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Showing papers on "Spectral efficiency published in 1998"


Journal ArticleDOI
TL;DR: The theory of conventional telecommunications is extended to chaotic communications, chaotic modulation techniques and receiver configurations are surveyed, and chaotic synchronization schemes are described.
Abstract: For pt. I see ibid., vol. 44, p. 927-36 (1997). In a digital communications system, data are transmitted from one location to another by mapping bit sequences to symbols, and symbols to sample functions of analog waveforms. The analog waveform passes through a bandlimited (possibly time-varying) analog channel, where the signal is distorted and noise is added. In a conventional system the analog sample functions sent through the channel are weighted sums of one or more sinusoids; in a chaotic communications system the sample functions are segments of chaotic waveforms. At the receiver, the symbol may be recovered by means of coherent detection, where all possible sample functions are known, or by noncoherent detection, where one or more characteristics of the sample functions are estimated. In a coherent receiver, synchronization is the most commonly used technique for recovering the sample functions from the received waveform. These sample functions are then used as reference signals for a correlator. Synchronization-based coherent receivers have advantages over noncoherent receivers in terms of noise performance, bandwidth efficiency (in narrow-band systems) and/or data rate (in chaotic systems). These advantages are lost if synchronization cannot be maintained, for example, under poor propagation conditions. In these circumstances, communication without synchronization may be preferable. The theory of conventional telecommunications is extended to chaotic communications, chaotic modulation techniques and receiver configurations are surveyed, and chaotic synchronization schemes are described.

474 citations


Journal ArticleDOI
TL;DR: The interference-limited performance of the PPM-OCDMA system is found to be superior to that of the original system when the number of simultaneous users is of the order of thePPM word length or larger.
Abstract: Spectral-amplitude-coding optical code-division multiple-access (OCDMA) systems are limited by interference between incoherent sources. A detailed analysis of this limit for a system with a balanced receiver is presented. Additional pulse-position modulation (PPM) coding is proposed as a method to improve the system performance beyond this limit. A simple and robust PPM decoding structure is proposed, and the performance analysis of the whole PPM-OCDMA system is presented. The interference-limited performance of the PPM-OCDMA system is found to be superior to that of the original system when the number of simultaneous users is of the order of the PPM word length or larger. In particular, for a PPM word length of two, an increase in spectral efficiency of up to 100% is possible with no change in the signaling rate, data rate, or bit-error rate (BER).

329 citations


Proceedings ArticleDOI
01 Nov 1998
TL;DR: The Imagine architecture supports the stream programming model by providing a bandwidth hierarchy tailored to the demands of media applications by reducing the global register and memory bandwidth required by typical applications by factors of 13 and 21 respectively.
Abstract: Media applications are characterized by large amounts of available parallelism, little data reuse, and a high computation to memory access ratio. While these characteristics are poorly matched to conventional microprocessor architectures, they are a good fit for modern VLSI technology with its high arithmetic capacity but limited global bandwidth. The stream programming model, in which an application is coded as streams of data records passing through computation kernels, exposes both parallelism and locality in media applications that can be exploited by VLSI architectures. The Imagine architecture supports the stream programming model by providing a bandwidth hierarchy tailored to the demands of media applications. Compared to a conventional scalar processor. Imagine reduces the global register and memory bandwidth required by typical applications by factors of 13 and 21 respectively. This bandwidth efficiency enables a single chip Imagine processor to achieve a peak performance of 16.2GFLOPS (single-precision floating point) and sustained performance of up to 8.5GFLOPS on media processing kernels.

280 citations


Journal ArticleDOI
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.

171 citations


Journal ArticleDOI
TL;DR: Frequency-domain correlative coding with correlation polynomial F(D)=1-D in OFDM mobile communication systems to compress the intercarrier interference caused by channel frequency errors shows that such a simple coding method enhances system CIR by 3.5 dB, without reducing the bandwidth efficiency.
Abstract: This study considers the use of frequency-domain correlative coding with correlation polynomial F(D)=1-D in OFDM mobile communication systems to compress the intercarrier interference caused by channel frequency errors. A theoretical expression of carrier-to-interference power ratio (CIR) has been derived. It shows that such a simple coding method enhances system CIR by 3.5 dB, without reducing the bandwidth efficiency.

