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Showing papers on "Frequency-division multiplexing published in 2013"


Journal ArticleDOI
TL;DR: JSDM achieves significant savings both in the downlink training and in the CSIT uplink feedback, thus making the use of large antenna arrays at the base station potentially suitable also for frequency division duplexing systems, for which uplink/downlink channel reciprocity cannot be exploited.
Abstract: We propose joint spatial division and multiplexing (JSDM), an approach to multiuser MIMO downlink that exploits the structure of the correlation of the channel vectors in order to allow for a large number of antennas at the base station while requiring reduced-dimensional channel state information at the transmitter (CSIT). JSDM achieves significant savings both in the downlink training and in the CSIT uplink feedback, thus making the use of large antenna arrays at the base station potentially suitable also for frequency division duplexing (FDD) systems, for which uplink/downlink channel reciprocity cannot be exploited. In the proposed scheme, the multiuser MIMO downlink precoder is obtained by concatenating a prebeamforming matrix, which depends only on the channel second-order statistics, with a classical multiuser precoder, based on the instantaneous knowledge of the resulting reduced dimensional “effective” channel matrix. We prove a simple condition under which JSDM incurs no loss of optimality with respect to the full CSIT case. For linear uniformly spaced arrays, we show that such condition is approached in the large number of antennas limit. For this case, we use Szego's asymptotic theory of Toeplitz matrices to show that a DFT-based prebeamforming matrix is near-optimal, requiring only coarse information about the users angles of arrival and angular spread. Finally, we extend these ideas to the case of a 2-D base station antenna array, with 3-D beamforming, including multiple beams in the elevation angle direction. We provide guidelines for the prebeamforming optimization and calculate the system spectral efficiency under proportional fairness and max-min fairness criteria, showing extremely attractive performance. Our numerical results are obtained via asymptotic random matrix theory, avoiding lengthy Monte Carlo simulations and providing accurate results for realistic (finite) number of antennas and users.

1,347 citations


Journal ArticleDOI
TL;DR: In this article, a closed-loop echo cancellation technique is proposed to cancel high-power echoes at the receive chain as echoes with powers much higher than the desired received signal, which can be implemented purely in the analogue domain.
Abstract: Full Duplex or Simultaneous transmission and reception (STR) in the same frequency at the same time can potentially double the physical layer capacity. However, high power transmit signal will appear at receive chain as echoes with powers much higher than the desired received signal. Therefore, in order to achieve the potential gain, it is imperative to cancel these echoes. As these high power echoes can saturate low noise amplifier (LNA) and also digital domain echo cancellation requires unrealistically high resolution analog-to-digital converter (ADC), the echoes should be cancelled or suppressed sufficiently before LNA. In this paper we present a closed-loop echo cancellation technique which can be implemented purely in analogue domain. The advantages of our method are multiple-fold: it is robust to phase noise, does not require additional set of antennas, can be applied to wideband signals and the performance is irrelevant to radio frequency (RF) impairments in transmit chain. Next, we study a few protocols for STR systems in carrier sense multiple access (CSMA) network and investigate MAC level throughput with realistic assumptions in both single cell and multiple cells. We show that STR can reduce hidden node problem in CSMA network and produce gains of up to 279% in maximum throughput in such networks. Moreover, at high traffic load, the gain of STR system can be tremendously large since the throughput of non-STR system is close to zero at heavy traffic due to severe collisions. Finally, we investigate the application of STR in cellular systems and study two new unique interferences introduced to the system due to STR, namely BS-BS interference and UE-UE interference. We show that these two new interferences will hugely degrade system performance if not treated appropriately. We propose novel methods to reduce both interferences and investigate the performances in system level. We show that BS-BS interference can be suppressed sufficiently enough to be less than thermal noise power, and with favorable UE-UE channel model, capacities close to double are observed both in downlink (DL) and uplink (UL). When UE-UE interference is larger than DL co-channel interferences, we propose a simple and "non-cooperative" technique in order to reduce UE-UE interference.

208 citations


Proceedings ArticleDOI
02 Jun 2013
TL;DR: A low complexity design for demodulating GFDM signals based on a sparse representation of the pulse-shaping filter in frequency domain and the results show, that for high-order QAM signaling, the error performance can be significantly improved with interference cancellation at reasonable computational cost.
Abstract: Generalized frequency division multiplexing (GFDM) is a multi-carrier modulation scheme. In contrast to the traditional orthogonal frequency division multiplexing (OFDM), it can benefit from transmitting multiple symbols per sub-carrier. GFDM targets block based transmission which is enabled by circular pulse shaping of the individual sub- carriers. In this paper we propose a low complexity design for demodulating GFDM signals based on a sparse representation of the pulse-shaping filter in frequency domain. The proposed scheme is compared to receiver concepts from previous work and the performance is assessed in terms of bit error rates for AWGN and Rayleigh multipath fading channels. The results show, that for high-order QAM signaling, the error performance can be significantly improved with interference cancellation at reasonable computational cost.

