This paper proposes a novel Bayesian receiver design for uplink signal detection in overloaded massive multi-user multi-input multi-output (MU-MIMO) systems. Iterative detection schemes are roughly classified into two types: iterative detection and decoding (IDD), in which log-likelihood ratios (LLRs) are exchanged between the detector and the channel decoder, and self-iterative detection (SID), in which a message passing algorithm (MPA) is operated without involving the channel decoder. In either scheme, the most vital mechanism of iterative signal detection is to decouple the self-feedback across iterations and propagate extrinsic values. As a receiver design to achieve an excellent performance-complexity trade-off while adhering to this mechanism, a concatenated structure of SID based on expectation propagation (EP) and IDD based on turbo equalization is proposed. Numerical simulations show that the proposed method outperforms the state-of-the-art alternatives in terms of bit error rate (BER) performance in coded systems, especially when the overloading ratio is high. In addition, the iterative behavior is analyzed by extrinsic information transfer (EXIT) chart to verify the efficacy of extrinsic value exchange.

We propose a novel joint channel and data estimation (JCDE) algorithm via bilinear Gaussian belief propagation (BiGaBP) for massive multi-user MIMO (MU-MIMO) systems with non-orthogonal pilot sequences. The contribution aims to reduce significantly the communication overhead required for channel acquisition by enabling the use of short non-orthogonal pilots, while maintaining multi-user detection (MUD) capability. Bilinear generalized approximate message passing (BiGAMP), which is systematically derived by extending approximate message passing (AMP) to the bilinear inference problem (BIP), provides computationally efficient approximate implementations of large-scale JCDE via sum-product algorithm (SPA); however, as the pilot length decreases, the estimation accuracy is severely degraded. To tackle this issue, the proposed BiGaBP algorithm generalizes BiGAMP by relaxing its dependence on the large-system limit approximation and leveraging the belief propagation (BP) concept. In addition, a novel belief scaling method complying with the data detection accuracy for each iteration step is designed to avoid the divergence behavior of iterative estimation in the early iterations due to the use of non-orthogonal pilots, especially in insufficient large-system conditions. Simulation results show that the proposed method outperforms the state-of-the-art schemes and approaches the performance of idealized (genie-aided) scheme in terms of mean square error (MSE) and bit error rate (BER) performances.

We propose a wireless localization algorithm based on complex-domain super multidimensional scaling (CD-SMDS) augmented with a self-localization (SL) component, whereby each target tracks its own motion by incorporating bearing information, obtained e.g., from integrated inertial sensors. The proposed method improves localization accuracy by simultaneously using the time series information of distance and angle associated to the SL information in order to construct the SMDS rank-one edge kernel matrix, maximizing the noise reduction effect of the low-rank truncation via singular value decomposition (SVD). The efficacy of the proposed method over the original CD-SMDS is confirmed via software simulations, and compared with an SL-aware Cramér-Rao lower bound (CRLB).

This paper proposes a novel angle-of-arrival (AoA) estimation-aided Bayesian joint channel and data estimation (JCDE) algorithm for uplink signal detection in millimeter-wave (mmWave) massive multi-user MIMO (MU-MIMO) systems with short non-orthogonal pilots. In the proposed method, the prior distribution of mmWave channels in the angular domain after digital beamforming is approximated by a Bernoulli-Gaussian (BG) distribution, and the mismatch with the actual distribution is corrected based on AoA estimation by low-complexity angle rotation (AR) method. The resultant beam-domain JCDE algorithm has an inherent mechanism to update path gains of the channels estimated based on AoA for every iteration. This receiver design allows us to take the advantage of both stochastic (i.e., Bayesian) and deterministic (i.e., AR) approaches. Efficacy of the proposed method over the state-of-the-art is confirmed via computer simulations in terms of bit error rate (BER) performance compared to the state-of-the-art alternatives.

This paper proposes a look-up table (LUT)-based multi-user detection (MUD) scheme imitating approximate message passing (AMP) for uplink signal detection in large multi-user multi-input multi-output (MU-MIMO) systems. When AMP is implemented with double-precision arithmetic, the increase in power consumption and memory occupation becomes a major obstacle to practical application as the system scale expands. To tackle this issue, we design a novel referential AMP detector composed by hierarchically cascading many small LUTs, where only informative integer-valued messages are exchanged on a factor graph. The quantization thresholds of LUTs are sequentially computed by tracking the discrete distribution of the LUT outputs at each layer to minimize the performance degradation owing to quantization errors. Based on the distribution at each layer, the thresholds are optimized by clustering with the Lloyd-Max algorithm using the initial values given by the k-means++ method. Simulation results demonstrate the efficacy of the proposed method in terms of the bit error rate (BER) performance and memory usage. Notably, we show that the referential AMP is robust to changes in communication environments, and then clarify the reason in terms of the algorithmic structure.

This paper deals with uplink multi-user detection (MUD) via generalized approximate message passing (GAMP) in highly correlated large multi-user multi-input multi-output (MUMIMO) systems. The most vital mechanism of GAMP is Onsager correction for decoupling the self-noise feedback of beliefs across iterations; this makes it possible to exchange extrinsic values. First, we show that by introducing the belief scaling method proposed in the context of Gaussian belief propagation (GaBP) for adjusting the convergence speed into GAMP, the Onsager correction works properly even under spatial fading correlation, which significantly improves detection capability. Surprisingly, the performance is much better compared to that of the GaBP with belief scaling, and even asymptotically approaches that of computationally expensive expectation propagation (EP) detectors. Based on the results, we clarify why such a dramatic performance improvement is possible only for GAMP in terms of the suppression mechanism of self-noise feedback.

Linear minimum mean square error (LMMSE) filters are often utilized to achieve low-complexity multi-user detection (MUD) in uplink large multi-input multi-output (MIMO) systems. As the scale and density of MIMO systems grow towards truly massive setups, however, the LMMSE detection requiring high-dimensional matrix inversion operations becomes computationally expensive. As a promising approach to tackle this issue, the local LMMSE (LLMMSE) detector was proposed, where a contiguous block of beams can be selected for each user to construct the reduced beam-domain channels, assuming the use of digital beamforming at a base station (BS). A main issue is the performance degradation according to the angular spread of the received signal, due to the information loss induced by an excessive dimensionality reduction aiming at the computational reduction. To alleviate this issue, this paper proposes to selectively combine the information from the overlapped LLMMSE filters in the log-likelihood ratio (LLR) domain. In addition, this method is extended to probabilistic data association (PDA)-based iterative detection scheme for further enhancement of communication reliability. The efficacy of the proposed methods is demonstrated by simulation results in terms of the bit error rate (BER) performance and the computational cost.

This paper proposes a high reliable demodulation method via phase-noise-aware log-likelihood ratios (LLRs) in millimeter-wave (mmWave) multi-user multi-input multi-output (MU-MIMO) systems with higher-order quadrature amplitude modulation (QAM). When using high-order QAM schemes in mmWave wide-band wireless communication systems, the phase noise severely degrades the demodulation performance at the operating point in the high signal-to-noise ratio (SNR) region. Typical two-stage processing, which consists of MIMO signal separation (i.e., multi-user detection (MUD)) and phase noise compensation via LLR calculation, cannot properly solve this inherent problem, because the spatial fading correlation in mmWave channels causes phase noise enhancement during MUD. To circumvent this issue, we formulate an approximate probability density function (PDF) of the received signals including phase noise, which enables us to jointly perform MUD and phase noise compensation; this makes it possible to compute reliable LLRs to be input to the channel decoder, without phase noise enhancement. Numerical results demonstrate the efficacy of the proposed method in terms of the bit error rate (BER) performance in coded mmWave MIMO systems.

