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Traditional OFDM systems present some embedded features that may be exploited in order to intercept the wireless transmitted signal. However, such a possibility is not accepted in military applications where security is a very important issue. Cyclic prefix is one of the most obvious OFDM parameters that induce cyclostationarity features. Aiming to suppress these features, some classical solutions...
This paper studies a spectrum sharing cognitive radio (CR) network coexisting with a primary network. In particular, the channel state information (CSI) between the secondary transmitter (STx) and the primary receiver (PRx) is assumed to be outdated due to channel feedback latency. We assume that the secondary user (SU) shall satisfy a given delay quality-of-service (QoS) constraint as well as the...
Carrier aggregation (CA) has been proposed as a key feature of the 4G cellular networks to achieve the very high data rates. It is known that the correlation between the subchannels, including both small- and large-scale fading, is critical in determining the performance gain we can obtain from the multicarrier transmission. However, due to the prohibitively high complexity and cost in simultaneously...
It has been shown that due to its smaller signal bandwidth (96 KHz), DRM+ signal could suffer from flat fading degradation at low receiver speeds, particularly in urban environments. To alleviate this problem, a simple transmit delay diversity (TDD) has been proposed in the standard. This paper tries to investigate this issue by presenting the performance results of multipath fading characterizations...
There are many studies dealt with handoff management in mobile communication systems and some of these studies presented handoff schemes to manage this important process in cellular network. All previous schemes used relative signal strength (RSS) measurements. In this work, a new proposed handoff scheme had been presented depending not only on the RSS measurements but also used the threshold distance...
Based on static outdoor channel measurements we evaluate the influence of a vehicle on the MIMO radio channel, from a base station antenna array, to a multiple antenna handset in the hand of a user placed inside a test car. The measurement scenario is chosen to mimic a 2.6 GHz (LTE) macro-cell urban or rural scenario with two locations and orientations of the car, one at an open parking lot with a...
In this paper, a generalized likelihood ratio test (GLRT) is adopted to realize optimum detection for differential UWB signal. Supposeing the channel circumstance is unknown, receiver presented in this paper is structured as follows. First of all, the maximum likelihood (ML) estimation of channel is completed. And then statistic detection of differential UWB signal is practiced. The receiver is approved...
In this paper, we study the impact of an important RF impairment inside direct-conversion receiver, namely the I/Q imbalance, on the performance of OFDM radio link over frequency-selective Rayleigh fading channel. Closed-form expressions for link performance, in terms of detection error rate, ergodic capacity and outage capacity, under both frequency-selective RX I/Q imbalance and noisy frequency-selective...
Multi-site measurements for urban macro cells at 2.66 GHz are performed with three base stations and one mobile station. In order to analyze the correlation properties of large scale parameters, we split up the routes into subsets, where it can be assumed that wide-sense stationarity (WSS) applies. The autocorrelation distance and correlation properties of large scale parameters for each link are...
In this paper, a novel OFDM symbol timing recovery method, which is robust to doubly selective fading channels and carrier frequency offset, is proposed for the mobile terminals of CMMB system. The time slot timing synchronization is accomplished by using the inverse sliding correlation between the segmenting Sync sequences, which possess the inverse conjugate symmetry (ICS) characteristic. Furthermore,...
Small-scale fading has its origin in the constructive and destructive superposition of electromagnetic waves. The fading process can be modeled by adding vectors in the complex plane using the so-called phasor model. Simulation results showed that this modeling allows very accurate reproduction of measured fading processes. The parameters of the phasor model can be obtained from measured Doppler power...
This paper investigates the performance of delay diversity with subcarrier-based signal phase rotation in an OFDM system. Delay diversity achieves transmit diversity with channel coding by intentionally ingenerating paths which have different delays at a transmitter side. However, the correlation between subcarriers is not always low. The proposed scheme which combines the delay diversity and the...
In cognitive radio networks, spectrum sensing is a fundamental function for detecting the presence of primary users in licensed frequency bands. Due to multipath fading and shadowing, the performance of detection may be considerably compromised. To improve the detection probability, cooperative sensing is an effective approach for secondary users to cooperate and combat channel impairments. This approach,...
It is known the operating efficiency of radio technical systems of different function (navigation, radar, communication), to a great extent depend on condition of propagation of radio-waves is conditioned on atmosphere refraction state. It for one's turn is conditioned on spatial-temporal distribution of refraction coefficient n. And variation of mean refraction and numerous cases of so called anomalous...
The impact of inaccurate channel knowledge on the system performance of a cooperative multi-cell system is studied. Using optimization theory, we investigate the performance degradation due to optimizing the collaborative downlink transmit signals of multiple base stations (BSs) based on inaccurate channel knowledge. Two important sources of channel knowledge inaccuracy are considered: quantization...
A channel model, based on stochastics and Ray tracing, is described for a communication system, in which moving participants communicate in the 24 GHz band. A realistic behaviour of propagation effects, both short-term and long-term, is modeled. This allows to simulate and design future vehicle-to-vehicle systems.
We analyze the outage probability of frequency domain minimum mean squared error turbo equalization over frequency-selective Rayleigh fading channels with exponential delay power profile. A correlation chart analysis is used to evaluate the convergence property of the iterative system. Based on the convergence characteristic of the equalizer and decoder, we derive a closed form approximation to the...
Spatial fading correlation is analyzed for an OFDM diversity receiver when network includes an RF repeater. Previously, it is reported that the effect of correlation can be reduced by the Time Shifted Sampling (TSS) technique which relies on multipath diversity. In this study, a multipath channel is constructed by repeated signal instead of natural multipath due to cluttered environments and the performance...
Many communication signals exhibit cyclostation-arity with some cycle frequencies and the cycle frequencies are related to signal parameters such as symbol rates, carrier frequencies. Dandawate proposed a statistical test to check the presence of cyclostationarity using a single cycle frequency. And recently, the statistical test has been applied to spectrum sensing. For most modulated communication...
A stochastic multiple-input multiple-output (MIMO) wireless channel model is discussed and its implementation scheme is proposed. An improved shaping-filter method, which can eliminate correlation of different paths by adding a random phase-shift and obtain the tap coefficient by using a double interpolation method, is proposed to simulate the MIMO fading channel. Simulation of 3GPP standard model...
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