Showing papers on "QAM published in 1998"

Signal space diversity: a power- and bandwidth-efficient diversity technique for the Rayleigh fading channel

Abstract: The increasing need for high data-rate transmissions over time- or frequency-selective fading channels has drawn attention to modulation schemes with high spectral efficiency such as QAM. With the aim of increasing the "diversity order" of the signal set we consider multidimensional rotated QAM constellations. Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, This multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense.

Impacts Of I/q Imbalance On Qpsk-ofdm-qam Detection

Abstract: The impacts of the I/Q imbalance in the quadrature down-converter on the performance of a QPSK-OFDM-QAM system are studied. Either amplitude or phase imbalance introduces inter-channel interference (ICI). In addition to the ICI, there is a cross-talk between in-phase and quadrature channels in each and every sub-carrier when both amplitude and phase imbalances are present. The BER (bit error ratio) performance of QPSK sub-carriers are also calculated to illustrate the impacts of the I/Q imbalance. It is observed that with the amplitude imbalance less than 1 dB and phase imbalance less than 5 degrees, the degradation of BER performance is less than 0.5 dB for a BER>10/sup -6/.

Reconfigurable radio system architecture

Abstract: A system and method for providing a digital field configurable radio frequency communication system that can be configured into a transmitter, or a receiver, to function with a plurality of signaling schemes, such as, AM, AME, A3E, H3E, J3E, CW, SSB, M-PSK, QAM, ASK, angular modulation, including FM, PM, FSK, CMP, MSK, CPFSK etc. The system includes a non volatile memory that is adapted to receive and store instructions for configuring the system. A user selects the mode of operation and the signaling scheme, and instructions and software are downloaded from the memory into the system and configure the system as selected by the user.

Blind decision feedback equalization for terrestrial television receivers

Abstract: In December 1996 the Federal Communications Commission (FCC) adopted the Grand Alliance (GA) system as the digital television broadcasting standard for the United States ending a seven-year-long search for a fully digital television standard. MPEG-2 was chosen as the video compression standard, and trellis-coded 8-vestigial sideband (VSB) with a training sequence was chosen as the transmission standard. The laboratory tests that were performed on the final two competing systems, 8-VSB with training sequence and 32-quadrature amplitude modulation (QAM) with blind equalization, showed a need for blind equalization in dynamic channels that could not be adequately handled by an equalizer training on the training sequence alone. Hence, the final GA system recommended the use of blind equalization in the receiver. In this paper, we describe the U.S. digital television transmission standard as it pertains to the equalization problem, typical transmission channel characteristics and the need for blind equalization in terrestrial television receivers.

Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals

Abstract: The multilevel modulation techniques of 64-quadrature amplitude modulation (QAM) and 64-differential amplitude and phase-shift keying (DAPSK) have been proposed in combination with the orthogonal frequency-division multiplexing (OFDM) scheme for digital terrestrial video broadcasting (DTVB). With this system a data rate of 34 Mb/s can be transmitted over an 8-MHz radio channel. A comparison of these modulation methods in the uncoded case has been presented by Engels and Rohling (see European Trans. Telecommun., vol.6, p.633-40, 1995). The channel coding scheme proposed for DTVB by Schafer (see Proc. Int. Broadcasting Convention, Amsterdam, The Netherlands, p.79-84, 1995) consists of an inner convolutional code concatenated with an outer Reed-Solomon (RS) code. In this paper the performance of the convolutional codes is analyzed for the two modulation techniques. This analysis includes soft decision Viterbi (1971) decoding of the convolutional code. For soft decision decoding of DAPSK modulated signals a new metric is developed.

Ethernet transport facility over digital subscriber lines

Abstract: A facility transport system for transporting Ethernet over digital subscriber lines. The system, termed 10BaseS, is capable of transmitting of 10 Mbps Ethernet over existing copper infrastructure. The system utilizes carrierless amplitude modulation phase modulation/quadrature amplitude modulation (CAP/QAM) to transport Ethernet frame data and utilizes splitter means (22) to separate both the downstream and upstream channels from POST signals.