In large multi-user multi-input multi-output systems, the computational cost and circuit scale of base stations (BSs) are effectively reduced using two-stage signal processing consisting of a slow varying outer beamformer (OBF) based on long-term channel statistics and group-specific multi-user detection for instantaneous channel variations. However, the dimensionality reduction of the group-specific beam-domain channel based on the OBF causes significant performance degradation in the subsequent spatial-filtering detection. To compensate for this drawback, this paper introduces a novel layered belief propagation (BP) detector with a concatenated structure of beam- and antenna-domain BP layers for post-stage OBF processing. The proposed detector is designed for improving the convergence of iterative detection by suppressing intra- and inter-group interference in stages. The layered structure provides the advantages of both beam and antenna domains while maintaining low signal-processing complexity. Numerical results show the validity of our proposed method in terms of the bit error rate performance in both the uncoded and coded cases and the computational complexity.

We consider large multi-user detection (MUD) via deep unfolding-aided belief propagation (BP) in coded multi-user MIMO (MU-MIMO) systems. A BP detector optimized (trained) by data-driven-tuning of embedded internal parameters achieves low-complexity and high-accuracy MUD while compensating practical imperfections. However, in actual implementation, these parameters should be optimized according to system parameters, e.g., modulation and coding scheme (MCS). In particular, when channel coding is used, it is vital not only to minimize the mean square error (MSE) but also to enhance the Gaussianity of the output log-likelihood ratio (LLR), in order to maximize the error correction capability of the subsequent soft-decision decoder. To that end, a novel loss function based on a weighted average of negentropy, which is a key measure to evaluate the Gaussianity, and MSE of the detector output is proposed. Simulation results show that the trainable Gaussian BP (T-GaBP) detector optimized with the proposed negentropy-aware loss function significantly improves the bit error rate (BER) performance of the decoder output and substantially outperforms the T-GaBP optimized with the typical MSE loss function.

We propose a novel joint channel and data estimation (JCDE) scheme for highly-correlated large multi-user multi-input multi-output (MIMO) systems with short non-orthogonal pilots. Bayesian JCDE via scalar-wise tensor products is a solid strategy for achieving multi-user detection (MUD) with extremely low computational cost, but the convergence property is significantly degraded in practical MIMO systems assuming spatially correlated fading channels. When using ultra-short pilots aiming at significant overhead reduction, the reliable MUD via JCDE becomes increasingly challenging. To address this issue, the proposed method estimates channel coefficients via a maximum a-posteriori (MAP)-like approach with the aid of long-term channel statistics. Furthermore, while the data detection is performed via probabilistic data association (PDA) to suppress the observation correlation, the channel estimation is performed via Gaussian belief propagation (GaBP) by leveraging the pseudo-orthogonality of the pilot-plus-data sequences, which makes it possible to realize low-complexity and high-accuracy Bayesian JCDE for highly-correlated MUD. Computer simulation demonstrates the validity of our proposed method in terms of bit error rate (BER) performance and computational cost.

This paper proposes bilinear Gaussian belief propagation (BiGaBP) for joint channel and data estimation (JCDE) in large multi-user multi-input multi-output (MU-MIMO) systems. JCDE is a well-known strategy for realizing a high-precision MU detection (MUD) with short pilots by utilizing the orthogonality of data sequences. For massive MIMO scenarios, the JCDE via bilinear generalized approximate message-passing (BiGAMP), which is systematically derived by extending AMP to the bilinear inference problem (BIP), achieves extremely low computational cost. However, the use of short non-orthogonal pilots to reduce the channel acquisition overhead significantly degrades the convergence property of BiGAMP. To resolve the lack of an appropriate JCDE scheme based on insufficient pilots, we design a novel MP rule based on GaBP, which is given by relaxing the large-system approximation from AMP. Furthermore, the belief scaling complying with the detection state in each iteration step is introduced to suppress the negative impact of non-orthogonal pilots even in the insufficient large-system conditions. Numerical results show the validity of our proposed method in terms of bit error rate (BER) and mean square error (MSE) performances.

This paper proposes a deep unfolding-aided belief propagation (BP) for large multi-user multi-input multi-output (MU-MIMO) detection under correlated fading channels. A BP-based detector is a well-known strategy for realizing large-scale MU detection (MUD) with low-complexity and high-accuracy. However, its convergence property is severely degraded under insufficient large-system conditions and spatial fading correlation among RX antenna elements. To compensate for this drawback, we design a trainable Gaussian BP (T-GaBP) having well-organized trainable internal parameters based on the BP structure. These parameters are optimized by the deep learning techniques in the signal-flow graph of unfolded GaBP; this approach is referred to as data-driven tuning. By training the parameters according to the system model, T-GaBP can maintain the high detection capability even in practical system configurations that differ from the ideal uncorrelated massive MIMO assumption. Numerical results show that the proposed detector improves the convergence property and achieves a comparable detection performance to the cutting-edge expectation propagation (EP) detector in correlated MUD, with a lower computational cost.

This paper deals with mmWave overloaded multiuser multi-input multi-output (MU-MIMO) detection, where the number of receive antennas is less than that of transmitted streams. Belief propagation (BP) is well known strategy for achieving large-scale MU detection (MUD) with low-complexity and high-accuracy. However, in mmWave massive MUD, the BP-based signal detector is subject to ill convergence behavior of iterative detection due to under-determined problem induced by spatial overloading and strong correlation among user channels induced by narrow angular spread of receive signal and line-of-sight (LOS) environments. To alleviate these impairments, we propose a novel iterative MUD approach based on beam-domain subspace marginalized BP (SMBP). Exploiting the approximate sparsity of beam-domain channels, the maximum likelihood (ML) principle is used to combine the strongly correlated signal subspace with reduced dimension while the BP-based detection is used for the remaining complementary subspace. The space partitioning criterion is adaptively determined based on channel state information (CSI) so that the two subspaces are as orthogonal as possible. Numerical results show that the proposed method is able to serve a massive number of wireless connections with low computational complexity even in the LOS environment, while providing excellent BER performance.

In this paper, we propose a novel soft interference cancellation scheme considering processing delay for uplink ultra-reliable and low latency communication (URLLC). For URLLC, repetition transmission was specified to satisfy a requirement of reliability. In a conventional scheme, the performance is improved by combining bit log-likelihood ratios (LLRs) at each repetition transmission. Although it is ordinal to secure radio resources for single URLLC user equipment (UE) to avoid severe inter-UE interference (IUI), it is effective to share a radio resource among plural UEs to increase spectrum efficiency. By introducing the soft interference cancelation, the proposed scheme can efficiently suppress the negative impact of IUI while keeping the similar processing delay as the conventional scheme.

This paper proposes low-complexity beam-domain channel estimation using long-term channel statistics in belief propagation (BP) based large multi-input multi-output (MIMO) detection. When the channel correlation matrix between the base station (BS) and each user equipment (UE) is available and used as prior information, maximum a-posteriori probability (MAP) estimation provides the optimal estimation performance. However, it requires undesirably complex large-scale matrix operations at any time the channel statistics is changed. By appropriately selecting beam-domain angular bins for each UE, the proposed method allows us to significantly reduce the computational cost while maintaining the near-optimal performance in terms of the mean square error (MSE) of estimated channel. The selection threshold is adaptively determined based on the prior information such as the channel correlation matrix, statistical beam, and receive SNR. For the subsequent BP-based signal detection, an appropriate covariance matrix is designed while considering the detrimental impact of channel estimation errors. Numerical results show that the proposed method can reduce the computational cost to less than 4% as compared to the MAP estimation, while providing similar MSE performance.

