Low Power Wide Area Networks (LPWAN) technologies in the 2.4 GHz band offer the opportunity to employ multiple antennas at the sensor, which can be used to create antenna diversity. In this paper, we present our software-defined, interference-robust, and highly mobile channel sounder architecture and experimentally evaluate the long-range outdoor-to- outdoor MIMO channel in a typical Smart City environment. Analyzing the measurements we have obtained over a wide area, we estimate path loss, coherence bandwidth, and antenna correlations. Link budget calculations show that, despite the higher frequency compared to popular LPWAN technologies such as LoRa or SigFox, multi-kilometer links are feasible. Furthermore, the comparison of an IEEE 802.15.4 PHY designed for LPWANs with a recently proposed multi-antenna scheme indicates that considerable performance gains are possible through antenna diversity schemes, even with rather high antenna correlation.

We present the design of a low-complexity air interface for the uplink in Low Power Wide Area Networks (LPWANs) based on a recently published Differential Spatial Modulation scheme for two transmit antennas achieving full transmit diversity (FD-DSM). Extending the authors' work, we derive an optimized assignment from bits to space-time matrices comparable to Gray coding, which improves the bit error rate by up to 1 dB. Furthermore, FD-DSM's superiority over single-antenna differential PSK schemes as used in current LPWAN technologies is evaluated in extensive simulations and confirmed in uncoded and coded scenarios, where a convolutional code with soft-input Viterbi decoding is employed. It is shown that existing systems are outperformed by at least 5 dB for packet error rates below 1%. Our system utilizes the DSSS technique to achieve the enormous processing gains required to enable links over many kilometers. We propose the insertion of time gaps between chip sequences to allow for the rise and fall time of conventional, spectrally-efficient pulse shaping filters and to thus facilitate antenna switching without spectral broadening, a challenging issue in Spatial Modulation (SM) systems. The resulting rate loss is negligible but allows the realization of practical SM systems with the theoretical minimum of a single RF chain.

Low Power Wide Area Networks (LPWANs) are an emerging paradigm for low-cost and long-range connection of sensor networks. While most technologies focus on sub-GHz frequencies for their low path loss, the 2.4 GHz band is also an interesting choice due to its high bandwidth and global availability. In this paper, we report our results from a measurement campaign performed in Karlsuhe, Germany, where we investigate the interference background in different scenarios typical for Smart City applications. Using our software implementation of the IEEE 802.15.4 LECIM DSSS PHY and the recorded noise and interference, we also quantify its impact on the performance of a practical LPWAN waveform in terms of packet error rate and effectively available bandwidth at different received signal strengths. Even though it turns out that link budget calculations based on AWGN might be too optimistic, promising results are presented for a two-way single-channel network with up to two retransmissions.

In this paper, we study the performance of hybrid cognitive radio systems that combine the benefits of interweave and underlay systems by employing a spectrum sensing and a power control mechanism at the Secondary Transmitter (ST). Existing baseline models considered for performance analysis assume perfect knowledge of the involved channels at the ST, however, such situations hardly exist in practical deployments. Motivated by this fact, we propose a novel approach that incorporates channel estimation at the ST, and consequently characterizes the performance of Hybrid Systems (HSs) under realistic scenarios. To capture the impact of imperfect channel knowledge, we propose outage constraints on the detection probability at the ST and on the interference power received at the primary receiver. Our analysis reveals that the baseline model overestimates the performance of the HS in terms of achievable secondary user throughput. Finally, based on the proposed estimation-sensing-throughput tradeoff, we determine suitable estimation and sensing durations that effectively capture the effect of imperfect channel knowledge and subsequently enhance the achievable secondary user throughput.

Knowledge of interacting channels is essential for characterizing the performance of a cognitive radio system in terms of interference power received by a primary receiver and throughput at a secondary receiver. Baseline models considered for the performance characterization assume perfect knowledge of the interacting channels. Recently, an analytical framework has been proposed that incorporates channel estimation and subsequently characterizes the performance of cognitive Interweave Systems (ISs). However, the analysis was pertained to the deterministic behaviour of the interacting channels. In this paper, we extend the characterization of the aforementioned framework to investigate the influence of channel fading on the performance of the IS. Our analysis indicate that an inappropriate choice of estimation time can severely degrade the performance of the IS in terms of achievable secondary throughput.

Cognitive Radio communication is foreseen as one of the possible candidates that can resolve spectrum scarcity currently faced by the upcoming wireless technologies. This scarcity can be solved by enabling secondary access to the licensed spectrum. The interference at the primary receiver can be avoided by employing a detector (spectrum sensing) at the Secondary Transmitter (ST). Energy detection is widely used due to its low complexity and applicability to a large range of primary user signals. Recently, antenna diversity techniques such as square-law selector and square-law combiner have been used to enhance the detection performance at the ST. In this context, the detector's performance pertaining to the antenna diversity techniques has been characterized analytically. However, issues such as RF impairments and deploying a fading model render hardware implementation of such techniques challenging. Motivated by this fact, this paper presents the deployment of a hardware, and subsequently utilize the theoretical expressions to validate the performance of a multi-antenna system at the ST that exploits antenna diversity techniques in a realistic environment. Finally, we emphasize the challenges faced during the hardware implementation and present our approach to address these challenges.

Secondary access to the licensed spectrum is viable only if the interference is avoided at the primary system. In this regard, different paradigms have been conceptualized in the existing literature. Among these, interweave systems (ISs) that employ spectrum sensing have been widely investigated. Baseline models investigated in the literature characterize the performance of the IS in terms of a sensing-throughput tradeoff, however, this characterization assumes perfect knowledge of the involved channels at the secondary transmitter, which is unavailable in practice. Motivated by this fact, we establish a novel approach that incorporates channel estimation in the system model, and consequently investigate the impact of imperfect channel knowledge on the performance of the IS. More particularly, the variation induced in the detection probability affects the detector’s performance at the secondary transmitter, which may result in severe interference at the primary receivers. In this view, we propose employing average and outage constraints on the detection probability, in order to capture the performance of the IS. Our analysis reveals that with an appropriate choice of the estimation time determined by the proposed approach, the performance degradation of the IS can be effectively controlled, and subsequently the achievable secondary throughput can be significantly enhanced.

