Showing papers on "Spectral efficiency published in 1995"

System and method for optimizing spectral efficiency using time-frequency-code slicing

Abstract: A system and method for optimizing usage of a communications transmission medium. The transmission medium may be sliced into time and frequency domains so as to create time-frequency slices for assignment to users having varying access rates and user-application requirements. Through scheduling of the various speed users within the frequency and time domains, the system and method can efficiently allocate and make use of the available spectrum, thereby accommodating higher rate users requiring greater bandwidths and time slot assignments while still preserving cost-efficient access for lower speed users. Depending on the signal modulation scheme, the time-frequency slices may be allocated on non-contiguous frequency bands. The system and method is also applicable to code-division multiple access (CDMA) techniques by slicing the available code space along time-code domains, frequency-code domains or, in three dimensions, along time-frequency-code domains. Users may be efficiently scheduled based on code space requirements so as to optimize use of the communication medium.

The spectrum efficiency of a base station antenna array system for spatially selective transmission

Abstract: In this paper we investigate the spectrum efficiency gain using transmitting antenna arrays at the base stations of a mobile cellular network. The proposed system estimates the angular positions of the mobiles from the received data, and allows multiple mobiles to be allocated to the same channel within a cell. This is possible by applying a transmit scheme which directs nulls against co-channel users within the cell. It is shown that multiple mobiles per cell is an efficient way of increasing capacity in comparison with reduced channel reuse distance and narrow beams (without directed nulls). The effect of the spatial spread angle of the locally scattered rays in the vicinity of the mobile is also investigated. >

On the performance of different detection techniques for OFDM-CDMA in fading channels

Abstract: The combination of orthogonal frequency division multiplexing (OFDM) with code division multiple access (CDMA) systems has attained increasing significance in mobile radio communications. In this paper basic OFDM-CDMA detection techniques based on simple equalization algorithms, and improved detection techniques, such as the newly proposed iterative detection applying the minimum mean square error (MMSE) criterion, are analyzed in the mobile radio environment. This analysis enables one a comparison between known and new OFDM-CDMA detection techniques in terms of spectral efficiency and receiver complexity.

Modulation analysis for wireless infrared communications

Abstract: The channel model for indoor wireless optical communication links is unusual in that it combines the intensity-modulation constraints of the Poisson photon-counting channel with the multipath dispersion, bandwidth constraints, and additive white Gaussian noise of the conventional radio channel. In this paper we examine the performance of several modulation schemes on the indoor wireless optical channel. Modulation schemes having low duty cycle, such as pulse-position modulation (PPM), offer improved power efficiency at the expense of decreased bandwidth efficiency. We compare the power and bandwidth efficiency of several forms of PPM, including multiple PPM, overlapping PPM, convolutional coded PPM, and trellis coded OPPM. We also examine the differences between the wireless infrared communications channel and the quantum-limited photon-counting channel.

OFDM-CDMA versus DS-CDMA: performance evaluation for fading channels

Abstract: In code division multiple access (CDMA) systems direct sequence (DS) applying maximum ratio combining (MRC) at the receiver has achieved high interest for mobile communications. A second and rather novel technique is orthogonal frequency division multiplexing (OFDM) applying maximum-likelihood detection (MLD) at the receiver. In this paper the performance of both techniques is compared considering the mobile radio environment. The analytical results for both DS-CDMA and OFDM-CDMA are confirmed by Monte Carlo simulations. The analysis enables a performance comparison between the DS-CDMA system and the OFDM-CDMA system with respect to the demands of low complexity receivers which is important for system design. The results show that OFDM-CDMA outperforms DS-CDMA in terms of spectral efficiency.

Transceiver algorithms of antenna arrays

Abstract: A transceiver for improving the spectral efficiency and the capacity of cellular communication systems is disclosed. The transceiver uses an antenna array for communicating in a cellular communication system with a plurality of mobile stations. In addition, the transceiver contains a spatial filter connected to an antenna array wherein the spatial filter has as many outputs as there are array elements and as many inputs as there are spatial channels. A splitter then splits data to be transmitted to each mobile station into a number of parallel data streams, the number of parallel data streams corresponds with the number of spatial channels in the system, wherein the data streams, are delayed based upon uplink measurements. Finally, power allocators are provided for allocating transmission power to each possible channel based upon long-term SNR measurements on the uplink.

