Cooperative Relaying with Carrier Frequency Uncertainty

A Low-Complexity Receiver for Cooperative Simultaneous Relaying

“…Note that the performance is sensitive to very small frequency offsets, and for frequency offsets around 0.2, the offsets are not negligible enough to ignore, and are not large enough to prevent the noise enhancement. Similar conclusions were arrived at by using other suboptimal receivers in [6]. This behavior suggests that the use of Alamouti space-time code is probably not suitable for relay channels with frequency offsets, necessitating the design of space-time codes that are more robust to frequency offsets.…”

“…detection with a conventional receiver degrades badly for some frequency offsets due to the time-varying system matrix, R t [n]A, as well as noise correlation. In some cases error floor on performance is observed [6].…”

“…Nevertheless, the symbol timing issues have been studied in, for example, [7], [8], [9]. This paper builds on our work in [6] wherein we have considered several suboptimal receivers for differential transmission using two relays. Our focus in this paper is on the design of a rank-based adaptive receiver whose complexity scales linearly as the number of relays increase.…”

“…The proposed receiver consists of a linear front-end that is designed to eliminate the effects of frequency offsets. Using such a front-end allows for the decisions of individual symbols to be decoupled, thereby eliminating the necessity of performing joint detection considered in [6]. The remainder of this paper is organized as follows.…”

“…The receiver is assumed to have knowledge of the carrier offsets since they remain constant for a relatively long period of time contrary to the channel fading realizations. We neglect the effects of symbol timing offsets which are less of a concern for low data-rate applications like sensor networks [6]. Nevertheless, the symbol timing issues have been studied in, for example, [7], [8], [9].…”