Showing papers on "Phase-shift keying published in 1998"
TL;DR: A minimum mean-square-error (MMSE) channel estimator is derived, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels and can significantly improve the performance of OFDM systems in a rapid dispersion fading channel.
Abstract: Orthogonal frequency-division multiplexing (OFDM) modulation is a promising technique for achieving the high bit rates required for a wireless multimedia service. Without channel estimation and tracking, OFDM systems have to use differential phase-shift keying (DPSK), which has a 3-dB signal-to-noise ratio (SNR) loss compared with coherent phase-shift keying (PSK). To improve the performance of OFDM systems by using coherent PSK, we investigate robust channel estimation for OFDM systems. We derive a minimum mean-square-error (MMSE) channel estimator, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. Since the channel statistics are usually unknown, we also analyze the mismatch of the estimator-to-channel statistics and propose a robust channel estimator that is insensitive to the channel statistics. The robust channel estimator can significantly improve the performance of OFDM systems in a rapid dispersive fading channel.
1,039 citations
TL;DR: Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, this multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense.
Abstract: The increasing need for high data-rate transmissions over time- or frequency-selective fading channels has drawn attention to modulation schemes with high spectral efficiency such as QAM. With the aim of increasing the "diversity order" of the signal set we consider multidimensional rotated QAM constellations. Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, This multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense.
1,030 citations
01 Sep 1998
TL;DR: It is shown that in the largest majority of cases, these error-rate expressions can be put in the form of a single integral with finite limits and an integrand composed of elementary functions, thus readily enabling numerical evaluation.
Abstract: Presented here is a unified approach to evaluating the error-rate performance of digital communication systems operating over a generalized fading channel. What enables the unification is the recognition of the desirable form for alternate representations of the Gaussian and Marcum Q-functions that are characteristic of error-probability expressions for coherent, differentially coherent, and noncoherent forms of detection. It is shown that in the largest majority of cases, these error-rate expressions can be put in the form of a single integral with finite limits and an integrand composed of elementary functions, thus readily enabling numerical evaluation.
851 citations
07 Jun 1998
TL;DR: A minimum mean-square-error (MSE) channel estimator is derived, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels and can significantly improve the performance of OFDM systems in a rapid dispersion fading channel.
Abstract: Orthogonal frequency division multiplexing (OFDM) modulation is a promising technique for achieving the high-bit-rates required for a wireless multimedia service. Without channel estimation and tracking, OFDM systems have to use differential phase-shift keying (DPSK), which has a 3 dB signal-to-noise ratio (SNR) loss compared with coherent phase-shift keying (PSK). To improve the performance of OFDM systems by using coherent PSK, we investigate robust channel estimation for OFDM systems. We derive a minimum mean-square-error (MSE) channel estimator, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. Since the channel statistics are usually unknown, we also analyze the mismatch of the estimator to channel statistics and propose a robust channel estimator that is insensitive to the channel statistics. The robust channel estimator can significantly improve the performance of OFDM systems in a rapid dispersive fading channel.
675 citations
18 May 1998
TL;DR: A space-time coded orthogonal frequency division multiplexing (OFDM) modulated physical layer is designed which combines coding and modulation and is attractive for delay-sensitive applications.
Abstract: There has been an increasing interest in providing high data-rate services such as video-conferencing, multimedia Internet access and wide area network over wideband wireless channels. Wideband wireless channels available in the PCS band (2 GHz) have been envisioned to be used by mobile (high Doppler) and stationary (low Doppler) units in a variety of delay spread profiles. This is a challenging task, given the limited link budget and severity of wireless environment, and calls for the development of novel robust bandwidth efficient techniques which work reliably at low SNRs. To this end, we design a space-time coded orthogonal frequency division multiplexing (OFDM) modulated physical layer. This combines coding and modulation. Space-time codes were previously proposed for narrowband wireless channels. These codes have high spectral efficiency and operate at very low SNR (within 2-3 dB of the capacity). On the other hand, OFDM has matured as a modulation scheme for wideband channels. We combine these two in a natural manner and propose a system achieving data rates of 1.5-3 Mbps over a 1 MHz bandwidth channel. This system requires 18-23 dB (resp. 9-14 dB) receive SNR at a frame error probability of 10/sup -2/ with two transmit and one receive antennas (resp. two transmit and two receive antennas). As space-time coding does not require any form of interleaving, the proposed system is attractive for delay-sensitive applications.
