FDMA System Research Articles

Carrier frequency offset estimation for MIMO single-carrier FDMA system in wireless communication

Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems and Single-Carrier Frequency-Division Multiple Access (SC-FDMA) are so susceptible to carrier frequency offset (CFO) between transceivers. In this paper, a novel sequence called CAZBAR is proposed. The proposed CAZBAR sequence is based on constant amplitude zero autocorrelation (CAZAC) sequence and barker code. CAZBAR sequence shows better autocorrelation with higher peak at zero shift without ripples, which facilitates estimating carrier frequency offset in communication systems compared to other compensation methods in terms of mean square error (MSE). By applying CAZBAR sequence in MIMO SC-FDMA system 2 × 2 and 4×4, the bit error rate (BER) performance has improved significantly. At a BER=10-2, a SNR reduction of 11 dB is achieved for 2 × 2 system and 7 dB reduction for 4 × 4 system compared to other sequences. Which improves the performance of the whole system MIMO SC-FDMA. The CAZBAR sequence can be applied in 5G techniques, MIMO-OFDM, and MIMO SC-FDMA systems.

Logarithmic Companding Technique to Improve Performance of SC-FDMA Systems

Objectives: This paper proposes logarithmic companding technique to improve PAPR and BER performance of conventional Single Carrier Frequency Division Multiple Access (SC-FDMA) system. Methods/Analysis: The lower signal envelope fluctuations in SC-FDMA signal results in low peak to average power ratio, in contrast to that of OFDMA. But still, there is a need to minimize PAPR in SC-FDMA systems. Although there are many techniques to minimize PAPR in SC-FDMA systems they are highly complex or need side information to be transmitted. This paper proposes a companding technique based on a logarithmic function which provides better PAPR reduction when compared to μ law companding. Findings: Simulation results demonstrate that proposed method provides better PAPR and BER performance when compared to conventional SC- FDMA system and μ law companding.

Uplink Achievable Rate and Power Allocation in Cooperative LTE-Advanced Networks

This paper studies the achievable rate and power allocation to improve the uplink (UL) spectrum efficiency in a Long-Term Evolution Advanced (LTE-A) cooperative cellular network with the deployment of Type-II in-band decode-and-forward (DF) relay stations (RSs). The physical-layer UL transmission technology is based on single-carrier frequency-division multiple access (SC-FDMA) with frequency-domain equalization (FDE). Different from the downlink (DL) orthogonal FDMA system, signals on all subcarriers in the SC-FDMA system are transmitted sequentially rather than in parallel; thus, the user's achievable rate is not simply the summation of the rates on all allocated subcarriers. Moreover, each user equipment (UE) device has its own transmission power constraint instead of a total power constraint at the base station in the DL case. Therefore, the UL resource allocation problem in the LTE-A system is more challenging. To this end, we first derive the achievable rates of the SC-FDMA system with two commonly used FDE techniques, namely, zero-forcing (ZF) equalization and minimum-mean-square-error (MMSE) equalization, based on the joint superposition coding for cooperative relaying. We then propose optimal power allocation schemes among subcarriers at both the UE and RS to maximize the overall throughput of the system. Both theoretical analysis and numerical results demonstrate that our proposed power allocation schemes can drastically improve system throughput.

Scheduling for virtual MIMO in single carrier FDMA (SC-FDMA) system

In this paper, we consider a joint frequency-domain scheduling and user-pairing problem for virtual MIMO in the single carrier frequency division multiple access (SC-FDMA) system, e.g., the uplink transmission for third generation partnership project-long term evolution (3GPP-LTE) standard. Due to the sub-carrier adjacency constraint inherent to SC-FDMA, its complexity becomes unmanageable. We propose a greedy heuristic algorithm for PF scheduling so as to deal with the complexity issue in this joint problem. It has been shown that its performance can reach up to 90% of its upper bound.

PAPR Distribution Analysis of OFDM signals with Partial Transmit Sequence

Third Generation Partnership Project (3GPP) LTE has adopted OFDMA as the uplink multiple access scheme. One of the major drawbacks is the high PAPR. Not only is the performance of PAPR with PTS technique influenced by the number of subblocks and the phase vector but also by the subblock partitioning. The Partial Transmit Sequence (PTS) technique suffers from the search complexity of finding the optimum set of phase vectors. We propose a suboptimal combination algorithm that reduces the search complexity. The number of commutations in the suboptimal combination algorithm is much lower than the required by the original PTS technique. In this paper, we propose a suboptimal combination algorithm to reduce the searching complexity of finding the optimum set of vectors to minimize PAPR. The performance of PAPR utilizing the PTS technique improves by the use of the proposed suboptimal combination algorithm. We also show that a SC- FDMA system with Interleaved-FDMA or Localized-FDMA performs better than Orthogonal- FDMA in the uplink direction where transmitter power efficiency is of great importance.

