Showing papers on "Spectral efficiency published in 2003"

Multi-Carrier and Spread Spectrum Systems

Abstract: From the Publisher: Frequency spectrum is a limited and valuable resource for wireless communications. A good example can be observed among network operators in Europe for the prices to pay for UMTS-frequency bands. Therefore, the first goal when designing future wireless communication systems (e.g. 4G - fourth generation) has to be the increase in spectral efficiency. The development in digital communications in the past years has enabled efficient modulation and coding techniques for robust and spectral efficient data, speech, audio and video transmission. These are the multi-carrier modulation (e.g. OFDM) and the spread spectrum technique (e.g. DS-CDMA), where OFDM was chosen for broadcast applications (DVB, DAB) as well as for broadband wireless indoor standards (ETSI HIPERLAN-II, IEEE-802.11) and the DS-CDMA was selected in mobile communications (IS-95, third generation mobile radio systems world wide, UMTS/IMT 2000). Since 1993 various combinations of multi-carrier (MC) modulation and the spread spectrum (SS) technique have been introduced and the field of MC-SS communications has become an independent and important research topic with increasing activities. New application fields have been proposed such as high rate cellular mobile, high rate wireless indoor and LMDS. It has been shown that MC-SS offers the high spectral efficiency, robustness and flexibility that is required for the next generation systems. Meanwhile, different alternative hybrid schemes such as OFDM/OFDMA, MC-TDMA, etc. have been deeply analysed and adopted in different international standards (ETSI-BRAN, IEEE-802 & MMAC). Multi-Carrier & Spread-Spectrum: Analysis of Hybrid Air Interfaces draws together all ofthe above mentioned hybrid schemes therefore providing a greatly needed resource for system engineers, telecommunication designers and researchers in order to enable them to develop, build and deploy several schemes based on MC-transmission for the next generation systems (which will be an integration of broadband multimedia services covering both 4G mobile and fixed wireless systems). Offers a complete treatment of multi-carrier, spread-spectrum (SS) and time division multiplexing (TDM) techniquesProvides an in-depth insight into hybrid multiple access techniques based on multi-carrier (MC) transmissionPresents numerous hybrid multiple access and air interface architectures including OFDM/CDMA, MC-CDMA, MC-DS-CDMA and MT-CDMACovers new techniques such as space-time coding and software radio Telecommunications engineers, hardware & software system designers and researchers as well as students, lecturers and technicians will all find this an invaluable addition to their bookshelf.

Universal space-time coding

Abstract: A universal framework is developed for constructing full-rate and full-diversity coherent space-time codes for systems with arbitrary numbers of transmit and receive antennas. The proposed framework combines space-time layering concepts with algebraic component codes optimized for single-input-single-output (SISO) channels. Each component code is assigned to a "thread" in the space-time matrix, allowing it thus full access to the channel spatial diversity in the absence of the other threads. Diophantine approximation theory is then used in order to make the different threads "transparent" to each other. Within this framework, a special class of signals which uses algebraic number-theoretic constellations as component codes is thoroughly investigated. The lattice structure of the proposed number-theoretic codes along with their minimal delay allow for polynomial complexity maximum-likelihood (ML) decoding using algorithms from lattice theory. Combining the design framework with the Cayley transform allows to construct full diversity differential and noncoherent space-time codes. The proposed framework subsumes many of the existing codes in the literature, extends naturally to time-selective and frequency-selective channels, and allows for more flexibility in the tradeoff between power efficiency, bandwidth efficiency, and receiver complexity. Simulation results that demonstrate the significant gains offered by the proposed codes are presented in certain representative scenarios.