126 citations


Journal ArticleDOI
TL;DR: It is revealed that introducing controlled interference can significantly increase the efficiency of realistic satellite communications systems, based on frequency-division-multiplexed linear modulations, where spectral efficiency is one of the main figures of merit.
Abstract: We consider realistic satellite communications systems for broadband and broadcasting applications, based on frequency-division-multiplexed linear modulations, where spectral efficiency is one of the main figures of merit. For these systems, we investigate their ultimate performance limits by using a framework to compute the spectral efficiency when suboptimal receivers are adopted and evaluating the performance improvements that can be obtained through the adoption of the time-frequency packing technique. Our analysis reveals that introducing controlled interference can significantly increase the efficiency of these systems. Moreover, if a receiver which is able to account for the interference and the nonlinear impairments is adopted, rather than a classical predistorter at the transmitter coupled with a simpler receiver, the benefits in terms of spectral efficiency can be even larger. Finally, we consider practical coded schemes and show the potential advantages of the optimized signaling formats when combined with iterative detection/decoding.

107 citations


01 Jan 2013
TL;DR: In this paper, an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks was proposed to solve the problem of spectrum reusability and flexible prototyping radio platform using software-defined radio (SDR).
Abstract: Mobile data traffic will continue its tremendous growth in some markets, and has already resulted in an apparent radio spectrum scarcity. There is a strong need for more efficient methods to use spectrum resources, leading to extensive research on increasing spectrum reusability on flexible radio platforms. This study solves this problem in two sub topics, millimeter wave communication on wireless backhaul for spectrum reusability, and flexible prototyping radio platform using software-defined radio (SDR). Wireless backhaul has received significant attention as a key technology affecting the development of future wireless cellular networks because it helps to easily deploy many small size cells, an essential part of a high capacity system. Millimeter wave is considered a possible candidate for cost-effective wireless backhaul. In the outdoor deployment using a millimeter wave, beamforming methods are key techniques to establish wireless links in the 60 GHz to 80 GHz to overcome pathloss constraints (i.e., rainfall effect and oxygen absorption). The millimeter wave communication system cannot directly access the channel knowledge. To overcome this, a beamforming method based on codebook search is considered. The millimeter wave communication cannot access channel knowledge, therefore alternatively a beamforming method based on a codebook search is considered. In the first part, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. Results show significant performance improvement with reduced search time. In the second part of this study, SDR is discussed as an approach toward flexible wireless communication systems. Most layers of SDR are implemented by software. Therefore, only a software change is needed to transform the type of radio system. The translation of the signal processing into software performed by a regular computer opens up a huge number of possibilities at a reasonable price and effort. SDR systems are widely used to build prototypes, saving time and money. In this project, a robust wireless communication system in high interference environment was developed. For the physical layer (PHY) of the system, we implemented a channel sub-bandding method that utilizes frequency division multiplexing to avoid interference. Then, to overcome a further interfered channel, Direct Spread Spectrum System (DSSS) was considered and implemented. These prototyped testbeds were evaluated for system performance in the interference environment.

103 citations


Journal ArticleDOI
TL;DR: An multipath delay commutator (MDC)-based architecture and memory scheduling to implement fast Fourier transform (FFT) processors for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems with variable length is presented.
Abstract: This paper presents an multipath delay commutator (MDC)-based architecture and memory scheduling to implement fast Fourier transform (FFT) processors for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems with variable length. Based on the MDC architecture, we propose to use radix-Ns butterflies at each stage, where Ns is the number of data streams, so that there is only one butterfly needed in each stage. Consequently, a 100% utilization rate in computational elements is achieved. Moreover, thanks to the simple control mechanism of the MDC, we propose simple memory scheduling methods for input data and output bit/set-reversing, which again results in a full utilization rate in memory usage. Since the memory requirements usually dominate the die area of FFT/inverse fast Fourier transform (IFFT) processors, the proposed scheme can effectively reduce the memory size and thus the die area as well. Furthermore, to apply the proposed scheme in practical applications, we let Ns=4 and implement a 4-stream FFT/IFFT processor with variable length including 2048, 1024, 512, and 128 for MIMO-OFDM systems. This processor can be used in IEEE 802.16 WiMAX and 3GPP long term evolution applications. The processor was implemented with an UMC 90-nm CMOS technology with a core area of 3.1 mm2. The power consumption at 40 MHz was 63.72/62.92/57.51/51.69 mW for 2048/1024/512/128-FFT, respectively in the post-layout simulation. Finally, we analyze the complexity and performance of the implemented processor and compare it with other processors. The results show advantages of the proposed scheme in terms of area and power consumption.