Understanding the performance of cognitive radio systems is of great interest. To perform dynamic spectrum access, different paradigms are conceptualized in the literature. Of these, Underlay System (US) has caught much attention in the recent past. According to US, a power control mechanism is employed at the Secondary Transmitter (ST) to constrain the interference at the Primary Receiver (PR) below a certain threshold. However, it requires the knowledge of channel towards PR at the ST. This knowledge can be obtained by estimating the received power, assuming a beacon or a pilot channel transmission by the PR. This estimation is never perfect, hence the induced error may distort the true performance of the US. Motivated by this fact, we propose a novel model that captures the effect of channel estimation errors on the performance of the system. More specifically, we characterize the performance of the US in terms of the estimation-throughput tradeoff. Furthermore, we determine the maximum achievable throughput for the secondary link. Based on numerical analysis, it is shown that the conventional model overestimates the performance of the US.

We present a stochastic model for analyzing the performance of multiple-input multiple-output (MIMO) diversity in a downlink heterogeneous cellular network. Multi-antenna receivers are assumed to perform maximal-ratio combining (MRC). We consider interference-blind (IB) MRC and interference-aware (IA) MRC, where the latter takes the interference power at each antenna into account. Using tools from stochastic geometry, we derive the coverage probability for both types of MRC as a function of various tier-specific system parameters, including the number of base station transmit antennas in each tier. The model is then used to compare the performance of IB-MRC and IA-MRC. One important insight is that IA-MRC becomes less favorable than IB-MRC in a transmit-diversity system due to a larger interference correlation across receive antennas.

The radar waveforms OFDM and chirp sequence are numerically compared in terms of receiver operating characteristic, accuracy in range and Doppler estimation and necessary signal bandwidth. By means of Monte Carlo simulations, fairly equal performace is shown, which supports a previous analytical result by the authors, which revealed that both signals yield the same baseband signal under narrowband assumption and negligible range-doppler-coupling in the chirp sequence waveform. However, as unambiguous range and Doppler get large, chirp sequence needs prohibitively more bandwidth than OFDM.

This paper presents a weighted least squares algorithm for passive localization using Time Difference of Arrival in multipath scenarios. The algorithm is based on the direct or one-step approach for position estimation using distributed sensors and requires no knowledge about the number of received multipaths, the transmitted signal or the transmit time. Delayed signal paths arriving due to multipath propagation are considered and treated as interference to the localization problem. Simulation results show a better and more robust performance of the algorithm, compared to conventional two-step localization algorithms.

Filter bank multicarrier is one of the candidates for next generation mobile radio systems. Using filtered sub-channels reduces side-lopes as well as interference among sub-channels. Symbols overlap in time and are not separated by a cyclic prefix resulting in inter-symbol inference as well as interference from adjacent sub-channels under multi-path propagation. Equalization methods known from OFDM can not be directly applied. However, a linear per-subchannel equalizer with minimum mean-squared error has been proposed. This has also been used for iterative decoding and equalization by remodulating decoded symbols to cancel-out interference. In this short paper, we extend this concept and derive a MMSE equalizer using soft interference cancellation. Using soft-information increases performance and enables turbo equalization for filter bank multicarrier systems.

Conventional peak detection algorithms are not designed to include information on the expected peak shape. Therefore, commonly used detectors discard this valuable information and do not perform optimally in regard to the given possibilities. Designed and evaluated is a detector based on an artificial neural network, which is employed for pattern recognition in order to exploit the peak shape information. The detector outperforms the best detector using no peak shape information with a detection rate increase of up to 10\% at a constant false alarm rate. The proposed detection method is compared with a threshold detector and an ordered statistics constant false alarm rate (OS-CFAR) detector commonly used in radar. The introduced detector provides useful information on the reliability of the peak detection. Furthermore, it is shown that the neural network based detection mechanism is easily employable on hardware because no knowledge about the signal-to-noise ratio of the training data is needed.

Industrial environments often exhibit harsh propagation conditions for wireless transmissions. This paper investigates the influence of different interference characteristics on the performance of IEEE 802.15.4 using the OQPSK and Chirp Spread Spectrum (CSS) PHY. Bit error rates are determined for AWGN, Rayleigh fading and self-interference scenarios. GNU Radio, a Software Defined Radio framework, serves as simulation environment. In addition to the implementation of the CSS transmitter and receiver, a low-complexity synchronization algorithm, which only consists of a correlator and a second order Phase Locked Loop (PLL), and its limitations are presented. Furthermore, MAC layer simulations are performed for beacon-enabled (slotted) as well as nonbeacon- enabled (unslotted) mode to make a statement about achievable throughput and latency in the presence of interference. It shows that the CSS PHY clearly surpasses the OQPSK PHY in throughput. Moreover, the simulation results are confirmed by the derivation of the theoretical maximum throughput for the investigated PHY layers.

We study multiple-input-multiple-output (MIMO)-based downlink heterogeneous cellular networks (HetNets) with joint transmit-receive diversity using orthogonal space-time block coding at the base stations (BSs) and maximal-ratio combining (MRC) at the users. MIMO diversity with MRC receivers is particularly appealing in cellular networks due to the relatively low hardware complexity at both the BS and the user device. Using stochastic geometry, we develop a tractable stochastic model for analyzing such HetNets taking into account the irregular and multitier BS deployment. We derive the coverage probability for both interference-blind (IB) and interference-aware (IA) MRC as a function of the relevant tier-specific system parameters such as BS density and transmit (Tx) power, number of Tx antennas, and path-loss law. Important insights arising from our analysis for typical HetNets are as follows: 1) IA-MRC becomes less favorable than IB-MRC with Tx diversity due to the smaller interference variance and increased interference correlation across receive (Rx) antennas; 2) ignoring spatial interference correlation significantly overestimates the performance of IA-MRC; and 3) for a small number of Rx antennas, selection combining may offer a better performance-complexity tradeoff than MRC.

Base station (BS) cooperation is set to play a key role in managing interference in dense heterogeneous cellular networks (HCNs). Non-coherent joint transmission (JT) is particularly appealing due to its low complexity, smaller overhead, and ability for load balancing. However, a general analysis of this technique is difficult mostly due to the lack of tractable models. This paper addresses this gap and presents a tractable model for analyzing non-coherent JT in HCNs, while incorporating key system parameters such as user-centric BS clustering and channel-dependent cooperation activation. Assuming all BSs of each tier follow a stationary Poisson point process, the coverage probability for non-coherent JT is derived. Using the developed model, it is shown that for small cooperative clusters of small-cell BSs, non-coherent JT by small cells provides spectral efficiency gains without significantly increasing cell load. Further, when cooperation is aggressively triggered intra-cluster frequency reuse within small cells is favorable over intra-cluster coordinated scheduling.

