Traffic volume is gradually increasing due to the development of technology and the concentration of people in cities. As the results, traffic congestion and traffic accidents are becoming social problems. Detecting and tracking a vehicle based on computer vision is a great helpful in providing important information such as identifying road traffic conditions and crime situations. However, vehicle detection and tracking using a camera is affected by environmental factors in which the camera is installed. In this paper, we thus propose a deep learning based on vehicle classification and tracking scheme to classify and track vehicles in a complex and diverse environment. Using YOLO model as deep learning model, it is possible to quickly and accurately perform robust vehicle tracking in various environments, compared to the traditional method.

Conventional channel estimation schemes may require for the use of orthogonal pilot signals for each antenna in frequency-division duplex (FDD) wireless systems. It is a very challenging issue to get channel information with an affordable signaling overhead in massive multi-input multi-output (m-MIMO) FDD transmission environments. The signaling overhead for the channel estimation can be reduced by exploiting the downlink channel correlation matrix (DCCM) of m-MIMO channel. With the use of DCCM, the channel information can be estimated using a reduced number of pilot signals. However, the accuracy of DCCM may seriously affect the estimation performance. In this paper, we consider the estimation of DCCM in m-MIMO transmission environments. Since the distance between a base station and a user is much larger than that between antennas, a set of antenna pairs of equal distance may experience similar spatial correlation due to the far-field effect. We consider the estimation of DCCM by averaging the correlation of these antenna pairs without reception of a large number of pilot signals, significantly reducing the pilot signaling overhead. We also consider the improvement of estimated DCCM by dropping out inaccurate correlation terms. Finally, we verify the proposed scheme by computer simulation.

Wireless sensor networks (WSNs) operating in 2.4 GHz ISM band may seriously experience interference from coexisting radio systems such as IEEE 802.11x wireless local area networks. In this paper, we consider improvement of transmission performance of WSNs by means of packet size adaptation in the presence of co-channel interference. We first analyze the probability of transmission failure and data throughput, and then determine the packet size to maximize the data throughput in the presence of co-channel interference. Exploiting the analytic results, we design a novel transmission scheme that can adjust the packet size in response to the change of transmission performance, maximizing the data throughput. Finally, the performance of the proposed scheme is verified by computer simulation, showing significant performance improvement over conventional schemes.

Data gathering is one of the most popular applications in multi-hop wireless sensor networks. Since resources are limited, it is important to efficiently allocate the resource while providing desired performance. In this paper, we consider resource allocation in the uplink of multi-hop wireless networks with the use of data buffers of finite size in the presence of transmission error. We first analyze the probability of buffer occupation of each router and then derive the outage probability associated with buffer overflow and transmission latency. Exploiting the analytic results, we design a resource allocation algorithm that minimally utilizes the resource in multi-hop wireless sensor networks, while guaranteeing desired performance. Finally, the proposed scheme is verified by computer simulation.

Wireless sensor networks operating in 2.4 GHz ISM band are seriously affected by interference from coexisting radio systems such as IEEE 802.11× wireless local area networks. In this paper, we investigate the transmission performance of wireless sensor networks in the presence of co-channel interference. We first analyze the probability of transmission failure and data throughput associated with transmission schemes in interference environments. The transmission schemes are modeled using a Markov chain taking into account the detection probability of channel sensing detector and the interference channel characteristics. Then, we determine the packet size to maximize the data throughput in the presence of co-channel interference. It is shown that the data throughput and energy consumption are affected by the packet size, data transmission rate, data transmission scheme, detection probability of channel sensing detector, and interference channel characteristics.

This paper presents a closed form of an optimal cooperative amplify-and-forward (AF) relay amplifying matrix for a distributed relay network of M-source-M-destination pairs and N relays, called a cooperative distributed AF relay network. The objective of this paper is to derive closed forms of minimum mean square error (MMSE)-based and zero-forcing (ZF)-based optimal AF relay amplifying matrices for the cooperative distributed AF relay network under the transmitter power constraint (TPC) at the relays, the receiver power constraint (RPC) at the destinations, and the no-power constraint (NPC) condition. Additionally, by substituting the derived optimum AF relay amplifying matrices into the original cost functions (CFs), the behavior of the optimum CFs and the total optimum signal component power (SCP) at the destinations are compared to each other for different cases. Finally, using the MMSE criterion, a novel relay selection scheme is proposed for the cooperative distributed AF relay network.

IEEE 802.15.4 networks operating in the 2.4 GHz ISM band are seriously affected by co-channel interference from coexisting radio systems such as IEEE 802.11x wireless local area networks. In this paper, we consider the beacon transmission in the presence of co-channel interference in the IEEE 802.15.4 beacon-enabled mode. For reliable transmission of the beacon frame, we propose repeated transmission of the beacon frame depending upon the channel characteristics. The network coordinator and its child nodes estimate the channel characteristics when they experience transmission failure of the beacon frame. The coordinator determines the number of repeated beacon transmissions and the timing gap between the beacon transmissions based on the estimated channel characteristics. Analytic and simulation results show that the proposed scheme can reliably transmit the beacon frame even in the presence of heavy co-channel interference, significantly reducing the network synchronization loss, power consumption as well as transmission delay.

IEEE 802.15.4 networks employ a medium access control scheme based on carrier sense multiple access with collision avoidance (CSMA/CA). However, CSMA/CA may seriously experience contention collision, suffering from resource wastage in time-varying operation environments. In this paper, we consider the alleviation of contention collision in IEEE 802.15.4 networks by partitioning the transmission period into a number of sub-transmission periods. To this end, the network coordinator and its child devices measure the transmission performance in a distributed manner. When the measured performance is not satisfactory, the coordinator adjusts the number of subtransmission periods considering the operation environment. Each child device uses one of the sub-transmission periods for its signal transmission, effectively reducing the probability of contention collision. Simulation results show that the proposed scheme remarkably reduces packet collision and thus energy consumption in time-varying network environments.

In this paper, we consider opportunistic feedback of channel state information (CSI) for multi-user multi-antenna transmission. The base station utilizes channel quality information (CQI) as the CSI for closed-loop multi-antenna transmission, which is often achieved from mobile stations in a quantized format. However, only the use of quantized CQI may noticeably deteriorate the transmission performance. We first analyze the effect of CSI quantization error on the multi-user beamforming performance. Then, we propose a novel scheme for opportunistic CSI feedback and user scheduling in multi-user multi-antenna transmission environments. Simulation results show that the proposed scheme can improve the spectral efficiency using a small amount of CSI feedback signaling overhead.