This paper proposes a novel layered belief propagation (BP) detector with a concatenated structure of two different BP layers for low-complexity large multi-user multi-input multi-output (MU-MIMO) detection based on statistical beams. To reduce the computational burden and the circuit scale on the base station (BS) side, the two-stage signal processing consisting of slow varying outer beamformer (OBF) and group-specific MU detection (MUD) for fast channel variations is effective. However, the dimensionality reduction of the equivalent channel based on the OBF results in significant performance degradation in subsequent spatial filtering detection. To compensate for the drawback, the proposed layered BP detector, which is designed for improving the detection capability by suppressing the intra- and inter-group interference in stages, is introduced as the poststage processing of the OBF. Finally, we demonstrate the validity of our proposed method in terms of the bit error rate (BER) performance and the computational complexity.

This paper focuses on multi-user detection in uplink Massive multiple-input multiple-output (MIMO) systems. As a low computational complexity signal detection algorithm, matched filter (MF)-based Gaussian belief propagation (MF-GaBP) using adaptively scaled belief (ASB) has been proposed. In addition, to suppress the negative impact of spatial correlation, an MMSE detector is introduced as the prior stage processing of MF-GaBP. Through computer simulations, this algorithm exhibits high performance even in high- spatially loaded Massive MIMO scenarios. However, in actual radio environments, there is a possibility to observe an extremely high channel correlation among some antenna elements or some users due to co-located polarization antenna elements or closely deployed mobile stations (MS). The highly correlated channel results in the performance degradation of MF-GaBP using ASB because of the low reliability of initial beliefs. This paper aims to verify the performances of MF- GaBP in the actual radio environments. The predetermined parameters in MF- GaBP are also adjusted according to actual environments for improving the convergence property of the iterative detection. To obtain propagation channel data for performance evaluation in the actual environments, an indoor experimental trial using Massive MMO equipment with 32 antenna elements was carried out under a condition that 16 MSs are closely deployed. Computer simulations using the obtained propagation channel data validate that simply applying the MMSE detector before MF-GaBP with ASB suppress an error floor in the bit error rate (BER) performance even in highly correlated channel.

This paper proposes a symbol replica generation method using look-up table (LUT) based on the information bottleneck (IB) theory in matched filter Gaussian belief propagation (MF-GaBP) for massive multi-input multi-output (MIMO) detection. MF-GaBP serves as an iterative signal detection scheme with low computational complexity by utilizing massive MIMO simplification owing to the law of large numbers. However, when the internal mathematical processes in MF-GaBP are conducted in double precision, a severe processing delay is inevitable. To avoid the impairment, we propose a quantized MF-GaBP detection scheme using predesigned LUTs. The quantization threshold is designed based on the sequential IB (sIB) method for minimizing the mutual information loss. Finally, computer simulations demonstrate that the proposed method significantly reduces the memory occupancy on the basis of table-based processing while suppressing error floor level of the bit error rate (BER) performance.

This paper proposes an adaptively scaled belief (ASB) in Gaussian belief propagation (GaBP) designed for use in large multi-user multi-input multi-output (MU-MIMO) detection under higher order modulation schemes. In practical MU-MIMO systems, the dominant factor in the poor convergence of GaBP iterative detection is approximation errors arising from the fact that the law of large numbers does not work well in many such applications as a result of physical system limitations. Unfortunately, the approximation errors become more severe when there is higher correlation among typical bit-wise prior beliefs when higher order quadrature amplitude modulation schemes are used. To cope with the impairments arising from inter-bit correlation, symbol-wise beliefs can be defined for GaBP self-iterative detection, although this still does not remove approximation errors. As a simple method for mitigating the harmful effects of approximation error, this paper proposes a novel method for adaptive belief scaling while stabilizing the dynamics of random MIMO channels. Based on the functionality of ASB, we also propose a method for approximately calculating conditional expectations with lower computational complexity without sacrificing detection capability. Finally, the validity of using ASB for symbol-wise iterative detection in suppressing the bit-error-rate floor level is confirmed.

This paper proposes a random codebook design and its constraints for Gaussian belief propagation (GaBP) in massive Sparse Code Multiple Access (SCMA). In typical SCMA, a message passing algorithm (MPA) is applicable as the detection scheme for multi-user detection (MUD) on the assumption of a predefined optimal codebook. As the number of transmit streams increases, however, it becomes quite difficult to design optimal codebook due to a large number of its candidates. To address such an inconvenient problem, we employ the structured random codebook and GaBP iterative detection, which may achieve the near-optimal performance thanks to the diversity gain in the large-scale MUD. Moreover, an abnormal noise enhancement induced in GaBP can be suppressed by appropriate constraints in random codebook design. To improve the convergence property of GaBP iterative detection, we propose a novel random codebook design and its constraints for GaBP. Finally, we demonstrate the validity of our proposed method, in terms of improvement of bit error rate (BER) performances.

Although Wireless Gigabit (WiGig) access operating in the 60 GHz band plays a significant role towards multi-Gbps WLANs, its transmission suffers from harsh propagation loss and path blocking reducing its transmission range to be few meters around a WiGig access point/station (AP/STA). Consequently, directional transmissions using antenna beamforming is tremendously used in WiGig communication. In this paper, a novel approach of leveraging Wi-Fi channel fingerprints for localizing WiGig coverage area along with reducing its beamforming training (BT) complexity over conventional exhaustive search BT is proposed. The proposed approach is motivated by the fact that Wi-Fi fingerprints, WiGig coverage area and the best beam identifications (IDs) of a WiGig AP and STA are all location dependent. Hence, by linking Wi-Fi fingerprints with WiGig information, e.g., WiGig coverage and the best AP/STA beam IDs, using statistical learning, Wi-Fi fingerprints comparisons can be used to detect if a WiGig STA is within the coverage area of a WiGig AP or not and which AP/STA beam IDs are expected to maximize the link quality. Experimental work in real indoor environment is conducted to prove the effectiveness of the proposed approach compared to the conventional exhaustive search BT.

This paper proposes a unified design of log likelihood ratio (LLR) quantization and joint reception (JR) to reduce the mobile fronthaul (MFH) bandwidth in the split-physical (PHY) processing (SPP). SPP is one of the schemes that redefine the base station (BS) functional split between a baseband unit (BBU) and a remote radio head (RRH) in cloud radio access network (C-RAN). SPP splits the BS functions between the channel encoder/decoder and the modulator/demodulator of the PHY layer functions. In the uplink scenarios, the RRH forwards demodulator output LLR to the channel decoder at the BBU through the MFH. To reduce the MFH bandwidth, the number of LLR quantization bits must be minimized while maintaining the requested quality after JR, for example in terms of bit error rate (BER) requirement. To deal with the minimization, the proposed scheme adaptively controls the LLR quantization threshold according to the received signal to noise ratio (SNR) as well as the capability of source coding for data compression of the quantized LLR. Numerical simulations show that the proposed scheme is capable of reducing the average number of LLR quantization bits to fewer than 2 bits and 1.1 bits at the minimum with a JR block error rate (BLER) performance superior to that of selection combining.