Understanding the performance of cognitive relay networks (CRNs) is of great interest. Recently, stochastic geometry is being used to model and characterize the performance of CRNs. It is a known fact that sensing is an integral part of the CRN, however, in most cases it is not perfect. Moreover, the model inaccuracies caused by simplifications and/or approximations when deriving the analytical expressions for characterizing CRNs may distort their true performance. With no sensing in the system, we determine a lower performance bound (LPB) that can be used to judge the reliability of other systems that include sensing and model approximations. Based on the LPB, the operating characteristics (OC) for the CRN are obtained, which determine the joint performance of the primary and secondary system. Finally, OC are used to investigate the system performance under different scenarios.

Coexistence by means of shared access is a cognitive radio application. The secondary user models the slotted primary users channel access as a Markov process. The model parameters, i.e, the state transition probabilities (α,β) help secondary user to determine the channel occupancy, thereby enables secondary user to rank the primary user channels. These parameters are unknown and need to be estimated by secondary users for each channel. To do so, the secondary users have to sense all the primary user channels in every time slot, which is unrealistic for a large and sparsely allocated primary user spectrum. With no other choice left, the secondary user has to sense a channel at random time intervals and estimate the parametric information for all the channels using the observed slots.

Despite being ubiquitous in practice, the performance of maximal-ratio combining (MRC) in the presence of interference is not well understood. Because the interference received at each antenna originates from the same set of interferers but partially decorrelates over the fading channel, it possesses a complex correlation structure. This paper develops a realistic analytic model that accurately accounts for the interference correlation using stochastic geometry. Modeling interference by a Poisson shot noise process with independent Nakagami fading, we derive the link success probability for dual-branch interference-aware MRC. Using this result, we show that the common assumption that all receive antennas experience equal interference power underestimates the true performance, although this gap rapidly decays with increasing the Nakagami parameter mIof the interfering links. In contrast, ignoring interference correlation leads to a highly optimistic performance estimate for MRC, especially for large mI. In the low outage probability regime, our success probability expression can be considerably simplified. Observations based from the analysis include the following: 1) For small path loss exponents, MRC and minimum mean square error combining exhibit similar performance, and 2) the gains of MRC over selection combining are smaller in the interference-limited case than in the well-studied noise-limited case.

While the performance of maximum ratio combining (MRC) is well understood for a single isolated link, the same is not true in the presence of interference, which is typically correlated across antennas due to the common locations of interferers. For tractability, prior work focuses on the two extreme cases where the interference power across antennas is either assumed to be fully correlated or fully uncorrelated. In this paper, we address this shortcoming and characterize the performance of MRC in the presence of spatially-correlated interference across antennas. Modeling the interference field as a Poisson point process, we derive the exact distribution of the signal-to-interference ratio (SIR) for the case of two receive antennas, and upper and lower bounds for the general case. Using these results, we study the diversity behavior of MRC and characterize the critical density of simultaneous transmissions for a given outage constraint. The exact SIR distribution is also useful in benchmarking simpler correlation models. We show that the full-correlation assumption is considerably pessimistic (up to 30% higher outage probability for typical values) and the no-correlation assumption is significantly optimistic compared to the true performance.

This paper presents a tractable model for analyzing noncoherent joint-transmission base station (BS) cooperation, taking into account the irregular BS deployment typically encountered in practice. In addition to cellular-network specific aspects, such as BS density, channel fading, average path loss, and interference, the model also captures relevant cooperation mechanisms, including user-centric BS clustering and channel-dependent cooperation activation. The locations of all BSs are modeled by a Poisson point process. Using tools from stochastic geometry, the signal-to-interference-plus-noise ratio (SINR) distribution with cooperation is precisely characterized in a generality-preserving form. The result is then applied to practical design problems of recent interest. We find that increasing the network-wide BS density improves the SINR, while the gains increase with the path loss exponent. For pilot-based channel estimation, the average spectral efficiency saturates at cluster sizes of around seven BSs for typical values, irrespective of backhaul quality. Finally, it is shown that intra-cluster frequency reuse is favorable in moderately loaded cells with generous cooperation activation, while intra-cluster coordinated scheduling may be better in lightly loaded cells with conservative cooperation activation.

This work analyzes the gains of cooperative relaying in interference-limited networks, in which outages can be due to interference and fading. A stochastic model based on point process theory is used to capture the spatial randomness present in contemporary wireless networks. Using a modification of the diversity order metric, the reliability gain of selection decode-and-forward is studied for several cases. The main results are as follows: the achievable spatial-contention diversity order (SC-DO) is equal to one irrespective of the type of channel which is due to the ineffectiveness of the relay in the MAC-phase (transmit diversity). In the BC-phase (receive diversity), the SC-DO depends on the amount of fading and spatial interference correlation. In the absence of fading, there is a hard transition between SC-DO of either one or two, depending on the system parameters.

Geolocation is an important topic nowadays. Among other applications, geolocation can be used by frequency regulators to monitor the time, frequency and space domain. In this case of a passive geolocation system, Time Difference of Arrival (TDOA) is often used. In this paper we analyze a geolocation system based on a combination of TDOA and Received Signal Strength Differences (RSSD). The benefit of combining the two measurement types is shown using the Cramer Rao Lower Bound (CRLB). The suitability of the Unscented Kalman Filter (UKF) as an algorithm for the hybrid geolocation system is investigated. Simulation results show that by using the UKF, the instability of RSSD geolocation, that is often caused by bad geometry, is compensated. The UKF nearly approaches the CRLB and greatly outperforms the previously proposed least squares hybrid solution. Using the UKF, the information about the signal power can be definitely used to enhance the position estimation accuracy.

Turbo equalization is a promising approach to deal with the inter-symbol interference when transmitting over frequency selective radio channels. The iterative exchange of soft information between the equalizer and the decoder improves the decision reliability and hence reduces the bit error probability compared to conventional receivers. However, the processing of real-valued soft information with floating point precision causes high memory consumption and complex arithmetic logic units. In this paper, the effects of a fixed-point implementation of linear minimum mean square error (MMSE) based turbo equalizers with soft cancellation (SC) are studied. The applied soft-input soft-output (SISO) algorithms are analyzed concerning the value range and efficient fixed-point representations are derived. Results show, that even for small word lengths of 8 bit, the performance loss is negligible.