99 citations


Proceedings ArticleDOI
01 Nov 2013
TL;DR: Generalized frequency division multiplexing (GFDM) is explored as a possible, non-orthogonal waveform for next generation cellular systems and shows that a non- OrthogonalWaveform brings additional degrees of freedom, which can be beneficial.
Abstract: With the Internet of Things on the horizon, novel services will impose new challenges upon future cellular systems. One key parameter that influences the energy efficiency is peak-to-average power ratio (PAPR). PAPR is particularly revelant for cheap mass market terminals. In the most recent cellular standard, Long Term Evolution, different waveforms are used in downlink and uplink transmission, to address the issue of nonlinear distortions as a consequence of high PAPR. In this work, generalized frequency division multiplexing (GFDM) is explored as a possible, non-orthogonal waveform for next generation cellular systems. Particular focus lies on the PAPR properties of the generated waveform. First, various filtered multi-carrier techniques, including OFDM, SC-FDE and GFDM, are presented in an unified framework. Second, the PAPR of those schemes is compared in an uplink multiple access scenario. The results show that a non-orthogonal waveform brings additional degrees of freedom, which can be beneficial.

82 citations


Journal ArticleDOI
Fan Li1, Zizheng Cao1, Xinying Li2, Ze Dong, Lin Chen1 
TL;DR: In this article, a fully integrated fiber-wireless system that delivers 30.67-Gb/s polarization division multiplexing (PDM-MIMO-OFDM) signal through 40-km fiber and 5-m wireless transmission over free-space at 100 GHz adopting heterodyne coherent detection is demonstrated.
Abstract: We experimentally demonstrated a seamlessly integrated fiber-wireless system that delivers 30.67-Gb/s polarization division multiplexing-multiple input multiple output-orthogonal frequency division multiplexing (PDM-MIMO-OFDM) signal through 40-km fiber and 5-m wireless transmission over free-space at 100 GHz adopting heterodyne coherent detection. De-multiplexing is realized by channel estimation based on a pair of time-interleaved training sequences (TSs). The bit-error ratio (BER) for the 30.67-Gb/s PDM-MIMO-OFDM signal is less than the pre-forward-error-correction (pre-FEC) threshold of 3.8 × 10-3 when the optical signal-to-noise ratio (OSNR) is larger than 19.3 dB after both 40-km single-mode fiber-28 (SMF-28) transmission and 5-m wireless delivery at 100 GHz. We also find that the BER performance is sensitive to the multipath effects induced by the transmission distance difference in the wireless link.

64 citations


Proceedings ArticleDOI
01 Dec 2013
TL;DR: This work presents non-coherent frequency shift keying (FSK) for bistatic backscatter radio; FSK is appropriate for the power limited regime and also allows many RF tags/sensors to convey information to a central reader simultaneously with simple frequency division multiplexing (FDM).
Abstract: For applications that require large numbers of wireless sensors spread in a field, backscatter radio can be utilized to minimize the monetary and energy cost of each sensor. Commercial backscatter systems such as those in radio frequency identification (RFID), utilize modulation designed for the bandwidth limited regime, and require medium access control (MAC) protocols for multiple access. High tag/sensor bitrate and monostatic reader architectures result in communication range reduction. In sharp contrast, sensing applications typically require the opposite: extended communication ranges that could be achieved with bitrate reduction and bistatic reader architectures. This work presents non-coherent frequency shift keying (FSK) for bistatic backscatter radio; FSK is appropriate for the power limited regime and also allows many RF tags/sensors to convey information to a central reader simultaneously with simple frequency division multiplexing (FDM). However, classic non-coherent FSK receivers are not directly applicable in bistatic backscatter radio. This work a) carefully derives the complete signal model for bistatic backscatter radio, b) describes the details of backscatter modulation with emphasis on FSK and its corresponding receiver, c) proposes techniques to overcome the difficulties introduced by the utilization of bistatic architectures, such as the carrier frequency offset (CFO), and d) presents bit error rate (BER) performance for the proposed receiver and carrier recovery techniques.

