Recently, the role of Low-Power Wide Area Networks (LPWANs) as enablers of the Internet of Things (IoT) is emerging. However, many concerns arise on the performance of LPWANs if higher Quality of Service (QoS) requirements are needed by certain classes of IoT services. In this work, we will focus on one of the most prominent of these technologies, i.e., Long-RangeTM(LoRa). Our aim is to study to what extent a LoRa network is able to support uplink (UL) traffic that requires to be confirmed by the Network Server (NS). The simulation results show that the network performance is severely impacted by the downlink (DL) traffic generated by feedback packets.

Water-filling methods is one of techniques to improve a performance of multiple input multiple output (MIMO) system. However, the application of water-filling method to multiple hops MIMO relay system hasn't been discussed, especially in amplify and forward scheme. In this paper, the water-filling method for multiple hops MIMO relay system with amplify and forward scheme is proposed and evaluated in both perfect channel state information (CSI) and imperfect CSI. The effect of imperfect CSI on water-filling and on co-channel interference is taken into account. Compared to average transmit power, the end-to-end channel capacity of proposed water-filling method is higher in perfect CSI, however, it is subject to the effect of imperfect CSI. Additionally, a half duplex and a full duplex transmission method are also discussed in this paper. The end-to-end channel capacity of full duplex is higher and more robust than that of half duplex due to a double of allocation time and a half of delay time.

Due to rapidly increasing of elderly population all over the world and quickly developing of entertainment devices, wireless body area network (WBAN) attracts attention. For both medical and non-medical applications, a reliability, high energy-efficiency and high throughput of WBAN communication are requested. The well-known cluster-based is proposed to obtain the high energy-efficiency, however the transmission in every cluster is controlled on MAC layer by superframe in order to obtain the high throughput. The performance of original cluster-based, complete control and spatial reuse superframe scenarios is analyzed and compared. The calculation result indicates that the spatial reuse superframe outperforms the original cluster-based when the access probability and/or the total number of sensors are high. Furthermore, there are the optimal number of clusters, the access probabilities and the total number of sensors that achieve the highest throughput. The optimization method of number of spatial reuse superframe (k) is proposed to obtain the highest throughput when another factors change. k increases when another factors of system model increase, excepted the payload. The optimization method of another factors is similar and the proposed method can be applied to not only IEEE802.15.6 WBAN but also another cluster-based wireless sensor networks.

A frame-patch matching based robust video watermarking using KAZE feature is proposed in this paper. We employed the KAZE feature for matching the feature points of frame-patch with those of all frames in video. In our method, the watermark information is embedded in Discrete Cosine Transform (DCT) domain of randomly generated blocks in the matched region. In the extraction process, we synchronized the embedded region from the distorted video by using KAZE feature matching. RST (rotation, scaling, translation) parameters are estimated and the watermark information can be extracted. Experimental results showed that our proposed method is very robust against geometrical attacks, video processing attacks, temporal attacks, and so on.

For high end-to-end channel capacity, the amplify-and-forward scheme multiple-hop MIMO relays system is considered. The distance between each transceiver and the transmit power of each relay node are optimized to prevent some relays from being the bottleneck and guarantee the high end-to-end channel capacity. By proposing the transmission environment coefficient, the path loss is described in a new way and then the distance of multiple-hop relay system can be optimized more simply than the original one. However, when the system has no control on Mac layer, the performance of system is deteriorated because of the presenting of interference signal. Thus the specific control protocol on MAC layer for multiple-hop system is proposed to reduce the power of interference signal and obtain the high end-to-end channel capacity. According to proposed control protocol on MAC layer, the system indicates the trade-off between the end-to-end channel capacity and the delay time.

Received signal's time-of-arrival (TOA) based real time ranging system is widely used for UWB geolocation. However, multipath radio wave propagation and Non-line-of-sight (NLOS) incidents can cause a large error in source localization. In order to mitigate these errors, this paper proposes and investigates a novel approach which makes a hybrid combination of fingerprinting (FP) positioning and an iterative Time of Arrival (TOA) real time positioning method. Moreover, to reduce the computational complexities in FP method, we introduce a unique idea for the arrangement of reference tags to create fingerprinting database. Each arrangement of reference tags resembles a shape of polygon, which size dominates the computational complexities of FP as well as proposed hybrid method. By analyzing the tradeoff between positioning accuracies and computational complexities in proposed method we determine the appropriate size of polygon to reduce the computational complexity while maintaining a higher positioning accuracy. Moreover, proposed method is the effective solution of geo-location in the dense multipath condition and in the worst cases of NLOS. Finally, in comparison with TOA only, FP only and a conventional iterative positioning method the proposed hybrid method yields better performance and is much more robust in dense multipath situations.

Recently, Impulse Radio Ultra Wideband (IR-UWB) signaling has become popular for providing precise location accuracy for device localization in the indoor environment due to its large bandwidth and high time resolution while performing ultra-high capacity of transmission. Received signal's time-of-arrival (TOA) based real time ranging system is widely used for UWB positioning. However, Non-line-of-sight (NLOS) propagation can cause a large error in source localization. Hence, mitigating NLOS errors is a great challenge for a positioning system. In order to mitigate NLOS errors this paper proposes and investigated a noble approach which makes a hybrid combination of fingerprinting (FP) positioning and an iterative Time of Arrival (TOA) real time positioning method. The proposed hybrid method follows an iterative process in which the initial values are estimated from FP positioning. We show that the computational complexity of the hybrid method can be significantly reduced when more appropriate initial values are considered. Finally, in comparison with TOA only, FP only and another iterative-TOA positioning methods the proposed hybrid method yields better performance and much more robust in NLOS error mitigation with improved positioning accuracy in various channel conditions.

The present paper considers how to improve estimation accuracy in a time of arrival (TOA) localization system using UWB in a non-line-of-sight (NLOS) environment for a sensor network. This algorithm consists of step-by-step compensation on the basis of two approaches considering a reference position which is estimated from data affected by NLOS delay. The first consideration consists of determining NLOS delays for each node, performing compensation to alleviate the effect on line of sight (LOS) nodes through a step-by-step compensation for the NLOS delay. The second consideration consists of compensating the effect of NLOS delay on the position determined on the basis of node distribution and geometrical relations of the estimated positions. Using these considerations, we show that the proposed algorithm outperforms the conventional algorithm in terms of estimation accuracy.

