Showing papers on "Frequency-division multiplexing published in 2011"
TL;DR: In this article, the authors provide a review of optical OFDM slanted towards emerging optical fiber networks, from its basic mathematical formation to its salient disadvantages and advantages, and reveal the unique characteristics of the fiber optical channel and identify the challenges and opportunities in the application of OFDM.
Abstract: Fast advancing silicon technology underpinned by Moore's law is creating a major transformation in optical fiber communications. The recent upsurge of interests in optical orthogonal frequency-division multiplexing (OFDM) as an efficient modulation and multiplexing scheme is merely a manifestation of this unmistakable trend. Since the formulation of the fundamental concept of OFDM by Chang in 1966 and many landmark works by others thereafter, OFDM has been triumphant in almost all the major RF communication standards. Nevertheless, its application to optical communications is rather nascent and its potential success in the optical domain remains an open question. This tutorial provides a review of optical OFDM slanted towards emerging optical fiber networks. The objective of the tutorial is two-fold: (i) to review OFDM fundamentals from its basic mathematical formation to its salient disadvantages and advantages, and (ii) to reveal the unique characteristics of the fiber optical channel and identify the challenges and opportunities in the application of optical OFDM.
152 citations
TL;DR: In this paper, the authors demonstrate that the number of kernels of a Volterra model based equalizer can be significantly reduced using the modified Gram-Schmidt method with reorthogonalization techniques.
Abstract: A main drawback of Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) system is its sensitivity to fiber nonlinearity. Nonlinear electrical equalizer based on Volterra model has been demonstrated capable of compensating fiber nonlinear distortion in an OOK or PSK optical communication system. However, the implementation complexity of a Volterra model based electrical equalizer prohibits its deployment in a real-life CO-OFDM system. In this paper, we demonstrate that the number of kernels of a Volterra model based equalizer can be significantly reduced using the modified Gram-Schmidt method with reorthogonalization techniques. The resulting “sparse” Volterra model based electrical equalizer and the electrical equalizer based on the “full” Volterra model have comparable performance and can compensate intra-channel nonlinearity of a 16-QAM 100 Gbit/s CO-OFDM System.
81 citations
TL;DR: In this paper, the authors studied the effect of the modal gains and losses on the average and outage capacities in the regime of strong mode coupling and found that the difference between the average capacity and outage capacity is inversely proportional to the square root of a diversity order that is given by the ratio of the signal bandwidth to the coherence bandwidth.
Abstract: In the regime of strong mode coupling, the modal gains and losses and the modal group delays of a multimode fiber are known to have well-defined statistical properties. In mode-division multiplexing, mode-dependent gains and losses are known to cause fluctuations in the channel capacity, so that the capacity at finite outage probability can be substantially lower than the average capacity. Mode-dependent gains and losses, when frequency-dependent, have a coherence bandwidth that is inversely proportional to the modal group delay spread. When mode-division-multiplexed signals occupy a bandwidth far larger than the coherence bandwidth, the mode-dependent gains and losses are averaged over frequency, causing the outage capacity to approach the average capacity. The difference between the average and outage capacities is found to be inversely proportional to the square-root of a diversity order that is given approximately by the ratio of the signal bandwidth to the coherence bandwidth.
63 citations
TL;DR: A new joint CFO and SFO maximum-likelihood (ML) estimation scheme extending Moose's CFO estimation scheme using two long training symbols in the frequency-domain (FD) is proposed, which derives FD Cramér-Rao bounds (CRBs) for the mean square errors (MSEs) of the CFOand SFO estimation.
Abstract: In orthogonal frequency-division multiplexing (OFDM) systems, carrier and sampling frequency offsets (CFO and SFO, respectively) can destroy the orthogonality of the subcarriers and degrade the system performance. In this paper, we propose a new joint CFO and SFO maximum-likelihood (ML) estimation scheme extending Moose's CFO estimation scheme using two long training symbols in the frequency-domain (FD). In particular, we derive FD Cramer-Rao bounds (CRBs) for the mean square errors (MSEs) of the CFO and SFO estimation. Simulation results show that the proposed ML scheme exhibits better performance than the other existing methods.