134 citations


Journal ArticleDOI
TL;DR: A basic service concept, advanced cellular Internet service (ACIS), and the technologies for achieving reliable high-speed transmission to wide-area mobile and portable cellular subscribers with very high spectrum efficiency are described.
Abstract: The public's desire for mobile communications and computing, as evidenced by the popularity of cellular phones and laptop computers combined with the explosive demand for Internet access suggest a very promising future for wireless data services. The key to realizing this potential is the development and deployment of high-performance radio systems. In this article we describe a basic service concept, advanced cellular Internet service (ACIS), and the technologies for achieving reliable high-speed transmission to wide-area mobile and portable cellular subscribers with very high spectrum efficiency. Such a wireless service, optimized to meet the needs of a client-server model for information retrieval and Web browsing, and combined with evolutionary enhancements in second-generation technologies, can provide an attractive option for third-generation systems. The radio link design combines OFDM with transmit and receive antenna diversity and Reed-Solomon coding to overcome the link budget and dispersive fading limitations of the cellular mobile radio environment. For access, a dynamic packet assignment algorithm is proposed which combines rapid interference measurements, priority ordering, and a staggered frame assignment schedule to provide spectrum efficiencies of two-to-four times existing approaches.

94 citations


Journal ArticleDOI
TL;DR: A dynamic packet assignment (DPA) scheme which, without coordinating base stations, allocates spectrum on demand with no collisions and low interference to provide high downlink throughput and is able to reuse spectrum efficiently in a large cellular system having many users with short active periods is proposed.
Abstract: The advanced cellular Internet service (ACIS) is targeted for applications such as Web browsing with a peak downlink transmission rate on the order of 1-2 Mbits/s using a wide-area cellular infrastructure. In order to provide bandwidth on demand using scarce radio spectrum, the medium-access control (MAC) protocol must: 1) handle dynamic and diverse traffic with high throughput, and 2) efficiently reuse limited spectrum with high peak rates and good quality. Most of the existing approaches do not sufficiently address the second aspect. This paper proposes a dynamic packet assignment (DPA) scheme which, without coordinating base stations, allocates spectrum on demand with no collisions and low interference to provide high downlink throughput. Interference sensing and priority ordering are employed to reduce interference probability. A staggered frame assignment schedule is also proposed to prevent adjacent base stations from allocating the same channel to multiple mobiles at the same time. Simulation results based on a packet data traffic model derived from wide-area network traffic statistics, which exhibit a "self-similar" property when aggregating multiple sources, confirm that this method is able to reuse spectrum efficiently in a large cellular system having many users with short active periods. Distributed iterative power control further enhances spectrum efficiency such that the same channel can be simultaneously reused in every base station.

82 citations


Proceedings ArticleDOI
18 May 1998
TL;DR: Simulations show that the introduction of EDGE significantly increases the user bit rates in both coverage and interference limited systems compared to standard GSM, and spectral efficiency is also increased considerably.
Abstract: The use of alternative modulation to provide Enhanced Data rates for Global Evolution (EDGE) is currently being standardized for GSM by the European Telecommunications Standards Institute (ETSI), and is also adopted for IS-136 evolution by the Universal Wireless Communications Consortium (UWCC) in the US. This paper analyzes the system performance of the EDGE concept. Two scenarios are studied: one where EDGE is introduced in an existing GSM system with 3/9 frequency reuse, and one where EDGE is introduced as an IS-136 overlay, using a very limited amount of spectrum and 1/3 frequency reuse. Both capacity and coverage results are provided. Simulations show that the introduction of EDGE significantly increases the user bit rates in both coverage and interference limited systems compared to standard GSM. The spectral efficiency is also increased considerably. It is also shown that spectral efficiencies exceeding 0.45 bps/Hz/site can be achieved when EDGE is introduced in an IS-136 system using a 1/3 frequency reuse pattern. Further, coverage simulations indicate that existing sites can be reused when EDGE is introduced.

76 citations


Book ChapterDOI
01 Jan 1998
TL;DR: It is shown how this detection scheme can be further improved by adaptive calculation of the soft-decision rule, which enables a significantly higher number of active users signaling within the same bandwidth to be detected, implying that spectral efficiency is increased.
Abstract: Multiuser detection by iterated soft-decision interference cancellation is known to achieve almost single user performance in low and moderate interference scenarios. In this paper, it is shown how this detection scheme can be further improved by adaptive calculation of the soft-decision rule. This enables a significantly higher number of active users signaling within the same bandwidth to be detected, implying that spectral efficiency is increased.

