Showing papers on "Frequency-division multiplexing published in 1993"
TL;DR: Experimental results indicate that the bit-error-rate performance achievable with the proposed scheme is within 1.5 dB of the performance obtained with ideal synchronization.
Abstract: A synchronization scheme enabling the use of orthogonal frequency division multiplexing (OFDM)/FM over a mobile radio channel in a pure ALOHA environment is proposed. The scheme encodes synchronization information in parallel with data in the same manner in which data is encoded in the OFDM/FM frame. The synchronization information is in the form of tones, centered in certain reserved frequency subchannels of the OFDM signal. The receiver uses a correlation detector, implemented in the frequency domain, to acquire synchronization accurately on a packet-by-packet basis. Experimental results indicate that the bit-error-rate performance achievable with the proposed scheme is within 1.5 dB of the performance obtained with ideal synchronization. >
194 citations
TL;DR: The Letter proposes new compensation methods for the fading distortion in OFDM signals, in which compensation is achieved in the frequency domain, by baseband simulation.
Abstract: In orthogonal frequency division multiplexing (OFDM) signal transmission via a frequency nonselective fading channel, multiplicative distortion in the time domain acts as intersymbol interference (ISI) in the frequency domain. The Letter proposes new compensation methods for the fading distortion in OFDM signals, in which compensation is achieved in the frequency domain. With the proposed methods, improved results can be obtained compared to previous schemes. The symbol error rate (SER) of each proposed scheme is obtained by baseband simulation.
118 citations
18 May 1993
TL;DR: Two signaling schemes that exploit the availability of multiple (N) antennas at the transmitter to provide diversity benefit to the receiver are proposed.
Abstract: Two signaling schemes that exploit the availability of multiple (N) antennas at the transmitter to provide diversity benefit to the receiver are proposed. In the first scheme, a channel code of length N and minimum Hamming distance d/sub min/ /spl les/ N is used to encode a group of K information bits. The channel code symbol c/sub i/ is transmitted with the i/sup th/ antenna. At the receiver, a maximum likelihood decoder for the channel code provides a diversity of d/sub min/, as long as each transmitted code symbol is subjected to independent fading. The second scheme introduces deliberate resolvable multipath distortion by transmitting the data bearing signal with antenna 1, and N - 1 delayed versions of it with antennas 2 through N. The delays are unique to each antenna and are chosen to be multiples of the symbol interval. At the receiver, a maximum likelihood sequence estimator resolves the multipath in an optimal manner to realize a diversity benefit of N.
104 citations
Patent•
09 Nov 1993
TL;DR: In this paper, the authors proposed a method and an arrangement for dynamic allocation of multiple carrier wave channels for multiple access by frequency division multiplexing (FDM) for flexible data speed and continuous transmission, where a wider frequency band is divided into a number of subbands with a modulated carrier wave in each subband.
Abstract: The invention relates to a method and an arrangement for dynamic allocation of multiple carrier wave channels for multiple access by frequency division multiplexing. The invention provides a number of mobile units with the possibility of flexible data speed and continuous transmission. On the fixed side, the number of transmitters and receivers can be minimized by utilizing broadband receivers which serve a number of mobiles. According to the invention, a wider frequency band is divided into a number of subbands with a modulated carrier wave in each subband. To vary the transmission speed, such a number of subbands is allocated as is needed by each user in order to cover the data clock requirement. Broadband transmitters/receivers handle the transmission over the entire accessible band. Oversampling is preferably carried out in the frequency demultiplexing in order to permit the best sampling time to be selected for the different frequency gaps.
83 citations
TL;DR: A digital modulation system using orthogonal frequency division and multiplexing (OFDM) is addressed, which presents the advantage of coping with echoes more easily than classical single-carrier modems, thanks to the insertion of a guard interval between two symbols.
Abstract: A digital modulation system using orthogonal frequency division and multiplexing (OFDM) is addressed in this paper. Such a system presents the advantage of coping with echoes more easily than classical single-carrier modems, thanks to the insertion of a guard interval between two symbols. The signal equalization is then achieved in the frequency domain. This OFDM modem is improved by using dual polarizations. In this configuration, it can convey a 70 Mbits/s (HDTV) bit stream in an 8 MHz UHF channel. Some experimental results relate field trials carried out in several countries with such equipment.