Rate control for multi-channel communication systems

Abstract: Techniques to determine a set of rates for a set of data streams to be transmitted in a multi-channel communication system A group of transmission channels to be used for each data stream is initially identified An equivalent system for each group is then defined to have an AWGN (or flat) channel and a spectral efficiency equal to the average spectral efficiency of the transmission channels in the group (216) A metric for each group is then derived based on the associated equivalent system, eg, set to the SNR needed by the equivalent system to support the average spectral efficiency (218) A rate for each data stream is then determined based on the metric associated with the data stream The rate is deemed to be supported by the communication system if the SNR required to support the data rate by the communication system is less than or equal to the metric (226)

Pilot-aided channel estimation for OFDM/OQAM

Abstract: OFDM/offsetQAM is an interesting alternative to classical OFDM modulation, as it does not require the use of guard interval. This characteristic makes its spectral efficiency optimal. On the other hand, this modulation is less robust to Rayleigh fading channel. Indeed, when classical channel estimation used for OFDM modulation is applied straightforwardly to OFDM/OQAM modulation, an intrinsic inter-symbol-interference is observed. This deeply degrades its performances. In this paper, we theoretically explain this phenomenon and propose a reliable method to significantly reduce it. Results of different methods of pilot-aided channel estimation over delay-Doppler channels are shown in this paper.

Ad-Hoc Control Protocol Governing Use of an Unlicensed or Shared Radio Frequency Band

Abstract: Systems and methods to enable different types of radio communication devices to communicate using a common language in order to enable the devices to regulate their use of the spectrum. Each device participating in the ad hoc control channel (ACC) protocol transmits information using a common signal format that each of the other participant devices is capable of recognizing, in order to share information about how it uses the radio frequency band. Each device receives the information transmitted by other participant devices and based on that information, controls one or more of its operational parameters that impact usage of the radio frequency band. The ACC protocol enables devices of the same or different type to harmonize (instead of alienate) themselves with each other by allowing them to communicate about their usage of the radio frequency band using a common signaling framework. Improvement can be achieved in spectrum efficiency and ultimately provide a more reliable and enjoyable experience for the end user of a device that operates in that radio frequency band.

Bandwidth-Efficient Digital Modulation with Application to Deep Space Communications

Abstract: Foreword. Preface. Chapter 1: Introduction. Chapter 2: Constant Envelope Modulations. 2.1 The Need for Constant Envelope. 2.2 Quadriphase-Shift-Keying and Offset (Staggered) Quadriphase-Shift-Keying. 2.3 Differentially Encoded QPSK and Offset (Staggered) QPSK. 2.4 /4-QPSK: A Variation of Differentially Encoded QPSK with Instantaneous Amplitude Fluctuation Halfway between That of QPSK and OQPSK. 2.5 Power Spectral Density Considerations. 2.6 Ideal Receiver Performance. 2.7 Performance in the Presence of Nonideal Transmitters. 2.7.1 Modulator Imbalance and Amplifier Nonlinearity. 2.7.2 Data Imbalance. 2.8 Continuous Phase Modulation. 2.8.1 Full Response-MSK and SFSK. 2.8.2 Partial Response-Gaussian MSK. 2.9 Simulation Performance. References. Chapter 3: Quasi-Constant Envelope Modulations. 3.1 Brief Review of IJF-QPSK and SQORC and their Relation to FQPSK. 3.2 A Symbol-by-Symbol Cross-Correlator Mapping for FQPSK. 3.3 Enhanced FQPSK. 3.4 Interpretation of FQPSK as a Trellis-Coded Modulation. 3.5 Optimum Detection. 3.6 Suboptimum Detection. 3.6.1 Symbol-by-Symbol Detection. 3.6.2 Average Bit-Error Probability Performance. 3.6.3 Further Receiver Simplifications and FQPSK-B Performance. 3.7 Cross-Correlated Trellis-Coded Quadrature Modulation. 3.7.1 Description of the Transmitter. 3.7.2 Specific Embodiments. 3.8 Other Techniques. 3.8.1 Shaped Offset QPSK. References. Chapter 4: Bandwidth-Efficient Modulations with More Envelope Fluctuation. 4.1 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Equal Signal Energie. 4.1.1 ISI-Based Transmitter Implementation. 4.1.2 Evaluation of the Power Spectral Density. 4.1.3 Optimizing the Bandwidth Efficiency. 4.2 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Unequal Signal Energies. References. Chapter 5: Strictly Bandlimited Modulations with Large Envelope Fluctuation (Nyquist Signaling). 5.1 Binary Nyquist Signaling. 5.2 Multilevel and Quadrature Nyquist Signaling. References. Chapter 6: Summary. 6.1 Throughput Performance Comparisons. References.