599 citations
TL;DR: A bandwidth-efficient channel coding scheme that has an overall structure similar to binary turbo codes, but employs trellis-coded modulation (TCM) codes (including multidimensional codes) as component codes and is very powerful, yet of modest complexity since simple component codes are used.
Abstract: We present a bandwidth-efficient channel coding scheme that has an overall structure similar to binary turbo codes, but employs trellis-coded modulation (TCM) codes (including multidimensional codes) as component codes. The combination of turbo codes with powerful bandwidth-efficient component codes leads to a straightforward encoder structure, and allows iterative decoding in analogy to the binary turbo decoder. However, certain special conditions may need to be met at the encoder, and the iterative decoder needs to be adapted to the decoding of the component TCM codes. The scheme has been investigated for 8-PSK, 16-QAM, and 64-QAM modulation schemes with varying overall bandwidth efficiencies. A simple code choice based on the minimal distance of the punctured component code has also been performed. The interset distances of the partitioning tree can be used to fix the number of coded and uncoded bits. We derive the symbol-by-symbol MAP component decoder operating in the log domain, and apply methods of reducing decoder complexity. Simulation results are presented and compare the scheme with traditional TCM as well as turbo codes with Gray mapping. The results show that the novel scheme is very powerful, yet of modest complexity since simple component codes are used.
529 citations
TL;DR: The theory and practice of a new advanced modem technology suitable for high-data-rate wireless communications and its performance over a frequency-flat Rayleigh fading channel are presented and it is concluded that STCM can provide significant SNR improvement over simple delay diversity.
Abstract: This paper presents the theory and practice of a new advanced modem technology suitable for high-data-rate wireless communications and presents its performance over a frequency-flat Rayleigh fading channel. The new technology is based on space-time coded modulation (STCM) with multiple transmit and/or multiple receive antennas and orthogonal pilot sequence insertion (O-PSI). In this approach, data is encoded by a space-time (ST) channel encoder and the output of the encoder is split into N streams to be simultaneously transmitted using N transmit antennas. The transmitter inserts periodic orthogonal pilot sequences in each of the simultaneously transmitted bursts. The receiver uses those pilot sequences to estimate the fading channel. When combined with an appropriately designed interpolation filter, accurate channel state information (CSI) can be estimated for the decoding process. Simulation results of the proposed modem, as applied to the IS-136 cellular standard, are presented. We present the frame error rate (FER) performance results as a function of the signal-to-noise ratio (SNR) and the maximum Doppler frequency, in the presence of timing and frequency offset errors. Simulation results show that for a 10% FER, a 32-state eight-phase-shift keyed (8-PSK) ST code with two transmit and two receive antennas can support data rates up to 55.8 kb/s on a 30-kHz channel, at an SNR of 11.7 dB and a maximum Doppler frequency of 180 Hz. Simulation results for other codes and other channel conditions are also provided. We also compare the performance of the proposed STCM scheme with delay diversity schemes and conclude that STCM can provide significant SNR improvement over simple delay diversity.
445 citations
TL;DR: An accurate method to determine the error probability of an orthogonal frequency-division multiplexing (OFDM) system in the presence of phase noise is presented.
Abstract: Multicarrier modulation exhibits a significant sensitivity to the phase noise of the oscillator used for frequency down-conversion at the portable receiver. For this reason, it is important to evaluate the impact of the phase noise on the system performance. We present an accurate method to determine the error probability of an orthogonal frequency-division multiplexing (OFDM) system in the presence of phase noise. In particular, four modulation schemes are analyzed and their performances are compared.
357 citations
TL;DR: It is shown that the solution to a number of previously considered communication problems can be simplified and, in some cases, made more accurate (i.e. exact rather than bounded).
