In recent years, indoor positioning has emerged as a critical function in many end-user applications; including military, civilian, disaster relief and peacekeeping missions. In comparison with outdoor environments, sensing location information in indoor environments requires a higher precision and is a more challenging task in part because various objects reflect and disperse signals. Ultra WideBand (UWB) is an emerging technology in the field of indoor positioning that has shown better performance compared to others. In order to set the stage for this work, we provide a survey of the state-of-the-art technologies in indoor positioning, followed by a detailed comparative analysis of UWB positioning technologies. We also provide an analysis of strengths, weaknesses, opportunities, and threats (SWOT) to analyze the present state of UWB positioning technologies. While SWOT is not a quantitative approach, it helps in assessing the real status and in revealing the potential of UWB positioning to effectively address the indoor positioning problem. Unlike previous studies, this paper presents new taxonomies, reviews some major recent advances, and argues for further exploration by the research community of this challenging problem space.

https://www.mdpi.com/1424-8220/16/5/707/pdf

Ultra Wideband Indoor Positioning Technologies: Analysis and Recent Advances.

Concrete mathematics, a foundation for computer science, by Ronald L. Graham, Donald E. Knuth and Oren Patashnik. Pp 625. £24·95. 1989. ISBN 0-201-14236-8 (Addison-Wesley)

Transmitter redundancy introduced using filterbank precoders generalizes existing modulations including OFDM, DMT, TDMA, and CDMA schemes encountered with single- and multiuser communications. Sufficient conditions are derived to guarantee that with FIR filterbank precoders FIR channels are equalized perfectly in the absence of noise by FIR zero-forcing equalizer filterbanks, irrespective of the channel zero locations. Multicarrier transmissions through frequency-selective channels can thus be recovered even when deep fades are present. Jointly optimal transmitter-receiver filterbank designs are also developed, based on maximum output SNR and minimum mean-square error criteria under zero-forcing and fixed transmitted power constraints. Analytical performance results are presented for the zero-forcing filterbanks and are compared with mean-square error and ideal designs using simulations.

Redundant filterbank precoders and equalizers. I. Unification and optimal designs

In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.

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Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

The spatial features of emitted wireless signals are the basis of location distinction and determination for wireless indoor localization. Available in mainstream wireless signal measurements, the Received Signal Strength Indicator (RSSI) has been adopted in vast indoor localization systems. However, it suffers from dramatic performance degradation in complex situations due to multipath fading and temporal dynamics. Break-through techniques resort to finer-grained wireless channel measurement than RSSI. Different from RSSI, the PHY layer power feature, channel response, is able to discriminate multipath characteristics, and thus holds the potential for the convergence of accurate and pervasive indoor localization. Channel State Information (CSI, reflecting channel response in 802.11 a/g/n) has attracted many research efforts and some pioneer works have demonstrated submeter or even centimeter-level accuracy. In this article, we survey this new trend of channel response in localization. The differences between CSI and RSSI are highlighted with respect to network layering, time resolution, frequency resolution, stability, and accessibility. Furthermore, we investigate a large body of recent works and classify them overall into three categories according to how to use CSI. For each category, we emphasize the basic principles and address future directions of research in this new and largely open area.

From RSSI to CSI: Indoor Localization via Channel Response, A survey on indoor localization using PHY-layer information

In this paper, the problem of channel equalization in filter bank multicarrier (FBMC) transmission based on the offset quadrature-amplitude modulation (OQAM) subcarrier modulation is addressed. Finite impulse response (FIR) per-subchannel equalizers are derived based on the frequency sampling (FS) approach, both for the single-input multiple-output (SIMO) receive diversity and the multiple-input multiple-output (MIMO) spatially multiplexed FBMC/OQAM systems. The FS design consists of computing the equalizer in the frequency domain at a number of frequency points within a subchannel bandwidth, and based on this, the coefficients of subcarrier-wise equalizers are derived. We evaluate the error rate performance and computational complexity of the proposed scheme for both antenna configurations and compare them with the SIMO/MIMO OFDM equalizers. The results obtained confirm the effectiveness of the proposed technique with channels that exhibit significant frequency selectivity at the subchannel level and show a performance comparable with the optimum minimum mean-square-error equalizer, despite a significantly lower computational complexity. The possibility of tolerating significant subchannel frequency selectivity gives more freedom in the multicarrier system parameterization. For example, it is possible to use significantly wider subcarrier spacing than what is feasible in OFDM, thus relieving various critical design constraints.

Channel Equalization for Multi-Antenna FBMC/OQAM Receivers

We consider OFDM (orthogonal frequency division multiplexing) transmission helped by a relay. Symbols sent by the source may or may not be retransmitted by a relay during a second time slot. The relay is supposed to operate in Decode-and-Forward (DF) mode. For each carrier the destination implements maximum ratio combining. Assuming perfect CSI (channel state information) knowledge the paper investigates the power allocation problem for rate maximization of the scheme. Both cases of a sum power constraint, and of individual power constraints at the source and at the relay are tackled. The theoretical analysis is illustrated by numerical results for both types of constraints.

Power Allocation for OFDM Transmission with DF Relaying

Iterative channel estimation can improve the channel-state information (CSI) with respect to noniterative estimation. New iterative channel estimators based on the expectation-maximization (EM) algorithm are proposed in this paper. A first estimator, called the unbiased EM (UEM), is designed to unbias the EM estimates. A second estimator is then put forward, which is based on the expectation-conditional-maximization (ECM) algorithm, and its complexity is lower than that of the EM. An unbiased ECM (UECM) estimator is also proposed. Although the unbiasedness of the UEM and UECM estimators is not rigorously proved, the use of these names is explained in the paper. The new estimators are compared with well-known ones, such as the EM, the decision-directed (DD), and the data-aided (DA) estimators. Simulations are reported for a turbo receiver operating over frequency-selective multiple-input multiple-output channels. It is shown that the UEM channel estimator outperforms the EM, and that the ECM-based estimators are very close to the EM-based ones

Comparison of EM-Based Algorithms for MIMO Channel Estimation

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,.

Fractionally spaced linear and decision-feedback detectors for transmultiplexers

We consider cyclic prefixed single carrier and adaptive multicarrier transmission over a frequency selective channel. We compare the achievable bit rate for a target bit error rate. We analytically prove that the bit rate achieved with multicarrier transmission with adaptive modulation is always higher than that obtained with single carrier transmission when a one-tap frequency domain equalizer is used. We also show that the same adaptively loaded multicarrier scheme reaches the performance of single carrier transmission with a block decision-feedback equalizer.

Jerome Louveaux

Papers

Channel Equalization for Multi-Antenna FBMC/OQAM Receivers

Power Allocation for OFDM Transmission with DF Relaying

Comparison of EM-Based Algorithms for MIMO Channel Estimation

Fractionally spaced linear and decision-feedback detectors for transmultiplexers

Cyclic prefixed single carrier and multicarrier transmission: bit rate comparison