Thresholded Interference Cancellation Algorithm for the LTE Uplink Multiuser MIMO

Ever since the adoption of the single carrier frequency division multiple access (SC-FDMA) scheme for the uplink in the Long Term Evolution (LTE) standard, there has been much interest in improved receiver algorithms for the same. Successive interference cancelation (SIC) based turbo receivers (Turbo SIC) have been proposed to tackle the multi-stream interference (MSI) for transmission modes such as spatial multiplexing (SM) and multiuser (MU) multiple input multiple output (MIMO). In addition, decision feedback equalizers (DFE) have been discussed as an alternative to the simple linear minimum mean square error (LMMSE) based receivers to suppress intersymbol interference (ISI) caused by the frequency selective multi-path channel. This paper proposes a DFE receiver variant based on parallel interference cancelation (PIC) with maximum likelihood detection (MLD) and ordered SIC (OSIC) principles to suppress ISI and MSI. Simulations show that the proposed receiver performs better than the existing SIC and DFE based receivers and achieves the matched filter bound (MFB) for both coded and uncoded systems.

Orthogonal frequency division multiple access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are the two major multiple access schemes for 4G wireless communications. In long term evolution (LTE) the downlink multiple access scheme is based on OFDMA and the uplink multiple access scheme is based on SC-FDMA. In this letter, we derive the fundamental performance difference between OFDMA and SC-FDMA, and present the general performance comparison between them. Analytical results show that OFDMA performance upper bounds SC-FDMA in the sense of capacity. The conclusion is further confirmed by numerical results.

Non-Gaussian noise is one of the most common noise models observed in wireless channels. This type of noise has severe impact on wireless systems detection devices. In this paper, the issue of OFDM and SCFDMA PAPR in non-Gaussian noise channel is addressed. Single carrier frequency division multiple access (SCFDMA) is developed form the Orthogonal Frequency Division Multiple access, (OFDM), and is a promising technique for high data rate uplink communications in the cellular systems. SCFDMA has similar throughput performance and essentially the same overall complexity as OFDM. One of the most important advantages of SCFDMA is the peak-to-average power ratio (PAPR), which is lower than that of OFDM. SCFDMA is employed in the uplink multiple access scheme in the Long Term Evolution (LTE) of cellular systems, and identified by the Third Generation Partnership Project (3GPP). In this paper, we show the performance differences of the OFDM and SCFDA system under different noise scenarios. The performance measure is the PAPR.

The Long Term Evolution (LTE) standards are generated by the Third Generation Partnership Project (3GPP) for the Fourth Generation (4G) wireless communication systems. The Fourth Generation (4G) wireless communication standards use new physical layer signaling techniques in their physical layer. Single Carrier Frequency Division Multiple Access (SC-FDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) are the two major signaling techniques used in LTE. OFDMA is used in the downlink of the Fourth Generation (4G) wireless communication systems for its high spectral efficiency and SC-FDMA is used in the uplink of the Fourth Generation (4G) wireless communication systems for its high power efficiency. The main objective of this paper is to design and implement the reliable and energy efficient architecture for LTE uplink system using FPGA. IFDMA is the most energy efficient subcarrier mapping scheme of SC-FDMA multiple access scheme. In IFDMA, the data symbols subcarrier mapping is not one to one instead each subcarrier carries a part from each data symbol transmitted at that time instant. The reason for the selection of IFDMA subcarrier mapping along with SC-FDMA multiple access scheme for LTE uplink comes mainly from its advantage to provide a low peak to average power ratio (PAPR) for the transmitted waveform. This results in less power consumption in the mobile station during uplink transmission. The reliability of the system is improved using interleaving process by avoiding packet loss. Convolution codes are less complex and are used to provide error free transmission. The enhancement of energy efficiency is done using the convolution coded IFDMA. The chosen energy efficient architecture must be more power efficient and support high data rates, which is the main requirement for the mobile user. The proposed reliable and energy efficient architecture for LTE uplink system is implemented using Xilinx system generator tool.

