Y. A. S. Dama

Optimizing Outdoor Propagation Model based on Measurements for Multiple RF Cell

This paper intends to study outdoor RF attenuation path loss behavior under certain restrictions. The study has been conducted in Nablus city to develop and optimize a suitable propagation model based on one of the existing propagation models based on outdoor measurements for 900 MHz, where a local GSM system is operating under sever geographical terrains and frequency limitations. The optimized model has been chosen such that certain error parameters are minimized. Some of the proposed models are; Bertoni-Walfish, Hat, Walfisch-Ikegami and the standard macrocell. In this paper a Tuned Bertoni-Walfisch model has outperformed the other models and has proven, to be the best suited for propagation analysis involving such terrain. This is achieved by varying the range dependence using Least Mean Square Error (LMSE) method

On the performance of DWT and WPT modulation for multicarrier systems

The discrete wavelet transform, DWT, is being considered for multicarrier modulation, and intensive investigations are underway on how this scheme can best be deployed. The performance of the DWT and wavelet packet transform (WPT) has been investigated and compared. There are more narrowband sub-channels in WPT than those that exist in DWT owing to the style of multiresolution adopted by the latter. However, it is found that DWT and WPT perform differently as multicarrier modulations over AWGN and multipath channels. This work helps to inform the selection of base-wavelet families when studying or designing a multicarrier system of this kind.

A New Approach for OSTBC and QOSTBC

ABSTRACT A new approach for Quasi-Orthogonal space time block coding (QO-STBC) is proposed, with simple linear decoding via maximum likelihood detection. The conventional QO-STBC can achieve the full communication rate, but at the expense of the decoding complexity and the diversity gain due to the interference terms in the detection matrix. In this paper we propose a QO-STBC scheme that will eliminate the interference from the detection matrix. The proposed code improves the diversity gain compared with the conventional QO-STBC scheme; it also reduces the decoding complexity. A full rate full diversity order DiagonalizedHadamard Space Time code (DHSTBC) is presented Keywords Quasi-Orthogonal space time block coding (QO-STBC), full rate, full diversity order,DiagonalizedHadamard Space Time code (DHSTBC). 1. INTRODUCTION In traditional communication systems there is only one antenna at both the transmitter and the receiver. This antenna system is known as Single Input Single Output (SISO). SISO systems have a major drawback in terms of the capacity, as stated by the well-known Shannon-Nyquist criterion. In order to increase the capacity of SISO systems to meet the high bit rate transmission demanded by modern communications, the bandwidth and the power have to increase significantly. Fortunately, using the Multiple-Input Multiple-Output (MIMO) system could increase the capacity of the wireless system without the need to increase the transmission power or the bandwidth. Transmit diversity is a well-known technique to mitigate fading effects over a communication link. Alamouti [1] proposed a transmit diversity scheme that offers maximum diversity gain using two antennas at the transmitter. The pioneering work of Alamouti has been the basis to create Orthogonal space time block coding systems (OSTBCs) for more than two transmit antennas. First of all, Tarokh studied the error performance associated with unitary signal matrices [2]. Sometime later, Ganesan streamlined the derivations of many of the results associated with OSTBC and established an important link to the theory of the orthogonal and ‘amicable orthogonal’ designs [3]. It has been proved that a complex orthogonal design of STBCs that provides full diversity and full transmission rate is not possible for more than two transmit antennas [1]. To achieve full-rate transmission while maintaining much of the orthogonality benefits of OSTBC, Quasi Orthogonal Space Time BlockCode(QO-STBC) has been proposed [4-6]. A QO-STBC can achieve full rate but interference terms will appear from the neighboring signals during the signal detection which will increase the detection complexity and decrease the gain performance.