73 citations


Journal ArticleDOI
T. Ono1, Y. Yano
TL;DR: In this paper, the authors investigated the key technologies to achieve terabit/second wavelength-division multiplexing (WDM) systems with over 1 bit/s/Hz spectral efficiency.
Abstract: To fully utilize a limited gain bandwidth of about 35 nm (4.4 THz) in an erbium-doped fiber amplifier, an increase in signal spectral efficiency is required. In this paper, we investigate the key technologies to achieve terabit/second wavelength-division multiplexing (WDM) systems with over 1 bit/s/Hz spectral efficiency. Optical duobinary signals, which have narrower optical spectra than conventional intensity modulation signals, were applied to such dense WDM systems. The measured minimum channel spacing for 20-Gbit/s optical duobinary signals was 32 GHz and a spectral efficiency of over 0.6 bit/s/Hz was reached. By using polarization interleave multiplexing, spectral efficiency was expected to reach 1.2 bit/s/Hz in an ideal case with no polarization dependencies along the transmission lines. In such ultradense WDM systems with narrower channel spacing, stabilizing the wavelengths of laser diodes is an important issue for achieving stable operation over long periods. To do this, we developed a simple and flexible wavelength stabilization system which uses a multiwavelength meter. The wavelengths for 116 channels with 35-GHz spacing were stabilized within /spl plusmn/150 MHz. The stabilization system is applicable to ultradense WDM signals with a spectral efficiency of over 1 bit/s/Hz by employing wavelength interleave multiplexing and an optical selector switch. On the basis of these investigations, we demonstrated a 2.6-Tbit/s (20 Gbit/s/spl times/132 channels) WDM transmission by using optical duobinary signals. In addition, 1.28-Tbit/s (20 Gbit/s/spl times/64 channels) WDM transmission with a high spectral efficiency of 1 bit/s/Hz was achieved by using polarization interleave multiplexing.

66 citations


Journal ArticleDOI
TL;DR: In this paper, the optical single-sideband (SSB) OFDM can achieve the highest spectrum efficiency of 0.25 b/s/Hz with error-free transport of two-channel 4.98 Gb/s BPSK signal on 10 GHz wireless carrier with the frequency channel interval of 20 GHz at 1550 nm over 50 km-long standard singlemode fiber link.
Abstract: Optical frequency division multiplexing (OFDM) wireless access network using optical single-sideband modulation is proposed, which allows to deliver different wireless signals from a central station to each base station over an optical fiber network. The optical single-sideband (SSB) OFDM can achieve the highest spectrum efficiency of 0.25 b/s/Hz. A 0.25 b/s/Hz has been experimentally verified by the error-free transport of two-channel 4.98 Gb/s BPSK signal on 10 GHz wireless carrier with the frequency channel interval of 20 GHz at 1550 nm over 50 km-long standard single-mode fiber link. Furthermore, it has been also experimentally confirmed that by introducing the polarization division multiplexing (PDM), the ultimate spectrum efficiency of 0.5 b/s/Hz can be achieved by the hybrid OFDM/PDM.

Proceedings ArticleDOI
18 May 1998
TL;DR: A high bandwidth efficiency variable rate adaptive channel coding scheme, ATCQAM, is proposed, which matches the variable modulation level with a variable rate channel coder, the physical bandwidth is maintained constant.
Abstract: A high bandwidth efficiency variable rate adaptive channel coding scheme, ATCQAM, is proposed. Known pilot symbols are transmitted periodically to aid demodulation. Past channel states are fed back to the transmitter with delay. Current channel state is then predicted at the transmitter to decide on the appropriate modulation mode for the current symbol. At good channel states, high level modulation is used to boost up the average throughput. At bad channel states, low level modulation is used to increase error protection. By matching the variable modulation level with a variable rate channel coder, the physical bandwidth is maintained constant. Design issues for the ATCQAM are considered. The effects of finite feedback delay, finite interleaving depth and mobile speed are investigated.

