Urban Mobile Environment Research Articles

Simulation Test Research on Typical Simulator NS-2 in Urban Vehicle Ad Hoc Network Based on Big Data

Abstract Vehicle ad hoc network (VANET) has gradually become a prominent research topic in the fields of wireless networks and intelligent vehicles. VANETs are unique mobile ad hoc networks with vehicles as their mobile nodes, presenting distinctive performance characteristics compared to traditional wireless self-organizing networks. In recent years, VANETs have gained significant attention in the wireless network and intelligent transportation domain. As an integral aspect of autonomous driving technology, vehicle-to-everything (V2X) communication spans multiple disciplines and is closely related to intelligent transportation, assisted driving, active safety, and smart vehicles. Evaluating VANET protocols and applications in real-world settings can be challenging. Therefore, utilizing simulation tools for VANET research is an effective approach. In this paper, we have designed and developed an optimized platform that uses IEEE 802.11a and IEEE 802.11p protocols for communication within a simulated urban traffic environment created with NS-2. The simulation results confirm the feasibility and rationale of applying the IEEE 802.11p protocol to wireless vehicular ad hoc networks. Within a distance of 300 m, at 0.0000 s, 14 key packets have not arrived in IEEE 802.11a, and 8 packets have not arrived in IEEE 802.11p; at 8.0000 s, 38 key packets have not arrived in IEEE802.11a, and 6 packets have not arrived in IEEE802.11p. Comparing the performance of IEEE 802.11a and IEEE 802.11p, the study concluded that the use of the 802.11p protocol in urban mobile environments can improve reliability and reduce average packet latency.

Accurate Variable-Order Approximations to the Sum of α – μ Variates With Application to MIMO Systems

Sum of fading signals arises in several communication applications such as maximal-ratio combining (MRC) used in multiple antenna systems and eliminating the inter-symbol interference in high speed wireless networks. The exact formulation of the statistics of the sum is known to be very complicated. This article presents two simple closed-form approximations to the probability density function (PDF) and cumulative distribution function (CDF) of the sum of $\alpha -\mu $ variates, resembling an urban mobile communication environment. By direct integration, it is demonstrated that the PDF of the sum of $\alpha -\mu $ random variables can be approximated by a weighted sum of few identical $\alpha -\mu $ distributions including order one coefficients. The proposed approximations are of variable-order to achieve the desired accuracy and also have specific parameters using which, multiple-input multiple-output (MIMO) diversity systems can be explicitly analyzed as simply as a single-input single-output (SISO) system. In addition, a MIMO wireless system utilizing orthogonal space-time block coding technique (OSTBC-MIMO) in an $\alpha -\mu $ frequency nonselective fading environment is analyzed, and expressions for outage probability (OP) and bit error rate (BER) of digital binary modulations as well as the capacity are obtained. Moreover, the asymptotic OP and BER expressions are derived from the declared approximate expressions. The asymptotic OP and BER performances clearly indicate a diversity order equal to the product of the $\frac {\alpha }{2}$ parameter, the $\mu $ parameter, the number of transmit antennas and the number of receive antennas. Analytical results are verified by simulation.

Next generation of broadcast multimedia services to mobile receivers in urban environments

This paper analyses the possibility of receiving high data rate multimedia services in the non-stationary urban mobile scenario using the digital video broadcast standard DVB-T2. The work focuses on the complex urban mobile environment and presents a comparison between the different configuration parameters and the data rates associated to different video services. The study is based on the experience operating an experimental DVB-T2 network in urban environments, where portable and vehicular reception scenarios have been tested. The results show the system performance and the feasible video quality. The paper explores the coverage for various video services, including HDTV and 3DTV options, and proposes some scenarios for the deployment of broadcasting networks transmitting multimedia services to mobile receivers.

An introduction to millimeter-wave mobile broadband systems

Almost all mobile communication systems today use spectrum in the range of 300 MHz-3 GHz. In this article, we reason why the wireless community should start looking at the 3-300 GHz spectrum for mobile broadband applications. We discuss propagation and device technology challenges associated with this band as well as its unique advantages for mobile communication. We introduce a millimeter-wave mobile broadband (MMB) system as a candidate next generation mobile communication system. We demonstrate the feasibility for MMB to achieve gigabit-per-second data rates at a distance up to 1 km in an urban mobile environment. A few key concepts in MMB network architecture such as the MMB base station grid, MMB interBS backhaul link, and a hybrid MMB + 4G system are described. We also discuss beamforming techniques and the frame structure of the MMB air interface.

