Blind carrier frequency offset mitigation in space–time block‐coded multicarrier code division multiple access uplink transmission

Abstract

In this paper, a novel blind carrier frequency offset (CFO) estimation is proposed on the basis of the linearly constrained optimization for the uplink transmission of space-time block-coded multicarrier code division multiple access systems. First, the full-dimensional spatial-and-temporal data are formed to avoid violation of the second-order statistics in the conventional receiver design. A set of weight vectors is then provided for acquiring each multipath signal from the desired user while the others get rejected. Finally, the estimated CFO is obtained in accordance with maximizing the well-defined measurement function, which is formulated by collecting all the output powers of the receiver. A space-time averaging technique is also proposed to enhance the robustness to the finite sample effect. Simulation study confirms that with the proposed CFO estimator used in the preceding, the receiver can successfully achieve the same performance of the optimal receiver working in the absence of CFO.Because the erroneous second-order statistics caused by CFO leads to failure in tracking the signalplus-noise subspace, these detectors exhibit severe performance degradation in the CFO estimation. To avoid this phenomenon, a two-level CFO estimator [20] was designed to maximize the figure of merit for an MC-CDMA downlink system incorporated with STBC, in which all users' CFOs are supposed to be aligned. However, in uplink transmission, this is typically impossible to achieve. The misaligned CFOs from different users destroy the convexity of the estimation merit figure and result in failure to accurately determine the CFO. As a remedy, an iterative estimation [21] without the time-consuming peak search was designed for a quasiorthogonal STBC uplink system [22,23]. In spite of the effectiveness in dealing with misaligned CFOs, this approach does not consider the relation between the consecutive time slot signals and works with the received array data associated with each time slot instead of the full-dimensional spatial-and-temporal data. This means that there is no combining gain at the receiver when constructing the measurement function. To the authors' knowledge, no prior works have been devoted to representing the blind CFO estimation using the full-dimensional spatial-and-temporal data for an uplink transmission of STBC MC-CDMA systems.In this paper, a novel blind CFO estimation is developed via the following implementation procedure. To avoid phase inversion, we first form the full-dimensional spatial-and-temporal data without taking the complex conjugate operation on the received data associated with the second time slot. A set of weight vectors is obtained on the basis of the linearly constrained optimization and is exploited to acquire each multipath signal from the desired user while the others get rejected [24]. Relying on point searching, we determine the estimated CFO by maximizing a well-defined measurement function, which is constructed by collecting all the output power of the receiver. On the basis of the S...

On the CFO/Channel estimation technique for MIMO-OFDM systems without using a prior knowledge of channel length

“…It can be found that the quadratic cost function with respect to in (7) reaches a minimum value while the condition of = 0 is satisfied [26]. In this way, the CFO estimate can be implemented by searching the minimum of the cost function.…”

“…SubstitutingL in (26) andˆ 0 in (29) into (23), we have the trimming estimate of the channel response.…”