Husameldin Mukhtar

Mitigation of DHCP starvation attack

DHCP starvation attack is an attack that targets DHCP servers whereby forged DHCP requests are crafted by an attacker with the intent of exhausting all available IP addresses that can be allocated by the DHCP server. Under this attack, legitimate network users can be denied service. In this paper, we describe the seriousness of the attack and survey and evaluate existing solutions designed to mitigate such an attack. In addition, we propose a novel mitigation solution. Our solution overcomes the limitations of existing solutions in terms of performance, effectiveness, and flexibility. Our solution is based on dynamic fair allocation of IP addresses and is suitable for unshared and shared (wireless) access networks. We study and analyze the proposed mitigation technique through numerical examples and simulations. Furthermore, simulation results show that our proposed solution is far superior in mitigating DHCP starvation attack when compared to other existing techniques such as fixed allocation and DHCP request rate detection.

Low Complexity Power Optimization Algorithm for Multimedia Transmission Over Wireless Networks

This paper considers the problem of transmit power optimization for multimedia applications in continuous high-speed transmission over wireless networks. The power optimization process is developed by noting that some performance metrics such as throughput, delay and peak signal-to-noise ratio (PSNR) for particular systems with hybrid automatic repeat request (HARQ) may exhibit a staircase behavior. In such scenarios, the corresponding metric remains fixed for a wide range of signal-to-noise ratios (SNRs). Consequently, the transmit power can be reduced significantly while the relevant metric remains almost unchanged. The obtained results reveal that invoking power optimization algorithms can achieve a significant power saving of about 80% for particular scenarios. The system considered in this work is a truncated HARQ with turbo product codes (TPC) and parallel concatenated convolutional codes (PCCC). Chase combining is also used to combine the retransmitted packets with the original transmission. An efficient semi-analytical model is developed to obtain the system throughput in additive white Gaussian noise (AWGN) and Rayleigh fading channels. The obtained results also show that using the throughput, delay or PSNR as performance metrics provides equivalent power saving results.

Adaptive Hybrid ARQ System Using Turbo Product Codes with Hard/Soft Decoding

The bit error rate (BER) performance of turbo product codes (TPC) has been considered extensively in the literature. However, other performance metrics such as throughput can be more informative in particular systems. In this letter, the throughput performance of hybrid automatic repeat request (HARQ) is considered using TPC with iterative hard and soft decision decoding. Monte Carlo simulation and semi-analytical solutions are developed to evaluate the throughput of HARQ-TPC system for a wide selection of codes. The obtained results reveal that the coding gain advantage of the soft over hard decoding is reduced significantly when throughput is adopted as the performance metric, and it actually vanishes completely for some codes. When adaptive coding is used, the soft decoding advantage is limited to about 1.4 dB.

An Adaptive Hierarchical QAM Scheme for Enhanced Bandwidth and Power Utilization

Hierarchical quadrature amplitude modulation (HQAM) enables unequal priority transmission through the use of non-uniformly spaced constellations. In this paper, we propose an adaptive HQAM (A-HQAM) scheme where the ratios between the constellation distances are regularly adjusted based on the channel condition with the objective of maximizing the transmission efficiency. The source bit stream is divided into multiple sub-streams which are simultaneously transmitted, each on a different priority level. When using A-HQAM, the high priority sub-stream maintains an acceptable bit error rate performance over all channel conditions. As the channel condition improves, the required protection for the high priority sub-stream is reduced allowing for increasing the protection level of lower priority sub-streams. Hence, the number of sub-streams with acceptable BER performances is incrementally increased as the channel condition improves. Analysis and simulation results show that the proposed A-HQAM not only enhances the transmission efficiency but also provides reduced peak to average power ratio (PAPR). The proposed scheme offers reduced complexity by using one constellation size, unlike conventional adaptive schemes which require the use of several constellation sizes. Moreover, a practical A-HQAM implementation is presented which enables the receiver to successfully demodulate the received signal without knowing the varying transmission parameters.

