Mohamed Fathy Feteiha

Enabling Cooperative Relaying VANET Clouds Over LTE-A Networks

This paper addresses the area of heterogeneous wireless relaying vehicular clouds. We devise an advanced vehicular relaying technique for enhanced connectivity in densely populated urban areas. We investigate the performance of a transmission scheme over a Long-Term Evolution-Advanced (LTE-A) network where vehicles act as relaying cooperating terminals for a downlink session between a base station and an end-user. The abundance of moving vehicles, operating in an ad hoc fashion, can eliminate the need for establishing a dedicated relaying infrastructure. However, the associated wireless links in vehicular clouds are characterized by a doubly selective fading channel; this causes performance degradation in terms of increased error probability. Hence, we propose a precoded cooperative transmission technique to extract the underlying rich multipath-Doppler-spatial diversity, which is a relay selection scheme to take advantage of the potentially large number of available relaying vehicles. We further contribute by the derivation of a closed-form error rate expression, diversity gain, and outage expressions and introduce our derived performance unconditional expressions as a benchmark to assess our analysis and future research studies of such an approach. Our analytical and simulation results indicate that significant diversity gains and reduced error rates are achievable. In addition, there is a noticeable reduction in the required transmitting power compared with traditional transmission schemes, as well as an increase in distance coverage.

Multipath-Doppler Diversity for Broadband Cooperative Vehicular Communications

Initial works on cooperative vehicular communications build upon the assumption of frequency-flat and quasi-static fading channels. This can be justified only for narrowband systems in very slow traffic flows such as in rush-hours. In this paper, we consider doubly-selective (i.e., time- and frequency-selective) vehicular channels and investigate multipath-Doppler diversity for a cooperative vehicular system to extract the underlying rich diversity. Our performance analysis through pairwise error probability derivation shows that, through proper precoding, the proposed system is able to extract maximum available diversity in time, frequency and space. Monte Carlo simulations are further presented to confirm the analytical derivations and corroborate on the analytical results.

Lookback scheduling for long-term Quality-of-Service over multiple cells

In current cellular networks, schedulers allocate wireless channel resources to users based on short-term moving averages of the channel gain and of the queuing state. Using only such short-term information, schedulers ignore the users service history in previous cells and, thus, cannot meet long-term Quality of Service (QoS) guarantees when users traverse cells with varying load and capacity. We propose a new scheduling framework, which extends conventional short-term scheduling with long-term QoS information from previously traversed cells. We demonstrate our scheme for relevant channel-aware as well as for channel and queue-aware schedulers. Our simulation results show high gains in long-term QoS while the average throughput of the network increases. Therefore, the proposed scheduling approach improves subscriber satisfaction while increasing operational efficiency.

Pairwise error probability evaluation of cooperative mobile femtocells

Cellular subscribers while travelling in public transportation vehicles, such as streetcars and buses, often experience poor signal reception and low bandwidth when using their cellular devises onboard. Small cell deployment of, for example, femtocells is considered as one of the most promising solutions for cellular operators to enhance coverage and meet the increasing need for capacity and QoS support expected by cellular subscribers. We consider a mobile Femto Base Station (mobFBS) installed in the public transportation vehicle, with an external antenna installed on the roof, to offer enhanced coverage and improved capacity onboard. We investigate the performance gains of a communication scheme in downlink LTE-A networks with mobFBSs. Users are assumed to be travelling using a public transportation vehicle, and the transmission between macroBS and users occurs through a mobFBS. The associated wireless links for this type of fast mobility are characterized by a doubly-selective fading channel. This causes performance degradation in terms of increased error probability. By taking advantage of the more powerful central processing mobFBS, we make use of a precoded technique to overcome the performance degradation that results from the wireless fading channel. We investigate the performance gain in terms of pairwise error probability (PEP) via a derived closed-form expression. Our analytical and simulation results indicate that significant diversity gains are achievable and error rates are tremendously reduced.

Opportunistic cooperation for infrastructure-to-relaying-vehicles over LTE-A networks

We extend vehicular cooperation into downlink LTE-A networks in what we call Infrastructure-to-Relaying-Vehicles (I2RV) cooperation. In I2RV, vehicles are used as relaying terminals between eNodeB/BS and a receiving user equipment located or mounted on another traveling vehicle, for the aim of extending coverage, improving performance, and attaining distributed transmission. Initial works on cooperative vehicular communications build upon the assumption of flat and quasi-static fading channels, this can be justified only for narrowband systems in very slow traffic flows such as in rush-hours. In this paper, we consider highway traffic with high-speed mobility resulting in doubly-selective (i.e., time- and frequency-selective) channels. To overcome the performance degradation, we make use of precoded cooperative transmission accompanied with an opportunistic best-relay selection technique to extract the rich underlying multipath-Doppler-spatial diversity gains. Our performance analysis through pairwise error probability (PEP) derivation shows that, through proper precoding, the proposed system is able to extract maximum available diversity in time, frequency and space. Furthermore, we derive a closed-form expressions for the outage probability as a bench-mark for future analysis for the proposed scheme. Through numerical analysis, we demonstrate that significant coverage advantage by extending the transmission distance targeting a specific error rate and using the same transmitting power can be achieved.

