Roshdy Hafez

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Verified

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• Doctor of Philosophy
• Profssor emeritus at Carleton University

In 5G Ultra-Dense Networks, a distributed wireless backhaul is an attractive solution for forwarding traffic to the core. The macro-cell coverage area is divided into many small cells. A few of these cells are designated as gateways and are linked to the core by high-capacity fiber optic links. Each small cell is associated with one gateway and all...

In 5G Ultra-Dense Networks, a distributed wireless backhaul is an attractive solution for forwarding traffic to the core. The macro-cell coverage area is divided into many small cells. A few of these cells are designated as gateways and are linked to the core by high-capacity fiber optic links. Each small cell is associated with one gateway and all...

In 5G Ultra-Dense Networks, a distributed wireless backhaul is an attractive solution for forwarding traffic to the core. The macro-cell coverage area is divided into many small cells. A few of these cells are designated as gateways and are linked to the core by high-capacity fiber optic links. Each small cell is associated with one gateway and all...

In 5G Ultra-Dense Networks, a distributed wireless backhaul is an attractive solution for forwarding traffic to the core. The coverage area is divided into many small cells. A few of these cells are designated as gateways, which are linked to the core by high capacity fiber optic links. Each small cell is associated with one gateway and all small c...

An Ultra-Dense Network (UDN) is foreseen as a key element of 5G, where small cells operating at millimeter-wave frequencies will be placed in hotspots to accommodate extreme traffic volumes. A fully distributed wired backhaul is not feasible in these UDN deployments because it is not practical to connect each small cell to the core over fiber. A li...

This paper presents a concise overview of current public safety communication networks known as LMR (Land Mobile Radio) and emerging LTE- (Long-Term Evolution-) based broadband public safety networks to be deployed in the 700 MHz band. A broadband nationwide network for public safety based on LTE is inevitable where shared or dedicated types of LTE...

To make the most efficient use of scarce bandwidth, channel assignment methods for wireless mesh networks (WMNs) should try to minimize the number of frequency channels used while achieving maximum network throughput. Beamforming is a well-known technique that improves spatial reuse in wireless networks. However, there are no channel assignment met...

In this paper we study the performance of the double orthogonal space-time block code (DOSTBC) scheme. In the DOSTBC, the transmitter simultaneously transmits its symbols using two OSTBC systems. In this paper, we consider the case where the receiver uses minimum mean square error detection to estimate the transmitted symbols. We derive an approxim...

Communication links connect pairs of wireless nodes in a wireless network. Links can interfere with each other due to their proximity and transmission power if they use the same frequency channel. Given that a frequency channel is the most important and scarce resource in a wireless network, we wish to minimize the total number of different frequen...

Reducing the energy consumption in wireless networks while maintaining the promised Long Term Evolution (LTE) high data rate has become a significant problem for network providers. To tackle these two conflicting objectives, this paper proposes to use Pico-eNBs in conjunction with a centralized switch on/off algorithm to create an adaptive radio co...

This paper presents a study of the mutual interference between a Macro cell and a Pico cell within LTE-A (Long Term Evolution — Advanced) framework. It is assumed that the Macro cell and the Pico cell share the same frequency channel and only the downlink (DL) performance is studied. In this paper, we introduce the idea that a Pico cell located wit...

Communication links in multi-radio multichannel (MRMC) wireless mesh networks (WMNs) can be beamformed by using the multiple omni-directional antennas of a multi-radio mesh node in the form of a linear antenna array. We recently developed the first channel assignment (CA) method for linear array beamformed (LAB) links in MRMC WMNs. In this paper we...

We study the impact of three different interference models on channel assignment in multi-radio multi-channel wireless mesh networks, namely the protocol model, the signal-to-interference ratio (SIR) model and the SIR model with shadowing. The main purpose is to determine the minimum number of non-overlapping frequency channels required to achieve...

In this paper, we study two-way relaying (TWR) using a detect-and-forward strategy, where two nodes exchange their data via a relay. We consider three TWR schemes: four-phase relaying, three-phase relaying and two-phase relaying. We limit our study to the case where the nodes and the relay have two antennas and use Alamouti coding. We derive approx...