Multiple-input multiple-output (MIMO) is known as an one of the most attractive candidates for large capacity. However, when signal to noise ratio (SNR) is decreased, the propagation character of MIMO is dropped rapidly. For re- maining the propagation character of MIMO and/or increasing a capacity, MIMO repeater systems have been discussed. In MIMO multi repeater system, called distributed MIMO repeater system, to obtain bound of capacity of two-way repeater system, we propose a simple mathematical method and statistical Markov chain Monte Carlo method for optimizing distances and transmit power simultaneously.

This paper describes the Impulse Radio Ultra-Wideband (IR-UWB) system using linear chirp UWB pulses as symbols. The novel method of coherent or differentially coherent detection of chirp pulses in multipath channels is introduced. The method divides detection in the receiver between its analog and digital part; in the analog part of the receiver, received signal is compressed in frequency by mixing with locally generated chirp pulse and low-pass filtering. In this way, the time-bandwidth (TB) product of the resulting signal is reduced compared to the received signal and made approximately independent of duration of the transmitted signal. This results in relatively low complexity digital back-end of the receiver that is able to capture a large portion of the multipath energy, regardless of duration of the transmitted waveform. The work includes derivation of analytical properties of the system, including derivation of loss parameters that quantify system multipath performance. Numerical results include discussion on the system multipath loss performance with varying chirp duration. As well, a comparison is made with error performance of sampling receivers featuring the same computational complexity. Analysis of the robustness of the system's performance to different chirp pulse implementation errors is also provided.

On-body communication channels are gaining increasing interests as more and more wireless devices are wearable in the fields of medicine, military, and personal communications. This paper presents an experimental investigation of the dynamic features of time-varying on-body channels with continuous movements of human body. Channel response at 10 antenna positions in two dynamic scenarios, walking and standing up and sitting down, have been measured in the anechoic chamber. Based on the statistical analyses of fading duration, a five-state Fritchman model that considers channel dwelling time at a given quality is proposed. Parameters of the Fritchman model are estimated from the measured data. The characteristics of simulated burst channels are in good agreement with the measurements.

It is important to estimate the accurate position of sensor tag in sensor network, for example, RFID. Time difference of arrival (TDOA) positioning algorithm is well known as the positioning algorithm of the sensor tag. Therefore, the positioning accuracy of conventional linear search algorithm is decreased exceedingly in non-line-of sight (NLOS) environment. Especially, we adopt IEEE 802.15.4a ultra wideband (UWB) channel model as NLOS condition in order to assume that UWB system is used at indoors for positioning system. In this paper, we propose the iterative NLOS delay compensation algorithm based on TDOA in order to fulfill high accuracy in the damaged propagation through NLOS environment. At first, the temporary position is estimated by normal TDOA method and transmission start time is estimated. Next, the time difference between transmission start time and node arrival time is compensated by delay compensation function (DCF), and reliability of each node is decided by reliability weight function (RWF). By those iterative processes, the positioning accuracy is improved.

Multiple-input multiple-output (MIMO) repeater systems have been discussed in several published papers. When a repeater has only one antenna element, the propagation environment is called keyhole. In this kind of scenario an achievable channel capacity and a link quality are decreased. Another limit is when the number of the antenna element of a repeater is larger than the one of a MIMO transceiver, the channel capacity cannot be increased. In this paper, to obtain an upper bound of the channel capacity, we express a propagation process of the distributed MIMO repeater system with decode-and-forward method by the numerical formula, and optimize the position of each repeater.

In this paper, ultra-wideband impulse radio(UWB-IR)system inside a vehicle is considered to construct internal vehicle wireless sensor network with better performance. In a vehicle, a direct path is likely to be blocked by the seat and passengers. The channel model characteristic in a vehicle is different from other wireless systems. When using UWB systems, other wireless systems in the same frequency band cannot be neglected. We propose equalization and interference cancellation using adaptive digital filters in order to remove the influence of the channel inside a vehicle and the narrowband interference. The cannel model and system model were constructed. The performance was analyzed by computer simulation. The simulation results showed that the performance could be improved by the proposed system. Moreover, the number of taps of ADF could be reduced from 10500 to 10000 by using band-pass filter(BPF). Therefore, the processing time could be decreased.

In this paper, one of new maximum a posteriori (MAP) estimation methods is introduced for signal detection in a magnetic recording channel with burst erasures. In signal detection for the recoded data sequence on the recording media, it needs to consider that there exists a fluctuation range for the variance of media noise according to the specific recorded bit patterns. Most of conventional signal estimation techniques assume to use the constant and invariant variance of media noise within the specified data fields. But, the readback signals happen to be faded in consequence of media defects or thermal asperities in several time intervals. These physical distortions cause burst erasures in magnetic recording. From a view point of signal estimation problem, the estimation technique is based on nonstationary time series analysis for a stochastic process is effective for attenuated signal sequences caused by burst errors. In this paper, it is shown that the estimation problem for burst erasures is solved by maximum a posteriori estimation with an autoregressive conditional heteroscedastic (ARCH) process (model) and burst error correcting non-binary array codes for 4K block sectors. For the given non-binary array coding system, the error rate performance using proposed channel predicting MAP estimation method is superior to the performance using the conventional MAP estimation.

Wireless communication devices in the field of medical implant, such as cardiac pacemakers, capsule endoscopes and micro or nano size of implant robots, have been studied and developed to improve healthcare systems. Especially it is very important to know the range and position of each device. Because it is useful and important for accurate sensing and controlling a capsule endoscope, micro or nano size of robot for a drug delivery system and a remote medical treatment system. We adopt the time-based approach of position estimation using ultra wideband (UWB) signals. Position estimation methods using the propagation velocity inside human body have been proposed [1]. However, the estimate position is mistaken when propagation velocity is not correctly calculated. In this paper, we proposed a system to estimate the position of medical implant device using slice photographs taken by CT or MRI systems as a map in addition to the estimation of propagation velocity. The compensation becomes possible by image information when the estimated position is an area where the device doesn't exist (ex: capsule endoscopes excluding the digestive system) and is calculated. This is similar to a car navigation system. We compared our proposed method to the method of estimation using only propagation velocity and showd the utility.

On-body communication channels are of increasing interest as more and more wireless devices are wearable in medical, military and personal communication applications. Based on the previous study at 4.5GHz, this paper investigates reasons for time-varying fading of dynamic on-body channels. Antenna movements during action are categorized into intentional movement which can be controlled and unintentional movement which cannot be controlled. We use commercial software POSER7 to generate intentional movements between on-body antennae, which include distance and direction mismatch. The unintentional movements are considered to be a Gaussian process. Combining antenna movements with a measured on-body antenna radiation pattern, dynamic relative path gains during an action are obtained. Through statistic analysis, it is found that the middle and long term dynamic fading are mainly attributed to intentional movements, and the dominant short term dynamic fading is mainly attributed to the mismatch of antenna direction resulting from unintentional movements. New discovered long term error channels indicate more states should be considered in the Fritchman model.

