Giambattista Carnevale

Optimum power control and ordering in SIC receivers for uplink CDMA systems

Successive interference cancellation (SIC) for code division multiple access (CDMA) systems, together with a suitable power control, is an attractive technique to reduce multiuser access interference in uplink transmissions. In this paper we propose a receiver design which minimizes the system transmit power while ensuring a constant signal to noise plus interference ratio (SNIR) at each user detection point by using a suitable order of user detection. Indeed, the problem is a joint optimization of power control and ordering of user detection and its optimum solution is NP-hard. Hence, we derive both a suboptimal greedy algorithm and a randomized search which explores many solutions. All these approaches are evaluated in an uplink multiuser scenario for the UMTS-TDD standard in terms of bit error rate and power consumption.

Energy optimization of CDMA transceivers using successive interference cancellation

In broadband code division multiple access (CDMA) communications, it has been shown that receivers based on successive interference cancellation (SIC) provide an effective reduction of multiuser access interference at an affordable complexity. We propose an optimization of CDMA systems by using power control and a suitable order of user detection at the SIC receiver. The aim is to minimize the total transmit power, while ensuring equal signal to noise plus interference ratio (SNIR) at the detection point for all users. Performance evaluation in an uplink multiuser scenario for the UMTS-TDD standard shows that the proposed algorithm provides energy saving of up to 7 dB in the absence of scrambling and up to 3 dB in the presence of scrambling, with respect to existing architectures based on SIC.

On low-complexity joint-detection techniques for TD-CDMA

This paper is focused on low-complexity joint-detection (JD) algorithms, where the computational complexity is reduced using banks of discrete Fourier transformations. Mainly, we have developed a fast hybrid zero-forcing block decision-feedback equalizer (H-ZF-BDFE) combining the Fourier-based JD scheme (IEEE J. Sel. Areas Commun., vol. 19, p. 1461, 2001) with the fast decision-feedback structure (F-ZF-BDFE) IEEE J. Sel. Areas Commun., vol. 19, p. 245, 2001. In a Rayleigh frequency-selective fading channel, the new structure yields an improvement in E/sub b//N/sub 0/ of almost 2 dB against the fast block linear equalizer (BLE) (IEEE J. Sel. Areas Commun., vol. 19, p. 1461, 2001) at a bit error rate (BER)=10/sup -3/. Moreover, it has the same performance as the F-ZF-BDFE, but the computational complexity for the signal processing is reduced by almost 50%.

MC-CDMA with SIC: Power Control by Discrete Stochastic Approximation and Comparison with OFDMA

Orthogonal frequency division multiple access (OFDMA) and multicarrier code division multiple access (MC-CDMA) are possible candidates for the next generation of mobile wireless systems. However, when applied to an uplink broadband communication, MC-CDMA suffers from multiuser access interference, which can be reduced by using successive interference cancellation (SIC) at the base station. With this regard, here we propose an optimization of the MC-CDMA receiver that jointly determines power control and user detection ordering based on a discrete stochastic approximation algorithm. For OFDMA, we consider instead interleaved transmission and optimization of transmission power for each user. A comparison of OFDMA and MC-CDMA with SIC is then given in a multiuser uplink scenario in terms of sum-power for a required signal to noise ratio at the detection point.

SIC-VBLAST receiver for coded uplink MIMO MC-CDMA systems

In this paper, a convolutionally-coded uplink multi-carrier code-division multiple-access (MC-CDMA) system with multiple transmit and receive antennas is considered, over multipath Rayleigh fading channels. In this framework, a new iterative hybrid scheme based on the combination of a successive interference cancellation (SIC) and a vertical-BLAST detector is presented, to cope, respectively, with multiple-access interference and multiple-substream interference. Based on simulation results, the performance of the uplink MC-CDMA system, decoded by hard or soft-input decoding methods, is found to improve significantly by the use of antenna arrays in conjunction with the proposed multi-user receiver

Space-time receivers realized in the frequency domain for dispersive wireless channels

We present a class of low complexity space-time receivers for frequency-selective channels in, multiple input and multiple output (MIMO) systems. In particular we extend to MIMO systems two approaches originally derived in the framework of joint detection techniques for code division multiple access by performing, in the frequency domain, feedback processing (Benvenuto, N. and Sostrato, G., IEEE J. Select. Areas Commun., vol.19, p.245-53, 2001) and block linear equalization (Vollmer, M. et al., IEEE J. Select. Areas Commun., vol.19, p.1461-75, 2001), while interference cancellation is performed in the time domain (Benvenuto et al., Proc. IEEE WPMC. 2004). Moreover, we extend to the frequency domain the fully connected ordered successive interference cancellation DFE (Lozano, A. and Papadias, C., IEEE Trans. Commun., vol.50, p.65-73, 2002). We show that these hybrid time-frequency domain space-time receivers yield almost the same performance with a much lower computational complexity than the original space-time receivers implemented in the time domain.

Optimization of SIC Receiver and CDMA Power Control by Discrete Stochastic Approximation

In an uplink CDMA transmission, we consider a base station that utilizes successive interference cancellation (SIC) and performs power control of the mobile terminals to minimize the system power. Since the joint optimization of power control and ordering (JOPCO) detection in SIC requires a computational effort that grows exponentially with the number of active users, in this paper we propose an approximated solution obtained by modelling JOPCO as a discrete stochastic optimization problem. The proposed algorithm is based on the construction of a Markov chain whose states are the orderings. Moreover, in order to further reduce complexity, an efficient description of the state probabilities is derived. Simulations performed on an UMTS scenario show that the proposed technique yields a performance close to the optimal JOPCO solution