Bojan Dimitrijevic

Adaptive self-reconfigurable interference suppression schemes for CDMA

In this paper we present a new approach to interference suppression in code-division multiple-access (CDMA) wireless networks. Depending on the interfering signal, these schemes adaptively change not only their parameters but their structures as well. For the relevant types of the interfering signal, suppression is also possible for the wideband interference occupying the same frequency band as the CDMA signal. Probability of error in these schemes is for several orders of magnitude better than in the existing solutions described in the open literature so far. The main applications are the CDMA overlay type wireless network collocated in the same frequency band with a high bit rate microwave communication system, and the multimedia CDMA network where high bit rate signal due to lower processing gain must use a higher level in order to provide the required quality of transmission.

Performance analysis of dual hop relay link in Nakagami-m fading channel with interference at relay

In this paper we consider performance of a dual hop amplify-and-forward system, with co-channel interference at relay. We consider channel state information assisted system in Nakagami-m channel. The outage probability and the average bit error probability of the system are determined. The influence of the interference, as well as the influence of other systems parameters, such as the fading parameter m and outage probability threshold γth on the systems performance is considered.

Multilayer LMS interference suppression algorithms for CDMA wireless networks

The general theory of adaptive self reconfigurable interference suppression schemes is applied to several specific practical problems mainly suppression of m-level m amplitude-shift keying, m phase-shift keying (PSK), and m quadrature amplitude modulation signals. This is a practical situation when a code-division multiple-access (CDMA) network is overlaid with standard microwave systems. Another example is a multirate CDMA network where a limited number of high bit rate CDMA signals are allowed to use much higher power level due to lower processing gain. The algorithm is well suited for a modular software radio concept, which we believe, will be more and more accepted in future wireless communications. Further modifications of the schemes necessary for these applications are described, and numerous results are presented to illustrate performance improvements. A general interpretation of these techniques based on so-called multilayer least mean squares (LMS) algorithm is introduced and discussed. The algorithm is based on estimating fast changing interfering signal parameters by using parallel structures, which are fast but complex. At the same time, estimation of slow-varying signal parameters over a large range is accomplished by using an LMS algorithm that is simple but slower. In this way, suppression of the interference occupying the same bandwidth as the CDMA signal is possible with reasonable implementation complexity. For this case, a BER 0 dB for binary PSK interference, J/S>17 dB for 8-PSK, J/S>27 dB for 32-PSK, and J/S>40 dB for 128-PSK.

Application of wireless sensors within a traffic monitoring system

The work describes a sensor system to monitor traffic-related data such as the number, type, and speed of vehicles on a road. Essential components like networked intelligent embedded systems for sensor data acquisition and aggregation and the antenna configuration are described and explained. Results of the application are illustrated.

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 analysis of reconfigurable receiver in DSSS system in the presence of interference

In this paper, we analyzed performance of DSSS/DPSK system in the presence of packet PSK interference. The results show that the proposed reconfiguration circuit decreases the error probability for at least an order of magnitude, compared to the system using only ¿-structure.

Three Dimensional Direction Lock Loop for DS/CDMA Systems

In this paper, an algorithm for three dimensional direction of arrival estimation is proposed. The proposed algorithm is presented using model of the mobile receiver having three antennas. It is shown that the proposed algorithm is able to track both azimuth and elevation by forming two S-curves, if the initial direction of arrival estimate is within a certain range which is referred to as the locking range like the DLL scheme in timing 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).

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.