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The foundations of the digital wireless world : selected works of A J Viterbi
\"Professor Andrew J. Viterbi has been extremely influential in the communications field via his invention of the Viterbi Algorithm, and his championing of CDMA technology developed by his company Qualcomm Inc. This book presents a selection of papers personally selected by him to mark his key technical contributions and his thoughts on CDMA technology as it evolved.\"--Jacket.
Book
Visible-Light CDMA Communications Using Inverted Spread Sequences
Visible-light communication (VLC) using light-emitting diodes (LEDs) is gaining attention in the wireless communication field. LEDs can be used as data transmitters without losing their main functionality as lighting devices. In some VLC applications, such as traffic signs and road signals in intelligent transportation systems, high brightness is required to help people recognize the signs and signals conveyed by the light sources. In this paper, the use of inverted modified prime sequence codes (MPSCs) is shown to be efficient for increasing brightness in an optical code-division multiple access (CDMA) system for VLC, while the original MPSCs, namely non-inverted codes, provide much lower brightness. The average light intensity of a system using an inverted MPSC is several times the intensity of a system using an original MPSC, without losing the capabilities of channel multiplexing and multi-user interference canceling. Average light intensity and normalized fluctuation are investigated for the optical CDMA systems with the original and inverted MPSCs. The results show that the systems with the inverted MPSCs provide higher average light intensity and lower normalized fluctuation than the systems with the original MPSCs do. Moreover, the bit error rates of the systems with the inverted MPSCs are evaluated by computer simulation and compared with those of the systems with the original MPSCs.
Journal Article
Application of Semiconductor Optical Amplifier (SOA) in Managing Chirp of Optical Code Division Multiple Access (OCDMA) Code Carriers in Temperature Affected Fibre Link
Chromatic and temperature induced dispersion can both severely affect incoherent high data rate communications in optical fibre. This is certainly also true for incoherent optical code division multiple access (OCDMA) systems with multi-wavelength picosecond code carriers. Here, even a relatively small deviation from a fully dispersion compensated transmission link can strongly impact the overall system performance, the number of simultaneous users, and the system cardinality due to the recovered OCDMA auto-correlation being strongly distorted, time-skewed, and having its full width at half maximum (FWHM) value changed. It is therefore imperative to have a simple tunable means for controlling fibre chromatic or temperature induced dispersion with high sub-picosecond accuracy. To help address this issue, we have investigated experimentally and by simulations the use of a semiconductor optical amplifier (SOA) for its ability to control the chirp of the passing optical signal (OCDMA codes) and to exploit the SOA ability for dispersion management of a fibre link in an incoherent OCDMA system. Our investigation is done using a 19.5 km long fibre transmission link that is exposed to different temperatures (20 °C and 50 °C) using an environmental chamber. By placing the SOA on a transmission site and using it to manipulate the code carrier’s chirp via SOA bias adjustments, we have shown that this approach can successfully control the overall fibre link dispersion, and it can also mitigate the impact on the received OCDMA auto-correlation and its FWHM. The experimental data obtained are in a very good agreement with our simulation results.
Journal Article
Capacity Enhancement for Free Space Optics Transmission System Using Orbital Angular Momentum Optical Code Division Multiple Access in 5G and beyond Networks
This paper introduces a novel free space optics (FSO) communication system for future-generation high-speed networks. The proposed system integrates orbital angular momentum (OAM) modes with an optical code division multiple access (OCDMA) technique. Two OAM beams are used (LG0,0 and LG0,10), each of which is used for transmitting three independent channels. Each channel is assigned by fixed right shift (FRS) codes and carries 10 Gbps of information data. The performance of the proposed model is evaluated under different foggy and dust storm conditions. Furthermore, the performance of two cities with different geographical locations, Alexandria city in Egypt and Srinagar city in India, is investigated to demonstrate its ability to be implemented in future generations. Bit error rate (BER), eye diagrams, received optical power (ROP), and channel capacity are used for studying the performance of the proposed system. The observed simulation results show successful transmission of 60 Gbps overall capacity with the longest propagation FSO range for Alexandria city, which is 1400 m. Because dust storms have a large attenuation when compared to different foggy conditions, the proposed model had the shortest propagation range of 315 m under low dust (LD), 105 m under moderate dust (MD), and 40 m under heavy dust (HD). Furthermore, the cloudy weather conditions that affect Srinagar city, which is considered a hilly area, make our suggested model achieve 1000 m.
Journal Article
3D Indoor Positioning of UAVs with Spread Spectrum Ultrasound and Time-of-Flight Cameras
This work proposes the use of a hybrid acoustic and optical indoor positioning system for the accurate 3D positioning of Unmanned Aerial Vehicles (UAVs). The acoustic module of this system is based on a Time-Code Division Multiple Access (T-CDMA) scheme, where the sequential emission of five spread spectrum ultrasonic codes is performed to compute the horizontal vehicle position following a 2D multilateration procedure. The optical module is based on a Time-Of-Flight (TOF) camera that provides an initial estimation for the vehicle height. A recursive algorithm programmed on an external computer is then proposed to refine the estimated position. Experimental results show that the proposed system can increase the accuracy of a solely acoustic system by 70–80% in terms of positioning mean square error.
