Physical Layer Algorithms Research Articles

Practical Steps towards Establishing an Underwater Acoustic Network in the Context of the Marine Internet of Things

When several hydroacoustic modems operate simultaneously in an area of mutual coverage, collisions of data packets received from several sources may occur, which lead to information loss. With an increase in the number of simultaneously operating hydroacoustic modems, physical layer algorithms do not provide stable data transmission and the likelihood of collisions increases, which makes the operation of modems ineffective. To ensure effective operation in a hydroacoustic signal propagation environment and to reduce collisions when exchanging data between two modems that do not have the ability to operate synchronously and to reduce the access time to the signal propagation environment, methods of the medium access control layer using link layer protocols are required. Typically, this problem is solved using code separation of hydroacoustic channels. If you need to transfer over a network, this option will not work, since network transfer involves working on the basis of “broadcast” messages, particularly between data source and data sink that remain too far from each other, outside of their mutual audibility. In practical use, it is convenient to place these protocols into a software environment for developing specific user applications for solving network communication problems. This software framework allows for custom modification of existing network algorithms, as well as the inclusion of new network hydroacoustic communication algorithms. To build a predictive model, the DACAP, T-Lohi, Flooding, and ICRP protocols were used in this work. The implementation is performed in Erlang. The paper presents algorithms for implementing these protocols. A comparative analysis of network operation with and without protocols is provided. Efficiency of operation, i.e., data rates and probabilities of data delivery, was assessed.

Comparison of Real- and Complex-Valued NN Equalizers for Photonics-Aided 90-Gbps D-band PAM-4 Coherent Detection

5G defines below 100 GHz as the millimeter-wave bands, whereas 100 GHz - 3 THz is categorized as THz band in 6G. Deep leraning (DL) is expected to enable a significant paradigm shift in 6G wireless networks. In this paper, D-band 90-Gbps single channel PAM-4 signal generation and transmission over 10-km SMF and 3-m wireless link at 140-GHz can be achieved. A novel complex-valued neural network (CVNN) equalizer using &#x2018;&Copf;ReLU&#x2019; activation function to directly recover PAM-4 signals from received noised signals is demonstrated. There are three DSP options in the experiment. In <i>Opt</i>.1, firstly conducted cascaded multi-modulus algorithm (CMMA) pre-equalization (pre-EQ) at transmitter, then processed via frequency offset estimation (FOE), carrier phase recovery (CPR) and finally real-valued neural network (RVNN) equalization at receiver. Here, the RVNN equalizers include DNN with a softmax output layer, two-step joint-DNN equalizer and LSTM. The experimental results show that LSTM-based equalizer outperforms the other real NN-based equalizers by average 0.5 to 1.5 dB at BER of 10^&#x2212;3 magnitude. Differently from <i>Opt</i>. 1, real-valued CMMA pre-EQ at transmitter is unexpected for CVNN in the other two options. In <i>Opt</i>. 2, we only combine down-conversion and CVNN regarded as &#x2018;pure data-driven&#x2019; training at receiver. This pure data-driven CVNN equalizer improves BER a lot and also has a larger computation burden, especially BER is as low as 1 &#x00D7; 10^&#x2212;4 with <i>n</i>₀ &#x003D; 571 and <i>n</i>₁ &#x003D; 200 training cells and the time complexity reaches 350000 in one iteration. Thanks to the aid of traditional mathematical-oriented models including FOE and CPR, the computation burden of CVNN in <i>Opt</i>. 3 is released significantly. Furthermore, we compare the performance of CVNN and RVNN in terms of BER decision accuracy, time complexity and receiver sensitivity. Followed by the same DSP with the same complexity, the comparison result between DNN and CVNN in the same structure of [371-260-1] with 11000 samples and 300 epochs shows that CVNN performs better due to its reservation of phase information. Therefore, we believe that the joint use of model-based, e.g., FOE, CPR steps and complex DL-based techniques has a potential for the future 6G wireless physical layer algorithms.

A Physical Layer Algorithm for Estimation of Number of Tags in UHF RFID Anti-Collision Design

A priori knowledge of the number of tags is crucial for anti-collision protocols in slotted UHF RFID systems. The number of tags is used to decide optimal frame length in dynamic frame slotted ALOHA (DFSA) and to adjust access probability in random access protocols. Conventional researches estimate the number of tags in MAC layer based on statistics of empty slots, collided slots and successful slots. Usually, a collision detection algorithm is employed to determine types of time slots. Only three types are distinguished because of lack of ability to detect the number of tags in single time slot. In this paper, a physical layer algorithm is proposed to detect the number of tags in a collided slot. Mean shift algorithm is utilized, and some properties of backscatter signals are investigated. Simulation results verify the effectiveness of the proposed solution in terms of low estimation error with a high SNR range, outperforming the existing MAC layer approaches.

