scispace - formally typeset
Search or ask a question

Maximum likelihood receiver for multiple channel transmission systems

01 Jan 2007-pp 305-312
TL;DR: In this article, a maximum likelihood estimator for digital sequences disturbed by Gaussian noise, intersymbol interference (ISI) and interchannel interference (ICI) is derived.
Abstract: A maximum likelihood (ML) estimator for digital sequences disturbed by Gaussian noise, intersymbol interference (ISI) and interchannel interference (ICI) is derived. It is shown that the sampled outputs of the multiple matched filter (MMF) form a set of sufficient statistics for estimating the input vector sequence. Two ML vector sequence estimation algorithms are presented. One makes use of the sampled output data of the multiple whitened matched filter and is called the vector Viterbi algorithm. The other one is modification of the vector Viterbi algorithm and uses directly the sampled output of the MMF. It appears that, under a certain condition, the error performance is asymptotically as good as if both ISI and ICI were absent.
Citations
More filters
01 Jan 2003
TL;DR: In this paper, the authors proposed a semi-OSDM system for complexity reduction by allowing the signal streams for a user to be non-orthogonal, but for each user, the multiple signaling streams are made triangular instead so that a simple backward substitution with symbol cancellation can be performed to maintain an accurate signal detection.
Abstract: Orthogonal space division multiplexing (OSDM) can be achieved by utilizing multiple antennas at the base station (BS) and all mobile stations (MS) (or multi-user MIMO) jointly. Recently, two iterative methods have been proposed to obtain the antenna weighting for realizing OSDM in the downlink (Kai-Kit Wong et al., IEEE Trans. Wireless Commun.; Zhengang Pan et al., IEEE Trans. Wireless Commun.). However, both suffer from high complexity if the number of BS antennas or users involved is large, as the computational complexity grows with the fourth power of the number of users. By allowing the signal streams for a user to be non-orthogonal, we propose a semi-OSDM system for complexity reduction. In the semi-OSDM system, the signals of multiple users are still orthogonal, but for each user, the multiple signaling streams are made triangular instead so that a simple backward substitution with symbol cancellation can be performed to maintain an accurate signal detection. Remarkably, the antenna weighting for semi-OSDM can be expressed in a closed form. Simulation results show that semi-OSDM has mild performance degradation, but it requires much lower computational complexity (by an order of magnitude) when compared with existing OSDM systems.

7 citations

Dissertation
01 Jan 2013
TL;DR: In this article, a wideband fractal monopole antenna is proposed to achieve the acceptable performance in terms of isolation, envelope correlation coefficient, capacity loss, radiation patterns and efficiency.
Abstract: Today’s small handheld and other portable devices challenge antenna designers for ultrathin, and high performances that have the ability to meet multi standards. In the context, fractal geometries have significant role for antenna applications with varying degree of success in improving antenna characteristics. In this thesis, we have investigated several wideband fractal monopole antennas. This work starts with design and implementation of Koch fractal, hybrid fractal, sectoral fractal, semi-circle fractal monopole antennas with discussion, covering their operations, electrical behavior and performances. The performances of these designs have been studied using standard simulation tools used in industry/academia and are experimentally verified. Frequency reconfigurable Koch snowflake fractal monopole antenna is also introduced. The present antenna can be used as an array element and has a wideband frequency of operation. A square Sierpinski monopole antenna has been designed, which is suitable for use in indoor UWB radio system and outdoor base station communication systems. Technique for obtaining a band stop function in the 5-6 GHz frequency band is numerically and experimentally presented. In addition to examining the performance of UWB system, the transfer function and waveform distortion are discussed. Finally, fractal antenna for array with MIMO environment is developed for mobile communication devices. Aim of this work is to achieve the acceptable performances in terms of isolation, envelope correlation coefficient, capacity loss, radiation patterns and efficiency. Furthermore, a wideband feed network prototype based on a modified Wilkinson power divider is designed. The designed feed network has been used in constructing 2-element and 4-element linear antenna arrays for high gain. This research work has addressed the effectiveness of fractal geometries in antenna and to bring-out the true advantages of their in antenna engineering.