A flexible and high performance cellular mobile communications system based on Orthogonal Multi-Carrier SSMA

Abstract: The conventional Direct-Sequence Spread-Spectrum-Multiple-Access (DS-SSMA) system with RAKE-receiver is an interesting approach in mobile communications in order to combat the frequency selectivity of the channel. The main advantages of DS-SSMA are well known, but its capacity is limited by other-user interference. Another interesting SSMA technique that combats the frequency selectivity of the channel and achieves high spectral efficiency is based on Orthogonal-Frequency-Division-Multiplexing (OFDM). This new SSMA technique combines the principles of DS-SSMA with OFDM and is called Multi-Carrier Spread-Spectrum-Multiple-Access (MC-SSMA). By providing high frequency diversity, this combination enables the possibility to perform a maximum-likelihood detection (MLD) resulting in high performance/capacity, to use the spectrum in an efficient way and to retain many advantages of the conventional DS-SSMA system. In addition, it allows both simple cell-separation by using frequency hopping and simple hardware realization. An example for the downlink of a mobile communications system, i.e. the transmission from the base station to a mobile station, using MC-SSMA with Walsh-Hadamard code spreading is studied. Different coherent detection algorithms such as conventional detection, MLD, and iterative detection are analyzed. The analytical performance of MLD is evaluated. It is also shown analytically, and by simulations that the MC-SSMA system with MLD outperforms the DS-SSMA system with RAKE-receiver. Up to 64 active users can be transmitted in a 1.25 MHz bandwidth. Each user has a rate of 16.0 kbit/s by using BPSK modulation. At a signal to noise ratio (SNR) of 13 dB a bit error probability ofP b =10−3 can be guaranteed without channel coding. This results in a spectral efficiency of about 0.8 bit/s/Hz. Under the same conditions the conventional DS-SSMA system results in a spectral efficiency of about 0.15 bit/s/Hz. Hence, using MC-SSMA for the downlink of a cellular mobile communications system is a promising approach.

ACE-8PSK: band-limited 8PSK with an Almost Constant Envelope

Abstract: 8PSK modulation is of increasing interest in satellite communications applications where bandwidth efficiency is a prime concern. However, its adoption in practical systems has been limited, largely due to its increased sensitivity to channel and transmitter imperfections as compared with QPSK and other modulation schemes. In particular, band-limited 8PSK is highly susceptible to the interference associated with adjacent channel spectral regrowth caused by transmitter nonlinearity. Spectral regrowth may lead to substantial performance degradation or make necessary an increase in the spacing between carriers. The transmitted carrier may suffer levels of spurious RF emission which exceed system specifications or spectral mask regulations. This paper proposes new low complexity trellis coding techniques which can be applied to conventional 8PSK modulation, and which lead to substantially reduced levels of spectral regrowth. When the coding is applied, the modulated signal exhibits a reduced degree of envelope fluctuation, and hence it is less affected by amplitude nonlinearity. The schemes are termed Almost-Constant-Envelope 8PSK (ACE-8PSK). Combined with outer FEC coding, ACE-8PSK can achieve greater power efficiency than QPSK, and provide significant performance advantages on the nonlinear channel in terms of bit error rate and the spectral purity of transmissions.

CD3-OFDM: a new channel estimation method to improve the spectrum efficiency in digital terrestrial television systems

