Minimum bit-error-rate decision fusion receivers for robust DS spread-spectrum communications

In this paper, we introduce Hyper-Dimensional Modulation (HDM) for massive machine-type communications (mMTC). HDM enables robust communication of short packets by spreading information bits across many elements in a hyper-dimensional vector and superimposing a set of such non-orthogonal vectors. The proposed CRC-aided K-best decoding algorithm for HDM can achieve a very low packet error rate (PER) in additive white Gaussian noise (AWGN) channels for short packets. Furthermore, extended decoding algorithms are proposed to combat overwhelming interference in an mMTC network. Comprehensive simulation and real-world experiment results show that HDM outperforms sparse superposition codes in AWGN channels and state-of-the-art short codes such as polar and tail-biting convolutional codes in interference-heavy channels for short packet transmissions.

This paper examines the bit error rate (BER) of a direct sequence spread spectrum (SS) system that uses bandlimited white Gaussian noise (BLWGN) as a spreading code. The performance of this bandlimited-SS system is examined in both additive white Gaussian noise (AWGN) and single tone jamming environments. The BLWGN spreading code is inferior to conventional codes in AWGN channels, but is more robust when a narrow band interference signal is present.

In this paper, we investigate a novel beam direction-based modulation transmit scheme for millimeter-wave (mmWave) communication systems equipped with distributed antennas, and propose an enhanced space-domain index modulation (ESDIM) scheme, in which the number of beamforming directions (BDs) for transmitting information bits can be one or two. The ESDIM system jointly utilizes the combination of the index of BDs and signal constellations to transmit information bits, in which one or two beam directions are considered. In addition, we propose power allocation (PA) aided schemes for ESDIM to further improve the system reliability by reducing the system symbol error rate (SER), where three constraints to the transmit power for beamforming are investigated. To be specific, a total transmit power constraint (TTPC) and two per-beamforming power constraints (PBPC) are considered. We first propose a suboptimal PA algorithm for the TTPC-PA aided ESDIM scheme using a powerful solver based on advanced algebra theories, which only considers the PA aspects for a given selected beamforming pair. Then, we extend the TTPC-PA aided scheme to the average per-beamforming power constraint (APBPC)-PA aided scheme and the strict per-beamforming power constraint (SPBPC)-PA aided scheme. Simulation results show that the proposed schemes improve the system SER performance compared to other existing counterparts.

Sparse vector coding (SVC) is a promising short-packet transmission method for ultra reliable low latency communication (URLLC) in next generation communication systems. In this paper, a dual-mapping SVC (DM-SVC) based short packet transmission scheme is proposed to further enhance the transmission performance of SVC. The core idea behind the proposed scheme lies in mapping the transmitted information bits onto sparse vectors via block and single-element sparse mappings. The block sparse mapping pattern is able to concentrate the transmit power in a small number of non-zero blocks thus improving the decoding accuracy, while the single-element sparse mapping pattern ensures that the code length does not increase dramatically with the number of transmitted information bits. At the receiver, a two-stage decoding algorithm is proposed to sequentially identify non-zero block indexes and single-element non-zero indexes. Extensive simulation results verify that proposed DM-SVC scheme outperforms the existing SVC schemes in terms of block error rate and spectral efficiency.

Automatic identification of digitally modulated signal has to be able to identify the digitally modulated signal correctly and accurately. Importance of automatic identification of digitally modulated signals are rising increasingly. In this paper an advanced technique is presented, that automatically identifies the multi-user chirp modulated signals in Additive White Gaussian Noise (AWGN) channel. The proposed technique is implementing high order moments (fourth, sixth, and eighth) of detail coefficients of discrete wavelet transform (DWT) as a feature extraction set. Adaptive Neural-Fuzzy Inference System (ANFIS) is proposed as a classifier. The proposed identification procedure is capable of identifying multi-user chirp modulated signals with high accuracy at 0dB, 5dB, and 10dB Signal to Noise Ratio (SNR), over AWGN channel.

