As the use of smartwatches continues to grow, improving the accuracy of tracking for smartwatch users has become increasingly important. Smartwatches are worn on the wrist, which means the sensors may detect free and independent hand movements while walking. This creates challenges for pedestrian dead reckoning (PDR) using the inertial sensors embedded in smartwatches because the data may lose information on walking characteristics. Therefore, it is essential to identify the user’s walking state first, whether moving or stationary, and then conduct precise step detection, which is a critical factor in reducing errors in PDR. In this study, we propose an adaptive step detection algorithm tailored to four categorized user activity states: walking, running, hand movements while standing, and hand movements while walking. We conducted human activity recognition (HAR) with these four categories to identify the user’s state and decide the appropriate method for step detection. To enable implementation on mobile devices, we propose a lightweight deep learning-based HAR network utilizing a grouped convolutional layer. The proposed network reduces the number of trainable parameters by approximately one-third compared to conventional CNN structures while achieving $\mathbf{9 6. 4 5 \%}$ accuracy in activity classification. For adaptive step detection, we utilize gyroscope data for normal walking, accelerometer data for running, and walking frequency obtained via fast Fourier transform (FFT) from normal walking data for segments of walking interspersed with hand movements. By applying these tailored step detection methods to each walking scenario, we enhance step detection accuracy, thereby improving smartwatch user position and distance estimation in overall PDR.

In this paper, unscented Kalman filter (UKF) based on maximum correntropy criterion (MCC) instead of minimum mean square error (MMSE) criterion, and it is applied to tightly coupled integration of inertial navigation system (INS) and ultra wide-band (UWB). UWB can measure distance with an accuracy of less than 30cm in line-of-sight environment, but provides distance measurement with various types of non-Gaussian uncertainty noise in non-line-of-sight environment. In this case, if the INS/UWB system is configured with the existing MMSE-based filter, a large error occurs. To solve this problem, in this paper, UKF is designed based on MCC. Through simulation analysis, it is confirmed that the proposed filter has robust characteristics against UWB uncertainty and enables stable INS/UWB integration.

In this paper, we investigate the user scheduling and power allocation scheme for a millimeter wave non-orthogonal multiple access system. To reduce the feedback overhead, random beamforming is adopted at a base station. The optimization problem is formulated to maximize the energy efficiency. To solve this problem, we first address the user scheduling and power allocation problem separately, then an iterative algorithm is proposed to jointly optimize the user scheduling and power allocation. Simulation results show that the proposed scheme achieves higher energy efficiency than the conventional scheme.

In this paper, we investigate a full-duplex relay system where a source communicates with a destination via a decode-and-forward relay in the presence of randomly located eavesdroppers. We derive analytical expressions for the secrecy outage probability and the average secrecy rate of the system. The validity of analysis is verified by computer simulations.

In this paper, we propose an optimal beamforming scheme for secure communication in a full duplex (FD) wireless powered communication (WPC) system. In the proposed scheme, the power beacon transmits an energy signal to a source which acts as a jamming signal to an eavesdropper. We formulate an optimization problem to find an optimal beamforming for the power beacon and propose an algorithm to solve the problem. Simulation results show the secrecy performance of FD WPC system with the proposed beamforming scheme.

In this paper, we investigate underlay device-to-device (D2D) communication in cellular networks where D2D transmitters transmit data to their receivers using cellular spectrum. We analyze the average sum throughput of D2D receivers in interference-limited channels. To enhance it, we propose a semi-distributed spectrum access scheme, which consists of two stages. In the first stage, the cellular base station divides whole D2D transmitters into multiple groups and assigns a different subchannel to each group. In the second stage, D2D transmitters in each group randomly access the subchannel assigned to it with predetermined access probability. We formulate an optimization problem to find groups and access probabilities, which maximize the average sum throughput. To overcome the prohibitive computational complexity to obtain its optimal solution, we decompose it into two subproblems: one to find groups and one to find access probabilities. A heuristic grouping algorithm is adopted to solve the former, and a branch-and-bound-based algorithm is proposed to solve the latter with achieving a target accuracy. The validity of the branch-and-bound-based algorithm is shown by performance comparison with an exhaustive search. It is shown that the heuristic grouping and the branch-and-bound-based algorithm achieve higher average sum throughput than conventional methods.

In this paper, we propose an optimal source power allocation scheme for a two-hop amplify-and-forward relaying network with cooperative jamming where a source and destination transmit jamming signals. For the full CSI of all link and the CSI for desired link, the source power is optimally splitted to minimize the secrecy outage probability. Simulation results show that the proposed power allocation scheme improves the secrecy rate and reliability.

In this paper, we investigate p-persistent random access used for a spectrum sensing cognitive radio network with multiple secondary users to avoid a collision. Effect of the imperfect sensing, false alarm and miss detection, is considered. We analyze the total throughput of the secondary network and propose throughput optimization algorithm. It is shown that simulation results well match with analysis results.