This paper proposes a successive interference cancellation (SIC) of independent component analysis (ICA) based spatial division multiple access (SDMA) differential detector for Bluetooth low energy (BLE) systems. Typical SDMA scheme requires estimations of channel state information (CSI) using orthogonal pilot sequences. However, the orthogonal pilot is not embedded in the BLE packet. This fact motivates us to apply ICA detector into BLE. In this case, there are three problems to be addressed. First, ICA requires a lot of samples for maintaining the accuracy of signal separation capability. Then, ICA suffers from phase ambiguity. Finally, noise enhancements are caused by ICA detector. To deal with all problems, we propose a unified design of ICA, differential detector, and SIC for SDMA of BLE. Regarding the packet error rate (PER) performance, computer simulations validate the proposed design.

Wireless Gigabit (WiGig) access points (APs) using 60 GHz unlicensed frequency band are considered as key enablers for future Gbps WLANs. Due to its short range transmission with high susceptibility to path blocking, a multiple number of WiGig APs should be installed to fully cover a typical target environment. However, using autonomously operated WiGig APs with IEEE 802.11ad DCF, the exhaustive search analog beamforming and the maximum received power based autonomous users association prevent the establishment of optimal WiGig concurrent links that maximize the total system throughput in random access scenarios. In this paper, we formulate the problem of WiGig concurrent transmissions in random access scenarios as an optimization problem, then we propose a Wi-Fi/WiGig coordination architecture to solve it. The proposed coordinated Wi-Fi/WiGig WLAN is based on a tight coordination between the 5 GHz (Wi-Fi) and the 60 GHz (WiGig) unlicensed frequency bands. By which, the wide coverage Wi-Fi band controls the establishment of the WiGig concurrent links. Statistical learning using Wi-Fi fingerprinting is used for estimating the best candidate AP and its best beam identification (ID) for establishing the WiGig concurrent link without making any interference to the existing WiGig data links.

This paper proposes a normalized matched filter (MF) belief in Gaussian belief propagation (GaBP) detection especially for a large multiple-input multiple-output (L-MIMO) configuration where a base station (BS) has tens of antennas. In a massive MIMO channel where the BS has hundreds of antennas, damped GaBP is known to be an effective detector in terms of low computational complexity and its detection capability. However, in L- MIMO channels, GaBP is subject to ill convergence behavior of iterative detection due to lack of channel hardening effects obtained by massive number of receive antennas. To improve the convergence property, we investigate the MF belief, instead of a traditional log likelihood ratio (LLR) belief. Then, we propose the novel normalized MF belief according to instantaneous channel state. As a side effect of the normalization, a noise variance estimator is not necessary. Finally, we demonstrate the validity of the normalized MF belief with the aid of damped processing, in terms of suppression of bit error rate (BER) floor as well as approach to maximum likelihood detection (MLD) limit.

Wireless Gigabit (WiGig) access points (APs) using the 60 GHz unlicensed frequency band are considered as key enablers for future Gbps wireless local area networks (WLANs). Exhaustive search analog beamforming (BF) is mainly used with WiGig transmissions to overcome channel propagation loss and accomplish data transmissions. Due to its short range transmission with high susceptibility to path blocking, a multiple number of WiGig APs should be installed to fully cover a typical target environment. Therefore, coordination among the installed APs is highly needed for enabling WiGig concurrent transmissions while overcoming packet collisions and reducing interference, which highly increases the total throughput of WiGig WLANs. In this paper, we propose a comprehensive architecture for coordinated WiGig WLANs. The proposed WiGig WLAN is based on a tight coordination between the 5 GHz (WiFi) and the 60 GHz (WiGig) unlicensed frequency bands. By which, the wide coverage WiFi band is used to do the signaling required for organizing WiGig concurrent data transmissions using control/user (C/U) plane splitting. To reduce the interference to existing WiGig data links while doing BF, a novel location based BF mechanism is also proposed based on WiFi fingerprinting.

This paper proposes an iterative cancellation scheme for adjacent channel interference (ACI) caused by nonlinear transmit power amplifier (PA) in millimeter wave (mmW) systems with the assistance of a nonlinear estimator and channel decoder's feedback. In this method, nonlinear distortion included in the transmit signal is estimated by polynomial regression analysis using not only the pilot signal but also the regenerated modulated signal in the receiver to enhance estimation accuracy in the higher signal level regions. Frequency selective fading is also compensated for. We have demonstrated that ACI cancellation with proposed nonlinearity estimation is capable of improving bit error rate (BER) performances in the presence of ACI, and have shown effectiveness and usefulness of the proposed scheme when IEEE 802.11ad using spectrum bands located adjacently in the same place.

This paper describes a virtual differentially coded system without a differential encoder at the transmitter and channel estimates at the receiver. Without the assistance of a differential encoder, a differential decoder detects a linearly multiplexed symbol that is constituted by two transmitted symbols in different times. In the virtual differentially coded system, the multiplexed symbol is regarded as a virtual symbol. In order to resolve the virtual symbol into the two original symbols, extrinsic log likelihood ratio (LLR), which is fed back from the channel decoder, is exploited with the aid of iterative decoding. For the sake of improving the convergence property of iterative decoding, sparse pilot symbols are doped in a stream of transmitted symbols. We demonstrate that the proposed system with a small number of sparse pilot tones is very assistive in terms of frame error rate (FER) performance. Furthermore, we explicitly show that the proposed approach outperforms the conventional differential and coherent detection schemes under the condition of a few sparse pilots.

Coordinated multipoint (CoMP) is one technique that can be used to extend the coverage area by solving the Inter Cell Interference (ICI) problem occurring at the cell-edge. On the other hand, Distributed Space-Time/Frequency Block Coding (DSTBC/DSFBC) technique is used to improve the reliability in large modern wireless networks e.g. 3GPP LTE advanced. The cell-edge user is usually power limited. Hence, reducing processing load in such a terminal is preferable. In this paper, we propose a low complexity decoding method named Adaptive K-Best Sphere Decoder (AKBSD) to serve a high mobility cell edge user facing different varying frequency selective channels from multiple base stations. AKBSD adapts the number of K-paths the decoder processes while performing the tree search depending on the estimated received signal strengths and the channel quality of each transmission link in a DSFBC open-loop CoMP environment. The simulation results confirm a good trade-off between performance and complexity achieved by AKBSD under this scenario where about 20% reduction in complexity is achieved over a high K-value fixed KBSD for the price of 0.4 dB reduction in performance at BER value of 10-4.

Increasing wireless cellular networks capacity is one of the major challenges for the coming years, especially if we consider the annual doubling of mobile user traffic. Towards that and thanks to the fact that a significant amount of mobile data is indeed delay tolerable, in this paper, we suggest embedding the delayed offloading of some user traffic to be a part of future wireless cellular networks. To accomplish this, user delayed files will be offloaded using ultra-high speed Millimeter Wave (Mm-W) gates. The Mm-W gate, which will be distributed inside the Macro basestation (BS) area, consists of number of Mm-W Access Points (APs) controlled by a local coordinator installed inside the gate. To effectively manage the delayed offloading mechanism, utilizing the concept of User/Control (U/C) data splitting, the gates coordinators and the Macro BS are connected to the Cloud Radio Access Network (C-RAN) through optical fiber links. Also, files offloading organizer software is used by the User Equipment (UE). A novel weighted proportional fairness (WPF) user scheduling algorithm is proposed to maximize the Gate Offloading Efficiency (GOFE) with maintaining long term fairness among the different mobility users pass through the gate. If the gate is properly designed and the files delay deadlines are properly set; near 100% GOFE with average reduction of 99.7% in UE energy consumption can be obtained, in time the user just passes through the gate.