IEEE 802.15.4 employs a medium access control protocol based on carrier sense multiple access with collision avoidance (CSMA/CA). Channel sensing may have critical impact on the system throughput and energy consumption as well. In this paper, we investigate the effect of channel sensing on the CSMA/CA performance in IEEE 802.15.4 star-topology configured networks. We show that the hidden node ratio (i.e., the probability that any two child nodes cannot hear each other in a star-topology configured network) is highly associated with the target false-alarm probability of the channel sensing detector. We show that the CSMA/CA performance of IEEE 802.15.4 network can significantly be improved by adjusting the hidden node ratio.

In this paper, we consider opportunistic user scheduling in heterogeneous channel environments where users experience different channel characteristics in average. For the user scheduling with fairness, we consider the use of instantaneous channel quality information (CQI) normalized in terms of its average and variance. The proposed scheme allows users to report their normalized CQI for service request only when it is higher than a threshold, exploiting multi-user diversity gain while reducing the signaling overhead for the reporting of CQI and/or the processing complexity for the user scheduling. Simulation results show that the proposed scheduling scheme can provide scheduling fairness similar to random user scheduling while achieving multi-user diversity gain.1

SUMMARY In most floating‐point operations related with 3D graphic applications for mobile devices, properly approximated data calculations with reduced complexity and low power are preferable to exactly rounded floating‐point operations with unnecessary preciseness of cost. Among all the sophisticated floating‐point arithmetic operations, division is the most complicated and time consuming. We adopted the concept of the logarithmic number system and proposed a novel approach of designing a hardware logarithm converter to utilize the advantage of the transformation of the division into a simple subtraction. The proposed piecewise interpolation method with differential coefficients for logarithmic conversion greatly reduces the error range compared with the previous studies. The comparison between our divider and the conventional precision divider shows that the throughput has been considerably improved with slightly increased gate counts, where the difference of the results is sufficiently tolerable for mobile 3D graphic applications. Copyright © 2010 John Wiley & Sons, Ltd.

In the uplink of orthogonal frequency division multiple access (OFDMA) systems, rate adaptation may not be exploitable mainly because of severe inter-carrier interference (ICI). In this study, the authors propose a novel hybrid link adaptation that simultaneously uses power adaptation for ICI adjustment and rate adaptation for capacity improvement in the uplink of OFDMA systems. The proposed hybrid link adaptation determines a maximum allowable transmission power according to the channel gain and velocity of each user, enabling all users to have a guaranteed loss of carrier to interference ratio (CIR). Moreover, the proposed hybrid link adaptation adjusts the transmission rate according to CIR of each user, while keeping the maximum allowable transmission power unchanged. The performance of the proposed hybrid link adaptation is analysed in OFDMA cellular uplink systems. Finally, the analytic results are verified by computer simulation.

In this letter, we consider the mitigation of co-channel interference in Bluetooth piconets. Prior to sending packets, the proposed scheme checks whether the next channel for the frequency hopping (FH) is in use by other signals or not. Then, it periodically detects busy channels subject to WLAN interference based on the packet error rate and interference signal detection rate in a group-wise manner and changes the set of hopping frequency. For further provision of channels for the FH, it maximized the number of channels for the FH by detecting additional channels which belong to groups classifies as being interrupted by WLAN, but not being used. The analytic design and simulation results show that the proposed scheme is quite robust to the presence of multiple WLAN and other Bluetooth signals, compared to the conventional mitigation schemes.

In this paper, we consider interference mitigation in IEEE 802.15.4 beacon-enabled cluster-tree networks. The proposed scheme first detects the presence of interference by means of packet-error detection and/or channel sensing in a clusterwise manner. In the presence of interference, the coordinator (or cluster head) fast notifies the presence of interference to its end devices by repeatedly transmitting the channel-handoff command. Then, it avoids the interference by the use of temporary channel hopping through predetermined hopping channels. Finally, it selects the best one among the hopping channels, which will be used as the final handoff channel. Simulation results show that the proposed scheme provides marked performance improvement over conventional schemes even in the presence of heavy interference.

Deployment of multiple femtocells in a confined area may cause serious interference problem to each other. To mitigate the inter-femtocell interference, we consider combined use of coordinated user scheduling with transmit beamforming in femtocell networks. Femto base stations collaboratively schedule users to minimize the interference in an average sense and employ a beamforming technique to maximize the network spectral efficiency. We assume that only the transmit spatial correlation coefficient is shared by femto base stations, making it quite feasible for implementation. The effectiveness of the proposed scheme is verifed by computer simulation in the presence of channel correlation.

In this paper, we consider channel estimation with the use of dedicated pilot signal in multiple-input multiple-output orthogonal frequency division multiplexing wireless systems. The dedicated pilot signal is transmitted through a channel virtually transformed by means of beam weighting. We consider the use of a minimum mean squared error (MMSE)-type estimator that fully exploits the statistics of beam-weighted channel. Without the statistics of the beam-weighted channel, conventional channel estimators cannot noticeably enhance the estimation performance even with the use of dedicated pilot signal. Obtaining the statistics of the beam-weighted channel from that of the common pilot channel, we design an affine MMSE channel estimator in consideration of biased beam weighting for the transmission of dedicated pilot signal. Simulation results show that the proposed scheme noticeably outperforms conventional estimation schemes in poor operation condition.

In this paper, we consider performance improvement of IEEE 802.15.4 systems in the presence of co-channel interference from other systems such as wireless local area networks (WLAN). The proposed scheme first detects the presence of interference by means of spectrum sensing or transmission performance testing. When the presence of interference signal is detected, the coordinator changes the carrier frequency for the signal transmission by means of frequency hopping through multiple channels which are predetermined according to the characteristics of interference signal. After signal transmission through these multiple channels for a while, the coordinator selects the best one among the multiple channels and then returns to the original transmission mode through the newly selected channel, efficiently alleviating the interference problem. Finally, the performance of the proposed scheme is verified by computer simulation in the presence of multiple WLANs.

This paper proposes a new method to automatically index searches for relevant images using geo-coded information. Photographic images are labeled with their GPS (Global Positioning System) coordinates and date/time at the moment of capture and this date is then utilized to create two layer spatial and temporal indexes for image searches. A simulation performed to estimate the effectiveness of the proposed method found that the combination of those indexes and visual features improving average recall by up to 59% and average precision by up to 49% compared to the use of visual content alone.

