Yeon Kyoon Jeong

Performance analysis of wide-band M-ary FSK systems in Rayleigh fading channels

Performance analysis schemes for wide-band M-ary frequency-shift keying systems with a limiter-discriminator-integrator receiver are presented along with analysis and simulation results for 4-ary and 8-ary systems. The probability distribution of clicks is required for performance analysis and is determined for Rayleigh fading channels.

Dual-phase continuous phase modulation for spread-spectrum multiple-access communication

A new class of direct-sequence spread-spectrum multiple-access (DS-SSMA) systems with continuous phase modulation (CPM) is defined. The signals are unique in that the spreading is done by adding an extra phase term to the information phase while maintaining phase continuity, constant envelope, and efficient bandwidth usage. The spreading phase is formed from the spreading code and is independent of the information phase, which allows despreading to be done separately before data detection, which, in turn, allows a simple CPM detector to be employed for data detection. The information phase is considered in the minimum-shift keying (MSK) format, and a serial-MSK-type spread-spectrum receiver is considered for performance analysis. Expressions for the signal-to-noise ratio, the power spectral density, and the probability of bit error are developed, along with methods for computing their values to an arbitrarily close approximation. Numerical results show that the proposed system is an attractive alternative to the conventional DS-SSMA systems.

Acquisition of packets with a short preamble for direct-sequence spread-spectrum multiple-access packet communications

Traditional methods for the acquisition of packets use the a priori information contained in the preamble, which is located at the start of each packet. For spread-spectrum systems such as a direct-sequence spread-spectrum packet communication, the preamble consists of a short period of known code sequence and the code sequence continues until the end of the packet, i.e., the information that may be useful for the acquisition continues even after the preamble period for spreading of message symbols. In this work, for direct-sequence packet communications we. propose a technique to enhance the performance of a packet acquisition system which uses not only the preamble but also the message payloads that follow the preamble. The proposed method is a tradeoff between the accuracy in the declaration of acquisition and receiver complexity. Using the proposed method we improve the probability of acquiring packets that leads to an increase in the throughput of the packet system, which is defined as the average number of successful packets given the offered traffic.

Performance bounds on chip-matched-filter receivers for bandlimited DS/SSMA communications

Performance bounds on chip-matched-filter (CMF) receivers for bandlimited direct-sequence spread-spectrum multiple-access (BL-DS/SSMA) systems with aperiodic random spreading sequences are obtained. First, the optimum transmit-receive chip waveform pairs that maximize the conditional signal-to-interference ratio are derived. This leads to performance bounds on CMF receivers when the conditional Gaussian approximation for cyclostationary multiple-access interference (MAI) is exploited. The bounds are used to examine the dependence of the MAI suppression capability of the CMF receivers on the excess bandwidth of the system and the delay profile of multiple-access users. The system employing the flat-spectrum chip waveform pair is shown to have near-optimum average bit-error rate performance among the fixed CMF (FCMF) receiver systems. Numerical results are provided for an adaptive CMF receiver and for FCMF receivers employing several different fixed chip waveforms.

An asymptotic analysis of band-limited DS/SSMA communication systems

A new asymptotic analysis is presented to establish whether or not commonly used techniques to approximate the performance of direct-sequence spread-spectrum multiple-access (DS/SSMA) systems still apply when the systems are strictly band limited. The results apply to any linear data modulation and spreading scheme. The interference components, including the interchip interference (ICI) of a linear receiver output, are shown to be asymptotically jointly Gaussian random variables conditioned on the phases and delays of the interfering signals. Expressions for the error probabilities of band-limited systems are also developed from this result.

Linear suppression of wideband data-like interference in DS/SS communications

In this paper, a linear receiver is proposed and its performance is analyzed for direct-sequence spread-spectrum communications with wideband data-like interference. Two groups of communicators employing generalized random spreading are considered, and the signals are assumed to have harmonically related cyclostationarity periods. First, the output signal-to-interference ratio (SIR) of a general correlation receiver is derived in the frequency domain, and the key system parameters that affect the structure of the interference are identified. Then, a linear interference suppression scheme based on the maximum SIR (MSIR) criterion is proposed, and a receiver structure similar to the cyclic Wiener filter is derived. Numerical results show that the proposed linear MSIR receiver significantly outperforms the conventional correlation receiver by effectively suppressing the wideband data-like interference.

A closed-form BER expression for band-limited DS/SSMA communications

An accurate closed-form expression of approximate average bit error rate (BER) is derived for band-limited direct-sequence spread-spectrum multiple access (DS/SSMA) communications with aperiodic random quadriphase spreading sequences and the conventional matched filter receiver. Although some closed-form BER expressions have been available, they are only for systems with chip-time-limited chip waveforms and even fail to accurately evaluate the BER for some combinations of system parameters. The proposed expression instantly evaluates the average BER for band-limited systems with arbitrary chip waveforms of interest. Monte-Carlo simulation results are also provided to show the accuracy.

An asymptotic analysis of band-limited DS/SSMA systems

Gaussian approximations to the overall interference at the output of linear receivers are commonly used to analyze the performance of asynchronous DS/SSMA communication systems. In this paper, a new asymptotic analysis is presented to establish the validity of Gaussian approximations for the systems employing more general chip waveforms of interest, which include strictly band-limited waveforms. The transmit and receive chip waveforms, can be either time-limited or band-limited with their energy normalized to unity.

A design of optimal overlay system

In this paper, the optimal design of a wideband overlay system is considered for communications over a white Gaussian noise channel corrupted by the signal from an existing system. Under the assumptions that the symbol transmission rate of the new system is an integer multiple of that of the existing system and that the transmit filter is time invariant, the optimum transmitter and receiver waveforms are derived that jointly minimize the average mean-squared error (MSE) at the output of the linear receiver of the new system. It is shown that this joint optimization technique leads to significant performance improvement through complete interference avoidance over the overlay systems with receiver-only optimization, and over those with no transmitter and receiver optimization. It is also shown that, if the existing system does not induce any self interference, the derived solution reduces to the generalized Nyquist condition for no mutual as well as self interference. The case where the symbol transmission rate of the existing system is an integer multiple of that of the new system is also briefly discussed.

Interference suppression capability of linear receivers for band-limited DS/SSMA communications

Interference suppression capabilities of linear receivers for band-limited direct-sequence spread-spectrum multiple-access (DS/SSMA) systems with aperiodic random spreading sequences are considered. First, bounds on the performance of systems with BPSK data symbols and QPSK spreading sequences are derived for fixed matched filter (MF) receivers and adaptive linear receivers. The bounds apply for the case in which the maximum conditional signal-to-interference ratio is obtained or, equivalently, for the case in which the linear minimum-mean-squared error (MMSE) criterion is used. The bounds are used to examine the dependence of the capability of the linear receivers to suppress multiple-access interference (MAI) on the system excess bandwidth and the profile of multiple-access users.