Saheed A. Adegbite

Least Squares Interpolation Methods for LTE System Channel Estimation over Extended ITU Channels

Abstract — Performance of pilot-aided channel estimation techniques such as the Least Squares (LS) method depends on not only on the signal-to-noise ratio (SNR), channel conditions and pilot ratio, but also on the choice of interpolation method for deriving channel estimates at non-pilot subcarriers. This paper investigates the bit-error-rate (BER) performance of linear, spline and Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) interpolation methods in LS channel estimation over the three extended ITU channel profiles defined for Long Term Evolution (LTE) testing. Simulation results show that applying the linear interpolation method produces the best BER performance over the fading channel with the smallest multipath delay spread. It is also shown that the choice of best interpolation method actually depends on the SNR in some of the fading channel profiles. Index Terms—ITU, LS, LTE, PCHIP, spline. I. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) technology has been adopted in many of the next generation communication systems such as Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) [1]. OFDM is preferred not only because it offers high data rate transmission but also because of its flexibility and robustness against multipath fading [1]. Multipath channel fading exists when multiple delayed copies of a transmitted signal are received at the receiver, thereby resulting in the distortion of the transmitted signal. These distortions are collectively termed „channel fading‟, causing reception errors and hence increased bit-error-rate (BER). Channel fading can be broadly classified as time-selective and/or frequency selective, depending on the relationship between the fading channel and the transmitted signal parameters [2]. To combat multipath fading and improve BER, some form of channel estimation method is required in order to estimate the channel distortion effect for each of the active subcarriers within an OFDM symbol [3].

Performance of a new joint PAPR reduction and SI estimation technique for pilot-aided SLM-OFDM systems

Selected mapping (SLM) is an effective method for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. However, it requires detection of some side information (SI) to achieve successful data recovery. Existing SI estimation schemes are unattractive because of their high computational complexity. To address this problem, a new SI estimation technique based on a modified SLM is proposed. This paper shows that the proposed method requires significantly reduced computational complexity and yet produces similar PAPR reduction and data recovery performance as conventional SLM and an existing SI estimation scheme based on a frequency-domain correlation respectively.

Time-Domain SI Estimation for SLM Based OFDM Systems Without SI Transmission

AbstractSide information (SI) detection is normally needed to achieve successful data reception when selected mapping is implemented for reducing peak-to-average power ratio in orthogonal frequency division multiplexing systems. In severe frequency selective channel fading, existing pilot-assisted SI estimation schemes are ineffective especially when the number of pilots is limited, resulting in performance degradation in the form of increased BER. To address this problem, an alternative pilot-assisted SI estimation method based on a time-domain decision metric is proposed. Simulations show that when compared to a pilot-assisted SI estimation scheme based on frequency domain correlation, the proposed method provides improved SI estimation performance in the form of reduced SI detection error rate.

Prolate-binary sequences for SLM based papr reduction in OFDM systems

To reduce the occurrence of high peak-to-average power ratio (PAPR), this paper introduces prolate-binary sequences, and their application in orthogonal frequency division multiplexing (OFDM) systems that implement selected mapping (SLM). Through computer simulation, it is shown that the proposed prolate-binary sequences offer combined improved PAPR reduction performance, and reduced computational complexity compared with Riemann-binary sequences.

A PAPR Reduction and Data Decoding for SLM Based OFDM Systems without SI

Selected mapping (SLM) is an effective method for addressing high peak-to-average power ratio (PAPR) issues in orthogonal frequency division multiplexing (OFDM) systems. However, the standard SLM approach introduces additional data decoding challenges in the form of side information (SI) transmission and estimation. In general, SI transmission reduces data throughput and SI estimation normally involves computationally complex procedures, which increase design costs. To eliminate the need for both SI transmission and SI estimation, this paper presents an investigation into the PAPR reduction and BER performance of a new technique based on a modified SLM approach. It is shown that the proposed method simplifies data decoding through SI cancellation without SI transmission. Results show that the proposed method produces similar PAPR reduction performance and BER performance as standard SLM based OFDM system, which presumes perfect SI estimation, within a frequency non-selective (flat) fading channel.