In a classical multi-radio multi-channel Wireless Mesh Network (WMN) architecture, mesh nodes use omni-directional antennas. Due to the circular radiation pattern of such antennas, when a mesh node communicates with its neighbor on a certain frequency channel, other mesh nodes within its range must remain silent. Directional antennas have been prop...

Traditional cellular network infrastructure provide fixed radio coverage. The temporal changes in user distribution throughout the day and from day to day leads to inefficient use of radio resources. Our position is to create an adaptive radio coverage to match the radio resources and user demand. The main approach for creating flexible radio cover...

We study the problem of achieving maximum network throughput with fairness among the flows at the nodes in a wireless mesh network, given their location and the number of their half-duplex radio interfaces. Our goal is to find the minimum number of non-overlapping frequency channels required to achieve interference-free communication. We use our ex...

In a multi-radio multi-channel wireless mesh network, a channel assignment that is based on a fixed number of available frequency channels may cause co-channel interference, which degrades the network throughput. We address this problem by ensuring interference-free communication among the mesh nodes. The main purpose of this work is to determine t...

In this paper we consider a multiuser detection scheme where K users, each with NT transmit antennas, transmit their symbols simultaneaously using space-time block coding (STBC). Previously, it was shown that a receiver can completely separate signals of K users, where each user has two antenna and uses Alamouti coding, using a number of receive an...

In this paper we propose a new Multiple-Input Multiple-Output (MIMO) transmission scheme that combines the generalised spatial modulation (GSM) with MIMO spatial multiplexing technique. Unlike the GSM which uses NA active antennas to transmit the same symbol, the proposed scheme uses the NA antennas to transmit different symbols simultaneously, whi...

Multi-radio multi-channel (MRMC) wireless mesh networks (WMNs) achieve higher throughput using multiple simultaneous transmissions and receptions. However, due to limited number of non-overlapping channels, such networks suffer from co-channel interference, which degrades their performance. To mitigate co-channel interference, effective channel ass...

In this paper we investigate the performance of two-way relaying that uses Alamouti space-time block code (STBC) and network coding. In this scheme, two nodes use Alamouti STBC to transmit their symbols to the relay consecutively in two phases. The relay detects and demodulates the transmitted symbols from the nodes, and then uses the bitwise-XOR o...

Spatial Modulation (SM) is a technique that can enhance the capacity of MIMO schemes by exploiting the index of transmit antenna to convey information bits. In this paper, we describe this technique, and present a new MIMO transmission scheme that combines SM and spatial multiplexing. In the basic form of SM, only one out of MT available antennas i...

In this paper we propose a new two-way relaying scheme using a quantize-and-forward strategy with space-time block coding (STBC). In this scheme two nodes use STBC to simultaneously transmit their signals to the relay. At the relay these signals are estimated by using minimum mean square error ordered successive interference cancellation and then a...

In this paper we propose a multiuser two-way relaying scheme using an XOR-and-forward strategy with space-time block coding (STBC). In this scheme, all users transmit their symbols simultaneously to the relay in the first phase. The relay uses minimum mean square error detection to estimate the transmitted symbols, and then it uses an XOR operation...

This paper presents a study of the Dedicated Short Range Communication (DSRC) Physical Layer in order to determine its reliability for Vehicle-2-Vehicle (V2V) communication under varying Signal-to-Noise Ratio (SNR), vehicle speed, delay spread, and packet lengths. In particular, we focus on computing the expected delay when packets with errors are...

Relays are being adopted as a cost effective solution to improve the coverage of cellular networks and provide ubiquitous service to all users. To meet the growing demand for mobile data, we need to improve radio resources reuse capability. Partitioning of radio resources is a common practice in cellular network as it provides a simple and reliable...

One of the challenges in Multi-Radio Multi-Channel Wireless Mesh Networks is the assignment of channels to links such that connectivity is ensured and interference is minimized. Two links that are within interference range of each other could be assigned the same channel, which causes co-channel interference and decreases network throughput. In thi...