A noncooperative power control game for multirate CDMA data networks

Abstract: The authors consider a multirate code-division multiple acess system, in which all users have the same chip rate and vary their data rate by adjusting the processing gain. The receivers are assumed to be implemented using conventional matched filters, whose performance is sensitive to the received power levels. The authors' goal is to maximize the total system throughput by means of power control. A game theoretic approach is adopted. It is shown that for a certain type of pricing function, a unique Nash equilibrium solution exists and it possesses nice global properties. For example, it can be shown that for the optimal solution a high-rate connection should maintain a higher energy per bit than low-rate ones. The asymptotic spectral efficiency is also derived.

Spectral efficiency of distributed antenna system with random antenna layout

Abstract: The downlink capacity potential of a distributed antenna system (DAS) with random antenna layout is investigated. A low complexity sub-optimal power allocation scheme among transmit antennas is proposed. Simulation results show that with the same antenna density DAS outperforms a co-located antenna system (CAS) in terms of average and outage spectral efficiency.

Power control for partial channel-state information (csi) multiple-input, multiple-output (mimo) systems

Abstract: Techniques for controlling the transmit power for a number of data streams in a wireless multi-channel (e.g., MIMO) communication system. In one method, a number of received symbol streams are initially processed in accordance with a particular (e.g., CCMI, CCMI-SC, MMSE, or MMSE-SC) receiver processing technique to provide a number of detected data streams. The post-detection SNRs of the detected data streams are estimated, and each SNR that exceeds a setpoint is identified. This setpoint may correspond to (1) the SNR needed to achieve the maximum allowed spectral efficiency or (2) the target SNR needed to achieve a specified spectral efficiency. A new (or adjusted) transmit power for each detected data stream associated with a post-detection SNR that exceeds the setpoint is determined and used for the data stream. Different power control schemes are provided for different classes of receiver processing techniques with different characteristics.

ESPDA: Energy-efficient and Secure Pattern-based Data Aggregation for wireless sensor networks

Abstract: Secure data transmission and data aggregation are critical in designing cluster-based sensor networks This paper presents an Energy-efficient and Secure Pattern-based Data Aggregation protocol (ESPDA) for wireless sensor networks ESPDA is energy and bandwidth efficient because cluster-heads prevent the transmission of redundant data from sensor nodes ESPDA is also secure because it does not require the encrypted data to be decrypted by cluster-heads to perform data aggregation In ESPDA, cluster-head first requests sensor nodes to send the corresponding pattern code for the sensed data If multiple sensor nodes send the same pattern code to the cluster-head, then only one of them is permitted to send the data to the cluster-head Hence, ESPDA has advantages over the conventional data aggregation techniques with respect to energy, bandwidth efficiency and security Simulations results show that as data redundancy increases, the amount of data transmitted from sensor nodes to cluster-head decreases up to 45% when compared to conventional algorithms

High Speed Downlink Packet Access: WCDMA Evolution

Abstract: This article gives an overview of the high speed downlink packet access (HSDPA) concept; a new feature which is coming to the Release 5 specifications of the 3GPP WCDMA/UTRA-FDD standard. To support an evolution towards more sophisticated network and multimedia services, the main target of HSDPA is to increase user peak data rates, quality of service, and to generally improve spectral efficiency for downlink asymmetrical and bursty packet data services. This is accomplished by introducing a fast and complex channel control mechanism based on a short and fixed packet transmission time interval (TTI), adaptive modulation and coding (AMC), and fast physical layer (L1) hybrid ARQ. To facilitate fast scheduling with a per-TTI resolution in coherence with the instantaneous air interface load, the HSDPA-related MAC functionality is moved to the Node-B. The HSDPA concept facilitates peak data rates exceeding 2 Mbps (theoretically up to and exceeding 10 Mbps), and the cell throughput gain over previous UTRA-FDD releases has been evaluated to be in the order of 50-100% or even more, highly dependent on factors such as the radio environment and the service provision strategy of the network operator.