Abstract: The paper describes a novel channel estimation scheme (identified as CD3, coded decision directed demodulation) for coherent demodulation of OFDM (orthogonal frequency division multiplex) signals making use of any constellation format (e.g. QPSK, 16 QAM, 64 QAM). The structure of the CD3-OFDM demodulator is described, based on a new channel estimation loop exploiting the error correction capability of a forward error correction (FEC) decoder and frequency and time domain filtering to mitigate the effects of noise and residual errors. In contrast to the conventional coherent OFDM demodulation schemes, CD3-OFDM does not require the transmission of a comb of pilot tones for channel estimation and equalisation, therefore yielding a significant improvement in spectrum efficiency (typically between 5% and 15%). The performance of the system with QPSK and 64 QAM modulations is analysed by computer simulations, on AWGN and frequency selective channels. The results indicate that CD3-OFDM allows to achieve C/N performance similar to coherent demodulation with pilot tones, when the same channel coding and modulation scheme is adopted. Otherwise, when the additional capacity is exploited to increase the FEC redundancy instead of the useful bit-rate, CD3 can offer significant C/N advantages (typically from 2 to 5 dB depending on the channel characteristics). Therefore CD3-OFDM can be suitable for digital television broadcasting services over selective radio channels.

Terrestrial digital video broadcasting for mobile reception using OFDM

Abstract: Performance of a system design for digital video broadcasting is examined with emphasis on mobile reception. Orthogonal frequency division multiplexing (OFDM) is used to achieve good bandwidth efficiency and to mitigate the intersymbol interference resulting from the channel delay spread. The resulting equivalent channel including OFDM can be modeled as a flat Rayleigh fading channel plus an interchannel interference (ICI) term due to the channel Doppler spread. This ICI term is analyzed and shown to result in an error floor. Performance improvements due to antenna diversity and trellis-coded modulation (TCM) are given. Finally, multiresolution modulation is discussed as a means of achieving graceful degradation and giving degrees of freedom for further performance improvement.

Spread-time code-division multiple access

Abstract: An alternative code-division multiple-access (CDMA) scheme to spread spectrum (SS), called spread time (ST) is proposed for bandlimited multiple-access channels. ST-CDMA can be considered the time-frequency dual of SS-CDMA. In ST-CDMA pseudorandom (PN) sequences are assigned to each user, and the Fourier transform of the transmitted pulse for a given user is determined by modulating the phase of the desired transmitted spectrum by the user's PN-sequence. The transmitted data for a particular user can be recovered by sampling the output of a filter matched to the user's pulse. Implementations are described in which surface acoustic wave devices are used to perform the matched filtering or Fourier transformation. Averaged signal-to-interference plus noise ratio (SIR) and spectral efficiency are computed for both asynchronous ST and direct-sequence SS-CDMA systems, assuming an arbitrary channel transfer function H(f), which is the same between all pairs of users. The results are the same for SS and ST provided that the magnitude of the Fourier transform of the chip shape in the SS system is the same as the magnitude of the Fourier transform of the ST pulse shape. The main advantage of the ST technique Is the flexibility with which the transmitted spectrum can be selected. We derive the transmitted spectrum that maximizes the SIR subject to an average power constraint. >

A trunked radio frequency communication system for accommodating both frequency and time division based rf communications

Abstract: In a trunked radio communications system, apparatus and methods are provided for transparently updating existing frequency division multiple access (FDMA) communications facilities to accommodate time division multiple access (TDMA) communications TDMA channels are added to existing FDMA sites on an individual basis to increase spectral efficiency and capacity while still being compatible with existing FDMA equipment and protocols For example, the existing FDMA control channel and protocols are used by dual mode sites and dual mode radios A dual mode radio transceiver selectively participates in trunked radio communications in either an FDMA mode and in a TDMA mode Each dual mode radio includes a memory for storing a mode identifier identifying each channel as an FDMA or a TDMA working channel When a channel assignment is made, the dual mode radio determines from that channel mode identifier stored in memory whether to operate in the FDMA or TDMA mode for that particular communication Moreover, dual mode radios expedite synchronization to a TDMA working channel (time slot) using a timing relationship established between the FDMA control channel and the TDMA working channels In the context of multiple site, trunked radio communications, the present invention provides for interoperability between sites and radios which have TDMA communications capabilities and sites and radios which have only FDMA capabilities

