Tone-Independent Orthogonalizing Lattice Equalization for Insufficient Cyclic-Prefix OFDM Transmissions

Tone-independent orthogonalizing lattice per tone equalizer (TOL-PTEQ) is introduced and its convergence is analyzed. Cyclic-prefix redundancy, one of the major drawbacks of orthogonal frequency division multiplexing (OFDM), can be reduced by TOL-PTEQ. Fast convergence and low computational complexity of TOL-PTEQ are also suitable properties for packet-based wireless communications and detections in which OFDM is widely deployed for their modulation technique. 1. Introduction PTEQ was originally proposed for optimizing bit rate of discrete-multitone (DMT) modem in wired communications such as digital subscriber lines (DSLs), where SNR of each tone can be independently maximized [1–4]. In these literatures, computational complexity is a major issue because they should cover a large number of tones, for example, DMTs with 512, 1024, or 2048 tones. Several types of stochastic-gradient algorithms for PTEQ have been proposed to reduce the computational complexity [1, 2]. But convergence rate is considered as a minor issue for DSLs because various DSLs have long training sequences in their initial set-up process. Wireless broadband communication technology is becoming more important for pervasive healthcare solutions as healthcare applications [5–7] are extending their coverage up to global scale as shown in Figure 1 [8]. According to [8], researches on more fast and reliable wireless infrastructures are conducted in order to improve the healthcare services in remote location. Candidate wireless technologies are as follows: IEEE 802.11x, IEEE 802.16x, ETSI HiperLAN, ETSI HiperMAN, and so on. A common feature of the candidates is that they use OFDM as their modulation method which is the promising technology because it is easy to handle the multipath channel problem by using fast Fourier transform. It is also widely utilized for multiple-access method, say OFDMA. It gives multiuser diversity taking advantage of channel frequency selectivity and good scalability over wide range of bandwidth that is achieved just by adjusting FFT size, where FFT stands for fast Fourier transform [9]. OFDM can also be utilized in the field of radar technologies as shown in Figure 2, where the multitone technique can be applied to enhance the radar scanning performance [10]. In this case, various OFDM technologies are essential to the multitone based radar systems. As shown in Figure 2, the radar transmits and receives the radar signal through the antennas. The received signal contains various reflection signals generated by the interfaces between two different layers. To obtain