A carrier frequency synchronization scheme is proposed for orthogonal frequency-division multiplexing (OFDM) systems in the presence of phase noise (PHN). In the proposed scheme, carrier frequency synchronization is performed based on the maximum-likelihood (ML) algorithm using an OFDM preamble symbol. The proposed scheme is compared with conventional methods. Simulation results are presented to illustrate the effectiveness of the proposed scheme in the presence of PHN.

This paper proposes the most effective deployment scenario of the passive double-star (PON) system to provide multiple broadband services, such as high speed Internet access and broadcast services. The deployment costs of the two major PON technologies, wavelength division multiplexing (WDM) and 10 Gbps time division multiplexing (TDM), are analyzed using the latest cost trend and the most popular access network architecture. These two technologies are compared using the cost analysis results to identify the cost-effective scenarios of PON system deployment. Based on the comparison, this paper reveals that the WDM network becomes cost effective when the service penetration and the shift ratio becomes high.

One approach to accommodating IP traffic on a wavelength division multiplexing (WDM) network is to construct a logical topology, establishing a set of lightpaths between nodes. The lightpaths carry IP traffic but do not require any electronic packet processing at intermediate nodes, thereby reducing the load on those nodes. When the IP and WDM networks have independent routing functions, however, the lightpaths in the WDM network may not be fully utilized by the IP router. It is therefore necessary to integrate the two routing mechanisms in order to utilize resources efficiently and adapt to changes in traffic. In this paper, we propose an integrated routing mechanism for IP over WDM networks. The key idea is to first prepare a set of virtual-links representing the lightpaths that can be established by the WDM network, then calculate the minimum cost route on an IP network including those links. Our simulation results show that when traffic patterns do not change, the throughput of our method is almost the same as that of a logical topology optimally designed for a given traffic demand. When traffic patterns change, the throughput of our method is about 50% higher than that of the logical topology.

Monolithically integrated four-channel distributed feedback (DFB) laser array has been fabricated by metal organic vapor phase epitaxy (MOVPE) selective area growth for 1.55 µm coarse-wavelength division multiplexing (CWDM) systems. Wide-stripe MOVPE selective area growth and electron-beam lithography are used to obtain wide CWDM channel spacing of 20 nm. Compared to hybrid integration of discrete lasers, monolithic integration of laser array on a single substrate greatly simplifies device alignment and packaging process.

This paper presents a novel threshold-based selection scheme to combine adaptive transmit antenna selection with an adaptive quadrature amplitude modulation (AQAM) for a spatial multiplexing (SM) multiple-input multiple-output (MIMO) system with linear receivers in practical uncorrelated and correlated channel conditions. The proposed scheme aims to maximize the average spectral efficiency (ASE) for a given bit error rate (BER) constraint and also to lower the hardware complexity. Our simulations are run on a general MIMO channel model, under the assumption that the channel state information (CSI) is known at the receiver and the adaptive control signaling can be perfectly fed back to the transmitter. We deploy the low rank-revealing QR (LRRQR) algorithm in transmit antenna subset selection. LRRQR is computationally less expensive than a singular value decomposition (SVD) based algorithm while the two algorithms achieve similar error rate performances. We show that both the conventional AQAM scheme (i.e., without adaptive transmit antenna selection) and the SM scheme perform poorly in a highly correlated channel environment. We demonstrate that our proposed scheme provides a well-behaved trade-off between the ASE and BER under various channel environments. The ASE (i.e., throughput) can be maximized with a proper choice of the channel quality threshold and AQAM mode switching threshold levels for a target BER.

Spatial multiplexing (SM) offers a linear increase in transmission rate without bandwidth expansion or power increase. In SM systems, the LMMSE receiver establishes a good tradeoff between the complexity and performance. The performance of the LMMSE receiver would be degraded by MIMO channel estimation errors. This letter focus on obtaining the asymptotic convergence of output interference power and SIR performance for the LMMSE receiver with channel uncertainty. Exactly matched simulation results verify the validity of analysis in the large-system assumption. Furthermore, we find that the analytical results are also valid in the sense of average results for limited-scale system in spite of the asymptotic assumption used in derivation.

Time-frequency-selective, equivalently time-variant multipath, fading channels in orthogonal frequency division multiplexing (OFDM) systems introduce intercarrier interference (ICI), resulting in severe performance degradation. To suppress the effect of ICI, several symbol detection methods have been proposed, all of which are based on the observation that most of the ICI's power is distributed near the desired subcarrier. However, these methods usually ignore the channel variation in a OFDM symbol block by fixing the number of considered ICI terms. Therefore, we propose a novel frequency-domain symbol detection method with moderate complexity, which adaptively determines the number of ICI terms within each OFDM symbol block.

