General ICI Self-Cancellation Scheme for OFDM Systems

Capacity Maximizing ICI Canceling Windows for OFDM in Time-Varying Channels

“…Second, the constrained nonlinear optimizer is employed to find the solution. 4 The optimizations are performed for several rate-t/k systems; rate-1/1, 1/2, 2/2, 2/4, 3/4, and 4/4. We have tried many randomly selected initial points to the optimizer and it appears that most of resulting C flat 's converge to the same value.…”

“…The conventional window for the rate-1/2 system in [4] (Design A) is also plotted for comparison. In the figure, the optimal windows for systems with the effective rate-1 (t = k) have flat shapes close to 1, and the optimal windows for systems with the effective rate less than 1 (t < k) have shapes similar to the conventional window in [4], which is designed to maximize a signal-to-interference ratio. Fig.…”

“…This happens because such a fast varying channel causes intercarrier interference (ICI). To compensate for the ICI, various techniques have been introduced including the frequency-and time-domain equalization (see, e.g., [1] and references therein), the ICI self-cancellation [2]- [4] and the frequency-domain partial response coding (PRC) [5], [6]. Among these approaches to ICI mitigation, the equalization would be the most common, but its implementation tends to require heavy computation when the channel varies fast.…”

“…In this paper, we present the rate-t/k (t ≤ k) OFDM systems with time-domain windowing by generalizing the rate- 1/k system in [4], where the rate-t/k system employs the first t subcarriers of every k subcarriers. For these systems, the capacity lower bounds are derived for the time-varying channels and the optimal time-domain windows are developed by maximizing these bounds.…”

“…Given a signalto-noise ratio (SNR), the capacity lower bound is maximized through a numerical procedure. When the rates are less than 1 (t < k), the resulting windows make the spectrum of each signal subcarrier, after suffering Doppler spread, have almost zero value at the frequency of the other signal subcarriers, as rate-1/k systems in [4]. Through comparing the systems with various rates, usefulness of ICI canceling schemes are examined, and the results indicate that the proposed rate-t/k (t < k) systems can provide the higher spectral efficiency when channel varies very rapidly.…”