A study of impact of inband signalling and realistic channel knowledge for an example dynamic OFDM–FDMA system

AbstractDynamically assigning sub‐carriers of orthogonal frequency division multiplexing (OFDM) systems to multiple different terminals in a cell has been shown to be beneficial in terms of different transmission metrics. The success of such a scheme, however depends on the ability of the access point to inform terminals of their newest sub‐carrier assignments as well as on the accuracy of the channel state information used to generate new assignments. It is not clear whether the overhead required to implement these two functions consumes all of the potential performance increase possible by dynamically assigning sub‐carriers. In this paper, a specific MAC structure is selected enabling the operation of a dynamic OFDM system, incorporating a signalling scheme for dynamically assigned sub‐carriers. Based on this structure, we study the overhead required for a dynamic sub‐carrier scheme; a static variant that serves as a comparison case. We investigate the performance difference of these two schemes for various scenarios where at first signalling and then realistic channel knowledge is added to the system model. Average throughput and goodput per terminal serve as figures of merit; the number of terminals in the cell, the transmission power per sub‐carrier, the delay spread and the movement speed of the terminals are varied. We find that a realistic overhead model decreases the performance of both static and dynamic schemes such that the overall ratio favours in all cases except for higher speeds the dynamic rather than the static scheme especially in realistic system environments. Copyright © 2005 AEIT.

Simulador de uma rede celular baseada no sistema FDMA (AMPS/TDMA).

This article describes the model and implementation of a cellular network simulator based on FDMA system (AMPS/TDMA). The purpose of the simulator is to evaluate the performance of the FDMA cellular network as well as the optimization of some parameters. Some results obtained from the simulator are also shown.

Spectrum and technology of a wireless local loop system

This article shows that the wireless local loop (WLL) may not necessarily provide more capacity than mobile cellular systems if an FDMA or TDMA system is used. CDMA has proven to have higher capacity than the other multiple access schemes due to the nature of CDMA systems. In industrial countries, the requirements of WLL are quality and service features. In developed countries, the requirement is a low-cost high-capacity system, even if voice quality must be sacrificed. Therefore, the system design aspects are different.

SAW filter matrix for SS/FDMA system

AbstractThe configuration and function of a surface acoustic wave (SAW) filter matrix used on board a satellite to implement a subchannel switched FDMA (SS/FDMA) system is described. The function and configuration of the SAW filter matrix (SFM) are described. Conditions imposed on the amplitude and phase of two adjacent subchannels to provide a broad channel by combining the outputs of the subchannels are investigated. Electrical and transmission characteristics of an SAW filter matrix used in four‐beam SS/FDMA system with a subchannel‐combining function are presented, demonstrating its technical feasibility.When implementing an SFM, it is important that the devices used for a satellite‐based SS/FDMA router are sufficiently reliable for the design life of the satellite. A methodology is shown that gives a redundant configuration with the lightest mass and that achieves the targeted reliability. Example calculations for a four‐beam SS/FDMA router are given.

The capacity of a spread spectrum CDMA system for cellular mobile radio with consideration of system imperfections

There has been much interest in the use of spread spectrum code division multiple access (CDMA) techniques for cellular mobile radio. To date, spread spectrum has been used mainly for military applications, in which the inherent transmission security and immunity to deliberate jamming are important. Spread spectrum systems, however, possess various other features such as multiple access and multipath rejection capability, which make their use attractive within the mobile radio environment. However, the current interest has been principally motivated by the work of Gilhousen et al. (see IEEE Trans. Vehic. Technol., vol.VT-40, no.2, p.303, 1991) in which it is claimed that the CDMA option may offer capacity improvement over more conventional frequency and time division multiple access, FDMA and TDMA, techniques. Within this paper, the relative capacities of a basic FDMA and CDMA system are examined. It is shown that, in the absence of capacity-enhancing features such as voice activity detection and cell sectorization, the capacity of each system is comparable. The paper then assesses the sensitivity of the CDMA system to typical propagation conditions, power control errors, and realistic antenna patterns and shows that the capacity of a CDMA system may be significantly reduced under nonideal conditions. >

Millimeter wave personal radio using an advanced communication satellite

THIS PAPER describes a millimeter-wave personal radio system using a communications satellite. It focuses on the development of a 50/40-GHz-band earth station. First, the trends of future satellite services are discussed. Satellite communications will be ready for personal utilization, namely the personalization of satellite communications, in the near future. The idea of a personal radio using a satellite and an example of an advanced communications satellite are introduced. The communications system and access method are also discussed and an FDMA system is recommended. Second, a small earth station for the millimeter-wave personal radio is proposed which has a 30-cm-diameter antenna, a transmission rate of 64 kb/s for wide applications, direct FSK modulation in the RF stage, the local signal fed from the transmit system, and link availability of 99%.