75 citations
TL;DR: In this article, a large capacity local access network providing users with a dedicated two-way link to a central office is presented, which is built along a single optical fiber ring.
Abstract: A large-capacity local access network providing users with a dedicated two-way link to a central office is presented. The network is built along a single optical fiber ring. Connection to the fiber is obtained by combining time-division-multiplexing (TDM) and frequency-division-multiplexing (FDM) techniques and by using a novel optical channel add-drop filter. Optical signals are generated at the central office. The users have a simple device integrated with the channel dropping filter to receive and transmit data without the use of an optical source. Such a system can support 210 users transmitting at 100 Mb/s. >
68 citations
TL;DR: Results show that in wide-area networks, very low outage probabilities may be achieved with very modest transmitter powers, which implies that good network planning results in low-power, closely spaced transmitters.
Abstract: The new digital modulation schemes (OFDM) proposed for broadcasting of sound and television allow for the use of simulcasting, i.e., letting all transmitters in a radio network transmit on the same frequency. Such single-frequency networks (SFNs) have the potential of providing good coverage and very good frequency economy in wide-area (nationwide) applications. An OFDM-based SFN is analyzed with respect to its coverage properties. The network performance is measured by the outage probability and frequency economy. Both wide and local area systems are considered. Results show that in wide-area networks, very low outage probabilities may be achieved with very modest transmitter powers. The main reason for this is the inherent diversity, the efficiency is of which is primarily dependent on the transmitter density. However, in local area systems with only a few transmitters in each region, the performance is shown to drop drastically, mainly due to the low degree of diversity. This work implies that good network planning results in low-power, closely spaced transmitters. >
67 citations
23 May 1993
TL;DR: It is shown that effective network failure restoration can be achieved with optical paths and the applicability of the wavelength path (WP) technique to global area networks is revealed.
Abstract: Path layer technologies play a key role in the development of a powerful and failure resilient broadband integrated services digital network (B-ISDN). The authors discuss wavelength division multiplexing/frequency division multiplexing (WDM/FDM) techniques and demonstrate that optical paths can greatly enhance the path layer capability and, therefore, network performance. It is shown that effective network failure restoration can be achieved with optical paths. The applicability of the wavelength path (WP) technique to global area networks is revealed. WPs are applied to the national backbone network example to evaluate the required number of wavelengths and to identify optical cross-connect node requirements. A new optical path concept is proposed, i.e., the virtual wavelength path (VWP). In the VWP scheme, wavelengths are assigned on a link-by-link basis. The wavelength assigned to a wavelength path has only local significance. Significant benefits of the VWP such as the simplified path accommodation design within a transmission facility network and the reduced number of wavelengths needed, are elucidated. >
64 citations
Patent•
12 Oct 1993TL;DR: In this article, a method and means for transmultiplexing a plurality of signals between signal terminals (17 or 29) and selected radio frequency channels is presented. But the method is not suitable for the use of a comb filter.
Abstract: A method and means are provided of transmultiplexing a plurality of signals between a plurality of signal terminals (17 or 29) and a plurality of selected radio frequency channels. The method includes the step of, and means for, frequency translating and filtering the plurality of signals between the plurality of selected channels and a polyphase discrete Fourier transform filter bank (16 or 21) within a comb filter (15 or 22). The method further includes the step of frequency division multiplexing the plurality of signals between the plurality of signal terminals and comb filter (15 or 22) within a polyphase discrete Fourier transform filter bank (16 or 21).
56 citations
TL;DR: In this article, two critical components, needed for optical networks based on frequency division multiplexing (FDM) and frequency reuse technologies, are presented: a fast tunable laser, yielding 24 discrete frequencies regularly spaced by 40 GHz around 1.53 mu m, and a broadband wavelength shifter capable of switching multigigabit data between optical frequencies in the 1.5- mu m region.
