Dynamic subcarrier allocation for single carrier - FDMA systems

Single carrier-frequency division multiple access (SC-FDMA) utilizes single carrier modulation at the transmitter and frequency domain equalization at the receiver. It has almost similar performance and essentially the same overall structure of an orthogonal frequency division multiple access (OFDMA) system with low peak to average power ratio (PAPR). Recently, the SC-FDMA has drawn great attention as an attractive alternative to OFDMA, in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of manufacturing cost as well as transmit power efficiency. Such power efficiency can provide considerable performance improvements in future wireless communication networks. This article outlines the basic principles of SC-FDMA systems with different types of sub-carrier mapping schemes. Simulation results demonstrate the performance of different sub-carrier mapping schemes under ideal and pedestrian channel condition.

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.

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.

Single-carrier frequency division multiple access (SC-FDMA) has been adopted as a possible air interface for future wireless networks. It combines most of the advantages of orthogonal frequency division multiple access and the low peak to average power ratio (PAPR) of single carrier (SC) transmission. Existing transmit antenna diversity techniques such as space-time block coding and space-frequency block coding are incompatible either with the system constraints or with the SC nature of SC-FDMA. We propose a novel space-frequency flexible coding scheme compatible with SC-FDMA and we prove its good performance both in terms of PAPR and bit error rate (BER) on frequency selective multiple input multiple output channels.

In this paper, subcarrier and power allocation are jointly considered in a three-node symmetric cooperation orthogonal frequency-division multiple access uplink system. With the help of Nash bargaining solution, the dynamic subcarrier allocation scheme and the adaptive power allocation scheme are proposed for joint optimization. The joint resource allocation is decomposed and solved by dynamic subcarrier allocation algorithm and adaptive power allocation algorithm. Simulation results show the effectiveness of the proposed cooperative scheme.

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.

This paper is dedicated to better understanding of the achievable sum rate in the single carrier FDMA (SC-FDMA) system. We investigate the achievable sum rate in a two-user SC-FDMA system, where a mix of SIMO (single input multiple output) and SDMA (space division multiple access) transmission mode is assumed for the wideband communication. The problem is formulated which appears to be non-convex. Relation to the conventional waterfilling solution is pointed out for single mode (SIMO or SDMA) transmission. We show that a mix of SIMO and SDMA transmission mode in the wideband is not favorable for any pair of the user equipments. A better strategy would be to switch to SIMO mode or SDMA mode adaptively. We also propose a simple algorithm to find the group of users for SDMA mode based on the wideband average spatial correlation. Performance improvement is shown by combining adaptive SIMO mode and SDMA mode selection with our proposed user grouping algorithm.

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.

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.

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

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.

Single carrier frequency division multiple access (SC-FDMA) has been adopted as uplink multiple access scheme for 3GPP LTE as it combines the advantages of orthogonal frequency division multiple access (OFDMA) and the low envelope variation properties of single carrier (SC) transmission. Moreover, the classical transmit antenna diversity technique as space-time block code (STBC) and space-frequency block code (SFBC) can improve the uplink performance combination with SC-FDMA schemes. In this paper, a signal-to-interference-plus-noise ratio (SINR) performance analysis method of SC-FDMA is proposed for STBC and SFBC schemes, respectively. The closed-form SINR expressions based on the modified SC-preserved implementation structure and MMSE equalization for receivers are derived by channel frequency response and noise variance, considering inter-symbol interference. Moreover, it can be easily extended to multi-receive antennas. By simulation results it is shown that with proposed equivalent SINR, the BLock Error Rate (BLER) performance of MIMO-SC-FDMA over slow fading channel is well matched with that over AWGN channel.

Single-carrier frequency division multiple access (SC-FDMA) is a promising alternative to orthogonal frequency division multiple access (OFDMA) for uplink wireless communications in frequency-selective fading environments. In this paper, we investigate the impact of the power amplifier (PA) on the performance of the SC-FDMA system. The suitable saturation level thresholds of the PA that can be utilized in the SC-FDMA system are studied and determined through simulations for different modulation formats. Simulation results show that the saturation level of the PA has a significant effect on the bit error rate (BER) performance of the SC-FDMA system, especially with high order modulation formats.

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.

Multiuser orthogonal frequency division multiplexing (OFDM) is a very promising multiple access technique to efficiently utilize limited RF bandwidth and transmit power in wideband transmission over multipath fading channels. When a wideband spectrum is shared by multiple users in multiuser OFDM-based systems, different users may experience different fading conditions at all subcarriers. Each user is assigned a subset of all subcarriers by some allocation algorithm. Thus, multiuser diversity can be achieved by adaptively adjusting subcarrier, bit, and power allocation depending on channel status among users at different locations (Wong et al., 1999a). In (Wong et al., 1999a), Wong applies a Lagrangian optimization technique and an iterative algorithm to solve the subcarrier, bit and power allocation problem. The suboptimal scheme for the NP-hard joint optimization problem is decoupled into two steps while it has a high computational complexity. A sub-optimal algorithm has been proposed to solve a related problem (Wong et al., 1999b). In (Wong et al., 1999b), Wong presents a real-time subcarrier allocation (SA) algorithm. It is a two-phase algorithm, including the constructive initial assignment (CIA) and the subcarrier swapping steps. The initial subcarrier allocation algorithm needs to pre-determine the numbers of subcarriers for each user before the allocation process starts. The performance of the SAbased algorithm will be compared in the simulation. In (Kim et al., 2006), Kim shows that the allocation problem in (Wong et al., 1999a) can be transformed into an integer programming (IP) problem. The branch-and-bound algorithm (Wolsey, 1998) can be employed to find the optimal solution of the allocation problem which has exponential computational complexity in the worse cases. We utilize the approach to obtain the optimal solution as the performance bound for comparison. Evolutionary algorithms (EA) are used to solve extremely complex search and optimization problems which are difficult to solve through simple methods. EAs are intended to provide a better solution, as it is based on the natural theory of evolution. Evolutionary algorithm (EA)-based schemes have been applied to solve subcarrier, bit, and power allocation problems (Wang et al., 2005) (Reddy et al., 2007) (Reddy & Phora, 2007) (Pao & Chen, 2008). In general, chromosomes can be designed with binary, integer, or real representation. The chromosome lengths are related to the number of subcarriers. Each element in the chromosome is a subcarrier allocated to a user. In this research, a subset of subcarriers can be assigned to one user depending upon the availability of subcarriers at a particular time