Journal ArticleDOI
TL;DR: This paper presents an application of a filtered decision feedback channel estimator for OFDM-based DTV systems using high order QAM modulations and the implementation and the performance of the channel estimators are discussed.
Abstract: Orthogonal frequency division multiplexing (OFDM) is one of the transmission techniques used for digital television (DTV) terrestrial broadcasting. A high quality channel estimator with a low training overhead is the key to the successful delivery of DTV services which require high spectrum efficiency and robustness to strong and dynamic ghosts. Robustness to multipath distortion is especially important in a single frequency emission environment. This paper presents an application of a filtered decision feedback channel estimator for OFDM-based DTV systems using high order QAM modulations. The implementation and the performance of the channel estimator are discussed. Computer simulations were conducted to evaluate the performance of the channel estimator. The channel estimation loss is about 1.2 dB from the ideal case where the channel is assumed to be known by the receiver. For a given multipath spread, the loss can be further reduced by increasing the FFT size. The FFT size is however subject to an upper limit imposed by the Doppler spread.

Journal ArticleDOI
TL;DR: This paper proposes several algorithms for scheduling the efficient transmission of data to multiple users that significantly outperform conventional schemes and provides a powerful approach to improving spectrum efficiency in forthcoming high-speed data cellular services.
Abstract: Next-generation wireless networks are expected to support a wide range of high-speed data services, with Web browsing as one of the major applications. Although high data rates have been shown feasible in a single-user setting, the resource allocation issues that arise in a multiple-user context remain extremely challenging. Compared with voice, data traffic is typically more bursty, while the users are less sensitive to delay. These characteristics require resource allocation strategies to operate in a fundamentally different manner if the spectrum is to be used efficiently. In this paper we propose several algorithms for scheduling the efficient transmission of data to multiple users. As a new feature, the various schemes exploit knowledge of the buffer contents to achieve high throughput, while maintaining fairness by providing quality of service (QoS) to individual users. The proposed algorithms are backward compatible with existing cellular and personal communications services (PCS) standards such as IS-136. They provide a powerful approach to improving spectrum efficiency in forthcoming high-speed data cellular services. The extensive simulation experiments we present in this paper demonstrate that the algorithms significantly outperform conventional schemes.

Proceedings ArticleDOI
01 Jan 1998
TL;DR: In this paper, a channel estimation method based on pilot symbols inserted both in time and frequency domains, and a linear interpolation algorithm has been proposed to minimize the system complexity and processing delay while giving a good approximation to the real mobile channel.
Abstract: Orthogonal Frequency Division Multiplexing ( OFDM ) is considered an effective technique in high speed digital transmission due to its spectral efficiency, its robustness in different multipath propagation environments and its ability to combat intersymbol interference ( ISI ). Coherent modulation combined with OFDM gives an optimum performance but needs a powerful channel estimator. In this paper we present a channel estimation method based on pilot symbols inserted both in time and frequency domains, and a linear interpolation algorithm. This linear interpolation algorithm has the advantage of minimising the system complexity and processing delay while giving a good approximation to the real mobile channel. The performance of the linear pilot aided estimation algorithm is compared to coherent modulation with perfect channel estimation as well as to differential modulation.

Patent
27 Jan 1998
TL;DR: In this article, a method and apparatus for allocating channels include making signal quality measurements for channels that are in use or available for use and for channels which may become available again.
Abstract: In a telecommunications network, a method and apparatus for allocating channels include making signal quality measurements for channels that are in use or available for use and for channels that may become available for use. Spectral efficiency is enhanced by considering the exclusionary bandwidths associated with combiner filters tuned to currently allocated frequencies.

Proceedings ArticleDOI
18 May 1998
TL;DR: In this paper, a simple, efficient, and robust voice activity detection (VAD) algorithm was developed to work in a mobile or portable environment exhibiting dynamically varying background noise, using probabilistic distances based on the energy content, the periodicity, the stationarity and the spectral distribution within the low frequency band to decide if the presented speech frame is speech or silence.
Abstract: Speech can be modeled as short bursts of vocal energy separated by silence gaps. During typical conversation talk-spurts comprise only 31.5% of each party's speech and the remaining 68.5% is silence. Communication systems can achieve significant gains in spectral efficiency and energy efficiency by disconnecting the users from the spectral resource during the silence periods. This paper develops a simple, efficient, and robust voice activity detection (VAD) algorithm to work in a mobile or portable environment exhibiting dynamically varying background noise. The VAD uses probabilistic distances based on the energy content, the periodicity, the stationarity and the spectral distribution within the low frequency band to decide if the presented speech frame is speech or silence.