A method previously reported by the authors for identifying simultaneous signals from different Tx antennas is applied for double-directional channel sounding between a channel sounder base station (CSBS) and a channel sounder mobile station (CSMS), as well as for single input single output (SISO) channel sounding on relay channels in urban microce...

In this paper, the information extracted from Single-Input Multiple-Output sounding measurements is used to study the effect of several aspects of the receive antenna arrays on system performance. The extracted multipath parameters are used to synthesize the MIMO channel matrices of a hypothesized communication system having a fixed microcellular b...

This paper presents a new scheme for demodulate-and-forward two-way relaying scheme based on Alamouti code. Two nodes, A and B, employ Space-Time Alamouti code to transmit their messages to each other through relay node (RN). The RN receiver uses Minimum Mean Square Error Successive Interference Cancellation (MMSE-SIC) to separate signals originati...

Single-radio mesh routers operating on a single channel suffer from low throughput due to collisions. Equipping mesh routers with multiple radios operating on non-overlapping channels can significantly improve the throughput. However, the assignment of channels to radios in a multi-radio mesh network is a challenging task. In this paper, we propose...

Wireless Mesh Networks aim to provide high-bandwidth broadband connections to a large community and thus, should be able to accommodate a large number of users accessing the Internet. Due to high estimated traffic volume in Wireless Mesh Networks, scalability and fault tolerance become important requirements in algorithm design. We propose a Failur...

In this paper, we introduce a new technique that allows the coexistence of secondary users (SUs) with a primary user (PU), in the same frequency and time. The proposed technique (i.e., the cluster-based spatial opportunistic spectrum sharing (CB-SOSS) technique) exploits the spatial degrees of freedom resulting from the use of multiple antennas at...

In this paper, a new algorithm that is able to identify and track multipath clusters in the delay-angular domain is introduced. The introduced algorithm avoids calculations of a single distance measure from quantities with different nature; instead it performs the clustering via extracting multiple 1D waveforms from the 2D delay-angular domain. The...

For simulating mobile MIMO performance, local area SNR variations can be reproduced if small-scale fading distributions are known, transmit bandwidths can be chosen appropriately if flat fading bandwidths are known, and, assuming plane waves, spatial covariance functions can be estimated if power-weighted histograms for angles of arrival (AOA) and...

This paper introduces a novel transmission technique for MIMO broadcasting directional channels, herein called the Angle-of-Departure-Aided Opportunistic Space-Division Multiple Access (AOD-OSDMA) technique. In AOD-OSDMA, the knowledge of angles-of-departure (AODs) at the BS of the strongest signal received by each user is used to design multiple o...

Cross layer optimization plays a key role in radio resource management of broadband wireless systems (BWS).Maximal SNR (MaxSNR) and Round Robin (RR) are two conventional scheduling strategies which emphasizeefficiency and fairness respectively. Proportional Fair (PF) provides a tradeoff between efficiency and fairness.Here, we tailor PF to OFDM-bas...

In this paper, a novel transmission technique for the multiple-input multiple-output (MIMO) broadcasting directional channels is introduced. During the training period, the base station sends a set of mutually orthogonal signals which enables each user to estimate the angle-of-departure of the anticipated strongest beam and the corresponding SNR. T...

A method is described for identifying simultaneous signals from different transmit antennas in multiantenna sounders. Multiple-orthogonal signals are produced from one pseudonoise code by using it to modulate RF carriers at precalculated offset frequencies. Although their frequency spectra are interleaved and they occupy the same band, the spectral...

TDMA-based MAC protocols are considered an energy efficient solution to prolong wireless sensor network lifetime. The topology learning and collection process, together with the used scheduling scheme, are essential parts in the design of such MAC protocols. Previous MAC and multihop scheduling protocols rely completely on CSMA to exchange topology...

This paper presents PROGRESSIVE, a topology discovery and multihop scheduling protocol that progressively collect network connectivity information and schedules nodes which have an identified routing path(s) to the sink. PROGRESSIVE saves energy by limiting the time during which CSMA is used for control message transmissions. In addition, it achiev...