We discuss the performance of an adaptive FH-CDMA ad hoc network under the influence of external interference where node positions are modeled by a homogeneous Poisson point process. The optimum channel assignment that balances internal network interference due to spatial reuse and external interference is derived analytically for a path loss and Rayleigh fading model. The performances of the resulting hopping strategies are then compared to various suboptimal hopping strategies such as non-adaptive hopping and min-max allocation with constant QoS. It is found that adaptivity offers a benefit only at low to medium node densities and that a good suboptimal strategy can be based on hard exclusion of bad channels (thresholding) with optional min-max allocation to balance the load of active channels.

We study the interference and outage statistics in a slotted Aloha ad hoc network, where the spatial distribution of nodes is non-stationary and isotropic. In such a network, outage probability and local throughput depend on both the particular location in the network and the shape of the spatial distribution. We derive in closed-form certain distributional properties of the interference that are important for analyzing wireless networks as a function of the location and the spatial shape. Our results focus on path loss exponents 2 and 4, the former case not being analyzable before due to the stationarity assumption of the spatial node distribution. We propose two metrics for measuring local throughput in non-stationary networks and discuss how our findings can be applied to both analysis and optimization.

Recently, OFDM radar has gained attention as new algorithms for range and Doppler estimation specific to OFDM signals have been developed. The major advantage of OFDM is that it is both well-suited for radar processing as well as being suitable for communication. In previous work, we have proposed parametrizations for OFDM signals which suit the radar problem well. However, the proposed algorithms are independent of the OFDM signal parametrization, and it is therefore interesting to see how well they work with other, more commonly available signals. For this paper, we examine a common type of signal-OFDM signals according to the IEEE 802.11a standard-and determine how they could be used in a radar application.

Orthogonal frequency division multiplexing (OFDM) is a transmission technique which divides a given frequency band into subbands such that the subcarriers are mutually orthogonal. Because of its favourable transmission properties, OFDM is widely used in wireless communications. Recently it was shown that it is possible to extract information about distance and speed of obstacles from OFDM scatterings as in a radar system. The combination of communications and radar in a single OFDM system for automotive applications was named OFDM Radar. In this paper a simple multi user access scheme for OFDM Radar is proposed and its implications on radar detector design are discussed. The proposed scheme is a variant of OFDMA based on the idea that each user chooses independently a subset of the available OFDM carriers for transmission. The chosen subcarriers can be spaced arbitrarily. A suitable detector which is furthermore capable of multiple target detection is derived and its performance in various scenarios is demonstrated using Monte Carlo simulations.

Automatic classification of the modulation type of an unknown communication signal is a challenging task, with applications in both commercial and military contexts, such as spectrum surveillance, cognitive radio, and electronic warfare systems. Most of the automatic modulation classification (AMC) algorithms found in the literature assume that the signal of interest has been transmitted using a single antenna. In this paper, a novel AMC algorithm for multiple input multiple output (MIMO) signals is proposed, which employs fourth-order cumulants as features for classification. First, perfect channel state information (CSI) is assumed. Subsequently, a case of more practical relevance is considered, where the channel matrix is unknown and has to be estimated blindly by employing independent component analysis (ICA). The performance of the proposed classification algorithm is investigated through simulations and compared with an average likelihood ratio test (ALRT) which can be considered as optimum in the Bayesian sense, but has a very high computational complexity.

We consider a single-hop frequency hopping (FH) mobile ad hoc network (MANET). To increase throughput orthogonal FH (O-FH) with hop-synchronous hopping can be used, thereby allowing collision-free transmissions under certain circumstances. However, as the MANET grows, hopping sequences must be re-used. As a result, nodes sharing the same sequence will experience deterministic collisions while others having a unique sequence will still communicate collision-free. This results in an \emph{unfair} interference situation and makes performance guarantees difficult to meet for all nodes simultaneously. In this paper, we propose a \emph{collision-balancing} FH (CB-FH) scheme to overcome this drawback. The CB scheme builds on O-FH and adapts the sequence set to balance interference among the nodes. We analytically study the characteristics of the adaptive sequences and analyze the resulting interference situation at the nodes. The performance is compared to uncoordinated FH (U-FH) and O-FH. It is found that CB-FH solves the problem of unfairness present in O-FH. Compared to U-FH, CB-FH yields considerable improvements in a wide range. Practical issues are discussed.

An analysis of narrow- and broadband interference robustness within an On-Off Keying/Binary Pulse Position Modulation based noncoherent multiband impulse radio ultra-wideband communication system is presented. Using the energy detector's processing gain closed-form expressions of the noise and interference related second order moment statistics at the output of an energy detection receiver are derived. This allows separate statements on the relative modulation specific processing gain with respect to various interference parameters.

Two OFDM radar algorithms (the Maximum Likelihood and a MUSIC-based algorithm) are introduced and their fundamental limits concerning accuracy are explained. To simplify the analysis, we research the special case of only one target in the radar's detection range, which facilitates the individual effects on the estimation quality. Through simulations, we can show that OFDM radar works well for this case.

We consider the influence of FDMA on the capacity region of wireless ad hoc networks with a small number of nodes. It is found that FDMA offers an additional degree of freedom that is beneficial in interference-limited networks. Furthermore, simulation results indicate that static FDMA channel assignment over a time division schedule can achieve rates comparable to dynamic channel assignment.

This paper investigates the performance of a wireless ad hoc network capable of dynamically coordinating a set of orthogonal frequency channels such that every receiver and its nearest interferer operate in different channels. The distribution of the ratio of the interference powers of the second and first interferer is derived to show that the nearest interferer has dominant character, particularly in the absence of fading. Lower and upper bounds on outage probability are derived for the path loss model. For Rayleigh fading, an approximation is presented. Simulation results show that nearest neighbor scheduling is beneficial, thereby avoiding interference effectively. In contrast to other techniques such as successive interference cancellation, the complexity of nearest neighbor scheduling remains comparatively low.

This paper studies the performance of ad hoc networks with local FDMA scheduling using stochastic point processes. In such networks, the Poisson assumption is not justified due to interdependencies between points introduced by scheduling. For this reason, an upper bound on the second reduced moment measure is derived. Using this result, two lower bounds on the success probability are given, based on the second order product density and a non-homogeneous Poisson approximation. The relative performance of local FDMA is compared to random channel access. It is shown that the relative outage probability reduction of local FDMA highly depends on the SIR threshold as well as on the ratio of transmission distance to orthogonalization distance. If these two quantities are small, the improvement is high; the number of channels has only a minor effect on the relative improvement.