This paper provides channel models for wireless body area network (WBAN) in UWB frequency band, and also presents performance evaluation using the derived channel models. The channel model is given by a statistical model in which parameters are derived from actually measured channel transfer function in a hospital room environment. These models enable us to evaluate performance of UWB-based WBAN. In this paper, bit error ratio (BER) and packet error ratio (PER) are shown for UWB-based WBAN which employs a signaling scheme among OOK, BPPM, BPSK, and DPSK. The results show that both OOK and BPPM which generally uses a non-coherent receiver provide severe performance when the target PER is set to 10-2under the packet size of 128 bytes. The other signaling schemes achieve the required performance from the viewpoint of such error ratio.

Biomedical sensors can be implanted and networked in the human body for health monitor, diagnosis, treatment or as a prosthetic device. Life time and heat generated by implant due to communication and circuitry power consumption are big concerns. This paper presents a new network architecture for long range communications in the implanted sensor networks. We measured the on-body propagation around body surface and in-body propagation through tissue in the frequency ranges of 403 MHz and 2.45 GHz. We have found that the in-body path loss is more than that of on-body. To exploit the path loss difference, we propose to introduce a body surface coordinator which has more resources to the implanted sensor networks. Instead of only routing data among implants, the coordinator on the body surface can forward data from one implant to another over long distance more safely and efficiently.

Wireless body area network (WBAN) solution is an emerging technology to resolve the small area connection issues around human body, especially for the medical applications. Based on the integrated superframe structure of IEEE 802.15.4, this paper proposes a modified medium access control (MAC) protocol for WBAN with focus on the simplicity, dependability and power efficiency. Considering the support to multiple physical layer (PHY) technologies including ultra-wide band (UWB), the slotted ALOHA is employed in the contention access period (CAP) to request the slot allocation. Mini-slot method is designed to enhance the efficiency of the contention. Moreover, sufficient slot allocation in the contention-free period (CFP) makes the proposed protocol adaptive to the different traffic including the medical and non-medical applications. Simulation results show that the protocol effectively decreases the probability of collision in a CAP and extends the CFP slots to support more traffic with quality of service (QoS) guarantee.

Spectrum sensing, as a key technology in cognitive radio networks, needs to detect signals from licensed primary radio systems to avoid harmful interference. However, due to the effects of fading, individual cognitive radios may not be able to reliably detect the existence of a primary radio. Cooperative sensing is proposed as a means to mitigate such effects. In this paper, we analyze a trade-off between the local processing overhead and the cooperation overhead. Numerical results show that the throughput of cognitive radio network decreases as the cooperation overhead increases due to the increase in the number of cooperation users.

Complementary WLAN and WPAN technologies, as well as other wireless technologies will play a fundamental role in the medical environments to support ubiquitous healthcare delivery. This paper investigates energy based carrier sensing and its impact on the coexistence of IEEE WLAN (802.11b) and WPAN (802.15.4) in the 2.4 GHz band. We derived closed-form expressions of energy based clear channel assessment (CCA) and qualified unequal sensing abilities between WLAN and WPAN in additive white Gaussian noise channel and fading channel. The asymmetric CCA is different from the traditional "hidden node" or "exposed node" issues in the homogeneous network. The WPAN is oversensitive to the 802.11b signals and the WLAN is insensitive to the 802.15.4 signals. Choosing an optimal CCA threshold requires some prior knowledge of the underlying signals. In the considered integrated medical environments, energy based CCA can effectively avoid possible packet collisions when they are close within the "heterogeneous exclusive CCA range". However, beyond this range, WPAN can still sense 802.11b signals, but WLAN lose its sense to 802.15.4 signals. This leads to WPAN traffic in a position secondary to the WLAN traffic.

A number of multitrack recording systems with multiple-head arrays have been developed for the future high density magnetic recoding systems. In this recording system, the signal detection scheme is needed to estimate the received sequence with media noise, intersymbol interference and inter-track interference. From the recent trend of high density magnetic recording, it is indispensable for any signal processing scheme to mitigate or reduce the effect of media noise such as mixture signal-dependent transition noise and colored Gaussian thermal noise. This paper proposes the statistical inference using the cointegrated process based on vector autoregressive (VAR) models for such a finite mixture of known number of noise and interference components. Our signal detection scheme is applied to maximum a posteriori (MAP) detection with the cointegrated VAR processes. Furthermore, a high rate low-density parity-check (LDPC) code is used for the error correcting code which satisfies the specific run-length limited condition in the proposed multitrack recording system. We show that the proposed multi-track system of error correcting and signal detection scheme is effective to estimate degraded signal sequences and improve the error rate performances with respect to the conventional multitrack system which has the LDPC coding scheme and MAP detector employing the BCJR algorithm.

The distance measurements are biased for various reasons in location systems, e.g. non-line-of-sight path, propagation speed, and sensor calibration error. The impact of measurement biases is investigated in the time of arrival (TOA) systems and time difference of arrival (TDOA) systems. The TDOA estimator is robust to biases when measurements bias their true values toward the same direction, either positive or negative. We thus present group biased-TOA difference (GBD) method to combat the mix of biased and unbiased measurements in location systems. The distance measurements are divided into biased group and unbiased group and time difference operation is conducted in the biased group. We verify the effectiveness of GBD through simulation and experiment by using an ultrasound location system.

Multiuser trellis shaping for space-time trellis codes (STTC) is proposed to realize dirty paper coding (DPC) in downlink multiuser channel, which is sometimes referred to as vector Gaussian broadcast channel. Our proposal considers not only the current transmit signal, but also the entire sequence of the signal for multiple users to achieve the higher capacity. In our proposal, the STTC is transmitted to each user and preceding is used to pre-subtract the interference among the users. An increase in transmit power due to the preceding is reduced by trellis shaping that adds trellis codewords to the information sequence for each user. The shaping code and the STTC are separated in order to systematically design both codes in our system. Simulation results indicate that the shaping gain of more than 3 dB is achieved by applying the different shaping codes for each user, and that frame error rate of the proposed scheme shows better performance than that of the conventional Tomlinson-Harashima precoding.

The 17 papers in this special issue focus on the theory and applications of cognitive radio.

