In this paper, we address a technique and related algorithms for precise detection, parametric imaging and classification of small marine targets in a harsh sensing environment attributed for heavy sea clutter via noncooperative processing of the GPS-based Forward Scatter Radar (FSR) data. In contrary to GPS L5 detection approach, the proposed technique utilizes civil GPS L1 signal formats in FSR exploiting GPS as a non-cooperative transmitter. In our previous studies it is shown that the use of the new power GPS signal L5, and the Forward Scattering effect providing a high SNR, at the detector input allows reliably to detect small air targets in conditions of the intense interference. In this paper we propose another approach, to enhance SNR, at the input of the detector in Forward Scattering Radar (FSR). The use of the effective filter (Local Variance Filter) for suppression of intensive sea clutter allows FSR reliably to detect small marine targets emerged in harsh sea clutter, but with GPS L1 signal, whose SNR is very small. At the classification level, the data mining approach is adopted, in which the target feature parameters are extracted from the preliminary filtered signals by utilizing the modified structure of a processor for target detection and parameter estimation in the time domain. Both, the decision tree-based and the neural network classifiers are featured and adapted for real-time implementation. The efficiency of the proposed technique is verified via analytical performance evaluations and experimental demonstrations.

Crosstalk (XT) is the main performance limiter in digital subscriber line (DSL) systems such as very-high-bit-rate digital subscriber line (VDSL) systems. In order to overcome these limitations various XT cancellation techniques have been proposed to mitigate this effect. While leading to very high performance gains, the computational complexity grows quadratically with the number of lines in a binder. This motivates partial cancellation schemes, maximising the capacity based on a given computational complexity. However, the data rate increase could still be very high above the quality of service (QoS) requirements that must be enforced for each user, leading to a ‘waste’ of computational resources. Therefore a QoS-based partial cancellation algorithm is presented in this study which selects the lines to be cancelled based on the desired data rates of the users. It relies on partial zero-forcing XT cancellation but the used selection algorithm [QoS-based joint tone-line selection (QoS-JTLS)] aims at QoS fulfilment instead of data rate maximisation. Simulation results show that compared with other QoS-based algorithms and conventional selection algorithms, QoS-JTLS leads to better fulfilment of QoS demands for the same given computational complexity. In other words, the computational complexity needed to achieve the target data rates of the users is reduced when applying QoS-JTLS.

Broadband digital transmission over cable wires, such as in very-high-speed digital subscriber line 2 systems, applies the discrete multitone technique in combination with a bit-loading procedure. The crosstalk interference among the different cables inside a binder is the major performance degradation in the systems. Different crosstalk cancellation schemes considering computation complexity as well as the quality-of-service (QoS) aspect have been investigated to improve the system performance. Nowadays, driven by the newest high-layer applications the QoS requirements are more critical and a dynamic situation happening quite often in reality has to be considered. In this situation, new active cable lines might significantly influence the existing running lines in terms of achieved data rates. Therefore a successive crosstalk cancellation scheme is presented in this study to deal with the dynamic situation. The performance degradation because of the new active lines is predicted. Based on the prediction a line-independent partial cancellation with successive procedure is performed until the QoS requirements are fulfilled again.

This paper presents a cross-layer concept with respect to a joint design of beamforming and scheduling in a cellular MIMO-OFDM-based network. Conventionally, the beamforming and scheduling processes are designed more or less independently of each other. In contrast, this paper describes a combined approach of the scheduling and beamforming procedure, with the aim to maximize the capacity and fulfill the QoS requirements for all users within the network. For the example of delay constraints, it is shown how a joint system design is beneficial to serve users with "urgent" data packets. This is accomplished by giving the scheduling unit a control over the beams to be applied, thus favorable radio channel conditions can be temporarily generated for specific users such that the associated packets are delivered in time.

