A general non-asymptotic theoretical analysis is developed for fingerprinting localization system designs. Based on this analysis, hybrid fingerprinting and propagation-based methods are proposed using 5G-like received signal strength (RSS), time of arrival (TOA), and direction of arrival (DOA) measurements which have been a focus in recent 3GPP Rel 16 and Rel 17 positioning activities. The proposed hybrid methods have the flexibility and robustness of fingerprinting methods in dealing with none-line-of-sight (NLOS) problem while inheriting the efficiency and accuracy of propagation-based methods in 3-D localization. Specifically, a ray extension technique is developed as the propagation-based method. Then the ray extension is combined with two fingerprinting methods, the conventional weighted k-nearest neighbors (WKNN) and the proposed optimal WKNN (OWKNN), in order to remedy the geometrical deficiency in fingerprinting methods. Based on the non-asymptotic study, the proposed hybrid methods are guaranteed to outperform the fingerprinting methods without ray extension. Verification of the proposed methods is performed in a large none-line-of-sight (NLOS) urban San Jose region using simulation data provided by a previously developed super-efficient ray launcher.

In a distributed massive multiple-input and multiple-output (DM-MIMO) orthogonal frequency division multiplexing (OFDM) system, each of the multiple receivers receives the OFDM signals simultaneously from all transmitters intended for itself and other receivers. Due to the distributed nature of the network and the differences in propagation delays, these OFDM signals received by any receiver are most likely not synchronized. We have analyzed analytically and numerically the asynchronous reception effects on a DM-MIMO OFDM system in this paper. It is shown that the desired signal power reduction due to phase shifts caused by timing offsets is the dominant performance degrading factor. Surprisingly, the increase of various interfering power (including multiuser, inter-carrier, and inter-symbol interference) due to timing offsets is negligible when compared with the desired signal power reduction. Two per-user rate lower bounds have been developed by averaging over small-scale fading. With the aids of these two lower bounds, averaged per-user rate over small- and large-scale fading have been simulated. It is found that around 50% reduction in per-user downlink rate could occur to the majority of users due to asynchronous reception in DM-MIMO OFDM systems. This important factor needs to be considered in implementing any future DM-MIMO system.

This study presents an unsaturated two‐dimensional (2D) Markov model to analyse the packet collision probability and the throughput performances of the stations (STAs) in a distributed coordination function network. Compared with the previous 2D models, it takes the flexible buffer size of the STA into consideration. Compared with the 3D models, it has the advantage of low complexity by avoiding matrix operations. From the numerical results, the authors explain the approximations used in the analytical models proposed in the common existing literatures, and discuss their effect on the model accuracy.

Presented in this study is a novel precoding scheme for orthogonal frequency division multiplexing systems to suppress the out‐of‐band emission (OOBE). The scheme suppresses the OOBE by making the transmitted signal satisfy the continuous derivative property and the notched frequency (NF) property, which have been proposed separately in some existing schemes. Unlike most of the continuous derivative related schemes that require iterative decoders, authors’ scheme employs a non‐iterative decoder. Numerical results show that their proposed scheme achieves superior OOBE suppression than the other non‐iterative continuous derivative precoding schemes and NF schemes. Computational complexity, peak‐to‐average power ratio, and bit error rate are also analysed.

Channel bonding proposed in IEEE 802.11ac has the potential to multiply the physical data rate with wider bandwidths. However, the backward compatibility with legacy 802.11 devices makes the available frequency resource severely underutilised. Furthermore, the design that allocates the entire extended bandwidth to a single user is very inefficient when the frame size is very small. In this study, the authors propose a novel channel access scheme, which has successfully mitigated these two problems by scheduling multiuser parallel transmission in both downlink and uplink. Simulation results show that the proposed scheme can improve the spectral efficiency of 801.11ac dramatically. In addition, same as the scheme in the 802.11ac draft, the proposed scheme guarantees the backward compatibility with legacy 802.11 devices, remains distributed and contention based and has the capability to multiply the physical data rates for 802.11ac devices.