In this paper, we consider channel sounding for multi-sector cooperative beamforming in othogonal frequency division multiplexing-based wireless cellular systems. To reduce sounding interference and signaling overhead, we allocate sounding physical resource units (PRUs) by exploiting the correlation characteristics in the frequency domain. The proposed scheme transmits sounding signal through PRUs which are not highly correlated to each other, significantly reducing the sounding interference and signaling overhead. Then, the whole channel information can be extracted by means of channel estimation based on the frequency correlation (e.g., minimum-mean-square-error estimation). Simulation results show that the proposed scheme provides remarkable performance improvement over conventional schemes in the presence of channel correlation in the frequency domain.

In this paper, we consider the use of fractional frequency reuse (FFR) to mitigate inter-femtocell interference in multi-femtocell environments. The use of universal frequency reuse can be said optimum in terms of the ergodic system spectral efficiency. However, it may cause inter-femtocell interference near the cell edge, making it difficult to serve the whole cell coverage. To alleviate this problem, we adjust the frequency reuse factor with the aid of femtocell location information. The proposed scheme can provide reasonably high ergodic system spectral efficiency, while assuring a desired performance near the cell boundary. Simulation results show that the proposed scheme is quite effective in indoor environments such as residential or office buildings.

This paper considers the channel estimation scheme using dedicated pilot signal in orthogonal frequency division multiplexing systems. To this end, we design a novel beam-weighted channel estimation scheme, called affine minimum mean squared error (AMMSE) estimator, for transmit beamforming. Although the use of dedicated pilot can provide merits such as the reduction of pilot signaling overhead and boosting of pilot power, it is not often employed in practical estimation schemes. This is mainly due to the difficulty in estimating the statistics of beamweighted channel from dedicated pilot signal. To alleviate this problem, we analytically estimate the statistics of beam-weighted channel from those of common pilot channel. Then, we consider an AMMSE estimator that can improve the estimation accuracy by utilizing the statistics of beam-weighted channel. Simulation results show that proposed estimation scheme remarkably outperforms conventional estimation schemes particularly near the cell boundary.

In this paper, we consider the sensing of primary user signal by exploiting the receive antenna correlation properties in cognitive radio systems. Since the signal and noise have different statistical correlation characteristics, it can be possible to design a detection scheme that does not need the apriori information on the noise, making it robust to noise uncertainty. Simulation results show that the proposed scheme is effective in the presence of antenna correlation.

In this paper, we propose a new cooperative spectrum sensing scheme to minimize the false alarm probability while satisfying the detection probability at a desired level. To improve the spectrum sensing performance, it is desirable for the cognitive base station to combine binary local decisions of secondary users by considering the local sensing reliability. In the proposed scheme, the local decisions are combined with weighting factors that reflect the local sensing reliability of each secondary user to optimize the probability distribution function of the test statistic. The detection and false alarm probabilities are also analytically determined in closed form. Finally, the performance of the proposed scheme is verified by computer simulation.

This letter investigates the effect of imperfect transmit correlation on the performance of statistical beamforming in terms of average signal-to-interference plus noise ratio (SINR) in a correlated multi-user multi-antenna cellular system. The average SINR of the statistical beamforming depends on the accuracy of transmit correlation information as well as the characteristics of co-channel interference (CCI) from adjacent base stations. It is shown by means of multivariate Taylor series expansion that the average SINR degradation due to imperfect transmit correlation is associated with the mean squared error (MSE) and the number of quantization bits, and that those effect significantly varies depending on the correlation magnitude and the phase difference between the transmit correlation coefficient of the intended and CCI channel.

This paper considers power allocation in a spatially correlated dual-hop multiple-input multiple-output (MIMO) relay channel. In a dual-hop MIMO relay channel, it is desirable to balance the capacity of each hop channel by dynamically allocating the transmit power according to the channel condition. In fact, the end-to-end capacity of a dual-hop relay channel can be maximized by means of max-min optimization with constraint on total power. This paper considers the improvement of the end-to-end capacity by allocating the transmit power according to the average channel gain and the spatial correlation between the dual-hop MIMO relay channels. Simulation results show that the proposed scheme provides significant performance improvement over the power allocation based on the average signal-to-noise ratio (SNR).

In this paper, we propose a cooperative spectrum sensing scheme to maximize the detection probability in cognitive radio systems. We first analytically derive a closed-form expression for the detection and false alarm probability in terms of the number of cooperating users, and then determine the number of cooperating users that maximizes the detection probability for a given false alarm probability. It is shown that the detection probability of cooperative sensing is maximized when the cooperation is performed among users with high signal-to-noise power ratio and interference-to noise-power ratio. Finally, the analytic results are verified by computer simulation.

This paper considers cooperative eigen beamforming with the use of partial channel information (e.g., transmit correlation) to maximize achievable sum-rate of multi-user dual-hop multiple-input single-output relay channels. By exploiting the transmit correlation in a cooperative manner, the proposed scheme selects a pair of users whose transmit correlation have the largest phase difference of the desired and interference channel from the relay. It is analytically shown that the achievable sum-rate of selected two-users is maximized when the principal eigenvectors of the transmit correlation matrix of the desired and interference channel from the relay are orthogonal to each other. By generating an eigen-beam by the principal eigenvector of the transmit correlation matrix of own desired channel, the proposed scheme can provide the achievable sum-rate comparable to the full channel information-based minimum mean square error beamforming scheme in correlated channel environments. Finally, the proposed scheme is verified by computer simulation.

We consider a power allocation strategy to maximize the end-to-end capacity of a regenerative dual-hop multiple-input single-output (MISO) relay channel with the use of transmit beamforming. In a dual-hop MISO relay channel, the optimum power allocation can be determined by means of a max-min technique with sum power constraints. The proposed scheme adaptively allocates the transmit power of the source and relay according to the achievable beamforming gain as well as the average channel gain to balance the capacity between the dual- hop MISO relay channels. Simulation results show that the proposed scheme can provide noticeable performance improvement over the average signal-to-noise ratio (SNR)-based power allocation scheme in a dual-hop MISO relay channel with the use of the transmit beamforming.

In this paper, we propose a complexity reduced spectrum sensing technique for Bluetooth to find channels free from the use of other communication devices in 2.4 GHz ISM band. By exploiting the spectrum characteristics of interference sources, the proposed scheme detects the availability of channels by comparing the power spectrum density (PSD) with a threshold. To reduce the implementation complexity, the PSD is calculated by means of fast Fourier transform and linear interpolation. The threshold for the detection is determined to maximize the detection probability. To further improve the transmission performance, the proposed scheme dynamically changes the channels by measuring the transmission performance.

