C. de Almeida

Two-dimensional interleaving using the set partitioning technique

We propose an efficient two-dimensional interleaving technique which spreads a cluster of errors having a circular shape. As a consequence of this technique, simple random-error-correcting codes can be used to correct cluster of errors, instead of the more complex burst-error-correcting codes. Interleaving techniques are mainly used in channels with memory. The combination of coding and interleaving, in general, leads to memoryless channels where modelling and performance analysis are amenable. The motivation for the use of this technique is related to applications such as in magnetic and optical data storage, or in digital image transmission, where a cluster of errors occurs in the first case due to dust particles, or defective regions, and in the second case due to noise. The 2D interleaving technique is used to separate the neighbors of any given point in a Q/spl times/Q square array, by a minimum squared Euclidean distance, d/sub min//spl les/Q, where Q is the order of the array. When d/sub min//spl les/=Q, we say that the interleaving is perfect, or it realizes a maximum distance spreading of points. We show by an example, the effectiveness of the interleaving scheme.<<ETX>>

On the interference of cellular CDMA systems

We obtain analytical values of the mean and the standard deviation of the own-cell and other-cell interference for the reverse link of CDMA systems. The outage probability is also obtained.

The fading effects on the CDMA/PRMA network performance

A system level network simulator is developed to assess and to compare some performance aspects of a joint code division multiple access/packet reservation multiple access (CDMA/PRMA) protocol and a random-access (RA)/CDMA protocol over lognormal shadowing, slow and fast fading Rayleigh channels.

Interference evaluation in CDMA Ad Hoc networks

This work presents an expression for the mean value of the interference in wireless code division multiple access (CDMA) ad hoc networks. CDMA is an interesting alternative for ad hoc networks, due to its characteristics, such as, multiple transmissions and interference rejection. Multihop CDMA network models generally consider network interference as a random variable with known distribution. Unlike the proposed model, this work analyses the performance of the CDMA ad hoc network as a function of the number of interferers deriving an expression for the mean value of the interference.

On the Performance of CDMA Systems Employing Multiuser Decorrelating Detector and Antenna Array

This paper presents analytical expressions to evaluate the capacity of code division multiple access (CDMA) cellular radio systems employing a joint antenna array and a multiuser decorrelating detector. The performance is evaluated for chip-synchronous and asynchronous baseband and bandpass CDMA systems on additive white Gaussian noise and flat-fading Rayleigh channels. Simulation results have shown that the analytical model developed to evaluate the performance of those systems is a very tight approximation.

Multiuser Decorrelating Detectors for DS-CDMA on Frequency-Selective Fading Channels

In this article two multiuser receivers for DS-CDMA systems on frequency-selective fading channels are analyzed and compared: the rake decorrelating detector (RDD) and the multipath decorrelating detector (MDD). Simple and precise expressions for the bit error probability and for the computational complexity for synchronous and asynchronous DS-CDMA cases are obtained. The analytic and simulations results have shown that the RDD detector achieves better performance than the MDD detector, with much lower computational complexity

Mean Spectral Efficiency Evaluation of the Uplink of MC-CDMA Cellular Systems

The mean spectral efficiency of the uplink of MC-CDMA cellular systems is evaluated. The complete system employs the multicarrier-code division multiple access (MC-CDMA) technique, a linear antenna array at the base stations, frequency interleaving, maximal ratio combining, adaptive modulation, perfect power control and a cyclic prefix large enough to eliminate the intersymbol and intercarrier interferences effects. This scenario assumes the presence of multiple access interference, co-channel interference, additive white Gaussian noise, exponential path-loss and slow and frequency selective Rayleigh fading channel. In this context, a procedure to calculate the mean spectral efficiency of the cellular network is proposed, which depends of the mean bit error rate, the channel reuse factor, the increase of bandwidth due to the cyclic prefix, the system load, the spreading factor, the cell radius and the modulation schemes. Results show that an unitary channel reuse factor is the most efficient way to use the spectrum, but it is critical in relation to the transmission rates. Also, as orthogonal frequency division multiple access technique is a particular case of MC-CDMA, the spectral efficiency of both techniques is compared.

New unit-memory codes obtained by puncturing periodically time-varying convolutional codes

New good high-rate punctured convolutional codes (PCC) are presented. While any previously known PCC was derived by puncturing a low-rate time-invariant mother code, the new PCC are shown to be derived by puncturing a periodically time-varying convolutional code (PTVCC) acting as the mother code. To find the new PCC, we first show that any PTVCC (hence, any PCC) is equivalent to a type of time-invariant convolutional code. Focusing on a fixed unit-memory (UM) code, we also show that under certain conditions there exists a PTVCC along with a puncturing pattern that is equivalent to that UM code. A combinatorial optimization algorithm is then used to search for the new good UM codes for which equivalent PCC do exist. We observe that the new PCC compare favorably to the previously known PCC in several respects.

On the frequency allocation for mobile radio telephone systems

We propose a technique that can be used to realize the optimum allocation of frequencies for a mobile radio telephone system and for multibeam satellites by employing the quadratic forms associated with the rectangular and the hexagonal grids.

Evaluation of the Effects of Co-Channel Interference on the Bit Error Rate of Wireless Networks with Error Correcting Codes in Fading Channels

This paper presents a performance analysis of wireless networks using error correcting codes on channels with Rayleigh fading in the presence of co-channel interference. The performance is evaluated in terms of the average bit error rate (BER) using TCM (Trellis-Coded Modulation) and TTCM (Turbo Trellis-Coded Modulation) schemes for QAM modulations. The effects of co-channel interference are evaluated through Monte Carlo simulation in scenarios where the system is affected by a dominant interfering synchronous and similar to the target user. For each coded-modulation schemes, the results show that there are BER floors, which vary according to the signal-interference (S/I).