Energy efficient wireless sensor networks with transmission diversity

Abstract: A new transmission scheme which uses two transmitting sensors and space-time block code to provide transmission diversity in distributed wireless sensor networks with neither antenna-array nor transmission synchronisation is proposed. Full diversity and full rate are achieved which enhances power/bandwidth efficiency and reliability. Simulations demonstrate its superior performance in saving transmission energy.

Capacity scaling and spectral efficiency in wide-band correlated MIMO channels

Abstract: The dramatic linear increase in ergodic capacity with the number of antennas promised by multiple-input multiple-output (MIMO) wireless communication systems is based on idealized channel models representing a rich scattering environment. Is such scaling sustainable in realistic scattering scenarios? Existing physical models, although realistic, are intractable for addressing this problem analytically due to their complicated nonlinear dependence on propagation path parameters, such as the angles of arrival and delays. In this paper, we leverage a recently introduced virtual representation of physical models that is essentially a Fourier series representation of wide-band MIMO channels in terms of fixed virtual angles and delays. Motivated by physical considerations, we propose a D-connected model for correlated channels defined by a virtual spatial channel matrix consisting of D nonvanishing diagonals with independent and identically distributed (i.i.d.) Gaussian entries. The parameter D provides a meaningful and tractable measure of the richness of scattering. We derive general bounds for the coherent ergodic capacity and investigate capacity scaling with the number of antennas and bandwidth. In the large antenna regime, we show that linear capacity scaling is possible if D scales linearly with the number of antennas. This, in turn, is possible if the number of resolvable paths grows quadratically with the number of antennas. The capacity saturates for linear growth in the number of paths (fixed D). The ergodic capacity does not depend on frequency selectivity of the channel in the wide-band case. Increasing bandwidth tightens the bounds and hastens the convergence of scaling behavior. For large bandwidth, the capacity scales linearly with the signal-to-noise ratio (SNR) as well. We also provide an explicit characterization of the wide-band slope recently proposed by Verdu. Numerical results are presented to illustrate the key theoretical results.

Reallocation of excess power for full channel-state information (CSI) multiple-input, multiple-output (MIMO) systems

Abstract: Techniques to allocate the total transmit power to the transmission channels in a multi-channel communication system such that higher overall system spectral efficiency and/or other benefits may be achieved. The total transmit power may be initially allocated to the transmission channels based on a particular power allocation scheme (e.g., the water-filling scheme). The initial allocation may result in more power being allocated to some transmission channels than needed to achieve the required SNR (e.g., the SNR needed to achieve the maximum allowed data rate), which would then result in these transmission channels being operated in the saturation region. In such situations, the techniques reallocate the excess transmit power of transmission channels operated in the saturation region to other transmission channels operated below the saturation region. In this way, higher data rate may be achieved for the “poorer” transmission channels without sacrificing the performance of the “better” transmission channels.

Adaptive subcarrier and power allocation in OFDM based on maximizing utility

Abstract: This paper investigates adaptive resource allocation on the downlink of multiuser OFDM networks to achieve both multiuser diversity and fairness. Utility functions are applied to quantify the level of users' satisfaction derived from the radio resources they occupy. We formulate cross-layer optimization problem as one that maximizes the sum of the utilities over all active users subject to the feasible rate region, which is determined by adaptive resource allocation schemes deployed and the current channel conditions. We present the conditions for optimal subcarrier assignment and power allocation based on utility, and investigate the optimality properties as well. It is also shown that the inherent mechanism of balancing spectral efficiency and fairness is associated with concave utility functions.

