Stefan Krone

Generalized frequency division multiplexing: Analysis of an alternative multi-carrier technique for next generation cellular systems

Generalized frequency division multiplexing (GFDM) is a new concept that can be seen as a generalization of traditional OFDM. The scheme is based on the filtered multi-carrier approach and can offer an increased flexibility, which will play a significant role in future cellular applications. In this paper we present the benefits of the pulse shaped carriers in GFDM. We show that based on the FFT/IFFT algorithm, the scheme can be implemented with reasonable computational effort. Further, to be able to relate the results to the recent LTE standard, we present a suitable set of parameters for GFDM.

5GNOW: Challenging the LTE Design Paradigms of Orthogonality and Synchronicity

LTE and LTE-Advanced have been optimized to deliver high bandwidth pipes to wireless users. The transport mechanisms have been tailored to maximize single cell performance by enforcing strict synchronism and orthogonality within a single cell and within a single contiguous frequency band. Various emerging trends reveal major shortcomings of those design criteria: (1) The fraction of machine-type-communications (MTC) is growing fast. Transmissions of this kind are suffering from the bulky procedures necessary to ensure strict synchronism. (2) Collaborative schemes have been introduced to boost capacity and coverage (CoMP), and wireless networks are becoming more and more heterogeneous following the non-uniform distribution of users. Tremendous efforts must be spent to collect the gains and to manage such systems under the premise of strict synchronism and orthogonality. (3) The advent of the Digital Agenda and the introduction of carrier aggregation are forcing the transmission systems to deal with fragmented spectrum. 5GNOW will question the design targets of LTE and LTE-Advanced having these shortcomings in mind. The obedience of LTE and LTE-Advanced to strict synchronism and orthogonality will be challenged. It will develop new PHY and MAC layer concepts being better suited to meet the upcoming needs with respect to service variety and heterogeneous transmission setups. A demonstrator will be built as Proof-of-Concept relying upon continuously growing capabilities of silicon based processing. Wireless transmission networks following the outcomes of 5GNOW will be better suited to meet the manifoldness of services, device classes and transmission setups being present in envisioned future scenarios like smart cities. The integration of systems relying heavily on MTC, e.g. sensor networks, into the communication network will be eased. The per-user experience will be more uniform and satisfying. To ensure this 5GNOW will contribute to upcoming 5G standardization.

Bit Error Rate Performance of Generalized Frequency Division Multiplexing

Generalized frequency division multiplexing is a non-orthogonal, digital multicarrier transmission scheme with attractive features that address the requirements of emerging applications of wireless communications systems in areas like cognitive radio and machine-to-machine communication. In this paper, first a linear system description is obtained for the transmitter by ordering data in a time-frequency block structure and representing the processing steps upconversion, pulse shaping and upsampling as matrix operations. Based on the transmitter, three standard ways of detecting the signal are derived and compared in terms of bit error performance in AWGN and Rayleigh multipath fading channels.

Low Complexity GFDM Receiver Based on Sparse Frequency Domain Processing

Generalized frequency division multiplexing (GFDM) is a multi-carrier modulation scheme. In contrast to the traditional orthogonal frequency division multiplexing (OFDM), it can benefit from transmitting multiple symbols per sub-carrier. GFDM targets block based transmission which is enabled by circular pulse shaping of the individual sub- carriers. In this paper we propose a low complexity design for demodulating GFDM signals based on a sparse representation of the pulse-shaping filter in frequency domain. The proposed scheme is compared to receiver concepts from previous work and the performance is assessed in terms of bit error rates for AWGN and Rayleigh multipath fading channels. The results show, that for high-order QAM signaling, the error performance can be significantly improved with interference cancellation at reasonable computational cost.

Capacity of communications channels with 1-bit quantization and oversampling at the receiver

Communications receivers that rely on 1-bit analog-to-digital conversion are advantageous in terms of hardware complexity and power dissipation. Performance limitations due to the 1-bit quantization can be tackled with oversampling. This paper considers the oversampling gain from an information-theoretic perspective by analyzing the channel capacity with 1-bit quantization and oversampling at the receiver for the particular case of AWGN channels. This includes a numerical computation of the capacity and optimal transmit symbol constellations, as well as the derivation of closed-form expressions for large oversampling ratios and for high signal-to-noise ratios of the channel.

