Earticle

In this paper, we present the block diagonalization (BD) algorithm for the multiple-user multiple input multiple output (MU-MIMO) $4{\times}4$ system using specific purpose processor (SPP) hardware. Our objective is to improve the single-user MIMO (SU-MIMO) system using the MU-MIMO technology, which is remarkably fast and allows more users to connect simultaneously. To that end, our MU-MIMO precoder uses the BD algorithm to ensure signal integrity when connecting multiple users; but remains accurate and stable. However, a precoder that uses the BD algorithm is computationally complex; therefore, we use an SPP with special functions designed to compute the BD algorithm. The implementation test results show that our SPP computes the BD algorithm faster than the software solution.

We present a practical design algorithm for quantizers at nodes in distributed systems in which each local measurement is quantized without communication between nodes and transmitted to a fusion node that conducts estimation of the parameter of interest. The benefits of vector quantization (VQ) motivate us to incorporate the VQ strategy into our design and we propose a low-complexity design technique that seeks to assign vector codewords into sets such that each codeword in the sets should be closest to its associated local codeword. In doing so, we introduce new distance metrics to measure the distance between vector codewords and local ones and construct the sets of vector codewords at each node to minimize the average distance, resulting in an efficient and independent encoding of the vector codewords. Through extensive experiments, we show that the proposed algorithm can maintain comparable performance with a substantially reduced design complexity.

The high peak to average power ratio (PAPR) is the main challenge facing asymmetrically clipped optical (ACO) orthogonal frequency division multiplexing (OFDM). We propose a new hybrid technique that incorporates a modified selective mapping (SLM) and companding called low complexity hybrid selective mapping (LCHSLM) for PAPR mitigation in ACO OFDM systems. It is demonstrated through computer simulations that our proposed system significantly reduces the PAPR compared with the conventional SLM or companding alone. In addition, LCHSLM achieves a significant reduction in complexity compared with conventional SLM without bit error rate (BER) degradation.

The newest video compression standard, called Versatile Video Coding (H.266/VVC), outperforms its predecessor High Efficiency Video Coding (HEVC) by up to 50% in the matter of coding performance. The achievement results from the integrating of several sophisticated tools such as 32 extended angular modes for intra coding, advanced partitioning structure, and additional transform selection. However, these tools negatively deliver the computational cost of the VVC Test Model (VTM) in all-intra encoding configuration. The existing fast intra coding algorithms achieve a significant saving in computational time with a comparable rate distortion (RD) performance of VVC plus additional computational complexity. In this paper, we study the original strategy of VVC intra mode decision and analyze the correlation among the sum of absolute transformed differences (SATD) costs of the rough mode decision (RMD) and the RD costs of the rate distortion optimization (RDO) processes. Based on the useful correlations with an effective threshold formulation, we propose a fast intra prediction mode selection for the most time-consuming RDO process by selecting a small candidate set based on the SATD costs and calculating the time-consuming RD costs for only intra prediction modes of the small candidate set without a significant overhead. According to the experimental results, our proposed system can reduce up to 27.38% and on average 21.07% of the computation complexity of VTM version 5.0 with an insignificant quality degradation.

This paper describes a low-complexity collision avoidance system for automated guided vehicles (AGVs) based on active ultra-wide band (UWB) modules. In particular, we consider an industrial warehouse where all the AGVs and target nodes (TNs) (e.g., people) are equipped with active UWB modules. A communication session between a pair of UWB modules permits the exchange of information and the estimation of the distance between them. The UWB module positioned on an AGV is connected to an on-board computer; whenever the UWB module on an AGV receives a message from a TN, it communicates all the received data to the on-board computer that can decide to stop the AGV if the range estimate is below a given threshold. This prevents undesired collisions between the AGV and the TN. In this paper, we present the experimental results of the proposed collision avoidance system obtained using the UWB modules, PulsON 410 ranging and communication modules (P410 RCMs), produced by Time Domain.