Non-reciprocal Transceivers in OFDMKDMA Systems: Impact and Mitigation'

Abstract: AEISTRACI Channel reciprocity is needed in SDMA or MIMO downlink pre-filtering when the channel knowledge is acquired in the n link We first show analytically that the non-reci roeity ofthe .&e station anal hardware which is part of the channel, introduces a veqxgh level ok multiuser interference and quantify the effect of the nonreciproeit by means of simulations We then prop a novel caliiratinn technique at the base station that enables to compensate for the non-reciprocity and reduce the MU to a negligible value while having a low implementation cat I. INTRODUIXION OFDM-SDMA is an attractive technique to enhance the capacity of future wireless LANs since it allows mitigating the frequency selective channel fading (OFWM) and increasing the spectral efficiency by accommodating several users in the same time-frequency slots (SDMA). In the downlink, pre-filtering at the base station (BS) side allows to pre-compensate the phase (and amplitude) of the channel in such a manner that all simultaneous users receive their own signal free of MLn 01, [4l. It is in fact this interference Cancellation property that makes SDMA possible in the downlink. Since the terminals have only one antenna, they have no means IO mitigate the spatial MUI. When the channel is estimated in the uplink, the downlink channel matrix is just the transpose of the uplink matrix, assuming the channel is reciprocal. However, the "channel" is actually made up of the propagation channel (the medium between the antennas), the antennas and the transceiver RF, IF and baseband circuits at both sides of the link. The transceiver circuits are usually not reciprml (the TX and RX frequency responses are different) and this can jeopardise the performance of the SDMA system. In this paper, we depart from the reciprocity assumption, analyse the impact of channel non-reciprocity and propose a mitigation method. The document is organised as fdlows. Section 2 introduces the OFDM-SDMA Uplink and Downlink model, including the impact of the composite channel. In section 3, the effects of non-reciprocities are estimated by simulations. Seaion 4 proposes a simple yet effective calibration method with minimal additional hardware requirement. Then, the conclusions are drawn. 11. SYSTEM MODEL

Analysis of multiple antenna wireless links at low SNR

Abstract: Wireless channels with multiple transmit/receive antennas are known to provide a high spectral efficiency both when the channel is known to the receiver, and when the channel is not known to the receiver if the signal-to-noise ratio (SNR) is high. Here we analyze such systems at low SNR, which may find application in sensor networks and other low-power devices. The key point is that, since channel estimates are not reliable, it is often not reasonable to assume that the channel is known at the receiver at low SNR. In this unknown channel case, we show that for sensible input distributions, in particular all practical modulation schemes, the capacity is asymptotically quadratic in the SNR, /spl rho/, and thus much less than the known channel case where it exhibits a linear growth in /spl rho/. We show that under various signaling constraints, e.g., Gaussian modulation, unitary space-time modulation, and peak constraints, that mutual information is maximized by using a single transmit antenna. We also show that at low SNR, sending training symbols leads to a rate reduction in proportion to the fraction of training duration time so that it is best not to perform training. Furthermore, we show that the per-channel use mutual information is linear in both the number of receive antennas and the channel coherence interval.

Multicarrier modulation with blind detection capability using cosine modulated filter banks

Abstract: The cosine modulated filter bank (CMFB) is introduced as a multicarrier modulation (MCM) technique for wideband data transmission over wireless channels. Under the name discrete wavelet multitone modulation, CMFB has been considered for data transmission over digital subscriber lines. We propose a new receiver structure that is different from those proposed previously. The new structure simplifies the task of channel equalization, by reducing the number of equalizer parameters significantly. We also propose a novel blind equalization algorithm that fits very nicely in the proposed structure. Moreover, we discuss the bandwidth efficiency of the proposed CMFB-MCM system and show that it is superior to the conventional (single carrier) quadrature amplitude modulation (QAM) and orthogonal frequency-division multiplexing (OFDM). The CMFB is found to be a signal processing block that stacks a number of vestigial sideband modulated signals in a number of overlapping subchannels in the most efficient way. The proposed CMFB-MCM is also compared to OFDM with respect to bit-error rate performance. Under the conditions that the channel impulse response duration remains less than the length of cyclic prefix, OFDM is found marginally superior to CMFB-MCM. However, OFDM degrades very fast when the channel impulse response duration exceeds the length of the cyclic prefix. CMFB-MCM, on the other hand, is found less sensitive to variations in channel impulse response duration.