60 citations
TL;DR: This paper develops several linear data estimators specifically designed for UW-OFDM, some based on classical and somebased on Bayesian estimation theory, and derives complexity optimized versions of these estimators and studies their individual complex multiplication count in detail.
Abstract: Unique word-orthogonal frequency division multiplexing (UW-OFDM) is a novel OFDM signaling concept, where the guard interval is built of a deterministic sequence - the so-called unique word - instead of the conventional random cyclic prefix. In contrast to previous attempts with deterministic sequences in the guard interval the addressed UW-OFDM signaling approach introduces correlations between the subcarrier symbols, which can be exploited by the receiver in order to improve the bit error ratio performance. In this paper we develop several linear data estimators specifically designed for UW-OFDM, some based on classical and some based on Bayesian estimation theory. Furthermore, we derive complexity optimized versions of these estimators, and we study their individual complex multiplication count in detail. Finally, we evaluate the estimators' performance for the additive white Gaussian noise channel as well as for selected indoor multipath channel scenarios.
59 citations
TL;DR: It is shown that cyclic prefix (CP) correlation coefficient (CPCC)-based spectrum sensing, which was previously introduced as a simple and computationally efficient spectrum-sensing method for OFDM signals, is a special case of the constrained generalized likelihood ratio test (GLRT) in the absence of multipath.
Abstract: Given the ever-growing demand for radio spectrum, cognitive radio has recently emerged as an attractive wireless technology. Since orthogonal frequency-division multiplexing (OFDM) is one of the major wideband transmission techniques, detection of OFDM signals in low-signal-to-noise-ratio scenario is an important research problem. In this paper, it is shown that cyclic prefix (CP) correlation coefficient (CPCC)-based spectrum sensing, which was previously introduced as a simple and computationally efficient spectrum-sensing method for OFDM signals, is a special case of the constrained generalized likelihood ratio test (GLRT) in the absence of multipath. As such, the performance of this algorithm degrades in a multipath scenario, where OFDM is usually implemented. Furthermore, by considering multipath correlation in the GLRT algorithm and employing the inherent structure of OFDM signals, a simple and low-complexity algorithm called the multipath-based constrained-GLRT (MP-based C-GLRT) algorithm is obtained. The MP-based C-GLRT algorithm is shown to outperform the CPCC-based algorithm in a rich multipath environment. Further performance improvement can be achieved by simply combining both the CPCC- and MP-based C-GLRT algorithms. A simple GLRT-based detection algorithm is also developed for unsynchronized OFDM signals, whose performance is only slightly degraded when compared with the synchronized detection in a rich multipath environment.
58 citations
28 Mar 2011
TL;DR: New SEFDM receivers that offer substantial complexity reduction with a competitive Bit Error Rate (BER) performance are presented and the Truncated Singular Value Decomposition (TSVD) is proposed as an efficient tool to overcome the ill conditioning of the system caused by the orthogonality collapse.
Abstract: Spectrally Efficient Frequency Division Multiplexing (SEFDM) systems aim to reduce the utilized spectrum by multiplexing non-orthogonal overlapped carriers. Since the per carrier transmission rate is maintained, SEFDM yields higher spectral efficiency relative to an equivalent Orthogonal Frequency Division Multiplexing (OFDM) system. Yet, due to the loss of the orthogonality, detection of the SEFDM system requires overly complex detectors. In this work, new SEFDM receivers that offer substantial complexity reduction with a competitive Bit Error Rate (BER) performance are presented. The Truncated Singular Value Decomposition (TSVD) is proposed as an efficient tool to overcome the ill conditioning of the system caused by the orthogonality collapse. The performance of the system with respect to the system size and spectrum saving is examined by extensive numerical simulations. It is shown that the TSVD detector outperforms linear detectors such as Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE) detectors in terms of BER. Furthermore, a combination of TSVD with the Fixed Sphere Decoder (FSD) algorithm is proposed and tested for the first time. This novel FSD-TSVD receiver achieves near -optimum performance in terms of BER with a fixed and reduced complexity for systems with bandwidth savings of up to 40%.