Closed-form expressions for the prediction of microcellular mobile radio propagation in urban environments

The paper derives two closed-form expressions for predicting microcellular mobile radio signal levels in urban street-grid environments. The results demonstrate that the two expressions are faster and more accurate than existing models and methods. Benefiting from physical optics and the conservation of energy, the two expressions are alternatives to available techniques such as ray tracing. The dielectric property (i.e., permittivity) of street buildings and other obstacles is essential to the ray tracing technique. However, there are no established, widely accepted techniques for selecting the permittivity in urban mobile environments, which varies in a wide range. Establishing a natural link between the received power after a street corner to the width of the street and the angle of incidence, our expressions show the possibility of making fast and accurate propagation predictions without having to use the permittivity.

EVM and BER Simulation of an NADC-TDMA Radiophone Influenced by theOperator's Body in Urban Mobile Environments

This paper presents the performance evaluation of a portable digital radiophone influenced by the operator's body in urban mobile environments, based on the EVM (error vector magnitude) and BER (bit error rate) simulation. The type of digital modulation follows to the NADC-TDMA standard. A new probability density function (pdf) is proposed to describe the statistic of the EVM in an AWGN channel under frequency non-selective slowly fading situation. The simulation combines the modified Doppler power spectrum (MDPS) method and a gray coding (π/4-DQPSK modulation with square-root raised cosine (SRRC) shaping filter. The performance evaluation based on BER uses an ideal matched-filter-based receiver. The results show that the closer of the distance between the radiophone antenna and the operator's head, the poorer of the EVM and BER performance.

Performance evaluation of a portable radio close to the operator's body in urban mobile environments

This paper presents computer simulation of the influence of the operator's body on the performance of a portable radio in mobile environments. Due to the human body blocking and absorption effects, the antenna pattern is significantly changed and a strong cross-polarized field is induced. An approach called modified Doppler power spectrum (MDPS) method is proposed to study the influence by an operator's body in mobile environments. To validate the results of the above method, we also present a second approach called direct discrete multipath (DDM) method which uses a defined a-profile distribution to relate with cross-polarization discrimination (XPD). Simulation results show that: (1) the signal envelope variations with human-body effects are also distributed according to the Rayleigh distribution, but the mean powers are decreased by a decay factor which varies according to the distance between antenna and head and (2) the closer the distance between the antenna and the head, the poorer the bit error rate (BER) performance of the radio. This means that more fading margin in the communication link budget must be counted in.

System capacity of F-TDMA cellular systems

We study the system capacity of cellular systems with time-division multiple access, slow time-frequency hopping (F-TDMA), and conventional single-user processing at the receivers. System capacity is formally defined as the maximum of the product of the number of users per cell times the user spectral efficiency for a given maximum outage probability. We adopt an information-theoretic definition of outage as the event that the mutual information of the block-interference channel resulting from a finite number of signal bursts spanned by the transmission of a user code word falls below the actual code rate, because of fading, shadowing, and interference. Starting from this definition, we develop a general framework which naturally takes into account many different aspects of F-TDMA cellular systems like channel reuse, channel utilization, waveform design, time-frequency hopping, voice activity exploitation, handoff, and power control strategies. Most importantly, our analysis does not rely on the choice of a particular coding scheme and can be applied to a very large class of systems in order to find guidelines for capacity-maximizing system design. A numerical example based on a typical urban mobile environment shows that there is a considerable capacity gap between actual F-TDMA systems and the limits predicted by our analysis. However, this gap can be filled by carefully designed (practical) systems, which make use of conventional single-user processing and simple coded modulation schemes.

UTD-based model for prediction of propagation path loss and shadowing variability in urban mobile environments

A new uniform-theory-of-diffraction- (UTD-) based approach for cellular-mobile-radio-propagation modelling is presented. Buildings are represented as conducting halfplanes or screens, and the model includes the effect of building-height variation along all intervening screens between base station and mobile. The proposed model has low computational complexity and could be applicable to small urban cells over regular terrain, with buildings of nonuniform height. It is shown that results from the model are in very close agreement with experimental observations, and that they accurately predict observed trends in the dependence of path loss and its variability on frequency, range, building-height variation and screen spacing.

Approximation of BER performance for adaptive 2-DPSK-RAKE receivers

A statistical model to evaluate the BER performance of an adaptive RAKE receiver in an urban mobile environment is presented. Path delay estimation using the maximum-likelihood estimation (MLE) technique is applied. The theoretical results are compared to computer calculations using the measured complex impulse responses of realistic mobile channels.

Shadowing variability in an urban land mobile environment at 900 MHz

Field tests have been performed in a high density urban environment to evaluate two important aspects of shadowing variability in land mobile radio links. These factors are the magnitude of variability and the rate at which variations decorrelate with time and spatial movement. The former was found to be significantly influenced by the size of the field test area. 1/e decorrelation times of the order of 15 s and decorrelation distances on the order of 100 m appear common.