Study of spread spectrum multiple access systems for satellite communications with overlay on current services

The feasibility of using spread spectrum techniques to provide a low-cost multiple access system for a very large number of low data terminals was investigated. Two applications of spread spectrum technology to very small aperture terminal (VSAT) satellite communication networks are presented. Two spread spectrum multiple access systems which use a form of noncoherent M-ary FSK (MFSK) as the primary modulation are described and the throughput analyzed. The analysis considers such factors as satellite power constraints and adjacent satellite interference. Also considered is the effect of on-board processing on the multiple access efficiency and the feasibility of overlaying low data rate spread spectrum signals on existing satellite traffic as a form of frequency reuse is investigated. The use of chirp is examined for spread spectrum communications. In a chirp communication system, each data bit is converted into one or more up or down sweeps of frequency, which spread the RF energy across a broad range of frequencies. Several different forms of chirp communication systems are considered, and a multiple-chirp coded system is proposed for overlay service. The mutual interference problem is examined in detail and a performance analysis undertaken for the case of a chirp data channel overlaid on a video channel

Performance Study of Hybrid Spread Spectrum Techniques

This thesis focuses on the performance analysis of hybrid direct sequence/slow frequency hopping (DS/SFH) and hybrid direct sequence/fast frequency hopping (DS/FFH) systems under multi-user interference and Rayleigh fading. First, we analyze the performance of direct sequence spread spectrum (DSSS), slow frequency hopping (SFH) and fast frequency hopping (FFH) systems for varying processing gains under interference environment assuming equal bandwidth constraint with Binary Phase Shift Keying (BPSK) modulation and synchronous system. After thorough literature survey, we show that hybrid DS/FFH systems outperform both SFH and hybrid DS/SFH systems under Rayleigh fading and multi-user interference. Also, both hybrid DS/SFH and hybrid DS/FFH show performance improvement with increasing spreading factor and decreasing number of hopping frequencies

Software Implementation of Orthogonal Frequency Division Multiplexing (OFDM)Scheme for Mobile Radio Channel

Orthogonal Frequency Division Multiplexing (OFDM) is a transmission technique which ensures efficient utilization of the spectrum by allowing overlap of carriers. OFDM is a combination of modulation and multiplexing that is used in the transmission of information and data. Compared with the other wireless transmission techniques like Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), OFDM has numerous advantages like high spectral density, its robustness to channel fading, its ability to overcome several radio impairment factors such as effect of AWGN, impulse noise, multipath fading, etc. Due to this it finds wide application in Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), and Wireless LAN. Most of the wireless LAN standards like IEEE 802.11a or IEEE 802.11g use the OFDM as the main multiplexing scheme for better use of spectrum. In fact in the 4G telecommunication system OFDMA is the backbone of it. This project deals with the software simulation of this OFDM system in a mobile radio channel using the software tools of MATLAB® and SIMULINK®. From this simulation the performance of OFDM system in mobile radio channel is studied. Apart from this we also compare the OFDM system performance with the performance of the DS-CDMA system in the mobile radio channel

Channel Estimation in Multicarrier Communication Systems

The data rate and spectrum efficiency of wireless mobile communications have been significantly improved over the last decade or so. Recently, the advanced systems such as 3GPP LTE and terrestrial digital TV broadcasting have been sophisticatedly developed using OFDM and CDMA technology. In general, most mobile communication systems transmit bits of information in the radio space to the receiver. The radio channels in mobile radio systems are usually multipath fading channels, which cause inter-symbol interference (ISI) in the received signal. To remove ISI from the signal, there is a need of strong equalizer which requires knowledge on the channel impulse response (CIR).This is primarily provided by a separate channel estimator. Usually the channel estimation is based on the known sequence of bits, which is unique for a certain transmitter and which is repeated in every transmission burst. Thus, the channel estimator is able to estimate CIR for each burst separately by exploiting the known transmitted bits and the corresponding received samples. In this thesis we investigate and compare various efficient channel estimation schemes for OFDM systems which can also be extended to MC DS-CDMA systems.The channel estimation can be performed by either inserting pilot tones into all subcarriers of OFDM symbols with a specific period or inserting pilot tones into each OFDM symbol. Two major types of pilot arrangement such as block type and comb type pilot have been focused employing Least Square Error (LSE) and Minimum Mean Square Error (MMSE) channel estimators. Block type pilot sub-carriers is especially suitable for slow-fading radio channels whereas comb type pilots provide better resistance to fast fading channels. Also comb type pilot arrangement is sensitive to frequency selectivity when comparing to block type arrangement. However, there is another supervised technique called Implicit Training (IT) based channel estimation which exploits the first order statistics in the received data, induced by superimposing periodic training sequences with good correlation properties, along with the information symbols. Hence, the need for additional time slots for training the equalizer is avoided. The performance of the estimators is presented in terms of the mean square estimation error (MSEE) and bit error rate (BER)

Co-Channel Interference Between IEEE 802.11 WLAN and Bluetooth

Electrical Engineering Technolog

Worst-Case Error Probability of a Spread-Spectrum System in Energy-Limited Interference

We consider a communication channel corrupted by thermal noise and by an unknown and arbitrary interference of bounded energy. For this channel, we derive a simple upper bound to the worst-case error probability suffered by a direct sequence (DS) communication system with error-correction coding, pseudorandom interleaving, and a correlation receiver. This bound is exponentially tight as the block length of the error correcting code becomes large. Numerical examples are given that illustrate the dependence of the bound on the choice of error correcting code, the type of interleaving used, and the relative energy of the Gaussian noise and arbitrary interferenc