System aspects of cellular radio

Abstract: The greatest single factor in enhancing spectral efficiency of a network is the mass deployment of microcells. By this simple technique we can repeatedly and efficiently reuse the precious spectrum. The number of users a network can support is fundamentally dependent on the common air interface (CAI) over which users communicate. User capacity is dependent on many factors, but the cardinal ones are the amount of spectrum the regulators allocate, the size of the radio coverage area from a base station (BS), and the amount of interference a particular radio link can tolerate. In this article we are primarily concerned with the system aspects associated with the CAI. We focus on the critical importance of BS siting. Starting with existing large cells, we deliberate on the problems that might arise in siting BSs in three dimensional microcells, in order to consider suitable multiple access methods for future cellular environments. >

A concept of digital terrestrial television broadcasting

Abstract: The future terrestrial television broadcasting system should support the transmission of a digital HDTV signal with a high spectral efficiency. In addition, this system should maintain graceful degradation as the actual analog systems, and should be compatible with the SDTV. The system compatibility can be achieved by using a hierarchical HDTV source-coding scheme that can provide at least two (HDTV, SDTV) or three (HDTV, EDTV, SDTV) hierarchy levels: SDTV image quality will be expected for portable receivers, and HDTV/EDTV image quality will destinate to stationary receivers with roof-top antennas. Taking into account the receivers' antenna gains and the different channel conditions, there will be a difference of 25–30 dB between the received powers of the stationary and the portable receivers. Therefore, the design of a powerful and a suitable transmission scheme for the future broadcasting of the digital HDTV signal will be a technological challenge. In this article we describe a concept of a flexible reconfigurable hierarchical digital terrestrial TV broadcasting system for clear and taboo channels. The flexibility of the proposed scheme easily permits the receivers to support different reconfigurable modes: One HDTV program or multi-programming EDTV or SDTV (for fixed receivers up to 5 × SDTV in clear and up to 2 × SDTV in taboo channels; for portable receivers up to 2 × SDTV.) The system achieves a high interoperability with the Satellite Baseline system. It maintains a graceful degradation and provides a hierarchical complexity. It is based on a concatenated coding scheme. The inner code of the concatenated coding scheme is combined with multi-resolution modulation. The basic constellation is a 64-QAM, which will be operated in clear channels. It can be reconfigured to a 16-QAM in the case of taboo channels. The principle of OFDM with very rugged frequency/time synchronization mechanisms is used to combat the frequency selectivity and the co-channel interference (CCI) in the channel. Known pilot symbols are sent regularly in order to perform coherent detection.

Transmitter design for data transmission in the presence of a data-like interferer

Abstract: In many digital communications systems, crosstalk, rather than additive noise, is the primary channel impairment. For such systems, it is known that the spectral support of the optimum transmitter is not, in general, restricted to a Nyquist set, in contrast to the case for the additive-noise channel. Nevertheless, the problem of determining the optimum transmitter shaping function for the crosstalk channel without the Nyquist restriction is a difficult one, and has so far remained unsolved. Motivated by current interest in the high-speed digital subscriber line (HDSL) and related crosstalk-dominated applications, we explore a subcase of this problem in which only a single interferer is present. When applied to HDSL-like systems with a single (or dominant) interferer, our analysis and numerical results confirm that wider-than-Nyquist transmitters provide a large performance advantage over Nyquist-limited transmitters. Several interesting and counter-intuitive results also arise. For example, PAM and QAM systems operating at the same spectral efficiency do not, in general, perform identically over the crosstalk channel, despite their essential equivalence in additive noise. We explain why this is so, and show that for channels qualitatively similar to the HDSL wire-pair, QAM has a significant advantage over PAM at high data rates. Finally, we show how the characteristics of HDSL-like channels can be exploited by optimizing the symbol rate. >

Modulation system for spread spectrum CDMA communication

Abstract: The OCDMA waveform of the present invention uses hi-phase PN modulation (BPSK PN chip modulation) in conjunction with MPSK or MQASK data modulation (QPSK data modulation is one preferred embodiment) to increase bandwidth efficiency. The number of orthogonal users that can be placed on a single carrier is equal to, at most, the length of the orthogonal binary sequence. The Radamacher-Walsh (RW) sequence chip rate must be 4" times the symbol rate (where n is a positive integer) since the symbol transitions must be synchronized to the RW period to guarantee orthogonality of the multiple users when data transitions are present. The symbol rate for QPSK modulation is one-half that for BPSK modulation. As a result, twice as many orthogonal functions are available for a given clock rate for QPSK as for BPSK modulation. That is, an OCDMA system with QPSK data can support twice as many users in a given bandwidth as an OCDMA system with BPSK data.

