The paper considers monostatic ISAC transceivers relying on in-band full-duplex (IBFD) capability to achieve simultaneous sensing and communication. These systems transmit a waveform for both communication and sensing and receive target echoes and incoming communication signals from other nodes. The major challenge is interference cancellation, suppressing self-interference (SI) from the leaked transmitted signal and the mutual interference (MI) between the echo for sensing and incoming signals for communication. This paper proposes an advanced joint analog and two-stage digital interference cancellation (DIC) structure to address this challenge, enabling simultaneous communication and sensing in IBFD ISAC systems. The analog SI cancellation structure leverages an analog least mean square (ALMS) loop with specific design constraints to preserve the integrity of sensing signals. A track-and-hold mechanism is employed to avoid ALMS weighting coefficient variation caused by the strong reflected sensing signal and uplink communication signal. The novel two-stage DIC first cancels residual SI for sensing and then mitigates echo sensing signals for communication. Doppler effects in the echo signals are compensated during the second stage to ensure effective suppression of sensing signals and accurate retrieval of communication signals. Simulation results validate the proposed approach, showcasing its strong communication and sensing performance and robust interference cancellation capabilities.

Self-interference (SI) cancellation for full-duplex (FD) multiple input multiple output (MIMO) systems is challenging due to both hardware and signal processing complexity. In this paper, a beam-based adaptive filter structure with analog least mean square (ALMS) loops is proposed to significantly reduce the complexity of SI cancellation for FD MIMO systems. With this structure, the number of adaptive filters required for SI cancellation scales linearly with the number of transmit beams rather than quadratically with the number of antennas. Furthermore, to avoid additional transmit chains used to up-convert the beam signals to generate reference signals for the ALMS loops, a novel method is proposed to select the optimized reference signals from all transmitted signals. In addition, our stationary analysis shows that the proposed structure for FD MIMO systems outperforms the ALMS loop employed for an FD single input single output system. Simulations are conducted to confirm the theoretical analyses.

In this paper, the performance of in-band full- duplex OFDM relaying systems with energy- harvesting and self-interference cancellation in the polarization domain is analyzed. Specifically, we use the time switching-based relaying protocol to implement energy harvesting. The harvested energy is used by the relay to forward the transmitted information from the source. To cancel the self-interference, the polarization-enabled digital self-interference cancellation scheme is deployed at the relay. Our simulation results show that the full-duplex OFDM energy harvesting relaying system almost doubles the throughput, while maintaining the same bit error performance by a modest increase in the signal-to-noise ratio compared to the half-duplex OFDM energy harvesting relaying system. It is also revealed that the optimal time splitting factor should be less than 0.3 to maximize the full-duplex system throughput.

Analog least mean square (ALMS) loop is a promising method to cancel self-interference (SI) in in-band full-duplex (IBFD) systems. In this paper, the steady state analyses of the residual SI powers in both analog and digital domains are firstly derived. The eigenvalue decomposition is then utilized to investigate the frequency domain characteristics of the ALMS loop. Our frequency domain analyses prove that the ALMS loop has an effect of amplifying the frequency components of the residual SI at the edges of the signal spectrum in the analog domain. However, the matched filter in the receiver chain will reduce this effect, resulting in a significant improvement of the interference suppression ratio (ISR). It means that the SI will be significantly suppressed in the digital domain before information data detection. This paper also derives the lower bounds of ISRs given by the ALMS loop in both analog and digital domains. These lower bounds are joint effects of the loop gain, tap delay, number of taps, and transmitted signal properties. The discovered relationship among these parameters allows the flexibility in choosing appropriate parameters when designing the IBFD systems under given constraints.

Generalized continuous wave synthetic aperture radar (GCW-SAR) is a promising new imaging radar system since it applies the full-duplex (FD) transmission technique to achieve continuous signaling in order to overcome several fundamental limitations of the conventional pulsed SARs. As in any FD wireless communication system, self-interference (SI) is also a key problem which can impact on the GCW-SAR system. In this paper, the analog least mean square (ALMS) loop in the radio frequency domain is adopted to cancel the SI for a GCW-SAR system with periodic chirp signaling. The average residual SI power after the ALMS loop is analyzed theoretically by a stationary analysis. It is found that the ALMS loop not only works with random signals in general FD communication systems, but also works well with the periodic signal in GCW-SAR systems. Simulation results show that over 45 dB SI cancellation can be achieved by the ALMS loop which ensures the proper operation of the GCW-SAR system.