On the Performance of MIMO Cooperative Transmission for Broadband Vehicular Networks

In this paper, we investigate the performance of a cooperative vehicular network over a doubly selective fading channel using multiple antennas at source and destination vehicles. Under the assumption of amplify-and-forward (AF) relaying with orthogonal cooperation protocol and Alamouti-type space-time block coding (STBC), we derive a pairwise error probability (PEP) expression and demonstrate the achievable diversity gains. Our results demonstrate that, via proper linear constellation precoding and digital phase sweeping (DPS), the cooperative vehicular scheme is able to extract the maximum available diversity in frequency (through multipath diversity), time (through Doppler diversity), and spatial (through antenna and cooperative diversity) dimensions. We further conduct Monte Carlo simulations to confirm the analytical derivations and present the error rate performance of the vehicular scheme under various mobility conditions and scenarios.

Cooperative vehicular ad-hoc transmission for LTE-A MIMO-downlink using Amplify-and-Forward relaying

Cooperative communication has been recently applied to vehicular networks to enable coverage extension and enhance link reliability through distributed spatial diversity. In this paper, we investigate the performance of cooperative vehicular relaying over a doubly-selective (i.e., frequency-selective and time-selective) fading channel for an LTE-Advanced downlink session. Using Amplify-and-Forward (AF) relaying with orthogonal cooperation protocol and Multiple-Input Multiple-Output (MIMO) deployment at the source and destination, we derive a pairwise error probability (PEP) expression and demonstrate the achievable diversity gains. Space-Time Block Coding (STBC) is used to ensure the orthogonality of the transmitted-received signals. Our results demonstrate that, via proper linear precoding constellation, the proposed cooperative-MIMO vehicular relaying is capable of extracting the maximum available diversity in frequency (through multipath diversity), time (through Doppler diversity) and space (through cooperative diversity as well as the MIMO deployment) dimensions. We further conduct numerical simulations to confirm the analytical derivations and present the error rate performance of the cooperative relaying vehicular scheme under consideration.

Infrastructure-to-vehicle cooperative communications with decode-and-forward relaying

In this paper, we consider infrastructure-to-vehicle cooperative communications in which roadside access points use vehicles as relaying terminals. This can be particularly useful in suburban or remote areas where the frequent deployment of roadside access points is not either possible or cost-effective. For the doubly-selective vehicular channel under consideration, we employ a precoded cooperative transmission technique to extract the underlying rich multipath-Doppler-spatial diversity. Under the assumption of decode-and-forward relaying, we derive a pairwise error probability expression and demonstrate the achievable diversity gains. We further provide Monte Carlo simulations to confirm the analytical derivations and provide insight into the error rate performance of infrastructure-to-vehicle cooperative communications.

Cooperative inter-vehicular communications in highway traffic

In this paper, we investigate the performance of a single-relay assisted cooperative vehicular network in a highway traffic scenario. Source and relaying vehicles are assumed to be traveling in the same direction with similar speeds. This results in a relative velocity nearly equal to zero and leads to a frequency-flat and time-flat fading in source-to-relay link. On the other hand, source-to-destination and relay-to-destination links are modeled as doubly-selective fading. To handle spreading in time and frequency, we propose a precoded cooperative scheme to exploit delay and Doppler spreads to our advantage. Under the assumption of amplify-and-forward relaying with orthogonal cooperation protocol, we derive a pairwise error probability expression and demonstrate the achievable diversity gains. We further conduct Monte Carlo simulations to confirm the analytical derivations and present the error rate performance of the proposed scheme with imperfect channel estimation.

Performance analysis of cooperative diversity networks with imperfect channel estimation over Rician fading channels

In this paper, we examine the effect of channel estimation error on the error and outage probabilities of a multi-relay system with amplify-and-forward relaying over frequency-flat Rician fading channel. We consider orthogonal relaying and study both conventional cooperative systems (i.e., all relays participate in the relaying phase) and opportunistic cooperative systems (i.e., only the best relay participates in the relaying phase). Based on the derivation of effective signal-to-ratio (SNR) at the receiver taking into account channel estimation error, we obtain closed-form expressions for error and outage probabilities in high SNR regime. Such closed form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Computer simulations are used to validate our analytical results.