It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

A historical perspective of orthogonal frequency-division multiplexing (OFDM) is given with reference to its literature. Its advantages and disadvantages are reviewed, and its performance is characterized over highly dispersive channels. The effects of both time- and frequency-domain synchronization errors are quantified, and a range of solutions proposed in the recent literature are reviewed. One of the main objectives of this review is to highlight the recent thinking behind adaptive bit allocation and turbo coding in the context of OFDM. This paper concludes with a wide-ranging throughput comparison of the schemes discussed herein under the unified constraint of a fixed target bit error rate of 10/sup -4/.

Prolog to adaptive multicarrier modulation: a convenient framework for time-frequency processing in wireless communications

Adaptive linear and decision feedback receiver structures for coherent demodulation in asynchronous code division multiple access (CDMA) systems are considered. It is assumed that the adaptive receiver has no knowledge of the signature waveforms and timing of other users. The receiver is trained by a known training sequence prior to data transmission and continuously adjusted by an adaptive algorithm during data transmission. The proposed linear receiver is as simple as a standard single-user detector receiver consisting of a matched filter with constant coefficients, but achieves essential advantages with respect to timing recovery, multiple access interference elimination, near/far effect, narrowband and frequency-selective fading interference suppression, and user privacy

Adaptive receiver structures for asynchronous CDMA systems

Acknowledgments.Historical Perspective, Motivation and Outline. I Convolutional and Block Coding. Convolutional Channel Coding. Block Coding. Soft Decoding and Performance of BCH Codes. II Turbo Convolutional and Turbo Block Coding. Turbo Convolutional Coding. The Super Trellis Structure of Convolutional Turbo Codes. Turbo BCH Coding. Redundant Residue Number System Codes. III Coded Modulation: TCM, TTCM, BICM, BICM ID. Coded Modulation Theory and Performance. IV Space Time Block and Space Time Trellis Coding. Space time Block Codes. Space Time Trellis Codes. Turbo coded Adaptive QAM versus Space time Trellis Coding. V Turbo Equalisation. Turbo coded Partial response Modulation. Turbo Equalisation for Partial response Systems. Turbo Equalisation Performance Bound. Comparative Study of Turbo Equalisers. Reduced complexity Turbo Equaliser. Turbo Equalisation for Space time Trellis coded Systems. Summary and Conclusions. Bibliography. Subject Index. Author Index. About the Authors.Other Related Wiley and IEEE Press Books.

Turbo Coding, Turbo Equalisation and Space-Time Coding for Transmission over Fading Channels

1) The Myth: Sixty years of research following Shannon's pioneering paper has led to telecommunications solutions operating arbitrarily close to the channel capacity-“flawless telepresence” with zero error is available to anyone, anywhere, anytime across the globe. 2)The Reality: Once we leave home or the office, even top of the range iPhones and tablet computers fail to maintain "flawless telepresence" quality. They also fail to approach the theoretical performance predictions. The 1000-fold throughput increase of the best third- generation (3G) phones over second-generation (2G) GSM phones and the 1000-fold increased teletraffic predictions of the next decade require substantial further bandwidth expansion toward ever increasing carrier frequencies, expanding beyond the radiofrequency (RF) band to optical frequencies, where substantial bandwidths are available. 3) The Future: However, optical and quantum-domain wireless communications is less developed than RF wireless. It is also widely recognized that the pathloss of RF wireless systems monotonically increases with the carrier frequency and this additional challenge has to be tackled by appropriate countermeasures in future research. Hence, we set out to seek promising techniques of tackling the aforementioned challenges and for resolving the conflicting design constraints imposed on the flawless telepresence systems of the future. To disspell the myth, we evaluate both the operational 3G as well as the emerging fourth-generation (4G) wireless systems and demonstrate that there is a substantial difference between their theoretical and their practically attainable performance. The reality is that the teletraffic predictions indicate further thirst for bandwidth, which cannot be readily satisfied within the most popular 1-2-GHz carrier-frequency range, where the best propagation conditions prevail. We briefly consider the 10-300-GHz unlicensed band as a potential source of further spectrum, followed by a review of advances way beyond the upper edge of the RF range at 300 GHz, namely to the realms of optical wireless (OW) communications. As the carrier frequency is increased, the pathloss is also increased, which results in ever smaller cells. Furthermore, the high-frequency RF waves predominantly obey line-of-sight (LOS) propagation-like visible light. The future requires advances in both infrared and visible-light communications for circumventing the LOS nature of light. We hypothesize that light-emitting diode (LED) arrays acting as "massive" multiple-input-multiple-output (MIMO) components as well as transmitter/receiver cooperation might be conceived. The heterogeneous networks of the near future will rely on seamless, near-instantaneous handovers among OW hotspots, RF hotspots, and oversailing larger cells. These "massive" MIMOs might impose a high complexity, hence their reduced-complexity noncoherently detected counterparts might be favored. Finally, we conclude by touching upon the promising research area of quantum-domain communications, which might be expected to circumvent the aforementioned complexity problem of massive MIMOs with the aid of efficient quantum-domain search techniques-a truly exciting research era