This paper considers orthogonal frequency division multiplexing (OFDM) systems with coherent and incoherent demodulation techniques in mobile radio channels with high terminal velocities. Coherent demodulated systems, using a scattered pilot based channel estimation or a decision directed channel estimation approach, is compared in terms of bit error rate (BER) performance and hardware complexity with an incoherent system with differential amplitude and phase shift keying (DAPSK) modulation schemes. It will be shown, that in high mobility scenarios, differential modulation schemes together with incoherent demodulation leads to an useful trade off between performance and hardware consumption. The hardware complexity results are acquired from field programmable gate array (FPGA) implementations

In this paper, a system concept is proposed and investigated for the downlink of a cellular network which combines a self-organised beamforming approach with an opportunistic scheduling concept. In the considered OFDM-based system, different beams or grids of beams are formed in time and frequency and the available space-time-frequency resources are allocated by intelligent scheduling algorithms to those mobile terminals with high instantaneous signal-to-interference-and-noise ratios (SINRs). Analysing the impact of various design criteria, such as the type of beamforming, scheduling concepts and frequency reuse factors, the performance in the cellular network regarding throughput and fairness is assessed

In this paper, orthogonal frequency division multiplexing (OFDM) systems with coherent, incoherent and quasi-coherent demodulation schemes will be considered respectively. Resulting system performance figures will be compared in terms of bit error rate (BER) and hardware complexity. It is well known that non-differential modulation and coherent demodulation techniques have optimum BER performance but lead to a significantly increased system overhead due to pilot signals and system complexity due to channel estimation procedure. This paper describes differential modulation schemes, which do not require any radio channel estimation, and two related incoherent and quasi-coherent demodulation techniques. The resulting BER performance is nearly identical compared with coherent demodulation, but the computation complexity is drastically reduced. A field programmable gate array (FPGA) based experimental system has been developed, which is used for BER performance measurements and system complexity considerations

Radar sensors in the 24- and 77-GHz frequency domain will be used to increase comfort and safety in many future automotive applications. In this paper, a radar network with four short-range radars is considered. Each sensor measures individually only the range information of all targets inside the observation area. The Cartesian coordinates of each target are calculated by a trilateration technique based on range measurements selected in a data-association procedure. Estimating a target position based on range measurements is called trilateration. In contrast to this, estimation of a target position based on pure angular measurements is called triangulation. In automotive applications, situations with multiple targets almost always occur. Therefore, a high-performance data association is very important to separate and to distinguish between these targets. To avoid errors in the data-association step and resulting ghost targets, this paper describes a technique that combines the procedures of data association and position estimation into a single step. This signal-processing technique shows very good results in multitarget situations and reduces the number of ghost targets drastically.

Intervehicle communication (IVC) is an emerging topic in research and application that is getting increasing attention from all major car manufacturers. In this paper, a novel method for scalable information dissemination in highly mobile ad hoc networks is proposed: segment-oriented data abstraction and dissemination (SODAD). With SODAD, information can be distributed in an information range multiple orders of magnitude larger than the transmission range of the air interface, even if only 1%-3% of all vehicles are equipped with an IVC system, e.g., during market introduction. By restricting the method to the dissemination of map/position-based data, scalability is achieved. In the second half of this paper, an example application for the SODAD method is presented: a self-organizing traffic-information system (SOTIS). In SOTIS, a car is equipped with a satellite navigation receiver, an IVC system, and a digital map. Each individual vehicle collects traffic information for its local area. Using the digital map, the traffic information is analyzed based on road segments. By distributing the information in the ad hoc intervehicle network using the SODAD method, a decentralized traffic information system is created. The performance of the proposed methods is evaluated using network simulation with vehicular mobility models. Simulation results for typical scenarios are presented. Furthermore, a prototype implementation based on commercially available standard hardware demonstrates the feasibility of the proposed approach.

Modern wireless communication standards like HiperLAN/2 or IEEE802.11a provide a high degree of flexibility on the physical layer (PHY) allowing the data link control (DLC) layer to choose transmission parameters with respect to the currently observed link quality. This possibility of so-called link adaptation (LA) is a key element for meeting quality of service (QoS) requirements and optimizing system performance. The decisions made by the LA algorithm are typically based on a prediction of the packet error rate (PER) implied by a certain transmit parameter setting. With most existing LA schemes, this prediction is based on the observed signal-to-noise ratio (SNR) or carrier-to-interference ratio (CIR), respectively. For frequency selective channels, however, the SNR alone does not adequately describe the channel quality. It is shown in this paper that LA schemes based on an accurate description of the momentary channel status can outperform conventional schemes with respect to throughput and reliability. Based on a novel "indicator" concept, schemes for obtaining an accurate prediction of the PER by evaluation of the channel transfer function are presented and evaluated by software simulation.

