One-shot Linear Decorrelating Detector Research Articles

O3BPSK-based Linear Decorrelating Detector for Asynchronous DS/CDMA Systems over Frequency-Selective Rayleigh Fading Channels

In this paper, a convenient signaling scheme, called orthogonal on---off BPSK (O3BPSK), along with a simple one-shot linear decorrelating detector (LDD) and a whitening Rake bank, is proposed for near---far resistant detection in asynchronous DS/CDMA systems. Based on the maximum multi-path spreading delay, a minimum duration of "off" is suggested, during which the temporally adjacent bits (TABs) that contain multi-user interference (MUI) and inter-symbol interference (ISI) from different users at the receiver are decoupled. The O3BPSK signaling scheme is combined with the whitening Rake receiver to preserve multi-path diversity gain in multi-path fading CDMA channels. The scheme offers low complexity, no detection delay, near---far resistance, and compensation for fading channels.

O [formula omitted]-based linear decorrelating detector for asynchronous UWB systems over multipath fading channels

In this paper, a convenient signaling scheme, termed orthogonal on–off Ultra wideband (UWB) (O 3 UWB), along with a simple one-shot linear decorrelating detector (LDD) and a Rake bank, is proposed. This scheme is useful for conducing multi-user detection because temporally adjacent bits in receiver signals from different users are decoupled using on–off signaling. This mechanism also leads to one-shot detection that overcomes the main disadvantage, long detection delay, of the conventional LDD. In addition, the data rate is maintained, with no increases in the transmission rate, by adopting an orthogonal structure. In this paper, we study the system performance over a flat fading channel. Four types of channel models, including Rayleigh fading, Nakagami- m fading, Rician fading, and Lognormal fading, are considered. Since multipath fading still significantly degrades UWB system performance, the Rake bank is included to recover multipath diversity gain. Numerical analysis and simulation results show that the O 3 UWB LDD receiver still offers a good near-far resistant property over fading channels compared to the conventional UWB receiver.

On the performance of O 3BPSK LDD with diversity combining techniques over fading channels

Zheng and Barton developed a convenient signaling scheme (orthogonal on-off BPSK (O 3BPSK)) with a simple one-shot linear decorrelating detector (LDD) for near–far resistant detection in asynchronous DS/CDMA systems. This paper studies the performance of the O 3BPSK LDD system over a frequency-nonselective and slowly fading channel. Three types of channel model are considered, namely Rayleigh fading, Nakagami- m fading, and Ricean fading. The analytical results show that channel fading causes a significant degradation in the performance of the O 3BPSK LDD receiver. Nevertheless, the receiver still demonstrates a better near–far resistant property than a conventional CDMA receiver over fading channels. This study also analyzes the effect of two well-known diversity combining techniques on the O 3BPSK LDD performance over Rayleigh fading channels. The results indicate that diversity combining techniques significantly improve the performance of the O 3BPSK LDD scheme over fading channels.

Orthogonal on–off-based near–far-resistant detection with diversity technique in UWB systems

A convenient signalling scheme, called orthogonal on–off (O3), together with a simple one-shot linear decorrelating detector (LDD) and a RAKE bank, is adopted in asynchronous ultra-wideband (UWB) systems. The performance of the proposed system is evaluated over multipath fading channels. This investigation also analyses mathematically the effect of the maximal-ratio combining diversity technique on the O3UWB LDD performance over lognormal fading channels. The analytical and simulation results indicate that the diversity technique significantly improves the performance of the O3UWB LDD scheme over fading channels, and the proposed receiver still demonstrates a better near–far-resistant property than a conventional UWB receiver.