In this paper, we consider the service of voice over internet protocol (VoIP) traffic with the service of non-real time traffic in the mobile WiMAX system. VoIP traffic is delay-sensitive and requires transmission at an almost constant rate. As a consequence, it may require a large amount of resource when users are in poor channel condition, leading to resource outage problem. To alleviate this problem, we consider the allocation of power according to the VoIP traffic load as well as the channel condition. When the VoIP traffic is fully loaded, the power is allocated to maximize the VoIP capacity. Otherwise, it is allocated to maximize the data throughput. Finally, the performance of the proposed scheme is verified by computer simulation.

This letter investigates the effect of the transmit correlation on the sum-rate capacity of a two-user broadcast channel (BC) with the use of equal-power allocation in high signal-to-noise ratio (SNR) environments. It is shown using an upper-bound analysis that the sum-rate capacity of a correlated two-user BC at high SNR highly depends on the phase difference between the transmit correlation coefficients of two users as well as the magnitude of the transmit correlation coefficients, and it is maximized (or minimized) when the principal eigenvectors of the transmit correlation matrix of two users are orthogonal (or parallel) to each other. The analytic results are verified by computer simulation.

In this paper, we propose an adaptive beamforming scheme that generates the beam weight using dominant eigenvectors of the spatial covariance matrix. The number of eigenvectors used for the generation of beam weight is determined to maximize the signal-to-noise ratio (SNR) for given feedback constraints (e.g., the amount of feedback information and feedback delay). It is shown that the conventional limited feedback beamforming and eigen-beamforming are special cases of the proposed scheme. Simulation results show that the proposed beamforming scheme can effectively be applied to spatially correlated channels.

In this paper, we propose a new beamforming scheme that utilizes both long-term and instantaneous channel state information (CSI). First, the dimension of the channel is effectively reduced by considering dominant eigen-dimensions of the channel covariance matrix. Then, the beam weight is generated using the instantaneous CSI of the effectively dimension-reduced channel. The reduction of the channel dimension is determined to maximize the signal-to-noise ratio (SNR) in an average sense considering the amount of feedback signaling burden and spatial correlation of the channel. It is analytically shown and verified by computer simulation that the proposed scheme outperforms conventional beamforming schemes when the same amount of feedback signaling burden is utilized.

In this paper, we propose a user scheduling scheme to maximize the ergodic capacity of multi-user MIMO uplink systems. The proposed scheduling scheme only considers the use of the receive correlation matrix of users, not the instantaneous channel state information of users. The proposed user scheduling scheme is applied to collaborative spatial multiplexing systems specified in the IEEE 802.16e, where the base station receives two user signals at each time slot using two receive antennas. Analytic and numerical results show that the proposed user scheduling scheme outperforms conventional random user scheduling scheme in terms of the ergodic capacity without loss of opportunity fairness.

In this paper, we propose a new beamforming scheme that generates beams by exploiting the spatial correlation in multiuser environments. The proposed scheme generates random beams using eigenvectors corresponding to dominant eigenvalues of the channel covariance matrix, increasing the multiuser diversity gain. Moreover, it can obtain an additional SNR gain by transmitting the signal with a beam weight coherent to the effective channel corresponding to dominant eigenvectors of the channel covariance matrix of a selected user. Simulation results show that the proposed scheme is quite effective in correlated channel environments.

In this paper, we consider novel cooperative transmission from multiple base stations in multi-user wireless systems. The proposed scheme generates multiple beams using partial channel state information, enabling to achieve both beamforming and spatial multiplexing gain. With the use of two- phase multi-user scheduling, it can also achieve multi-user diversity gain. The performance of the proposed scheme is analyzed and verified by computer simulation. Simulation results show the proposed scheme is quite effective as the spatial correlation and/or the number of users increase.

This paper considers a transmit beamforming scheme that works with reduced feedback information in OFDM based multiple-input single-output (MISO) wireless systems. The proposed scheme generates the beamforming weight using information on the previous beamforming weights and channel correlation, significantly reducing the amount of feedback signaling burden. The feedback signaling overhead can further be reduced with the use of clustering and interpolation techniques. Simulation results show that the proposed scheme outperforms conventional beamforming techniques, while using the same amount of feedback signaling overhead.

SUMMARY: Genomes of more than 60 fungal species have been sequenced to date, yet there has been no systematic approach to analyze fungal transcription factors (TFs) kingdom widely. We developed a standardized pipeline for annotating TFs in fungal genomes. Resulting data have been archived in a new database termed the Fungal Transcription Factor Database (FTFD). In FTFD, 31,832 putative fungal TFs, identified from 62 fungal and 3 Oomycete species, were classified into 61 families and phylogenetically analyzed. The FTFD will serve as a community resource supporting comparative analyses of the distribution and domain structure of TFs within and across species. AVAILABILITY: All data described in this study can be browsed through the FTFD web site at http://ftfd.snu.ac.kr/.

In this paper, we propose a new beamforming scheme that can work with partial channel information. The proposed beamforming scheme can simultaneously achieve multiuser diversity (MUD) gain and beamforming gain by utilizing the beam weight information of the selected user in addition to the signal-to-noise ratio (SNR) information of all users. To fully exploit spatial multiplexing gain, we further consider the use of multiple beams. Multiple beams are generated in a sequential manner to reduce the interference among users, while virtually increasing the desired signal power. Finally, we analyze the performance of the proposed scheme and verify it by computer simulation. Although the proposed scheme is somewhat affected by the user mobility, numerical results show that the proposed scheme is quite effective in low mobility environments.

In orthogonal frequency division multiple access \n(OFDMA)-based uplink systems, it may not be feasible \nto exploit the rate adaptation due to severe intercarrier \ninterference (ICI). In this paper, we propose a \nnovel hybrid link adaptation scheme that employs \npower adaptation for ICI adjustment and rate \nadaptation for capacity improvement in OFDMAbased \nuplink systems. The proposed scheme determines \nthe maximum allowable transmit power in response to \nthe channel gain and mobility of the user, \nguaranteeing the carrier to interference power ratio \n(CIR) loss of all users.

