Topic
Pulse-position modulation
About: Pulse-position modulation is a research topic. Over the lifetime, 3916 publications have been published within this topic receiving 72057 citations. The topic is also known as: PPM.
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19 May 1991
TL;DR: A base station modulation diversity scheme is proposed for simulcast systems which use linear QAM (quadrature amplitude modulation) type modulation and the impact of the choice of tap weights on the energy efficiency, the system complexity, and the performance in the presence of a propagation delay difference between the signals of different base stations is demonstrated.
Abstract: A base station modulation diversity scheme is proposed for simulcast systems which use linear QAM (quadrature amplitude modulation) type modulation. With this method the bandwidth efficiency is fully preserved because each base station uses the same base pulse. Modulation diversity is achieved by filtering the input symbols with a symbol-spaced finite impulse response (FIR) filter prior to QAM modulation. The tap weights of the FIR filters at different base stations are different. They are chosen such that a necessary condition for optimum diversity gain in time-selective fading is satisfied. Examples for simulcast with two base stations are given. They demonstrate the impact of the choice of tap weights on the energy efficiency, the system complexity, and the performance in the presence of a propagation delay difference between the signals of different base stations. >
325 citations
TL;DR: It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty, and that aligning transmit and receive units creates nearly uncorrelated channel paths.
Abstract: In this paper, a power and bandwidth efficient pulsed modulation technique for optical wireless (OW) communication is proposed. The scheme is called optical spatial modulation (OSM). In OSM, multiple transmit units exist where only one transmitter is active at any given time instance. The spatially separated transmit units are considered as spatial constellation points. Each unique sequence of incoming data bits is mapped to one of the spatial constellation points, i.e., activating one of the transmit units. This is the fundamental concept of the spatial modulation (SM) technique. In OW communication systems, the active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, the optimal SM detector is used to estimate the active transmitter index. An overall increase in the data rate by the base 2 logarithm of the number of transmit units is achieved. The optical MIMO (multiple-input multiple-output) channel and the channel impulse response are obtained via Monte Carlo simulations by applying ray tracing techniques. It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty. The power efficiency can be improved by increasing the number of receive units to enhance receive diversity and/or by using soft and hard channel coding techniques. Conversely, it is shown that aligning transmit and receive units creates nearly uncorrelated channel paths and results in substantial enhancements in system performance even as compared to the diversity or coding gain. The resultant aligned scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying, pulse position modulation, and pulse amplitude modulation. In this paper also, the upper bound bit error ratios of coded and uncoded OSM are analyzed. The analytical results are validated via Monte Carlo simulations and the results demonstrate a close match.
277 citations
TL;DR: In this article, multiple pulse position modulation (MPPMPM) is proposed as a modulation method to improve the band-utilization efficiency in optical PPM, where multiple pulses are transmitted using different combinations of the positions of these pulses.
Abstract: Multiple pulse position modulation (MPPM) is proposed as a modulation method to improve the band-utilization efficiency in optical pulse position modulation (PPM). Optical PPM gives higher transmission efficiency (bit/photon) in optical communications but degrades band-utilization efficiency. The proposed method reduces the required transmission bandwidth in optical PPM to about half with the same transmission efficiency, thus increasing band-utilization efficiency. While in conventional optical PPM, only one optical pulse is transmitted in every signal block, multiple pulses are transmitted using this method. Information is represented by different combinations of the positions of these pulses. The principle of bandwidth reduction applied, the transmission characteristics of the proposed method, and examples of improvement in band-utilization efficiency are also shown. >
245 citations
TL;DR: The performance of a direct-detection, avalanche photodiode-based free-space optical (FSO) communication system in terms of the overall bit-error rate is characterized in order to shed light on the impact of turbulence on the overall performance.
Abstract: In this paper, we characterize the performance of a direct-detection, avalanche photodiode-based free-space optical (FSO) communication system in terms of the overall bit-error rate. The system of interest uses pulse-position modulation (PPM) and is subjected to scintillation due to optical turbulence. Two scenarios are considered. In one case, a weak turbulence (clear-air) scenario is considered, for which the received signal intensity may be modeled as a log-normal random process. In the other case, we consider a negative exponentially distributed received signal intensity. To arrive at the desired results, it is assumed that the system uses a binary PPM (BPPM) modulation scheme. Furthermore, it is assumed that the receiver thermal noise is nonnegligible, and that the average signal intensity is large enough to justify a Gaussian approximation at the receiver. Union bound is used to assess the performance of M-ary PPM systems using the results of the BPPM scenario. Numerical results are presented for the BPPM case to shed light on the impact of turbulence on the overall performance.
242 citations
TL;DR: The performance of OFDM-IM is studied in terms of the achievable rate assuming an M-ary constellation and that channel state information is available at the receiver, and an interleaved grouping method is proposed for the use of subcarriers.
Abstract: Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a recently developed transmission technique that extends the principle of spatial modulation to OFDM subcarriers. In this paper, the performance of OFDM-IM is studied in terms of the achievable rate assuming an $M$ -ary constellation and that channel state information is available at the receiver. A closed-form lower bound is derived, based on which an interleaved grouping method is proposed for the use of subcarriers. In comparison with the existing grouping method, the proposed one can better benefit from the diversity effects over frequency-selective fading channels, especially when the spacing of any two subcarriers within a subcarrier group is larger than the coherence bandwidth. Through numerical results, it is revealed that OFDM-IM with interleaved grouping outperforms classical OFDM for small $M$ and certain ranges of signal-to-noise ratio. Finally, the effects of modulation types on the performance of OFDM-IM are studied. It is found that the superiority of OFDM-IM over classical OFDM is greater for phase-shift keying than for quadrature amplitude modulation.
241 citations