Yasmine A. Fahmy

Multi-User MIMO Mobile CDMA Uplink System Employing Turbo Coding and Joint Detection Through a Multipath Rayleigh Fading Channel

In this paper, a generalized multiple-input multiple-output (MIMO) antenna system that can be fitted to the uplink of a wireless communication system is considered for the general case of multi-user. At the transmitter, the information bits are Turbo coded, then interleaved and passed through a serial-to-parallel converter. The channel is assumed bad urban suffering from multipath Rayleigh fading resulting in inter-symbol and multiple access interferences (ISI and MAI). At the front-end of the receiver, a number of receiving antennas are used followed by a joint multi-user estimator based on the Minimum Mean Square Error Block Linear Equalizer (MMSE-BLE).Computer simulations demonstrate a significant performance improvement in both single user and multi-user cases.

LTE and WiMAX: performance and complexity comparison for possible channel estimation techniques

SUMMARY The similarities between the physical layer of LTE and WiMAX systems trigger the design of a unified hardware platform. As a consequence, there exists a great need to design common blocks that can be adapted to support both of them. In this paper, the choice of the channel estimator is studied where the performance and complexity trade-off is investigated to seek a unified channel estimation design that can suit both systems under different channel conditions. The performance of different channel estimation techniques when applied to LTE and WiMAX systems is assessed and compared. Two channel profiles with different delay spreads are considered for urban macrocell and bad urban macrocell channels. Three different Doppler frequencies are assumed to illustrate the effect of users’ mobility. The estimators’ computational complexity is also thoroughly studied.Copyright

Two-way TOA with limited dead reckoning for GPS-free vehicle localization using single RSU

Road safety applications in Vehicular Ad Hoc Networks (VANETs) necessitate highly accurate vehicle localization techniques. Unfortunately, Global Positioning System (GPS)-based localization techniques do not only suffer from the lack of ubiquitous GPS coverage but also are susceptible to high localization errors (10 m to 30 m). Consequently, such techniques are not suitable for road safety applications. Recently, GPS-free localization based on vehicle communication with installed roadside units (RSUs) has emerged as a more accurate alternative. However, existing GPS-free techniques require the vehicle to communicate with two RSUs in order to achieve high localization accuracy. Such techniques either increase the system cost due to the high number of needed RSUs or delay the localization decisions. In this paper, we propose a GPS-free localization framework that uses two-way time of arrival with partial use of dead reckoning to locate the vehicles based on communication with a single RSU. Our results show that the accuracy of the proposed framework is 13.1% to 20.1% better than the techniques that use 1 RSUs while completely depending on dead reckoning, and only 3% to 8.9% worse than those techniques that use 2 RSUs on both sides on the road.

High accuracy GPS-Free vehicle localization framework via an INS-Assisted single RSU

Collision avoidance and road safety applications require highly accurate vehicle localization techniques. Unfortunately, the existing localization techniques are not suitable for road safety applications as they rely on the error-prone Global Positioning System (GPS). Likewise, cooperative localization techniques that use intervehicle communications experience high errors due to hidden vehicles and the limited sensing/communication range. Recently, GPS-free localization based on vehicle communication with a low cost infrastructure installed on the roadsides has emerged as a more accurate alternative. However, existing techniques require the vehicle to communicate with two roadside units (RSUs) in order to achieve high localization accuracy. In contrast, this paper presents a GPS-free localization framework that uses two-way time of arrival to locate the vehicles based on communication with a single RSU. Furthermore, our framework uses the vehicle kinematics information obtained via the vehicles onboard inertial navigation system (INS) to further improve the accuracy of the vehicle location using Kalman filters. Our results show that the localization error of the proposed framework is as low as 1.8 meters. The resulting localization accuracy is up to 65% and 47.5% better than GPS-based techniques used without/with INS, respectively. This accuracy gain becomes around 73.3% when compared to existing RSU-based techniques.

