Emerging healthcare radio technologies are designed to operate in the 2.4GHz industrial, scientific and medical (ISM) band. Since both standardized (Bluetooth and Wi-Fi) and non-standardized (proprietary) devices use the same frequency band, the aggregate interference may significantly affect the performance of medical wireless systems. This paper characterizes the spatiotemporal spectrum occupancy and proposes models for the aggregate interference in hospital environments. In particular, time-frequency and cluster-based statistical models for the aggregate interference are developed based on network experimentation. The proposed models enable the design of wireless networks for e-health applications and medical services.

Bluetooth Low Energy (BLE) devices are becoming common in hospital scenarios. This technology is widely employed to collect patients' vital signs, to provide wireless connectivity to medical equipment, and to enable communications between devices carried by hospital personnel, patients and visitors. This paper presents a mathematical model to evaluate the impact of the interferences, from different wireless technologies, on the performance of a BLE-based body area networks operating over the 1 Mbit/s physical layer (PHY). The interfering technologies addressed are ZigBee (802.15.4), Wi-Fi (802.11), and the newly introduced BLE version 5.0 (coded PHY). The results for the latter are supported by real-life measurements, which are reported in this paper, thus giving some insight into the practical performance of this new technology. The presented numerical results provide guidance on how to manage these various technologies to minimize the packet error rate (PER) of the communications emanating from the on-body BLE enabled devices.

Dynamic off-body ultra wideband channels are examined by way of anechoic chamber measurements at a 3-5 GHz frequency band in frequency domain with a help of a fast sweeping vector network analyzer. Five antenna locations on the body are selected: right wrist, left wrist with an antenna on the palm or back side, left arm (AL) and left ankle (LA). The off body node is set at a pole (PO). Two in-house designed and manufactured prototype antennas, dipole and double loop, are used in cases with both similar and dissimilar antennas in a link. Depending on the case, the path loss (PL) ranges between 46.2-87.9 dB. The LA-PO has the highest and AL-PO the lowest average PLs. The PL amplitudes follow the inverse Gaussian distribution. Based on the level crossing rate the LA-PO has the deepest fading conditions and the AL-PO is the most stable link. The LA-PO has the largest average fade duration (AFD) at the thresholds below 0 dB. The AFD is larger on the average with the dipole than the double loop. The comparison of similar vs. dissimilar antenna pairs shows no major difference in the performance.

The smart home is an environment, where heterogeneous electronic devices and appliances are networked together to provide smart services in a ubiquitous manner to the individuals. As the homes become smarter, more complex, and technology dependent, the need for an adequate security mechanism with minimum individual's intervention is growing. The recent serious security attacks have shown how the Internet-enabled smart homes can be turned into very dangerous spots for various ill intentions, and thus lead the privacy concerns for the individuals. For instance, an eavesdropper is able to derive the identity of a particular device/appliance via public channels that can be used to infer in the life pattern of an individual within the home area network. This paper proposes an anonymous secure framework (ASF) in connected smart home environments, using solely lightweight operations. The proposed framework in this paper provides efficient authentication and key agreement, and enables devices (identity and data) anonymity and unlinkability. One-time session key progression regularly renews the session key for the smart devices and dilutes the risk of using a compromised session key in the ASF. It is demonstrated that computation complexity of the proposed framework is low as compared with the existing schemes, while security has been significantly improved.

To avoid idle listening and to improve energy efficiency in short range communication networks, a generic wake-up radio (WUR) based medium access control (GWR-MAC) protocol is proposed. GWR-MAC is not restricted to a specific WUR technology or data radio technology, and therefore it is suitable for a variety of scenarios in wireless sensor and body area networks. GWR-MAC includes a bidirectional wake-up procedure and a transmission period for data communication. Two different options for the wake-up procedure are defined: source-initiated and sink-initiated. The data transmission period can be implemented by using different type of channel access methods, which enables scalability. This paper describes the GWR-MAC protocol and an analytical model which is used to explore the energy efficiency of the proposed GWR-MAC based network and conventional duty cycle MAC based network. The comparison is done as a function of number of events to enable the selection of a correct radio technology for different application scenarios. The results clearly illustrate the usefulness and energy efficiency of the proposed protocol especially in applications that have low event frequency and require a low delay wake-up procedure.

