Mohammed Abd-Elnaby

Efficient contention-based MAC protocol using adaptive fuzzy controlled sliding backoff interval for wireless networks

Efficient medium access control (MAC) protocol should be able to provide high throughput performance and efficient share of the medium. In this paper, a new contention-based MAC protocol based on adaptive fuzzy controlled sliding backoff interval is proposed to maximize the channel throughput and improve the fairness of random access channels. In the proposed protocol, every node that experiences packet collisions increases its sliding backoff interval (SB) range by a forward sliding factor (FSF). In case of successful transmission the node decreases its SB range by a backward sliding factor (BSF). Forward and backward sliding factors are controlled by the channel offered traffic using a fuzzy controller. Furthermore, the operation of the proposed backoff algorithm does not depend on the knowledge of the number of active nodes. A computer simulation is developed using MATLAB to evaluate the performance of the proposed algorithm and compare it with other backoff schemes. Simulation results show that the proposed algorithm significantly outperforms other backoff schemes, such as binary exponential backoff (BEB) and the fast collision resolution (FCR) scheme. It provides a significant efficient fair sharing performance improvement which converges to the ideal fairness performance while providing high throughput performance.

Self-organised dynamic resource allocation scheme using enhanced fractional frequency reuse in long term evolution-advanced relay-based networks

Inter-cell interference (ICI) from neighbouring cells is a major challenge that severely degrade the performance of cellular mobile communication systems, particularly for cell-edge users. An efficient technique to mitigate ICI is interference coordination. The most common ICI coordination technique is fractional frequency reuse (FFR). Furthermore in order to effectively improve cell-edge performance in terms of coverage extension and throughput, the third generation partnership project introduced the use of relays in long term evolution-advanced (LTE-A) networks. This paper presents a self-organized dynamic resource allocation scheme using enhanced FFR (SODRA-EFFR) which dynamically allocates resources to cell inner and outer regions in LTE-A relay-based networks. In this scheme, the downlink power and frequency resources allocation for cell inner and outer regions and the outer regions frequency resources allocation between evolved nodeBs (eNBs) and relay stations in each cell are dynamically allocated based on coordination between neighbouring eNBs and relay stations through LTE-X2 interfaces. The performance of the proposed scheme without and with relays is evaluated using MATLAB simulations and compared with different reference resource allocation schemes. Simulation results show that the proposed scheme improves cell-edge performance and achieves high degree of fairness among users’ equipment (UEs) compared with reference resource allocation schemes.

Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.

Fair Delay Optimization-based Resource Allocation Algorithm for Video Traffic over Wireless Multimedia System

The major issue related to the realization of wireless multimedia system is the design of suitable medium access control (MAC) protocol. The design challenge is to maximize the utilization of the limited wireless resources while guaranteeing the various quality of service requirements for all traffic classes especially for the stringent real-time constraint of real time variable bit rate (rt-VBR) video service. In this paper a novel resource allocation algorithm for video traffic is proposed. The proposed allocation algorithm aims to provide fair delay for video packets by minimizing the delay difference among transmitted video packets. At the same time it adaptively controls the allocated resources (bandwidth) for video traffic around the corresponding average bit rate, and has the ability of controlling the quality of service (QoS) offered for video traffic in terms of packet loss probability and average delay. A minimized control overhead of only two bits is needed to increase the utilization efficiency. Simulation results show that the proposed algorithm achieves very high utilization and provides nearly fair delay among video packets. Its efficiency is also investigated under traffic integration condition with voice and data traffic to show that the QoS offered to video traffic does not change in the presence of the highest priority voice traffic while data traffic increases the channel utilization to 98% by using the remaining bandwidth after voice and video traffic while a good QoS is offered to voice and data traffic.

Efficient compression and reconstruction of speech signals using compressed sensing

Speech compression is the process of compressing a speech signal to reduce its size for easy transmission. This paper investigates two techniques to compress the speech signal and reconstruct it. The first technique is based on a decimation process. This process reduces the sampling rate and consequently saves time, storage capacity, and cost. The decimation process comprises a low-pass filtering stage followed by a down-sampling stage. The recovery of the original speech signal from the decimation-based compressed signal can be accomplished using the inverse interpolation techniques, namely, the maximum entropy and the regularization methods. The second technique is based on the concept of compressed sensing (CS). CS has a very vital role in signal compression and reconstruction because of its ability to sample the signal at a rate smaller than the Nyquist rate. It depends on non-adaptive linear projections that save the structure of the signal and the reconstruction of the original signal is performed by solving a linear optimization problem. Finally, the quality of the recovered signal is assessed using signal-to-noise ratio (SNR), spectral distortion (SD), and correlation coefficient (cr).

