Approaching MIMO-OFDM Capacity with Per-Antenna Power and Rate Feedback

This paper presents power-efficient transmission schemes for the multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) block-fading channel under the assumption that the channel during each fading block is known perfectly at the receiver, but is unavailable at the transmitter. Based on the well-known vertical Bell Labs layered space-time (V-BLAST) architecture that employs independent encoding for each transmit antenna and successive decoding at the receiver, this paper presents a per-antenna-based power and rate feedback scheme, termed the "closed-loop" V- BLAST, for which the receiver jointly optimizes the power and rate assignments for all transmit antennas, and then returns them to the transmitter via a low-rate feedback channel. The power and rate optimization minimizes the total transmit power for support of an aggregate transmission rate during each fading block. Convex optimization techniques are used to design efficient algorithms for optimal power and rate allocation. The proposed algorithms are also modified to incorporate practical system constraints on feedback complexity and on modulation and coding. Furthermore, this paper shows that the per-antenna-based power and rate control can be readily modified to combine with the conventional linear MIMO transmit preceding technique as an efficient and capacity-approaching partial-channel-feedback scheme. Simulation results show that the closed-loop V-BLAST is able to approach closely the MIMO-OFDM channel capacity assuming availability of perfect channel knowledge at both the transmitter and the receiver.     

MMSE design of redundant FIR precoders for arbitrary channel lengths

The joint design of transmitter and receiver for multichannel data transmission over dispersive channels is considered. The design criterion is the minimization of the mean squared error (MSE) at the receiver output under the constraint of a fixed transmit power. The focus is on the practically important case where the transmitter employs finite impulse response (FIR) filters, and the channel impulse response has arbitrary length. The proposed algorithm allows a straightforward transmitter design and generally yields near-optimal solutions for the transmit filters. Under certain conditions, the exact solutions for optimum block transmission, as known from the literature, are obtained.     

Detection and correction of transmission errors in facsimile images

Today, facsimile is recognized as the primary communication tool for both printed and written materials. Most facsimile machines operating on public switched telephone networks use the Group 3 (G3) facsimile compression standards, in which images are entropy-coded. Although the synchronization codeword end of line (EOL) is employed, a transmission error in a codeword may cause the current codeword, the subsequent codewords in the current line, even the codewords in the subsequent lines to be misinterpreted, resulting in a great degradation of the received image. The objective of the proposed error detection and correction approaches is to completely or partially eliminate transmission errors in G3 facsimile images, requiring no extra transmission bit rate and without changing the transmitter and the receiver. The proposed approaches are based on the error checking conditions derived from the relationship between the current line and the previous line as well as the constraints on compressed image data. A corrupted line is detected if any of the error checking conditions is satisfied. When a corrupted line is detected, a sequence of bit inversions and redecoding operations are performed on the current corrupted line and/or its previous lines so that at least one possible (feasible) redecoding solution can be found. Then, the best solution is selected by using some selection criterion. Based on simulation results, the proposed approaches can recover the original or high-quality facsimile images from their corresponding corrupted facsimile images. This shows the feasibility of the proposed approaches     

A High-Speed Facsimile Apparatus for Satellite Communication

This paper outlines a newly developed high-speed facsimile apparatus for satellite communication. An ISO A4 size document can be transmitted in about 3 s at a transmission rate of 1.536 Mbits/s using the apparatus. In the transmitter, a CCD linear image sensor and a fluorescent lamp are used for photoelectric conversion. In the receiver, an electrostatic recording technique using a multistylus electrode is applied. Furthermore, this apparatus applies a new tone-reproduction technique involving electrostatic recording, which makes it possible to reproduce documents, such as photographs, that have gray-level information without reducing the character quality. A facsimile control procedure which takes into consideration satellite communication circuit characteristics is established. The transmitter sends all documents to be sent continuously, receiving the message confirmation response for one document while transmitting the next one. The results of message transmission tests over experimental satellite communication circuits are described.     

