Frequency Hopping Code-division Multiple-access System Research Articles

Two classes of optimal frequency-hopping sequences with new parameters

Direct-sequence spread spectrum and frequency-hopping (FH) spread spectrum are two main spread-coding technologies. Frequency-hopping sequences (FHSs) achieving the well-known Lempel–Greenberger bound play an important part in FH code-division multiple-access systems. Our objective is to construct more FHSs with new parameters attaining the above bound. In this paper, two classes of FHSs are proposed by means of two partitions of $${{\mathbb {Z}}_{v}}$$ , where v is an odd positive integer. It is shown that all the constructed FHSs are optimal with respect to the Lempel–Greenberger bound. By choosing appropriate injective functions, infinitely many optimal FHSs can be recursively obtained. Above all, these FHSs have new parameters which are not covered in the former literature.

Chip-Level Detection in Optical Frequency Hopping Code Division Multiple Access

In this paper we propose a chip-level receiver for optical frequency hopping code-division multiple-access (FH-OCDMA) systems. The proposed chip-level receiver for FH-OCDMA consists of an arrayed waveguide grating (AWG), and photo-detector (PD) for each mark chip, and uses the principles of the chip-level receiver. We analyze the error rate performance of the FH-OCDMA system with the proposed chip-level receiver with treating APD noise, thermal noise, and multi-user interference (MUI) using a Gaussian approximation. We compare the performance of the proposed chip-level receiver to that of the conventional correlation receiver. We show that the proposed chip-level receiver has a better bit error probability and can accommodate more users than the conventional correlation receiver.

On the Cutoff Rates of a Multiclass OFFH-CDMA System

We consider an optical code-division multiple-access (OCDMA) network that supports multiple traffic classes. Each class has different processing gain and performance requirements. In this paper, a new method is proposed to analyze the cutoff rates for a multiclass, multirate optical frequency-hopping code-division multiple-access system using fiber Bragg gratings and direct detection. This approach exploits the linear structure of passive OCDMA systems and the nominal time required to accomplish the encoding-decoding operations in such systems. A system model is presented and analyzed, based on a newly introduced bit-overlap procedure. An expression for the cutoff rate of a single-class system is derived. In addition, for a multiclass system, an expression that relates the cutoff rates of the offered classes is introduced, and it is called the service curve. It is shown that for a required quality of service guarantee, a number of active users, and a given probability of hit, the system's data rate can be increased beyond the nominal limit imposed by the physical constraint of the encoder-decoder set.

Mobile frequency-hopping CDMA systems

Through analysis and simulation, a unified evaluation of the potential performance of both mobile peer-to-peer and sectorized cellular frequency-hopping code-division multiple-access (CDMA) systems is presented. The equivalent number of frequency channels and the minimum area-mean signal-to-noise ratio are defined and shown to be important parameters in understanding and predicting network capacity. The effects of spectral splatter are analyzed. Separated orthogonality is defined and shown to be useful in completely eliminating intracell or intrasector interference. Spatial diversity by postdetection rather than predetection combining is proposed and shown to be invaluable. Noncoherent demodulation by a frequency discriminator rather than parallel matched filters and envelope detectors is proposed and shown to be effective. It is shown that even without exploiting either its natural bandwidth advantage or power control, frequency-hopping CDMA provides a reverse-link capacity nearly the same as direct-sequence CDMA with realistic power-control imperfections.

Performance improvement of a frequency hopping-CDMA system utilizing memorized prior data

An algorithm for improving the stability and throughput of a frequency hopping code-division multiple-access system (FH-CDMA) is presented. The algorithm includes a multiple block transmission with error-detection block(s) and a logical AND-operation between previously received (erroneous but saved) data, and retransmitted data. The packet success probability of the new algorithm is formulated and the improvement in stability is shown in terms of the proportion of retransmission users in the system under various conditions, including the new packet generation probability, retransmission probability, different signal-to-noise ratio in the channel, and the number of blocks in a packet. The average drift of retransmission users and the analysis of the expected number of retransmissions were used to evaluate the stability performance of the retransmission strategy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Code Acquisition for a Frequency-Hopping System

Code acquisition for a frequency-hopping code-division multiple-access system using Reed-Solomon coding is investigated. The one-coincidence codes which minimize the user interference are shown to be well suited for initial synchronization but are less appropriate for regaining synchronism during transmission. A modified code construction is proposed, which has good capability of both startup and resynchronization.