Khairi Ashour Hamdi

A useful lemma for capacity analysis of fading interference channels

This paper presents a simple new expression for the exact evaluation of averages of the form E [ln (1+x₁+...x_N/y₁+...+y_M+1)], where x₁,..., x_N, y₁..., y_M are arbitrary non-negative random variables, in terms of the joint moment generating functions of these random variables. Application examples are given for the ergodic capacity evaluation of some multiuser wireless communication systems which are difficult to solve by the known classical methods.

Capacity of MRC on Correlated Rician Fading Channels

A new exact explicit expression is derived for the ergodic capacity of maximal ratio combining (MRC) schemes over arbitrarily correlated Rician fading channels. This is used to study the effects of channel correlation on the ergodic capacity. Numerical results reveal that both the phase and the magnitude of correlation have an impact on the ergodic capacity of Rician fading channels. This is in contrast to correlated Rayleigh fading, where the phase of the correlation has no effect on the ergodic capacity. It is also observed that negatively correlated branches in Rician fading may lead to an increase in ergodic capacity beyond that obtained by uncorrelated branches.

Resource Efficiency: A New Paradigm on Energy Efficiency and Spectral Efficiency Tradeoff

Spectral efficiency (SE) and energy efficiency (EE) are the main metrics for designing wireless networks. Rather than focusing on either SE or EE separately, recent works have focused on the relationship between EE and SE and provided good insight into the joint EE-SE tradeoff. However, such works have assumed that the bandwidth was fully occupied regardless of the transmission requirements and therefore are only valid for this type of scenario. In this paper, we propose a new paradigm for EE-SE tradeoff, namely the resource efficiency (RE) for orthogonal frequency division multiple access (OFDMA) cellular network in which we take into consideration different transmission-bandwidth requirements. We analyse the properties of the proposed RE and prove that it is capable of exploiting the tradeoff between EE and SE by balancing consumption power and occupied bandwidth; hence simultaneously optimizing both EE and SE. We then formulate the generalized RE optimization problem with guaranteed quality of service (QoS) and provide a gradient based optimal power adaptation scheme to solve it. We also provide an upper bound near optimal method to jointly solve the optimization problem. Furthermore, a low-complexity suboptimal algorithm based on a uniform power allocation scheme is proposed to reduce the complexity. Numerical results confirm the analytical findings and demonstrate the effectiveness of the proposed resource allocation schemes for efficient resource usage.

A unified model for interference analysis in unlicensed frequency bands

This paper presents a unified framework for interference characterizations and analysis in the unlicensed frequency bands and the like, where many narrowband heterogeneous terminals coexist and share a common wideband channel using less-restrictive transmission etiquettes. Here, each transmitter/receiver pair makes his own decision regarding when to access the channel without any direct coordination with the other users. This is usually based on the local channel conditions at the receiver or/and the transmitter. Due to the nature of the wireless channel, communication in such environments is usually prone to arbitrary partial-band interference which can be generated anywhere in the space and frequency domains. In this paper, a new spatial-spectral interference model is introduced, where interferers can be of any power spectral density and are distributed according to a Poisson process in space and frequency domains. This basic model is extended to include the effects of channelization, where users are allowed only to transmit at a preassigned set of discrete frequencies. This is further extended to include also the effects of spectral-spatial guard zones, where the interferers can not exist in a given band nearby the victim receiver. Based on this multidimensional spatial-spectral Poisson model and the accurate conditional Gaussian analysis, explicit expressions are derived for average error rates of different communication systems.

Resource Allocation for Energy Efficiency Optimization in Heterogeneous Networks

Heterogeneous network (HetNet) deployment is considered a de facto solution for meeting the ever increasing mobile traffic demand. However, excessive power usage in such networks is a critical issue, particularly for mobile operators. Characterizing the fundamental energy efficiency (EE) performance of HetNets is therefore important for the design of green wireless systems. In this paper, we address the EE optimization problem for downlink two-tier HetNets comprised of a single macro-cell and multiple pico-cells. Considering a heterogeneous real-time and non-real-time traffic, transmit beamforming design and power allocation policies are jointly considered in order to optimize the system energy efficiency. The EE resource allocation problem under consideration is a mixed combinatorial and non-convex optimization problem, which is extremely difficult to solve. In order to reduce the computational complexity, we decompose the original problem with multiple inequality constraints into multiple optimization problems with single inequality constraint. For the latter problem, a two-layer resource allocation algorithm is proposed based on the quasiconcavity property of EE. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE.