Direct multilevel carrier modulation using millimeter-wave balanced vector modulators

Abstract: The importance of being able to design affordable, high-performance, millimeter-wave transmitters for digital communications and radar applications is increasing. To this end, two monolithic millimeter-wave vector modulators have been realized at 38 and 60 GHz for use in direct multilevel carrier modulation. It is shown that, by employing balanced biphase amplitude modulator elements, accurate constellations are achieved with broad-band operation from 20 to 40 GHz and 55 to 65 GHz. Modulations of 16- and 256-QAM have been demonstrated, both at 38 and 60 GHz, using this technique. Each balanced biphase amplitude modulator uses a pair of reflection-type attenuators operated in push-pull mode. This study investigates the suitability of this topology for use as a full biphase amplitude modulator for multilevel digital modulation schemes. It is found that the technique is very robust and the resulting analog vector modulator can be a very important component for many future millimeter-wave applications.

Subchannel modulation scheme for carrying management and control data outside the regular data channel

Abstract: A method and apparatus for implementing a subchannel for management and control or other supplemental data on a media shared with a high speed data link Several FDMA approaches are disclosed including AM, FM, PM, phase, QAM, QPSK etc modulation of a subcarrier having a frequency which is in the bandwidth provided by the shared media which is not used by the DC balanced high speed data stream A preferred species which is compatible with existing high speed data transmitters and receivers comprises a subchannel transmitter which frequency shift keys a subchannel carrier of about 1 mHz with the subchannel data The modulated subchannel carrier is summed by superposition with a DC balanced NRZ format gigabit data stream and coupled onto the media Injection power levels of the subchannel carrier are controlled so as to not cause excessive jitter in the high speed data receivers but so as to provide sufficient amplitude in the face of noise sources including random variations in transition density to be recovered by a subchannel receiver At the destination node, the combined signal is directly coupled to the input of the high speed data receiver, but is coupled to the input of the subchannel receiver through a low pass filter The subchannel receiver is narrowband and includes an FSK demodulator

TCM/SSMA communication systems with cascaded sequences and PAM/QAM signal sets

Abstract: An expression in matrix form for the multiple-access interference (MAI) in an asynchronous direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system with cascaded sequences (CVs), arbitrary chip waveforms, and trellis-coded modulation (TCM) with a pulse amplitude modulation (PAM) or quadrature amplitude modulation (QAM) signal set is obtained. TCM provides significant coding gain while the CVs decrease the correlation between the MAI of adjacent data intervals. The expression is used to calculate arbitrarily accurate probability density functions (PDFs) of the MAI in the TCM system and to derive an accurate approximation of the MAI variance. It also helps illustrate some properties of the MAI by separating contributing parameters into different matrices. We derive an approximation of the upper union bound on the bit-error probability and investigate its applicability. The results show that CV schemes can greatly reduce the pairwise error probabilities (PEPs) until the length of the CV becomes greater than that of the error weight sequence (EWS) under consideration.

Comparison of single-carrier and multitone digital modulation for ADSL applications

Abstract: Single-carrier modulation such as quadrature amplitude modulation (QAM) or carrierless amplitude modulation-phase modulation (CAP), and DMT are alternative techniques for providing digital communication in a variety of applications, in particular ADSL for communication over the telephone company subscriber lines. Although theory predicts comparable performance under ideal implementations, a definitive comparison of performance over a wide range of conditions will require more experience from field trials. Similarly, accurate comparison of implementation costs must await the greater availability of commercial-grade devices. However, enough is now known about these modulation schemes to compare their inherent similarities and differences in performance and cost. Overall, a present view of single-carrier and multitone modulation indicates comparable performance with some differences depending on the type of degradation. Costs should also be approximately equal, with multitone having some advantage in digital processing, but requiring greater cost in analog circuitry.

Reception mode control in radio receivers for receiving both VSB and QAM digital television signals

Abstract: A radio receiver uses the same tuner for receiving a selected digital television (DTV) signal, irrespective of whether it is a quadrature-amplitude-modulation (QAM) or a vestigial sideband (VSB) signal. The tuner supplies a final IF signal in a 6-MHz-wide frequency band, the lowest frequency of which is not appreciably more than 2.69 MHz. The final IF signal is digitized at a rate that is a multiple of both the symbol frequencies of the QAM and VSB signals, for synchrodyning to baseband, with the 2.69 MHz difference between the carrier frequencies of QAM and VSB signals being taken into account in the digital synchrodyning circuitry. The carrier frequencies of the QAM and VSB final IF signals are regulated to be submultiples of the multiple of both the symbol frequencies of the QAM and VSB signals by applying automatic frequency and phase control signals developed in the digital circuitry to a local oscillator of the tuner.

