OFDM for Optical Communications Armstrong, J.
Journal of lightwave technology,
02/2009, Letnik:
27, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective ...solution to intersymbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a tutorial overview of OFDM highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by single mode optical fiber, multimode optical fiber and optical wireless are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.
Over the past 40 years, telecommunications policy worldwide has been dominated by the privatisation of former government-owned firms, the pursuit of increasing competition as well as the delegation ...of day-to-day operations of industry decision-making and oversight from core governments to autonomous regulators sitting at arms-length from political decision-making. One of the most (apparently) dramatic reversals of this trend has occurred in Australia where the federal government has set up a state-owned company (NBN Co) to fully replace and upgrade the fixed-line infrastructure for voice and broadband communications for the entire country. Some argued that the NBN heralded a reversal of a “failed, neoliberal” deregulation and pro-competition policy agenda in Australia, and a return to “social democratic” values. The NBN has attracted interest as a possible model for other governments looking to fund broadband infrastructure.
The NBN Co's network is nearing completion. It has proved disappointing in many ways, with costs escalations, missed deadlines and a downscaling of the original full-fibre footprint to a mixed technology model (MTM). It has also proved politically divisive, with some claiming the MTM changes represent the reassertion of a neoliberal political agenda. In this paper, we trace the evolution of the fixed-line telecommunications industry in Australia from the 1980s to the present along the dimensions of privatisation, deregulation and competition in voice, broadband and policy settings. We find that contrary to popular political rhetoric, the Australian industry reforms have been characterised by only a partial and inconsistent progression towards the international policy objectives. In particular, ongoing government ownership of the incumbent created perverse incentives for both regulatory and industry actors and ensured political involvement in import network investment and operations decisions which in other jurisdictions are delegated to private-sector owners and regulators at arms-length from political influence. We contend that the NBN was not a social democratic response to failed neoliberal policies, nor was the MTM a neoliberal reassertion. Rather, the politicisation of the NBN is a function of the inability to decentralise ownership and control of the industry away from the government. These issues will continue to dominate the Australian debate, as the statutory context requires the privatisation of the NBN within five years of its projected 2021 completion. Extreme caution is warranted for jurisdictions looking to the NBN model for guidance.
•The trend of privatisation and deregulation in telecommunications was reversed by Australia's National Broadband Network.•The NBN was not a social democratic response to failed neoliberal policies, nor was the MTM a neoliberal reassertion.•Rather, the politicisation of the NBN is a function of the inability to decentralise ownership and control of the industry.•The paper plots the history of liberalisation and deregulation (and partial reversal) over the past 40 years.•The politicisation of Australian broadband investment cannot be described as a rejection of liberalisation policies.•Despite a promising start with institutions to govern a liberalising industry, the requisite privatisation did not occur.•The dilemma of competing interests of government ownership and oversight in the industry (Telstra) has returned with the NBN.
A large electronically reconfigurable reflectarray antenna that has 160 × 160 reflecting elements was designed, fabricated, and evaluated so that it could be applied to a millimeter-wave imaging ...system operating in the 60-GHz band. To make it feasible to construct such a large reflectarray, the reflecting element structure had to be simple and easily controlled; therefore, a reflecting element consisting of a microstrip patch and a single-bit digital phase shifter using a p-i-n diode was employed. A large reflectarray antenna was fabricated using the reflecting elements. The measured radiation patterns and antenna gain were in good agreement with those that were calculated. Furthermore, the near-field beam focusing capabilities, which was required to image near-field objects, were also verified through an experiment. Finally, the response time for beamforming was measured, which was far less than the system requirements.
A joint TOA/AOA estimator is proposed for UWB indoor ranging under LOS operating conditions. The estimator employs an array of antennas, each feeding a demodulator consisting in a squarer and a ...low-pass filter. Signal samples taken at Nyquist rate at the filter outputs are processed to produce TOA and AOA estimates. Performance is assessed with transmitted pulses with a bandwidth of either 1.5 GHz (type-1 pulses) or 0.5 GHz (type-2 pulses), which correspond to sampling rates of 3 GHz and 1 GHz, respectively. As expected, the estimation accuracy decreases with the pulse bandwidth. Ranging errors of about 10 cm and angular errors of about 1° are achieved at SNR of practical interest with type-1 pulses and two antennas at a distance of 50 cm. With type-2 pulses the errors increase to 35 cm and 3°. Comparisons are made with other schemes discussed in literature.
