Joe McGeehan

Performance comparison of cooperative and non-cooperative relaying mechanisms in wireless networks

Relaying is a known method for increasing coverage in wireless communication systems. In addition to coverage increase, new cooperative relaying methods have been proposed that may increase the wireless system capacity by taking advantage of higher data rates in intermediate cooperating relaying nodes. This paper investigates the performance of several of these relaying methods in terms of maximum achievable throughput at MAC service access point for single-frequency wireless ad-hoc networks. The simulation framework used is described, and the performance limitations of the relaying methods are analysed. We find that relaying, cooperative or not, does not significantly increase maximum achievable throughput for line-of-sight (LOS) propagation environments. The achievable throughput can be significantly increased for non-line of sight (NLOS) environments under specific conditions for source/destination and intermediate relaying nodes

Adaptive frequency-domain equalization for single-carrier multiple-input multiple-output wireless transmissions

Channel estimation and tracking pose real problems in broadband single-carrier wireless communication systems employing multiple transmit and receive antennas. An alternative to estimating the channel is to adaptively equalize the received symbols. Several adaptive equalization solutions have been researched for systems operating in the time domain. However, these solutions tend to be computationally intensive. A low-complexity alternative is to adaptively equalize the received message in the frequency domain. In this paper, we present an adaptive frequency-domain equalization (FDE) algorithm for implementation in single-carrier (SC) multiple-input multiple-output (MIMO) systems. Furthermore, we outline a novel method of reducing the overhead required to train the proposed equalizer. Finally, we address the issues of complexity and training sequence design. Other computationally efficient adaptive FDE algorithms for use in SC systems employing single transmit and receive antennas, receive diversity, or space-time block codes (STBC) can be found in the literature. However, the algorithm detailed in this paper can be implemented in STBC systems as well as in broadband spatial multiplexing systems, making it suitable for use in high data rate MIMO applications.

Channel and noise variance estimation and tracking algorithms for unique-word based single-carrier systems

Single-carrier (SC) wireless communication systems generally require knowledge of the channel and the variance of the additive noise process to equalize a received message. Obtaining this information can be straightforward in stationary environments; however, these parameters constantly change in mobile environments. In this paper, we propose novel algorithms for estimating and tracking the channel and noise variance in SC systems by exploiting a unique word (UW) extension. These UW-based algorithms benefit from low complexity and lend themselves to SC systems employing frequency-domain equalization at the receiver

Optimal training sequences for channel estimation in cyclic-prefix-based single-carrier systems with transmit diversity

We investigate a new class of training sequences that are optimal for least squares (LS) channel estimation in systems employing transmit diversity and single-carrier (SC) modulation with a cyclic prefix (CP) extension. The sequences have a constant envelope in the time domain and are orthogonal in the frequency domain. Transmission of these sequences facilitates optimal (in the LS sense) estimation of the channel impulse response at the receiver while precluding the peak-to-average power ratio problem that is inherent in other CP-based architectures such as orthogonal frequency division multiplexing.

Path Loss Models for Air-to-Ground Radio Channels in Urban Environments

This paper provides new statistical models for air-to-ground channels in an urban environment. The model is derived to operate at frequencies from 200 MHz to 5 GHz. Issues such as path loss and shadowing are evaluated as a function of the elevation angle to the airborne platform, rather than the more usual separation distance used for terrestrial mobile communications. Results demonstrate the advantages of an air-to-ground channel for urban communication, and relayed peer-to-peer links in particular

A channel estimation algorithm for MIMO-SCFDE

This letter proposes a novel method for channel estimation in a single-carrier multiple input-multiple output (MIMO) system with frequency-domain equalization/detection. To this end, we construct novel short MIMO training sequences that have constant envelope in the time domain to preclude the peak-to-average power ratio problem encountered in many systems that utilize the frequency domain for data recovery. Simultaneously, the spectrum in the frequency domain is flat except for a grid of nulls for predefined frequency tones. Armed with these sequences, we provide an algorithm that is optimal in the least squares (LS) sense at a potentially low computational cost. Results show that the algorithm performs identically to other proposed LS techniques. Furthermore, the algorithm is extremely bandwidth efficient in that the total training overhead required to obtain full CSI is just one block.