One of the most important aspects of a wireless health monitoring system is the security of data. In this paper, security attacks against the complete transmission chain of a medical health monitoring system are enumerated and classified based on their threat to three security principles: confidentiality, integrity and availability. The communication chain is divided in a standard way into three tiers and relevant threats are identified for each tier. Security requirements corresponding to these threats are presented. It is noted that end-to-end security is not feasible due to distributed computing and the incompatibility of the data standards of different tiers.

In this paper, we analyze the effects of guaranteed time slots (GTSs) to the performance of IEEE 802.15.4 slotted Aloha (S-Aloha) medium access control (MAC) protocol utilizing impulse radio ultrawideband (IR-UWB) technology. IEEE 802.15.4e, amendment to IEEE 802.15.4 standard, defines an optional MAC scheme termed as deterministic and synchronous multi-channel extension (DSME). One of the key features of DSME is that it enables the MAC to operate in fully scheduled mode utilizing DSME-GTS slots for communications. The feasibility of DSME-GTSs is analytically derived in terms of throughput and it is verified by simulations performed in Opnet. Furthermore, the impact of DSME-GTSs for packet delivery ratio and delay is simulated in wireless hospital room scenario and the results are compared to contention-based operation of IEEE 802.15.4 MAC. The results show that significantly higher throughput and packet delivery ratio is achieved when IEEE 802.15.4 MAC operates in fully scheduled mode. In addition, fully scheduled mode guarantees upper bound for end-to-end data packet delay, and therefore it is the preferable mode for transmitting vital biomedical information.

New automated solutions are needed, e.g., in mining industry to improve efficiency and productivity of every process. In addition, costs have to be reduced, and health and safety of employees need to be enhanced. This paper studies vehicle-to-vehicle (V2V) communication to be utilized in, e.g., mining vehicles in a tunnel to increase safety and productivity of a transportation of mining goods. The objective of the paper is to experimentally evaluate maximum achievable range of WiFi radio in a real tunnel environment including line-of-sight (LOS) and non-LOS (NLOS) links. The measurement campaign was carried out in an artificial tunnel using commercial off-the-shelf WiFi radios and antennas. The experimental system was able to reach 150 m range when applying a single data stream, and 100 m for two simultaneous data streams without loss in throughput.

In this paper, we present statistical models for wideband and ultra-wideband (UWB) radio channels for working machine cabin environment. Based on a set of measurements, it was found that such a small and confined space causes mostly diffuse multipath scattering rather than specular paths. The amplitude of the channel impulse responses in the wideband case is mostly Rayleigh distributed small-scale fading signal, with only few paths exhibiting Ricean distributions, whereas the ones in the UWB case tend to be log-normally distributed. For the path amplitude, we suggest an exponential decay profile, which has a constant slope in dB scale, with the corresponding parameters for the UWB case. For the wideband case, a two-fold exponential decay profile provides excellent fits to the measured data. It was also noted that the root-mean-square (RMS) delay spread is independent of line-of-sight (LOS)/obstructed line-of-sight (OLOS) situations of the channel. The multipath components contributing significant energy play a major role in such a small environment if compared to the direct path. In addition, the radio channel gains are attenuated with the presence of a driver inside the cabin.

This paper investigates several maximum selection and serial search based code acquisition techniques for direct sequence spread spectrum receivers, which utilize either a single or multiple antenna elements. The techniques are studied with different combinations of threshold comparison and verification. Paper includes large number of analytical results calculated in static, fast and slow fading channels to obtain an insight of the performances of these methods. Numerical results will give an overview of the methods relative performance in different channels.

