Rohit Datta

GFDM Interference Cancellation for Flexible Cognitive Radio PHY Design

Generalized frequency division multiplexing (GFDM) is a new digital multicarrier concept. The GFDM modulation technique is extremely attractive for applications in a fragmented spectrum, as it provides the flexibility to choose a pulse shape and thus allows reduction of the out-of-band leakage of opportunistic cognitive radio signals into incumbent frequency space. However, this degree of freedom is obtained at the cost of loss of subcarrier orthogonality, which leads to self-inter-carrier-interference. This paper will explain how self-interference can be reduced by a basic and a double-sided serial interference cancellation technique and show that these interference cancellation techniques improve the GFDM bit error rate to match the theoretical performance of the well studied orthogonal frequency division multiplexing (OFDM).

FBMC and GFDM Interference Cancellation Schemes for Flexible Digital Radio PHY Design

With the opening up of white spaces, efficient use of the fragmented spectrum - TV white space in particular - has become an extremely important focus of research. Apart from efficient spectrum usage, special care needs to be taken to maintain low out-of-band radiation to avoid harmful interference to incumbent services like TV signals and wireless microphones. For this reason, a flexible digital radio with multicarrier modulation scheme is the only solution. In this paper, we show the performance of two innovative multicarrier systems, Filter Bank Multi Carrier (FBMC) and Generalized Frequency Division Multiplexing (GFDM). A simple interference cancellation technique called serial inter-carrier interference cancellation scheme has been used to improve performance of the GFDM system. Channel equalization techniques have been implemented for FBMC.

Experimental testbed for 5G cognitive radio access in 4G LTE cellular systems

Cognitive radio technology addresses the limited availability of wireless spectrum and inefficiency of spectrum usage. Cognitive Radio (CR) devices sense their environment, detect spatially unused spectrum and opportunistically access available spectrum without creating harmful interference to the incumbents. In cellular systems with licensed spectrum, the efficient utilization of the spectrum as well as the protection of primary users is equally important, which imposes opportunities and challenges for the application of CR. This paper introduces an experimental framework for 5G cognitive radio access in current 4G LTE cellular systems. It can be used to study CR concepts in different scenarios, such as 4G to 5G system migrations, machine-type communications, device-to-device communications, and load balancing. Using our framework, selected measurement results are presented that compare Long Term Evolution (LTE) Orthogonal Frequency Division Multiplex (OFDM) with a candidate 5G waveform called Generalized Frequency Division Multiplexing (GFDM) and quantify the benefits of GFDM in CR scenarios.

Cyclostationary detection of cognitive radio systems using GFDM modulation

A cognitive radio should be able to detect unused spectrum band and to change its transmission parameters in order to transmit within these free bands. To achieve this, reliable detection of incumbent signals as well as of other opportunistic signals that are using the said spectrum, is necessary. Generalized Frequency Division Multiplexing (GFDM) is a recent multicarrier modulation technique with extremely low out-of-band radiation that makes it an attractive choice for the PHY layer of cognitive radio. GFDM has an innovative tail biting cyclic prefix which shows unique circular detection properties. In this paper, we consider the cyclostationarity properties of GFDM and compare this with well studied OFDM. Detection of GFDM based opportunistic signal by cyclostationary detection is shown and compared to OFDM detection by the same method.

Analysis of cyclostationary GFDM signal properties in flexible cognitive radio

Generalized Frequency Division Multiplexing (GFDM) is a recent multicarrier modulation technique with extremely low out-of-band radiation that makes it an attractive choice for the PHY layer of cognitive radio. GFDM has a flexible pulse shaping technique which reduces the out of band leakage. It also has an innovative tail biting cyclic prefix (CP) which shows unique circular detection properties. Compared to OFDM, only the GFDM signal presents side peaks characteristics in the cyclostationary autocorrelation function (CAF). Following this observation, in this paper we analyze the impact of the roll-off factor on the detection result when the cyclostationary detector uses the CAF side peaks. We have also studied the trade-off between the length of the CP and the roll-off factor for the detection performance. The results show that if the roll-off factor is properly designed, it can increase the detection capability even when the CP is very low, thus allowing to transmit more useful data in the same time without decreasing the detection performance.

