Fabbryccio A. C. M. Cardoso

Efficient FPGA-based implementation of a CAZAC sequence generator for 3GPP LTE

This paper presents a configurable and optimized hardware architecture for computing Zadoff-Chu (ZC) complex sequences in the frequency domain. It is a hardware-efficient and accurate architecture for computing ZC sequences in realtime. The architecture is mainly based on the CORDIC algorithm for computing complex exponentials using only shift and add operations. Due to transformations applied to the Zadoff-Chu equation it is possible to eliminate the use of multipliers with non-constant terms. This hardware architecture is employed by the Physical Random Access Channel (PRACH) in LTE and LTE-A systems during the reception and detection of random access preambles. Its main advantage is that it eliminates the need for storing a large number of long complex ZC sequences. Simulation results show that the proposed architecture is accurate, efficient and renders the resulting PRACH receiver fully compliant with 3GPPs detection requirements.

On the application of massive MU-MIMO in the uplink of machine type communication systems

The development of next-generation networks has been driven by a number of use cases aimed at supporting innovative applications and services. Among these drivers the Internet of Things has gained momentum due to its potential to leverage Machine Type Communications (MTC), a term used to denote machine-centered communications among sporadic, bursty traffic generating devices. While scalability issues have been addressed by the community, less is understood to date about the use of Multiple Input Multiple Output (MIMO) techniques in the context of MTC networks. In this paper, we propose the use of a Massive Multiuser (MU)-MIMO1 setup as means to tackle the uplink mixed-service communication problem. Under the assumption of an available physical narrowband shared channel, the capacity of the MTC network and, in turn, that of the whole system, can be increased by grouping MTC devices into clusters and letting each cluster share the same time-frequency physical resource blocks. The individual data streams conveyed by spatially spread MTC signals can be separated thanks to the powerful processing gain of our Massive MU-MIMO setup, where we consider K single-antenna MTC devices served by a BS equipped with an array of M antennas, M >> K. Our simulation results suggest that, as M is made progressively larger, the performance of sub-optimal linear filtering methods approach the matched filter bound, also known as perfect interference-cancellation bound. Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE) approach the bound at a faster pace than simple Maximum Ratio Combining (MRC), although the performance gap of the latter is of only 2 dB for M = 500 antennas. Due to its better balance between interference suppression and noise enhancement, MMSE outperforms MRC and ZF in all cases studied. The gap in the performance of ZF, however, is negligible for array sizes around 50 antennas, and entirely vanishes when the BS is equipped with M > 100 antennas.

A modified CA-CFAR method for LTE random access detection

Random Access is an important aspect of mobile systems where multiple users are always competing for resources. However, noise imposes a significant problem to those systems causing them to falsely detect access requests. In consequence, unnecessary processing and air traffic are generated based upon these unreal request events. This paper presents a modified Cell-Average Constant False Alarm Rate (CA-CFAR) strategy used for random access detection of CAZAC preambles in the presence of noise. Simulation results indicate that the proposed method performs well even in the case of low SNR.

Channel Estimation for Massive MIMO TDD Systems Assuming Pilot Contamination and Frequency Selective Fading

Channel estimation is crucial for massive multiple-input multiple-output (MIMO) systems to scale up multi-user MIMO, providing significant improvement in spectral and energy efficiency. In this paper, we present a simple and practical channel estimator for multipath multi-cell massive MIMO time division duplex systems with pilot contamination, which poses significant challenges to channel estimation. The proposed estimator addresses performance under moderate to strong pilot contamination without previous knowledge of the inter-cell large-scale fading coefficients and noise power. Additionally, we derive and assess an approximate analytical mean square error (MSE) expression for the proposed channel estimator. We show through simulations that the proposed estimator performs asymptotically as well as the minimum MSE estimator with respect to the number of antennas and multipath coefficients.

Efficient Frequency Domain Zadoff-Chu generator with application to LTE and LTE-A systems

This paper presents a configurable and optimized hardware architecture for computing Zadoff-Chu (ZC) complex sequences in the Frequency Domain (FD). It is a hardware-efficient and accurate architecture for computing ZC sequences in real-time. The architecture is mainly based on the CORDIC algorithm for computing complex exponentials using only shift and add operations. Due to transformations applied to the Zadoff-Chu equation it is possible to eliminate the use of multipliers with non-constant terms. This hardware architecture is employed by the Physical Random Access Channel (PRACH) in LTE and LTE-A systems during the reception and detection of random access preambles. Its main advantage is that it eliminates the need for storing a large number of long complex ZC sequences.

An FPGA-based time-domain frequency shifter with application to LTE and LTE-A systems

This paper presents the hardware architecture and the corresponding implementation details of a configurable and optimized FPGA-based time-domain frequency shifter with application to Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A) systems. The architecture is mainly based on a customized Numerically Controlled Oscillator (NCO) that is used for generating complex exponentials employing only adders, a Look-Up Table (LUT) and plain logic resources.

A case study on protocol stack integration for 3GPP LTE evolved node B

This paper presents a case study of the integration of the Long Term Evolution (LTE) physical layer into the radio protocol subsystem of a macrocell base station. We conduct tests in the laboratory using a modular experimental setup aimed at validating this protocol stack integration. Measurements and analysis are carried out with the aid of Wireshark, a well-known protocol analyzer tool. This choice allows the inspection of data packets at the application program interface between PHY and MAC subsystems. Our results suggest that the LTE protocol stack can operate synchronously, thus supporting message sequences conveyed within both random access and radio-resource-control connection procedures. The proposed experimental setup and test methodology make it possible to validate the control plane operation of the protocol stack without the need of a core network interface.

Design of an efficient uplink time alignment module for Long Term Evolution

This paper deals with architectural and practical design aspects to estimate the frame misalignment of LTE uplink transmissions on field programmable gate array devices. Timing adjustments are calculated and delivered to the User Equipment in conformance to Long Term Evolution specifications. Performance results as well as amount of resources necessary for the implementation of the proposed method are assessed. Moreover, the issue regarding the resulting digital circuitry is also considered. Results indicate that the proposed architecture is capable of calculating timing adjustments for SNR as low as -10dB with no constraints on the number of users multiplexed within a time transmission interval.