For quite a while, it has been evident that homogeneous network architectures, based on cells with a uniform radiation pattern, cannot fulfill the ever increasing demand of mobile users for capacity and service quality while still preserving spectrum and energy. However, only with the introduction of the Fourth Generation mobile communication networks to deal with the surging data traffic of multimedia applications, have smaller cells been widely used to break down service zone areas of macro base stations into multiple tiers, thus improving network performance, reducing traffic congestion, and enabling better management of spectrum and energy consumption in a macro network. In this paper, we present an analytical model for assessing the efficiency of bandwidth and energy usage, as well as of network deployment, taking into account overall network investment and maintenance costs. This paves the way to the improved planning of network coverage, and its capacity and reliability, thus preserving its spectrum and energy, as well as the environment. The analysis considers the downlink of an arbitrary heterogeneous cellular network by using tools of stochastic geometry that adopt the distribution of base stations in the form of a Poisson Point Process. The proposed analytical model is verified by the according software simulations using the ns-3 network simulator. The obtained results closely match the theoretically predicted values and boundaries, clearly indicating that, in all three analyzed aspects: spectral, energy, and deploymental, the efficiency of small-cell networks was higher with respect to traditional large-cell networks and increased even further for heterogeneous (two-tier in our tests) networks.

The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR), which both degrade the Bit Error Rate (BER). Specifically, we consider here clipping or any other PAPR reduction method sufficient to prevent the nonlinear high-power amplifier from generating errors. Moreover, in small cells, the signal-to-noise ratio is large, while the small time dispersion allows the OFDM symbol cyclic prefix to prevent intersymbol interference. This retains the CFO to solely determine the BER and vice versa, enabling indirect estimation of CFO-induced phase distortion by simple BER testing. However, a particular problem is measuring very low BER values (generated by alike residual CFO), which could last a long time in order to acquire statistically enough errors. The test time can be drastically reduced if the noise margin is reduced in a controllable way, by adding the interfering signal to each subcarrier at the receiver. This approach is shown to enable efficient and accurate short-term BER (and so CFO phase error) testing.

This article proposes geometrically-based stochastic channel model with scatterers homogeneously distributed within <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-dimensional (<inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-D) hyperspherical-shaped scattering region for single-bounce propagation scenario, with arbitrary positions of base station (BS) and mobile station (MS). For such defined geometrically-based stochastic channel model, the angular and temporal statistics are determined by introducing the projective approach. Accordingly, azimuthal angle and time of arrival marginal PDFs are derived in closed form, while the elevation angle PDF can be delivered numerically in general, and in closed-form for specific environmental parameters. The fidelity of the analytically obtained results is evaluated by their comparison to the corresponding normalized histograms. Also, it is shown that the proposed <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-D model can be used to analyze some of the existing channel models like 2-D uniform disk and 3-D uniform (hemi)sphere models. Additionally, by introducing the mentioned projective approach, it is shown that the angular statistics of the proposed <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-D model are the same as the angular statistics of some nonuniform 2-D and 3-D models, which is an important property of the proposed model. Such observation enabled us, for the first time in the literature, to determinate angular statistics for geometrically-based stochastic channel models such as inverted parabolic scattering model, 2-D Gaussian model and 3-D Gaussian hemisphere model, for arbitrary positions of BS and MS. Such angular characteristics of proposed channel model are validated through several empirical datasets.

: T his paper provides a simple estimation of the Long Term Evolution (LTE) physical and Medium Access Control (MAC) layer peak transmission performanc e-the irr educible Block - Error - Rate (BLER) that determines the Hybrid Automatic Repeat Request (HARQ) residual channel available to higher - layer protocols. With this regard, the general pre - HARQ BLER prediction is developed for the redundancy version 0 (RV0) codeword transmission, expressed by the Bit - Error - Rate (BER)), considering the cyclic prefix protection against inter - symbol interference sufficient to prevent long error bursts. This implies only sporadic bit error occurrences, exhibiting moderate mutual interdependence that we modelled considering errored bits of each block of data as a sample without replacement and consequently describing it with the hypergeometric distribution instead of the mostly used binomial one. The HARQ BLER estimation model is verified by both problem - dedicated Monte - Carlo simulations and industry - standard LTE software simulation tool, specifically for the LTE FDD downlink channel environment, as the test results exhibit excellent matching with the residual BLER prediction.