Abstract: Using an alternate form of the Gaussian probability integral discovered a number of years ago, it is shown that the solution to a number of previously considered communication problems can be simplified and, in some cases, made more accurate (i.e. exact rather than bounded). These problems include the evaluation of: (1) the bit-error probability of uncoded phase shift keying (PSK) with Costas loop tracking; (2) word-error probability of antipodal modulation in the presence of fading; (3) bit-error probability of coded M-ary PSK (MPSK) over the memoryless fading channel with given channel-state information; (4) conditional symbol-error probability of MPSK in the presence of carrier synchronization error; and (5) the average error probability for the binary additive white Gaussian noise (AWGN) intersymbol interference channel. Also obtained is a generalization of this new alternate form to the case of a two-dimensional Gaussian probability integral with arbitrary correlation which can be used to evaluate the symbol-error probability of MPSK with I-Q unbalance.
250 citations
TL;DR: A new kind of adaptive equalizer that operates in the spatial-frequency domain and uses either least mean square (LMS) or recursive least squares (RLS) adaptive processing and requires only /spl sim/50 complex operations per detected bit, which is close to achievable with state-of-the-art digital signal processing technology.
Abstract: We introduce a new kind of adaptive equalizer that operates in the spatial-frequency domain and uses either least mean square (LMS) or recursive least squares (RLS) adaptive processing. We simulate the equalizer's performance in an 8-Mb/s quaternary phase-shift keying (QPSK) link over a frequency-selective Rayleigh fading multipath channel with /spl sim/3 /spl mu/s RMS delay spread, corresponding to 60 symbols of dispersion. With the RLS algorithm and two diversity branches, our results show rapid convergence and channel tracking for a range of mobile speeds (up to /spl sim/100 mi/h). With a mobile speed of 40 mi/h, for example, the equalizer achieves an average bit error rate (BER) of 10/sup -4/ at a signal-to-noise ratio (SNR) of 15 dB, falling short of optimum linear receiver performance by about 4 dB. Moreover, it requires only /spl sim/50 complex operations per detected bit, i.e., /spl sim/400 M operations per second, which is close to achievable with state-of-the-art digital signal processing technology. An equivalent time-domain equalizer, if it converged at all, would require orders-of-magnitude more processing.
231 citations
01 Aug 1998
TL;DR: The impacts of the I/Q imbalance in the quadrature down-converter on the performance of a QPSK-OFDM-QAM system are studied and it is observed that the degradation of BER performance is less than 0.5 dB for a BER>10/sup -6/.
Abstract: The impacts of the I/Q imbalance in the quadrature down-converter on the performance of a QPSK-OFDM-QAM system are studied. Either amplitude or phase imbalance introduces inter-channel interference (ICI). In addition to the ICI, there is a cross-talk between in-phase and quadrature channels in each and every sub-carrier when both amplitude and phase imbalances are present. The BER (bit error ratio) performance of QPSK sub-carriers are also calculated to illustrate the impacts of the I/Q imbalance. It is observed that with the amplitude imbalance less than 1 dB and phase imbalance less than 5 degrees, the degradation of BER performance is less than 0.5 dB for a BER>10/sup -6/.
TL;DR: It is shown that the probability density function of the maximum signal-to-interference ratio (SIR) at the output of the optimum combiner has a Hotelling T/sup 2/ distribution.
Abstract: Optimum combining for space diversity reception is studied in digital cellular mobile radio communication systems with Rayleigh fading and multiple cochannel interferers. This paper considers binary phase-shift keying (BPSK) modulation in a flat Rayleigh-fading environment when the number of interferences L is no less than the number of antenna elements N(L/spl ges/N). The approach of this paper and its main contribution is to carry out the analysis in a multivariate framework. Using this approach and with the assumption of equal-power interferers, it is shown that the probability density function of the maximum signal-to-interference ratio (SIR) at the output of the optimum combiner has a Hotelling T/sup 2/ distribution. Closed form expressions using hypergeometric functions are derived for the outage probability and the average probability of bit error. Theoretical results are demonstrated by Monte Carlo simulations.
TL;DR: An iterative decoder structure is presented, which combines channel equalization and turbo decoding, and results are presented for a rate 1/2 turbo code with binary phase-shift keying modulation, transmitted over an intersymbol interference channel having severe frequency distortion.