55 citations
TL;DR: An on-chip multiplexed multichannel resistive pulse sensor (Coulter counter) for high throughput counting of microscale particles and can be extended to a larger number of channels to further improve the throughput, without increasing the external detection electronics.
Abstract: In this work we demonstrate an on-chip multiplexed multichannel resistive pulse sensor (Coulter counter) for high throughput counting of microscale particles. The design, fabrication and testing of this device are presented. The high throughput counting is a result of using multiple parallel microfluidic channels to analyze the sample. Detection is achieved by using frequency division multiplexing; each microchannel is modulated with its own known and unique frequency, a combined measurement is made across a single pair of electrodes, and the measured signal is demodulated to determine the signal across each individual channel. Testing results using 30 µm polystyrene particles demonstrate that the throughput of the multiplexed device gets improved 300% over a single-channel device; this is achieved by simultaneously detecting particles through the device's four parallel channels. In addition, the ac modulation method used in this paper reduces the polarization effect on the microelectrodes, and thereby allows for measurement of the particle sizes with significantly reduced error. The multiplexed detection principle can be extended to a larger number of channels to further improve the throughput, without increasing the external detection electronics.
49 citations
15 May 2011
TL;DR: This paper presents the first VLSI digital baseband transmitter architecture for SEFDM, implemented using a 65nm CMOS cell library to provide analysis of area and power compared to a baseline OFDM transmitter.
Abstract: Spectrally Efficient FDM (SEFDM) systems employ non-orthogonal overlapped carriers to improve spectral efficiency for future communication systems. One of the challenges for SEFDM systems is to demonstrate efficient hardware implementations for transmitters and receivers. This paper presents the first VLSI digital baseband transmitter architecture for SEFDM. The transmitter is reconfigurable between three bandwidth compression ratios, including OFDM and Fast OFDM, therefore supporting operation with current OFDM systems. Complexity analysis is presented of the proposed architecture, along with an area and power efficient hardware mapping, implemented using a 65nm CMOS cell library to provide analysis of area and power compared to a baseline OFDM transmitter.
44 citations
TL;DR: A lower bound on the two-way transmission capacity with transmit beamforming using limited feedback is derived as a function of bandwidth and the number of bits allocated for feedback, which is shown to perform better than allocating bandwidth proportional to the desired rate in both directions.
Abstract: The transmission capacity of an ad-hoc network is the maximum density of active transmitters per unit area, given an outage constraint at each receiver for a fixed rate of transmission. Most prior work on finding the transmission capacity of ad-hoc networks has focused only on one-way communication where a source communicates with a destination and no data is sent from the destination to the source. In practice, however, two-way or bidirectional data transmission is required to support control functions like packet acknowledgements and channel feedback. This paper extends the concept of transmission capacity to two-way wireless ad-hoc networks by incorporating the concept of a two-way outage with different rate requirements in both directions. Tight upper and lower bounds on the two-way transmission capacity are derived for frequency division duplexing. The obtained bounds are used to derive the optimal solution for bidirectional bandwidth allocation that maximizes the two-way transmission capacity, which is shown to perform better than allocating bandwidth proportional to the desired rate in both directions. Using the proposed two-way transmission capacity framework, a lower bound on the two-way transmission capacity with transmit beamforming using limited feedback is derived as a function of bandwidth and the number of bits allocated for feedback.
44 citations
01 Sep 2011
TL;DR: It is shown that with a proper sensing and transmission scheme the capacity of the CRFN can be increased by simultaneous transmissions on multiple channels, water-filling further improves the result when interference from the macrocell basestation is large.
Abstract: Deploying cognitive radio femtocell network (CRFN) inside a macrocell network can significantly increase the utilization of the available macrocell bandwidth and increase the capacity of the macrocell. However, the success of this deployment in terms of performance degradation of the macrocell and the acceptable throughput for the CRFN is not well defined. In this paper, we propose a time division duplex (TDD) operation of a CRFN and investigate its performance inside a macrocell operating in frequency division duplex (FDD) mode. It is shown that with a proper sensing and transmission scheme the capacity of the CRFN can be increased by simultaneous transmissions on multiple channels, water-filling further improves the result when interference from the macrocell basestation is large. The proposed scheme is applicable to full duplex networks, such as LTE and GSM.
