Ahmed Dooguy Kora

New List Sphere Decoding (LSD) and Iterative Synchronization Algorithms for MIMO-OFDM Detection With LDPC FEC

New sphere decoding and synchronization algorithms for multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems are proposed in this paper. In particular, an iterative list branch-and-bound (BB) algorithm based on the basic BB algorithm is described to obtain a candidate list to compute soft information that is used in the iterative detector. Furthermore, an improved algorithm that uses prior information from the preceding iteration to calculate the lower bound is proposed, and the candidate list is updated every iteration. To obtain a complete modem architecture, we propose an efficient expectation-maximization (EM)-based iterative algorithm for synchronization and channel estimation to interface with the proposed list-sphere-decoding detector, and we investigate the performance of the designed MIMO-OFDM modem on a realistic fading channel. The obtained performance results show that it is possible to practically design a performing MIMO-OFDM modem with high spectral efficiency, i.e., 8 bit/s/Hz with a 4times4 16-QAM MIMO-OFDM system.

Accurate radio coverage assessment methods investigation for 3G/4G networks

Sufficient wireless coverage is necessary to initiate communication with mobile terminals. Mobile network operators must guarantee good radio coverage. Telecommunication regulatory services (TRS) and technicians are assigned the duty of regularly verifying the conformity of the radio coverage at least once a year. However, it is not possible to collect data at every point in a given area. Therefore, TRS have defined a methodology called Random Drive Test Route (RDTR) to measure the provided radio coverage. The objective of this work is to investigate the weakness of the RDTRs that TRS are using. We used ATOLL for radio planning. The coverage prediction is adjusted to actual field measurements. We propose a novel methodology, called Special Drive Test Routes (SDTR) for assessing the radio coverage level of existing and future mobile network technologies. We defined for the SDTR a set of parameters such as minimum number of samples to be collected, the speed range and the route according to the network density in the considered area. We collected the radio coverage channel performances using TEMS Investigation 15.1 (a tool for 3G/4G). The performance results showed that a type of SDTR processes better than RDTR in a given area (open or with obstacles).

Optical orthogonal codes over wavelength division multiplexing in passive optical network communication system and its performance analysis

The paper presents a generalized analytical model of error probability in passive optical network (PON) in which optical orthogonal codes (OOC) and (dense) wavelength division multiplexing (WDM) have been considered. Low cost deployment of these networks is determined by several parameters characterizing this system such as optic transmitters with a relatively large spectrum. The distance between the wavelengths used at the transmitters, the code length, the code weight and the correlation values are taken into account in the formulation of a user communication link performance. This work evaluates the relationship between a network using OOC and WDM parameters in crosstalk situation. Simulations results are provided to validate the model and prove the practical significance of the approach.

Universal Access Index assessment and appropriate optimization strategy

Abstract Information and communications technologies (ICTs) are the basis of globalization evolution. In Africa, particularly, the lightning mobile telephony evolution marked by the implementation of wide-band infrastructures has promoted the evolution of ICT in urban areas. It is important, on the other hand, to underline that this evolution in a country is not observed in a proportional way among the various urban and rural areas. In this context, an overall approach of assessment and optimization of the universal access service index in a country, called Universal Access Index, is proposed in this paper. The optimization approach suggested is based on the implementation of corrective actions related to the Universal Service Access Fund and takes into account the intrinsic technical–economic constraints in every area. To assimilate the updated definition of the International Telecommunications Union on the universal access, two significant indicators representing the voice services and data services were integrated in the modelling approach. This approach is applied to a real case study of the state of Ouaddaï in Chad which makes it possible to highlight its relative simplicity of implementation.

EM Based Channel Estimation and Decoding in OFDM Turbo Blast Detectors

Channel parameter estimation is an important task for coherent detection and constitutes a key challenge in MIMO systems. Turbo-Bell Labs Laboratory Architecture Systems (T-BLAST) with orthogonal frequency division multiplexing (OFDM) can be used to improve communication quality and capacity. This paper proposed a modified expectation maximization (EM) algorithm for T-BLAST systems in frequency selective channels. It is based on a combination of data and pilot based channel estimate with approximated coefficients. These coefficients are obtained by resolving an optimization problem using the Lagrangian multipliers. The algorithm we present takes advantage of the exchange message between the two soft input soft output (SISO) modules of the turbo receiver to attain the best estimation performance. The effectiveness of this technique is demonstrated through the simulation of an OFDM T-BLAST system with two-transmit and three-receive antennas.

Radio access model for universal service

This paper proposes a mathematical model as a decision tool for the choice of radio access solutions adapted to a geographical region through universal access. It integrates the formalism related to engineering radio network access in general as well as financial constraints imposed by the access and universal service funds. Services considered are voice and data services. This approach has helped to derive a general expression set for radio technologies. The coverage and capacity deployment strategy has also been combined to clarify the optimal implementation based on financial constraints. A case study on the Ouaddai region in Chad accompanied by simulations curves for wireless technologies as Wi-Fi, WiMAX and CDMA for example has shown the efficiency of such approach.

Free Space Passive Optical Network

This paper proposes free space passive optical network (FSPON) as a potential candidate of high data rate access network based on optical wireless transmission. FSPON could be considered for indoor as well as outdoor deployments. Pending the progress in FSO range, it is appropriate for short range communication network. The system architecture and network architecture are depicted. A key component for the deployment success is the alignment of the remote terminal equipment’s with the free space optical splitter (FSOS). The main advantages and performances of a user terminal station are discussed. The performance comparison has been made with a simple point to point free space optical link. The FSPON capacity is limited to 6 users at the cost of low modulation scheme and high signal to noise ratio.

Geometric Approach of Blind Channel Estimation

This paper introduces a geometric approach of channel estimation (GACE). It is a blind channel estimation method for multiple input multiple output systems. GACE is based on a two-step geometric approach of source separation (GASS) that outperforms the existing ones. It is an approximated maximum likelihood estimation method which proceeds by the determination of the polyhedral edges tilts representing the matrix parameters. It operates by identifying matrix parameters using a geometric consideration depending on the probabilistic hypothesis of the sources. The simplicity of this method is based on a cloud observation, which is used to determine the edge of parallelogram describing the matrix channel parameters. In this paper, the case of real channel parameters and complex data sources for higher modulation order are performed. The simulation results show the efficiency of the proposed approach.

Assessing the Radio Access Technologies Impact on the Universal Access Index

On all continents, assessing efforts to make information and communication technologies available throughout a territory has become a necessity. As part of universal access and service, this paper aims at assessing the impact of radio access technologies on universal access indicator. To achieve this, a mathematical model has been developed to deal with locality coverage and broadband needs, based on a methodological approach consisting in integrating parameters linked to access index through radio technologies. This approach has been applied to a real case study of the state of Ouaddaï in Chad, which has contributed to highlight its relative simplicity of implementation.

Limits of relays in cascade for wireless optical communications networks

Turbulence is one key limitation factor of wireless optical transmission. In this paper a combined modulation and relays schemes as solutions to extend the free space optics (FSO) range are studied. The objective were to find the limitations in wireless communication range extension. Since turbulence limits the communication link of wireless optical communication, coding and diversity are considered as potential solution to overcome this limitation. Decode and forward (DF) relays and two modulations scheme as pulse position modulation (PPM) and multi pulse position modulation are addressed. It has been estimated the number of relays with efficient performance for PPM and MPPM.