Performance Evaluation of DWT-OFDM and FFT-OFDM for Multicarrier Communications Systems using Time Domain Zero Forcing Equalization

Other than the conventional fast Fourier transform (FFT) for multicarrier modulation, a new approach for multicarrier modulation (MCM) has been known. Meanwhile, multicarrier modulation involves dividing the broadband channel into many orthogonal but overlapping narrowband carriers. In an OFDM modulation based multicarrier system using the FFT, a cyclic prefix (CP) is inserted after each symbol frame to combat the effects of inter symbol interference (ISI). By inserting the CP, which results in spectral inefficiency OFDM schemes trades up to 25% of the transmit bandwidth. A new MCM approach that is void of the expense is the wavelet transform-based systems. These systems also have very suppressed side-lobes and exhibit improved BER performance. In wavelet based systems, the latest challenge in its implementation is in the channel estimation. In this work we have studied the performance of the FFT based OFDM system against wavelet transform (WT) based multicarrier system using a simple zero forcing (ZF) equalization in time domain. The studied system shows some improved BER performance.

Linear and nonlinear crosstalk in MIMO OFDM transceivers

This paper studies the effect of nonlinear and linear crosstalk in a MIMO (multiple in, multiple out) transceiver. These effects are mainly due to the power amplifier (PA) nonlinear behaviour and mutual coupling of antennas in the MIMO transmitter. The effects of the crosstalk interference on the signal performance are studied based on the measured error vector magnitude (EVM) at the transmitting antennas. The simulation and measurement results show that PA nonlinearity and RF crosstalk need to be considered in the design process.

Secondary User Power Saving in Overlay Cognitive Radio Networks

The secondary user power saving in the overlay based Hybrid Automatic Repeat request cognitive radio has been investigated. The effect of the power splitting ratio on the secondary transmissions has been studied and a simple power saving technique for secondary users is proposed. Extensive simulation runs have been carried out to validate our results. General Terms:

Indoor Channel Measurement and Prediction for 802.11n System

Significant improvements in the quality and reliability of indoor WLAN communications are claimed for devices with MIMO technology applying 802.11n standards, that allow users to achieve a theoretical data rate up to 300-600 Mbps on a single transmission. This paper presents an analysis of a commercial 802.11n MIMO 2¿e3 dual band (2.4 and 5 GHz) system focusing on the operational throughput performance over an indoor environment for Line of Sight (LOS) and Non Line of Sight (NLOS) scenarios. Efforts on combined field strength distribution, throughput, propagation-channel environments, of this system will be elucidated. The work is focusing on the operational performance of the physical measurements and results compared with simulation model over an indoor environment.

Envelope correlation formula for (N, N) MIMO antenna array including power losses

The scattering parameter formulation for the envelope correlation in an (N, N) MIMO antenna array has been modified to take the intrinsic antenna power losses into account. This method of calculation provides a major simplification over the use of antenna radiation field patterns. Its accuracy is illustrated in three examples, which also show that the locations of the correlation minima are sensitive to the intrinsic losses.

An Evaluation of Spatial Modulation for MIMO Systems with QO-STBC

Simplified designs of multi-antenna systems with optimum efficiency are receiving attentions. Such simplicities also involve low cost architectures. In this study, we report an evaluation of a new multi-antenna scheme, namely, spatial modulation (SM) that is compared with quasi-orthogonal space time block codes (QOSTBC) scheme over Rayleigh fading channel. The SM scheme has been, earlier, compared with space time block codes (STBC) – a two antenna transmit diversity scheme that achieves full diversity when only two antennas are used. This is extended to QOSTBC scheme that absolves some decoding limitations to attain full diversity. It will be shown that, using the QOSTBC of similar architecture with the SM, even better performance can be achieved in favour of QOSTBC.

A Multi-service Cluster-Based Decentralized Group Key Management Scheme for High Mobility Users

Previous cluster based group key management schemes for wireless mobile multicast communication lack efficiency in rekeying the group key if high mobility users concurrently subscribe to multiple multicast services that co-exist in the same network. This paper proposes an efficient multi-service group key management scheme suitable for high mobility users which perform frequent handoffs while participating seamlessly in multiple multicast services. The users are expected to drop subscriptions after multiple cluster visits hence inducing huge key management overhead due to rekeying the previously visited cluster keys. However we adopt our already proposed SMGKM system with completely decentralised authentication and key management functions to address demands for high mobility environment with same level of security and less overhead. Through comparisons with existing schemes and simulations, SMGKM shows resource economy in terms of rekeying communication overhead in high mobility environment with multi-leaves.