This paper provides a model for received power estimation in 802.11a wireless point-to-point (PTP) links using commercially available WLAN cards in single or multi-hop configurations. The model describes in some details the link attenuation as a function of the antenna heights. Within this model, a simple model for parabolic reflector antennas is i...

A method is described for identifying simultaneous signals from different transmit antennas in multi-antenna sounders. Multiple orthogonal signals are produced from one pseudorandom code by using it to modulate RF carriers at pre-calculated offset frequencies. Although their frequency spectra are interleaved, the spectral lines from different trans...

TDMA scheduling for data gathering in wireless sensor networks can potentially save energy by eliminating collisions and avoiding idle listening due to its built in duty cycle. Furthermore, temporal and spatial correlation in the sensed data gives room for better delay and energy efficiency. Several TDMA scheduling schemes have been suggested in th...

We consider wireless sensor networks where a number of unconstrained nodes (Access Points) with unlimited power source can be deployed together with constrained and limited energy sensor nodes. The presence of unconstrained nodes promotes the use of centralized TDMA scheduling mechanisms that can potentially reduce the delay and save power by elimi...

This paper provides an extension of our previous work in which we provided a model for received power estimation in 802.11a wireless point-to-point (PTP) links using commercially available WLAN cards in single or multi-hop configurations. The model describes how the link attenuation changes with environmental factors such as the ambient humidity an...

This paper proposes ISS-Mac, an efficient MAC protocol for Infrastructure-Supported low-power wire- less sensor networks. A central base station (sink node) is responsible for wide-network synchronization and multi-hop TDMA slots allocation. Providing an accurate topology information to the base station re- quires a lot of signaling overhead which...

This paper addresses some basic issues related to protecting the energy infrastructure in the Persian Gulf region. The analysis and models presented in this paper are applicable in Canada and any other part of the world as well. The study describes the general characteristics of the oil production and transportation and their vulnerabilities to ter...

Scheduling schemes play a key role in the system performance of broadband wireless systems such as WLANs/WMANs. Maximal SNR and round robin are two conventional scheduling strategies that emphasize efficiency and fairness, respectively. The proportional fair scheme provides a trade-off between efficiency and fairness, and has been well studied in T...

There is a market need for higher data rates than that offered by WiMAX. An algorithm that will greatly enhance, up to several times, the downlink data rate of WiMAX is proposed in this paper. We propose to use a SDMA signaling scheme over each tone with multi-user diversity based on inter-user correlations.

Scheduling algorithms are playing a key role in overall system performance of broadband wireless systems (BWS). Maximal SNR (MaxSNR) and Round Robin (RR) are two conventional scheduling strategies which emphasize efficiency and fairness respectively. Proportional Fair (PF) algorithm provides tradeoff between efficiency and fairness. In this paper,...

For planning purposes, there is a need for the evaluation of expected performance on mobile radio links in anticipated new frequency bands and comparison of results with 2 GHz band performance estimates evaluated by the same methods. To that end, this paper reports the application of a semi-analytical technique to estimate average binary phase shif...

Mobile users scattered in a microcell and communicating with co-located base station antennas, may cause a severe near-far problem for an uplink space division multiple access (SDMA) system. Also correlations within the multi-input multi-output (MIMO) channel matrix, in such uplink SDMA propagation scenario, can cause significant degradation in sys...

Scheduling algorithms play a key role in overall system performance of broadband wireless systems (BWS) such as WLAN/WMAN. Maximal SNR (MaxSNR) and Round Robin (RR) are two conventional scheduling strategies which emphasize efficiency and fairness respectively. Proportional Fair (PF) algorithm provides tradeoff between efficiency and fairness and i...

The near-far problem and the correlations in a MIMO channel are two major obstacles in the way of widely implementing space division multiple access (SDMA) systems. In this paper we investigate the effect of distributing the basestation antennas and the reduction of intra-user correlations on the performance of a MIMO-OFDM system in which a basesta...

Space-division multiple-access (SDMA) is a communication technique that enables a base station to communicate with several mobile users simultaneously. The ability of the base station to spatially separate several users depends on the pairwise cross correlations between the channel matrices of the users (the inter-user correlation). In this paper,...