Orthogonal frequency division multiplexing (OFDM) is considered as one of the most promising techniques for next generation mobile systems. When the OFDM is applied to cellular environments, it may suffer from so-called other-cell interference (OCI). In this paper, we propose a novel resource allocation scheme in OFDM-based asynchronous cellular systems. It can reduce the OCI by exploiting the repetitive property of a cyclic prefix (CP) of OFDM symbols. The proposed scheme can be applied to OFDM-frequency division multiple access (FDMA) and OFDM-code division multiple access (CDMA) systems. Computer simulation results show that the proposed scheme can reduce the OCI by nearly up to 1 dB in a typical cellular OFDM environment, compared to the conventional scheme.

This paper considers opportunistic packet scheduling with the use of reduced channel information in multiuser OFDM wireless systems. The amount of channel information can be reduced by exploiting the correlation characteristics in the frequency domain. For a given amount of feedback information, the subcarriers are selected to maximize the system capacity. A simplified algorithm is proposed for the selection of subcarriers, making the proposed scheme realizable. Simulation results show that the proposed scheme provides significant performance improvement over conventional schemes especially when the channel is highly correlated in the frequency domain and/or the amount of allowable feedback information is small.

The transmission performance of an OFDM system can significantly be improved by exploiting the channel characteristics. In this paper, we consider the design of a channel-aware OFDM transceiver whose parameters are adjusted in response to the change of channel condition. To this end, we first estimate the channel state information (CSI), such as the signal to interference power ratio, low order moments of Doppler spectrum and power-delay profile of the channel. The proposed CSI estimator can estimate these CSI parameters altogether in a unique manner by exploiting the autocorrelation properties of the channel impulse response (CIR). Then, we design a CIR estimator and adaptive OFDM modulator that adjust their parameters according to the estimated CSI. Finally, we verify the performance of the proposed OFDM transceiver by computer simulation

In this paper, we propose a new multiple-antenna transmission scheme that can simultaneously achieve both diversity and multiplexing gain in the multiuser domain, by using multiple random beams. Multiple beams are generated so that the users encounter multiple channels at the same time, enabling the use of multiuser diversity through each channel. Although the signal-to-noise power ratio (SNR) of each channel is reduced in proportion to the number of beams, multiple beams are generated so that the multiplexing gain is larger than the decrease of SNR, increasing the overall system capacity

In this paper, we consider fast cell site selection (FCS) in the downlink of a packet based orthogonal frequency division multiplexing cellular system. Mobile stations near the cell boundary can have opportunities to encounter a link that can provide better condition than the link in service due to the nature of fading effect. Conventional FCS schemes can track the variation of channel fading, exploiting a site selection diversity gain. However, mobile stations near the cell boundary may suffer from other cell interference (OCI) which is highly time-varying and unpredictable. To mitigate the OCI effect, we propose a new FCS scheme that exploits cell selection diversity while preventing adjacent cells from using the same sub-channels. We also consider the selection of candidate cells. The performance of the proposed FSC scheme is analyzed in terms of the capacity using an upper bound. Finally, analytic results are verified by computer simulation.

In this paper, we propose a beamforming scheme that exploits the advantages of opportunistic beamforming and coherent beamforming in multi-user environment. It is analytically shown that the proposed scheme achieves multi-user diversity gain and beamforming gain simultaneously, providing much better performance over the conventional ones. The performance of the proposed scheme is analyzed using an upper bound method. Although the proposed scheme involves an additional feedback delay, the analytical result implies that the use of the proposed scheme is quite effective unless the user mobility is too high. Finally, the analytic results are verified by computer simulation.

In this paper, we propose a multi-beam multiplexing scheme that can simultaneously achieve spatial multiplexing gain and multi-user diversity (MUD) gain by generating coherent multiple beams in the multi-user domain. Multiple beams are generated to provide multiple channels in parallel, making it possible to achieve the MUD gain through each channel. Since the transmission power is spilt into multiple channels, the signal-to-noise power ratio (SNR) of each channel is reduced inversely proportional to the number of beams. However, multiple beams are utilized to make the multiplexing gain much larger than the decrease of SNR, increasing the overall system capacity. The proposed scheme is applicable to both multi-input multi-output (MIMO) and multi-input single-output (MISO) schemes, enabling the use of flexible antenna structures in the receiver.

Adaptive modulation with coding (AMC) is often employed to enhance the throughput of OFDM based wireless systems. The AMC mode is usually adjusted according to the signal to interference ratio (SIR) of the received signal. Most of the conventional schemes use fixed thresholds for the selection of AMC mode, yielding a large performance variation depending on the channel characteristics. This paper proposes the use of adaptive SIR thresholds for the mode selection in response to the channel condition, providing significant improvement in throughput performance in a wide range of channel environments

Extensive use of the Internet and huge demands for multimedia services via portable devices require the development of packet-based radio access systems with high transmission efficiency. Advanced radio transmission technologies have recently been proposed to achieve this challenging task. However, few researches have been reported on the design of an integrated system that can efficiently exploit the advantages of these transmission technologies. This paper considers the design of a packet-based cellular system for next-generation radio access. We propose a novel system framework that can incorporate various advanced transmission technologies such as link adaptation, opportunistic packet scheduling, channel coding, and multiantenna techniques. For efficient use of these technologies together, we first investigate the interoperability between these technologies by proposing a so-called cause and effect analysis. Based on this investigation, we design a differentiated-segments-based orthogonal frequency-division multiplexing system, called DiffSeg, to accommodate heterogeneous operating conditions in a seamless manner. Simulation results show that the proposed DiffSeg system can provide a nearly optimum performance with flexible configuration in a wide range of wireless channel conditions.

We consider the crosstalk cancellation problem when the transmit and receive signal spectrum are partially overlapped with each other in the frequency domain. In this case, the use of conventional crosstalk cancellers may not be practical due to the computational complexity. When the overlapped bandwidth of the crosstalk signal is less than the bandwidth of the transmit signal, the crosstalk cancellation can be realized efficiently by processing in the baseband. The use of interpolation and decimation processing in the baseband makes it possible to realize the crosstalk canceller with low computational complexity. The proposed scheme can provide crosstalk cancellation performance comparable to the conventional one, while requiring the computational complexity less than one half the conventional one

Digital subscriber lines (DSL) technology provides a transport of high-bit-rate digital information over the public telephone lines. Recently, a new technique has been proposed to increase the overall data rate by coordinating all the wires in the same DSL cable. However, this coordination method cannot be applied when the cable lines are used for different types of xDSL services. This paper proposes a dimensional decision-feedback equalizer (M-D DFE) and precoding method that can simultaneously coordinate the lines in the time and user domain. A modified decision-feedback substitution is proposed by applying a generalized DFE (G-DFE) scheme into the two dimensional domain to increase the cable capacity. The performance of the proposed scheme is verified by computer simulation.