Abstract: In this letter, the subject of turbo coding in the presence of an intersymbol interference channel is investigated. An iterative decoder structure is presented, which combines channel equalization and turbo decoding. At each iteration extrinsic information from the channel detector is fed into the turbo decoders, and then their extrinsic information is fed back to the channel detector. Simulation results are presented for a rate 1/2 turbo code with binary phase-shift keying (BPSK) modulation, transmitted over an intersymbol interference (ISI) channel having severe frequency distortion. The performance is about 0.8 dB from the ISI channel capacity at a bit-error rate of 10/sup -5/.
TL;DR: In this paper, an iterative decoding scheme for quadrature phase shift keying (QPSK) modulation with anti-gray mapping is presented, where a soft demapper accepting a priori information and a convolutional decoder are applied in a serial concatenation.
Abstract: The authors present an iterative decoding scheme which is particularly suited for quadrature phase shift keying (QPSK) modulation with anti-Gray mapping. At the receiver, a soft demapper accepting a priori information and a convolutional decoder are applied in a serial concatenation. Numerical results are presented for QPSK in additive white Gaussian noise and Rayleigh-fading channels. The iterated system applying anti-Gray mapping outperforms the conventional system using Gray mapping after only one iteration.
TL;DR: This paper looks into modulation formats which minimize peak power and retain high spectral efficiency, and a generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats.
Abstract: In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. The peak suppression algorithm is also applicable to /spl pi//4-QPSK and was found to improve peak power efficiency of that format by about 1.25 dB over a Rayleigh fading channel.
18 May 1998
TL;DR: A method is proposed which considerably reduces the peak-to-average power ratio of the OFDM signal by means of signal processing.
Abstract: An important difficulty which has to be solved in OFDM transmission systems is the large peak-to-average power ratio of the OFDM signal. Without any measures, the signal is limited by the power amplifier in the transmitter which causes interference both of the signal itself and in adjacent frequency bands. A method is proposed which considerably reduces the peak-to-average power ratio of the OFDM signal by means of signal processing.
TL;DR: It is demonstrated by computer simulation and laboratory experiments that the proposed time-division multiple-access/time-division duplex system can achieve a higher average bit rate with higher transmission quality in comparison with the fixed-rate quaternary phase-shift keying system and modulation level-controlled adaptive modulation system in both flat Rayleigh and frequency-selective fading environments.
Abstract: This paper proposes a time-division multiple-access/time-division duplex (TDMA/TDD)-based symbol rate and modulation level-controlled adaptive modulation system for high-bit-rate data transmission. The proposed system controls both the symbol rate and modulation level for the next transmission time slot according to the estimated carrier power to noise spectral density ratio (C/N/sub 0/) and delay spread for the time slot to achieve higher bit rate and higher transmission quality as well as higher delay-spread immunity. It is demonstrated by computer simulation and laboratory experiments that the proposed system can achieve a higher average bit rate with higher transmission quality in comparison with the fixed-rate quaternary phase-shift keying (QPSK) system and modulation level-controlled adaptive modulation system in both flat Rayleigh and frequency-selective fading environments. The simulated and experimental results also show that the proposed adaptive modulation techniques can be applied to 1-2-Mb/s indoor and outdoor microcellular systems with its delay spread of up to 250 ns and its terminal mobility of up to pedestrian speed without employing any special antifrequency-selective fading techniques, such as the adaptive equalizer and space diversity.
18 May 1998
TL;DR: In this paper, a new kind of adaptive equalizer that operates in the spatial-frequency domain, and uses either least mean square (LMS) or recursive least squares (RLS) adaptive processing, is introduced.
Abstract: We introduce a new kind of adaptive equalizer that operates in the spatial-frequency domain, and uses either least mean square (LMS) or recursive least squares (RLS) adaptive processing. We simulate the equalizer's performance in an 8 Mb/s QPSK (quaternary phase shift keying) link over a frequency-selective, Rayleigh fading multipath channel with /spl sim/3 /spl mu/s RMS delay spread, corresponding to 60 symbols of dispersion. Our results show rapid convergence and tracking for a range of mobile speeds (up to /spl sim/100 mph). Moreover, a 2-branch RLS equalizer requires only /spl sim/50 complex operations per detected bit, which, at 8 Mb/s, is close to achievable with state-of-the-art digital signal processing technology.
