two efficient weighted fair queueing (WFQ) scheduling algorithms leaned on the well-known token bucket and leaky bucket shaping/policing algorithms. The performance of the presented algorithms is compared to those of the state-of-the-art WFQ approximations such as weighted round robin (WRR) and the recently proposed bin sort fair queueing (BSFQ). Our simulation results show that the proposed algorithms provide a better fairness at a lower implementation complexity while simultaneously achieving a comparable network utilization.     

Yield enhancement and manufacturing throughput of redundant memories by repairability/unrepairability detection

In this article, yield enhancement and manufacturing throughput of large repairable memories are analyzed. These objectives are met by repairability/unrepairability detection. Initially two new techniques for detection of memory chips with redundancy are presented. Initially, a heuristic, yet efficient approach is proposed. This first approach is based on finding a very good approximation to the minimum covering set. An algorithm, which executes in quadratic time with respect to the largest dimension of the memory, is presented. This algorithm is executed off-line, that is, when the memory has been fully diagnosed. New conditions for detection are presented and fully analyzed. These are based on a more accurate estimation of the regions of repairability and unrepairability. Hence, this results in a reduction of the uncertainty region, where the status of a memory cannot be established without executing a fully exhaustive search algorithm. The second approach to repairability/unrepairability detection is based on a more complex covering relationship, namely the generalized leading element. A model for manufacturing throughput of large repairable memories is presented.A new repair algorithm which utilizes a ternary tree approach, is also presented. This repair algorithm is perfect in the sense that it finds the optimal repair-solution (whenever one exists) after the memory has not been diagnosed unrepairable.Illustrative examples and simulation results show that considerable improvements for average and the worst-case analysis over existing techniques can be achieved.This research was supported in part by grants from AT&T and NATO.     

Range and throughput enhancement of wireless local area networks using smart sectorised antennas

At present, wireless local area networks (WLANs) such as HiperLAN2 and 802.11a are being developed and deployed around the world. In this letter, the use of sectorized antennas is considered as a means to improve the physical layer performance of WLANs. Results demonstrate that throughput and range can be enhanced and/or the transmit power can be reduced. However, these benefits are achieved with a small increase in multiple access protocol overhead. Simulations are performed using measured wideband channels in the 5-GHz band. In cases where the channel exhibits strong Rician characteristics, gains as high as 13 dB are demonstrated. These benefits substantially outweigh the associated medium access control overhead.     

On the throughput enhancement of the downstream channel in cellular radio networks through multihop relaying

In this paper, we study the effect of multihop relaying on the throughput of the downstream channel in cellular networks. In particular, we compare the throughput of the multihop system with that of the conventional cellular system, demonstrating the achievable throughput improvement by the multihop relaying. We also propose a hybrid control strategy for the multihop relaying, in which we advocate the use of both, the direct transmission and the multihop relaying. Our study shows that most of the throughput gain can be obtained with the use of a two- and three-hop relaying scheme. Substantial throughput improvement could be additionally obtained by operating the concurrent relaying transmission in conjunction with the nonconcurrent transmission. We also argue here that the multihop relaying technology can be utilized for mitigating unfairness in quality-of-service (QoS), which comes about due to the location-dependent signal quality. Our results show that the multihop system can provide more even QoS over the cell area. The multihop cellular network architecture can also be utilized as a self-configuring network mechanism that efficiently accommodates variability of traffic distribution. We have studied the throughput improvement for the uniform, as well as for the nonuniform traffic distribution, and we conclude that the use of multihop relaying in cellular networks would be relatively robust to changes in the actual traffic distribution.     