This paper investigates robustness of a non-coherent multi-band impulse radio ultra-wideband communication system with respect to narrow-band interference. A statistical analysis of interference at the energy detector output gives insight into its impact and system dependency. Furthermore, the potential of interference mitigation is shown and verified with respect to the processing gain.

We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for small signal-to-noise ratios when incremental relaying is used. We show that the ratio between the outage capacities of BAF and the cut-set bound is independent of the relay position and that BAF is outage optimal for certain conditions on the target rate R. This is in contrast to decode-and-forward with incremental relaying, where the relay location strongly determines the performance of the cooperative protocol. We further derive the outage capacity for a network consisting of an arbitrary number of relay nodes. In this case the relays transmit in subsequent partitions of the overall transmission block and the destination accumulates signal-to-noise ratio until it is able to decode.

We analyse mobile propagation channels which occur in the context of car-to-car communications in the 24~GHz ISM band. From the information gathered, we design robust frame designs for combined radar and communication systems using high-bandwidth OFDM signals. Two solutions are proposed: the combination of a spread spectrum technique and a standard convolutional encoder, as well as a low rate Reed-Muller code. We can show that while both perform well enough for the channels analysed, the Reed-Muller code has some advantages for the RF system, but achieves lower data rates.

We present the ε-outage capacity in the low signal-to-noise ratio (SNR) regime of an incremental relaying network. The network consists of one source, one destination, and two half-duplex relays. The one-bit feedback from the destination node is considered to be imperfect and is modeled as binary symmetric channel. The basic idea is that in each block only one terminal transmits depending on the feedback information in order to achieve a better use of the degrees of freedom of the channel. We derive a closed-form expression of the ε-outage capacity and show that the quality of the feedback link has a great influence on the ε-outage capacity of the network. We further examine an extension to the "usual" incremental relaying protocol by allowing the relays to overhear the transmissions of each other in order to increase their own decoding probability. This novel incremental relaying protocol performs close to the cut-set bound (within 0.5 bit/s/Hz).

In this paper we investigate a cooperative mobile network with respect to error performance. Power allocation is applied between source and relay. The relay cooperates after having received a request from the destination which decides upon successful or non-successful transmission based on a threshold criterion. We show that with respect to the relay's location a suitable power allocation technique can increase performance enormously. Our results reveal that a practical implementation strategy for cooperative networks first proposed in can easily be adopted to cognitive networks where a relay senses its environment for feedback signals from the destination. Depending on the applied services, however, it may be beneficial to always cooperate, since this creates spatial diversity at the destination.

The design process of a joint radar and communication system employing OFDM is analyzed. In particular, the question on how to choose OFDM modulation parameters such as carrier distance, guard interval length, frame length or pilot design is studied. Such systems use the same OFDM frames to transmit data and image the surroundings, so both radar and communication are affected by the choice of these parameters. The main design criteria for the radar component are accuracy of distance and speed measurements, whereas the communication subsystem needs to be designed such that it transmits robustly through a mobile communication channel. As these design criteria often are antipodal, arguments for choosing a particular set of modulation parameters are discussed. The presented design process is applied to the case of a vehicular (car-to-car) communication, in which moving participants communicate in the 24 GHz range.

Compressed sensing and the related recently introduced smashed filter are novel signal processing methods, which allow for low-complexity parameter estimation by projecting the signal under analysis on a random subspace. In this paper the smashed filter of Davenport et al. is applied to a principal problem of digital communications: pilot-based time offset and frequency offset estimation. An application, motivated by current cognitive radio research, is wide-band detection of a narrowband signal, e.g. to synchronize terminals without prior channel or frequency allocation. Smashed filter estimation and maximum likelihood-based, uncompressed estimation for a signal corrupted by additive white Gaussian noise (matched filter estimation) are compared. Smashed Filtering adds a degree of freedom to signal detection and estimation problems, which effectively allows to trade signal-to-noise ratio against processing bandwidth for arbitrary signals.

We consider a wireless relay network in a Rayleigh fading scenario where transmission power as well as transmission time per user are optimized. The criterion of optimization is the capacity. We apply an optimization algorithm based on Brent's method. Hence, we employ parabolic interpolation for finding the optimum whenever possible in order to achieve a faster convergence. If parabolic interpolation is not suitable, we use golden section search which is a robust root-finding method. Optimization takes place in two steps. First, we optimize power allocation and consider time as parameter. Second, time is optimized. We demonstrate that, depending on the cooperation strategy, remarkable capacity gains over direct transmission can be achieved by multi-routing. However, for a high overall transmission power, direct transmission outperforms multi-hopping. Generally, capacity gains increase with decreasing overall system power, which demonstrates that relaying is beneficial for low overall transmission powers.

We derive the e-outage capacity of a wireless relay network where relaying only takes place if the destination has not been able to decode the source message. We refer to this scheme as incremental relaying. The relays use space-time block coding and perform decode-and-forward. We compare incremental relaying to transmit diversity in terms of e-outage capacity and signal-to-noise ratio gain. It is demonstrated that incremental relaying outperforms transmit diversity only in certain regions that determine the relay locations. Moreover, our results confirm the well-known fact that decode-and-forward is especially preferable if the relays are located close to the source.

We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the e-outage capacity of the cut-set bound and demonstrate that the ratio between the e-outage capacity of incremental relaying and the cut-set bound lies within 1/¿2 and 1. Furthermore, we derive lower bounds on the e-outage capacity for the case of K relays.

We perform market-oriented management of the reverse link of a CDMA cell populated by data terminals, each with its own data rate, channel gain, willingness to pay (wtp), and link-layer configuration, and with energy supplies that are limited for some, and inexhaustible for others. For both types, appropriate performance indices are specified. A terminal pays in proportion to its fraction of the total power at the receiver, which directly determines its signal-to-interference ratio (SIR), and hence its performance. Hence, a terminal can individually choose its optimal power fraction without knowing the choices made by others. The network sets for each terminal an individual price that drives the terminal to the "revenue per Watt" maximiser. An optimal link-layer configuration can be identified through this analysis. Distinguishing features of our model are: (i) the simultaneous consideration of both limited and unlimited energy supplies, (ii) the performance metrics utilised (one for each type of energy supply), (iii) the generality of our physical model, and (iv) our focus on the fraction of total power at the receiver allocated to a terminal.