31 Aug 2011
TL;DR: A simple interference cancellation technique called serial inter-carrier interference cancellation scheme has been used to improve performance of the GFDM system and channel equalization techniques have been implemented for FBMC.
Abstract: With the opening up of white spaces, efficient use of the fragmented spectrum - TV white space in particular - has become an extremely important focus of research. Apart from efficient spectrum usage, special care needs to be taken to maintain low out-of-band radiation to avoid harmful interference to incumbent services like TV signals and wireless microphones. For this reason, a flexible digital radio with multicarrier modulation scheme is the only solution. In this paper, we show the performance of two innovative multicarrier systems, Filter Bank Multi Carrier (FBMC) and Generalized Frequency Division Multiplexing (GFDM). A simple interference cancellation technique called serial inter-carrier interference cancellation scheme has been used to improve performance of the GFDM system. Channel equalization techniques have been implemented for FBMC.
TL;DR: In this article, the authors proposed a nonlinear electrical equalization scheme based on the Wiener-Hammerstein model for coherent optical orthogonal frequency division multiplexing system.
Abstract: Nonlinear distortion caused by fiber nonlinearity is a major performance-limiting factor in advanced optical communication systems. We proposed a nonlinear electrical equalization scheme based on the Wiener-Hammerstein model. Compared with other popular nonlinear compensation techniques such as the Volterra model, the Wiener-Hammerstein model approach has a simpler structure and requires less calculation. Simulation results are presented to demonstrate the capability of a Wiener-Hammerstein model based electrical equalizer used in a coherent optical orthogonal frequency division multiplexing system. It is shown that the Wiener-Hammerstein model based equalizer can significantly reduce nonlinear distortion and can deliver a performance comparable to the Volterra model based equalizer.
Patent•
TL;DR: In this paper, a beam steering direction is made a function of frequency by driving each element of a uniformly spaced line array by a signal which leads or lags its nearest neighbor by a fixed phase shift, Δφ.
Abstract: A sonar array for forming multiple transmit and/or receive acoustic beams by a frequency beamforming technique. In frequency division beamforming, beam steering direction is made a function of frequency by driving (receiving) each element of a uniformly spaced line array by a signal which leads or lags its nearest neighbor by a fixed phase shift, Δφ. This permits scanning a transmit and/or receive beam through a range of angles by changing its frequency. The same principle can be used to form multiple simultaneous transmit and/or receive beams. This is accomplished by transmitting a wide bandwidth signal and receiving the echoes through a spectrum analyzer. Each frequency bin of the spectrum analyzer then corresponds to a beam pointing in its own unique direction. Advantages of such a sonar system include improved cost, weight, and size versus performance for a variety of systems including ahead looking sonars and bottom mapping sonars.
TL;DR: An optical orthogonal frequency division multiplexing (OFDM) demultiplexer with an optical discrete Fourier transform circuit fabricated using silica planar lightwave circuit technology is demonstrated.
Abstract: We demonstrate an optical orthogonal frequency division multiplexing (OFDM) demultiplexer with an optical discrete Fourier transform circuit fabricated using silica planar lightwave circuit technology. This compact device can process an arbitrary number of subcarriers. The operation of a ten-channel device is demonstrated by demultiplexing a 100 Gbit/s (10 subcarrier×10 Gbits/s) OFDM signal. We also discuss a main factor affecting characteristics degradation of the device.
TL;DR: In this article, the authors proposed a method to develop an all-optical arithmetic and logic unit by means of which so many binary logic operations such as AND, OR, NAND, NOR, EXOR, data comparator etc., as well as some arithmetic operations, such as half-addition, half-subtraction, full addition, full-add addition, full subtraction multiplication, etc., can be performed by properly selecting the frequencies of the control signals and using the frequency encoded input data.
