Performance Analysis of Repetition Coded OFDM Systems with Diversity Combining and Higher-Level Modulation

Abstract

SUMMARYOrthogonal frequency division multiplexing (OFDM) communication systems have great advantages, such as high spectrum efficiency and robustness against multipath fading. In order to enhance the advantages, this paper investigates an efficient utilization of both diversity combining and higher-level modulation (adaptive modulation) with a repetition code on the frequency domain in the OFDM systems. The repetition coded OFDM systems can achieve an improvement of performance with such a simple structure as one pair of transmit/receive antennas. In this paper, we derive simple closed-form equations for bit error probability (BEP) and throughput, and then improvements of those performances in the proposed OFDM systems are verified by both theoretical analysis and Monte Carlo simulation.

Performance Analysis of Hermite-Symmetric Subcarrier Coding for OFDM Systems over Fading Channels

“…It is found from the figure that the BER varies depending on the frequency correlation characteristics, which is shown in Fig. 3 of [18], at any rms delay spread σ τ normalized by OFDM symbol duration T s (= T d + T g ). That is, the average BER is more degraded around the center of all subcarriers because of less frequency diversity gain.…”

“…1(a). Figure 1(b) shows the repetition coding scheme [18]. The symbols {D j } j=1,2,··· ,N c /2 are duplicated with N c /2 subcarriers spacing at a transmitter and the two symbols are combined with MRC at a receiver to acquire the frequency diversity gain.…”

“…The average BERs with Gray-mapped M-PSK or M-QAM in the OFDM and the RC-OFDM systems over Rayleigh fading channels can be calculated by [18] …”

“…The repetition coded OFDM (RC-OFDM) scheme brings many good results, such as inter-carrier interference (ICI) cancellation [15], [16], blind channel estimation [17], and bit error rate (BER) improvement owing to diversity gain [16], [18]. In [18], we have introduced the RC-OFDM systems employing diversity combining and higher-level modulation with such a simple structure as one pair of transmit/receive antennas. All subcarriers of OFDM are divided into two regions (low and high subcarrier frequencies), then PSK or QAM symbols are duplicated with half the subcarriers spacing.…”

“…Therefore, the signal power per channel in the HC-OFDM systems should be reduced by half in order to keep the same condition. But, by enhancing the analytical method in [18], it can be theoretically and quantitatively indicated that the HC-OFDM systems achieve the improvement of BER and Copyright c 2012 The Institute of Electronics, Information and Communication Engineers throughput performances owing to the frequency diversity gain and the dual channel transmission. The derived equation of throughput can be also utilized for verifying the advantage of the HC-OFDM systems when applying the adaptive modulation.…”