Time domain leakage in DFT-based channel estimation for OFDM systems with guard bands

In this paper, a mathematical analysis of the time domain leakage problem in the discrete Fourier transform DFT based channel estimation technique is presented. The time domain leakage is because of the absence of pilots in the guard band. Several solutions to this problem were previously proposed based on reducing the leakage in the frequency domain. These solutions significantly increase the receiver complexity. In this paper, the root cause of the leakage problem is linked to the time domain and a modification is proposed carrying slight additional complexity over the conventional DFT-based estimator. Performance evaluation is assessed in terms of the bit error rate and the mean square error. The proposed modification significantly decreases the error floor of the conventional DFT-based channel estimation technique. In addition, its performance is comparable to other more complex techniques recently proposed.Copyright

Opportunistic splitting algorithm for underlay cognitive radio networks

Dynamic Resource Allocation (DRA) is one of the essential enabling techniques for Cognitive Radio (CR) technology. In this paper, the Opportunistic Splitting Algorithm (OSA), previously proposed for conventional systems, is exploited to allocate the resources in a CR system. The CR system is allowed to underlay the sub-carriers of an OFDM-based primary system. Several modifications are proposed to the OSA to suit a CR system without losing the main advantages of the OSA. The proposed CR-OSA can allocate resources without the need of a centralized controller and the decision is taken on the average in less than 2.5 mini-slots regardless of the number of users in the CR system. These results are shown analytically and using simulations. Different scenarios based on the nature of the rate needed by the CR system are also compared.

On the Distributed Resource Allocation of MIMO Cognitive Radio Networks

One of the key challenges of cognitive radio networks is the design of efficient resource allocation schemes. Here we propose a distributed resource allocation algorithm for an underlay multiple-input multiple-output (MIMO) cognitive radio network. To reduce the complexity and cost, we introduce two different antenna selection techniques to allow the secondary communication via a single radio frequency (RF) chain. We show that the proposed distributed algorithm approaches the centralized performance while reducing the delay and overhead. Moreover, the simulation results compare the performance of the two proposed techniques showing their merits and demerits. The results show that the proposed algorithm achieves high throughput with low complexity.

Designing near Shannon limit LDPC codes using particle swarm optimization algorithm

This paper presents a new design methodology/process for low-density parity-check codes (LDPC). To minimize the gap to Shannon limit, the particle swarm optimizer is applied to optimize the variable and check node degree distribution lambda and p respectively in case of irregular LDPC codes. discrete fast density evolution (FDE) is used (as the analysis technique) to compute the threshold value of LDPC code and the Shannon limit is evaluated based on Butman and McEliece formula. The results conducted show that, our proposed distributions with low degrees of (lambda, p) outperform other comparable distributions.

Phase ambiguity mitigation for per-cell codebookbased limited feedback coordinated multi-point transmission systems

Limited feedback techniques, that employ codebook-based quantisation, are used in coordinated multi-point (CoMP) transmission to convey the channel direction information between the mobile user and each base station in the cooperative set and also among the cooperating base stations. However, unlike single-cell multiple-user multiple input multiple output (MU-MIMO) systems, CoMP systems face additional challenges in this codebook design. Among these challenges are the huge feedback overhead and the need for dynamic codebook size. These problems are solved when CoMP uses the so-called per-cell codebook, in which the channel to each cell is quantised separately. However, this results in a further problem, that is having random phase values between the quantised per-cell channels of the same user. In this study, the phase ambiguity problem is explained and its effect on performance degradation is quantified. A new quantisation technique is proposed where the quantisation of each of the real and the imaginary parts is performed independently using the same real codebook. This novel solution prevents the phase ambiguity problem instead of trying to mitigate its effects, in addition to simplifying the codebook design. The proposed quantisation technique outperforms two recently introduced solutions in the literature. The first solution is to quantise phase ambiguity as part of channel state information (CSI), whereas the other avoids phase ambiguity by an iterative selection procedure. Mathematical validations and simulations are provided to verify these findings.

Iterative channel estimation and turbo decoding for OFDM systems

In this paper, an iterative channel estimation algorithm for Turbo coded OFDM based systems is proposed. The first channel estimate is derived from the known pilots and fed to the decoder which will generate the Log Likelihood Ratios (LLR) for the decoded bits. These LLRs are used to get a better estimate of the channel, while keeping the decoders previously calculated parameters. The proposed technique is applied to Long Term Evolution (LTE Rel. 8) standard. Simulation results show the bit error rate (BER) performance improvement using the proposed estimator.