Tobias Frank

IFDMA: A Scheme Combining the Advantages of OFDMA and CDMA

Future mobile radio systems must fulfill challenging requirements. Some requirements are met by single-carrier-based multiple access (MA) schemes such as CDMA and others by multi-carrier-based MA schemes like OFDMA. MA schemes integrating the characteristics of both are receiving more and more attention. In this article, candidate MA schemes based on the idea of integration are summarized and classified using a new framework. Moreover, interleaved frequency division multiple access (IFDMA) is shown to be a scheme that combines the advantages of both CDMA and OFDMA and is a promising candidate MA scheme, especially for non-adaptive transmission in the uplink of future mobile radio systems.

B-IFDMA - A Power Efficient Multiple Access Scheme for Non-frequency-adaptive Transmission

Within the EU FP6 Integrated Projects WINNER and WINNER II, multiple access schemes for frequency-adaptive and non-frequency-adaptive transmission for a future broadband mobile wireless system are investigated. This paper presents a novel power efficient multiple access scheme for non-frequency-adaptive uplink transmission denoted Block Interleaved Frequency Division Multiple Access (B-IFDMA), which provides large frequency-diversity, potential power savings by user terminal sleep mode, modest high power amplifier backoff and robustness to frequency-offsets, and phase noise.

IFDMA - a promising multiple access scheme for future mobile radio systems

The interleaved frequency division multiple access (IFDMA) scheme is based on compression, repetition and subsequent user dependent frequency shift of a modulated signal. Multiple access is enabled by the assignment of overlapping but mutually orthogonal subcarriers to each user. In this paper it is shown that IFDMA can be regarded as unitary precoded OFDMA with interleaved subcarriers. On the other hand, IFDMA is shown to be a CDMA variant with frequency domain orthogonal signature sequences and chip interleaving. Thus, it combines the advantages of single and multi-carrier transmission such as low peak to average power ratio, orthogonality of the signals of different users even for transmission over a time dispersive channel and low complexity. Simulation results show the good performance of coded IFDMA transmission over a mobile radio channel for different data rates

A Survey on the Envelope Fluctuations of DFT Precoded OFDMA Signals

Discrete Fourier transform (DFT) preceding is a promising approach for reduction of the envelope fluctuations of orthogonal frequency division multiple access (OFDMA) signals. However, the envelope fluctuations of DFT precoded OFDMA signals strongly depend on the subcarrier allocation used. In this work, the envelope fluctuations of DFT precoded OFDMA signals with different subcarrier allocations are analyzed based on various metrics. The mutual dependency of the metrics is addressed and a set of suitable metrics for the design of appropriate DFT precoded OFDMA solutions for the uplink of future mobile radio systems is proposed. New results for oversampled signals considering pulse shaping and windowing are presented and analyzed.

Low complexity equalization with and without decision feedback and its application to IFDMA

The interleaved frequency division multiple access (IFDMA) scheme is a promising candidate for next generation mobile radio systems. IFDMA is based on compression, repetition and subsequent user dependent frequency shift of a modulated signal. As in OFDMA, multiple access is enabled by the assignment of overlapping but mutually orthogonal subcarriers to each user. It combines the advantages of single and multicarrier transmission such as low peak to average power ratio, orthogonality of the signals of different users even for transmission over a time dispersive channel and low complexity. In this paper, a linear low complexity frequency domain equalizer for IFDMA is presented and extended by subsequent decision feedback with initialization. Simulation results show the good performance for data transmission using IFDMA with frequency domain equalization over a mobile radio channel

Block interleaved frequency division multiple access for power efficiency, robustness, flexibility, and scalability

The multiple access solution in an IMT-Advanced mobile radio system has to meet challenging requirements such as high throughput, low delays, high flexibility, good robustness, low computational complexity, and a high power efficiency, especially in the uplink. In this paper, a novel multiple access scheme for uplinks denoted as B-IFDMA is presented. We show that this scheme is able to provide equal or better error rate performance than the Single-Carrier Frequency Division Multiple Access (SCFDMA) schemes IFDMA and LFDMA, when considering realistic channel estimation performance at the receiver and no reliable channel state information at the transmitter. We also show that B-IFDMA provides better amplifier efficiency than OFDMA and can provide better end-to-end energy efficiency than IFDMA and LFDMA. Moreover, the scheme shows a promisingly high robustness to frequency-offsets and Doppler spread. Thus, this scheme can be regarded as a promising solution for the uplink of future mobile radio systems.

An Efficient Implementation for Block-IFDMA

Recently, a new multiple access (MA) scheme denoted Block-Interleaved Frequency Division Multiple Access (B-IFDMA) has been proposed which can be regarded as a generalization of Interleaved Frequency Division Multiple Access (IFDMA). Compared to IFDMA, B-IFDMA provides higher flexibility, increased robustness to carrier frequency offsets and additional power savings at the mobile terminal at the expense of increased envelope fluctuations and higher complexity. In this paper, different variants of B-IFDMA are presented and their properties are discussed. Moreover, new algorithms for a low complexity implementation of B-IFDMA providing low envelope fluctuations are introduced. The complexity of B-IFDMA is shown to be lower than for OFDMA. New performance results for coded transmission over a mobile radio channel are given.

Channel Estimation for Block-IFDMA

In this paper, pilot multiplexing and channel estimation is investigated for two different signal models of DFT precoded OFDMA with block-interleaved subcarrier allocation (B-IFDMA). The influence of the B-IFDMA signal model on the bit error rate performance with and without perfect channel knowledge is presented. Moreover, the Peak-to-Average Power Ratio of the transmit signal, as well as the pilot symbol overhead required for channel estimation is given for the two signal models.

On combining SDMA and B-IFDMA: Multi-user detection and channel estimation

In this paper, we combine two different multiple access, namely, Space Division Multiple Access (SDMA) and Block-Interleaved Division Multiple Access (B-IFDMA), for uplink transmission, and we name the combined multiple access SD/B-IFDMA. Since SDMA suffers from multiple access interference (MAI) and B-IFDMA from intersymbol interference (ISI), a multi-user detector that can counteract both MAI and ISI is needed for SD/B-IFDMA. We propose three low complexity linear multi-user detectors for SD/B-IFDMA, namely, Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Non-Iterative Constrained Least Squares (NICLS). The NICLS is a heuristic multi-user detector that tries to improve the performance of ZF without the necessity of having to estimate the noise variance. Additionally, we also address the channel estimation procedure for SD/B-IFDMA by applying orthogonal time multiplexing training and using Chu sequence as the training sequence. Two estimators are considered for channel estimation for SD/B-IFDMA, namely, frequency domain Least Squares (LS) and time domain low complexity Maximum Likelihood (lcML). From bit error performance, it is shown that the MMSE multiuser detector performs best followed by NICLS and ZF. For performance assessment of the channel estimators, ZF multiuser detection is used. It is shown that the lcML outperforms LS with the penalty of having higher computational complexity.