Orthogonal frequency division multiplexing (OFDM) is a system which is used to encode data using multiple carriers instead of the traditional single carrier system. This method improves the spectral efficiency (optimum use of bandwidth). It also lessens the effect of fading and intersymbol interference (ISI). In 1995, digital audio broadcast (DAB) adopted OFDM as the first standard using OFDM. Later in 1997, it was adopted for digital video broadcast (DVB). Currently, it has been adopted for WiMAX and LTE standards. In this project, a Verilog design is employed to implement an OFDM transmitter (DAC block) and receiver (FFT and ADC block). Generally, OFDM uses FFT and IFFT for modulation and demodulation. In this paper, 16-point FFT decimation-in-frequency (DIF) with the radix-2 algorithm and direct summation method have been analyzed. ADC and DAC in OFDM are used for conversion of the signal from analog to digital or vice-versa has also been analyzed. All the designs are simulated using Verilog on ModelSim simulator. The result generated from the FFT block after Verilog simulation has also been verified with MATLAB.

This article presents a quick overview of conventional precoding and beamforming techniques in the cellular networks and proposes a novel coordinated beamforming technique for coordinated multipoint (CoMP) networks, which is based upon signal-to-leakage-plus-noise ratio (SLNR) metric. The proposed scheme has reduced computational cost and offers improved performance compared to the conventional multi-cell precoding schemes in the noise-dominated environments. Simulation results reveal that proposed scheme offers a spectrally efficient, low complexity solution with improved average user throughput and sum rate in the CoMP enabled networks.

In this letter a new detection scheme combining the conventional Sphere decoders and best detection algorithm is proposed. This algorithm leverages the Sphere decoder (SD) results to use smaller values of in best algorithm to achieve better performance. Post best detection algorithm Darlington pairs of SD- SD, SD- SD, and -1 SD are used to get the final detection results. The proposed best detection algorithm finds out smallest paths by counting and sorting the bits of every candidate, which is much simpler as used in conventional sphere decoders. The computational complexity has been calculated in terms of time taken to visit the average number of K paths taken by Conventional SDs -SDs and Darlington pair of SDs. Extensive Monte Carlo simulations are used to demonstrate that the proposed approach exhibits significant performance gain over conventional SD schemes in terms of bit error rate and computational time. Besides, a complete analytical approach is provided to validate the simulation results.

In this paper, we propose a novel successive cancellation flip (SCF) decoding to reduce the computational complexity compared to the conventional SCF decoding by using distributed CRC bits. The proposed decoding reduces the number of estimations for information bits by early termination of decodings for failed frames of the first SC decoding, while trying to minimize the additional sorting operations. Simulation results show that the proposed SCF decoding reduces the computational complexity of repeated SC decoding at least 27% compared to the conventional SCF decoding.

The authors propose the side information-free low-computational complexity Time Domain Sequence Superposition - Selected Mapping (TDSS-SLM) scheme for PAPR suppression. We adopt IFFT point reduction for transmitter and reception technique using pilot subcarriers for side information estimation. The simulation results show the [R1-1]TDSS-SLM transmitter achieves PAPR reduction of 2.3 dB which corresponds to the 1.5 times larger PAE than that in the conventional transmitter. In addition, the proposed receiver shows loss-less BER performances for both AWGN channel and two types of fading channels, while the computational complexity of the proposed receiver is nearly the same as the conventional OFDM receiver, which is less than 1/10 of the ML receiver.

In this paper, we propose an image interpolator for low computational complexity. The proposed image interpolator supports the image scaling using a modified cubic convolution interpolation between the input and output resolutions for a full screen display. In order to reduce the computational complexity, we use the difference in value of the adjacent pixels for selecting interpolation methods and linear function of the cubic convolution. The proposed image interpolator is compared with the conventional one for the computational complexity and image quality. The proposed image interpolator has been designed and verified by Verilog HDL(Hardware Description Language). It has been synthesized using the Xilinx VirtexE FPGA, and implemented using an FPGA-based prototype board.

