Code Division Multiple Access Frequency Research Articles

Doppler frequency code division multiple access method for LEO mega-constellation navigation systems

Doppler frequency code division multiple access method for LEO mega-constellation navigation systems

An Efficient Code Domain NOMA Scheme with Enhanced Spectral and Energy Efficiency for Networks Beyond 5G

Non-Orthogonal Multiple Access (NOMA) is an efficient multiple access scheme which augments the capacity and overall throughput in LTE and 5G networks. Tackling the high system throughput and device connectivity of multiple users with different channel state information is a key challenge at this juncture. The joint detection and decoding using parity check polar coding (PCPC) and the utilization of Sparse Code Multiple Access (SCMA) in Code domain NOMA improves throughput supporting an overloaded number of users. Also, Multiple-Input Multiple-Output (MIMO)-SCMA scheme has potential in providing spectrum and energy efficiency. MIMO-SCMA superimposes multiple users in the code domain and utilizes the channel gain difference between multiplexed users. Hence, this paper aims to propose a proficient code domain NOMA scheme, the PCPC SCMA multiplexed over Orthogonal Frequency Code Division Multiple Access (OFCDMA), implementing a joint detection and decoding with user scheduling. Signals of numerous users are superimposed and transmitted over a channel. At the receiver, Multi-User Detection (MUD) exploiting the Message Passing Algorithm (MPA) is used to identify the desired user. To ensure proper resource utilization of multiple data blocks, the users are scheduled by implementing the Invasive Weed Optimization (IWO) technique along with the MPA. The proposed scheme, which engages an IWO-MPA based MUD scheme, improves the convergence rate, in terms of the number of iterations thereby leading to lower complexity, as well as reduces the Bit Error Rate (BER). Computer simulations reveal that the proposed scheme achieves high spectrum and energy efficiency, higher throughput and overloaded user fairness compared with recent researches.

Particle Filter-Based Inter-System Positioning Model for Non-Overlapping Frequency Code Division Multiple Access Systems

In the process of composing a double-differenced positioning model, it is difficult to separate different frequency signals between code division multiple access (CDMA) systems, the single-difference ambiguity of the pivot satellite and phase differential inter-system biases (PDISBs). Hence it is difficult to calibrate in advance the bias between systems in order to build an inter-system model which only needs one pivot satellite. Based on analysis of the stability of PDISB parameters for non-overlapping frequency CDMA systems, this study adopts a particle filter to estimate the fractional part of the PDISBs (F-PDISBs) between the systems and proposes a particle filter-based inter-system positioning model. Results show that the F-PDISBs and code DISBs for the baselines with the same receiver types and some with different receiver types are rather stable over time and for these baselines it is feasible to use a particle filter to estimate the F-PDISB parameters in the initial stage. Having attained the F-PDISBs, the inter-system model can be constructed to improve positioning accuracy in complex operational environments.

Pixels of Interest (POI) empowered higher speed CAOS camera imaging and spectrometry for multi-target applications

Designed and demonstrated for the first time is Pixels of Interest (POI) centric camera design empowered higher speed, better computational efficiency, Coded Access Optical Sensor (CAOS) time–frequency Code Division Multiple Access (CDMA)-mode imaging versus the classic Hadamard (H) spatial transform-based imaging. The showcased CAOS camera is highly suited for faster tracking of multiple distributed targets within a large pixel count full Field of View (FOV) over a full multi-band optical spectrum. A demonstration white light experiment with 3 different shaped targets distributed in a 16384 pixels full FOV shows an 6.12 times faster CAOS imaging operation versus Hadamard Transform (HT)-imaging with a CAOS POI frame update time of 143.4 ms. An additional experiment using 3 similar shaped white light targets with different brightness values also demonstrates the CAOS CDMA-mode speed advantage. Potential areas of use are multi-target tracking in manufacturing, microscopy, security such as Unmanned Aerial Vehicles based surveillance, air traffic monitoring, and astronomy. Apart from imaging applications, the CAOS CDMA-mode is also suited for higher speed spectrometry across a broad optical spectrum with distributed discrete targeted spectral lines.

Fifth Generation promising integrated full loaded MIMO space‐time spreading‐aided‐orthogonal frequency code division multiple access system

The optimisation of a communication system becomes a difficult objective if distinct techniques are utilised to resolve different problems of the same system. Accordingly, the main target of future mobile communication systems (e.g. fifth generation) is to integrate different techniques under a unified framework for the optimisation purpose. This study proposes a downlink air interface that targets maximum capacity and bit error rate (BER) performance enhancement. The proposed system is an integration of a full loaded multi-code transmission orthogonal frequency code division multiple access and space-time spreading that exploits transmit diversity needed for BER enhancement and data rate optimisation. Further BER improvement was achieved through applying an effective iterative interference cancellation in the space domain combined with multi-code interference suppression algorithm at the receiver. The authors present a system performance analysis in addition to simulation results for the proposed system. The BER performance improvement was emphasised through comparing the proposed system with a similar system that uses joint iterative detection. Finally, the effect of frequency domain spreading factor with different number of iteration loops was investigated for further BER system performance enhancement. The achieved BER performance outperforms the maximal ratio receive combining diversity system performance with 1Tx and 8Rx.

