Low-latency polyphase filter scheme based on the IIR filter for the OFDM repeater

Recently, the orthogonal frequency division multiplexing (OFDM) technique has been recommended as an access scheme for high-speed wireless broadband internet service [1] due to its high-data-rate and robustness for multipath fading channels. When OFDM operates in the time division duplex (TDD) style, a guard interval is usually inserted so as to prevent the system from inter-symbol interference. Here, the length of the guard interval is nominally determined by observing the maximum delay spread [1]. Due to the usage of the wireless repeater, the outage in this shadowed region can be avoide, and the service range can be extended. However, the problem to be resolved is shortening the processing time for relaying the data from the base station to the terminal or vice versa. Otherwise, the uplink and downlink slot can overlap either at the base station or the terminal, resulting in major performance degradation [2]. Therefore, the primary concern in the realization of the wireless repeater is how to effectively reduce the processing time needed for down- and up-conversion of the signal to be relayed. With the TDD system, strict requirements relating to processing delay must be taken into account to avoid interference. This kind of interference results in outage because it causes the deterioration of signal quality. The primary concern is how to diminish the processing delay intrinsically occurring at the repeater so that the TDD system works properly [3].