Keying

About: Keying is a research topic. Over the lifetime, 6598 publications have been published within this topic receiving 82943 citations.

Multidimensional modulation for ultra-wideband multiple-access impulse radio in wireless multipath channels

Abstract: In this paper, we develop multidimensional modulation for ultra-wideband (UWB) multiple-access (MA) impulse-radio communications in wireless multipath environments. An important advantage of multidimensional modulation over single-dimensional modulation is the possibility of higher power efficiency, and this may be critical in UWB communications. For this reason, we propose a 2MN-ary biorthogonal keying (BOK) scheme, in which N orthogonal pulse shapes in conjunction with M orthogonal codes are employed to construct MN-dimensional biorthogonal modulation. The direct sequence (DS) MA performance of the proposed scheme is analyzed. A closed-form bit-error-rate expression is derived and compared with simulations based on the Intel Labs' UWB channel model. Orthogonal pulse shapes that comply with the Federal Communications Commission UWB indoor-emission limits are used in simulations. Our results confirm the power-efficiency improvement achieved by multidimensional modulation for UWB MA communications under multipath fading.

Transmit Optimization for Symbol-Level Spoofing

Abstract: With recent developments of wireless communication technologies, malicious users can use them to commit crimes or launch terror attacks, thus imposing new threats on the public security. To quickly respond to defend these attacks, authorized parities (e.g., the National Security Agency of the USA) need to intervene in the malicious communication links over the air. This paper investigates this emerging wireless communication intervention problem at the physical layer. Unlike prior studies using jamming to disrupt or disable the targeted wireless communications, we propose a new physical-layer spoofing approach to change their communicated information. Consider a fundamental three-node system over additive white Gaussian noise (AWGN) channels, in which an intermediary legitimate spoofer aims to spoof a malicious communication link from Alice to Bob, such that the received message at Bob is changed from Alice's originally sent message to the one desired by the spoofer. We propose a new symbol-level spoofing scheme, where the spoofer designs the spoofing signal via exploiting the symbol-level relationship between each original constellation point of Alice and the desirable one of the spoofer. In particular, the spoofer aims to minimize the average spoofing-symbol-error-rate (SSER), which is defined as the average probability that the symbols decoded by Bob fail to be changed or spoofed, by designing its spoofing signals over symbols subject to the average transmit power constraint. By considering two cases when Alice employs the widely-used binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulations, we obtain the respective optimal solutions to the two average SSER minimization problems. Numerical results show that the symbol-level spoofing scheme with optimized transmission achieves a much lower average SSER, as compared to other benchmark schemes.

Cost-Effective Multiservices Hybrid Access Networks With no Optical Filter at Remote Nodes

Abstract: This letter experimentally demonstrates a multiservices hybrid access network integrated radio-over-fiber and fiber-to-the-home systems which share the same distributed architecture. A 1.25-Gb/s baseband signal and a 14.375-GHz radio-frequency (RF) signal with 625-Mb/s binary phase-shift keying data are generated and transmitted employing a commercially available dual-electrode Mach-Zehnder modulator. The proposed scheme offers better performance, has no RF fading issue, can carry vector signals, and requires no optical filter at remote nodes. After transmission over 25-km single-mode fiber, the proposed scheme successfully achieves less than 0.5-dB sensitivity penalties.

Power efficient subcarrier modulation for intensity modulated channels

Abstract: We compare formats for optical intensity modulation limited by thermal noise with the assumption of having ideal devices. At the same bitrate and bandwidth, a hitherto unknown format turns out to be more power efficient than known formats. This new modulation, which is a hybrid between on-off keying and phase-shift keying, belongs to the subcarrier modulation family. At asymptotically high signal-to-noise ratios, this hybrid scheme has a 1.2 dB average electrical power gain and 0.6 dB average optical power gain compared to OOK, while it has a 3.0 dB average electrical power gain and 2.1 dB average optical power gain compared to subcarrier QPSK.

Multicarrier modulation for narrowband PCS

Abstract: Investigation of multicarrier modulation has demonstrated the feasibility of using this modulation format to deliver relatively high channel bit rates (24 kbps) to a low cost, pager-like personal communications service (PCS) terminal that enjoys long battery life (e.g., one month on a few pen-light cells). This is to be compared to the 1200 bps carried by typical current paging systems or the 6250 bps attained by the new ERMES paging system. While more complex modulation formats, such as PSK and QAM, might achieve higher bit rates in less (power, size, cost) constrained environments, amplitude keying of the component subcarriers allows simple noncoherent energy detection that is found to be robust in this short message delivery application. >