Modified shapiro-rudin sequences for SLM-PAPR reduction in wireless OFDM systems

Using selected mapping (SLM), chaotic-binary (CB) sequences have been successfully applied to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. However, high computational complexity associated with the construction of CB sequences make them unattractive in practical system. This paper presents an alternative source of SLM sequences, namely Modified Shapiro-Rudin (MSR) sequences. Simulations compare PAPR reduction performance and computational complexity of MSR sequences over CB and conventional Shapiro-Rudin (SR) sequences. Results demonstrate that MSR sequences provide equivalent PAPR reduction to CB sequences but have the advantage of reduced computational complexity.

Computational efficient SLM–OFDM receiver for time-invariant indoor fading channel

This paper addresses receiver related side information (SI) estimation issues when selected mapping is used to reduce peak-to-average power ratio in orthogonal frequency division multiplexing (OFDM) systems. The SI contains critical information and its accurate estimation is required to enable successful recovery of payload data regardless of the channel condition. However, the need for SI estimation poses some practical issues in the form of high computational complexity and implementation challenges. Through simulations, this paper investigates the performance of an alternative data decoding approach called Embedded Coded Modulation (ECM), which requires no SI estimation. Using a form of block-type OFDM frame structure, results show that the ECM technique produces identical data decoding performance as other methods even in the presence of some non-linear amplifier distortions. In addition, it is shown that the ECM method eliminates SI related computational complexity and implementation problems.

Evaluation of selective control information detection scheme in orthogonal frequency division multiplexing-based radio-over-fiber and visible light communication links

Abstract. Block-level detection is required to decode what may be classified as selective control information (SCI) such as control format indicator in 4G-long-term evolution systems. Using optical orthogonal frequency division multiplexing over radio-over-fiber (RoF) links, we report the experimental evaluation of an SCI detection scheme based on a time-domain correlation (TDC) technique in comparison with the conventional maximum likelihood (ML) approach. When compared with the ML method, it is shown that the TDC method improves detection performance over both 20 and 40 km of standard single mode fiber (SSMF) links. We also report a performance analysis of the TDC scheme in noisy visible light communication channel models after propagation through 40 km of SSMF. Experimental and simulation results confirm that the TDC method is attractive for practical orthogonal frequency division multiplexing-based RoF and fiber-wireless systems. Unlike the ML method, another key benefit of the TDC is that it requires no channel estimation.

Selective Control Information Detection in 5G Frame Transmissions

Control signalling information within wireless communication systems facilitates efficient management of limited wireless resources, plays a key role in improving system performance and meets performance requirements of 5G systems. This chapter focuses on one particular form of control information, namely, selective control information (SCI). The SCI is a type of control information currently used in physical control channels of 4G wireless systems and will be extensively implemented in 5G wireless systems to encode essential system information such as signal format, frame structure, modulation scheme and coding rate. Maximumlikelihood (ML) is one of the conventional SCI detection techniques. Unfortunately, it requires channel estimation, which introduces some implementation constraints and practical challenges. This chapter uses generalized frequency division multiplexing (GFDM) to evaluate and demonstrate the detection performance of a new form of SCI detection that uses a time-domain correlation (TDC) technique. Unlike the ML scheme, the TDC technique is a form of blind detection that has the capability to improve detection performance with no need for channel estimation. In comparison with the ML based receiver, results show that the TDC technique achieves improved detection performance. In addition, the detection performance of the TDC technique is improved with GFDM receivers that use the minimum mean square error (MMSE) scheme compared with the zero-forcing (ZF) technique. It is also shown that the use of a raised cosine (RC) shaped GFDM transmit filter improves detection performance in comparison with filters that employ root raised cosine (RRC) pulse shape.

Improved PCFICH decoding in LTE systems

This paper studies control format indicator (CFI) estimation methods in 4G-LTE communication systems. CFI is an essential control signal in LTE, and must be correctly detected at the receiver to avoid degraded system performance. The standard method of CFI detection involves the use of the Maximum Likelihood (ML) estimation criterion. Unfortunately, ML decoding performance relies on accurate channel estimation, and as a consequence may result in poor CFI decoding when channel estimates are poor. To improve CFI detection in severe fading channel conditions, a time-domain decision rule that requires no channel estimation, is proposed. Results show that when compared with the ML approach, the proposed method reduces the probability of CFI estimation error in the form of reduced block error rate.