This paper proposes a frequency-domain (FD) scheduling for an uplink single carrier non-orthogonal multiple access (SC-NOMA) with the assistance of iterative interference cancellation (IC). In the SC-NOMA, an evolved Node B (eNB) with an iterative IC receiver is capable of allocating overlapped spectra to plural intra-cell user equipments (UEs) exceeding the number of receive antennas. As a result, the SC-NOMA can enhance the spectral efficiency owing to the non-orthogonal multiplexing. However, when the subband (SB) criterion scheduling, that assigns an SB to a UE on the basis of the metric only on an SB, is applied, this scheduling is not suitable in the SC-NOMA. This is because the throughput in single carrier transmission depends on all the allocated SBs. Therefore, we propose a novel FD scheduling based on the expected value of cell throughput which is calculated by both the SB selected by the metric as a candidate and the previously allocated SBs. The eNB assigns the candidate SB if the expected cell throughput increases after allocating the candidate SB. Computer simulations confirm that the proposal can improve throughput performances compared to the SB criterion scheduling in the SC-NOMA.

This paper presents an indoor experiment to verify the battery-less sensor activation via multi-point wireless energy transmission with carrier shift diversity which realizes seamless coverage extension of the sensor activation. The multi-point scheme is employed to overcome path-loss attenuation. The carrier shift diversity has been developed to achieve uniform coverage of power transmission by combating standing-wave problem caused by multi-point transmitters as well as multipath waves, while its effectiveness on activation of battery-less sensors has never been studied in real environments. In this paper, we develop prototype hardware of battery-less sensor and conduct an indoor experiment with the developed sensor node. The experimental results show that the coverage of single-point and simple multi-point wireless energy transmission are limited at 44% and 70% respectively, while that of the proposed multi-point wireless energy transmission with carrier shift diversity achieves 100% to activate the developed sensor node which consumes -4 dBm for a transmission period of 1s.

The authors have proposed a distributed-transmission-based secure wireless link creation scheme by providing multiple transmission routes to a destination. In the proposed scheme, the transmitted information is divided into pieces of “shared information” by a secret-sharing method, and the pieces of information are separately transmitted to the destination through different transmission routes with individually controlled antenna directivities. In this paper, we focus on the performance of the proposed scheme in a non-line-of-sight (NLOS) propagation environment and propose a joint receiver beamforming in accordance with the controlled transmitter antenna directivity. The computer simulations clarify that the degree of spatial distribution of the transmission routes is enhanced by the joint beamforming. Therefore, it can improve the secrecy of the transmitted information by the distributed transmission in the wireless space.

This paper proposes a design strategy for decode- quantize-forward (DQF) relaying in which two relay nodes parallelly forward quantized a-posteriori loglikelihood ratio (LLR) after channel decoding. A primary focus is on cross correlation among quantized bits. When the source signal is received by plural relays and they are transmitted independently, the parallel streams can be regarded as an imperfect parallel repetition streams, and the final destination can detect the concatenated code sequences. In the proposed scheme, taking into account this feature, we have designed its iterative unified decoding modules, in which we have a novel iterative unified decoding schemes that consists of vertical and horizontal iterations. We have demonstrated that the iterative unified decoding is capable of obtaining large iterative gain in terms of bit error rate (BER).

This paper proposes a novel extrinsic log likelihood ratio (LLR) of soft demapper to be conveyed to maximum a-posteriori probability (MAP) decoder under the presence of channel estimation errors. In principle, the extrinsic LLR should obey Gaussian distribution for the sake of reducing computational complexity in the MAP decoder. However, channel estimation errors deteriorate Gaussianity of the LLR derived by conventional definition. In order to guarantee the Gaussianity, this paper defines alternative extrinsic LLR according to mean square error (MSE) of channel estimates. The derivation of proposed LLR is extended to an iterative channel estimation scenario. We will demonstrate that the proposed extrinsic LLR is capable of improving bit error rate (BER) performances.

This paper proposes an autonomous grouping in subsystem band for spectrum sharing with the aid of selfish dynamic spectrum control (S-DSC) for asynchronous private wireless networks. When S-DSC, in which each transmitter maps its original spectrum to spectrum with higher channel gain of a system band in a selfish manner, is employed in each link of a shared band, and their transmission timing is asynchronous, there arises mutual interference components in the receiver even at null spectrum positions of the original interference signal, and this causes a so-called near-far problem, which is much severer than the transmit timing synchronous case. To alleviate the critical problem, the proposed scheme introduces an autonomous subsystem band grouping in which each user autonomously selects one of the subsystem band in a system band to maximize its expected average capacity, thereby user links with moderate mutual interference are grouped in the same subsystem band autonomously. Computer simulations confirm that the proposed scheme mitigates the impact of the aforementioned near-far problem. Moreover, the simulations confirm that the frame error rate (FER) performance of the proposed scheme is better than that for the centralized control assumed orthogonal frequency division multiple access (OFDMA).

This paper deals with an adaptive bit-wise switching strategy for hybrid decode-forward (DF) and decode-amplify-forward (DAF) relaying and proposes a novel bit-wise partial noise elimination technique. In relay nodes of DAF relaying, bit log likelihood ratios (LLR)s with high reliability is proactively hard-decoded to cut noise propagation. With this method, we have a difficulty to calculate LLRs in the destination node, due to multi-modality of probability density function (PDF) caused by nonlinear operations of the noise elimination. In order to resolve this issue, a classification problem is formulated in this paper. We will demonstrate that DAF with the bit-wise noise elimination functionality is capable of improving frame error rate (FER) performance in the destination node.

This paper proposes an antenna directivity control method of adaptive array antenna for secure wireless transmission by dividing the transmitted information into pieces of divided-information and sending each pieces of information in a spatially distributed manner along multiple paths in a wireless space. Based on the DCMP weight control algorithm, the authors propose an antenna directivity control method not only to steer its main lobe to one targeted path but also to suppress other side lobes to suppress unnecessary signal radiation. Computer simulation confirms that by suppressing the side lobes of the antenna directivity, the transmitted signal power can be concentrated along the targeted path. It is effective to provide multiple transmission routes for signal delivery in the wireless space. Therefore better performance in regard with the secrecy of the transmitted information can be achieved in the wireless space by sending the transmitted information in a spatially distributed manner along the selected paths between the sender and the destination.

In this paper, we propose a new criterion for the extrinsic information transfer (EXIT) analysis in the spectrum-overlapped resource management (SORM) for a broadband single carrier transmission. In the SORM technique, each user can ideally obtain a maximum channel gain by allowing overlapped allocation, assuming the soft canceller with minimum mean square error (SC/MMSE) turbo equalization for multi-user detection. When the interference is not completely removed by SC/MMSE turbo equalization, frame error rate (FER) remarkably degrades. To solve this problem, we proposed a new criterion which is used for design of error correcting code in order to improve convergence property of SC/MMSE turbo equalization without large redundancy of channel code. In the proposed criterion, we design the decoder so that the decoder's EXIT property is fitted to the upper bound of equalizer's property and the channel code sharply improves mutual information (MI) in the lower amount of input MI. This paper evaluates FER performance with the irregular low-density parity-check (LDPC) codes designed based on this criterion. As a result, this paper shows that the irregular LDPC code designed based on the proposed criterion for the SORM outperforms conventional codes.

This paper presents a novel base station (BS) cooperation scheme to address issues on fatal links experienced by cell-edge users based on bit interleaved repetition coded (BIRC) concatenated structures for downlink OFDM scenarios. A primary focus is on employing independent random interleavers in cooperating BSs following by BS cooperation which may be regarded as the repetition code. In early works related to the BS cooperation, the main paradigm was just for an enhancement of signal levels after a signal combining, in terms of improvements of channel capacity. However, in order to achieve the enhanced channel capacity, we have to design not only appropriate channel codes but also perfect channel state information (CSI) notifications. The proposed simple BIRC based BS cooperation technique has a potential to overcome above mentioned issues through unified design via an iterative fashion. In this paper, high diversity and coding gains of BIRC based BS cooperation are observed in computer simulations, comparing to an Alamouti's STBC based BS cooperation scheme.