TL;DR: In this article, a spectrally efficient millimeter-wave (mm-wave) fiber-wireless transmission system is presented demonstrating downstream transportation of 155-Mb/s BPSK data at 38 GHz over 50 km of standard singlemode fiber and a 5m wireless link.
Abstract: A spectrally efficient millimeter-wave (mm-wave) fiber-wireless transmission system is presented demonstrating downstream transportation of 155-Mb/s BPSK data at 38 GHz over 50 km of standard single-mode fiber and a 5-m wireless link. The effect of fiber chromatic dispersion on the transmission of the mm-wave optical carrier was overcome by using a single dual-electrode Mach-Zehnder modulator to generate optical single-sideband (SSB) modulation with carrier. We also demonstrate a simple technique for obtaining electrical SSB that will allow the effect of fiber dispersion across the bandwidth of the information to be overcome with simple electrical delay equalization. We predict that this fiber-wireless system could permit the transportation of mm-wave signals with large bit rates over long optical fiber distances.
TL;DR: The concept of a virtual optical code path (VOCP) is introduced within the transport layer of the network and it is demonstrated that this is a potential solution to wavelength path (WP) allocation problems which may plague WDM based transport networks of the future.
Abstract: Lightwave networks realized through code division multiple access techniques are extensively studied to determine their ultimate capabilities. Here, these concepts are extended to network implementation by introducing an optical code division multiplexing (OCDM) multihop strategy using optical coding. It is shown that this approach is effective in scaling up existing wavelength division multiplexing (WDM) networks without a significant drain of the wavelength resources. The concept of a virtual optical code path (VOCP) is introduced within the transport layer of the network. It is demonstrated that this is a potential solution to wavelength path (WP) allocation problems which may plague WDM based transport networks of the future. Crucial to the VOCP concept is optical code conversion. The interplay between this added functionality and the optical cross-connect is highlighted; the optical cross-connect serves to establish VOCP/VWP (virtual wavelength path) in the hybrid transport layer. An example of optical code conversion is introduced. It is based on coherent OCDM principles in which bipolar phase-shift keyed (PSK) optical pulse sequences are used as the signature codes. Error-free code conversion using a four-chip optical encoder/decoder is successfully performed at 1.24 Gbit/s. The results show the feasibility of high bit rate OCDM transmission with optical code conversion.
Patent•
26 Feb 1998TL;DR: In this article, the authors proposed a spread spectrum radio transceiver with a modulator for spread spectrum phase shift keying (PSK) modulating information for transmission via the radio circuit.
Abstract: A spread spectrum radio transceiver includes a high data rate baseband processor and a radio circuit connected thereto. The baseband processor preferably includes a modulator for spread spectrum phase shift keying (PSK) modulating information for transmission via the radio circuit. The modulator may include at least one modified Walsh code function encoder for encoding information according to a modified Walsh code for substantially reducing an average DC signal component to thereby enhance overall system performance when AC-coupling the received signal through at least one analog-to-digital converter to the demodulator. The demodulator is for spread spectrum PSK demodulating information received from the radio circuit. The modulator and demodulator are each preferably operable in one of a bi-phase PSK (BPSK) mode at a first data rate and a quadrature PSK (QPSK) mode at a second data rate. These formats may also be switched on-the-fly in the demodulator. Method aspects are also disclosed.
TL;DR: An accurate approximation for calculating bit error rates in direct sequence code division multiple access (CDMA) radio systems using binary phase shift keyed (BPSK) signaling is presented.
Abstract: An accurate approximation for calculating bit error rates in direct sequence code division multiple access (CDMA) radio systems using binary phase shift keyed (BPSK) signaling is presented. All interfering users are assumed to employ random signature sequences, but the desired signal can be structured with either a random or a deterministic spreading code. Bit error probabilities are given for signals having carrier phase or chip offsets that are either deterministic or random. Computational complexity of all calculations is O(1).