High peak‐to‐average‐ratio (PAPR) and large out‐of‐band emission (OOBE) are the two main shortcomings of orthogonal frequency division multiplexing (OFDM) signals for cognitive radios. Among all the existing techniques, it has been shown that precoding is an effective way for either reducing the PAPR or suppressing the OOBE. However, no work has focused on designing an effective precoding approach to reduce the PAPR and suppress the OOBE simultaneously. In this study, three new precoding approaches that can jointly suppress OOBE and reduce PAPR simultaneously are presented. The simulation results show that, firstly, all the three proposed precoding approaches can achieve the same power spectral density performance as the typical OOBE‐suppression precoding approach with the same spectral efficiency. Secondly, their PAPR performances are only slightly worse than the typical PAPR‐reduction precoding approach with a similar computational complexity. Finally, two of the three proposed precoding approaches do not cause any bit error rate (BER) performance degradation with respect to the conventional OFDM system. The abilities to suppress OOBE and PAPR jointly and to maintain the good BER performance make two of the three proposed approaches very favourable for practical applications.

In multiple-input multiple-output–orthogonal frequency division multiplexing (MIMO–OFDM) communications, the channel state information (CSI) of the forward link at each subcarrier is needed for precoder design at the transmitter to achieve the maximal diversity and/or multiplexing gains. In frequency division duplex (FDD) systems, the CSI needs to be estimated at the receivers and fed back to the transmitters. Owing to the limited network resources, there will be CSI feedback errors due to quantisation, delay and clustering (where one CSI feedback is used to represent a cluster of adjacent subcarriers for feedback reduction). Consequently, the system performance degrades and the gains expected from using MIMO diminish. To mitigate this performance degradation, an adaptive codebook-based CSI prediction and interpolation scheme is proposed for multiuser MIMO–OFDM systems. In this scheme, geodesic CSI prediction is employed at the receiver to mitigate the feedback delay effect and geodesic CSI interpolation is performed at the transmitter to mitigate the clustering feedback effect. Since the performance gain assumed by the CSI prediction and interpolation is limited by the low-resolution CSI quantisation, an adaptive codebook scheme is proposed to be used to support the CSI prediction and interpolation. Simulation results show that the proposed scheme is effective in mitigating the performance loss due to quantisation, feedback delay and clustering feedback.

In frequency division duplex (FDD) wireless MIMO communications, the channel state information (CSI) of the forward link needs to be fed back to the transmitter for precoder design. In practice, the inevitable CSI feedback delay results in system performance degradation. In this paper, to mitigate the CSI feedback delay, an efficient adaptive double codebook based CSI prediction scheme is proposed by exploiting the LTE Release 10 double codebook framework. Simulation results demonstrate that the proposed scheme is effective in mitigating the CSI feedback delay in single- and multi-user (SU/MU) MIMO-OFDM systems.

Interference Alignment (IA) transceiver designs are currently of great interest to the community. They are, however, limited to certain configurations. This paper seeks to show that for general multiuser MIMO systems, a) there is a relationship between MMSE designs and IA, and b) MMSE designs should be used instead of IA ones. The former is done by proving that MMSE designs naturally have IA-like behaviors. The latter is done using several arguments. One of them is based on the MIMO X network numerical results involving the generalized iterative approach (GIA) and the previously proposed MMSE-IA. In the simulation, the hybrid IA approach is clearly outperformed by the purely MMSE based GIA. The GIA is also run for the MIMO M network.

This paper considers a two-way multiple-input multiple-output (MIMO) relay system with multiple relay nodes between two end nodes. A novel iterative approach is introduced for jointly designing the precoders and decoders at the two end nodes, and the processors at the relays to maximize the system capacity. Numerical results for the per-node power constraint show the convergence behavior of the proposed approach and give a performance benchmark for the analog network coding scheme.

In MIMO-OFDM communications, the channel state information (CSI) of the forward link is needed for precoder design at the transmitter to achieve the maximal performance gains. In frequency division duplex (FDD) systems, the CSI estimated at the receivers needs to be fed back to the transmitters. Because of the limited network resources, there will be CSI feedback errors due to quantization, delay and clustering (where one CSI feedback is used to represent a cluster of adjacent subcarriers for feedback reduction). Consequently, the system performance degrades and the gains expected from using MIMO diminish. To mitigate this performance degradation, an adaptive codebook-based CSI prediction and interpolation scheme is proposed for multiuser MIMO-OFDM systems. In this scheme, geodesic CSI prediction is employed at the receiver to mitigate the feedback delay and geodesic CSI interpolation is performed at the transmitter to mitigate the cluster feedback effect. Since the performance gain assumed by the CSI prediction and interpolation is limited by the low resolution CSI quantization, a simplified adaptive codebook is developed to support the CSI prediction and interpolation. Simulation results show that the proposed scheme is effective in mitigating the performance loss due to quantization, feedback delay and cluster feedback.