Advances in FAX

One of the most important techniques introduced into the recent facsimile is redundancy-reduction coding. The CCITT already standardized the coding schemes to be employed in Group 3 and Group 4. There are, however, left for further study the optional non-information-preserving coding scheme for black-and-white pictures and the coding scheme for multilevel and color pictures. Much work has been carried out with respect to these kinds of coding, including pattern-matching coding for black-and-white pictures and various information-preserving and non-information-preserving coding for multilevel and color pictures. The Group 4 apparatus is a new generation facsimile apparatus, which is mainly operated on public switched data networks. This kind of facsimile apparatus features higher resolution and error-free reception, and has the teletex-facsimile mixed mode capability as an option. The most important technical problem in the standardization of the Group 4 facsimile is the communication protocol which has been developed based on the existing teletex protocol. Facsimile communication is carried out not only on general public switched telephone or data networks, but also on specialized networks dedicated to it. Some sorts of communication processing such as speed conversion, automatic appending function, repeated delivery attempt, etc., are incorporated into these networks. The development of facsimile equipment has also shown progress in these few years. For example, a very compact apparatus has been developed using a new contact type imager and a codec built by special-purpose LSIs. The press fax apparatus employing flat-bed scanner and multicolor facsimile apparatus have also been put into market. This paper describes the outline of recent advances in facsimile, including the above-mentioned items.     

Optical Wireless Systems Employing Adaptive Collaborative Transmitters in an Indoor Channel

We propose a novel optical wireless (OW) system based on a power adaptive multibeam spot-diffusing transmitter serving multiple seven-segment maximum ratio combining (MRC) angle diversity receivers. A feedback link is assumed between the transceivers so that each receiver conveys to the multibeam transmitter the new beams transmit power weights to be used to achieve the best signal quality at a given receiver location. Two cases involving three and five receivers are considered. Four different configurations for the placement of the three-receiver case in the room are also examined. The system's performance in each case is evaluated in terms of signal-to-noise ratio (SNR) and is compared with the single receiver scenario with and without power adaptation. In the presence of one receiver, the transmit spot powers can be adjusted for optimum performance at that receiver location. For multiple receivers, there is conflict, and we propose spot power adaptation based on the average requirements (power distribution in spots), i.e., transmit equal gain combining (EGC) of spot power or MRC of transmit spot powers. The results show that the three receivers benefit most from an adaptive transmitter when each is placed at a corner of the room. In this case, an SNR increase of as much as 2.6 dB is achieved for all three receivers at the corners by both MRC and EGC. Moreover, when all receivers are placed away from the line of diffusing spots, our proposed MRC collaborative approach is 1 dB better than the noncollaborative system. This gain reduces the difference from the upper bound set by the single receiver adaptation, which is 3 dB. For a mobile transmitter, MRC also significantly improved the SNR for the farthest receivers at the opposite end from the transmitter located near one room corner.      

Distance measures for viterbi decoding of coded and bandlimited 8PSK signals

The paper studies a digital modem that transmits a convolutionally encoded eight-phase-shift keyed (CE8PSK) signal over a satellite channel and employs a near-maximum-likelihood decoder at the receiver. Several different earth-stations are assumed to have simultaneous access to a given transponder in the satellite as an arrangement of frequency-division multiple access. Adjacent channel interference (ACI) is neglected here. The high-power amplifier (HPA) at the earth-station transmitter and the satellite transponder are assumed to be linear. The channel distorts the data signal, through the bandlimiting introduced by the equipment filters, and it adds stationary white Gaussian noise to the data signal at the receiver input. The resulting noisy and distorted data signal is coherently demodulated. Four different bandwidths of the transmitted CE8PSK signal are considered, together with three different demodulation processes. The decoder uses the Viterbi algorithm, together with one of six different distance measures to determine the costs of the stored vectors (survivors). The paper describes the various techniques involved in the modem, and presents the results of an extensive series of computer-simulation tests to measure the performances of the system with all appropriate combinations of the signal bandwidth, demodulation process and distance measure. The results of the tests are then used to determine the preferred modem design.     