This paper presents a relay activation scheme designed for joint channel-and-network (JCN) coded systems relying on an iterative decoding. A primary focus is on proposing criteria of the relay activation to find the best user combination for cooperative relaying, which exploits extrinsic information transfer (EXIT) chart analysis. We will demonstrate that the EXIT chart aided relay activation scheme is capable of reducing the probability of outages, despite increasing the effective throughput of network.

This paper proposes an adaptive bandwidth control scheme for autonomous distributed networks. Based on the consideration that the carrier sense multiple access with collision avoidance (CSMA/CA) is not efficient in terms of throughput due to its strict collision avoidance process, this paper employs a dynamic spectrum control (DSC) in which a certain number of discrete spectra having the highest signal to interference power ratio (SINR) is selected in a selfish manner in each link allowing a partial band interference, and such interference is suppressed by the equalizer in the receiver. For optimal selection of the band activity ratio (BAR) for the selfish DSC in the sense of throughput maximization, this paper also proposes a channel capacity maximization-based BAR control scheme. Computer simulation confirms that the proposed scheme is achieving high throughput efficiency in the autonomous distributed networks.

This paper proposes a cooperative relay transmission exploiting a concatenated structure composed of a simple exclusive OR (XOR) network code and channel codes. A main contribution of this paper is to clarify the joint network-and-channel coding combined with an iterative decoding is effective in providing highly reliable wireless communications even in the case where distances from one destination node to two source nodes are not the same in the case of triangular topology network. In this case, it is subject to imbalanced signal powers at the destination node, resulting in imbalanced link quality. In this paper, we focus on an analogy between the triangular topology network and a quaternary PSK (QPSK) symbol with a rectangular shape, i.e., imbalanced the in-phase and quadrature-phase (I-Q). After demonstrating that the rectangular QPSK has a potential to detect signals with high accuracy by iterative decoding, a configuration of the cooperative relay to be proposed in this paper is revealed. Computer simulation confirms that both the rectangular QPSK and the cooperation are effective to solve the imbalanced problem.

This paper investigates the minimum number of antenna elements of an adaptive array antenna (AAA) required to suppress unnecessary radiation to a single location in an indoor ubiquitous communication environment. In the investigation the relationship between the number of antenna elements of an AAA and its digitally-created antenna null width is demonstrated using antenna directivity control technique that has been proposed by the authors. Also, the angular spread around a terminal to a single location in an indoor communication environment is demonstrated with propagation measurements. Based on the computer simulation results and the angular spread obtained by propagation measurements, the authors specify that at least 6 antenna elements are required to suppress radiation to a single location in an indoor communication environment up to -60 dB.

This paper proposes a scheduling and adaptive rate control scheme for multi-user multiple-input multiple-output (MIMO) systems in the uplink, designed to improve system throughput in single-carrier broadband wireless systems exploiting a frequency domain soft canceller with minimum mean square error (FD-SC/MMSE) turbo equalizer. Aiming at the reduction of computational burden involved in the scheduling and adaptive rate control while maintaining high throughput efficiency, scheduling including a stream selection is first conducted in the base station (BS) based on the expected signal to noise power ratio (SNR) under an assumption that the turbo receiver is converged. The BS then conducts a coding rate optimization for each scheduled stream to maximize the throughput efficiency. A main contribution is to reveal a mechanism that the convergence property is controlled to maximize the throughput efficiency by a prediction of the iterative behavior based on extrinsic information transfer (EXIT) trajectory which is predicted from channel transfer functions and a window control proposed in this paper. Computer simulation confirms that the achievable average system throughput can be significantly improved by the proposed scheme.

This paper proposes a spectrum-overlapped resource management (SORM) technique using a dynamic spectrum control (DSC) and turbo equalizer for flexible frequency domain resource management under multiuser conditions. In the proposed technique, discrete spectrum of the transmitted signal is mapped onto spectrum components having the highest channel gain in the system band while accepting partial spectrum overlapping between users, and a frequency domain soft-canceller with minimum mean square error (FD-SC/MMSE) turbo equalizer is applied as the signal detection scheme for multiuser detection (MUD) in order to cancel not only inter-symbol interference (ISI) but also inter-user interference (IUI). Computer simulation including extrinsic information transfer (EXIT) analysis confirms that the proposed scheme can achieve high frequency selection diversity and realize flexible frequency domain resource management.

This paper proposes a relay-assisted re-transmission scheme based on mutual information for wireless mesh networks. In the proposed scheme, re-transmission is done not from the source node but from the relay node, and minimal amount of spectrum corresponding to the remaining uncertainty for the data sequence is re-transmitted, where the number of spectrum components to be fed back is determined based on expected mutual information after re-transmission. Moreover, to directly convert reduction of feedback spectrum to spectrum efficiency improvement in carrier sense multiple access with collision avoidance (CSMA/CA) introduced systems, the re-transmitted spectrum is mapped on whole the bandwidth with equal spacing, thereby the time duration for the re-transmission is reduced. Computer simulation confirms that the proposed scheme can achieve much higher system throughput efficiency especially than the conventional two-hop transmission schemes.

This paper proposes a partial spectrum retransmission scheme using a dynamic spectrum control for broadband single carrier transmission systems. In the proposed scheme, using a dynamic spectrum control in which discrete spectrum of the transmitted signal is mapped onto an arbitrary part of the assigned spectrum, only a certain amount of deeply faded spectrum components are retransmitted via a part of channel having relatively a higher channel gain. The amount of retransmitted components are determined based on mutual information between the transmitted signal and the output of an minimum mean square error (MMSE) based frequency domain equalizer (FDE). Moreover, plural retransmission frames are multiplexed in a retransmitted frame for efficient utilization of the retransmitted spectrum component reduction. Computer simulation confirms that the proposed scheme can achieve high throughput performances even under low terminal mobility or quasi-static conditions.

This paper propose an unnecessary radiation power suppressing technique to electromagnetically restricted areas in ubiquitous communication environments. An adaptive array antenna is employed in each terminal to control a directivity of transmit antenna not to radiate unnecessary power to the electromagnetically restricted areas while keeping sufficient gain to a target terminal. To identify angle of departures to the electromagnetically restricted areas, a radio power sensor network is assumed. Moreover, channel sounding based delay profile estimation is conducted to identify the strongest path direction for the desired signal. Based on the identified strongest path for the desired signal and the direction of the unwanted radiation detected using the radio power sensor network, artificial delay profile for a transmitted signal is created, and antenna directivity for the transmitted signal is created using a deep and wide null creation technique based on the artificial delay profile. Computer simulation confirms that the unnecessary radiation to the electromagnetically restricted areas is sufficiently suppressed while keeping throughput at a satisfactory level.

