Abstract
In this paper, we propose a modified dynamic decode-and-forward (MoDDF) relaying protocol to meet the critical requirements for user equipment (UE) relays in next-generation cellular systems (e.g., LTE-Advanced and beyond). The proposed MoDDF realizes the fast jump-in relaying and the sequential decoding with an application of random codeset to encoding and re-encoding process at the source and the multiple UE relays, respectively. A subframe-by-subframe decoding based on the accumulated (or buffered) messages is employed to achieve energy, information, or mixed combining. Finally, possible early termination of decoding at the end user can lead to the higher spectral efficiency and more energy saving by reducing the frequency of redundant subframe transmission and decoding. These attractive features eliminate the need of directly exchanging control messages between multiple UE relays and the end user, which is an important prerequisite for the practical UE relay deployment.
Highlights
Relay transmission can help increase both the cell coverage and the data rate of the cutting edge cellular systems without creating undue inter-cell interference, and as such, has been considered in the latest cellular standards (e.g., LTE-Advanced) [1]
We have proposed modified dynamic decode-and-forward (MoDDF) which can be applied to the type II relay for the nextgeneration cellular systems (e.g., LTE-Advanced and beyond)
The end user can perform the joint and sequential decoding without exchanging the control message with user equipment (UE) relays, because it does not need to know whether a UE relay is participating in the transmission or not
Summary
Relay transmission can help increase both the cell coverage and the data rate of the cutting edge cellular systems without creating undue inter-cell interference, and as such, has been considered in the latest cellular standards (e.g., LTE-Advanced) [1]. To enable joint decoding at the end user with the openloop retransmissions from multiple UE relays, we propose several subchannel/code selection strategies based on the rateless codes at UE relays [18]. With the proposed relaying protocol, each relay and the end user can attempt to perform the subframe-by-subframe message decoding. The end user can blindly search for the forwarded messages from UE relays based on the pre-determined subchannel/code selection strategies. When the correct message decoding occurs at the i-th UE relay after receiving (j − 1) subframes, this relay begins to re-encode and forward the message to D at the j-th subframe duration using the pre-determined subchannel/codes sequences. DT occurs when the number of activated relays at all previous subframes and current subframe is 0, providing the instantaneous rate as log(1 + γSD) where γSD is the signal-to-noise ratio (SNR) of the S-D link. If we let ARðgjR1 1⁄4 n1; Á Á Á ; RN 1⁄4 nNÞ be the conditional average AR per frame at a given Rj as a function of g which is the common average SNR of the received signal at D, an average AR, AR, per frame can be derived based on the given number of new active relays at each subframe, Rj, as XM MXÀ n1
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