A novel generalized iterative approach is proposed for designing the MMSE MIMO processors (precoders, relay processors and decoders) for two amplify-and-forward relaying schemes: two-hop (2Hop) and cooperative (Coop) relaying schemes. The MMSE design can be achieved for communication links with two end nodes and multiple relay nodes (all nodes with multiple antennas) subject to either the per-node power constraint or the per-antenna power constraint. Simulation results show that there exist circumstances where 2Hop performs as well as Coop. In addition, there exist scenarios that the conventional Direct Transmission (DT) scheme can actually outperform Coop if optimum modulation coding schemes and sophisticated cooperation protocols are not employed for Coop.

Network MIMO (multiple-input multiple output), also known as Coordinated Multipoint (CoMP), is a key enabling technology of future cellular systems. A unified framework and a novel generalized iterative approach (GIA) is proposed for the minimum mean square error (MMSE) transceiver design of general MTMR (multiple-transmitter multiple-receiver) MIMO systems with different CoMP configurations (including Non-Coordinated Multipoint, Coordinated Beamforming, Joint Processing Downlink, Joint Processing Uplink and Joint Processing Single User) subject to general linear power constraints. Performance analysis of the different CoMP configurations is provided for the per-antenna and total power constraints at each base station or user equipment. The result provides a benchmark for joint transceiver designs based on other criteria.

The novel fast iterative approach (FIA), transmit covariance optimization approach (TCOA) and decoder covariance optimization approach (DCOA) are proposed for jointly designing the minimum mean square error (MMSE) precoder and decoder of single-user multiple-input and multiple-output (MIMO) systems subject to general power constraints. Specifically, the total power constraint and the more practical per-antenna power constraint are discussed. With the rank constraint on the precoder or decoder relaxed, both the TCOA and DCOA are shown to yield the global optimum solution. The FIA is also shown to provide the global optimum solution when the transmit covariance matrix is full rank (equivalent to the TCOA) and/or the decoder covariance matrix is full rank (equivalent to the DCOA). These three approaches form a unified framwork for MMSE transceiver designs for both single-user and multiuser MIMO systems. The global optimality and comparison of the proposed three approaches are supported by numerical results.

To mitigate the sum rate ceiling problems, high-resolution quantization and feedback schemes for the channel state information (CSI) are highly demanded in multi-user (MU) multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. In this paper, we investigate three adaptive codebook-based limited feedback techniques for MU-MIMO-OFDM broadcast systems. Using the channel covariance and mean respectively, adaptive codebook techniques I and II are extensions of two adaptive codebook techniques proposed for single-user MIMO single-carrier systems. Technique III is a totally novel proposal wherein both channel covariance and mean are exploited in the adaptive codebook construction. Numerical results show that the adaptive codebook approaches have significant sum rate gain compared to the fixed codebook solution and technique III outperforms techniques I and II.

In this paper, we have developed a novel unified approach to deal with arbitrary transmitted power constraints for designing jointly the MMSE precoders and decoders in uplink multiuser MIMO systems. This work is an extension of the first iterative approach developed by Serbetli and Yener for per-user power constraint. An explicit expression relating Lagrange multipliers with the per-user constraint can be obtained using the proposed approach to mitigate the time consuming root searching for the Lagrange multipliers. Moreover, the explicit expression allows the MMSE solution subject to arbitrary transmit power constraints including the practical per-antenna power and peak power constraints. It is shown in some two-user numerical examples that the raw BER performance obtained from per-antenna power constraint is similar to that of the per-user power constraint and is 1-2.5 dB better than that of the peak power constraint.

This paper addresses the coded cooperation in single carrier transmission with frequency-domain equalization. A practical cooperation strategy is provided to facilitate the time-frequency-space diversity for the coded single carrier frequency division multiple access system over frequency-selective Rayleigh block fading channels. To take advantage of the time-frequency dispersion and to facilitate the space diversity through cooperation, each user transmits his partner's and his own interleaved data on different subcarriers spreading over the entire available bandwidth. The allocation of subcarriers to each user and his partners can be either pre-specified or dynamically determined. Numerical simulations show that the proposed scheme outperforms the direct transmission with improved diversity gains.

A practical cooperation strategy is provided to facilitate the time-frequency-space diversity for the coded OFDMA system over frequency-selective Rayleigh block fading channels. To take advantage of the time-frequency dispersion and to facilitate the space diversity through cooperation, each user transmits his partner's and his own interleaved data on different subcarriers spreading over the entire available bandwidth. The allocation of subcarriers to each user and his partners can be either pre-specified or dynamically determined. Theoretical analysis on pairwise error probability and frame error probability is given to illustrate the improved diversity gain which is further verified by computer simulation results.