63 citations


Journal ArticleDOI
TL;DR: In this article, simulations have been performed to evaluate and compare the link power budget and power dissipation of 100 Gb/s carrierless amplitude and phase modulation (CAP-16/64) and 16/64-quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) systems over feedforward error correction (FEC) enhanced single mode fiber (SMF) links using an 18.6 GHz bandwidth directly modulated laser.
Abstract: For the first time, simulations have been performed to evaluate and compare the link power budget and power dissipation of 100 Gb/s carrierless amplitude and phase modulation-16/64 (CAP-16/64) and 16/64-quadrature amplitude modulation-orthogonal frequency division multiplexing (16/64-QAM-OFDM) systems over feedforward error correction (FEC) enhanced single mode fiber (SMF) links using an 18.6 GHz bandwidth directly modulated laser, for both single channel and two coarse wavelength division multiplexing (CWDM) channel cases. It is shown that single channel CAP-16 and 16-QAM-OFDM links can successfully support transmission over 5 km SMF, with a power dissipation of ~ 2 times that of a 4 × 25 Gb/s NRZ system. Even when the loss of the optical multiplexing/demultiplexing operations is considered, the use of two CWDM channels supports transmission over 5 km SMF with CAP-16 and 16-QAM-OFDM. The CWDM systems do not increase transceiver power dissipation greatly.

55 citations


Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a proof-of-principle multiplexed, multichannel, inductive pulse sensor based on resonant frequency division multiplexing for high throughput detection of micro-scale metallic debris in lubricants.
Abstract: With a long time goal of detecting signs of potential machine failure, we demonstrate a proof-of-principle multiplexed, multichannel, inductive pulse sensor based on resonant frequency division multiplexing for high throughput detection of micro-scale metallic debris in lubricants. In the four-channel sensor, each sensing coil is connected to a specific external capacitance to form a parallel LC circuit that has a unique resonant frequency. Only one combined sinusoidal excitation signal consisting of four frequencies components that are close to the 4 sensing channels’ resonant frequencies was applied to the sensor, and only one combined voltage response was measured. Because each sensing channel exhibited a peak amplitude at its resonant frequency, the signals for each individual channel were recovered from the combined response by taking the spectrum components at each resonant frequency with an improved signal-to-noise ratio. Inductance change for each channel was then calculated from signals of individual channels. Testing results show that the use of resonant frequency division multiplexing allows simultaneous detection of debris in lubricants using only one set of detection electronics; for the four-channel sensor, there is a 300 % increase in throughput. The resonant frequency division multiplexing concept can be potentially applied to a multichannel oil debris sensor with a large number of sensing channels to achieve a very high throughput, which is necessary for online health monitoring of rotating and reciprocal mechanical components.

Proceedings ArticleDOI
02 Dec 2013
TL;DR: A dynamic cancellation technique is proposed, enabling sufficient TX-RX isolation in FDD mode without any extra analog/RF filtering, based on creating a replica of the undesired transmitter leakage signal and subtracting it from the down-converted signal in the receiver path.
Abstract: Frequency division duplex (FDD) transceivers employing the direct-conversion radio architecture are known to suffer from transmitter-receiver signal leakage problems. The presence of such leakage signal can impose stringent linearity requirements in receiver components that are difficult to fulfill in practice. Good example is second-order intermodulation distortion (IM2) due to transmitter leakage signal, stemming from finite IIP2 of receiver mixers, falling directly on top of the weak received signal. This paper carries out detailed modeling and proposes a dynamic cancellation technique for such TX-RX leakage, enabling sufficient TX-RX isolation in FDD mode without any extra analog/RF filtering. The technique is based on creating a replica of the undesired transmitter leakage signal and subtracting it from the down-converted signal in the receiver path, taking also the essential transmitter nonidealities into account. Simulation results show that the proposed method is able to effectively push transmitter leakage induced IM2 below the receiver noise floor.

Journal ArticleDOI
TL;DR: A spectral precoding approach for multiple OFDM-based CR users to reduce OOB leakage and enhance spectrum compactness and ensures user independence thus with low encoding and decoding complexities is proposed.
Abstract: Orthogonal frequency-division multiplexing (OFDM) is an ideal transmission technique for cognitive radio (CR) systems because of its flexible nature to support dynamic spectrum access. However, the out-of-band (OOB) radiation of OFDM signals from different CR users must be strictly controlled to protect licensed users operating in the adjacent frequency bands. In this paper, we propose a spectral precoding approach for multiple OFDM-based CR users to reduce OOB leakage and enhance spectrum compactness. By constructing individual precoders to render selected spectrum nulls, our approach suppresses the overall OOB radiation without sacrificing bit-error rate performance of CR users. The proposed approach also ensures user independence thus with low encoding and decoding complexities. Furthermore, our approach can improve bandwidth efficiency by carefully selecting notched frequencies. As a comprehensive application of the proposed approach, two simplified multiuser spectral precoding schemes are provided to reduce the computational complexity. Simulation results demonstrate that our spectral precoding schemes effectively limit OOB radiation and enable efficient spectrum sharing.