Abstract: Two critical components, needed for optical networks based on frequency division multiplexing (FDM) and frequency reuse technologies, are presented. One is a fast tunable laser, yielding 24 discrete frequencies regularly spaced by 40 GHz around 1.53 mu m. The laser can be switched randomly in less than 8 ns among these frequencies. Frequency routing of a 3-Gb/s bit stream in 10-ns packets between ten different destinations has been demonstrated with this laser. The second component is a broadband wavelength shifter capable of switching multigigabit data between optical frequencies in the 1.5- mu m region. The device is tunable and cascadable, provides conversion gain, and is nearly polarization insensitive. Data degradation after wavelength shifting is negligible. Such a device provides the means of reusing the limited set of frequencies given by the lasers and thus of realizing large size networks. >
52 citations
TL;DR: In this paper, the future outlook for communication networks based on optical frequency division multiplexing (optical FDM) technology is assessed based on the technical results obtained from a 100-channel optical FDM experiment.
Abstract: Optical frequency division multiplexing (optical FDM) technology, which allows the use of an extremely broad lightwave bandwidth (10-200 THz and over) and can realize transport systems that could replace the current digital (time division multiplexing based) transport networks, is described. The future outlook for communication networks based on optical FDM technology is assessed. Based on the technical results obtained from a 100-channel optical FDM experiment, of an optical FDM channel concept is proposed and a viable architecture for optical FDM-channel-based networks is developed. >
23 May 1993
TL;DR: An example of a modem for two-resolution digital terrestrial transmission, providing two programs in a single 8 MHz channel is described, using a two- resolution quadrature amplitude modulation (QAM) signal constellation.
Abstract: An example of a modem for two-resolution digital terrestrial transmission, providing two programs in a single 8 MHz channel is described. For each program, it is desired to transmit 5 Mb/s to portable receivers and additionally 5 Mb/s to fixed receivers. In the example, orthogonal frequency division multiplexing (OFDM) is used with guard intervals as in digital audio broadcasting. The two-resolution transmission is achieved by using a two-resolution quadrature amplitude modulation (QAM) signal constellation. Reed-Solomon coding gives burst error correction capability to combat the frequency selective nature of the transmission channel. The two-resolution system can easily be reconfigured into a compatible system, providing high-definition television to fixed receivers. >
TL;DR: The question of whether multilevel signaling can improve the spectral efficiency of optical frequency division multiplexing (FDM) systems is investigated and it is shown that there is no advantage to going beyond binary signaling.
Abstract: The question of whether multilevel signaling can improve the spectral efficiency of optical frequency division multiplexing (FDM) systems is investigated. Multilevel amplitude-shift keying (ASK) and a receiver consisting of an optical channel selection filter (specifically, a single-stage Fabry-Perot), a pin diode for direct detection, and an integrator are assumed. It is also assumed that additive noise is negligible and that the major impairments are adjacent channel interference and intersymbol interference. The analysis shows that, for such a receiver, there is no advantage to going beyond binary signaling. It is also shown that this finding holds up when additive and phase noises and alternative approaches to filtering are considered. >
29 Nov 1993
TL;DR: A transmission scheme for broadcasting a hierarchical HDTV signal in an 8 MHz terrestrial channel for stationary and portable receivers, is proposed, based on a concatenated coding scheme, where the inner multilevel coding is combined with multiresolution modulation.
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 the graceful degradation as the actual analog systems, and should be compatible with the standard definition-TV (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. A transmission scheme for broadcasting a hierarchical HDTV signal in an 8 MHz terrestrial channel for stationary and portable receivers, is proposed. The system is based on a concatenated coding scheme, where the inner multilevel coding is combined with multiresolution modulation. The principle of OFDM is used to combat the multipath propagation. This combination will allow one to perform a coherent detection with a simple channel estimation algorithm, to use the available spectrum in an efficient way, to achieve high spectral efficiencies, to assume a graceful degradation, and to maintain the compatibility between the different receivers by providing different receiver complexities depending on the desired image quality. >
29 Nov 1993
TL;DR: The paper investigates a system proposal for transmitting digital high-definition television (HDTV) signals over terrestrial UHF channels by comparing uncoded 16-QAM and trellis-coded 32-CROSS modulation in conjunction with an orthogonal frequency division multiplexing (OFDM) procedure.
