Baseband Digital Signal Research Articles

Development of MIMO-SDR Platform and Its Application to Real-Time Channel Measurements

A multiple-input multiple-output software defined radio (MIMO-SDR) platform was developed for implementation of MIMO transmission and propagation measurement systems. This platform consists of multiple functional boards for baseband (BB) digital signal processing and frequency conversion of 5 GHz-band radio frequency (RF) signals. The BB boards have capability of arbitrary system implementation by rewriting software on reconfigurable devices such as field programmable gate arrays (FPGAs) and digital signal processors (DSPs). The MIMO-SDR platform employs hybrid implementation architecture by taking advantages of FPGA, DSP, and CPU, where functional blocks with the needs for real-time processing are implemented on the FPGAs/DSPs, and other blocks are processed off-line on the CPU. In order to realize the hybrid implementation, driver software was developed as an application program interface (API) of the MIMO-SDR platform. In this paper, hardware architecture of the developed MIMO-SDR platform and its software implementation architecture are explained. As an application example, implementation of a real-time MIMO channel measurement system and initial measurement results are presented.

Performance analysis of a wavelength-locked Fabry-Perot laser diode by light injection of an external spectrally sliced Fabry-Perot laser diode

We have analyzed and experimentally demonstrated the performance of a wavelength-locked Fabry-Perot laser diode (FP-LD) with a spectrally sliced FP-LD as an external-injection optical source. A high side-mode suppression ratio exceeding 30 dB was obtained, and the noise characteristic of the wavelength-locked FP-LD was analyzed in terms of both mode partition noise and interferometric noise. The measured relative intensity noise had a minimum value of -140 dB/Hz. We also investigated the transmission characteristics such as the Q factor and extinction ratio for a 622 Mbits/s and 2.5 Gbits/s baseband digital signal.

A new adaptive delay method for wideband wireless Kahn's RF power amplifiers

This paper presents an adaptive delay control method used in wideband Kahn's envelope elimination and restoration (EER) RF power amplifiers (PAs). Besides control circuits, envelope and phase signals are also implemented by baseband digital signal processing (DSP) technique. It avoids using not only nonlinear limiter and envelope detector, but also difficult RF delay module or complicated feedback loop, each of which is necessary in conventional EER PA's structure. With the help of applying phase detector, counter, and latch register, the delay varies adaptively with circuit parameters, and then the new PA maintains performance at all times. With the application of this method we can realize a PA applicable to IEEE 802.11b standard with 11 MHz signal bandwidth, of which adjacent channel power ratio (ACPR) is better than -40 dBc at the first side lobe

A 900 MHz CMOS RF transceiver including digital baseband and hardware‐MAC for IEEE 802.15.4/ZigBeeTM applications

AbstractThis paper presents a fully‐integrated RF transceiver operating from 860 to 930 MHz. The device parameters are compliant to the IEEE 802.15.4 standard. The analogue portion of the chip contains a direct‐conversion receiver, a fractional‐N PLL, a direct‐conversion transmitter and a TR‐switch. Digital baseband signal processing as well as MAC support are also implemented on the same chip. Only minimal external components are needed to form a complete wireless network application two low‐cost crystals, the PLL loop filter, an antenna and a low‐cost 8 bit microcontroller. Therefore, this chip is one of the most integrated 802.15.4 transceiver ICs presented to date. The receiver input sensitivity is −98 dBm. The chip is fabricated in a 0.25 μm CMOS technology with MIM‐capacitors, deep n‐well and a thick top metal layer. Copyright © 2005 AEIT.

Hybrid wavelength-division-multiplexing transport systems based on praseodymium-doped fiber amplifiers

A hybrid wavelength-division-multiplexing transport system based on 1.3-µm optical transmitters and praseodymium-doped fiber amplifiers is proposed and demonstrated. It uses one wavelength for AM vestigial-sideband CATV, one wavelength for 256-QAM digital passband, and one wavelength for OC-48 digital baseband signals. Good performance with respect to composite second order and composite triple beat has been obtained at an acceptable carrier-to-noise ratio for CATV; and a low bit error rate has been achieved for 256-QAM and OC-48 digital signals over a 70-km single-mode fiber transport.

2.4 GHz direct-digital binary phase shift keying modulator using MEMS switch

A novel MEMS-based binary phase shift keying direct-digital modulator operating at a carrier frequency of 2.4 GHz is presented. The circuit is composed of a rat-race coupler and a single-pole double-throw MEMS switch controlled by a digital baseband signal. The coupler divides the input waveform into two signals that are 180° out of phase and the MEMS switch is used to select between these two signals. This circuit has been experimentally verified and results are reported.

