Sharif Digital Repository

In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quantum-classical dense-wavelength-division-multiplexing systems. The transmission of intense classical signals alongside weak quantum ones on the same fiber introduces some crosstalk noise, mainly due to Raman scattering and non-ideal channel isolation, that may severely affect the performance of quantum key distribution systems. We examine the conventional methods of suppressing this crosstalk noise, and enhance them by proposing an appropriate channel allocation method that reduces the background crosstalk effectively. Another approach proposed in this paper is the usage of orthogonal frequency... 

An efficient, easy to implement method for OFDM and DMT Peak to Average Power Ratio (PAPR) reduction is proposed based on constellation extension. A PAPR reduction of more than 5 dB at clip rate of 10-5, is achieved with no rate loss and improved noise margin with low complexity. Various versions of the proposed method have been studied and compared in terms of PAPR reduction, complexity and average power, with each other and earlier methods. © Springer-Verlag Berlin Heidelberg 2002  

The vertical plane launching ray tracing method has been applied for a real urban scenario and the delay characteristics of received signals in the overall coverage area have been extracted. Using these parameters, an equivalent channel impulse response (ECIR) has been introduced for the overall coverage area. For an orthogonal frequency division multiplexing system, the optimum guard interval, which maximises the number of points with symbol error rate less than a threshold, has been simulated. Using the defined ECIR, the optimum guard interval could be analytically extracted  

Clipping and filtering is a well-known technique used at the transmitter side of Orthogonal Frequency Division Multiplexing (OFDM) systems to reduce the Peak to Average Power Ratio (PAPR). In this paper, the extension of clipping and filtering to spatially multiplexed OFDM systems will be introduced. In the proposed scheme, the channel coding and clipping operations are performed at the transmitter branches independently. Based on this scheme, a receiver is proposed, which is based on the detection method of Nulling Cancellation (NC). In this method, the layer with the minimum average noise power over all subcarriers is selected and an iterative method is used to compensate for its clipping... 

The ways in which an innovation (e.g., new behaviour, idea, technology, product) diffuses among people can determine its success or failure. In this paper, we address the problem of diffusion of innovations over multiplex social networks where the neighbours of a person belong to one or multiple networks (or layers) such as friends, families, or colleagues. To this end, we generalise one of the basic game-theoretic diffusion models, called networked coordination game, for multiplex networks. We present analytical results for this extended model and validate them through a simulation study, finding among other properties a lower bound for the success of an innovation. While simple and leading... 

Two gains play key roles in recently developed multiple-input-multiple-output (MIMO) wireless communication systems: 'spatial diversity' gain and 'spatial multiplexing' gain. The diversity gain (DG) refers to the capability to decrease the error rate of the MIMO channel, whereas the multiplexing gain (MG) implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the DG) and increasing data rate (via an increase in the MG). On the other hand, recently, MIMO radars have attracted much attention for their superior... 

It is proved that the out-of-phase autocorrelation of a well-known class of multiplexed sequences for cryptographic and spread spectrum applications is necessarily high for relatively small values of the phase shifts. Related design criteria for the multiplexer generator including the use of full positive difference sets are proposed. By generalizing the classical occupancy problem, higher order statistical weaknesses of multiplexed sequences are also established. © 2002 Elsevier Science (USA)  

In this article we present a new scheme to support multirate and multi-quality-of-service transmission in passive optical networks based on a hybrid wavelength-division multiplexing/optical code-division multiplexing scheme. The idea is to use multilength variable-weight optical orthogonal codes as signature sequences of a hybrid WDM/OCDM system. To provide the requested classes of service, the code weight and code length of MLVW-OOCs are designed based on the characteristics of the requested classes of service. In order to mitigate multiple access interference, we propose to utilize a multilevel signaling technique and interference remover structure based on advanced optical logic gate... 

In this paper, we propose a new scheme to provide multiservice transmission on generalized multiprotocol label switching (GMPLS) networks using optical code-division multiplexing (OCDM) in each wavelength of a wavelength-division multiplexing system. To provide multiservice transmission in a typical GMPLS network, we propose to classify the fiber bandwidth into a number of waveband and consider the wavelengths of each waveband for a specific class-of-service such that the corresponding codes to be used are designed based on the characteristics of the class-of-service. The traffic behavior of the network is examined using Erlang's model, and the probability density functions (PDF) of the... 

