Young Serk Shim

Wibro Usage Scenarios and Requirements in Tactical Environment

WiBro (wireless broadband) that provide portable Internet service is standardized in South Korea. It is incorporating the Institute of Electrical and Electronics Engineering (IEEE) 802.16e standards. As wireless mobile network technologies continue to develop, customers want more high data rate telecommunication services in addition to mobility. WiBro is an effective communication method in terms of providing better mobility compared to WLAN networks and a higher transmission rate than cellular networks. These service benefits of WiBro are expected to encompass the military applicability, as the military desires the simultaneous use of high bandwidth communications and mobile supporting networks. This paper presents an overview of WiBro and discusses a hypothetical military application usage scenario focusing on the requirements needed in a tactical environment. The paper addresses three technical aspects of tactical WiBro. Tactical WiBro means a WiBro that is enhanced by networking technologies (e.g., ad-hoc network architecture design, service coverage extension, a vertical handover) for military needs. These aspects are investigated in a tactical scenario, which will identify military requirements

A frequency domain approach for complexity reduction in wideband radio interference cancellation repeaters

To cancel wideband feedback interference signals that enter the receive antenna via near-by reflectors from the transmit antenna of the radio repeater, the wideband input signal is first split into several narrowband signals by narrowband filters. Interference cancellation (ICAN) is then performed on each split narrowband signal separately. As a result, the major portion of the complexity of a feedback ICAN system in a wideband radio repeater is accounted for by input and output filtering for spectrum control instead of the complexity of the ICAN algorithm itself. In this work, to reduce the overall complexity of the feedback ICAN system, a frequency sampling filter that is efficiently designed in the frequency domain when the filterpsilas frequency response has a narrow bandwidth is applied to input and output filtering for spectrum control. The proposed filtering method reduces the complexity of the feedback ICAN system to less than a half that of the conventional system with no performance deterioration.

A scheme to compensate for the input multipath channel effect in an interference cancellation repeater for mobile communication systems

Conventional interference cancellation (ICAN) techniques are mainly used to prevent feedback oscillation of a radio repeater when the repeaterpsilas gain is larger than the isolation between the transmit and receive antennas of the repeater. Therefore, the output signal distortion of the radio repeater, which is caused by the multipath channel between the repeaterpsilas input antenna and a base station, is not properly compensated. In this paper, a scheme to compensate for the output signal distortion in conventional ICAN repeaters is proposed. The compensation is performed by estimating the input multipath channel, inverting the estimated channel, and compensating the input signal using the inverted channel prior to feedback signal cancellation. The validity of the proposed scheme is confirmed by showing that the output signal quality of a conventional ICAN repeater is considerably improved by this scheme.

A software-based receiver running on a single DSP for terrestrial digital multimedia broadcasting

This paper presents the design and implementation of a software (SW)-based receiver running on a single digital signal processor (DSP) for terrestrial digital multimedia broadcasting (TDMB). Implementing the functions of the physical layer such as synchronization and channel decoding as well as codec decoders for a TDMB receiver in software running a DPS raises numerous design and implementation issues. We present solutions to these issues including an efficient software receiver structure, efficient algorithms with low complexity, real-time scheduling, reduction of the execution cycle number, and data transfer and communication between function blocks in the receiver, with a focus on the physical layer. The SW-based TDMB receiver developed in the present work can change and upgrade its functions and adapt to new standards. The performance of the implemented receiver was verified through successful decoding of live audio and video signals.

Parallel Data Processing Based on EDMA to Save the Processing Power of a T-DMB Software Baseband Receiver Running on a Digital Signal Processor

Unlike symbol decoding and channel decoding, which perform a variety of computationally simple or complex algorithms in the T-DMB baseband receiver, time de-interleaving simply moves data between two buffers according to a specified rule. Nonetheless, such simple data movement consumes considerable processing power if the T-DMB baseband receiver is implemented in software running on a digital signal processor (DSP). In this work, we present a parallel data processing approach based on the enhanced direct memory access (EDMA) to perform time deinterleaving in a T-DMB software baseband receiver with the view of saving the DSP processing power. Results demonstrating the validity of the presented parallel data processing are presented in terms of the execution cycle count and bit error rate of an implemented T-DMB software baseband receiver.

Improving BER Performance of T-DMB System by Error/Erasure Correction in RS Codes

In this paper, we introduce a new scheme to improve the performance of the terrestrial-digital multimedia broadcasting (T-DMB) system, which exploits the properties of the Reed-Solomon (RS) decoder to correct more errors by predicting as many erasures as possible in each RS packet in advance before decoding in the RS decoder. The concept depth of prediction (DoP) used for predicting erasures is introduced and derived. Simulation results show that with optimal DoP values, the new scheme yields performance gain of around 1dB at BER of 10-8 resulting in the extended coverage area of the T-DMB system.

A Real-time Input Data Buffering Scheme Based on Time Synchronization for a T-DMB Software Baseband Receiver

To decode a broadcasting signal such as a T-DMB signal using a software baseband receiver running on a digital signal processor (DSP), real-time input data buffering is important. A time offset of each received frame, which is caused by a difference in the sampling frequency between the transmitter and the receiver, makes input buffer management difficult, eventually resulting in the performance deterioration of the receiver. This work proposes an input data buffering scheme based on a ring buffer for a T-DMB software baseband receiver running on a DSP. The time offset of each received frame is estimated by a time synchronization block using a phase reference symbol and is used by a buffer controller to control the ring buffer so that the receiver on the DSP always reads valid data for data decoding. The validity of the proposed scheme is confirmed by showing that the ring buffer never goes into an overflow state when buffering the input data with a time-varying time offset. Thus, the specified receiver performance is guaranteed over time.