Basuki Endah Priyanto

Initial Performance Evaluation of DFT-Spread OFDM Based SC-FDMA for UTRA LTE Uplink

In this paper we present an initial performance evaluation of the 3GPP UTRA long term evolution (UTRA LTE) uplink with baseline settings. The performance results are obtained from a detailed UTRA LTE uplink link level simulator supporting OFDMA and SC-FDMA schemes. The basic transmission scheme for uplink direction is based on single-carrier transmission in the form of DFT spread OFDM with an MMSE receiver. Two antenna configurations, SISO and 1times2 SIMO are considered in the analysis of spectral efficiency in addition to adaptive modulation and coding (AMC) and L1-HARQ. For assessment purposes, the performance results of SC-FDMA are compared with OFDMA. It is shown that 1times2 SIMO greatly increases the spectral efficiency of SC-FDMA making it comparable to OFDMA, especially for high coding rate. Furthermore, SC-FDMA has a flexibility to increase BLER performance by exploiting frequency diversity.

Improving SC-FDMA Performance by Turbo Equalization in UTRA LTE Uplink

Turbo equalization is known as an advanced iterative equalization and decoding technique that allows to enhance the performance of the data transmission over a frequency selective fading channel. The turbo equalizer will result in extra receiver complexity, but isolated to the base-station, which does not have stringent power constraints. In this paper, a turbo equalization technique to improve Single Carrier Frequency Division Multiple Access (SC-FDMA) performance is proposed. A new adaptive coefficients solution for frequency domain equalization is considered. The work is in the context of UTRA Long Term Evolution (LTE) Uplink. The performance is evaluated for 1x2 Single Input Multiple Output (SIMO) antenna configuration in a 6 paths Typical Urban (TU-06) channel profile. For assessment purpose, the results are compared with SC-FDMA MMSE and OFDMA schemes. Simulation results show that the turbo equalizer can improve the BLER performance around 1 dB with only a few iterations, and improve the SC-FDMA performance over OFDM, especially at high coding rate.

Baseline E-UTRA Downlink Spectral Efficiency Evaluation

This paper evaluates spectral efficiency performance of the 3GPP Evolved UTRA (E-UTRA) downlink with baseline settings. A detailed link level tool has been developed including the majority of 3GPP E-UTRA link chain processing modules such as time-domain link adaptation and LI HARQ. Since MIMO is an integral part of the new system, we include four basic multiple antenna configurations in the analysis, namely the SISO, 1x2 SIMO, 2x2 SFC and 2x2 BLAST schemes. Since the BLAST is very sensitive to channel estimation error in cell edge, a case denoted as adapMIMO is considered as well, where the SFC is taken as a backup for the BLAST in cell edge. The system bandwidth is fixed at 20 MHz and a Typical Urban channel model is assumed for both macrocell and microcell evaluations. Simulation results show that in macrocell scenario, the spectral efficiency performance gain of SIMO over SISO is up to 54%, while SFC shows an additional gain of 14% over SIMO. Although the adapMIMO scheme has similar performance as SFC in the macrocellular case, it produces about 30% spectral efficiency gain in the microcell scenario.

Assessing and Modeling the Effect of RF Impairments on UTRA LTE Uplink Performance

In this paper we investigate the effect of modelled RF transmitter impairments on UTRA Long Term Evolution (LTE) uplink link performance. Nonlinear power amplifier, gain imbalance, phase imbalance, and phase noise are considered. The main contributions of this work is assessment of the relation between Error Vector Magnitude (EVM) and link performance loss due to each impairment and the investigation of a white Gaussian noise source in the transmitter as an equivalent model of the impairment. The results obtained are based on the UTRA LTE uplink parameter settings. Results show that the EVM is a good measure to estimate the link level performance loss for numerous impairments. The performance degradation in AWGN and a frequency selective fading when using a white noise source as an equivalent transmitter RF impairment model, fits well with the other impairments in the anticipated range of EVM. An analytical formulation describing the effect of the white noise source in the SNR loss fits similarly with the simulation results. With 16 QAM rate 3/4, an EVM value of 8% corresponds to an SNR loss of approximately 0.5 dB.