In this paper, we investigate an underlay relay-assisted cognitive radio network where a secondary relay harvests energy from a secondary source's signal. Outage probability of the secondary network is derived in closed form under a harvested energy constraint at the relay and an interference constraint at the primary user. Also, optimal energy harvesting duration is obtained. Analytical results are verified by computer simulation.

We propose a resource allocation scheme for the downlink of a two-tier wireless network in which femto-base stations are used as relays to macro- users. In the proposed scheme, subcarriers and relays are assigned to users assuming equal power allocation by all base stations to all subcarriers, and then, power is allocated to users. Simulation results show that the proposed scheme achieves higher sum rate of users than the random subcarrier assignment (RSA) scheme, more fair resource allocation to users than the greedy scheme, and lower total transmit power of base stations than the greedy and the RSA schemes.

In this paper, an inter-cell interference coordination algorithm is proposed for a downlink OFDMA relay network with multicells. In the proposed algorithm, the resource allocation problem is heuristically divided into subchannel allocation and subchannel restriction for interference coordination. Simulation results show that the proposed algorithm achieves higher cell edge user throughput and cell throughput than the proportional fair algorithm.

We propose a new resource allocation scheme for a downlink orthogonal frequency division multiple access (OFDMA) relay network with imperfect channel state information (CSI). In the proposed scheme, resources are allocated to the channels between a base station, relays, and users such that the weighted sum of goodput is maximized under power constraints of the base station and relays. Simulation results show that the proposed scheme achieves much higher weighted sum of goodput than a conventional scheme.

In this paper, we analyze the outage probability and average throughput of opportunistic relaying with ARQ when the outdated channel state information (CSI) is available for relay selection. Its diversity order is analyzed to show that it is determined by the number of relays and the maximum number of ARQ rounds. Numerical results verify our analysis by comparison with computer simulation and show the effect of outdated CSI on its outage probability, diversity order, and average throughput.

In this paper, we analyze the amplify-and-forward (AF) opportunistic relaying with multiple interferers over Rayleigh fading channels. We derive the closed-form expression of the outage probability for the AF opportunistic relaying with multiple interferers which have arbitrary transmit power. Numerical results verify the validity of our theoretical analysis by comparison with Monte Carlo simulations and demonstrate the excellence of the AF opportunistic relaying by comparison with conventional relaying systems.

In this paper, a multiuser DF-AF cooperative wireless network is considered. When a user is assigned to another user by a base station, the user relays the received signal from another user by using either the DF or the AF protocol. We consider two types of feedbacks: full feedback and limited feedback. For full feedback cases, three relay assignment schemes are considered. The relay assignment scheme with limited feedback is also considered to reduce the signaling overhead caused by full feedback. The simulation results show that in full feedback case, the worst user outage probability of the min-max assignment scheme is much lower than that of the greedy assignment scheme.

In this paper, we investigate a joint resource allocation for a multiuser two-way OFDMA relay network. To reduce the computational complexity, we separate the joint resource allocation into two stages, subcarrier allocation and power allocation, and propose resource allocation schemes. In the proposed schemes, resources are allocated to the user-pairs and relays to maximize the achievable sum-rate over all user-pairs under proportional fairness constraints. Simulation results show that the proposed schemes achieve higher spectral efficiency and fairness index, and lower outage probability compared with the static scheme.

In this paper, we propose a new resource allocation scheme for an OFDMA relay network with multicells. In the proposed scheme, by sharing the channel state information (CSI) between base stations, resources are allocated to users and relays to maximize the overall sum of the achievable rate under fairness constraints. Simulation results show that the proposed scheme achieves higher spectral efficiency per subcarrier than the static scheme and reduces the outage probability compared to the static and greedy schemes.

In this paper, we introduce a collision model for vehicular cluster and we propose path selection algorithms for multi-hop VANETs. That is, we propose the intuitive algorithm named range-aware broadcasting (RAB), the collisions minimized optimal path selection algorithm (CM-Opt), SNR-guaranteed optimal path selection algorithm (SNRG-Opt), low-complexity SNR-guaranteed path selection algorithm (Low-SNRG), and distributed algorithms to reduce the number of collisions and/or reduce the complexity. We show that Low-SNRG has same performance as SNRG-Opt. Through computer simulations, it is shown that the proposed algorithms reduce the number of collision significantly. Also, it is shown that Low-SNRG has almost same average number of collisions as CM-Opt in spite of its low complexity. Also, the distributed path selection algorithm has similar performance to the non-distributed algorithms.

In this paper, randomized distributed space-frequency coding (R-DSFC) scheme is proposed for decentralized wireless relay networks. We consider relay-assisted ARQ to overcome the problem such as transmission failure caused by lack of the knowledge of the number of relays. We analyze the throughput, the maximum achievable diversity order, and the coding gain of the proposed scheme and show that the proposed scheme achieves multipath diversity. Also, we formulate the optimization problem for a randomization matrix to maximize the coding gain. Simulation results show that the proposed scheme improves the throughput and the reliability.