5 citations

01 Jan 2007
TL;DR: An optimum linear receiver for multiple channel digital transmission systems is developed for the minimum P e and for the zero-forcing criterion and an algorithm is given to calculate the tap settings of this multiple tapped delay line.
Abstract: An optimum linear receiver for multiple channel digital transmission systems is developed for the minimum P and for the zero-forcing criterion A multidimensional Nyquist criterion is defined together with a theorem on the optimality of a finite length multiple tapped delay line Furthermore an algorithm is given to calculate the tap settings of this multiple tapped delay line This algorithm simplifies in those cases where the noise is so small that it can be neglected Finally as an example the transmission of binary data over the cable, consisting of four identical wires, symmetrically situated inside a cylindrical shield, is considered

5 citations

Dissertation
01 Jan 2012
TL;DR: In this article, a dissertation submitted to the Departamento de Engenharia Electrotecnica of Faculdade de Ciencias e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy was presented.
Abstract: A dissertation submitted to Departamento de Engenharia Electrotecnica of Faculdade de Ciencias e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotecnica e de Computadores

4 citations

Dissertation
01 Nov 2008
TL;DR: In this article, a relay-assisted direct-sequence code-division multiple access (DS-CDMA) system with multiple relays is considered and the achievable bit error ratio (BER) performance is investigated.
Abstract: In relay-assisted direct-sequence code-division multiple-access (DS-CDMA) systems, the distance between the relay and the destination receiver may be significantly shorter than that between the source transmitter and the destination receiver. Therefore, the transmission power of the relay may be significantly reduced in comparison to that of the source transmitter. In this thesis, we investigate the dependence of the achievable bit error ratio (BER) performance of DS-CDMA systems on the specific locations of the relays as well as on the power-sharing among the source transmitters and relays, when considering different propagation pathloss exponents. This thesis is focused on the class of repetition-based cooperation aided schemes, including both amplify-and-forward (AF) as well as decode-and-forward (DF) schemes, with an emphasis on lowcomplexity AF schemes. In our study, the signals received at the destination receiver from the source transmitters as well as from the relays are detected based on a range of diversity combining schemes having a relatively low-complexity. Specifically, the maximal ratio combining (MRC), the maximum signal-to-interference-plus-noise ratio (MSINR) and the minimum mean-square error (MMSE) principles are considered. We propose a novel cooperation aided DS-CDMA uplink scheme, where all the source mobile terminals (MTs) share a common set of relays for the sake of achieving relay diversity. As shown in our study, this low-complexity AF-based cooperation strategy is readily applicable to the challenging scenario where each source MT requires the assistance of several separate relays in order to achieve relay diversity. Another novel cooperation scheme is proposed for the downlink of DS-CDMAsystems, where the downlink multiuser interference (MUI) is suppressed with the aid of transmitter preprocessing, while maintaining the relay diversity order facilitated by the specific number of relays employed, despite using simple matched-filter (MF) based receivers. The transmitter preprocessing schemes considered include both the zero-forcing (ZF) and the MMSE-assisted arrangements, which belong to the class of linear transmitter preprocessing schemes. Furthermore, these transmitter preprocessing schemes are operated under the assumption that the base station’s transmitter employs explicit knowledge about the spreading sequences assigned to the destination MTs, but requires no knowledge about the downlink channels. Our study demonstrates that the proposed relay-assisted DS-CDMA systems using transmitter preprocessing are capable of substantially mitigating the downlink MUI, despite using low-complexity MF receivers.

3 citations

References
More filters
Journal ArticleDOI
TL;DR: The results show that the proposed multiuser detectors afford important performance gains over conventional single-user systems, in which the signal constellation carries the entire burden of complexity required to achieve a given performance level.
Abstract: Consider a Gaussian multiple-access channel shared by K users who transmit asynchronously independent data streams by modulating a set of assigned signal waveforms. The uncoded probability of error achievable by optimum multiuser detectors is investigated. It is shown that the K -user maximum-likelihood sequence detector consists of a bank of single-user matched filters followed by a Viterbi algorithm whose complexity per binary decision is O(2^{K}) . The upper bound analysis of this detector follows an approach based on the decomposition of error sequences. The issues of convergence and tightness of the bounds are examined, and it is shown that the minimum multiuser error probability is equivalent in the Iow-noise region to that of a single-user system with reduced power. These results show that the proposed multiuser detectors afford important performance gains over conventional single-user systems, in which the signal constellation carries the entire burden of complexity required to achieve a given performance level.

