Principal investigator: Prof. Bor-Sen Chen
Motivation and Target
Wireless communication is currently an astonishingly prosperous high-technology industry in the world. At present, Taiwan has very large productivity in this industry. However, Taiwan only plays a role of OEM. Actually, the research and development in wireless communication has been quite flourishing in Taiwan, especially playing a leading role in many relevant cutting-edge academic researches. In this subproject, we would like to focus on the following research topics to further promote wireless communication in Taiwan to the world-class level: (1) Cognitive Radio Systems, (2) Cooperative and Secure Wireless Communications, (3) Broadband Wireless Communications, (4) Coding Theory and System Optimization, (5) Communication IC. If these researches can be thoroughly studied and the research results can be advisably integrated in an optimal fashion, we will provide a great platform for training talented creative researchers and capable engineers to significantly promote the wireless communication industry of Taiwan.
The research topics of Subproject 3 have 5 items. They include Wireless Sensing, Cooperative Wireless Communication and It Security, Broadband Wireless Communications, Coding Theory and System Optimization and Low- Power Cognitive Radio SOC System. They are described in detais as follows:
Because the mobile location and tracking becomes important in user location, mobile tracking, security and military targeting, National Security Committee of Europe, Japan and USA have required mobile should have the location function in future. Therefore, the design of mobile location and tracking becomes an important topic in wireless communication network and has much potential in commercial product. In the urban area, due to complex environment such as shadowing, channel fading and non-line of sight, there exist severe interferences in mobile location and tracking. It is a challenge for robust design of mobile location and tracking. Further, in wireless sensor network there are still some problems like target location, power allocation and lifetime.
Therefore, we integrate some techniques such as fuzzy estimation, Markov jumping, extended kalman filter, data fusion, convex optimization and multi-objective optimization to solve the difficult design problems such as robust location and tracking of mobile, and location detection, power allocation and lifetime of wireless sensor network.
Cooperative wireless communications have been recognized as a promising approach in enhancing communication reliability and communication ranges. In these systems, multiple users or multiple relays cooperate with each other to send a common message to the destination in order to achieve desired diversity gains and improved symbol error performance. However, this distributed system is vulnerable to information security (secrecy). In particular, the common message that needs to be distributed across the cooperative users may be subject to overhearing by some nearby passive eavesdroppers. It is also possible that there exist some (active) malicious users who intend to disturb the communication between the other normal users and the destination. In view of these issues, we will investigate the following advanced research topics in the subproject:
In future wireless communications, the demand for multimedia streaming services is expected to increase dramatically. To meet this demand, a broadband wireless communication system must increase the transmission rate and enhance the bandwidth efficiency. The orthogonal frequency division multiplexing (OFDM) technology is a promising solution for future broadband wireless communications because of its high bandwidth efficiency and superior resistance to multipath interference. Being standardized by the 3GPP (3rd Generation Partnership Project) community, LTE (Long Term Evolution)/LTE-A (LTE-Advanced) is the newest radio access system technology based on OFDM, which aims at providing higher data rate services with lower latency. LTE/LTE-A can support not only fundamental telecommunication services but also interactive multimedia applications, and thus will become the main stream of broadband wireless communications in the future.
There are still numerous unsolved problems related to the OFDM technology and future broadband wireless communication systems, including
Bandwidth-efficient modulation schemes can increase the available data rate and reduce the transmission latency; while energy-efficient modulation schemes can reduce the energy consumption and improve the receiving performance. In future broadband wireless communications, modulation schemes with high bandwidth efficiency and energy efficiency are essential and worthy of studying thoroughly.
MBMS is an efficient approach to provide multimedia services in wireless communication systems. By sharing the same data stream, multiple interested users can acquire the desired service simultaneously, thereby reducing the consumption of radio resources. To support multiple multimedia streams in OFDM-based MBMS, efficient radio resource allocation is a key issue and worthy of studying in the future.
