Koji Maeda

Recognition Among OFDM-Based Systems Utilizing Cyclostationarity-Inducing Transmission

This paper presents cyclostationarity-inducing transmission techniques that enable the receiver to distinguish among different systems employing OFDM (Orthogonal Frequency Division Multiplexing) as a common air interface. Several systems using different air interfaces may have different properties of cyclostationarity that can be utilized to distinguish among them. However, this is usually not possible when the same air interface is used. To address this problem for systems using OFDM as an air interface, we consider methods that induce different properties of cyclostationarity in the transmitter of different systems. Specifically, we configure the OFDM signal before transmission such that its cyclic autocorrelation function (CAF) has peaks at certain pre-chosen cycle frequencies. The difference in the cycle frequencies, at which the CAF peaks occur for the configured OFDM signals, is utilized to distinguish among several systems even when OFDM is used as a common air interface. Two configuration methods for the OFDM signal are proposed. The first proposed method inserts a specific preamble at the head of each OFDM frame. Each preamble is configured such that only a selected subset of subcarriers is used for transmission. A different subset of subcarriers results in the occurrence of CAF peaks at different cycle frequencies for the OFDM signal. The second proposed method is based on dedicating a few subcarriers in an OFDM frame to the transmission of specific signals so that the whole frame exhibits cyclostationarity at pre-chosen cycle frequencies. For this method, we introduce a method for generating signals on the dedicated subcarriers and describe their relation to the cycle frequencies of the configured OFDM frame. Both proposed methods are evaluated by computer simulation in a multipath Rayleigh fading environment. Simulation results show that system recognition based on the proposed methods exhibits excellent detection probability.

Cyclostationarity-inducing transmission methods for recognition among OFDM-based systems

This paper proposes two cyclostationarity-inducing transmission methods that enable the receiver to distinguish among different systems that use a common orthogonal frequency division multiplexing- (OFDM-) based air interface. Specifically, the OFDM signal is configured before transmission such that its cyclic autocorrelation function (CAF) has peaks at certain preselected cycle frequencies. The first proposed method inserts a specific preamble where only a selected subset of subcarriers is used for transmission. The second proposed method dedicates a few subcarriers in the OFDM frame to transmit specific signals that are designed so that the whole frame exhibits cyclostationarity at preselected cycle frequencies. The detection probabilities for the proposed cyclostationarity-inducing transmission methods are evaluated based on computer simulation when optimum and suboptimum detectors are used at the receiver.

Performance Evaluation of Overhead Reduction Method for Cyclostationarity-Inducing Transmission

This paper proposes an overhead reduction method for cyclostationarity-inducing transmission which enables the receiver to distinguish among different signals that use a common orthogonal frequency division multiplexing (OFDM)-based air interface. Although the proposed method dedicates some subcarriers to give the specific feature to the OFDM signal as well as our previous proposal, this new proposed method even with half amount of overhead can create various cyclic auto-correlation function (CAF) peak patterns and achieve the detection probability almost equal to that of the previous proposed method. Both previous and new proposed methods are evaluated by computer simulations and test-bed experiments.

Successive multi-user detector with ordering for signals having different symbol rates

This paper proposes a successive multi-user detector that detects signals with different symbol rates. The proposed multi-user detector successively detects signals based on rejection of out-of-band signals and replica generation using soft-decision outputs from channel decoders. Moreover, an ordering method, which decides the detection order of the proposed multi-user detector based on the signal-to-interference-plus-noise ratio in consideration of the signal bandwidths of each signal, is proposed in order to enhance the multi-user detection performance. Simulation results show that employing the proposed ordering method can greatly improve the multi-user detection performance when the training periods of each signal are overlapped, as in the case when the frames of each signal are synchronized. The results also show that the BER performance of the proposed detector can be further improved by using the ordering method for the case when the training periods of each signal are not overlapped, as in the case when the frames of each signal are not synchronized