The optical ZCZ code, which is a set of pairs of binary and biphase sequences with zero correlation zone, can provide code division multiple access (CDMA) communication system without co-channel interference. The M-ary amplitude shift keying spread spectrum (M-ary/ASK-SS) system using this code can detect a desired sequence without interference of undesired sequences. We have proposed the compact construction of a matched filter bank for this code, which is called the compact-type matched filter bank. However, M-ary/ASK-SS system using this filter bank might go down the bit error rate (BER) performance because input-output characteristics of this filter bank for this code with zero correlation zone 4n - 2 are nonlinear characteristics. In this paper, we clarify that BER performance in the M-ary/ASK-SS system over the additive white Gaussian noise (AWGN) channels is not influenced by nonlinear characteristics of this filter bank by the theoretical formula of BER characteristics and the computer simulation. The BER performance in the ASK-SS system using compact-type matched filter under the AWGN environment go down compared to that using direct-type matched filter as expected. But the BER performance in the M-ary/ASK-SS system using this compact-type matched filter bank under the AWGN environment is almost equal compared to that using parallel-type matched filter bank. In fact, this compact-type matched filter bank is effective in the M-ary/ASK-SS system.

We analyze the effect of a nonlinearity on the bit error rate performance of multicarrier spread spectrum (MCSS) systems in the presence of multipath fading. A 5th order polynomial model is used to represent the amplifier amplitude nonlinearities (AM/AM) and a flat Rayleigh fading channel is assumed for each modulated carrier. It is found that for the additive white Gaussian noise and multipath fading channel, the bit error degradation from a nonlinear amplification is not as significant as in the additive white Gaussian noise channel alone.

Soft demodulation is a basic module of traditional communication receivers. It converts received symbols into soft bits, that is, log likelihood ratios (LLRs). However, in the nonideal additive white Gaussian noise (AWGN) channel, it is difficult to accurately calculate the LLR. In this letter, we propose a demodulator, DemodNet, based on a fully convolutional neural network with variable input and output length. We use hard bit information to train the DemodNet, and we propose log probability ratio (LPR) based on the output layer of the trained DemodNet to realize soft demodulation. The simulation results show that under the AWGN channel, the performance of both hard demodulation and soft demodulation of DemodNet is very close to the traditional methods. In three non-ideal channel scenarios, i.e., the presence of frequency deviation, additive generalized Gaussian noise (AGGN) channel, and Rayleigh fading channel, the performance of channel decoding using the soft information LPR obtained by DemodNet is better than the performance of decoding using the exact LLR calculated under the ideal AWGN assumption.

Compared with the SAW convolver and the digital correlator, the SAW matched filter (tapped delay line) has many advantages in commercial wireless LAN applications, because of its high efficiency and simple configuration. A new type of SAW device for the spread spectrum (SS) transceiver and a low-loss SAW matched filter for the wireless LAN system is described. Two matched filters which correspond to bi-phase data modulation and bandpass filters for the intermediate frequency (IF) section are combined into one device. This SAW matched filter fabricated on ST cut quartz has been practically used in commercial wireless LAN systems and has good temperature stability. To reduce the conversion loss further we have developed an extremely low loss SAW matched filter. The output correlation peak of the matched filter is 3 dB larger than the input level at a 50 /spl Omega/ input and output impedance. This low loss SAW matched filter is fabricated on 128/spl deg/ Y-X LiNbO/sub 3/ substrate and consists of unidirectional transducers. The phase error caused by the temperature coefficient of delay is compensated by using a temperature dependent change of local frequency in the spread spectrum receiver. Under the critical conditions of a 2.4 GHz wireless LAN (data rate is 1.4 Mbps, C/N>2 dB, that is E/sub b//N/sub 0/>13.6 dB, and operation temperature is from -20/spl deg/C to +60/spl deg/C), good performance is achieved with less than a 10/sup -5/ bit error rate.

This paper considers an improved single-user detection technique for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems using long sequence spreading (random-CDMA) Most of the known detection schemes for DS-CDMA suffer from either poor performance under power-imbalance (near-far like) conditions, excessive complexity, or incompatibility with systems employing long sequence spreading. To address these problems, this paper considers a signal-to-noise ratio maximizing linear time-invariant filter for one-shot bit symbol detection exploiting some information about the interferers. This filter, referred to as the chip-delay locked matched filter (CLMF), exploits the cyclostationarity in multiple-access interference, and it can offer good near-far resistance while remaining suitable for systems with long sequence spreading. The CLMF requires knowledge of interferers chip delays and signal powers; however, knowledge of their pseudonoise sequences is unnecessary. This paper also demonstrates the improvement in performances offered by the CLMF over other single-user receivers such as the conventional matched filter and noise-whitening matched filter performance is evaluated in terms of probability of outage for single-rate and dual-rate DS-CDMA systems using bandwidth-efficient chip pulses, over a single-path additive white Gaussian noise channel. Errors in the interferer chip delay estimates degrade the CLMF performance. However, if the root-mean-square value of these errors is less than 5% of the chip interval, then this degradation is small.