Journal ArticleDOI
TL;DR: There is a considerable capacity gap between actual F-TDMA systems and the limits predicted by the analysis, but this gap can be filled by carefully designed (practical) systems, which make use of conventional single-user processing and simple coded modulation schemes.
Abstract: We study the system capacity of cellular systems with time-division multiple access, slow time-frequency hopping (F-TDMA), and conventional single-user processing at the receivers. System capacity is formally defined as the maximum of the product of the number of users per cell times the user spectral efficiency for a given maximum outage probability. We adopt an information-theoretic definition of outage as the event that the mutual information of the block-interference channel resulting from a finite number of signal bursts spanned by the transmission of a user code word falls below the actual code rate, because of fading, shadowing, and interference. Starting from this definition, we develop a general framework which naturally takes into account many different aspects of F-TDMA cellular systems like channel reuse, channel utilization, waveform design, time-frequency hopping, voice activity exploitation, handoff, and power control strategies. Most importantly, our analysis does not rely on the choice of a particular coding scheme and can be applied to a very large class of systems in order to find guidelines for capacity-maximizing system design. A numerical example based on a typical urban mobile environment shows that there is a considerable capacity gap between actual F-TDMA systems and the limits predicted by our analysis. However, this gap can be filled by carefully designed (practical) systems, which make use of conventional single-user processing and simple coded modulation schemes.

Proceedings ArticleDOI
31 May 1998
TL;DR: This paper compares CAP versus QAM modulation and highlights some practical implementation issues, and three different CAP-like architectures are compared according to A/D sampling-rates, A/ D resolutions and jitter requirements.
Abstract: Recently CAP modulation (Carrierless Amplitude and Phase modulation) has been of wide interest to industry because of its simplicity, bandwidth efficiency and zero dc component. This paper compares CAP versus QAM modulation and highlights some practical implementation issues. In addition, three different CAP-like architectures are compared according to A/D sampling-rates, A/D resolutions and jitter requirements.

Proceedings ArticleDOI
K. Chawla1, Xiaoxin Qiu
05 Oct 1998
TL;DR: Numerical analysis shows that adaptive modulation even without power control has significant throughput advantage over SIR-balancing power control and an iterative algorithm that converges to the optimal in very few steps is proposed.
Abstract: Adaptive modulation techniques have the potential to substantially increase the spectrum efficiency and to provide different levels of service to users, both of which are considered important for third generation cellular systems. In this work, we propose a general framework to quantify the potential gains of such techniques. We characterize the optimum throughput of the system with adaptive modulation and power control, and then propose an iterative algorithm that converges to this optimum. Numerical analysis shows that (i) adaptive modulation even without power control has significant throughput advantage over SIR-balancing power control; and (ii) the proposed iterative algorithm converges to the optimal in very few steps. The first observation is especially important from an implementation point of view. Adjusting the modulation level without changing the transmission power does not involve the repeated measurements and feedback, which significantly simplifies the implementation. This work provides valuable insight into the performance of adaptive modulation in multi-user environments.

Proceedings ArticleDOI
08 Sep 1998
TL;DR: A blind method using the correlation of the samples at the output of the discrete Fourier transform (DFT) to estimate and correct the frequency offset is proposed and an adaptive algorithm for the Frequency offset correction is developed.
Abstract: Orthogonal frequency division multiplexing (OFDM) is believed to be an important technique for future wireline and wireless communications. One of the major disadvantages of such a multi-carrier modulation is the sensitivity of the performance to a frequency offset. The frequency offset can result from a Doppler shift due to mobile movement as well as from a carrier frequency synchronization error. Such a frequency offset causes a loss of the carriers' orthogonality, and hence inter-carrier interference (ICI). A previously proposed method to estimate and correct the frequency offset uses the retransmission of a data symbol, thus reducing the bandwidth efficiency. Another method, which merely reduces the effects of the ICI instead of completely correcting for effects of the frequency offset is based on repetition coding in the frequency domain, hence also reducing the throughput. In this paper, we propose a blind method using the correlation of the samples at the output of the discrete Fourier transform (DFT) to estimate the frequency offset. As no training sequence or symbol retransmission is required there is no loss in bandwidth efficiency. Additionally, we develop an adaptive algorithm for the frequency offset correction. The derived algorithm is basically a stochastic gradient algorithm which minimizes the mean squared frequency offset error.

