Sharif Digital Repository

Exponential backoff is an intrinsic feature of MAC-layer standards of most types of ad hoc networks. It leads to random access channels with memory. In this paper we propose a new network coding-based packet forwarding scheme suitable for multiple unicast scenarios in downlink direction of a wireless network. The wireless nodes as well as the access point attempt to access the channel, based on slotted Aloha with exponential backoff. In the proposed scheme we convert multiple unicast scenario to a combination of several anycast and a multicast scenarios. By proposing an open multiclass queueing network, we are able to derive the maximum stable download throughput of the network. The... 

In this paper, we propose a new scenario in order to increase the total throughput of a WLAN. In this scenario, some secondary users (SUs) are considered in a primary WLAN such that SUs cooperate with primary users (PUs) in transmitting the primary packets. Each SU sends its packets as well as the primary packets collided at the access point, but overheard successfully at the SU, by random access the primary WLAN. We show that SUs cooperation is able to compensate their adverse effect in the WLAN, so total throughput in the WLAN increases without a significant degrading effect for the stability region of PUs. To this end, we use an analytical model based on open queueing networks. By solving... 

We study myopic sensing policy for an opportunistic communication system in which the states of channels evolve as independent Markov chains. A Secondary User (SU) takes one channel to sense and access in each time slot by myopic sensing policy. In the myopic policy, SU ignores the impact of the current action on the future decisions and tries to maximize the expected immediate reward. We propose an upper bound on the throughput achieved by the myopic sensing policy for general case in which channels have different Markov models. In particular, the proposed bound is compared with the Zhao et. al's upper bound (UZhao) for the channels with identical models. We prove that there are conditions... 

In this paper, we consider a new scheme based on jointly network and rateless coding for a multiple-access relay channel. In the scheme, whenever the relay can decode multiple messages of the users, it jointly encodes them using a larger rateless code. This scheme is compared with direct transmission and the conventional relaying scheme in which the relay helps each user independently at orthogonal channels. The comparison is made by evaluating the throughput of different schemes. The analytical and the simulation results show that the proposed scheme outperforms the other ones at the cases considered  

This paper presents a VLSI architecture of a novel softoutput K-Best MIMO detector. The proposed detector attains low computational complexity using three improvement ideas: relevant discarded paths selection, last stage on-demand expansion, and relaxed LLR computation. A deeply pipelined architecture for a soft-output MIMO detector is implemented for a 4x4 64-QAM MIMO system realizing a peak throughput of 655Mbps, while consuming 174K gates and 195mW in 0.13um CMOS. Synthesis results in 65nm CMOS show the potential to support a sustained throughput up to 2Gbps achieving the data rates envisioned by emerging IEEE 802.16m and LTE-Advanced wireless standards  

In this paper, we evaluate the saturation throughput for an IEEE 802.11 based wireless network considering capture effect at the receiver, while nodes transmit with random powers. In this respect, we consider a scenario consisting of a specific number of wireless nodes. Then, we derive the transmission as well as collision probabilities with respect to the perfect capture effect. In order to maximize the saturation throughput we set up an optimization problem and obtain how to compute optimum values for the probabilities corresponding to different power levels. By providing the numerical results, we deduce that power randomization may lead to a significant improvement in saturation... 

Caching has been widely considered an efficient way of reducing and balancing the growing traffic in communications networks in recent years. The cache network of interest consists of one content server connected via a shared link to a number of caching nodes, also known as a single bottleneck caching network. In this paper, for the first time, the stochastic requests traffic model in such networks is considered and a performance analysis is provided based on such a realistic assumption. In addition, we introduce new comprehensive performance metrics, which simultaneously take into account, the cache hit probability, load on the bottleneck link, and requests arrival rates. The main... 

In communications, the nodes with the ability of harvesting energy potentially can prolong the overall network lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our goal is to find an online algorithm for the throughput maximization problem, which only needs the causal information of the arrival processes. We propose a heuristic online algorithm which is efficient for both discrete and continuous models, even when the distributions of harvested energy and arrival data are unknown  

In this study, the average throughput maximisation of a secondary user (SU) by optimising its spectrum sensing time is formulated, assuming that a priori knowledge of the presence and absence probabilities of the primary users (PUs) is available. The energy consumed to find a transmission opportunity is evaluated, and a discussion on the impacts of the number of PUs on SU throughput and consumed energy are presented. To avoid the challenges associated with the analytical method, as a second solution, a systematic adaptive neural network-based sensing time optimisation approach is also proposed. The proposed scheme is able to find the optimum value of the channel sensing time without any... 

Contraflow or lane reversal is an efficient way for increasing the outbound capacity of a network by reversing the direction of in-bound roads during evacuations. Hence, it can be considered as a potential remedy for solving congestion problems during evacuation in the context of homeland security, natural disasters and urban evacuations, especially in response to an expected disaster. Most of the contraflow studies are performed offline, thus strategies are generated beforehand for future implementation. Online contraflow models, however, would be often computationally demanding and time-consuming. This study contributes to the state of the art of contraflow modelling in two regards. First,... 

This paper quantifies the difference in resource demand between modern and classic NoC workloads. In the paper, we show that modern workloads are able to better utilize higher numbers of VCs and smaller C factors in order to attain performance and energy efficiency. This is because of the high throughput and possible local congestions in their traffic pattern. As a result, such workloads are more suitable for concurrency and redundancy energy reduction techniques where the voltage and frequency are reduced simultaneously and the increased power budget is used for introducing additional resources to the network in order to improve the performance  

A novel method involving focusing of magnetic particles at the inner wall of a curved microchannel and secondary Dean flow-based exchange of their fluid was investigated. Solution exchange occurred in a hybrid microchip at very high throughput and with unprecedented solution exchange and particle isolation efficiencies of 99.2% and 90%, respectively. © 17CBMS-0001  

the parallel form in adaptive HR filtering is an efficient realization that provides robust stability monitoring with less complexity than that of the direct form. This paper presents an implementation of two line parallel structure employing a real orthogonal transform and real coefficients second-order section as sub filters on FPGA. Architecture that is implemented is in pipeline fashion and it is independent from its building blocks and they may have its own implementation or in other system numbering. In the last section, we compared throughput of our architecture with a Ti DSP (TMS320C3x/4x), the results show that this architecture works better than the DSP  

Transmission Control Protocol (TCP) uses multiple timers to do its work. The most important of these is the retransmission timer. In this paper, the TCP retransmission timer adjustment mechanism is approached from a system point of view and a new mechanism is proposed. A simple recursive system identification algorithm is used to capture both time variant and time invariant Internet behavior. Also a dynamic model-based Round-Trip Time (RTT) predictor was provided. Based on network simulation and real Internet data collection, it was observed that when the retransmission timer is adjusted by the proposed predictor instead of the traditional RTT estimator, performance increased significantly  

In this paper, we focus on a cognitive network scenario, comprised of a WLAN overlaid on a network with time-scheduled primary users. WiMAX is an example of such primary networks. For time-scheduled primary users simple On-Off traffic model with exponential durations is not valid anymore. In this scenario, the cognitive nodes (CNs) hear downlink map (DL-MAP) and thus, know the frequency and time locations of all allocated slots at each frame. Then, cognitive nodes contend with each other in order to transmit their fixed size packets based on IEEE 802.11 MAC protocol. Since the number of empty slots at each frame is variable each packet transmission in cognitive network prolongs a random...