A Useful Technique for Interference Analysis in Nakagami Fading

This paper presents a unified analytical method for computing the average E[g(x/(Sigma_k=1 ^K y_k + b))] of some arbitrary function g(.) when x is a gamma random variable and independent of the arbitrary random variables y₁, y₂, ..., y_k. This leads to new explicit expressions for the averages of some specific functions including, erfc(radicz), exp(-z), zⁿ, and In(1 + z), in terms of the moment generating functions of y₁, y₂, ..., y_K.

Exact probability of error of BPSK communication links subjected to asynchronous interference in Rayleigh fading environment

We derive a new expression for the exact bit-error probability for the detection of a coherent binary phase-shift keying signal experiencing a number of asynchronous interferers having unequal power levels in Rayleigh fading channels. The new expression is readily computed in terms of the coefficients of a Hermite polynomial.

Precise interference analysis of OFDMA time-asynchronous wireless ad-hoc networks

This paper presents a unified mathematical performance analysis of the physical layer in orthogonal frequency division multiple access (OFDMA) wireless ad hoc networks, where several independent transmitter-receiver pairs share a common wideband channel in a local area environment. Multiuser interference (MUI) occurs when the signals from different users arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of the orthogonality between subcarriers. Precise interference analysis in white Gaussian noise and Rayleigh multipath fading is developed in a partially loaded OFDMA network. New exact expressions of symbol and bit error rates are given in the case of interleaved subcarrier assignment schemes. On the other hand, tight upper bounds and accurate improved Gaussian approximations are developed for arbitrary subcarrier assignment schemes. Furthermore, expressions of the cutoff rates are derived and employed to estimate the spectral efficiency in bits/sec./Hz. These are used to quantify the improvement in the spectral efficiency that can be achieved by a common MUI mitigating technique based on the extension of guard intervals and dynamic positioning of FFT windows.

Physical Layer Security With RF Energy Harvesting in AF Multi-Antenna Relaying Networks

In this paper, we analyze the secrecy capacity of a half-duplex energy harvesting (EH)-based multi-antenna amplify-and-forward relay network in the presence of a passive eavesdropper. During the first phase, while the source is in the transmission mode, the legitimate destination transmits an auxiliary artificial noise (AN) signal which has two distinct purposes: 1) to transfer power to the relay and 2) to improve system security. Since the AN is known at the legitimate destination, it is easily cancelled at the intended destination, which is not the case at the eavesdropper. In this respect, we derive new exact analytical expressions for the ergodic secrecy capacity for various well-known EH relaying protocols, namely, time switching relaying (TSR), power splitting relaying (PSR), and ideal relaying receiver (IRR). Monte Carlo simulations are also provided throughout our investigations to validate the analysis. The impacts of some important system parameters, such as EH time, power splitting ratio, relay location, AN power, EH efficiency, and the number of relay antennas, on the system performance are investigated. The results reveal that the PSR protocol generally outperforms the TSR approach in terms of the secrecy capacity.

A Unified Framework for the Analysis of Fractional Frequency Reuse Techniques

Fractional frequency reuse (FFR) and soft frequency reuse (SFR) systems are an efficient cellular interference management technique to reduce inter-cell interference in multi-cell OFDMA networks. In this paper, a new and unified analytical framework for performance evaluation for both systems over a composite fading environment is presented. Explicit expressions are obtained for the area spectral efficiency (ASE) with both FFR and SFR, under fully loaded and partially loaded systems for downlink and uplink, and in generalized frequency reuse factor. The presented numerical result provides useful system design guidelines between the two systems. It is demonstrated that SFR outperforms FFR in a partially loaded scenario while the opposite is true for fully loaded system. The mathematical model is then extended to include the analysis of elastic data traffic in FFR system.