Reduced-complexity Receiver Research Articles

Differential Modulation in Massive MIMO With Low-Resolution ADCs

In this paper, we present a differential modulation and detection scheme for use in the uplink of a system with a large number of antennas at the base station, each equipped with low-resolution analog-to-digital converters (ADCs). We derive an expression for the maximum likelihood (ML) detector of a differentially encoded phase information symbol received by a base station operating in the low-resolution ADC regime. We also present an equal performing reduced complexity receiver for detecting the phase information. To increase the supported data rate, we also present a maximum likelihood expression to detect differential amplitude phase shift keying symbols with low-resolution ADCs. We note that the derived detectors are unable to detect the amplitude information. To overcome this limitation, we use the Bussgang Theorem and the Central Limit Theorem (CLT) to develop two detectors capable of detecting the amplitude information. We numerically show that while the first amplitude detector requires multiple quantization bits for acceptable performance, similar performance can be achieved using one-bit ADCs by grouping the receive antennas and employing variable quantization levels (VQL) across distinct antenna groups. We validate the performance of the proposed detectors through simulations and show a comparison with corresponding coherent detectors. Finally, we present a complexity analysis of the proposed low-resolution differential detectors

Universal Filtered Multicarrier Receiver Complexity Reduction to Orthogonal Frequency Division Multiplexing Receiver

The Universal Filtered Multicarrier (UFMC) waveform technology is one of the promising waveforms for 5G and beyond 5G networks. Owing 2N-point Fast Fourier Transform (FFT) processor at the UFMC receiver, the computational and implementation complexity is two times more than the conventional Orthogonal Frequency Division Multiplexing (OFDM) receiver system. In this paper, we proposed a simplified UFMC receiver structure to reduce computational complexity as well as hardware requirements. The received UFMC symbol simplified exactly to its equivalent after performing 2N-point FFT and decimation operations. In which, the mathematical model of the frequency-domain UFMC signal is rederived after processing through 2N-point FFT and decimator, and the simplified signal is generated with an N-point FFT. Accordingly, the 2N-point FFT processor and decimator are replaced with a single N-point FFT processor. This approach reduces the 50% computational complexity at the FFT processor level hence the hardware and processing time. The computational complexity of the proposed receiver model is approximately equivalent to the OFDM receiver. Additionally, analyzed the mathematical model for the simplified UFMC receiver and the comparative performance of the UFMC system with the conventional model.

FDA Based QSM for mmWave Wireless Communications: Frequency Diverse Transmitter and Reduced Complexity Receiver

Quadrature spatial modulation (QSM) based millimeter wave (mmWave) communication system design using frequency diverse array (FDA) is proposed in this article. Since spatial modulation techniques (SMT) employ maximum likelihood (ML) based detector at receiver, the computational complexity increases vastly. Moreover, numerous existing SMT methods utilize phased array (PA), where only angle dependent communication is possible. In this article, we propose to use a standard FDA that exploits a small linearly increasing frequency offset across the array for range-angle dependent QSM wireless communications. That is, the in-phase and quadrature components of transmission vector utilize slightly different frequencies to deliver the information. Furthermore, we propose a suboptimal multi-stage (MS) detector in the receiver, which applies a matched filtering (i.e., bandpass filters matched to the corresponding frequency offsets) approach to decode the index bits at first step, whereas, merely, two most probable estimated indices are utilized further to decode associated data bits using a standard ML method. Adhering an improved signal to noise ratio (SNR) due to an FDA based range-angle dependent transmission, simulation and numerical results show the improved performance of the proposed design over existing SM and QSM based schemes, while MS approach reduces the receiver's computational complexity.