In this paper, we propose a new adaptive subcarrier allocation for a multiuser two-way OFDMA relay network. In the proposed algorithm, subcarriers are allocated to the user-pairs and relays to maximize the achievable sum-rate over all user-pairs while satisfying the minimum rate requirement for each user-pair. Simulation results show that the proposed algorithm improves spectral efficiency and fairness.

In this paper, a new subcarrier allocation algorithm is proposed for an uplink multiuser OFDM relay network. To achieve fairness for a source and relay, we consider the minimum rate requirement for a source and the power constraint on a relay, respectively. An optimization problem with fairness constraints is formulated and the subcarrier allocation criterion is obtained by using convex optimization. In the proposed algorithm, if all sources meet the minimum rate requirement, a subcarrier is allocated to a source-relay pair which has the largest instantaneous rate to maximize the sum of the achievable rate of a source. Otherwise, a subcarrier is allocated to a source-relay pair which has the smallest achievable rate to improve fairness for a source. Simulation results show that the proposed algorithm improves fairness and spectral efficiency for a source.

In this paper, a new resource allocation scheme is proposed for a two-way OFDM relay network. In the proposed scheme, two terminals exchange information with the help of multiple relays, and subcarriers and their power are successively allocated to the relays to maximize sum capacity. To achieve fairness for the relays, power constraint on each relay is imposed. Simulation results show that the proposed scheme improves sum capacity and fairness significantly.

Opportunistic relaying has been shown to be an effective and practical method for implementing the cooperative diversity. However, most of previous works have focused on single cell environments and ignored the effects of interference from neighboring cells. In this paper, opportunistic relaying for cooperative diversity is investigated on multicell environments. We provide a closed form expression for its outage probability. Simulation results show the outage probability for various considerations on multicell environments.

In this paper, we propose a novel detection algorithm for the elementary signal estimator of an IDMA system considering channel estimation error. To develop the algorithm, we derive new probability density function of decision variable reflecting channel estimation error and modify the conventional algorithm based on it. Through computer simulations, it is shown that the proposed algorithm achieves lower bit error rate than the conventional one. This performance enhancement is provided with negligible increase of its computational complexity.

We propose an adaptive relay selection scheme for a regenerative orthogonal frequency division multiplexing access (OFDMA) relay network with fairness constraints. The proposed scheme selects the best M relays out of a set of K potential relays to maximize the system capacity. Among these selected relays, subcarriers are reallocated to satisfy fairness constraints as well as to minimize the decrease of the system capacity. The simulation results show that the proposed scheme achieves significant performance improvement over direct transmission and opportunistic relaying with OFDM (OR-OFDM). In addition, multiuser diversity is achieved as the number of potential relays increases with proposed scheme.

In this paper, we propose the opportunistic cooperation based on delayed retransmissions (OC-DR) for a multi-user uplink system. There are N users and one destination (Base station). At a given timeslot, a user who has the best channel condition to the destination is selected to transmit its data. Adaptively dividing the allocated timeslot into the sub-timeslots for its own data and other users' data, the user sequentially transmits its data and previously received other users' data during each sub-timeslot, respectively. Using this cooperation protocol, we can achieve maximally N2diversity order, the second power of number of users. Additionally, the OC-DR can improve resource fairness in asymmetric multi-user systems.

In this paper, the cooperative coding using cyclic delay diversity (CDD) for multiuser OFDM systems is introduced. In proposed scheme, multiple terminals with a single antenna share their resources and exploit spatial diversity. Also, in order to increase frequency selectivity in the relay channel, different cyclic time delay is used at the relays. Analysis of frame error probability (FEP) for proposed cooperative coding using CDD is shown. Simulation results show the frame error rate (FER) for various consideration. The proposed scheme provides the diversity gain according to the number of relays and cyclic delay.

In this paper, we propose a novel adaptive selection cooperation scheme using prediction-based decision combined with a new relay selection strategy. In the proposed scheme, the destination predicts whether the transmission from a selected relay would be successful or not by utilizing instantaneous state information about the channel from the relay to the destination. Then the destination gives back a command determined by the prediction to the whole network. Numerical results show that the proposed adaptive selection cooperation scheme combined with the new relay selection strategy improves its throughput, saves transmission power, and prolongs the lifetime of the network, while having the same outage probability as a conventional selection cooperation scheme combined with the best relay selection strategy.

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the OFDM signal. In this paper, we propose the use of hexagonal constellation for PAPR reduction of an OFDM signal. Because hexagonal constellation is the densest packing of regularly spaced points in two dimensions, we can have more signal points in a given area with hexagonal constellation than with quadrature amplitude modulation (QAM) constellation. We can exploit these extra degrees of freedom provided by the hexagonal constellation for PAPR reduction of an OFDM signal. We will apply the proposed technique to eliminate data rate loss due to the side information in partial transmit sequence (PTS) technique and selected mapping (SLM) technique.

