Nenad Milosevic

The CoordSS experimentation framework ontologies

The CoordSS experimentation framework aims to provide a solid practical evidence that testbeds and other experimentation infrastructure provided by EU FP7 FLEX project is capable of supporting advanced experimentation with proposed use of LTE Advanced in unlicensed 5 GHz spectrum (LTE-U). By integrating technologies such as spectrum sensing, various coexistence mechanisms between legacy unlicensed technologies (primarily WiFi) and LTE, and a range of coordination protocols, the frameworks primary objective is to enable experimentation with SDR based LTE in unlicensed spectrum. The flexibility of such experimental environment is addressed by adoption of domain and system ontologies for formal representation of semantics of the problem. This paper deals with ontologies that are needed for the CoordSS experimentation framework implementation.

Performance analysis of FFH/FSK system using diversity

We consider a binary orthogonal frequency-shift-keying receiver employing fast frequency hopping waveforms transmitted over a frequency-nonselective slowly fading channel with partial-band interference. The diversity is performed using multiple hops per data bit. It was shown that the system with diversity has better performances in the case of strong fading or strong interference than the system without diversity.

Performance Improvement of MDPSK Signal Reception in the Presence of Carrier Frequency Offset

Performance of mobile systems is significantly influenced by the carrier frequency offset caused by a Doppler shift, which leads to deployment of differential modulation schemes instead of coherent detection-based schemes. In this paper, we propose a novel M-ary differential phase-shift keying (MDPSK) receiver that performs better than the receiver with MDPSK differential detection and is very close to the performance of a coherent MDPSK detector. The symbol error probability of the proposed MDPSK receiver is approximately constant within the practical frequency offset range. The proposed receiver may be used in the systems that work in fading and with high-frequency offset environments.

Low computing complexity frame synchronization for OFDM communication

The paper deals with a new frame synchronization scheme for OFDM systems. The scheme is based on the computing of the detection window variance. The variance is computed in two delayed times, so a modified Early-Late loop is used for the frame position detection. The proposed algorithm has good properties regarding the choice of the algorithms parameters since the parameters may be chosen within a wide range without having high influence on system performance. The verification of the proposed algorithm functionality has been performed on a development environment using universal software radio peripheral (USRP) hardware. The experimental results are compared to the simulation results, where the simulated system was an equivalent OFDM system with ideal time synchronization.

Performance of ultra wide band system using nonlinear receiver in the presence of interference

The performance of a time hopping combined with pulse position modulation ultra wide band system with a nonlinear receiver using an adaptive filter and a soft-limiter in the presence of narrowband interference has been considered. This system brings a significant performance improvement compared with the system that uses an adaptive filter and a linear receiver, particularly in the case of high-interference power where its absence leads to the reception loss. Also, the proposed receiver has much better interference rejection performance compared with minimal mean-square error interference rejection, in case of high-interference power (interference to signal ratios from 30 to 65 dB).

Modal density of sound pressure level in a room

Modal analysis of the sound field in a rectangular room at low frequencies, based on the physics of the modal sound field, is presented in this paper. The eigenfrequencies and the modal density, which can be calculated with the well-known formulas and obtained by the calculated characteristic sound pressure level for three rooms with the same volume but different dimensions, is analysed. One of the main conclusions are that the sound field is determined, not by all eigenfrequencies that can be excited in the room, but only by extremely excited modes in a given band. Because of that, the spatial distribution of the sound field is a practically determined by these modes.

Performance Analysis of Interference-Limited Mobile-to-Mobile κ–μ Fading Channel

In this paper, a wireless cooperative network, with two sections, operating over multipath mobile-to-mobile interference-limited fading channel is considered. The desired signal and the cochannel interference experience κ–μ short term fading. The source and destination mobile stations are connected by an amplify-and-forward relay mobile station. The destination station signal-to-interference ratio probability density function and the outage probability closed-form expressions are derived. The closed form approximate expressions for the average fade duration and the level crossing rate are also derived. The influence of the fading channel parameters on these statistical measures are studied. The Monte-Carlo simulations are used to validate the theoretical results.

Wireless Networks Coexistence in Unlicensed Bands

Mobile communication networks are constantly evolving and each new generation provides considerably higher data transmission capabilities. Having in mind predictions of high cellular data traffic growth over the next few years, it is clear that the licensed band communications would have problems to support such a high bandwidth demand. One of the possible solutions to this problem is to adaptively use some additional spectrum out of the dedicated licensed band, such as the unlicensed bands. LTE-A standard introduced a new mechanism, named Carrier Aggregation, which provides the possibility to simultaneously use multiple frequency bands, such as the licensed and unlicensed bands. In order to work in an unlicensed band, LTE has to employ some new procedures that provide shared access with other systems using the same frequency band, such as WiFi. These procedures include spectrum sensing, dynamic frequency selection, as well as the coordination of the shared access. Performance measurements and the analysis of the procedures in 5 GHz frequency band will be shown in this paper. Since there is no available LTE hardware operating in 5 GHz band, it has to be made in a laboratory using the software radio approach. The description of such an experiment may be complex, and therefore we describe and propose the concept of the automatic experiment code generation. The automatic code generation is based on the semantic descriptions of experiments, and it is flexible due to the adoption of the domain and system ontologies for formal representation of the semantics of the problem.

STATISTICS OF SIGNAL TO INTERFERENCE RATIO PROCESS AT OUTPUT OF MOBILE-TO-MOBILE RAYLEIGH FADING CHANNEL IN THE PRESENCE OF COCHANNEL INTERFERENCE

Dual-hop cooperative communications in interference-limited Rayleigh fading channel will be investigated in this paper. The paper considers the first- and second-order statistics of the signal to interference ratio process at the input of the destination mobile station. The exact closed-form expressions for the first-order statistical measures, the probability density function and cumulative distribution function, will be derived. We will also derive approximate closed form expressions for the second-order statistics, the level crossing rate and the average fade duration. The obtained theoretical results will be verified by the Monte-Carlo simulations.

Semantic coordination protocol for LTE and Wi-Fi coexistence

In this paper, we address the challenges in facilitating the intra-band coexistence of WiFi and LTE technologies in multi-RAT networks and propose a semantic coordination protocol that improves the communication performance among inter-network devices. Effective communication in LTE networks is a critical task to achieve as the heterogeneity of the devices and coexisting technologies arises. This paper introduces an internetwork spectrum coordination across Wi-Fi and LTE systems based on an ontological framework as a possible solution for improved coexistence. We develop and evaluate our approach under real-world settings. The results we obtained using the proposed semantic coordination protocol have shown significant gains for both the under-study Wi-Fi and LTE networks.