Adaptive modulation, i.e. subcarrier-specific selection of the modulation scheme, is a well-known technique for enhancing the performance of multi-carrier systems. The adaptation to the frequency selective characteristics of the channel leads to considerable SNR gains for transmission over non-line-of-sight multipath channels. The actual assignment of modulation schemes to the individual subcarriers must be known to both the transmitter and the receiver. Conventionally this is achieved by exchanging information about the assignment over the communication link. i.e. a certain amount of signalling overhead is introduced. In this paper a signalling-free approach for reconstructing the assignment of modulation schemes in the receiver is presented. The decision about the modulation scheme used on each individual subcarrier is incorporated into the process of channel decoding.

The objective of the presented work is the design of flexible data link control (DLC) protocols with the focus on scheduling policies, which combine the information of the time variant radio channel (described by the channel transfer function) and the incoming data streams from real time video applications with variable data rates. The goal is to fulfil the quality of service (QoS) requirements in terms of data rate, reliability and delay for all wireless terminals and to improve the average system throughput. Fairness between the wireless terminals (WTs) is also a very important aspect of scheduling.

Within the FleetNet project an ad hoc radio network for intervehicle communications (IVC) and road telematics is being developed. For the air interface, the framework of the UMTS Terrestrial Radio Access time division duplex (UTRA TDD) standard has been selected as the most promising candidate. The requirements and challenges for synchronization in an ad hoc network with rapidly changing topology and high velocities are discussed. Solutions for synchronization in ad hoc networks based on UTRA TDD are proposed and evaluated by means of link-level simulations. The results indicate promising performance with only minor changes to the UTRA TDD standard specifications.

Modern wireless communication standards like HiperLAN/2 or IEEE 802.11a provide a high degree of flexibility on the physical layer (PHY) allowing the data link control (DLC) layer to choose transmission parameters with respect to the currently observed link quality. This possibility of so-called link adaptation (LA) is also a key element for meeting quality of service (QoS) requirements of higher layers. Most LA algorithms take an estimate of the signal-to-noise ratio (SNR) or carrier-to-interference ratio (CIR), respectively, as the only input from the PHY layer. For frequency selective channels, however, the SNR alone does not adequately describe the channel quality. It is shown in this paper that system performance can be significantly improved if the LA scheme is based on a more detailed description of the channel situation. Methods for selecting the PHY mode based on the estimated channel transfer function are presented and compared to conventional algorithms.

The orthogonal frequency division multiplex (OFDM) transmission technique can efficiently deal with the effects of multipath propagation in the broadband radio channel. It also has a high system inherent flexibility for designing a multiple access scheme by combining the conventional TDMA, FDMA and CDMA approaches with the OFDM modulation scheme. The FDMA multiple access scheme is especially interesting for an uplink of a communication system since it can completely avoid any multiple access interference (MAI). Moreover, the peak-to-average ratio (PAR) of the uplink OFDM transmit signal can be greatly reduced if this OFDM-FDMA multiple access scheme is additionally combined with a data spreading technique based on a discrete Fourier transform (DFT) spreading matrix using only the user specific subcarriers. Since the DFT spreading operation and the IDFT operation used as a part of the OFDM modulation scheme cancel out each other the complexity of the transmitter structure for an OFDM-FDMA uplink can be greatly reduced.

The OFDM transmission technique has the inherent flexibility to adapt the modulation scheme on each subcarrier according to the reception quality, i.e. the signal-to-noise ratio (SNR) on a subcarrier. The allocation of bits to subcarriers is performed by so-called loading algorithms. In this paper, a new and rather simple loading algorithm is introduced which shows comparable performance and lower computational complexity compared to the well-known algorithm of Chow et al. (1995). In the proposed algorithm, subcarriers are clustered in blocks, which are allocated the same modulation scheme. This way, the signalling overhead can be reduced in comparison with standard subcarrier bit loading algorithms.

