Performance of parallel combinatorial CDMA systems with side information

This paper proposes an algorithm that improves the mean code acquisition time using an energy estimation mode (EEM) and dwell time values from direct-sequence spread spectrum (DS-SS) System. Until recently, DS-SS System has been used in many areas from Wireless LAN, cellular phone, and GPS to telecommunication. Meanwhile, the development of reducing of pseudonoise (PN) code acquisition time, the core technique of DS-SS system, is continuously explored. The algorithm in this paper added the EEM before a search mode (SM) from the conventional PN code acquisition system, which is composed of a SM and a verification mode (VM). In the EEM, dwell time and threshold values are determined for use in the SM and the VM depending on the correlation energy. This paper applies the proposed technique under Rayleigh-fading channel in performing a simulation of PN code acquisition time by a mathematical modeling to evaluate the proposed algorithm. Numerical results show that the proposed method improves the detection performance and the rejection performance of false code phases not only in the VM but also in the SM. Furthermore, the proposed algorithm reduces the mean code acquisition time by maximum 29% than the conventional algorithm.

This paper presents performance evaluation and comparison analysis of Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) systems. The evaluation and analysis are done based on the systems performance against wideband interferences. The interferences are signals with similar spectrum characteristic to the transmitted signals of DSSS and FHSS systems. Bit Error Ratio (BER) is used as evaluation parameter to assess the performance of both systems. Simulation and mathematical analysis are performed to test and verify the performance of both systems. Mathematical analysis also verifies that increasing Spreading Frequency on certain conditions will reduce the BER. This research also points out that FHSS system has a better performance compared to DSSS system indicated by smaller BER.

This paper presents a novel technique to save the transmitting power of spread-spectrum communication systems based on the application of delay diversity. The core idea of this delay-diversity system is to delay two spreading sequences that carry the same information of a bit with respect to each other in order to statistically separate the influence of fading on the same bit in time domain. The theoretical bit error rate (BER) expression of the proposed system is derived and verified by simulations. According to the numerical results, it is found that this technique save significant amount of transmitting power, and it may be used to extend the life-time of energy-constrained devices such as sensor nodes in wireless sensor networks.

We analyzed the bit error probability of a single RS codeword with symbol overlapping. By symbol overlapping, we mean that the bits in each modulation symbol can belong to 2 or more RS symbols and vice versa. We propose two novel designs for Reed-Solomon (RS) coded modulation with symbol overlapping. For an RS code with symbol size GF(2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> ), the information bits are first RS coded. For the first strategy, the coded bits are matrix interleaved prior to modulation and for the second strategy, the RS symbols are matrix interleaved and the resulting coded symbols are shifted circularly by n/2 bits prior to modulation. In this paper, we considered a M = 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> -ary modulation scheme. The received signal is demodulated appropriately, de-interleaved and RS decoded. The decoded symbols are interleaved and sent to the demodulator where it makes use of the decoded symbols from other codewords to re-demodulate the signals. This process is repeated until there is no improvement in the bit error rate. It is observed that this simple coded modulation design scheme has about 0.5 dB better performance than one that does not employ symbol overlapping over an AWGN channel at bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . An improvement of 1 dB is observed over a Rayleigh fading channel

Under the software environment of MATLAB/Simulink, the communication system of direct sequence spread spectrum (DSSS) is dynamically modeled and simulated over a new practical Rayleigh channel, and the relationship curves of the bit error rate (BER) with the signal-to-noise ratio (SNR) of DSSS communication systems are presented. It is analyzed that DSSS system can effectively overcome multipath fading in multipath Rayleigh Fading Channel (RFC). In addition, the anti-multipath fading performance improved by the way of increasing pseudo noise (PN) code length is better than that by the way of increasing the spread spectrum gain in the condition of strong multipath fading.

In this paper, we theoretically analyse the influence by intersymbol interference (ISI) on the bit error rate (BER) performance of the spread spectrum (SS) system using a real-valued Huffman sequence whose aperiodic correlation function has zero sidelobes except at the left and right shift-ends, under the quasi-static Rayleigh fading environment. The system can give the unified communication and ranging system because the output of a matched filter (MF) is the ideal impulse by overlap of 1 chip. As a result, the BER performance of the system under the quasi-static Rayleigh fading environment is improved with decrease in the absolute value of the shift-end value, is not influenced by ISI if the shift-end value is almost zero-value.

The performance of anti narrowband noise of direct sequence spread spectrum (DSSS) communication system is investigated in this paper. The new result given in the paper shows that performance of anti noise in DSSS system is different from classic result. The attenuation of narrowband noise in DSSS system is the function of the relative distance between the narrowband noise and carrier frequency of DSSS system, and it is discontinuous. The attenuation of broadband noise is little, and the process gain is about 0.46dB. The results can be utilized in design and application of spread spectrum system.