In order to alleviate development cost, many application-oriented wireless networks make use of the off-the- shelf wireless standards such as the Bluetooth, IEEE802.15.4 (Zigbee), and IEEE802.11, which are originally developed for personal area networks (PAN) and local area networks (LAN). Examples of such applications are medical monitoring and control. These applications do not require data rates as high as these standards, but instead they require higher reliability with lower latency. As a means to meet such requirements based on these standards, we propose an efficient error control technique named embedded forward error control technique (EFECT). This technique enables an additional forward error correction to the existing standards without any additional costs. Some design guidelines based on Reed-Solomon (RS) codes are proposed and, as a specific example, achievable gains by applying the EFECT are studied for the Bluetooth standard.

In order to alleviate development cost, many application-oriented wireless networks make use of the off-the- shelf wireless standards such as the Bluetooth, IEEE802.15.4 (Zigbee), and IEEE802.11, which are originally developed for personal area networks (PAN) and local area networks (LAN). Examples of such applications are medical monitoring and control. These applications do not require data rates as high as these standards, but instead they require higher reliability with lower latency. As a means to meet such requirements based on these standards, we propose an efficient error control technique named Embedded Forward Error Control Technique (EFECT). This technique enables an additional forward error correction to the existing standards without any additional costs. Some design guidelines based on Reed-Solomon (RS) codes and sphere packing bound are proposed and, as a specific example, achievable gains by applying the EFECT are studied for the Bluetooth standard.

In this paper, a method for the design of non-linear phase, full-band, UWB pulses that satisfy any given spectrum mask is described. The method uses convex programming in each step of the iterative procedure that updates the phase distribution of the goal function. Thanks to its mathematical structure, method performance is much better than the performance of similar methods found in literature. Techniques of adapting pulses waveforms for the cognitive radio applications are described; pulses waveforms are modified in order to achieve low interference to the victim systems.

In this paper, Tomlinson-Harashima precoding with differential detection for MIMO communications is proposed. It is shown that our proposed nonlinear preequalization with differential detection can achieve space division multiplexing and significant robustness compared with coherent detection even with carrier tracking error.

In this paper, we propose a low complexity bit-interleaved coded DAPSK in combination with cyclic delay diversity, which transmits delayed replicas of an orthogonal frequency division multiplexing (OFDM) signal in cyclic manner and thereby enjoys full diversity without loss of bandwidth efficiency. Here, the frequency diversity induced by delayed replicas can be exploited by a subsequent channel decoder. The performance of the proposed system is evaluated over frequency selective block Rayleigh fading channels. We also show that our proposed system is robust against the blockage effect caused by some obstacles.

In this paper, cognitive radio technology is considered, which has gained much attention around the world. The coexistence between decentralized cognitive radio and primary radio systems is focused. Specifically, by introducing two benchmarks, the network performance without and with cognitive radio technology with the function of detecting radio signals to avoid the primary radio system is studied. From these results, it is shown that cognitive radio can avoid interference. However, according to the condition, cognitive radio cannot get the opportunity of communication. Therefore, an additional function for the sake of avoiding an unavailable arbitrary spectrum band is proposed. Moreover, we show that cognitive radio technology cannot avoid the interference to primary systems whenever hidden primary terminals exist in the network.

In ultra-wideband (UWB) ad-hoc networks, the performance degrades due to the severe near-far problem. In this paper, we aim to reduce the effect of large near-far ratio interfering users in UWB ad-hoc networks. We proposed a low-complexity decision-feedback interference suppression scheme where the decoder output is used to estimate the reliability of the channel. Then, the received samples are combined according to the estimated reliability level. The proposed technique can be used without knowledge of spreading sequence, received timing and power of the other users. It is shown that by using the proposed scheme, the error rate performance improves drastically compared to the conventional MF receiver when the near-far ratio is relatively large. Furthermore, we examine the effect of coding and spreading parameters on the performance of the proposed technique. As a result, the number of required retransmission is reduced, and thus, high power efficient transmission can be achieved.

In practical magnetic recording channel, burst erasures occur in addition to random error. It is well known that burst erasures are caused by thermal asperity (TA) and media defect (MD). In this paper, the detection scheme of the position of burst erasures is proposed. Proposed scheme utilizes the power monitoring of the read signal after equalization and calculates the erasure position and the erasure length. We show that the sequence estimation with Viterbi algorithm using this burst erasure position and burst erasure depth as channel state information (CSI) outperforms the conventional scheme in perpendicular magnetic recording channels. Furthermore, we studied joint design schemes with error correcting code (ECC).

Centralized maximum likelihood (ML) data aided channel estimation for wavelet packets based ultra wideband (WP-UWB) transmissions is investigated. Training pilot symbols are employed for joint ML channel estimation based on a least square algorithm derived from the optimum ML approach. An optimum training sequence criterion is derived. Based on this, nearly optimum perfect root of unity sequences (PRUS) are tested and compared to Gold sequences and random sequences. In this estimation strategy, a generalized inverse of the training pilot symbols matrix can be pre-computed and stored in memory. Furthermore, PRUS allows to save the inverse matrix operation and so reducing the complexity of the joint ML estimator significantly. This technique is especially attractive for low data rate transmissions as in sensor networks because of its low complex implementation. Performance analysis results in terms of the MSE and BER for a single user matched filter are provided. Trade-offs between performance and complexity are described as well. The investigated channel estimation algorithms for UWB channels offer flexibility, low complexity and robustness, making channel estimation fairly simple and effective.

In this paper, a new calibration matrix is proposed which helps to remove the effect of mutual coupling for transmitting and receiving uniform linear arrays (ULA) consisting of dipole antennas. In general, a calibration matrix has close relations with the impedance matrix defined by an equivalent circuit of antenna array. In our method, the circuit equation is re-defined whereby the terminal current is separated into two parts according to the different current distributions flowing over the surface of antennas, i.e., radiating and re-radiating current for transmitting mode, receiving and re-radiating current for receiving mode. In order to calculate the calibration matrix, the authors solve a coupling equation which is nonlinear simultaneous equations obtained by measuring the current (or voltage) of antenna terminals in the transmitting mode. This paper shows that the proposed technique allows more precise calibration compared to conventional calibration techniques.

This paper presents a performance evaluation in terms of bit error rate (BER) of a 26 GHz-band ultra-wideband (UWB) communication system through measurement-based simulation. We measured real channel responses in an office to obtain responses for use in simulations. The simulation results demonstrate that the 26-GHz-band UWB system can achieve high-speed data transmission of 500 Mbps or more, in and indoor office by using a directional antenna.