Future multimedia services will require the transmission of very high data rates over broad-band radio channels. In order to provide these services to mobile users, an appropriate transmission technique has to cope with frequency-selective and time-variant radio channels. The computation complexity for an equalizer increases in a frequency-selective radio channel for high data rate applications. Furthermore, the overhead for channel estimation procedures increases in time-variant channels. To overcome these drawbacks orthogonal frequency division multiplexing (OFDM) has been considered for broadband applications in many publications. The objective of this paper is to describe the large potential, the flexibility and adaptivity of the OFDM transmission technique in frequency-selective and time variant radio channels. Several technical aspects of OFDM transmission systems are discussed, especially the topics of differential modulation for which we compare different demodulation methods and channel coding with soft decision decoding. For higher level differential modulation, multilevel coding is taken into consideration.

The FRAMES multiple access (FMA) in order to meet the UMTS requirements and thereby also the IMT2000, has proposed a harmonized platform based in two access techniques, i.e. time division multiple access (TDMA) and code division multiple access (CDMA). Thus, the MA concept has two modes: FMA1, wideband TDMA with and without spreading, and FMA2, wideband CDMA. The FMA1 included several options such as spreading (CDMA features) and orthogonal frequency division multiplexing (OFDM) modulation. This paper presents the performance of this latter option in order to outline the flexibility of the FMA1 and the advantages of the OFDM modulation when used instead of the single carrier setting following the classical TDMA approach. Link level results illustrate that the E/sub h//N/sub 0/, values are comparable or even better than the ones obtained following traditional modulation techniques.

The multilevel modulation techniques of 64-quadrature amplitude modulation (QAM) and 64-differential amplitude and phase-shift keying (DAPSK) have been proposed in combination with the orthogonal frequency-division multiplexing (OFDM) scheme for digital terrestrial video broadcasting (DTVB). With this system a data rate of 34 Mb/s can be transmitted over an 8-MHz radio channel. A comparison of these modulation methods in the uncoded case has been presented by Engels and Rohling (see European Trans. Telecommun., vol.6, p.633-40, 1995). The channel coding scheme proposed for DTVB by Schafer (see Proc. Int. Broadcasting Convention, Amsterdam, The Netherlands, p.79-84, 1995) consists of an inner convolutional code concatenated with an outer Reed-Solomon (RS) code. In this paper the performance of the convolutional codes is analyzed for the two modulation techniques. This analysis includes soft decision Viterbi (1971) decoding of the convolutional code. For soft decision decoding of DAPSK modulated signals a new metric is developed.

For digital transmission over frequency-nonselective fading channels, data security can be obtained by error correction coding, but the coding scheme has to be adapted to the channel properties. For many vehicular applications, the range of possible vehicle speeds is large and in the UHF band the resulting Doppler frequency may not be small relative to the symbol rate-suggesting a differential detection scheme. Therefore, the channel coding should be robust against changes in Doppler spread. A combination of a convolutional code (soft-decision decoding) and a Reed-Solomon (RS) code is considered, and the performance in a narrow-band Rayleigh-fading channel with differential quaternary phase shift keying (DQPSK) modulation without interleaving is evaluated as a function of signal-to-noise ratio (SNR) and Doppler spread by computer simulations. This transmission scheme is proved to have good performance over a large variety of vehicle speeds.

The field of application for a radar sensor is outlined and a requirement profile is derived therefrom. A standard hardware platform for a CWFM radar is described. By step-form modification of known modulation signals, new methods for the elimination of phantom objects and for the correction of typical receiver errors are made possible. The application of a residual-class code with its special correlation properties ensures high level detection probability of all objects.>

The well known orthogonal frequency division multiplexing (OFDM) multicarrier transmission technique is tailored for a broadband cellular mobile communications system. A performance analysis in multipath fading radio channels is presented and the average bit error rate (BER) is calculated in dependence of the signal-to-noise ratio for bad urban and hilly terrain channel models, following the COST-207 report. Pros and cons for OFDM and code division multiple access (CDMA) techniques are discussed on the basis system robustness, receiver complexity and bandwidth efficiency.>