Jong-Hyune Kim

Adaptive data transmission based on band-selection for MC-CDMA systems

We introduce an adaptive band-selection (ABS) scheme for Multi Carrier-Code Division Multiple Access (MC-CDMA) systems to improve system capacity. Instead of using all subcarriers, mobile stations transmit message data only through the selected frequency bands based on band-selection coefficients from the base station. By using the adaptive band-selection scheme, ABS MC-CDMA systems accommodate more users than MC-CDMA systems that use all frequency bands for message data transmission. Due to the time-varying wireless channel conditions and dynamic power allocations, band-selection coefficients should be adaptively determined at the base station every update period. In our ABS MC-CDMA systems, the processing gain, the transmitted power and the data rate depend on the number of selected bands. Under the assumption that the total transmission power and the total amount of transmission data are the same for both MC-CDMA systems and ABS MC-CDMA systems, SNR behaviors are investigated and BER performances are presented in terms of the number of users and the normalized Doppler frequencies.

Performance Enhancement in a Low Rate Wireless PAN

The low rate wireless personal network (LR-WPAN) is a new standard uniquely designed for low data rates and low energy consumption. Each device has a limited energy supply and generates information that needs to be communicated to a sink node, but traffic generation from the network device may depend on the sensor type. Some sensors generate information regularly, but other sensors may generate information in an event-driven manner. Consequently, a static contention access period is not desirable for event-driven information because it cannot cope well with the variations of network traffic volume and patterns. In this paper, we suggest a new traffic adaptation scheduling mechanism that is based on the network traffic volume and pattern. The PAN coordinator can configure its beacon order (BO) and superframe order (SO) parameters based on the channel contention situation and broadcast a beacon message including a new SO and BO at every beacon interval (BI). Therefore, we will allow a network device to access the channel more frequently according to the traffic model. We will show the improvement of the throughput, the energy efficiency, and the end-to-end delay. The performance enhancement will be confirmed by the network simulation (NS-2) results.

Performance optimization over channel model for a Low Rate Wireless Personal Area Network

The low rate wireless personal network (LR-WPAN) is a new standard uniquely designed for low data rates and low energy consumption. LR-WPAN researchers are focusing extensively on the wireless technology and energy consumption, but many papers do not cover channel characterization and link quality assessment in LR-WPANs, even though we could reasonably surmise that the network performance will be optimized only when the channel and link information are provided. In this paper, we will suggest a new mechanism for performance enhancement in the presence of a time-varying channel response. First, we will regard the link quality indicator (LQI) as a channel state indicator. Second, we will modify the pure CSMA-CA procedure by reflecting the LQI measurement. Finally, we roughly observe the time-varying channel, and then we assign a weight to the L2 scheduling parameter known as the backoff exponent (BE). This mechanism upgrades the network performance when there is a time-varying channel. This paper addresses the problem by creating an efficient scheduling scheme that is based on the channel memory. The result of an NS-2 simulation indicates an overall improvement in the effective throughput, energy consumption, and end-to-end delay.