Showing papers on "Spread spectrum published in 2003"

Improved spread spectrum: a new modulation technique for robust watermarking

Abstract: This paper introduces a new watermarking modulation technique, which we call improved spread spectrum (ISS). When compared with traditional spread spectrum (SS), the signal does not act as a noise source, leading to significant gains. In some examples, performance improvements over SS are 20 dB in signal-to-noise ratio (SNR) or ten or more orders of magnitude in the error probability. The proposed method achieves roughly the same noise robustness gain as quantization index modulation (QIM) but without the amplitude scale sensitivity of QIM. Our proposed ISS is as robust in practice as traditional SS.

Steganalysis of additive-noise modelable information hiding

Abstract: The process of information hiding is modeled in the context of additive noise. Under an independence assumption, the histogram of the stegomessage is a convolution of the noise probability mass function (PMF) and the original histogram. In the frequency domain this convolution is viewed as a multiplication of the histogram characteristic function (HCF) and the noise characteristic function. Least significant bit, spread spectrum, and DCT hiding methods for images are analyzed in this framework. It is shown that these embedding methods are equivalent to a lowpass filtering of histograms that is quantified by a decrease in the HCF center of mass (COM). These decreases are exploited in a known scheme detection to classify unaltered and spread spectrum images using a bivariate classifier. Finally, a blind detection scheme is built that uses only statistics from unaltered images. By calculating the Mahalanobis distance from a test COM to the training distribution, a threshold is used to identify steganographic images. At an embedding rate of 1 b.p.p. greater than 95% of the stegoimages are detected with false alarm rate of 5%.

Modern Communications Jamming Principles and Techniques

Abstract: This newly revised and greatly expanded edition of the popular Artech House book, Modern Communications Jamming Principles and Techniques, provides an up-to-date, exhaustive treatment of the techniques and methods available to create countermeasures against anti-jam, over-the-air communications. The Second Edition features a wealth of new material on urban warfare, including a computer simulation of EW architecture alternatives for land-based forces based on urban constraints. The new edition also includes an expanded section on time-hopped spread spectrum communications, more details on modern communication system technologies such as CDMA and OFDM, and an in-depth discussion on sources of urban noise. This practical resource is focused on showing you how to design and build jammers specifically targeted at spread spectrum, anti-jam communications. Moreover, you find assistance in evaluating the expected performance of jamming systems against modern communications systems, and discover the best waveform to use to counter communication systems designed to be effective in jamming environments. While mathematical derivations in general are avoided, the book presents error rate performance equations for most modern digital anti-jam communication systems.

A channelized digital ultrawideband receiver

Abstract: A channelized digital ultrawideband (UWB) receiver that efficiently samples the UWB signal at a fraction of the chip frequency is proposed. The received signal is channelized in the frequency domain by employing a bank of mixers and low-pass filters. After sampling at a much reduced frequency, digital synthesis filters optimally estimate the transmitted signals. The signal-to-noise ratio (SNR) of the proposed receiver has been solved and compared against an ideal conventional receiver, which is defined as a receiver that samples at the signal Nyquist rate. When finite resolution analog-to-digital converters (ADC) are employed in the presence of a large narrowband interferer, the proposed receiver significantly outperforms the ideal conventional receiver. For example, the SNR of the proposed receiver is as much as 20 dB higher than the ideal conventional receiver when a 4-bit ADC is used in the presence of a 50 dB (relative to the noise floor) brickwall narrowband interferer with a bandwidth of 15% of the chip frequency.

Digital spread spectrum methods and apparatus for testing aircraft wiring

Abstract: A system and method that utilizes direct sequence spread spectrum signal (DSSS) encoding to enable testing of a live wire, wherein an original data signal is modified and then transmitted along the wire, and a reflected signal is collected and analyzed using correlation techniques to determine characteristics of the live wire, including the location of a fault.