The performance of channel estimation can be improved by employing a channel estimation filter (CEF) that can adjust its bandwidth in response to the channel condition. For coherent OFDM receiver, we consider the use of two-dimensional (2-D) moving average (MA) FIR filter with a linear interpolation filter as the CEF that can provide good performance without requiring large implementation complexity. The optimum tap size of 2-D MA FIR CEF is analytically determined in terms of the pilot spacing, the channel spectrum and pilot signal to interference power ratio. The performance of the proposed channel estimator is evaluated by computer simulation.

In this paper, we propose a new multiple-access transmission scheme that can simultaneously achieve both diversity and multiplexing gain in the multi-user domain, by using multiple random beams. Multiple beams are generated so that the users encounter multiple channels at the same rime, enabling the use of multi-user diversity through each channel. Since the transmit power is spilt into multiple channels, the signal-to-noise power ratio (SNR) of each channel is reduced in proportion to the number of beams. However, multiple beams are generated so that the multiplexing gain is much larger than the decrease of SNR, increasing the overall system capacity. The proposed scheme works well in both Rician and Rayleigh fading channels regardless of the channel correlation, providing the maximum capacity in multiuser and multi-antenna systems in practice. The proposed scheme is applicable to both MIMO and MISO systems, enabling the use of receivers with flexible antenna structure.

BACKGROUND: Recent advances in sequencing techniques leading to cost reduction have resulted in the generation of a growing number of sequenced eukaryotic genomes. Computational tools greatly assist in defining open reading frames and assigning tentative annotations. However, gene functions cannot be asserted without biological support through, among other things, mutational analysis. In taking a genome-wide approach to functionally annotate an entire organism, in this application the approximately 11,000 predicted genes in the rice blast fungus (Magnaporthe grisea), an effective platform for tracking and storing both the biological materials created and the data produced across several participating institutions was required. RESULTS: The platform designed, named PACLIMS, was built to support our high throughput pipeline for generating 50,000 random insertion mutants of Magnaporthe grisea. To be a useful tool for materials and data tracking and storage, PACLIMS was designed to be simple to use, modifiable to accommodate refinement of research protocols, and cost-efficient. Data entry into PACLIMS was simplified through the use of barcodes and scanners, thus reducing the potential human error, time constraints, and labor. This platform was designed in concert with our experimental protocol so that it leads the researchers through each step of the process from mutant generation through phenotypic assays, thus ensuring that every mutant produced is handled in an identical manner and all necessary data is captured. CONCLUSION: Many sequenced eukaryotes have reached the point where computational analyses are no longer sufficient and require biological support for their predicted genes. Consequently, there is an increasing need for platforms that support high throughput genome-wide mutational analyses. While PACLIMS was designed specifically for this project, the source and ideas present in its implementation can be used as a model for other high throughput mutational endeavors.

The performance of channel estimation in orthogonal frequency division multiplexing (OFDM) systems significantly depends on the pilot signal, which is usually scattered in time and frequency domains. For a given pilot density, the authors optimally design the pilot pattern so as to minimize the mean squared error (MSE) of the channel estimate with the use of a general interpolator. The analytic results are verified by computer simulation.

Slot synchronization is the most challenging step for rapid cell search in intercell asynchronous code division multiple access systems such as wide-band code division multiple access (WCDMA). For rapid cell search, it is desirable to design the receiver robust to initial frequency offset and Doppler spread. In this letter, we consider combining schemes for rapid slot synchronization of WCDMA signals in such channel impairments. We propose an inner-slot differential combining scheme that exploits partial correlation of slot synchronization code, making the receiver tolerable to a large amount of initial frequency offset and Doppler spread. Unlike conventional differential combining schemes, the proposed scheme is also applicable to the use of transmit antenna diversity. The detection performance of the proposed combining scheme is analyzed with the use of transmit antenna diversity. Finally, the analytic results are verified by computer simulation.

The performance of channel estimation in OFDM systems significantly depends on the pilot signal, which is usually scattered in the time and frequency domains. For a given pilot density, we analytically design the optimum pilot pattern that minimizes the mean square error of the channel estimate obtained with the use of general interpolators. The analytic results are verified by computer simulation.

Coherent demodulation needs to maintain the symbol timing synchronization and to estimate the channel response in multicarrier code division multiple access systems. The use of inverse DFT (IDFT) is often considered to generate a pilot signal for this propose. However it requires a large implementation complexity, making it impractical for real applications. In this paper, we consider the design of a novel pilot signal for both symbol synchronization and channel estimation. By controlling the design parameters, the pilot signal can be generated to provide a desired signal-to- interference noise power ratio, while maintaining an acceptable peak-to-average power ratio. Simulation results show that the use of the proposed pilot signal can improve the detection performance compared to the use of conventional IDFT-based pilot signal, while significantly reducing the implementation complexity.

We consider an equalization problem when the transmitted symbol rate is higher than the available channel bandwidth. This situation can happen in the uplink of the voiceband pulse-code modulation (PCM) modems whose transmit signal bandwidth is larger than the available channel bandwidth. Although the use of a minimum mean-squared error (MMSE) pre-equalizer is considered in the International Telecommunications Union (ITU)-T V.92 Recommendation, it may not provide an acceptable performance unless the channel condition is mild. As another approach to this problem, we consider the use of a bank of subequalizers, each of which compensates the part of the channel distortion, enabling the PCM-mode transmission over the channel where the V.92 scheme may fail. In this paper, a multiple subequalizer scheme is optimally designed in the MMSE sense, and its performance is compared with the MMSE pre-equalizer of V.92 in terms of the bit-rate-normalized signal-to-noise ratio.

In this paper, a new direction-of-arrival (DOA) tracking algorithm, direction lock loop (DiLL), is proposed for wireless direct-sequence code-division multiple-access systems. It has a similar concept to the delay lock loop that is used for timing synchronization. It may track the DOA of sources by iterations. Its computational requirements are NK+O(K) for coherent DiLL and 2NK+O(K) for noncoherent DiLL, where N is the number of antenna elements and K is the number of signal sources, which is less than that of the projection approximation subspace tracking with deflation algorithm. The DOA tracking accuracy is demonstrated by analysis and computer simulations.