Abstract: An all-optical arithmetic and logic unit is the integral part of optical computing and data processing. In this paper, the author proposes a method to develop an all-optical arithmetic and logic unit by means of which so many binary logic operations such as AND, OR, NAND, NOR, EXOR, data comparator etc., as well as some arithmetic operations, such as half-addition, half-subtraction, full-addition, full-subtraction multiplication, etc., can be performed by properly selecting the frequencies of the control signals and using the frequency encoded input data. For this purpose, the author has exploited the frequency conversion scheme of semiconductor optical amplifier (SOA) using nonlinear polarization rotation character of the probe beam in SOA and, cross-gain modulation character of reflecting semiconductor optical amplifier (RSOA). Frequency-dependent optical beam routing to different channels have done using optical add/drop multiplexer made of SOA with multiquantum well structure. Frequency conversion efficiency of SOA and RSOA are very high as well as switching speed of SOA is very fast with very good ON-OFF contrast ratio.
TL;DR: A general framework adopting generalized signal expansion functions for representation of physical-layer radio resources as well as for synthesis of transmitter and receiver waveforms is presented, which allow us to join DRA with waveform adaptation, two procedures that are currently carried out separately.
Abstract: This paper investigates the issue of dynamic resource allocation (DRA) in the context of multi-user cognitive radio networks. We present a general framework adopting generalized signal expansion functions for representation of physical-layer radio resources as well as for synthesis of transmitter and receiver waveforms, which allow us to join DRA with waveform adaptation, two procedures that are currently carried out separately. Based on the signal expansion framework, we develop noncooperative games for distributed DRA, which seek to improve the spectrum utilization on a per-user basis under both transmit power and cognitive spectral mask constraints. The proposed DRA games can handle many radio platforms such as frequency, time or code division multiplexing (FDM, TDM, CDM), and even agile platforms with combinations of different types of expansion functions. To avoid the complications of having too many active expansion functions after optimization, we also propose to combine DRA with sparsity constraints. Generally, the sparsity-constrained DRA approach improves convergence of distributed games at little performance loss, since the effective resources required by a cognitive radio are in fact sparse. Finally, to acquire the channel and interference parameters needed for DRA, we develop compressed sensing techniques that capitalize on the sparse properties of the wideband signals to reduce the number of samples used for sensing and hence the sensing time.
TL;DR: Two novel spread coding schemes for NC-SOFDM for cognitive radio in a DSA network are proposed and improve the performance by exploiting the diversity gain and eliminating the orthogonality loss.
Abstract: In a dynamic spectrum access (DSA) network, multi-carrier-based cognitive radio transceivers need to deactivate some of their subcarriers to avoid interference to primary users. In a mobile environment, the spread orthogonal frequency-division multiplexing (SOFDM) system has demonstrated excellent performance in multipath fading channels, outperforming the traditional OFDM system due to the diversity gain. The traditional SOFDM uses Hadamard-Walsh code as the spreading code set, in which case, when deactivating subcarriers, orthogonality among different spreading codes will be lost, leading to poor bit error ratio (BER) performance. The performance of the SOFDM system can be improved by using adaptive spreading code adjustment to compensate for the loss of orthogonality. Because Hadamard-Walsh codes only exist for certain code length, in many cases, the SOFDM system based on Hadamard-Walsh code set needs to deactivate more subcarriers. Otherwise, loss of orthogonality cannot be eliminated. Instead, it can only be minimized. Moreover, deactivating more subcarriers will force the system to reduce the data rate. By treating the system as subsystems, we can generate binary orthogonal code set based on Hadamard-Walsh code to maintain the data rate. On the other hand, if the spreading code is not limited to be binary, orthogonal carrier interferometry (CI) codes exist for code length of any integer. Hence, by applying non-contiguous SOFDM (NC-SOFDM) with CI code to DSA, the loss of orthogonality among spreading codes caused by deactivating subcarriers can be eliminated. In this paper, we propose two novel spread coding schemes for NC-SOFDM for cognitive radio in a DSA network. The new spreading code sets help the system to maintain the same data rate as that of the traditional OFDM and improve the performance by exploiting the diversity gain and eliminating the orthogonality loss. The NC-SOFDM with the proposed spreading code outperforms the traditional NC-OFDM and the adaptive NC-SOFDM with Hadamard-Walsh code.
