High Chip Rate Research Articles

Effect of Polarization Mode Dispersion on the BER Performance of Optical CDMA

In this paper, impact of polarization mode dispersion (PMD) on the bit error rate (BER) performance of direct sequence optical code division multiple access with in-line optical amplifiers is analytically investigated. Intensity modulation direct detection technique is employed in optical correlator receiver. Optical orthogonal codes are used as address sequence. The system BER performance is determined in presence of PMD and different noises induced from receiver, optical amplifiers, and multiple access interference. The power penalty suffered by the system is evaluated at BER of 10 -9 . It is found that the BER performance of the proposed system degraded more at high chip rate, chirp parameter and long fiber length due to the effect of PMD. Further, the BER performance of the proposed system is studied in presence of PMD compensation with frequency advanced higher order PMD vectors. The results demonstrate that the system BER performance is improved significantly for a particular fiber length and third-order PMD compensation technique shows better performance compared to first-, and second-order compensations.

Direct P-Code Acquisition Technique Based on the Data Resource Pool

In GPS system, the P-code can offer higher accuracy and better anti-jamming property than C/A code. However, the direct P-code acquisition is difficult as its long period and high chip rate. To solve the problem, the idea of expanding the code sequence to a three-dimensional space is put forward. The concept of data resource pool is defined, and the fast direct P code acquisition technique based on the data resource pool is proposed to improve the acquisition efficiency. By effect compression, the acquisition technique can enlarge the uncertainty search coverage and accelerate the search process. Furthermore, the technique based on the data resource pool can get different sub-algorithms according to the different compression method. The simulation results show that the proposed technique can achieve fast direct P code acquisition by the reasonable choice of compression parameters and the compression mode of code sequence.

Mapping and overlapping based carrier frequency searching technique for rapid GNSS long PN-code acquisition

In global navigation satellite systems (GNSS), because of the long period and high chip rate of long pseudo-noise (PN) code, the rapid acquisition is hard to accomplish. To speed up search process, in the paper, a mapping and overlapping based carrier frequency searching technique is proposed. By mapping incoming signals of the same interval to different carrier frequency cells and overlapping together the mapped incoming signals that correspond to the same code phase, the technique reduces the number of the cells to be searched. The effect of the technique on detection and mean acquisition time performance is analyzed. It is shown that the technique reduces the cells to be searched and shortens mean acquisition time at the expense of degrading detection performance. The technique is fit to the previously published acquisition methods and is capable of improving their mean acquisition time performance. Numerical and simulation results validate the analysis.

Generalized zero-padding scheme for direct GPS P-code acquisition

Because of the long period and high chip rate of GPS P-code, direct acquisition is challenging. In the letter, the widely used zero-padding scheme (ZPS) for direct GPS P-code acquisition is generalized to investigate the effects of the ZPS on detection performance, parallel searching capability, and mean acquisition time. It is shown that, by adjusting the zeros padded to received signal according to signal to noise ratio, the generalized zero-padding scheme (GZPS) makes a better tradeoff between detection performance and parallel searching capability and further reduces mean acquisition time. The generalized zero-padding scheme can be easily applied to the previously proposed zero-padding method (ZPM) and the direct average method (DAM) to improve their mean acquisition time performance and it does not increase the implementation complexity of a receiver.

Mathematical modelling and performance analysis for average-based rapid search method for direct global position system precision code acquisition

Direct global position system precision code acquisition is desirable for providing stronger anti-jamming and anti-spoofing capabilities than the handover from a coarse acquisition code. Because of the high chip rate and long period of the precision code (P-code), direct acquisition is challenging. By averaging incoming and local signals respectively, to reduce the number of code phases to be searched, previously proposed direct and overlap average methods provide an efficient way to rapid acquisition. To further analyse the performance of average methods the previously proposed direct and overlap average methods are generalised, the corresponding mathematical modelling is established, the correlation properties of the averaged P-code are studied and the detection and mean acquisition time performances are investigated. By increasing the weighting of the local signal, which has a code phase shift in samples of half of the average length, improved overlap average methods are proposed. Compared with the previously proposed direct and overlap average methods, the improved overlap average methods have better detection performance and can further improve acquisition performance, that is, shorten the mean acquisition time. Numerical results demonstrate the enhancement.