For the precise measurement of 3D object coordinates a high precision radio location system is introduced for 3D applications and optimized for very high precision. In different test scenarios the system is evaluated with regards to precision, resolution, reproducibility, and robustness. Based on a direct sequence spread spectrum transmission at 24 GHz the radio location system shows high robustness against interferers as well as a high suppression of reflections. After adequate object tracking using a Kalman filter it offers a very high precision with an uncertainty of 0.1 mm also in very general highly reflective indoor environment.

A noncentralized fully distributed mobile communication network with directive/adaptive antennas is proposed. The spatial and temporal synchronization of transmitting and receiving antenna beams is accomplished by employing the global positioning system information and a synchronized spatial search algorithm. The link setup between a communication transmitter (CT) and a communication receiver (CR) depends on the success of both forward and reverse links. A two-way communication link protocol is defined as a basic agreement for the link activation in the network. Two link search algorithms, for additive white Gaussian noise channels, are proposed for use in hostile communication environments as follows: (1) a sequential ascending search power algorithm using an optimal set of link power levels and (2) a sequential Bayesian search algorithm (SBSA) using Bayes rule to update the CR location information. The optimal SBSA can be obtained by using dynamic programming, but the computational complexity is unfeasibly high. The experimental results in which the CT uses a noncoherent matched filter receiver for spread-spectrum code acquisition and the unfriendly interceptor uses a wide-band energy detector for both link search algorithms are presented.

A semiconductor laser diode direct detection optical communication system suitable for use in an intersatellite communication link was constructed, and its performance was measured. The system used Q = 4 pulse position modulation (PPM) to transmit binary source data at a rate of 25 Mbit/s and contained a low-noise silicon avalanche photodiode (APD) as a photodetector. Use of the conventional Gaussian model for the output of the low-noise APD (RCA C30902S) was shown to be inappropriate under low-background radiation levels because its use caused a severe underestimate of the optical APD gain and an overestimate of a system bit error rate. A numerical procedure was developed that made use of the Conradi distribution for the APD output which gave good agreement with the results of the experimental measurements of system performance. A slot clock recovery subsystem was also provided in the receiver. It consisted of a nonlinearity which is easy to implement and a narrow bandpass filter centered at the slot clock frequency. Use of the recovered timing signal showed no penalty in the minimal input optical power required to maintain a specified error rate. The system achieved a bit error rate of 10−6 at a received signal level corresponding to an average of 60 detected photons per transmitted information bit (120 photons per PPM symbol).

In this paper, we study transmit codebook designs for spatial modulation with analog phase shifters. The proposed spatial modulation with analog phase shifters can send more spatial symbols than conventional spatial modulation, while reserving the low complexity of single RF-chain MIMO structure. The main idea is to transmit N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> different phase-shifted copies of a digitally modulated signal through N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> transmit antennas. In each time slot, the transmitted information bits are divided into two groups. The first group of the bits is mapped to the digitally modulated signal symbol. The second group of the bits is mapped to the spatial symbol, which determines the phase shift of each antenna. The transmit signal designs are carried out in open loop and closed loop scenarios, respectively. In open loop scenario, the transmit codebook is designed in two steps, i.e., generate the optimal spatial codebook according to Grassmannian line packing criterion, and find the optimal tradeoff between the cardinality of spatial codebook and the modulation order of signal symbol. In the closed loop scenario, the transmit codebook is designed according to the structure of Huffman tree. Extensive simulation results are given to validate the effectiveness of the proposed scheme in open loop scenario and close loop scenario, respectively.

Transmission efficiency, defined as the ratio of successfully transmitted information bits to overall bits transmitted, can be used for evaluating the transmission performance of wireless links. As a function of received signal to noise ratio (SNR), transmission efficiency is determined by physical layer technologies, such as channel coding, interleaving, modulation and other error-recovery techniques of wireless links. In this paper we first analyze the form of transmission efficiency function in wireless links, then based on that we propose an adaptive coding scheme that maximizes the transmission efficiency according to wireless channel conditions (received SNR). Simulation results show that with the proposed adaptive coding, transmission efficiency of wireless links can be significantly enhanced.