The ability of the basestation to separate several users spatially depends on the pair wise cross-correlations between the channel matrices of the users. In this paper we propose an improved null steering downlink MIMO-OFDM system that reduces the intra-user correlations resulting in significant enhancement in system performance. In this system, se...

The RF issues that concern the development and deployment of wireless sensor systems are discussed. Such issues include the impact of the RF propagation channel on the communications range, where the sensor nodes are hidden or covered with vegetation or any other obstructing objects. In sensor systems, the low RF transmit power of the nodes makes t...

The ability of the base station to separate several users spatially depends on the pair-wise cross-correlations between the channel vectors of the users. In this paper we propose an improved uplink multi-user MIMO-OFDM system that reduces the intra-user correlations resulting in significant enhancement in the SDMA system performance. In this system...

This paper studies the measured behavior of point-to-point 802.11a links at low and high antenna elevations. The purpose of the project is to investigate the possibility of using 802.11a links to interconnect houses and community centers in rural areas with minimum cost. We built an experimental setup using commercial WLAN cards and high gain anten...

Summary form only given. This tutorial addresses recent developments in broadband wireless technologies and networking. The tutorial starts by providing a quick overview of the different classes of wireless systems and their respective applications and limitations, then it moves on to describe the most recent techniques that are opening the way for...

This paper presents a localized routing protocol for both hybrid ad-hoc/infrastructure networks and conventional ad-hoc networks. The goal is to extend the network lifetime and to reduce power consumption. Several performance metrics are proposed considering nodes transmission power and/or remaining battery capacity. The proposed protocol avoids en...

The performance of a RAKE receiver in a mobile terminal is analysed for a WCDMA downlink. Bit error rates as a function of signal-to-noise ratio are computed for the case when channel estimates are in error as a result of self-interference due to multipath propagation and thermal noise. Channel estimation errors are described using Gaussian approxi...

This paper presents a system concept for Radio-over-Optical transmission in order to increase the radio spectrum efficiency. Cellular operators are seeking large amounts of new spectrum in order to deploy the third generation (3G) and fourth generation (4G) wireless systems, while it is difficult to find new spectrum allocations below the 10 GHz ba...

A service specification of third generation wireless systems using wideband CDMA is to enable the delivery of data rates up to 2 Mbps to a single user on the downlink channel. One implication of such high data rates is the reduction of spreading gain, which results in increased multiple-access interference and also self-interference (SI). The latte...

With advances in wireless and portable devices technologies, a new paradigm called mobile computing is promising to make it possible for mobile users to access information "anywhere anytime". This paradigm, however, faces many technical challenges such as limited wireless bandwidth and high error rate. Moreover, mobile devices widely differ with re...

Third-generation (3G) wireless systems need strategies to further improve performance, increase data rates and at the same time provide flexible and affordable support for multi-services and multi-standards. Software radio technology is promising to provide the required flexibility in radio frequency (RF), intermediate frequency (IF) and baseband s...

Mobile devices/clients vary in their hardware and software resources such as screen size, color depth, effective bandwidth, processing power, and the ability to handle different data formats. This makes it difficult for servers to support a wide range of client variations. In our research, we introduce an image transcoding proxy server placed betwe...

In this paper, the impact of co-channel and adjacent channel interference in mobile cellular radio systems on the cellular system capacity are studied. Simple empirical expressions for average signal to co-channel, signal to adjacent channel and signal to total interference ratios are obtained. The simple empirical results developed in this paper a...

This paper addresses some challenges that face multimedia CDMA wireless networks. We highlight problems related to power assignment, admission control, and other radio resource management functions. At the core of our approach is a novel definition of an index for Quality of Service (QoS). The proposed QoS vector can easily be defined on a network...

In this letter, we propose a new technique for power assignment in outdoor code-division multiple access cell supporting bursty multimedia traffic. The proposed scheme takes into consideration both average signal-to-interference ratios and outage probability required by multimedia traffic.

In this paper we propose a new technique for access control in an outdoor CDMA cell supporting multimedia traffic. The proposed scheme controls the flow of the traffic at both packet and call level. Delay scheduling at packet level is employed to minimize the variance of intra-cell interference while a call admission control based on a modified equ...