PAPR Reduction in OFDM Systems: Polynomial-Based Compressing and Iterative Expanding

In this paper a companding-based scheme is proposed to reduce the Peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing system. At the transmitter side, a compressing polynomial function is appended to the inverse discrete Fourier transform block; and at the receiver the transmitted signal is retrieved iteratively through combining the discrete Fourier transform block with a reverse expanding function. In the iterative algorithm the Jacobi’s method is used for solving the equations. Also, the general form of the compressing polynomial functions is attained through the use of Daubechies wavelet functions. As an advantage, the proposed method involves less complexity at the transmitter compared to other PAPR reduction methods. Furthermore, it requires less increasing to signal-to-noise ratio for the same bit error rate in comparison with other companding methods. The order of compressing polynomial and the number of iterations for the proposed algorithm at the receiver can be set in accordance with the performance-complexity trade off.     

An ISDN echo-cancelling transceiver chip set for 2B1Q coded U-interface

A three-chip set for a 2B1Q U-interface transceiver has been developed. The chip set is composed of an analog front-end (AFE), echo-canceller (EC), and receiver (RCV) LSIs. The AFE LSI includes a 12-b accuracy oversampling analog/digital converter. The EC and RCV LSIs are 26- and 16-bit microprogrammable digital signal processors, respectively. A digital phase-locked loop is used to minimize the analog part. Residual echo increase by a timing phase jump is compensated for by a newly introduced additional adaptive filter. Infinite impulse response filters and multiresponse filters reduce the necessary number of taps for both the echo canceller and the decision-feedback equalizer. The AFE and the two digital signal processor LSIs are implemented in 1.6- and 1.2-μm double-metal layer CMOS processes, respectively. A 6-km loop coverage was realized with a less than 10^-7 error rate. Total power consumption by the chip set is 580 mW at 5-V single supply     

An Experimental Microprocessor-Implemented 4800 Bit/s Limited Distance Voice Band PSK Modem

A low-cost 4800 bit/s modem is described which is applicable to limited distance, direct-copper channels. The modulation technique is eight-phase PSK and both the transmitter and receiver algorithms are aimed at economy of implementation in digital circuitry. The transmitter uses digitally stored waveform elements, and the detection and clock recovery techniques are based on received signal polarity. The implementation of the transmitter and receiver algorithms in a 6800 microprocessor is described. Some experimental results are given.     

A 26-GHz Miniaturized Mic Transmitter/Receiver

A very compact 26-GHz transmitter/receiver for high-speed digital radio subscriber systems has been developed. The transmitter/receiver makes extensive use of MIC technology in the RF sections. Transmitting power of 18 dBm and a receiving noise figure of less than 12 dB is obtained. The freqnency of the local oscillator is stabilized to within +-100 ppm by means of a high-Q dielectric resonator. The bit error rate is measured in order to evaluate the overall system, and good performance of the equipment is obtained. A field test rising this equipment is now under way. The technique described in the text can be extended to transmitter/receiver for terrestrial radio relay systems and satellite communication systems. In addition, the various MIC components developed here can be scaled to the millimeter-wave region.     

Development of the Base Station Transceiver Subsystem in the CDMA Mobile System

The base station transceiver subsystem (BTS) of the CDMA Mobile System is interfaced to mobile stations over the air and to the wired network through a packet switched interconnection network. The potential benefits of CDMA technology are achieved when the transmitter and the receiver are properly designed and implemented. The physical layer of the air interface at the base station is implemented with the CDMA ASICs and control circuits in the channel card of the BTS. We present the design perspectives and structural illustration of the BTS. Base station modem ASICs and their control to implement the CDMA receiver, baseband and RF signal processing blocks, and BTS controller are described. Elaborate power control is essential to ensure the high capacity which is one of advantages of the CDMA technology. The closed loop reverse link power control and the forward link power control operated in the BTS are described.     