In this paper, we propose a computationally efficient algorithm for transmit power and bit allocations in wireless OFDM systems aiming at maximization of data rate under the constraint of total transmit power and bit error rate. Although the proposed algorithm is based on the water-filling approach, the computational complexity is only O(k/spl times/M), where k denotes the number of iterations required to meet the constraints and M is the number of subchannels. By computer simulations, we verify that 10 iterations are sufficient to satisfy the constraints, and the decrease of data rate for the proposed algorithm is shown to be less than one percent relative to the optimal method at the average SNR above 4 dB. The proposed algorithm is appropriate for OFDM systems in a time varying wireless channel for its low computational complexity and good performance.

In this paper, we consider combined equalization and nonlinear distortion cancellation for transmission of QAM signals in fixed wireless channel with nonlinear distortion. To reduce nonlinear intersymbol interference (ISI) due to the use of high power amplifiers in the transmitter, we design a nonlinear equalization scheme by approximating the Volterra series model for the nonlinear distortion. The proposed equalization scheme employs two memoryless nonlinear modules, one at the input of the feedback filter and the other at the input of the decision device of the conventional minimum mean-squared-error decision-feedback equalizer (MMSE-DFE). The performance of the proposed scheme is analyzed in terms of the symbol error rate and verified by computer simulation. The SNR gain of the proposed scheme over the conventional MMSE-DFE increases as the QAM constellation size and/or the roll-off factor of the transmit and receive filters increase, enabling the transmission of high-level QAM signals in fixed wireless channel.

The receiver performance with the use of space time transmit diversity (STTD) scheme is more susceptible to the accuracy of channel estimate than that without the use of the STTD scheme since the despreading signals suffer from the effect of crosstalk and the transmit power is equally divided into multiple transmit antennas. As a result, the efficiency of channel estimation in the WCDMA STTD system becomes an important issue more than that in the non-STTD system. In this paper, an adaptive channel estimator (ACE) is designed to mitigate the performance degradation due to inaccurate channel estimation. Numerical results show that the performance improvement significantly increases with the use of the proposed ACE, particularly when the channel condition becomes worse.

We design an adaptive channel estimator (ACE) in the DS-CDMA downlink that has a common pilot channel (CPICH). The proposed ACE first estimates the channel condition, including the maximum Doppler frequency, without requiring exact a priori information on the operating condition. Then, it adjusts the impulse response of the channel estimation filter in response to the estimated channel condition. The performance of the proposed ACE is verified by computer simulation. The performance improvement with the use of the proposed ACE increases as the channel experiences severe frequency selective fading or the mobile is getting closer to the cell boundary.

Some blind beamformers require the direction of the desired signal. The performance of such type beam-formers can be severely degraded by a small directional error. We propose a blind beamforming scheme robust to directional error by employing a simple steering vector estimator. The performance of the proposed beamformer can be further improved by re-initializing the weights of the beamformer.

A multicarrier system, which is under consideration for high data rate transmission in the future, offers robustness to multipath fading in a wireless channel. We develop the optimal transmit power adaptation method to maximize the channel capacity of a multicarrier system, considering both frequency and time domains. The optimal transmit power adaptation policy with average transmit power constraint is found to be "water-pouring" in the frequency-time domain. We also show that the channel capacity with the frequency-time domain transmit power adaptation is greater than that with only the frequency domain transmit power adaptation.

The WCDMA system, an asynchronous CDMA scheme, uses different downlink scrambling codes for each base station, not requiring synchronization between the base stations as in the synchronous CDMA systems. However, the mobile station needs to obtain initial code synchronization by resolving both the code and timing uncertainty. The 3GPP Group adopts the use of a three-step cell search scheme. For ease of initial cell search, the base station transmits two synchronization codes through the synchronization channel. The mobile station searches the peak correlation value of the primary synchronization code to acquire the slot timing. For reliable detection, the receiver combines the correlation values from several slots. In this paper, we propose a new combining scheme that can reduce search time and also provide performance robust to a wide range of initial frequency offset. The proposed scheme utilizes a differential detection method, applicable to the transmit antenna diversity mode as well as the single antenna mode. The proposed scheme can also estimate the initial frequency offset for the automatic frequency control (AFC) performance, eliminating the need for an initial frequency acquisition circuit.

We propose an improved scheme for parallel acquisition of PN sequences of multi-carrier direct-sequence spread spectrum systems in the Rayleigh fading channel. Unlike conventional parallel acquisition schemes, the search region of each searcher in the proposed scheme is modified so that it is overlapped with that of other searchers. The use of the proposed search scheme enables us to obtain multiple information on the same code phase at different time instants, providing the time diversity effect. This effect results in acquisition performance robust to fading. The performance of the proposed acquisition scheme is analytically evaluated in terms of the detection probability and the mean acquisition time in the Rayleigh fading channel. Numerical results show that the proposed scheme can provide acquisition performance robust to channel conditions, including fading and correlation between the subchannels.

The performance of a coherent RAKE receiver for DS-CDMA systems is significantly affected by the accuracy of channel estimation. The performance of the channel estimator can be improved by employing a channel estimation filter (CEF) whose impulse response is adjusted according to the channel condition. In this paper, we consider the analytic design of an adaptive channel estimator for DS-CDMA systems with a pilot channel. The proposed channel estimator estimates the channel condition including the maximum Doppler frequency, which can be performed without having exact a priori information on the operating condition. The estimated channel condition adjusts the impulse response of the CEF. Numerical results show that the use of the proposed channel estimator can provide BER performance quite robust to a wide range of channel condition.

To reduce the equalizer training time with robustness to the timing phase error in fixed wireless channels, we propose a fractionally-spaced modified DFE (FS-MDFE) scheme. The proposed FS-MDFE is an extension of the previously proposed symbol-spaced modified DFE (SS-MDFE) (see Ariyavisitakul, S. and Greenstein, L.J., IEEE J. Select. Areas Commun., vol.15, no.1, p.5-15, 1997). The performance of the FS-MDFE is analytically evaluated in terms of the mean squared error. The optimum MMSE solution is derived for initialization of the feedforward filter of the MDFE. We also propose a simplified initialization method to reduce the implementation complexity.

When a multi-level quadrature amplitude modulation (QAM) signal is transmitted over the wireless channel, transmit power needs to be controlled to avoid severe performance degradation due to the fading. Most studies on the transmit power control (TPC) were considered in the flat fading channel. In this paper, we propose a power control scheme in the frequency selective fading channel, where the transmit power is controlled based on the mean-squared error (MSE) of the equalizer output. The performance of the proposed scheme is analytically evaluated and verified by computer simulation in the fixed wireless channel with low Doppler frequency.

