Non-binary symbol transmission such as Ternary Phase Shift Keying (TPSK) and Hexagonal Quadrature Amplitude Modulation (HQAM) can achieve the superior performance to the PSK or square QAM in the band-limited and peak-to-average power ratio (PAPR) limited channel due to its excellent natures of PAPR, spurious characteristic, and minimum Euclidean distance. However, these non-binary symbol transmissions are not suitable for the transmission of binary information, because there is mapping loss in the bit-to-symbol mapping due to non-power-of-two number of constellation points. The aim of this work is to alleviate its loss by using spatial modulation and then improve the bit-error performance. Spatial modulation has been proposed as a spatial domain modulation, which can efficiently work only in the case of power-of-two number of antennas. By jointly desingning spatial modulation and non-binary amplitude phase modulation, the system can be more flexibly designed and then achieve better performance. Furthermore, we study the coding scheme for this non-binary symbol transmission in the PAPR limited channel. Computer simulations confirm that the proposed system with non-binary turbo code can significantly improve BER performance.

In order to guarantee the QoS (Quality of Service) for current or future multimedia application services over wireless networks, we have proposed a cross-layer design framework which is jointly optimized among physical, data link, and network layers. In our proposed scheme, we classify the various application services into two QoS classes, i.e., streaming and downloading types of data transmissions. This paper focuses on a frame fragmentation method in data link layer to improve both latency and throughput performances in network layer. The proposed scheme properly controls the packet length based on the QoS classes as well as CSI (Channel State Information). The computer simulations reveal that our proposed scheme improves latency and throughput performances by 8.52-10.5 dB and 12.4-12.7%, respectively.

This paper provides the practical design of the transmit diversity technique with a nested coding technique and evaluates its performance via computer simulations. Similar to network coding techniques, the nested transmit diversity combines the transmit data with XOR operation. As a characteristic of the proposed transmit diversity, it can obtain diversity gain without some extra resources (e.g., transmit/receive antenna). In the proposed system, the transmitter simultaneously transmits two or more data sequences with a superposition technique, namely, nested coding technique. Suppose the case of two data superposing, the transmitting signal is composed of two data sequences, one is the data sequence to be currently transmitted, the other is the previously transmitted data sequence. In this case, the receiver has two types of decoding method corresponding to the previous decoding result. When successfully decoded at previous time slot, since the receiver knows the data-sequence transmitted at previous time slot which is referred to as superposition factor, it can completely remove the superposition factor with XOR manner. Different from a network coding, even if the receiver does not know the superposition factor (failed to decode the data), it can attempt to decode both data sequences. In this paper, we focus on the pragmatic design of nested transmit diversity. In order to achieve further improvement, we propose a reverse order decoding scheme. We reveal that the proposed nested transmit diversity can achieve diversity gain without extra resources.

Recently, wireless sensor networks have received considerable attention. In order to realize these networks, it is very important to estimate the position of indivisual nodes. The purpose of this study is to improve the accuracy of positioning. In wireless sensor networks, since a large number of sensor nodes are densely distributed over the target field, the sensor are closely located. As a result, the sensing data of nearby nodes have some correlation. Moreover, the closer the sensors are located, the higher the correlation the sensing data have. We propose a novel positioning method based on the above fact. Concretely, we combine the conventional positioning method which consists of the ToA ranging method and the proposed method considering the relationship between the data correlation and the distance. Computer simulations show that our proposed positioning method can improve the accuracy of positioning compared with the conventional ones.

Wireless communications are expected to be the dominant mode of access technology in the next century. Besides voice, a new range of services such as multimedia, high-speed data, etc. are being offered for delivery over wireless networks. Mobility will be seamless, realizing the concept of persons being in contact anywhere, at any time. Two developments are likely to have a substantial impact on the mobile communications systems deployed in the twenty-first century: the adoption of International Mobile Telecommunications-2000 and wireless asynchronous transfer mode (ATM). They are two different but cooperative approaches to providing high-speed wireless access. The limitations of the radio-frequency spectrum and radio channel propagation impose special constraints on the technologies of systems to be deployed. To make future mobile systems globally acceptable, standardization efforts are underway in the International Telecommunications Union and the ATM Forum. This paper reviews the international standardization efforts, the challenges to the technologies imposed by the radio spectrum limitations, radio channel propagation-induced distortions, and possible solutions. Evolution, migration, and architecture issues also are discussed.