Single-channel blind equalization for GSM cellular systems

Abstract: This paper focuses on the study of blind equalization global system for mobile communications (GSM) systems using a single antenna. In order to utilize the well-known linear system model in conventional studies of blind equalization, an equivalent baseband quadrature amplitude modulation (QAM) approximation is used for the nonlinear GMSK signal in GSM systems. Since the GMSK signal in GSM has very little excess bandwidth to warrant oversampling, a derotation scheme is developed to create two subchannels for each received GMSK signal sampled at the baud rate. Linear approximation of the GMSK signal makes the traditional QAM blind equalization system model applicable for GSM. Derotation induces channel diversity without an additional antenna and reduces the number of necessary radio frequency (RF) receivers (sensors) without increasing hardware or computational costs. Several second-order statistical and higher order statistical methods of blind equalization are adopted for GSM signals.

QAM receiver with improved immunity to crosstalk noise

Abstract: The invention discloses a novel equalization system for reducing the deleterious effects of crosstalk on signals received at a modem, with particular regard to QAM signals transmitted over copper twisted pairs. The equalization system employs the common combination of a linear equalizer followed by a decision-feedback equalizer (DFE). However, instead of aiming for perfect equalization of channel distortion, the overall frequency response of the channel plus the linear equalizer is skewed such that higher frequencies are attenuated relative to lower ones. More generally, the spectral regions where crosstalk is strongest are attenuated, which reduces the crosstalk noise present at the input to the DFE at the expense of introducing inter-symbol interference (ISI). Fortunately, most DFEs are capable of handling the added ISI, leading to data decisions that are relatively unaffected by crosstalk noise.

Multiple hypothesis modulation classification based on cyclic cumulants of different orders

Abstract: A multiple hypothesis modulation QAM classification task is addressed. The classifier is designed within the rigorous framework of decision theory. A characteristic feature is extracted from the signal, and is compared to the possible theoretical features in the maximum likelihood sense. This feature is composed of a combination between fourth-order and squared second-order cyclic temporal cumulants. No assumption about the power of the signal is made. It is shown that this uncertainty about the power of the signal does not affect the decision rule. As an application, we present simulated performance in the context of 4-QAM vs 16-QAM vs 64-QAM classification.

Filtered decision feedback channel estimation for OFDM-based DTV terrestrial broadcasting system

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

Method and transceiver using an improved protocol for a frequency hop communication system

Abstract: A frequency hopping transceiver having a protocol for selecting a clear channel for exchanging QAM payload data signals. An energy level in a current channel is sounded by to determine whether it is clear or busy. When the current channel is clear an outgoing frequency shift key (FSK) handshake signal is transmitted. When the current channel is busy or an incoming handshake signal is not received, the transceiver hops to the next channel without waiting until the dwell time has elapsed for the current channel. When a channel is clear and the FSK handshake signal is received the transceiver uses a differential synchronization time for exchanging QAM acquisition signals and payload data in unison.

Method and system for cable modem management of a data-over-cable system

Abstract: A method and system for providing management functionality with a cable modem with telephony return is provided. The cable modem with telephony return is used for providing management functionality such as maintenance and signaling via the lower bandwidth telephony return path, leaving more higher bandwidth cable television channels free for data transmission. Since routine management functions such as maintenance are completed on the cable television channels via the telephony return path, the overall costs of maintaining the higher bandwidth cable television channels are reduced. In addition, since routine management functions are carried out via the telephony return path, fewer overall maintenance functions need to be carried out on the higher bandwidth cable television channels, requiring less down time and generating more revenues for the cable television network providers.

Upper bounds on the bit-error rate of optimum combining in wireless systems

Abstract: This paper presents upper bounds on the bit-error rate (BER) of optimum combining in wireless systems with multiple cochannel interferers in a Rayleigh fading environment. We present closed-form expressions for the upper bound on the bit-error rate with optimum combining, for any number of antennas and interferers, with coherent detection of BPSK and QAM signals, and differential detection of DPSK. We also present bounds on the performance gain of optimum combining over maximal ratio combining. These bounds are asymptotically tight with decreasing BER, and results show that the asymptotic gain is within 2 dB of the gain as determined by computer simulation for a variety of cases at a 10/sup -3/ BER. The closed-form expressions for the bound permit rapid calculation of the improvement with optimum combining for any number of interferers and antennas, as compared with the CPU hours previously required by Monte Carlo simulation. Thus these bounds allow calculation of the performance of optimum combining under a variety of conditions where it was not possible previously, including analysis of the outage probability with shadow fading and the combined effect of adaptive arrays and dynamic channel assignment in mobile radio systems.