Proceedings ArticleDOI
02 Sep 1998
TL;DR: A bandwidth efficiency plan for the different MC multiple access schemes in fading channels, the influence of the channel code rate, the system load, and the spreading code length is presented.
Abstract: The multi-carrier (MC) multiple access schemes MC-FDMA, MC-TDMA, MC-CDMA and the previously proposed SS-MC-MA scheme are investigated and compared for the suitability in the uplink and the downlink of a mobile radio system. By presenting a bandwidth efficiency plan for the different MC multiple access schemes in fading channels, the influence of the channel code rate, the system load, and the spreading code length is presented. Moreover, results with oneand two-dimensional pilot symbol aided channel estimation are shown for the various MC multiple access schemes considering typical multipath propagation scenarios in the uplink and the downlink.

Proceedings ArticleDOI
Justin C. Chuang1
08 Nov 1998
TL;DR: In this paper, a dynamic packet assignment (DPA) method has been proposed as a key component of the MAC protocol for an OFDM-based advanced cellular Internet service (ACIS) system, which is targeted for applications such as Web browsing, with a peak downlink transmission rate on the order of 1 Mb/s using a wide-area cellular infrastructure.
Abstract: Future wireless networks are expected to employ packet access with high peak-bandwidth demands. This will impose a significant challenge for frequency reuse, especially for services deployed in a wide area. A dynamic packet assignment (DPA) method has been proposed as a key component of the MAC protocol for an OFDM-based advanced cellular Internet service (ACIS) system, which is targeted for applications such as Web browsing, with a peak downlink transmission rate on the order of 1 Mb/s using a wide-area cellular infrastructure. This method is able to allocate radio resources on a packet time scale and reassign them in about 100 msec, thereby gaining advantages in both statistical multiplexing of packet access and spectrum efficiency of dynamic channel assignment (DCA). Interference suppression is considered in this paper as method for performance enhancement. Following a detailed discussion of the frame structure and the DPA algorithm, comprehensive performance evaluation on the downlink delay and throughput characteristics is presented. It is found that this method achieves significant performance without requiring additional overhead.

Journal ArticleDOI
TL;DR: In this article, a high bandwidth efficiency variable rate adaptive channel coding scheme, ATC-QAM, is proposed, where known pilot symbols are transmitted periodically to aid demodulation.
Abstract: A high bandwidth efficiency variable rate adaptive channel coding scheme, ATC-QAM, is proposed. Known pilot symbols are transmitted periodically to aid demodulation. Past channel states are fed back to the transmitter with delay. Current channel state is then predicted at the transmitter to decide on the appropriate modulation mode for the current symbol. At good channel state, high level modulation is used to boost up the average throughput. At bad channel state, how level modulation is used to increase error protection. By matching the variable modulation level with a variable rate channel coder, the physical bandwidth is maintained constant. Design issues for the ATCQAM are considered. Pradicol schmes to maintain transmitter-receiver synchranization, namely the quasi-Closed loop control and the closed-loop control, are discussed. The effects offinite feedback delay, finite interleaving depth and mobile speed are Investigated. Keywords: Adaptive Channel Coding

Proceedings ArticleDOI
A. Jalali1, A. Gutierrez
18 May 1998
TL;DR: In this article, the forward link performance of a direct spread CDMA system with a spreading bandwidth of 3.6864 MHz and a multicarrier system consisting of 3 carriers each with a 1.2288 MHz is compared.
Abstract: The objective of this paper is to compare the forward link performance of a direct spread CDMA system with a spreading bandwidth of 3.6864 MHz and a multicarrier system consisting of 3 carriers each with a spreading bandwidth of 1.2288 MHz. In addition to providing a description of a multicarrier method, which is under consideration for the forward link of the next generation CDMA cellular/PCS systems, this paper summarizes performance comparison results of the two systems for a data rate of 9.6 kbps with the IMT-2000 vehicular and pedestrian channel models. The results indicate that the two systems have comparable performance for the above data rate and the IMT-2000 channel models.