Abstract: The paper investigates a system proposal for transmitting digital high-definition television (HDTV) signals over terrestrial UHF channels The authors compare uncoded 16-QAM and trellis-coded 32-CROSS modulation in conjunction with an orthogonal frequency division multiplexing (OFDM) procedure The simulations show the influence of the nonlinear distortions introduced by the high-power amplifier (HPA) of the transmitter As HPA the authors consider a travelling wave tube amplifier (TWTA) and a solid state power amplifier (SSPA) The characteristics of the channel for HDTV in a single frequency network (SFN) is simulated using a time-invariant multipath model >
TL;DR: An overview of supervisory control and data acquisition (SCADA) communication techniques is provided in this article, where modulation techniques, frequency division multiplexing (FDM) and time division multiple access (TDM) are discussed.
Abstract: An overview of supervisory control and data acquisition (SCADA) communication techniques is provided. Modulation techniques, frequency division multiplexing (FDM) and time division multiplexing (TDM), are discussed. Message formats and data transfer are detailed. An update on the development of standards for SCADA systems is given. >
18 May 1993
TL;DR: In this article, the minimum-mean-squared-error block linear equalizer (MSEQE) was used for the orthogonal frequency division multiplexing (OFDM) system.
Abstract: Multipath distortion in a digital mobile channel can be alleviated by using the orthogonal frequency division multiplexing system in which the discrete Fourier transform is used for multiplexing N subchannels. Albeit every subchannel is subject to a flat fading, the difference in fading level results in intersymbol interference. Five equalization methods are studied, and their performance is compared. It is concluded that the minimum-mean-squared-error block linear equalizer is a good compromise between complexity and performance.
TL;DR: Cochlear prosthesis systems for postlingually deaf individuals (those who have become deaf due to disease or injury after having developed mature speech capability) are considered.
Abstract: Cochlear prosthesis systems for postlingually deaf individuals (those who have become deaf due to disease or injury after having developed mature speech capability) are considered. These systems require the surgical implantation of an array of electrodes within the cochlea and are driven by processed sound signals from outside the body. A system that uses an analog signal approach for transcutaneous transfer of six processed speech data channels using frequency multiplexing is described. The system utilizes a filterbank of six narrowband surface acoustic wave (SAW) filters in the range 72-78 MHz with a 1.2-MHz channel spacing to multiplex the six carrier signals, frequency modulated, by the processed speech signals, onto a composite signal. The same SAW filters are used in the receiver filterbank for signal separation, but are housed in a miniaturized package. The system includes a portable transmitter and a receiver package which is to be implanted in the patient. The implanted circuits are supplied exclusively from power transferred from outside the body via a separate 10-MHz transcutaneous link. >
12 Oct 1993
TL;DR: A protocol is described which allows a wireless access communication system (WACS) to dynamically allocate bandwidth on its system-wide broadcast radio channel among the alerting, system information, and priority access request subchannels, and efficiently accommodates a wide range of alerting traffic levels.
Abstract: A protocol is described which allows a wireless access communication system (WACS) to dynamically allocate bandwidth on its system-wide broadcast radio channel among the alerting, system information, and priority access request subchannels. These subchannels each have different requirements with respect to the message length and position within the framing structure; the described protocol meets each of their requirements. The protocol efficiently accommodates a wide range of alerting traffic levels, and provides for efficient downloading of system information to subscriber units by using excess capacity when alerting traffic is low. It has error detection capabilities above that provided by the radio channel alone, and is easily extendible to accommodate other services such as paging and low bandwidth broadcast messaging. This work is targeted towards understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks.
Patent•
22 Dec 1993
TL;DR: In this article, the authors proposed an error correction method where the speedup of transmission speed is easy and the degradation of the error ratio of a frequency selective phasing is small, in an FDM transmission system.
Abstract: PURPOSE: To realize an error correcting method where the speed-up of transmission speed is easy and the degradation of the error ratio of a frequency selective phasing is small, in an FDM transmission system. CONSTITUTION: A transmitter 301 is composed of (n) error correction encoders 101-1 to 101-n (n is ≥2) performing an error correction encoding for transmission data, a mapping circuit 102 outputting m of data arranged so as to disperse each of n encoded data sequence on a frequency axis or a time axis and an FDM modulator 103 outputting signal where m of data is modulated into each of m carrier waves and is multiplexed. Therefore, plural error correction encoders 101-1 to 101-n and a decoder are provided, the application of high transmission speed to a system is easy. Because the burst error by a selective fading is effectively dispersed by a mapping means, the reliability of decoded data is improved. When a user receives only part of data in a multiconnection and a broadcasting system, the miniaturization of a receiver and low power consumption is performed. COPYRIGHT: (C)1995,JPO
TL;DR: In this article, the design and performance of all-fiber video distribution (AFVD) systems based on AM/FM FDM subcarrier multiplexing (SCM) and erbium-doped fiber amplifiers (EDFAs) are investigated.