Performance of adaptive MC-CDMA detectors in rapidly fading Rayleigh channels

Abstract: Multicarrier code-division multiple access (MC-CDMA) combines multicarrier transmission with direct sequence spread spectrum. Different approaches have been adopted which do not assume a perfectly known channel. We examine the forward-link performance of decision-directed adaptive detection schemes, with and without explicit channel estimation, for MC-CDMA systems operating in fast fading channels. We analyze theoretically the impact of channel estimation errors by first considering a simpler system employing a threshold orthogonality restoring combining (TORC) detector with a Kalman channel estimator. We show that the performance deteriorates significantly as the channel fading rate increases and that the fading rate affects the selection of system parameters. We examine the performance of more realistic schemes based on the minimum mean square error (MMSE) criterion using least mean square (LMS) and recursive least square (RLS) adaptation. We present a discussion which compares the decision-directed and pilot-aided approaches and explores the tradeoffs between channel estimation overhead and performance. We find that there is a fading rate range where each method provides a good tradeoff between performance and overhead. We conclude that the MMSE per carrier decision-directed detector with RLS estimation combines good performance in low to moderate fading rates, robustness in parameter variations, and relatively low complexity and overhead. For higher fading rates, however, only pilot-symbol-aided detectors are appropriate.

Receiver processing systems

Abstract: Spread spectrum receiver architectures and methods are described for reducing interference, particularly the interference observed at a user-end terminal in a W-CDMA 3G mobile communications system. Interpath interference which arises due to non-zero cross and auto correlation of more than one spreading code is suppressed by estimating a transmitted signal stream, or a plurality of such signal streams in the case of a plurality of multipath components, respreading this estimated signal and subtracting non-orthogonal interference contributions from a received signal. The techniques provide an improved bit error rate or equivalently, enhanced capacity for a digital mobile communications network.

Integrated radar and communications based on chirped spread-spectrum techniques

Abstract: Linear frequency modulated (LFM) signals and the associated pulse compression techniques are attractive in applications where highly secure and robust communication is needed. This paper investigates the novel integration of radar and communications utilizing LFM waveforms. The simulations suggest that the performance of the communications-receiver deviates at most 2 dB from the theoretical probability of bit error for /spl pi//4-differential phase shift keying. The simulated radar receiver-operating characteristics for false-alarm probabilities between 10/sup -2/ and 10/sup -4/ also compares very well with the theoretical limits for a coherent system.

Coexistence mechanisms for interference mitigation in the 2.4-GHz ISM band

Abstract: Wireless technologies sharing the same frequency band and operating in the same environment often interfere with each other, causing severe decrease in performance. We propose two coexistence mechanisms based on traffic scheduling techniques that mitigate interference between different wireless systems operating in the 2.4-GHz industrial, medical, and scientific band. In particular, we consider IEEE 802.11 wireless local area networks (WLANs) and Bluetooth (BT) voice and data nodes, showing that the proposed algorithms can work when the two systems are able to exchange information as well as when they operate independently of one another. Results indicate that the proposed algorithms remarkably mitigate the interference between the IEEE 802.11 and BT technologies at the expense of a small additional delay in the data transfer. It is also shown that the impact of the interference generated by microwave ovens on the IEEE 802.11 WLANs performance can be significantly reduced through the mechanisms presented.

Adaptive multirate CDMA for uplink throughput maximization

Abstract: We determine the optimal adaptive rate and power control strategies to maximize the total throughput in a multirate code-division multiple-access system. The total throughput of the system provides a meaningful baseline in the form of an upper bound to the throughput achievable with additional restrictions imposed on the system to guarantee fairness. Peak power and instantaneous bit energy-to-noise spectral density constraints are assumed at the transmitter with matched filter detection at the receiver. Our results apply to frequency selective fading in so far as the bit energy-to-equivalent noise power spectral density ratio definition can be used as the quality-of-service metric. The bit energy-to-equivalent noise power spectral density ratio metric coincides with the bit-error rate metric under the assumption that the processing gains and the number of users are high enough so that self-interference can be neglected. We first obtain results for the case where the rates available to each user are unrestricted, and we then consider the more practical scenario where each user has a finite discrete set of rates. An upper bound to the maximum average throughput is obtained and evaluated for Rayleigh fading. Suboptimal low-complexity schemes are considered to illustrate the performance tradeoffs between optimality and complexity. We also show that the optimum rate and power adaptation scheme with unconstrained rates is in fact just a rate adaptation scheme with fixed transmit powers, and it performs significantly better than a scheme that uses power adaptation alone.