This paper evaluates the performance of an analog least mean square (ALMS) loop employed to cancel self-interference in in-band full-duplex (IBFD) orthogonal frequency division multiplexing (OFDM) systems. Cyclostationary analysis is applied to investigate the behavior of the ALMS filter. It is revealed that the performance of the ALMS filter for OFDM systems primarily depends on windowing function rather than pulse shaping as in single carrier systems. It is also noticed that the ALMS loop in OFDM systems provides a much higher level of sel-interference (SI) suppression because OFDM signals lead to reduced the error of the interference channel modelling with the adaptive filter. Simulations are then conducted to verify the theoretical findings.

In Wireless Body Area Networks (WBANs), on-body channels undergo temporal variations predominantly because of the body motion and shadowing of tissue. This paper focuses on a common human activity, walking, to explore the characteristics of the dynamic on-body propagation channel. A customized portable wireless sounder is built and utilized to collect the original on-body channel data both for the indoor and outdoor environments. We focus on exploring the second-order statistics of the on-channel data during walking, including the temporal autocorrelation, the cross- correlation and the path loss discrepancy between the two correlated links. This channel characterization facilitates more efficient designs and evaluations of WBAN systems, including more efficient network resource allocation and more efficient deployment of cooperative communication.

In Wireless Body Area Networks (WBANs), the tradeoff between network throughput and energy efficiency remains a key challenge. Most current transmission schemes try to cope with the challenge from the perspective of general Wireless Sensor Networks (WSNs), which may not take the peculiarities of WBAN channels into account. In this paper, we take advantage of the correlation of on-body channels in walking scenarios to achieve a better tradeoff between throughput and energy consumption. We first analyze the characteristics of on-body channels based on realistic channel gain datasets, which are collected by our customized wireless transceivers in walking scenarios. The analytical results confirm the rationale of our newly proposed transmission scheme A3NC, which explores the combination of the aggregative allocation (AA) mechanism in MAC layer and the Analog Network Coding (ANC) technique in PHY layer. Both theoretical analyses and simulation results show that the A3NC scheme achieves significant improvement in upload throughput and energy efficiency, compared to the conventional approaches.

Wireless Body Area Network (WBAN) has been considered as a revolutionary technology to address current healthcare needs. However, before the extensive deployment of WBAN, one main challenge to be met is how to balance the trade-off between data transmission rate and energy efficiency. In this paper, we utilize WBAN's spatial correlation characteristics during movement and propose an efficient cross-layer scheme, named A3NC, which combines analog network coding (ANC) and MAC layer channel allocation. Our simulation results show that the A3NC scheme achieves significant improvement in upload throughput and energy efficiency compared to the conventional approaches. Meanwhile, our scheme also maintains a better balance between correlated sensors' upload throughput.

This study devises for the first time a comprehensive analysis of decode‐and‐forward, space–time coded, fully cooperative orthogonal frequency division multiplexing (OFDM) systems from both error performance and energy efficiency perspectives, in either identically or non‐identically distributed frequency selective Rayleigh fading channels. The authors’ analyses show the interesting result that the fully cooperative OFDM is better than direct OFDM transmission from both perspectives in many cases, especially at a low power and low signal‐to‐noise ratio regime, making it particularly useful for emerging low power applications, such as wireless body area networks.

In this study, the authors investigate energy efficiency in antenna selection multi‐input multi‐output automatic repeat request (MIMO ARQ) wireless systems. The authors first derive an approximate expression for the average frame‐error rate (FER) in antenna selection MIMO systems over quasi‐static Nakagami‐ m fading channels. The FER approximation is then used to obtain an analytical expression of an energy‐efficiency metric that is defined as the total energy required to successfully deliver one information bit. The authors prove that this energy‐efficiency metric is a quasi‐convex function with respect to the average signal‐to‐noise ratio value. Based on this analysis, the authors obtain the optimal value of the average energy per transmitted data symbol such that the total energy consumption in the system is minimised. The results show that the energy efficiency in antenna selection MIMO ARQ systems is improved when the number of equipped antennas is increased. Simulation results are provided to validate the analysis.