640-Gb/s high-speed ATM switching system based on 0.25-μm CMOS,MCM-C, and optical WDM interconnection

A 640-Gb/s high-speed ATM switching system that is based on the technologies of advanced MCM-C, 0.25-μm CMOS, and optical wavelength-division-multiplexing (WDM) interconnection is fabricated for future broadband backbone networks. A 40-layer, 160×114 mm ceramic MCM forms the basic ATM switch module with 80-Gb/s throughput. It consists of 8 advanced 0.25-μm CMOS LSIs and 32 I/O bipolar LSIs. The MCM has a 7-layer high-speed signal line structure having 50-Ω strip lines, high-speed signal lines, and 33 power supply layers formed using 50-μm thick ceramic layers to achieve high capacity. A uniquely structured closed-loop-type liquid cooling system for the MCM is used to cope with its high power dissipation of 230 W. A three-stage ATM switch is made using the optical WDM interconnection between high-performance MCMs. For WDM interconnection, newly developed compact 10-Gb/s, 8-WDM optical transmitter and receiver modules are used. These modules are each only 80×120×20 mm and dissipate 9.65 W and 22.5 W, respectively. They have a special chassis for cooling, which contains high-performance heat-conductive plates and micro-fans. An optical WDM router based on an arrayed waveguide router is used for mesh interconnection of boards. The optical WDM interconnect has 640-Gb/s throughput and simple interconnection     

On the error exponent for memoryless flat fading channels withchannel-state-information feedback

We derive the random coding error exponent for the time-independent flat fading channel with perfect knowledge of the channel state information (CSI) at both the receiver and the transmitter. That is, the CSI is feedback from the receiver to the transmitter. In such a situation, the transmitter is capable of optimizing the power allocation of the transmitted signal according to the fading state in order to obtain, for our case, the best error exponent. The power scheme obtained here is different from the water-pouring one, which is known to maximize the channel capacity     

An innovative power regulation method applied for wireless magnetic-energy transportation

An innovative power regulation design and realization is proposed for wireless micro-power transmission. The proposed power regulation method is employed to regulate the power intensity transmitted by magnetic flux transmitter, based on distance change and angle misalignment between transmitter and receiver. Therefore, not only the power transmitted by magnetic flux transmitter is adjustable, but also consistent power received by locomotive devices can be achieved. Firstly, by Faraday’s law and Kirchhoff’s circuit law, the dynamic equation for proposed wireless power transmission is constructed. The distance change and angle misalignment between transmitter and receiver are also considered to reflect the influence on power received by micro-devices. In order to ensure that the power received by receiver is consistent at various locations along an ellipse trajectory, the sliding mode controller is synthesized to regulate the power transmitted by the magnetic energy source. In addition, the sliding mode estimator is also employed so that not only the system states can be estimated, but also the cost for sensors and the physical size of secondary side can be much reduced. By intensive simulation, no matter which distance and misalignment angle between transmitter and receiver is present, stable and consistent power at receiver can be achieved. Finally, the test rig for wireless micro-power transmission is constructed for performance verification. The experimental result shows that the constant power at receiver can be obtained if the SMC controller is applied to regulate the output power by transmitter.     

OFDM power loading using limited feedback

Orthogonal frequency division multiplexing (OFDM) is a practical broadband signaling technique for use in multipath fading channels. Over the past ten years, research has shown that power loading, where the power allocations on the OFDM frequency tones are jointly optimized, can improve error rate or capacity performance. The implementation of power loading, however, is dependent on the presence of complete forward link channel knowledge at the transmitter. In systems using frequency division duplexing (FDD), this assumption is unrealistic. In this paper, we propose power loading for OFDM symbols using a limited number of feedback bits sent from the receiver to the transmitter. The power loading vector is designed at the receiver, which is assumed to have perfect knowledge of the forward link channel, and conveyed back to the transmitter over a limited rate feedback channel. To allow for the vector to be represented by a small number of bits, the power loading vector is restricted to lie in a finite set, or codebook, of power loading vectors. This codebook is designed offline and known a priori to both the transmitter and receiver. We present two power allocation selection algorithms that optimize the probability of symbol error and capacity, respectively. Simulation results show that the proposed limited feedback techniques provide performance close to full channel knowledge power loading.     