TL;DR: The cyclostationarity properties of received OFDM signal in time-dispersive channel is exploited to estimate the OFDM parameters, which includes OFDM symbolperiod, useful symbol period, cyclic prefix factor, number of subcarriers and carrier frequency offset.
Abstract: This paper presents a blind parameter estimation algorithm for orthogonal frequency division multiplexing (OFDM) signal affected by a time-dispersive channel, timing offset, carrier frequency offset and additive Gaussian noise. Unlike the previous studies, this paper presents the second-order cyclostationarity of OFDM signal considering the effect of time-dispersive channel. The cyclostationarity properties of received OFDM signal in time-dispersive channel is exploited to estimate the OFDM parameters. These parameters includes OFDM symbol period, useful symbol period, cyclic prefix factor, number of subcarriers and carrier frequency offset. Simulations are performed to investigate the performance of OFDM parameter estimation algorithm in diverse channel conditions.
15 May 2011
TL;DR: This paper proposes a heuristic subcarrier and power allocation algorithm to maximize the weighted sum-rate of LDS-OFDM system and shows that the proposed algorithm can significantly increase the spectral efficiency of the system.
Abstract: Low Density Signature-Orthogonal Frequency Division Multiplexing (LDS-OFDM) has been introduced recently as an efficient multiple access technique. In this paper, we focus on the subcarrier and power allocation scheme for uplink LDS-OFDM system. Since the resource allocation problem is not convex due to the discrete nature of subcarrier allocation, the complexity of finding the optimal solutions is extremely high. We propose a heuristic subcarrier and power allocation algorithm to maximize the weighted sum-rate. The simulation results show that the proposed algorithm can significantly increase the spectral efficiency of the system. Furthermore, it is shown that LDS-OFDM system can achieve an outage probability much less than that for OFDMA system.
TL;DR: The equivalence of the IDFT generated signal and the modulators based signal is proved mathematically, nonetheless, numerical simulations were performed to verify that equivalence and to test for the performance of the digitally generated signal in AWGN channel.
Abstract: Problem statement: Spectrally Efficient Frequency Division Multiplexing (SEFDM) system promises bandwidth savings by multiplexing overlapped non-orthogonal sub-carriers. However, the loss of orthogonality results in increasing the complexity of generation and detection of the signal. In this work, we propose simple framework for the generation of the SEFDM signal based on the Inverse Discrete Fourier Transform (IDFT). Approach: This study further proposes the use of the Discrete Fourier Transform (DFT) as the receiver front end, specifically for extracting the statistics of the signal needed for recovering the transmitted signal. The proposed transmitter designs employ similar building blocks as Orthogonal Frequency Division Multiplexing (OFDM) based systems, hence, would facilitate an easy migration and/or coexistence with OFDMon the transmitter side. Furthermore, the proposed framework may facilitate the IDFT design for any Frequency Division Multiplexed (FDM) signal with arbitrary sub-carriers spacing. Results and Conclusion: The equivalence of the IDFT generated signal and the modulators based signal is proved mathematically, nonetheless, numerical simulations were performed to verify that equivalence and to test for the performance of the digitally generated signal in AWGN channel. Numerical results confirmed the required spectrum compression and Bit Error Rate (BER) performance at a much reduced complexity.
01 Jan 2011
TL;DR: This work presents the hardware design of a novel algorithm using Field Programmable Gate Arrays (FPGAs) for the detection of Spectrally Efficient Frequency Division Multiplexing (SEFDM) signals and shows excellent fixed-point performance which are comparable to existing floating-point computer-based simulations.