Spread spectrum communication has good performances such as anti-noise, anti-interference and fast transmission rate, so it has been widely used in military communication and civil communication fields and others. The M-ary spread spectrum system has its unique advantages and strong practical application background with respect to direct sequence spread spectrum, and effectively solves the problem of limited bandwidth of direct spread spectrum. This paper firstly expounds the principle of traditional direct sequence spread spectrum system and then focuses on the research of the principle and system model of M-ary spread spectrum system. The error performance of M-ary spread spectrum system is also simulated and analyzed. The simulation results show that M-ary spread spectrum has a greater advantage in the bandwidth-constrained field, where high-speed data transmission is required and certain anti-noise capability is required.

In this paper, a fast convergent nonlinear adaptive algorithm for narrow-band interference rejection in direct sequence spread spectrum (DS-SS) systems is proposed. The new algorithm can significantly increase the convergence rate of the nonlinear adaptive filter by computer simulations.

Tone interference suppression in DS-SS systems with modified DFT

The study on the Doppler frequency search strategy in direct sequence spread spectrum (DSSS) systems has been addressed in this article. To reduce the estimation error and alleviate the possible false detection, a novel Doppler search algorithm that combines the serial-based search and the fuzzy-logic (FL)-based search is presented. At first, the serial-based search is used until the decision variable exceeds a preset threshold; the FL-based search is then performed for a second search and the final decision is made. In the second search stage, Doppler search step size is adaptively adjusted by an FL controller. To design a robust FL controller, the characteristics of the spectrum distribution and several possible abnormal conditions are analyzed, input and output fuzzy membership functions are derived, and a set of fuzzy rules is formulated. Finally, the effectiveness of the proposed approach is evaluated through Monte Carlo simulations. The obtained results show that a smaller estimation error is achieved when the proposed algorithm is used; further, reasonable mean acquisition times are attained compared with other existing search techniques. Furthermore, the proposed algorithm can alleviate possible false detection in the abnormal conditions.

The performance of the data-aided nonlinear filter (DNF), for combating narrowband interference (NBI) in direct sequence spread spectrum (DS-SS) systems, is analyzed. Closed-form analytical expressions for improvement in signal to interference-plus-noise ratio (SINR) are derived under the condition of single tone interference. Results show that the DNF structure outperforms conventional nonlinear prediction filter.

In this paper, we propose a new PAPR reduction by using a partial transmit sequences (PTS) method with coded side information (SI) technique. These methods are used in an orthogonal frequency division multiplexing (OFDM) system. The OFDM employs orthogonal sub-carriers for data modulation. These sub-carriers unexpectedly present a large peak to average power ratio (PAPR) in some cases. In order to reduce PAPR, the sequence of input data is partitioned into disjoint sub-block of PTS. If number of sub-block increases, high efficiency of PAPR reduction can be obtained. However, a quite large calculation cost must be demanded and thus it is impossible to obtain the optimum PTS. In the proposed method, we introduce a coded side information technique assuming the pseudo-optimum condition into the PTS. The total calculation cost becomes drastically reduced and side information bits for recovering original data in demodulation. In simulation results, the proposed method demonstrated the improvement of PAPR and bit error rate (BER) performance.

This paper presents a comparative study of the use of two modulation techniques for a fast frequency hopping (FFH) spread spectrum system for wireless communication over a non-selective Rayleigh fading channel. The modulation techniques considered are binary frequency shift keying (BFSK) and differential phase shift keying (DPSK). The comparison standard chosen is that of the signal-to-noise ratio (SNR) for achieving a given bit error rate (BER). It is found that DPSK is capable of giving a gain of about 3 dB over BFSK indicating the potential for employing DPSK for such a spread spectrum. A square law combiner for the case of DPSK has also been suggested.

Bit-error rate (BER) performance analyses are presented for Reed-Solomon coded fast frequency-hopping binary frequency-shift-keying (FFH/BFSK) spread-spectrum (SS) systems under the conditions of additive white Gaussian noise (AWGN) and the worst-case band multitone jamming (MTJ). The FFH system employs the soft-decision linear-combining receiver to obtain the diversity-combining output. The corresponding hard decision of the diversity-combining output is then used to decode the Reed-Solomon codes. The analytical expressions of the BER performance of the coded FFH systems are derived and shown to be applicable to higher diversity levels without much more computational complexity. Numerical results show that there is an optimum code rate for the Reed-Solomon coded system under the worst-case multitone jamming conditions.