In this paper, we propose a novel cooperative ARQ scheme for static channel. The relay nodes, who decode the source's packet correctly, participate in the cooperation to retransmit the packet erroneously received by the destination node. In the cooperative retransmission, we consider simultaneous transmissions, where the phase pre-compensation method is introduced at each relay node to prevent the signals from summing destructively at the destination node. The phase information is obtained by the estimation at each of the relay nodes. The analysis and simulation results are provided to evaluate the proposed scheme in terms of the packet error rate (PER). The proposed cooperative ARQ scheme provides significant performance gain compared to conventional one.

Sounding provides a BS with knowledge of the channel state information of a user in an orthogonal frequency division multiple access (OFDMA) full duplex division (FDD) uplink. In this paper, we propose a novel sounding subband allocation algorithm for the proportional fair (PF) scheduler. Simulation results show that our proposed sounding method enables the PF scheduler to achieve the throughput gain and guarantee fairness at the same time.

Cooperative diversity obtains the spatial diversity gains created by sharing antennas of terminals in wireless networks. In this paper, adaptive amplify-and-forward (AF) cooperative diversity with multiple relays using phase feedback is introduced. Adaptive algorithm depending on channel condition and threshold obtained by computer simulation are introduced. Simple power allocation for proposed scheme is introduced. Adaptive AF cooperative diversity using phase feedback provides improved performance than the conventional AF cooperative diversity using phase feedback.

An initial timing offset estimation method for orthogonal frequency-division multiplexing (OFDM) systems is proposed. Conventional preamble-based synchronization methods result in performance degradation due to the time variation in the power delay profile of the channel. We propose a simple but efficient synchronization method using a specifically designed preamble. The performance of the proposed estimator is evaluated by computer simulations. The simulation results show that the proposed estimator has a significantly smaller mean squared error (MSE) than other estimators even in the fast varying channel.

In the interleaved orthogonal frequency-division multiple access (OFDMA) uplink, the received signal from a user is corrupted by the intercarrier interferences (ICI) which result from both his own signal and other users' signals due to Doppler spreads. Furthermore, different received signal powers and Doppler spreads between users may increase the effect of the ICI. Among the schemes which have been proposed to reduce the ICI in OFDM, the ICI self-canceling scheme is easily applicable to the interleaved OFDMA uplink. In this paper, we investigate the performance of the interleaved OFDMA uplink with and without ICI self-canceling over doubly dispersive channels. We analyzed the signal-to-intercarrier-interference-plus-noise ratio (SINR) improvement and we examined the symbol error rates and the error floors through simulation.

Most work on cooperative diversity has assumed that the cooperating group (source and partners) and the associated average channel conditions between terminals (source, partners, and destination) are predetermined. In practical situations, however, it is important to develop the efficient algorithms for assigning the terminals with good inter-user channels for cooperating groups. In this paper, we propose the partner assignment algorithm for cooperative diversity in mobile communication systems. The proposed partner assignment algorithm is investigated by using the path loss model for mobile communication systems. Numerical results show that the proposed partner assignment algorithm provides the comparable probability of cooperative transmission to the partner assignment algorithm using exhaustive search. The probability of cooperative transmission increases with the number of users, which gives potential benefits of practical implementation to user cooperation in mobile communication systems. The proposed partner assignment algorithm also provides the tradeoff between probability of cooperative transmission, cooperative diversity gain, and the amount of average SNR information of inter-user channels.

Cooperative transmission obtains the spatial diversity gains created by sharing antennas of terminals in wireless networks. Although the amplify-and-forward (AF) cooperative transmission has the advantages of low implementation complexity and simplicity compared to the decode-and- forward (DF) cooperative transmission, studies on the AF cooperative transmission with multiple relays have not been sufficiently investigated. In this paper, we introduce the AF cooperative transmission with multiple relays using phase feedback. Simulation results show that the proposed schemes obtain the diversity gain according to the number of the cooperating terminals. The performance of proposed scheme using tolerable quantized feedback is close to that of proposed scheme using full feedback.

In this paper, two channel estimation schemes for OFDM systems are investigated in a time-variant channel. The orthogonality of the subcarriers is destroyed in a time-variant channel, resulting in intercarrier interference (ICI). To mitigate the ICI, the 2D Kalman filtering (2D KF) scheme estimates the channel in time domain by using the Kalman filters in both time and frequency domains and the iterative Wiener filtering (IWF) scheme calculates the ICI through the iteration. To mitigate error propagation, comb-type pilots are adopted in the two proposed schemes. Simulation results show that the proposed schemes have better performance than the conventional schemes.