This paper investigates three code acquisition methods for direct sequence spread spectrum systems (DS/SS) utilizing smart antennas. The methods are suitable especially for receivers that consist of a smart antenna followed by a single correlator or a matched filter (IMF). The first method is the known fixed beam strategy where the whole angular uncertainty region is divided into small cells using conventional beamforming techniques. Therein, the receiver searches through all angular and delay cells via a serial search procedure. In the second method, the fixed division is made using advanced beamforming techniques, which provide improved tolerance against interference. In the third strategy, the direction-of-arrival (DOA) of incoming signals are estimated and utilized in the acquisition process. An advantage of this DOA estimation-based strategy, when compared to fixed beamforming methods, is a decrease in the region of uncertainty. Disadvantages are increased computational complexity and signal-to-noise ratio (SNR) limitations. The acquisition strategies are compared when the serial search acquisition of the code phase is made using either the correlator or the matched filter. The results indicate that a single antenna receiver gives the best acquisition performance when SNR is high. However, single antenna methods are sensitive to interference. On the other hand, DOA estimation-based methods offer shorter mean acquisition times than fixed beam methods, especially when the number of arriving signals is small.

In this paper, a performance analysis of orthogonal frequency-division multiplexing (OFDM) based ultra-wideband (UWB) systems with frequency-domain spreading is presented. A continuum of schemes from a plain nonspread OFDM scheme to a maximally spread multicode scheme via medium-spread combinations of the variable spreading factor (VSF) and multi- code transmissions is considered. The channel is assumed to be Rayleigh fading with exponentially decaying delay power profile. Furthermore, the analysis takes into account the intersymbol interference (ISI) caused by the multipath delay components exceeding the guard interval. Numerical results demonstrate that frequency-domain spreading can improve the performance remarkably when sufficient spreading factors and a suitable combining method is used.

In this paper, code synchronization probabilities of the direct sequence spread spectrum (DS/SS) system are investigated when the receiver utilizes an adaptive antenna array. Performance studies of three beam forming algorithms in the presence of direction-of-arrival (DOA) errors are presented. The investigated algorithms are the conventional, the minimum variance distortionless response (MVDR), and the MVDR+ADL where the MVDR algorithm is enhanced against DOA error via the adaptive diagonal loading (ADL). The paper includes a large number of analytical and simulation results where the effects of DOA errors are investigated. It can be concluded that the MVDR beam former is more sensitive to DOA errors than the conventional beam former, especially, at large DOA errors and high signal-to-noise-ratio (SNR) values. However, this sensitivity can be reduced notably by using the ADL.

This paper studies the performance differences of three low data rate ultra wideband (UWB) systems in interfered AWGN and multipath channels. The studied systems are based on ultra wideband frequency modulation (UWB-FM), direct sequence UWB (DS-UWB) and multiband orthogonal frequency division multiplexing (MB-OFDM). The systems are studied in very high and ultra high frequency bands (VHF/UHF), i.e. 230 - 390 MHz, and 6.336 - 7.920 GHz. The VHF/UHF channel model is based on the measurements carried out in typical Finnish forest, whereas channel model for 6.336 - 7.920 GHz band is based on the modified Saleh-Valenzuela model. The intentional interference locates at the centre of the studied band having a 20 MHz bandwidth. In the literature, the comparison of the different low data rate UWB systems is rather insignificant. Therefore, the results of this paper are filling up this evident gap. The same spectral allocation and data rate are used as a starting point for a study. In the lower band, DS-UWB seems to tolerate more interference than UWB-FM in AWGN and multipath channels. The interference power can be higher for UWB-FM than MB-OFDM without performance degradation in AWGN channel in the upper band. The system performance starts to decrease with the same interference power in the case of MB- OFDM and UWB-FM in the interfered multipath channels in the upper band.

In the simulation of multiple-input multiple-output (MIMO) radio systems, accurate channel models are needed. Channel models have to be approximated to reach reasonable complexity of practical radio channel simulators, but the approximation should not cause too high error in the simulation. The error of the MIMO correlation matrix can be measured via different metrics such as correlation matrix distance (CMD) and mean square error (MSE). This paper compares the different metrics of correlation error, and investigates the impact of different approximations on the MIMO correlation matrix. From the results it was found that a modified MSE (Mod-MSE) presented in this paper and CMD have quite similar behavior, but Mod-MSE is independent of the correlation matrix size and the level of the original correlation. Thus, Mod-MSE shows only the error on correlation. Channel model approximations are, e.g., limited number of impulse responses, phase error between the channels, and synchronization error in simulator start-up. The impact of the approximations is investigated via the CMD and Mod-MSE analysis. The results show that the number of impulse responses should be in the order of 100 000 or more, phase error of less than 5 degrees is acceptable, and the synchronization error is critical when highly correlated channels are simulated. Another result of this paper is that the Mod-MSE is more recommendable metric than CMD.