Machine Learning Tips and Tricks for Power Line Communications

A great deal of attention has been recently given to Machine Learning (ML) techniques in many different application fields. This paper provides a vision of what ML can do in Power Line Communications (PLC). We first and briefly describe classical formulations of the ML, and distinguish deterministic from statistical learning models with relevance to communications. We then discuss ML applications in PLC for each layer, namely, for characterization and modeling, for the development of physical layer algorithms, for media access control and networking. Finally, other applications of the PLC that can benefit from the usage of ML, as grid diagnostics, are analyzed. Illustrative numerical examples are reported to serve the purpose of validating the ideas and motivate future research endeavors in this stimulating signal/data processing field.

Research and implementation of synchronization for ultra-wide bandwidth receiver within enclosed metal cabin

Aiming at solving the problem of wireless communications within the enclosed metal cabin, such as, spacecraft and aircraft cabin, the enclosed metal cabin statistical channel parameters are given based on channel measurements which prove the channel characteristics of the strong multipath channel environments. Ultra-wideband wireless communications technology is suitable to apply in such enclosed metal cabin with the strong anti-multipath ability. Due to the extremely wide bandwidth, design and implementation of synchronization with low complexity is important for the receiver. In this paper, an improved parallel synchronization scheme consists of 1-bit quantization and multipath energy accumulation is proposed. Owing to 1-bit quantization, the computation of correlation can be simplified by transferring complex operation of multiplication into the easy operation of addition in FPGA. The synchronization performance is observed through analytical expressions corroborated by simulations which show that the 1-bit quantization can reduce the complexity significantly with a little loss in signal noise ratio. By investigating the probabilities of false alarm and missed detection in simulation, the optical threshold of synchronization is also obtained. On this basis, the hardware implementation of the physical layer algorithm and the experimental verification in the enclosed metal cabin are performed. Experiments show that the design of synchronization scheme can overcome the strong multipath effect and achieve large capacity and low bit error rate transmission.

A software-defined radio FPGA implementation of OFDM-based PHY transceiver for 5G

This paper introduces a software-defined radio implementation of an OFDM-based transceiver for the prototyping and testing of 5G physical layer algorithms. The implementation uses high level abstraction tools to develop and test the algorithms, significantly reducing the time and effort needed to test new features. The proposed architecture adopts interconnecting FIFOs between each functional block, reducing the critical paths and enabling complex designs to be implemented at higher clock rates. The proposed LTE-like transceiver is implemented using COTS FPGA and RF development boards. The real-time over-the-air demonstrator has an on-the-fly scalable bandwidth from 20 to 61.44 MHz, attaining close to 500 Mb/s when using 256-QAM modulation.

TxCP: A Coprocessor for LTE-A

With the widely use of 4G network, the corresponding bandwidth processing has become a critical issue. The current recognized 4G network is LTE-A. In the baseband processing for LTE-A, the processing of its physical layer algorithm is the biggest bottleneck for current processors. The use of application specific integrated circuit (ASIC) design has become necessary. This article will introduce a communication dedicated coprocessor (TxCP), specifically for LTE-A physical layer uplink shared/control channel (PUSCH/PUCCH) algorithm for bit-level acceleration. Its internal support for PUSCH/PUCCH CRC, Turbo encoding, equation definable convolutional encoding, data channel and control channel rate matching, channel interleaving, scrambling and modulation supporting QPSK, 16QAM and 64QAM. And in order to ensure that the coprocessor has a certain degree of flexibility, its internal controller design will support a variety of modes to ensure that some of the algorithm modules can be run separately. The programming model of the processor is relatively simple, and the user does not need to go through a complicated design.

Modelling and simulation of channel power delay profile under indoor stair environment

An empirical stochastic discrete tapped delay line (DTDL) power delay profile (PDP) model is presented. It is used for characterising the multipath effects under indoor stair environment. In this model, the amplitude at each DTDL tap and stair step follows the Nakagami distribution. Its scale parameters are lognormally distributed, and its shape parameters are distance and propagation delay dependent. Then, the procedure for simulating the PDPs is given. In addition, the average PDP, root mean square delay spread and capacity extracted using the measured and simulated channels are compared to validate the accuracy of the proposed model. Finally, a measurement-based channel simulator is developed by implementing an orthogonal frequency division multiplexing communication procedure on the simulated channel. These works can provide important information about the designs of the physical layer algorithms in small cells scenarios.

Measurement and Modeling of Wireless Off-Body Propagation Characteristics Under Hospital Environment at 6–8.5 GHz

A measurement-based novel statistical path-loss model with a height-dependent factor and a body obstruction (BO) attenuation factor for off-body channel under a hospital environment at 6–8.5 GHz is proposed. The height-dependent factor is introduced to emulate different access point (AP) arrangement scenarios, and the BO factor is employed to describe the effect caused by different body-worn positions. The height-dependent path-loss exponent is validated to fluctuate from 2 to 4 with AP height increasing by employing both computer simulation and classical two-ray model theory. As further validated, the proposed model can provide more flexibility and higher accuracy compared with its existing counterparts. The presented channel model is expected to provide wireless link budget estimation and to further develop the physical layer algorithms for body-centric communication systems under hospital environments.

