This paper suggests modified LZSS which is suitable for compressing Hangul data by Hangul character token and the string token with small size based on Hangul properties. The Hangul properties can be described in 2 ways. 1) The structure of a Hangul character consists of 3 letters: The first sound letter, the middle sound letter, and the last sound letter which are called Cho-seong, Jung-seong, and Jong-seong, respectively. 2) The code of Hangul is represented by 2 bytes. The first property is used for making the character token processing Hangul characters which occupies most of the unmatched characters. That is, the unmatched Hangul characters are replaced with one Hangul character token represented by Huffman codes of Cho-seong, Jung-seong, and Jong-seong in regular sequence, instead of 2 character tokens. The second property is used to shorten the size of the string token processing matched string. In other words, since more than 75% of Hangul data are Hangul and Hangul codes are constructed in 2 bytes, the addresses of the window of LZSS can be assigned in 2-byte unit. As a result, the distance field and the length field of the string token can be lessened by one bit each. After compressing Hangul data through these tokens, about 3% of improvement could be made in compression ratio.

Although each application has its own quality of service (QoS) requirements, the resource allocation for multiclass services has not been studied adequately in multiuser orthogonal frequency division multiplexing (OFDM) systems. In this paper, a total transmit power minimization problem for downlink transmission is examined while satisfying multiclass services consisting of different data rates and target bit-error rates (BER). Lagrangian relaxation is used to find an optimal subcarrier allocation criterion in the context of subcarrier time-sharing by all users. We suggest an iterative algorithm using this criterion to find the upper and lower bounds of optimal power consumption. We also propose a prioritized subcarrier allocation (PSA) algorithm that provides low computation cost and performance very close to that of the iterative algorithm. The PSA algorithm employs subcarrier selection order (SSO) in order to decide which user takes its best subcarrier first over other users. The SSO is determined by the data rates, channel gain, and target BER of each user. The proposed algorithms are simulated in various QoS parameters and the fading channel model. Furthermore, resource allocation is performed not only subcarrier by subcarrier but also frequency block by frequency block (comprises several subcarriers). These extensive simulation environments provide a more complete assessment of the proposed algorithms. Simulation results show that the proposed algorithms significantly outperform existing algorithms in terms of total transmit power consumption.