2D-to-3D 비디오 변환 기술은 2D 비디오 속에 내재하는 깊이 단서를 이용하여 스테레오 영상을 생성함으로써 2D 비디오에 3D 효과를 부여한다. 이 기술은 완전한 3D 비디오 시대로 가는 과도 기간 동안 3D 콘텐츠의 부족문제를 해결할 수 있는 유용한 기술이다. 본 논문은 2D-to-3D 비디오 변환의 저 복잡도 구현을 위한 새로운 깊이 생성 방안을 제시한다. 제안 기법에서는 전역 깊이의 시방향 일관성을 위하여 패턴 기반의 전역 깊이 생성 기법을 제안하였다. 뿐만 아니라 객체 영역의 3D 입체감 개선을 위한 저 복잡도의 객체 깊이 개선 알고리즘도 추가적으로 제시하였다. 실험을 통해 제안 알고리즘이 복잡도와 주관적 화질 측면에서 기존 방식들에 비해 우수한 성능을 나타냄을 보인다.

2D-to-3D video conversion vests 3D effects in a 2D video by generating stereoscopic views using depth cues inherent in the 2D video. This technology would be a good solution to resolve the problem of 3D content shortage during the transition period to the full ripe 3D video era. In this paper, a low-complexity depth generation method for 2D-to-3D video conversion is presented. For temporal consistency in global depth, a pattern-based depth generation method is newly introduced. A low-complexity refinement algorithm for local depth is also provided to improve 3D perception in object regions. Experimental results show that the proposed method outperforms conventional methods in terms of complexity and subjective quality.

본 논문에서는 MIMO(Multi Input Multi Output) 시스템을 위한 적응형 검색범위 기반 복잡도 감소 QRD-M 기법을 제안한다. 기존 의 fixed QRD-M 기법은 각 단계에서 survivor path들을 현 단계의 모든 가능한 성상도 심벌들로 확장하여 그 중 가장 작은 path metric을 가지는 M개를 선택한다. 성능의 저하를 최소화 하기 위해서는 큰 값의 M을 사용해야 하지만, 계산양 또한 증가하는 단점 을 가진다. 이러한 단점을 보완하기 위해 측정된 평균 잡음 전력 값에 따라 survivor path의 개수나, 검색 범위를 적절히 조절하는 기법들이 제안 되었다. 하지만 이 기법들에 채널 상태를 판별하기 위해 사용된 지표는 평균 잡음 전력 정보이므로 잡음 전력 값이 순간적으로 크게 변하는 경우 성능 저하를 가져올 수 있다. 제안된 기법에서는 수신 심벌 벡터와 QRD에 의해 임시적으로 추정된 심벌 벡터와의 Euclidean distance와 채널 행렬의 대각성분을 이용하여 순시적인 채널 정보를 추정하여 검색 범위를 적절히 조절하 므로 기존의 기 법의 단점을 보완한다. 실험 결과에서는 제안된 기법이 MLD(Maximum Likelihood Detection)의 성능에 근접하면서, 동일한 성능을 가지는 기존의 QRD-M 기법들에 비해 확연히 작은 복잡도를 가지는 것을 보인다.

A very low complexity QRD-M algorithm based on limited search area is proposed for MIMO systems. The conventional QRD-M algorithm calculates Euclidean distance between all constellation symbols and the temporary detection symbol at each layer. We found that performance will not be degraded even if we adaptively restrict the search area of the candidate symbols only to the neighboring points of temporary detection symbol according to the channel condition at each layer. As a channel condition indicator, we employ the channel gain ratio among the layers without necessity of SNR estimation. The simulation results show that the proposed scheme effectively achieves near optimal performance while maintaining the overall average computation complexity much smaller than the conventional QRD-M algorithm.

최근 모바일 환경에서 고화질 멀티미디어 서비스 수요가 늘어감에 따라, 다중안테나(MIMO, Multiple-Input Multiple-Output) 시스템에 대한 연구가 활발히 진행되고 있으며, 최신무선 통신 시스템에 적용되고 있다. 이와 함께, 휴대폰, 테블릿 등 모바일 디바이스용 MIMO 시스템은 물리적 크기의 한계로 인하여 최대 2개의 송수신 안테나(2×2)를 고려하고 있으며, 따라서 본 논문에서도 2×2 MIMO 시스템을 고려하여 모바일 디바이스용 다중안테나 시스템을 위한 저복잡도 특성을 갖는 심볼 검출 알고리즘을 제안한다. 제안된 심볼 검출 기법은 비록 Modified-SQRD 알고리즘을 통해 검출된 1차원 상의 신호를 제안된 심볼 확장 기법을 통해 2차원 신호로 확장한 다음 연판정을 위한 LLR 연산이 가능하도록 제안하였다.