Abstract: This work presents the hardware design of a novel algorithm using Field Programmable Gate Arrays (FPGAs) for the detection of Spectrally Efficient Frequency Division Multiplexing (SEFDM) signals. Previous work has shown that a sub-optimal Truncated Singular Value Decomposition (TSVD) approach is well-suited for use in SEFDM systems. TSVD offers a targeted reduction in complexity while outperforming linear detectors, such as Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE), in terms of Bit Error Rate (BER). This is the first time a hardware design for the TSVD algorithm has been devised for implementation on an FPGA device using Very high speed integrated circuit Hardware Description Language (VHDL). Results show excellent fixed-point performance which are comparable to existing floating-point computer-based simulations. The optimal parameters required to achieve this outcome combined with their effect on system performance are identified. The impact of finite FPGA resources against performance gain is also examined.
TL;DR: An iterative algorithm employing decision feedback provided by either an equalizer or a channel decoder in order to compensate for the phase noise resulting from imperfect oscillators in orthogonal frequency-division multiplexing (OFDM) systems achieves performance close to that of an OFDM system without phase noise over a wide range of conditions.
Abstract: An iterative algorithm employing decision feedback provided by either an equalizer or a channel decoder is proposed in order to compensate for the phase noise resulting from imperfect oscillators in orthogonal frequency-division multiplexing (OFDM) systems. In the proposed algorithm, the received OFDM symbol is partitioned into subblocks in the time domain and the estimate of the time-average of the phase noise at each subblock is used to compensate for the phase noise. A formula for the signal-to-interference-plus-noise ratio (SINR) after phase noise compensation is derived and its values are evaluated under a variety of conditions in order to demonstrate the efficiency of the proposed algorithm. Numerical results show that the proposed algorithm achieves performance close to that of an OFDM system without phase noise over a wide range of conditions, while requiring only one-half the complexity of the partial intercarrier interference reduction algorithm.
TL;DR: In this paper, two fiber types have been identified as candidates for transmission of multiple signals at the same wavelength inside a single cladding: fibers with multiple single mode cores and single core multi-mode fibers.
TL;DR: The results indicate that the proposed method for distributed interference cancellation leads to performance benefit, in particular under heterogeneous path loss conditions between the helper and the primary/secondary nodes.
Abstract: This paper considers secondary usage of spectrum resources that are allocated to frequency division duplexing (FDD)-based cellular systems. We propose an interference cancellation technique using the concept of distributed antenna array. We show that the interference from the primary cellular system can be cancelled at a secondary node equipped with single antenna by introducing a helper that decodes the interference and transfers it to the secondary node. Interference is forwarded during the time periods in which training signals are transmitted within the primary cellular system. Since the duration of those intervals is short relative to periods for data transmission in the primary system, we introduce a scheme by which the helper compresses the interference before forwarding it. The performance advantage of our scheme is verified by computer simulation, where both analytical and measured channel models are used. The measurement data used in evaluations have been obtained through outdoor experiments while assuming a short-range secondary system. The results indicate that the proposed method for distributed interference cancellation leads to performance benefit, in particular under heterogeneous path loss conditions between the helper and the primary/secondary nodes.
TL;DR: A novel method based on Hadamard precoding is proposed to reduce the peak-to-average power ratio in optical direct detection OFDM system and is successfully applied to an experimental system of optical direct-detection OFDM signal transmission through fiber.
Abstract: The high peak-to-average power ration (PAPR) values of optical orthogond frequency division multiplexing (OFDM) signal limit the system nonlinear tolerance (NLT). In this paper, a novel method based on Hadamard precoding is proposed to reduce the peak-to-average power ratio in optical direct detection OFDM system. The proposed scheme is successfully applied to an experimental system of optical direct-detection OFDM signal transmission through fiber. In this experiment, the 2.5 Gbit/s binary phase shift keying (BPSK) optical OFDM signals with Hadamard precoding are generated and transmitted though a single mode fiber. The experimental results show that the proposed scheme can reduce PAPR by almost 1.5 dB. Meantime the received sensitivity is improved by 2 dB with 100 km fiber transmission compared with that of an ordinary optical direct detection OFDM system.
TL;DR: Numerical simulations of a 58 Gb/s single polarization 2375 km system with inline dispersion compensation show that the signal quality, Q, at the optimal launch power is increased by 2.4 dB if SPM compensation is used before the PB-NLC, compared with only a 0.9 dB improvement if the PB -NLC is used without an SPM compensator for the same link.
