Tongyang Xu

Optical SEFDM System; Bandwidth Saving Using Non-Orthogonal Sub-Carriers

We propose and demonstrate a new optical spectrally efficient frequency division multiplexing (O-SEFDM) system, where non-orthogonal and overlapping sub-carriers are employed to provide higher spectral efficiency relative to optical-orthogonal frequency division multiplexing (O-OFDM). The O-SEFDM technique can increase spectral efficiency in both the electrical and optical domains. It is experimentally shown that for bandwidth saving up to 25%, we can achieve the same performance as O-OFDM. This is the first experimental verification of 25% optical faster than the Nyquist rate. Furthermore, for approximately the same spectral efficiency, 4QAM O-SEFDM outperforms standard 8QAM by 1.6 dB. It is experimentally shown that a lower-order modulation format can achieve a better performance by replacing a higher one.

An Improved Fixed Sphere Decoder Employing Soft Decision for the Detection of Non-orthogonal Signals

This letter proposes a hybrid soft iterative method together with Fixed Sphere Decoding (FSD) concurrently optimize performance and complexity. We show that for bandwidth compression factors of up to 25 percent, we can achieve the same performance as Orthogonal Frequency Division Multiplexing (OFDM). For systems with bandwidth compression higher than 25 percent, the complexity/performance trade-offs of the hybrid method are better than those of Truncated Singular Value Decomposition-FSD (TSVD-FSD).

Multi-band carrier-less amplitude and phase modulation for bandlimited visible light communications systems

Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370-780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems.

A Soft Detector for Spectrally Efficient Systems With Non-Orthogonal Overlapped Sub-Carriers

Spectrally efficient frequency division multiplexing (SEFDM) improves spectral efficiency, relative to the well known orthogonal frequency division multiplexing (OFDM). A fast Fourier transform (FFT) detector working with a standard Bahl-Cocke-Jelinek-Raviv (BCJR) decoder based on the Turbo principle is proposed to improve iteratively the system performance. In the presence of multipath fading channel, system modelling results show that the new system with 1024 sub-carriers can save up to 40% of bandwidth compared to the OFDM system. In addition, this work proves that by using the FFT detector, complexity is reduced.

Dual Polarization Coherent Optical Spectrally Efficient Frequency Division Multiplexing

A new optical spectrally efficient frequency division multiplexing technique, utilizing coherent detection and polarization division multiplexing, is proposed and demonstrated. The proposed system uses non-orthogonal and overlapping subcarriers to provide a significant reduction in both the electrical and optical bandwidth of up to 33%, relative to dual polarization orthogonal frequency division multiplexing (DP-OFDM), with an implementation penalty <;3.2 dB. After transmission over 80 km of single mode fiber, it is shown that quadrature phase shift keying-based DP coherent optical spectrally efficient frequency division multiplexing, achieves a 2-dB gain in optical signal-to-noise ratio performance relative to eight-quadrature amplitude modulation-based DP-OFDM, which has approximately the same spectral efficiency.

Bandwidth compressed carrier aggregation

Carrier aggregation (CA) is a technique introduced in LTE-Advanced to achieve a higher throughput by increasing bandwidth. In this work, the spectrally efficient frequency division multiplexing (SEFDM) bandwidth compression technique is utilized to enhance CA performance. This work reports experimental demonstration of SEFDM and shows that up to 7 component carriers (CCs) can be aggregated in a given bandwidth with guaranteed bit error rate (BER), while orthogonal frequency division multiplexing (OFDM) can only pack 5 CCs in the same bandwidth. Full system description and experimental set up are given in the paper together with BER results for SEFDM and OFDM based systems using LTE-like frame and signal formats and transmitted over an LTE standard fading channel. Experimental results show the bandwidth advantages of SEFDM and confirm that the effective spectral efficiency of aggregated SEFDM is much higher than that of aggregated OFDM.

Multi-band reduced complexity spectrally efficient FDM systems

Spectrally Efficient Frequency Division Multiplexing (SEFDM) is a non-orthogonal multicarrier communication technique that can pack more sub-carriers than Orthogonal Frequency Division Multiplexing (OFDM) in a given bandwidth. In this work, we propose a multi-band architecture named Block-Spectrally Efficient Frequency Division Multiplexing (B-SEFDM) for a large non-orthogonal system. Furthermore, a Block Efficient Detector (BED) is presented in this work and computer simulations show that the performance is improved by at most 4.5 dB while the complexity is decreased by one order of magnitude. Finally, a butterfly structure, which is reconfigurable according to required complexity/throughput, is proposed here for the detection.

Bandwidth Compressed Waveform for 60-GHz Millimeter-Wave Radio Over Fiber Experiment

A bandwidth compressed waveform termed spectrally efficient frequency division multiplexing (SEFDM) is experimentally demonstrated in a 60-GHz millimeter-wave (mm-wave) radio-over-fiber scenario to increase transmission data rates without changing signal bandwidth and modulation format. Experimental results show the advantages of SEFDM and confirm that the bit rate of SEFDM signals can be substantially higher than that of orthogonal frequency-division multiplexing (OFDM) signals. Experimentally, a 2.25 Gbit/s 4QAM OFDM signal is transmitted through 250 m of OM-1 multi-mode fiber and then it is optically up converted to 60 GHz band at the photodiode before delivery to a mm-wave antenna for transmission over a 3 meter wireless link. The work demonstrates that when the OFDM signal is replaced by an SEFDM signal using the same modulation format and occupying the same bandwidth, the bit rate can be increased, by a factor of up to 67%, to 3.75 Gbit/s at the expense of a 3-dB power penalty. Additionally, a bandwidth compressed 4QAM SEFDM is shown to outperform an 8QAM OFDM of the same spectral efficiency, thereby verifying that a lower order modulation format may replace a higher order one and achieve performance gain.

First demonstration of a spectrally efficient FDM radio over fiber system topology for beyond 4G cellular networking

In this work, a spectrally efficient frequency division multiplexing (SEFDM) scheme based on radio over fiber (RoF) technology is proposed for the first time, so as to address next generation wireless data traffic demands on a cost, energy & spectrally efficient way. A proposed radio over fiber topology for beyond 4G deployment is addressed and a proof-of-concept SEFDM long term evolution (LTE) type radio over multimode fiber transmission is successfully demonstrated at 36Mb/s.

FPGA implementations of real-time detectors for a spectrally efficient FDM system

A new method for detecting Spectrally Efficient Frequency Division Multiplexing (SEFDM) is proposed and verified through modelling and practical FPGA implementation. The method is derived through studies of two sphere decoding techniques, namely Fixed SD (FSD) with Sort-Free (SF) and Non-Sort-Free (NSF) algorithms. We report a co-simulation verification framework to verify the performance of these detectors and to choose an optimum design. Finally, a hybrid detector Truncated Singular Value Decomposition-Fixed Sphere Detector (TSVD-FSD) is tested on the FPGA platform. Error behaviour is studied for the practical FPGA system and then compared with theoretical/ideal modelling. Detailed analysis indicates the suitability of our design and implementation methods for SEFDM detection with 16 carriers and 25% bandwidth saving.