TL;DR: It is proven that for large L the coherent capacity is approached and an analytic asymptotic expression for low L/spl middot/SNR is derived exhibiting the expected quadratic dependence on the SNR.
Abstract: The capacity of M-ary phase-shift keying (MPSK) over an additive white Gaussian noise (AWGN) channel with carrier phase unknown but constant over L symbols is investigated. It is shown that capacity-achieving channel inputs are uniformly distributed and independent MPSK symbols. Capacity over a range of signal-to-noise ratio (SNR) and L is presented for binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK). Upper and lower easy-to-compute bounds on capacity are derived. It is proven that for large L the coherent capacity is approached. An analytic asymptotic expression for low L/spl middot/SNR is derived exhibiting the expected quadratic dependence on the SNR.
Patent•
20 Apr 1998TL;DR: In this paper, a method and apparatus for implementing a subchannel for management and control or other supplemental data on a media shared with a high speed data link is proposed, which is compatible with existing high-speed data transmitters and receivers.
Abstract: A method and apparatus for implementing a subchannel for management and control or other supplemental data on a media shared with a high speed data link Several FDMA approaches are disclosed including AM, FM, PM, phase, QAM, QPSK etc modulation of a subcarrier having a frequency which is in the bandwidth provided by the shared media which is not used by the DC balanced high speed data stream A preferred species which is compatible with existing high speed data transmitters and receivers comprises a subchannel transmitter which frequency shift keys a subchannel carrier of about 1 mHz with the subchannel data The modulated subchannel carrier is summed by superposition with a DC balanced NRZ format gigabit data stream and coupled onto the media Injection power levels of the subchannel carrier are controlled so as to not cause excessive jitter in the high speed data receivers but so as to provide sufficient amplitude in the face of noise sources including random variations in transition density to be recovered by a subchannel receiver At the destination node, the combined signal is directly coupled to the input of the high speed data receiver, but is coupled to the input of the subchannel receiver through a low pass filter The subchannel receiver is narrowband and includes an FSK demodulator
TL;DR: A present view of single-carrier and multitone modulation indicates comparable performance with some differences depending on the type of degradation, and costs should also be approximately equal, with multitone having some advantage in digital processing, but requiring greater cost in analog circuitry.
Abstract: Single-carrier modulation such as quadrature amplitude modulation (QAM) or carrierless amplitude modulation-phase modulation (CAP), and DMT are alternative techniques for providing digital communication in a variety of applications, in particular ADSL for communication over the telephone company subscriber lines. Although theory predicts comparable performance under ideal implementations, a definitive comparison of performance over a wide range of conditions will require more experience from field trials. Similarly, accurate comparison of implementation costs must await the greater availability of commercial-grade devices. However, enough is now known about these modulation schemes to compare their inherent similarities and differences in performance and cost. Overall, a present view of single-carrier and multitone modulation indicates comparable performance with some differences depending on the type of degradation. Costs should also be approximately equal, with multitone having some advantage in digital processing, but requiring greater cost in analog circuitry.
TL;DR: Closed form bit-error rate (BER) expressions for differentially detected /spl pi//4-shifted differentially encoded quadrature phase-shift keying (QPSK) modulation and Rayleigh-fading channels are derived for both additive white Gaussian noise (AWGN), and L-fold diversity combining.
Abstract: Closed form bit-error rate (BER) expressions for differentially detected /spl pi//4-shifted differentially encoded quadrature phase-shift keying (QPSK) modulation (/spl pi//4 DQPSK) are derived for both additive white Gaussian noise (AWGN) and Rayleigh-fading channels. The derivations are carried out in an exact and most general manner in that in-phase (I) and quadrature (Q) channel bit-error probabilities P/sub cl/ and P/sub cQ/ are separately obtained in terms of the same-quadrature and cross-quadrature noise Correlation functions, including a measure of noise nonstationarity. We then specialize the general expressions for uncorrelated noise and equal noise powers in successive symbol periods to obtain a useful bit-error probability expression for the AWGN channel in the form P/sub e//spl ap/Q(/spl radic/(1.1716/spl middot/E/sub b//N/sub 0/)) where Q(/spl middot/) is the Gaussian distribution Q-function and E/sub b//N/sub 0/ is the bit energy-to-noise density ratio. Exact BER expressions for the Rayleigh-fading channel that involve the noise parameters are also given and are extended to the case of L-fold diversity combining.