In this paper, a performance analysis for the frequency-domain code-division multiple-access (CDMA) of multiple simultaneously operating piconets (SOPs) in orthogonal frequency-division multiplexing (OFDM) based ultra-wideband (UWB) systems is presented. Two different strategies for the accommodation of multiples SOPs, namely, the variable spreading factor (VSF) scheme with minimal spreading and the multicode scheme with maximal spreading, were considered. The channel is assumed to be Rayleigh fading with exponentially decaying delay power profile. Furthermore, the analysis takes into account the intersymbol interference (ISI) caused by the multipath delay components exceeding the guard interval. Numerical results demonstrate that the frequency-domain CDMA can be employed to accommodate multiple SOPs while maintaining acceptable performance when a suitable subcarrier combining method is used. The VSF and multicode schemes result in a similar performance when the number of SOPs is large, while notable differences are pointed out when there are only a few SOPs.

A statistical characterisation of a small-scale fading mobile radio channel is presented and a fading simulator for the simulation of multiple input–multiple output multicarrier systems is introduced. The derivation of the equivalent lowpass channel as a function of time, transmit and receive antenna positions and subcarrier frequency, leads to a tapped delay-line model with time, space and frequency-selective taps. The taps are modelled as a sum of a deterministic line-of-sight or dominant scattered path and a zero-mean Gaussian part composed of a number of unresolvable scattered paths, and are therefore Rice fading. The Gaussian parts can have the desired temporal and spatiospectral correlations generated by time-correlation shaping filtering and a space–frequency correlation transformation, respectively. The structure and details of the simulator are presented, and the simulator is shown to achieve good accuracy while retaining a reasonable computational complexity.

This paper studies the effects of channel estimation in ultra wideband (UWB) systems using a multiband-OFDM (MB-OFDM) approach. The system used consists of a three-band OFDM transmitter, each band having 128 equally spaced subcarriers, which carry both the information data and the pilot signals. The channel estimation is based on the principle of pilot-symbol aided channel estimation (PACE), and it has been implemented using comb-type and block-type pilot subcarrier arrangements. The algorithms used here are based on the least squares (LS) and the linear minimum mean-square error (LMMSE) approaches supported by linear and cubic interpolation, and an IFFT-based time channel estimation, which uses a zero-padding interpolation approach with and without Wiener filtering. In frequency domain algorithms, phase compensation is also taken into account. Bit error rate (BER) versus signal-to-noise ratio Eb/N0results show that the frequency based methods generally perform better than the corresponding time based ones. Furthermore, the performances of LS and LMMSE methods are quite similar, leading us to suggest the use of LS estimator for uncoded MB-OFDM systems. Phase compensation is required in comb-type pilot sub-carrier arrangement when a low number of pilot sub-carriers is used

Multiband orthogonal frequency division multiplexing (MB-OFDM) and direct sequence ultra wideband (DS-UWB) systems' performances are studied in interfered AWGN channel. Co-existing systems, i.e., interference, are assumed to be based on the forth-coming 4G. The other source is 100 MHz interference located at IEEE802.11a band. The published studies related to the comparison between MB-OFDM and DS-UWB in interfering environments seems to be unsubstantial in the literature. Therefore, it is crucial to fill this gap. We focus more on MB-OFDM systems, whereas the DS-UWB is applied as a reference. The studied victim systems share the same frequency band and have similar data rates. Simulation results indicate that MB-OFDM system can slightly tolerate interference to achieve reasonable bit error rate level. DS-UWB achieves similar bit error rate level with higher interference-to-signal power ratio than MB-OFDM is able to do. The center frequency of interference has only minor effect on systems' performances. Increasing the bandwidth of the interference reduces the performance in the case of MB-OFDM, whereas DS-UWB seems to be quite resilient to it

Multicarrier code-division multiple access (MC-CDMA) is a promising multiplexing technique for future mobile radio systems, which require multirate transmission capability to efficiently support various services with wide range of data rates. In this paper, a generic performance analysis for the multicode and variable spreading factor multirate schemes in MC-CDMA is presented. Results comparing and pointing out notable differences in the error rate performance of these multirate schemes in conjunction with six different combining techniques are presented for the synchronous downlink and both the synchronous and asynchronous uplink. Furthermore, the analysis takes into account also the intersymbol interference caused by the multipath delay components exceeding the guard interval, which is commonly omitted in the literature.