Journal ArticleDOI
TL;DR: The proposed reconfigurable adaptive SVD engine design is very suitable for high-throughput wireless communication applications and an orthogonal reconstruction scheme to obtain more accurate SVD outputs is proposed.
Abstract: Singular value decomposition (SVD) is an optimal method to obtain spatial multiplexing gain in multi-input multi-output (MIMO) channels. However, the high cost of implementation and high decomposing latency of the SVD restricts its usage in current wireless communication applications. In this paper, we present a complete adaptive SVD algorithm and a reconfigurable architecture for high-throughput MIMO-orthogonal frequency division multiplexing systems. There are several proposed architectural design techniques: reconfigurable scheme, division-free adaptive step size scheme, early termination scheme, and data interleaving scheme. The reconfigurable scheme can support all antenna configurations in a MIMO system. The division-free adaptive step size and early termination schemes are used to effectively reduce the decomposing latency and improve hardware utilization. The data interleaving scheme helps to deal with several channel matrices concurrently. Besides, we propose an orthogonal reconstruction scheme to obtain more accurate SVD outputs, and then the system performance will be greatly enhanced. We apply our SVD design to the IEEE 802.11 n applications. This design is implemented and fabricated in UMC 90 nm 1P9M CMOS technology. The maximum operating frequency is measured to be at 101.2 MHz, and the corresponding power dissipation is at 125 mW. The core size is 2.17 mm2 and the die size occupies 4.93 mm2. The chip result shows that the average latency is only 0.33% of the wireless local area network coherence time. Hence, the proposed reconfigurable adaptive SVD engine design is very suitable for high-throughput wireless communication applications.

Journal ArticleDOI
TL;DR: In this work, the problem of cross-tier interference in a two-tiered (macro-cell and cognitive small-cells) network, under the complete spectrum sharing paradigm, is studied and a new orthogonal precoder transmit scheme for the small base stations, called multi-user Vandermonde-subspace frequency division multiplexing (MU-VFDM), is proposed.
Abstract: In this work, the problem of cross-tier interference in a two-tiered (macro-cell and cognitive small-cells) network, under the complete spectrum sharing paradigm, is studied. A new orthogonal precoder transmit scheme for the small base stations, called multi-user Vandermonde-subspace frequency division multiplexing (MU-VFDM), is proposed. MU-VFDM allows several cognitive small base stations to coexist with legacy macro-cell receivers, by nulling the small- to macro-cell cross-tier interference, without any cooperation between the two tiers. This cleverly designed cascaded precoder structure, not only cancels the cross-tier interference, but avoids the co-tier interference for the small-cell network. The achievable sum-rate of the small-cell network, satisfying the interference cancelation requirements, is evaluated for perfect and imperfect channel state information at the transmitter. Simulation results for the cascaded MU-VFDM precoder show a comparable performance to that of state-of-the-art dirty paper coding technique, for the case of a dense cellular layout. Finally, a comparison between MU-VFDM and a standard complete spectrum separation strategy is proposed. Promising gains in terms of achievable sum-rate are shown for the two-tiered network w.r.t. the traditional bandwidth management approach.

Journal ArticleDOI
TL;DR: In this paper, a numerical model of Semiconductor Optical Amplifiers (SOA) is experimentally validated in terms of the Alpha Factor (αH) and the Four-Wave Mixing (FWM).
Abstract: In this paper, a numerical model of Semiconductor Optical Amplifiers (SOA) is experimentally validated in terms of the Alpha Factor (αH) and the Four-Wave Mixing (FWM). Besides, a Coherent Optical-Orthogonal Frequency Division Multiplexing (CO-OFDM) simulation platform is used to confirm the good agreement between the measured and the simulated Error Vector Magnitude (EVM) of a received signal amplified by the studied SOA in an optical transmission link. In addition, the performance of the SOA on the amplification of a 10.94 Gb/s QPSK CO-OFDM signal is numerically analyzed with respect to the Amplified Spontaneous Emission (ASE) noise, the Alpha Factor, the output saturation power of the SOA and the bit rate.