Automatic characterization of a television signal

Abstract: A method and apparatus in a client processing system are provided for characterizing (401, 402) an input television signal as broadcast television (403) or cable television (409) and, if the signal is cable television (409), as IRC cable, HRC cable, or standard cable. The client processing system includes processing circuitry configured to receive hypertext pages from a remote server and to display the hypertext pages on a display device, such as a conventional television set. The client system further includes a television tuner for receiving either cable television or broadcast television signals. When a television signal is initially provided to the client system, the client system executes a routine to automatically characterize the received television signal as broadcast (408), HRC cable (410), IRC cable (407), or standard cable. The characterization (401, 402) is made based upon one or more frequencies at which the incoming television signal is detected.

A 70 Mb/s variable-rate 1024-QAM cable receiver IC with integrated 10 b ADC and FEC decoder

Abstract: A 70 Mb/s variable-rate 1024-quadrature amplitude modulated (QAM) cable receiver IC with integrated 10 b analog-to-digital converter (ADC) and forward error correction (FEC) decoder is presented. The chip accepts an analog 2 V/sub pp/ differential QAM signal centered at an intermediate frequency. The integrated 10 b ADC digitizes the IF signal, and all subsequent signal processing, including demodulation, timing/carrier recovers, adaptive equalization, and FEC, is performed digitally. The receiver IC is capable of receiving 4, 16, 32, 63, 128, 256, and 1024-QAM modulation formats. The 0.5-/spl mu/m triple level metal N-well CMOS chip has a complexity of 650 k transistors with a core area of 1.9/spl times/4.9 mm/sup 2/. Power dissipation is 1.8 W at 7 MBaud and 5 V.

For atsc digital television standard

Abstract: This paper describes a system structure of a DTV receiver capable of decoding a terrestrial broadcast signal which conforms to the ATSC digital television standard[ I]. A newly developed chip set is used to realize a compact decoder unit.

Adjustment of the sampling frequency in a multicarrier receiver

Abstract: In a multicarrier QAM system, a receiver comprises a data directed phase error estimator (21) which determines a phase rotation direction of each received complex QAM data value (YK) with respect to the complex default QAM data value (CK) used by a quantizer/decoder (11, 12) for decoding. The data directed phase error estimator (21) averages the phase rotation directions for all carriers and adjusts the phase of a sample frequency (fsampR) output by a numerically-controlled oscillator (15) on the basis of this overall average phase rotation direction value (D). Thus, an overall estimate of the missing phase synchronization to the sample frequency used in the transmitter can be obtained such that the data symbols can be more accurately decoded.

Precoder for DMT with insufficient cyclic prefix

Abstract: Multi-carrier modulation is a modulation technique that enables higher transmission rate than traditional techniques, such as single-carrier quadrature amplitude modulation (QAM) systems. One implementation of multi-carrier modulation technique is discrete multi-tone (DMT). DMT used in asymmetric digital subscriber lines (ADSL) and very high speed DSL (VDSL) systems has a fixed cyclic prefix length. When the impulse response of the channel is longer than the designed prefix length, for instance when the length of the line impulse response is very long, distortion will appear at the channel output in the form of interference between the carriers. This paper describes a method to remove this distortion by introducing a precoder at the transmitter. Although there will be a power increase when the precoder is used, the distortion is significantly reduced, yielding a performance improvement.

Method and apparatus for monitoring and controlling a local area network

Abstract: A method and an apparatus for establishing a local area network (LAN) using a channel stripper, a LAN controller and a cable television cable that couples peripheral devices to the LAN controller. The channel stripper removes signals from one or more selected channels from a cable television signal path. The channels form a signal path between the LAN controller and peripheral devices connected to the LAN. The remaining channels provide a digital cable television signal. Both the LAN channels and the digital cable television channels are combined onto a common coaxial cable. The cable stripper may be a multiplexer/demultiplexer or a notch filter. Alternately, the channel stripper can assign frequency channels outside the frequency bandwidth of to the LAN and maintain the cable television signals as received. The LAN controller can create additional communications channels by using Time Division Multiple Access protocols to assign time slots to each of the peripheral devices that are coupled to the LAN.