A bit error rate (BER) estimation-based adaptive space-time-frequency coded (STFC) multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) wireless body area network (WBAN) system is proposed in this paper. It is designed to improve the average BER performance for high data rate applications while maintaining a reasonably high throughput in body-to-external links of a WBAN. The performance improvement fundamentally translates to power saving at the transmitter and/or receiver, thus reducing battery requirements and size of WBAN devices. Two novel blocks, namely the BER estimation-based adaptive algorithm which controls the set of modulation, STFC coding rate, and power of signal constellations, and the linearly interpolated CM4 WBAN channel model are implemented in the proposed adaptive STFC MB-OFDM UWB WBAN system. Three sets of adaptive schemes are defined, each of which is determined by two BER thresholds, i.e. the lower and upper thresholds, which are in turns calculated from the non-adaptive average BER performance as the benchmark. Simulation results show a significant improvement in the performance and/or Tx/Rx power saving, with the cost of a slight reduction in the throughput.

In a multiple-input multiple-output (MIMO), multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system, coherent detection requires the transmission of a large number of symbols for channel estimation, thus reducing the bandwidth efficiency. For the first time, this paper proposes unitary differential space-time-frequency codes (DSTFCs) for MB-OFDM UWB communications, which increase the system bandwidth efficiency because no channel state information (CSI) is required. The proposed system would be useful when CSI is unavailable at the receiver, such as when the transmission of multiple channel estimation symbols is impractical or uneconomical. The coding and decoding algorithms for the proposed DSTFCs are then derived for both constant envelope modulation scheme, such as PSK (phase shift keying) and 4QAM (quadrature amplitude modulation), and multi-dimensional modulation scheme, such as DCM (dual carrier modulation). The paper also quantifies for the first time the diversity order of a DSTFC MB-OFDM system. Simulation results show that the application of DSTFCs can significantly improve the bit error performance of conventional differential MB-OFDM system (without MIMO), and even provide much better bit error performance than the conventional coherent MB-OFDM system (without MIMO) at high signal-to-noise ratios.

This paper investigates the performance of the space-time-frequency coded (STFC) multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) system over wireless body area network (WBAN) channels, using the Alamouti code. Different MIMO configurations and different modulations are used for comparison. The effect of body directions is also assessed by simulation in this paper. Simulation results show that the proposed STFC MB-OFDM UWB system provides a significantly better BER performance, compared to the conventional MB-OFDM system, even from a reasonably low Eb/Norange. The simulations also confirm that the body direction affects the system performance significantly due to the availability of line-of-sight (LOS) or partial LOS paths. Overall, the STFC MB-OFDM UWB system can provide an energy efficient and robust, high data rate transmission for WBAN applications.

In this paper, the application of space time trellis codes to multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems is investigated. We propose a coding scheme that could fully exploit all the available channel diversity, including space diversity, frequency diversity and inter-subband diversity. Performance of the proposed system is compared with that of the conventional MB-OFDM UWB system in terms of packet error rate (PER). Simulation results show that this system outperforms the conventional one. As an example, an improvement of at least 5 dB at PER=10-2 could be achieved over the IEEE 802.15.3a channel models of CM1 and CM2 in the system equipped with only two transmit antennas and one receive antenna. Moreover, the system performance could be further improved when the number of antennas and/or the number of trellis states is increased.

In a multiple-input multiple-output (MIMO) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system, coherent detection where the channel state information (CSI) is assumed to be exactly known at the receiver requires the transmission of a large number of symbols for channel estimation, thus reducing the bandwidth efficiency. This paper examines the use of unitary differential space-time frequency codes (DSTFCs) in MB-OFDM UWB, which increases the system bandwidth efficiency due to the fact that no CSI is required for differential detection. The proposed DSTFC MB-OFDM system would be useful when the transmission of multiple channel estimation symbols is impractical or uneconomical. Simulation results show that the application of DSTFCs associated with dual carrier modulation (DCM) can significantly improve the bit error performance of conventional differential MB-OFDM system (without MIMO), and even provide better bit error performance than the DSTFC MB-OFDM system associated with constant envelope modulation schemes.

Constructions of square, maximum rate complex orthogonal space–time block codes (CO STBCs) are well known, however codes constructed via the known methods include numerous zeros, which impede their practical implementation. By modifying the Williamson and Wallis-Whiteman arrays to apply to complex matrices, we propose two methods of construction ofsquare, order-$4n$CO STBCs fromsquare, order-$n$codes which satisfy certain properties. Applying the proposed methods, we constructsquare,maximum rate, order-8 CO STBCs with no zeros, such that the transmitted symbols are equally dispersed through transmit antennas. Those codes, referred to as theimproved square CO STBCs, have the advantages that the power is equally transmitted via each transmit antenna during every symbol time slot and that a lower peak-to-average power ratio (PAPR) is required to achieve the same bit error rates as the conventional CO STBCs with zeros.