OTFS Signaling for Uplink NOMA of Heterogeneous Mobility Users

We investigate a coded uplink non-orthogonal multiple access (NOMA) configuration in which groups of co-channel users are modulated in accordance with orthogonal time frequency space (OTFS). We take advantage of OTFS characteristics to achieve NOMA spectrum sharing in the delay-Doppler domain between stationary and mobile users. We develop an efficient iterative turbo receiver based on the principle of successive interference cancellation (SIC) to overcome the co-channel interference (CCI). We propose two turbo detector algorithms: orthogonal approximate message passing with linear minimum mean squared error (OAMP-LMMSE) and Gaussian approximate message passing with expectation propagation (GAMP-EP). The interactive OAMP-LMMSE detector and GAMP-EP detector are respectively assigned for the reception of the stationary and mobile users. We analyze the convergence performance of our proposed iterative SIC turbo receiver by utilizing a customized extrinsic information transfer (EXIT) chart and simplify the corresponding detector algorithms to further reduce receiver complexity. Our proposed iterative SIC turbo receiver demonstrates performance improvement over existing receivers and robustness against imperfect SIC process and channel state information uncertainty.

Double Antenna-Transitions Spatial Modulation Performance Evaluation Over Nakagami- m Wireless Fading Channels

Recently, a novel spatial modulation (SM) scheme; termed Mid-symbol Antenna transition (MAT) spatial modulation, was developed to reduce the number of utilized transmitting antennas and improve the average bit error rate (ABER) performance. In this paper, the structure of the original MAT is extended to adapt Double-antenna transitions (DAT) during the symbol's transmission duration. Compared to the mid-symbol antenna-transition (MAT), the DAT scheme allows more reduction in the number of required transmitter antennas (TAs) and more enhancement of ABER performance, while achieving the same spectral efficiency (SE). DAT scheme reduces receiver complexity in comparison with generic SM, generalized SM (GSM), variable generalized SM (VGSM), and MAT schemes. The detailed DAT system design is presented. Furthermore, the theoretical closed-form of the ABER upper bound of the DAT system is quantified. The validity of the derived ABER upper bound is proved by contrasting it with the simulated ABER. Monte-Carlo simulations are utilized to evaluate the ABER of the DAT scheme over nakagami-m fading channels with respect to competing schemes. Furthermore, we study the impact of the spatial correlation on the considered schemes and the impact of varying nakagami-m factor on the performance of the DAT scheme. Our simulations demonstrate that DAT significantly outperforms the aforementioned rival schemes in terms of the average bit error rate (ABER) performance.

Optimal-Power Superposition Modulation for Scalable Video Broadcasting

To mitigate the burden of the tele-traffic imposed by video streaming, Scalable Video Coding (SVC) is invoked for mapping the video clips to multiple layers, which allows us to improve the coverage quality. Although numerous non-orthogonal techniques have been conceived in the literature for maximizing the theoretical capacity relying on the idealized simplifying assumption of perfect channel coding. There is a paucity of practical finite-delay channel-coded solutions capable of mitigating the avalanche-like error proliferation routinely encountered in the face of hostile channels. Against this background, we propose SVC based Superposition Coding (SC) assisted video broadcasting, which curbs the error propagation introduced both by the inter-layer dependency and the Successive Interference Cancellation (SIC) required by the superimposed signal. Specifically, we formulate an Objective Function (OF) based on the average video quality across the Base Station's (BS) coverage area and then determine the optimal power scaling coefficients of each video layer using a bespoke Evolutionary Algorithm (EA). Our solution strikes a compelling compromise between the best possible video service provided for the cell-centre and the cell-edge users. Explicitly, our simulation results show that the optimal-power SC system guarantees a better compromise than its Time Division Multiplexing (TDM) and conventional QAM assisted counterparts, despite its reduced receiver complexity.

