A new training symbol weighted by pseudo-noise(PN) sequence is designed and an efficient timing and fre-quency offset estimation scheme for orthogonal frequency division multiplexing(OFDM) systems is proposed. The timing synchronization is accomplished by using the piecewise symmetric conjugate of the primitive training symbol and the good autocorrelation of PN weighted factor. The frequency synchronization is finished by utilizing the training symbol whose PN weighted factor is removed after the timing synchronization. Compared with conventional schemes, the pro-posed scheme can achieve a smaller mean square error and provide a wider frequency acquisition range.
In order to obtain coding gain along with diversity gain,rotation code was applied to cooperative diversity employing decoded-and-forward cooperative protocol.Different from the same two symbols transmitted in conventional repetition-coded scheme,two different symbols were transmitted separately in two successive timeslots in the proposed rotation-coded cooperative diversity.In this way,constellation spread in the available two-dimensional signal space rather than on a single-dimensional line in repetition-coded scheme,which was supposed to be responsible for the additional coding gain.Under the proposed cooperative transmission model,upper bounds for the symbol-error-rate(SER)of cooperative diversity based on repetition code and rotation code were derived respectively.Both analytical and simulated results show that cooperative diversity based on rotation code can obtain an improved coding gain(by about 2 dB)than repetition-coded scheme without the expense of power or bandwidth.