At present, high data services are only available for fixed or low-mobility users. In future broadband wireless communications, supporting high data services for high-mobility users is attractive and essential. To meet this demand, user mobility estimation techniques and inter-carrier interference (ICI) cancellation techniques for OFDM systems are vital for performance improvement. These topics are worthy of studying in detail.
Low-density parity-check (LDPC) codes have attracted considerable attention in recent years because they can achieve near-Shannon-limit performance. However, most methods of designing LDPC codes are based on random construction techniques; the lack of structure implied by this randomness presents serious disadvantages in terms of the large complexity of encoding and decoding. Therefore, design of structured LDPC block and convolutional codes with reduced decoding complexity is very important for practical applications.
For LDPC block codes, we will develop new algebraic constructions of quasi-cyclic (QC) LDPC codes with enlarged minimum distance for good error performance. New unequal error protection (UEP) schemes based on QC-LDPC codes will also be investigated for practical applications. For LDPC convolutional codes, we will study new algebraic constructions with guaranteed girth and corresponding efficient encoding/decoding algorithms.
Network coding can increase the achievable throughput in a network by allowing intermediate nodes not only to route but also to perform operations on the incoming data. It has been considered as a conceptual breakthrough for network transmission and receiving extensive interests from the academia and industry in recent years. There are two types of network coding problems, coherent and noncoherent, depending on the assumption whether the network topology is known. Both approaches are susceptible to transmission errors caused by noise, interference, or malicious jamming. Hence, the problem of error control for network-coded transmission is very interesting and important.
For coherent network coding, we will conduct a well-round investigation of performance evaluation of error control for noisy channel networks, starting from a simple network topology and then to a general network setting. For noncoherent network coding, we will perform further study of the rank-metric approach for error control. We will develop new types of rank-metric codes and corresponding decoding algorithms. We will also conduct probabilistic performance evaluation of the rank-metric approach for error control, which has not been done in the literature.
Both centralized and distributed multi-input multi-output (MIMO) systems are highly attractive due to their appealing capability of achieving large capacity over fading channels. For high mobility, the fading is rapid and the coherence interval is short. Consequently, non-coherent techniques, which avoid the use of pilots for channel estimation, can be adopted in MIMO systems designed for fast-fading channels. In order to increase the transmission reliability, powerful outer channel codes, such as turbo codes or low-density parity-check (LDPC) codes, can be serially concatenated with the inner MIMO mapper suitable for non-coherent detection. This research topic focuses on designing several advanced non-coherent coded communication systems, especially for channels with short coherence intervals.
This research investigates the low-power cognitive radio SOC system, including cognitive radio SOC, low-power multi-standard FEC codec, and power-cognitive communication ICs.
This topic focuses on SoC for cognitive radio, which can provide much more spectrum efficiency than current communications under the techniques of spectrum sensing/detection and efficient spectrum management. There are many researches for algorithms and protocols; however, there are very few on the low complexity implementation and system integration solutions. Therefore, based on our preliminary studies and results on spectrum sensing/detection, we will continue to focus on more robust spectrum sensing/detection algorithms, low complexity/high power efficiency DSP, efficient spectrum management, and interference cancellation techniques. Combined with the developed SoC demo platform, we can provide high performance algorithms, SoCs and platform demo by the end of the project.
All the wireless transmission standards such as cellular, broadcast, and connectivity standards employ FEC (forward error correction) coding scheme in order to achieve high transmission reliability over noisy channel. In the future, multi-standard FEC codecs (encoders and decoders) will become key components for a variety of products such as mobile phones, portable entertainment and notebooks. Since CMOS scaling predicted by Moore’s law has significantly slowed down, in this research topic, we will use algorithmic and architectural approaches to design multi-standard FEC codec that achieves throughput values of Gb/s with lower complexities and power consumption levels within tight budgets imposed by the battery capacity.
The research of power-cognitive communication chip investigates to design the communication chip or manage the power-consumption of the chip according to the channel state information, including analog front-end circuits and baseband signal processing circuits.