OFDM Applications Research Articles

Design of N -way distributed Doherty amplifier for WCDMA and OFDM applications

A novel three-way distributed Doherty power amplifier with an extended efficiency range for WCDMA or OFDM repeater or base-station applications is presented. This distributed Doherty amplifier consists of one main amplifier and two peaking amplifiers. To achieve high efficiency at a high back-off power, the peaking amplifier structure is based on the dual-fed distributed amplifier form. The 2140 MHz measured results of the three-way distributed Doherty amplifier yielded an 11 dB power gain, with 39.5% power added efficiency at 9.5 dB back-off power

A Dual-Antenna Phased-Array UWB Transceiver in 0.18-$\mu{\hbox {m}}$ CMOS

A dual-antenna ultra-wideband (UWB) transceiver in 0.18-mum CMOS for mode-1 OFDM applications employs the techniques of antenna diversity and integrated RF selectivity to improve robustness to interferers. Optimal selectivity in receiver and band flatness in transmitter are achieved by on-chip calibration of each band. The packaged device achieves an overall noise figure of 4.7 dB, an IIP3 of -0.8 dBm, a TX P1 dB of 3.1 dBm, and an error vector magnitude (EVM) of -27.2 dB for 480 Mb/s. The transmit output spectrum is fully compliant with FCC mask for UWB without any external bandpass filter

An approach to simplify the design of IFFT/FFT cores for OFDM systems

In this paper we present an approach to simplify the design of IFFT/FFT cores for OFDM applications, A novel software tool is proposed, called AFORE. It is able to generate efficient single and multiple mode IFFT/FFT processors. AFORE employs a parallel architecture, where the degree of parallelism can be varied. This way, the tool can find a trade off between area and processing time to meet the system specification. In order to assess the quality of the proposed approach, results are provided for some of the most widely used OFDM standards, such as, WLAN 802.11a/g, WMAN 802.16a, DVB-T.

A family of low-complexity binary linear codes for bluetooth and BLAST signaling applications

We construct a family of linear binary block codes that are useful for Bluetooth, OFDM and BLAST applications. These codes are derived from ordinary block repetition codes using cyclic shifts of the input information vector which greatly simplifies encoding. We find several sets of cyclic shifts that constrain the search for good codes. We consider code lengthening and the input-output weight enumerators. We show that the codes are good candidates for low-power, low-cost and high data-rate applications using fixed code rate and variable codeword length, or adaptive coding with variable minimum Hamming distance. We propose a parallel structure of the encoder well-suited to OFDM and BLAST systems. Finally, we give an example of code design for use in retransmission schemes, and another example of a concatenated rate 2/3 code well-suited to the Bluetooth system.

A UWB CMOS transceiver

A direct-conversion ultra-wideband (UWB) transceiver for Mode 1 OFDM applications employs three resonant networks and three phase-locked loops. Using a common-gate input stage, the receiver allows direct sharing of the antenna with the transmitter. Designed in 0.13-/spl mu/m CMOS technology, the transceiver provides a total gain of 69-73 dB and a noise figure of 6.5-8.4 dB across three bands, and a TX 1-dB compression point of -10 dBm. The circuit consumes 105 mW from a 1.5-V supply.

New Radix-2 to the 4th Power Pipeline FFT Processor

This paper proposes a new modified radix-2 4 FFT algorithm and an efficient pipeline FFT architecture based on this algorithm for OFDM systems. This pipeline FFT architecture has the same number of multipliers as that of the radix-2 2 algorithm. However, the multiplication complexity could be reduced by more than 30% by replacing one half of the programmable multipliers by the newly proposed CSD constant multipliers. From the synthesis simulations of a standard 0.35μm CMOS SAMSUNG process, a proposed CSD constant complex multiplier achieved more than 60% area efficiency when compared to the conventional programmable complex multiplier. This promoted efficiency could be used to the design of a long length FFT processor in wireless OFDM applications, which needs more power and area efficiency.

Design of wide-bandwidth envelope-tracking power amplifiers for OFDM applications

An efficiency-enhanced power-amplifier system design is presented based on wide-bandwidth envelope tracking (WBET) with application to orthogonal frequency-division multiplexing wireless local area network systems. Envelope elimination and restoration (EER) and WBET are compared in terms of the time mismatch sensitivity between the base-band amplitude path and the RF path, and it is demonstrated that WBET is much less sensitive than EER to these effects. An adaptive time-alignment algorithm for the WBET system is developed and demonstrated. The analysis and algorithm are verified by experimental results. The measurement shows that the peak drain efficiency of the complete system was 30% at a 2.4-GHz orthogonal frequency-division multiplexing output power of 20 dBm.

Adaptive Algorithm Based on Accumulated Signal Processing for Fast Fading Channels with Application to OFDM Mobile Radio

In this paper, we propose an adaptive algorithm based on accumulated signal processing, which could be applicable to Post-FFT-type OFDM adaptive array antennas. Proposed scheme calculates the weight of each element at a particular instant t, by considering both post- and pre-received symbols. Because of the use of additional forthcoming information on channel behavior in the weight calculation scheme, one can expect an improved performance in fast fading conditions by using the proposed adaptive algorithm. This paper also discusses the application of the proposed adaptive algorithm to OFDM adaptive array. In OFDM application, a few subchannels are being used to transmit pilot symbols, and at the receiver, the proposed adaptive algorithm is applied to those pilot subchannels, and interpolates the weights for the data subchannels which are allocated between the pilot subchannels. Finally, the system performance improvement with the application of the proposed adaptive algorithm is verified by computer simulation.

Feedback frequency synchronization for OFDM applications

Maximum-likelihood estimation methods are often used to derive carrier frequency recovery schemes for digital receivers. Unfortunately, their rigorous application is generally hindered by analytical difficulties and, in consequence, some approximations must be made to achieve practical results. In this paper we concentrate on frequency recovery for orthogonal frequency division multiplexing signals. Following Daffara and Chouly (see Proc. ICC, p.766-71, June 1993), we derive a feedback synchronizer based on maximum-likelihood methods. Making different approximations, however, we come up with a scheme that is superior in terms of estimation accuracy. Comparisons are also made with other feedback schemes based on heuristic reasoning.

An improved frequency offset estimator for OFDM applications

An efficient algorithm has been proposed by Schmidl and Cox (see IEEE Trans. Commun., vol.45, p.1613-21, 1997) for carrier frequency estimation in orthogonal frequency-division multiplexing systems. The scheme is based on the transmission of a training symbol composed of two identical halves in the time domain. We extend this algorithm by considering a training symbol composed of L>2 identical parts. This makes it possible to achieve a better accuracy at the cost of some increase in computational load. The estimation range can be made as large as desired without the need of a second training symbol, as required by the Schmidl and Cox method.

Calibrated Fabry-Perot etalon as an absolute frequency reference for OFDM communications

The frequency locking of a large number of lasers in OFDM applications requires an equally large number of stable references at predictable frequencies. The authors present a technique to lock a Fabry-Perot etalon on an atomic reference to provide multiple and evenly spaced absolute frequency references. Absolute etalon spacing is calibrated by matching two atomic references with two corresponding etalon modes. To maintain long-term stability in channel spacing, the etalon is locked to an atomic resonance using an electrical feedback loop to control mirror separation. This technique can be used for close spacing or coherent applications where channel separation and reproducibility is critical between transmitter and receiver.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>