This paper presents an admission control technique for multi-carrier systems with an FRF(frequency reuse factor) of 1. The FRF of 1 is very attrative for more improved channel throughput but the forward link capacity is rapidly decreased at the cell boundary region due to the increase in the ICI(InterCell Interference). By measuring a region-based channel capacity and deriving a closed form of blocking probability, a QoS(Quality of Service) maintenance technique and mobility model can be acquired. In the simulation, the proposed scheme demonstrates a blocking probability reduction of up to 40% compared to the cell-based link capacity scheme.

We introduce an adaptive subchannel, bit, and power allocation (ASBPA) algorithm to maximize the bandwidth efficiency of the mobile communication system that use orthogonal frequency division multiplexing (OFDM). We propose a suboptimal rate adaptive ASBPA algorithm that guarantees fairness in resource allocation and overcomes inherent co-channel interference (CCI) in the cellular system. Furthermore, we evaluate the maximum possible bandwidth efficiency of the cellular OFDM system achieved by the ASBPA algorithm which is practical to implement. Our simulation results show that the proposed algorithm outperforms the existing ones and achieves the cellular bandwidth efficiency of up to 5 b/s/Hz/cell. We also investigate some of the conditions that govern the bandwidth efficiency of the cellular OFDM system using the proposed ASBPA algorithm.

In this letter, the system capacity of multiuser diversity combined with spatial multiplexing schemes is analyzed. An analytic expression is derived for the ergodic system capacity with multiuser scheduling and dual multi-input multi-output (MIMO) systems by using a tight lower bound of the link capacity. The proposed analytic approach is verified through comparisons between analytic and simulated results, and is shown to make fairly precise predictions of the ergodic system capacity and the scheduling gains even when the numbers of antennas and users are small.

This paper reports on a fiber-optic system for in-building wireless communication/broadcast systems developed in Samsung Electronics. Our system delivers the third generation mobile system, satellite-digital multimedia broadcast, and wireless local access network services over a single strand of single-mode fiber or multi-mode fiber. We present the design issue and experimental results of the radio-over-fiber link.

This paper presents a numerical analysis of reverse link capacity by obtaining a closed form of ICI (InterCell Interference) over OFDM (Orthogonal Frequency Division Multiplexing)-based broadband wireless networks. In the analysis, shadowing factors are taken into account for determining the home BS (Base Station) of each MS (Mobile Station) over multicell environments. Under the consideration, a more accurate analysis of link capacity can be performed compared to Gilhousen's approximation. In the numerical results, it turns out that the actual interference is lower than Gilhousen's approximation with a decrease of around 20% in the interference.

We derived explicit formulas for evaluating the error vector magnitude (EVM) from the amplitude distortion (AM-AM) and phase distortion (AM-PM) of power amplifiers (PAs) in orthogonal frequency-division multiplexing (OFDM) systems, such as the IEEE 802.11a/g wireless local area networks (WLANs) standards. We demonstrated that the developed formulas allowed EVM simulation of a memoryless PA using only a single-tone response (i.e. without OFDM modulation and demodulation), thus enabling us to easily simulate the EVM using a harmonic-balance (HB) simulator. This HB simulation technique reduced the processing time required to simulate the EVM of a PA for the IEEE 802.11a standard by a factor of ten compared to a system-level (SL) simulation. We also demonstrated that the measured EVM of a PA module for the IEEE 802.11g could accurately be predicted by applying the measured static AM-AM and AM-PM characteristics to the derived formulas.

We have developed a code-division-multiplexing (CDM) transmission scheme for future road-vehicle communication systems, which uses cyclic shifted-and-extended (CSE) codes generated from a basic code with superior auto-correlation characteristics. This paper proposes to use a Quasi-Orthogonal (QO) sequence as the basic code. Its auto-correlation values are zero except at zero and middle shifts. When the CDM transmission is performed by the CSE codes based on the QO sequence, a desired correlation value is, at a receiver, interfered by the auto-correlation value at middle shift. Therefore, an elimination technique for the interfered correlation value is proposed and realizes zero cross-correlation characteristics within the cyclical shift interval. The new CDM transmission scheme based on the proposed scheme is evaluated by computer simulations in terms of the bit-error-rate performance.

In this letter, a blind frequency offset estimation algorithm is proposed for OFDM systems. The proposed method exploits the intrinsic phase shift between neighboring samples in a single OFDM symbol, incurred by a frequency offset. The proposed algorithm minimizes a novel cost function, which is the squared error of the candidate frequency offset compensated signals from two different observation windows. Also, the solution of the proposed algorithm is given by an explicit equation, which does not require any iterative calculation. It is shown that the performance of the proposed method is better than those of the conventional methods, especially in the presence of multipath channels. This is due to the fact that the proposed method is insensitive to inter-symbol interference (ISI).

