We consider the joint detection and decoding of m-sequences. The receiver has to decide whether an m-sequence is received and possibly to decode its initial state. To do so, it implements an iterative message-passing decoding algorithm that operates on a parity check matrix, built upon a number of reference parity-check equations satisfied by the m-sequence. This matrix concatenates several elementary parity check matrices which are derived from reference equations. Unlike the conventional decoding case, the detection problem imposes to consider false alarms that may occur when the decoder is only fed with noise. While absorbing sets are known to be responsible for the error floor phenomenon of iterative message-passing decoders, we show that they may have a beneficial effect on the detection performance, in that they may prevent the decoder to produce false alarms. We further compute the number of hybrid cycles of length six and eight in the Tanner graph of the decoder and use the minimization of this number as criterion to derive an algorithm for selecting the reference parity check equations. This algorithm was found to be efficient for minimizing the probability of false alarm and decreases also the probability of wrong detection in the very small SNR region. This has been achieved at the cost of a reduction of the probability of correct detection.

Gold sequences are widely used in communications and positioning systems for synchronization purposes or spread spectrum transmissions. This paper addresses the decoding of the initial state of a Gold sequence. This can be used to detect a harmful interferer closed to a 3G femtocell base station and implement interference mitigation techniques. The decoder implements an iterative message-passing algorithm which is built upon a parity check matrix. Thus, it depends on the coding properties of Gold codes. In this paper, we synthesize the coding properties of Gold codes and use them to compute the number of parity check equations of weight t = 3, 4 or 5. Eventually, the impact of the parity check equations used for decoding is highlighted.

Interference between macro and femtocells is an important issue for the development of WCDMA femtocell networks. More specifically, the uplink signal of a macro User Equipment may generate an unacceptable level of interference at the femto Base Station. To avoid this situation, interference mitigation techniques could be implemented. All the proposed techniques require the knowledge of the uplink scrambling code index of the interferer. Unfortunately, if the femto BS is in a closed access mode, there are no signalling links with the surrounding macro BSs. The femto BS has to estimate blindly this scrambling code index. An algorithm which performs a blind identification of the uplink scrambling code index of a WCDMA transmission is proposed in this article. This gives the possibility to implement interference cancelation algorithm at the femto BS.

Interference between macro and femtocells is an important issue for the development of CDMA2000 femtocell networks. More specifically, the reverse link signal of a macro User Equipment may generate an unacceptable level of interference at the femto Base Station. To avoid this situation, interference mitigation techniques could be implemented. All the proposed techniques require to know the state of the scrambling code of the interferer in the reverse link. Unfortunately, it depends on the code mask of the terminal which is unknown by the femto BS. The femto BS has to estimate blindly the state of the scrambling code. An algorithm which performs a blind identification of the scrambling code of a CDMA2000 reverse link transmission is proposed in this article. This gives the possibility to implement interference cancelation algorithm at the femto BS.

Phase noise is a topic of theoretical and practical interest in electronic circuits. Although progress has been made in the characterization of its description, there are still considerable gaps in its effects especially on multi-carrier spreading systems. In this paper, we investigate the impact of a local oscillator phase noise on the multi-carrier 2 dimensional (2D) spreading systems based on a combination of orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) and known as OFDM-CDMA. The contribution of this paper is multifold. First, we use some properties of random matrix and free probability theory to give a simplified expression of signal to interference and noise ratio (SINR) obtained after equalization and despreading. This expression is independent of the actual value of the spreading codes and depends mainly on the complex amplitudes of estimated channel coefficients. Secondly, we use this expression to derive new weighting functions which are very interesting for the radio frequency (RF) engineers when they design the frequency synthesizer. Therefore, based on these asymptotic results, we adapt a new method to predict the bit error rate (BER) at the output of the channel decoder by using an effective SINR value. We show by simulations the validity of our models and that at a given BER, the required signal to noise ratio (SNR) may easily increase due to the carrier phase noise.

This paper presents the impact of a carrier frequency offset on the performance of 2 dimensional spreading OFDM-CDMA systems. This is measured by the degradation of the Signal to Interference plus Noise Ratio (SINR) obtained after despreading and equalization. Using some properties of random matrix and free probability theories, a new expression of the SINR is derived. It is independent of the actual value of the spreading codes while still accounting for the orthogonality between codes. This model is validated by means of Monte-Carlo simulations. It is also exploited to compare the sensitivities of MC-CDMA and MC-DS-CDMA systems to carrier offset in a frequency selective channel. This work is carried out for zero forcing (ZF) and minimum mean square error (MMSE) equalizers.

Multi carrier communication systems are very sensitive to phase noise caused by oscillator at the receiver front-end. This paper presents a new approach for evaluating the degradation introduced by phase noise on a MC-CDMA receiver. Using the random matrix theory, a new analytical model of signal to interference plus noise ratio (SINR) has been developed. It is validated thanks to link level simulation based on behavioral phase noise models. Moreover, it allows us to derive a new weighting function, analog as the one proposed by Stott for OFDM systems (1998). This weighting function is very interesting for RF engineer when they design the receiver frequency synthesizer

This article presents the impact of a constant timing error on the performance of a downlink 2 dimensional spreading OFDM-CDMA system. This impact is measured by the Signal to Interference plus Noise Ratio (SINR) degradation after equalization and despreading. Using random matrix theory, an asymptotic evaluation of the SINR is obtained. It is independent of the value of users' spreading code while taking into account their orthogonality. Simulation results are provided to evaluate and discuss the validity of this model.