Distance between a pair of UWB sensor nodes without common time reference can be obtained by measuring round trip time. Because of difficulties in synchronization and channel estimate, the response delay of impulse UWB node is the order of milliseconds. Comparing with the nanosecond propagation delay, relative crystal offset between UWB nodes introduces big error in two way ranging. This paper estimates relative crystal offset through measuring the ranging frame duration in the counting window after synchronization. Simulation shows the relative crystal offset can be reduced to less than plusmn2 ppm

This paper presents an analysis of iterative demapping and decoding for coded M-ary bi-orthogonal keying direct sequence UWB (MBOK DS-UWB) systems via an extrinsic information transfer chart (EXIT chart). In MBOK DS-UWB systems, which have been considered a type of PHYs suitable for high-speed wireless personal area networks (WPANs) in IEEE802.15.3a, one of useful error correction techniques is iterative demapping and decoding between soft-input/soft-output (SISO) MBOK demapper and SISO channel decoder. The EXIT chart has been invented by ten Brink (1999) to allow the prediction of turbo cliff position and bit error rate after arbitrary number of iterations. Through analyses, the bit error rate performance of the iterative demapping and decoding highly depends on the UWB channel conditions in multipath fading UWB channels. We show that the use of RAKE reception is effective approach in multipath fading UWB channels for the iterative demapping and decoding via the EXIT chart.

We analyze the achievable performance of bit-interleaved coded differential amplitude and phase-shift keying (DAPSK) systems over frequency nonselective Rayleigh-fading channels with suboptimal differential detection assuming an ideal bit interleaving. The suboptimal differential detection in this work refers to the bit metric calculation based only on the difference between two consecutive symbols, in contrast to more complex maximum-likelihood (ML)-based differential detection, which makes use of all the observed consecutive symbols for its metric calculation in channel decoding. As benchmarks of coded system performance, we analyze the average mutual information (AMI) and cutoff rate of this system. Exact probability density functions of the suboptimal differential detector outputs are derived for this purpose. Comparative studies suggest that the performance loss of the suboptimal approach is in fact noticeable. Therefore, we also develop a low-complexity receiver structure in the framework of suboptimal differential detection that can approach the performance of ML-based system by suitably incorporating the amplitude statistics of received symbols. The theoretical framework developed in this paper is also confirmed by simulations using convolutional and turbo codes.

This paper describes low-complexity rake reception and Viterbi equalization techniques for M-ary bi-orthogonal keying direct sequence UWB (MBOK DS-UWB) systems, which have been considered a type of PHY suitable for high-speed WPANs in IEEE802.15.3a. In MBOK DS-UWB systems, rake reception and equalization are essential to compensate interpulse interference generated by multipath fading. For rake reception, we derive a novel technique to reduce its implementation complexity by setting a limit on the number of delay devices. For Viterbi equalization, we provide a reduced-state sequence estimation algorithm that reduces the computation complexity for MBOK DS-UWB systems. By employing the proposed rake reception and Viterbi equalization techniques, the complexity can be reduced to less than half of ordinary rake and equalization techniques. Simulation results show that our rake reception and Viterbi equalization techniques enable almost the same performance as existing techniques despite the lower complexity.

We analyze the achievable performance of the coded differential amplitude and phase shift keying (DAPSK) over a frequency non-selective Rayleigh fading channel with ideal bit interleaving. The bit metrics based on the exact probability density of detector output and the average mutual information of the system with conventional differential detection are derived and compared with that of multiple-symbol differential detection (MSDD). It is shown that by suitably incorporating the amplitude statistics of transmitted signals into bit metrics, the performance of conventional DAPSK can be significantly improved without increasing complexity. Theoretical framework developed above is also justified by the comparative simulation results using convolutional and turbo codes.

With respect to soft-spectrum adaptation (SSA) UWB wireless system with multiband pulse waveform shaping and adaptation, we investigate a design scheme for pulse waveform optimization based on prolate spheroidal wave functions (PSWF). The PSWF-based pulse shaping is then applied to M-ary signaling for high data rate and multiple accessing environment expected by multiuser services. Moreover, double water-filling (DWF) method is combined with the PSWF-based pulse shaping for achieving high system capacity performance, efficient local power control and interference avoidance.

The design of a class of Hermite pulses for pulse shape modulated (PSM) ultra-wideband (UWB) communications is presented. The proposed pulses offer robustness against jitter or small imperfections in synchronization between received waveforms and their matched templates. Close form expressions of the auto- and cross-correlation functions of the proposed and conventional Hermite pulses are given, which are used to model the jitter channel as a simple distortive matrix. The set of jitter-robust orthogonal pulses is then obtained by simultaneously diagonalizing a subset of selected samples of such channel matrix realizations for different jitter values. Examples of waveforms derived with the method and simulation results showing the effectiveness of the proposed pulses in combatting jitter in PSM-UWB systems are given.

A soft-spectrum impulse radio scheme with multi-band pulse waveform adaptation and shaping is proposed, which can be applied to the co-existence, the interference avoidance, the matching with regulatory spectral mask (e.g. FCC spectrum mask), and high data rate. In the paper, the soft-spectrum adaptation proposal has been discussed in detail. Different kinds of soft-spectrum pulse waveforms with various shapes, envelopes, as well as their corresponding spectral features are investigated. Achievable BER performance simulations for these multi-band pulse waveforms are also carried out under AWGN environment.

This paper investigates multi-user detection in multiple-access communication systems based on ultrawideband (UWB) technology. As user numbers increase and the bandwidth to pulse repetition frequency (PRF) decreases, multiple-access interference (MAI) is expected to adversely affect system capacity and performance. The paper presents a framework for the design of multi-user detectors and proposes the optimum multi-user detector for UWB. Numerical examples illustrate the performance of the optimum detector versus that of the conventional single-user UWB detector.

A simple method to enhance the performance of simplified decoding of block space-time codes (STC) is proposed. The method is capable of removing the error floor observed when conventionally decoded STC is applied under fast fading conditions, provided that the channel is known, or accurately enough estimated, across the block. This requirement can be reached by interpolating channel estimates from pre- and post-posted pilot symbols, which allows several blocks to be framed together, enhancing spectral efficiency.

In order to obtain an appropriate, high level of security, a number of architectural elements for secure downloading of software to a software defined radio (SDR) terminal have been pointed out. They include four different cryptographic techniques and employment of tamper resistant hardware. The cryptographic techniques employed are: (a) a secret key encryption technique; (b) a public key encryption technique; (c) a technique for cryptographic hashing and (d) a technique for digital signature. Particularly, a protocol for exchanging cryptographic components in an automatic manner without any assistance from the user, is proposed. Implementation characteristics of certain cryptographic components are also discussed.