Cl. Subcarrier Gain basedPower Allocation in Multicarrier Systems

The Orthogonal Frequency Division MuItiplexing (OFDM) transnussIOn scheme is the optimum version of the muIticarrier transmission scheme which has the capability to achieve high data rate transmission. The key issue of OFDM system is the allocation of bit and power over number of subcarriers. In this paper, a new power allocation algorithm based on subcarrier gain is proposed to maximize the bit rate. For OFDM system, the subcarrier gain based power allocation (SGPA) algorithm is addressed and compared with the standard greedy power allocation (GPA). We demonstrate by analysis and simulation that the proposed algorithm greatly reduces the computational complexity and achieves near optimal performance in maximization the bit rate over number of subcarrier.

A novel fair random access scheme with throughput optimization using fuzzy controller for wireless systems

Good backoff algorithms should be able to achieve high channel throughput while maintaining fairness among active nodes. In this paper, we propose a novel backoff algorithm to improve the fairness of random access channels, while maximizing channel throughput. The mechanism of the proposed backoff algorithm uses backoff delay (retransmission delay) and channel-offered traffic to dynamically control the backoff interval, so that each active node increases its backoff interval in the case of collision by a factor which exponentially decreases as the backoff delay increases, and decreases its backoff interval in the case of successful transmission by a factor which exponentially decreases as the backoff delay of previous retransmission attempts increases. Also, the backoff interval is controlled according to the channel offered, traffic using a fuzzy controller to maximize channel throughput. Furthermore, the operation of the proposed backoff algorithm does not depend on knowledge of the number of active nodes. A computer simulation is developed using MATLAB to evaluate the performance of the proposed backoff algorithm and compare it with the binary exponential backoff (BEB) scheme, which is widely used owing to its high channel throughput, while its fairness is relatively poor. It is shown that the proposed backoff algorithm significantly outperforms the BEB scheme in terms of improving the performance of fairness, and converges to the ideal performance as the minimum backoff interval increases, while achieving high channel throughput.

Near optimal fair delay based resource allocation for video traffic over wireless multimedia system

The major issue related to the realization of wireless multimedia system is the design of suitable medium access control (MAC) protocol. The design challenge is to maximize the utilization of the limited wireless resources while guaranteeing the various quality of service requirements for all traffic classes especially for the stringent real-time constraint of real-time variable bit rate (rt-VBR) video service. In this paper a novel resource allocation algorithm for video traffic is proposed. The proposed allocation algorithm aims to provide fair delay for video packets by minimizing the delay difference among transmitted video packets. At the same time it adaptively controls the allocated resources (bandwidth) for video traffic around the corresponding average bit rate, and has the ability of controlling the quality of service (QoS) offered for video traffic in terms of packet loss probability and average delay. A minimized control overhead of only two bits is needed to increase the utilization efficiency. Simulation results show that the proposed algorithm achieves very high utilization and provides nearly fair delay among video packets. Its efficiency is also investigated under traffic integration condition with voice and data traffic to show that the QoS offered to video traffic does not change in the presence of the highest priority voice traffic while data traffic increases the channel utilization to 98% by using the remaining bandwidth after voice and video traffic while a good QoS is offered to voice and data traffic.

Spectrum Allocation for Enhanced Cross-Tier Interference Mitigation with Throughput Improvement for Femtocells in a Heterogeneous LTE Cellular Network

Femtocells are the solution to improve cellular system capacity in indoor coverage. In two-tier networks, co-channel interference is a serious problem. In this paper, an efficient spectrum allocation scheme is proposed to improve signal to interference plus noise ratio (SINR) and the throughput for femtocell users. The proposed spectrum allocation scheme is based on reducing the cross-tier interference by allocating the best group of the available resource blocks (RBs) that achieve minimum interference level for femtocell users. The soft frequency reuse scheme is considered for long term evolution cellular system due to its ability to decrease the inter-cell interference and enhances the throughput for macrocells. Simulation results show that the proposed spectrum allocation scheme efficiently increases the SINR for femtocell users and enhances both the femtocell throughput and the total cell throughput compared to the conventional random allocation scheme. In addition, it is shown that the best performance of proposed scheme in terms of highest SINR and highest throughput is achieved by allocating only one-third of the available RBs for femtocell.

Efficient coding techniques for ADO-OFDM in IM/DD systems

Optical wireless communication (OWC) is an age-long technology, which is based on optical data transmission through free space, and it can be implemented in both indoor and outdoor applications. Asymmetrically clipped DC-biased optical orthogonal frequency division multiplexing (ADO-OFDM) is a modulation scheme that can be utilized in indoor OWC systems. It is based on transmitting DC-biased optical OFDM (DCO-OFDM) for even-frequency subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) for odd-frequency subcarriers. The ADO-OFDM exhibits better optical power performance than those of the conventional ACO-OFDM and DCO-OFDM. The main disadvantage of ADO-OFDM is the clipping noise, which mainly affects the even subcarriers. So, in this paper, convolutional and turbo coding techniques are investigated to improve the bit error rate performance of the ADO-OFDM over Additive white Gaussian noise and diffuse channels. Simulation results show that the proposed coded ADO-OFDM using convolutional and turbo coding techniques achieves significantly lower BERs compared to that of the uncoded ADO-OFDM. In addition, turbo-coded ADO-OFDM gives the best BER performance.