In this paper, we address the time-of-arrival (TOA) based localization problem in an adverse environment, where line-of-sight (LOS) signal propagation between the source and the sensor is not readily ...available, in which case we have to resort to non-line-of-sight (NLOS) signals. Two convex relaxation methods, i.e., the semidefinite relaxation (SDR) and the second-order cone relaxation (SOCR) methods, are proposed to mitigate the effect of NLOS errors on the localization performance. We consider two separate cases in which the information of the NLOS status is totally unknown and perfectly known, respectively. The proposed methods can be applied without knowing the distribution of NLOS errors. Moreover, we propose a NLOS error mitigation method that is robust to detection errors, which are generated in the process of detecting NLOS paths. Simulation results show that the proposed convex relaxation methods outperform some existing state-of-the-art methods.
Cooperative communication with single relay selection is a simple but effective communication scheme for energy-constrained networks. In this paper, we propose a novel selective single-relay ...cooperative scheme, combining selective-relay cooperative communication with physical-layer power control. Based on the MAC-layer RTS-CTS signaling, a set of potential relays compute individually the required transmission power to participate in the cooperative communication, and compete within a window of fixed length. The "best" relay is selected in a distributed fashion with minimum signaling overhead. We derive power-control solutions corresponding to two policies on relay selection: one is to minimize the energy consumption per data packet, and the other is to maximize the network lifetime. Our numerical and simulation results confirm that the proposed scheme achieves significant energy savings and prolongs the network lifetime considerably.
In this communication, the simulation and experimental results of a novel wideband wearable circularly polarized textile antenna for low-power transmission in the 2.45 GHz ISM band are presented. The ...wide impedance and axial ratio bandwidths make it perfect for low microwave power transmission to a wearable sensor system. The antenna is flexible, robust and light weight so that it can be easily integrated into clothes. It is shown that the circularly polarized textile antenna has a 3-dB axial ratio bandwidth of 564 MHz (23%) and a {-}10 dB impedance bandwidth of 1086 MHz (44%) on a human body with the maximum gain of 4.9 dBic. Lastly, the textile antenna is employed on the battery-less temperature sensor system on a human arm to demonstrate the effective power transmission over a metre distance.
In this paper, we begin by presenting a multiband antenna for mobile phone applications operating in GSM, DCS, PCS, UMTS, Bluetooth, and LTE bands. The antenna platform includes the ground plane, the ...battery, the camera, and other paraphernalia that the mobile phone environment typically comprises. Results show that the platform has a significant effect on the performance of the antenna, both in terms of its bandwidth and the number of its resonance frequencies. In addition, metal rings, frequently used in a mobile phone for mechanical reasons, can also have a significant influence on the performance of the antenna in the phone. Equivalent circuits and current distributions have been derived with the objective of investigating the effects of the metal ring that embrace the mobile phone. We investigate ways in which we can modify the ring so as to restore the desired performance of the antenna, which has been previously designed to operate in the phone environment but without the presence of the ring. We show how we can control the resonances of the ring by using capacitance loading and lower its Q by loading the ring resistively at a number of different strategic locations along the ring.
This paper focuses on the relay selection problem in amplify-and-forward (AF) cooperative communication with full-duplex (FD) operation. Different relay selection schemes assuming the availability of ...different instantaneous information are studied. We consider optimal relay selection that maximizes the instantaneous FD channel capacity and requires global channel state information (CSI) as well as several sub-optimal relay selection policies that utilize partial CSI knowledge such as a) source-relay and relay-destination links b) loop interference c) source-relay links and loop interference. To facilitate comparison, exact outage probability expressions and asymptotic approximations of these policies that show a zero diversity order are derived. In addition, an optimal relay selection procedure that incorporates a hybrid relaying strategy, which dynamically switches between FD and half-duplex relaying according to the instantaneous CSI, is also investigated.
In this paper, we present simple opportunistic relaying with decode-and-forward (DaF) and amplify-and-forward (AaF) strategies under an aggregate power constraint. In particular, we consider ...distributed relay-selection algorithms requiring only local channel knowledge. We show that opportunistic DaF relaying is outage-optimal, that is, it is equivalent in outage behavior to the optimal DaF strategy that employs all potential relays. We further show that opportunistic AaF relaying is outage-optimal among single-relay selection methods and significantly outperforms an AaF strategy based on equal-power multiple-relay transmissions with local channel knowledge. These findings reveal that cooperation offers diversity benefits even when cooperative relays choose not to transmit but rather choose to cooperatively listen; they act as passive relays and give priority to the transmission of a single opportunistic relay. Numerical and simulation results are presented to verify our analysis.
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