In this paper, we investigate the performance of orthogonal frequency division multiplexed quantum key distribution (OFDM-QKD) in an integrated quantum-classical wavelength-division-multiplexing system. The presence of an intense classical signal alongside the quantum one generates Raman background noise. Noise reduction techniques should, then, be carried out at the receiver to suppress this crosstalk noise. In this work, we show that OFDM-QKD enables efficient filtering, in time and frequency domains, making it an attractive solution for the high-rate links at the core of quantum-classical networks  

We propose orthogonal frequency-division multiplexing (OFDM), as a spectrally efficient multiplexing technique, for quantum key distribution at the core of trusted-node quantum networks. Two main schemes are proposed and analyzed in detail, considering system imperfections, specifically, time misalignment issues. It turns out that while multiple service providers can share the network infrastructure using the proposed multiplexing techniques, no gain in the total secret key generation rate is obtained if one uses conventional passive all-optical OFDM decoders. To achieve a linear increase in the key rate with the number of channels, an alternative active setup for OFDM decoding is proposed,... 

This paper addresses the problem of frame detection in orthogonal frequency-division multiplexing (OFDM) systems. Using fourth-order statistics, a novel approach is presented for detection of a preamble composed of two identical parts in the time domain. First, it is demonstrated that sufficient statistics for detection of a periodic preamble do not exist, and conventional methods are not optimal. Next, looking at the detection of a preamble from the viewpoints of hypothesis testing and classification, a new method is presented based on the idea that fourth-order statistics can increase class separability (between-class distance) and consequently improve detection performance. It is proven... 

In this paper, the problem of coarse timing synchronization in orthogonal frequency-division multiplexing (OFDM) systems is investigated, and two new timing metrics with better performance are presented. The new metrics take advantage of two novel differential normalization functions that are based on the fourth-order statistics and are designed depending on the value of carrier frequency offset (CFO). The proposed timing metrics are theoretically evaluated using two different class separability criteria. It is shown that the new schemes considerably increase the difference between the correct and wrong timing points in comparison with previous methods. The computational complexity of the... 

Abstract Reducing the NoC power is critical for scaling up the number of nodes in future many-core systems. Most NoC designs adopt packet-switching to benefit from its high throughput and excellent scalability. These benefits, however, come at the price of the power consumption and latency overheads of routers. Circuit-switching, on the other hand, enjoys a significant reduction in power and latency of communication by directing data over pre-established circuits, but the relatively large circuit setup time and low resource utilization of this switching mechanism is often prohibitive. In this paper, we address one of the major problems of circuit-switching, i.e. the circuit setup time... 

We propose and experimentally demonstrate a receiver structure for direct detection optical orthogonal frequency-multiplexing systems that improves the spectral efficiency by reducing the guard band between the carrier and the OFDM signal while mitigating signal-signal mixing interference  

Interconnect networks employing wormhole-switching play a critical role in shared memory multiprocessor systems-on-chip (MPSoC) designs, Multicomputer systems and System Area Networks. Virtual channels greatly improve the performance of wormhole-switched networks because they reduce blocking by acting as "bypass" lanes for non-blocked messages. Capturing the effects of virtual channel multiplexing has always been a crucial issue for any analytical model proposed for wormhole-switched networks. Dally [8] has developed a model to investigate the behaviour of this multiplexing which have been widely employed in the subsequent analytical models of most routing algorithms suggested in the... 

A novel packet-based photonic label switching router for a multirate all-optical switch using generalized multiprotocol label switching is proposed. The idea is based on using optical code-division multiple access (OCDMA) as multiplexing technique and treating OCDMA codes as labels. The system can coexist with current wavelength division multiplexing systems on the same infrastructure. The concept of switch fabric is introduced. Label processing and label swapping functionalities of the switch are discussed. In-depth analyses are made for spectrally phase-encoded OCDMA (SPE-OCDMA) due to its capabilities of supporting high data rates, large code cardinality, and its secure transmission.... 

Orthogonal frequency division multiplexing (OFDM) is one of the widely used multiplexing techniques in wireless communications and especially cognitive radio networks. One of the key challenges of this technique is its high peak to average power ratio (PAPR) of the transmitted signal. This paper, introduces a new approach to PAPR reduction of OFDM signals using harmony search algorithm (HSA) based on the partial transmit sequence (PTS) method. The simulation results demonstrate that the proposed algorithm has better PAPR reduction performance as an accurate and low complexity approach for OFDM systems