Journal Article
Optimal power allocation and relay selection for multiple code division multiple access peer-to-peer communication
The authors consider a half-duplex asynchronous code division multiple access cooperative network with N source–destination (SD) pairs and a number of relay nodes where the nodes of all pairs have to exchange data in two hops via assistance of one of the available relays. In this study, they minimise the total transmit power and derive the closed-form solution for choosing the best relay, the best relay gain and the transmit powers of all sources where some predefined signal-to-interference plus noise-ratios (SINRs) are guaranteed. Interestingly, the feasibility condition of the problem depends only on the required SINRs, the number of SD pairs and the maximum cross-correlation of users’ codes. They suggest two control procedures for admitting or dropping of users to the network to satisfy the feasibility condition. For a reciprocal environment, the best relay and its gain are proved to remain unchanged for reversing the communication directions. In addition, the authors’ power control algorithm can be directly applied to the case of two-hop two-way relaying. Computer simulations are used to demonstrate the system performance.
Journal Article
SAC-OCDMA system performance using narrowband Bragg filter encoders and decoders
In this paper, we have studied a Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system performance using fiber Bragg gratings equivalent to very narrow filters used in the system as encoders and decoders in both the transmitter and the receiver block. The system performance depends on several variables such as: the optical power; the fiber length; the data rate and the bandwidth. Different simulations have been realized in terms of the bit error rate (BER) and the quality factor (Q) to evaluate the effect of each parameter on the system performance and also to examine the impact of number of users. The obtained results using Optisystem network show clearly that the studied SAC-OCDMA system of three users remains efficient for fiber lengths up to 25 km at a data rate of 200 Mbits/s and a FBGs bandwidth of 0.6 nm. These results are realized with an acceptable bit error rate
B
E
R
<
10
-
9
. In addition, a SAC-OCDMA system of 9 users was also simulated to assess the effect of the number of users. The results obtained show that for a fiber length
L
=
5
Km, the system remains efficient for a number of users set at 8 users, then the longer the fiber length increases the more the number of possible users decreases. For
L
=
35
Km, the number of users for whom all users obtain a good BER value is 6 users.
Journal Article
Coded downlink MIMO MC-CDMA system for cognitive radio network: performance results
In this letter, the error-rate (ER) performance of multiple input and multiple output multi-carrier code-division-multiple-access (MIMO MC-CDMA) is evaluated with the aid of cognitive radio network (CRN). MIMO is proven to be useful for high data rate application. MC-CDMA is used to accommodate higher number of user by eliminating channel impairments. CRN is suggested for 5G network to offer higher bandwidth by exposing idle spectrum. Multi-carrier modulation is processed inverse fast-Fourier transform at transmitter and demodulation at each receiver using fast-Fourier transform. Multi-carrier technique is introduced to obtain bandwidth efficiency and overcome the problem of frequency selectivity. At each mobile station, we estimate user’s information using MMSE based iterative algorithm. Further; the system performance is tested using channel encoder. We structure channel encoder using turbo code which is designed with the help of two convolutional encoder. The input information is interleaved using random interleaver and is fed to second convolutional encoder. We create puncturing matrix using input information and output of two convolutional encoders. Then we puncture parity bit information to obtain necessary code rate. Further, we decode and estimate information using iterative decoder which ensure higher performance with lower signal-to-noise ratio. It is vindicated from simulations that CRN based MIMO MC-CDMA system with iterative decoder swell better ER while ensuring higher data rate for downlink signal transmission.
Journal Article
Performance of adaptive MIMO switching for cognitive MC-CDMA system
The future 5G wireless network will be identified by flexibility design, high combination of services, and higher data rate. In this treatise, we present the performance evaluation physical layer design for multi-carrier code-division-multiple-access (MC-CDMA) system for cognitive radio network (CRN) employing link adaptive multiple-input multiple- output (MIMO). CRN in conjunction with MIMO promises to achieve massive amelioration in system bandwidth. We consider link adaption scheme (LAS) which will select modulation scheme and MIMO profile based on channel parameters. CRN is a device in wireless communication which can sense the idle unused spectrum and allocate the spectrum dynamically to base station. We utilize sub-band frequency of CRN for multi-carrier communication and to extract for user-specific spreader in CDMA system. Further, we realize iterative decoder at the receiver to achieve better error-rate performance for CRN based MIMO MC-CDMA system with less signal-to-noise ratio (SNR). Furthermore,We study the performance of adaptive MIMO scheme with CRN defined MC-CDMA for Stanford University Interim channel model specifications. We discern through computer simulations that CRN based MC-CDMA system with adaptive MIMO scheme achieves significant performance enhancement both in error-rate and data rate.
Journal Article
Empirical Evaluation of High-speed Cost-effective Ro-FSO System by Incorporating OCDMA-PDM Scheme under the Presence of Fog
Radio over free space optics (Ro-FSO) innovation saddles the vast limit of optical fiber and the portability from local to remote systems. To enhance the capacity of Ro-FSO systems without compromising the bandwidth, this work incorporates use of hybrid polarization division multiplexing (PDM) with optical code division multiplexing (OCDMA) schemes. Due to low deployment time and support cost, the vast majority of the current optical network application systems adopts free space optics (FSO) as the elective answer for suitably supplanting fiber optical cable. This study has incorporated PDM and OCDMA schemes to design a 50 Gbps Ro-FSO link. Ten channels, each with 5 Gbps of data, are transported via FSO link of 3500 m. In addition, the proposed PDM-OCDMA-Ro-FSO link is evaluated under various atmospheric commotions.
Journal Article