In this paper, we propose a QR-based detection scheme of orthogonal space-time block codes for very fast fading channels. The proposed detection scheme employs a QR decomposition on the channel matrix and minimizes noise enhancement which occurs in an existing detection scheme. The performance of the proposed detection scheme is evaluated by computer simulations for various very fast fading channels. It is shown that when the channel fading is very fast, the proposed detection scheme outperforms the existing detection scheme.

We put forth a saddlepoint approximation for the outage capacity of multiple-input multiple-output (MIMO) systems using the exact moment generating function of the capacity. We consider both uncorrelated and spatially correlated Rayleigh-fading channels. Our results show that the saddlepoint method gives a remarkably accurate approximation to the outage capacity even at extremely low outage probabilities

In this paper, we analyze the capacity of multiple-input multiple-output (MIMO) Rayleigh-fading channels in the presence of spatial fading correlation at both the transmitter and the receiver, assuming the channel is unknown at the transmitter and perfectly known at the receiver. We first derive the determinant representation for the exact characteristic function of the capacity, which is then used to determine the trace representations for the mean, variance, skewness, kurtosis, and other higher-order statistics (HOS). These results allow us to exactly evaluate two relevant information-theoretic capacity measures - ergodic capacity and outage capacity - and the HOS of the capacity for such a MIMO channel. The analytical framework presented in the paper is valid for arbitrary numbers of antennas, and generalizes the previously known results for independent and identically distributed or one-sided correlated MIMO channels to the case when fading correlation exists on both sides. We verify our analytical results by comparing them with Monte Carlo simulations for a correlation model based on realistic channel measurements as well as a classical exponential correlation model

A major drawback of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted signal. In this paper, we propose a novel technique to reduce PAPR in an OFDM signal. Proposed technique is based on signal set expansion. Each point in the original signal set is associated with two or more points in the expanded signal set. Each symbol in an OFDM data block is mapped into a point among associated points in the expanded signal set so as to achieve PAPR reduction. The proposed technique is very simple and does not require any side information to be transmitted from the transmitter to the receiver.

A major drawback of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of OFDM signals. In the PTS technique, the data block to be transmitted is partitioned into disjoint subblocks and the subblocks are combined using phase factors to minimize PAPR. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of subblocks. In the proposed technique, a gradient descent search is performed to find the phase factors. It is shown that the proposed technique achieves significant reduction in search complexity with little performance degradation.

In this letter, we present new closed-form formulas for the exact average symbol-error rate (SER) of binary and M-ary signals over Nakagami-m fading channels with arbitrary fading index m. Using the well-known moment generating function-based analysis approach, we express the average SER in terms of the higher transcendental functions such as the Gauss hypergeometric function, Appell hypergeometric function, or Lauricella function. The results are generally applicable to arbitrary real-valued m. Furthermore, with the aid of reduction formulas of hypergeometric functions, we show previously published results for Rayleigh fading (m=1) as special cases of our expressions.

In this paper, an infrared intervehicle ranging and vehicle-to-roadside communication systems are studied. A direct-sequence spread-spectrum (DS-SS) technology is employed to obtain the robustness against multiuser interference and ambient light noise. We compare the correlation properties for various optical spreading codes such as an optical orthogonal code (OOC), a prime code, an extended prime code, and a modified m-sequence. The performance of the infrared DS-SS ranging and communication system is evaluated by computer simulation over a channel in consideration of multipath dispersion, multiuser interference, and a background light noise. The infrared DS-SS intervehicle ranging system using an OOC has lower ranging error rate (RER) than ranging systems using a prime code, an extended prime code, and modified m-sequences even if there is the interference from other users and lightwave dispersion. In the infrared DS-SS vehicle-to-roadside communication system, L-ary pulse position modulation (L-PPM) is used as a modulation scheme due to high average power efficiency. It is shown that the proposed system achieves smaller BER performance as the modulation order L increases and the proposed system with a (361,6,1,1) OOC has a smaller BER than that with a (181,6,1,1) OOC.

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. In the PTS technique, the data block to be transmitted is partitioned into disjoint sub-blocks and the sub-blocks are combined using phase factors to minimize PAPR. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub-blocks. In this paper, we propose a novel PTS technique with reduced complexity that achieves significant reduction in search complexity with little performance degradation.

We present a new closed-form formula for the ergodic capacity of multiple-input multiple-output (MIMO) wireless channels. Assuming independent and identically distributed (i.i.d.) Rayleigh flat-fading between antenna pairs and equal power allocation to each of the transmit antennas, the channel capacity is expressed in closed form as finite sums of the exponential integrals which are the special cases of the complementary incomplete gamma function. Using the well-known asymptotic behavior of the MIMO capacity, we also give a simple approximate expression for the channel capacity. Numerical results show that the approximation is quite accurate for the entire range of average signal-to-noise ratios.

