A Direct Sequence Code-Division Multiple-Access Local Area Network Model

The United States Air Force relies heavily on computer networks for every-day operations. The medium access control (MAC) protocol currently used by most local area (LAN) permits a single station to access the network at a time (e.g. CSMA/CD or Ethernet). This limits network throughput to, at most, the maximum transmission rate of a single node with overhead neglected. Significant delays are observed when a LAN is overloaded by multiple users attempting to access the common medium. In CSMA/CD, collisions are detected and the data sent by the nodes involved are delayed and transmitted at a later time. The retransmission time is determined with a binary exponential back-off-algorithm. Code Division Multiple Access (CDMA) is a technique that increases channel capacity by allowing multiple signals to occupy the same bandwidth simultaneously. Each signal is spread through multiplication with a unique pseudo-random code that distinguishes it from all other signals. Upon reception, the signal of interest is despread and separated from other incoming signals by multiplying it with the same exact code. With this technique, it is possible for multiple stations to transmit simultaneously with minimal ill effects. A simulation model is developed for a direct sequence spread spectrum CDMA (DS/CDMA) channel that incorporates the effects of multiple access interferers (MAI) having spreading codes from the same or different code families. The model introduces cross-correlation coefficients to calculate the signal-to-interference ratio and determine channel bit error performance. Transmission media attenuation and the near-far effects are accounted for in the model design. The model utility is demonstrated by determining the loss characteristics of a coaxial spread spectrum network. Due to the modular design, other transmission media characteristic can be easily incorporated. A bus network topology is simulated using 10Base2 coaxial cable. The model is compared and validated against a spread spectrum local area network hardware test bed

Some aspects of a code division multiple access local area network

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Using Direct-Sequenced Spread Spectrum in a Wired Local Area Network

Code division multiple access provides an ability to share channel bandwidth amongst users at the same time. Individual user performance is not degraded with the addition of more users, unlike traditional Ethernet. Using direct sequenced spread spectrum in a wired local area network, network performance is improved. For a network in overload conditions, individual station throughput is increased by nearly 212% while mean end-to-end delay was reduced by 800%. The vast improvement demonstrated by this research has the capability to extend legacy-cabling infrastructures for many years to come while easily accommodating new bandwidth intensive multimedia applications

Selective mode excitation in SCM-OCDMA

A six-channel 2.4GHz subcarrier multiplexing - optical code division multiple access (SCM-OCDMA) system in conjunction with the selective excitation of LP01 and LP02 modes is presented for a multimode fiber Local Area Network. Simulation results demonstrate that mode selectivity increases the bandwidth-distance product and improves the BER performance of the channel

Development of User-Interface Software Program for Double Weight Code Family for OCDMA

Optical Code Division Multiple Access (OCDMA) offers high statistical multiplexing gain in a busty traffic environment and is thought to be a more suitable solution in local-area network. There have been many codes proposed OCDMA systems, such as Hadamard code, Modified Frequency Hopping (MFH) code and Double Weight (DW) code family. The inspiration of this study is to improve the Modified Double Weight (MDW) code to give a better performance and to enhance the detection technique of DW code family. There are few aspects that have been identified in this study. First of all, the construction of MDW code is studied. Besides, the equation-based construction technique is examined and is then simulated using Virtual Basic software version 6.0. The findings of the project will lead to a new development of the MDW code by having new user-interface software program to generate the DW codeword with an ease

Importance of Fifth Generation Wireless Systems

Fifth generation wireless communications are denoted by 5G technology. 5G schemes are coming from first generation analog communication, 2G of Global System for Mobile communication (GSM), then 3G of Code Division Multiple Access (CDMA), after that fourth generation of long-term evaluation (LTE), and now fifth generation World Wide Wireless Web (WWWW). This research investigation presents issues, challenges, and the importance of 5G Wifi communication. In the 5G digital cellular network, the coverage area of the service providers is separated into small area called cells. All the audio, video, and image files are digitized and converted by an ADC (Analog to Digital Converter) and transmitted through stream of bits. 5G wireless devices are communicated using radio waves in a geographically reusable common pool of frequency band. Using wireless backhaul connection, the local antennas are connected with the internet/telephone network. Spectrum speed is substantially higher in millimeter wave. Hence, this was considered in this work

Multi-User Detection for the Optical Code Division Multiple Access (OCDMA): Optical Parallel Interference Cancellation (OPIC)