Performance evaluation of direct-sequence spread spectrum multiple-access for indoor wireless communication in a Rician fading channel

Abstract: The bit error probability in a Rician fading channel is evaluated for indoor wireless communications considering direct-sequence spread spectrum multiple access (DS/SSMA) with differential phase shift keying (DPSK) modulation and two types of diversity: selection diversity and maximal ratio combining. The performance of the indoor radio system is also obtained in terms of outage probability and bandwidth efficiency. The analysis is done for a star-connected multiple access radio network. Furthermore the influence of three types of forward error correcting (FEC) codes namely, the (15,7) BCH code, the (7,4) Hamming code and the (23,12) Golay code, on the performance is studied. Computational results are presented for suitable values of Rician parameters in an indoor environment and using Gold codes as spread spectrum codes. >

Diversity combining considerations for incoherent frequency hopping multiple access systems

Abstract: This paper studies the problem of diversity combining for frequency hopped multiple access (FHMA) systems that operate in a mobile satellite environment characterized by frequency-nonselective Rician multipath fading. The modulation scheme considered is the incoherent M-ary frequency-shift keying (MFSK). The optimal diversity combining rule is derived under the assumptions that the number of active users (K) in the system is known, all users are chip (hop)-synchronous, and each user employs a random FH address. We suggest practical implementations that are close approximations of the optimal rule and examine the effects of various system parameters on the resulting receivers. The bit error probability performance is analyzed and numerical examples are provided. The effects of the diversity order (L), the signaling size (M) and unequal received powers are examined and related system design concerns such as system capacity and spectral efficiency are evaluated as well. >

Spectrum efficiency of multilevel modulation schemes in mobile radio communications

Abstract: Lee (1989) has produced equations describing spectrum efficiency for modulation schemes operating in cellular environments. The present authors consider the performance of a range of multilevel modulation schemes when these spectrum efficiency equations are applied. They then proceed to adapt these efficiency equations for use in microcells before considering the performance of multilevel modulation within this environment. The results show that the preferred modulation scheme depends on the BER required, with 4 level PSK being preferred in conventional cells, and variable 16 level QAM, or 32 or 64 level QAM being suitable in microcells, particularly when a high SNR is available. >

Performance bounds for power control supported DCA-algorithms in highway micro cellular radio systems

Abstract: To achieve a high spectrum efficiency in cellular radio systems, the radio resource allocation algorithms have to be adaptive to the actual traffic and interference situation. The focus of the paper is on performance bounds of a cellular radio system using dynamic channel assignment (DCA) combined with power control (PC). A trivial upper bound on the performance is identified. The bound is given by the performance of a hypothetical system which is able to use all channels simultaneously in all cells. A lower bound on the performance is derived from a theoretical PC supported DCA-algorithm. For a highway micro cellular system and a deterministic propagation model, numerical results show that the lower and upper bounds are tight. That is, the results indicate that it is possible to use all channels in all cells simultaneously and still provide an acceptable signal-to interference ratio in all assigned communication links. >

Adaptive modulation/TDMA with a BDDFE for 2 Mbit/s multi-media wireless communication systems

Abstract: This paper proposes an adaptive modulation/time division multiple access (TDMA) system using a bi-directional decision feedback equalizer (BDDFE) and space diversity to support multi-media wireless communication systems with a bit rate of up to 2 Mbit/s under frequency selective fading conditions. A 7-tap BDDFE and space diversity are employed to cope with a delay time of up to 3-symbol duration. When the maximum delay time (/spl tau//sub max/) is shorter than 3-symbol duration for the full rate, the full rate is employed. When /spl tau//sub max/ is longer than that, the symbol rate is lowered to half-rate, quarter-rate or 1/8 -rate to satisfy the condition that /spl tau//sub max/ is shorter than 3-symbol duration. The modulation level is also selected from 16QAM and QPSK according to the channel conditions to increase spectral efficiency. Computer simulation confirms that the proposed scheme is effective to achieve 2 Mbit/s transmission at /spl tau//sub max/=10 /spl mu/s and 1 Mbit/s at /spl tau//sub max/=20 /spl mu/s.