An adaptive air interface waveform

Abstract: In one embodiment, a method for generating an adaptive air interface waveform includes generating a waveform that includes a variable carrier frequency and variable bandwidth signal. The variable bandwidth signal includes one or more subcarriers that are dynamically placeable over a range of frequencies, and each subcarrier is separately modulated according to a direct sequence (DS) spread spectrum (SS) technique. The waveform has an embedded pilot usable to optimize one or more spectrum efficiencies of the waveform. A modulation constellation, a code rate, and a code length of the generated waveform are adapted according to an available spectrum and one or more sub-carrier conditions.

A spread-spectrum clock generator with triangular modulation

Abstract: In this paper, a spread-spectrum clock generator (SSCG) with triangular modulation is presented Only a divider and a programmable charge pump are added into a conventional clock generator to accomplish the spread-spectrum function The proposed circuit has been fabricated in a 035-/spl mu/m CMOS single-poly quadruple-metal process The proposed SSCG can generate clocks of 66, 133, and 266 MHz with center spread ratios of 05%, 1%, 15%, 2%, and 25% Experimental results confirm the theoretical analyses

System for direct acquisition of received signals

Abstract: Signal processing architectures for direct acquisition of spread spectrum signals using long codes. Techniques are described for achieving a high of parallelism, employing code matched filter banks and other hardware sharing. In one embodiment, upper and lower sidebands are treated as two independent signals with identical spreading codes. Cross-correlators, in preferred embodiments, are comprised of a one or more banks of CMFs for computing parallel short-time correlations (STCs) of received signal samples and replica code sequence samples, and a means for calculating the cross-correlation values utilizing discrete-time Fourier analysis of the computed STCs. One or more intermediate quantizers may optionally be disposed between the bank of code matched filters and the cross-correlation calculation means for reducing word-sizes of the STCs prior to Fourier analysis. The techniques described may be used with BOC modulated signals or with any signal having at least two distinct sidebands.

Wideband measurements of angle and delay dispersion for outdoor and indoor peer-to-peer radio channels at 1920 MHz

Abstract: The paper presents spatio-temporal measurements for the peer-to-peer radio channel at a center frequency of 1920 MHz with 140 MHz of radio-frequency bandwidth. The measurements were taken using a spread-spectrum channel sounder and an automated spatial probing system that uses precise computer-controlled positioning and orientation of omnidirectional and directional (30/spl deg/ beamwidth) antennas to measure both the angles-of-arrival and time-delays of multipath components. We use a unitless definition of angular spread which we proposed previously (see Durgin, G.D. and Rappaport, T.S., IEE Electron. Lett., vol.34, no.25, p.2431-2, 1998). Transmitter-receiver configurations include six outdoor-to-outdoor cross-campus locations at Virginia Polytechnic Institute and State University (17-219 ns rms delay spread, 0.36-0.91 angular spread), three outdoor-to-indoor locations (27-34 ns rms delay spread, 0.78-0.98 angular spread), and three indoor-to-indoor locations (29-45 ns rms delay spread, 0.73-0.90 angular spread). The paper also quantitatively describes a trend that shows how angular spread increases with increasing delay spread.

EM-based joint data detection and channel estimation of DS-CDMA signals

Abstract: We present two efficient iterative receiver structures of tractable complexity for joint multiuser detection and multichannel estimation (JDE) of direct-sequence code-division multiple-access signals. The schemes result from an application of the expectation-maximization (EM) and the space-alternating generalized expectation-maximization (SAGE) algorithms, respectively. The EM-JDE receiver updates the data bit sequences in parallel, while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. The EM algorithm provides a set of free parameters, called weight coefficients, which can be selected to optimize its performance. Two optimality criteria are defined and analytical expressions for the corresponding optimized weight coefficients are given. Monte-Carlo simulations of a synchronous scenario show that the proposed JDE receivers have excellent multiuser efficiency and are robust against errors in the estimation of the channel parameters. Moreover, very short training sequences are required for the JDE schemes to converge. Simulation results further demonstrate that the SAGE-JDE receiver exhibits a better performance when the users' bit sequences are updated in the order of increasing signal strength, i.e., the bit sequence of the user with the weakest signal strength is updated first at each stage.

An asymmetric watermarking method

Abstract: This paper presents an asymmetric watermarking method as an alternative to classical direct sequence spread spectrum and watermarking Costa (1983) schemes techniques. This new method provides a higher security level against malicious attacks threatening watermarking techniques used for a copy protection purpose. This application, which is quite different from the classical copyright enforcement issue, is extremely challenging as no public algorithm is yet known to be secure enough, and some proposed proprietary techniques have been already hacked. Our method is thus an attempt toward the proof that the Kerckhoff's (1883) principle can be stated in the copy protection framework.