Improved ACLR by Cancellation Carrier Insertion in GFDM Based Cognitive Radios

Generalized Frequency Division Multiplexing (GFDM) is a recent multicarrier modulation technique with low out-of-band radiation that makes it an attractive choice for the PHY layer of cognitive radio. In orthogonal frequency division multiplexing (OFDM) the out of band leakage is around -13 dB; with raised cosine or root raised cosine pulses, the out of band leakage of a GFDM system is -35 dB. To improve the adjacent channel leakage ratio (ACLR) even further, a technique of inserting cancellation carriers is implemented. Cancellation carriers are inserted at the vicinity of interference avoidance notch and are designed such that these cancellation carriers mitigate the interference from other subcarriers to the adjacent band. With this technique the out of band leakage is lowered to around -65 dB. This stunning improvement in the GFDM adjacent channel leakage ratio satisfies stringent FCC requirements for cognitive radio transmissions in TV white space scenarios.

Experimental Testbed for Dynamic Spectrum Access and Sensing of 5G GFDM Waveforms

Generalized frequency division multiplexing (GFDM) is a new candidate waveform for 5G applications. With flexible pulse shaping filtering and tail-biting cyclic prefix, GFDM has lower out of band leakage and hence is more suitable as an opportunistic cognitive radio waveform. Improved adjacent channel leakage ratio (ACLR) of GFDM makes the coexistence of secondary signals easier, with lower adjacent channel interference to legacy users. This paper details the experimental validation of the coexistence study of this 5G waveform in an LTE system. The paper also highlights the improved sensing performance of GFDM- CR waveform compared to traditional OFDM. OFDM with implicit rectangular pulse shaping has higher out of band leakage and increases the probability of false alarm; while sharper GFDM waveform demonstrates substantial spectral efficiency and produces lesser number of false alarms.

TVWS regulation and QoSMOS requirements

Regulatory regimes for opportunistic usage is being discussed in many countries for the so called TV White Space channels. The key objective of the regulators is to ensure that opportunistic systems can coexist with incumbent systems without causing harmful interference. However, they do not specify how these opportunistic systems must be designed to guarantee these requirements and to exploit White Spaces in an optimal way. This paper gathers key regulatory rules for opportunistic usage in the TV bands, and illustrates how these rules are turned into technical requirements within the framework of the European FP7 QoSMOS project.

PSO-based output matching network for concurrent dual-band LNA

This article presents an original design methodology for the selection of output matching load network for a dual-band Low Noise Amplifier (LNA) that is targeted for the use in the GSM 1.8 GHz and WLAN 2.4 GHz range. A particle swarm optimization (PSO) based technique is used to get the optimized values of the output load network components. The concurrent dual-band LNA is simulated with these entire component values in CADENCE with CMOS 0.18μm technology.

Cyclostationary detection of 5G GFDM waveform in cognitive radio transmission

Generalized frequency division multiplexing (GFDM) is a new flexible multicarrier waveform. With the flexibility of pulse shaping techniques and a tail-biting cyclic prefix, it has very low out of band leakage. This makes this potential 5G waveform suitable for cognitive radio opportunistic access with lower interference to the adjacent legacy/primary users. Because of the per-subcarrier pulse shaping technique, the cyclostationary autocorrelation properties of GFDM produces extra correlation peaks at particular cyclic frequencies. Cyclostationary detection based on these side peaks improve the spectrum sensing of GFDM over traditional OFDM. The GFDM receiver with ICI cancellation unit mitigates the ICI for any values of the roll-off factor, and hence, increasing the roll-off factor does not impact the BER performance of the GFDM system. This paper highlights the innovative cyclostationary properties of GFDM and studies the effect of pulse shaping roll-off factors on detection performance.