PC-notebook based mobile networking: algorithms, architectures and implementation

Abstract: The integration of multimedia adaptive wireless networking capabilities in a PC-notebook platform are investigated. To support mobile networking, while providing compatibility with the wired infrastructure, new functions are required for topology creation using multihop protocols. To support mobility in a wireless environment, power control and bandwidth allocation are required in conjunction with adaptive wireless modems and rate-adaptive video codecs. A prototype implementation of a wireless node with these capabilities reveals several performance and complexity limitations with current technology. In particular the DOS operating system, the PC shared bus architecture and traditional partitioning of the network and modem functions lead to severe performance losses that are detrimental in wireless networking. For mobile wireless nodes, these limitations are unacceptable. Several ideas are presented for re-architecting the PC-notebook for wireless networking nodes that can substantially improve bandwidth efficiency while overcoming the complexity and power limitations of current technology.

Bit error rate performance and power spectral density of a noncoherent hybrid frequency-phase modulation system

Abstract: This paper studies the design and performance analysis of a noncoherent hybrid modulation scheme derived from multifrequency and multiphase signals, and referred to as joint frequency-phase modulation (JFPM). This modulation class includes many formats, which can be classified as efficient bandwidth-limited modulation or power-limited modulation techniques. A noncoherent receiver structure for JFPM signals is introduced, and an exact expression for the probability of a bit error over AWGN channels is obtained. The results show that noncoherent JFPM perform better than M-ary DPSK and/or noncoherent M-ary FSK systems. The power spectral density and the spectral efficiency of JFPM are analyzed. Fractional out-of-band power containment bandwidths are obtained numerically for different JFPM formats. These analytical results show that the power spectral density of JFPM does not contain a discrete component and the same bandwidth efficiency can be obtained by using different JFPM formats. Overall, JFPM can be classified as a bandwidth- and power-efficient modulation technique. >

Multilevel block codes for Rayleigh-fading channels

Abstract: New multilevel block codes for Rayleigh-fading channels are presented. At high signal-to-noise ratios (SNRs), the proposed block codes can achieve better bit error performance over TCM codes, optimum for fading channels, with comparable decoder complexity and bandwidth efficiency. The code construction is based on variant length binary component block codes. As component codes for the 8-PSK multilevel block construction, the authors propose two modified forms of Reed-Muller codes giving a good trade-off between the decoder complexity and the effective code rates. Code design criteria are derived from the error performance analysis. Multistage decoding shows very slight degradation of bit error performance relative to the maximum likelihood algorithm. >

Modulation/microwave integrated digital wireless developments

Abstract: Simultaneous study and joint optimization of digital modulation techniques and of microwave components, presented in this paper, lead to spectrally efficient, high capacity, fast transmission, and throughput rate wireless systems. The choice of a particular modulation/demodulation (modem) technique has a major impact on the overall microwave system design, transceiver architecture and on the choice of all intermediate frequency (IF) as well as radio frequency (RF) component specifications. The performances of the most frequently used digital modulation techniques, including /spl pi//4-DQPSK, conventional BPSK, DQPSK, GMSK, GFSK, 4FSK, and FQPSK systems are compared. Study of crosscorrelated quadrature modulated GMSK systems used in GSM, PCS-1900, and other standards indicate that the subject technologies applied to GMSK improve the performance of these systems. We demonstrate that with the patented family of digitally modulated Feher's FQPSK systems, the power efficiency of conventional QPSK systems, which require linear microwave amplifiers, can be increased by about 300%, and the spectral efficiency of standardized nonlinearly amplified microwave integrated circuit GMSK systems can be increased by 60-200%. Similar advantages are obtained with our new FBPSK over BPSK modulated systems. >

Neural network based adaptive predistortion for the linearization of nonlinear RF amplifiers