Diversity comparison of spreading transforms for multicarrier spread spectrum transmission

Abstract: Multicarrier spread spectrum transmission methods based on orthogonal frequency division multiplexing employ a linear transform to spread energy of transmitted symbols over statistically independent Rayleigh fading subcarriers, in order to enable a diversity gain at the receiver. We jointly treat the mapping from bits into transmit symbols and the spreading transform as a code in Euclidean space. We describe criteria to identify good and bad spreading transforms, in terms of the asymptotic bit-error probability (BEP) at high signal-to-noise ratio. Upper and lower bounds on the BEP are derived. It is shown that the BEP performance of the commonly used Hadamard transform is asymptotically bad. Alternative orthogonal transforms with better asymptotic performance are proposed. Simulation results are given for the example of 2-phase-shift keying, block length 8.

Coded Modulation Systems

Abstract: Coded Modulation Systems is an introduction to the subject of coded modulation in digital communication. It is designed for classroom use and for anyone wanting to learn the ideas behind this modern kind of coding. Coded modulation is signal encoding that takes into account the nature of the channel over which it is used. Traditional error correcting codes work with bits and add redundant bits in order to correct transmission errors. In coded modulation, continuous time signals and their phases and amplitudes play the major role. The coding can be seen as a patterning of these quantities. The object is still to correct errors, but more fundamentally, it is to conserve signal energy and bandwidth at a given error performance. The book divides coded modulation into three major parts. Trellis coded modulation (TCM) schemes encode the points of QAM constellations; lattice coding and set-partition techniques play major roles here. Continuous-phase modulation (CPM) codes encode the signal phase, and create constant envelope RF signals. The partial-response signaling (PRS) field includes intersymbol interference problems, signals generated by real convolution, and signals created by lowpass filtering. In addition to these topics, the book covers coding techniques of several kinds for fading channels, spread spectrum and repeat-request systems. The history of the subject is fully traced back to the formative work of Shannon in 1949. Full explanation of the basics and complete homework problems make the book ideal for self-study or classroom use.

Ultra wideband DSSS for multiple access communications using antipodal signaling

Abstract: Ultra wideband (UWB) technology is characterized by transmitting extremely short duration radio impulses. To improve its multiple access (MA) capability, UWB technology can be combined with traditional spread spectrum techniques. So far, much of the research has focused on employing time hopping spread spectrum with impulse radio using pulse position modulated (PPM) signals. In this paper, we outline the attractive features of direct sequence (DS) ultra wideband multiple access systems employing antipodal signaling and compare it with time hopping (TH). An appropriate DS-UWB transmitter and receiver are designed, and the system signal processing formulation is investigated. Performance of such communication systems in terms of multiple access capability, error rate performance, and achievable transmission rate are evaluated. An upper bound on the maximum number of users supported by the system is discussed.

A low-latency and energy-efficient algorithm for convergecast in wireless sensor networks

Abstract: In wireless sensor networks (WSN) the process of dissemination of data among various sensors (broadcast) and collection of data from all sensors (convergecast or data aggregation) are common communication operations. With increasing demands on efficient use of battery power, many efficient broadcast tree construction and channel allocation algorithms have been proposed. Generally convergecast is preceded by broadcast. Hence the tree used for broadcast is also used for convergecast. Our research shows that this approach is inefficient in terms of latency and energy consumption. In this paper we propose a heuristic solution for the problem of minimum energy convergecast which also works toward minimizing data latency. This algorithm constructs a tree using a greedy approach where new nodes are added to the tree such that weight on the branch to which it is added is less. The algorithm then allocates direct sequence spread spectrum or frequency hopping spread spectrum codes. Simulation results show that energy consumed and communication latency of our approach is lower than some of the existing approaches for convergecast. We have then used our algorithm to perform broadcast. Surprisingly our results show that this algorithms performance for broadcasting is better compared to other broadcast techniques.