TL;DR: Simulation results show that the proposed detection strategy, implemented via a standard Viterbi algorithm, provides improved performance over differential detection, with a moderate increase in receiver complexity and without requiring the periodic transmission of training blocks.
Abstract: A novel equalization/detection algorithm for orthogonal frequency division multiplexing (OFDM) signals transmitted over frequency-selective channels is introduced and investigated. The algorithm stems from the recognition that the Fourier transform processing inherent in OFDM turns a single wideband frequency-selective channel into a set of correlated narrowband frequency-flat fading channels. This suggests that sequence detection techniques, such as those discussed by Vitetta et al. (see IEEE Trans. Commun., vol.43, p.2750-8, 1995, IEEE Trans. Commun., vol.43, pt.II, p.1256-9, 1995, and Proc. IEEE Commun. Theory Mini-Conf (Globecom '96), London, UK, p.153-7, 1996), for time-selective flat-fading channels, can be also profitably utilized for joint equalization and decoding of OFDM signals in the frequency domain. Simulation results show that the proposed detection strategy, implemented via a standard Viterbi algorithm, provides improved performance over differential detection, with a moderate increase in receiver complexity and without requiring the periodic transmission of training blocks.
TL;DR: The estimation range can be greatly extended without sacrificing the estimation accuracy and a simple technique is indicated to measure the Doppler bandwidth, which allows the algorithm to operate in an adaptive manner in a time-varying environment.
Abstract: A data-aided feedforward algorithm has been proposed by Kuo and Fitz (see IEEE Trans. Commun., vol.45, p.1412-26, 1997) for carrier frequency estimation in M-ary phase-shift keying (PSK) transmissions over frequency-flat Rayleigh fading channels. Its accuracy is very good but the estimation range may be limited under certain operating conditions. Also, its application requires a knowledge of the Doppler bandwidth. We show that the estimation range can be greatly extended without sacrificing the estimation accuracy and a simple technique is indicated to measure the Doppler bandwidth. This allows the algorithm to operate in an adaptive manner in a time-varying environment.
TL;DR: It is shown that by using interleaving combined with a proper signal constellations and still using symbol-by-symbol detection, a higher diversity is obtained and the performance of uncoded PSK schemes over fading channels is considerably improved.
Abstract: The performance of uncoded phase-shift-keying (PSK) schemes over fading channels is only inversely proportional to the signal-to-noise ratio, which is not very reliable for digital communication applications. Improving their performance has been approached by means of coded modulation schemes, where code redundancy combined with interleaving introduces some degree of diversity that depends on the complexity of the code. This paper proposes an alternative way in improving the performance of PSK schemes over fading channels by looking at the reference scheme first. It is shown that by using interleaving combined with a proper signal constellations and still using symbol-by-symbol detection, a higher diversity is obtained and the performance of uncoded PSK schemes over fading channels is considerably improved. With this simple modification, the obtained performance is comparable to that of the best four-state trellis-coded-modulation (TCM) 8PSK schemes reported in the literature. By optimizing the reference scheme first, it is shown that this technique optimizes the performance of Ungerboeck's trellis-coded 8PSK schemes over fading channels. In fact, without altering their performance over the additive white Gaussian noise (AWGN) channel, significant coding gain over fading channels is achieved.
TL;DR: The loss due to imperfect channel estimation is derived for pilot symbol assisted binary phase-shift keying (BPSK) on fading channels with diversity and analytical optimization of pilot symbol spacing is provided.
Abstract: The loss due to imperfect channel estimation is derived for pilot symbol assisted binary phase-shift keying (BPSK) on fading channels with diversity. The presented approach, which holds for both narrow-band and spread spectrum communication, further provides an analytical optimization of pilot symbol spacing. The loss due to channel estimation is demonstrated to be low if the maximum Doppler frequency is significantly less than the bit rate.