Recently, the demand has continued to increase for higher data rates and improved multimedia services through wireless internet access. In order to increase the data rate and link reliability, 3GPP LTE/A and IEEE 802.16e/m WiMAX systems incorporate MIMO transmission schemes. Since the hardware complexity increases with the number of transmit data streams and mobile devices have limited physical dimensions, an multiple input multiple output (MIMO) ystem with two antennas at both the transmitter and the receiver (2×2) is considered to be a possible solution for mobile devices. In this paper, a low-complexity soft output MIMO symbol detector based on Modified-SQRD is proposed for mobile devices with two transmit and two receive antennas.

Bluetooth는 다양한 소비자 전자 장치 간의 연결 매체로 널리 사용되는 공통 무선 기술이다. Bluetooth 수신기 는 주로 신호 대 잡음비 성능 개선을 위해 일반적으로 Viterbi 알고리즘을 채택하지만 전송단에서의 irrational modulation index(무리수 변조 지수)로 수신단의 지속적인 탐색 및 추정이 필요하며 이를 위한 복잡한 하드웨어와 계산을 요구한다. 본 논문에서는 이러한 복잡도 문제를 해결하기 위해 비동기 최대 우도 추정(MLE, Maximum-likelihood Estimation) 기반 8-state Viterbi FSM을 제안한다. 본 논문에서 제안한 최적의 Viterbi FSM 은 전송단에서의 변조 지수에 대한 사전 정보 및 추정이 필요 없으며 GFSK(Gaussian Frequency Shift Keying) 심볼 검출이 가능하다. 제안한 알고리즘에 대한 성능은 HV1/HV2 패킷을 사용하여 평가하였으며, 시뮬레이션 결과는 DD(Decision Direct)와 같은 이상적인 접근 방식과 비교하여 10-3 BER에서 약 2dB 성능 향상을 보여주었다.

Bluetooth is a common wireless technology that is widely used as a connection medium between various consumer electronic devices. The Bluetooth receiver usually adopts a Viterbi algorithm to improve signal-to-noise ratio performance, but requires complex hardware and calculations for continuous search and estimation for the irrational modulation indexes at the transmission. This paper proposes a non-coherent maximum estimation based 8-State Viterbi FSM to solve these complexity problems. The proposed optimal Viterbi FSM can detect Gaussian frequency-shfit keying symbol without any prior information and estimation for the modulation indexes. The HV1/HV2 packets are used for the estimation of the proposed algorithm and the simulation results have shown performance improvements with about 2dB for 10-3 BER compared to other ideal approaches such as decision direct method.

To lower the mapping complexity of designing analog decoders, a method to optimize the design of low-density parity-check (LDPC) analog decoders is proposed in this paper. Based on factor graphs and the sum-product algorithm, the LDPC decoding process on the factor graph and the construction of analog decoders are exploited. Then the frequent subgraph mining algorithm is introduced to search the isomorphic subgraphs in factor graphs. According to the output of the frequent subgraph mining algorithm which enumerates all the subgraphs in factor graphs, the mapping complexity of a LDPC analog decoder can be significantly reduced. Finally, a (40, 16) LDPC analog decoder is constructed using the proposed method. Simulation results show that the need to place gates and connections can be reduced 90% and 23%, respectively, and the ideal performance is obtained by carefully choosing unit currents and decoding time.

A promising choice for signal generation in modern communications systems is direct digital frequency synthesis (DDFS) which is capable of well controlled, rapid changes in signal frequency, over a relatively large frequency range. Unfortunately, a conventional DDFS system requires a high frequency read only memory (ROM) which consumes most of the power. This paper describes a novel low complexity DDFS with smaller lookup table size and lesser hardware overhead. It is based on the Taylor series expansion method for sinusoidal and co-sinusoidal functions combined with an approximation algorithm. It has the advantages of high speed, low complexity, low computational delay and high spectral purity. The proposed DDFS has high SFDR (spurious free dynamic range) and the spectral purity can be as good as 135 dBc.