The Development of Base-band Digital Signal Generator for SAR

The Development of Base-band Digital Signal Generator for SAR

A hybrid CATV/256-QAM/OC-48 DWDM system over an 80-km LEAF transport

A hybrid dense-wavelength-division-multiplexing (DWDM) system for CATV, 256-QAM and OC-48 trunking is proposed and demonstrated. It used two wavelengths for AM-VSB CATV, one wavelength for 256-QAM digital passband signals and four wavelengths for OC-48 (2.5 Gb/s) digital baseband signals transport. Good performances of carrier-to-noise ratio (CNR) /spl ges/ 50 dB, composite second order (CSO) /spl ges/ 67 dB and composite triple beat (CTB) /spl ges/ 65 dB were obtained for AM-VSB CATV; and low bit error rate (BER < 10/sup -9/) had been achieved for 256-QAM and OC-48 digital signals over an 80 km large effective area fiber (LEAF) transport.

A hybrid DWDM system based on a Fabry–Perot laser diode and an optical circulator with a fiber Bragg grating

AbstractA hybrid dense‐wavelength‐division‐multiplexing (DWDM) system using a combination of a Fabry–Perot (FP) laser diode, an optical circulator (OC), and a fiber Bragg grating (FBG), as well as half‐split‐band and WDM techniques, is demonstrated. It is a four‐wavelength system, in which two wavelengths are for AM–VSB video, one wavelength is for a 256‐QAM digital signal, and one wavelength is for OC‐48 digital baseband signal transmission. © 2002 John Wiley &amp; Sons, Inc. Microwave Opt Technol Lett 32: 390–393, 2002.

A bidirectional hybrid DWDM system for CATV and OC-48 trunking

We propose and demonstrate, for the first time, a bidirectional hybrid dense wavelength-division-multiplexing (DWDM) system for CATV and OC-48 trunking with two wavelengths for AM-VSB video and two wavelengths for OC-48 baseband digital signal transport. Not only twice of the channel capacity, but also good performances of carrier-to-noise ratio /spl ges/50 db, composite second order (CSO)/spl ges/65 db, composite triple beat /spl ges/63 dB and low bit-error rate (<10/sup -9/) were obtained over an 80-km large effective area fiber transport.

A Hybrid DWDM System for CATV and Multimedia Trunking

A Hybrid DWDM System for CATV and Multimedia Trunking A hybrid dense-wavelength-division-multiplexing (DWDM) system for CATV and multimedia trunking is demonstrated. It is a 5-wavelength system, in which two wavelengths for AM-VSB NTSC video, two wavelengths for 64-QAM PAL digital signal and one wavelength for OC-48 digital baseband signal transmission. For 77 AM-VSB NTSC video channels, carrier-to-noise ratio (CNR) > 49 dB, composite second order (CSO) < -68 dBc and composite triple beat (CTB) < -60 dBc were obtained; low bit error rate (BER < 10 -9 ) has been achieved for both the eight 64-QAM digital channels (at 40 Mbit/s each) and the baseband digital OC-48 signal (2.5 Gbit/s).

Design Methodology of a Low-Energy Reconfigurable Single-Chip DSP System

In this paper, we first present a reconfigurable architecture template for low-power digital signal processing, and then an energy conscious design methodology to bridge the algorithm to architecture gap. The energy efficiency of such an architecture and the effectiveness of the methodology are demonstrated in case study implementations targeting baseband voice processing and digital signal processing.

Advanced methods for I/Q imbalance compensation in communication receivers

I/Q signal processing is widely utilized in today's communication receivers. However, all I/Q processing receiver structures, such as the low-IF receiver, face a common problem of matching the amplitudes and phases of the I and Q branches. In practice, imbalances are unavoidable in the analog front-end, which results in finite and usually insufficient rejection of the image frequency band. This causes the image signal to appear as interference on top of the desired signal. We carry out general signal analysis of an imbalanced I/Q processing receiver and propose novel methods for I/Q imbalance compensation using baseband digital signal processing. A simple structure for compensation is derived, based on a traditional adaptive interference canceller. Improved image rejection can also be obtained by using more advanced blind source separation techniques. Theoretical analysis of the performance of the proposed imbalance compensation structures is presented. In addition, some simulation results are provided in order to further evaluate the performance of the proposed methods. The results indicate that the I/Q imbalance can be effectively compensated during the normal operation of the receiver even in the rapidly changing case, as long as a linear system model for the imbalance is valid.

Gain/phase imbalance-minimization techniques for LINC transmitters

Two simple calibration schemes for the correction of the path imbalance in a linear amplification with nonlinear components (LINC) transmitter have been demonstrated. In the foreground algorithm, a baseband digital signal processor (DSP) evaluates the gain and phase imbalance with a set of calibration signals, while in the background algorithm, the imbalance is characterized by exchanging the two LINC vector components. In both cases, the compensation of the path imbalance is accomplished within the DSP by introducing a predistortion term. A prototype LINC system has been tested for CDMA IS-95 baseband input, and -38 and -35-dBc adjacent channel interference were achieved for the foreground and background schemes, respectively. The quadrature errors of the in-phase/quadrature modulators set a limit on the overall performance of both algorithms.

