Mamiko Inamori

IQ imbalance compensation scheme in the presence of frequency offset and dynamic DC offset for a direct conversion receiver

A direct conversion architecture reduces the cost and power consumption of a receiver. However, a direct conversion receiver may suffer from direct current (DC) offset, frequency offset, and IQ imbalance. This paper presents an IQ imbalance estimation scheme for orthogonal frequency division multiplexing (OFDM) direct conversion receivers. The proposed IQ imbalance estimation scheme operates in the presence of dynamic DC offset and frequency offset. The proposed scheme calculates IQ imbalance from a simple equation. It employs the knowledge of the preamble symbols of the IEEE 802.11 a/g standards, while it does not require the impulse response of the channel. Numerical results obtained through computer simulation show that the bit error rate (BER) performance for the proposed IQ imbalance estimation scheme has a degradation of about 4 dB with a large DC offset, frequency offset, and IQ imbalance.

Frequency Offset Estimation Scheme in the Presence of Time-Varying DC Offset for OFDM Direct Conversion Receivers

This paper presents a frequency offset estimation scheme for Orthogonal Frequency Division Multiplex (OFDM) direct conversion receivers. The key idea is to use a differential filter for reduction of DC offset. Frequency offset is estimated in the presence of time-varying DC offset. In order to overcome the varying DC levels under automatic gain control (AGC) circuits, a threshold level is set for the output of the differential filter. The proposed compensation scheme offers superior frequency offset estimation when compared with a conventional scheme with a high pass filter.

Sampling Rate Selection for Fractional Sampling in OFDM

Through fractional sampling, it is possible to separate multi- path components and achieve diversity. However, power consumption grows as the sampling rate increases. In this paper, a novel sampling rate selection scheme in OFDM according to multipath environments is proposed. Numerical results through computer simulation show that the proposed sampling rate selection scheme reduces power consumption by decreasing the sampling rate when delay spread is small.

Frequency Offset Estimation Scheme in the Presence of Time-Varying DC Offset and IQ Imbalance for OFDM Direct Conversion Receivers

In WLAN systems, direct conversion architecture has been implemented. Though this architecture reduces the cost and power consumption, it may suffer from DC offset, frequency offset, and IQ imbalance. This paper presents a frequency offset estimation scheme for OFDM direct conversion receivers. In this paper, a frequency offset estimation scheme in the presence of time-varying DC offset and IQ imbalance is proposed. The novelty of this scheme is in its usage of a differential filter to reduce DC offset. Evaluation of the presented estimation scheme was carried out on an OFDM communication system designed to the specifications of the IEEE 802.11a/g standard for WLANs. Numerical results through computer simulation show that the proposed frequency offset estimation scheme works well even with large DC offset and IQ imbalance.

Non-uniform sampling point selection in OFDM receiver with fractional sampling

To achieve diversity with a single antenna, a fractional sampling (FS) scheme in OFDM has been proposed. In the previous literatures for FS, the sampling interval is fixed. An oversampling rate needs to be large to obtain more path diversity gain through FS. This leads to the increase of a circuit size for demodulation in a mobile terminal. In this paper, sampling point selection according to the frequency response of a channel has been proposed. The proposed scheme reduces the number of demodulation branches to a half as compared to the conventional FS scheme to achieve the same bit error rate. Moreover, by eliminating the specific sets of the sampling points, the computational complexity for sampling point selection is also reduced by a factor of 2.

Non-Orthogonal Access Scheme over Multiple Channels with Iterative Interference Cancellation and Fractional Sampling in MIMO-OFDM Receiver

A diversity scheme with Fractional Sampling (FS) in OFDM receivers has been investigated recently. FS path diversity makes use of the imaging components of the desired signal transmitted on the adjacent channel. In this paper nonorthogonal access over multiple channels with iterative interference cancellation (IIC) and FS is proposed. The proposed scheme transmits the imaging component non- orthogonally on the adjacent channel. In order to accommodate the imaging component, it is underlaid on the other desired signal. Through diversity with FS and IIC, non-orthogonal access on multiple channels is realized. Our propose scheme can accommodate nonorthogonal signals with limited diversity gains.

Sampling rate selection for fractional sampling in OFDM

Through fractional sampling, it is possible to separate multipath components and achieve diversity gain. However, power consumption grows as the sampling rate increases. This paper proposes a novel scheme for OFDM systems that selects the sampling rate according to the channels frequency response. Numerical results through computer simulation show that the proposed sampling rate selection scheme reduces power consumption by reducing oversampling ratio when delay spread is small.

Direct-Sequence/Spread-Spectrum Communication System with Sampling Rate Selection Diversity

In this paper, sampling rate selection diversity (SRSD) scheme for Direct-Sequence/Spread-Spectrum (DS/SS) is proposed. In DS/SS communication systems, oversampling may be employed to increase the signal-to-noise ratio (SNR). However, oversampling enlarges the power consumption because signal processing of the receiver has to be carried out at a higher clock rate. Higher sampling rate does not always maximize the SNR. In the proposed SRSD scheme, the power consumption can be reduced by selecting the optimum sampling rate depending on the characteristics of the channel. The proposed SRSD scheme can also reduce the BER more than the conventional oversampling scheme under certain channel conditions.

Adjacent Channel Interference Cancelation in Fractional Sampling OFDM Receiver

A diversity scheme with Fractional Sampling (FS) in OFDM receivers has been investigated recently. In the previous literature it has been shown that performance improvement with path diversity through FS depends on the bandwidth of the total channel response including transmit and receive baseband filters. However, if the signal on the adjacent channel exists, that signal causes interference to the desired signal with FS. In this paper, an adjacent channel interference cancellation scheme has been proposed for the FS OFDM receiver. The proposed scheme demodulates the signal on the adjacent channel and regenerates it to be subtracted from the received signal. Numerical results through computer simulation show that the proposed scheme achieves BER improvement under low signal-to-interference-ratio (SIR) conditions.

Non-uniform sampling point selection in orthogonal frequency division multiplexing receiver with fractional sampling

To achieve diversity with a single antenna, a fractional sampling (FS) scheme in OFDM has been proposed. FS achieves path diversity with a higher sampling rate and multiple demodulation branches. In the previous literatures for FS, the sampling interval is fixed even though the initial phase selection of the sampling has been investigated. The fixed sampling interval limits the diversity gain through FS. Thus, in this study, a non-uniform sampling point selection scheme according to the frequency response of a channel is proposed. Numerical results through computer simulation show that the proposed scheme improves the BER performance by about 2 dB when the number of the demodulation branches is 2. While the proposed scheme further improves bit error rate (BER) performance it requires a larger rate and more computational complexity for the selection of the sampling points. Therefore the complexity reduction for the sampling point selection is also investigated. The complexity reduction scheme eliminates the specific sets of the sampling points and reduces the computational complexity of the sampling point selection for the proposed scheme by a factor of 2. Computer simulation also shows that the low complexity version of the proposed scheme even achieves the equivalent BER compared to the original proposed scheme.