Performance analysis of O/sup 3/ BPSK LDD for asynchronous CDMA systems in the presence of synchronization errors

A convenient signaling scheme, termed orthogonal on-off binary phase-shift keying (O/sup 3/BPSK), along with a simple one-shot linear decorrelating detector (LDD), was proposed by F.C. Zheng and S.K. Barton (see ibid., vol.47, p.969-76, 1998; Proc. IEEE PIMRC'94, p.194-8, 1994) as a technique for near-far resistant detection in asynchronous direct-sequence code-division multiple-access (DS/CDMA) systems. The temporally adjacent bits from different users in the received signals are decoupled by using on-off signaling, and the data rate is maintained with no increase in the transmission rate by adopting an orthogonal structure. The paper examines the effects of three classes of synchronization errors (time-delay errors, carrier phase errors, and carrier frequency errors) on the performance of the O/sup 3/BPSK LDD in an asynchronous CDMA near-far environment. It is shown that the performance of the O/sup 3/BPSK LDD has an advantage over that of the isolation bit insertion detector in the presence of synchronization errors. In addition, numerical results show that the O/sup 3/BPSK LDD still offers a good near-far resistant property as long as synchronization errors do not exceed some practical limit.

A one-shot LDD with pre-SDC/post-MRC for random CDMA over asynchronous Rayleigh channels

It is well known that conventional detectors of direct sequence-code division multiple access systems are interference-limited. Multiuser detection has been considered as a promising approach to combat this problem. Since an optimal multiuser detector is too complex to implement, several suboptimal multiuser detector techniques have been developed. The one-shot linear decorrelating detector (LDD) was proposed to reduce the computational complexity and delay required in the conventional LDD, but it still require high complexity. Another one-shot LDD with low complexity was proposed. To improve its performance, this detector uses a maximal ratio combining (MRC) at the two outputs of the left piece of the present bit and the right piece of the next bit in an one-shot window; this detector is called as a one-shot LDD with post-MRC. In spite of the aid of MRC, the performance of the one-shot LDD with post-MRC is worse than the one-shot LDD. To overcome this problem, we propose the one-shot LDD with pre-SDC/post-MRC that employs selection diversity combining (SDC) with multiple antenna elements in front of the one-shot LDD with post-MRC. In asynchronous random code division multiple access systems over fading channels, the largest signal-to-noise ratio (SNR) of SDC, near-far resistance (NFR) of the one-shot LDD, and the output SNR of MRC are random variables. We derive the probability density functions (PDFs) for these random variables and calculate the bit error rate) of the proposed detector using the obtained PDFs. In a comparison of mathematical analysis and computer simulation results, we observe good agreement.

Multiuser detection of asynchronous CDMA with frequency offset

This article presents a near-far resistant detection scheme for asynchronous code-division multiple access with frequency offset. Based on a one-shot technique and Taylor expansion, a zeroth-order and a first-order one-shot linear decorrelating detector (LDD) are proposed. The zeroth-order LDD has simple architecture but suffers performance degradation for large frequency offset. The first-order one-shot LDD, with increased complexity, has very good near-far resistant property even for large frequency offset. Two versions of the first-order one-shot LDD are investigated according to different Taylor expansion approaches. The feasibility of the proposed detectors is demonstrated by computer simulations.

Frame-extended linear decorrelating detector for asynchronous CDMA

The standard linear decorrelating detector (LDD) for asynchronous code-division multiple access involves complicated computations and long detection delay. The one-shot LDD with a frame of 1-bit period length leads to a simpler architecture with less than 1-bit detection delay but significant noise enhancement compared with the standard LDD. In this paper, extending the frame to more than one bit period, a frame-extended LDD (FELDD) is proposed. With a slight increase of complexity and detection delay, the noise enhancement of the FELDD is greatly reduced compared with the one-shot LDD and approaches that of the standard DD. The total number of users supported is also increased compared with that of the one-shot LDD. Theoretical analysis and computer simulations are used to demonstrate the feasibility of the proposed scheme.

Orthogonal on-off BPSK: a convenient signaling scheme for near-far resistant detection in DS/CDMA

This paper proposes a convenient signaling scheme-orthogonal on-off BPSK (O/sup 3/BPSK)-for near-far (NF) resistant detection in asynchronous direct-sequence code-division multiple-access (DS/CDMA) systems (uplink). The temporally adjacent bits from different users in the received signals are decoupled by using the on-off signaling, and the original data rate is maintained with no increase in transmission rate by adopting an orthogonal structure. The detector at the receiver is a one-shot linear decorrelating detector, which depends upon neither hard decision nor specific channel coding. The application of O/sup 3/ strategy to the differentially encoded BPSK (D-BPSK) sequences is also presented. Finally, some computer simulations are shown to confirm the theoretical analysis.