The UMTS Long Term Evolution (LTE) is an emerging technology in the evolution of 3G networks. LTE runs on an advancement of the obtainable UMTS infrastructure already used by over 80 percent of mobile subscribers worldwide. We have very inadequate resources in cellular technologies and it is important to utilize them with high efficiency. Single Carrier Frequency Division Multiple Access (SC-FDMA) & Orthogonal Division Multiple Access (OFDMA) are most important division of LTE. OFDMA was well utilized for achieving high spectral efficiency in communication method. SC-FDMA is introduced in recent times and it became handy candidate for uplink multiple access scheme in LTE system that is a project of Third Generation Partnership Project (3GPP). The Multiple Access Scheme in Advanced Mobile radio system has to meet the challenging requirements for example high throughput, fine robustness, capable Bit Error Rate (BER), high spectral efficiency, small delays, low computational difficulty, less Peak to Average Power Ratio (PAPR), low error probability etc. In our paper, we investigate the performance of SC-FDMA in LTE physical layer by considering different modulation schemes (QPSK, 16QAM and 64QAM) on the basis of BER vs Eb/No. Additive White Gaussian Noise (AWGN) and fading channel are used to evaluate the performance in presence of noise and fading.

Long Term Evolution (LTE) has adopted Single Carrier Frequency Division Multiple Access (SCFDMA) technique for uplink and Orthogonal Frequency Division Multiple Access (OFDMA) for downlink. SCFDMA is often called as Discrete Fourier Transform (DFT) spread OFDMA. In this paper, Wavelet based SCFDMA is proposed for analyzing Bit Error Rate (BER) performance. Analysis is carried out using different wavelets and different modulation schemes under AWGN channel. This analysis will show that the reduction in BER takes place by using wavelet transform in SCFDMA. Thus wavelet based SCFDMA provides better BER performance than that of DFT based SCFDMA.

Multiple access techniques like single carrier frequency division multiple access (SC-FDMA) requires orthogonal subcarriers to be distributed among various active users by the base station (BS). Intelligent scheduling of available subcarriers can significantly improve the quality of service (QoS) by employing SC-FDMA for uplink mobile communication. The BS scheduler must efficiently utilize the available frequency and multi-user diversity with limited side information exchange. In this regard, a simplified mathematical approach is first discussed for symbol error rate (SER) analysis of SC-FDMA system over a generalized multipath channel utilizing the statistical characterization of effective noise after equalization. The derived expressions of SER are generalized and simplified as it only depends on the equalizer amplification factor (EAF). The analysis is then used as a quick and accurate method to compare performance over various available subbands (SB's) for subcarrier distribution by BS scheduler with less side information to be exchanged. Since the error rate is directly dependent on EAF, we have used EAF for channel-dependent scheduling (CDS) performed by the base station (BS) for SC-FDMA.

Channel interpolation for LTE uplink systems with high mobility using Slepian sequences

Single carrier frequency division multiple access (SC-FDMA) which utilizes single carrier modulation at the transmitter and frequency domain equalization at the receiver is a technique that has similar performance and essentially the same overall structure as those of an OFDMA system. One prominent advantage over OFDMA is that the SC-FDMA signal has lower peak-to-average power ratio (PAPR). SC-FDMA has drawn great attention as an attractive alternative to OFDMA, especially in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of the transmit power efficiency. SC-FDMA is currently a working assumption for the uplink multiple access scheme in 3GPP Long Term Evolution (LTE). To achieve low PAPR, a novel scheme, SC-OFDMA with super frame using intermediate mapping (SF-IFDMA), is proposed in this paper. In our proposed scheme, B frames with N subcarriers will be combined into one super frame, then SC-OFDM technique is applied to reduce the PAPR of the super frame, the super frame with lowered PAPR will finally be divided into B OFDM frames for the transmission. The combining and dividing process is equivalent to the concatenation process. The proposed scheme requires no side information and can significantly reduce PAPR while maintaining small number of subcarriers.