In this paper, we introduce adaptive link control techniques for multiple-input multiple-output (MIMO) systems with broadband single-carrier signaling. Soft cancellation and minimum mean squared error turbo equalization is assumed, where matching between coding and equalization plays crucial roles to achieve high throughput. This paper uses multilevel coded bit-interleaved coded modulation (ML-BICM) with linear mapping as a core part of the transmission, on top of which this paper applies automatic repeat request (ARQ) with adaptive coding (AC) for link control. The reason behind the use of the linear mapping ML-BICM is the separability between the layers in the modulation format: This should bring us a significant benefit in designing the link control strategies because each layer has its own reliability, and the adaptive link control should be optimized based on the each layer's reliabilities. For ARQ with ML-BICM, we introduce layer-by-layer retransmission control, where turbo equalization and retransmission control can be performed independently over the layers because of the layer-separability. The layer-by-layer concept is then applied to AC with ML-BICM, where the code parameters such as code rate and generator polynomials are chosen so that after several iterations the mutual information between the transmitted and the soft-input soft-output decoder output information can reach a value very close to one while minimizing the rate loss due to the mismatch between the equalization and decoder. Extrinsic information transfer analysis is performed for the MIMO channel realization being given. The transmitter is notified of the selected codes for the each layer via the feedback channel, and uses the selected codes for the following transmission, assuming that the channel state information (CSI) stays the same at least over two consecutive frames. Finally, this paper evaluates the throughput performances of the ML-BICM ARQ and AC techniques using multidimensional field measurement data. The performance tendencies are correlated with propagation properties, obtained as results of the high-resolution channel analysis, such as spatial spreads at the transmitter and receiver sides.

This paper discusses system design strategies and performance evaluation for adaptive modulation techniques used in new and up-and-coming wireless access systems. After a brief discussion on basic modulation parameter (MP) settings as well as functionalities specific for adaptive modulation systems, this paper discusses how to design a narrowband time-division multiple-access/time-division duplex (TDMA/TDD)-based adaptive modulation system and confirms through laboratory experiments that the narrowband TDMA/TDD-based adaptive modulation system dramatically enhances system robustness to multipath fading and flexibility in throughput and transmission quality control. Next, as an extension to many fields of application for adaptive modulation, this paper discusses subcarrier-level adaptive modulation for orthogonal frequency-division multiplexing (OFDM)-based one-cell reuse broadband cellular systems. One key result is that nonsubcarrier transmit power control (TPC) applied adaptive modulation systems can achieve almost the same performance as subcarrier TPC applied adaptive modulation systems provided that the required signal-to-noise-plus-interference power ratio increment in the MP sets is designed to be sufficiently small. Finally, this paper explains the dynamic parameter controlled OFDM/TDMA system as an example of a practical scheme for one-cell reuse broadband wireless access systems. The analysis confirms that this adaptive system can achieve a spatial reuse efficiency defined by (average throughput in multicell conditions)/(average throughput in single cell conditions) of 0.8 as well as an average media access control payload throughput of about 150 Mb/s using about 100 MHz of bandwidth.

This paper proposes a microscopic spectrum control technique using a carrier interferometry (CI) to achieve an adaptive modulation based one-cell reuse broadband single carrier time division multiple access (TDMA) system. In the proposed systems, in order to reduce peak to average power ratio (PAPR) and to improve robustness to inter-cell interference (ICI), we employ a CI technique that equivalently generate a single carrier waveform using the same waveform generation with orthogonal frequency division multiplexing (OFDM). As for improvement of robustness to ICI, an adaptive spectrum selection according to the received signal to interference plus noise power ratio (SINR) is introduced as a microscopic spectrum control technique when lower symbol rate is selected in the adaptive modulation scheme (AMS). Computer simulation confirms that the proposed scheme is effective in improvement of ICI immunity

This paper will discuss trend and our views on the flexible spectrum control and receiver performance improvement technologies as a part of capacity maximization technologies for beyond third generation (B3G) systems. First of all, we will discuss dynamic spectrum control techniques that can minimize intra- and inter-system interference for both multi-carrier (MC) and single-carrier (SC) systems, thereby maximizing upper-limit of channel capacity. We will also discuss receiver performance improvement strategies as a part of capacity maximization technologies for MC and SC systems, especially joint operation of the adaptive equalizer and decoder using EXIT chart analysis for MC and SC systems

This paper proposes a channel estimation technique for multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM)/time division multiple access (TDMA) (MIMO-OFDM/TDMA) cellular systems based on the dynamic parameter controlled-OF/TDMA (DPC-OF/TDMA) systems. In the proposed scheme, impulse responses of all the transmit antennas are multiplexed in the time domain using a carrier interferometry (CI) signal, which is equivalent to an impulse signal, and each impulse response is discriminated using a time window with the length of the maximum delay time of delayed paths, in order to estimate a channel state information (CSI) using only 64 subcarriers. Computer simulation confirms that the proposed channel estimation scheme is effective even in the case of 64 subcarriers under MIMO and multi-cell conditions

In one-cell-frequency-reuse MIMO (multi input multi output) - OFDMA based TDMA (OF/TDMA) systems, we face a problem that communication is blocked by interferences from adjacent cells. To solve this problem, an AMC (adaptive modulation and coding) scheme that is controlled by estimating DUR (desired signal to undesired signal power ratio) would be most promising. However, there is no accurate DUR estimation method using spreading codes for OF/TDMA systems due to the asynchronous FFT so far. In this paper, we propose a novel DUR estimation method by adding IFFT and time-window and introducing CI (carrier interferometry). The proposed DUR estimation method can separate the desired signal from a received signal even if FFT is asynchronous

This paper proposes a channel estimation technique for the dynamic parameter controlled - orthogonal frequency and time division multiple access (DPC-OF/TDMA) system. In the proposed scheme, channel impulse response that represents channel state information (CSI) is measured using a carrier interferometry (CI) which is equivalent to impulse transmission. Moreover, because the minimum unit (subchannel block) of subcarriers to be allocated to each terminal is 64 subcarriers, to achieve high accuracy of the estimated CSI with a spreading factor of 64, code-multiplexed pilot signal is applied to identify base station (BS) in the cell search process, and CSI between a terminal and each transmit antenna element in the BS is detected using a time-domain-multiplexed CI signal for ease of extension of the DPC-OF/TDMA to multi-input multi-output (IMO) systems. Furthermore, we will also propose a CSI estimation scheme flexible to the plural subchannel block assignment cases. Conmputer simulation confirms that the proposed scheme can estimate the CSI regardless of the number of subchannel blocks assigned to each terminal.

We propose a new generation mobile communication system that can realize 100 Mbps carrier bit rate under high mobility environment and can access the IP network easily. The new system is based on dynamic parameter controlled orthogonal frequency and time division multiple access (DPC-OF/TDMA) in which users share "slots" that use a certain number of subcarriers and a certain number of OFDM symbols. To access the slots, mobile stations use a packet-reservation-based protocol: packet reservation dynamic time-slotted multiple access (PR-DSMA). In addition, to avoid cochannel interference from adjacent cells and increase frequency utilization efficiency, we use an adaptive modulation scheme that is based on an interference detection algorithm. We mention the concept and the basic transmission performance of the proposed system.

This paper proposes a spatial filtering technique to effectively receive narrow angle spread multipath signals incoming to the typical macro cell base station in DS/CDMA cellular systems. In the proposed system, a hypothetical received signal for each antenna element is generated in the receiver using the measured delay profiles and known QPSK symbol sequences, and this signal is employed for antenna weight calculation. At this stage to create high gain pointing toward all the desired multipath components in the spatial filter, phase and delay time of the measured delay profiles for the hypothetical received signal is adjusted to be equal to enhance the generated hypothetical received signal with inphase. Computer simulation confirms that the proposed algorithm can create an effective spatial filter for receiving narrow angle multipath and achieves better performance than the conventional algorithm.