Proceedings ArticleDOI
18 May 1998
TL;DR: It is found that several iterations are required, upon changes of co-channel interference, to update the transmit powers for all active links in order to achieve desirable improvement, and for a system having many data terminals with short duty cycles, significant overhead may be required for iterative power control.
Abstract: Wireless broadband networks are expected to employ packet access with high peak-bandwidth demands. This will impose a significant challenge for frequency reuse, especially for the case of ubiquitous services deployed in a wide area. A dynamic packet assignment (DPA) method has been proposed as a key component of the MAC protocol for an OFDM-based advanced cellular Internet service (ACIS) system, which is targeted for applications such as Web browsing, with a peak downlink transmission rate on the order of 1 Mb/s using a wide-area cellular infrastructure. This method is able to allocate radio resources on a packet time scale and reassign them in less than 100 msec, thereby gaining advantages in both statistical multiplexing of packet access and spectrum efficiency of dynamic channel assignment (DCA). One way to achieve very high spectrum efficiency is by using closed-loop SIR-based power control. This paper studies the implementation and performance of various power control methods for DPA in the ACIS environment. It is found that several iterations are required, upon changes of co-channel interference, to update the transmit powers for all active links in order to achieve desirable improvement. However, for a system having many data terminals with short duty cycles, significant overhead may be required for iterative power control. Alternative techniques such as interference suppression, which does not require high iteration overhead, may be attractive options.

Patent
22 Jul 1998
TL;DR: In this paper, the authors proposed an improved communication system which provides improved spectral efficiency as well as relatively low co-channel interference modulation characteristics relative to known communication systems, in particular, the communication system includes a modem that includes an arbitrary or chaotic waveform generator and a chaotic wave-form demodulator configured as a sliding window correlator.
Abstract: An improved communication system which provides improved spectral efficiency as well as relatively low co-channel interference modulation characteristics relative to known communication systems. In particular, the communication system includes a modem that includes an arbitrary or chaotic waveform generator and a chaotic waveform demodulator configured as a sliding window correlator that is adapted to modulate and demodulate an arbitrary or chaotic waveforms. The modulator includes a finite impulse response (FIR) filter, for example, formed from tapped delay lines with unequal time delays. The demodulator is formed as a matched filter for recovery of the input data signals. The modem is adapted to transmit either optical or RF waveforms. In order to prevent drift of the tap weights due to temperature drift of the tapped delay lines and other factors, a closed servo loop may be provided for each tap weight. By maintaining the accuracy of the tap weights, the system in accordance with the present invention is adapted to provide arbitrary or chaotic modulation and demodulation of the input data signal thereby providing increased spectral efficiency and improved performance which provides increased data output relative to known communication systems based on modulation of periodic signals while minimizing auto correlation errors.

Proceedings ArticleDOI
09 Aug 1998
TL;DR: Analysis of cellular systems where the base stations are placed at random compares the base station to mobile link in random systems to ideal hexagonal systems and shows how deployment costs and deployment speed can be greatly reduced.
Abstract: This paper analyzes cellular systems where the base stations are placed at random. Analysis compares the base station to mobile link in random systems to ideal hexagonal systems. Under log-normal shadow fading and sectorizing-but no channel planning-the random system has carrier to interference levels within 4 dB and spectral efficiency within 2 dB of the hexagonal system. A simple linear-time channel assignment algorithm reduces each of these differences by 1 dB. Thus, at a modest cost in performance, deployment costs and deployment speed can be greatly reduced.

Proceedings ArticleDOI
18 May 1998
TL;DR: The spectral efficiency of four channel coding schemes for GPRS is analyzed in a cellular system with different omnicell frequency reuse patterns, and shows that a frequency reuse of 3 and a code rate of 2/3-3/4 is the most spectrum efficient combination.
Abstract: In the Global System for Mobile Communications (GSM) phase 2+ development, one major activity has been to specify the General Packet Radio Service (GPRS). The purpose of GPRS is to accomplish efficient dynamic spectrum resource sharing between data sources that are bursty in nature, GPRS is well integrated in the overall GSM structure, to allow smooth introduction in existing GSM networks. Four channel coding schemes are defined for GPRS, which facilitates high throughput in a variety of radio conditions. The spectral efficiency of these schemes is analyzed in a cellular system with different omnicell frequency reuse patterns (1, 3 and 7). The results show that a frequency reuse of 3 and a code rate of 2/3-3/4 is the most spectrum efficient combination.

Proceedings ArticleDOI
20 Sep 1998
TL;DR: A new class of transmission line codes, called PASS codes, capable of dramatically increasing the spectral efficiency of DWDM transmission are proposed, and generalize the spectral shaping characteristics of duobinary signaling to multi-bit data representations.
Abstract: We propose and analyze a new class of transmission line codes, called PASS codes, capable of dramatically increasing the spectral efficiency of DWDM transmission. PASS codes generalize the spectral shaping characteristics of duobinary signaling to multi-bit data representations.