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The study of propagation inside confined environments leads to very specific results. Specular reflections are not dominant and the result is more comparable with diffuse scattering. Evaluating this channel can be done using acoustic theory. However, this theory is described by a parameter, eta whose physical meaning lacks of description. Reverberation chamber theory can therefore be applied to estimate...
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This paper is the extension of the first paper (Rashad et al., 2007) that described the modification of rectangular pilot pattern applied in OFDM-based cognitive radio system. In this paper, a new concept for pilot symbols arrangement in OFDM transmission system is introduced. The new idea is the virtual pilot symbols concept which is based on the interpolation of the received pilot symbols. Further...
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Adaptive resource allocation has been shown to provide substantial performance gain in OFDMA based wireless systems when perfect channel state information (CSI) is available at the transmitter. However, perfect CSI at the transmitter (CSIT) is rarely possible due to channel estimation errors and channel feedback delay. In this paper, we consider practical resource allocation strategies for downlink...
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The current service-and device discovery protocols are not platform-and network independent. Therefore, proxy servers will be needed to extend the range of IP-based discovery protocols to non-IP domains. We developed an architecture of a proxy that enables Universal Plug and Play (UPnP) devices and services to be discovered and accessed on the Bluetooth network and vice versa. We optimized and implemented...
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In this work, we introduce a new approach for channel estimation in single frequency networks (SFN). The intention is to exploit the a-priori knowledge of the SFN scenario. Conventional pilot schemes for SFN design the pilot scheme to deal with the aggregate channel. In this paper, we show that by being aware of how this long channel is generated, we can design a more efficient pilot scheme. The core...
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A broadband, continuously tunable receiver system for phased array antennas is described. It uses a ring resonator-based optical beamforming network, filter-based optical SSB-SC modulation and balanced coherent detection. The system is modeled as an equivalent RF two-port system and its performance is analyzed, identifying and modeling dominant noise and distortion sources. Numerical theoretical performance...
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The 60 GHz band, with a large unlicensed bandwidth, is an excellent choice for short distance high-speed communications. However, radio frequency (RF) circuit limitations at 60 GHz give rise to impairments such as phase noise, in-phase/quadrature-phase (I/Q) imbalance and amplifier nonlinearities. The candidate transmission schemes, in addition to multi-path fading, should therefore be fairly robust...
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Multi-carrier CDMA takes advantage of frequency diversity by spreading each user symbol across multiple sub-carriers to improve the transmission performance. However, the performance of linear detection schemes is affected by the residual inter-symbol interference (ISI) and the correlated noise present in decision variables. In order to improve the performance, a decision feedback equalization (DFE)...
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The influence of nonlinear high power amplifier (HPA) at transmit side on single-and multi-carrier block transmission systems is studied in wireless mutipath environments. We consider the single carrier block transmission with frequency domain equalization (SC-FDE), OFDM and MC-CDMA. The effective signal-to-noise ratio (SNR) and SNR penalty caused by the nonlinearity are derived and analyzed. In addition,...
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Hierarchical modulation, used in DVB-{T, H} (digital video broadcasting - terrestrial and handheld), allows two separate bit streams to be modulated on one single stream according to their relative priority (high priority and low priority stream). We investigate the robustness of coupled OFDM (orthogonal frequency division multiplex) and hierarchical modulation systems under impulse noise as it appears...
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Multi-hop relay is essential for ad-hoc networking in order to interconnect remote communication devices. This enables information exchange in areas without a pre-deployed communications infrastructure, making it an appealing technology for the military community. The focus of this article is on TCP throughput measurements for multi-hop networking based on WLAN technology using COTS devices. The present...
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Nowadays research in the area of Cognitive Radio has grown tremendously. In the application of spectrum pooling in OFDM-based Cognitive Radio system there will be subcarriers that are deactivated due to the access of Licensed Users. The unloaded subcarriers that are caused by Licensed Users access create problems in performing channel estimation. The unloaded subcarriers restrict putting the pilot...
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In this paper we consider an OFDM (orthogonal frequency division multiplexing) transmission scheme with a relay. Symbols sent by the source may or may not be retransmitted during a second time slot by the relay, which is assumed to be of the decode-and-forward (DF) type. For each carrier the destination implements maximum ratio combining. Assuming perfect CSI (channel state information) knowledge...
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The dense multipath scattering typical of ultra-wideband (UWB) wireless channels provides very large multipath diversity, but from the other side makes the receiver design a demanding task as far as channel estimation and timing recovery are concerned. The contribution of this paper is to derive a novel receiver structure based on the multiple symbols differential detection (MSDD) framework with particular...
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Many performance evaluations for distributed coordination function (DCF) for IEEE 802.11 Wireless LANs have been previously reported in the literature; most studies based on are saturation analysis, and a few models under a finite load condition adopt an M/G/l queuing system. However, using M/G/l queuing only considers the first moment of frame service time to derive the probability of transmission...
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Localization using Ultra Wide Band (UWB) signals can show large errors. Due to Non-Line-of-Sight (NLOS) propagation and low signal to nosie ratio (SNR), it is possible to expect that the first arriving path and the strongest path are not equal to each other. This problem can be modeled as a multihypothesis problem. We base our decision on matched subspace detectors. The case where we deal both with...
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In this paper we apply predictive vector quantization (PVQ) to quantize time-correlated broadcast channels. PVQ exploits the time-correlation of the channel to reduce the quantization error of the channels, and thus to improve the sum rate of the system. PVQ predicts the actual channel based on a number of previous channels, and then quantizes the difference between the prediction and the true channel...
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Modern wireless networks need to integrate different types of traditional and multimedia traffic. This paper proposes a new WLAN access mechanism as an alternative to the HCF (Hybrid Coordination Function) scheme defined by the IEEE 802.1 le workgroup to provide QoS in wireless LANs. POHA (Priority Oriented Hybrid Access) is a complete medium control protocol, it combines a polling based and a TDM...
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Co-ordinate interleaving (also known as signal space diversity (SSO)) with the rotation of signal constellation of multilevel modulation schemes with bit interleaved coded modulation (BICM) is known to provide good performance for single carrier systems. This paper studies the extension of SSD with recursive systematic convolutional (RSC) coded BICM and constellation rotation in an orthogonal frequency...
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In order to enable efficient implementation of wireless systems with high signal dynamics, this paper proposes an approach to estimate and correct for the amplitude and phase distortion caused by nonlinear power amplifiers. The approach comprises a preamble design, an estimation method and a digital compensation algorithm. Correction for the nonlinearities is applied in the receiver, which requires...