Variable-rate variable-power hybrid M-FSK M-QAM for fading channels

Abstract: This paper investigates a variable-rate variable-power hybrid non-coherent M-FSK M-QAM system. The goal is to combine the spectral efficiency merit of M-QAM with the power efficiency advantage of M-FSK and as such extend the region of availability even at very low channel gain values. A basic system is first designed to maximize the average spectral efficiency while meeting average power and target bit error rate constraints. In addition, a peak power constraint is imposed in a more general system. The optimization procedure leads to optimum rate and power loading functions which are compared for the different modes of operation.

Impact of multiuser diversity and channel variability on adaptive OFDM

Abstract: A downlink radio interface for cellular packet data systems with wide area coverage and high spectral efficiency is evaluated. A slotted OFDM radio interface is used, in which time-frequency bins are allocated adaptively to different mobile users within a downlink beam, or sector, based on their channel quality. Frequency division duplex (FDD) is assumed, which requires channel prediction in the terminals and feedback of this information to a packet scheduler. The adaptive modulation scheme is optimized by a novel approach which maximizes the throughput, including also the ARQ part of the transmission. A theoretical evaluation of the resulting multiuser diversity under some idealized assumptions shows that the spectral efficiency increases significantly with the number of active users. The simulations indicate that the loss of performance due to channel variability within the bins for vehicular users in frequency-selective fading environments is rather small.

The perspectives of large area synchronous CDMA technology for the fourth-generation mobile radio

Abstract: Some basic relations among system bandwidth, threshold SIR, maximum number of access users, as well as system spectral efficiency are studied for both traditional CDMA and large area synchronous CDMA (LAS-CDMA). The perspectives of LAS-CDMA for the 4G are also studied.

Performance analysis of cellular mobile systems with successive co-channel interference cancellation

Abstract: This paper presents an analytical framework for the performance evaluation of cellular mobile radio systems equipped with smart antenna systems. In particular, the paper focuses on low-complexity systems which are able to successively suppress the strongest active interferers. The desired user fading statistics is assumed to be flat Rayleigh, Rician, or Nakagami, whereas the interfering signals are assumed to be independent and subject to slow flat Rayleigh fading. The paper starts by presenting generic closed-form expressions for the the carrier-to-interference ratio probability density function after interference cancellation. Based on that, exact closed-form expressions for the outage probability and average error rate formulas are derived. Finally, a comparison with a practical cancellation scheme and the impact of some practical considerations on the performance of successive interference cancellation are investigated. More specifically, the effect of traffic loading, the overall spectral efficiency gain, and the impact of time delay are studied.

Asymptotic spectral efficiency of multicell MIMO systems with frequency-flat fading

Abstract: The spectral efficiency of multiple-input multiple-output (MIMO) systems operating in multicell frequency-flat fading environments is studied for situations in which co-channel interference is the dominant channel impairment instead of ambient noise. The following detectors are analyzed: the joint optimum detector, a group linear minimum-mean-square-error (MMSE) detector and its generalized version, a group MMSE successive interference cancellation detector, and an adaptive multiuser detector, with the focus on their large-system asymptotic (nonrandom) expressions. Analytical and numerical results based on these asymptotic multicell MIMO spectral efficiencies are explored to gain insights into the behavior of interference-limited multicell MIMO systems.

1-Tb/s (6 x 170.6 Gb/s) transmission over 2000-km NZDF using OTDM and RZ-DPSK format

Abstract: We demonstrate six-channel 160-Gb/s wavelength-division-multiplexed transmission over 20 100-km spans of nonzero-dispersion fiber, with a spectral efficiency of 0.53 b/s/Hz. We achieve this result using optical-time-division multiplexing with polarization bit interleaving and return-to-zero differential-phase-shift-keying modulation format. We also operate at 170.6 Gb/s per channel to emulate the use of forward error correction.