To increase area spectral efficiency, overlay use of spectrum already assigned to a primary system is considered in the context of cognitive radio research. Minimizing interference with the primary system is a key requirement and equivalent to the problem of transmission opportunity identification. Transmission opportunities are unused slots in the communication space which is spanned by time, frequency, and location. In this paper we describe a method to identify transmission opportunities by modeling the spatial power distribution with Gaussian processes. This approach to distributed sensing is verified with real-world measurements using the GSM downlink band as the primary system and contrasted with traditional wave propagation modeling approaches.

Overlay systems are a feasible approach to increase the efficiency of spectrum use. An independent secondary user (SU) system operates in the same frequency band as a primary user (PU) system. In order to avoid mutual interference, an important task of every SU system is to periodically monitor the PU system's allocation. In this paper, we investigate the question how many SUs have to be deployed in the system area of an ad hoc network in order to meet a given network wide detection probability and how this effects the false alarm probability (and thus the performance of the SU system). This is achieved with the help of geometric random graph theory and results from a distributed detection approach. In our investigations we consider a scenario with an infinite system area, and therefore neglecting border effects, as well as a scenario including border effects.

Dynamic spectrum allocation is a key technique to face spectrum scarcity and inefficient pre-allocation of resources in an environment of rapidly growing demands for mobile communications. By allowing operators to adaptively exchange transmission resources of their communication systems with each other by way of trading, short-term traffic variations can be addressed based on local actual demand. Concatenating trading areas and coarsening the time scale, pre-allocation of resources can be adapted with respect to long-term estimations of traffic, thereby building a hierarchic market framework for trading transmission resources. Numerical simulations show, that our approach can lead to a significant increase in resource usage.

On-off-keying with energy detection is a promising candidate when aiming at simple receiver concepts, due to the fact that simple energy detection reduces receiver complexity. On the other hand, data rates are low and interference mitigation by correlation is no longer possible. This paper proposes and analyzes a method for mitigating asynchronous interferers in energy detection receivers by adapting the maximum likelihood decision rule. It is shown that detection in the presence of interferers is improved and detection in absence of interferers is not declined.

In future multi-media applications dynamic access to spectral resources will play an important role. However, regulation of spectrum will only change very slowly and spectrum rights holders might not be willing to share their resources without gaining something out of it. Therefore the authors analyse the suitability of WiMAX as an overlay system on GSM where available resources will be auctioned among several competitors. The authors design a cross-layer approach to facilitate dynamic resource allocation. It is demonstrated that, with minor changes of the original WiMAX frame and a small signalling overhead which is currently unused, GSM resources can be allocated efficiently without decreasing system performance. Thus, this adapted WiMAX system used in opportunistic coexistence to GSM offers a suitable alternative to broadband service access.

The experience of ubiquitous and seamless ac- cess to heterogeneous mobile communication networks is one of the core issues of today's research. This comes along with an increasing demand in bandwidth. However, bandwidth as a natural resource is limited by technical constraints and, as several measurements have shown, is currently used very in- efficiently due to a static allocation. Consequently, we have to consider spectrum allocation techniques and employ use- ful applications for the detection of vacant frequency bands. In this paper, we present a novel, swarm-behavior based ap- proach for the detection of spectrum holes in cognitive wire- less networks. It is based on the fact that several cogni- tive radios form a cognitive network. This network is then split up into several cognitive sub-networks that collaborate among each other and scan the frequency range simultane- ously. Thus, several vacant frequency bands can be found and the overall processing time can be reduced. In addition, fading effects due to multi-path propagation can be met in a more efficient way.

With an increasing demand for mobile communications an efficient usage of the available spectral resources gains importance, since suitable frequency bands are limited. Although nearly all frequency bands are assigned to specified services and users causing a frequency shortage, measurements show that nevertheless there are a lot of unused spectrum holes in the time frequency domain, leading to an overall low spectral efficiency (M.A. McHenry et al., 2006). In this paper we consider an overlay scenario with an OFDM (orthogonal frequency division multiple access) based additional ad hoc overlay system operating in the same frequency band as the licensed system and exploiting the spectrum holes. Since spectrum sensing is a key issue for the coexistence of both systems we propose a method in the MAC (medium access control) layer for frame synchronization, enabling the coordination of allocation measurements. Furthermore, we point out some signal processing aspects regarding overlay systems.

Mismatches of the amplitudes and phases of the I and Q signal branches in quadrature receivers result in insufficient rejection of the image frequency band. Particular sensitiveness of modern re-configurable transceivers reinforces the need for efficient mitigation of I/Q imbalance. This paper introduces two algorithms for I/Q imbalance compensation: blind source separation and a novel low order statistics method. A signal-to-noise-and-distortion ratio based measure to evaluate the performance of the algorithms is used. It is observed that the results of I/Q imbalance compensation are highly coupled with the dependencies between the mismatches in the transmitter and the receiver. Therefore a known frequency offset in the transmitter is introduced. Due to this operation, the mismatches may be treated as two independent impairment sources, and the compensation is performed in two stages. Results of a theoretical study are verified by extensive Monte Carlo simulations for multipath fading environments.

With respect to the ever-growing demand for mobile communications on the one hand and spectral scarcity on the other hand it is necessary to increase spectral efficiency. In this paper, we focus on OFDM (Orthogonal Frequency-Division Multiplex) based overlay systems, which share a frequency band with already existing systems by adaptively filling the spectral holes. In order to enable such a co-existence, on the physical (PHY) layer promising methods for minimising mutual interference between the overlay system and the licensed systems are presented. The medium-access control (MAC) layer protocols are designed such as to be able to efficiently signal the available subcarriers as well as to handle the changing available bandwidth. A third issue is the joint optimisation of PHY and MAC parameters which is essential in order to optimally exploit the available spectrum with minimum signalling overhead.

The technical-economic performances of static (traditional) and auction-driven dynamic radio-spectrum allocation (FSA and DSA), and of an Utopian "federated" network (with all spectrum and customers) are compared. Spectrum licensees operate cellular CDMA networks populated by heterogeneous data-downloading terminals, which may coexist with ultra-wide-band (UWB) devices. A terminal has its own data rate, channel state, and "willingness to pay". The key performance figure is the economic value of total bits transferred. The Utopian regime always performs best, but is often nearly matched by DSA. The DSA "gain" over FSA ranges from a few percentage points to as high as (in idealised cases) 200%. The technical-economic impact of "high power" UWB under all regimes is considered.

