Mohammed Hafez

• PhD
• Research Assistant at University of South Florida

In this paper, we introduce a secure multiple access scheme which exploits the multipath structure of the channel to create a multi-user interference environment. The generated interference enables legitimate users to share time and frequency resources over spatially secure communication links. Utilizing directional modulation, we ensure secrecy fo...

Abstract: Increasing the spectral efficiency was always the motivation behind the evolution of wireless communication systems. Also, due to the widespread usage of wireless systems, securing the transmitted data rises as a main concern nowadays. Hereby, we introduce a scheme that increases the capacity of wireless systems by transmitting multiple i...

We propose a new one-bit feedback scheme with scheduling decision based on the maximum expected weighted rate. We show the concavity of the $2$-user case and provide the optimal solution which achieves the maximum weighted rate of the users. For the general asymmetric M-user case, we provide a heuristic method to achieve the maximum expected weight...

A blind (non-data-aided) SNR estimator using the statistical moments of the received signal is proposed. The proposed envelope-based non-data-aided estimator works for any time-domain Gaussian-distributed signal (e.g., OFDM signals). A closed-form expression for the estimated SNR as a function of the moments of the received signal and the Nakagami-...

Practical multiple-input-multiple-output (MIMO) systems depend on a predefined set of precoders to provide spatial multiplexing gain. This limitation on the flexibility of the precoders affects the overall performance. Here, we propose a transmission scheme that can reduce the effect of mismatch between users’ channels and precoders. The scheme use...

Practical multiple-input-multiple-output (MIMO) systems depend on a predefined set of precoders to provide spatial multiplexing gain. This limitation on the flexibility of the precoders affects the overall performance. Here, we propose a transmission scheme that can reduce the effect of mismatch between users' channels and precoders. The scheme use...

In this paper, a physically secure multi-directions directional modulation scheme is proposed. The scheme provides an adaptive beam-width assignment, where each user is granted a different beam width based on its channel condition. The scheme can be efficiently implemented using a DFT-based algorithm that divides the spatial dimension into orthogon...

We propose a new one-bit feedback scheme with scheduling decision based on the maximum expected weighted rate. We show the concavity of the $2$-user case and provide the optimal solution which achieves the maximum weighted rate of the users. For the general asymmetric M-user case, we provide a heuristic method to achieve the maximum expected weight...

Security is one of the key requirements of wireless communication systems. By exploiting the broadcast nature of wireless medium, a malicious user might attempt to mislead the legitimate nodes, intercept the communication and overhear the private information. In order to combat against such malicious attacks, various encryption using security techn...

Limitations on the wireless communication resources (i.e., time and frequency) introduces the need for another domain that can help communication systems to match the increasing demand on high data transfer rates and quality of service (QoS). By using multiple antennas. Besides, the widespread use of wireless technology and its ease of access makes...

A signal-to-noise ratio estimator for OFDM signals in Nakagami-m fading channels is proposed. This estimator can be used with any signal constellation. It is an envelope-based non-data-aided estimator that makes use of statistical-moments of the received OFDM signals to get an estimate of the SNR in time domain. A mathematical derivation of the est...