Sharif Digital Repository

Classifying the modulation type of radio signals plays an important role in current and future wireless communication systems. We present a modulation classification method based on convolutional neural networks that reaches high accuracy in face of various channel characteristics and signal conditions without requiring the network to have a very large depth. Experiment results show that the proposed method reaches accurate classification under different system impairment settings that include sampling rate offset, carrier frequency offset, multi-path fading, and additive white Gaussian noise. For instance, compared to a state-of-the-art method, accuracy is improved up to 25% in classifying... 

A novel architecture for efficient time and frequency synchronization, applied to the long-term evolution (LTE) standard, is proposed. For symbol timing, we propose applying a symbol-folding method on top of the sign-bit reduction technique, leading to a novel algorithm for the cyclic prefix-type recognition in LTE. Following the symbol timing, the fractional carrier frequency offset is estimated and compensated using an adaptive gain loop, which allows for a high-accuracy compensation in a short interval. In the frequency domain, for cell search, we propose a sign-bit reduction technique on top of the matched filter method for the primary synchronization signal detection. In addition, we... 

In this article, the authors introduce and propose an overloaded Synchronous Optical Code Division Multiple Access (SOCDMA) based on Unipolar Walsh Code (UWC) for fiberoptic communication systems. Given μ as the number of chips, it is shown that 2L - 2 active users can be supported by the proposed system. In this system the users of the network are categorized into two groups. Users of each group transmit at the same power level but different from the level of the other group's users. Using the UWC properties we propose a simple receiver that cancels multiple-user interference (MUI) completely. Moreover, we obtain the optimal power level of each group in order to minimize the probability of... 

In this article we present an all passive optical iterative interference cancellation method for optical CDMA. We propose the receiver structure based on advanced binary optical logic gates (ABOLGs). Since the performance bottleneck in optical communication systems is the conversion from optical to electronic domains for optical detectors, the interference cancellation has been performed in the optical domain. In incoherent optical communication systems, we have only the positive values for the optical signals. In the proposed system, we bypass the negative values using logic arrays. In the simulations we consider multiple access interference and neglect other sources of noise. Simulation... 

In this work we present a high-throughput, low-complexity design for linear precoding in massive Multiple-Input Multiple-Output (MIMO) systems. Large number of Base Station (BS) antennas in massive MIMO at one hand has caused the performance of linear precoders to be near-optimal and at the other hand has increased their complexity due to the need for the inversion of matrices with large dimensions. To avoid this complexity, approximate inversion methods based on Neumann Series have been proposed. However, in this work, we propose an architecture for Zero Forcing (ZF) precoder based on the Neumann Series approximate inversion that further reduces the complexity by replacing matrix-matrix... 

We propose and demonstrate a novel architecture for four-wave mixing (FWM)-based recognition of spectral amplitude code (SAC) labels in optical packet-switched networks. With a proper code design, a unique FWM idler for each SAC label, referred to as a label identifier (LI), is generated in a nonlinear medium. A serial array of fiber Bragg gratings is then used to reflect the LI wavelengths. Each LI is associated with a unique amount of delay between two optical signals received at two photodiodes (PDs). Label recognition is then achieved by measuring this unique time delay (referred to as the characteristic delay). The main advantages of the proposed method include the following: no... 

We propose a flexible four-wave mixing-based label recognition technique for low-weight spectral amplitude codes in optical packet-switched networks. We experimentally demonstrate label recognition, packet switching, and error-free transmission  

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  

We theoretically and experimentally evaluate a beat interference cancellation receiver (BICR) for direct detection optical orthogonal frequencydivision multiplexing (DD-OFDM) systems that improves the spectral efficiency (SE) by reducing the guard band between the optical carrier and the optical OFDM signal while mitigating the impact of signal-signal mixing interference (SSMI). Experimental results show that the bit-errorrate (BER) is improved by about three orders of magnitude compared to the conventional receiver after 320 km single-mode fiber (SMF) transmission for 10 Gb/s data with a 4-QAM modulation using reduced guard band single-sideband OFDM (RSSB-OFDM) signal with 1.67 bits/s/Hz SE... 

Centralized and cloud computing-based network architectures are the promising tracks of future communication systems where a large scale compute power can be virtualized for various algorithms. These architectures rely on high-performance communication links between the base stations and the central computing systems. On the other hand, massive Multiple-Input Multiple-Output (MIMO) technology is a promising solution for base stations toward higher spectral efficiency. To reduce system complexity and energy consumption, 1-bit analog-to-digital converters (ADCs) are leveraged with the cost of lowering the signal quality. To recover the lost information, more sophisticated algorithms, like...