Cross layer design for service differentiation in mobile ad hoc networks

Cross layer design is a promising approach in mobile ad hoc networks (MANET) to combat the fast time-varying characteristics of wireless links, network topology, and application traffic. In this paper, we employ cross layer design to develop a novel scheduling scheme with two optimizations aimed at service differentiation. The scheduling scheme is executed at the network layer of every station according to the channel conditions estimated by the MAC layer. The optimizations are based on traffic property sharing and packet timeout period interaction to reduce the packet collisions and improve network performance. We evaluate the proposed scheme under different network loads in terms of packet delivery ratio, average end-to-end delay and delay jitter. The simulation results show that our scheme can provide different service differentiations for time-bounded and best effort traffics. In particular, we can guarantee the delay and delay jitter requirements of time-bounded traffic. © 2003 IEEE.published_or_final_versio

Performance Evaluation of Training Based Channel Estimation in MIMO-OFDM Wireless SystemÂ

In modern wireless communication systems, multiple input multiple output (MIMO) combined with orthogonal frequency division multiplexing (OFDM) can achieve reliable high data rate and better spectral efficiency. Channel estimation technique based on pilot arrangement for multiple input multiple output (MIMO) for Rayleigh fading channel is proposed in this paper. The channel estimation using block type pilot arrangement is carried out with Least square (LS) and Minimum mean square (MMSE) estimation algorithms through matlab simulation. The performance of channel estimation techniques LS and MMSE are compared on the basis of mean square error (MSE) for 2x2 and 4x4 MIMO-OFDM system

A Novel SAGE Algorithm for Estimating Parameters of Wideband Spatial Nonstationary Wireless Channels with Antenna Polarization

In this article, a novel space-alternating generalized expectation-maximization (SAGE) algorithm is proposed for parameter estimations of wideband spatial nonstationary wireless channels with antenna polarization (SAGE-WSNSAP). Compared with the traditional SAGE algorithm, the proposed SAGE-WSNSAP algorithm adds spatial nonstationarity by introducing birth-death coefficients at both transmitter (Tx) and receiver (Rx) sides into the parametric model. To reduce the complexity of the SAGE-WSNSAP algorithm, a coarse-to-fine search method is adopted in the initialization step. In addition, multiple-input multiple-output (MIMO) channel measurements are conducted to validate the proposed algorithm. The measurement results of the angle-delay power spectral density (PSD) and average delay PSD are compared with those estimated by the far-field SAGE algorithm, the near-field SAGE algorithm, and the proposed algorithm. It is found that the estimation results using the proposed SAGE-WSNSAP algorithm show higher similarity to measurement results than using the other two SAGE algorithms. In comparison to the far-field and near-field SAGE algorithms, the SAGE-WSNSAP algorithm can extract more effective multipath components (MPCs) and improve the power extraction ratios.</p

A combined MMSE-ML detection for a spectrally efficient non orthogonal FDM signal

In this paper, we investigate the possibility of reliable and computationally efficient detection for spectrally efficient non-orthogonal Multiplexing (FDM) system, exhibiting varying levels of intercarrier interference. Optimum detection is based on the Maximum Likelihood (ML) principle. However, ML is impractical due to its computational complexity. On the other hand, linear detection techniques such as Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) exhibit poor performance. Consequently, we explore the combination of MMSE estimation with ML estimation around a neighborhood of the MMSE estimate. We evaluate the performance of the different schemes in Additive White Gaussian Noise (AWGN), with reference to the number of FDM carriers and their frequency separation. The combined MMSE-ML scheme achieves a near optimum error performance with polynomial complexity for a small number of BPSK FDM carriers. For QPSK modulation the performance of the proposed system improves for a large number of ML comparisons. In all cases, the detectability of the FDM signal is bounded by the signal dimension and the carriers frequency distance

Broadband Spectrum Survey Measurements for Cognitive Radio Applications

It is well known that the existing spectrum licensing system results in a gross under-utilization of the frequency spectrum. Spectrum background measurements – spectrum surveys – provide useful data for spectrum regulation, planning or finding frequency niches for spectrum sharing. Dynamic spectrum sharing as a main goal of cognitive radio (CR) is the modern option on how to optimize usage of the frequency spectrum. A spectrum survey measurement system is introduced with results obtained from a variety of markedly different scenarios allowing us, unlike other studies, to focus on wideband and fast spectrum scans. The sensitivity of the receiver is no worse than -113 dBm in the whole band. The utilization of the frequency spectrum is analyzed to prove its under-utilization and to show spectrum sharing opportunities. This was shown to be true in the frequency band higher than 2.5 GHz. A comparison with other spectrum survey campaigns is provided