In this paper, a generic performance analysis for the multicode and variable spreading factor (VSF) multirate schemes in a multicarrier code division multiple access (MC-CDMA) system is presented. In addition to the downlink channel, the analysis includes also both the synchronous and asynchronous uplink channels. Furthermore, the analysis takes into account the intersymbol interference (ISI) caused by the multipath delay components exceeding the guard interval, which is commonly omitted in the literature. Numerical results comparing and pointing out notable differences in the error rate performance of the two multirate schemes, different combining techniques, and spreading sequences are presented

A statistical characterization of a small-scale fading mobile radio channel is presented, and a fading simulator for the simulation of multiple input - multiple output (MIMO) multi-carrier systems is introduced. The derivation of the equivalent lowpass channel as a function of time, transmit and receive antenna locations, and subcarrier frequency, leads to a tapped delay line model with time, space, and frequency selective taps. The taps are modeled as a sum of a deterministic line-of-sight (LOS) or dominant scattered path and a zero-mean Gaussian part composed of a number of unresolvable scattered paths, and are therefore Rice fading. The Gaussian parts can have the desired temporal and spatiospectral correlations generated by time correlation shaping filtering and a space-frequency correlation transformation, respectively. The simulator is shown to achieve a good accuracy while retaining a reasonable computational load.

This paper introduces a method used for code synchronization in direct sequence spread spectrum (DS/SS) systems when the receiver is equipped with a smart antenna followed by the matched filter (MF). The presented method first estimates the direction-of-arrival (DOA) of the DS-signal, then performs beamforming, and finally makes synchronization decision based on the maximum output of the MF. Because the amount of data needed in DOA estimation depends on the prevailing signal-to-noise ratio (SNR), the proposed method operates iteratively. The method starts by collecting a piece of data for DOA estimation. Due to the inaccurate DOA estimation, the main beam of the radiation pattern may be steered to erroneous direction and code acquisition may be failed. After a fail more data is collected and the accuracy of DOA estimate improves. This process is repeated until DOA and delay estimation succeeds. The results show that it is advantageous to start by collecting only a small amount of data for DOA estimation because the shortest mean acquisition times are achieved in that case

Noncoherent detection is usually applied in frequency hopping (FH) systems, because reliable coherent detection is very difficult. With multiple symbol differential detection (MSDD) a noncoherent system can achieve the performance of coherent differentially encoded systems. Due to its is complexity, two computationally simpler hard-decision feedback algorithms, multiple-symbol based decision-feedback differential detection (MSD DF-DD) and multiple symbol observation interval (MSOI), are studied and compared in partial-band jammed FH system. Additionally the system which uses maximum-a-posteriori (MAP) algorithm as inner decoder is studied and its performance is compared to MSD DF-DD and MSOI. The performance improvement of the MSD DF-DD and MSOI using two simple limiters are also studied. The noniterative versions of MSD DF-DD and MSOI have very similar performance. MSD DF-DD benefits from the iterative processing more effectively than MSOI in jammed and nonjammed simulations. The impact of jamming depends strongly on its bandwidth. The narrower the jamming band is, the more the performance of the algorithms decrease. MAP-based decoding performs significantly better than either of the algorithms

In this paper, we investigate code acquisition in the delay and angular domain in environments where interference and noise are nonuniformly distributed in the spatial (angular) domain. It is seen that performance is clearly degraded by the presence of nonuniform spatial distributions of interference. The degree of impairment is related to the actual shape of the distribution and becomes more significant when large amounts of interfering power are concentrated in one or more angular directions. As compared to a reference case with a uniform distribution of equivalent interfering power, the mean acquisition time could increase by factors of up to four. Some effective approaches to compensate for the loss of performance due to the uneven nature of interference are also studied. First, the effect of search strategies in the delay and angular domains on acquisition performance is assessed. A searching algorithm up-ranking angular cells according to the amount of associated interference is proposed as one solution to reduce the performance gap. It is shown that applying this search strategy can considerably reduce the mean acquisition time. Finally, two adaptive schemes based on setting integration times or threshold values according to the level of interference prevailing in each angular cell, are discussed. The former approach returns performance figures similar to those obtained with the uniform equivalent interference distribution while the latter provide moderate performance gains.