Multiple-input multiple-output (MIMO) systems using eigenbeam space division multiplexing (E-SDM) perform well and have increased capacities compared with those using conventional space division multiplexing (SDM). However, channel state information (CSI) is required at a transmitter, and the performance of E-SDM systems depends much on the accuracy of the CSI at a transmitter and a receiver. In time-varying fading environments, the channel change between the transmit weight determination time and the actual data transmission time causes the system performance to degrade. To compensate for the channel error, a linear extrapolation method has been proposed for a time division duplexing system. Unfortunately, the system performance still deteriorates as the maximum Doppler frequency increases. Here, two new techniques of channel extrapolation are proposed. One is second order extrapolation, and the other is exponential extrapolation. Also, we propose maximum Doppler frequency estimation methods for exponential extrapolation. Simulation results for 4tx 4rx MIMO systems showed that using the proposed techniques, E-SDM system performs better in a higher Doppler frequency region.

We introduce an extension of Golay complementary sequences in which, for each sequence, there exists another sequence such that the sum of aperiodic autocorrelation functions of these two sequences for a given multiple L-shift (L≥1) is zero except for the zero shift. We call these sequences multiple L-shift complementary sequences. It is well-known that the peak-to-average power ratio (PAPR) value of any Golay complementary sequence is less than or equal to 2. In this paper, we show that the PAPR of each multiple L-shift complementary sequence is less than or equal to 2L. We also discuss other properties of the sequences and consider their construction.

Recently, lattice reduction aided (LRA) detectors have been introduced into Vertical Bell-Labs Layered Space-Time (V-BLAST) systems to obtain nearly optimal bit error rate (BER) performance for only small additional complexity. In this paper, the layer error characteristics of LRA-V-BLAST detectors are investigated and compared with those of conventional V-BLAST ones. Two important conclusions are drawn for the LRA-V-BLAST detectors. First, the variation of their mean square error (MSE) within each detection iteration is not as large as in conventional V-BLAST detectors. Second, thanks to lattice reduction there exists an inherent sub-optimal detection order from the last to the first layer. These conclusions allow LRA-V-BLAST detectors to avoid optimal ordering to further reduce the complexity. LRA-V-BLAST detectors without optimal ordering are shown to obtain almost the same BER performance of LRA-V-BLAST detector with optimal ordering.

Wavelength division multiplexing (WDM) technology offers the capability of building wide-area networks with high speed. Reconfigurability is a key feature of a WDM network that enables the network logical topology to change dynamically in response to the changing traffic patterns. There are two important issues involved in the reconfiguration of a network logical topology. One is how to determine the new logical topology corresponding to the current topology. It needs to consider a trade-off between the performance of the new target topology and the cost of the topology transition from the current topology to the new one. The other is how to determine the transition sequence from the current topology to the new one. It needs to control the disruption to the network as less as possible during the reconfiguration process. In this paper, we focus on the latter problem and propose several heuristic algorithms that reconfigure logical topologies in wide-area wavelength-routed optical networks. Our reconfiguration algorithms attempt to control the disruption to the network as less as possible during the reconfiguration process. For this purpose, a lightpath is taken as the minimum reconfiguration unit. The proposed algorithms are evaluated by using an NFSNET-like network model with 16 nodes and 25 links. The results show that very simple algorithms provide very small computational complexity but poor performance, i.e., large network disruption, and that an efficient algorithm provides reasonable computational complexity and very good performance. More complex algorithms may improve performance somewhat further but have unrealistically large computational complexity.

This paper discusses a cyclic prefixed single carrier frequency-domain equalization (SC-FDE) scheme with two types of transmit diversity. Firstly, we propose a SC-FDE system with space-frequency block coding (SFBC). The transmit sequence of the proposed system is designed to have spatial and frequency diversities, which is equivalent to the SFBC. The corresponding combining receiver is derived under a minimum mean square error (MMSE) criterion. It is shown that the proposed system significantly outperforms the SC-FDE system with space-time block coding (STBC) over fast fading channels, while providing lower computational complexity than orthogonal frequency division multiplexing (OFDM) combined with SFBC. We verify the performance of two-branch transmit diversity systems including the proposed one through bit error rate (BER) analysis. Secondly, as a scheme that combines STBC and SFBC, a space-time-frequency block code (STFBC) SC-FDE system is presented. Computer simulation results show that the proposed STFBC SC-FDE system has better immunity to the distortion caused by both fast fading and severe frequency selective fading, compared to the SC-FDE system with the STBC or the SFBC scheme. Complexity analysis is also conducted to compare their computational loads of the transceiver. It is shown that the proposed STFBC SC-FDE system has lower computational complexity than the STFBC OFDM system.