Analyses of constraints on high speed optical code division multiplexing access (OCDMA) link parameters due to fiber optic chromatic dispersion

In direct sequence-optical code division multiplexing access (DS-OCDMA) system networks, data rate and data spreading technique involved in such systems require a high chip rate. Transmission link in these systems is significantly affected by the fiber chromatic dispersion. In this study, we have developed and employed a simple model to estimate the G652 fiber dispersion effects. OCDMA technique has been employed to investigate fiber chromatic dispersion effects on multiple access interference (MAI). We have found that, at a short optical fiber length, the optical fiber dispersion has a significant impact on the high data rate transmission systems (higher than 750Mbit/s). The performance and optimization of optical orthogonal code (OOC) in the OCDMA system is reported. We have demonstrated that, for a high data rate, even if dispersion compensated devices are not deployed, the BER can be significantly improved when the OOC desired length is selected. We have shown that when compensation dispersion devices are not deployed in the system, there is a trade off between the limited dispersion effects and the MAI.

Spreading Code Selection for Multiple Chip Rate DS-CDMA Systems

In this paper, we analyze the interuser interference (IUI) in multiple chip rate (MCR) direct-sequence code-division multiple-access (DS-CDMA) systems employing realistic chip waveforms. In MCR DS-CDMA systems, different users may have different chip rates, which makes IUI unavoidable even if the employed spreading codes are orthogonal. Here, we consider orthogonal variable spreading factor (OVSF) codes and random spreading codes. We find that the spreading code of the low chip rate user does not affect the IUI at all. The IUI depends only on the bit patterns of the high chip rate user corresponding to one chip duration of the low chip rate user and on the carrier frequency separation of the users. We provide a closed-form equation for the IUI power of random codes, and we show that a judicious choice of the spreading codes can reduce the IUI significantly for OVSF codes.

Hybrid TDOA/AOA mobile user location for wideband CDMA cellular systems

This paper proposes a mobile user location scheme for wideband code-division multiple-access (CDMA) wireless communication systems. To achieve high location accuracy and low cost of the mobile receiver, the location scheme combines the time difference of arrival (TDOA) measurements from the forward link pilot signals with the angle of arrival (AOA) measurement from the reverse link pilot signal. High chip rates in wideband CDMA systems facilitate accurate TDOA measurements, and a smart antenna used at the home base station (BS) can provide accurate AOA measurement in a macrocell environment. A two-step least square location estimator is developed based on a linear form of the AOA equation in the small error region. Numerical results demonstrate that the proposed hybrid TDOA/AOA location scheme gives a much higher location accuracy than TDOA only location, when the number of base stations is small and/or when the TDOA measurements have a relatively poor accuracy.

On the feasibility of a 2-Mb/s bearer service in a future cellular radio system using code-division multiple access

The universal mobile telecommunications system (UMTS) and other third-generation mobile radio systems will be required to support data rates up to 2 Mb/s. This paper examines whether a direct-sequence spread-spectrum air interface can support such a high data rate in an outdoor environment. A mathematical analysis of the operation of a RAKE receiver is presented. Monte-Carlo methods are used to establish the probability that a 2-Mb/s link is possible and the proportion of system capacity such a link would consume. It is concluded that with sufficiently complex RAKE receivers and a high enough chip rate, it is certainly practical for a direct-sequence code-division multiple-access (DS-CDMA) mobile radio system to offer a 2-Mb/s service and that the overall spectrum efficiency will be high provided that the majority of users of the system use much lower data rates.

A noise whitening approach to multiple-access noise rejection .II. Implementation issues

Several practical methods are proposed for the implementation of linear filters that reject multiple-access noise in direct sequence code-division multiple-access (DS-CDMA) receivers. These methods rely on taking advantage of variations in the received chip spectrum, and do not require locking and despreading multiple signals. The resulting structures are simple, and some can operate at a high chip rate. Adaptive structures are also proposed. It is shown that a close relationship exists between noise whitening and chip-equalization for a DS-CDMA receiver. System issues affecting the choice of the chip spectrum, and thus the applicability of these methods, are described.

Effect of system imperfections on BER performance of a CDMA receiver with multipath diversity combining

The bit error rate performance of a high chip rate, indoor code division multiple access multipath combining receiver with imperfections in power control, estimation of channel parameters (path amplitude and phase), and estimation of spreading code phase is analyzed. Imperfection in power control is taken into account by modeling the received signal power as a log normally distributed random variable. The estimate errors are modeled as zero mean Gaussian random variables. It is shown that the performance of such a receiver degrades when the variance of power control imperfection is above 0 dB, mean square error in channel parameter estimation is above 0.01, or standard deviation of the code phase error is above 0.1.