O. van de Wiel

Per tone equalization for DMT-based systems

An alternative receiver structure is presented for discrete multitone-based systems. The usual structure consisting of a (real) time-domain equalizer in combination with a (complex) 1-tap frequency-domain equalizer (FEQ) per tone, is modified into a structure with a (complex) multitap FEQ per tone. By solving a minimum mean-square-error problem, the signal-to-noise ratio is maximized for each individual tone. The result is a larger bit rate while complexity during data transmission is kept at the same level. Moreover, the per tone equalization is shown to have a reduced sensitivity to the synchronization delay.

Fractionally spaced linear and decision-feedback detectors for transmultiplexers

We investigate improved detectors for transmultiplexer-based high bit rate transmission over dispersive channels like telephone wires. The transmitter is based on a synthesis stage. For the receiver, we design fractionally spaced single-input/multiple-output linear detectors, possibly upgraded with a multiple-input/multiple-output decision-feedback section, for an MMSE criterion. The performance of the system is investigated for filter banks, classical DMT, and different channels. The potential of these detectors is demonstrated,.

MIMO DFE equalization for multitone DS/SS systems over multipath channels

The combination of multitone modulation with direct sequence spectrum spreading (DS/SS) has been introduced in the past. The performance of a correlation receiver has been evaluated for a multipath channel and in the presence of an additional multiple access interference. We analyze the problem of decision feedback equalization (DFE) for such a system. In order to understand the potential of the system with equalization, we first study the steady-state behavior of the equalizer for a minimum mean square error (MMSE) criterion. The investigation is carried out for a receiver made of a bank of filters matched to both the symbol shape and the channel, and for a two path channel. Assuming transmission of binary phase shift keying (BPSK) symbols, an exact expression of the bit error probability is obtained in the form of an integral. Then adaptive least mean square (LMS) and recursive least square (RLS) structures are derived. The performance of the adaptive RLS algorithm is demonstrated by means of computer simulations.

Performance analysis of linear MIMO equalizers for multitone DS/SS systems in multipath channels

In [11] the combination of multitone modulation with direct sequence spectrum spreading has been introduced. The performance of a correlation receiver has been evaluated for a multipath channel. In [12] the analysis has been extended to the presence of a multiple access interference. In the present paper we analyze the equalization problem of such a system for a single user scenario. In order to understand the potential of the system we first investigate the steady-state behavior of the MIMO equalizer for an MMSE design. The investigation is carried out for an equalizer following a receiver made of a bank of filters matched to both the symbol shape and the channel, which is a two-path channel. Assuming BPSK symbols an exact expression of the bit error probability before and after equalization is obtained in the form of an integral by means of the characteristic function method. Next adaptive LMS and RLS structures are proposed. The performance of the RLS algorithm is demonstrated.

Performance analysis of linear joint equalization and multiple access interference cancellation for multitone CDMA

In [18] the combination of multitone modulation with direct sequence spectrum spreading has been introduced. The performance of a correlation receiver with diversity has been evaluated for a multipath channel in the presence of a multiple access interference (MAI) using the Gaussian assumption. In the present paper we analyze the problem of joint equalization and cancellation of the multipath and multiple access interferences for these multitone CDMA (Code Division Multiple Access) systems. A linear structure is first investigated for a mean square error (MSE) criterion. In order to understand the potential of the system we study the steady-state behavior of the joint equalizer-canceler. The investigation is carried out for a joint device following a bank of matched filters and assuming perfect carrier phase and timing recovery. An exact expression for the bit error probability of BPSK symbols before and after cancellation, is obtained in the form of an integral The performance of the joint device is investigated for different types of channels. The resistance to the near-far effect is also demonstrated. Then adaptive structures are derived from a least square approach. Their performance is demonstrated by means of computer simulations.

Adaptive equalization structures for multitone CDMA systems

The combination of multitone transmission (also known as orthogonal frequency division multiplexing (OFDM)) with direct sequence spread spectrum (DS/SS) is suitable for the design of a multiuser system robust against channel impairments. For high bit rate applications in indoor channels, the need for equalization is high, because guard intervals would lead to poor spectral efficiency. This paper presents a comparison between a recursive least square (RLS) scheme and a least mean square (LMS) algorithm, both extended for the linear equalization of OFDM/DS systems.

Performance analysis of linear joint multiple access interference cancellation-equalization for asynchronous multitone CDMA

We analyze the problem of joint equalization and cancellation of the multipath and multiple access interference for multitone CDMA introduced by Vandendorpe (see IEEE Transactions on Vehicular Technology, vol.44, no. 2, p.327, 1995). A linear structure is investigated for an MMSE criterion. In order to understand the potential of the system we first study the steady-state behaviour of the joint equalizer-canceller. The investigation is carried out for a joint device following a receiver made of a bank of matched filters and assuming perfect carrier phase and timing recovery. The scenario is asynchronous. An exact expression in the form of an integral is obtained for the bit error probability of the BPSK symbols before and after cancellation, by means of the characteristic function method. The performance of different systems is obtained for a constrained comparison and the near-far resistance of the detector is demonstrated.

Linear and decision-feedback MIMO equalization for transmultiplexer-based high bit rate transmission over copper wires

In this paper, we investigate detectors for transmultiplexer-based high bit rate transmission over dispersive channels like telephone wires. The transmitter is based on a synthesis stage. At the receiver we design, for an MMSE criterion, fractionally spaced multiple-input/multiple-output (MIMO) linear detectors applied after an analysis stage. The receiver may be upgraded with a MIMO decision-feedback (DF) section. The performance of the system is investigated for filter banks and a twisted pair channel. The influence of the forward section rate is investigated. The potential of these detectors is clearly demonstrated. Besides, reduced complexity solutions are also put forward.

A comparison of bidimensional RLS and LMS equalizers for OFDM/DS transmission in an indoor environment

The combination of multitone transmission (also known as orthogonal frequency division multiplexing (OFDM)) with direct sequence spread spectrum (DS/SS) is suitable for the design of a multiuser system robust against channel impairments. For high bit rate applications in indoor channels, the need for equalization is high, because guard intervals cannot be used due to the CDMA feature introduced in the system. The paper presents a comparison between a recursive least square (RLS) scheme and a least mean square (LMS) algorithm, both extended for the equalization of OFDM/DS systems, implemented in linear or DFE modes.

Fractionally spaced decision feedback joint detection for multitone CDMA systems

We consider a fractionally spaced decision feedback joint detector (FS-DFJD) for multitone code division multiple access (CDMA) systems. We first derive the structure of the receiver for an minimum mean-squared error (MMSE) criterion. Then we investigate the bit-error rate (BER) performance achieved by this detector for binary phase-shift keying (BPSK) modulation in steady-state conditions. We consider an asynchronous scenario where the signal of each user propagates over a two-path channel. The resistance of the detector against timing errors is studied, and the resistance against a near-far scenario is also demonstrated.