Journal ArticleDOI
TL;DR: In this paper, the authors present new trends in the performance evaluation of submarine fiber cable system with different ultra-high multiplexing and propagation techniques over a wide range of the affecting parameters.
Abstract: We present new trends in the performance evaluation of submarine fiber cable system with different ultrahigh multiplexing and propagation techniques over a wide range of the affecting parameters. Our model takes into account the ultimate optical transmission of huge submarine cables with 14,400 channels under different depth conditions. We employ Raman and erbium-doped fiber amplifiers in our study. We investigate the double impact of both temperature and pressure through the defined depth penalty. We also study the soliton transmission technique using two multiplexing methods considered in the design of ultra-wide wavelength division multiplexing (UW-WDM) with 14,400 optical channels and ultra-wide space division multiplexing (UW-SDM) with 440 fiber links. Based on experimental data, both the deep ocean water temperature and pressure are obtained as functions of the water depth.

Journal ArticleDOI
TL;DR: In this paper, a remotely seeded flexible passive optical network (PON) with multiple low-speed subscribers but only a single optical line terminal transceiver operating at a data rate of 31.25 Gbps/s is demonstrated.
Abstract: We demonstrate a remotely seeded flexible passive optical network (PON) with multiple low-speed subscribers but only a single optical line terminal transceiver operating at a data rate of 31.25 Gbits/s. The scheme is based on a colorless frequency division multiplexing (FDM)-PON with centralized wavelength control. Multiplexing and demultiplexing in the optical network unit (ONU) is performed in the electronic domain and relies either on FDM with Nyquist sinc-pulse shaping or on orthogonal frequency division multiplexing (OFDM). This way the ONU can perform processing at low speed in the baseband. Further, the ONU is colorless by means of a remote seed for upstream transmission and a remote local oscillator for heterodyne reception, all of which helps in keeping maintenance and costs for an ONU potentially low and will simplify wavelength allocation in a future software defined network architecture. To extend the reach, semiconductor optical amplifiers are used for optical amplification in the downstream and upstream.

Journal ArticleDOI
TL;DR: In this article, the authors proposed an intra-symbol carrier phase recovery (IS-CPR) algorithm for reduced-guard-interval (RGI) CO-OFDM in order to compensate for the intrasymbol phase shift (ISPS) between subcarriers that is caused by the dispersionenhanced phase noise (DEPN).
Abstract: We propose intra-symbol carrier phase recovery (IS-CPR) for reduced-guard-interval (RGI) CO-OFDM in order to compensate for the intra-symbol phase shift (ISPS) between subcarriers that is caused by the dispersion-enhanced phase noise (DEPN). We begin by proposing a pre-emphasized pilot subcarrier (PEPS) approach to reduce the pilot subcarrier overhead for the following IS-CPR algorithms. Then, we show a statistical analysis of the DEPN-induced ISPS between subcarriers within one symbol, which is related to the accumulated chromatic dispersion (CD). Next, three algorithms are proposed for IS-CPR including maximum-likelihood (ML) phase estimation, digital phase-locked loop (DPLL), and feedforward carrier recovery (FFCR) employing either the Mth power scheme in case of QPSK modulation or the QPSK partitioning scheme for the 16-QAM case. The performance and complexity of these algorithms are compared. Through simulations, we show that in comparison to conventional common phase error (CPE) compensation, IS-CPR significantly improves the linewidth tolerance at 1 dB signal-to-noise ratio (SNR) penalty for a bit error rate (BER) = 10-3 from 300 kHz to 2 MHz for 112 Gb/s systems (28 Gbaud QPSK) at 3200 km transmission distance, and from 70 kHz to 550 kHz for 448 Gb/s (56 Gbaud 16-QAM) systems at 1600 km transmission distance.

Journal ArticleDOI
TL;DR: The optimal resource allocation is realised under the individual power constraints in source and relays, so that the sum rate is maximised, whereas the interference induced to the primary system is kept below a pre-specified interference temperature limit.
Abstract: In this study, the problem of resource allocation in multiple-input multiple-output-orthogonal frequency division multiplexing-based cooperative cognitive radio networks is considered. The cooperation strategies between the secondary users is the decode-and-forward (DF) strategies. In order to obtain an optimal subcarrier pairing, relay assignment and power allocation in the system, the dual decomposition technique is recruited. The optimal resource allocation is realised under the individual power constraints in source and relays, so that the sum rate is maximised, whereas the interference induced to the primary system is kept below a pre-specified interference temperature limit. Moreover, because of the high computational complexity of the optimal approach, a suboptimal algorithm is further proposed. The joint allocation of the resources in suboptimal algorithm is carried out taking into account the channel qualities, the DF cooperation strategy, the interference induced to the primary system and the individual power budgets. The performance of the different approaches and the impact of the constraint values and deploying multiple antennas at users are discussed through the numerical simulation results.