Zero-IF (direct conversion) receivers are very sensitive to non-linearities of analog hardware. A phase and/or amplitude imbalance between the inphase and quadrature signal branch results in a base band signal deterioration known as I/Q imbalance. Especially OFDM and the OFDM-based MC-CDMA modulation technique are affected by this error. This paper proposes a novel orthogonal quaternary MC-CDMA spreading code scheme that uses the inherent mathematical symmetry to mitigate I/Q imbalance without additional computational cost.

The spectrum pooling strategy allows a license owner to share a part of his licensed spectrum with a secondary wireless system (the rental system, RS) during its idle times. The coexistence of two mobile systems on the same frequency band poses many new challenges, one of which is the reliable extraction of the channel allocation information (CAI), i.e. the channel occupation of the licensed system (LS). This paper presents a strategy for the extraction of the CAI based on exploiting the distinct cyclostationary characteristics of the LS and RS signals and demonstrates, via simulations, its application on a specific spectrum pooling scenario, where the LS is a GSM network and the RS is an OFDM based WLAN system

A critical obstacle for ultra wideband (UWB) communications is conformity to restrictions set on the allowed interference with other wireless devices. Using trains of N amplitude modulated basic pulses gives an FIR filter like design when disregarding the power spectral density (PSD) of the basic pulse. These leads to implementation losses and should be avoided. We quantify these losses and introduce an FIR filter design using semidefinite programming which can incorporate the basic pulse PSD by introducing non-constant upper bounds in the design. This leads to optimal designs and increases available signal power at no extra implementation complexity, just by choosing more optimal filter coefficients

The direct-conversion or homodyne receiver principle has received lots of interest in recent years for building flexible and compact radios. The homodyne architecture is, however, found to be rather sensitive to certain non-idealities of the analog front-end components. One big concern here is the amplitude and phase mismatches of the I and Q signal branches, resulting in insufficient rejection of the mirror frequency band. This paper presents an efficient low-order statistics based method (stat) for digital I/Q mismatch compensation, and compares the proposed technique with the blind signal separation (BSS) and hard decision (HD) based compensators proposed earlier by the authors. In addition to algorithm developments, big emphasis in the paper is on performance measurements and verifications carried out using measured true-world receiver front-end signals obtained from a laboratory homodyne measurement system. In general, the obtained results indicate that I/Q imbalance can be efficiently compensated using the proposed ideas. Even with really high-order modulation techniques, such as 64-QAM, close-to additive noise bound compensator performance is demonstrated using the measured signals

Investigations performed for future applications in various research areas allow users to communicate over more than one radio access technology with one single device. Thus, user terminals need methods to specify the quality of service provided by a radio access technology in order to decide about the radio access technology being used for a certain service or even to consider a possible change of an operator. In this paper a quality of service measure is proposed that allows the evaluation of services by certain service parameters, as, for example, a data transmission may be judged by the bit error rate, the overall network data rate or the delay. The measure defined in this paper bases on simple observation of frames resp. packets and can be applied for the assessment of any service property whose validity can be characterized by a simple decision whether or not a given quality of service was fulfilled.

The interference of ultra wideband (UWB) signals on conventional radio systems, called victims, is still an open issue. In this paper we show that not only the interference power but also the amplitude statistics have significant influence on the bit error rate (BER) of the victim. The amplitude probability distribution (APD) of UWB signals at the channel and inside the victim's receiver is studied analytically and verified by simulation. It is shown under which boundary conditions the UWB signal looses its pulsed behavior inside the victim's receiver. From this an interference model for the additional BER caused by UWB is proposed. The theoretical model is evaluated by simulations with a WLAN and a UMTS victim

Radio networks are designed to guarantee quality of service (QoS). This QoS guarantee is offered for customers with time varying load characteristics. Since the peak to average load of a network is usually very high the network utilizes the maximum capacity only for a fraction of time. Radio spectrum is a scarce resource and radio network providers pay huge amounts of money for licenses. For this reason applications with high QoS requirements are usually very expensive. For a better subscriber satisfaction the price for QoS should be as low as possible. From an economic perspective (X. R. et al., 2002), (U. Savagoankar et al.) the excess bandwidth could be disposed of in a secondary market. This would mean additional profit and by lowering the price for primary users the user satisfaction will increase. Surely there will be an optimum pricing strategy to maximize the profit. As a matter of fact, the QoS which can be offered in the secondary market is lower than the QoS which is offered in the primary market. In This work we will model a network which offers high QoS services to primary users and low QoS services for secondary users. The primary user applications are not queued whereas the secondary user applications are queued. Our focus is on a spectrum band at a dedicated frequency which is shared using a TDMA access scheme. We will model the traffic as Poisson arrival processes. Since the achievable QoS depends on the queue state of the network a state dependent pricing scheme for services in the secondary market will be applied. An acceptance function will characterize the behavior of the users in the secondary market.

The spectrum pooling concept allows the license owner of a spectral band to share a sporadically used part of his licensed spectrum with a renter system, until he needs it himself. For the smooth operation of a spectrum pooling system, the license owner has to have absolute priority to access the shared spectrum. This means that the renter system has to monitor the channel and extract the channel allocation information (CAI), i.e. it has to detect which parts of the shared spectrum the owner system accesses in order to vacate immediately the frequency bands being required by the license owner and to gain access to the frequency bands which the license owner has stopped using. The paper proposes exploiting the cyclostationary properties of the spectrum owner signal for the extraction of the CAI in a specific spectrum pooling scenario, where the license owner is a GSM network and the spectrum renter is an OFDM based WLAN system.

Reconfigurable software radio equipment is seen as the key technology in the evolution of mobile communications. One of the most important properties of a software radio terminal is that it is capable of using a wide range of air interface standards, providing a seamless interoperability between different standards and an enhanced roaming capability. One of the key functions supporting this multimode operation is the air interface recognition. A Software radio terminal has to be capable of detecting, recognizing and monitoring the air interfaces available in the frequency environment. In our paper, we propose exploiting the distinct cyclostationary properties of different air interface signals as features for air interface recognition.

The understanding of design approaches to modular software defined radio (mod-SDR) are of immediate relevance for offering flexible services to mobile users, by means of a single communication device. Both the potential of modular hardware/software for short time to market and the capability of mastering diverse data transmission modes under a unified multiprocessing framework are the motivation for research efforts in this field. In the present paper we continue to study half-frame pipelining (HFP) as a method for scheduling software modules on a particular two-processor hardware. We compare the properties of HFP to those of graph duplication pipelining (GDP) for both circuit-switched and packet-switched services. Based on computer simulations of both a generalized SDR environment and the example of an IEEE 802.11a WLAN communication system, we conclude on the utility of these pipelining methods for operating Mod-SDR terminals.