Wireless Myths, Realities, and Futures: From 3G/4G to Optical and Quantum Wireless

Adaptive Wireless Transceivers provides the reader with a broad overview of near-instantaneously adaptive transceivers in the context of TDMA, CDMA and OFDM systems The adaptive transceivers examined employ powerful turbo codecs, turbo equalisers and space-time codecs, equipping the reader with a future-proof technological road map It demonstrates that adaptive transceivers are capable of mitigating the channel quality fluctuations of the wireless channel as a lower-complexity alternative to space-time coding By contrast, if the higher complexity of multiple transmitters and multiple receiver-assisted systems is deemed acceptable, the advantages of adaptability erode • Provides an in-depth introduction to channel equalisers and Kalman filtering and discusses the associated complexity versus performance trade-offs • Introduces wideband near-instantaneously adaptive transceivers and studies their performance both with and without turbo channel coding • Describes how to optimise adaptive modulation mode switching and highlights a range of practical considerations • Introduces neural network based channel equalisers and discusses Radial Basis Function (RBF) assisted equalisers embedded into adaptive modems supported by turbo channel coding and turbo channel equalisation • Employs the above adaptive principles also in the context of CDMA and OFDM transceivers and discusses the pros and cons of space-time coding versus adaptive modulation Researchers, advanced students and practising development engineers working in wireless communications will all find this valuable text an informative read

Adaptive Wireless Transceivers: Turbo-Coded, Turbo-Equalized and Space-Time Coded TDMA, CDMA and OFDM Systems

A reduced complexity trellis-based turbo equalizer known as the in-phase (I)/quadrature-phase (Q) turbo equalizer (TEQ-IQ) invoking iterative channel impulse response (CIR) estimation is proposed. The underlying principle of TEQ-IQ is based on equalizing the I and Q component of the transmitted signal independently. This requires the equalization of a reduced set of separate I and Q signal components in comparison to all of the possible I/Q phasor combinations considered by the conventional trellis-based equalizer. It was observed that the TEQ-IQ operating in conjunction with iterative CIR estimation was capable of achieving the same performance as the full-complexity conventional turbo equalizer (TEQ-CT) benefiting from perfect CIR information for both 4- and 16-quadrature amplitude modulation (QAM) transmissions, while attaining a complexity reduction factor of 1.1 and 12.2, respectively. For 64-QAM, the TEQ-CT receiver was too complex to be investigated by simulation. However, by assuming that only two turbo equalization iterations were required, which is the lowest possible number of iterations, the complexity of the TEQ-IQ was estimated to be a factor of 51.5 lower than that of the TEQ-CT. Furthermore, at BER = 10/sup -3/ the performance of the TEQ-IQ 64-QAM receiver using iterative CIR estimation was only 1.5 dB away from the associated decoding performance curve of the nondispersive Gaussian channel.