A fractionally-spaced frequency domain equalizer (FS-FDE) is needed to transform a received signal into the frequency domain. We consider two fast Fourier transform (FFT) schemes, one with a single 2N-point FFT and one with two N-point FFTs, for the transform of oversampled N symbol data in the FS-FDE receiver. It is shown that the two receiver schemes are equivalent in terms of the characteristics of the FFT output, per-bin SNR after maximum-ratio combining, computational complexity and the residual out-of-band noise rejection property. These properties are verified by computer simulation in additive white Gaussian noise (AWGN) and typical multipath channel.

The near-far problem and multipath fading degrade the performance of the CDMA transceiver. The use of transmit power control (TPC) is widely applied to alleviate these effects. It is required to estimate signal-to-interference power ratio (SIR) of the received signal for the TPC. As the accuracy of the SIR increases, the transmit power can be reduced without degrading the bit error rate (BER) performance, increasing the system capacity. In this paper, we propose an improved SIR estimate scheme. The proposed scheme increases the SIR accuracy by considering not only present slot information but also previous slot information. The number of previous slots is adjusted in response to the channel condition. The performance of the proposed SIR estimator is verified by computer simulation.

For full-duplex high-speed data transmission over the two-wire line using the same frequency band, it is required to sufficiently suppress the echo. The use of a conventional adaptation method may take a long time to train the echo canceler. Fast training can be achieved by initializing the coefficients of the echo canceler with an estimate of the impulse response of the echo path. We propose a method for fast initialization of the echo canceler by using a circular convolution technique. The proposed method enables the use of real-valued training signals instead of complex-valued ones, resulting in significant reduction of the initialization time as well as the implementation complexity. Finally, the performance of the proposed method is analyzed and verified by computer simulation.

The characteristics of spreading sequences significantly affect the performance of the forward link DS-CDMA system in a fading channel. The bit error rate (BER) is a function of the signal-to-interference ratio (SIR) which has different characteristics depending upon the spreading sequence. In this paper, the SIR is analyzed when orthogonal codes and pseudo random codes are used as the spreading sequence. The BER performance is analyzed with and without the use of convolutional codes. The use of orthogonal codes can cancel out the interference signals having the same path delay, but the use of random codes cannot, resulting in significant performance degradation. As a result, the BER performance of the orthogonal spreading system is much better than that of the random spreading system. Even in the case of many multipaths, the number of users achieving a fixed BER value in the orthogonal spreading system is twice larger than that in the random spreading system. The analytical results are verified by computer simulation.

We propose a new scheme for rapid acquisition of PN signals in direct-sequence spread spectrum (DS/SS) systems by estimating the phase of the received PN signal with the use of an auxiliary signal. The auxiliary signal can be generated by a sum of the phase shifted PN signals. The phase of the incoming PN signal is estimated using the properties of cross correlation between the PN signal and the auxiliary signal. True phase alignment is detected using a conventional serial search scheme, where the initial phase of the local PN generators is set to a value obtained by the phase estimator. The performance of the proposed acquisition scheme is analytically evaluated in terms of the mean acquisition time. Numerical results show that the proposed scheme can achieve acquisition at least two times faster than the conventional scheme in the nominal operating condition.

The performance of sequence acquisition for Gold sequence based DS-CDMA systems is studied in this paper. We consider the use of a sliding correlator-type structure for the acquisition scheme. Since acquisition of a PN sequence in DS-CDMA systems can be formulated as testing two simple hypotheses, we apply fixed sample size for the synchronization test. The acquisition schemes require the knowledge of the partial correlation of Gold sequences, which is difficult to model. We propose the use of an approximate upper bound and then further linearize it for ease of designing the test scheme. The acquisition performance of Gold sequence based DS-CDMA systems is analyzed and is compared to that of m-sequence based ones. Numerical results indicate that the use of Gold sequences is very suitable for DS-CDMA systems. In addition, analytical results are verified by computer simulation.

The performance of sequential acquisition of m sequences, based on the sequential probability ratio test (SPRT), is studied. The authors consider a sliding correlator-type structure for the acquisition scheme, which the mean acquisition time is proportional to the average number of samples used for a synchronization test. Sequential acquisition requires the knowledge of the partial correlation of the pseudonoise (PN) sequence, however, as the partial correlation of an m sequence is difficult to model the authors propose an approximate upper bound. This is then piecewise linearized and used for designing the SPRT which is then compared to the fixed-dwell time technique, a scheme using the fixed sample size test. Numerical results show that the saving of acquisition time by the SPRT increases as the desired probabilities of errors and/or the input SNR decrease. Analytic results are verified by computer simulation.>

A filter which combines L-type structure with a modified median filter (MMF) is proposed for suppressing nonimpulsive as well as impulsive noise. The MMF is designed to reduce edge jitter caused by the median filter. The MMF output is obtained by modifying the median filter output, based on results of hypothesis tests. The proposed filter, named the decision-based order statistic filter (DBOSF), generates the output by using asymmetrical alpha -trimming with respect to the MMF output. In addition to noise suppression, the DBOSF can enhance the gradient of blurred edges provided that the size of the window is greater than twice the transition with width of the blurred edges. Experimental results for one- and two-dimensional signals are presented to demonstrate performances of the proposed filter.>

In this paper the performance of delta modulation (DM) systems have been studied by computer simulation when the input signal to the DM coder is a voiceband data signal. First, the parameter values of three DM systems, linear DM (LDM), constant factor DM (CFDM), and continuously variable slope DM (CVSD) has been optimized for 4800 bits/s differential phase shift keying (DPSK) signal. Then, the performance of the three DM systems have been studied for ideal and noisy channels. It has been found that the peak signal-to-quantization-noise ratio (SQNR) is nearly the same regardless of coding scheme used, but CFDM yields the widest dynamic range. In a noisy channel, however, CFDM is very sensitive to channel bit errors. Considering the overall performance, CVSD appears to be the best among the three DM systems studied. Also, the performances of DM's have been compared with those of PCM and DPCM systems. In addition, we have studied the effect of DM quantization noise on modem bit error rate by the Monte Carlo simulation method. It is possible to transmit a 4800 bits/s DPSK signal at a bit error rate below 10-5by CVSD with the rate of 32 kbits/s.