Journal ArticleDOI
TL;DR: A global view of VFDM is presented, showing that it provides a spectral efficiency increase of up to 1 bps/Hz over cognitive radio systems based on unused band detection and some key design parameters for its future implementation and a feasible channel estimation protocol.
Abstract: Vandermonde-subspace frequency division multiplexing (VFDM) is an overlay spectrum sharing technique for cognitive radio. VFDM makes use of a precoder based on a Vandermonde structure to transmit information over a secondary system, while keeping an orthogonal frequency division multiplexing (OFDM)-based primary system interference-free. To do so, VFDM exploits frequency selectivity and the use of cyclic prefixes by the primary system. Herein, a global view of VFDM is presented, including also practical aspects such as linear receivers and the impact of channel estimation. We show that VFDM provides a spectral efficiency increase of up to 1 bps/Hz over cognitive radio systems based on unused band detection. We also present some key design parameters for its future implementation and a feasible channel estimation protocol. Finally we show that, even when some of the theoretical assumptions are relaxed, VFDM provides non-negligible rates while protecting the primary system.


Patent
09 Sep 2013
TL;DR: A magnetic recording system includes an array of analog inputs operable to receive analog signals retrieved from a magnetic storage medium, a modulator that combines the analog signals to yield a frequency division multiplexed signal, a demodulator that yields a plurality of demodulated signals from the FDM signal corresponding to each channel of the array, and a joint equalizer that filters the plurality of signals from each channel to yield an equalized output as discussed by the authors.
Abstract: A magnetic recording system includes an array of analog inputs operable to receive analog signals retrieved from a magnetic storage medium, a modulator operable to combine the analog signals to yield a frequency division multiplexed signal, a demodulator operable to yield a plurality of demodulated signals from the frequency division multiplexed signal corresponding to each channel of the array, and a joint equalizer operable to filter the plurality of demodulated signals to yield an equalized output.

Patent
11 Sep 2013
TL;DR: In this paper, a spatial orthogonality-based large-scale MIMO system pilot frequency distribution method was proposed to reduce the influence caused by pilot frequency pollution and improve the system throughput performance.
Abstract: The invention relates to a spatial-orthogonality-based large-scale MIMO system pilot frequency distribution method. The method comprises the following steps: 1) obtaining the statistical covariance matrix information of every user terminal channel through a base station; 2) under the condition that the statistical covariance matrix information is known, obtaining the condition for achieving no-speed-loss transmission when two users located in different cells on the same time-frequency block perform pilot frequency multiplexing; 3) according to the information obtained in step 1), contrasting and calculating the spatial orthogonality degree among the channels of different users through the base station, and utilizing the condition of achieving the no-speed-loss transmission in step 2) to perform greedy packet scheduling on the users under the principle of maximizing the system sum speed; and 4) performing pilot frequency distribution on every user group. Under the condition that the user side does not know instantaneous channel state information, the spatial-orthogonality-based large-scale MIMO system pilot frequency distribution method can achieve the pilot frequency multiplexing and meanwhile effectively reduce the influence caused by the problem of pilot frequency pollution and improve the system throughput performance.

Journal ArticleDOI
TL;DR: This paper gives a great insight of major problems like high peak-to-average power ratio (PAPR) problem, synchronization (time and frequency) problems, and the methods of inter-carrier interference (ICI) reduction available in literature.
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) has been adopted as a major data transmission technique by many wireless communication standards. Despite its several advantageous features, there are some major issues which should be resolved for getting its full advantages. This paper reviews these concerns of OFDM system in detail and present different available solutions of these problems. This paper gives a great insight of major problems like high peak-to-average power ratio (PAPR) problem, synchronization (time and frequency) problems. This paper also highlights the methods of inter-carrier interference (ICI) reduction available in literature.