Performance Evaluation of Channel Estimation in OFDM System for Different QAM and PSK Modulations

To recover accurate transmitted data at the receiver end, the information regarding channel state derived from channel estimation methods play a very important role in any communication system. In this paper the performance evaluation of different types of QAM and PSK modulations with three different channel estimation methods in OFDM system for wireless communication in frequency domain for slow fading channel is compared. The results must be useful in OFDM based applications like IEEE 802.16(d) and equivalent standards.DOI:http://dx.doi.org/10.11591/ijece.v1i2.14

Power control approach for IEEE 802.11 ad hoc networks

In packet radio networks, especially an ad hoc wireless network using IEEE 802.11 as the MAC (media access control) protocol, power control is a crucial issue. By using a judicious power control mechanism, co-channel interference can be significantly reduced, thus improving the channel spatial reuse and network capacity. However, efficient power control in an IEEE 802.11 system is very challenging because according to the standard, fixed power is used for transmitting packets, and there is only one channel. In this paper, we propose an enhancement to the standard IEEE 802.11 MAC protocol by improving the handshaking mechanisms and adding one separate power control channel. With the control channel, the receiver notifies its neighbors its noise tolerance. Thus, the neighbors can adjust their transmission power levels to avoid packet collisions at the receiver. Through extensive simulations using NS-2, our proposed power control mechanism is found to be effective in that network throughput can be increased by about 10%, and the battery utilization can also be improved at the same time.published_or_final_versio

Investigation into the design of broadband singly-fed electromagnetically coupled patch (EMCP) antenna elements and arrays for circular polarisation

University of Technology, Sydney. Faculty of Engineering.The rapid development of satellite and wireless communications pose extraordinary demands on broadband circularly polarised (CP) antenna elements and high-performance antenna arrays. The use of high-dielectric-constant materials as the substrate for the driven layer and a low-dielectric-constant material as superstrate for the radiating patch overcomes the conflict between circuit integration and antenna radiation. The aim of the research presented in this thesis is to design and develop high performance singly-fed microstrip patch antennas and arrays for CP applications. Firstly, we introduce a singly-fed cross-aperture coupled patch antenna and a stacked patch antenna using high and low dielectric materials known as Type-F and Type-E elements, respectively. As the physical structure of the Type-E element is close to the conventional linearly-polarised electromagnetically coupled patch (LP-EMCP) antennas, we have also denoted it as CP-EMCP antenna. The development of CP-EMCP antennas addresses the drawbacks of the cross-aperture patch antenna. A systematic optimisation method is developed for the design of CP-EMCP elements, at which the mean frequencies of the bandwidths can be adjusted in order to achieve a wide overlaid bandwidth. Secondly, we investigate the effects of perturbation on the parasitic patch, layer displacements, material tolerances and superstrate thicknesses on the broadband performance as well as the mutual coupling of the CP-EMCP elements. Both our theoretical and experimental results show that the CP-EMCP elements are robust in performance and have a low mutual coupling. When compared to the conventional stacked EMCP antennas and to the reduced surface-wave antenna, the mutual coupling between CP-EMCP elements is lower which allows the use of small element spacings to avoid grating lobes, which therefore make these elements good candidates for high-performance CP arrays. Following a parametric study on the effect of displacements between stacked patches and the loss consideration of the coplanar feed network printed on high dielectric constant substrates, the modified Type-E elements whose parasitic patch have a zero perturbation are developed for the design of high performance CP arrays. The low mutual coupling allows short feed-lines to connect with the spatially offset elements so as to minimise the feed loss. Consequently, it became possible to develop the novel sequentially rotating feed networks which incorporate the modified elements with a small element spacing of 2/3/λₒ for the 4- and 16-element planar antenna arrays. The results indicate that these arrays have high gain, low axial ratio, high antenna efficiency low sidelobe levels, and wide overlaid bandwidth