Changeon Kang

A novel timing estimation method for OFDM systems

We present a novel timing offset estimation method for orthogonal frequency division multiplexing systems. The estimator proposed here is designed to avoid the ambiguity which occurs in Schmidls (1997) timing offset estimation method. The performance of the proposed scheme is presented in terms of mean and mean-square error (MSE) obtained by simulations. The simulation results show that the proposed estimator has a significantly smaller MSE than the other estimators.

A blind OFDM synchronization algorithm based on cyclic correlation

Future wireless systems will need to employ blind estimation to achieve better spectral efficiency. In this letter, we introduce a blind synchronization algorithm for jointly estimating timing and frequency offset in orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator exploits the second-order cyclostationarity of received signals and then uses the symbol-timing and carrier frequency offset information appearing in the cyclic correlation. Because it is a blind estimator, no channel impulse response information is required. Simulations demonstrate that the proposed estimator performs at a sufficiently high level, thus indicating its suitability for use over fading channels.

Performance of an MC-CDMA system with frequency offsets in correlated fading

The performance of an MC-CDMA system with carrier frequency offsets in correlated multipath fading is mathematically analyzed. The bit error rate is obtained from such analysis for the uplink Rayleigh fading channel. The derived results show that the performance of the MC-CDMA system is sensitive to the frequency offset, and the correlation of the subcarriers. That is, the performance degradation of the MC-CDMA system is caused by both carrier frequency offset and correlation among subcarriers. From the derived results, however, the performance degradation due to correlation among subcarriers is more severe than effect of frequency offset.

Level crossing rate estimation with Doppler adaptive noise suppression technique in frequency domain

The maximum Doppler frequency, or, equivalently, the mobile speed, is very useful information for optimizing the performance of many wireless communication systems. The paper proposes an improved method for estimating the maximum Doppler frequency based on the level crossing rate (LCR) estimator. To reduce the effect of additive noise, the proposed algorithm uses a novel Doppler adaptive noise suppression (DANS) process in the frequency domain. The proposed DANS process does not require additional channel information such as signal-to-noise ratio (SNR).

Effect of Bluetooth interference on OFDM-based WLAN

Bluetooth systems result in unintentional interference to OFDM systems using industry, science and medical (ISM) bands. The performance degradation of orthogonal frequency division multiplexing (OFDM) systems from Bluetooth interference is analyzed numerically. Bluetooth interference is modeled on partial band jamming with a rectangular spectrum. Bit error probability (BEP) performance based on the effective signal-to-noise power ratio (SNR) is provided for OFDM systems in Rayleigh fading channels in addition to AWGN. Additionally, coding gain over Bluetooth interference is evaluated for an OFDM-based wireless local area network (WLAN) in IEEE 802.11g.

Performance analysis of channel estimation for OFDM systems with residual timing offset

The authors present an analysis of the effect of timing offset on channel estimation for comb-type pilot-aided orthogonal frequency division multiplexing (OFDM) systems. Residual timing offset does not negatively affect the channel estimation of the pilot subcarrier, but does corrupt the channel information obtained via interpolation. This paper provides the mean square error (MSE) channel estimation performance when a linear interpolation technique is used in a comb-type pilot-aided OFDM system. Analysis shows that the performance degradation of the channel estimator due to imperfect frame synchronization is dependent on the frequency correlation of the channels and the amount of timing offset

A simple preamble for OFDM timing offset estimation

An efficient timing offset estimation method for orthogonal frequency division multiplexing(OFDM) systems is presented. The performances of the timing offset estimators in multipath fading channel are compared in terms of mean and mean-square error (MSE). The simulation results show that the proposed estimator is unbiased and has significantly smaller MSE.

Robust frequency offset estimation for pilot symbol assisted packet CDMA with MIMO antenna systems

We propose frequency offset estimation and combining techniques for pilot symbol assisted (PSA) packet downlink code-division multiple access (CDMA) with multiple-input and multiple-output (MIMO) antenna systems. Orthogonal Walsh codes are used for dedicated pilot symbols at the transmit antennas. The discrete Fourier transform (DFT)-based frequency offset estimation is used for simple implementation. In addition, simple interpolation is also used for resolution improvement of the DFT. When identical frequency offset is assumed, the frequency offset estimates for each single-input single-output (SISO) sub-stream (i.e., transmit/receive antenna pair) can be combined at the receiver. Simulation results show that the estimation and combining techniques proposed deliver improvement in the frequency offset estimation performance.

A channel assignment scheme for reducing call blocking rate in a DS-CDMA cellular system

We propose a channel assignment scheme for reducing call blocking rate in a base station (BS) of DS-CDMA cellular systems. The proposed scheme can be applied to the case where the reverse link capacity is enough, but all traffic channels are in a busy state. The proposed scheme takes advantage of the feature of soft handoff in which a mobile station holds its communication link even if one of the two communication links is released. The scheme estimates the mean and variance of the total received power level measured at the BS before assigning a traffic channel for a new call request. The BS makes a decision based on the estimated values whether the new call request will be accepted or not. If it is decided that the capacity of the reverse radio link is enough, but the traffic channel is not available, then the BS increases the value of the soft handoff parameter T_DROP to release the traffic channel of mobile stations located in the soft handoff area. The BS assigns the released traffic channel to a new call or a handoff call. The performance of the proposed channel assignment scheme is evaluated by computer simulation. The results show that the call blocking rate for new calls and handoff calls is reduced.

RBF multiuser detector with channel estimation capability in a synchronous MC-CDMA system

The authors propose a multiuser detector with channel estimation capability using a radial basis function (RBF) network in a synchronous multicarrier-code division multiple access (MC-CDMA) system. The authors propose to connect an RBF network to the frequency domain to effectively utilize the frequency diversity. Simulations were performed over frequency-selective and multi-path fading channels. These simulations confirmed that the proposed receiver can be used both for the channel estimation and as a multi-user receiver, thus permitting an increase in the number of active users.