Performance evaluation of frequency hopping schemes in UTRA-ITE uplink

This paper presents the performance of various frequency hopping schemes in UTRA-Long Term Evolution (LTE) uplink. SC-FDMA is the multiple access technique for LTE uplink in which the signals can be transmitted in localized and distributed mode. Frequency hopping mechanism can be combined with localized mode to obtain frequency diversity gain. Two frequency hopping mechanisms are evaluated, which are the intra and inter sub-frame frequency hopping. The results are obtained from LTE uplink link level simulations. Simulation results for 16 QAM 4/5 in typical urban channel model shows that the localized transmission with frequency hopping provide a diversity gain of around 0.3 dB to 0.7 dB over conventional localized transmission. Moreover, an inclusion of HARQ retransmission provides significant additional gain in low SNR region.

A spectrum shaping technique to control spectrum emission of UTRA LTE user equipment

For the UTRA long term evolution (LTE), the transmit signal spectrum must comply with stringent spectrum emission mask requirements because of very low guard band size for high spectral efficiency. Compared to e.g. WCDMA, the requirements are tightened, which calls for efficient user equipment (UE) transmitter design, to balance the tradeoff among performance and hardware complexity. In this paper a spectrum shaping technique suitable for LTE user equipment is proposed and evaluated. The key component of this technique is an inverse Chebyshev digital IIR filter which has maximally flat in the passband and sharp transition from passband to stopband. We compare this technique with the well-known time windowing method which offers low implementation complexity. We study the two techniques impact on both error vector magnitude (EVM) and spectrum emission for two different LTE system bandwidths and for various bandwidth allocations for the user. Results show that for wideband setting (10 MHz) both techniques are able to produce acceptable EVM values less than 0.2%. However, for narrowband setting (1.4 MHz), only digital filtering performs sufficiently well since the time windowing method fails when the window overlap size is greater than the cyclic prefix length.

Effect of Phase Noise on Spectral Efficiency for Utra Long Term Evolution

In this paper, the effects of phase noise on the spectral efficiency of the next generation of OFDM based mobile systems with channel estimation is investigated. The simulation context and parameter settings are taken from the 3GPP Evolved UTRA (E-UTRA) study item, focusing on an OFDM downlink single antenna system in 20 MHz bandwidth. Phase noise is modeled as a Wiener-Levy process and several phase noise powers are evaluated. The OFDM coherent detection method is based on pilot assisted channel estimation (PACE) with Wiener based frequency domain interpolation and second order Gaussian interpolation for the time domain interpolation. The cell level spectral efficiency is also evaluated for micro and macro-cell scenarios. The simulation results indicate that the phase noise effect in E-UTRA downlink can be reduced by using high performance local oscillator or by placing pilots in every OFDM symbols

Impact of polar transmitter imperfections on UTRA LTE uplink performance

The polar transmitter is an alternative RF transmitter architecture solution to achieve a high-efficiency power amplifier. In this paper the impact of polar transmitter imperfections on the UTRA long term evolution (LTE) link level performance is investigated. The most common imperfections in a polar transmitter are modelled, such as timing delay alignment and power amplifier non-idealities. Our approach is to analyze the relation between error vector magnitude (EVM) and link performance loss due to each imperfection. The results obtained are based on LTE uplink parameter settings and show that the most severe polar transmitter problem in LTE uplink is the timing delay alignment, especially for higher order modulation and coding scheme. Results also show that the EVM is a good direct measure to estimate the link level performance loss for various imperfections in the anticipated EVM range. For 16 QAM rate 3/4, an SNR loss of approximately 0.5 dB can be estimated by an EVM value of 8%.