Contemporary wireless networks dramatically enhance data rates and latency to become a key enabler of massive communication among various low-cost devices of limited computational power, standardized by the Long-Term Evolution (LTE) downscaled derivations LTE-M or narrowband Internet of Things (NB IoT), in particular. Specifically, assessment of the physical-layer transmission performance is important for higher-layer protocols determining the extent of the potential error recovery escalation upwards the protocol stack. Thereby, it is needed that the end-points of low processing capacity most efficiently estimate the residual bit error rate (BER) solely determined by the main orthogonal frequency-division multiplexing (OFDM) impairment–carrier frequency offset (CFO), specifically in small cells, where the signal-to-noise ratio is large enough, as well as the OFDM symbol cyclic prefix, preventing inter-symbol interference. However, in contrast to earlier analytical models with computationally demanding estimation of BER from the phase deviation caused by CFO, in this paper, after identifying the optimal sample instant in a power delay profile, we abstract the CFO by equivalent time dispersion (i.e., by additional spreading of the power delay profile that would produce the same BER degradation as the CFO). The proposed BER estimation is verified by means of the industry-standard LTE software simulator.

Nakagami-m probability density function (pdf) is one of the frequently used distributions for describing fast received signal variations in radio channels, obtained as a result of multipath phenomenon. It is foremost derived by assuming the most general multipath channel model but applying mathematical approximations. Afterward, it is derived without approximations, but based on dedicated physical models with many constraints. Consequently, neither approach can be considered both, universally applicable and exact. Accordingly, in this paper, a novel approach in deriving Nakagami-m pdf is provided, being based on fewer constraints on propagation phenomena than others. Herein, it is shown that Nakagami-m pdf can be obtained as a distribution of a Euclidean distance of a point orthogonally projected from homogeneous distributed n-dimensional hypersphere on N-dimensional space, where received signal envelope is interpreted as mentioned Euclidean distance, with $n$ being a total number of orthogonal multipath components which can reach the receiver in idealized condition and $N$ being a number of these components which reach the receiver in reality (with N < n).

In this paper we present an analytical model for planning and using network resources to improve network coverage, capacity and reliability, reduce network investment and maintenance costs, as well as reduce the electrical power consumption. The analysis considers the downlink of an arbitrary heterogeneous cellular network by using tools of stochastic geometry that adopts the distribution of base stations in the form of Poisson Point Process (PPP). To prove the analytical model, simulation based on ns-3 network simulator has been conducted, with accurately matching the theoretical values and boundaries.

The ability to simulate various mobile radio channel impairments, particularly, multipath fading, in the products design phase, before equalizer algorithms have been implemented as custom ASICs, is critical. This paper presents the test procedure, developed for type-approval testing of a multipath fading simulator, as well as corresponding practical measurement results in terms of spurious signals and intermodulation products, transfer functions, amplitude statistics, Doppler spectra, delay power profiles, and impulse responses, which can be used as a reference in similar situations.

Carrier Frequency Offset (CFO) and (high) Peak-to-Average Power Ratio (PAPR) are well-known major drawbacks of the Orthogonal Frequency-Division Multiplexing (OFDM) signal. So, in many practical situations, specifically with LTE-Advanced downlink introducing carrier aggregation, estimation of PAPR and CFO-induced OFDM symbol phase deviation is of interest. However, this demands complex test equipment, such as e.g. Vector Signal Analyzer (VSA), which might not be always and everywhere available. Therefore, we applied the link abstraction principle on the residual BER that is considered to be determined just by the CFO-caused phase deviation, i.e. as if the channel is noiseless and time-dispersion-free (so that evident errors occur just due to actual CFO). Moreover, as recently it has been shown that the phase deviation is linear with the instantaneous (per-OFDM-symbol) PAPR, we develop a simple model for analytical estimating of BER-based CFO, considering the easy-to-measure BER degradation as resulting just from the according additive white Gaussian noise (AWGN) power level, which abstracts the CFO distortion. The proposed analytical model is validated by according Monte-Carlo simulations.