Abstract: this paper describe the design and performance of all-fiber video distribution (AFVD) systems based on AM/FM FDM subcarrier multiplexing (SCM) and erbium-doped fiber amplifiers (EDFAs). The impact of applying EDFAs to SCM analog video distribution systems is investigated. AM/FM hybrid systems, which can simultaneously distribute 11 AM TV channels and 50 FM TV channels are proposed and discussed. Four-stage amplifier-branch transmission experiments are introduced. The construction and performance of a newly designed 50-channel FM tuner are also presented.
TL;DR: Simulation results for such systems show that an order of magnitude reduction in the sampling rate is possible while producing only minimal error in the bit error rate estimate.
Abstract: When simulating multicarrier digital communication systems operating over nonlinear channels, the required high sampling rate contributes significantly to long execution times. A new method that reduces the sampling rate of simulations of such systems is developed. The partial rate of products (ParSOP) method reduces the sampling rate by generating only the intermodulation products that lie in a frequency band of interest. The ParSOP method requires that the bandpass nonlinearity be represented by memoryless operations on the complex envelope of the signal and that the subcarriers constituting the frequency-division multiplexed signal are sufficiently separated to prevent significant adjacent channel interference. Simulation results for such systems show that an order of magnitude reduction in the sampling rate is possible while producing only minimal error in the bit error rate estimate. >
TL;DR: Transmission aspects of the advanced digital high definition television (AD-HDTV) system, for terrestrial simulcast delivery of HDTV are described, and the NTSC planning factors, suitably modified for HDTV delivery, are used to estimate the coverage area.
Abstract: Transmission aspects of the advanced digital high definition television (AD-HDTV) system, for terrestrial simulcast delivery of HDTV are described. In AD-HDTV, two quadrature-amplitude-modulated (QAM) carriers, with different power spectral densities, are employed in a frequency division multiplex (FDM) mode within the standard 6-MHz channel. The resulting spectral shaping allows a larger power to be transmitted, compared to that for a single QAM carrier, for the same level of perceptual interference into cochannel NTSC. The coded video data are split into high-priority (HP) data and standard-priority (SP) data, and the vital information is sent on the appropriate QAM carrier, resulting in a robust audio and video transmission system. The availability is higher in scenarios where the carrier-to-noise ratio (CNR) is above the threshold for HP reception but below the threshold for SP reception; this is important in fringe areas. The NTSC planning factors, suitably modified for HDTV delivery, are used to estimate the coverage area for AD-HDTV. The calculated AD-HDTV coverage area of 54.5 miles is comparable to that for NTSC transmission. >
Proceedings Article•
02 May 1993TL;DR: Distinguished features of recent optical IC devices are 1) larger-scale substrates, 2) low-loss waveguides, 3) a higher degree of integration, 4) higher speed, 5) aHigher degree of function, 6) frequency multiplexing, 7) alignment stability, and 8) nonlinear-optic effects.
Abstract: More than twenty years have passed since the concept of "Optical Integrated Circuits" was proposed, and their theory, design, fabrication, and evaluation have improved greatly. Distinguished features of recent optical IC devices are 1) larger-scale substrates, 2) low-loss waveguides, 3) a higher degree of integration, 4) higher speed, 5) a higher degree of function, 6) frequency multiplexing, 7) alignment stability, and 8) nonlinear-optic effects. These aspects will be discussed using several examples.
01 Nov 1993
TL;DR: In this article, the authors examined the extent to which optical signal processing can be brought into use instead of present-day electronic signal processing in such switching elements and several experiments involving OFDM technologies are described which are intended to underline the significance of those technologies for future telecommunication networks.