In OFDM systems the oscillators used at the digital to analog converter (DAC) and analog to digital converter (ADC) to derive sampling instants at the transmitter and receiver will never have exactly the same period. Thus sampling instants slowly shift relative to each other. In this paper we investigate the performance of a frequency domain re-sampler for a MIMO OFDM system which was developed for a proposed IEEE 802.11n TGn proposal. We present analysis and simulation to demonstrate that this technique results in negligible performance loss relative to perfect sample timing. In addition, the complexity of the technique is compared to a competing technique based upon a variable digital delay filter (Farrow filter). It is shown that the frequency domain re-sampler results in a lower complexity design. Also memory requirements for the design are causal and very low.

A modified asymptotic linear solver is proposed to estimate emitter locations by solving the intersections of hyperbolas defined by measured time differences of arrivals. The algorithm achieves simplicity and computational efficiency by removing the nonlinearity inherent in hyperbolic localization problems. Off-line parameter optimization is required to minimize the estimation error. Simulation results show that performance of the proposed new algorithm is similar to that of a maximum-likelihood estimator in regions of interest.

Novel space-time processing techniques are developed to determine the weights of broadband multiple antenna systems so that independent wireless channels can be established between two localized transceivers in the same bandwidth and the same time (and the same spreading code, if there is any) by taking advantages of the multipath propagation feature.

Spread spectrum techniques and collision avoidance multiple access protocols are combined to form a new set of medium access protocols for mobile wireless ad hoc networks. The request-to-send and clear-to-send message dialogue solves the "hidden terminal" and the "exposed terminal" problems and speeds up the retransmission. The spreading code assignment avoids disruption of any ongoing transmission by an intruder. Simulation results confirm that a higher channel throughput is achieved by the new protocols even in a dense network.

A new global positioning system (GPS)-based routing protocol for ad hoc networks, called zone-based hierarchical link state (ZHLS) routing protocol, is proposed. In this protocol, the network is divided into nonoverlapping zones. Each node only knows the node connectivity within its zone and the zone connectivity of the whole network. The link state routing is performed on two levels: focal node and global zone levels. Unlike other hierarchical protocols, there is no cluster head in this protocol. The zone level topological information is distributed to all nodes. This "peer-to-peer" manner mitigates traffic bottleneck, avoids single point of failure, and simplifies mobility management. Since only zone ID and node ID of a destination are needed for routing, the route from a source to a destination is adaptable to changing topology. The zone ID of the destination is found by sending one location request to every zone. Simulation results show that our location search scheme generates less overhead than the schemes based on flooding. The results also confirm that the communication overhead for creating and maintaining the topology in the proposed protocol is smaller than that in the flat LSR protocol. This new routing protocol provides a flexible, efficient, and effective approach to accommodate the changing topology in a wireless network environment.

A novel blind space-time algorithm for multiuser detection with interference rejection in DS-CDMA cellular communication systems is presented. Beamforming and equalization are performed simultaneously where complex weights are adaptively determined by a hybrid combination of the constant modulus algorithm and the decision-directed algorithm. The adaptive scheme converges approximately after 100 iteration steps when the input SNR is 10 dB. The performance of the proposed approach is as good as the least mean square approach using training sequences. A 20 dB enhancement of SINR is obtained when the maximum difference of the received signal power is up to 6 dB.

A novel approach is developed to determine the weights of broadband multiple antenna systems so that independent wireless channels (channel diversity) can be established between two localized transceivers in the same bandwidth and the same time (and the same spreading code, if there is any) by taking advantages of the multipath propagation feature.

The location dependent effect of the acoustic field received by a linear array is modeled as an extra "loss" factor in the complex spectral variable. A high-resolution algorithm combining the singular value decomposition method and the eigen-matrix pencil method is then employed to find the complex directions representing the incoming directions and the location dependent factors of multipath and multimode arrivals. Five key features (namely, noise immunity, robustness, resolution, accuracy, and physical insight) of the proposed algorithm are studied using numerical examples.

Multiple ray paths are resolved using high-resolution digital signal processing algorithms. The conventional complex channel model for wireless indoor propagation is extended to include the frequency dependence of individual rays which can be used to classify the ray arrivals and provide physical insight of the channel. This approach may be crucial to broadband CDMA systems.