Bluetooth adaptive frequency hopping and scheduling

Abstract: In this paper, we investigate the use of adaptive frequency hopping (AFH) techniques aimed at modifying the Bluetooth frequency hopping sequence in the presence of WLAN direct sequence spread spectrum devices. We examine the conditions such as the applications, topologies, and scenarios under which AFH techniques improve performance that is measured in terms of packet loss, TCP delay, and channel efficiency. We also compare the results obtained with AFH to others obtained using a scheduling technique that consist in delaying the transmission of a Bluetooth packet until the medium is "idle". Our results show that an obvious performance improvement with AFH is in terms of delay and throughput. AFH brings the delay down to the same level than when no interference is present. On the other hand, AFH is rather slow in responding to changes in the environment and the packet loss is more significant than with the scheduling. This is probably due to the limitations imposed by the communication overhead. The main difficulty for AFH is having to dynamically communicate the changes to all slaves in the piconet in order to keep the synchronization.

Global positioning system code phase detector with multipath compensation and method for reducing multipath components associated with a received signal

Abstract: A method for compensating for multipath components in a received CDMA signal comprising a repetitive PRN code uses delay times in addition to the early, late and prompt delay times for determining if a multipath component is present in the received signal, and if so, making an adjustment to the delay time of the replica code generated by a receiver so as to minimize the difference between the correlation values for a delay time equal to −1 chip and a delay time more negative than −1 chip. In this manner, adjustments to the estimation time for the start of the PRN code can be made in a manner which minimizes the effects of multipath components. A system using additional delays and correlators in association with the code phase detector, a code numerical control oscillator and replica code generator is described for performing the above methodology. The methodology is particularly suitable for GPS receivers and may further be used in receivers that receive any type of digital sequence spread spectrum, code division multiple access signals. Compensation for multipath components with 180 degree phase shifts is also made as well as compensation due to smoothing of the triangular correlation function due to RF characteristics and non-ideal PRN codes.

Orthogonal multiple access over time- and frequency-selective channels

Abstract: Suppression of multiuser interference (MUI) and mitigation of time- and frequency-selective (doubly selective) channel effects constitute major challenges in the design of third-generation wireless mobile systems. Relying on a basis expansion model (BEM) for doubly selective channels, we develop a channel-independent block spreading scheme that preserves mutual orthogonality among single-cell users at the receiver. This alleviates the need for complex multiuser detection, and enables separation of the desired user by a simple code-matched channel-independent block despreading scheme that is maximum-likelihood (ML) optimal under the BEM plus white Gaussian noise assumption on the channel. In addition, each user achieves the maximum delay-Doppler diversity for Gaussian distributed BEM coefficients. Issues like links with existing multiuser transceivers, existence, user efficiency, special cases, backward compatibility with direct-sequence code-division multiple access (DS-CDMA), and error control coding, are briefly discussed.

DS-CDMA: the modulation technology of choice for UWB communications

Abstract: We show that because of drastic differences in the fading statistics between ultra wide bandwidth (UWB) multicarrier and direct sequence code division multiple access (DS-CDMA) approaches, DS easily scales to Gbps rates while multicarrier architectures have severe difficulty. Both DS-CDMA and orthogonal frequency division multiple access (OFDM) are well understood and proven modulation techniques in conventional (narrowband) commercial technologies (e.g. DS-CDMA in cell phones; OFDM in IEEE 802.11a/g). The maturity of these approaches, however, is vastly different when applied to ultrawideband (UWB) systems. Already implemented and operating in silicon, DS-CDMA architectures have proven to be the most mature and scaleable for UWB on both a theoretical as well as implementation basis. Among the proposed approaches before the IEEE 802.15.3a standards committee, the DS-CDMA transmitted waveform (which is the "thing" being standardized) is uniquely capable of serving the broadest diversity of applications. It can, for example, allow very low-cost low-power transmit-only devices (even at Gbps rates) because it requires no FFT or DAC or DSP. At the same time, receivers can incorporate varying degrees of DSP to provide scaleable power/cost versus performance. We present performance comparisons of DS-CDMA [Document IEEE.15-03/153r10, July 2003] vs. the proposed multiband MB-OFDM architecture [Document IEEE 802.15-03/267r0, July 2003] for outage range in a variety of multipath environments. Moreover, we describe how DS-CDMA UWB architectures can support robust and flexible multiuser capabilities, protect against in-band interference, and provide high-resolution ranging capabilities for safety-of-life applications.