We focus attention on the development of security techniques using software defined radio (SDR) technologies. We propose a new secure download system which uses the characteristics of the field programmable gate arrays (FPGAs) composing the SDR. The proposed system has the novelty that realization of high security encipherment is possible. This is achieved using the characteristic of FPGAs which allows systems to be arranged in a variety of different layouts, as well as by using the configuration information as the key. This unifies the renewal of the key and the encipherment. In addition the proposed system has the merit that it has high security against illegal acquisition such as a wiretapping, and can also be used in conjunction with any other current cipher algorithm. As an evaluation of the security, we show that the proposed system has high immunity to illegal acquisition of software using replay attack, by verification of the protocol as well as by numerical computation. The proposed system can therefore realize high security software downloads based on SDR.

Some arguments more are presented to illustrate a need for careful security evaluation of the encryption algorithms for possible use in the wireless networks. Particularly, the security evaluation of a previously proposed fast encryption for multimedia FEA-M is presented. It is shown that the effective secret key size is much smaller than its nominal one, which is a very undesirable and potentially dangerous characteristic.

An ideal broadband beamformer requires an increased number of taps for each filter, which in turn increases the complexity of the design. It is shown that for angles near the broadside of the antenna the beamforming is more accurate compared to the angles near the endfire, and it is advantageous to use recursive filters combined with a computed number of zeros for angles near the endfire. The proposed method is used for estimating the arrival angle of the incoming signals and displays uniform accuracy for all angles.

Recent research activities in the area of mobile radio communications have moved to third generation (3G) cellular systems to achieve higher quality with variable transmission rate of multimedia information. In this paper, an overview is presented of various interference cancellation and iterative detection techniques that are believed to be suitable for 3G wireless communications systems. Key concepts are space-time processing and space-division multiple access (or SDMA) techniques. SDMA techniques are possible with software antennas. Furthermore, to reduce receiver implementation complexity, iterative detection techniques are considered. A particularly attractive method uses tentative hard decisions, made on the received positions with the highest reliability, according to some criterion, and can potentially yield an important reduction in the computational requirements of an iterative receiver, with minimum penalty in error performance. A study of the tradeoffs between complexity and performance loss of iterative multiuser detection techniques is a good research topic.

Proposes a method for designing spread sequences for a spread spectrum (SS) communication and ranging system. The proposed sequence is composed by concatenated equivalently odd and even (EOE) inner-sequences and an M outer sequence. We have previously proposed EOE sequences that have equivalently good properties of both even and odd correlation, what are important features for acquisition and demodulation in SS communications. Usually, simple concatenation of pseudonoise-sequences results in sequences with bad autocorrelation properties. Unlike the latter, concatenation of EOE inner sequences result in sequences with good correlation properties, exhibiting low sidelobe peaks, what is useful for achieving stable acquisition. The proposed sequences have long period. Therefore, the single concatenated EOE sequence is suitable for a spread spectrum system with both communication and ranging functions.

Smart antenna technology has proved to be a valuable add-in feature for communication systems. However, its application indoors, in particular to the unlicensed 2.4-GHz industrial, scientific and medical (ISM) band has not been accomplished yet, mainly due to the problem of near-field distortion that upsurges from the indoor channel characteristics at the mentioned band. We evaluate the compensation scheme to eliminate such near field distortion presented by Abren and Kohno (see Proc. of the ICT2000, vol.2, p.900-906, 2000) under the IEEE 802.11 standard's specifications.

This paper investigates improvement of the radiation pattern design of the transmitting array antenna beamforming and transmission power control (TPC) for the forward link of DS-CDMA/FDD system. Optimum transmission beamforming and power can be derived with the information of the propagation channel of the forward link in order to improve user capacity. It is assumed that a channel is static, all mobile stations (MSs) report measured channel characteristics to a base station (BS) and that controls received SIRs of all MSs by using this information. Then, the optimum control of transmitting beam pattern based on linear goal programming is proposed to improve user capacity.

This paper investigates the optimal access point placement in a simultaneous broadcast system using orthogonal frequency division multiplexing (OFDM) for high data rate indoor wireless LAN. We aim to determine the best combination of multiple AP placements that minimizes the average bit error rate (BER) of terminals when input information including an indoor configuration, a number of APs, and total transmission power is given a priori. Since this AP placement problem is categorized as a hard combinatorial problem with many variables and constraints, we applied a nonlinear optimization scheme called very fast simulated annealing to search for an approximate optimal solution. The simulation results demonstrate that the algorithm has been successfully applied to the AP placement problem and its effectiveness was also confirmed in comparison with a local search algorithm.

This paper proposes and investigates optimum band allocation scheme and modulation assignment for band-segmented transmission OFDM (BST-OFDM) according to different environment characteristics of each segmented band or subband channel. The proposed system can adaptively optimize the allocation of subbands according to a conditional parameter, that is, the CNR under independently fading subband channels. The optimization criterion is the minimum total BER performance under the constraint conditions that are the total bandwidth, the number of subbands and the constant total information bit rate. The subband condition is updated by the feedback information from the receiver. The proposed adaptive band allocation BST-OFDM system can overperform the conventional BST-OFDM system in which subbands are divided with equal bandwidth.

A software defined radio (SDR) system is used to reconfigure all or many specifications such as modulation scheme, demodulation, coding etc. Therefore, supplementary information allow recognition of these specifications by the receiver is required. Since much redundant supplementary information reduces efficiency in transmission, we have aimed to carry out blind adaptive demodulation which, can adaptively demodulate without supplementary information. This paper proposes and investigates both a blind adaptive algorithm for estimating channel and that for estimating a modulation scheme. Computer simulation evaluates the proposed blind estimation algorithm.

We propose and investigate a new type of satellite multiple access protocol that combines the characteristics of the spread slotted (SS)-ALOHA protocol, code division multiple access (CDMA), and the hybrid automatic repeat request (ARQ) error controlling and retransmission scheme, in order to increase the throughput by reducing the number of retransmissions and to keep the bit error rate (BER) of the satellite link low when the channel experiences heavy traffic. The main feature of our proposed system is the utilization of two different fields in the analysis of the satellite multiple access problem. Since the hub now possesses the forward error correction (FEC) capability to correct errors that appear after the CDMA despreading of the packets, the satellite does not need to ask so often for the retransmission of erroneous packets and will ask for retransmission only when the FEC error correcting capability is exceeded. This paper also presents the adaptive optimization of the balance between the CDMA processing gain and FEC coding gain in order to obtain a better throughput for the SS-CDMA/ALOHA with hybrid ARQ protocol for satellite multiple access. The optimization is made with the constraint of keeping the bandwidth of the transmitted packets constant during all times. According to this, the effective throughput of the protocol (information bits over total transmitted bits ratio) is improved by adaptively changing the CDMA and FEC codes used in the transmission. This adaptive optimization is done by observing the channel status or load and increasing or decreasing both coding schemes' gains. Computer simulations show the performance of the proposed multiple access scheme.