Low Duty-cycle based Optimized Sleep-schedule (LDCOS) Cross Layer Design for WSN

Energy based design in Wireless sensor network (WSN) is the emerging trend. Different optimization methods are introduced in traditional layering approach create unaddressed open issues. WSN layers are interlinked and a change in one layering parameter needed to update in another linked layer also. A cross layer design creates understanding between layers and its parameters to reduce the open issues. New Cross layer design proposal considered Physical and MAC layers. Low duty cycle concept and nodes remaining energy consideration concepts covered by physical layer and sleep scheduling algorithm controlled by MAC layer. The new design also considered nodes residual energy and distance between node and base for hop-count choice. Simulation results show the comparative improvement in energy consumption, network average delay and lifetime of the network.

Reconfigurable antennas and link adaptation algorithms for MIMO-OFDM wireless systems

In this work, we study and analyze the performance of physical layer algorithms for adaptive multiple input-multiple output orthogonal frequency-division multiplexing (MIMO-OFDM) wireless systems that employ a new class of adaptive antenna systems known as reconfigurable antennas. These antennas are capable of adaptively modifying their radiation characteristics and thus leverage pattern diversity to affect how the transmitter and receiver perceive the wireless channel. We propose a low complexity spatial adaptive modulation and coding (AMC) algorithm that uses the advantages of pattern reconfigurable antennas in concert with link adaptation to improve MIMO-OFDM link throughput. The algorithm operates in two main stages; first, it searches for the antenna configuration that yields the highest post processing signal-to-noise ratio (ppSNR) and, then, applies AMC to improve spectral efficiency. The performance of the proposed scheme is experimentally evaluated for a 2×2 MIMO-OFDM wireless system in an indoor environment.

Design and Study of Cognitive Network Physical Layer Simulation Platform

Cognitive radio technology has received wide attention for its ability to sense and use idle frequency. IEEE 802.22 WRAN, the first to follow the standard in cognitive radio technology, is featured by spectrum sensing and wireless data transmission. As far as wireless transmission is concerned, the availability and implementation of a mature and robust physical layer algorithm are essential to high performance. For the physical layer of WRAN using OFDMA technology, this paper proposes a synchronization algorithm and at the same time provides a public platform for the improvement and verification of that new algorithm. The simulation results show that the performance of the platform is highly close to the theoretical value.

A Novel Dynamic Adjusting Algorithm for Load Balancing and Handover Co-Optimization in LTE SON

With the development of mobile internet and multi-media service, advanced techniques need to be applied in wireless network to improve user experience. Long term evolution (LTE) systems, which can offer up to 100Mbps downlink date rates, have been deployed in USA and Korea. However, because plenty of complex physical layer algorithms are utilized, network planning and optimization become heavy burdens for LTE network operators. Self-organizing network (SON) is a promising method to overcome this problem by automatically selecting and adjusting key parameters in LTE systems. In this paper, we present a dynamic adjusting algorithm to improve both handover and load balancing performance by introducing a weighted co-satisfaction factor (CSF). Analysis and system level simulation are conducted to exhibit the performance improvement of the proposed scheme. Results show that the proposed method outperforms the conventional solutions in terms of the network handover success ratio and load balancing gains significantly.

Radio communications: components, systems, and networks [Guest editorial

Dear readers: Continuing our series in 2011, our challenge remains: bring timely, highly relevant contributions of a tutorial nature that can bring new ideas and concepts closer to the Communications Society readership. Radio Communications topics are diverse in nature, spanning components and subsystem enabling technologies, physical and radio access layer approaches, and network techniques. The complexity of modern systems brings all of the disciplines together with a crossdisciplinary emphasis, with enabling solutions being distributed across all aspects of the system. Taking the low power challenge (or maybe calling it the green approach) is an excellent example: savings can come from protocol design, low-complexity physical layer algorithms, and efficient implementations all the way to advances in semiconductor technology. Add on top of this energy harvesting as part of the solution, and one can imagine how important a cross-disciplinary approach is today.

Capacity analysis for a multiuser cross-layer downlink model in the presence of fading and interference

A system model that employs beamforming at the physical (PHY) layer and different scheduling algorithms at the medium access control (MAC) layer is used in a downlink environment where two users are served simultaneously. The effect of the scheduling algorithms on the system performance is assessed in terms of total system capacity. The scheduling algorithms considered, choose users either randomly, or on the basis of their instantaneous signal-to-noise ratio (SNR) and/or their angular location around the base station. A semi-analytical framework for the capacity analysis is also presented. The results obtained from the numerical model are shown to be consistent with those based on the semi-analytical framework. It is shown that explicitly taking into consideration at the MAC layer the angular location of mobile users around the base station along with instantaneous SNR for the selection of users that are served simultaneously leads to an improved system capacity. This improvement is the result of reduced interference that simultaneously served users cause on each other. The results show that joint addressing of the PHY and MAC layer issues in an integrated cross-layer framework is important for achieving maximal system performance.