Multicarrier CDMA systems using time-domain and frequency-domain spreading codes

Abstract: For wideband code-division multiple-access systems, the paper introduces a multicarrier modulation scheme that performs the spreading simultaneously in the time and frequency domains. This scheme attains higher flexibility and spectrum efficiency because system parameters can be selected at will. The performance is compared with that of a single carrier RAKE system by calculating the probability of error over a frequency-selective Rayleigh fading channel. The proposed scheme outperforms the single carrier RAKE system if the system parameters are selected properly for given conditions, such as bandwidth and delay spread.

Transmitting and receiving spread spectrum signals using continuous waveforms

Abstract: Systems and methods are described for transmitting and receiving spread spectrum signals using continuous waveforms. A method of transmitting a spread spectrum signal includes: generating a plurality of substantially continuous waveforms; summing the plurality of substantially continuous waveforms; modulating the summed plurality of substantially continuous waveforms to generate the spread spectrum signal; and transmitting the spread spectrum signal. A method of receiving a spread spectrum signal includes: generating a plurality of substantially continuous waveforms; summing the plurality of substantially continuous waveforms; modulating the summed plurality of substantially continuous waveforms with a code; mixing the modulated summed plurality of substantially continuous waveforms with the spread spectrum signal to produce a baseband signal; integrating the baseband signal; and detecting data.

Wideband air-to-ground radio channel measurements using an antenna array at 2 GHz for low-altitude operations

Abstract: Wideband measurements were performed using a direct-sequence spread-spectrum measurement system in the air-to-ground radio environment to characterize propagation between an airborne transmitter and a ground-based receiving antenna array at a center frequency of 205 GHz The transmitter was flown along constant-radius arcs at low altitudes around the receiver location to obtain measurement results for 75, 15, 225, and 30 degree elevation angles An 80 megachip per second (Mcps) modulating PN sequence was transmitted by the airborne station The receiver was located in a campus environment of four- to six-story buildings and rolling terrain The receiver used a four-element antenna array and sampled received signals at 1 gigasample per second (Gsps) per channel Power-delay profiles that approximated channel impulse responses were used to measure magnitude, phase, and delay of multipath signal components received at each element Characterization parameters produced from the measurements include RMS delay spread, excess delay spread, multipath fading CDFs, antenna diversity gain, and gain achieved through spatial-temporal combining The measurements presented here support analysis of wireless systems for intentional transmissions, such as data communications between ground nodes and low-altitude aircraft In addition, these measurements support investigations into interference from ground sources to low-altitude aircraft (eg, on instrument approaches) or interception of signals originating from ground sources

Spread spectrum clock generation circuit, jitter generation circuit and semiconductor device

Abstract: A spread spectrum clock generation circuit capable of further reducing the electromagnetic wave radiation with a simple configuration has been disclosed and, particularly in a spread spectrum clock generation circuit using a current control oscillator (ICO), a differential signal to which a spread spectrum modulation signal, the period or amplitude of which changes, is added is generated, and the differential signal is applied to the ICO and a clock is generated.

Spread spectrum transmitter and spread spectrum receiver

Abstract: A spread spectrum transmitter provides delays having different magnitudes to spread spectrum (SS) signals for a plurality of channels, and multiplexes the SS signals to generate transmission multiplex SS signal. A spread spectrum receiver calculates a partial correlation value between the transmission multiplex SS signal and spreading codes multiplied to the SS signals, multiplies the partial correlation values by a prescribed matrix prepared based on each orthogonal code sequence to calculate a plurality of orthogonal correlation values. The receiver identifies for a respective channel each parallel data sequence related in advance to an orthogonal code sequence whose orthogonal correlation value is a maximum, corrects delay differences of the parallel data sequences, and then performs sampling and parallel-serial conversion to obtain a serial demodulated data sequence.

Wireless, frequency-agile spread spectrum ground link-based aircraft data communication system with wireless unit in communication therewith

Abstract: A system and method provides a retrievable record of the flight performance of the aircraft and includes a ground data link unit that obtains flight performance data representative of aircraft flight performance during flight of the aircraft. A spread spectrum transceiver is coupled to a data store and operative to download flight performance data that has been accumulated and stored by the data store over a spread spectrum communication signal. A ground base spread spectrum transceiver receives the spread spectrum communication signal from the aircraft and demodulates the signal to obtain flight performance data. A wireless unit is operative with the ground data link unit. This wireless unit could be for inventory control of products during in-flight servicing of passengers.