This paper proposes a general framework of space-time-frequency codes (STFCs) for multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wide band (UWB) communications systems. A great similarity between the STFC MB-OFDM UWB systems and conventional wireless complex orthogonal space-time block code (CO STBC) multiple-input multiple-output (MIMO) systems is discovered. This allows us to quantify the pairwise error probability (PEP) of the proposed system and derive the general decoding method for the implemented STFCs. Based on the theoretical analysis results of PEP, we can further quantify the diversity order and coding gain of MB-OFDM UWB systems, and derive the design criteria for STFCs, namely diversity gain criterion and coding gain criterion. The maximum achievable diversity order is found to be the product of the number of transmit antennas, the number of receive antennas, and the FFT size. We also show that all STFCs constructed based on the conventional CO STBCs can satisfy the diversity gain criterion. Various baseband simulation results are shown for the Alamouti code and a code of order 8. Simulation results indicate the significant improvement achieved in the proposed STFC MB-OFDM UWB systems, compared to the conventional MB-OFDM UWB ones.

Though cooperative communication has been intensively examined for general wireless systems, such as mobile and ad-hoc networks, it has been almost unexplored in the case of space-time-frequency coded multi-band OFDM ultra-wideband (STFC MB-OFDM UWB). This paper proposes a framework of cooperative communication in such systems where nodes are equipped with only one antenna. Simulation results show that cooperative communication might, in some cases, provide better error performance than non-cooperative communication without any additional transmission power.

In this paper, we expand the idea of spreading the transmitted symbols in OFDM systems by unitary spreading matrices based on the rotated Hadamard or rotated Discrete Fourier Transform (DFT) matrices proposed in the literature to apply to Space-Time Coded Multiple-Input Multiple- Output OFDM (STC-MIMO-OFDM) systems. We refer the resulting systems to as STC-MIMO Block Spread OFDM (STC-MIMO-BOFDM) systems. In the proposed systems, a multi-dimensional diversity, including time, frequency, space and modulation diversities, can be used, resulting in better bit error performance in frequency selective Rayleigh fading channels compared to the conventional OFDM systems with or without STCs. Simulations carried out with the Alamouti code confirm the advantage of the proposed STC-MIMO-BOFDM systems.

Constructions of square, maximum rate complex orthogonal space-time block codes (CO STBCs) are well known, however codes constructed via the known methods include numerous zeros, which impede their practical implementation. By modifying the Williamson and Wallis-Whiteman arrays to apply to complex matrices, we propose two methods of construction or square, order-4n CO STBCs from square, order-n codes, which satisfy certain properties. Applying the proposed methods, we construct square, maximum rate, order-8 CO STBCs with no zeros, such that the transmitted symbols equally disperse through transmit antennas. Those codes, referred to as the improved square CO STBCs, have the advantages that the power is equally transmitted via each transmit antenna during every symbol time slot and that a lower peak-to-mean power ratio per each antenna is required to achieve the same bit error rates as for the conventional CO STBCs with zeros

Although the generation of correlated Rayleigh fading envelopes has been intensively considered in the literature, all conventional methods have their own particular shortcomings, which seriously impedes their applicability. A very general, straightforward algorithm is proposed for the generation of an arbitrary number of Rayleigh envelopes with any desired, equal or unequal power in wireless channels, either with or without Doppler frequency shifts. The proposed algorithm can be applied in the case of spatial correlation, such as with antenna arrays in multiple input multiple output (MIMO) systems, or spectral correlation between random processes, as in orthogonal frequency division multiplexing (OFDM) systems. It can also be used for generating correlated Rayleigh fading envelopes in either discrete-time instants or a real-time scenario. Besides being more generalized, our proposed algorithm is more precise, while overcoming all the shortcomings of conventional methods.

The paper deals with antenna selection techniques for wireless channels utilizing differential space-time modulation. We propose here the restricted N-out-of-M antenna selection technique providing relatively good bit error performance, while using only one feedback bit for transmit diversity purpose. In addition, we also present an improved N-out-of-(N+1) antenna selection technique, which shortens the time required for processing feedback information. These techniques remarkably improve performance of wireless channels using differential detection.