A time and frequency synchronization scheme for multiuser OFDM

Abstract

We present a multiuser synchronization scheme for tracking the mobile's uplink time and frequency offsets. It uses the redundancy introduced by the cyclic prefix and does not need additional pilots. We show performance results of an orthogonal frequency division multiplexing (OFDM)-based radio interface based on universal mobile telecommunication system (UMTS) parameters. For a UMTS-typical mobile channel environment, the performance of a coherent system employing the scheme is virtually indistinguishable from the performance of a perfectly synchronized system. In a differentially modulated system, synchronization errors decrease the system performance by about 0.7 dB compared to a perfectly synchronized system.

Channel estimation in OFDM systems operating under high mobility using Wiener filter combined basis expansion model

“…If we want to compensate this effect, we are dealing with the problem of fine-frequency adjustment. One effect of carrier frequency offset is the detrimental effect of a rotation of the subcarriers [23,24]. This effect will be recognized by a channel estimator, which does not distinguish between phase offsets caused by the channel and those caused by a frequency offset.…”

Asynchronous multicarrier multiple access: Optimal and sub-optimal detection and decoding

“…To reduce the complexity of the detection stage, we can pursue an ad hoc design of the system, such as • Introduce some level of time and frequency synchronization among users. For instance, a control loop from the base station can be deployed such that the terminals can adjust their local oscillators and timing [45].…”

“…The effect of the time offsets in a DMT-MA system with suboptimal single-user detection can be found in [21]. A technique for compensating time and frequency misalignments based on feedback control in a DMT-MA system is presented in [45]. On the other hand, a rich body of literature can be found on the study of receivers for DMT modulation in single-user applications in the presence of timing errors, frequency offsets, and multipath fading, e.g., [30,31] and associated references.…”

Carrier Frequency Offset Estimation for Uplink OFDMA Using Partial FFT Demodulation

“…Filter-banks separate different users in [9], enabling per user CFO estimation and is suitable for SCAS. Energy minimization of null subcarriers is This research has been funded in part by the following grants and organizations: ONR MURI grant N00014-07-1-0738, ONR N00014-09-1-0700, ONR N00014-10-1-0576, NSF 0831728, NSF CNS-0832186, NSF CNS-0821750 (MRI), NSF OCE-0520324 and the University of Southern California's Provost Office.…”