This paper studies in-band interference of different kind of ultra wideband (UWB) signals. UWB frequency spectra are produced by using several types of narrow pulse waveforms, all based on the Gaussian pulse. Due to the extremely wide bandwidth, these signals spread over the frequency bands allocated to other radio systems. In-band interference power is calculated over the IF bandwidths of two victim receivers as a function of pulse width. Also, the signal attenuation with distance is presented. The victim systems under the study are GPS (L1-band) and GSM900. Based on the results, the 3/sup rd/ derivative of a Gaussian pulse seems to be the best choice, from the interference point of view, among the waveforms included in this study. It causes less interference than the Gaussian pulse or Gaussian doublet if the pulse widths are shorter than 1 ns. The system utilizing the direct sequence concept caused less in-band interference power than the system utilizing time hopping amongst all waveforms studied. The studied UWB systems are based on bi-phase baseband data modulation.

Analytical results are presented for a direct sequence spread spectrum system code acquisition in a static multipath channel. The performance measure is the mean acquisition time. The constant false alarm rate criterion is used as threshold setting rule for comparator. The energies of the multipath components are combined already in the acquisition process by using a modified chip level post detection integration. Therefore, diversity combining in the acquisition is used. The method increases the probability of detection of the burst of multipath components, ie, it decreases the mean acquisition time for finding the existence of a multipath profile. The numerical results indicate that the method improves the acquisition performance significantly. Also total acquisition time, ie, time to acquire all the multipaths can be decreased by the proposed method.

This paper evaluates the level of interference caused by different ultra-wideband (UWB) signals to other various radio systems, as well as the performance degradation of UWB systems in the presence of narrowband interference and pulsed jamming. The in-band interference caused by a selection of UWB signals is calculated at GSM900, UMTS/wideband code-division multiple-access (WCDMA), and Global Position System (GPS) frequency bands as a function of the UWB pulsewidth. Several short-pulse waveforms, based on the Gaussian pulse, can be used to generate UWB transmission. The two UWB system concepts studied here are time hopping and direct sequence spread spectrum. Baseband binary pulse amplitude modulation is used as the data modulation scheme. Proper selection of pulse waveform and pulsewidth allows one to avoid some rejected frequency bands up to a certain limit. However, the pulse shape is also intertwined with the data rate demands. If short-pulses are used in UWB communication the high-pass filtered waveforms are preferred according to the results. The use of long pulses, however, favors the generic Gaussian waveform instead. An UWB system suffers most from narrowband systems if the narrowband interference and the nominal center frequency of the UWB signal overlap. This is proved by bit-error rate simulations in an additive white Gaussian noise (AWGN) channel with interference at global system for mobile communication (GSM) and UMTS/WCDMA frequencies.

The extension of conventional delay-domain code acquisition to the angular domain is explored. The uncertainty region is partitioned into a number of delay and angular cells. In single-path channels where the interference is modeled as temporarily and spatially white, there exists an optimum number of angular cells minimizing the mean acquisition time. Mean acquisition times up to three times shorter can be attained with the two-dimensional approach. A rather similar behavior is in general found in Lth-order equal amplitude multipath channels, where paths are contiguous in the delay or angular domains. The strategy employed to search through the uncertainty region may have a considerable impact on acquisition performance. The results reveal that the search should proceed not in the direction of the multipath spread but in the other available domain. Proper selection of the search strategy can reduce the synchronization time by a factor of up to two. Two-dimensional code acquisition in scenarios with spatially nonuniform interference is also investigated. In general, the acquisition performance is degraded by the presence of nonuniform interference in the angular domain.

This paper introduces analytical results for code acquisition of a DS spread spectrum system in which either continuous pilot (CP) or burst pilot (BP) is used. Emphasis is in the performance and restrictions of Doppler shift, which is taken into account as signal-to-noise decreases. The performance measure is the mean acquisition time. Constant false alarm rate criteria are used as threshold setting rules for comparison. Numerical results indicate that the burst pilot method outperforms the continuous pilot method significantly when the average transmitter power is kept the same.