Abstract: The good spectral efficiency of linear modulation techniques makes them attractive for use in high data rate digital radio systems. Unfortunately, the fluctuating envelopes of such systems combined with the nonlinear nature of the high power RF amplifiers commonly used gives rise to spectral spreading, adjacent channel interference, I-Q crosstalk, and degraded bit error rates. A possible solution to these problems is the linearization of the transmitter system by predistortion of the baseband digital signal using a nonlinear filter which is the inverse of the amplifier response. We realize the inverse filter using a backpropagation neural network. A coupler and demodulator provide a feedback path which provides the input to the neural network while the desired signal is the original waveform. The shaped waveform is passed through the network which adaptively corrects for the changing response of the high power RF amplifier. This technique allows us to correct for quite general nonlinearities, significantly reduce spectral spreading, and to improve the bit error rate.

Efficiency of data-aided timing recovery techniques

Abstract: This paper assesses the tracking capabilities of data-aided timing recovery schemes in terms of an efficiency that characterizes, coarsely speaking, the amount of timing information that the scheme manages to extract from the incoming signal per unit of time and signal-to-noise ratio. Efficiencies of maximum-likelihood and various baud-rate timing recovery schemes are determined as a function of the data and channel parameters, and are optimized with respect to design freedoms of the schemes. These results are illustrated for partial-response channels and idealized digital recording channels. >

OFDM performance evaluation over measured indoor radio propagation channels

Abstract: Transmission of a multi-carrier (MC) signal through the multipath fading indoor channel is explained and its capability to combat the frequency selectivity of the channel as well as to provide spectral efficiency and also its effective implementation with discrete Fourier techniques is described. Performance of orthogonal frequency division multiplexing (OFDM) with BPSK modulation is evaluated over a large empirical data base of indoor radio propagation channels. These indoor channels have lognormal amplitude fading and modified Poisson distribution of the arrival time of multipath components. The performance is evaluated in terms of the average probability of bit error as a function of signal-to-noise ratio. The influence of changing the number of tones as well as the guard interval on the average bit error rate is investigated. Results can be used in design and assessment of high speed indoor wireless communication systems.

Aggressive fuzzy distributed dynamic channel assignment algorithm

Abstract: Constraint based channel assignment schemes often rely on crisp evaluations of radio interference constraints to determine if an open channel is feasible for assignment. Such an approach has been popularly adopted to formulate fixed channel assignment (FCA) schemes, dynamic channel assignment (DCA) schemes, and more recently distributed DCA (DDCA) schemes. DDCA schemes are localized DCA schemes where every cell site is responsible for channel assignments to calls generated within that cell. The paper introduces the aggressive fuzzy DDCA (AFDDCA) scheme in which the feasibility evaluation of the constraints is soft. The scheme is in the polite mode when a perfectly feasible channel exists, and in an aggressive mode otherwise. The aggressive policy is progressive. We demonstrate that, when the traffic is heavy, AFDDCA scheme can outperform globally optimal DCA in terms of spectral efficiency while the voice quality degradation is surprisingly mild.

A new FQPSK modem/radio architecture for PCS and mobile satellite communications

Abstract: A newly developed constant envelope FQPSK modem/radio architecture, which employs a modified double-jump (DJ) filter in the cross-correlated FQPSK system, is proposed for personal communications systems (PCS) and mobile satellite applications. The power efficiency and spectrum efficiency of this system are investigated in a nonlinear amplified (NLA) environment. The bit error rate (BER) performance is evaluated in a noisy Rayleigh fading channel. We demonstrate that with the simplest threshold detectors (binary robust eye diagrams in I and Q channels), this system is 4-7 dB more power efficient than the US digital cellular and Japanese Handyphone standard /spl pi//4-QPSK (50%-100% more spectrally efficient than the recently adopted wireless local area network (LAN) standard GFSK and the European standard GMSK). The results indicate that the proposed DJ filtered FQPSK is a power and spectrally efficient modem/radio technique. By selecting different system parameters, this system can be optimized for a wide range of applications in PCS and mobile satellite communications. >