Broadband acoustic local positioning system for mobile devices with multiple access interference cancellation

This paper presents an Acoustic Local Positioning System (ALPS) suitable for indoor localization of mobile devices, based on the transmission of high frequency Code Division Multiple Access (CDMA) audio signals from a fixed beacon network to a tablet computer. The system permits positioning of the device (and the user carrying it) within a few centimeters, which is accurate enough for most location-based applications. It also implements a CDMA scheme for localization, including compensation for the limited transmission frequency band of the sensors which causes Intersymbol Interference (ISI), as well as Multiple Access Interference (MAI) between the different beacons. Signal reception, processing and estimation of position all take place within the tablet, operating at real time and with an update rate of 2 Hz. Experimental results show that the MAI/ISI compensation algorithm increase both the system’s robustness (availability ⩾90%) and accuracy (errors ⩽10 cm) under adverse circumstances such as near-far effect or noisy conditions.

Transmitter diversity scheme for OFCDMA systems based on space‐time spreading with iterative detection receiver

Orthogonal frequency code division multiple access (OFCDMA) system is one of the most promising multi-user wireless communications systems. It outperforms orthogonal frequency division multiplexing (OFDM) and multi-carrier CDMA (MC-CDMA) through utilisation of two-dimensional spreading. This study proposes a downlink air interface that targets data rate increase and bit error rate (BER) performance enhancement with low complexity receiver. The proposed system is an integration of space-time spreading (STS) and OFCDMA that exploits transmit diversity needed for BER enhancing and data rate boosting with low complexity advantage. Further BER improvement was achieved using an effective iterative interference cancellation (IIC) algorithm at the receiver. Analytical and complexity analyses for the proposed system performance are presented in addition to simulation results. The proposed system attains better performance with lower complexity compared to the STS-aided direct sequence MC-CDMA that uses beamforming as a closed-loop transmit diversity. Moreover, the effect of frequency domain spreading factor with different number of iteration loops is investigated. The achieved BER performance was very close to maximal ratio receive combining system with 1Tx and 4Rx. A considerable improvement was obtained by increasing the number of IIC iteration loops. The system performance was enhanced significantly with the frequency domain spreading factor increase.

EV-do revision C: Evolution of the cdma2000* data optimized system to higher spectral efficiencies and enhanced services

Wireless packet data services are poised to be a major growth area, as wireless voice services have reached a fair level of maturity. An effort by the 3rd Generation Partnership Project 2 (3GPP2) standards body to continue to develop the successful data-optimized 1x EV-DO high rate packet data (HRPD) 3G system is under way. Alcatel-Lucent along with partners is proposing several novel techniques beyond the state of the art. Some of the key technologies are orthogonal frequency code division multiple access (OFCDMA), multi-carrier as well as wideband transmission, both frequency division duplex (FDD) and time division duplex (TDD) modes, multiple antenna techniques such as space division multiple access (SDMA) and multiple input multiple output (MIMO), interference mitigation techniques, and frequency domain interference cancellation. These are described in detail along with the resulting benefits. The design goals are to provide flexibility, backward compatibility (both loose and strict), a boost in the spectral efficiency and peak rates, a reduction in latency for real-time services, and a reduction in complexity in the base stations (BS) and mobile stations (MS). In this paper, we describe the underlying design philosophy and the associated technologies of 1x EV-DO Revision C with a focus on Alcatel-Lucent's contribution and provide associated performance results. The standard is expected to be completed in 2Q 2007. © 2007 Alcatel-Lucent.

A Ferroelectric-Capacitor-Based Tunable Matching Network for Quad-Band Cellular Power Amplifiers

A tunable matching network (TMN) based on ferroelectric capacitors for cellular power-amplifier applications was designed, fabricated, and tested. When the matching network is operated for GSM850/900 frequency bands, the input impedance varied from 3.44-j1.87 to 3.55-j0.02 Omega with a power gain variation of -1.35 to -1.62 dB. When the circuit is operated for digital communication system/personal communication system/wideband code division multiple access frequency bands, the input impedance varied from 4.28-j0.06 to 4.31+j0.97 Omega with a power gain variation of -2.05 to -1.79 dB. The nonlinearity of the TMN was also characterized on an on-wafer load-pull system using a 1.95-GHz test signal with CDMA2000 and high-speed downlink packet access modulation strings