This paper compares the meaning of different threshold setting principles in the code acquisition process of a direct sequence (DS) spread spectrum (SS) receiver. The consideration is made mainly in one-path additive white Gaussian noise (AWGN) channel. A consideration to a fixed multipath channel is given to see its effect on the results. Also, a consideration for a certain type of fading is given in a case where the signal power is assumed to be considerably lower, i.e., faded, part of the time. For the possible performance measures of code acquisition, the main interest is in the mean acquisition time T/sub MA/. The probability of the acquisition in a given observation interval P/sub acq/ is also considered to see if different measures have different demands. A matched filter (MF) acquisition is used with and without a verification mode using an active integration. In the comparisons, fixed thresholds, thresholds based on constant false alarm rate (CFAR) criteria, and optimal thresholds in the sense to give either the minimum T/sub MA/ or the maximum P/sub acq/ are used. The results, which are obtained by using a method of selecting the maximum value at the output of the MF, are compared to the threshold cases. The results can be summarized as follows: when the performance measure is T/sub MA/, the best results are obtained by using CFAR-based threshold comparison. By a proper selection of the probability of a false alarm, the same performance is obtained as by using the optimal thresholds. When the performance measure is P/sub acq/, the maximum-selection method is the best choice.

This paper introduces analytical results for a DS spread spectrum system with matched filter code acquisition in a fixed multipath channel. The performance measure is the mean acquisition time. Constant false alarm rate criteria are used as the threshold setting rule for the comparator. The energies of the multipath components are combined already in the acquisition process by using a chip level post detection integration. The method increases the probability of detection of the burst of multipath components, i.e., it decreases the mean acquisition time for finding the existence of the multipath profile. The numerical results indicate that the method improves the acquisition performance significantly, without requiring knowledge of the number of multipath components.

In this paper, the performance of some code acquisition schemes are studied in the downlink of DS-CDMA systems. The conventional matched filter, the minimum variance method, the MUSIC algorithms and the eigenvector method based delay acquisition schemes are studied in a frequency-selective fading channel. The three last algorithms are based on different estimation schemes for the inverse of the sample-covariance matrix. Based on the results, the minimum variance based method can be used to improve the acquisition performance in comparison to the conventional non-coherent matched filter method. The MUSIC algorithm becomes useless in highly loaded systems. The best performance, however, was obtained by using a longer despreading interval in the conventional delay estimator. Unfortunately, it would require either unmodulated pilot channel or a control channel with lower data rate, which may not be available in all applications.

The performance analysis of a new concept of a code-division multiple-access (CDMA) based low Earth orbit (LEO) satellite network for mobile satellite communications is presented and discussed. The starting point was to analyze the feasibility of implementing multisatellite and multipath diversity reception in a CDMA network for LEO satellites. The results are used to specify the design parameters for a system experimental test bed. Due to the extremely high Doppler, which is characteristic of LEO satellites, code acquisition is significantly simplified by using a continuous wave (CW) pilot carrier for Doppler estimation and compensation. The basic elements for the analysis presented are: the channel model, the pilot carrier frequency estimation for Doppler compensation, and multipath and multisatellite diversity combining.

This paper introduces analysis and simulation results of a DS spread spectrum system in which data detection is based on a matched filter. An approximation is made of the probability of bit error in the AWGN channel and with continuous tone jamming when a complementary code pair is used as the spreading code. It is shown that the median filter causes a loss of about 3 dB in the AWGN channel, but the dramatic effect of continuous jamming can be efficiently eliminated using a median filter.

This paper introduces the analysis and simulation results of a DS spread spectrum system in which the principle of matched filter synchronization for acquisition of code synchronization is used. Upper bounds (due to the upper bound of P/sub d/) of mean acquisition time of coherent matched filter synchronization in continuous tone jamming, when complementary codes are used as the spreading codes, are indicated. The idea of using median type filtering as an aiding device for the matched filter is presented. It is shown that continuous jamming can have a very dramatic influence on mean acquisition time if the imbalances of the codes have large values, but the influence is totally eliminated by using a median filter.>