Jaekwon Lee

A New Spectral Correlation Approach to Spectrum Sensing for 802.22 WRAN System

rapidly, much attention has been paid on the use of spectrum resources. Recently, a new technology called Cognitive Radio (CR) was developed for using the unused spectrum band efficiently. In the CR systems, one possible approach is to allocate the unused spectrum band to the usage spectrum band provided by spectrum sensing technique. In this paper, we propose a new spectral correlation based signal feature detection method for spectrum sensing. To improve spectrum sensing sensitivity, the proposed method computes the autocorrelation of received signal before the spectral correlation detection. Simulation results show that the proposed method provides better performance of spectrum sensing than conventional spectral correlation detection method even in the low SNR environment. Index Terms--Cognitive radio, Cyclostationary, Spectrum sensing.

Component-interleaved Alamouti coding with rotated constellations for signal space diversity

A signal space diversity (SSD) scheme combined with Alamouti coding is investigated to achieve more diversity gain in fading channels. By approximating noise as a Gaussian distribution after Alamouti decoding, an exact expression for the SER for SSD schemes with Alamouti coding in Rayleigh fading channels can be derived for 4-QAM and 16-QAM. Using the formula derived by using upper bound approach, it can be confirmed that the diversity order is 4MR, where 2 stems from SSD and 2MR from Alamouti coding with receive MRC. Numerical evaluation performed using the formula developed for evaluating performance under various conditions indicated that the rotation angle affects the performance; this numerical evaluation had low computational complexity.

Definition and Properties of the Erasure Effect in Single-Frequency Network With Two Synchronized Transmitters

In this letter, the erasure probability of a received signal in a single-frequency network (SFN) is investigated. In particular, the definition and properties of such for a two-transmitter (two-TX) SFN are derived, which is known as the worst case of an erasure event. By definition, the erasure probability of a two-TX SFN is determined by the threshold level and the relative amplitude, and the relative delay does not have any effect on the erasure probability. Furthermore, the condition and the value of the maximum erasure probability are derived along with the erasure-free condition. Using the definition and properties, the erasure probability can be easily calculated and predicted for a given SFN condition.

Adaptive HPA Linearization Technique for Practical ATSC DTV System

In the digital television (DTV) broadcasting system, high power amplifier (HPA) is the most essential device to expand the service availability and coverage. However, as the input power level of HPA increases, the HPA is driven into the saturation mode and HPA output signal suffers nonlinear distortion. HPA nonlinearity is potentially responsible for adjacent channel interference and inter-symbol interference (ISI). To prevent these negative effects, digital pre-distortion (DPD) is one of the most widely used techniques for the HPA linearization. In order to estimate the HPA nonlinearity, DPD technique requires a feedback signal, which needs to be appropriately down converted and digitized from HPA output. However, since the feedback signal might be generally influenced by offset error, it is important to reduce the offset error in order to improve HPA linearization. In this paper, an adaptive DPD technique based on iterative look-up table (LUT) update and adaptive acquisition is proposed. The proposed DPD technique is validated on the advanced television systems committee (ATSC) terrestrial DTV broadcasting system by computer simulation and laboratory test.

A novel receive power analysis system for DTV broadcasting network

This paper presents a receive power analysis system for DTV broadcasting networks. This system measures the receive power and channel information simultaneously, analyzes the receive power of the measured multipath components and constructs 360 degree receive power profile by repeating analysis in all antenna directions. The proposed receive power analysis algorithm is proved by laboratory tests with two distributed translators. Field test results are briefly introduced and discussed for the evaluation of the proposed system.

On the condition of adaptive digital predistorter with real-time update

This paper investigates the reason why the predistorted signal is sampled and feeds back to an adaptation block as reference for digital predistorter (DPD) to be updated in real-time (RT) by comparing a non-real-time (NRT) method with off-time processing. In addition, by deriving a simple algorithm based on gradient descent algorithm with minimum square error criterion, the steady-state condition can be obtained. In simulation, it is confirmed that RT method converges to the exact high power amplifier (HPA) model. Also, RT method can rapidly cope with the change of HPA characteristics caused during the operation, which is a major advantage with emphasis on the operation of real-time update. In addition, RT method shows more accurate performance and stability consistently compared to NRT method.

An improved LUT based DPD technique for nonlinear HPA in ATSC DTV system

It is well known that high power amplifier (HPA) induces nonlinear distortion around its saturation region. It causes the inter-modulation distortion (IMD) and spectrum re-growth problems. Thus, the digital pre-distortion (DPD) technique is used to improve the linearity of HPA. This paper proposes the adaptive DPD technique, which is composed of a look-up table (LUT) based adaptive update algorithm, for the compensation of HPA nonlinearity. From the simulation results, the proposed technique shows the better convergence speed and spectrum re-growth suppression compared with conventional LUT technique.

Modified Dummy Sequence Insertion Method for PAPR Reduction of OFDM Signal

One of the major drawbacks of the OFDM system is a large peak to average power ratio. This leads to performance degradation due to nonlinear distortion in the high power amplifier. In this paper, we propose a modified dummy sequence insertion (m-DSI) method whereby low complexity and high PAPR reduction can be realized in OFDM system. The m-DSI method designs the sequence that achieves low covariance value with other sequences. After IFFT operation, the m-DSI sequence with the lowest PAPR is selected for transmission. Also, in order to reduce the IFFT complexity, the N-point IFFT block is divided into two sub-IFFT blocks due to avoiding the repeated calculation of IFFT operation. Simulation results of the m-DSI method in comparison with the DSI method are presented. The results demonstrate that the m-DSI method yields superior PAPR performance and lower IFFT complexity than the DSI method with almost the same BER performance while utilizing the same number of dummy bits.

A novel TxID insertion system for ATSC DTV auxiliary data transmission

This paper presents a new TxID (Transmitter Identification) data insertion system for ATSC DTV auxiliary data transmission. Because the functional description of TxID was not included in the early ATSC transmission standard, most of the conventional DTV transmitters and translators cannot transmit TxID signal which should be generated during 8-VSB (Vestigial Side Band) symbol generation process. The proposed system generates RF signal of TxID and then combines it synchronously with the RF signal of the legacy ATSC transmitter. This combination enables the conventional DTV transmitters and translators to transmit TxID signal with auxiliary data based on RF watermark technique. The proposed system is implemented and its performance is evaluated through laboratory tests.

A new synchronous watermark data insertion method for ATSC transmission systems

In this paper, a new synchronous insertion method of the uniquely assigned RF watermark data into ATSC transmitters and translators is proposed. Watermark data is generated, VSB filtered and up-converted to the same IF or RF frequency with the target transmission system. Frequency and timing of the generated RF watermark data are synchronized with the target system by extracting synchronization information from the exciter module of the target system. The generated synchronized RF watermark signal is combined with the output signal of the exciter of target transmitter at the level of the designated bury ratio. Performance of the proposed method is evaluated and compared with the conventional RF watermark insertion method through computer simulations.