CRC-Free Hybrid ARQ System Using Turbo Product Codes

This paper presents a hybrid automatic repeat request (HARQ) system using turbo product codes (TPC). The inherent word-error detection capability of TPC is exploited to replace the conventional cyclic redundancy check (CRC) used for packet error detection in conventional HARQ systems. Therefore, TPC are used for joint bit error correction and packet error detection. Consequently, the HARQ system efficiency is improved by increasing the system throughput when short packets are transmitted or by reducing the computational complexity/delay when the packets transmitted are long. Monte Carlo simulation results reveal that the CRC-free TPC-HARQ system consistently provides equivalent or higher throughput than CRC-based HARQ systems. Moreover, numerical results show that TPC self-detection has lower computational complexity than CRC detection, particularly for TPCs with high code rates. In particular scenarios, the relative complexity of the self-detection approach with respect to popular CRC techniques is about 0.3%.

An occupancy-based and channel-aware multi-level adaptive scheme for video communications over wireless channels

Video streaming over wireless channels is challenged with the time-varying nature of the underlying channels and the stringent requirements of video applications. In particular, video streaming has strict requirements on bandwidth, delay, and loss rate while wireless channels are dynamic and error-prone by nature. In this article, we propose a novel multilevel adaptive scheme that is designed to mitigate the challenges facing video streaming over unreliable channels. This is done while preventing potential playback discontinuities and guaranteeing a graceful degradation of the rendered video quality. Scalable video coding, adaptive modulation, and adaptive channel coding are integrated to achieve the objectives of the proposed scheme. If adaptive modulation and channel coding are not enough to guarantee the on-time delivery of decodable video frames, we adopt scalable coding. Simulation results show that the proposed adaptive scheme achieves an improvement of about 2.5 dB in the peak signal-to-noise ratio over a nonadaptive one. In addition, the proposed scheme reduces the number of starvation instances by 50 and 90% in the cases of Stop-and-Wait and Go-Back-N automatic repeat requests, respectively.

Hybrid ARQ with partial retransmission using turbo product codes

This paper presents a hybrid automatic repeat request (HARQ) scheme based on turbo product codes (TPC) error correction and self-detection. The TPC inherent error detection is used as an alternative to the conventional cyclic redundancy check (CRC) process and is utilized to implement partial retransmission. The proposed HARQ system attempts to identify the location of errors within the TPC codeword. Consequently, only parts of the codeword which are declared erroneous are retransmitted. The performance of the proposed TPC-based HARQ is evaluated with hard and soft decision decoding in additive white Gaussian noise (AWGN) channels. Packet combining and adaptive channel coding are also considered. The obtained results show that the proposed HARQ scheme provides higher or equivalent throughput when compared to CRC-based HARQ in most test scenarios.

A Multi-Level Adaptive Scheme for Multimedia Transmission over Wireless Channels

Delivery of multimedia contents over unreliable channels poses several challenges. In particular, video streaming has strict requirements on bandwidth, delay, and loss rate. In this paper, we propose the integration of several approaches to overcome these challenges. These approaches are adaptive modulation, adaptive channel coding, adaptive playback, and bitstream switching. The proposed adaptive scheme significantly improves the effective channel bitrate. It also accommodates variations in the channel condition and subsequently ensuring uninterrupted video playback.

Turbo Product Codes: Applications, Challenges, and Future Directions

Turbo product codes (TPCs) have been integrated in several practical applications, and hence, they have been considered widely in the literature where the main aim is improving the error performance and/or reducing the computational and implementation complexity. This paper presents a comprehensive survey of the research that focuses on TPCs in terms of encoding, decoding, error performance, and complexity. Moreover, this paper also considers the advantages of integrating TPCs in hybrid automatic repeat request systems where power optimization becomes very efficient and the complexity can be reduced using the unique properties of TPCs such as error self-detection capabilities. Based on the surveyed literature, the pivotal open research issues in TPCs are presented and discussed.

On the performance of adaptive HARQ with no channel state information feedback

This paper presents an adaptive power control scheme for hybrid automatic repeat request (HARQ) systems with no channel state information feedback. The power control process is developed by noting that the throughput of particular HARQ systems may exhibit a staircase behavior. In such scenarios, the throughput remains fixed for a wide range of signal-to-noise ratios (SNRs). Consequently, the transmit power can be reduced significantly while the throughput remains almost unchanged. The obtained results reveal that invoking power optimization algorithms can achieve a significant power saving of about 80% for particular scenarios. The system considered in this work is a truncated HARQ with turbo product codes (TPC). Chase combining is also used to combine the retransmitted packets with the original transmission. HARQ acknowledgment/negative acknowledgment (ACK/NACK) feedback is used to estimate the packet error rate from which the system throughput is computed.