IEEE 802.11n: Joint modulation‐coding and guard interval adaptation scheme for throughput enhancement

IEEE 802.11n is a high‐speed wireless broadband local area networking standard. IEEE 802.11n‐based devices are using some kind of adaptive modulation‐coding (AMC) scheme to adjust its transmission rate according to the radio channel condition. In these devices, however, the concept of guard interval adaptation is not been considered. Normally, orthogonal frequency division multiplexing (OFDM) technology‐based systems are using the guard interval much greater than the length of the channel impulse response. However, many previous works have shown that the choice of the larger guard interval is inefficient in terms of achievable throughput. IEEE802.11n supports using two guard intervals (short = 400 ns or long = 800 ns). Indeed, the shorter guard interval evidently results in intersymbol interference (ISI) and intercarrier interference (ICI), but the gain offered by shortened guard interval may exceed the loss caused by interference. In this paper, we propose a novel but simple solution for the guard interval adaptation joint with an adaptive modulation‐coding scheme to optimize the throughput performance of a wireless local area network (WLAN) system. This paper aims to analyze the effect of joint adaptive modulation‐coding and the guard interval (JAMCGI) algorithm on the WLAN system under bit‐error‐rate (BER) constraints. Simulation results and their analysis show a significant increase in the throughput performance of the WLAN system with our proposed algorithm.     

Credit-based fair queueing for ATM networks

A simple and practically attractive rate-based scheduling algorithm for ATM networks is presented. By using simple counters to keep track of the transmission credits earned by each traffic stream, the algorithm decides which stream to serve next, based on their bandwidth shares and the values of the counters     

Extended distributed queueing for integrated services

A method for supporting time-constrained and nontime-constrained integrated services on a shared dual bus network is presented. The method is an extension of the basic distributed queue protocol defined in the IEEE 802.6 distributed-queue dual-bus (DQDB) MAN standard. The extended distributed queueing protocol differs from the basic protocol in allowing more than one outstanding request in the distributed queue at any one time. Used at the high priority and in conjunction with segment stream shaping and subscribed service limiting, the extended protocol provides bearer services with guaranteed bandwidth and bounded delays. Bearer services with fair but nonguaranteed bandwidth shares, suitable for nontime-constrained applications, are provided by the same protocol and bandwidth balancing operating at the lowest priority. A number of the desirable attributes of the proposed scheme are identified including the optimality of the delay variance introduced by the access protocol. An approximate analysis of the access delay experience by time-constrained streams is presented     

Competing for throughput in the local loop

The voice-grade telephone channel is the communication medium most widely available throughout the world. Its limitations, a relatively narrow bandwidth and a moderate SNR figure, have challenged telecommunication researchers and engineers over several decades to develop technologies able to pass higher and higher data rates. The sophisticated combination of trellis coding and quadrature amplitude modulation increases the bandwidth utilization close to the Shannon limit of 10 b/s/Hz for the 3.1 kHz bandwidth voice channel. However, the resultant data rate of about 30 kb/s does not even begin to approach the throughput needed by multimedia applications. Fortunately, twisted pair bandwidth reaches up to several megahertz, so multilevel signaling implemented as in the xDSF family of modems enables data rates of several megabits per second to be reached. Standard ADSL modems are able to deliver 8 Mb/s to a subscriber in the best case. VDSL modems can deliver 52 Mb/s, but only up to 300 m, so their mass implementation will only become possible when fiber migrates into an access network closer to the user premises. Both broadband xDSL solutions approach the Shannon limit and the related spectral efficiency as well, so there is not much room left for a transmission improvement     

Efficient fair queueing algorithms for packet-switched networks

Although weighted fair queueing (WFQ) has been regarded as an ideal scheduling algorithm in terms of its combined delay bound and proportional fairness properties, its asymptotic time complexity increases linearly with the number of sessions serviced by the scheduler, thus limiting its use in high-speed networks. An algorithm that combines the delay and fairness bounds of WFQ with O(1) timestamp computations had remained elusive so far. In this paper we present two novel scheduling algorithms that have O(1) complexity for timestamp computations and provide the same bounds on end-to-end delay and buffer requirements as those of WFQ. The first algorithm, frame-based fair queueing (FFQ), uses a framing mechanism to periodically recalibrate a global variable tracking the progress of work in the system, limiting any short-term unfairness to within a frame period. The second algorithm, starting potential based fair queueing (SPFQ), performs the recalibration at packet boundaries, resulting in improved fairness while still maintaining the O(1) timestamp computations. Both algorithms are based on the general framework of rate-proportional servers (RPSs) introduced by Stiliadis and Varma (see ibid., vol.6, no.2, p.164-74, 1998). The algorithms may be used in both general packet networks with variable packet sizes and in asynchronous transfer mode (ATM) networks