In multiple-input multiple-output (MIMO) fading environments, degenerate channel phenomena, so-called keyholes or pinholes, may exist under realistic assumptions that the spatial fading is uncorrelated at the transmitter and the receiver but the channel has a rank-deficient transfer matrix. In this paper, we analyze the average symbol error rate (SER) of a space-time block coded MIMO link in the presence of the keyhole. We also study an effective diversity order, which quantifies the influence of the keyhole on the diversity gain offered by space-time block codes.

In this paper, differential unitary space-time modulation (DUSTM) is combined with multiple trellis codes. The set partitioning of a unitary space-time constellation for multiple trellis code is described, and several code constructed are provided. The computational complexity of multiple trellis coded DUSTM is considered. Numerical results are given.

In this paper, differential unitary space-time modulation (DUSTM) is combined with multiple trellis codes. The set partitioning of a unitary space-time constellation for multiple trellis code is described, and several code constructed are provided. The computational complexity of multiple trellis coded DUSTM is considered. Numerical results are given.

In a multi-rate DS-CDMA system with multiple modulation, modulation format is adjusted according to the data rate of each user while symbol duration is fixed for all users. In this paper, two types of multi-stage partial parallel interference cancellation (PIC) receivers are considered for multi-rate DS-CDMA system with multiple modulation: multi-stage PIC receiver with partial cancellation factors and multi-stage PIC receiver with decision thresholds. Performance of the receivers is evaluated by simulation in a Rayleigh fading channel. It is shown that the multi-stage PIC receiver with partial cancellation factors achieves significant performance improvement over the matched filter (MF) receiver and has much lower symbol error rate (SER) than multi-stage PIC receiver for multi-rate DS-CDMA system with multiple modulation in a Rayleigh fading channel.

The capacity of multiple-input multiple-output (MIMO) wireless channels is limited by both the spatial fading correlation and rank deficiency of the channel. While spatial fading correlation reduces the diversity gains, rank deficiency due to double scattering or keyhole effects decreases the spatial multiplexing gains of multiple-antenna channels. In this paper, taking into account realistic propagation environments in the presence of spatial fading correlation, double scattering, and keyhole effects, we analyze the ergodic (or mean) MIMO capacity for an arbitrary finite number of transmit and receive antennas. We assume that the channel is unknown at the transmitter and perfectly known at the receiver so that equal power is allocated to each of the transmit antennas. Using some statistical properties of complex random matrices such as Gaussian matrices, Wishart (1928) matrices, and quadratic forms in the Gaussian matrix, we present a closed-form expression for the ergodic capacity of independent Rayleigh-fading MIMO channels and a tight upper bound for spatially correlated/double scattering MIMO channels. We also derive a closed-form capacity formula for keyhole MIMO channels. This analytic formula explicitly shows that the use of multiple antennas in keyhole channels only offers the diversity advantage, but provides no spatial multiplexing gains. Numerical results demonstrate the accuracy of our analytical expressions and the tightness of upper bounds.

In this paper, group-wise successive interference cancellation (GSIC) receiver with adaptive minimum mean squared error (MMSE) detection and extended GSIC (EGSIC) receiver with adaptive MMSE detection are proposed for dual-rate DS-CDMA system. Users are divided into 2 groups for their data rates: high-rate (HR) users and low-rate (LR) users. Initial bit estimates for the HR users are obtained by adaptive MMSE detection. Multiple access interference (MAI) between the HR users is cancelled by parallel interference cancellation (PIC) and updated bit estimates for the HR users are obtained. Then, the estimates for the received signals of the HR users are regenerated using the updated bit estimates and summed up to be subtracted from the received signal. The initial bit estimates for the LR users are obtained by adaptive MMSE detection using the received signal with MAI from the HR users being subtracted. MAI between the LR users is cancelled by PIC and updated bit estimates for the LR users are obtained. It is possible to extend the proposed receiver. In the extended GSIC (EGSIC) receiver with adaptive MMSE detection, an extra stage is added which takes the interference from the LR users to the HR users into account. It is shown that the EGSIC receiver with adaptive MMSE detection achieves significant performance improvement over the MF receiver, EGSIC receiver for dual-rate DS-CDMA system in a Rayleigh fading channel.

Space-time block coding is a modulation scheme for the use of multiple transmit antennas providing a simple transmit diversity scheme with the same diversity order as maximal-ratio receiver combining. Using the equivalent single-input single-out (SISO) model, we present a closed-form expression for the exact symbol error rate (SER) of orthogonal space-time block codes (STBC) over flat Rayleigh fading channels.