Multichannel and Wideband Power Amplifier Design Methodology for 4G Communication Systems Based on Hybrid Class-J Operation

A methodology for the design of multichannel, wideband, highly efficient hybrid Class-J power amplifiers for fourth-generation (4G) communication transmitters is proposed. The design procedure is based on the automatic generation and evaluation of a vast number of output matching networks of the same topology but different dimensions, with respect to efficiency, output power, and linearity. The approach can find application in the management of the efficiency/linearity/bandwidth tradeoff in amplifier design. In this paper, two matching network architectures have been considered. One multistubbed network and a stepped-impedance microstrip line network. The approach has been validated through the design, simulation, and measurement of two power amplifiers realized using the aforementioned procedure. The first amplifier covers 1.6-2.2 GHz (31.6% fractional bandwidth) with 55%-68% drain efficiency at the 2-dB compression point and worst case adjacent channel power ratio (ACRP) and error vector magnitude (EVM) of - 21.8 dBc and 8.35%, respectively, over the bandwidth. The second covers 0.5-1.8 GHz (113% fractional bandwidth) with 50%-69% drain efficiency at the 2-dB compression point and worst case ACRP of - 27.5 dBc and EVM of 4.22%. Both amplifiers are based on a commercial, packaged 10-W GaN HEMT transistor.

Analysis of microstrip discontinuities using the finite difference time domain technique

The authors demonstrate the potential of the finite-difference time-domain technique for analyzing MMIC (monolithic microwave integrated circuit) structures of arbitrary complexity with moderate computational effort and for meeting the requirement for CAD (computer-aided design) tools capable of treating high-density MMICs. Results are presented for the propagation constant of a uniform microstrip, calculated using this method, which show excellent agreement with those obtained using the SDM (spectral domain method). Results are also presented for the parameters of structures containing a right-angle bend in microstrip and an abrupt termination in microstrip. The latter results are compared to those obtained by means of the SDM, and good agreement can be seen.<<ETX>>

Impact of Body and Clothing on a Wearable Textile Dual Band Antenna at Digital Television and Wireless Communications Bands

A dual band textile antenna designed for Digital Television (DTV) and many wireless standards including GSM 900, WLAN 2.45/5.8 GHz, Wimax 3.5 GHz, Hyperlan 5.2 GHz and UMTS-LTE-advanced is described. The impact of the body on antenna performance is assessed for return loss, radiation patterns and antenna efficiency in a wide frequency range. Full three dimensional radiation patterns were measured with the antenna backed by a phantom in order to simulate a human body. While the return loss was found to be only marginally affected when the antenna was mounted at various positions on the human body, the measured efficiency was observed to decrease by up to 90% when the antenna was positioned flush to the phantom. The return loss response was little affected when the antenna was worn on the back and further covered with a number of garments including a thick woolen jumper and a ski jacket. Although antenna efficiency was substantially affected by the presence of the body, interposing a layer of felt fabric between the antenna and the phantom typically improved efficiency by over 50%. This unique soft antenna is a good candidate for receiving digital television and wireless communications in a smart clothing environment.

A comparison of MIMO-OFDM and MIMO-SCFDE in WLAN environments

Recent developments in orthogonal frequency division multiplexing (OFDM) and single-carrier frequency-domain equalization (SCFDE) have sparked debate about the superiority of one method over the other. In this paper, we further this debate by comparing the theoretical performance of OFDM and SCFDE when each is implemented in one of two different multiple-input multiple-output (MIMO) architectures: spatial multiplexing and space-time block codes. This study focuses on the use of MIMO-OFDM and MIMO-SCFDE in wireless local area network (WLAN) applications. Performance is given in terms of the packet error rate (PER) and the throughput of the systems.