Carrier frequency offset (CFO) and phase noise are challenging problems in single carrier frequency division multiple access (SC-FDMA) system. In this study, the authors have studied single-carrier space frequency block coding (SC-SFBC) to reduce the peak to average power ratio (PAPR) of the multiple-input multiple-output (MIMO) SC-FDMA signal, in which Alamouti SFBC will change the signal spectrum structure, break the single-carrier property and increase PAPR. Also, the authors propose a joint algorithm to suppress the inter-carrier interference (ICI) caused by phase noise and CFO. Conventional methods are to estimate phase noise and CFO in other algorithms, which are pretty difficult and complicated to obtain accurate estimation results. Unlike the conventional works, the novelty of the authors proposed algorithm is that it directly calculates the interference components and then reconstructs the ICI matrix. Thus, it avoids the degrading interactions between phase noise and CFO estimations. The proposed algorithm exploits block-type pilot, which is a common pilot pattern in SC-FDMA communications and is used in other wireless communication standards. Simulation results show that the suppression performance keeps smooth while phase noise and CFO varies, and BER performance degradation can be significantly reduced in 3 dB.

A low complexity iterative equalization technique for OFDMA and SC-FDMA uplink systems with Tx-Rx IQ imbalance and CFO under doubly selective channels

We propose a simple and flexible peak-to-average power ratio (PAPR) reduction scheme for coded single carrier frequency division multiple access (SC-FDMA) signals in the uplink of the Long Term Evolution (LTE). The proposed scheme is based on the introduction of few bit errors to modify the few complex modulated symbols of each data SC-FDMA symbol in a sub-frame, which cause peaks of the output signal samples to be larger than a predetermined threshold value. In addition, the effect on the bit error rate (BER) performance of the few deliberately corrupted bits can be greatly mitigated by using the channel decoding at the receiver. Computer simulations show that the proposed scheme can reduce the PAPR of SC-FDMA signals effectively with almost the same BER as the conventional SC-FDMA signals when the signal-to-noise ratio (SNR) is below 35 dB.

Long Term Evolution (LTE) chose Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink communications due to lower signal envelope changes in SC-FDMA signal. This enables low peak to average power ratio (PAPR) in SC-FDMA in contrast to Orthogonal Frequency Division Multiple Access (OFDMA). High PAPR cannot be ignored as it reduces energy efficiency due to the requirement of large range linear power amplifiers. As the mobile devices are power restricted, there is a requirement to mitigate PAPR in the uplink SC-FDMA systems, especially for higher order modulations. Companding is an attractive technique to mitigate PAPR without any bandwidth extension. This paper suggests a companding transform using exponential function to mitigate PAPR in SC-FDMA systems. The suggested transform maintains the average signal power contrary to $\mu$ law companding. Simulation results demonstrate that exponential companding technique without any decompanding operation reduces PAPR by a significant value by maintaining the average signal power and BER performance.

In recent years, secure, reliable and high speed data transmission have become key elements for cooperative based communication systems. Conventional communication methods are no longer sufficiently fulfilling the demands of next generation communication systems. In this paper, in order to establish communication between sensor nodes with the 3GPP LTE standard and achieve better communication values in terms of low Signal to Noise Ratio (SNR) regimes, four different Multi-Carrier modulation scenarios were investigated for relay network configuration of Wireless Sensor Networks' (WSNs) Physical Layer (PHY). Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) modulation techniques were selected due to their wide usage areas in broadband wireless communication as LTE. Optimal simulation results were achieved when the SC-FDMA was employed for all relay network configurations.

The Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard is becoming the appropriate choice to pave the way for the next generation wireless and cellular standards. While the popular OFDM technique has been adopted and implemented in previous standards and also in the LTE downlink, it suffers from high peak-to-average-power ratio (PAPR). High PAPR requires more sophisticated power amplifiers (PAs) in the handsets and would result in lower efficiency PAs. In order to combat such effects, the LTE uplink choice of transmission is the novel Single Carrier Frequency Division Multiple Access (SC-FDMA) scheme which has lower PAPR due to its inherent signal structure. While reducing the PAPR, the SC-FDMA requires a more complicated detector structure in the base station for multi-antenna and multi-user scenarios. Since the multi-antenna and multi-user scenarios are critical parts of the LTE standard to deliver high performance and data rate, it is important to design novel architectures to ensure high reliability and data rate in the receiver. In this paper, we propose a flexible architecture of a high data rate LTE uplink receiver with multiple receive antennas and implemented a single FPGA prototype of this architecture. The architecture is verified on the WARPLab (a software defined radio platform based on Rice Wireless Open-access Research Platform) and tested in the real over-the-air indoor channel.