Fast Convergence and Reduced Complexity Receiver Design for LDS-OFDM System

Low density signature for OFDM (LDS-OFDM) is able to achieve satisfactory performance in overloaded conditions, but the existing LDS-OFDM has the drawback of slow convergence rate for multiuser detection (MUD) and high receiver complexity. To tackle these problems, we propose a serial schedule for the iterative MUD. By doing so, the convergence rate of MUD is accelerated and the detection iterations can be decreased. Furthermore, in order to exploit the similar sparse structure of LDS-OFDM and LDPC code, we utilize LDPC codes for LDS-OFDM system. Simulations show that compared with existing LDS-OFDM, the LDPC code improves the system performance

On receiver design for low density signature OFDM (LDS-OFDM)

Low density signature orthogonal frequency division multiplexing (LDS-OFDM) is an uplink multi-carrier multiple access scheme that uses low density signatures (LDS) for spreading the symbols in the frequency domain. In this paper, we introduce an effective receiver for the LDS-OFDM scheme. We propose a framework to analyze and design this iterative receiver using extrinsic information transfer (EXIT) charts. Furthermore, a turbo multi-user detector/decoder (MUDD) is proposed for the LDS-OFDM receiver. We show how the turbo MUDD is tuned using EXIT charts analysis. By tuning the turbo-style processing, the turbo MUDD can approach the performance of optimum MUDD with a smaller number of inner iterations. Using the suggested design guidelines in this paper, we show that the proposed structure brings about 2.3 dB performance improvement at a bit error rate (BER) equal to 10-5 over conventional LDS-OFDM while keeping the complexity affordable. Simulations for different scenarios also show that the LDS-OFDM outperforms similar well-known multiple access techniques such as multi-carrier code division multiple access (MC-CDMA) and group-orthogonal MC-CDMA

Waveform Design for 5G and beyond Systems

5G traffic has very diverse requirements with respect to data rate, delay, and reliability. The concept of using multiple OFDM numerologies adopted in the 5G NR standard will likely meet these multiple requirements to some extent. However, the traffic is radically accruing different characteristics and requirements when compared with the initial stage of 5G, which focused mainly on high-speed multimedia data applications. For instance, applications such as vehicular communications and robotics control require a highly reliable and ultra-low delay. In addition, various emerging M2M applications have sparse traffic with a small amount of data to be delivered. The state-of-the-art OFDM technique has some limitations when addressing the aforementioned requirements at the same time. Meanwhile, numerous waveform alternatives, such as FBMC, GFDM, and UFMC, have been explored. They also have their own pros and cons due to their intrinsic waveform properties. Hence, it is the opportune moment to come up with modification/variations/combinations to the aforementioned techniques or a new waveform design for 5G systems and beyond. The aim of this Special Issue is to provide the latest research and advances in the field of waveform design for 5G systems and beyond

EXIT chart analysis for turbo LDS-OFDM receivers

In this paper, the mutual information transfer characteristics of turbo Multiuser Detector (MUD) for a novel air interface scheme, called Low Density Signature Orthogonal Frequency Division Multiplexing (LDS-OFDM) are investigated using Extrinsic Information Transfer (EXIT) charts. LDS-OFDM uses Low Density Signature structure for spreading the data symbols in frequency domain. This technique benefits from frequency diversity besides its ability of supporting parallel data streams more than the number of subcarriers (overloaded condition). The turbo MUD couples the data symbols' detector of LDS scheme with users' FEC (Forward Error Correction) decoders through the message passing principle. The effect of overloading on LDS scheme's performance is evaluated using EXIT chart. The results show that at Eb/N0 as low as 0.3, LDS-OFDM can support loads up to 300%

Single-Frequency Network Terrestrial Broadcasting with 5GNR Numerology

L'abstract è presente nell'allegato / the abstract is in the attachmen

Low density spreading multiple access

The need for ubiquitous coverage and the increasing demand for high data rate services, keeps constant pressure on the cellular network infrastructure. There has been intense research to improve the system spectral efficiency and coverage, and a significant part of this effort focused on developing and optimizing the multiple access techniques. One such technique that has been recently proposed is the low density spreading (LDS), which manages the multiple access interference to offer efficient and low complexity multiuser detection. The LDS technique has shown a promising performance as a multiple access technique for cellular systems. This chapter will give an overview on the LDS multiple access technique. The motivations for the LDS design will be highlighted by comparing it to conventional spreading techniques, including brief history of the early work on LDS. Furthermore, a background on the design of LDS in multicarrier communications, such as signatures design, a belief propagation multiuser detection, etc., will be presented along with the challenges and opportunities associated with the multicarrier LDS multiple access

Performance Evaluation of Multi-gigabit Indoor Visible Light Communication System

This paper presents a performance evaluation of a mobile multi-gigabit visible light communication (VLC) system in two different environments. The VLC channel characteristics and links were evaluated under the diverse situations of an empty room and a room with very strong shadowing effects resulting from mini cubicle offices. RGB laser diodes (LDs) were used to mitigate the low modulation bandwidth of conventional transmitters (light emitting diodes, LEDs) in the VLC system. In addition, an angle diversity receiver (ADR) was introduced to mitigate intersymbol- interference (ISI). Furthermore, a delay adaptation technique was used to further reduce the effect of ISI and multipath dispersion. The combination of delay adaptation and ADR (DAT ADR system) added a degree of freedom to the link design, which resulted in a VLC system that has the ability to provide high data rates (i.e. 5 Gbps) in the considered harsh indoor environment. Our proposed system used a simple on-off keying (OOK) modulation format and it was able to provide data rates of 5 Gbps and a bit-error-rate (BER) of 10-3 in the worst case scenario in the considered realistic indoor environment