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The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot. [ABSTRACT FROM AUTHOR]

Next generation wireless networks (i.e., WiMAX, LTE) provide higher bandwidth and spectrum efficiency leveraging smaller (femto) cells with orthogonal frequency division multiple access (OFDMA). The uncoordinated, dense deployments of femtocells however, pose several unique challenges relating to interference and resource management in OFDMA femtocell networks. Towards addressing these challenges, we propose RADION, a distributed resource management framework that effectively manages interference across femtocells. RADION’s core building blocks enable femtocells to opportunistically determine the available resources in a completely distributed and efficient manner. Further, RADION’s modular nature paves the way for different resource management solutions to be incorporated in the framework. We implement RADION on a real WiMAX femtocell testbed deployed in a typical indoor setting. Two distributed solutions are enabled through RADION and their performance is studied to highlight their quick self-organization into efficient resource allocations. [ABSTRACT FROM PUBLISHER]

Multihop cellular networks (MCNs) have drawn tremendous attention due to its high throughput and extensive coverage. However, there are still three issues not well addressed. With the existence of relay stations (RSs), how to efficiently allocate frequency resource to relay links becomes a challenging design issue. For mobile stations (MSs) near the cell edge, cochannel interference (CCI) become severe, which significantly affects the network performance. Furthermore, the unbalanced user distribution will result in traffic congestion and inability to guarantee quality of service (QoS). To address these problems, we propose a quantitative study on adaptive resource allocation schemes by jointly considering interference coordination (IC) and load balancing (LB) in MCNs. In this paper, we focus on the downlink of OFDMA-based MCNs with time division duplex (TDD) mode, and analyze the characteristics of resource allocation according to IEEE 802.16j/m specification. We also design a novel frequency reuse scheme to mitigate interference and maintain high spectral efficiency, and provide practical LB-based handover mechanisms which can evenly distribute the traffic and guarantee users' QoS. Our study shows that our scheme not only meets the requirement on coverage, but also improves the throughput while accommodating more users in MCNs. [ABSTRACT FROM AUTHOR]

Multiple-input-multiple-output (MIMO) technique for wireless communications is extensively used these days, especially to increase the spectral efficiency of new wireless communication systems like LTE, WiMAX, etc. MIMO in combination with robust modulation techniques like orthogonal frequency division multiplexing (OFDM) provides a good solution for high data rate wireless links. In this paper, the performance of MIMO for a 60 GHz OFDM radio over fiber link is analyzed. System performance of the MIMO system for different antenna spacing is also studied. Using the optimum system parameters, a MIMO OFDM wireless link of up to 51 Gb/s was successfully demonstrated at 60 GHz in a bandwidth of <7 GHz, with a wireless transmission distance of up to 4 m and optical fiber transmission of \>1 km. To our knowledge this is the highest data rate demonstrated in the 7 GHz band of 60 GHz. [ABSTRACT FROM PUBLISHER]

This brief compares the use of multiplierless and DSP slice-based cross-correlation for IEEE 802.16d orthogonal frequency division multiplexing (OFDM) timing synchronization on Xilinx Virtex-6 and Spartan-6 field programmable gate arrays (FPGAs). The natural approach, given the availability of embedded DSP blocks on these FPGAs, would be to implement standard multiplier-based cross-correlation. However, this can consume a significant number of DSP blocks, which may not fit on low-power devices. Hence, we compare a DSP48E1 slice-based design to four different quantizations of multiplierless correlation in terms of resource utilization and power consumption. OFDM timing synchronization accuracy is evaluated for each system at different signal-to-noise ratios. Results show that even relatively coarse multiplierless coefficient quantization can yield accurate timing synchronization, and does so at high clock speeds. Multiplierless designs enjoy reduced power consumption over the DSP48E1 Slice-based design, and can be used where DSP Slice resources are insufficient, such as on low-power FPGA devices. [ABSTRACT FROM PUBLISHER]

Use of Wireless communications for Metropolitan Area Network (MAN) in consumer electronics has increased significantly in the recent past. This paper, presents the performance analysis of four different channel coding and interleaving schemes for MIMO-OFDM communications systems. A comparison is done based on the BER, hardware implementation resources requirement, and power dissipation. It also presents a memory-efficient and low-latency interleaver implementation technique for the MIMO-OFDM communication system. It is shown that among the four coding and interleaving schemes studied, the crossantenna coding and per-antenna interleaving performs the best under all SNR conditions and for all modulation schemes. It is also the best scheme as far as the hardware resource implication and power dissipation are concerned, which are particularly important in the context of consumer electronics. Next, using the proposed interleaver, a MIMO-OFDM based transmitter employing a double data stream 2?2 MIMO spatial multiplexing system is built. [ABSTRACT FROM PUBLISHER]

This paper describes a fully integrated 130 nm CMOS 2x2 MIMO tri-band dual-mode transceiver for fixed and mobile WiMAX and IEEE 802.11a/b/g/n applications. The proposed transceiver features reduced RF interface (only 4 RF pins) with the wideband circuit topology of the LNA and drive amplifier that minimizes the performance degradation. With carefully chosen LO frequency planning, the transceiver is capable of operating at 2.3–2.7 GHz, 3.3–3.9 GHz, and as well as 5.1–5.9 GHz bands covering whole frequency spectrum of fixed and mobile WiMAX and WLAN. The measured noise figure of the receiver is 3.6–4.2, 4.2–4.7, and 5.4–6.2 dB for each 2/3/5 GHz bands respectively. The measured PLL phase noise from 1 kHz to 10 MHz is 0.5/0.8/0.95 rms degree for 2/3/5 GHz bands respectively. The transceiver ensures low EVM over the wide dynamic range due to linear RX and TX signal paths and low integrated PLL phase noise characteristics. [ABSTRACT FROM AUTHOR]