This paper presents a technique for designing a broad-band partially adaptive antenna using a new recursive fan filter. Each beamformer is designed using recursive two-pole sections. This method reduces the number of taps of the fan filter considerably. Interferences occurring in the sidelobes as well as the mainlobe of the desired pattern and having the same frequency as the desired signal and overlap in bandwidths are cancelled effectively independent of frequency.

The maximum-likelihood (ML) detector for direct-sequence spread-spectrum signaling over ISI channels is developed for both symbol-length and long spreading sequences. The approach is based on a delay-domain orthogonal decomposition of a joint specular/diffuse dispersive multipath channel. The detector, which extends the Ungerboeck symbol-spaced structure, demonstrates the path diversity inherent in spread spectrum ML detection. The RAKE detector is shown to be the ML detector under a set of ideal conditions, one of which cannot be obtained in practice. As an intermediate result, the DS/SS decision-feedback equalizing detector is shown to be a suboptimum approximation of the ML detector.

A multi-carrier transmission system performs high-speed data transmission for multimedia information in digital audio and video broadcasting and wireless ATM. However, it has significant performance degradation due to offset of carrier frequency and multipath in a channel. This paper proposes and investigates adaptive linear and Viterbi equalizers including frequency-offset compensator for a multi-carrier system such as OFDM. Computer simulation illustrates improvement of performance.

This paper proposes and investigates a dynamic cell size controlling scheme based on macro-diversity transmission for DS/CDMA. According to the time-variance of geographical mobile distribution, the transmission power of several base-stations is adaptively controlled considering the measured signal-to-interference power ratios of the received signals from mobile stations in order to minimize the calculated outage probabilities of the whole cells in the service area. Computer simulation shows the performance improvement.

Both classes of adaptive algorithm based on temporal update, e.g. LMS and spatial spectral estimation, e.g. DFT have advantages and disadvantages relatively. In order to compensate for their problems while maintaining advantages, this paper proposes and investigates an adaptive array antenna using a combined DFT and LMS algorithm. The proposed combined algorithm can improve the convergence speed of the weight coefficients in the temporal updating algorithm and the accuracy of the weight coefficients in the spatial spectral estimation algorithm.

Pieter van Rooyen and Kohno proposed a combination receiver of adaptive arrays and MRC diversity, named a double spatial and temporal filter (DSTF) receiver. Each of the diversity branches consist of an array antenna. Each of the branches are separated spatially and independent. This assumption differs from the plane waves model. This paper discusses a method of combining an array antenna and a diversity antenna in plane waves model.

Unequal error-protection (UEP) codes that are designed using trellis-coded modulation (TCM) are proposed for use with a single data stream consisting of information with two levels of importance. To achieve UEP, the proposed scheme encodes the data according to the importance of the information by switching between two codes which use different signal constellations. Using simple trellis codes, it is shown that the error rate of the important information is lower than the error rate for an equivalent equal error-protection scheme.

There are many requirements for increasing the user capacity in radio wireless communication. Adaptive array antennas are useful for reducing the interference signal. This paper proposes multiuser equalization based on an adaptive array antenna for DS/CDMA. This approach is considered as the joint transmitter and receiver multiuser equalizer in spatial and temporal domains. First, this paper describes the channel model for DS/CDMA in spatial and temporal domains. Then, the proposed system is described. Finally the system is evaluated by computer simulations.

When multimedia information including speech, image, data etc. are transmitted, the difference in information rates, required quality, and traffic performance should be taken into account. A wireless spread spectrum system can achieve a flexible balance of these differences because of inherent asynchronous code-division multiple-access (CDMA) capability. In order to accomplish wireless multimedia communication, three parameters are investigated: the transmission power, packet length, and time slot. We propose and investigate two methods to accomplish wireless multimedia communication by using these parameters: (1) a method based on control of both transmission power and transmission packet length and (2) a method based on control of both transmission power and adaptive time slot. We derive the optimal transmission packet length and transmission power in (1) and derive optimal adaptive time slot and transmission power in (2) by using traffic of measurement and nonlinear programming. By the comparison, the two proposed methods are compared to the minislotted alternating priority (MSAP). Numerical results demonstrate that the proposed methods, when the priority of each medium is graded, show better performance than other systems in terms of average throughput and delay time of all media.

This paper proposes a wireless multimedia code division multiple access (CDMA) system based on transmission power control. When we transmit multimedia information (i.e., speech, image, and data), differences in information rate, traffic performance, and required quality should be taken into account. The wireless CDMA system can achieve a flexible balance if transmission power distribution is controlled by using channel measurement information, i.e., traffic. In this paper, the optimal control of transmission power is derived by linear programming and nonlinear programming. Numerical results using a LAN demonstrate that the proposed method can satisfy the required quality.

This paper proposes a wireless multimedia CDMA system based on transmission power control. When we transmit multimedia information such as speech, image and data, differences in the information rate, traffic performance and required quality should be taken into account. The wireless CDMA system can achieve a flexible balance of these differences if the transmission power distribution is controlled using channel measurement information such as traffic. The optimal control of transmission power is derived by linear programming and nonlinear programming. Numerical results demonstrate that the proposed method can satisfy the required quality.

This paper describes spatial and temporal modeling of a multipath channel which is useful in array antenna environment for mobile radio communications. From this modeling, a no distortion condition that is the Nyquist theorem, is derived for total equalization in both spatial and temporal domains. We use an adaptive tapped-delay-line array antenna as a tool of equalization in spatial and temporal domains. Several criteria for such spatial and temporal equalization are available to update weight and tap coefficients such as ZF (zero forcing), MSE (mean square error) and so on. In this paper, we discuss the optimum weight based on ZF criteria in spatial and temporal domains. Moreover, computer simulations show the performance of an adaptive array antenna based on the ZF criteria in spatial and temporal domains.