Capacity Analysis for OFDM Systems with Transceiver I/Q Imbalance

OFDM systems have gained utmost importance for wireless communications requiring ever higher data rates. The maximum data rate that can be achieved is, however, limited by the wireless communications channel as well as by hardware imperfections that can not be avoided in practice. One of the most serious hardware imperfections affecting the performance of OFDM systems is transceiver I/Q imbalance. This paper studies the maximum data rate, i.e. the capacity of OFDM systems that are impaired by transceiver I/Q imbalance of low-cost mobile terminals. Both, the downlink and the uplink case are considered. Closed-form expressions are derived for the ergodic system capacity and the outage probability considering different types of Rayleigh fading channels. Numerical examples are given to provide clear insight into the system capacity degradation due to transceiver I/Q imbalance.

Fading channels with 1-bit output quantization: Optimal modulation, ergodic capacity and outage probability

The achievable rate of communications systems depends on the quantization resolution at the receiver. Earlier work has shown that the capacity of real-valued AWGN channels with 1-bit output quantization is achieved with BPSK. This paper studies optimal modulation schemes, the ergodic capacity and the outage probability for complex-valued fading channels with 1-bit output quantization, assuming full channel knowledge at the receiver. It is shown that circular symmetry with at most one amplitude per phase is a necessary condition for optimal modulation. Circular-symmetric PSK achieves the ergodic capacity in case of Rayleigh fading. Considering the outage probability for Rayleigh fading, L-PSK with large L shows the best performance among conventional modulation schemes.

Entering the path towards terabit/s wireless links

Wireless communications has been a hot area of technology advancement for the past two decades. As long as memory sizes increase, the demand for higher data rates of communications increases on the same scale. This means that one must understand todays high-end 10 Gbit/s wireless technology to get prepared for 100 Gbit/s and 1 Tbit/s data rates of tomorrow. This paper presents key boundary conditions learned by understanding leading edge wireless links of today to prepare for the Tbit/s technology of the year 2020.

Achievable rate of single-carrier systems with optimal uniform quantization at the receiver

The performance of digital communications systems can be affected by limitations of the analog-to-digital conversion at the receiver. To cope with finite sampling frequency and limited quantization resolution it is important to know about the impact on the achievable rate. This paper studies the achievable rate of single-carrier systems that employ analog-to-digital-conversion with uniform quantization. The achievable rate is evaluated in terms of the average mutual information between the transmitted symbols and the quantized received samples. Complex-valued modulation schemes are considered and a phase offset between the transmitter and the receiver is taken into account. System design constraints that derive from general upper bounds are discussed, and the achievable rate with optimal uniform quantization is evaluated numerically. The results show that a phase offset can significantly degrade the performance even in case of optimal quantization. This degradation cannot be compensated by means of any digital post-processing but requires either sufficiently high quantization resolution or an analog compensation, both of which has to be traded off for receiver complexity.

Evaluation of Efficient Modes of Operation of GSM/GPRS Modules for M2M Communications

The field of machine-to-machine (M2M) communications has gained wide popularity and is steadily growing. This paper studies the feasibility of using the Global System for Mobile Communications and in particular the General Packet Radio Service (GPRS) for a low data rate long- lasting battery-powered operation of M2M devices. A model is introduced to estimate the power consumption of a GPRS connection. It allows the identification and evaluation of optimizations of the data transmission procedures. Two M2M modes of GPRS operation are introduced. For applications with frequent transmissions, an Always- on-mode turns out to be most reasonable. For infrequent transmissions, e.g., one transmission every 2 hours, an On/off-mode reduces the power consumption of M2M devices by 93% as compared to the Always-on-mode. With a 3-cell battery providing 25.9 Wh of energy and considering only the power consumption of the communication module, a battery lifetime of up to 5 years is feasible. Measurements show that usually 40% of the energy spent for a short data transmission is wasted by one particular GPRS procedure called non-DRX period. Avoiding this saves up to 35% of total average power, depending on the rate of data transmissions.