Co-channel interference cancellation for space-time coded OFDM systems

Abstract: Space-time coded orthogonal frequency division multiplexing (OFDM) is a promising scheme for future wideband multimedia wireless communication systems. The combination of space-time coding (STC) and OFDM modulation promises an enhanced performance in terms of power and spectral efficiency. Such combination benefits from the diversity gain within the multiple-input-multiple-output ST coded system and the matured OFDM modulation for wideband wireless transmission. However, STC transmit diversity impairs the system's interference suppression ability due to the use of multiple transmitters at each mobile. We propose an effective co-channel interference (CCI) cancellation method that employs angle diversity based on null-steering beamforming or minimum variance distortion response beamforming. It is shown that the proposed method can effectively mitigate CCI while preserving the space-time structure, thereby, significantly improving the system's interference suppression ability without significant bit-error rate performance degradation. Furthermore, it is demonstrated that the proposed method can significantly combat the delay spread detrimental effects over multipath fading channels without the use of interleaving.

25 x 40-Gb/s copolarized DPSK transmission over 12 x 100-km NZDF with 50-GHz channel spacing

Abstract: We report the first transmission of copolarized 40-Gb/s channels with 0.8-b/s/Hz spectral efficiency. We transmit 25 channels over 1200 km of nonzero-dispersion fiber (1600 km with adjacent channels orthogonally polarized). This result was obtained using differential phase-shift keying, and without forward error correction.

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

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

An FPGA based rapid prototyping platform for MIMO systems

Abstract: Multiple input multiple output (MIMO) techniques hold the potential of dramatically increasing the data rates and spectral efficiency of wireless communications systems. Even with extensive research on the design of transmission and reception algorithms, little is known as to how much of the predicted gains are actually achievable on real wireless channels. In this paper, we present a MIMO testbed, which enables the rapid prototyping of MIMO transceivers for wideband channels. Such prototypes provide experimental quantification of achievable gains from MIMO algorithms. The testbed design allows real-time operation of baseband processing and RF up/down-conversion. The choice of testbed components is made to allow maximum, flexibility for research purposes, including monitoring and control of all subsystems. In addition to discussing the testbed's design, we present the implementation of two wireless systems. The first is a spread-spectrum system based on IEEE 802.11b. The second is an implementation of Alamouti's transmit diversity scheme.

Forward high-speed wireless packet data service in IS-2000 - 1/spl times/EV-DV

Abstract: This article describes enhancements to the physical layer design of single-carrier (1/spl times/) cdma2000/sup /spl reg// wireless networks introduced by Revision C of the IS-2000 standard (commonly referred to as 1/spl times/EV-DV). These improvements are mainly for the support of high-speed wireless packet data service on the forward (base station to mobile station) link. A new shared channel, the forward packet data channel, F-PDCH, is introduced to significantly increase spectral efficiency. This is accomplished through smart, channel-dependent scheduling of base station, BS, resources by taking advantage of the delay-tolerant nature of data traffic. This shared channel utilizes fast link adaptation through adaptive modulation and coding supported by the feedback of channel quality information. A form of hybrid ARQ type II technique commonly referred to as asynchronous adaptive incremental redundancy compensates for frame error events due to imperfect link adaptation. The impact of the new channel on voice capacity of the system is designed to be minimal because the F-PDCH utilizes resources that are not consumed by real-time users.

Introduction to OFDMOFDM and MCCDMA for Broadband Multiuser Communications WLANS and Broadcasting. L.Hanzo, Mnster, T. Keller and B.J. Choi,

Abstract: This chapter contains sections titled: Introduction Principles of QAM-OFDM Modulation by DFT Transmission via Bandlimited Channels Generalised Nyquist Criterion Basic OFDM Modem Implementations Cyclic OFDM Symbol Extension Reducing MDI by Compensation [15] Decision-Directed Adaptive Channel Equalisation OFDM Bandwidth Efficiency Chapter Summary and Conclusion