Proposes and investigates a method for designing pseudonoise (PN) sequences having both good odd and even correlation properties, which are important for acquisition and demodulation in spread spectrum (SS) communications. Odd correlation properties of PN sequences should be designed as well as their even or periodic correlation properties so that the cochannel interference can be reduced as small as possible. Polyphase PN sequences with such good correlation properties can be derived from biphase PN sequences with a good aperiodic correlation property under a certain condition. Absolute values of odd and even correlation functions of these sequences are equal at each shift. The authors evaluated their peak correlations properties and bit error rate performance. Numerical evaluations show that the derived polyphase sequences have lower peaks of correlations and lower bit error rate than their original sequences. Furthermore, the authors defined the generalized odd correlation function for polyphase SS systems, and derived a way to improve the generalized odd correlation properties.>

The paper proposes and investigates a multiuser detection scheme baseEEon canceling cochannel interference (CCI) to improve spectral efficiency or to increase user capacity in an MFSK (multilevel frequency shift keying)/FH-SSMA (frequency hopping-spread spectrum multiple access) system. In the MFSK/FH-SSMA system, an address code is employed as a hopping sequence to hop the carrier frequency in MFSK. In the proposed scheme, it is assumed that the address codes of all users in MFSK/FH-SSMA are known. Then, candidates of the transmitted vector which are regenerated from the time-frequency matrices decoded by all the users' address codes are added with logical OR operation to produce candidates of the received matrix. The candidates of the received matrix are utilized in order to estimate a pattern of all users' data symbols which has the most number of coincident entries with the received matrix. Its BER (bit error rate) performance is evaluated by theoretical analysis and computer simulation in order to show the improvement of user capacity. Moreover, the authors investigate a hybrid scheme combining a multiuser detection scheme and the decoding scheme of an error-correcting code for the coded MFSK/FH-SSMA system.>

The authors propose and analyze a direct-sequence spread-spectrum multiaccess (DS/SSMA) receiver that employs a cascade of cochannel interference (CCl) cancellers for communication over multipath fading channels. The receiver first coherently demodulates and despreads the received signal to produce correlator outputs and initial data estimates. Based on these estimates, the cancellation scheme essentially creates replicas of the contributions of the CCl embedded in the correlator outputs and removes them for a second improved hard data decision. By repeating this operation over and over, a cascade of CCl cancellers is derived. Through theoretical analysis and simulation, the authors investigate the canceller's bit error rate (BER) performance in both the absence and presence of errors in the amplitude and phase estimates of each user's received signal. Numerical results show the considerably large improvement in performance that can be attained by the cancellation scheme, even under partially degraded estimates.>

The paper first proposes a method to correctly update the weights of an adaptive array antenna using the inherent processing gain of a spread spectrum (SS) receiver, even for received signals with very low desired-to-undesired signal power ratio (DUR). Since the method reduces effect of the delay in the controlling loop, stable convergence can be guaranteed in a fading channel. Secondly the method is applied to a tapped delay line (TDL) adaptive array antenna in order to improve performance of rejecting co-channel interference in CDMA. The array is investigated corresponding to the DUR and bandwidth of SS signals.>

This paper proposes image compression using an advanced neural network in which a variable input-output function of a neural unit can be learnt as well as a weight coefficient of a neural connection corresponding to information source and application. Since the neural network has the improved learning capability for local nonlinearity of information source, its application to compression of nonlinear information such as image is investigated. A learning algorithm and adaptive controlling schemes of input-output functions are derived. Simulation results show that the neural network can achieve higher SNR and shorter learning time than a conventional network having only variable weights.

In the realization of code-division multiple access based on a spread-spectrum communication system, i.e. spread-spectrum multiple access (SSMA), reduction of cochannel interference is an important problem. An adaptive array antenna system is proposed that includes a cancellor of cochannel interference, which can improve performance by a combination of temporal and spatial filtering. While the adaptive array suppresses interference sources with arrival angles different from those of the desired user, the adaptive digital filter-canceller rejects those whose arrival angles are the same as those of the desired user. The proposed system can achieve stable acquisition and low error rate of demodulated data even in a heavy-interference channel where a conventional array antenna system cannot achieve satisfactory acquisition.>

The authors propose and investigate an adaptive canceller of intersymbol and cochannel interference due to channel distortion and cross-correlation among pseudonoise sequences assigned to individual users of a DS-SSMA (direct-sequence spread-spectrum multiple-access) system. In order to implement a local area network (LAN) by using a power line installed in a building wall as a transmission channel, the authors have investigated utilization of DS-SSMA which has advantages such as robustness against narrow-band interference and noise and realization of asynchronous code division multiple access. In a power line, however, restriction of transmission bandwidth for communications makes it difficult to suppress cochannel interference and the channel is also time-varying due to fluctuation of loads. Since the proposed canceller adaptively eliminates cochannel interference as well as intersymbol interference, it can facilitate synchronization and increase the number of the simultaneously accessing users on a power line with restricted processing gain. The error probability in the output of the canceller is theoretically calculated for the steady-state case by using a Markov model. Computer simulations illustrate stable convergence properties of the canceller.>

The authors propose an automatic equalizer, applicable to trellis-coded modulation, that includes a Viterbi decoder and a carrier-phase controller and achieves reliable high-speed voiceband data transmission at 14.4 kb/s and above. The equalizer can perform the operations of equalization, demodulation, and decoding. Since the system reduces misadjustment of tap values and estimated carrier-phase shift due to decision errors, stable convergence can be achieved. Also presented is a method to utilize the reliability of decoded data in order to minimize misadjustment of the adaptive digital filters and the phase controller owing to undetected errors and miscorrected data in decoding.>

Effective utilization of an error-correcting code (ECC) is proposed in order to make a low-hit-rate adaptive differential PCM (ADPCM) system robust against bit errors in noisy channels, such as mobile radio. In 16 kb/s ADPCM systems, the inverse-quantizers with a small number (four) of levels lead to large offsets in stepsizes due to channel errors, and high-order all-pole predictors are very sensitive to them. For the purpose of solving these problems, we present a robust ADPCM system using an ECC, in which the reliability of words decoded by the ECC decoder is utilized to control the updating of the inverse-quantizer and also to stabilize the predictor in the receiver. Moreover, on condition that a sampling rate of the system is reduced from 8 to 6.4 kHz, the proposed system is compared with a forward adaptation system [8]. A computer simulation shows a maximum of 1.8 dB improvement over an usual system using the same ECC in segmental SNR forBER\geq10^{-2}.

A new proposed automatic equalizer including a decoder of error-correcting code (AEDEC) is obtained by the joint adaptive operation of an automatic equalizer and a decoder. This AEDEC can reduce misadjustment of tap values and error propagation owing to decision errors, and stabilize convergence even without a known training signal in noisy channels.