Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field of the Invention
The invention relates to a guard section length detection method and system.
2. Description of the Related Art
Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-user version of the popular OFDM digital modulation scheme. Multiple accesses are achieved in OFDMA by assigning subsets of subcarriers to individual users. Compared with the conventional single carrier communication system, the OFDM communication system allocates data in several subcarriers, thus, the data transmission speed can be increased. Because the OFDM system is increasingly being used in wireless communication systems, a guard section is used to reduce inter-symbol interference (ISI). Inter-symbol interference (ISI) is a form of signal distortion that causes previously transmitted symbols to have an effect on the currently received symbol. Adding the guard section reduces ISI, but, also reduces transmission efficiency because the guard section does not carry information. If the OFDM symbol length is NFFT points and the guard section length is NGI points, for example, the transmission rate after adding the guard section is
      N    FFT              N      FFT        +          N      GI      of the transmission rate without an added guard section. Generally speaking, ISI can be avoided when the guard section is longer than the channel length and a longer guard section length decreases the transmission rate and cannot increase the OFDM system performance.
As selection of the length of the guard interval depends on the channel condition, the length of the guard interval will dynamically change. For example, the IEEE 802.16 standard defines a guard section having a length of ¼, ⅛, 1/16 or 1/32 (hereinafter, called a ¼ mode, ⅛ mode, 1/16 mode and 1/32 mode) of an actual OFDM symbol length, and the base station selects a proper guard section length based on the channel length and the environment. Thus, a method for synchronizing the guard section parameter between the transmitter and the receivers is desirable.