Yutaka Jitsumatsu

CTH12-3: Gaussian Chip Waveform Together with Markovian Spreading Codes Improve BER Performance in Chip-Asynchronous CDMA Systems

Performance of chip-asynchronous DS/CDMA system depends on chip waveform as well as spread spectrum (SS) codes. In case of rectangular chip waveform, SS codes generated by a Markov chain were shown to improve bit error rate (BER) performance. However, in commercial CDMA systems, a band-limited root raised cosine (RRC) pulse is used, where the superiority of Markov codes is reduced. RRC pulse fulfills inter-chip interference (ICI)-free condition. In CDMA systems, multiple-access interference (MAI) is of crucial importance. Gaussian pulse used in conjunction with Markovian codes reduces MAI although it does not has the ICI-free property. Computer simulations show that Gaussian pulse with same excess bandwidth energy as the RRC pulse significantly reduces BER.

Design and implementation of low power digital phase-locked loop

This paper proposes a low power architecture for second order digital phase-locked loop (DPLL). High power consumption of DPLL results from using a look-up table (LUT) in implementing the numerically controlled oscillator (NCO). A new design for NCO is presented in which no LUT is used. Proposed architecture implemented using field programmable gate array (FPGA) consumed 15.44 mw at 100 MHz clock frequency which means a more than 25% saving in power consumption compared to traditional NCO. Furthermore, proposed method also saves FPGA resources and works at faster clock frequency.

A low-power implementation of arctangent function for communication applications using FPGA

A low power architecture to compute arctangent function which is suitable for broad-band communication applications is presented. This architecture aims to avoid high power consumption and long latency which are the main disadvantages to other methods based on CORDIC algorithm or conventional LUT methods or polynomial approximation. The architecture is implemented using FPGA, computes arctangent function with 3 clock pulses, and it is power dissipation is lower than Cordic algorithm by 80%.

Quasi-Orthogonal Multi-Carrier CDMA

It is believed that the dimension of the signal space with interval T and bandwidth W is 2WT, while we cannot make the out-of-band and out-of-time energies of any waveform zero. We propose a Gaussian pulse shaping for multi-carrier CDMA systems to utilize the time and frequency resources effectively. Gaussian pulses have ICI and ISI; they are not orthogonal. Markovity of spreading codes save the drawback of ICI and ISI. Overlapped Gaussian pulses increase the spectral efficiency.

Bit error rate in an asynchronous DS/CDMA system using Markovian SS codes

SS codes generated by a Markov chain are shown to be superior to LFSR-based codes and i.i.d. codes in an asynchronous DS/CDMA system in terms of the following two common performance measures: 1) acquisition rate; and 2) bit error rate of the correlator using all accumulated version of the serial search acquisition method.

Markovian SS codes imply inversion-free code acquisition in asynchronous DS/CDMA systems

Conventional single user correlators for asynchronous DS/CDMA systems provide only one scalar value for each data period. Code acquisition is expected to be improved if sampling is performed once each chip time. This accurate code acquisition method is shown to require the covariance matrix of SS codes, while the optimum method needs inversion of the covariance matrix. However, Markovian SS codes with eigen value -2+/spl radic/3 do not need matrix inversion, which is the same value needed to achieve minimum bit error rate.

Code acquisition of Markovian SS codes in a chip-synchronous DS-CDMA system

A decorrelator for chip-synchronous DS-CDMA systems using Markovian SS codes, which makes observed data at each chip-time uncorrelated is proposed in this article. Moreover, using the decorrelator output a posteriori probability is calculated by applying a very simple expression.

PLL-free receiver for Gabor division/spread spectrum system

Non-coherent signal with unknown delay and Doppler is recovered by Gabor division/spread spectrum system. Separable property (SP) condition for time and frequency synchronization leads us to determine delay and Doppler precisely. This paper gives an enlargement of acceptable delay and Doppler region by using multiple codes and their associated receivers simultaneously without increasing computation time. As its application, two-target simultaneous determination is discussed.

Gabor Division/Spread Spectrum System Is Separable in Time and Frequency Synchronization

Recently proposed new Time-Domain (TD) synchronization using frequency integration and TD Spread Spectrum (SS) codes has been shown to be robust to frequency offset, that has its dual Frequency-Domain (FD) synchronization using time integration and FD SS codes which is robust to timing offset. Separable Property (SP) is defined for time-frequency synchronization under the condition containing time and frequency deviations to be performed separately and cooperatively. The SP compels us to design phase correction on SS codes and transmitted data.

2D Markovian SS codes flatten time-frequency distribution of signals in asynchronous Gabor division CDMA systems

We propose a Gabor division (GD)-CDMA system which permits time and frequency offsets. Negatively correlated time- and frequency-domain spreading codes have shown to reduce the variances of mutual- and self-interferences. In this paper, we show that such negatively correlated spreading codes have another important property that they flatten the time-frequency energy distributions of signals in GD-CDMA system.