In this paper, we summarize the known definitions of the spectrum utilization and discuss their applicability to existing radio services and their practical usefulness. An important parameter that limits the full utilization of the available radio spectrum is the non-uniformity of the user density. We illustrate that when users are clustered in sma...

Video transmission over wireless packet networks is gaining importance due to the concept of universal personal communication. Further, it is considered an important step towards wireless multimedia. The challenge however is to achieve good video quality over mobile channels, where typically the channel conditions vary due to signal fading. Hence t...

This paper deals with the problem of admission control when different traffic media with different quality of service (QOS) requirements are sharing a CDMA (code division multiple access) channel. We propose an adaptive access control method based on the equivalent bandwidth theory and cell load measurements. Our algorithm allows efficient integrat...

This paper deals with the problem of admission control when different media with different quality of service requirements (QOS) are present in a CDMA (code division multiple access) environment. We propose an adaptive access control method based on the equivalent bandwidth theory and the cell load measurement. Our algorithm allows efficient integr...

The rapid development of wireless in-building communication systems, has widened the scope of supported applications. Remote terminals may be capable of producing broadband real-time traffic such as variable bit-rate (VBR) video or bursty data transfers. Consequently one of the important issues in indoor broadband wireless networks (IBWN) is employ...

This paper investigates the adaptive dynamic rate controlled video transmission for robust video communication under packet wireless environment. The video coder comprises of a wavelet transform (WT), multi-resolution motion estimation (MRME) and a robust zero tree coder. The robust zero tree coder is a modification of the basic coder proposed by S...

The performance of multi-resolution motion estimation schemes in low bit-rate video coding are presented. Video frames are individually wavelet decomposed and motion activity is detected using variable block size multi-resolution motion estimation (MRME) schemes. The residual frames are coded using zero tree quantization, followed by arithmetic ent...

We compare the performance of two TDMA-ATM-based access methods for indoor broadband wireless systems. The first scheme is a non-uniform polling and the second is reservation. Although the non-uniform polling has a lower delay than reservation schemes, it has the the disadvantage of requiring the base station and remotes to switch between receive a...

We describe a broadband indoor wireless system, where the base stations are connected through an ATM network. The ATM switch provides backbone connectivity among microcells as well as with the outside world. This paper investigates a broadband indoor wireless network (BIWN), employing time division multiple access (TDMA), based on polling for dynam...

In FDMA digital cellular systems significant enhancement to capacity may be achieved if overlap of adjacent channel signal spectra could be tolerated. A receiver structure is proposed to recover data in the presence of significant interchannel interference. The proposed receiver takes full advantage of spectral redundancies in the digitally modulat...

In a hybrid (terrestrial + satellite) mobile personal communications networks environment, a large size satellite footprint (supercell) overlays on a large number of smaller size, contiguous terrestrial cells. We assume that the users have either a terrestrial only single mode terminal (SMT) or a terrestrial/satellite dual mode terminal (DMT) and t...

Future wireless communication systems designed for indoor environments are expected to handle integrated voice, data, and video services. The use of millimeter waves in the 20GHz to 60GHz band for future indoor wireless communications appears to be a favorable choice as it provides sufficient bandwidth to support broadband services, current sparse...

In recent years Demand Time Assigned Speech Interpolation (D-TASI) system has been proposed to alleviate the problem of spectrum shortages. In D-TASI system, delay in accessing message channel to transmit a voice packet is identified as a major obstacle in its practical implementation. Theoretical models and computer simulation packages have been d...

The results of field trials conducted in the urban and sub-urban areas in Ottawa/Hull region are reported. These tests were conducted at 150, 450 and 820 HHz bands selecting synchronous and asynchronous transmissions. The collected data has been analysed for bit error, character error rates, and error free gaps distributions for different signal to...

One of the WCDMA service specifications is the delivery of data rates up to 2 Mbps to a single user on a downlink channel. The transmission of such high data rates in an urban propagation environment, however, poses unique problems not encountered previously in DSSS systems intended primarily for voice and low data rate traffic. At high data rates,...