Ibrahim A. Ghaleb

Coordinated partial co-channel deployment in two-layer networks

Reducing the interference level between the overlapped femtocells and macrocells is one of the main issues facing femtocells deployment. In this paper, a new coordinated scheduling technique based on femtocell-aware frequency planning is proposed. This technique is based on partial co-channel deployment between the macrocell and the femtocell. The main idea of the proposed scheme is to enable the coordination of the spectrum arrangement schemes between the overlapped macrocells and femtocells based on the requested user traffic, taking into consideration the different Quality of Service (QoS) requirements for the different users applications. The macro base station uses the information about the femtocells used frequency band as well as the information about the requested macro user traffic in making the scheduling decisions so that the cross-layer interference between macrocells and femtocells is reduced. Extensive simulations are conducted to demonstrate the performance improvements of the proposed scheme in terms of the macro user blocking probability and the throughput.

Femtocells interference avoidance using Femtocell Identification

Femtocells are cost-effective means of providing indoor coverage in LTE cellular system. Furthermore, their decreased cell sizes provide improved cell capacity through increased spatial reuse. However, co-channel interference is one of the most critical challenges facing LTE femtocell deployment. This paper proposes to use Femtocell Identification (FID) approach to avoid co-channel interference between neighbour femtocells without operator intervention. Each femtocell has to cognitively detect other femtocells FID and their frequency allocation from the network environment and allocate the unoccupied resource blocks for interference avoidance. FID is designed such that each resource blocks assignment to a femtocell has a unique FID frequency allocation that distinguishes this assignment. Each femtocell through its FID allocation sends a message to the nearby femtocells. The simulation results show that the FID detection can be achieved even at low SNR region.

A new fuzzy adaptive perceptual image coding system

A new adaptive, perceptual image coding system in the framework of fuzzy logic is proposed. The image is decomposed into 8/spl times/8 blocks that are then subjected to the discrete cosine transform (DCT). The image DCT blocks are then classified using the fuzzy c-medians (FCMED) clustering algorithm into four fuzzy classes. Coding bits are then adaptively and perceptually allocated to the DCT coefficients in each class. DCT coefficients are then normalized, optimally quantized, coded, and transmitted, accompanied by their overhead information over a channel. The performance of the proposed system is evaluated using the peak signal-to-noise ratio (PSNR) measure and a just noticeable distortion (JND) based perceptual measure.

A modified joint processing technique for Coordinated Multi-Point Transmission in LTE-advanced

Coordinated Multi-Point Transmission (CoMP) was presented in LTE-Advanced standard to enhance the LTE performance and reduce the effect of intercell interference. In the downlink, there are two CoMP techniques used; one of these techniques is the Joint Processing (JP) technique. In this paper, a modified-JP technique is proposed. In the conventional JP, the second best base station (BS) is used to enhance the quality of the user signal while in the modified-JP, the second best BS is used so that the users are prevented from service blocking. Extensive simulations are conducted to illustrate the benefits achieved by applying the modified-JP techniques compared to the conventional JP one.

The enhanced performance of combined multicarrier and CDMA techniques in multipath fading channels

The enhanced performance of combined multicarrier and code division multiple-access techniques in multipath fading mobile communication channels is investigated in this paper. In particular, computer simulation is used for the comparison between three multiuser multicarrier CDMA modulation techniques, including OFDM, multicarrier code division multiple-access (MC-CDMA) and multicarrier-direct sequence (MC-DS-CDMA). The point of comparison, here, is the performance of these different schemes in the presence of a Rayleigh fading channel. Both slow and fast fading is considered in the simulations. It is required to investigate which system gives the best performance if different path channels with different values for the Doppler shift are taken into consideration. The paper also includes a detailed review of the three considered systems and their properties, advantages and limitations as well as a description of the fading channel model.

