Multiple carrier-frequency offsets (CFO) arise in a distributed antenna system, where data are transmitted simultaneously from multiple antennas. In such systems the received signal contains multiple CFOs due to mismatch between the local oscillators of transmitters and receiver. This results in a time-varying rotation of the data constellation, which needs to be compensated for at the receiver before symbol recovery. This paper proposes a new approach for blind CFO estimation and symbol recovery. The received base-band signal is over-sampled, and its polyphase components are used to formulate a virtual Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system estimation techniques, the system response is estimated and used to subsequently transform the multiple CFOs estimation problem into many independent single CFO estimation problems. Furthermore, an initial estimate of the CFO is obtained from the phase of the MIMO system response. The Cramer-Rao Lower bound is also derived, and the large sample performance of the proposed estimator is compared to the bound.
In spatially distributed multiuser antenna systems, the received signal contains multiple carrier-frequency offsets (CFOs) arising from mismatch between the oscillators of transmitters and receivers. This results in a time-varying rotation of the data constellation, which needs to be compensated at the receiver before symbol recovery. In this paper, a new approach for blind CFO estimation and symbol recovery is proposed. The received base-band signal is over-sampled, and its polyphase components are used to formulate a virtual Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system estimation techniques, the system response can be estimated and decoupled versions of the user symbols can be recovered, each one of which contains a distinct CFO. By applying a decision feedback Phase Lock Loop (PLL), the CFO can be mitigated and the transmitted symbols can be recovered. The estimated MIMO system response provides information about the CFOs that can be used to initialize the PLL, speed up its convergence, and avoid ambiguities usually linked with PLL.keywords-Multi-user Systems, Distributed Antenna Systems, Carrier Frequency Offset, Blind MIMO System Identification BACKGROUNDIn both wireless and wireline communication systems, received signals are often corrupted by carrier-frequency offsets (CFOs), due to Doppler shift and/or local oscillator drift. The CFO causes a time-varying rotation of the data symbols, and thus before symbol recovery, it must be estimated and accurately compensated for by the receiver. The CFO can be estimated via the use of pilots symbols; however, even a small error in this estimation tends to cause large data recovery errors. This necessitates transmission of pilot symbols rather often. In single user systems, or in multiuser systems where the transmitters are physically connected to the same oscillator, there is only one CFO that needs to be estimated. This is typically done via a decision feedback Phase Lock Loop (PLL) at the receiver. The PLL is a closed-loop feedback control system that can adaptively track both frequency and phase offsets between the equalized signals and the reference constellation. However, depending on the constellation used during transmission, the PLL can have an M -fold symmetric ambiguity, and thus it has limited CFO acquisition range; e.g., |f k | < 1/8 for 4QAM signals. Moreover, the PLL require a long convergence time. To solve these problems, several methods have been proposed [3], [5], [6], [9] [11] that allow for blind estimation of the CFO and symbols using the second-order cyclo-stationary statistics of the over-sampled received signal. Blind CFO estimation has also been studied in the context of orthogonal In a spatially distributed multiuser antenna system where data are transmitted simultaneously from multiple antennas, the received signal contains multiple CFOs, one for each transmit antenna. A PLL does not work in this case as there is no single frequency to lock onto. The literature on estimation of multiple CFOs is rat...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.