| Description |
Filter Bank Multicarrier (FB-MC) is a technique similar to Orthogonal Frequency Division Multiplexing (OFDM), used to divide the spectrum of a transceiver into multiple subcarriers or channels. When a single symbol is repeated across all subcarriers, its energy is spread across the entire spectrum. This is referred to as Filter Bank Multicarrier Spread Spectrum (FB-MC-SS). The design of a preamble or training sequence used in the packet construction of a FB-MC-SS transceiver system is explored in this thesis. The preamble is used to acquire an estimate of the channel impulse response and noise variance for each subcarrier. This information is then used to undo the effect of the channel and perform Maximum Ratio Combining (MRC) across all subcarriers. An alternating {+1, âˆ'1} sequence has been previously proposed for its implementation simplicity. An alternating {+1,âˆ'1} sequence leads to detection advantages as a result of the impulse response of the matched filter. An alternating {+1,âˆ'1} sequence also presents many disadvantages. Mainly, the sequence is susceptible to interference because of its distinct frequency. The alternating {+1, âˆ'1} sequence also has a higher probability of detection by unauthorized users. To combat these deficiencies of the alternating {+1,âˆ'1} sequence, pseudorandom sequences are explored in this thesis. The goal of the pseudorandom sequence is to gain ro- bustness without forfeiting the packet’s detectability by intended receivers. Pseudorandom Polyphase and Maximum Length Binary sequences are explored as randomized preambles. Both the alternating {+1, âˆ'1} sequence and the pseudorandom sequence are implemented separately in the FB-MC-SS transceiver on a Xilinx FPGA to compare resource utilizations. Pseudorandom Polyphase preamble sequences lead to robust channel frequency response and noise variance estimation in interfered environments. Although alternating {+1, âˆ'1} sequence leads to straightforward packet detection and simple FPGA implementation, the susceptibility of an alternating {+1, âˆ'1} preamble to interference makes a pseudorandom preamble sequence more desirable. |