The application of orthogonal designs to wireless communication

Abstract: We introduce space-block coding, a new paradigm for transmission over Rayleigh fading channels using multiple transmit antennas. Data is encoded using a space-block code and the encoded data is split into n streams which are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signal perturbed by noise. Decoding is achieved in a simple way using the orthogonal structure of the space-block code and the maximum likelihood decoding algorithm is totally based on linear processing at the receiver. Space-block codes are designed to achieve the maximum diversity gain of transmit and receive antennas with the constraint of having a simple decoding algorithm. It is shown that the classical mathematical framework of orthogonal designs can be applied to construct channel codes which have a simple decoding algorithm, while providing the full spatial diversity order. Space-block codes constructed in this way only exist for few sporadic values of n and therefore there is a need for a new mathematical theory. We introduce the theory of generalized designs which provides codes for both real and complex constellations for any number of transmit antennas. Using this theory, we construct space-block codes that achieve the maximum possible transmission rate for any number of transmit antennas using any arbitrary real constellation such as PAM. For any arbitrary complex constellation such as PSK and QAM, we construct space-block codes that achieve half of the maximum possible transmission rate for any number of transmit antennas. For the specific cases of two, three and four transmit antennas, we provide space-block codes that achieve respectively the whole, 3/4 and 3/4 of maximum possible transmission rate using arbitrary complex constellations.

Performance characteristics and applications of hybrid multichannel ANI-VSB/M-QAM video lightwave transmission systems

Abstract: The performance characteristics and applications of hybrid multichannel amplitude modulation vestigal sideband (AM-VSB)/M-quadrature amplitude modulation (QAM) video lightwave transmission systems operating at either 1310 or 1550 nm are reviewed. These systems can transport up to 80 AM-VSB video channels and more than 30 64/256-QAM digital video channels over a standard single-mode fiber (SMF) using a single laser transmitter. Five main transmission impairment mechanisms for these systems are reviewed as follows: (a) clipping-induced impulse noise, (b) bursty nonlinear distortions, (c) multiple optical reflections, (d) stimulated Brillouin scattering, and (e) self-phase modulation. For AM-QAM video lightwave trunking applications, the in-line erbium-doped fiber amplifier (EDFA) selection is discussed using a frequency-domain simulation model. Such lightwave trunking systems can provide an AM carrier-to-noise ratio (CNR) greater than 50 dB with composite second order (CSO) and composite-triple-beat (CTB) distortions less than -65 dBc, and nearly error-free transmission (BER/spl les/10/sup -9/) for the 64-QAM channels with signal-to-noise ratio (SNR) of 30-dB or better. Comparison between 64-QAM and 256-QAM video channel transmission and the effect of the QAM channels on the AM-VSB channels are also presented. The implications of these results and others in hybrid multichannel AM-QAM video lightwave trunking systems are discussed.

Cosimulating synchronous DSP applications with analog RF circuits

Abstract: This paper introduces timed synchronous dataflow (TSDF) which enables the codesign of the synchronous DSP and analog RF portions of an application. The semantics and scheduling techniques of TSDF are detailed. A 16 QAM modem with a QAM synthesizable DSP transmitter cosimulating with a RF modulator and RF power amplifier is demonstrated.

Method and system for enhancing digital video transmission to a set-top box

Abstract: A method and system for enhancing digital video transmission to set-top boxes improves the performance of a hybrid analog and digital video transmission system, for example, an AM-VSB QAM video transmission system, by selecting a digital channel map based on the relative magnitude and frequency locations of CSO and CTB distortions and the analog channel frequency plan. A variable interleaver may also be implemented in the video transmission system to further reduce the CSO and CTB distortions.

64/256 quadrature amplitude modulation trellis coded modulation decoder

Abstract: A quadrature amplitude modulation (QAM) trellis coded modulation (TCM) decoder for decoding a stream of QAM TCM signals is disclosed. Each of the signals has a plurality of associated branch metrics and has an in-phase component and a quadrature component. The in-phase component is defined by a plurality of in-phase symbols and the quadrature component is defined by a plurality of quadrature symbols. The QAM TCM decoder includes a first Viterbi decoder and a second Viterbi decoder. The first Viterbi decoder is configured to receive an in-phase component of a QAM TCM signal for decoding the associated in-phase symbols into an in-phase decoded bit and a plurality of uncoded in-phase bits. The second Viterbi decoder configured to receive a quadrature component of the QAM TCM signal for decoding the associated quadrature symbols into a quadrature decoded bit and a plurality of uncoded quadrature bits. The first and second Viterbi decoders are adapted to decode 64- or 256-QAM TCM signals.