Low Rate High Frequency Data Transmission from Very Remote Sensors

This chapter deals with the difficulties of transmitting data gathered from sensors placedin very remote areas where energy supplies are scarce. The data link is established bymeans of the ionosphere, a layer of the upper atmosphere that is ionized by solar radiation.Communications through the ionosphere have persisted, although the use of artificialrepeaters, such as satellites, has provided more reliable communication. In spite of beingrandom, noisy and susceptible to interference, ionospheric transmission still has favorablecharacteristics (e.g. low cost equipment, worldwide coverage, invulnerability, etc.) thatappeal to current communications engineering.The Research Group in Electromagnetism and Communications (GRECO) from La Salle -Universitat Ramon Llull (Spain) is investigating techniques for the improvement of remotesensing and skywave digital communications. The GRECO has focused its attention on thelink between Antarctica and Spain. The main objectives of this study are: to implementa long-haul oblique ionospheric sounder and to transmit data from sensors located at theSpanish Antarctic Station (SAS) Juan Carlos I to Spain.The SAS is located on Livingston Island (62.7◦S, 299.6◦E; geomagnetic latitude 52.6◦S) in theSouth Shetlands archipelago. Spanish research is focused on the study of the biological andgeological environment, and also the physical geography. Many of the research activitiesundertaken at the SAS collect data on temperature, position, magnetic field, height, etc.which is temporarily stored in data loggers on-site. Part of this data is then transmittedto research laboratories in Spain. Even though the SAS is only manned during the australsummer, data collection never stops. While the station is left unmanned, the sets of dataare stored in memory devices, and are not downloaded until the next Antarctic season. Theinformation that has to be analyzed in almost real-time is transmitted to Spain through asatellite link. The skywave digital communication system, presented here, is intended totransmit the information from the Antarctic sensors as a backup, or even as an alternativeto the satellite, without depending on other entities for support or funding.Antarctica is a continent of great scientific interest in terms of remote sensing experimentsrelated to physics and geology. Due to the peculiarities of Antarctica, some of theseexperiments cannot be conducted anywhere else on the Earth and this fact might obligethe researchers to transmit gathered data to laboratories placed on other continents for intensivestudy. Because of the remoteness of the transmitter placed at the SAS, the system suffers frompower restrictions mainly during austral winter. Therefore, maintaining the radio link, evenat a reduced throughput, is a challenge. One possible solution to increase data rate, withminimal power, is to improve the spectral efficiency of the physical layer of the radio linkwhile maintaining acceptable performance. The outcomes and conclusions of this researchwork may be extrapolated to other environments where communication is scarcely possibledue to economic or coverage problems. Therefore, the solutions presented in this study maybe adopted in other situations, such as communications in developing countries or inanyother remote area

Simulations of Implementation of Advanced Communication Technologies

Wireless communication systems have seen significant advancements with the introduction of 3G, 4G, and 5G mobile standards. Since the simulation of entire systems is complex and may not allow evaluation of the impact of individual techniques, this thesis presents techniques and results for simulating the performance of advanced signaling techniques used in 3G, 4G, and 5G systems, including Code division multiple access (CDMA), Multiple Input Multiple Output (MIMO) systems, and Low-Density Parity Check (LDPC) codes. One implementation issue that is explored is the use of quantized Analog to Digital Converter (ADC) outputs and their impact on system performance. Code division multiple access (CDMA) is a popular wireless technique, but its effectiveness is limited by factors such as multiple access interference (MAI) and the near far effect (NFE). The joint effect of sampling and quantization on the analog-digital converter (ADC) at the receiver\u27s front end has also been evaluated for different quantization bits. It has been demonstrated that 4 bits is the minimum ADC resolution sensitivity required for a reliable connection for a quantized signal with 3- and 6-dB power levels in noisy and interference-prone environments. The demand for high data rate, reliable transmission, low bit error rate, and maximum transmission with low power has increased in wireless systems. Multiple Input Multiple Output (MIMO) systems with multiple antennas at both the transmitter and receiver side can meet these requirements by exploiting diversity and multipath propagation. The focus of MIMO systems is on improving reliability and maximizing throughput. Performance analysis of single input single output (SISO), single input multiple output (SIMO), multiple input single output (MISO), and MIMO systems is conducted using Alamouti space time block code (STBC) and Maximum Ratio Combining (MRC) technique used for transmit and receive diversity for Rayleigh fading channel under AWGN environment for BPSK and QPSK modulation schemes. Spatial Multiplexing (SM) is used to enhance spectral efficiency without additional bandwidth and power requirements. Minimum mean square error (MMSE) method is used for signal detection at the receiver end due to its low complexity and better performance. The performance of MIMO SM technique is compared for different antenna configurations and modulation schemes, and the MMSE detector is employed at the receiving end. Advanced error correction techniques for channel coding are necessary to meet the demand for Mobile Internet in 5G wireless communications, particularly for the Internet of Things. Low Density Parity Check (LDPC) codes are used for error correction in 5G, offering high coding gain, high throughput, low latency, low power dissipation, low complexity, and rate compatibility. LDPC codes use base matrices of 5G New Radio (NR) for LDPC encoding, and a soft decision decoding algorithm is used for efficient Frame Error Rate (FER) performance. The performance of LDPC codes is assessed using a soft decision decoding layered message passing algorithm, with BPSK modulation and AWGN channel. Furthermore, the effects of quantization on LDPC codes are analyzed for both small and large numbers of quantization bits