This paper proposes an adaptive resolution control scheme for a RAKE receiver in direct sequence/code division multiple access (DS/CDMA) systems to effectively resolve and combine multipaths for high-bit-rate wireless multimedia services. In the proposed scheme, the receiver measures a delay profile for the received signal with its resolution equal to the highest chip rate, estimates delay profiles for lower chip rates using a delay profile conversion technique, and selects a chip rate that maximizes the received signal to noise plus interference power ratio (SNIR) under a condition that the number of RAKE fingers is limited by a certain number. Computer simulation confirms that the proposed scheme with a 3-finger RAKE receiver can reduce the average transmit power by about 5 dB without degrading the transmission quality under a 30-ray Rayleigh fading channel.

This paper proposes an accurate signal to interference plus noise power ratio (SINR) measurement technique to correctly proceed transmit power control (TPC) in M-sequence-based M-ary/spreading spectrum (M-ary/SS) scheme to realize high bit rate transmission for M-ary/SS/code division multiple access (M-ary/SS/CDMA) systems. Because the accuracy of TPC depends largely on the accuracy of SINR measurement, to sufficiently proceed TPC, the proposed scheme measures power ratio of the correlation peak to the other correlations in the correlator for M-ary/SS employing a correlation peak detector that regenerates the spreading sequence from the Viterbi decoded output data. Computer simulation confirms that the M-ary/SS scheme with regenerating spreading sequence can achieve much better bit error rate (BER) performance with decrease of peak transmit power of 5 dB in comparison with the conventional direct sequence/spread spectrum (DS/SS) scheme under ITU-Vehicular B model.

This paper proposes a delay profile information based subcarrier power control combined with a partial non-power allocation technique for OFDM/FDD systems to achieve high bit-rate and high quality non-voice data transmission for wireless communication systems. To improve the bit error rate (BER) performances for the convolutionally encoded OFDM system, the proposed system controls the transmit power for each subcarrier in order to keep the received power of each subcarrier constant using a measured delay profile and noise level given by a delay profile information (DPI) channel in the return-link. To further reduce the transmit power needed to achieve high quality data transmission, a partial non-power allocation (PNPA) scheme combined with a punctured coding technique is further applied to the subcarrier power control. In this scheme, the deleted bits by the punctured coding are allocated to the nonreliable subcarriers and transmit power for these subcarriers are power-suppressed. Computer simulation confirms that the proposed system can achieve high quality data transmission and reduction of transmit power as compared with that of a conventional system in frequency selective fading environments.

This paper evaluates the effect of angle spread on the system capacity for a DS/CDMA system using a delay profile measurement based adaptive array antenna combined with beam pattern selection diversity and carrier-to-interference plus noise (CINR) based transmit power control (TPC) techniques. In the proposed system, beam directivity is controlled by the delay profiles for each terminal measured in each antenna element. Moreover, to reduce the number of computation for the beam directivity control, the proposed system calculates the optimum beam directivity for only a limited number of terminals that locates far from the base station, and signals from the rest of the terminals are demodulated by selecting one of the most reliable adaptive array combined signals. This technique is called beam pattern diversity. For the evaluation of impact of the angle spread of the multipath components on the capacity of DS/CDMA systems with an adaptive array antenna, computer simulation is conducted. The results show that the proposed scheme gives better performance than the sector antenna systems under practical angle spread conditions; i.e. less than 10 degree, with relatively a small number of computation.

This paper discusses intelligent and flexible radio access/transmission technologies necessary to smoothly upgrade supported services as well as to economically extend coverage and operational environments. After a brief discussion on classification of key technologies for intelligent and flexible radio access/transmission technologies, the paper discusses the adaptive transmission parameter (TP) control techniques for both time division multiple access (TDMA) based and code division multiple access (CDMA) based systems. Finally, this paper proposes a time division multiplex (TDM) based adaptive access control technique to further enhance system capacity and to introduce higher grade services for CDMA-based wireless multimedia communication systems.

This paper proposes an adaptive modulation system (AMS) with a discrete power control combined with a predistortion (PD)-type nonlinear distortion compensation technique for high quality and high power efficient high-bit-rate wireless communication systems. In the PD-type nonlinear distortion compensator, predistortion look-up table is updated using a teaching signal embedded in the guard time. In this process, nonlinear input signal vs. output distortion performance is discretely measured during the guard time period, and at the end of the guard time, a sequence of the measured distortion is interpolated using a cubic spline function to reduce memory size and the number of computation. More over, in the power control section, three levels of transmitter power attenuation, i.e., 0, 10 and 20 dB are prepared, and they are selected according to the expected carrier power to noise power spectral density (C/N/sub 0/) of the transmitter. Computer simulation confirms that the proposed method can sufficiently suppress the non-linear distortion in the adaptive modulation TDMA/TDD systems.

This paper proposes a direct sequence/code division multiple access (DS/CDMA) cellular system using channel activation and soft power control techniques to increase both the forward and reverse link capacities. To equivalently control the received signal to interference and noise power ratio (CINR) to be constant, the proposed system employs a channel activation technique in which higher channel coding gain and small processing gain are employed with a shorter burst length during higher CINR period, and a lower channel coding gain and larger processing gain are employed with longer burst during lower CINR. Moreover, the proposed system employs a soft power control technique to enhance the advantages of the channel activation technique. Computer simulation confirms that the proposed system can achieve a higher system capacity with a smaller soft hand-off margin and a smaller average transmitter power.

This paper proposes automatic repeat request (ARQ) protocols combined with an adaptive modulation system (AMS) (ARQ/AMS) to achieve high throughput data transmission for wireless multimedia communication services. First, it analyses the cause of the throughput limitation of the conventional fixed modulation ARQ system, and discusses basic strategies to improve the throughput performance by effectively combining ARQ and AMS. Next, it proposes a selective repeat ARQ (SR-ARQ) with AMS (SR-ARQ/AMS), and shows its throughput performance improvement effect. Finally, this paper proposes a type-II hybrid ARQ with a punctured convolutional coding combined with the AMS (type-II hybrid ARQ/AMS) to further improve the throughput performance. Computer simulation confirms that the proposed type-II hybrid ARQ/AMS can achieve higher throughput performance than the conventional selective repeat ARQ with QPSK under any channel conditions.

This paper reports laboratory experimental results of a time division multiple access/time division duplex (TDMA/TDD) based adaptive modulation system to verify feasibility and its usefulness for future wireless multimedia communication systems. The developed system employs a symbol rate and modulation level controlled adaptive modulation in which the modulation scheme is selected from full-rate 64-ary quadrature amplitude modulation (64 QAM), full-rate 16 QAM, full-rate quaternary phase shift keying (QPSK), 1/2-rate QPSK, 1/4-rate QPSK, 1/8-rate QPSK and no transmission according to the expected channel condition for the transmitted signal. The experimental results confirm that the developed system is very effective in achieving high quality and high bit rate transmission of around 1 Mbit/s without any special anti-frequency selective fading techniques even under frequency selective fading conditions with its d delay spread of less than 250 ns and f/sub d/ of less than 10 Hz.

This paper proposes a complexity-reduced decision feedback equalization (DFE) scheme for 16-ary quadrature amplitude modulation (16 QAM) over frequency-selective fading channels. The proposed DFE uses bidirectional equalizing (BDE), and space diversity combining (SDC) to achieve high-spectral-efficiency, high-quality data transmission. To reduce the amount of computation of both BDE and SDC for 16 QAM, this paper proposes a tap gain interpolation scheme, new selection schemes of both the equalizing direction of the BDE and the selection of diversity branch. Using these techniques, a 16 QAM/time division multiple access (TDMA) system with 448 ksymbol/s is designed. The system performance is evaluated by computer simulation, assuming a maximum delay of 13 msec. The results confirm that the proposed system is effective and also simple for high-speed data transmission in land mobile communications.