Public cellular networks have experienced exponential increase in service demand in recent years. Hence, the public mobile radio spectrum has become a scarce resource while other spectral ranges are only rarely used. Here, a new strategy called spectrum pooling is considered. It aims at enabling public access to rarely used spectral ranges without sacrificing the transmission quality of the actual license owners. The quality of service boundaries in such a system are investigated as demanding wireless multimedia applications produce more and more interest among wireless users. Simulations have been conducted in a spectrum pooling specifically modified HIPERLAN/2 testbed, revealing achievable service guarantees with respect to throughput and delay under different wireless weighted fair scheduling policies. Simulation results show that service guarantees can be met across a wide range of activity (arrival rate) of the accessing license owners. However, if certain activity thresholds are exceeded, service guarantees - especially delay guarantees - have to be renegotiated. Furthermore, performance evaluations concerning the different scheduling policies in a spectrum pooling system are given.

Ultra wideband (UWB) radios are characterized by the extreme wide bandwidth of their radiated signal. Although in the last years the research and development was focused on systems which use baseband pulse transmission, UWB is defined by its power spectral density and is therefore not restricted to baseband impulse radios. In this paper we propose an alternative system based on multicarrier code division multiple access (MC-CDMA). In addition to the general advantages of multicarrier transmission, MC-CDMA UWB promises also benefits especially in UWB radios, like transmitter range, frequency notching and narrowband suppression, which are described in this paper.

Spectrum for mobile networks is becoming scarce and on the other hand plenty of sporadically used frequencies exist. The spectrum utilization of such spectra is very low, which is a reason to think about a way to make them available for commercial purpose without a drawback for the license owners. We recommend a strategy called spectrum pooling which is based on this idea. The notion spectrum pool was first mentioned by Mitola III (see Proc. IEEE International Workshop on Mobile Multimedia Communications, p.3-10, 1999). In a spectrum pooling system the license owner of the spectrum allows priorly specified candidate renters to use his spectrum until he needs his spectrum himself. The renters of the spectrum may be treated in two different ways. One way is that communication processes of spectrum renters can persist as long as there are channels for the processes of the license owners. The other way is that the owner has no knowledge whether the channels are occupied by renters or not and treat the channels used by renters like free channels. In both cases the renters have to measure the interference level in the channel after dedicated time intervals and have to leave the channel within the time interval T/sub p/ as soon as the interference exceeds a prior specified threshold. We compare the spectrum utilization, blocking probability and forced termination probability for these two different channel access schemes.

The family of international standards for mobile communications IMT-2000 includes amongst others the Universal Terrestrial Radio Access (UTRA) proposal, which consists of two modes: frequency division duplex (FDD) and time division duplex (TDD). Both are in principle wideband CDMA (W-CDMA) systems. Conventional detectors like the RAKE receiver do not decrease the multiple access interference (MAI). For a further improvement of system capacity multiuser detectors (MUD) should be applied. But the computational effort for such algorithms is high. In this paper a new approach based on linear MUD with FFT speed (Vollmer et al. 1999) is investigated for the high rate data transfer mode in UTRA-FDD.

In this paper the use of the polynomial expansion (PE) detector as a multiuser detector (MUD) for UTRA-TDD is discussed. The PE detector can iteratively approximate either the decorrelating or the MMSE (minimum mean-squared error) MUD. This is possible without the computationally intense matrix inversion operation (cubic complexity in the number of users: O(K/sup 3/)), which is needed for the decorrelating and the MMSE detector. In this paper it is shown that the operations for the PE detector can be arranged such that they only have a complexity of O(K/sup 2/), in all processing levels. New simulation results for an UTRA-TDD simulation environment show that the detector achieves a performance (in terms of BER) close to that of the MUD which it approximates (decorrelating or MMSE). Additionally, it is shown how the number of iterations can be reduced significantly, while achieving the same BER performance.

Two radial-basis function (RBF) based detectors which are used as multiuser detectors (MUD) for the UTRA-TDD mode of IMT-2000, are presented. One of the RBF detectors is chip level based (CLB) and the other is preprocessesing based (PPB). A detailed performance evaluation, based on new simulation results of the RBF detectors in the UTRA-TDD system, is presented. These results illustrate that the detectors achieve low BERs, even for time-variant multipath propagation channels (pedestrian, vehicular test environment). Furthermore, it is shown that the BER of the RBF based detector is virtually independent of the number of users. On the down side, the complexity of the detectors is significantly affected by the number of users.

This paper proposes a new technique for feature extraction of modulated signals which is based on a pattern recognition approach. The new algorithm uses the cross Margenau-Hill distribution, autoregressive modeling, and amplitude variations to detect phase shifts, frequency shifts, and amplitude shifts, respectively. Our method is capable of classifying PSK2, PSK4, PSK8, PSK16, FSK2, FSK4, QAM8 and OOK signals. Unlike most of the existing decision-theoretic approaches, no explicit a priori information is required by our algorithm. Consequently, the method is suitable for application in a general noncooperative environment. Furthermore, our approach is computationally inexpensive. Simulation results on both synthetic and "real world" short-wave signals show that our approach is robust against noise up to a signal-to-noise ratio (SNR) of approximately 10 dB. A success rate greater than 94 percent is obtained.

The classification of transient time-varying signals is important for industrial, biomedical and military applications. The attack phase of piano sounds is used as an example for transient, time-varying signals in a real data application. Discrete Fourier transform and time-invariant wavelet packet based algorithms are used alternatively for feature extraction. The training set is used for determining an appropriate feature selection. A classifier checks whether the generated features are sufficient in order to identify the correct piano. Classification results are presented and discussed.

A topical task is the classification of burst-like signals, e.g. in signal detection. Piano sounds are used here as an example. Different time-frequency methods including wavelet processing are used alternatively for feature extraction. A classifier checks whether the generated features are sufficient to identify the correct piano. Results of the real data signal processing are presented and discussed.

In today's SATCOM systems transparent transponders are widely used. This device is the most vulnerable component of the whole system. Signals which are received accidentally or introduced intentionally into the transponder band will be retransmitted, generating IM products and therefore reducing the available energy to the user signal. It is shown, that the bandwidth spreading of the user signal reduces the vulnerability. Two techniques, frequency hopping (FH) and direct sequence spread spectrum (DS-SS), are considered.