Techniques for indoor positioning systems (IPSs) can be categorised as range‐based or range‐free. Range‐based methods rely on geometric mappings to approximate a location given the calculated distances or angles from multiple reference points. In contrast, range‐free strategies utilise fingerprinting, wherein an acquired fingerprint data is compared to a pre‐collected dataset to identify the best position estimate. Among these, fingerprinting of channel state information (CSI) is preferred over other information such as received signal strength indicator as the former can exploit the effect of multipath propagation and is robust against non‐line‐of‐sight channels. CSI has the potential to achieve cm‐level positioning accuracy with a single reference point only. In this study, the authors survey CSI fingerprinting‐based indoor positioning and mobility tracking systems. The process of fingerprinting that includes site surveying and signal preprocessing is discussed in detail. They determine the potential challenges of such systems and propose remedies to improve positioning accuracy. In general, spatial diversity, such as multiple‐input multiple‐output antennas and wireless sensor networks, or frequency diversity (e.g. high subcarrier count, frequency hopping mechanism) are exploited to achieve high positioning resolution. Such IPS can also be enhanced via additional sensors or spatial graphs for motion detection and tracking.

Spectrally efficient frequency division multiplexing (SEFDM) has been recognised as a promising multi‐carrier technology since it can offer a higher spectral efficiency than orthogonal frequency division multiplexing (OFDM). In this study, the authors provide a framework for SEFDM transceiver design and investigate the techniques of channel equalisation and data detection of SEFDM over frequency selective fading scenarios. Specifically, they first demonstrate through mathematical analysis that SEFDM with the proposed frequency‐domain equalisation scheme can benefit from the frequency diversity, and thus, performs more robust to the frequency selective fading environment than OFDM. To effectively mitigate inter‐carrier interference raised by the non‐orthogonality between sub‐carriers of SEFDM, they then propose a low‐computational data detection scheme based on the Viterbi principle and maximum a posteriori criterion. The proposed detector can provide an indistinguishable performance from the maximum likelihood detection using sphere decoding while entailing a much lower computation. Numerical results validate the superiority of SEFDM to OFDM over frequency selective fading channels.

In a system utilizing multiuser diversity, regular feedback of channel-quality predictions to the base station is required for each user. Typically, the measure of channel quality must be quantized at each mobile station before it can be sent back. In this paper, we present two distributed scalar quantization schemes that optimize two different performance criteria: a) the minimization of the probability Peof incorrectly identifying the user with the best channel quality and b) maximization of the resulting throughput R. For a typical Rayleigh-fading system with 30 users per sector, numerical optimization results show that the Peand R realized by the uniform quantization strategy with 16 quantization levels for each user can be achieved by only three quantization levels using the two proposed strategies. A practical approximation of the proposed schemes is studied and is shown to provide near-optimal performance for both performance criteria as the number of quantization levels becomes large

Energy-constrained multihop wireless links are considered, where the total power consumption is minimized under given requirements on the end-to-end bit error rate (BER). As multihop transmissions are known to be able to save transmission energy in a wireless environment, we study the optimal power scheduling schemes over intermediate hops when the source- relays-destination link can be modeled as cascaded binary symmetric channels. The problem is formulated with an end- to-end BER constraint, and the resulting power consumption is compared with that of the individual link requirement strategy where each hop assigns power under a per-link BER constraint. Results show that the proposed joint power scheduling strategy can achieve a maximum power reduction factor of M in an M-hop route.

We consider energy-constrained multihop wireless links where the power consumption must be minimized under given requirements on the end-to-end bit error probability. As multihop is known to be able to save transmission energy in a wireless environment, we study the power scheduling schemes over intermediate hops where each source-relay-destination link is modeled as a cascaded binary symmetric channel. The optimal power scheduling problem is formulated with the end-to-end bit error probability constraints. Results show that with the proposed joint power scheduling strategy, a maximum power reduction factor of M is possible in a M-hop route compared with the individual link requirement strategy where each hop assigns power individually to meet certain bit error probability at each intermediate link.

Conventional matched-filter detectors for code-division multiple-access (CDMA) systems suffer from multiple-access interference (MAI) caused by nonzero correlation between spreading codes at the receiver. A host of advanced detector structures have been proposed to reduce the effect of MAI and, hence, improve performance. However, most multiuser detectors suffer from their relatively complex implementations. A simple method is proposed to improve the performance of the conventional detector by detecting and correcting decision errors at its output without the use of forward error correcting (FEC) codes. The proposed post-detection error control method is shown to substantially improve the performance of the conventional detector, but has a much lower complexity than most other multiuser detectors.