Abstract: A pilot-based nonlinearity compensator (PB-NLC) is shown in this Letter to be an effective method for compensating cross-phase modulation (XPM) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An unmodulated pilot tone is transmitted at the center of each OFDM channel to detect phase errors caused by the Kerr effect, which converts intensity fluctuations from all channels to phase errors. The pilots are then used to cancel the XPM phase errors for each OFDM channel at the receiver after each channel’s self-phase modulation (SPM) has been compensated, using its intensity waveform to determine its SPM. Numerical simulations of a 58 Gb/s single polarization 2375 km system with inline dispersion compensation show that the signal quality, Q, at the optimal launch power is increased by 2.4 dB if SPM compensation is used before the PB-NLC. This contrasts with only a 0.9 dB improvement if the PB-NLC is used without an SPM compensator for the same link. This shows the PB-NLC can effectively mitigate XPM but not SPM.
15 May 2011
TL;DR: A serial codeword selection method is proposed, whose complexity is quite low but the performance approaches that of the optimal codewords selection for CoMP channel.
Abstract: Coherent multi-cell cooperative transmission, also referred to as coordinated multi-point transmission (CoMP), is a promising way to provide high spectral efficiency for universal frequency reuse cellular systems. To report the required channel information to the transmitter in frequency division duplexing systems, limited feedback techniques are often applied. Considering that the large scale fading gains of channels from multiple base stations (BSs) to one mobile station are different and the number of cooperative BSs may be dynamic, it is not flexible nor compatible to employ a large codebook for directly quantizing the CoMP channel. In this paper, per-cell codebook for separately quantizing local and cross channels are studied. We first optimize the bit allocation among per-cell codebooks, aiming at minimizing the average quantization error of the aggregated CoMP channel. A closed-form codebook size allocation method is proposed, which only depends on the large scale fading gains of per-cell channels. Considering that the optimal per-cell codeword selection for CoMP channel is of high complexity, we propose a serial codeword selection method, whose complexity is quite low but the performance approaches that of the optimal codeword selection. Simulation results validate our analysis and demonstrate an evident performance gain of our methods.
TL;DR: It is expected that MIMO strategies can provide significant benefits to local and metropolitan area networks in terms of network cost and complexity, power budget, and data rate.
Abstract: We evaluate the performance of multiple-input multiple-output (MIMO) concepts and their applicability in increasing data rates achievable in multimode fibers. We draw on several MIMO techniques used commonly in wireless standards, and experimentally evaluate their performance benefits to a 3-km multimode fiber link. Using two transmitters and two detectors in concert, with orthogonal frequency-division multiplexing (OFDM), we achieved a data rate of 12 Gb/s, exceeding the fiber's characteristic bandwidth length product by over 20-fold. It is expected that MIMO strategies can provide significant benefits to local and metropolitan area networks in terms of network cost and complexity, power budget, and data rate.
TL;DR: An analytical model for calculating the saturation throughput performance of a medium transparent medium access control (MAC) protocol in 60 GHz radio-over-fiber (RoF) networks is demonstrated and confirms that the proposed medium transparent MAC protocol can effectively operate in high-speed 60 GHz RoF LAN environments.
Abstract: We demonstrate an analytical model for calculating the saturation throughput performance of a medium transparent medium access control (MAC) protocol in 60 GHz radio-over-fiber (RoF) networks. The proposed model incorporates effectively the medium transparent MAC mechanism, assuming a finite number of terminals and ideal channel conditions. It takes into account contention both at the optical and wireless layer, ensuring seamless and dynamic capacity allocation over both transmission media. This model enables extensive saturation throughput performance analysis for the medium transparent MAC and has been applied to 60 GHz RoF network scenarios considering variable numbers of available optical wavelengths, wireless nodes and serving antenna elements and for two different data rate values, namely 155 Mbps and 1 Gbps. Comparison between the model-based throughput results and respective simulation-based outcomes reveals that our model is extremely accurate in predicting the system throughput. Moreover, it confirms that the proposed medium transparent MAC protocol can effectively operate in high-speed 60 GHz RoF LAN environments.