A 1-V heterogeneous reconfigurable DSP IC for wireless baseband digital signal processing

A heterogeneous reconfigurable platform enables the flexible implementation of baseband wireless functions at energy levels between 10 and 100 MOPS/mW, six times higher than traditional digital signal processors. A 5.2 mm/spl times/6.7 mm prototype processor, targeted for voice compression, is implemented in a 0.25-/spl mu/m 6-metal CMOS process, and consumes 1.8 mW at an average operation rate of 40 MHz. It combines an embedded microprocessor with an array of computational units of different granularities, connected by a hierarchical reconfigurable interconnect network.

Optical channel upgradability of multiwavelength erbium-doped fiber amplifier for hybrid digital/analog dense wavelength-division-multiplexing systems

We investigate theoretically the impact of optical channel upgradability on the design of erbium-doped fiber amplifier (EDFA), in terms of guard band, channel number and input signal power level for simultaneously amplifying amplitude-modulated vestigial-sideband analog cable television signal and multiple optical digital baseband signals in hybrid dense wavelength-division-multiplexing (H-DWDM) systems. The single-staged forward and backward bidirectional pumping scheme for EDFA without using any inter-staged components is adopted because it is the best amplifier configuration to offer the highest output power with fairly low noise figure and highly satisfied carrier-to-noise ratio performance. In this work, we define the guard band Δλ GB as the channel spacing between the analog channel and the nearest digital channel. We find that various guard bands (Δλ GB =6.45–1.61 nm) do not affect the noise figure (3.36–3.38 dB) and channel gain variation (ΔG D =0.12–0.13 dB) . However, the channel number (10–32, Δλ D =0.8 nm) influences the gain variations (ΔG D =0.12–3.62 dB) evidently. The gain variation of H-DWDM EDFA for a launched 10, 16, 20 and 24 digital channels is 0.12, 0.65, 0.71 and 0.74 dB, respectively, but that for 28 and 32 digital channels is degraded to 2.47 and 3.95 dB, respectively, because the left-most digital channel is very close to the 1530 nm spectrum so as to degrade the gain flattening. This degradation can be improved by shifting the digital channels away from the 1530 nm band.

Optimum configuration and characteristic comparisons of multiwavelength erbium-doped fiber amplifier for hybrid digital/analog WDM systems

We theoretically investigate various configurations of erbium-doped fiber amplifier (EDFA) for simultaneously amplifying AM-VSB analog CATV signal and multiple optical digital baseband signals in hybrid wavelength-division multiplexing (H-WDM) systems. The design criterion of H-WDM EDFA is to keep the differential channel output power among digital channels at ≤0.2 dB while providing a high saturated output power of ≥60 mW and a low noise figure of ≤4 dB for the analog channel. A total of nine EDFA configurations are examined and compared in this work, including the dual-forward, dual-backward, and different bidirectional pumping schemes, each with and without the midway optical isolator. The investigation provides the optimum EDFA configuration to design both power and in-line amplifiers for hybrid analog/digital WDM lightwave systems. Such H-WDM technology allows direct transmission of AM-VSB/QAM video traffic from the fiber backbone supertrunking networks to the hybrid-fiber-coaxial (HFC), fiber-to-the-curb (FTTC), or fiber-to-the-home (FTTH) broadband access networks without the complicated and costly signal format conversion at the CATV head-end and hubs.

Temperature insensitive spectrally encoded optical multichannel system for simultaneous transmission of digital baseband and subcarrier signals

In an optical code division multiplexed system digital baseband and subcarrier signals have been simultaneously transmitted over the same fibre using spectrally encoded LEDs. Electrical frequency reuse for the subcarrier signals is demonstrated. The insensitivity of the optical multiplexing approach with respect to temperature variations of the transmitters is experimentally proven.

Optical single sideband transmission at 10 Gb/s using only electrical dispersion compensation

A system is presented which uses optical single sideband transmission at 10 Gb/s together with electrical dispersion compensation at the receiver. Transmission with a bit error rate better than 10/sup -10/ on nondispersion shifted fiber is experimentally demonstrated over 320 km and the dispersion from 1000 km of fiber was effectively equalized in simulation. In the transmitter, driving one or two modulators with a combination of a baseband digital signal and the Hilbert transform of that signal creates an optical single sideband signal. In terms of reducing the effects of chromatic dispersion, transmitting the signal in a single sideband format has two advantages over a double sideband format. First, the optical bandwidth of the transmitted single sideband signal is approximately one half of a conventional double sideband signal. Second, an optical single sideband signal with transmitted carrier can be "self-homodyne" detected and the majority of the phase information preserved since no spectrum back folding occurs upon detection. This allows the received signal to be partially equalized in the electrical domain.

Clipping noise effects on the performance of digital baseband signal in lightwave hybrid digital and analogue transmission systems

Accurate modelling of the clipping effects in lightwave hybrid SCM carrier and digital baseband transmission systems is presented using newly derived formulae. Unlike the cases of bandpass transmission, the PDF of clipping noise in the baseband receiver is found to be asymmetrical. Numerical simulation is described for a system with a 140 Mb/s baseband channel and 33 microwave FM video channels. Results show that clipping noise can have a serious impact on the baseband transmission of digital signals, although its influence on analogue signals is moderate. It is also shown that the decision level may be adjusted to give an optimum BER in the presence of clipping noise.