Locally Decodable Index Codes

An index code for broadcast channel with receiver side information is locally decodable if each receiver can decode its demand by observing only a subset of the transmitted codeword symbols instead of the entire codeword. Local decodability in index coding is known to reduce receiver complexity, improve user privacy and decrease decoding error probability in wireless fading channels. Conventional index coding solutions assume that the receivers observe the entire codeword, and as a result, for these codes the number of codeword symbols queried by a user per decoded message symbol, which we refer to as locality , could be large. In this paper, we pose the index coding problem as that of minimizing the broadcast rate for a given value of locality (or vice versa) and designing codes that achieve the optimal trade-off between locality and rate. We identify the optimal broadcast rate corresponding to the minimum possible value of locality for all single unicast problems. We present new structural properties of index codes which allow us to characterize the optimal trade-off achieved by: vector linear codes when the side information graph is a directed cycle; and scalar linear codes when the minrank of the side information graph is one less than the order of the problem. We also identify the optimal trade-off among all codes, including non-linear codes, when the side information graph is a directed 3-cycle. Finally, we present techniques to design locally decodable index codes for arbitrary single unicast problems and arbitrary values of locality.

Split labeling diversity for wireless half-duplex relay assisted cooperative communication systems

Labeling diversity (LD) is a well-known technique proposed for multi-antenna Wireless local area network (WLAN) applications . In this paper, we propose LD for three-terminal cooperative communication schemes i.e., Decode and Forward (DF) and Coded-cooperative (CC) schemes with each terminal using a single antenna for transmission. The Boosted space-time codeword is jointly constructed by source and a relay node in two phases and joint iterative detection and decoding are used at the destination node. This technique shows that the gains from LD can be further enhanced when used in cooperative communication schemes. Numerical analysis reveal that the proposed schemes DF and CC provide full diversity gains, over non-cooperative schemes, later scheme being the most successful one, under identical conditions using less number of antennas at each communication node and with reduced receiver complexity.

Analysis of Selection Combining Receiver Performance for Time Successive SSK-M-ary Modulation

Space shift keying (SSK) is a single radio frequency (RF) chain multiple-input multiple-output (MIMO) scheme which uses the indices of transmit antennas for information transmission. Time successive SSK-M-ary modulation (TSSM) is a second order transmit diversity scheme based on single RF chain multiple antenna transmitter. In this letter, TSSM based on selection combining (TSSM-SC) is conceived to realize a single RF chain receiver for TSSM without compromise on the diversity order. The metric of receiver antenna selection is proposed for TSSM-SC. A novel approach is given to find a tight upper bound on the bit error rate (BER) of TSSM-SC in simple closed form. Further, the diversity order of TSSM-SC is analyzed with asymptotic expression. Simulation results that validate the analyses are given to show the diversity gain at reduced receiver complexity. The performance of TSSM-SC is compared with other schemes with selection combining to highlight its performance advantage.

Frequency reconfigurable monopole antenna with harmonic suppression for IoT applications

This work proposes a new reconfigurable printed monopole antenna for IoT devices working with the promising wireless technology Wi-Fi 6. Based on effective resonant length value, the antenna has the ability to reconfigure its operating band between 2.4 GHz and 5 GHz ISM bands. Therefore, the designed antenna works as an RF band-pass filter which reduces receiver complexity and supports network scalability. One PIN diode with complete biasing circuit is integrated to the antenna radiator to obtain re-configurability. Furthermore, two stubs are added to the antenna structure in order to suppress harmonic component which appears near to the higher band (5 GHz) when antenna forced to work at the lower band (2.4 GHz). The design built over commercially available FR-4 substrate with a compact size of (33.5x16x1.6) mm 3 . CST software is used to simulate antenna performance in terms of flection coefficient, radiation pattern, efficiency, and gain.