An Interference-Aware Cognitive Radio UWB (IA-CR-UWB) system using Eigen pulse shaping

To protect the performance of the UWB system against undesired interference and to avoid deterioration of the coexisting systems, special transmit and receive (T-R) pulses are designed. In this paper, we propose a Interference Aware Cognitive) Radio (IA-CR) Ultra Wide-Band (UWB) system which will have superior performance over noncognitive ultra wide band systems. A modified Eigen-analysis method is used to design the UWB pulse shapes and the T-R filters. This method allows the imposing of sharp spectrum nulls at the frequency bands of the interferers. In practical scenarios, when the interference activity is not static, static transmit and receive filters will have degraded performance. With our proposed IA-CR capability, the UWB system performs spectrum sensing to pick the most suitable transmit and receive filters that will minimize its error rate performance. The coexistence of a practical UWB system with other narrow band systems as IEEE 802.11 wireless LAN systems operating at 5.2 GHz and radio location services operating at 8.5 GHz is considered in this paper. The proposed IA-CR UWB system is shown to outperform static interference rejection systems. The simulations are performed using the system parameters and channel models for the IEEE 802.15.4a UWB system.

A new finite alphabet based blind channel estimation algorithm for OFDM systems

A new blind channel estimation algorithm is proposed based on the finite alphabet property of the transmitted symbols and the correlation between the channel attenuations at the adjacent subcarriers. The new method preserves the classical OFDM transmitter structure with cyclic prefix (CP) used in all standardized multicarrier systems (such as DAB, IEEE802.Ha, Hiperlan/2, etc.) as well as the newly proposed OFDM with zero padding (ZP). The new method proves via simulations to provide an unbiased channel estimates and its performance is independent of the channel zero locations.

Multiple Routing Configurations for Datacenter Disaster Recovery Applicability and Challenges

Cloud services based on data center networks are becoming very important. Data centers host computing and storage resources, and these resources are served to customers through a network of data centers. Protecting such a network from disasters like earthquakes, hurricanes and terrorist attacks is crucial. In this paper, we propose the use of multiple routing configurations (MRC) IP fast reroute recovery process for data center disaster recovery. A demonstration of how this recovery scheme can be applied is shown. Also, we discuss the impact of the MRC recovery process on the post failure load distribution over network links and how this impact can be minimized. We propose a manual technique to minimize the impact of MRC and compare it to an automatic technique called modified MRC. Both the advantages and disadvantages of the two techniques are outlined. We conclude that a newer technique is needed that overcome the above mentioned disadvantages. The new technique should not manipulate link weights to achieve good load distribution. Our proposed new technique will implement unequal weight load balance inside open shortest path first (OSPF) and it is used with MRC. The new technique achieves good load distribution while overcoming all disadvantages.

A New Multirate Multiple-Access Technique Based on the Combination of Space-Time Coding and Wavelet Modulation

A new multirate multiple-access technique based on the combination of space-time coding and wavelet modulation is presented in this paper. The proposed technique makes use of the good properties of space-time coding (STC) technique with multiple transmitting and receiving antennas which has enhanced performance in fading channels. However, STC was originally proposed for single user systems. To generalize it to multi-user systems, we propose to combine STC with wavelet modulation to provide both orthogonality among different users as well as multi-rate transmission capability in a way similar to wavelet-packet division multiplexing (WPDM) systems. This technique provides a high multiple-access interference rejection performance. Simulation show its good performance in Rayleigh fading channels

Improving channel estimation using a modified root selection algorithm with model order estimation in OFDM systems

In this paper a new algorithm for blind channel estimation in orthogonal frequency division multiplexing (OFDM) systems is described. The proposed algorithm uses a modification to the root-selection algorithm for channel estimation and a generalized Akaike information criterion to estimate the channel length. The new algorithm is termed, the modified root-selection (MRS) algorithm. This algorithm together with the channel order estimation effectively reduces the signal space of the estimator, and hence improves the estimation performance as demonstrated using computer simulations. The proposed MRS with channel estimation algorithm has a 5 dB lower mean square error in channel estimation when compared to the conventional RS approach which translates to approximately 0.5 dB improvement in SNR at receiver. In addition, the proposed modification to the RS algorithm results in a more computationally efficient algorithm. It is applicable not only to standard OFDM transmitters with cyclic prefix, but also to the recently proposed zero padded OFDM transmissions