Simultaneous broadcasting of analog FM and digital audio signals bymeans of adaptive precanceling techniques

A method for broadcasting digital audio simultaneously with existing analog frequency modulation (FM) radio is presented. The method is based on precomputing the response of the host analog FM signal at the digital receiver and precanceling it at the transmitter. As a result, the digital transmission is free from interference from analog FM. We select the rate and power level of the digital transmission in a manner that the interference the digital data incur on the analog FM signal remains at acceptably low levels. The digital transmission is based on adaptive orthogonal frequency-division multiplexing (OFDM) (adaptive multicarrier). The frequencies and number of carriers of the digital multicarrier modem are judiciously selected in a time-varying fashion so as to cause a negligible distortion in a standard receiver for analog FM. Simulations based on conservative nonoptimized signal design indicate that data rates up to about 130 kb/s inside the 200-kHz FM channel are achievable for acoustic test signals. We present a number of numerical examples where the average digital data use up to 50% of the 200-kHz power spectrum with digital signal power levels 25-35 dB below the analog signal. Due to the resulting variable-rate digital transmission, a control channel is required. A method of precanceling with multiple orthogonal direct-sequence spread-spectrum schemes is also presented     

一种新型水声信号发射机的设计与研究

设计并实现了一种体积小、效率高的水声信号发射机,是一些使用电池供电的水声设备(如便携式水声通信设备、便携式水下探测设备等)的关键技术。为满足这些需求,该文从基本理论出发,结合现代音响功放的理论、经验和设计方法,提出了一种全新的微型水声信号发射机设计方案,且通过2007年3月的湖上试验验证了所提出的方案。     

Pre-Compensation for Rayleigh Fading Channels in Time Division Duplex OFDM Systems

Coherent demodulation results in good detection performance but requires channel estimation. Fading pre-compensation (precoding) at the transmitter can lead to low-complex receiver structures with good performance capabilities, without the need for channel estimation. Time division duplex systems based on orthogonal frequency division multiplex (OFDM) are particularly suited to this because intersymbol interference effects can be neglected, simplifying transmitter adjustments. Methods that involve amplitude and/or phase pre-compensation are compared in terms of resulting bit error rate and increase in peak-to-average power ratio. Dynamic channels degrade the performance as the block lengths get longer. For a certain block length the performance degrades below that of traditional differential decoding. A block length of up to 40 times that used in the Digital European Cordless Telephone system, DECT, is possible using channel estimation and ideal Wiener prediction.     

A design of a high-speed and high-efficiency capsule endoscopy system

This paper presents a high-speed and high-efficiency capsule endoscopy system. Both a transmitter and a receiver were optimized for its application through an analysis of the human body channel. ON-OFF keying modulation is utilized to achieve low power consumption of the in-body transmitter. A low drop output regulator is adopted to prevent performance degradation in the event of a voltage drop in the battery. The receiver adopts superheterodyne structure to obtain high sensitivity, considering the link budget from the previous analysis. The receiver and transmitter were fabricated using the CMOS 0.13-μm process. The output power of the transmitter is -1.6 dB·m and its efficiency is 27.7%. The minimum sensitivity of the receiver is -80 dB·m at a bit error ratio (BER) of 3 × 10 (-6). An outer wall loop antenna is adopted for the capsule system to ensure a small size. The integrated system is evaluated using a liquid human phantom and a living pig, resulting in clean captured images.