2,300 citations

Journal ArticleDOI
01 Dec 2017
TL;DR: This work provides a comprehensive overview of the state of the art in power-domain multiplexing-aided NOMA, with a focus on the theoretical N OMA principles, multiple-antenna- aided NomA design, and on the interplay between NOMa and cooperative transmission.
Abstract: Driven by the rapid escalation of the wireless capacity requirements imposed by advanced multimedia applications (e.g., ultrahigh-definition video, virtual reality, etc.), as well as the dramatically increasing demand for user access required for the Internet of Things (IoT), the fifth-generation (5G) networks face challenges in terms of supporting large-scale heterogeneous data traffic. Nonorthogonal multiple access (NOMA), which has been recently proposed for the third-generation partnership projects long-term evolution advanced (3GPP-LTE-A), constitutes a promising technology of addressing the aforementioned challenges in 5G networks by accommodating several users within the same orthogonal resource block. By doing so, significant bandwidth efficiency enhancement can be attained over conventional orthogonal multiple-access (OMA) techniques. This motivated numerous researchers to dedicate substantial research contributions to this field. In this context, we provide a comprehensive overview of the state of the art in power-domain multiplexing-aided NOMA, with a focus on the theoretical NOMA principles, multiple-antenna-aided NOMA design, on the interplay between NOMA and cooperative transmission, on the resource control of NOMA, on the coexistence of NOMA with other emerging potential 5G techniques and on the comparison with other NOMA variants. We highlight the main advantages of power-domain multiplexing NOMA compared to other existing NOMA techniques. We summarize the challenges of existing research contributions of NOMA and provide potential solutions. Finally, we offer some design guidelines for NOMA systems and identify promising research opportunities for the future.

1,008 citations

Journal ArticleDOI
Jack Harriman Winters1
TL;DR: Results show that with optimum linear processing at the receiver, up to M/2 channels can be established with approximately the same maximum data rate as a single channel with the potential for large capacity in systems with limited bandwidth.
Abstract: In this paper, we study the fundamental limits on the data rate of multiple antenna systems in a Rayleigh fading environment. With M transmit and M receive antennas, up to M independent channels can be established in the same bandwidth. We study the distribution of the maximum data rate at a given error rate in the channels between up to M transmit antennas and M receive antennas and determine the outage probability for systems that use various signal processing techniques. We analyze the performance of the optimum linear and nonlinear receiver processor and the optimum linear transmitter/receiver processor pair, and the capacity of these channels. Results show that with optimum linear processing at the receiver, up to M/2 channels can be established with approximately the same maximum data rate as a single channel. With either nonlinear processing at the receiver or optimum linear transmitter/receiver processing, up to M channels can be established with approximately the same maximum data rate as a single channel. Results show the potential for large capacity in systems with limited bandwidth.

997 citations

Journal ArticleDOI
TL;DR: How current and future trends increases the need for and viability of multi-user receivers for both the uplink, where many asynchronous users are simultaneously detected, and the downlink, where users are scheduled and largely orthogonalized is discussed.
Abstract: Cellular networks today are interference-limited and only becomes increasingly so in the future due to the many users that need to share the spectrum to achieve high-rate multimedia communication. Despite the enormous amount of academic and industrial research in the past 20 years on interference-aware receivers and the large performance improvements promised by these multi-user techniques, today's receivers still generally treat interference as background noise. In this article, we enumerate the reasons for this widespread scepticism, and discuss how current and future trends increases the need for and viability of multi-user receivers for both the uplink, where many asynchronous users are simultaneously detected, and the downlink, where users are scheduled and largely orthogonalized; but the mobile handset still needs to cope with a few dominant interfering base stations. New results for interference cancelling receivers that use conventional front-ends are shown to alleviate many of the shortcomings of prior techniques, particularly for the challenging uplink. This article gives an overview of key recent research breakthroughs on interference cancellation and highlights system-level considerations for future multi-user receivers.

740 citations

Journal ArticleDOI
TL;DR: Four suboptimum detection techniques based on zero forcing and minimum mean-square-error equalization with and without decision feedback (DF) are presented and compared and it is shown that the performance of the MMSE equalizers is better than that of the corresponding ZF equalizers.
Abstract: In code-division multiple-access (CDMA) systems transmitting over time-varying multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) arise. The conventional suboptimum receiver consisting of a bank of matched filters is often inefficient because interference is treated as noise. The optimum multiuser detector is too complex to be implemented at present. Four suboptimum detection techniques based on zero forcing (ZF) and minimum mean-square-error (MMSE) equalization with and without decision feedback (DF) are presented and compared. They combat both ISI and MAI. The computational complexity of all four equalizers is essentially the same. All four equalizers are independent of the size of the data symbol alphabet. It is shown that the performance of the MMSE equalizers is better than that of the corresponding ZF equalizers. Furthermore, the performance of the equalizers with DF is better than that of the corresponding equalizers without DF. The impairing effect of error propagation on the equalizers with DF is reduced by channel sorting.

581 citations