This correspondence presents an algorithm for compensation of I/Q imbalance for a direct-conversion packet-switched orthogonal frequency-division-multiplexing (OFDM) communications system, which accounts for transmitter I/Q imbalance, receiver I/Q imbalance, phase/frequency error, and dispersive multipath fading. The proposed estimation algorithm is then presented, which operates within the framework of existing multiuser OFDM radio standards (802.11a). It is shown that this algorithm accurately estimates and corrects transceiver I/Q imbalance on a packet-by-packet basis, all within the receiver's digital baseband. [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of a new estimator for Fine Frequency Offset in OFDM packed-based applications. The estimator, which operates in the frequency domain, is based on the Inter-Carrier Interference (ICI) in the received preamble. A new theoretical expression for the estimator as a function of the input frequency offset is proposed. The estimator performance is evaluated for WIMAX receivers, showing an estimation error variance similar to that obtained with other well-known methods based on the processing in the time domain. [ABSTRACT FROM AUTHOR]

A framework for analyzing the performance of coded OSTBC-OFDM systems over arbitrary correlated generalized Ricean fading channels is established. The moment generating function of the signal-to-noise ratio at the input to the channel decoder is derived assuming correlated transmitter and receiver antennas and correlated paths in frequency selective channels. The probability of outage, the pairwise error probability, and the bit error rate are then evaluated. Bit-interleaved and iteratively decoded turbo product codes, Gray encoded M-ary quadrature amplitude modulation, and other parameters of the IEEE 802.16 Standard are used to illustrate numerical results. [ABSTRACT FROM AUTHOR]

We consider improving the performance of orthogonal frequency-division multiplexing (OFDM)-based mobile broadband wireless communication (MBWC) systems. We show that a recently approved packet-based MBWC standard can cause the resulting systems to suffer from severe performance degradations for time-varying channels due to the lack of a mechanism for tracking the time-varying channels needed for coherent detection. We consider both packet design and signal processing to deal with time-varying channels. For the packet design, we segment an entire packet into multiple subpackets—with each subpacket having zero tail bits to reset the convolutional channel encoder—so that the detection/decoding result of each subpacket can be used to update the channel response for this subpacket. For signal processing, we use weighted polynomial fitting and prediction at the receiver to improve the channel tracking accuracy. Simulation results show that the coherent detection based on our new scheme can significantly outperform the commonly suggested differential modulation/detection methods. [ABSTRACT FROM AUTHOR]

We propose a novel pilot-aided algorithm for estimation of rapidly varying wireless channels in OFDM systems. Our approach is specifically designed for channels varying on the scale of a single OFDM symbol duration, which occur, for example, in mobile WiMAX, WAVE, and DVB-T. From the pilot information, we recover information about the channel taps in the framework of the Basis Expansion Model (BEM). We derive explicit formulas for the BEM coefficients in terms of the receive signal. Algebraically, the algorithm is FFT-based, and can be easily implemented in hardware. For a system with L channels taps, our method uses \cal O(L log L) operations and \cal O(L) memory per OFDM symbol. This complexity is the best possible up to the order of magnitude. Previously published methods require \cal O(L^2) operations and \cal O(L^2) memory. Numerical simulations illustrate performance gains achieved by our estimator at sufficiently high Doppler frequencies. Our approach does not assume any prior statistical information. [ABSTRACT FROM AUTHOR]

The term WiMAX is used to refer to a collection of standards, products, and service offerings derived from the IEEE 802.16 family of standards for wireless networks. These standards define physical and MAC layer elements that ensure interoperability of compatible equipment. However, the standards leave both the details of the packet scheduling algorithms and the values of performance related configuration parameters to the discretion of the equipment vendor or network operator. These algorithms and parameters ultimately determine fundamental performance characteristics such as round-trip latency and sustainable throughput on the network. In this paper, we examine performance characteristics of an operational WiMAX testbed upon which we were able to conduct controlled experiments in the absence of competing traffic. We characterize latency, throughput, protocol overhead, and the impact of WiMAX on TCP dynamics. We show that scheduling policies and parameter values impact actual performance in ways that are not possible to characterize in generic studies of WiMAX. [ABSTRACT FROM AUTHOR]

In this paper a novel technique for reducing the peak to average power ratio (PAPR) in OFDM systems by using the combination of the dummy sequence insertion (DSI) and partial transmit sequence (PTS) is proposed. In DSI increasing the number of dummy sequence decrease the transmission efficiency (TE) and in PTS the complexity increases when the number of subblock increases. Unlike the conventional PTS which needs several inverse fast fourier transform (IFFT) operations, the proposed DSI-PTS technique requires half IFFT operations only, while the PAPR performance is even better. So, it can remarkably reduce the computational complexity. Simulation results are examined with IEEE 802.16-2004 standard. By applying the DSI-PTS method about 0.5 dB reduction in PAPR at complementary cumulative distribution function (CCDF) of 0.01% is achieved compared to the conventional PTS while the complexity is reduced1. [ABSTRACT FROM AUTHOR]