25 Feb 2013
TL;DR: This paper discusses the channel estimation in OFDM and its implementation in MATLAB using pilot based block type channel estimation techniques by LS and MMSE algorithms, concluding that LS algorithm gives less complexity but MMSE algorithm provides comparatively better results.
Abstract: During the past few years, the developments in digital communication are rapidly increasing to meet the ever increasing demand of higher data rates. Orthogonal Frequency Division Multiplexing (OFDM) has an edge over other frequency multiplexing techniques by using more densely packed carriers, thus achieving higher data rates using similar channels. This paper discusses the channel estimation in OFDM and its implementation in MATLAB using pilot based block type channel estimation techniques by LS and MMSE algorithms. This paper starts with comparisons of OFDM using BPSK and QPSK on different channels, followed by modeling the LS and MMSE estimators on MATLAB. In the end, results of different simulations are compared to conclude that LS algorithm gives less complexity but MMSE algorithm provides comparatively better results

Journal ArticleDOI
TL;DR: An adaptive multiuser detection (MUD) technique using the complex radial basis function (CRBF) network is proposed for space division multiple access-orthogonal frequency division multiplexing (SDMA-OFDM) system and has low complexity, better performance compared with MSER MUD and also supports overload scenario.
Abstract: An adaptive multiuser detection (MUD) technique using the complex radial basis function (CRBF) network is proposed for space division multiple access-orthogonal frequency division multiplexing (SDMA-OFDM) system. Among various MUDs, the linear minimum mean-square error (MMSE) MUD suffers from poor performance and the maximum likelihood (ML) detector is restricted by high computational complexity. Hence, the cost function minimisation-based detector like minimum symbol error rate (MSER) is preferred because of significant performance gain over MMSE MUD and complexity gain over ML detector. Moreover, the MSER detector also has a potential of surviving in overload scenario, where the number of users are more than that of the number of receiving antennas. However, in all these techniques, the requirement of channel estimation adds an extra complexity whereas, the proposed CRBF detector approximates the channel parameters in training phase and detects signals in testing phase. It also has low complexity, better performance compared with MSER MUD and also supports overload scenario. Each neuron in the proposed CRBF network is assembled with ` sech ' activation function, as this function can do better complex non-linear mapping than Gaussian activation. The simulation study and performance evaluation of CRBF MUD is investigated, considering both data and image transmission.

Journal Article
TL;DR: A global view of VFDM is presented, showing that it provides a spectral efficiency increase of up to 1 bps/Hz over cognitive radio systems based on unused band detection and some key design parameters for its future implementation and a feasible channel estimation protocol.
Abstract: Vandermonde-subspace frequency division multiplexing (VFDM) is an overlay spectrum sharing technique for cognitive radio. VFDM makes use of a precoder based on a Vandermonde structure to transmit information over a secondary system, while keeping an orthogonal frequency division multiplexing (OFDM)-based primary system interference-free. To do so, VFDM exploits frequency selectivity and the use of cyclic prefixes by the primary system. Herein, a global view of VFDM is presented, including also practical aspects such as linear receivers and the impact of channel estimation. We show that VFDM provides a spectral efficiency increase of up to 1 bps/Hz over cognitive radio systems based on unused band detection. We also present some key design parameters for its future implementation and a feasible channel estimation protocol. Finally we show that, even when some of the theoretical assumptions are relaxed, VFDM provides non-negligible rates while protecting the primary system.

Journal ArticleDOI
TL;DR: A demodulation algorithm and schemes on how to optimize performances in detail based on the idea of software radio are presented, suitable for sensor signal detection with AC signal excitation and can also improve overall system performance.

Journal ArticleDOI
TL;DR: The theoretical analysis and numerical results demonstrate that DF relaying has better performance in the low to moderate SNR regime, while AF relaying is more appropriate in the highSNR regime.
Abstract: Most of the existing works on two-way frequency division multiplexing (OFDM) relay channels was centered on per-subcarrier decode-and-forward (DF) relaying, where each subcarrier is treated as a separate channel, and channel coding is performed separately over each subcarrier. In this paper, we show that this per-subcarrier DF relay strategy is suboptimal. More specifically, we present a multi-subcarrier DF relay strategy which achieves a larger rate region by adopting cross-subcarrier channel coding. Then we develop an optimal resource allocation algorithm to characterize the achievable rate region of the proposed multi-subcarrier DF relay strategy. Compared to standard Lagrangian duality optimization algorithms, our algorithm has a much smaller computational complexity due to the use of the structure property of the optimal resource allocation solution. We further prove that our multi-subcarrier DF relay strategy tends to achieve the capacity region of the two-way OFDM relay channels in the low signal-to-noise ratio (SNR) regime, and the amplify-and-forward (AF) relay strategy tends to achieve the multiplexing gain region of the two-way OFDM relay channels in the high SNR regime. Our theoretical analysis and numerical results demonstrate that DF relaying has better performance in the low to moderate SNR regime, while AF relaying is more appropriate in the high SNR regime.