Jaehwang Yu

A Performance Evaluation of Vertical Handoff Scheme between Mobile-WiMax and Cellular Networks

In multi-access network environments, interworking technologies has become a very important issue these days. This interworking would deliver optimized services to users and also benefit service providers by reducing network construction and maintenance costs. This paper proposes a cost-effective scheme for fast handoff between mobile WiMax and cdma2000 networks. The smoothly integration scheme proposed in this paper adopts the advantages of both loosely integration and tightly integration schemes: cdma2000 and Mobile-WiMax networks provide their own services independently and, on vertical handoff between them, support seamless services by fast handoff. Since we present protocol stacks as well as operation flows considering cdma2000 and Mobile-WiMax standard specifications, the proposed scheme can be implemented with minimal modification of existing Mobile-WiMax and cdma2000 networks. As result of simulation, we proved performance of the proposed scheme compared with others.

Multi data rate signaling based on IEEE 802.15.4

The IEEE 802.15.4 standard was brought up for the use in wireless personal area networks (WPANs) and is widely known as ZigBee. It employs spread spectrum techniques to obtain a robust transmission at comparatively low data rates of up to 250 kbit/s. In order to better match a certain transmission environment, different spreading factors could be used to obtain additional data rate modes. This approach appears to be a feasible extension to IEEE 802.15.4 allowing the coverage of a wider range of the signal to interference and noise ratio (SINR). However, a signaling scheme must be added to distinguish the additional modes from the native ZigBee mode. This scheme should also allow the operation of extended devices without interfering native ZigBee devices. Based on the structure of an IEEE 802.15.4 frame a method is presented that will allow extending the specified frame structure to a multi data rate system without interfering IEEE 802.15.4 compliant devices.

Performance comparison of audio codecs for high-quality color ring-back-tone services over CDMA

In this paper, we investigate the use of existing audio codecs for the purpose of a high quality color ring-back- tone service. First of all, we exploit the limitations of the enhanced variable rate codec (EVRC) in a view of music quality because EVRC is a standard speech coder employed in a code division multiple access (CDMA) system. In order to figure it out which current existing audio codec is suitable to deliver music over CDMA or wideband CDMA (W-CDMA), several audio codecs such as two different versions of MPEG AAC and the Enhanced AAC+ codec are reviewed. Next, the music quality of the audio codecs is compared with that of EVRC, where the bit-rates of the audio codecs are set to be around 10 kbit/s because the color ring-back-tone service using one of the audio codecs should be realized by replacing EVRC with it. The quality comparison is performed by an informal listening test as well as an objective quality test. It is shown from the experiments that the audio codecs provide better music quality than EVRC and among them, the Enhance AAC+ codec operated at a bit-rate of 10 kbit/s with a sampling rate of 32 kHz can be considered as a new candidate for the high quality color ring-back-tone service.

Effects of Gradual Enhancement for Receivers at Mobile Terminals in Different Locations with Greedy Scheduling

Receiver enhancement at mobile terminals such as using receiver diversity is a way of achieving greater downlink capacity. The enhancement, however, is achieved not instantaneously by a network operator but gradually by the individual users that choose and purchase their own mobile terminals. We investigate in this letter the effect of gradually introducing enhanced receivers at mobiles in different locations. With greedy scheduling, capacity, fairness and coverage are quantified and numerically compared according to locations of enhanced mobiles. The results show that the enhancement made at mobiles nearer to the base provides the greater capacity but this capacity-driving introduction of the enhancement makes the fairness and the coverage poorer.

Design and development of compact UHF RFID reader using SD interface

In this study, we developed UHF RFID reader on microSD which can be inserted into external memory on smartphone. A RFID application on smartphone controls RFID reader on microSD card and acquires information from RFID tag via SD interface which mainly uses the external memory. We applied flexible antenna to UHF RFID reader on microSD to guarantee tagging performance within few centimeters. The UHF RFID reader on microSD card which implemented in this research can utilizes development of new smartphone service base on individual item tagging, and provides advantage which expands B2B application to B2C application area.

Outdoor radio channel measurements at 2.35 GHz for WiBro systems

In this paper we present the results of measurements using a wideband wireless channel sounder and its analysis methods to propose the channel models of 2.35 GHz frequency band for wireless high speed portable internet which is named Wireless Broadband (WiBro) systems in Korea. It is important to know the characterization of the wireless radio channel for planning and developing a wireless system. This paper compares of fixed-point measurements with mobile-site measurements, and two post-processing methods called Pre-PDP and Post-PDP respectively. In addition, we have proposed the tapped delay line models of the Single-Input Single-Output (SISO) channel impulse response data obtained from the measurements in different radio environments.