New OSTBC for Blind Channel Estimation and Tracking in MIMO-OFDM Systems

Applying orthogonal space time block coding (OSTBC) to multiple-input multiple-output (MIMO) systems helps reduce receiver complexity. However, this approach has been applied only to flat fading channels, as when the channel is a frequency selective fading MIMO channel, OSTBC cannot be used directly since its orthogonal propriety may be lost. Furthermore, the MIMO channel is not always known. To deal with this problem, many techniques were proposed to estimate the channel using a training sequence. Unfortunately, these techniques reduce the useful spectral bandwidth. This paper proposes OSTBC for blind channel estimation and data detection in the case of a MIMO frequency selective channel. The aim of this new OSTBC is twofold: to solve the ambiguity of channel estimation and to reduce the complexity of the detector. By exploiting the well-known technique of orthogonal frequency division multiplexing (OFDM), the frequency selective fading MIMO channel is split into a set of flat fading subchannels. Moreover, to accommodate the fact that a MIMO channel can be time varying, the steady state Kalman channel estimator (SS-KCE) is extended to track the channel’s fast variations. The performance of the proposed blind algorithm is related by the adequate choice of the number of subcarriers and it is compared with other existing approaches by means of Monte Carlo simulations.

Reduced-Complexity Receiver for Free-Space Optical Communication over Orbital Angular Momentum Partial-Pattern Modes

This paper explores the effect of a partial-pattern receiver for transmitted orbital angular momentum (OAM) multimodes included in the Laguerre-Gaussian beam propagating under non-Kolomogorov weak-to-moderate turbulence on the achievable capacity and the error rates with introduced controlled parameters. We deduce the necessary conditions for reducing the receiver’s area to guarantee that the modes are decoupled when the area is reduced. Furthermore, we derive the conditions at which area reduction yields a performance gain over the complete-area reception. For that, some use cases are introduced and discussed and the basic building block for multibeam MIMO receivers with a reduced area is developed and analyzed.

Underwater wireless optical MIMO system with spatial modulation and adaptive power allocation

In this paper, we investigate the performance of underwater wireless optical multiple-input multiple-output communication system combining spatial modulation (SM-UOMIMO) with flag dual amplitude pulse position modulation (FDAPPM). Channel impulse response for coastal and harbor ocean water links are obtained by Monte Carlo (MC) simulation. Moreover, we obtain the closed-form and upper bound average bit error rate (BER) expressions for receiver diversity including optical combining, equal gain combining and selected combining. And a novel adaptive power allocation algorithm (PAA) is proposed to minimize the average BER of SM-UOMIMO system. Our numeric results indicate an excellent match between the analytical results and numerical simulations, which confirms the accuracy of our derived expressions. Furthermore, the results show that adaptive PAA outperforms conventional fixed factor PAA and equal PAA obviously. Multiple-input single-output system with adaptive PAA obtains even better BER performance than MIMO one, at the same time reducing receiver complexity effectively.

Mode Division Multiplexing Communication Using Microwave Orbital Angular Momentum: An Experimental Study

Mode division multiplexing (MDM) using orbital angular momentum (OAM) is a recently developed physical layer transmission technique, which has obtained intensive interest among optics, millimeter-wave, and radio frequency due to its capability to enhance communication capacity while retaining an ultra-low receiver complexity. In this paper, the system model based on OAM-MDM is mathematically analyzed and it is theoretically concluded that such system architecture can bring a vast reduction in receiver complexity without capacity penalty compared with conventional line-of-sight multiple-in-multiple-out systems under the same physical constraint. Furthermore, a $4\times 4$ OAM-MDM communication experiment adopting a pair of easily realized Cassegrain reflector antennas capable of multiplexing/demultiplexing four orthogonal OAM modes of $l = {-3}$ , −2, +2, and +3 is carried out at a microwave frequency of 10 GHz. The experimental results show high spectral efficiency as well as low receiver complexity.