A joint interference cancellation and maximum likelihood (ML) decoding scheme is proposed for a space-time coded DS-CDMA system in a multipath fading channel. Arrival time difference between multiple transmit antennas by multipaths causes not only inter-symbol interference but also multiple-access interference and inter-antenna interference between the desired signals transmitted from different antennas. To mitigate the effect of the interferences a joint algorithm for the proposed scheme is presented, in which an adaptation process for the AIC is merged in the conventional ML decoding algorithm. The performance of the proposed scheme is evaluated for the space-time coded DS-CDMA system with two transmit antennas. It is shown that the proposed scheme achieves significant performance improvement over the conventional ML decoding scheme.

We investigate an improved upper bound on the bit error probability of turbo codes for the maximum likelihood (ML) decoding with imperfect channel state information (CSI) in a fully interleaved Rayleigh fading channel. The upper bound is based on the Viterbi & Viterbi (see Proc. of the IEEE Inform. Theory Workshop '98, San Diego, CA, Feb. 1998, p.72) bound and is also compared with iterative decoding using the log-MAP algorithm. It is shown that the upper bound well approximates the simulation results of the iterative decoding below a BER of 10/sup -5/.

Like differential phase shift keying (DPSK), a differential space-time block code has recursive encoding structure and then, when it is concatenated serially with a channel code, additional coding gain from the concatenation is obtained. To obtain the additional gain, recent research has introduced serial concatenation of the differential space-time block code and channel code, and its sub-optimal iterative receiver. The receiver consists of two APP decoders, which not only has considerable computational complexity, but also is not suitable, especially for the differential space-time block code. This paper proposes a simpler, more suitable decoder for the differential space-time block code in the serial concatenation than the APP decoder. The core idea of the proposed decoder is to employ a maximum likelihood decoding method. With low complexity, a receiver with the proposed decoder shows performance almost identical to the conventional one in a time-correlated fading channel.

An objective function based group-wise successive interference cancellation (GSIC) receiver is proposed for a dual-rate DS-CDMA system. In the receiver, user signals are divided into 2 groups for their data rates. Initial bit estimates for the users in group 1 are obtained by its matched filter (MF) bank. The initial bit estimates for the group 1 users are fed into the multiuser detection (MUD) algorithm that is based on iterative objective function optimization. The objective function is derived from the optimum multiuser detection. Then the estimates for the received signals of the group 1 users are regenerated and summed before being subtracted from the received signal. The initial bit estimates for the users in group 2 are obtained by its MF bank using the received signal with multiple access interference from the group 1 users subtracted. The initial bit estimates for the group 2 users are also fed into the MUD algorithm based on iterative objective function optimization. These procedures are done in multiple stages to achieve the desired performance. It is shown that the proposed receiver achieves significant performance improvement over the MF receiver, GSIC receiver, multi-stage PIC (parallel interference cancellation) receiver, and multi-stage partial PIC receiver for a Rayleigh fading channel.

In this paper, the performance of M-ary signals for optimum combining with multiple co-channel interferers is analyzed in a flat Rayleigh fading channel. The closed-form expressions of average symbol error rates of M-ary phase shift keying and M-ary differential phase shift keying are derived by using the moment generating function-based approach and the orthogonal approximation which is employed to evaluate the eigenvalues of the covariance matrix of the received interference-plus-noise. This analysis is a convenient way of evaluating the performance of optimum combining and comparing it with that of maximal-ratio combining. In the cases of single and multiple interferer(s), the accuracy of the approximation is assessed through computer simulations.

An interference cancellation scheme is applied to the space-time coded DS-CDMA system in a Rayleigh fading channel having arrival time difference from multiple transmit antennas. Arrival time difference causes not only multiple-access interference but also intersymbol interference between the desired signals transmitted from different antennas. To mitigate the effect of the interferences, an adaptive interference canceller (AIC) and maximum likelihood (ML) joint decoding scheme is proposed for a space-time coded DS-CDMA system in which an adaptation process for the AIC is merged in the conventional ML decoding scheme. The performance of the proposed decoding scheme is evaluated for the space-time coded DS-CDMA system with two transmit antennas. It is shown that the proposed decoding scheme achieves significant performance improvement over the conventional ML decoding scheme.

An adaptive multi-stage parallel interference cancellation (PIC) receiver is considered for a multi-rate DS-CDMA system. In each stage of the adaptive multi-stage PIC receiver, multiple access interference (MAI) estimates are obtained using the sub-bit estimates from the previous stage and the adaptive weights for the sub-bit estimates. The adaptive weights are obtained by minimizing the mean squared error between the received signal and its estimate through a least mean square (LMS) algorithm. It is shown that the adaptive multi-stage PIC receiver achieves smaller BER than the matched filter receiver, multi-stage PIC receiver, and multi-stage partial PIC receiver for the multi-rate DS-CDMA system in a Rayleigh fading channel.

An iterative multiuser detection scheme is proposed for a DS-CDMA system. The iterative multiuser detection has a partial parallel interference cancellation (PIC) detector and serially concatenated codes. Taking the expectation value of a coded bit, the partial PIC detector produces a metric which becomes an input to the decoders. It is shown that the proposed iterative multiuser detector has near single user performance as MAI is effectively cancelled out and a high coding gain is obtained.