Abstract: In future telecommunication systems, efforts will be made to exhaust the almost unlimited transmission capacity of optical fibers by applying optical frequency-division-multiplexing (OFDM) techniques. The switching elements of such networks must be able to process OFDM signals as well as time-division-multiplexing (TDM) signals. The extent to which optical signal processing can be brought into use instead of present-day electronic signal processing in such switching elements is examined. Several experiments involving OFDM technologies are described which are intended to underline the significance of those technologies for future telecommunication networks. Various techniques for and experiments on the optical switching of signals in the frequency, space, and time domain are described. Experiments dealing with optical signal regeneration are described. >
01 Dec 1993
TL;DR: In this paper, the application of the microwave subcarrier multiplexing technique (SCM) in an OFDM system which employs an optical FM direct detection scheme was described, and the effect of laser diode phase noise and relative intensity noise as well as the intermodulation product of sub-carrier channels was analyzed and the results presented.
Abstract: This paper describes the application of the microwave subcarrier multiplexing technique (SCM) in an optical frequency division multiplexing (OFDM) system which employs an optical FM direct detection scheme. Direct frequency modulation of a laser diode offers the advantages of compact optical spectrum and simple driving circuit; it also permits a more effective utilisation of optical channel capacity. The carrier-to-noise ratio performance of each subcarrier channel is evaluated. The effect of laser diode phase noise and relative intensity noise as well as the intermodulation product of subcarrier channels on the overall system performance is analysed and the results presented.
01 Aug 1993
TL;DR: Field trials have been carried out on the digital transmission of color TV signals in a standard European terrestrial channel of 8 MHz bandwidth to obtain first practical results on the general properties of OFDM modulated digital TV signals under real transmission and reception conditions.
Abstract: Field trials have been carried out on the digital transmission of color TV signals in a standard European terrestrial channel of 8 MHz bandwidth. The goal was to obtain first practical results on the general properties of OFDM modulated digital TV signals under real transmission and reception conditions. A comparison of digitally modulated broadcast TV signals and VSB (vestigial sideband) modulated PAL signals was carried out in a UHF channel under normal and severe reception conditions. The field trials were carried out in September 1992 in a hilly region. The results of measurements for normal reception at a distance of 12 km from the transmitter are shown. For OFDM transmission the presentation of absolutely noise-free and interference-free pictures is possible down to a transmitter output power of 2 dBW (1.6 W) and a SNR in the received signal of 29 dB. To achieve the minimum requirements needed for analog PAL transmission (field strength 69 dBV/m and SNR of 38 dB) a peak power of 13 dBW (20 W) in the synch-pulse has to be used. >
Patent•
11 May 1993TL;DR: In this article, a frequency-multiplexed video signal is generated in which a color-under signal and a second under signal are linearly combined with at least partially overlapping frequency spectra to form a composite under signal.
Abstract: A frequency-multiplexed video signal is generated in which a color-under signal and a second under signal are linearly combined with at least partially overlapping frequency spectra to form a composite under signal for an FM luma signal. The frequency-multiplexed video signal is suited for recording on magnetic tape using helical scanning methods and for being played back from the magnetic tape using helical scanning methods. The second under signal is generated in such way that line-comb filtering can be used during playback to separate color-under signal and second under signal each from the composite signal despite their frequency spectra being at least partially overlapping in the composite signal.
TL;DR: The analysis estimates the adjacent channel interference (ACI)-induced floor on BER for the middle of three FDM channels, as a function of frequency spacing and linewidth-to-bit rate ratio ( beta T).
Abstract: The required frequency spacings between channels in an optical frequency division multiplexing (FDM) network are considered. The minimum permissible spacings consistent with meeting bit error rate (BER) objectives are derived. The assumed transmission uses on-off keying (OOK), at a data rate 1/T (in bits per second), via external modulation of a laser source having linewidth beta (in hertz). The assumed receiver consists of an optical channel selection filter followed by a p-i-n photodiode and a postdetection integrate-and-dump circuit. The analysis estimates the adjacent channel interference (ACI)-induced floor on BER for the middle of three FDM channels, as a function of frequency spacing and linewidth-to-bit rate ratio ( beta T). For BER=10/sup -9/ and beta T ranging from 0.32 to 5.12, the required channel spacing ranges from 5.2 to 27.5 bit rates. The multiplying factors associated with using (wide-deviation) frequency shift keying (FSK), coherent (heterodyne) detection, and infinitely many FDM channels, respectively, are estimated to be 2.0, at most 3.0, and at most 1.37. >