Channel‐independent 3D‐EXIT chart‐based path scheduling for serially concatenated decoders

SummaryIn this paper a generic method for determining optimal activation cycle scheduling for serially concatenated decoders using three‐dimensional Extrinsic Information Transfer charts is proposed. The complexity of a turbo decoding receiver can be reduced considerably by adopting an optimal activation cycle within the component decoders. However, this optimum scheduled path varies with channel conditions for a given modulation and coding scheme. Thus a real‐time evaluation of the activation path is required, which results in an added computational overhead and storage requirement. Therefore, a channel‐independent method of optimal activation path scheduling using three‐dimensional extrinsic information transfer chart analysis has been proposed where the activation cycle needs to be evaluated once offline and stored as lookup tables as a function of an appropriate compression parameter. The average mutual information of the codeword has been adopted as this compression parameter. It has been demonstrated that the proposed reduced complexity receiver's performance is very close to the more complex conventional fixed activation cycle schemes and superior to the signal to noise ratio‐based dynamic scheduling schemes. Copyright © 2016 John Wiley & Sons, Ltd.

Underwater acoustic communication using orthogonal signal division multiplexing scheme with time diversity

In this paper, an underwater acoustic (UWA) communication scheme for mobile platforms is proposed. The proposed scheme is based on the orthogonal signal division multiplexing (OSDM) scheme, which offers highly reliable UWA communication. However, OSDM is not suitable for mobile platforms as it is — it requires a receiver array and a large calculation cost for equalization. To establish a reliable link with small communication platforms, we design OSDM that can perform reliable communication without the need for an array and can reduce receiver complexity using the time-diversity technique (TD), and evaluate its performance in experiments. The experimental results suggest that OSDM-TD can simultaneously achieve power-efficient communications and receiver complexity reduction, and can realize small-scale communication platforms. In detail, OSDM-TD achieved almost the same communication quality as conventional OSDM, in exchange for an effective data rate. Moreover, the power efficiency of OSDM-TD was almost the same as that of conventional OSDM with two receiver array elements, although the calculation cost of OSDM-TD was far below that of conventional OSDM. As a result, it was found that OSDM-TD is suitable for UWA communication for mobile nodes whose capacity and computational resources are severely limited.

Optical communication system for high‐capacity LAN

ABSTRACTIn this article, it is proposed a model for multilevel polarization modulation tailored to Local Area Networks (LAN's), which exploits optical fiber intrinsic properties to obtain, with the same bandwidth, a higher single‐channel throughput with a reduced receiver complexity. This is achieved through a “fluid” constellation of confined bands. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:389–393, 2016

Adaptive Rate-Maximizing Channel-Shortening for ISI Channels

We consider detection over intersymbol interference channels that are unknown at the receiver. For such a kind of systems, we consider an alternative approach to the design of a reduced-complexity receiver based on channel shortening without the explicit estimation of the channel impulse response. The proposed solution allows a simplification of the receiver architecture and a faster convergence for channels with a long memory and a few number of poles.

GA based adaptive receiver for MC-CDMA system

Multicarrier systems like the multicarrier code division multiple access (MC-CDMA) systems are designed for maximum usability of available bandwidth. We use the MC-CDMA system with Alamouti's space time coding in this paper. We propose the genetic algorithm (GA) in order to calculate MC-CDMA receiver weights with two variation schemes. The proposed schemes reduce receiver complexity. The bit error rate and convergence rate are also improved by increasing the number of genes and chromosomes of the GA in both schemes as compared with conventional LMS based receivers of the MC-CDMA system. This is verified via simulations.

Electrical filter-based and low-complexity DPSK coherent optical receiver.

Direct-detection of differential phase shifted keying (DPSK) optical signals is implemented either by ad hoc optical filtering or one-bit delayed optical interferometers. We show a coherent receiver where the filtering is performed in the electrical domain after down-converting the incoming signal to the baseband or to an intermediate frequency. This can be particularly advantageous whenever optical filters cannot be used or when extremely narrow filtering (sub-GHz) would be required [for example ultra-dense wavelength division multiplexing (WDM) passive optical networks]. Electrical filters can be realized more accurately than their optical counterpart. In addition, in a coherent receiver, this operation is colorless and avoids digital signal processing. We show experimentally this reduced complexity receiver and compare it with the classical one based on the delay and multiply block.