In this paper, two multirate transmission schemes are considered for an asynchronous multicarrier (MC) DS/CDMA system: multicode scheme and multiple processing gain (MPG) scheme. A successive interference canceller (SIC) is applied to the two multirate MC-DS/CDMA systems to cancel multiple access interference (MAI). The bit error rate (BER) of each system is obtained by analysis and simulation in a Rayleigh fading channel with perfect channel estimation. It is shown that higher rate users have smaller BER than lower rate users in both systems. It is shown that the system with the multicode scheme has better performance than the system with the MPG scheme for high processing gain. Also, it is shown that the former has even better performance than the latter when SIC is applied.

A sequence inverse keyed (SIK) code-division multiple-access (CDMA) system is proposed for an indoor wireless infrared channel. The proposed system employs an m-sequence as a signature sequence. On-off keying (OOK) is used as a modulation scheme. The bit error rate of the proposed system is evaluated by analysis and computer simulation. It is shown that the SIK OOK-CDMA system is more robust against multi-user interference than the OOK-CDMA system with an optical orthogonal code (OOC) in an indoor environment and the former has lower complexity than the latter due to zero-valued threshold detector in the receiver.

In this paper, a successive interference canceller (SIC) is adopted for the performance enhancement of a multicarrier DS/CDMA system and its performance is analyzed in a Rayleigh fading channel. A successive interference canceller is employed for each subcarrier of a multicarrier DS/CDMA system and the outputs of SICs are combined through the maximal-ratio or equal-gain combining. Numerical results show that the considered system achieves a significant performance improvement over a conventional multicarrier DS/CDMA system. It is robust to the multiple access interference coupled with a near-far problem and therefore it achieves a significant increase in system capacity.

The performance of a decorrelating receiver is analyzed for a cost-effective and throughput-efficient optical orthogonal code-division multiple-access (CDMA) system. The analysis is carried out for a chip-synchronous system and the effects of the avalanche photo diode (APD) and the thermal noise as well as the multiple-access interference (MAI) are considered. Through the theoretical analysis and the numerical results, it is shown that the decorrelating receiver provides a significantly improved performance over the conventional correlation receiver.

A multicarrier DS/CDMA system with adaptive antenna array is proposed for a multipath fading channel. A multipath fading channel is modeled as a Nakagami-m (1960) fading channel. The performance is evaluated in terms of the bit error probability, and system capacity for the multicarrier DS/CDMA system with an adaptive antenna array is estimated. From the analytic and simulation results, it is shown that the overall system capacity increases significantly compared to the system without an adaptive antenna array.

A new multiuser detection scheme is proposed which employs adaptive minimum mean square error (MMSE) detection in combination with successive interference cancellation (SIC). Through theoretical analysis and numerical examples, it is shown that the proposed detector provides superior performance to existing ones in terms of asymptotic multiuser efficiency (AME) and bit error rate (BER).

A new pulse position modulation code division multiple access (PPM-CDMA) system is proposed for an indoor optical wireless channel. As a signature sequence for CDMA an optical orthogonal code (OOC) is used. To reduce multiple access interference two interference cancellation schemes are employed: decorrelating detection and successive interference cancellation (SIC). The bit error rate of the proposed system is calculated for a conventional receiver, a decorrelating receiver, and a receiver with SIC. It is shown that PPM-CDMA systems with both decorrelating detection and SIC achieve significant SNR improvement over the system with a conventional receiver.

We propose a new ordered decoding scheme for a product code for mobile data communications. The ordered decoding scheme determines the order of decoding for both row and column component codewords according to the probability of decoding the component codeword correctly. Component codewords are decoded independently. To randomize burst errors in both row and column codewords, a diagonal interleaving scheme is used for code symbols in the codeword. It is shown that the ordered decoding scheme combined with diagonal interleaving improves the performance of a product code with reasonably long code length for mobile data communications.

We investigate the undetected error probabilities for bounded-distance decoding of binary primitive BCH codes when they are used for both error correction and detection on a binary symmetric channel. We show that the undetected error probability of binary linear codes can be simplified and quantified if the weight distribution of the code is binomial-like. We obtain bounds on the undetected error probability of binary primitive BCH codes by applying the result to the code and show that the bounds are quantified by the deviation factor of the true weight distribution from the binomial-like weight distribution.

In this paper, a new hybrid automatic repeat request (ARQ) scheme is proposed for data transmission in a power controlled DS-CDMA cellular system. Data frame is composed of interleaved Reed-Solomon codes. The depth of interleaving is determined by a power control interval. After decoding each codeword, the post decoding processor decides whether to accept the codeword or to discard it by utilizing channel state information from the power control processor. The proposed hybrid ARQ scheme reduces the probability of undetected error among accepted codewords significantly without reducing the throughput much.>