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Reduced complexity in-phase/quadrature-phase M-QAM turbo equalization using iterative channel estimation

The video performance benefits of burst-by-burst adaptive modulation are studied, employing a higher-order modulation scheme when the channel is favorable, in order to increase the system's bits per symbol capacity and conversely, invoking a more robust lower order modulation scheme when the channel exhibits inferior channel quality. It is shown that due to the proposed adaptive modem mode switching regime, a seamless video quality versus channel quality relationship can be established, resulting in error-free video quality right actress the operating channel signal-to-noise ratio (SNR) range. The main advantage of the proposed burst-by-burst adaptive transceiver technique is that irrespective of the prevailing channel conditions, the transceiver achieves always the best possible source-signal representation quality-such as video, speech, or audio quality-by automatically adjusting the achievable bit rate and the associated multimedia source-signal representation quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path loss, fast-fading, slow-fading, dispersion, co-channel interference, etc. Furthermore, when the mobile is roaming in a hostile out-doors-or even hilly terrain-propagation environment, typically low-order low-rate modem modes are invoked, while in benign indoor environments, predominantly the high-rate high source-signal representation quality modes are employed.

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Turbo- and BCH-coded wide-band burst-by-burst adaptive H.263-assisted wireless video telephony

The design trade-offs of interactive wireless video systems are discussed and performance comparisons are provided both in the context of second- and third-generation wireless videophone systems. We commence our discussions by a comparative study of arbitrarily programmable, but fixed-rate, videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s. These proprietary codecs were designed to allow direct replacement of mobile radio voice codecs in second generation wireless systems, such as the Pan-European GSM, the American IS-54 and IS-95 as well as the Japanese systems, operating at 13, 8, 9.6 and 6.7 kbps, respectively, although better video quality is maintained over higher-rate, 32 kbps cordless systems, such as the Japanese PHS and the European DECT and CT2 systems. From the range of codecs investigated, best overall performance was achieved by our vector-quantised codecs, followed by the discrete cosine transformed and the quadtree-based schemes. The associated video peak signal-to-noise ratio (PSNR) was around 30 dB, while the subjective video quality can be assessed under http://www-mobile.ecs.soton.ac.uk. A range of multimode wireless transceivers is also proposed. The second part of the paper is dedicated to burst-by-burst (BbB) adaptive wireless video transceivers employing the standard H.263 codec. It is demonstrated that the proposed BbB adaptive transceivers provide an improved video performance in comparison to their statically reconfigured counterparts in the context of both wideband BbB adaptive quadrature amplitude modulation (AQAM) transceivers and the joint-detection based code division multiple access (CDMA) transceivers of the third generation systems.

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Burst-by-burst adaptive wideband wireless video telephony

The performance of adaptive modulation-applied in conjunction with turbo equalization (TE)-is characterized in a noise limited environment over a slowly varying wideband multi-path Rayleigh fading channel. The iterative structure of the turbo equalizer was also exploited in order to invoke an iterative least mean square (LMS) channel estimator. Finally, the throughput performance of the adaptive modulation scheme was compared to that of its constituent modulation modes, where a gain of 1.5 dB to 1.7 dB was recorded.

/pdf/wideband-burst-by-burst-adaptive-modulation-with-turbo-tmbucvs3xo.pdf

C. H. Wong

Papers

Adaptive Wireless Transceivers: Turbo-Coded, Turbo-Equalized and Space-Time Coded TDMA, CDMA and OFDM Systems

Reduced complexity in-phase/quadrature-phase M-QAM turbo equalization using iterative channel estimation

Turbo- and BCH-coded wide-band burst-by-burst adaptive H.263-assisted wireless video telephony

Burst-by-burst adaptive wideband wireless video telephony

Wideband burst-by-burst adaptive modulation with turbo equalization and iterative channel estimation