Optical Code Division Multiple Access (OCDMA) has recently been proposed as an alternative to frequency and time based multiple access methods for the next generation high-speed optical fiber networks. This is because such system offers a large bandwidth. Based on the vast amount of bandwidth available in optical line, OCDMA system has received much attention in fiber optic Local Area Network (LAN) where the traffic is typically bursty. However, Multiple Access Interference (MAl), which is originated from other simultaneous users, severely limits the capacity of the system. In addition, the need for dynamic threshold in the Conventional Correlation Receiver (CCR) is a very demanding requirement particularly in the high speed LANs. To overcome the stated problems, Optical Parallel Interference Cancellation is used throughout this thesis. Optical Hard Limiter (OHL) has been placed at the front of the OPIC receiver to reduce the effect of MAl and fixed threshold is used to overcome the problem of dynamic threshold. The study carried out using theoretical and simulation. The results reveal that, OPJC system is attractive technology for next generation optical networks. The drawback of OPIC is the increases in the demand for hardware in each receiver. As a result, it requires more complex hardware, higher processing time and cost. To overcome these difficulties, an efficient method is proposed called, One Stage Optical Parallel Interference Cancellation (OS-OPIC) which is based mainly on the OPIC. Performance analysis of the proposed design is done using Optical Orthogonal Code (OOC) as a signature sequence and a new expression for error probability is demonstrated. It is shown that, the proposed method is effective to reduce the hardware complexity, processing time and cost while maintaining the same BER at the cost of increasing threshold value

COSSAP simulation model of DS-CDMA indoor microwave ATM LAN

This thesis presents an original work in the area of designing and implementing a simulation testbed for modelling a high speed spread spectrum Asynchronous Transfer Mode (ATM) Local Area Network (LAN). The spread spectrum technique used in this LAN model is Direct Sequence Code Division Multiple Access (DS-CDMA). The simulation model includes at least a physical layer of such a LAN, embedded into the COSSAP1 simulation environment, and has been fully tested. All the newly developed building blocks are comprised of standard blocks from the COSSAP libraries or compatible user-built primitive blocks (only where it is absolutely necessary), and are flexible enough to allow the modification of simulation or model parameters; such as the number of signal channels, modulation method used, different spreading code sequences and so on. All these changes can be made with minimal effort. Another significant contribution made in this thesis is the extended research into evaluating the Bit Error Rate (BER) performance of different spread spectrum COMA coding schemes for an indoor microwave A1M LAN [8]. Different spread spectrum CDMA coding schemes are compared for their transmission error rate in Additive White Gaussian Noise (AWGN) channel with varying transmitted signal power and at different channel Signal to Noise Ratio (SNR) levels. Since a wireless microwave channel is very prone to transmission errors, a major contribution of the simulation testbed developed in this thesis is its use in the finding of an optimal physical layer transmission scheme with the best Bit Error Rate (BER) performance in an indoor environment

A NOVEL CONSTRUCTION OF VECTOR COMBINATORIAL (VC) CODE FAMILIES AND DETECTION SCHEME FOR SAC OCDMA SYSTEMS

There has been growing interests in using optical code division multiple access (OCDMA) systems for the next generation high-speed optical fiber networks. The advantage of spectral amplitude coding (SAC-OCDMA) over conventional OCDMA systems is that, when using appropriate detection technique, the multiple access interference (MAI) can totally be canceled. The motivation of this research is to develop new code families to enhance the overall performance of optical OCDMA systems. Four aspects are tackled in this research. Firstly, a comprehensive discussion takes place on all important aspects of existing codes from advantages and disadvantages point of view. Two algorithms are proposed to construct several code families namely Vector Combinatorial (VC). Secondly, a new detection technique based on exclusive-OR (XOR) logic is developed and compared to the reported detection techniques. Thirdly, a software simulation for SAC OCDMA system with the VC families using a commercial optical system, Virtual Photonic Instrument, “VPITM TransmissionMaker 7.1” is conducted. Finally, an extensive investigation to study and characterize the VC-OCDMA in local area network (LAN) is conducted. For the performance analysis, the effects of phase-induced intensity noise (PIIN), shot noise, and thermal noise are considered simultaneously. The performances of the system compared to reported systems were characterized by referring to the signal to noise ratio (SNR), the bit error rate (BER) and the effective power (Psr). Numerical results show that, an acceptable BER of 10−9 was achieved by the VC codes with 120 active users while a much better performance can be achieved when the effective received power Psr > -26 dBm. In particular, the BER can be significantly improved when the VC optimal channel spacing width is carefully selected; best performance occurs at a spacing bandwidth between 0.8 and 1 nm. The simulation results indicate that VC code has a superior performance compared to other reported codes for the same transmission quality. It is also found that for a transmitted power at 0 dBm, the BER specified by eye diagrams patterns are 10-14 and 10-5 for VC and Modified Quadratic Congruence (MQC) codes respectively